EP1461651A1 - Optical waveguide termination with vertical and horizontal mode shaping - Google Patents
Optical waveguide termination with vertical and horizontal mode shapingInfo
- Publication number
- EP1461651A1 EP1461651A1 EP02786857A EP02786857A EP1461651A1 EP 1461651 A1 EP1461651 A1 EP 1461651A1 EP 02786857 A EP02786857 A EP 02786857A EP 02786857 A EP02786857 A EP 02786857A EP 1461651 A1 EP1461651 A1 EP 1461651A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- guiding layer
- recited
- waveguide
- optical device
- mode
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
Links
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
- G02B6/42—Coupling light guides with opto-electronic elements
-
- 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
- G02B6/42—Coupling light guides with opto-electronic elements
- G02B6/4201—Packages, e.g. shape, construction, internal or external details
- G02B6/4204—Packages, e.g. shape, construction, internal or external details the coupling comprising intermediate optical elements, e.g. lenses, holograms
- G02B6/4214—Packages, e.g. shape, construction, internal or external details the coupling comprising intermediate optical elements, e.g. lenses, holograms the intermediate optical element having redirecting reflective means, e.g. mirrors, prisms for deflecting the radiation from horizontal to down- or upward direction toward a device
Definitions
- the present invention relates generally to optical integrated circuits (OIC), and particularly to, a structure for coupling optical waveguides.
- OIC optical integrated circuits
- Optical communications are evolving as the chosen technique for data and voice communications.
- OICs in the optical network are passive components that are discretely packaged, providing a singular functionality such as power splitting an optical signal into several signals (1 X N), creating (N x M) switches for optical signals, equalizing or attenuating signals, wavelength demultiplexing via arrayed waveguide gratings, or adding and dropping selected wavelengths into the optical path (Optical Add -Drop Multiplexing).
- Higher levels of integration may combine several of these functions on a single OIC chip.
- active dies such as lasers, modulators, and photodetectors has been accomplished and is gaining in popularity as more mature manufacturing methods are developed.
- planar waveguide cores that have the same mode field diameter of current telecommunications fiber can cause an 8x8 optical switch with power equalization to consume an entire 100 mm wafer.
- the reason large core size and low index contrast between the core and cladding are presently used in the current generation of OICs is to achieve a mode match between the current single mode optical fiber used in the networks and the OIC. Such mode matching achieves low coupling loss between the OIC and the optical fibers that connect it to the rest of the network.
- high index contrast OICs are often referred to as "high delta-n" waveguides, referring to a large (e.g., 2% - 10%) difference between the core and cladding refractive indices in the OIC planar waveguides.
- the difference in refractive index between the core and the cladding should be increased so that the core size may be reduced. Accordingly, high delta-n waveguides allow for decreased core size and tighter turning radii at equal energy loss, and allow for less crosstalk for closely spaced waveguides due to better mode confinement in the core. In addition, since the core in a high delta-n waveguide may be thinner and the mode is more tightly confined, the thickness of the core and cladding layers used to make the planar waveguide of the OIC become thinner. This can reduce the costs and challenges in fabricating a high delta-n OIC, especially those made using traditional inorganic glasses that utilize etched cores.
- high delta-n waveguides yet remain to be adopted due to a number of challenges.
- One of the greatest challenges preventing the commercial use of high delta-n waveguides is that high delta-n waveguides are not well suited for direct coupling to commonly used single mode optical fiber that typically has a 7 ⁇ m to 9 ⁇ m mode field diameter. The lack of compatibility between such components is understood in terms of optical mode theory.
- Planar optical waveguides including high delta-n waveguides, and optical fiber waveguides useful in high-speed and long-haul optical transmission systems often are designed to support a single mode.
- the waveguides are designed such that the wave equation has one discrete solution; although an infinite number of continuous solutions (propagation constants) may be had.
- the discrete solution is that of a confined mode, while the continuous solutions are those of radiation modes. Because each waveguide will have a different discrete (eigenvalue) solution for its confined mode, it is fair to say that two disparate waveguides, such as an optical fiber and a planar waveguide, generally will not have the same solution for a single confined mode.
- This transition region ideally enables adiabatic compression or expansion of the mode so that efficient coupling of the mode from one type of waveguide to another can be carried out.
- optical fibers typically support mode sizes (electromagnetic field spatial distributions) that are much larger, both in the horizontal and vertical directions than modes supported by high delta-n waveguide structures, such as planar waveguides.
- a challenge is to provide a waveguide transition region that enables adiabatic expansion of the mode so that it is supported by the optical fiber. Moreover, it is useful to achieve the adiabatic expansion of the mode in both the horizontal and vertical directions. Fabricating a waveguide to effect adiabatic expansion of the mode in the vertical direction has proven difficult using conventional fabrication techniques. For example, tapering the thickness of the waveguide to effect the vertical adiabatic expansion of the mode is exceedingly difficult by conventional techniques.
- an optical device comprising a single-mode waveguide which supports a first optical mode in a first region and a second optical mode in a second region, the waveguide including a guiding layer having at least one wing extending outwardly from the guiding layer.
- the waveguide may have two wings so that the waveguide may have a cross- sectional shape of a rib waveguide for coupling an optical device of the present invention to a rib waveguide device.
- the wings may decrease in width along the length of the guiding layer to convert a mode from a rib waveguide mode to a channel waveguide mode.
- the waveguide may also include a guiding layer having a lower portion with a first taper and an upper portion with a second taper.
- the lower portion of the guiding layer may taper from a first width to a second width, and the upper portion may taper from the first width to a point.
- the guiding layer made desirably be provided as a single material layer.
- Figure 1(a) is a top view of waveguide according to an illustrative embodiment of the present invention.
- Figure 1(b) is a perspective view of the waveguide shown in Figure 1(a);
- Figure 1(c) is a side elevational view of the waveguide of Figure 1(a) of a waveguide according to an illustrative embodiment of the present invention;
- Figure 2(a) is a perspective view of a waveguide coupled to an optical fiber in accordance with an illustrative embodiment of the present invention
- Figure 2(b) is a top view of a waveguide according to an illustrative embodiment of the present invention.
- Figures 3(a)-3(f) are graphical representations of the electric field distributions of optical modes at various regions of a waveguide according to an illustrative embodiment of the present invention.
- Figures 4(a)-4(d) are top views of guiding layers of waveguides in accordance with illustrative embodiments of the present invention.
- Figure 5 is a perspective view of an illustrative embodiment of the present invention.
- Figure 6 is a perspective view of an illustrative embodiment of the present invention
- Figure 7(a) is a perspective view of a waveguide according to an illustrative embodiment of the present invention in which the waveguide includes wings for coupling to a rib waveguide;
- Figure 7(b) is an end elevational view of the waveguide of Figure 7(a) showing the end of the waveguide that includes the wings;
- Figure 7(c) is a top view of the waveguide of Figure 7(a);
- Figure 7(d) is aperspective view a waveguide similar in configuration to that shown in Figure 7(a), but having wings of tapered thickness;
- Figures 8(a) and 8(b) are top views of waveguides according to the present invention having further exemplary wing configurations; and Figure 9 is a top view of a waveguide according to an illustrative embodiment of the present invention similar to that of Figure 8(a), but having an upper waveguide portion of decreased width.
- the term "on” may mean directly on or having one or more layers therebetween.
- single material includes materials having a substantially uniform stoichiometry. These materials may or may not be doped. Illustrative materials include, but are in no way limited to silicon, SiO x N y , SiO x , Si 3 N 4 and InP. Moreover, as used herein, the term single material includes nanocomposite materials, organic glass materials.
- bisect may mean to divide into two equal parts.
- bisect may mean to divide into two unequal parts.
- the present invention relates to an optical waveguide which fosters adiabatic mode expansion/compression thereby enabling optical coupling between a first waveguide, which supports a first optical mode and a second waveguide, which supports a second optical mode.
- the waveguide supports a first optical mode in a first region and a second optical mode in a second region.
- the waveguide of the present invention illustratively couples a planar waveguide, such as a channel waveguide or a rib waveguide, of the OIC to an optical fiber or another waveguide of an optical communications system.
- the waveguide may include a single material guiding layer having a lower portion with a first taper and an upper portion with a second taper.
- an optical device which includes a waveguide having a single material guiding layer.
- the single material guiding layer has a lower portion, which tapers from a first width to a second width, and an upper portion which tapers from the first width to a point.
- the single material may be disposed on a stress compensating layer, which is used to reduce stress induced polarization mode dispersion and temperature induced polarization mode dispersion. This stress compensating layer will not substantially impact the optical characteristics of a waveguide.
- an optical device is disclosed which includes a waveguide having a guiding layer with two wings extending outwardly from the guiding layer. The wings are provided at a selected end of the waveguide to provide an endface of the waveguide well-suited to coupling to a rib waveguide of the OIC.
- the waveguide according to exemplary embodiments described herein may be an integral part of an OIC formed during the fabrication of the OIC.
- multiple waveguides may be used to couple multiple optical fibers at various locations of the
- an 8 channel fiber array could be efficiently coupled to a 8 channel SOI waveguide by utilizing a device incorporating multiple waveguides of the present invention.
- Such a configuration prevents the need for expensive up-tapers in the SOI waveguide by solving the mode matching challenges in one interposer chip of the present invention.
- Figs. 1(a) and 1(b) show a waveguide 100 according to an illustrative embodiment of the present invention.
- a guiding layer 101 is disposed on a lower cladding layer 102.
- the guiding layer 101 is illustratively a single material.
- An upper cladding layer (not shown) covers the guiding layer 101.
- the indices of refraction of the upper and lower cladding layers may or may not be the same. In all cases, the indices of refraction of the upper and lower cladding layers are less than the index of refraction (n g ) of the guiding layer 101.
- the waveguide 100 includes a first region 103 and a second region 104.
- the guiding layer 101 further includes an upper portion 105 and a lower portion 106.
- the upper portion 105 tapers at an angle ⁇ 2 relative to the edge 107 of the guiding layer 101.
- the lower portion 106 tapers at an angle 0 ! relative to the edge 107 of the guiding layer 101. Reducing the thickness and width of the guiding layer 101 effects substantially adiabatic expansion/compression of an optical mode traversing the waveguide. (As would be readily apparent to one having ordinary skill in the art, adiabatic expansion of a mode occurs when the mode is traveling in the +z-direction; while from the reciprocity principle of optics, adiabatic compression occurs when the mode is traveling in the -z- direction).
- the effective index of refraction decreases as the width of the guiding layer 101 decreases. Due to the reduction in the effective index of refraction, the horizontal portion of the optical mode expands (is less confined in the guiding layer 101) as the mode traverses the waveguide in the +z-direction.
- Fabrication of the first taper 108 and second taper 111 of the guiding layer 101 may be carried out by well known techniques, as described in further detail below. Of course, it is also useful to adiabatically expand/compress the vertical portion of the optical mode. In order that the vertical portion of the optical mode undergoes substantially adiabatic expansion/compression, the thickness of the guiding layer is reduced.
- Fig. 1(c) a side elevational view of the illustrative embodiment of Fig. 1 (a) is shown.
- the thickness of guiding layer 101 reduces in the +z- direction from a thickness t x to a thickness t 2 as shown.
- An upper cladding layer (not shown) may cover the guiding layer 101.
- the single material used for guiding layer 101 has an index of refraction n g as the thickness of the guiding layer 101 is reduced from a thickness t j to a thickness t 2 , the effective thickness of refraction is reduced. Accordingly, the vertical portion of an optical mode traversing the guiding layer 101 in the +z-direction will expand, as it is less confined to the guiding layer 101.
- the endface 110 of the guiding layer 101 has a width w 2 , thickness t 2 and index of refraction that produce an optical mode well matched to that of an optical fiber. Accordingly, the single optical mode supported by the waveguide 100 at endface 110 will also be one which is supported by an optical fiber. As such, good optical coupling between the guiding layer 101 of the waveguide 100 and the guiding layer of an optical fiber (not shown) results.
- the waveguide 100 may be fabricated so that the upper portion and lower portion of the guiding layer 101 are symmetric about a plane which longitudinally bisects the guiding layer 101.
- the waveguide 100 according to exemplary embodiments of the present invention may be fabricated so that the upper portion, or the upper portion and the lower portion, of the guiding layer 101 are asymmetric about an axis which bisects the waveguide 100.
- a waveguide according to exemplary embodiment of the present invention may be fabricated to include one or more wings extending outwardly from the guiding layer. The wings may be disposed at an endface of the waveguide so that that endface is particularly suited to coupling to a rib waveguide.
- FIG. 2(a) a perspective view of a waveguide 200 according to an exemplary embodiment of the present invention is shown.
- a lower cladding layer 202 is disposed on a substrate 201.
- a guiding layer 203 is disposed on lower cladding layer 202.
- Waveguide 200 has a first region 204 and a second region 205.
- the guiding layer 203 includes a lower portion 206 and an upper portion 207.
- An optical mode is coupled from an endface 209 to an optical fiber 208.
- an upper cladding layer is not shown in Fig. 2(a). This upper cladding layer would cover the guiding layer 203.
- the upper cladding layer, guiding layer 203 and lower cladding layer 202 form a waveguide 200 according to an illustrative embodiment of the present invention.
- the upper cladding layer may have the same index of refraction as the lower cladding layer 202.
- the upper cladding layer may have a higher (or lower) index of refraction as the lower cladding layer 202.
- the guiding layer 203 has an index of refraction, n g , which is greater than the indices of refraction of both the upper cladding layer and lower cladding layer 202.
- the upper portion 207 and lower portion 206 are symmetric about an axis 210 that bisects guiding layer 200, as shown in Fig. 2(b).
- an optical fiber 208 may be desirable to couple to an OIC (not shown). This coupling may be achieved by coupling the optical fiber to a planar waveguide (not shown) of the OIC.
- the planar waveguide supports a first optical mode and the optical fiber 208 supports a second optical mode.
- the first optical mode of the planar waveguide will not be support by the optical fiber in an efficient manner, and a significant portion of the energy of the first optical mode of the planar waveguide could be transformed into radiation modes in the optical fiber 208.
- Waveguide 200 may be disposed between the planar waveguide of the OIC and the optical fiber 208 to facilitate efficient optical coupling therebetween.
- the first optical mode of the planar waveguide is physically more confined to the guiding layer of the planar waveguide than the second optical mode is in the guiding layer of the optical fiber. That is, the confined mode of the planar optical waveguide is smaller than the confined mode of an optical fiber. Accordingly, waveguide 200 is useful in efficiently transferring the energy of the first optical mode of the planar waveguide into optical fiber 208 by substantially adiabatic expansion of the mode.
- the solution to the wave equation for the planar waveguide is a first optical mode.
- the waveguide 200 is undergoes a transformation to a second optical mode that is supported by a cylindrical optical waveguide (optical fiber 208).
- the transformation of the mode which is supported by the planar waveguide, to a mode which is supported by waveguide 200, and ultimately to a mode which is supported by optical fiber 208 is substantially an adiabatic transformation.
- transition losses from the planar waveguide to the optical fiber 208 are minimal.
- transition losses are approximately 0.1% or less.
- the second region 205 of the waveguide 200 effects both horizontal and vertical transformation of the mode.
- the above discussion is drawn to the adiabatic expansion of a mode in waveguide 200.
- a mode traveling from optical fiber 208 (-z-direction) to a planar waveguide wold undergo an adiabatic compression by identical principles of physics.
- Fig.2(b) shows a top-view of the waveguide 200 of Fig. 2(a).
- the guiding layer 203 of waveguide 200 includes a first region 204 which is coupled to (or is a part of) another waveguide, such as a planar waveguide (not shown).
- the second region 205 is the region in which the transformation of the mode supported in the planar waveguide into one which is supported by another waveguide (e.g. optical fiber 208) occurs.
- This second region 205 includes a lower portion 206 and an upper portion 207.
- the single confined mode is one which is supported by optical fiber 208. Accordingly, a significant proportion of the energy of the mode is not lost to radiation modes in the optical fiber.
- the structure of the illustrative embodiment of Fig. 2(a) and Fig. 2(b) results in efficient coupling of both the horizontal portion and the vertical portion of the optical mode.
- the structure is readily manufacturable by standard semiconductor fabrication techniques.
- the lower portion 206 is at a first angle, ⁇ l5 relative to the edge of waveguide 203; and the upper portion 207 at a second angle, ⁇ 2 , again relative to the edge of waveguide 203.
- the angles are in the range of approximately 0° to approximately 0.5°. Sometimes, it is preferable that the angles are in the range of greater than 0° to approximately 0.5°.
- the greater the angle of the taper the shorter the length of the taper. Contrastingly, the smaller the taper angle, the longer the length of the taper. As will be described in greater detail herein, a greater taper length may require more chip area, which can be disadvantageous from an integration perspective, but may result in a more adiabatic transformation (expansion/compression) of the mode. Ultimately, this may reduce transition losses and radiation modes in the second region 205 of the waveguide and the optical fiber 208, respectively. Finally, it is of interest to note that angle ⁇ 1; and the angle ⁇ 2 are not necessarily equal. Illustratively, the angle ⁇ 2 may be greater than angle ⁇ .
- the length of taper of lower portion 206 (shown in Fig. 2(b) as L 2 ) is on the order of approximately 100 ⁇ m to 1 ,500 ⁇ m.
- Fig. 2(b) is not drawn to scale as the width of the waveguide (shown as w g ) is hundreds of times smaller than the length L 2 of the taper portion (e.g. 1-10 microns wide).
- the length of the taper of the upper portion 207 of the waveguide (shown at L t ) is on the order of approximately 100 ⁇ m to approximately 1,500 ⁇ m.
- smaller taper angles will result in longer taper lengths (L j ) and consequently may require more chip surface area, which can be less desirable in highly integrated structures.
- the length of the taper (L ) also dictates the efficiency of the mode shaping. To this end, longer tapers may provide more efficient mode shaping because the mode transformation is more adiabatic.
- the upper portion 207 and the lower portion 206 of guiding layer 203 are substantially symmetric about an axis 210 that bisects the guiding layer 203.
- the first angle 0 X of the lower portion is the same on both sides of the axis 210.
- second angle ⁇ 2 of upper portion is the same on both sides of the axis 210.
- the lengths L x and L 2 are the same on both sides of the axis 210.
- the tapering of the waveguide reduces the width (w g ) of the guiding layer 203, which enables substantially adiabatic expansion/compression of the horizontal portion of the mode.
- the width is reduced to a width w 2 as shown.
- this width w 2 is in the range of approximately 0.5 ⁇ m to approximately 2.0 ⁇ m. While the embodiment shows that guiding layer 203 terminates at this width rather abruptly, of course, as in the illustrative embodiment of Figs. 1 (a) and 1 (b), it is possible to continue the guiding layer 203 at the reduced width, w g , for a finite length, which ultimately terminates at an endface.
- Fabrication of the waveguide 200 may be effected by relatively standard semiconductor fabrication process technology. Particularly advantageous is the fact that the guiding layer 203 may be fabricated of a single layer, illustratively a single layer of a single material.
- a suitable material is deposited in a single deposition step.
- a conventional photolithographic step is thereafter carried out, and a conventional etch, such as a reactive ion etching (RIE) technique may be carried out to form the waveguide 203 and to define the lower portion 206.
- RIE reactive ion etching
- the upper portion 207 may be fabricated by a second conventional photolithography/etch sequence.
- a monolithic material may be deposited on layer 202, and in the deposition step, the taper in the lower portion 206 of second region 205 may be formed.
- the guiding layer 203 may be partially etched to form the taper in the top portion 207.
- the top portion 207 can be etched by standard dry or wet etch techniques, both isotropically and anisotropically. While the illustrative embodiment described thus far is drawn to the guiding layer 203 being formed of a single layer, it is clear that this waveguide may be formed of multiple layers of a single material as well.
- the guiding layer 203 may be comprised of a lower layer which includes the lower portion 206 and an upper layer (not shown) which includes the upper portion 207.
- the top layer is thereafter etched by standard technique to form the taper in the top portion 207 of the second region 205 of the guiding layer 203.
- the lower cladding layer 202 is silicon dioxide (SiO 2 ) having an index of refraction on the order of approximately 1.46.
- the guiding layer 203 is illustratively silicon oxynitride (SiO x N y ), and the upper cladding layer (not shown) is also SiO 2 .
- guiding layer 203 in the first region 204, guiding layer 203 has a thickness (shown at t j in Fig. 2(a)) on the order of approximately 2.0 ⁇ m to approximately 4.0 ⁇ m. As can be seen in Fig.
- the thickness of guiding layer 203 reduces from t x to t 2 . Moreover, as can be seen in Fig. 2(a), at 213 guiding layer 203 has a thickness t 1; which is the sum of the thickness t 3 of upper portion 207 and thickness t 2 lower portion 206. At section 211, the thickness of guiding layer 203 is reduced to t 2 which is the thickness of lower portion 206.
- the taper (reduction of the width, w g ) of the upper portion 207 and lower portion 206 results in the adiabatic expansion of the horizontal portion of the confined mode
- the reduction in the thickness from tj to t 2 results in the adiabatic expansion of the vertical portion of the confined mode.
- the reduction of the thickness of the guiding layer 203 results in a reduction in the effective index of refraction (n eff ) for the vertical portion of the mode.
- the mode is less confined vertically in the guiding layer 203, and is progressively expanded as it traverses the waveguide 200 in the +z-direction.
- the mode is effectively matched to the guiding layer characteristics of optical fiber 208.
- the lower portion 206 has an illustrative thickness
- the upper portion 207 illustratively has a thickness (t 3 ) in the range of approximately 1.0 ⁇ m to approximately 2.0 ⁇ m.
- Figs. 3(a) and 3(b) show the electric field distribution of the confined mode in the first portion 204 of waveguide 200 along the x-axis at a point z 0 and along the y-axis at point z 0 , respectively.
- Fig. 3(a) shows the horizontal portion of the electric field of the confined mode in first region 204
- Fig.3(b) shows the vertical portion of the electric field of the mode.
- the mode energy is particularly confined in the first region 204 of the waveguide 200. Characteristically, this is an energy distribution of a supported eigen ode of a planar waveguide (not shown), which is readily coupled to the first region 204 of waveguide 200 having virtually the same physical characteristics as the planar waveguide.
- Figs .3 (c) and 3 (d) show the electric field of the confined mode in the second region 205 of the waveguide 200, particularly near point 212. More particularly, Figs. 3(c) and 3(d) show the horizontal and vertical portions of the electric field distribution of the confined mode, respectively, in second region 205 of waveguide 200. As can be seen, the supported mode in this portion of waveguide 200 is slightly expanded (less confined to the guiding layer 203) compared to the supported mode in the first portion 204.
- Figs. 3(e) and 3(f) show the horizontal and vertical portion of the electric field distribution, respectively, of the confined mode at approximately endface 209 of the second region 205 of waveguide 200.
- the electric field distribution of the confined mode is significantly greater in both the horizontal direction (Fig.3(e)) and the vertical direction (Fig. 3(f)).
- the adiabatic transformation of the mode from the relatively confined mode of the first region 204 to the relatively expanded mode at endface 209 is relatively adiabatic, and results in transition losses which are substantially negligible.
- FIG. 3(a)-3(f) A review of Figs. 3(a)-3(f) reveals the adiabatic expansion of the confined mode traversing the guiding layer 203 in the +z-direction.
- the tapers of the lower portion 206 and the upper portion 207 result in a reduction in the width, w g , of guiding layer 203.
- the horizontal portion of the mode is less confined to the guiding layer 203. Accordingly, the mode is expanded as it traverses the waveguide 200.
- the reduction in the thickness of the guiding layer 203 from t x to t 2 results in a reduction in the effective index of refraction (n eff ) for the vertical portion of the mode.
- the mode is less confined in the guiding layer 203.
- the mode as represented in Figs. 3(d) and 3(f) will be supported by an optical fiber.
- the upper portion 207 and lower portion 206 of the guiding layer 203 in Example I were substantially symmetric about an axis 210 bisecting the guiding layer 203.
- the upper portion 407 of the guiding layer 401 may be asymmetric about an axis 413 bisecting the guiding layer 401.
- the lower portion 402 may be symmetric about the axis 413 bisecting the guiding layer 401.
- both the upper portion 407 and the lower portion 402 may be asymmetric about an axis 413 bisecting the guiding layer 401.
- the asymmetry of either the upper portion 407 of the guiding layer 401 alone or of the upper and lower portions 407 of the guiding layer 401 about an axis 413 which bisects the guiding layer 401 may be beneficial from the perspective of manufacturing and fabrication.
- the asymmetry of the taper of either the upper portion 407 or the upper portion 407 and lower portion 401 of the guiding layer 401 offers more tolerance during fabrication. To this end, mask positioning tolerances are greater when fabricating tapers that are asymmetric.
- waveguides according to the illustrative embodiments of Example I facilitate efficient optical coupling between two waveguides by adiabatically expanding/compressing an optical mode.
- waveguides according to the exemplary embodiments of Example II illustratively couple optical fibers of an optical communication system to planar waveguides of an OIC.
- a top view of guiding layer 401 of a waveguide is shown.
- a lower cladding layer (not shown) and an upper cladding layer (not shown) may be disposed under and over the guiding layer 401, respectively, thereby forming a waveguide.
- the upper and lower cladding layers are substantially the same as described in connection with the illustrative embodiments described fully above.
- a lower portion 402 of guiding layer 401 has a lower portion first taper 403 and a lower portion second taper 404.
- the lower portion first taper 403 is defined by an angle ⁇ 3 and length 405.
- the length 405 of the lower portion first taper 403 is readily determined by dropping a perpendicular to the terminal point of the first taper 403.
- Lower portion second taper 404 is defined by an angle ⁇ 4 , a length 406, again defined by dropping a perpendicular to the terminal point.
- An upper portion 407 of guiding layer 401 is disposed on the lower portion 402.
- the upper portion 407 of guiding layer 401 is disposed on the lower portion 402.
- the upper portion 407 has an upper portion first taper 408 which is defined by an angle Q ⁇ and a length 410, which may be found by dropping a perpendicular from the terminal point of upper portion first taper 408.
- the guiding layer 401 has an illustrative width w g , which decreases to a width w 2 at endface 410.
- Section 412 is illustrative, and the endface having reduced widthw 2 may be located at the termination of lower portion 402.
- an axis 413 bisects the guiding layer 401.
- the upper portion 407 is asymmetric about the axis 413.
- the lower portion 402 is substantially symmetric about the axis 413.
- the angles ⁇ 3 and ⁇ 4 are substantially identical.
- the lengths 405 and 406 of lower portion first and second tapers 403 and 404, respectively, are substantially identical, as well.
- the constraints on mask location tolerances in forming the upper portion 407 of guiding layer 401 are lessened, when compared to the embodiments described above where the upper portion is symmetric about an axis that bisects the guiding layer 401.
- a variety of structures for guiding layer 401 may be realized.
- both upper portion 407 and lower portion 402 of guiding layer 401 may be asymmetric about axis 400.
- Fig. 4(b) a top view of an illustrative embodiment of the present invention is shown.
- the lower portion 402 of the guiding layer 401 is substantially symmetric about axis 413. That is, angle ⁇ 3 is substantially identical to angle ⁇ 4 , and the length 405 is substantially the same as second length 406. However, angle ⁇ 2 and length 411 are essentially zero. As such, there is no second taper of upper portion 407.
- Upper portion 407 is substantially defined by ⁇ x and length 410. This embodiment is particularly advantageous in that a mask used to define the upper portion 407 need be only semi-self-aligning.
- Guiding layer 401 includes lower portion 402 and upper portion 407.
- angles ⁇ ! and ⁇ 4 are essentially zero.
- Upper portion 407 includes upper portion second taper 409 having a taper length 411.
- Lower portion 402 has a first taper 403 having a taper length 405.
- both the upper portion 407 and the lower portion '402 are asymmetric about axis 413 that bisects the guiding layer 401.
- Guiding layer 401 includes lower portion 402 and upper portion 407. In this illustrative embodiment, angles ⁇ j and ⁇ 4 are essentially zero.
- Upper portion 407 includes upper portion second taper 409 having a taper length 411.
- Lower portion 402 has a first taper 403 having a taper length 405.
- both the upper portion 407 and the lower portion 402 are asymmetric about axis 413 that bisects the guiding layer 401.
- FIG. 4(d) another illustrative embodiment of the present invention is shown.
- both the lower portion 402 and the upper portion are shown.
- angles ⁇ j and ⁇ 2 in conjunction with lengths 410 and 411, may be used to define the taper of upper portion 407.
- angle ⁇ 3 and length 405 may be used to define the taper of the lower portion 402 of guiding layer 401.
- the guiding layer may be of a variety of structures.
- the embodiments described are merely exemplary of the waveguide of the present invention. As such, these exemplary embodiments are intended to be illustrative and in no way limiting of the invention.
- FIG.5 shows a perspective view according to another illustrative embodiment of the present invention.
- a waveguide 500 includes a lower cladding layer 502.
- the lower cladding layer 502 may be disposed on a substrate 501.
- a guiding layer 503 is disposed on the lower cladding layer 502.
- An upper cladding layer (not shown) may be disposed on the guiding layer 503.
- the lower portion 507 of the guiding layer 503 is a diffused guiding layer.
- the lower portion 507 is illustratively a TiLiNbO 3 waveguide.
- the top portion 506 of waveguide 503 is a material having an index of refraction that is substantially the same as that of the lower portion 507 (the diffused waveguide).
- the embodiment shown in Fig. 5 is useful because diffused guiding layers are often wider (along x axis) than they are deep (along y axis) .
- the second region 505 of the top portion 506 is tapered in a manner similar to that shown in previous embodiments, for example that of Fig. 1.
- the top portion 506 of the second region 505 is useful in providing both vertical and horizontal mode transformation.
- waveguide 600 has a second region 605 that illustratively includes three layers.
- the substrate 601 has a lower cladding layer 602 disposed thereon.
- the guiding layer 603 has a first region 604 and a second region 605.
- the second region 605 has a lower portion 606 and an intermediate portion 607 and a top portion 610.
- An upper cladding layer 611 may be disposed over guiding layer 603.
- a waveguide couples to the end face 608; and illustratively the waveguide is an optical fiber (not shown).
- the second region 605 is symmetric about an axis 609 which bisects the lower portion 606.
- the fabrication sequence and materials are substantially the same in the embodiment shown in Fig. 6.
- a third photolithography/etching step would have to be carried out in the embodiment in which one layer of material is deposited to form the guiding layer 603.
- multiple depositions of the same material could be carried out in a manner consistent with that described in connection with Fig. 1.
- a sequence of photolithographic and etching steps would be carried out to realize the lower portion 606, intermediate portion 607 and top portion 610 of the second region 605.
- embodiments of this example include a waveguide end which has a cross-sectional shape compatible with that of a rib waveguide, as shown for example, in Fig. 7(b).
- a waveguide 700 which includes a guiding layer 703 which has two wings 750 extending outwardly from the guiding layer 703 at an endface 710 of the waveguide 700.
- the waveguide 700 includes a lower cladding layer 702 on which the guiding layer 703 is disposed.
- the upper cladding layer may have the same index of refraction as the lower cladding layer 702.
- the upper cladding layer may have a higher (or lower) index of refraction than that of the lower cladding layer 702.
- the guiding layer 703 has an index of refraction, n g , which is greater than the indices of refraction of both the upper cladding layer and lower cladding layer 702.
- the guiding layer 703 includes an upper portion 707 and a lower portion 706 which may have the same configuration as that of the above embodiments.
- the upper and lower portions 707, 706 may be tapered in a manner similar to that shown in previous embodiments, for example that of Fig. 1.
- the guiding layer 703 may be provided without tapers.
- Each wing 750 may be formed of the same material as the lower portion 706 as well as the upper portion 707 to provide a single material structure, as illustrated in the end view of Fig. 7(b).
- one or both of the wings 750 may comprise a material different from that of lower portion 706 and/or upper portion 707.
- Each wing 750 has a width, w w , and thickness, t 3 , at the endface 710 so that the combined structure of the guiding layer 703 and the wings 750 has the cross-sectional shape of a rib waveguide.
- the portion of the waveguide 700 at the rib end 710 is well-suited to coupling to a rib waveguide, such as one provided on an OIC.
- the thickness, t 3 , of the wings 750 may be the same as that of the lower portion 706 or may be different from that of the lower portion 706.
- the wings 750 decrease in width along the length of the guiding layer 703 to convert a mode in the waveguide 700 from a rib waveguide mode at endface 710 to a channel waveguide mode at the opposing endface 709 of the waveguide 700 (or vice versa depending on the direction of propagation in the waveguide 700).
- the thickness, t 3 , of the wings 750 may decrease along the length of the guiding layer 703 from a maximum value at the endface 710, as illustrated in Fig. 7(d).
- the rate at which the wing width, w w , decreases is controlled by the choice of the wing angle, Q w , shown in Fig. 7(c), which in turn dictates how adiabatic the mode transformation may be.
- a wing angle, ⁇ w of 1° or less may be sufficiently small to provide for adiabatic mode transformation from a rib mode to a channel mode.
- each wing 750 may have the same wing angle, ⁇ w .
- each wing 750 may have differing wing angles, ⁇ w .
- the wing angles, ⁇ w may have a value less than that or greater than that of the taper angle, ⁇ j, of the lower portion 706.
- the wing angle, ⁇ w may have a value equal to the taper angle, ⁇ ls of the lower portion 806, as illustrated in the embodiment of Fig. 8(a).
- the waveguide 800 of Fig. 8(a) illustrates a top view of another exemplary embodiment of a winged waveguide, which is similar in many respects to the embodiment of Figs. 7(a)-(d).
- the waveguide 800 includes a guiding layer 803 which has two wings 850 extending outwardly from the guiding layer 803 at an endface 810 of the waveguide 800.
- the waveguide 800 includes a lower cladding layer 802 on which the guiding layer 803 is disposed.
- An upper cladding layer (not shown) may be disposed on the guiding layer 803 in a similar manner as described with regard to the waveguide 700.
- the guiding layer 803 includes an upper portion 807 and a lower portion 806, which may be similar to corresponding structures shown in the above embodiments.
- the wing angle, ⁇ w has the same value as the taper angle, ⁇ ,.
- the wings 850 optionally have a length, l w , that extends from the endface 810 to the taper point 852 where the lower portion taper begins. Accordingly, for such a configuration of the wings 850 and lower portion 806, the wing sidewalls 851 and the taper sidewalls 817 of the lower portion taper are coplanar.
- Such a configuration of a waveguide 800 also provides for mode conversion between a rib waveguide mode and a channel waveguide mode.
- the wing angle, ⁇ w may be greater than the lower portion taper angle, ⁇ l5 as illustrated in the waveguide 860 of Fig. 8(b).
- the waveguide 860 includes a guiding layer 863 which has two wings 880 extending outwardly from the guiding layer 863 at an endface 870 of the waveguide 860.
- the waveguide 860 includes a lower cladding layer 862 on which the guiding layer 863 is disposed.
- An upper cladding layer (not shown) may be disposed on the guiding layer 863 in a similar manner as described with regard to the waveguide 800.
- the guiding layer 863 includes an upper portion 867 and a lower portion 866, which maybe similar to corresponding structures shown in the above embodiments.
- the wing angle, ⁇ w has a larger value than the taper angle, ⁇
- the wings 880 optionally have a length, l w , that extends from the endface 810 to the taper point 854 where the lower portion taper begins.
- the waveguide 860 also provides for mode conversion between a rib waveguide mode and a channel waveguide mode.
- the waveguide 900 is similar in several respects to the waveguide 800 of Fig. 8(a). Like the waveguide 800, the waveguide 900 includes a guiding layer 903 which has two wings 950 extending outwardly from the guiding layer 903 at an endface 910 of the waveguide 900.
- the waveguide 900 includes a lower cladding layer 902 on which the guiding layer 903 is disposed.
- An upper cladding layer (not shown) may be disposed on the guiding layer 903 in a similar manner as described with regard to the waveguide 800.
- the guiding layer 903 includes an upper portion 907 and a lower portion 906, similar to the corresponding structures shown in Fig. 8(a).
- the wing angle has the same value as the taper angle so that the wing sidewalls and the taper sidewalls of the lower portion taper are coplanar.
- the upper portion 907 of the waveguide 900 has a width, w u , which at all points along a length of the waveguide 900 is less than the width across the lower portion 906 and the wings 950.
- standard masking and etching steps as described in connection with the illustrative embodiments in Examples I-IH may be used in fabricating the waveguides of the present example.
- waveguides have been described as being made with tapers that vary in horizontal width, that is, width that changes in the direction of the plane of the substrate that the waveguide is fabricated on. This is an advantage of the invention, for while waveguides with vertical taper could also be fabricated as an embodiment of the present invention, these may be much more difficult to manufacture.
- tapered sections have been illustrated as having planar walls, the tapered sections could also have arcuate walls to provide a curved taper.
Abstract
Description
Claims
Applications Claiming Priority (5)
Application Number | Priority Date | Filing Date | Title |
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US33693301P | 2001-12-05 | 2001-12-05 | |
US336933P | 2001-12-05 | ||
PCT/US2001/051497 WO2002095453A2 (en) | 2000-12-14 | 2001-12-14 | Optical waveguide termination with vertical and horizontal mode shaping |
WOPCT/US01/51497 | 2001-12-14 | ||
PCT/US2002/038553 WO2003050580A1 (en) | 2001-12-05 | 2002-12-05 | Optical waveguide termination with vertical and horizontal mode shaping |
Publications (2)
Publication Number | Publication Date |
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EP1461651A1 true EP1461651A1 (en) | 2004-09-29 |
EP1461651A4 EP1461651A4 (en) | 2005-04-27 |
Family
ID=26680611
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
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EP02786857A Withdrawn EP1461651A4 (en) | 2001-12-05 | 2002-12-05 | Optical waveguide termination with vertical and horizontal mode shaping |
Country Status (4)
Country | Link |
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EP (1) | EP1461651A4 (en) |
JP (1) | JP2006517673A (en) |
AU (1) | AU2002351211A1 (en) |
WO (1) | WO2003050580A1 (en) |
Families Citing this family (21)
Publication number | Priority date | Publication date | Assignee | Title |
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US7068870B2 (en) | 2000-10-26 | 2006-06-27 | Shipley Company, L.L.C. | Variable width waveguide for mode-matching and method for making |
US7251406B2 (en) | 2000-12-14 | 2007-07-31 | Shipley Company, L.L.C. | Optical waveguide termination with vertical and horizontal mode shaping |
EP1356327B1 (en) | 2000-12-14 | 2008-04-16 | Shipley Company LLC | Optical mode size converter with vertical and horizontal mode shaping |
US7158701B2 (en) | 2001-02-21 | 2007-01-02 | Shipley Company, L.L.C. | Method for making optical devices with a moving mask and optical devices made thereby |
US6912345B2 (en) | 2001-03-30 | 2005-06-28 | Shipley Company, L.L.C. | Tapered optical fiber for coupling to diffused optical waveguides |
US20050067037A1 (en) * | 2003-09-30 | 2005-03-31 | Conocophillips Company | Collapse resistant composite riser |
TW200533972A (en) * | 2004-03-01 | 2005-10-16 | Univ Mcgill | Apparatus for efficient optical frequency conversion |
JP4868763B2 (en) * | 2005-03-31 | 2012-02-01 | 住友大阪セメント株式会社 | Light modulator |
WO2008014606A1 (en) * | 2006-07-31 | 2008-02-07 | Onechip Photonics Inc. | Integrated vertical wavelength (de)multiplexer using tapered waveguides |
JP2011164376A (en) * | 2010-02-10 | 2011-08-25 | Mitsubishi Electric Corp | Spot size conversion waveguide |
WO2012042708A1 (en) * | 2010-09-28 | 2012-04-05 | 日本電気株式会社 | Optical waveguide structure and optical waveguide device |
US9128242B2 (en) | 2011-12-15 | 2015-09-08 | Mitsubishi Electric Research Laboratories, Inc. | Mode-evolution compound converter |
WO2013146818A1 (en) * | 2012-03-28 | 2013-10-03 | 日本電気株式会社 | Light waveguide structure and light waveguide device |
JP2013231753A (en) * | 2012-04-27 | 2013-11-14 | Nippon Telegr & Teleph Corp <Ntt> | Spot size converter and manufacturing method thereof |
JP2013238708A (en) * | 2012-05-15 | 2013-11-28 | Nippon Telegr & Teleph Corp <Ntt> | Spot size converter and method for manufacturing the same |
JP6065663B2 (en) * | 2013-03-08 | 2017-01-25 | 住友電気工業株式会社 | Method for fabricating a semiconductor optical waveguide device |
KR102037759B1 (en) * | 2013-03-25 | 2019-10-30 | 한국전자통신연구원 | optical coupler and optical device module used the same |
WO2014196103A1 (en) | 2013-06-07 | 2014-12-11 | 日本電気株式会社 | Waveguide mode conversion element, orthomode transducer, and optical device |
JP2015191029A (en) * | 2014-03-27 | 2015-11-02 | 沖電気工業株式会社 | spot size converter |
WO2016008114A1 (en) * | 2014-07-16 | 2016-01-21 | 华为技术有限公司 | Spotsize converter and apparatus for optical conduction |
US10359569B2 (en) * | 2016-05-09 | 2019-07-23 | Huawei Technologies Co., Ltd. | Optical waveguide termination having a doped, light-absorbing slab |
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JPH0281005A (en) * | 1988-09-19 | 1990-03-22 | Nec Corp | Waveguide type optical device |
WO2001027670A1 (en) * | 1999-10-13 | 2001-04-19 | Bookham Technology Plc | Method of fabricating an integrated optical component |
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US6229947B1 (en) * | 1997-10-06 | 2001-05-08 | Sandia Corporation | Tapered rib fiber coupler for semiconductor optical devices |
US6317445B1 (en) * | 2000-04-11 | 2001-11-13 | The Board Of Trustees Of The University Of Illinois | Flared and tapered rib waveguide semiconductor laser and method for making same |
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2002
- 2002-12-05 EP EP02786857A patent/EP1461651A4/en not_active Withdrawn
- 2002-12-05 AU AU2002351211A patent/AU2002351211A1/en not_active Abandoned
- 2002-12-05 WO PCT/US2002/038553 patent/WO2003050580A1/en active Application Filing
- 2002-12-05 JP JP2003551579A patent/JP2006517673A/en active Pending
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JPH0281005A (en) * | 1988-09-19 | 1990-03-22 | Nec Corp | Waveguide type optical device |
WO2001027670A1 (en) * | 1999-10-13 | 2001-04-19 | Bookham Technology Plc | Method of fabricating an integrated optical component |
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BAUER J.G. ET AL: 'HIGH RESPONSIVITY INTEGRATED TAPERED WAVEGUIDE PIN PHOTODIODE' PROCEEDINGS OF THE EUROPEAN CONFERENCE ON OPTICAL COMMUNICATION (ECOC) MONTREUX, SEPT. 12 - 16, 1993. REGULAR PAPERS, ZURICH, SEV, CH vol. 2, 12 September 1993, pages 277 - 280, XP000492220 * |
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No further relevant documents disclosed * |
See also references of WO03050580A1 * |
Also Published As
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EP1461651A4 (en) | 2005-04-27 |
AU2002351211A1 (en) | 2003-06-23 |
JP2006517673A (en) | 2006-07-27 |
WO2003050580A1 (en) | 2003-06-19 |
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