Optical multimode interference coupler based on a hybrid structure of a strip ridge waveguide

Abstract

The application provides an optical multimode interference coupler based on a bar-ridge waveguide hybrid structure, and relates to the field of integrated optics. The coupler is integrally formed and sequentially comprises a single-mode input waveguide with a ridge structure, a tapered input waveguide, a multimode waveguide with a bar structure, a tapered output waveguide with a ridge structure and a single-mode output waveguide from the input to the output of the signal. The waveguide with the ridge structure comprises a ridge waveguide and a flat plate area waveguide; the ridge waveguide width of the single-mode input waveguide is equal to the minimum ridge waveguide width of the tapered input waveguide; the sum of the maximum ridge waveguide widths of the tapered input waveguide is less than the width of the multimode waveguide; the sum of the maximum ridge waveguide widths of the tapered output waveguide is less than the width of the multimode waveguide; and the minimum ridge waveguide width of the tapered output waveguide is equal to the ridge width of the single-mode output waveguide. Based on the above coupler, the structure of an electronic component is formed without using a traditional tapered conversion structure.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of integrated optics, in particular to an optical multimode interference coupler based on a bar-ridge waveguide hybrid structure. BACKGROUND

[0002] In modern optical communication systems, with the continuous improvement of optical function requirements, a large number of optical switch modulation units need to be used on the optical chip to realize complex optical routing and optical information processing functions. Typical applications are high-speed electro-optical switch arrays.

[0003] In existing optical switch modulation units, a transition structure of bar waveguide and ridge waveguide is often used to connect bar optical beam splitters, bar optical beam combiners and ridge modulation arm waveguides. Therefore, a large number of transition structures of bar waveguide and ridge waveguide are needed inside the optical chip.

[0004] Due to the long length of the transition structure, in the case of a large number of repeated use of the transition structure, the size of the optical device and the overall area of the optical chip will be increased, thereby reducing the integration level of the system chip. SUMMARY

[0005] (I) Technical problems solved

[0006] In view of the deficiencies of the prior art, the present application provides an optical multimode interference coupler based on a bar-ridge waveguide hybrid structure, which solves the problem of low integration level of the system chip in the prior art.

[0007] (II) Technical solutions

[0008] To achieve the above purpose, the present application is implemented by the following technical solutions:

[0009] In the first aspect of the present application, an optical multimode interference coupler based on a bar-ridge waveguide hybrid structure is provided,

[0010] The optical multimode interference coupler comprises, in order from the input to the output direction of the signal, a single-mode input waveguide with a ridge structure, a tapered input waveguide with a ridge structure, a multimode waveguide with a bar structure, a tapered output waveguide with a ridge structure, and a single-mode output waveguide with a ridge structure.

[0011] All waveguides with a ridge structure include a ridge waveguide and a flat plate region waveguide.

[0012] The ridge waveguide width of the single-mode input waveguide is equal to the minimum ridge waveguide width of the tapered input waveguide.

[0013] The sum of the maximum ridge waveguide widths of the tapered input waveguide is less than the width of the multimode waveguide.

[0014] the sum of the maximum ridge waveguide widths of the tapering output waveguides is less than the width of the multimode waveguide;

[0015] the minimum ridge waveguide width of the tapering output waveguide is equal to the ridge width of the single-mode output waveguide.

[0016] Optionally, the ridge waveguide of the single-mode input waveguide is of the same size as the ridge waveguide of the single-mode output waveguide.

[0017] the ridge waveguide of the tapering input waveguide and the ridge waveguide of the tapering output waveguide are of the same size.

[0018] Optionally, the multimode waveguide is located in the middle region of the optical multimode interference coupler; the tapering input waveguide and the tapering output waveguide are respectively located on both sides of the multimode waveguide and are directly connected to the multimode waveguide.

[0019] Optionally, if the optical multimode interference coupler is a 1x2 coupler, the number of single-mode input waveguides, tapering input waveguides and multimode waveguides is 1, and the number of tapering output waveguides and single-mode output waveguides is 2.

[0020] The two tapering output waveguides and the two single-mode output waveguides are symmetrically distributed about the transverse central axis of the multimode waveguide.

[0021] Optionally, if the optical multimode interference coupler is a 2x1 coupler, the number of single-mode input waveguides and tapering input waveguides is 2, and the number of multimode waveguides, tapering output waveguides and single-mode output waveguides is 1.

[0022] The two tapering input waveguides and the two single-mode input waveguides are symmetrically distributed about the transverse central axis of the multimode waveguide.

[0023] Optionally, the thickness of the slab region waveguide is adjusted according to the thickness of the top silicon layer of the optical multimode interference coupler; the ridge waveguide width of all ridge waveguides is adjusted according to the thickness of the top silicon layer of the optical multimode interference coupler.

[0024] Specifically, the thickness of the top silicon layer is 3 μm, the thickness of the slab region waveguide is 1.3 μm, the minimum ridge waveguide width of the tapering input waveguide is 2.2 μm, and the maximum ridge waveguide width of the tapering input waveguide is 2.5 μm.

[0025] Optionally, in the optical multimode interference coupler, the length of the multimode waveguide is 70 μm, and the length of the ridge waveguide of the tapering output waveguide is 10 μm.

[0026] (III) Beneficial Effects

[0027] The present application provides an optical multimode interference coupler based on a hybrid structure of a strip ridge waveguide. Compared with the prior art, the following beneficial effects are achieved:

[0028] The present application provides an optical multimode interference coupler based on a hybrid structure of a strip ridge waveguide. The optical multimode interference coupler is integrally formed and sequentially includes, from the input direction of a signal to the output direction, a single-mode input waveguide of a ridge structure, a tapered input waveguide of a ridge structure, a multimode waveguide of a strip structure, a tapered output waveguide of a ridge structure, and a single-mode output waveguide of a ridge structure. All waveguides of the ridge structure include a ridge waveguide and a flat plate region waveguide. The ridge waveguide width of the single-mode input waveguide is equal to the minimum ridge waveguide width of the tapered input waveguide. The sum of the maximum ridge waveguide widths of the tapered input waveguide is less than the width of the multimode waveguide. The sum of the maximum ridge waveguide widths of the tapered output waveguide is less than the width of the multimode waveguide. The minimum ridge waveguide width of the tapered output waveguide is equal to the ridge width of the single-mode output waveguide. Based on the above processing, the present application directly connects the ridge transmission waveguide and the strip multimode waveguide interface. Based on the multimode excitation principle of the multimode interference coupler, the optical signal in the ridge single-mode waveguide is simultaneously excited and the waveguide structure is converted at the interface of the strip structure multimode waveguide. The traditional tapered strip ridge waveguide conversion structure is not used, the length of the electronic component is effectively reduced, and the integration of the device is improved. BRIEF DESCRIPTION OF DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort based on these drawings.

[0030] Figure 1 A structural schematic diagram of a 1x2 port coupler in the prior art;

[0031] Figure 2 A principle schematic diagram of an electro-optical switch unit based on MZI provided by the present application;

[0032] Figure 3 A structural schematic diagram of an electro-optical switch unit provided by the present application;

[0033] Figure 4 A schematic diagram of a conventional strip ridge waveguide conversion structure provided by the present application;

[0034] Figure 5A structure schematic diagram of a MZI optical switch unit connected with a single-mode transmission waveguide provided by the present application;

[0035] Figure 6 A structure schematic diagram of an optical multimode interference coupler based on a bar-ridge waveguide hybrid structure provided by the present application;

[0036] Figure 7 A top view of a 1x2 optical multimode interference coupler provided by the present application;

[0037] Figure 8 A cross section of a ridge waveguide of a 1x2 coupler provided by the present application;

[0038] Figure 9 A cross section of a bar multimode waveguide of a 1x2 coupler provided by the present application;

[0039] Figure 10 A 1x1 MZI optical switch principle diagram based on a bar-ridge waveguide hybrid structure provided by the present application. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical scheme and advantages of the embodiments of the present application more clear, the technical scheme in the embodiments of the present application is described clearly and completely. Obviously, the described embodiments are part of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the present application.

[0041] The embodiments of the present application provide an optical multimode interference coupler based on a bar-ridge waveguide hybrid structure, avoid the traditional conversion structure between a bar waveguide and a ridge waveguide, and solve the problem of low integration of a system chip in the prior art.

[0042] The technical scheme in the embodiments of the present application is as follows to solve the above technical problem:

[0043] In the application scenario of a thick silicon platform, a single-mode waveguide with a ridge structure can realize ultra-low-loss optical transmission, and an optical beam splitter with a bar structure can complete the optical beam splitting function in a compact size.

[0044] In actual application, the ridge single-mode transmission waveguide and the bar multimode waveguide are often used simultaneously. For example, in an electro-optical switch based on a Mach-Zehnder phase shift modulation, two bar 1x2 optical beam splitters, two ridge modulation arm waveguides, two input and output transmission waveguides are included. At the connection of the bar waveguide and the ridge waveguide, the waveguide structure conversion is needed.

[0045] The prior art solution is a transition conversion structure based on a gradual change structure, but the length of the unit device is increased, especially when a phase shift modulation switch array is used in large scale, a large number of gradual transition strip ridge waveguide conversion structures are needed.

[0046] The application provides an optical multimode interference coupler based on a strip ridge waveguide hybrid structure, a ridge transmission waveguide is directly connected with a strip multimode waveguide at an interface, based on a multimode excitation principle of the multimode interference coupler, light signals in the ridge single-mode waveguide are simultaneously excited in the multimode waveguide at the interface of the strip structure, the multimode excitation in the waveguide and the transition of the waveguide structure are completed, a traditional gradual change strip ridge waveguide conversion structure is not needed, the length of the electronic unit device is effectively reduced, and the integration degree of the device is improved.

[0047] In order to better understand the above technical solution, the above technical solution will be described in detail in combination with the description of the drawings and the specific embodiments.

[0048] Firstly, the basic concept in the application is introduced.

[0049] At present, in the field of silicon-based photonics, optical couplers based on the principle of multimode interference coupling are widely used in various optical functional structures.

[0050] Among them, the multimode interference coupling principle uses the transmission effect between different modes in the multimode optical waveguide: the propagation constants of different light modes are different, so different phase multimode interference superpositions occur at different distances along the propagation direction, and then different interference patterns are formed and the light splitting effect of different output ports is realized.

[0051] From the waveguide structure, the core region of the multimode interference coupler is a wide waveguide that supports different light mode transmissions. The core region can adopt a strip structure or a ridge structure. Usually, a certain number of input waveguides and output waveguides are arranged on both sides of the wide waveguide core region, and the input waveguides and output waveguides are responsible for connecting the wide waveguide core region and the single-mode transmission waveguide outside the coupler. Referring to Figure 1 , Figure 1 A structural diagram of a 1x2 port coupler in the prior art. For a common 1x2 port coupler, the two structures are as shown in Figure 1 .

[0052] An electro-optical switch is an optical router widely used in communication systems. For example, an optical switch unit based on MZI (Mach-Zehnder Interferometer) is a 1x1 port structure, which uses an electrical Mach-Zehnder modulation arm waveguide, an optical beam splitter and an optical beam combiner inside. Referring to Figure 2 , Figure 2A schematic diagram of a principle of an electro-optical switch unit based on MZI is provided.

[0053] In the prior art, an electro-optical switch unit based on the principle of free carrier dispersion is widely used in high-speed optoelectronic integrated chips. In order to perform carrier doping of different concentrations and types on the modulation arm waveguide in the electro-optical switch unit, the two modulation arm waveguides are often in a ridge structure. In order to realize electro-optical modulation in the electro-optical switch unit, a 1x2 optical splitter and a 2x1 optical combiner are arranged on the two sides of the modulation arm waveguide. The 1x2 optical splitter and the 2x1 optical combiner can be realized by a 1x2 port multimode interference coupler.

[0054] Under a thick silicon platform, the performance of a bar-shaped structure optical splitter based on the principle of multimode interference coupling is often better than that of a ridge-shaped structure optical splitter. Therefore, in order to constitute an electro-optical switch based on MZI, the ridge-shaped structure modulation arm waveguide needs to be combined with the bar-shaped structure optical splitter, and a schematic diagram is as shown in Figure 3 . Figure 3 A structural schematic diagram of an electro-optical switch unit is provided.

[0055] As Figure 3 can be seen, when the electro-optical switch unit simultaneously contains the ridge-shaped structure modulation arm waveguide and the bar-shaped structure multimode interference coupler, a conversion transition structure is often needed between the bar-shaped waveguide and the ridge-shaped waveguide to realize the conversion of different optical waveguide structures. In the present application, the conversion structure between the bar-shaped waveguide and the ridge-shaped waveguide is referred to as a bar-ridge transition structure.

[0056] A traditional bar-ridge waveguide conversion structure is an adiabatic gradual transition waveguide structure, and a structure thereof is as shown in Figure 4 . Figure 4 A schematic diagram of a traditional bar-ridge waveguide conversion structure is provided.

[0057] In a thick silicon platform, the bar-shaped structure optical splitter and the ridge-shaped structure waveguide modulation arm have good optical transmission characteristics. In order to realize an optical switch unit based on the principle of MZI modulation, a conversion transition structure of the bar-shaped waveguide and the ridge-shaped waveguide needs to be used to connect the bar-shaped optical splitter, the optical combiner and the ridge-shaped modulation arm waveguide.

[0058] In addition to the need to use the conversion structure of the bar-shaped waveguide and the ridge-shaped waveguide inside the MZI electro-optical switch unit, a single-mode ridge-shaped waveguide can realize ultra-low loss optical transmission in a thick silicon platform. Therefore, in addition to the electro-optical switch unit, a ridge-shaped optical waveguide is used as an optical path transmission structure, and the external interface of the optical switch unit is a 1x2 optical splitter and a 2x1 optical combiner. As Figure 5 is shown, Figure 5 A schematic diagram of a structure after a MZI optical switch unit is connected with a single-mode transmission waveguide is provided.

[0059] Because the light splitters and light combiners adopt high-efficiency strip-shaped structures, when connecting the MZI optical switch unit with the low-loss thick silicon ridge-shaped transmission waveguide, the input and output ports of the optical switch unit also face the conversion problem of strip-shaped waveguides and ridge-shaped waveguides, and the conversion structure of strip-shaped waveguides and ridge-shaped waveguides is also needed.

[0060] In summary, in the application scenario of the thick silicon platform, the ridge-shaped single-mode waveguide can realize super-low-loss optical transmission, and the strip-shaped light splitter can complete the light splitting function in a compact size. In actual applications, ridge-shaped single-mode transmission waveguides and strip-shaped optical coupler multi-mode waveguides are often used simultaneously. For example, in the Mach-Zehnder phase shift modulation-based electro-optical switch, two strip-shaped 1x2 light splitters, two ridge-shaped modulation arm waveguides, two input and output transmission waveguides are included.

[0061] Therefore, the waveguide structure conversion is needed at the connection of the strip-shaped waveguide and the ridge-shaped waveguide, and the traditional scheme is the transition conversion structure based on the gradual structure, but the conversion structure needed by this scheme will increase the length size of the unit device, especially in the case of large-scale use of the phase shift modulation switch array, a large number of gradual transition-shaped strip-shaped ridge-shaped waveguide conversion structures will be used.

[0062] In order to avoid the use of the conversion structure of the strip-shaped waveguide and the ridge-shaped waveguide, the application provides an optical multi-mode interference coupler based on a strip-shaped ridge-shaped waveguide hybrid structure, which is shown in Figure 6 , Figure 6 The application provides a structural schematic diagram of the optical multi-mode interference coupler based on the strip-shaped ridge-shaped waveguide hybrid structure.

[0063] As shown in Figure 6 , the optical multi-mode interference coupler is integrally formed, and sequentially includes, from the signal input to the output direction (i.e. from left to right), a ridge-shaped single-mode input waveguide, a ridge-shaped tapered input waveguide, a strip-shaped multi-mode waveguide, a ridge-shaped tapered output waveguide, and a ridge-shaped single-mode output waveguide.

[0064] All the ridge-shaped waveguides include ridge waveguides and flat plate region waveguides.

[0065] The ridge waveguide width of the single-mode input waveguide is equal to the minimum ridge waveguide width of the tapered input waveguide.

[0066] The sum of the maximum ridge waveguide widths of the tapered input waveguide is less than the width of the multi-mode waveguide.

[0067] The sum of the maximum ridge waveguide widths of the tapered output waveguide is less than the width of the multi-mode waveguide.

[0068] The minimum ridge waveguide width of the tapered output waveguide is equal to the ridge width of the single-mode output waveguide.

[0069] Specifically, the ridge waveguide of the single-mode input waveguide has the same size as the ridge waveguide of the single-mode output waveguide.

[0070] The ridge waveguide of the tapered input waveguide and the ridge waveguide of the tapered output waveguide have the same size.

[0071] Specifically, the multimode waveguide is located in the middle region of the optical multimode interference coupler; the tapered input waveguide and the tapered output waveguide are respectively located on both sides of the multimode waveguide and are directly connected to the multimode waveguide.

[0072] If the optical multimode interference coupler is a 1x2 coupler, the number of single-mode input waveguides, tapered input waveguides and multimode waveguides is 1, and the number of tapered output waveguides and single-mode output waveguides is 2.

[0073] The two tapered output waveguides and the two single-mode output waveguides are symmetrically distributed about the transverse center axis of the multimode waveguide.

[0074] If the optical multimode interference coupler is a 2x1 coupler, the number of single-mode input waveguides and tapered input waveguides is 2, and the number of multimode waveguides, tapered output waveguides and single-mode output waveguides is 1.

[0075] The two tapered input waveguides and the two single-mode input waveguides are symmetrically distributed about the transverse center axis of the multimode waveguide.

[0076] The thickness of the slab region waveguide is adjusted according to the thickness of the top silicon layer of the optical multimode interference coupler; the ridge waveguide width of the ridge waveguide is adjusted according to the thickness of the top silicon layer of the optical multimode interference coupler.

[0077] Specifically, the thickness of the top silicon layer is 3 μm, the thickness of the slab region waveguide is 1.3 μm, the minimum ridge waveguide width of the tapered input waveguide is 2.2 μm, and the maximum ridge waveguide width of the tapered input waveguide is 2.5 μm.

[0078] In some embodiments, the length of the multimode waveguide is 70 μm, and the length l2 of the ridge waveguide of the tapered output waveguide is 10 μm.

[0079] Referring to Figure 7 , Figure 7 A top view of a 1x2 optical multimode interference coupler provided by the present application is shown in FIG. 1. Figure 7As shown, the 1x2 optical multimode interference coupler from left to right is a single-mode input waveguide of ridge structure, a tapered input waveguide of ridge structure, a multimode waveguide of strip structure, a tapered output waveguide of ridge structure, and a single-mode output waveguide of ridge structure.

[0080] Referring to Figure 8 , Figure 8 The cross section of the 1x2 coupler ridge waveguide provided by the present application is shown in FIG. 2. In combination with Figure 8 Firstly, the single-mode condition of the input ridge waveguide needs to be determined to achieve a low-loss thick silicon ridge single-mode waveguide. Under the condition of a 3μm-thick silicon platform, the width of the ridge waveguide that satisfies the single-mode condition can be obtained by using optical simulation software. In the present application, the length of w1 is 2.2μm to achieve a single-mode ridge waveguide.

[0081] The ridge waveguide part of the tapered input waveguide is a section of ridge waveguide with a gradually changing width, which gradually widens from the minimum width (2.2μm) of the ridge waveguide to the maximum width w2 (2.5μm) of the strip multimode interference coupling waveguide.

[0082] Further, the length of the input tapered waveguide needs to be selected to enable the light field to complete the gradual transition during the transmission from the input end of the input tapered waveguide to the output end of the input tapered waveguide. In the embodiment of the present application, the length l2 of the tapered waveguide is 10μm.

[0083] The strip structure multimode waveguide is the core structure of the multimode interference coupler. Referring to Figure 9 , Figure 9 The cross-sectional view of the strip multimode waveguide of the 1x2 coupler provided by the present application is shown in FIG. 3. Under the condition of a 3μm-thick top silicon layer, the length and width of the strip multimode waveguide need to be determined.

[0084] In the embodiment of the present application, the width w3 of the strip multimode waveguide is 8μm to ensure that a sufficient number of optical modes are supported in the multimode waveguide region. Further, the length of the strip multimode waveguide needs to be optimized to maximize the optical transmission efficiency of the 1x2 coupler. In the embodiment of the present application, the length l3 of the multimode waveguide is 70μm.

[0085] At present, the application of the multimode interference coupler based on a thin silicon platform can achieve the light splitting effect of different ports in a small size, but it is difficult to achieve ultra-low loss optical transmission based on thin silicon waveguides due to the distribution of optical mode fields in thin silicon waveguides and the etching roughness of waveguide sidewalls.

[0086] Optical devices under a thin silicon platform have a top silicon layer thickness of 100nm to 300nm, while optical devices based on a thick silicon platform have a top silicon layer thickness of 2μm or more.

[0087] Based on the optical device under the thick silicon platform, the confinement of the mode field in the waveguide is weaker than that under the thin silicon platform, and the sensitivity of optical loss to the sidewall roughness is also lower than that of the thin silicon material, especially the ridge waveguide under the thick silicon platform, which can realize ultra-low loss optical transmission.

[0088] Therefore, the application provides an optical multimode interference coupler based on a bar-shaped ridge waveguide hybrid structure.

[0089] The optical multimode interference coupler based on the bar-shaped ridge waveguide hybrid structure provided by the application can be a 1x2 optical coupler. Based on the multimode interference coupling effect in the multimode waveguide, the 1x2 optical coupler can be an optical beam splitter. The bar-shaped waveguide and the ridge waveguide are used in the optical beam splitter.

[0090] The core region of the beam splitter is a multimode waveguide with a bar-shaped structure, and the two sides of the core region are tapered waveguides with a ridge-shaped structure and input and output single-mode waveguides. At the interface between the core region and the tapered waveguide, the cross section of the waveguide is suddenly changed, that is, the use of the traditional tapered cross-section bar-shaped ridge-shaped conversion structure is avoided.

[0091] The 1x2 optical beam splitter with the bar-shaped ridge waveguide hybrid structure realizes the functions of optical power splitting and waveguide structure conversion. Specifically, the thickness of the top silicon layer of the optical beam splitter is 3 microns, and the thickness of the flat plate region of the ridge waveguide is 1.3 microns, so as to realize a low-loss single-mode waveguide. The input end of the optical beam splitter is connected with a low-loss ridge input waveguide, and the output end is connected with a ridge electro-optic modulation arm waveguide.

[0092] Similarly, the 1x2 optical beam splitter based on the bar-shaped ridge waveguide hybrid structure can also be used to realize a 2x1 port optical combiner. Only the input port and the output port are interchanged, and the optical signal is input from the double-port side of the multimode interference coupler and output from the single-port side, so as to realize the combiner effect.

[0093] Similarly, for the 2x1 optical combiner with the bar-shaped ridge waveguide hybrid structure, the waveguide thickness of the top silicon layer and the flat plate waveguide is the same as that of the optical beam splitter. The input end of the 2x1 optical combiner is connected with a ridge electro-optic modulation arm waveguide, and the output end is connected with a low-loss ridge output waveguide.

[0094] In some embodiments, when the optical multimode interference coupler based on the bar-shaped ridge waveguide hybrid structure provided by the application is used to realize a 2x1 port optical combiner, the corresponding multimode interference coupler of the optical combiner should be a double-port input. Two-way signal light is input from the double-port side of the multimode interference coupler at the same time, and by adjusting the relative amplitude and phase difference between the two-way signal light, the interference output of the two-way optical signal can be realized.

[0095] It is worth noting that the optical multimode interference coupler based on a hybrid strip-ridge waveguide structure provided by this invention represents a groundbreaking advancement. For the first time, a high-efficiency 1×2 optical coupler capable of direct connection to a ridge single-mode waveguide has been achieved on a 3-micron SOI thick silicon optical platform. Specifically, this optical multimode interference coupler achieves an optical transmission efficiency of 99.6% at a wavelength of 1550 nm, comparable to a pure strip coupler, while significantly improving upon the 94.2% efficiency of ridge waveguide couplers.

[0096] See Figure 10 , Figure 10 The schematic diagram of a 1×1 MZI optical switch based on a hybrid strip-ridge waveguide structure provided by this invention is shown below. Figure 10 As shown, a 1×1 MZI optical switch contains two 1×2 multimode interference couplers with a hybrid structure of strip-ridge waveguides, which are the optical beam splitter and optical beam combiner in the MZI optical switch, respectively.

[0097] In a high-speed MZI electro-optic switch unit based on electro-optic modulation on a thick silicon optical platform, the modulation arm waveguide is a ridge waveguide, while the efficient optical beam splitter and optical beam combiner are strip waveguides. Therefore, using a 1×2 multimode interference coupler based on a hybrid strip-ridge waveguide structure as the beam splitter and beam combiner within the MZI electro-optic switch avoids the use of traditional strip-ridge waveguide gradient transition structures.

[0098] like Figure 10 As shown, in the 1×1 MZI optical switch based on a hybrid strip-ridge waveguide structure provided by this invention, there are four waveguide transition regions: the junction of the ridge input waveguide and the 1×2 optical beamsplitter, the junction of the 1×2 optical beamsplitter and the ridge electro-optic modulation arm waveguide, the junction of the ridge electro-optic modulation arm waveguide and the 2×1 optical combiner, and the junction of the 2×1 optical combiner and the ridge output waveguide. Because a hybrid strip-ridge waveguide optical coupler is used, the above four waveguide transition regions do not require the use of traditional strip-ridge waveguide gradient transition structures, thus ensuring high-efficiency optical signal transmission within the MZI optical switch while effectively reducing device size.

[0099] In summary, compared with existing technologies, it has the following beneficial effects:

[0100] 1. This invention provides an optical multimode interference coupler based on a hybrid structure of strip-ridge waveguide and strip-shaped waveguide. The interface between the ridge-shaped transmission waveguide and the strip-shaped multimode waveguide is directly connected. Based on the multimode excitation principle of the multimode interference coupler, the optical signal in the ridge-shaped single-mode waveguide can simultaneously complete the excitation of multiple modes in the waveguide and the transformation of the waveguide structure at the interface of the strip-shaped multimode waveguide. This eliminates the need for the traditional gradient-shaped strip-ridge waveguide conversion structure, effectively reducing the length of the electrical unit device and improving the integration of the device.

[0101] 2. The application provides an optical multimode interference coupler based on a bar-ridge waveguide hybrid structure, which solves the transition problem between a bar waveguide and a ridge waveguide in a thick silicon optical platform. The idea of mode field expansion and excitation of optical signals in a multimode waveguide is used to complete the conversion of the optical waveguide structure at the input and output cross sections of the multimode waveguide, i.e. a bar multimode waveguide is directly connected with a ridge input and output waveguide to realize a high-efficiency multimode interference coupler. The optical splitting and combining in the waveguide in the thick silicon platform is realized, and the traditional gradual transition structure between the bar waveguide and the ridge waveguide can be avoided.

[0102] It is worth noting that the length and width of the bar structure multimode waveguide in the optical multimode interference coupler of the application comply with the multimode interference principle, and the working wavelength can cover the common infrared waveband range.

[0103] 3. The application provides an optical multimode interference coupler based on a bar-ridge waveguide hybrid structure, which reduces the structural complexity of an optical unit device in which a bar waveguide and a ridge waveguide coexist, and can effectively reduce the device size while ensuring high-efficiency optical signal transmission.

[0104] 4. In the optical multimode interference coupler based on the bar-ridge waveguide hybrid structure provided by the application, the traditional transition structure between the bar multimode interference coupler and the ridge transmission waveguide is avoided, and a low-loss thick silicon 1x2 optical splitter and a 2x1 optical combiner device are realized in a compact area.

[0105] In addition, the optical splitter and the optical combiner in the Mach-Zehnder electro-optical switch unit are based on the above-mentioned bar-ridge hybrid waveguide structure, which realizes the direct conversion of the waveguide structure between the optical splitter, the optical combiner and the electro-optical modulation arm waveguide. Meanwhile, the input and output ends of the Mach-Zehnder electro-optical switch unit are directly connected with the ridge low-loss waveguide, and the traditional transition structure between the bar waveguide and the ridge waveguide is avoided.

[0106] It should be noted that in this document, relational terms such as first and second and the like can only be used to distinguish one entity or action from another entity or action, without necessarily requiring or implying that there is any such actual relationship or order between these entities or actions. Moreover, the terms "comprises", "comprising", or any other variations thereof are intended to cover non-exclusive inclusions, so that a process, method, article, or apparatus that includes a list of elements does not only include those elements, but also includes other elements not explicitly listed, or other elements inherent to such a process, method, article, or apparatus. Without more limitations, an element defined by the statement "comprising a" does not exclude the presence of additional identical elements in the process, method, article, or apparatus that includes the element.

[0107] The above examples are only used to illustrate the technical solutions of the present application, but not to limit the present application; although the present application has been described in detail with reference to the foregoing examples, those ordinarily skilled in the art should understand: the technical solutions recorded in the foregoing examples can still be modified, or some technical features can be replaced equivalently; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. An optical multimode interference coupler based on a hybrid structure of a strip ridge waveguide, characterized in that, the optical multimode interference coupler is integrally formed, and from the input to the output of a signal, comprises in sequence: a single-mode input waveguide of a ridge structure, a tapered input waveguide of a ridge structure, a multimode waveguide of a strip structure, a tapered output waveguide of a ridge structure, and a single-mode output waveguide of a ridge structure; all the waveguides of the ridge structure comprise a ridge waveguide and a slab region waveguide; wherein the ridge waveguide width of the single-mode input waveguide is equal to the minimum ridge waveguide width of the tapered input waveguide; the sum of the maximum ridge waveguide widths of the tapered input waveguide is less than the width of the multimode waveguide; the sum of the maximum ridge waveguide widths of the tapered output waveguide is less than the width of the multimode waveguide; the minimum ridge waveguide width of the tapered output waveguide is equal to the ridge width of the single-mode output waveguide; the ridge waveguide of the single-mode input waveguide and the ridge waveguide of the single-mode output waveguide are of the same size; the ridge waveguides of the tapered input waveguide and the tapered output waveguide are of the same size.

2. The optical multimode interference coupler of claim 1, wherein, If the optical multimode interference coupler is a 1x2 coupler, the number of single-mode input waveguides, tapered input waveguides and multimode waveguides is 1, and the number of tapered output waveguides and single-mode output waveguides is 2; the two tapered output waveguides and the two single-mode output waveguides are symmetrically distributed about the transverse center axis of the multimode waveguide.

3. The optical multimode coupler of claim 1, wherein, If the optical multimode interference coupler is a 2x1 coupler, the number of single-mode input waveguides and tapered input waveguides is 2, and the number of multimode waveguides, tapered output waveguides and single-mode output waveguides is 1; the two tapered input waveguides and the two single-mode input waveguides are symmetrically distributed about the transverse center axis of the multimode waveguide.

4. The optical multimode coupler according to any of claims 2 or 3, characterized in that The thickness of the slab region waveguide is adjusted according to the thickness of the top silicon layer of the optical multimode interference coupler; the ridge waveguide width of the ridge waveguide is adjusted according to the thickness of the top silicon layer of the optical multimode interference coupler; Specifically, the thickness of the top silicon layer is 3 μm, the thickness of the slab region waveguide is 1.3 μm, the minimum ridge waveguide width of the tapered input waveguide is 2.2 μm, the maximum ridge waveguide width of the tapered input waveguide is 2.5 μm, and the width of the multimode waveguide is 8 μm.

5. The optical multimode coupler of claim 4, wherein, In the optical multimode interference coupler, the length of the multimode waveguide is 70 μm, and the length of the ridge waveguide of the tapered output waveguide is 10 μm.

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