CA1242907A - Compound optical phase grating and switching devices comprising such a grating - Google Patents
Compound optical phase grating and switching devices comprising such a gratingInfo
- Publication number
- CA1242907A CA1242907A CA000446587A CA446587A CA1242907A CA 1242907 A CA1242907 A CA 1242907A CA 000446587 A CA000446587 A CA 000446587A CA 446587 A CA446587 A CA 446587A CA 1242907 A CA1242907 A CA 1242907A
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- grating
- optical
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Classifications
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/26—Optical coupling means
- G02B6/35—Optical coupling means having switching means
- G02B6/354—Switching arrangements, i.e. number of input/output ports and interconnection types
- G02B6/3544—2D constellations, i.e. with switching elements and switched beams located in a plane
- G02B6/3546—NxM switch, i.e. a regular array of switches elements of matrix type constellation
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
- G02B27/42—Diffraction optics, i.e. systems including a diffractive element being designed for providing a diffractive effect
- G02B27/4272—Diffraction optics, i.e. systems including a diffractive element being designed for providing a diffractive effect having plural diffractive elements positioned sequentially along the optical path
- G02B27/4277—Diffraction optics, i.e. systems including a diffractive element being designed for providing a diffractive effect having plural diffractive elements positioned sequentially along the optical path being separated by an air space
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/26—Optical coupling means
- G02B6/35—Optical coupling means having switching means
- G02B6/351—Optical coupling means having switching means involving stationary waveguides with moving interposed optical elements
Abstract
ABSTRACT
The invention relates to a compound blazed opti-cal phase grating comprising at least two grating sections (U1, U2) which are disposed opposite each other in parallel planes and which have grooves which extend parallel to each other, the grating sections comprising equal grating per-iods and being movable relative to each other within their planes perpendicularly to the grooves. Over one grating period (.DELTA.) the optical pathlength varies at least sub-stantially parabolically and symmetrically relative to the grating period, in such a manner that in the case of a symmetrical position of the grating section relative to a common line perpendicular to the grating planes the opti-cal pathlength through the compound grating is constant.
Various optical switches and switching matrixes can be formed by means of such a compound phase grating.
The invention relates to a compound blazed opti-cal phase grating comprising at least two grating sections (U1, U2) which are disposed opposite each other in parallel planes and which have grooves which extend parallel to each other, the grating sections comprising equal grating per-iods and being movable relative to each other within their planes perpendicularly to the grooves. Over one grating period (.DELTA.) the optical pathlength varies at least sub-stantially parabolically and symmetrically relative to the grating period, in such a manner that in the case of a symmetrical position of the grating section relative to a common line perpendicular to the grating planes the opti-cal pathlength through the compound grating is constant.
Various optical switches and switching matrixes can be formed by means of such a compound phase grating.
Description
PIID.S3 0~1 l 5.1.8L,' Compound optical phase grating and switching devices comprising suctl a gra-ting.
The invention re:La-tes to a cornpouncL blazecl op-t:ical phase grating.
SLLCII a grat:ing is general:Ly known, for exarnple rrom ~'~ppl:Lecl Op-tics", Vol.19, No.1~, 15 J-uly 'l9~O, pages
The invention re:La-tes to a cornpouncL blazecl op-t:ical phase grating.
SLLCII a grat:ing is general:Ly known, for exarnple rrom ~'~ppl:Lecl Op-tics", Vol.19, No.1~, 15 J-uly 'l9~O, pages
2~76 -to 2278. Bla~ecl phase gratings of the type described in this maga~ine, whose grating profiles are subs-tantially sawtooth-shaped, have -the proper-ty -tha-t they cle`1ect light in a specific diffrac-tion order of` the grating with a hig'h efficiency, which diffrac-tiorl order inter a:Lia depends on the inclina-tion of the groove walls. IIow -the remainder of -the light is distribu-ted over the o-ther dif~raction orders is generally irrelevan-t.
However, gra-tings of this -type clo not permit deflec-tion ~ith a high efficiency in other dif~rac-tion orders. This means tha-t -the dif-frac-tion order determined by the selected grating profile cannot be varied.
It is the objec-t of -the invention to provide a compound optical phase gra-ting w'hose sawtoo-th-shaped optical profile can be variecl simply, so -that at op-tion the ligh-t can be deflec-ted in different cliffrac-tion orders, -thereby enabling optical switches to be construc-ted in a simple manner.
~ ccorcling -to -t'he invention -this obJec-t is achle~ecl in tha-t the compo--lnd phase-gra-tiIlg comprises at least two gra-ting sec-t:ioILs wh:ictl are clisposecl oppos:ite one another :in para:Lle:I p:Lanes ancl WIL:;CII have g~:rooves WtLiCh e~tend parallel -to eact-l otller, in -Lhat thQ grat:ing sections have equal gra-t:ing periods ancl are movab:Le :re:Lat:Lve to each other w:ithin their ~planes in a direction perpenclicnlar to -the g:rooves, ancl :in -tt-lat over one gla-ting period -the grating prof:ile :is at :Least subs-ttarlt:ially parabol:ic and is symnle-trical re:lt~t:ive -to -the gra-ting per:iocl, -tl-le gra-ting profi:Les ~)e-ing sIlch tlLat in a symme-tr:ical pos:it-ion of th-~h. S ,~
PIID.~3-011 2 5.1.~L~
grating sections relative -to a common line perpenclicular to -the gra-ting planes -the opiical pathleng-t:h through -the com-pound grat:ing is constan-t.
I:~ the gra-ting sections are in a symme-trical 5 position relati.ve to a line which extencls perpenclicularly -to -the gra-ting planes~ -this means -that in -the case of, for exam~ple, -two grating sections :E'or example one g:ra-ting h:il:L
o:E' one g:rat:ing sec-tion is si-tuated exactly above a gra-ting hill of' t:he other gra-ting sec-tion. A:Lter:nativel.y, a grating .h:ill cLnd a grati.ng va:Lley rnay be sit-uated on t:he comrrlon lin.e whic:h ex-tends perpenclicular:Ly -to -t:he grating planes. This posi-tion o:E'-the grating sections is hereinafter :referred -to as in:i-tial posi-tion and is -the posi-tion in which t:he grating see-t:ions are no-t shi:~ted relative to eae:h other.
In -this position -the sum of -the optical pa-thlengt:h through the grating sec-tions, viewed perpendicularly -to -the grating~Lanes, is cons-tant over all the gra-ting periods.
This means -that a ligh-t beam which is incident, preferably at right angles, upon the compound hase grating is no-t influenced at all by -the grating structure of -the gra-ting sec-tions, because there is no ef~ec-tive optical grating s-tructure. As a resul-t o~ this, -the light beam is no-t def]ected; -t:he compound grating is then bla~ed for -the ~ero order. However, if -the grating sections are shif-ted rela-tive to each o-t:her by a frac-tion of -the:ir gra-ting per~.ods ou-t of the:ini-tial pos:ition, the e:~fec-tive op-tical s-truc-ture o:E' the compouncl phase g:rat:ing is also c:hangecl. Depending on the magni-t-ucle ancl t:he clirec-tion o~ the clisplacerncant O:r the gra-ting sec-t:io:ns :reLa-tive -to each o-the:r a blazecl g:rcLting s-t:ruc-t1.Lre is ~orme~l w:h:ic:h, ow:ing -to t;:he speci.a:L p:ro:E'i:Le O:e the grating soc-tions, cle:Flects an inc:iclent :L.igtlt beam in a hif,r~her o:rcler, ~'or e.Yarrlp:Le in the -~ 'Ist ror in :hi~tle:r orcle:rs.
This enables t:t-le blcn~e o:E'-t:he compo-L:Lncl ph.se g:r~t:i.ng to be sw:i-tc'hed betweerl d:i:rl'erc-~nt cl:i:r:E':rac-ti.on o:rclers, permitting it to be employed as arl op-tical swi-r;ch.
In ~a sui.tab:Le emboclirrlerl-t o:E' the i:n-ve:nt:ion t:he gra-ting sect:ions are d.if!;-i tal p:tlase g:ra-t:i:ngs, :i..e. the PIID.S3-~11 3 5.1.8ll gra-ting prof:i.le changes in a plurality o~ s-teps within one grating period. T:his may be achieved :E'or example in -tha-t a transparen-t substra-te having a constan-t refractive index is ~ormecl wi-th s-teps Or di~:E'eren-t height or in tha-t adjacen-t areas with cli~reren-t :re~rac-tive indexes are rorrnecl in a su~strate oE' constan-t -thickness. Dig-i.-tal p:hase gratings ha-ve t:he advanta{e -tha-t -they can 'be manu:E`actu:red in a com-pa:rat.i.ve:ly s:impLe mclnner and tha-t; they perm:i-t -the construc-t-ion of' cornpound p:t-l.ase g:rat:ings with a cornparatively hig'h bla~e e:~f`iciency wh:ich compol:lncl gratings d:i~:E`ract a substan-t.ia:l por-t:ion o:f the inciclent :Ligh-t iil a desired cli:E'~rac-tion order only a very srnall amoun-t o:E' light being di:i`rractecl in the acdjacen-t dif`frac-tion orders.
In ano-ther embodirnen-t the gra-ting sections comprise 5 ana:Log phase gratings whic:h may also be constructed as rel:ief and/or ref:ractive-index gra-tings. Analog phase gra-tings wi-th sui-table re~rac-tive index pro-~iles have -the advan-tage tha-t -they can be shi~-ted rela-tive -to each other in a simple manner because -they comprise -~la-t pla-tes of cons-tan-t -thickness which are superimposed. This also applies to digital re-~rac-tive-index gra-tings.
In anot:her advan-tageous em~odimen-t of -the inven-tion a gra-ting sec-tion in -the :E`orrn o~ a relief gra-ting is provided wi-th a re~lec-t:ive l.ayer on its upper surface enabling a : compound phase gra-ting -thus construc-ted -to be nsed as a re~lec-tion grat:in.g~
A pa:r-ticu:La-rly advan-tageous ernbodi.ment o~ the inverl-tion is fornrle(l by an optical swi-tch w:h:ic:h comprises a rirst op-t:ical port ancl a p:Lura]:i-ty o:E` second opt:ical ports ancl Wil:i.Cil rlurt:her coml)rises a lig:il-t-cle:i`:lecti:rlg e.Lemen-t fo:r optica:LLy connect:ing the ~i:rs-t port -to on:l.y one o:E` tile secolld po:rts. Crl t~l:is opt:ica:L sw-i.tch the :L:ig:ll-t-clef`:Lecting elerment is a compoLIncl phase g:ra-ting in accorclance ~.ith the invention and the seconcl optical ga-tes are cl:isposecl in ~t:he cent:ral di:~:~raction orclers o~ the phase-~ra~ting a-rrangerrlerlt.
Var.io~ls types o~` optical sw:i-tciles wit!lrnecilanic-al:ly rno-vecl parts are krlowl-l. For exarnp:le penca p:r:isrrls are ~2'~Z~
PHD.S3-~'l1 4 5.1.8L~
employecl (J. Minowa, ~. ~ujii, Y. Naga-ta, T. Aoyarrla, K. Doi:
Non-l~locking ~ x S op-tieal ma-trix swi-tch for fibre-op-tical comrmlnica-tion~ Electron. Le-t-ters 19SO, vol. 6, no.11, pages 422-Ll23), which prisms are moved in-to -the radiation path hy means of srnall electromagnets, de~lec-t -the beam and -thereby prov-icLe the swi-tehing aetion. Alternatively~ optieal glass fibres Inay be movecl relative -to eaeh o-ther parallel -to their encl faces (see E`or exarnple T.P. Tanaka, M. Maeda, Y. Shlrrlohori, Il. Takastlirrla, I. Kondo: Simple and reliab:Le 10 optica:L bypass swi-tcll E'or fibre-op-tie data bus app:L:ieation, 7-th European Cone. on Opt:ieal Comm.~ 198'1, Copenhagen, page 15-1), to enable eo-upling in-to differen-t :E`ibres.
Non-mee'hanieal optieal switehes ean be eonstr~Leted usintt,r magneto-optieal or eleetro-optieal e:E'feets. In prin-15 ciple, magne-to-optical swi-tches (see for example M.Shirasaki, H. Takamatsu, T. O'boka-ta: Bi-s-table magne-to op-tie swi-teh for multimode op-tieal fibre, Appl. Op-t. 21 (1982), pages 1943-Ll9) operate only wi-th polarized light and ean be used only with non-polarized light with -the aid of addi-tional, very in-tri-20 eate means. Eleetro-op-ticaL ef:~ects are utilized for switching in integra-ted op-tical -technology (see for exarnple E.M. Philipp-Rutz, R. Linares, M. Eakuda: Electro-op-tic Bragg di-fE`raetion swi-tehes in low erosstalk in-tegrated op-tic swi-tching ma-trix, Appl. Opt. 21 (1982), pages 2189-94).
In comparison with all -these op-tical swi-te'hes -the swi-teh in aeeoranee with the inven-tion has the advan-tage of a eomparati-vely simple eonstrue-tion wi-th georne-trieally prede-termined radia-tion pa-ths, only a ~Low power eonsurnp-tion -for shiE`-ting t'he grating see-tions, a low-:Loss po:la-r:ization-30 independen-t operation, and a 'h:ittrh eross-ta:Lk-atterl-lLatiorl.
It is obv:io-us that by rneans o:E' sucl-l op-t:ica:L
s-witehes it :is poss:i'ble to eonstruet arrays oE' optiea:L
switeh:irlg ma-t;rixes witll a p:l-ura:Li-ty oI' :inpllt and O~ltp~lt ports. In such matrixes eaetl inpllt and Outpllt por-t eompriSes 35 a first port oE' an op-t:ic~a:L swi-tell in aecordance W-ittl the invcntion, -thenurrlber o-f seconcl ports oE` an :input or OUtpllt sw:itch corresponcling to the nurrlber of OUt~pllt or inpllt 2~7 PIID.~3-O1'l 5 5.1.~
switches, and tihe seconcl por-ts of every inpu-t or ou-tput sw-itch -being opt:ically connectecl to a seconcl por-t of clifL'eren-t inpu-t or ou-tpu-t swi-tches. This swi-tching rna-tri~
en.bles informa-tion7 for e~ample moclulated ligh-t, -to be transm-it-tecl f-rom any of -the inpu-t por-ts -to any desired OlltpUt port, wi-tholl-t information being applied -to the other OUtp~lt por-ts.
~ nol;her acl-van-tageous emboclimen-t of -the in-ven-tion erlabLes the construc-tiorl oL~ op-tica:L concentrators -wi-th a l0 plnraLity oL' op-ticaL input ports ancl --~ srnalLer mlrnber of O~tpllt ports. In -these concen-tra-tors groups o~ input ports' are -those of an opticaL sw:L-tching matri~ in accordance wi-th -the invention, one output por-t of the concentra-tor being -the firs-t port oL` an op-tical switch according to the inven-t-ion 15 and the outp-u-t por-ts, which each form part of an op-tical switching ma-tri~, being connec-ted to a seconcl por-t of difLferent optical swi-tches.
Concen-trators of this type are used for -trans-mi-t-t-ing light which is received via a plurality of inpu-t 20 lines at option -to a specific ou-tput line, for example a trunk line, the nnrn'ber of ou-tpu-t lines being smaller than -the number of input lines. Concen-trators fur-ther have the advan-tage -tha-t -the number of second ports of the optical sw:itches can be cornparati-vely small.
~mbocliments Or -the inven-tion will now be clescribed in more cletail, by way of e~ample, wi-th reference to the clrawings, in which:
~ ig. 1a shows a compouncl pl~ase-gra-t:ing comprising two steppecd (d:igital) grating sec-tions in -tthe in:itial 30 poslt:ion, the grat:ing sec-l-ions compr:isingr an oclcl nurrlber Or steps per grat:LrLg periocl, Fig. 'I'b Sl-IOWS tt-le same com-pourlcl phase gra-t:ing in the sh:i~`-te(L position, ~ ig. 'Ic stlows tile resuLt:ing optical grat:ing 35 prori:Le oL' -tlle conlpound ~phase grating sLhown in ~ig. 'Ib, F:ig. 2a shows a compollncL pllase gra-ting comprising -two steppecl (cLig:ital) grat:inlg sectioIls ir-tLIe init:i.l:L
position, I;he grat:irllg sec-lions c~mprisin~; an i?verl nllmher P~D.S3-o11 6 5.1.84 of steps per grating period, Fig. 2b sho~s -this compound phase gra-ting in the shif-tecl posi-t:ion, Fig. 2c shows -the resulting optical gra-ting profile of tlle cornpound phase grating shown in Fig. 2b, F:ig. 3a S}lOWS -the phase pro-file of a cornpouncl phase gra-t:ing whose gra-ting sections comprise con-tinuous (analog) phaso gra-t:irlgs which are sh:Lftecl re:La-tive -to each o-ther ~y a clistance , F:ig. 3b shows -the res-u1 ting phase prof:i.1e Or the compouncl pt-Lase gra-ting shown in F:ig. 3a, Fig. ~I shows a cornpouncl phase gra-ting comprising two cligital gra-ting sec-tions, -the upper sLIrface O r one grating section being provided wi-th a reflective layer, Fig. 5 shows an optical swi-tch cornprising a com-po-lnd phase gra-ting in accorclance wi-th the inven-tion, Fig. 6 shows an op-tical swi-tching matrixcomprising a plurali-ty of optical switches, and Fig. '7 shows an op-tical concen-trator comprising 20 nine inpu-ts and -three ou-tputs.
Firstly, i-t will be illustratecl by means of the sirnple exarnple of Fig. 1 how the blaze in a compouncl -trans-mission phase gra-ting comprising two steppecl grating sections U1 and U2 can be swi-tchecl be-tween for exampLe the 25 -three cen-tral diffrac-tion orclers -1, O and -~1. The groove profiles of the two gra-ting sections U1, U2 are s-tepped surface relieL's (also referrecl Lo as cdigital surface struc-tllres), wh-ich exac-tly ma-tch ono ano-ther an{l which are made Or -the sarno rnate:r:ia'l. Onc prof:ile is an ex~c-t irnpression 30 of -the other profilo ,:i.e. a (no~at:i-ve) copy. In ttlC
origina:L sLIch proL`i:Les can bo forrrled by :LocaLLy se:Lect:ive e-tching processes. Copies of these origirl.-Ls ancl coples o:~
coples can he manu['ilc-tnrecl frorn speciL'ic pLast:ics, f<)r ex~lrnp'L~ by rn~.lns O r c. I,tlO to-po:l yrrl~r i ~a-t i O~rl :[~r Occss .
'rhe grat:ing soct:ior-ls 'Ul ancl U2 compr:iso an oclcl nLIlnbor7 for oxalrlple 5,oL'steps per ~ra-t:in~- periocl~, so -that there :is ono step of clollble w:icltll, wtlicll in a symrrletr:ica:L
arrangement may be :re~ardo(l as tho bas:ic step.
PIID.S3-0'l1 7 5.1.8L~
TlIe s-tep he-igrh-t from t:his cen-tral basi.c s-tep towarcls -the ends of -tlle gra-ting, period ~ of -tile gra-ting section U2, :E`or example comp:Lies wi-t:h:
s-tep he:iglIt = O,d,3d,6d, ...., 1/2N(N-~1).cl, (1) wlIere (2N+1) is t:he number of steps per grating periocl.
The :increasc of the s-tep :height from -the centre -towarcds -the edges i.s in p:rlnciple clefined by a parabolic law;in addition to t}-lis there is a :Iinea:r porti.on as a result of -the pre-sence o:l` the cloub:Le bas:ic step. T:he same also app:Lies -to tlIe grclt:ing section 'U1.
Thus, t:he geometric step helgh-t in the g:rating section U1 in Fig. 1a varies (frorn left to right for equal s-tep I~id-ths in -t:he cross-sec-tion in ~ig. 1a) frorn ..., 2d, O, 2d, 3d, 3d, 2d, O, 2d, ... . The geome-tric s-tep heigh-ts in -the grating sec-tion U2 are the same:
... d, 3d, d, O, O, d, 3d, d, ... .
[n order to enable a movement of the gra-ting sec-tions U~l and U2 rela-tive -to each other in a direc-tion perpendicular -to -the gra-ting grooves, -the -two gra-ting SeCtions are spaced :E`rom each ot:her by a distance 2d.
The op-tical pa-thlength s (in the -transrnission mode) 'between -the -two planes a and b, shown in broken lines, in the -two gra-ting sec-tions U1, U2 is constant in ~ig. 1a (i.e. inclependent of the ioca-tion), namely SO = (3n-~2)d (2) w'lIere n is the :refract:i-ve index o:E`-the d:ie:Lectr:i.c rna-Le:rial ancl d is the uni.t O r eeorne-t:rical s-tep tIe:igh-t This means l;hat in -the cornpou:ncl g:rat:irlg shown .in ~`ig. 'ia -the:re :is no e:E`:E`ect:i.ve optica:L. grating st:ruc-Lurc at aL:L~ i.e. t;lIe pl-Lase-g~ra-t:ing arrangelllerIt :is bl.a~ed :E`or tlle .e:ro o:rcle:r (tlIe no:rlrIcll (:I:irect:ion).
'[:r, as -is sllown :in :li`ig. 'Ib, for exarrlp:Le the g:ra-t:ing section U.l is sll:i.:rtecl by one s-top wi.dl;ll (-ty~pically app:rox. 10/l.~rrl) to tlle Left~ tt~e opt:ica.L patlIl.e7lg-tl-- s.l between the two p:lanes a an(.l b, stlown in l,:ro:ken I..:i.nes, :in t:l-~e successi-ve are<.as :L`:rom :Le:E'-t -to :ri.gtIt is:
s.l = ..,(n+Ii)d,5r~ lrl-~1)cl~(3r~-~2)(l~(2n-~3)(l~(rl~ 5ncl (~IrI-~'I)cl~... (3) PIID.S3-o-l'l c~ 5.1.c~II
TiIe op-tiea:L pa-thlerlgth clifference ~ith respec-t -to -the patlI length sO = (3n~2)d in -the successive areas is:
S1-So = ~ 2(n-1)cl~2(n-1)d~(n-1)cl~o~-(n-1) -2(n-'l)d~2(n-1)d~(n-1)d~
The op-tical pa-th1eIlg-tll prof:ile o:f t'he cornpound grating is shown :in 'Fig. 1c. I-t ~ill be seen t:hat sl (ancl s1-sO) is a reg-llar five-step pro:fi:Le having a "di~i-tal" b:Laze if the opt:iea:L step :lle.igl-lt (di:f:fererlee 'be-tl~een the phase deLays o:f two adjacent steps) is /~/5 (,i~- wave~leng-th of -the :Ligh-t).
In Fig~. 1'b t~iis op-tica:l step heig:ll-t is (n-1)cl, so that (n-'l)d = ~/5. Phase gratings wi-th sllch prof:iles are known and have al:ready 'been investiga-ted ex-tensively (see for eYamp1e H. Darnman : Spec-tral characteris-tic of s-teppecl phase gra-tings, Op-tik 53 (1979), pages L~o9_L~17; Blazed synthe-tic phase-only holograms, Op-tik 31 (197O), pages 95-1 o4) .
Frorn the same li-terature referen.ce i-t -is also kno~n -tha-t-~i-th such a five-s-tep phase profiles (grating grooves) a bla~e efficiency o:f (-theore-tically) 87.4 /0 can be aehievecl for the firs-t diffraction order, no ligh-t being 20 deflected in the adjacen-t diffraction orders. The general requiremen-t for -this is:
~ (l) - 2JL 7~ = k.2 (5) (~ = ~avelength o:f the lighti q = number of the diffrac-tion order, in -the presen-t ease: q = ~1, P = number o:f s-teps per gra-ting period ~, in -the presen-t case P = 5; k = an integer).~7(,~) is -t'he phase cle:Lay producecl in E~ 'basic s-tep o:f t:he profi1.e. .Cn accorclance w.it:h F:ig. 'Ic the co:rrespo:ncl:ing pat:h:Lengt:lI cli:fference ~= (n-'l)cl, so -t:hat it f`o:L:Lows from ~p (;~) = 2 1~ S (6) t:na t;
(n-~l)~l = (k ~ (7) Fo:r a simp:Le pract-ic<l:l e:Yarrlp'le (k=O, q='l, P=5, n-'l=0.5, m) this yie~Lcls cl=().4/urrl. Gra-ting sections w-it:h -the reqllireclrrla:.Yirrlllrll elc~-l:ing clept}l of al)proYimate:Ly 1 /nIll can be ma:n~lfact-lrecl w:it:lloilt any p:rol):lelrls.
The gratirIg sect:iorls U1, 'U2 usecl in Fii~. 1 have syrnrrI(?trical. pro:L`:i:Les. Tl-lereforo, it wi:l:l. be evide:rIt that - ~2~
PIID.~3-011 9 5.1.~
a corresponding shif-t of -the grating section U1 to the righ-t (lnstead of to the lef-t as is shown in Figo 1b)~ will yielcl a bl.aYe effect for the other first diffrac-tion order (diffractinn order =-1). Thus, by rneehanically shifting the gra-ting sections rela-tive -to each o-ther -the 'blaze effect can be switc:hed be-tween -the three cen-tral diffrac-tion orders +1, 0, -1. T:he rnagni-tude of -t:he shif-t~ which corresponds -to one step wid-th, is si-tuated typically :in the range around approxirnately -lO /uIn The grating s-tructure itself imposes a Lower lirn:it of approx:irnately 1 /um for physical/optical and technological reasons, an upper li.mit 'being imposed by -the possi'b:i.Li-t:ies of realiYing -the shif-t (requiremen-t:
simple, fas-t 7 cheap, low power consump-tion) and -the require-men-t -t:ha-t the construc-tion of -the compound gra-ting rn-us-t be compact.
~ ig. 1 shows an example of sui-table stepped ("digital~) grating structnres for the -transmission of ligh-t. However, t:here are o-ther s-ui-table digi-ta:L s-truc-tures as well as suitable continuous ("analog") gra-ting s-truc-t-ures and it is alterna-tively possible to use reflection gra-tings. In many cases more -than the three cen-tral difrrac-tion orders -1, ~, ~1, for example also the + 2nd diffraction orders, can be obtained by further shifting the grating sections relative to each o-ther. However, -the -technological complexl-ty of such gra-tings then increases because a larger number of s-teps is ~then required.
Figs. 2 -to ~I show fl-lr-ther examples of cornpound phase gra-tings with suitable gra-ting s-truc-tures.
'L~`ig. 2 shows a compourlcl phase grating opera-ti.ng in transrrlissiorl, w:llose digi-ta:L gra-t:ing sec-tions~U'~I, 'U~2 yield a four-ste[) blaYe profilo (compare :~lg. 2c).
T:he grating sec-tiorls U'1, 'U'2 .havc-~ even n-umbers of s-teps per grating pe:r.iod ~, narrle:Ly foll:r.
'V:iewecl l'rorrl tlle centre towards t:he ends o:f t:he gratirlg pe:r:iocl ~ -the s-teps :in the g:ra-t:iI-lg sec-t:ioIl U~2 :have fo:L:Low:irle hcig~hts: ~, d, ~d, 9d, ..., N cl, where 2N is t:he nurnber of s-tep wiclttls pcr gra-tiIlg per.iod.~.. The s~tep hcights w-it:h-irl Ihc g:rating pori.o(l~ us va:ry in. conformi-ty P~ID.83-01l 10 5~ L~
wi-th a purely paraboLic Eunc-tion, which obviously -then also applies to the op-t:ical pa-thleng-ths. SirnilarLy, the s-teps and -the op-tical pa-thlengths in t'he grating section U'1 vary sirnilarly, because in -t'he same way as :in -the gra-ting shown in Fig. '1, it is an impression o:E -the gra-ting section U'2 (nega-tive copy).
Fig. 2b shows -the two gra-ting sec~tions'U'1~ U'2 -in a posit-ion irL Wh:iCIl -they are shiftecl by one s-tep wiclth, so that the Eollr-step op-tica] pa-thleng-t'h proEi~Le s1-sO
l shown in F:ig. 2c :i9 o'b-ta:inecl. Equations 5 -to 7 are -then valid Eor -the calcula-t:ion oE -the step heights. Ho-wever, now P = 4 (mlnl'ber o-E s-teps per grating period ~). In this case S is 2(n-1)d, as Eollows Erorn Fig. 2'b.
Figs. 3a, 'b show an example oE a compouncl phase 15 gra-ting comprising analog gra-ting sec-tions U''1, U''2, in which -the optical pathlength varies contin-uously wi-thin the grating periocl ~ as a square-law function, Eor example in tha-t -the surface proEile oE the grating section has a corresponding undulating shape.
2L Fig. 3a shows -the corresponding curves of -the phase delays ~1 and ~2 Eor -the two gra-ting sections U''1, U''2, which also vary in conEc,rmi-ty with a square-law ~Eunc~tion.
The Eollowing equa-tion is then ~alid C~ = Cg O ( ~/ ) , (8) where x is the pos:i-t:ion coorclinate in a clirection perpen-d:icu:lar -to the grating grooves, xln -the coorcl:ina-te in the cr_ntre oE the groo~es, :i.e. Eor ~/2, L being tllc grat:in~;
However, gra-tings of this -type clo not permit deflec-tion ~ith a high efficiency in other dif~rac-tion orders. This means tha-t -the dif-frac-tion order determined by the selected grating profile cannot be varied.
It is the objec-t of -the invention to provide a compound optical phase gra-ting w'hose sawtoo-th-shaped optical profile can be variecl simply, so -that at op-tion the ligh-t can be deflec-ted in different cliffrac-tion orders, -thereby enabling optical switches to be construc-ted in a simple manner.
~ ccorcling -to -t'he invention -this obJec-t is achle~ecl in tha-t the compo--lnd phase-gra-tiIlg comprises at least two gra-ting sec-t:ioILs wh:ictl are clisposecl oppos:ite one another :in para:Lle:I p:Lanes ancl WIL:;CII have g~:rooves WtLiCh e~tend parallel -to eact-l otller, in -Lhat thQ grat:ing sections have equal gra-t:ing periods ancl are movab:Le :re:Lat:Lve to each other w:ithin their ~planes in a direction perpenclicnlar to -the g:rooves, ancl :in -tt-lat over one gla-ting period -the grating prof:ile :is at :Least subs-ttarlt:ially parabol:ic and is symnle-trical re:lt~t:ive -to -the gra-ting per:iocl, -tl-le gra-ting profi:Les ~)e-ing sIlch tlLat in a symme-tr:ical pos:it-ion of th-~h. S ,~
PIID.~3-011 2 5.1.~L~
grating sections relative -to a common line perpenclicular to -the gra-ting planes -the opiical pathleng-t:h through -the com-pound grat:ing is constan-t.
I:~ the gra-ting sections are in a symme-trical 5 position relati.ve to a line which extencls perpenclicularly -to -the gra-ting planes~ -this means -that in -the case of, for exam~ple, -two grating sections :E'or example one g:ra-ting h:il:L
o:E' one g:rat:ing sec-tion is si-tuated exactly above a gra-ting hill of' t:he other gra-ting sec-tion. A:Lter:nativel.y, a grating .h:ill cLnd a grati.ng va:Lley rnay be sit-uated on t:he comrrlon lin.e whic:h ex-tends perpenclicular:Ly -to -t:he grating planes. This posi-tion o:E'-the grating sections is hereinafter :referred -to as in:i-tial posi-tion and is -the posi-tion in which t:he grating see-t:ions are no-t shi:~ted relative to eae:h other.
In -this position -the sum of -the optical pa-thlengt:h through the grating sec-tions, viewed perpendicularly -to -the grating~Lanes, is cons-tant over all the gra-ting periods.
This means -that a ligh-t beam which is incident, preferably at right angles, upon the compound hase grating is no-t influenced at all by -the grating structure of -the gra-ting sec-tions, because there is no ef~ec-tive optical grating s-tructure. As a resul-t o~ this, -the light beam is no-t def]ected; -t:he compound grating is then bla~ed for -the ~ero order. However, if -the grating sections are shif-ted rela-tive to each o-t:her by a frac-tion of -the:ir gra-ting per~.ods ou-t of the:ini-tial pos:ition, the e:~fec-tive op-tical s-truc-ture o:E' the compouncl phase g:rat:ing is also c:hangecl. Depending on the magni-t-ucle ancl t:he clirec-tion o~ the clisplacerncant O:r the gra-ting sec-t:io:ns :reLa-tive -to each o-the:r a blazecl g:rcLting s-t:ruc-t1.Lre is ~orme~l w:h:ic:h, ow:ing -to t;:he speci.a:L p:ro:E'i:Le O:e the grating soc-tions, cle:Flects an inc:iclent :L.igtlt beam in a hif,r~her o:rcler, ~'or e.Yarrlp:Le in the -~ 'Ist ror in :hi~tle:r orcle:rs.
This enables t:t-le blcn~e o:E'-t:he compo-L:Lncl ph.se g:r~t:i.ng to be sw:i-tc'hed betweerl d:i:rl'erc-~nt cl:i:r:E':rac-ti.on o:rclers, permitting it to be employed as arl op-tical swi-r;ch.
In ~a sui.tab:Le emboclirrlerl-t o:E' the i:n-ve:nt:ion t:he gra-ting sect:ions are d.if!;-i tal p:tlase g:ra-t:i:ngs, :i..e. the PIID.S3-~11 3 5.1.8ll gra-ting prof:i.le changes in a plurality o~ s-teps within one grating period. T:his may be achieved :E'or example in -tha-t a transparen-t substra-te having a constan-t refractive index is ~ormecl wi-th s-teps Or di~:E'eren-t height or in tha-t adjacen-t areas with cli~reren-t :re~rac-tive indexes are rorrnecl in a su~strate oE' constan-t -thickness. Dig-i.-tal p:hase gratings ha-ve t:he advanta{e -tha-t -they can 'be manu:E`actu:red in a com-pa:rat.i.ve:ly s:impLe mclnner and tha-t; they perm:i-t -the construc-t-ion of' cornpound p:t-l.ase g:rat:ings with a cornparatively hig'h bla~e e:~f`iciency wh:ich compol:lncl gratings d:i~:E`ract a substan-t.ia:l por-t:ion o:f the inciclent :Ligh-t iil a desired cli:E'~rac-tion order only a very srnall amoun-t o:E' light being di:i`rractecl in the acdjacen-t dif`frac-tion orders.
In ano-ther embodirnen-t the gra-ting sections comprise 5 ana:Log phase gratings whic:h may also be constructed as rel:ief and/or ref:ractive-index gra-tings. Analog phase gra-tings wi-th sui-table re~rac-tive index pro-~iles have -the advan-tage tha-t -they can be shi~-ted rela-tive -to each other in a simple manner because -they comprise -~la-t pla-tes of cons-tan-t -thickness which are superimposed. This also applies to digital re-~rac-tive-index gra-tings.
In anot:her advan-tageous em~odimen-t of -the inven-tion a gra-ting sec-tion in -the :E`orrn o~ a relief gra-ting is provided wi-th a re~lec-t:ive l.ayer on its upper surface enabling a : compound phase gra-ting -thus construc-ted -to be nsed as a re~lec-tion grat:in.g~
A pa:r-ticu:La-rly advan-tageous ernbodi.ment o~ the inverl-tion is fornrle(l by an optical swi-tch w:h:ic:h comprises a rirst op-t:ical port ancl a p:Lura]:i-ty o:E` second opt:ical ports ancl Wil:i.Cil rlurt:her coml)rises a lig:il-t-cle:i`:lecti:rlg e.Lemen-t fo:r optica:LLy connect:ing the ~i:rs-t port -to on:l.y one o:E` tile secolld po:rts. Crl t~l:is opt:ica:L sw-i.tch the :L:ig:ll-t-clef`:Lecting elerment is a compoLIncl phase g:ra-ting in accorclance ~.ith the invention and the seconcl optical ga-tes are cl:isposecl in ~t:he cent:ral di:~:~raction orclers o~ the phase-~ra~ting a-rrangerrlerlt.
Var.io~ls types o~` optical sw:i-tciles wit!lrnecilanic-al:ly rno-vecl parts are krlowl-l. For exarnp:le penca p:r:isrrls are ~2'~Z~
PHD.S3-~'l1 4 5.1.8L~
employecl (J. Minowa, ~. ~ujii, Y. Naga-ta, T. Aoyarrla, K. Doi:
Non-l~locking ~ x S op-tieal ma-trix swi-tch for fibre-op-tical comrmlnica-tion~ Electron. Le-t-ters 19SO, vol. 6, no.11, pages 422-Ll23), which prisms are moved in-to -the radiation path hy means of srnall electromagnets, de~lec-t -the beam and -thereby prov-icLe the swi-tehing aetion. Alternatively~ optieal glass fibres Inay be movecl relative -to eaeh o-ther parallel -to their encl faces (see E`or exarnple T.P. Tanaka, M. Maeda, Y. Shlrrlohori, Il. Takastlirrla, I. Kondo: Simple and reliab:Le 10 optica:L bypass swi-tcll E'or fibre-op-tie data bus app:L:ieation, 7-th European Cone. on Opt:ieal Comm.~ 198'1, Copenhagen, page 15-1), to enable eo-upling in-to differen-t :E`ibres.
Non-mee'hanieal optieal switehes ean be eonstr~Leted usintt,r magneto-optieal or eleetro-optieal e:E'feets. In prin-15 ciple, magne-to-optical swi-tches (see for example M.Shirasaki, H. Takamatsu, T. O'boka-ta: Bi-s-table magne-to op-tie swi-teh for multimode op-tieal fibre, Appl. Op-t. 21 (1982), pages 1943-Ll9) operate only wi-th polarized light and ean be used only with non-polarized light with -the aid of addi-tional, very in-tri-20 eate means. Eleetro-op-ticaL ef:~ects are utilized for switching in integra-ted op-tical -technology (see for exarnple E.M. Philipp-Rutz, R. Linares, M. Eakuda: Electro-op-tic Bragg di-fE`raetion swi-tehes in low erosstalk in-tegrated op-tic swi-tching ma-trix, Appl. Opt. 21 (1982), pages 2189-94).
In comparison with all -these op-tical swi-te'hes -the swi-teh in aeeoranee with the inven-tion has the advan-tage of a eomparati-vely simple eonstrue-tion wi-th georne-trieally prede-termined radia-tion pa-ths, only a ~Low power eonsurnp-tion -for shiE`-ting t'he grating see-tions, a low-:Loss po:la-r:ization-30 independen-t operation, and a 'h:ittrh eross-ta:Lk-atterl-lLatiorl.
It is obv:io-us that by rneans o:E' sucl-l op-t:ica:L
s-witehes it :is poss:i'ble to eonstruet arrays oE' optiea:L
switeh:irlg ma-t;rixes witll a p:l-ura:Li-ty oI' :inpllt and O~ltp~lt ports. In such matrixes eaetl inpllt and Outpllt por-t eompriSes 35 a first port oE' an op-t:ic~a:L swi-tell in aecordance W-ittl the invcntion, -thenurrlber o-f seconcl ports oE` an :input or OUtpllt sw:itch corresponcling to the nurrlber of OUt~pllt or inpllt 2~7 PIID.~3-O1'l 5 5.1.~
switches, and tihe seconcl por-ts of every inpu-t or ou-tput sw-itch -being opt:ically connectecl to a seconcl por-t of clifL'eren-t inpu-t or ou-tpu-t swi-tches. This swi-tching rna-tri~
en.bles informa-tion7 for e~ample moclulated ligh-t, -to be transm-it-tecl f-rom any of -the inpu-t por-ts -to any desired OlltpUt port, wi-tholl-t information being applied -to the other OUtp~lt por-ts.
~ nol;her acl-van-tageous emboclimen-t of -the in-ven-tion erlabLes the construc-tiorl oL~ op-tica:L concentrators -wi-th a l0 plnraLity oL' op-ticaL input ports ancl --~ srnalLer mlrnber of O~tpllt ports. In -these concen-tra-tors groups o~ input ports' are -those of an opticaL sw:L-tching matri~ in accordance wi-th -the invention, one output por-t of the concentra-tor being -the firs-t port oL` an op-tical switch according to the inven-t-ion 15 and the outp-u-t por-ts, which each form part of an op-tical switching ma-tri~, being connec-ted to a seconcl por-t of difLferent optical swi-tches.
Concen-trators of this type are used for -trans-mi-t-t-ing light which is received via a plurality of inpu-t 20 lines at option -to a specific ou-tput line, for example a trunk line, the nnrn'ber of ou-tpu-t lines being smaller than -the number of input lines. Concen-trators fur-ther have the advan-tage -tha-t -the number of second ports of the optical sw:itches can be cornparati-vely small.
~mbocliments Or -the inven-tion will now be clescribed in more cletail, by way of e~ample, wi-th reference to the clrawings, in which:
~ ig. 1a shows a compouncl pl~ase-gra-t:ing comprising two steppecd (d:igital) grating sec-tions in -tthe in:itial 30 poslt:ion, the grat:ing sec-l-ions compr:isingr an oclcl nurrlber Or steps per grat:LrLg periocl, Fig. 'I'b Sl-IOWS tt-le same com-pourlcl phase gra-t:ing in the sh:i~`-te(L position, ~ ig. 'Ic stlows tile resuLt:ing optical grat:ing 35 prori:Le oL' -tlle conlpound ~phase grating sLhown in ~ig. 'Ib, F:ig. 2a shows a compollncL pllase gra-ting comprising -two steppecl (cLig:ital) grat:inlg sectioIls ir-tLIe init:i.l:L
position, I;he grat:irllg sec-lions c~mprisin~; an i?verl nllmher P~D.S3-o11 6 5.1.84 of steps per grating period, Fig. 2b sho~s -this compound phase gra-ting in the shif-tecl posi-t:ion, Fig. 2c shows -the resulting optical gra-ting profile of tlle cornpound phase grating shown in Fig. 2b, F:ig. 3a S}lOWS -the phase pro-file of a cornpouncl phase gra-t:ing whose gra-ting sections comprise con-tinuous (analog) phaso gra-t:irlgs which are sh:Lftecl re:La-tive -to each o-ther ~y a clistance , F:ig. 3b shows -the res-u1 ting phase prof:i.1e Or the compouncl pt-Lase gra-ting shown in F:ig. 3a, Fig. ~I shows a cornpouncl phase gra-ting comprising two cligital gra-ting sec-tions, -the upper sLIrface O r one grating section being provided wi-th a reflective layer, Fig. 5 shows an optical swi-tch cornprising a com-po-lnd phase gra-ting in accorclance wi-th the inven-tion, Fig. 6 shows an op-tical swi-tching matrixcomprising a plurali-ty of optical switches, and Fig. '7 shows an op-tical concen-trator comprising 20 nine inpu-ts and -three ou-tputs.
Firstly, i-t will be illustratecl by means of the sirnple exarnple of Fig. 1 how the blaze in a compouncl -trans-mission phase gra-ting comprising two steppecl grating sections U1 and U2 can be swi-tchecl be-tween for exampLe the 25 -three cen-tral diffrac-tion orclers -1, O and -~1. The groove profiles of the two gra-ting sections U1, U2 are s-tepped surface relieL's (also referrecl Lo as cdigital surface struc-tllres), wh-ich exac-tly ma-tch ono ano-ther an{l which are made Or -the sarno rnate:r:ia'l. Onc prof:ile is an ex~c-t irnpression 30 of -the other profilo ,:i.e. a (no~at:i-ve) copy. In ttlC
origina:L sLIch proL`i:Les can bo forrrled by :LocaLLy se:Lect:ive e-tching processes. Copies of these origirl.-Ls ancl coples o:~
coples can he manu['ilc-tnrecl frorn speciL'ic pLast:ics, f<)r ex~lrnp'L~ by rn~.lns O r c. I,tlO to-po:l yrrl~r i ~a-t i O~rl :[~r Occss .
'rhe grat:ing soct:ior-ls 'Ul ancl U2 compr:iso an oclcl nLIlnbor7 for oxalrlple 5,oL'steps per ~ra-t:in~- periocl~, so -that there :is ono step of clollble w:icltll, wtlicll in a symrrletr:ica:L
arrangement may be :re~ardo(l as tho bas:ic step.
PIID.S3-0'l1 7 5.1.8L~
TlIe s-tep he-igrh-t from t:his cen-tral basi.c s-tep towarcls -the ends of -tlle gra-ting, period ~ of -tile gra-ting section U2, :E`or example comp:Lies wi-t:h:
s-tep he:iglIt = O,d,3d,6d, ...., 1/2N(N-~1).cl, (1) wlIere (2N+1) is t:he number of steps per grating periocl.
The :increasc of the s-tep :height from -the centre -towarcds -the edges i.s in p:rlnciple clefined by a parabolic law;in addition to t}-lis there is a :Iinea:r porti.on as a result of -the pre-sence o:l` the cloub:Le bas:ic step. T:he same also app:Lies -to tlIe grclt:ing section 'U1.
Thus, t:he geometric step helgh-t in the g:rating section U1 in Fig. 1a varies (frorn left to right for equal s-tep I~id-ths in -t:he cross-sec-tion in ~ig. 1a) frorn ..., 2d, O, 2d, 3d, 3d, 2d, O, 2d, ... . The geome-tric s-tep heigh-ts in -the grating sec-tion U2 are the same:
... d, 3d, d, O, O, d, 3d, d, ... .
[n order to enable a movement of the gra-ting sec-tions U~l and U2 rela-tive -to each other in a direc-tion perpendicular -to -the gra-ting grooves, -the -two gra-ting SeCtions are spaced :E`rom each ot:her by a distance 2d.
The op-tical pa-thlength s (in the -transrnission mode) 'between -the -two planes a and b, shown in broken lines, in the -two gra-ting sec-tions U1, U2 is constant in ~ig. 1a (i.e. inclependent of the ioca-tion), namely SO = (3n-~2)d (2) w'lIere n is the :refract:i-ve index o:E`-the d:ie:Lectr:i.c rna-Le:rial ancl d is the uni.t O r eeorne-t:rical s-tep tIe:igh-t This means l;hat in -the cornpou:ncl g:rat:irlg shown .in ~`ig. 'ia -the:re :is no e:E`:E`ect:i.ve optica:L. grating st:ruc-Lurc at aL:L~ i.e. t;lIe pl-Lase-g~ra-t:ing arrangelllerIt :is bl.a~ed :E`or tlle .e:ro o:rcle:r (tlIe no:rlrIcll (:I:irect:ion).
'[:r, as -is sllown :in :li`ig. 'Ib, for exarrlp:Le the g:ra-t:ing section U.l is sll:i.:rtecl by one s-top wi.dl;ll (-ty~pically app:rox. 10/l.~rrl) to tlle Left~ tt~e opt:ica.L patlIl.e7lg-tl-- s.l between the two p:lanes a an(.l b, stlown in l,:ro:ken I..:i.nes, :in t:l-~e successi-ve are<.as :L`:rom :Le:E'-t -to :ri.gtIt is:
s.l = ..,(n+Ii)d,5r~ lrl-~1)cl~(3r~-~2)(l~(2n-~3)(l~(rl~ 5ncl (~IrI-~'I)cl~... (3) PIID.S3-o-l'l c~ 5.1.c~II
TiIe op-tiea:L pa-thlerlgth clifference ~ith respec-t -to -the patlI length sO = (3n~2)d in -the successive areas is:
S1-So = ~ 2(n-1)cl~2(n-1)d~(n-1)cl~o~-(n-1) -2(n-'l)d~2(n-1)d~(n-1)d~
The op-tical pa-th1eIlg-tll prof:ile o:f t'he cornpound grating is shown :in 'Fig. 1c. I-t ~ill be seen t:hat sl (ancl s1-sO) is a reg-llar five-step pro:fi:Le having a "di~i-tal" b:Laze if the opt:iea:L step :lle.igl-lt (di:f:fererlee 'be-tl~een the phase deLays o:f two adjacent steps) is /~/5 (,i~- wave~leng-th of -the :Ligh-t).
In Fig~. 1'b t~iis op-tica:l step heig:ll-t is (n-1)cl, so that (n-'l)d = ~/5. Phase gratings wi-th sllch prof:iles are known and have al:ready 'been investiga-ted ex-tensively (see for eYamp1e H. Darnman : Spec-tral characteris-tic of s-teppecl phase gra-tings, Op-tik 53 (1979), pages L~o9_L~17; Blazed synthe-tic phase-only holograms, Op-tik 31 (197O), pages 95-1 o4) .
Frorn the same li-terature referen.ce i-t -is also kno~n -tha-t-~i-th such a five-s-tep phase profiles (grating grooves) a bla~e efficiency o:f (-theore-tically) 87.4 /0 can be aehievecl for the firs-t diffraction order, no ligh-t being 20 deflected in the adjacen-t diffraction orders. The general requiremen-t for -this is:
~ (l) - 2JL 7~ = k.2 (5) (~ = ~avelength o:f the lighti q = number of the diffrac-tion order, in -the presen-t ease: q = ~1, P = number o:f s-teps per gra-ting period ~, in -the presen-t case P = 5; k = an integer).~7(,~) is -t'he phase cle:Lay producecl in E~ 'basic s-tep o:f t:he profi1.e. .Cn accorclance w.it:h F:ig. 'Ic the co:rrespo:ncl:ing pat:h:Lengt:lI cli:fference ~= (n-'l)cl, so -t:hat it f`o:L:Lows from ~p (;~) = 2 1~ S (6) t:na t;
(n-~l)~l = (k ~ (7) Fo:r a simp:Le pract-ic<l:l e:Yarrlp'le (k=O, q='l, P=5, n-'l=0.5, m) this yie~Lcls cl=().4/urrl. Gra-ting sections w-it:h -the reqllireclrrla:.Yirrlllrll elc~-l:ing clept}l of al)proYimate:Ly 1 /nIll can be ma:n~lfact-lrecl w:it:lloilt any p:rol):lelrls.
The gratirIg sect:iorls U1, 'U2 usecl in Fii~. 1 have syrnrrI(?trical. pro:L`:i:Les. Tl-lereforo, it wi:l:l. be evide:rIt that - ~2~
PIID.~3-011 9 5.1.~
a corresponding shif-t of -the grating section U1 to the righ-t (lnstead of to the lef-t as is shown in Figo 1b)~ will yielcl a bl.aYe effect for the other first diffrac-tion order (diffractinn order =-1). Thus, by rneehanically shifting the gra-ting sections rela-tive -to each o-ther -the 'blaze effect can be switc:hed be-tween -the three cen-tral diffrac-tion orders +1, 0, -1. T:he rnagni-tude of -t:he shif-t~ which corresponds -to one step wid-th, is si-tuated typically :in the range around approxirnately -lO /uIn The grating s-tructure itself imposes a Lower lirn:it of approx:irnately 1 /um for physical/optical and technological reasons, an upper li.mit 'being imposed by -the possi'b:i.Li-t:ies of realiYing -the shif-t (requiremen-t:
simple, fas-t 7 cheap, low power consump-tion) and -the require-men-t -t:ha-t the construc-tion of -the compound gra-ting rn-us-t be compact.
~ ig. 1 shows an example of sui-table stepped ("digital~) grating structnres for the -transmission of ligh-t. However, t:here are o-ther s-ui-table digi-ta:L s-truc-tures as well as suitable continuous ("analog") gra-ting s-truc-t-ures and it is alterna-tively possible to use reflection gra-tings. In many cases more -than the three cen-tral difrrac-tion orders -1, ~, ~1, for example also the + 2nd diffraction orders, can be obtained by further shifting the grating sections relative to each o-ther. However, -the -technological complexl-ty of such gra-tings then increases because a larger number of s-teps is ~then required.
Figs. 2 -to ~I show fl-lr-ther examples of cornpound phase gra-tings with suitable gra-ting s-truc-tures.
'L~`ig. 2 shows a compourlcl phase grating opera-ti.ng in transrrlissiorl, w:llose digi-ta:L gra-t:ing sec-tions~U'~I, 'U~2 yield a four-ste[) blaYe profilo (compare :~lg. 2c).
T:he grating sec-tiorls U'1, 'U'2 .havc-~ even n-umbers of s-teps per grating pe:r.iod ~, narrle:Ly foll:r.
'V:iewecl l'rorrl tlle centre towards t:he ends o:f t:he gratirlg pe:r:iocl ~ -the s-teps :in the g:ra-t:iI-lg sec-t:ioIl U~2 :have fo:L:Low:irle hcig~hts: ~, d, ~d, 9d, ..., N cl, where 2N is t:he nurnber of s-tep wiclttls pcr gra-tiIlg per.iod.~.. The s~tep hcights w-it:h-irl Ihc g:rating pori.o(l~ us va:ry in. conformi-ty P~ID.83-01l 10 5~ L~
wi-th a purely paraboLic Eunc-tion, which obviously -then also applies to the op-t:ical pa-thleng-ths. SirnilarLy, the s-teps and -the op-tical pa-thlengths in t'he grating section U'1 vary sirnilarly, because in -t'he same way as :in -the gra-ting shown in Fig. '1, it is an impression o:E -the gra-ting section U'2 (nega-tive copy).
Fig. 2b shows -the two gra-ting sec~tions'U'1~ U'2 -in a posit-ion irL Wh:iCIl -they are shiftecl by one s-tep wiclth, so that the Eollr-step op-tica] pa-thleng-t'h proEi~Le s1-sO
l shown in F:ig. 2c :i9 o'b-ta:inecl. Equations 5 -to 7 are -then valid Eor -the calcula-t:ion oE -the step heights. Ho-wever, now P = 4 (mlnl'ber o-E s-teps per grating period ~). In this case S is 2(n-1)d, as Eollows Erorn Fig. 2'b.
Figs. 3a, 'b show an example oE a compouncl phase 15 gra-ting comprising analog gra-ting sec-tions U''1, U''2, in which -the optical pathlength varies contin-uously wi-thin the grating periocl ~ as a square-law function, Eor example in tha-t -the surface proEile oE the grating section has a corresponding undulating shape.
2L Fig. 3a shows -the corresponding curves of -the phase delays ~1 and ~2 Eor -the two gra-ting sections U''1, U''2, which also vary in conEc,rmi-ty with a square-law ~Eunc~tion.
The Eollowing equa-tion is then ~alid C~ = Cg O ( ~/ ) , (8) where x is the pos:i-t:ion coorclinate in a clirection perpen-d:icu:lar -to the grating grooves, xln -the coorcl:ina-te in the cr_ntre oE the groo~es, :i.e. Eor ~/2, L being tllc grat:in~;
3~ periocl and ~ yO -the rnaxirnuln o-r m:in:irn-lnrl phase.
Ti~e g-ra-t;:irLg section 'U2 Eor examp:Le compl:ies w:ith ~2 = ~ (:in the non-sh:iL`tecL position)~ so ttla-l; the grat:ing S r3 C t:ion 'U 1 rn L l s t co m p Ly w :i th ~ I?:ig. 3a these two prori:Les are shown supc~:rirllposecl~ shii`-te(l b-~ a cl:is-tancc~
re:lat:ive to each ottler~ ancl Fig. 3b shows -tl-le resu:Lting pl~ase proEi:Le ~1 +'-~'2 ~rlliS p~-asr~ I~rofiLe CP1 ~ ~2 I~;LS tl~
well- known sawtootl-l-stlape~cl'b:La~e p:roL'i:Le. The"cl-iEErac-tion"
angle oE -th-is proEiLe c'an bc acljllsted by a su:it~lbLe cho:icr_ P~ID.~3-011 '11 5.'l.S~
of tlle s~lift~ . Thus, i-t is possible -to select for ~hich cen-traL diffrac-tion order -t'he 'blaze effec-t occurs~ For a specific diffrac-tion order -the necessary shif-t depencls on tl1e max:imurn phase shift yO. The necessary shift c~ decreases as this phase-;~O increases. mus-t be small in comparison with ~ , because an excessive slope of -the edges of -the sawtoo-th profile rnus-t 'be avoided. ~or example, ~or yO = 2 a shit`t ~ of` approximate:Ly 1/8 ~ is req-uired in orcler to obtairl the bla~e for -the firs-t order.
Analog phase gra-tings with -parabo:lic phase profile, cc~n 'be construc-ted 'by means oE' relief grati,ngs or refrac-t:ive-index gratings. In any case the optical pa-th-leng-th difference be-tween the centre and -the encls of a gra-ting period rmlst be greater -than -the wavelength ~of -the incident ligh-t wave if -the bla~e must be obtained for a shift of 1/8 of -the gra-ting period. In the case of relief gratings the surface is rnodulated -to such an ex-ten-t that the periodic phase shif-t of -the incident light wave is obtained by a varia-tion in the -thickness of -the layer of a rna-terial wi-th a homogeneous refrac-tive index n. Relief gra-tings can be manufac-tured cheaply by embossing plastics plates~ -the die being made of a hard metal by reac-tive spu-tter etching. The shape of -the die is con-trolled by a suitable set-ting of the press-ure oC -the reac-tive gas, -the energy and -the angle of incidence of the sputter ions (Ar+), and -the rnask profile.
A rnethocl whicll is less s-usceptible -to faul-ts is the (pi,e~oel,ec-tric shift:ing of plane-paral:Lel plates 'hav:ing an arlalog refrac-ti-ve-inclex grating s-truc-tLIre. The maxirrll:lm index step wi-ttl:in il g~rati,rlg -period mus-t be greater ttlan t'he qlloti,ent oL` the p:late -th,i,ckness d ancl the wa-ve:Lengti (approx. 1.5~/cl). For a pla-te th:ickrless of d = 'I mrrl-the :incLex s-tep mu s-t be at Leas-t '1.5 . 'IO 3 .
-[t is known -tha-t when Illanut`.acturirlg synthetic crys-ta:Ls in accorclance W:itLI the C~ochraLsk:i-llle-tL-Iocl-ttle refractive inclex can be :inf:L~Iencecl :Loca:L:Ly 'by nleans of externa:L eiLectric f:i,eLcls, By e'1ectron transport processes an inclex gra-ting wi-tll contro'l:l,oble refract:i,ve i~1d(?x pro-f'iLe 2~
PllD.o3-011 12 5~1.oLL
is formecl itl the crys-tal by periodically varying -the electric cnrrent during -the crys-tal growth. From -t'his crys-tal p:Lates with a suitable geometry ancl a substan-tially congruen-t gra-ting s-tructure can be cu-t.
~ simi:Lar me-t'hod is -the doping of ma-terials wi-th impur:ities e:ither by ion 'bombardmen-t, which is modulated periodicaLly by sui-table mask profiles, or by therrnal dirfusion of impuri-t-ies which are depos:ited on t'he surface of the transpQrent e'Lectro-o-p-tica:L crystals :in suitable concentra-t:ions. Again -the para'bolic refractive-inclex profi:Le can be formed in a con-trolled manner by means of a sui-ta'ble mask profile and thro-ugh -the diffusion dep-ths of -the irnpuri-t:ies - which de-pend on -the diffl~sion -time as a subs-tantia'lly square-:Law function.
Fig. ~I shows an exarnple of a componnd phase gra-ting with adjus-table 'bla~e, which opera-tes in -t'he reflec-tion mode and whose grating sec-tions 'U'''1, U'''2 are digital s-tepped gra-tings. The grating section U'''1 is a transmission phase grating cornprising five steps per gra-ting period ~ , whilst -the gra-ting section Ul''2 is a five-step digi-tal grating, whose surface is provided wi-th a light-reflec-ting layer. The structures of these gra-ting sections correspond -tothe s-truc-tures of -the phase gra-tings described with reference to Fig. 1. However, as a resul-t of -the reflec-tion from the grating section U~'2 and -the conseqnent repea-ted passage of -the ligh-t -throngh the gra-ting sec-tion 'U'''1 differerl-t s-tep heights a:re o'b-tained.
In general:
(n-'l)~ 0 = ~ 3) where /~ is -the wave:Leng-th Or -the :L-ight, _ is l;he refracti-ve index, ancl ~ -the step helghl; of the gratirlg sect:ion of 'U~'''l, ancl cl -tho step heigllt of tlle gra-t-irlg sect:ion 'U'''2.
~or shifl;il-lg -the g~ra-t:ing sections ShOWII in F:igures 1 to ll pie70 e:Lec-tr:ic ac-tu.lt:ions are par-ticLI:Larly s~litable~ which actlLators have ex-tremely :lo~ switch:ing powers (~.'lO 5 J pe:r stlif-t) ancl h:igll swi-tching freclLLencies ( > 1 ~c:l:l~ ) .
PIID.83-011 13 5,'l.~' By means o~ compound phase gratin,,s wi-th mechanical:Ly acljustabLe blaze it is possible -to construct optical switches 9 Fig. 5 by way Or e.Yample illustrates -the principle o~ such an op-tical swi-tch, by rneans o~ which a glass fibre 'I can be optically connec-ted to one o~ -three fur-tller g:lass E`ibres 2, 3, ~L-. Op-tically eonnec-ted means tha-t a pa-th is pro-viclecl ror -the op-tical signals which propagate in the grlass fibres.
In -the sw-i-tctl sho-wn in '~ig. 5 the encl face '1' of lO ~Ghe glass E~ihre 1 (E':irs-t optical port) is irrlaged on -tho end ~ace 2 t ( seconcl op-tical por-t) of` a second glass fi'bre 2 by an irrlaging system cornprising t-wo convex lenses 5 and 6, so that an optical connec-tion (an optical pa-t'h) is esta-b:Lished be-tween the two ~ibres 'I ancl 2. By incl-lcling a l5 transmission phase grat-ing 7 comprising -two grating sections "o and 9 which are rnovahle relative -to each other and arranged between the two lenses 5 and 6, it is possible to select the second glass fibre 2 of a group o~ -three glass fibrds 2, 3, Ll which are arranged a-t the location of -the 20 three central diffraction orders -~1, O, -1 and have end faces 2', 3', LL I . As explained in the ~oregoing, -the blaze oE` the grating can be switched mechanically bet~een the three central difrrac-tion orders, for example by means o~ a piezo-electric actuator 10. In Fig. 5 it is assumed that -this 25 b:Laze has been set to -the -'Is-t difE`raction order.
The opt:ical signals in -the glass fibres (~ig. 5) can travel E`rom the :Iert to the right or E`rom tt-le r:ight -to the left. In -the ~irst case the op-t:ica:L sw:i-tch carl connect an optical :inpllt channe:L -to any one Or -three o~ltpllt chanrlels, 30 wh:i:Lst in the Ottlor case one oE' tllree input channe:Ls is connected -to arl outI)-It channeL.
I~l-lerl a rerlect:ion gratirl,g (ror exalrlp:lo as showrl in F:ig.~ is -usocl-tlle second Iens in the arrallgelrlerlt shown in '~:ig. 5 may be cl:ispensocl w:ith. ~:LI the g:Lass ~:ihres aro 35 Lhen d:isposecl on one sido; the gra-tin~,r is sL:ightLy inclirLed.
t~:ig. 6 scherrla-t:ically shows how an o-pt-icaL
switchirlg matr-iY l)etween three :input ancl output ports PilD.S3-0'l1 1~L 5.1.æ4 (ror example glass L'ibre encl-faces 11~, 127 7 'l3' ancl 1~', 15', l6' (can be ~ormecL'by means o~ 6 op-tical swi-tches 11-'l6 each having three switching posi-tions -1, 0, ~'l.
Each Or -the :inp-u-t ancl output por-ts 117-16', a-t different -times, corresponds -to -the first optical port 1' of the op-tical switch shown in Fig. ~. It can be seen-tLlat for establishing a connection (for example, be-tween the fibres 'l1'' and 15'') -the gra-ti,ng switches 11 and 15 must be se-t to -the correc-t posi-ti,ons. It follows -tha-t the crosstalk in a swi-tch may be compara-tively high. For example, if in a switch 2% is deflec-ted -to -the "wrong"fibre, -the crosstalk at-tenua-tion of the sw;-tching matrix remains ~10 3 or ~30 dB.
Fig. 7 fin,ally shows how an op-tical concen-tra-tion comprising nine inputs and three ou-tpu-ts in -total can be formed b-y means of, for e~ample, -three optical swi-tching ma-tri~e,s 17, 18, 19 as shown in Fig. 6 and three separate o ~ C 6 ~
switches 20, 21, 22, corresponcLing to -the switches 1~, 15~ 16 as shown in Fig. ~. A group of -three inputs is then connec-ted -to an optical switching matrix as shown in Fig. 6. Each inpu-t line E can be connec-ted -to any output line A. This concen-trator can be called a concen-tra-tor in -the -full beam. In a similar manner concentrators eornprising more -than nire inpu-ts or more -than three outpu-ts can be cons-tructed, a suitable arrangemen-t also permit-ting in-complete 'beams -to be for7rlecL, in which case aninput cannot be switched to every ou-tput.,
Ti~e g-ra-t;:irLg section 'U2 Eor examp:Le compl:ies w:ith ~2 = ~ (:in the non-sh:iL`tecL position)~ so ttla-l; the grat:ing S r3 C t:ion 'U 1 rn L l s t co m p Ly w :i th ~ I?:ig. 3a these two prori:Les are shown supc~:rirllposecl~ shii`-te(l b-~ a cl:is-tancc~
re:lat:ive to each ottler~ ancl Fig. 3b shows -tl-le resu:Lting pl~ase proEi:Le ~1 +'-~'2 ~rlliS p~-asr~ I~rofiLe CP1 ~ ~2 I~;LS tl~
well- known sawtootl-l-stlape~cl'b:La~e p:roL'i:Le. The"cl-iEErac-tion"
angle oE -th-is proEiLe c'an bc acljllsted by a su:it~lbLe cho:icr_ P~ID.~3-011 '11 5.'l.S~
of tlle s~lift~ . Thus, i-t is possible -to select for ~hich cen-traL diffrac-tion order -t'he 'blaze effec-t occurs~ For a specific diffrac-tion order -the necessary shif-t depencls on tl1e max:imurn phase shift yO. The necessary shift c~ decreases as this phase-;~O increases. mus-t be small in comparison with ~ , because an excessive slope of -the edges of -the sawtoo-th profile rnus-t 'be avoided. ~or example, ~or yO = 2 a shit`t ~ of` approximate:Ly 1/8 ~ is req-uired in orcler to obtairl the bla~e for -the firs-t order.
Analog phase gra-tings with -parabo:lic phase profile, cc~n 'be construc-ted 'by means oE' relief grati,ngs or refrac-t:ive-index gratings. In any case the optical pa-th-leng-th difference be-tween the centre and -the encls of a gra-ting period rmlst be greater -than -the wavelength ~of -the incident ligh-t wave if -the bla~e must be obtained for a shift of 1/8 of -the gra-ting period. In the case of relief gratings the surface is rnodulated -to such an ex-ten-t that the periodic phase shif-t of -the incident light wave is obtained by a varia-tion in the -thickness of -the layer of a rna-terial wi-th a homogeneous refrac-tive index n. Relief gra-tings can be manufac-tured cheaply by embossing plastics plates~ -the die being made of a hard metal by reac-tive spu-tter etching. The shape of -the die is con-trolled by a suitable set-ting of the press-ure oC -the reac-tive gas, -the energy and -the angle of incidence of the sputter ions (Ar+), and -the rnask profile.
A rnethocl whicll is less s-usceptible -to faul-ts is the (pi,e~oel,ec-tric shift:ing of plane-paral:Lel plates 'hav:ing an arlalog refrac-ti-ve-inclex grating s-truc-tLIre. The maxirrll:lm index step wi-ttl:in il g~rati,rlg -period mus-t be greater ttlan t'he qlloti,ent oL` the p:late -th,i,ckness d ancl the wa-ve:Lengti (approx. 1.5~/cl). For a pla-te th:ickrless of d = 'I mrrl-the :incLex s-tep mu s-t be at Leas-t '1.5 . 'IO 3 .
-[t is known -tha-t when Illanut`.acturirlg synthetic crys-ta:Ls in accorclance W:itLI the C~ochraLsk:i-llle-tL-Iocl-ttle refractive inclex can be :inf:L~Iencecl :Loca:L:Ly 'by nleans of externa:L eiLectric f:i,eLcls, By e'1ectron transport processes an inclex gra-ting wi-tll contro'l:l,oble refract:i,ve i~1d(?x pro-f'iLe 2~
PllD.o3-011 12 5~1.oLL
is formecl itl the crys-tal by periodically varying -the electric cnrrent during -the crys-tal growth. From -t'his crys-tal p:Lates with a suitable geometry ancl a substan-tially congruen-t gra-ting s-tructure can be cu-t.
~ simi:Lar me-t'hod is -the doping of ma-terials wi-th impur:ities e:ither by ion 'bombardmen-t, which is modulated periodicaLly by sui-table mask profiles, or by therrnal dirfusion of impuri-t-ies which are depos:ited on t'he surface of the transpQrent e'Lectro-o-p-tica:L crystals :in suitable concentra-t:ions. Again -the para'bolic refractive-inclex profi:Le can be formed in a con-trolled manner by means of a sui-ta'ble mask profile and thro-ugh -the diffusion dep-ths of -the irnpuri-t:ies - which de-pend on -the diffl~sion -time as a subs-tantia'lly square-:Law function.
Fig. ~I shows an exarnple of a componnd phase gra-ting with adjus-table 'bla~e, which opera-tes in -t'he reflec-tion mode and whose grating sec-tions 'U'''1, U'''2 are digital s-tepped gra-tings. The grating section U'''1 is a transmission phase grating cornprising five steps per gra-ting period ~ , whilst -the gra-ting section Ul''2 is a five-step digi-tal grating, whose surface is provided wi-th a light-reflec-ting layer. The structures of these gra-ting sections correspond -tothe s-truc-tures of -the phase gra-tings described with reference to Fig. 1. However, as a resul-t of -the reflec-tion from the grating section U~'2 and -the conseqnent repea-ted passage of -the ligh-t -throngh the gra-ting sec-tion 'U'''1 differerl-t s-tep heights a:re o'b-tained.
In general:
(n-'l)~ 0 = ~ 3) where /~ is -the wave:Leng-th Or -the :L-ight, _ is l;he refracti-ve index, ancl ~ -the step helghl; of the gratirlg sect:ion of 'U~'''l, ancl cl -tho step heigllt of tlle gra-t-irlg sect:ion 'U'''2.
~or shifl;il-lg -the g~ra-t:ing sections ShOWII in F:igures 1 to ll pie70 e:Lec-tr:ic ac-tu.lt:ions are par-ticLI:Larly s~litable~ which actlLators have ex-tremely :lo~ switch:ing powers (~.'lO 5 J pe:r stlif-t) ancl h:igll swi-tching freclLLencies ( > 1 ~c:l:l~ ) .
PIID.83-011 13 5,'l.~' By means o~ compound phase gratin,,s wi-th mechanical:Ly acljustabLe blaze it is possible -to construct optical switches 9 Fig. 5 by way Or e.Yample illustrates -the principle o~ such an op-tical swi-tch, by rneans o~ which a glass fibre 'I can be optically connec-ted to one o~ -three fur-tller g:lass E`ibres 2, 3, ~L-. Op-tically eonnec-ted means tha-t a pa-th is pro-viclecl ror -the op-tical signals which propagate in the grlass fibres.
In -the sw-i-tctl sho-wn in '~ig. 5 the encl face '1' of lO ~Ghe glass E~ihre 1 (E':irs-t optical port) is irrlaged on -tho end ~ace 2 t ( seconcl op-tical por-t) of` a second glass fi'bre 2 by an irrlaging system cornprising t-wo convex lenses 5 and 6, so that an optical connec-tion (an optical pa-t'h) is esta-b:Lished be-tween the two ~ibres 'I ancl 2. By incl-lcling a l5 transmission phase grat-ing 7 comprising -two grating sections "o and 9 which are rnovahle relative -to each other and arranged between the two lenses 5 and 6, it is possible to select the second glass fibre 2 of a group o~ -three glass fibrds 2, 3, Ll which are arranged a-t the location of -the 20 three central diffraction orders -~1, O, -1 and have end faces 2', 3', LL I . As explained in the ~oregoing, -the blaze oE` the grating can be switched mechanically bet~een the three central difrrac-tion orders, for example by means o~ a piezo-electric actuator 10. In Fig. 5 it is assumed that -this 25 b:Laze has been set to -the -'Is-t difE`raction order.
The opt:ical signals in -the glass fibres (~ig. 5) can travel E`rom the :Iert to the right or E`rom tt-le r:ight -to the left. In -the ~irst case the op-t:ica:L sw:i-tch carl connect an optical :inpllt channe:L -to any one Or -three o~ltpllt chanrlels, 30 wh:i:Lst in the Ottlor case one oE' tllree input channe:Ls is connected -to arl outI)-It channeL.
I~l-lerl a rerlect:ion gratirl,g (ror exalrlp:lo as showrl in F:ig.~ is -usocl-tlle second Iens in the arrallgelrlerlt shown in '~:ig. 5 may be cl:ispensocl w:ith. ~:LI the g:Lass ~:ihres aro 35 Lhen d:isposecl on one sido; the gra-tin~,r is sL:ightLy inclirLed.
t~:ig. 6 scherrla-t:ically shows how an o-pt-icaL
switchirlg matr-iY l)etween three :input ancl output ports PilD.S3-0'l1 1~L 5.1.æ4 (ror example glass L'ibre encl-faces 11~, 127 7 'l3' ancl 1~', 15', l6' (can be ~ormecL'by means o~ 6 op-tical swi-tches 11-'l6 each having three switching posi-tions -1, 0, ~'l.
Each Or -the :inp-u-t ancl output por-ts 117-16', a-t different -times, corresponds -to -the first optical port 1' of the op-tical switch shown in Fig. ~. It can be seen-tLlat for establishing a connection (for example, be-tween the fibres 'l1'' and 15'') -the gra-ti,ng switches 11 and 15 must be se-t to -the correc-t posi-ti,ons. It follows -tha-t the crosstalk in a swi-tch may be compara-tively high. For example, if in a switch 2% is deflec-ted -to -the "wrong"fibre, -the crosstalk at-tenua-tion of the sw;-tching matrix remains ~10 3 or ~30 dB.
Fig. 7 fin,ally shows how an op-tical concen-tra-tion comprising nine inputs and three ou-tpu-ts in -total can be formed b-y means of, for e~ample, -three optical swi-tching ma-tri~e,s 17, 18, 19 as shown in Fig. 6 and three separate o ~ C 6 ~
switches 20, 21, 22, corresponcLing to -the switches 1~, 15~ 16 as shown in Fig. ~. A group of -three inputs is then connec-ted -to an optical switching matrix as shown in Fig. 6. Each inpu-t line E can be connec-ted -to any output line A. This concen-trator can be called a concen-tra-tor in -the -full beam. In a similar manner concentrators eornprising more -than nire inpu-ts or more -than three outpu-ts can be cons-tructed, a suitable arrangemen-t also permit-ting in-complete 'beams -to be for7rlecL, in which case aninput cannot be switched to every ou-tput.,
Claims (15)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A compound blazed optical phase grating, charac-terized in that it comprises at least two grating sections which are disposed opposite one another in parallel planes and which have grooves which extend parallel to each other, the grating sections have equal grating periods and are movable relative to each other within their planes in a direction perpendicular to the grooves, and over one grat-ing period, the grating profile is at least substantially parabolic and is symmetrical relative to the grating per-iod, the grating profiles being such that in a symmetrical position of the grating sections relative to a common line perpendicular to the grating the optical path length through the compound grating is constant.
2. A compound phase grating as claimed in Claim 1, characterized in that in the grating sections are digital phase gratings.
3. A compound phase grating as claimed in Claim 1, characterized in that the grating sections are analog phase gratings.
4. A compound phase grating as claimed in Claim 2, characterized in that the grating sections are constructed as relief and/or refractive-index gratings.
5. A compound phase grating as claimed in Claim 4, characterized in that a grating section in the form of a relief grating is provided with a reflective layer on one surface.
6. A compound phase grating as claimed in Claim 2, characterized in that the number of grating steps within one grating period is odd and the optical pathlength varies from grating step to grating step in conformity with a parabolic function on which a linear portion is superposed.
7. A compound phase grating as claimed in Claim 2, characterized in that the number of grating steps within one grating period is even and the optical pathlength varies from grating step to grating step as a purely para-bolic function.
8. A compound phase grating as claimed in Claim 1, 2 or 3, characterized in that a piezo-electric actuator is used for shifting the grating sections.
9. An optical switch, comprising a first optical port and a plurality of second optical ports, and a light-deflecting element for optically connecting the first port to one of the second ports, characterized in that the light-deflecting element comprises a compound phase-grating as claimed in Claim 1, and the second ports are positioned in the central diffraction orders of the compound phase grating.
10. An optical switching matrix comprising a plural-ity of optical input and output ports, characterized in that each input port and output port is a first port of an optical switch as claimed in Claim 9, the number of second ports of an input or output switch corresponds to the number of input or output switches, and each second port forming part of one of the input or output switches may optically be connected to a second port of different output or input switches.
11. An optical concentrator comprising a number of optical input ports and a smaller number of output ports, characterized in that groups of input ports may constitute those of an optical switching matrix as claimed in Claim 10, an output port of the concentrator is the first port of the optical switch, and the output port which form part of an optical switching matrix each time connected to a second port of different optical switches.
12. An optical switch as claimed in Claim 10 or 11, characterized in that the number of input ports is equal to the number of output ports.
13. An optical switch as claimed in Claim 9, 10 or 11, characterized in that the optical ports are the end faces of optical fibre guides.
14. A compound phase grating as claimed in Claim 3, characterized in that the grating sections are constructed as relief and/or refractive-index gratings.
15. A compound phase grating as claimed in Claim 14, characterized in that a grating section in the form of a relief grating is provided with a reflective layer on one surface.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE19833303623 DE3303623A1 (en) | 1983-02-03 | 1983-02-03 | OPTICAL PHASE GRID ARRANGEMENT AND SWITCHING DEVICES WITH SUCH AN ARRANGEMENT |
| DEP3303623.3 | 1983-02-03 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1242907A true CA1242907A (en) | 1988-10-11 |
Family
ID=6189932
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000446587A Expired CA1242907A (en) | 1983-02-03 | 1984-02-02 | Compound optical phase grating and switching devices comprising such a grating |
Country Status (5)
| Country | Link |
|---|---|
| US (2) | US4585307A (en) |
| EP (1) | EP0121270B1 (en) |
| JP (1) | JPS59143110A (en) |
| CA (1) | CA1242907A (en) |
| DE (2) | DE3303623A1 (en) |
Families Citing this family (28)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3543179A1 (en) * | 1985-12-06 | 1987-06-11 | Philips Patentverwaltung | OPTICAL TRAVEL SENSOR WITH A FILTER |
| US4999234A (en) * | 1987-08-10 | 1991-03-12 | Polaroid Corporation | Holographic optical data storage medium |
| US4888260A (en) * | 1987-08-10 | 1989-12-19 | Polaroid Corporation | Volume phase reflection holograms and methods for fabricating them |
| US5089835A (en) * | 1989-02-28 | 1992-02-18 | Canon Kabushiki Kaisha | Phase-type diffusing plate |
| US5227915A (en) * | 1990-02-13 | 1993-07-13 | Holo-Or Ltd. | Diffractive optical element |
| JPH0834532B2 (en) * | 1990-05-15 | 1996-03-29 | キヤノン株式会社 | Color image reader |
| US5161045A (en) * | 1990-06-28 | 1992-11-03 | The United States Of America As Represented By The Secretary Of The Air Force | Large field of view light beam transceiver having small motion of optics |
| US5113286A (en) * | 1990-09-27 | 1992-05-12 | At&T Bell Laboratories | Diffraction grating apparatus and method of forming a surface relief pattern in diffraction grating apparatus |
| DE69311638T2 (en) * | 1992-07-15 | 1998-01-22 | Nippon Telegraph & Telephone | Optical switch |
| US5255332A (en) * | 1992-07-16 | 1993-10-19 | Sdl, Inc. | NxN Optical crossbar switch matrix |
| US5537252A (en) * | 1993-12-23 | 1996-07-16 | Xerox Corporation | Double blazed binary diffraction optical element beam splitter |
| US6480334B1 (en) * | 1994-01-18 | 2002-11-12 | Massachusetts Institute Of Technology | Agile beam steering using phased-array-like elements |
| US6404553B1 (en) * | 1994-02-07 | 2002-06-11 | Engineered Support Systems, Inc. | Phase active diffractive optical method |
| US5687264A (en) * | 1995-08-24 | 1997-11-11 | Sandia Corporation | Apparatus for injecting high power laser light into a fiber optic cable |
| US5982545A (en) * | 1997-10-17 | 1999-11-09 | Industrial Technology Research Institute | Structure and method for manufacturing surface relief diffractive optical elements |
| GB9811195D0 (en) * | 1998-05-22 | 1998-07-22 | Sira Ltd | Diffractive optical element |
| JP4336412B2 (en) * | 1998-06-16 | 2009-09-30 | キヤノン株式会社 | Diffractive optical element and optical system using the same |
| AU2001237168A1 (en) | 2000-02-22 | 2001-09-03 | Light Management Group Inc. | Acousto-optical switch for fiber optic lines |
| DE60330521D1 (en) * | 2002-04-04 | 2010-01-28 | Canon Kk | Diffractive optical element with a variety of diffraction gratings and optical system |
| US7189497B2 (en) * | 2002-07-24 | 2007-03-13 | Intel Corporation | Method for writing a planar waveguide having gratings of different center wavelengths |
| WO2005012948A2 (en) * | 2003-08-04 | 2005-02-10 | Yissum Research Development Company Of The Hebrew University Of Jerusalem | Stable dielectric gratings implemented by composition striations in paraelectric crystals |
| US20080031627A1 (en) * | 2006-08-04 | 2008-02-07 | Smith Irl W | Optical communication system |
| US7989250B2 (en) | 2007-04-06 | 2011-08-02 | Rosemount Aerospace Inc. | Membrane grating for beam steering device and method of fabricating same |
| US7566173B2 (en) * | 2007-07-09 | 2009-07-28 | Alcon, Inc. | Multi-spot ophthalmic laser probe |
| US8116632B2 (en) * | 2007-11-30 | 2012-02-14 | Raytheon Company | Space-time division multiple-access laser communications system |
| AU2010325048B2 (en) * | 2009-11-24 | 2015-04-02 | Alcon Inc. | Single-fiber multi-spot laser probe for ophthalmic endoillumination |
| CN102655906B (en) * | 2009-12-15 | 2015-03-25 | 爱尔康研究有限公司 | Multi-spot laser probe |
| US10245181B2 (en) | 2012-12-21 | 2019-04-02 | Alcon Research, Ltd. | Grin fiber multi-spot laser probe |
Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS4824480U (en) * | 1971-07-17 | 1973-03-22 | ||
| DE2316248A1 (en) * | 1973-03-31 | 1974-10-10 | Leitz Ernst Gmbh | PHOTOELECTRIC STEPPER |
| DE2747243A1 (en) * | 1977-10-21 | 1979-04-26 | Philips Patentverwaltung | Diffraction grating for prodn. of colour components - has staged profile with selected peak valve for each stage |
| NL7714270A (en) * | 1977-12-22 | 1979-06-26 | Nederlanden Staat | DEVICE FOR COUPLING AT LEAST THREE LIGHT GUIDES. |
| US4360251A (en) * | 1979-11-02 | 1982-11-23 | Rajchman Jan A | Display device and method utilizing phase gratings |
| DE3118582A1 (en) * | 1981-05-11 | 1982-12-02 | Philips Patentverwaltung Gmbh, 2000 Hamburg | Optical coupler |
-
1983
- 1983-02-03 DE DE19833303623 patent/DE3303623A1/en not_active Withdrawn
-
1984
- 1984-01-27 US US06/574,775 patent/US4585307A/en not_active Expired - Fee Related
- 1984-01-31 DE DE8484200125T patent/DE3463185D1/en not_active Expired
- 1984-01-31 JP JP59015963A patent/JPS59143110A/en active Pending
- 1984-01-31 EP EP84200125A patent/EP0121270B1/en not_active Expired
- 1984-02-02 CA CA000446587A patent/CA1242907A/en not_active Expired
-
1985
- 1985-11-21 US US06/800,576 patent/US4679901A/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| US4679901A (en) | 1987-07-14 |
| US4585307A (en) | 1986-04-29 |
| EP0121270A1 (en) | 1984-10-10 |
| DE3303623A1 (en) | 1984-08-09 |
| EP0121270B1 (en) | 1987-04-15 |
| DE3463185D1 (en) | 1987-05-21 |
| JPS59143110A (en) | 1984-08-16 |
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