CA2201371C - Raman fibre laser, bragg fibre-optical grating and method for changing the refraction index in germanium silicate glass - Google Patents

Abstract

The invention pertains to laser technology, fibre optics and integrated optics and has industrial applicability in the field of fibre-optical and waveguide elements made from germano-silicate glass, in particular in fibre-optical Bragg and long-period gratings, dispersion compensators, integrated optical waveguides and so forth. The invention solves the problem of simplifying Raman fibre-optical lasers operating at wavelengths of 1.24 µm and 1.48 µm and enhancing the efficiency of the radiation conversion associated with Raman scattering. The 1.24 µm laser comprises a pumping source (1), a fibre-optical waveguide (2) containing 1-30 Mol % P2O5; sections of the fibre-optical waveguide containing 11-39 Mol % GeO2 form Bragg fibre-optical gratings (3, 4). The grating (3) forms an opaque dispersion mirror of an optical resonator for a first Stokes component, while the grating (4) is an output dispersion mirror for the same resonator; the first Stokes component issues at the output. In the 1.48 µm Raman fibre-optical laser, the second Stokes component issues at the output. The refractive index in the section of fibre-optical waveguide (11) is altered by directing 270-390 nm laser radiation (12) onto the section, said radiation passing through the protective polymer sheath of the fibre-optical waveguide (11).

Description

~20 ~ 37 ~

RAMAN FIBRE LASER, BR~4GG FIBRE-OPTICAL GRATl~G
METEIOD FOR CHANI~IN13 THE REFRACTION INDEX IN
GERMhNlUM SILICATE GLASS

1. FIEL~ OF THE IN~ENTION
The~e inve~ti~ relate to the ~pherc of the laser technology7 ~e ~bre and ~ntegrated ~ptics.

2. DESCRlPTION OF THE REiLATEI~ ~RT
A ~?~m~n fibre laser is known r~ ~ waYelt~ngth h =1.48 mc and c~nn~.~in~ a ~bre li~ht guide based aql SiO2 + Ge(~ as the actiYc me~ n, an yl~ laser ~.";lt;.~ in the wavel~ngth 1.117 mc as ~G ~ ;n~ source, and S Bragg fibrc-op~cal ~ratin~ aS the ~ ~uLed rcflectors fa~ waYcl~ngth~
of 1.175 mc~ 1.24 mc, 1.31 mc, 1.40 mc a~d 1.48 that faqm, r~iLisrcly, 5 res~n~t~ for 1st, 2nd, 3d, 4th and ~th Stokcs components of R~ n (stlm~ t~l cc~mhin~ti~ S.G. Gnibb, T. S~ , W.Y. Cheung, W.~ Reed, ~ h~ri, T. Erdogan, P.J. I~airc, A.M VG.~ C) J.
DiGiovanni, :~.W. Pcck~7~m, B.E. Rocl~hey. High-Powcr 1.48 mc C~cr~defl R~m~m I,aser in Ce~ te Fibrcs. Optical Amp. and Their A~pl., 20 ~avos, USA, 1~-17 J~mc 199~, p 197-1991l.
The &~w~aGks of this lascr is its cc~ln~le~ity c~s~l by the neccssity to ~
five pails of Bra~ tin~C and a relativcly low effif~ency of c~verting the radiation into ~th Stokes coqnponent. Fu~he~nore, Bragg ~i-t;.~c do not have a s~ irnt dcpth ~the refraction index modulation.
AR~m~nfibre~erell7;L~ gwavel~n~ = 1.48mc, coi.~ )gafibre light g~de based on SiO2 + GeO2 as thc ac~ve medium, a solid body 1ase~
CJII;~ g in the wave1engt1~ of about 1 mc as the ~Ir~ ~ solIrce, and 6 Bragg fibre-~ptical ~til~gS as the d;~ll~uled reilcctoqs for wavcleng~.~ of 1.117 mc, 1.175 mc, 1.24 mc, 1.31 mc, 1.40 mc a~d 1.48 mc that f~m, rc~pcctively, 5 30 rest n~to~ fc~ 1st, 2nd, 3d, 4th, 5th and 6th Stokes c~poncnts of R~man sc~tt~ing, ix known lS.G. Gr~b, T. Sha~r, W.Y. Chclmg, W.A. Recd, V.
M-i7.h~ri, T. Erdogan, P.J. Lem~c, A.M.Ven~-~r, D.J. DiGiovaImi, r}.W.

~2 2 0 1! 3 7 1 Peçkhan~ B.H. Rockhey. EIigh-Power 1.4~ mc C~ded R$man ~in C~-...a~ . Silic~tGFl~res. OpticalAmpl. andTharAppl., Davos~ USA, 15-17 June 1995, p. 197-1~9l.
T~e drawbacl~s of t~is laser is its comrl~xity caused by the necessi~ to use six p~rs of Bragg gratings, and a relatiYely low efliciency of cc~nYer~ng the radiatioq~ into 5th Stokes component. Mc~eover, Bragg gratirlgs have not a fficie}~t dept~ of ~he refra~ion index modulation.
T~e most ~ .Yi~late to the claimed lasers is t~e known R~man laser, co~ n~ a fibre light guide based on SiO~ + GeC~2 as the aGtive me~ilnn, a lo neody~ laser e.~;L~ g in the waYeler~ll of 1.06 mc a~ the ~
so~Ge, and 3 Bragg ~br~o~tical ~atill~s as ~he di~uted re~ect~¢s for wavelen~ of 1.117 mc~ 1.17~ mc and 1.24 mc ffiat form, respectiYely, 3 resonators for 1st, 2nd and 3d Stokes Gomponent~ of R~man ~tt~rir~ lS.G.
Grubb, T. Lfd~al~, V. Mi7.h~ri, T. S~ser, ~Y.Y. Cheung, W.A. Reed, P.J.
Lemaire, A.E. Miller, S.C. Ko~inP1ri, G. Nykolak, P.C Becker, D.W.
Pecl~am. 1.~ mc C~ ded ~ n ~m~lifier in Ge~m~ni~nn Silicate Fl~res.
{)pticalA~pl. andThe~A~l.., Col~ado, USA, ~-5Aug. 1994? 187-190].
The dr~ acks of tbis la~qer is its com~ ity cau~ed by ~e necessity to use three pairs of Bra~g gratin~q, and a relatiYely low efflciency of caqlYerting the ~o radiation into ~d Stokes co~nponent.
An optical fibre is known that cont~ q phosphoruq to re~uce the pe~iod of ~llJiulll ionq relaxation and, aq the re~ult, the ~tte~ tjon of the energy reYerqe tran~fer fro~ ion~q to ytt~ io~L~. [US patent 5 225 925, dated 06 07 9~, rPC H 01 S ~J16].
2s The drawback of this fibre iq the impo~bility to obtain radiation in ~e wa~elcne~hq of 1.24 mc and 1.4~ owing to the pre~qence of ~lbiu compoqitioIl of the optical fibre.
A Bragg grating is known ~hat L~ u~ed a~ a digkibuted re~ect~ and impl~nted in the form of a p<)rtion of a fibre light guide, the corc refracticn 30 index of w~ich light g~de having beGn modulated [US patent 5 2~7 576, dated 07 08 95. IPC H 01 S ~/171.

~0 ~ ~7 ~

The d~awbaGk of ~i~ ~ating i~ its low effici~ncy for~ the res~~ tha~e çhemi~l ç4,~ ;0n of the optical fibre core ~ not u~ ed.
~ e method i~ l~nown for ch~ngin~ the refraGtion index in a~ ~p~cal waveguide of ~,er~ te glass, in~lusiYe of the ~tep of ac~ng c~ a i~re 5 li~t guide along the ~ptical a~Ls by a laser radiatioq~ in the w~.Y-,lr~ .t~
a~ tinp 480 nm lKO. E~ill, Y. F~, ~.C. Johnson and B.S. Kawasaki.
PhotosensitiYity in ~ptical ~re waYe~nlles; applicatio¢L to rcflectio~ filt~r f~bn~tion. A~l. Phy~. I~tt. Vol. 32910~, ~47-~49 ~197B)l. Hcrc a~ argoa~
laser haYing output power about 1 W and cohcrent waYe about L = 30 Gm in 1~ length was uscd. ~ this method thc tw~photo¢l int~ction takes place, i.e. a ch~nge in the rciiactio¢l index was achieYed wh~n ~he ab~pti~ band of 240 nm was cxcit~. In a fibre light guide the int~ ncc of thc inc~ ~ and reflected from ~he face beams occurred, ~,Yhercby a gr~ting was fo~ned in a ~ht guide.
The dl~ack of thi~ method is a alight cl~an~~ of the refractia~ index 10 ~ and the ;m~bility to ~y the ~çin~ of a g~atil~g being fa¢med.
The mo~t ~f~ e to the cl~imed method i~ the h~own method fo~
ch~n~ the rei~action index in an ~ptical waYegllide of g~ ~te glas~, ;nC~ ive of the step of act~ on a fibre light guide at an an~le to the 20 ~a~uide sl~ceby a la~er radiation having waYelen~t~ a~ t;..g 240 nm lG. Melt~, W.W. Moqey, W.H. Glen. Fo~matio~ of Bragg gratings in optical fibres by a tra~erse holographic mcthod. Opt. Lett. Vol. 14 ~15), 82~-82~ ~1989)]. In particular, in the said method, a ch~r~ge of the refracti~ indexcan be ~ttaiTl~d by action of radia~on of seco~d haIm~nic of an argon laser ~
= 244 nm~, four~ monic of a neo~ laser ~ = 266 nm), an ç~imer laser based on KrF ~ = 248 nm), or a dye laser ~= 240 nm). In the real practice an excimer lasGr is coqnmaq~ly uscd, which is the most unreliable, the mo~ co.~ and e~pcnsiYc am~st the lasers mentioned above.
tion of second halmanic of an argon la~r has a s~ ~tly great 30 oulput power ~Y~ 0.2 W) alld coherent le~ (L ~ ~ cm~, therefore using the same a grating in a fibre light gmde is f~rm~ by the int,,f~.Gllce effect directing two bcams at a;n~e :pto the Iight guide s~ce. Honr~,,.,L the L~

220 ~ ~ 7 ~

effie~tive length i~ not ~lfficie~t to f~rm a ~tine in~ the ~e~ e radiation i~ directed along the a~ of a fibre light ~de due to a~ high absorptio~, which is ..~ ~le. Ch~ng~np an~le ~p the ~np of thc .g be~ foqmed can be varied. By a ~imil~r method a eh~r~gr o~ the S rc~action in~ex can bc achicved by acti~ of r~ tif~n a~ four~ h~ nic of a neody~ . lascr (W '~ 1 W), coherent le~ of which i$ L ~ 2-3 c~n.
Unfortlm~trly, usc of this laser is not cffici-nt enough, as the radiati~ hits the edge of the band of ab$~tio¢1 ~f p,erm~ni~ ilics-tr g~s, which i$ m~Yiml7nn 24~ nm. A ~l~'ul r~7f1i~tif~n of all ex~imer laser ~W ~ 2 W~ and ~ccond 10 harmonic of a dye lascr that hit the centre of the band of absa~on of 5~msmi7nT .~ili~te ~lass cIL3ures a 5~7ff~ tlr great .h~ c, of the refrac~a~
indcx ~ '~ 10~ ut radiation emitteJ~ by these la~e~ has a ~ittle cohe~cnt le~ ~L < 1 mm), and ~t make~ the usc of thG inte. ~r~nce effect ~;ng fcemation of gratings rather diffic~t (thc grating~ are foImcd us~ng $pecial 1~ e~pensi~re and non-d~rable q~z m~ , whereth~-~ugh the laser radiation is p~ssed~.
The main drawback of ffle said method i~ ~he u~e of a too 3h~t-waYe laser IadiatiOn rG;~ il~ in degradation of the optical elementq ~that increaseq a~ t~eou~put power grow~) and additi~al ~im~ ted lo~c~ in the ~ptical ele~ents ~o and iibre light guides (in pa:~ticular~ a wide band of absorption of fibre li~ht , being 2~0 nm at most~ and this ~ ts f~natioIl of e~tencled and sever~l grdlill3~S. Such radia~ q not allowed to be passed by polymer cl~d~1in~q of the st~n(:l~rd i~bre light guides~ which makes the fo~nation of gratings therein di~icult ~the light g~ides are to be relieYed froqn the cl~d~9ing~.
25 MoreoYer~ the la,qer sources used in the prototype do not proYide a ,~fficient reliability.

SUMMARY OF INVENTrON

The cl~imed i~ ti~q are int~f1ed to .~ the R~man fibre lasers e~nitting in the waYel~ng~1lq àbout 1.24 mc and 1.48 mc, and enh~ne~e the effici~ncy of the radiatioql C~lIVC~iaq~ m E~ n S~tt~in~.

~2 n 1 ~ 7 1 S

The set o~jectiYe LS to be achieYed as foLtows. 1~ a l~n~m R~ n- fibre~e~
that co..~ a fibre lig:ht g~de ba~ed ~ SiO2 ha~ng at least ~e ;.~
dope as the actiYe me~iltm, a laser ej~;LI;I~, in the waY~ t~ range from 1.0 to 1.1 mc a~ t~e ~ "l';'~ source, and two Bragg ~atings as the di~ibuted rcflect~s fo~ wav~le Igt~ n~ fro~ 1.20 mc to 1.28 mc that fc~ a resollato~l an aptical fi~re co~t~ ax the i r;ly dope, and the digkibuted reflectors farm a re~n~tnr for first Stoke$ component, the ~ptical fibre col.tPi~l;l7g ~0~ e amount ii~om 1 to ~0 mole %~
The set objectiYe i$ al~o ~7ttPined as follows. 1~ a known R~7~n fi~re la$er 10 that c~ a fibre light guide based ~ SiO~ ha~ at lea$t ~e ~
d~pe as the actiYe medium, a laser ~...ill;ng in the waYelLI~l~. raIIge fr~n 1.0to 1.1 mc as the ~ source, two Bragg ~til~s a$ the di~ uled re~ecta¢s for a ~ra~ l7~t~7 ra~ge froqn 1.2Q mc to 1.28 mc, and two Bragg ~rat~$ as the dig~uted reflectors for a waY-,le~ . range from 1.46 to 1.
5 mc fQrminp t.~vo resonat~, cha~ct~ ed in that an ~cal fibre C~nt7in~
P2CsS a$ the it~ d~pe, and the ~3ist~buted reflect~s f~m re~ to~$ for fi~st and $ec~d Stoke$ compone~ts, ~aid ~ptis~l fibre c~nta;~ in the ~mo~mt la~ n 1 to 3û mole ~.
Particularly, the ~P4re light guide can additi~nally car~tain F, N, Ge, Al, Ti ~o andfor Bi f~ the p~e to improve its mechan~ ~tical and other pr~es as well as foq varying the Stokes components waYel~l~ within na~row li~nits, ~aid additional ;~ d~pe being c4nt~in~ in the amo~mt ra~ng fr~ 1~4to lû mole ~.
PaIticularly, thc ~ ~ source can be imI~J~mente~ as a neodymi~n laser, ~s ytt~ laser, scmiconductor lase~, or a ~re laser. Co¢ltent of Nd in the actiYe element in a nc~l~ la~ can be in the an~ouIlt from 0.1 to 2 ~ by weight.
Pa~ticularly, the ~ lp;~g source, comri.~in~ a neo~ laser, can additiona~ly COl--pl i.~c a restr~ member based on LiF:F2.
~o Partic~ rly~ t;he actiYe member of a neod~mium laser can be implGmente~
on the basi~ of ytt;d~m almninate7 litllimn f~ c7 yt~rium-a~ , gamet, = ~ =
~a~ 11 37 ~

gad~ P~ nn g~net, gadolinil~-c~tçi~n-m~il-trn-zirconi~
gamet o~ c~l~nn-niobi~ linm gamet.
Particularly, i~ a i~re laser, leIlg~h of the iibre light guide caII be f~ 1 to lOOm.
Pa~tic~ar~y, lengt~ of the fibre li~ht guide Gan be ~om 1 to 10 km. Further, the ~bre light g~de can be implelnentecl as haYi~g a ste~t~pe refraction index pro~le. ln an ~lt~n~t;ye Yersic~n, the ~bre light g~de core can be imr~eme~t~
as haYing th~ refractian index that c1~ e.~ oYer it~ cro~s ~tion.
Par~cularly~ e be~ refiacti~ inlli~q o~ the core and the ~re lo lig~t guide c-1~d~n~ can be not le~s than 10 ~he ~et o~jectiYe is fi~ther ~ in~3 as folla4Ys. ~n a Bragg fibre gr~ti in~rlemerlted in the f~¢m of a porti~ of ~e i~re light guide based on SiO~
ha~ng at least one ;I~,p-lr;~ d~pc, inclll~iYe of GeO2, wherein the light gaide core rei~action index was mo~ te~1 along its ler~, c~tent of GeO2 Lq within the ~ge from 11 to 3~ mole ~i.
Particwl~1y, the fibre light guide of Bragg grating for the ~U~ c of i"lp~o~ ent of the optical and mech~niç~l p~op~llieq can ~d(1ition~lly cc,lLtaill F, N, P, Al, Ti a;nd,J~ Bi a~ the il~lyu~ d~pe, co~tent of said additianal ~y~il~ d~pe can be within the range fr~m 10 to 10 mole %.
Pa~ic~l~rly~ in ~ragg grating, the periodic ctl~nge of the mod~ ted refractian index oYer the 1cn~ of the fibre lig~t guide can be within the range fraq~ o 10-2.
Partic~arly, length of a po~ion of the fibre light guide can be wit~in the ra~ge from 1 to 100 m.
~s Particlll~rly, the reflection factor in a Bragg ~ng m the waYelengt~ raDge firam 1.20 to 1.28 r~c can bc from ~5 to 100~i.
Particularly, the reflectio~ factor in a Bragg gra~ng in the waY~lengtl~ range from 1.~0 to 1.28 mc can be from 10 to 80%.
Partic~rly, the reflectioll factor in a Bra8g grating irl the ~f~y~lC~ range from 1.46 to 1.50 mc can be fr~n ~ to 100%.
Particllt~r1y~ the re~ection factor in a ~gg ~rd~ g in the wa~ve1en~ range from 1.46 to 1.56 mc can be from lO~o to 80%.

_ The set objectiYe is fitrther attS~;ne~ as follows. 1~ the ~own me~h~or çhal7~ there~aGti~indexinp~ 7 silicateglas~thatCf)..~p~ the step of acting OIl a glass by a laser r~di7ti~n~ this action is executed by radiati~ haY~ waYelength w~thin the r~e from 270 to ~û nm.
5 Part~ slrly~ a ~ radiatioql c~ be direGted al~g the optic~ axis of a~
element made of p~7St7il~7 ~ 7te glass.' ~ ~lt~7s7tiye Yersio¢ls, a laser radiation is direGted at an angle to the eletnent surfa~e made of ~,4r..~a~
~ilicate glag~, or ~iml~ltsneously ~l~ng t~e optical axis and at an ~e to the element sllrfS~ce Parti~ , thc eleme~t can be im~lc.~.LI~ed as a portion of the fibrc li~ht g~de, a protecti~ polymer çl~dflin~, being applied thereon.
Par~icularly, said element can be imrl~mented in the form of a plate.
Particlllslrly~ the action to be done on the glass can be executed by the iltraYiolet radiation of an argon la~er. In s ltems ti~re element~, the actioll to be 5 done on the glass is executed by third ll~rmf~nic of radiation emitte~l by a neodymium laser, ~ko~ L laser, krypton laser o¢ the ultraYio~et radiation by a h~ m-c~f~ laser.
~ e cla~ned two Rannan fibre la~, Bragg i~rc optical ~ g used ~erein, and a method fo~ cl~ ~ the refraction index in ~rmanilmn ~ili~te g~s ~o used to form a Bragg ef~hn~ are all linked by ~gle la~er of the il~ tion and E~oYide acllieY~l~cl.t of the said tef~hni~l ~~eGtiYe.

4~ Brief Description of Drawings The mventia~ will be d~ed in cf~nr~nf~tion ~ith the acco 2~ drawings. Figs. 1 and 2 ~hffw v~i~ of a R~m~ fibre la~cr e,~l,;ll;~ waYe-en~ of 1.24 mc and 1.48 mc, respectiYely. Fig. 3 s~l~em~ti~ y illl~te~ a Bragg fibre-oE)tical grating. Fig. 4 ~how~ the ab~ption ~pectr~m that LS
characterig~c of gcrm~n;lmn ~ilic~te glass. Fig~ ~, 6 and 7 srhem~fi~lly 8how ver~i~ of l~lati~c po~ti~ns of a p~¢~on of a fibre light guidc and a lascr 30 radiatioq~ beam during fc~mation of a Bragg ~¢ating.

~ 220137 1 ~. Description of In~ention Embodimenl~
A R~ laser e~ n~ waYel~th of 1.24 mc (Fig. 1~ c~mrri~, a ~ p;~
source 1, a fibre light guide 2, porti~s of the ~re light guide being Bragg fibre-optical ~ 3 a~d 4, ~ltill~ 3 f~rming a blanlc distributed re~ecto~ of s an op~cal resonator for first Stokes co~ ent, and re~ector 4 is the output dîstrl~uted reflector for the same resc:nator. Type of the ~ ~ source 1 and?
if feasl~le, that of its restn~ing, and length of waYe of its radiation are selected on ~e basis of the necess,ity of fine tlming of a R~m~n iibrc laser radiation ~Y~
lo Laser ~Fig. 1) ~perates in the following m~nn~r P~ ?il-~ radiati~ froq~ the sourGe 1 is converted in the ~bre light guide ~ owing to the forced G~mhin~ti~n~t sc~ttkring rn the prototype, at t~e output, third Stokes componc~t was dc~ l, in the claimed lase~ (Fig. 1~ derivcd i~ first Stokes component. PffiGienGy of conversion into first Stoke~ c~npa~ent is ob~oualy 15 hig~er than that into third one, and the c~versio.n itself is ~im~l~r. To el7h~nce the e.fficiency, in the la~ Fig. 1~, as in the prototype, the resananceconversion during a 1~ L;l~le p~ ofthe fi~st Stokes c~p~ent.radiation thr~llgl. the resqn~t~r f~ned by reflecta~s ~Bragg gratings) ~ and 4 is used.
How~v~f, in the proto~ype, crcation of optica~ re~t~rs not only faq fir~t, but ~o also for seco.nd and third Stokes G~m~ent~ is re~red.
The l~ n fibre la~er f~ wavelcn~ of 1.48 mc ~Fig. 2~ in co.~
with the first ver~ion ~Fig. 1) additionally GOl~ portions of thc iibrc waveguide that are Bragg fibre a~ical grat~gs 5 and 6, grating 5 fa~ a blank di~lf~suled re~ect~ of the optical resQn~tQr for second Stokes con~ponent, and reflector 6 - the output digt~ibuted reflector for t~c same resonator. MoreoYer, there is second gLati~g 3 in~e~d of grating 4. ln this laser ~Fig. 2) second Stokes co~nponent is derived, while in the most L)r~ate allalogue - si~th < ne. Ffficiency c~ c~versia~ into sec~nd Stokes c~lll)ollent is obviou~ly higher than that into si~ one, and thc colw~on itself is ~ pl~.
30 The analogue rc.lui~es creaticn of optical res~n~t~ fo~ first, second, t~ird,fourth, fi~h and si~th Stokes co~ ents, while in the cl~imed laser ~Fig. 2) -only for first and se~nd ones.

~ 22n 1 3 7 1 g The claimed Bragg fibre-optic~l grating~ (Fig. 3~ as in the prototype~is a po~tioql of t~c i~bre light guide, co.~ a co~e 7 and a cl~d~in~ 8, in said core sectia~s of a higher 9 and a no~mal ~i.e. a lower than the avelage value~
10 refraction index are periodically ~ltern~ted . This grating ~perates exactly in the same m~nner a~ in the prototype. The a~ly di~tincti~ is that in the claimed grating ~Fig.3~ a greater di~ ce bel~ the m~ and the values of the refra~tion index ~moch~ n dept~) is provided ow~ng to a new composition of the iibre light guide. Stokes camponents associated with the d~pes were ~ul)~re3~ ing an additional long-~ing grating or a 1~ spe~l ~ ~ introduced into the reson~t~r.
ln the course of ff~ "~ n of a Bragg fibre-o~tical ~lil~g in ~ase of t~e lc~n~itl~in~l geometry (Fig. 5~, the la~er radiation 11 is directed along the optical a~is ofthe light guide 12~ in ca~e ofthe t~ c p~omçtry (Fig. 6), thc l~er radiatio~ 11 is directcd at a~e q~ to the xUlra~ of thc li~t ~ide 12;
5 and in case of the l~t~n~ erse geo~netry (Fig. 7), the lager r~ tion is directed ~;""J~ alang the o$~cal axis of the light guide 12 and at an angle to its sl~ce. Figs. 5, ~ and 7 show also an area 13 where~n a ~tin~ is ~ in Fig. S it oc~lIJie,s the entire portion of the fibre light guide 12~. Direction of laser beams 11 in Figs. 5, 6 and 7 are shown by arrows.
~0 lix.~. i.. ~ent~ have shown that the ch~nge of the refr~ ( n index of pe- "-~ ic~te glass re~ired for the infhlgtn~l a~li~bility can be provided by acti~ of the laser radiati~ haYing a waY~ , hitting not a~ly the ~fliti~n~lly utili~ bands of absorption near wal,. k .-g~h~ of 180 and 240 nm, but also a wcaker band of abs~ion haYing a wa~l.,l~th a~lo ;..~
330 nm ~Fig. 4). Such r~fli~tif~n is passed tl.lou~ll a protection polymer c1qflflin~ of fibrc light guidcs. For pro~ ion of a r~tic~n w-dY~ ~h within the range from 270 to 390 nm, lascrs that are morc reliable and durable than those of the prototype can be uscd. Par~icularly, it is clear that a ncodymium lascr is a more reliable r~fli~tiQn source, when third h~n~nic of its radiati~n is 30 uscd (as in thc claimcd method), not fourth onc (as in the prototypc). 'rhe same is true for an argon laser: in the claimcd method one of the main lines of radiation is used, while in the prototype - second h~rmonic.

2 a n ~ 3 7 1 1~

Our ~f.rii~ t has ~mcngtrated that -a le~ ¢ption by p~m~
~ilic~te ~pass in thc ~aid ~ge in no way prcvcnts cl:eation of a dc~rcd ~h~r~ge of the re~ index. Also it wa~ discovered that at the ~ band of absorptio~ Ilear 2~0 nm, there are no stim~ te~ lo~ at all. Slight lo~ses in the said range al~ow to form ~atil~ not only in the t~ c ~Fig. 6)~ but also in the l~ nal ~F~g. ~) and the t~sver~longitl~inal ~Fig. 7) gea~et~ies. 1 n the longitlldinat gea~netry (Fig. 5) the gL~ n~, iS
in~iable~ and in the t~ r~3e geo$ne~y ~Fig. 6~ a~d the ~ ~d;t?Dl-sverse geoqnc~y ~Fig. 7) it can be valied by ch~ p an~e.
lo ~ cfJ...l~-ixon with the prototype, a radiati~ w.ith l~nger waYçlcng~h~ ~w.ith a le~ser cner~ of phota~ ed in the claimed method docs not res~t in a nohceilble ~ d~h~ n of the optical elem~nts~
A known fibre neo~,..iu,~ laser hay~ng au~ut power of 1.~ W~ with leng~h of a fibrc light guide of 30 m, core of which laser cC~nt~in~ 0.5 ~o by weight of 15 Nd, was uscd as the ~ g source 1. Bra~g ~hng~ 3, 4, ~ and 6 werc imrl~ r~lt~ in the foqm of p~ions of the ~ptical fibre 1 m long, the core 7 of which fibre Cf...t~ 21 mole ~o of GeO2, and its re~action index ha boen ~ ly mo~ d~r~1~ and ~he m~llqh~n dcpth r~h~ 8 x 10-4. The reflection factor of ~r,tl;..~ 3 and ~ at waYçlen~ of 1.24 mc and 1.48 mc ~o was, re~pectiYely, 999b, and the rl flrcti~n factor of grq-tings 4 and 6 at waYes 1.24 mc and 1.48 mc long was, respu~Ycly, 205~. The ~re light guide 2 was 10 m lcxng, and its ca~e contqined 19 mole ~ of P2(~. The f~re l~ght guide of the neo~l.liuul laser 1, the i~re light guide 2 and the fibre light guides of Bragg grqtings ~, 4, 5 and 6 had stq-ncl~rd LI~V~ ..c...4.;aq~s, These lght ~s guides werc fabricqte~l acc~ding to the standard technology using the method of ch mic,~l precirit~tion froq~ eollx phase [DeYyatykh G.G., Dianov E.M.
Fibre l~ight Guides with Low C~ptid l~es. USSR ~cad of Sc. Courier, 1~81, iss. 10, p. 54-66]. They were welded into an entity.
~ the ~ x re~lixing the Gl~imr~ ~n tho~l one of the following las~rs was 30 used; 1~ argaa~ laser (ultraYiolet radiation with w~ 11. of 333, 350 and/or 364 nm); 2~ neo~lr~ laser based on ylL~ .. galnet (third h7.. ~ iC ~rith waYrl~ h of 3~ ; 3~, iL,ogc., laser ~with way~lc~ h of ~ 2ao ~ 3 7 1 ~0 nm); 4~ krypt~ ~r ~ waYc~el-a~h of ~50 nm~; ~) hPlimn~
la~ il~aYiolet radia~ nth wayelengt~ of ~0 andfa~ ~0 nm~ the~e lase~ are es~nti~lly maqe reliable and dllrable than the kaditio~ally used E~rF-ba~ed eY~imer ~ne. Provi~ion of a ~lffi~ently powerfill radiati~ of ~ d ha~ llG of an arg~n laser having wavelength of 244 nm fo~ the purpose to fo¢m ~atings i~ more ~liffiGlllt ~an to obtain the ~adiatiall of its ba~ic i~e~l~7lCy. Simil~r1y, it is more ~iffi~lt to proYide and u~e ff~e Iadiatian of fou~th haImanic ~a~ its ~hird h~rrn~iG, ln the a.~alu~ that wolild reali~e the Glaimed method, e~cimer lasers e.~ p in the waveler~ of 308 nm, 351 lQ nm, 352 nm can be u~ed, but in thi~ ca~e ~e~H~ of a31 the benefits of the claimed method will not be caI~ied out. Par~met~ of the used l~ser~ and the geoqnetry of t~e ~ ent are given in the Table below.
~ tl pa~tiGlilal, Ugillg thc claimed metho~ a l~g-~q~n~ ~flt;~ in a fibre l~ht g~de of ~,er~ te gla~s wa~ created. A iibre ~ght gl~ide wa~
5 imrlem~nted both u~ he hydrogen ~tmosphere, a~d without ~ sffoll of a proce~in~ by hydrogcn. t~f~ltill8S wcrc fa~ned both by the ink~ Lrcl~ce me~hod ~Fig. 5, 6 and 7), and us~ng oqLe foGuscd la~er beam ~padnt-by~ int" mode).
Te~ng of ~n~ ;..~ haYing ~pfl~n~, of 200 mc ~ri~ted ~ r~ the claimed method dem~ Gd that they ~re as semceable a~ those u~ing the prototype, thc rcfi~ n index ch~ge t~,~ceefling ~n ~ 10-4. Mo~ , thc additi~al 1osses ~h~r~ct~ri c of the prototypc were abscnt. When the ~ te ~lasg obt~cd ~ the prcscnce of hydrogen wag uscd, an e~ l ru*l~tif~n af the ~ lo~sex was observed.
Tcs~ng of R~ n fibre laserg (Figs. 1 and ~) having Bragg ~ting~ (Fig. ~) 2s exccu~ed according to thc ~ A i~ ~ that thc ~et objcctivc is ~ in-d whcn thcy arc used, i.c. ~ tif~n of l~m~n fibrc lasers c,..;ll;..~ in the wavelengll~ of 1.24 mc and 1.48 mc i5 provided, and inR~m~n sc~çTing the effi~ir,ncy of the r~ h~n cc~ ion in~lea~cx.

6. Industrial Applicability Thc imrcnhQn.c are int~u~ y ap~ ~bl- in deviceg for ~ 8 devices in i~brc ~ ~ of the ggr~lx ~at arc uscd in the bro~ n~1 fibrc-optical -~ ~ O ~ 3 7 1 ~ t;~ ~stem~ in~te~d of the ol~~ c r~te~ cl~d method caI~ a~o bc uscd for l'~r;.~ g t~e ~bre alld ~ 5uide o~c5 elç~nçnt~
made of EÇ~ n~n;~l.n ~ili~te gla~, and in particular - t;he i;bre-optical Bragg alld long-~nP ~ratings, ~tt~ring co~ -~tOM~ ~te~ated-a~tical w~eg~ G~, etc.

Table Examples of s~ iric Embodiments I ~r A Mode W L Geomc~y nm Argon 333-364 coq~t 5 30 Figs. S a~d 7 Nd; Yag 355 pul~e 3 3 Fig. 6 ~3d hann~ c) Nil~ 337 p~lsc 0.5 O.I Fig. 6 ~o Hc-Cd 325 pul~e 0.07 50 Figs. S and 7 }~ypton 338-356 cont 1 30 Fig. S and 7 Arg~n 244 COIlt 0.2 5 Fig. 6 (2nd ha~
Nd:YAG 266 pulse 1 1 Fig. 6 2s (4th h~monic~) F.ycimM KrF 248 puLse 2 ~0.1 Fi~. 6 F.Y~im~ XcCl 308 pu13c 2 ~0.1 Fig. 6 E~:cimcrXcF 352, 352 pul~e 2 ~0.1 Fig. 6

Claims (12)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. ~A Raman fiber laser, comprising a fiber light guide based on SiO2 having at least one impurity dope as the active medium, a laser emitting in the wavelength range from 1.0 to 1.1 mc as the pumping source, and two Bragg gratings as the distributed reflectors for wavelength within the range from 1.20 to 1.28 mc forming a resonator, wherein an optical fiber contains P2O5 as the impurity dope, and the distributed reflectors form a resonator for first Stokes component, the optical fiber containing P2O5 in the amount from 1 to 30 mole %.

2. ~A Raman fiber laser, comprising a fiber light guide based on SiO2 having at least one impurity dope as the active medium, a laser emitting in the wavelength range from 1.0 to 1.1 me as the pumping source, two Bragg gratings as the distributed reflectors for wavelength within the range from 1.20 to 1.28 mc, and two Bragg gratings as the distributed reflectors for wavelength within the range from 1.46 to 1.50 mc forming two resonators, wherein an optical fiber contains P2O5 as the impurity dope, and the distributed reflectors form resonators for first and second Stokes components, the optical fiber containing P2O5 in the amount from 1 to 30 mole %.

3. ~A laser as claimed in claim 1, wherein the fiber light guide additionally contains F, N, Ge, Al, Ti and/or Bi as the impurity dope, the additional impurity dope being contained in the amount from 10 -3 to 10 mole %.

4. A laser as claimed in claim 1, wherein the pumping source is a neodymium laser, ytterbium laser, semiconductor laser, or a fiber laser.

5. ~A laser as claimed in claim 4, wherein the content of Nd in the active element of the neodymium laser is in the amount from 0.1 to 2% by weight.

6. ~A laser as claimed in claim 1, wherein the pumping source, comprising the neodymium laser, additionally contains a restructuring element based on LiF:F2.

7. ~A laser as claimed in claim 1, wherein the pumping source is a neodymium laser, and wherein the active element of the neodymium laser is yttrium aluminate, lithium fluoride, yttrium-aluminum garnet, gadolinium-gallium garnet, gadolinium-calcium-magnesium-zirconium-gallium garnet, or calcium-niobium-gallium garnet.

8. ~A laser as claimed in claim 1, wherein the length of the fiber light guide is within the range from 1 to 100 m.

9. ~A laser as claimed in claim 1, wherein the fiber light guide is from 1 to 10 km long.

10. ~A laser as claimed in claim 1, wherein the fiber light guide has a step-type profile of the refraction index.

11. ~A laser as claimed in claim 1, wherein the core of the fiber light guide has a refraction index that varies across its cross-section.

12. ~A laser as claimed in claim 1, wherein the difference between the refraction indices of the core and of the cladding of the fiber light guide is not less than 10 -5.