Double-ridge-shaped end face coupler based on thick silicon platform

Abstract

The utility model provides a double-ridge-shaped end face coupler based on a thick silicon platform. The double-ridge-shaped end face coupler comprises a substrate and a coupling waveguide structure. The substrate comprises a bottom silicon layer and a buried oxide layer, and a coupling waveguide structure is arranged on the buried oxide layer; the coupling waveguide structure comprises a double-ridge-shaped inverted-cone waveguide and a strip-shaped waveguide which are connected with each other. By adopting the thick silicon platform, the polarization dependent loss can be reduced; by adopting the double-ridge inverted-cone waveguide, the unification of low loss and high tolerance can be obtained; in addition, the coupler can be processed based on an SOI wafer, the device is of a single-layer silicon design, additional multi-layer manufacturing is not needed, the photoetching and etching cost can be saved, the process is simple, and the coupler is good in compatibility with a CMOS (Complementary Metal-Oxide-Semiconductor Transistor) platform.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of silicon optoelectronics, and in particular to a double-ridge-shaped end-face coupler based on a thick silicon platform. BACKGROUND

[0002] Since silicon is an indirect bandgap semiconductor material, a light source cannot be integrated based on a silicon-based platform, so an external optical fiber is generally used, which inevitably causes a problem that the mode field diameter of a traditional optical fiber is several orders of magnitude larger than the size of a waveguide, and the loss problem is a great challenge. Currently, the mainstream coupling schemes are two kinds: vertical coupling (also known as grating coupling) and end-face coupling. However, the grating coupling has the disadvantages of low coupling efficiency, limited optical bandwidth, strong polarization dependence, and the like, so the research on the end-face coupler is more important than that on the grating coupler.

[0003] However, after comparing and researching some typical end-face couplers, it is found that there are problems as follows: the end-face coupler with small insertion loss has poor alignment tolerance or process tolerance, that is, the tolerance performance is poor. Taking a 220-nm traditional thin silicon platform as an example, the basic principle of coupling at the end face is to make the width of the waveguide smaller, generally several hundred nanometers or tens of nanometers, so that the ability of the waveguide to bind the light field is weakened, and part of the light field is distributed in the oxide layer and the upper cladding layer, so that the mode spot size is increased. When actually produced, the width of the waveguide will have a process error, so that the insertion loss of the coupler of this type will be significantly increased. In addition, the end-face coupler with good tolerance performance has low efficiency, or the end-face coupler with both good performance has a complex process, is not compatible with the CMOS platform, has huge cost, and has low yield.

[0004] Therefore, based on the above problems, the present application provides an end-face coupler based on a thick silicon platform, which has low loss, low cost, large tolerance, and low polarization-dependent loss.

[0005] It should be noted that the above introduction to the technical background is only for the convenience of clearly and completely describing the technical scheme of the present application and facilitating the understanding of those skilled in the art. The above technical scheme cannot be considered as known to those skilled in the art only because it is described in the background section of the present application. CONTENT OF THE UTILITY MODEL

[0006] The utility model discloses to solve all or part problems of the prior art, provide a double-ridge-shaped end-face coupler based on thick silicon platform, to realize the unification of high coupling efficiency, high tolerance and simple preparation process.

[0007] In order to achieve the above object, the utility model provides a kind of double-ridge end face coupler based on thick silicon platform, including substrate and coupling waveguide structure;The substrate includes bottom silicon layer and buried oxygen layer, and coupling waveguide structure is arranged on the buried oxygen layer;The coupling waveguide structure includes the double-ridge inverted taper waveguide and bar waveguide connected.The polarization-dependent loss can be reduced by using thick silicon platform;Double-ridge inverted taper waveguide can not only get high tolerance of ridge structure, but also improve the spot matching of coupler and optical fiber by introducing double-ridge input end face, reduce the mode field mismatch loss of end face;By using inverted taper structure, the internal mode evolution and transmission loss of the device are reduced;Finally, the unification of low loss and high tolerance is realized;In addition, the coupler can be processed based on SOI wafer, and the device is single-layer silicon design, without additional PLCVD or PECVD for multilayer manufacturing, can save the cost of lithography and etching, process is simple and has good compatibility with CMOS platform.

[0008] In some embodiments, the double-ridge inverted taper waveguide includes a double-ridge inverted taper waveguide flat layer and a double-ridge inverted taper waveguide ridge layer arranged from bottom to top;The bar waveguide includes a bar waveguide flat layer and a bar waveguide ridge layer arranged from bottom to top.

[0009] In some embodiments, the width of the inverted taper structure of the double-ridge inverted taper waveguide ridge layer increases linearly from the front end to the rear end.

[0010] In some embodiments, the width of the inverted taper structure of the double-ridge inverted taper waveguide ridge layer increases parabolically from the front end to the rear end.

[0011] In some embodiments, the width difference between the front and rear ends of the inverted taper structure of the double-ridge inverted taper waveguide ridge layer is between 3-4 microns.

[0012] In some embodiments, the length of the double-ridge inverted taper waveguide is more than 135 microns.

[0013] In some embodiments, the thickness of the double-ridge inverted taper waveguide flat layer and the bar waveguide flat layer is the same.

[0014] In some embodiments, the bar waveguide flat layer is a trapezoidal structure, and the width decreases linearly from the end of the bar waveguide flat layer connected to the double-ridge inverted taper waveguide flat layer to the rear.

[0015] In some embodiments, it further includes a cladding layer, the cladding layer covers the coupling waveguide structure, and the cladding layer is a silicon dioxide layer.

[0016] In some embodiments, it is used for coupling with a lens optical fiber.

[0017] Compared with the prior art, the main beneficial effects of the utility model are as follows: 1) low polarization dependent loss: the coupler adopts thick silicon process, which means that the effective refractive indexes of TE and TM modes are close to equal, and the main reason for the polarization dependent loss is the effective refractive index difference between TM and TE modes, for the traditional thin silicon or silicon nitride, their width is generally tens to hundreds of nanometers, in this case, the effective refractive index difference between TM and TE is larger, and the polarization dependent loss is difficult to reduce; 2) low insertion loss: because the coupler is well matched with the optical fiber in the end face part, one is that the thickness of the waveguide is not much different from the mode field diameter of the optical fiber, and two is that the structure after the end face adopts an inverted taper structure, and the width difference of the inverted taper two ends is only 3 to 4 microns, so the transmission loss is small; 3) low cost: the design does not use lithium niobate or silicon nitride and other special materials, but only uses silicon material. Most importantly, the device only has one layer of silicon design, does not need to use PLCVD or PECVD for multi-layer manufacturing, and can also save the cost of lithography and etching. BRIEF DESCRIPTION OF DRAWINGS

[0018] In order to more clearly illustrate the technical scheme in the specific embodiments of the utility model, the drawings needed to be used in the embodiment description will be briefly introduced, obviously, the drawings described below are only some embodiments of the utility model, and for those skilled in the art, other drawings can also be obtained according to these drawings without creating labor.

[0019] Figure 1 The three-dimensional structure schematic diagram of the double-ridge end face coupler provided for the application.

[0020] Figure 2 The input end face sectional view of the double-ridge end face coupler provided for the application.

[0021] Figure 3 The plan view of the double-ridge end face coupler provided for the application.

[0022] Figure 4 The end face mode spot schematic diagram of the ridge waveguide in the prior art.

[0023] Figure 5 The end face mode spot schematic diagram of the double-ridge waveguide provided for the application. DETAILED DESCRIPTION

[0024] The foregoing and other technical contents, features and effects of the present application will be clearly presented in the following detailed description of the preferred embodiments with reference to the accompanying drawings. The directional terms mentioned in the following embodiments, such as up, down, left, right, front or back, etc., are only for reference to the directions of the accompanying drawings. Therefore, the directional terms used are for illustration and not for limitation of the present application.

[0025] Embodiment one:

[0026] There is a large mode spot size mismatch and effective refractive index mismatch between the silicon-based single-mode waveguide and the single-mode optical fiber. If the optical signal is directly input from the optical fiber into the silicon waveguide, there will be very large loss. Therefore, a coupler with high coupling efficiency is needed. The function of the end-face coupler is to realize the coupling between the optical fiber and the chip, that is, to couple the optical signal input by the optical fiber into the device waveguide of the chip through the end-face coupler.

[0027] The present application provides a double-ridge end-face coupler based on a thick silicon platform, a three-dimensional structural schematic diagram of which is shown in Figure 1 , a top view of which is shown in Figure 2 , and an input end-face cross-sectional view of which is shown in Figure 3 . The structure of the coupler includes a bottom silicon layer (not shown in the figure) and a buried oxygen layer (not shown in the figure); the buried oxygen layer is arranged on the bottom silicon layer, and a coupling waveguide structure is arranged on the buried oxygen layer; the coupling waveguide structure includes a double-ridge inverted taper waveguide 1 in contact with an optical fiber inputting an optical signal and a strip waveguide 2 in the rear; in addition, the end-face coupler further includes a cladding layer (not shown in the figure) covering the coupling waveguide structure.

[0028] The working process of the double-ridge end-face coupler based on a thick silicon platform provided in the present embodiment is as follows: signal light is transmitted to the input end-face of the coupler through an optical fiber and coupled into the double-ridge inverted taper waveguide 1 and then transmitted to the strip waveguide 2 in the rear, and finally input to a device waveguide, realizing the coupling input of the optical field from the optical fiber to the chip. In the present embodiment, the optical fiber coupled with the double-ridge end-face coupler is a lens optical fiber, which is a specially designed optical fiber combining the functions of an optical fiber and a lens, and integrates a micro-lens at one end of the optical fiber to realize the focusing or divergence of light. In other embodiments, a common optical fiber can also be used.

[0029] In the present embodiment, the double-ridge inverted taper waveguide 1 includes a double-ridge inverted taper waveguide flat plate layer 10 and a double-ridge inverted taper waveguide ridge layer 11 arranged from bottom to top; and the strip waveguide 2 includes a strip waveguide flat plate layer 20 and a strip waveguide ridge layer 21 arranged from bottom to top.

[0030] Specifically, the inverted cone width of the double-ridged inverted cone waveguide ridge layer 11 (i.e., the width of each ridge structure in the double-ridged inverted cone waveguide ridge layer 11) gradually increases from the front end to the rear end, and its inverted cone width changes linearly, so that the refractive index of the double-ridged inverted cone waveguide 1 gradually changes from the front end to the rear end. It should be noted that in this embodiment, the inverted cone width of the double-ridged inverted cone waveguide 1 adopts a linear change setting; in other embodiments, the inverted cone width of the double-ridged inverted cone waveguide 1 can also be set to a parabola or other linear gradient according to actual needs. In this embodiment, the length of the double-ridged inverted cone waveguide 1 is 135 microns. 135um meets adiabatic transmission requirements, and the width difference between the front and rear ends of the inverted cone is only 3 to 4 microns, so the transmission loss is relatively small. In other embodiments, the length of the double-ridged inverted cone waveguide 1 can be greater than 135 microns.

[0031] In the prior art, the contact portion between the end face coupler and the end face of the optical fiber is usually a single-ridge waveguide structure. The ridge waveguide structure can provide precise alignment and stability, thereby achieving a higher tolerance. However, the traditional single-ridge waveguide structure has a large optical mode field mismatch loss with the optical fiber. Figure 4 Schematic diagram of the end face mode spot of a single ridge waveguide in the prior art. Figure 1 It can be seen that for traditional single-ridge waveguides, there are certain limitations on the light spot in the waveguide, but the degree of limitation is limited. It is impossible to confine the waveguide light spot to a circular shape that closely matches the optical fiber. This will cause the end coupler to produce relatively large losses at the contact part with the end face of the optical fiber. This loss mainly comes from the mismatch of the end face mode spot.

[0032] Generally speaking, the closer the shape and area of ​​the end coupler's mode spot are to those of the fiber's end face, the smaller the end face's mode field mismatch loss will be. Therefore, this embodiment proposes the use of a double-ridge waveguide structure as the contact portion between the end coupler and the fiber's end face. With a double-ridge structure, its end face mode spot area can be larger, and the oxide layer (silicon dioxide) covering the waveguide can also be used to expand it into a circular mode spot. The results are shown in Figure 1. Figure 5As shown in the figure, the blue area represents the end face of the double-ridge inverted taper waveguide 1, and the white area in the center represents the mode spot 3. The design of the end face can make the overlap integral of the TE (Transverse Electric) mode and TM (Transverse Magnetic) mode of the end face reach above 0.9, thus solving the problem of the end face part loss. The loss of the end face coupler generally comes from three aspects: 1, the mode field mismatch loss of the end face; 2, the Fresnel reflection loss; 3, the mode evolution and transmission loss inside the device. In order to further reduce the loss of the end face coupler, an inverted taper structure is adopted in the rear end part of the end face coupler, and the transmission loss is also relatively small. Therefore, in the embodiment, through the contact end face of the double-ridge structure of the double-ridge inverted taper waveguide 1 and the rear end transmission part of the inverted taper structure, high tolerance and low loss are achieved.

[0033] In the embodiment, the double-ridge inverted taper waveguide 1 is connected with a strip waveguide 2, which includes a strip waveguide flat layer 20 and a strip waveguide ridge layer 21 arranged from bottom to top. The thickness of the strip waveguide flat layer 20 is the same as the thickness (H1) of the double-ridge inverted taper waveguide flat layer 10, and the thickness is between 1-2 microns; similarly, the thickness of the strip waveguide ridge layer 21 is the same as the thickness of the double-ridge inverted taper waveguide ridge layer 21; the strip waveguide flat layer 20 presents an isosceles trapezoidal structure, and the width of the end connected with the double-ridge inverted taper waveguide flat layer 10 is larger, and the width linearly decreases to the rear end.

[0034] It should be noted that the double-ridge end face coupler provided in the present application is prepared by thick silicon technology, that is, the thickness of the double-ridge end face coupler is generally in the order of several microns. For example, in the embodiment, it is based on a 3-micron-thick silicon platform, that is, the total thickness of the coupling waveguide structure of the end face coupler is 3 microns, as shown by the thickness H2 in Figure 3 In other embodiments, the thickness of the coupling waveguide structure can be changed according to the selected optical fiber. For example, preferably, the thickness of the coupling waveguide structure of the end face coupler can be 1-10 microns.

[0035] Since the thick silicon technology is adopted, that is, the thickness of the end face coupler is large, the end face coupler provided in the present application can obtain less polarization-dependent loss. This is because the main reason for the polarization-dependent loss is that the effective refractive index difference between TM and TE modes is large, and in the end face coupler of the present application, the effective refractive indices of TE and TM modes are close to equal, while for traditional thin silicon or silicon nitride, since their thickness is generally in the order of tens to hundreds of nanometers, in this case, the effective refractive index difference between TM and TE is large, so it is difficult to make the polarization-dependent loss small for these couplers.

[0036] On the other hand, the end face coupler in the application is based on SOI wafer processing, the structures are formed in the top silicon layer of the SOI wafer, and the device only has one layer of silicon design, without additional use of LPCVD (low pressure chemical vapor deposition) or PECVD (plasma enhanced chemical vapor deposition) for multi-layer manufacturing, so that the cost of photolithography and etching can be saved.

[0037] The common English nouns or letters used for the convenience of clear description in the utility model are only used for exemplary reference, and are not limited to the non-limiting interpretation or specific usage, and the protection scope of the utility model should not be limited by the possible Chinese translation or specific letters.

[0038] It should also be noted that in this paper, such as "first" and "second" and other relational terms are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between the entities or operations.

Claims

1. A double-ridge end-face coupler based on a thick silicon platform, characterized in that, The application relates to a coupling waveguide structure, which comprises a substrate and a coupling waveguide structure; the substrate comprises a bottom silicon layer and a buried oxygen layer, and the buried oxygen layer is provided with the coupling waveguide structure; The coupling waveguide structure comprises a double-ridge inverted taper waveguide and a strip waveguide connected with each other; The double-ridge inverted taper waveguide comprises a double-ridge inverted taper waveguide flat layer and a double-ridge inverted taper waveguide ridge layer arranged from bottom to top, and the strip waveguide comprises a strip waveguide flat layer and a strip waveguide ridge layer arranged from bottom to top; The application further discloses a cladding layer, which covers the coupling waveguide structure, and the cladding layer is a silicon dioxide layer.

2. The dual-ridge end-coupler based on thick-silicon platform according to claim 1, wherein, The width of the inverted taper structure of the double-ridge inverted taper waveguide ridge layer linearly increases from the front end to the rear end.

3. The dual-ridge end-coupler based on thick-silicon platform according to claim 1, wherein, The width of the inverted taper structure of the double-ridge inverted taper waveguide ridge layer parabolically increases from the front end to the rear end.

4. The dual-ridge end-coupler based on thick-silicon platform according to claim 2, wherein, The width difference between the front end and the rear end of the inverted taper structure of the double-ridge inverted taper waveguide ridge layer is between 3-4 microns.

5. The dual-ridge end-coupler based on thick-silicon platform according to claim 1, wherein, The length of the double-ridge inverted taper waveguide is above 135 microns.

6. The dual-ridge end-coupler based on thick-silicon platform according to claim 1, wherein, The thickness of the double-ridge inverted taper waveguide flat layer and the strip waveguide flat layer is the same.

7. The dual-ridge end-coupler based on thick-silicon platform according to claim 1, wherein, The strip waveguide flat layer is a trapezoidal structure, and the width linearly decreases from the end, where the strip waveguide flat layer is connected with the double-ridge inverted taper waveguide flat layer, to the rear end.

8. The dual-ridge end-coupler based on thick-silicon platform according to claim 1, wherein, The application is used for coupling with a lens optical fiber.

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