High efficiency optical waveguide chip-fiber coupler

Abstract

The application discloses a high-efficiency optical waveguide chip-few-mode fiber coupler. The coupler comprises a few-mode fiber-multimode waveguide mode spot conversion module on a low-contrast conversion chip, a polarization-insensitive mode multiplexing / demultiplexing module, a low-high-contrast waveguide mode spot conversion module and a polarization control module on a high-contrast chip. 2n linear polarization modes of the few-mode fiber are coupled into a multimode waveguide through the end face of the few-mode fiber-multimode waveguide mode spot conversion module, and then are demultiplexed into n base modes through the mode multiplexing / demultiplexing module, and then are coupled into n high-contrast waveguides through the low-high-contrast waveguide mode spot conversion module to obtain TE0 / TM0 mode pairs, and finally are divided into 2n linear polarization modes of the high-contrast waveguide through the polarization control module. The application can realize high-efficiency coupling of linear polarization modes in the few-mode fiber and linear polarization modes in the high-contrast optical waveguide chip, has the advantages of large bandwidth, large tolerance, low crosstalk, semiconductor process compatibility and the like, and effectively solves the problem of multimode coupling from the optical fiber to the chip.

Description

Technical Field

[0001] This invention relates to waveguide-chip couplers, and more particularly to a high-efficiency optical waveguide chip-few-mode fiber coupler. Background Technology

[0002] With the advent of the era of big data and the internet, the demand for communication transmission capacity is increasing daily. Traditional electrical interconnects face development bottlenecks due to limited transmission capacity and high power consumption. In contrast, on-chip optical interconnects offer advantages such as high bandwidth, high transmission rate, and low power consumption, which can improve the problems existing in electrical interconnects. By utilizing various multiplexing technologies, the communication capacity in optical interconnects can be further improved. Traditional wavelength division multiplexing (WDM) technology uses multiple wavelength channels to transmit signals to increase transmission capacity and has been widely used in practice, especially in long-distance communication where it has demonstrated unique advantages. However, the need for multiple light sources inevitably leads to an increasing cost burden. Mode division multiplexing (MDM) technology utilizes multiple mutually orthogonal mode channels in few-mode fibers to effectively improve transmission capacity and can effectively suppress inter-mode crosstalk, and is considered the next-generation cutting-edge technology in the field of optical communication. In addition, various high-performance photonic integrated functional devices, such as on-chip optical field manipulation, optical signal modulation, and detection devices, can now be realized on-chip. Therefore, achieving high-efficiency coupling between optical waveguide chips and few-mode fibers is of great significance.

[0003] Existing optical waveguide-few-mode fiber coupler schemes can generally be divided into grating coupling and end-face coupling. For grating coupling, a two-dimensional grating is typically constructed to change the light transmission direction, allowing each mode to be emitted through the surface into the few-mode fiber. Its advantage is ease of testing, but this grating-based scheme usually has relatively small tolerances and bandwidths, and its coupling efficiency is limited, failing to meet the actual performance requirements of the coupler. For end-face coupling, the structure of mode evolution is generally designed to separate the peaks of higher-order modes, which are then coupled separately into the few-mode fiber at the end face. However, existing methods generally cannot achieve coupling of higher-order modes in the height direction, lacking mode scalability. Some schemes also achieve coupling based on multi-stage adiabatic mode evolution structures. The problem with this approach is incompatibility with manufacturing processes, making it difficult to fabricate and lacking practicality.

[0004] Therefore, existing technologies cannot simultaneously meet the technical requirements of high coupling efficiency, scalability, large bandwidth, large tolerance, and low inter-mode crosstalk in optical waveguide-few-mode fiber couplers, which greatly limits the further development of mode division multiplexing technology and optical communication and optical interconnection systems. Summary of the Invention

[0005] To address the problems existing in the background technology, the purpose of this invention is to provide an optical waveguide chip-few-mode fiber coupler that supports high coupling efficiency, scalability, large bandwidth, large tolerance and low inter-mode crosstalk. It can effectively couple multiple modes in the few-mode fiber into multiple linear polarization modes in the optical waveguide chip, and has important application value.

[0006] This invention enables highly efficient coupling between linearly polarized modes in few-mode optical fibers and linearly polarized modes in high-refractive-index-difference optical waveguide chips. It has advantages such as large bandwidth, large tolerance, low crosstalk, and semiconductor process compatibility. It effectively solves the multi-mode coupling problem from fiber to chip and is of great significance for further improving communication capacity and developing next-generation optical communication and optical interconnect systems.

[0007] The technical solution adopted in this invention is:

[0008] This invention includes a few-mode fiber, a low refractive index difference conversion chip, and a high refractive index difference chip, which are connected sequentially by end-face coupling.

[0009] The low refractive index difference conversion chip includes a few-mode fiber-to-multimode waveguide mode spot conversion module and a polarization-insensitive mode multiplexing / demultiplexing module connected sequentially along the conduction direction. The input end of the few-mode fiber-to-multimode waveguide mode spot conversion module and the output port of the few-mode fiber are arranged in corresponding docking arrangements.

[0010] The few-mode fiber to multimode waveguide mode conversion module is mainly composed of a multimode end-face coupler.

[0011] The polarization-insensitive mode multiplexing / demultiplexing module mainly consists of a low refractive index difference multimode waveguide, a polarization-insensitive mode multiplexer / demultiplexer, and n low refractive index difference single-mode waveguides connected sequentially along the propagation direction. The polarization-insensitive mode multiplexer / demultiplexer has n output ports, and the n output ports of the polarization-insensitive mode multiplexer / demultiplexer are respectively connected to the input terminals of the n low refractive index difference single-mode waveguides.

[0012] The high refractive index difference chip includes a low-to-high refractive index difference waveguide mode conversion module and a polarization control module connected sequentially along the conduction direction;

[0013] The low-to-high refractive index difference waveguide mode conversion module mainly consists of n single-mode end-face couplers and n high refractive index difference single-mode waveguides connected thereafter. The input ends of the n single-mode end-face couplers are respectively connected to the output ends of the n low refractive index difference single-mode waveguides, and the output ends of the n single-mode end-face couplers are respectively connected to the input ends of the n high refractive index difference single-mode waveguides.

[0014] The polarization control module mainly consists of n polarization control devices and 2n high refractive index difference single-mode waveguides connected to them. The input terminals of the n polarization control devices are respectively connected to the output terminals of the n high refractive index difference single-mode waveguides. Each polarization control device has two output terminals. The 2n output terminals of the n polarization control devices are respectively connected to the input terminals of the 2n high refractive index difference single-mode waveguides. The output terminals of the 2n high refractive index difference single-mode waveguides serve as the output terminals of the optical waveguide chip-few-mode fiber coupler.

[0015] The low refractive index difference described in this invention refers to a low refractive index between the waveguide and its cladding, while a high refractive index difference refers to a higher refractive index between the waveguide and its cladding. A high refractive index difference, compared to a low refractive index difference, means the refractive index between the waveguide and its cladding is significantly higher. Generally, waveguides with low refractive index differences are on the micrometer scale and have a birefringence of less than 10⁻⁴, making them polarization-insensitive. Waveguides with high refractive index differences are on the nanometer scale and have a birefringence greater than 10⁻⁴, making them polarization-sensitive.

[0016] The number of modes supported by the few-mode fiber is between that of multimode and single-mode fibers.

[0017] The multimode end-face coupler is composed of a segmented waveguide with a periodic, linearly varying duty cycle. The segmented waveguide is formed by multiple waveguide segments arranged at intervals along the propagation direction, and the duty cycle of the segmented waveguide decreases sequentially along the propagation direction.

[0018] The duty cycle refers to the proportion of the waveguide length along the propagation direction to the total length of the waveguide along the propagation direction within a single period. The segmented waveguide has the largest duty cycle near the end of the low-refractive-index-difference multimode waveguide and the smallest duty cycle near the end of the few-mode fiber. This periodic segmented waveguide structure with a gradually changing duty cycle improves the coupling efficiency from the few-mode fiber to the multimode waveguide.

[0019] The polarization-insensitive mode multiplexer / demultiplexer mainly consists of a low refractive index difference multimode bus waveguide, a laterally distributed high-order mode coupler, and a longitudinally distributed high-order mode coupler connected sequentially along the transmission direction. One end of the laterally distributed high-order mode coupler is connected to the low refractive index difference multimode waveguide via the low refractive index difference multimode bus waveguide, and the other end is connected to one end of the longitudinally distributed high-order mode coupler. The other end of the longitudinally distributed high-order mode coupler outputs n ports, which are respectively connected to n low refractive index difference single-mode waveguides.

[0020] The polarization-insensitive mode multiplexer / demultiplexer is a 1*3 multiplexer / demultiplexer, specifically as follows:

[0021] The aforementioned laterally distributed high-order mode coupler mainly consists of a lateral bus waveguide, a lateral access waveguide, a lateral S-shaped bend waveguide, and an angled height conversion waveguide.

[0022] The input end of the lateral bus waveguide is connected to the output end of the low refractive index difference multimode bus waveguide, and the output end of the lateral bus waveguide is connected to the input end of the oblique mode rotating waveguide of the longitudinally distributed high-order mode coupler; parallel and coupled lateral access waveguides are provided on the side of the lateral bus waveguide; the output end of the lateral access waveguide is connected to one end of the lateral S-shaped bend waveguide, the other end of the lateral S-shaped bend waveguide is connected to the input end of the oblique height conversion waveguide, and the output end of the oblique height conversion waveguide is connected to the input end of a corresponding low refractive index difference single-mode output waveguide;

[0023] The aforementioned longitudinally distributed high-order mode coupler mainly consists of an angled mode rotating waveguide, a longitudinal bus waveguide, a longitudinal access waveguide, and a longitudinal S-shaped bend waveguide.

[0024] The output of the angled mode rotating waveguide is connected to the input of the longitudinal bus waveguide, and the output of the longitudinal bus waveguide is connected to the input of its corresponding low refractive index difference single-mode waveguide. Parallel and coupled longitudinal access waveguides are provided on the side of the longitudinal bus waveguide. The output of the longitudinal access waveguide is connected to one end of the longitudinal S-shaped bend waveguide, and the other end of the longitudinal S-shaped bend waveguide is connected to the input of its corresponding low refractive index difference single-mode waveguide.

[0025] The output of each low refractive index difference single-mode output waveguide is connected to a corresponding low refractive index difference single-mode waveguide, and the output of each low refractive index difference single-mode waveguide serves as the output of the low refractive index difference conversion chip.

[0026] The arrangement relationship between the transverse bus waveguide and the transverse access waveguide is the same as that between the longitudinal bus waveguide and the longitudinal access waveguide, which is: the width of the bus waveguide gradually decreases and the width of the access waveguide gradually increases along the conduction direction. The bus waveguide and the access waveguide are arranged facing each other with their respective sides flush to form parallel sides, and their respective other sides are set as side slopes with their own tapered slopes.

[0027] The oblique height conversion waveguide and oblique mode rotating waveguide have the same structure, consisting of two waveguide segments connected sequentially along the conduction direction: an input segment and an output segment. The input segment and the output segment are connected by vertically arranged, inclined end faces that are tilted towards the conduction direction. The width of the input segment gradually decreases along the conduction direction, while the width of the output segment gradually increases along the conduction direction. The thickness of the input segment is greater than the thickness of the output segment.

[0028] To design both laterally and longitudinally distributed high-order mode couplers, first determine the widths at both ends of the bus waveguide and the access waveguide to ensure that the modes can be coupled from the bus waveguide to the access waveguide. Then, determine the spacing between the bus waveguide and the access waveguide, and finally, determine the coupling length.

[0029] Design an angled height conversion waveguide and an angled mode rotation waveguide, determine the widths at both ends, and determine the lengths of both waveguides by monitoring the transmittance of the mode at the other end to ensure complete mode rotation.

[0030] The low-to-high refractive index difference waveguide mode conversion module mainly consists of n single-mode end-face couplers placed side by side. The input end of the single-mode end-face coupler is flush with the end face of the high refractive index difference chip. The input end of each single-mode end-face coupler is coaxially aligned with its corresponding low refractive index difference single-mode waveguide. Each low refractive index difference single-mode waveguide in the high refractive index difference chip is connected to the input end of its corresponding low refractive index difference single-mode waveguide. The output ends of the n single-mode end-face couplers are respectively connected to n high refractive index difference single-mode waveguides.

[0031] The single-mode end-face coupler structure is inverted cone, double-layer, or trident type, etc., and n single-mode end-face couplers adopt the same structure.

[0032] The polarization control device mentioned above includes polarization beam splitters, polarization beam rotators, etc.

[0033] The few-mode fiber receives optical signals of 2n linearly polarized modes and outputs them to a multimode end-face coupler. The signals are then coupled into a low-refractive-index-difference multimode waveguide and transmitted through the low-refractive-index-difference multimode waveguide to a polarization-insensitive mode multiplexer / demultiplexer. The polarization-insensitive mode multiplexer / demultiplexer demultiplexes the 2n linearly polarized modes into n fundamental mode optical signals, which are output from the n low-refractive-index-difference single-mode waveguides respectively. Each fundamental mode optical signal is a transverse electric fundamental mode, a transverse magnetic fundamental mode, or a coexisting transverse electric fundamental mode and a transverse magnetic fundamental mode mode pair.

[0034] Subsequently, the refractive index difference is converted through mode field matching using a single-mode end-face coupler, and then coupled into n high-refractive-index-difference single-mode waveguides. These n high-refractive-index-difference single-mode waveguides then conduct the signals to n polarization control modules, which separate the optical signals into different linearly polarized modes. Finally, the 2n linearly polarized optical signals are separately input into the 2n high-refractive-index-difference single-mode waveguides to achieve signal coupling.

[0035] This invention is based on end-face coupling and consists of four parts: a few-mode fiber-to-multimode waveguide mode conversion module on a low-refractive-index-difference conversion chip, a polarization-insensitive mode multiplexing / demultiplexing module, a low-to-high refractive-index-difference waveguide mode conversion module on a high-refractive-index-difference chip, and a polarization modulation module. Taking the coupling of a few-mode fiber to the chip as an example (the reverse is also true as a coupler), the 2n linearly polarized modes (including x and y polarization) in the few-mode fiber are input to the multimode waveguide in the form of end-face coupling through the few-mode fiber-to-multimode waveguide mode conversion module. Then, they are demultiplexed into n fundamental modes by the polarization-insensitive mode multiplexing / demultiplexing module, and then coupled to the TE0 / TM0 mode pairs in the n high-refractive-index-difference waveguides by the low-to-high refractive-index-difference waveguide mode conversion module. Finally, they are divided into 2n linearly polarized modes in the high-refractive-index-difference waveguides by the polarization modulation module.

[0036] The beneficial effects of this invention are:

[0037] This invention utilizes a low-refractive-index-difference conversion chip as a transition, enabling highly efficient coupling of 2n linearly polarized modes (including x and y polarizations) in a few-mode fiber with 2n linearly polarized modes in a high-refractive-index-difference optical waveguide chip. Compared to existing multi-mode coupling schemes, this optical waveguide chip-few-mode fiber coupler features large bandwidth, high tolerance, and low inter-mode crosstalk.

[0038] This invention utilizes a segmented waveguide with a certain period and a gradually changing duty cycle as a coupler between a few-mode fiber and a low-refractive-index waveguide. This segmented waveguide design can further expand the mode field diameter of the fundamental and higher-order modes in the low-refractive-index waveguide, thereby achieving mode field matching with the modes in the few-mode fiber. While ensuring the coupling efficiency of the fundamental mode, it can effectively improve the end-face coupling efficiency of the higher-order modes. The gradually changing duty cycle design can reduce on-chip transmission loss.

[0039] This invention is highly scalable and has the ability to couple higher-order modes distributed in both the horizontal and vertical directions. The number of coupled modes can be increased by designing polarization-insensitive mode multiplexers / demultiplexers with different numbers of channels on a low refractive index difference chip.

[0040] The structures mentioned in this invention are all easy to implement in terms of manufacturing process and have high practical value. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of an embodiment of the present invention.

[0042] Figure 2 This is a schematic diagram of the device structure in the embodiment.

[0043] Figure 3 This is a schematic diagram of the oblique height conversion waveguide and the oblique mode rotating waveguide.

[0044] Figure 4 This is a mode field diagram of a few-mode fiber.

[0045] Figure 5 This is a simulated loss spectrum of a multimode end-face coupler based on a segmented waveguide with a gradually varying duty cycle.

[0046] Figure 6 This is a simulation loss spectrum of a polarization-insensitive mode multiplexing / demultiplexing module.

[0047] Figure 7 This is a schematic diagram of a polarization beam splitter rotator. Detailed Implementation

[0048] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0049] like Figure 1 As shown, it includes a few-mode fiber i, a low refractive index difference conversion chip ii, and a high refractive index difference chip iii connected in sequence, and the three are connected in sequence by end-face coupling.

[0050] The low refractive index difference conversion chip ii includes a few-mode fiber-to-multimode waveguide mode spot conversion module a and a polarization-insensitive mode multiplexing / demultiplexing module b connected sequentially along the transmission direction. The input end of the few-mode fiber-to-multimode waveguide mode spot conversion module a and the output port of the few-mode fiber i are arranged in corresponding docking.

[0051] The few-mode fiber to multimode waveguide mode conversion module a mainly consists of a multimode end-face coupler 1;

[0052] The polarization-insensitive mode multiplexing / demultiplexing module b mainly consists of a low refractive index difference multimode waveguide 2, a polarization-insensitive mode multiplexer / demultiplexer 3, and n low refractive index difference single-mode waveguides 41, 42, ..., 4n connected sequentially along the conduction direction. The polarization-insensitive mode multiplexer / demultiplexer 3 has n output ports, and the n output ports of the polarization-insensitive mode multiplexer / demultiplexer 3 are respectively connected to the input terminals of the n low refractive index difference single-mode waveguides 41, 42, ..., 4n.

[0053] The high refractive index difference chip iii includes a low-to-high refractive index difference waveguide mode conversion module c and a polarization control module d connected sequentially along the conduction direction;

[0054] The low-to-high refractive index difference waveguide mode conversion module c mainly consists of n single-mode end-face couplers 51, 52, ..., 5n and n high refractive index difference single-mode waveguides 61, 62, ..., 6n connected to them. The input ends of the n single-mode end-face couplers 51, 52, ..., 5n are respectively connected to the output ends of the n low refractive index difference single-mode waveguides 41, 42, ..., 4n. The output ends of the n single-mode end-face couplers 51, 52, ..., 5n are respectively connected to the input ends of the n high refractive index difference single-mode waveguides 61, 62, ..., 6n.

[0055] The polarization control module d mainly consists of n polarization control devices 71, 72, ..., 7n and 2n high refractive index difference single-mode waveguides 801, 802, ..., 8n1, 8n2 connected thereafter. The input terminals of the n polarization control devices 71, 72, ..., 7n are respectively connected to the output terminals of the n high refractive index difference single-mode waveguides 61, 62, ..., 6n. Each polarization control device 71, 72, ..., 7n has two output terminals. The 2n output terminals of the n polarization control devices 71, 72, ..., 7n are respectively connected to the input terminals of the 2n high refractive index difference single-mode waveguides 801, 802, ..., 8n1, 8n2. The output terminals of the 2n high refractive index difference single-mode waveguides 801, 802, ..., 8n1, 8n2 serve as the output terminals of the optical waveguide chip-few-mode fiber coupler of this invention.

[0056] like Figure 1 As shown, the few-mode fiber i receives optical signals from 2n linearly polarized modes and outputs them to the multimode end-face coupler 1. The linearly polarized modes contain two two-dimensional polarization directions, x and y. They are coupled into the low refractive index difference multimode waveguide 2 through the multimode end-face coupler 1 and then transmitted to the polarization-insensitive mode multiplexer / demultiplexer 3 through the low refractive index difference multimode waveguide 2.

[0057] The polarization-insensitive mode multiplexer / demultiplexer 3 demultiplexes the optical signals of 2n linearly polarized modes into n fundamental mode optical signals and outputs them from n low refractive index difference single-mode waveguides 41, 42, ..., 4n respectively. Each fundamental mode optical signal is an optical signal of a low refractive index difference transverse electric fundamental mode, transverse magnetic fundamental mode, or a coexisting transverse electric fundamental mode (hereinafter referred to as TE0 mode) and transverse magnetic fundamental mode (hereinafter referred to as TM0 mode) mode pair.

[0058] Subsequently, the refractive index difference is converted through single-mode end-face couplers 51, 52, ..., 5n, that is, the low refractive index difference is converted into the fundamental mode optical signal with a high refractive index difference. Then, it is coupled into n single-mode waveguides with high refractive index difference 61, 62, ..., 6n respectively. After being conducted through the n single-mode waveguides with high refractive index difference 61, 62, ..., 6n, it is transmitted to n polarization control modules 71, 72, ..., 7n respectively. The polarization control modules 71, 72, ..., 7n perform polarization separation into optical signals with different linear polarization modes. Finally, the 2n linear polarization modes of the optical signals are separately input into 2n single-mode waveguides with high refractive index difference 801, 802, ..., 8n1, 8n2 to achieve signal coupling.

[0059] like Figure 2 As shown, the multimode end-face coupler 1 is composed of periodic segmented waveguides 11, 12, ..., 1n with linearly varying duty cycles. The segmented waveguides 11, 12, ..., 1n are composed of multiple waveguide segments arranged at intervals along the propagation direction, with the intervals decreasing sequentially. The duty cycles of the segmented waveguides 11, 12, ..., 1n decrease sequentially along the propagation direction.

[0060] Duty cycle refers to the proportion of the waveguide length along the propagation direction to the total length of the waveguide along the propagation direction in a single period. In segmented waveguides 11, 12, ..., 1n, the duty cycle is largest at the end near the low refractive index difference multimode waveguide 2, and smallest at the end near the few-mode fiber i.

[0061] To fabricate a segmented waveguide, the first step is to determine the optimal matching duty cycle near the few-mode fiber end. A smaller waveguide duty cycle results in a larger mode field diameter. Next, determine the duty cycle near the low-refractive-index-difference multimode waveguide end. Generally, a smaller duty cycle results in lower insertion loss. Then, determine the optimal period size and number of periods. A period that is too large will lead to excessive loss, while a period that is too small will prevent the optimal duty cycle from being achieved near the few-mode fiber end. Finally, simulate the energy of each mode (including the fundamental mode and higher-order modes) in the few-mode fiber coupled to the low-refractive-index-difference multimode waveguide after passing through the segmented waveguide to evaluate the coupling performance of the segmented waveguide.

[0062] like Figure 2 As shown, the polarization-insensitive mode multiplexer / demultiplexer 3 mainly consists of a low refractive index difference multimode bus waveguide 301, a laterally distributed high-order mode coupler H, and a longitudinally distributed high-order mode coupler V connected sequentially along the transmission direction. One end of the laterally distributed high-order mode coupler H is connected to the low refractive index difference multimode waveguide 2 via the low refractive index difference multimode bus waveguide 301, and the other end is connected to one end of the longitudinally distributed high-order mode coupler V. The other end of the longitudinally distributed high-order mode coupler V outputs n ports, which are respectively connected to n low refractive index difference single-mode waveguides 41, 42, ..., 4n.

[0063] For ease of description, in the polarization-insensitive mode multiplexer / demultiplexer 3, the end closer to the low refractive index difference multimode bus waveguide 301 is defined as the input end, and the end closer to the low refractive index difference single-mode waveguides 311, 312, ..., 31n is defined as the output end.

[0064] The polarization-insensitive mode multiplexer / demultiplexer 3 is a 1*3 multiplexer / demultiplexer, specifically as follows:

[0065] The laterally distributed high-order mode coupler H is mainly composed of a lateral bus waveguide 302, a lateral access waveguide 303, a lateral S-shaped bend waveguide 304, an oblique height conversion waveguide 305, and a low refractive index difference single-mode waveguide 311. It is mainly composed of the lateral bus waveguide 302 and the lateral access waveguide 303 arranged close to each other to form an adiabatic conical asymmetric directional coupler.

[0066] The input end of the low refractive index difference multimode bus waveguide 301 is connected to the output end of the low refractive index difference multimode waveguide 2. The input end of the lateral bus waveguide 302 is connected to the output end of the low refractive index difference multimode bus waveguide 301. The output end of the lateral bus waveguide 302 is connected to the input end of the angled mode rotating waveguide 306 of the longitudinally distributed high-order mode coupler V. Parallel and coupled lateral access waveguides 303 are provided on the side of the lateral bus waveguide 302. From the input end to the output end of the laterally distributed high-order mode coupler H, the width of the lateral bus waveguide 302 gradually decreases along the propagation direction, while the width of the lateral access waveguide 303 gradually increases. Linear waveguide 302 and lateral access waveguide 303 are arranged opposite each other with their sides flush to form parallel sides, i.e., the spacing between all points on the parallel sides is equal; their other sides are respectively set as side slopes with their own tapered slopes; the input end of lateral access waveguide 303 is empty or connected to an S-shaped curved waveguide, the output end of lateral access waveguide 303 is connected to one end of lateral S-shaped curved waveguide 304, the other end of lateral S-shaped curved waveguide 304 is connected to the input end of angle height conversion waveguide 305, and the output end of angle height conversion waveguide 305 is connected to the input end of a corresponding low refractive index difference single-mode output waveguide 311.

[0067] The longitudinally distributed high-order mode coupler V is mainly composed of an angled mode rotating waveguide 306, a longitudinal bus waveguide 307, a longitudinal access waveguide 308, a longitudinal S-shaped bending waveguide 309, and low refractive index difference single-mode waveguides 312 and 313. It is mainly composed of the longitudinal bus waveguide 307 and the longitudinal access waveguide 308 arranged close to each other to form an adiabatic conical asymmetric directional coupler.

[0068] The input terminal of the angled mode rotating waveguide 306 is connected to the lateral bus waveguide 302 of the laterally distributed high-order mode coupler H, as follows: Figure 3The output of the angled mode rotating waveguide 306 is connected to the input of the longitudinal bus waveguide 307. The output of the longitudinal bus waveguide 307 is connected to the input of its corresponding low refractive index difference single-mode waveguide 312. Parallel and coupled longitudinal access waveguides 308 are arranged beside the longitudinal bus waveguide 307. From the input to the output of the laterally distributed high-order mode coupler H, the width of the longitudinal bus waveguide 307 gradually decreases along the propagation direction, while the width of the longitudinal access waveguide 308 gradually increases. 307 and the longitudinal access waveguide 308 are arranged opposite each other with their sides flush to form parallel sides, that is, the spacing between all points on the parallel sides is equal; their other sides are respectively set as side slopes with their own tapered slopes; the input end of the longitudinal access waveguide 308 is empty or connected to an S-shaped curved waveguide, the output end of the longitudinal access waveguide 308 is connected to one end of the longitudinal S-shaped curved waveguide 309, and the other end of the longitudinal S-shaped curved waveguide 309 is connected to the input end of a corresponding low refractive index difference single-mode waveguide 313.

[0069] The output ends of each low-refractive-index-difference single-mode output waveguide 311, 312, 313 are flush with the end face of the low-refractive-index-difference conversion chip ii. Each low-refractive-index-difference single-mode output waveguide 311, 312, 313 is connected to its corresponding low-refractive-index-difference single-mode waveguide 41, 42, 43. The output ends of each low-refractive-index-difference single-mode waveguide 41, 42, 43 serve as the output ends of the low-refractive-index-difference conversion chip ii. The output ends of the low-refractive-index-difference single-mode waveguides 41, 42, ..., 4n are coaxially aligned with the single-mode end-face couplers 51, 52, ..., 5n in the low-to-high-refractive-index-difference waveguide mode conversion module c.

[0070] The arrangement relationship between the transverse bus waveguide 302 and the transverse access waveguide 303 and the arrangement relationship between the longitudinal bus waveguide 307 and the longitudinal access waveguide 308 are the same: the width of the bus waveguide gradually decreases and the width of the access waveguide gradually increases along the conduction direction. The bus waveguide and the access waveguide are arranged facing each other with their respective sides flush to form parallel sides, that is, the spacing between the parallel sides is equal at all points. Their respective other sides are set as side slopes with their own tapered slopes.

[0071] The low refractive index difference multimode bus waveguide 301 is connected to the low refractive index difference multimode waveguide 2. It is multimode in both height and width directions, and can support the stable transmission of the fundamental mode and higher-order modes.

[0072] Low-refractive-index-difference single-mode waveguides 311, 312, ..., 31n are connected to low-refractive-index-difference single-mode waveguides 41, 42, ..., 4n. They are single-mode in both height and width directions, and can support stable transmission of the fundamental mode.

[0073] like Figure 2As shown, the low-to-high refractive index difference waveguide mode conversion module c mainly consists of n single-mode end-face couplers 51, 52, ..., 5n placed side by side. The input ends of the single-mode end-face couplers 51, 52, ..., 5n are flush with the end face of the high refractive index difference chip ii. The input end of each single-mode end-face coupler 51, 52, ..., 5n is coaxially aligned with its corresponding low refractive index difference single-mode waveguide 41, 42, ..., 4n. Each low refractive index difference single-mode waveguide 311, 312, ..., 31n in the high refractive index difference chip ii is connected to its corresponding input end of its corresponding low refractive index difference single-mode waveguide 41, 42, ..., 4n. The output ends of the n single-mode end-face couplers 51, 52, ..., 5n are respectively connected to n high refractive index difference single-mode waveguides 61, 62, ..., 6n.

[0074] The polarization control devices 71, 72, ..., 7n are polarization beam splitters, polarization beam rotators, etc., and the n polarization control devices adopt the same structure.

[0075] If the polarization control devices 71, 72, ..., 7n are polarization beam splitters, then the two output terminals of the polarization beam splitter will output optical signals of the two fundamental modes TM0 and TE0 respectively.

[0076] If the polarization control devices 71, 72, ..., 7n are polarization beam splitters, then the optical signals of the same fundamental mode TE0 and TE0 are output through both output terminals of the polarization beam splitter.

[0077] The following describes the application of the present invention in mode (here referred to as LP). 01 LP 11a and LP 11b (Taking the mode (including x and y polarization) as an example, the working process when coupled from a few-mode fiber to an optical waveguide chip is as follows:

[0078] LP in few-mode fiber 01 The mode is coupled to the LP of the low refractive index difference multimode waveguide via a multimode end-face coupler. 01 The mode is first transmitted through a horizontally distributed high-order mode coupler and a vertically distributed high-order mode coupler in a polarization-insensitive mode multiplexer / demultiplexer, and then continuously propagated in the bus waveguide until it reaches the end face of the low refractive index difference conversion chip. Subsequently, it is coupled to the TE0 / TM0 mode pair in the high refractive index difference waveguide through a low-to-high refractive index difference mode spot conversion module, and finally split into two path polarization modes by a polarization control module. If the device in the polarization control module is a polarization beam splitter, the two path polarization modes are TE0 and TM0 modes, respectively; if it is a polarization beam rotator, both path polarization modes are TE0 modes, facilitating integration with other subsequent devices, such as modulators and detectors.

[0079] LP in few-mode fiber 11aThe mode is coupled to the LP of the low refractive index difference multimode waveguide via a multimode end-face coupler. 11a After passing through the polarization-insensitive mode multiplexer / demultiplexer, the mode first passes through the laterally distributed high-order mode coupler in the polarization-insensitive mode multiplexer / demultiplexer, then is coupled to the access waveguide and transmitted to the angled height conversion waveguide, and then to the low refractive index difference single-mode waveguide. At the end face of the low refractive index difference chip, it is coupled to the TE0 / TM0 mode pair in the single-mode waveguide of the high refractive index difference chip through the low refractive index difference-high refractive index difference mode spot conversion module, and finally passes through the polarization control module to split into two path polarization modes.

[0080] LP in few-mode fiber 11b LP multimode end-face coupler coupled to low refractive index difference multimode waveguide 11a After passing through the polarization-insensitive mode multiplexer / demultiplexer, the mode first passes through the laterally distributed higher-order mode coupler in the polarization-insensitive mode multiplexer / demultiplexer, and then continues to propagate in the bus waveguide. When it reaches the longitudinally distributed higher-order mode coupler, it first passes through the angled mode rotating waveguide to be converted into LP mode. 11a The mode is then coupled to the access waveguide, and then transmitted to the low refractive index difference single-mode waveguide. At the end face of the low refractive index difference chip, it is coupled to the TE0 / TM0 mode pair in the single-mode waveguide of the high refractive index difference chip through the low refractive index difference-high refractive index difference mode spot conversion module. Finally, it is split into two path polarization modes by the polarization control module.

[0081] Specific embodiments of the present invention are as follows:

[0082] The schematic diagram of the device structure in the embodiment is shown below. Figure 2 As shown, a center wavelength of 1550 nm is considered. The core diameter of few-mode fiber i is 14 μm, NA ~ 0.11, and the supported LP... 01 LP 11a and LP 11b The model field diagram is as follows Figure 4 As shown. The core layer of the low refractive index difference chip ii is made of silicon dioxide (SiO2) material, with a refractive index difference of about 1.5% and a core layer height of 6.5μm; the high refractive index difference chip iii is made of silicon nanowire waveguide based on silicon insulator (SOI) material. Its core layer material is silicon, with a thickness of 220nm and a refractive index of 3.476. Its lower and upper cladding layers are both made of SiO2, with a thickness of 3μm and a refractive index of 1.444.

[0083] For the multimode coupler 1 in this embodiment, the segmented waveguides 11, 12, ..., 1n have a period of 5.4 μm and a duty cycle that linearly varies from 77% to 40.7%. The low refractive index difference multimode waveguide 2 has a height of 6.5 μm and a width of 7 μm. LP 01 LP 11a and LP 11bThe coupling efficiencies of the few-mode fiber i coupled to the low-refractive-index-difference multimode waveguide 2 are 81.1%, 84.7%, and 83.8%, respectively, with crosstalk all less than -30dB. The simulated loss spectrum in the 1500nm-1600nm band is as follows: Figure 5 As shown.

[0084] For the laterally distributed high-order mode coupler H, the lateral bus waveguide 302 has a height of h1 = 6.5 μm, widths of 7 μm and 4.5 μm at its two ends, and a length of 2000 μm; the lateral access waveguide 303 has widths of 1.5 μm and 2.5 μm at its two ends, and a length of 3500 μm; the spacing between the bus waveguide and the access waveguide is 2.5 μm. The lateral S-shaped curved waveguide 304 has a width of 2.5 μm at both ends and a length of 600 μm. The angled height conversion waveguide 305 has heights of 6.5 μm and 4 μm at its two ends, widths of 2.5 μm and 4 μm, and a length of 1000 μm.

[0085] For the longitudinally distributed high-order mode coupler V, the angled mode rotating waveguide 306 has heights of 6.5 μm and 4 μm at its two ends, widths of 4 μm and 7 μm, and a length of 1500 μm. The longitudinal bus waveguide 307 has a height of h² = 4 μm, widths of 7 μm and 4.5 μm at its two ends, and a length of 2000 μm; the longitudinal access waveguide 308 has widths of 1.5 μm and 2.5 μm at its two ends, and a length of 2000 μm; the spacing between the bus waveguide and the access waveguide is 2.5 μm. The longitudinal S-shaped curved waveguide 309 has a width of 2.5 μm at both ends and a length of 1500 μm. The low refractive index difference single-mode output waveguide has a height and width of 4 μm and supports single-mode transmission.

[0086] The simulated loss spectrum of the polarization-insensitive mode multiplexing / demultiplexing module b in the 1500nm-1600nm band in this embodiment is as follows: Figure 6 As shown.

[0087] For the inverted conical single-mode end coupler in this embodiment, the waveguide tip width is 0.14μm, the single-mode waveguide width at the other end is 0.45μm, and the length is 200μm.

[0088] For the polarization beam splitter rotator in this embodiment, such as Figure 7 As shown, wb1=0.4μm, wb2=0.8μm, ws=2.4μm, L1=100μm, L2=30μm, gs=15μm, wb3=0.72μm m, wb4=0.42μm, wa1=0.18μm, wa2=0.3μm, g=0.18μm, L3=20μm, L4=60μm, Ls=50μm.

[0089] Simulation results show that the coupling loss of the low-to-high refractive index difference waveguide mode conversion module of this invention is 0.3dB (TE0) and 1.6dB (TM0) in the C-band; the TE0 mode and TM0 mode loss of the polarization beam splitter are less than 0.03dB, and the crosstalk is less than -30dB.

[0090] As can be seen from this implementation, the present invention couples six linearly polarized modes (including x and y polarization) in a few-mode fiber to six linearly polarized modes in a high refractive index difference waveguide, which has the advantages of low crosstalk, large bandwidth, large tolerance, and scalability.

[0091] The above embodiments are used to explain and illustrate the present invention, but not to limit the present invention. Any modifications and changes made to the present invention within the spirit and scope of the claims shall fall within the protection scope of the present invention.

Claims

1. A high-efficiency optical waveguide chip-fiber coupler, characterized in that: comprising a few-mode fiber (i), a low-contrast conversion chip (ii) and a high-contrast chip (iii), which are sequentially connected in the form of end-face coupling; the low-contrast conversion chip (ii) comprises a few-mode fiber-multimode waveguide mode spot conversion module (a) and a polarization-insensitive mode multiplexing / demultiplexing module (b) connected in sequence along the transmission direction, and the input end of the few-mode fiber-multimode waveguide mode spot conversion module (a) is arranged in corresponding butt joint with the output port of the few-mode fiber (i); the few-mode fiber-multimode waveguide mode spot conversion module (a) is composed of a multimode end-face coupler (1); the polarization-insensitive mode multiplexing / demultiplexing module (b) is composed of a low-contrast multimode waveguide (2), a polarization-insensitive mode multiplexing / demultiplexing device (3) and n low-contrast single-mode waveguides (41, 42, …, 4n) connected in sequence along the transmission direction, the polarization-insensitive mode multiplexing / demultiplexing device (3) has n output ports, and the n output ports of the polarization-insensitive mode multiplexing / demultiplexing device (3) are connected with the input ends of the n low-contrast single-mode waveguides (41, 42, …, 4n) respectively; the high-contrast chip (iii) comprises a low-high-contrast waveguide mode spot conversion module (c) and a polarization control module (d) connected in sequence along the transmission direction; the low-high-contrast waveguide mode spot conversion module (c) is composed of n single-mode end-face couplers (51, 52, …, 5n) and n high-contrast single-mode waveguides (61, 62, …, 6n) connected behind the n single-mode end-face couplers (51, 52, …, 5n), the input ends of the n single-mode end-face couplers (51, 52, …, 5n) are arranged in corresponding butt joint with the output ends of the n low-contrast single-mode waveguides (41, 42, …, 4n) respectively, and the output ends of the n single-mode end-face couplers (51, 52, …, 5n) are connected with the input ends of the n high-contrast single-mode waveguides (61, 62, …, 6n) respectively; the polarization control module (d) is composed of n polarization control devices (71, 72, …, 7n) and 2n high-contrast single-mode waveguides (801, 802, …, 8n1, 8n2) connected behind the n polarization control devices (71, 72, …, 7n), the input ends of the n polarization control devices (71, 72, …, 7n) are connected with the output ends of the n high-contrast single-mode waveguides (61, 62, …, 6n) respectively, each polarization control device (71, 72, …, 7n) has two output ends, the 2n output ends of the n polarization control devices (71, 72, …, 7n) are connected with the input ends of the 2n high-contrast single-mode waveguides (801, 802, …, 8n1, 8n2) respectively, and the output ends of the 2n high-contrast single-mode waveguides (801, 802, …, 8n1, 8n2) serve as the output ends of the optical waveguide chip-fiber coupler. ​ ​ ​ ​ ​ ​ ​ 2. A high efficiency optical waveguide chip-fiber coupler according to claim 1, characterized in that: The multi-mode end face coupler (1) is composed of segmented waveguides (11, 12, …, 1n) with periodicity and linearly changing duty cycle, the segmented waveguides (11, 12, …, 1n) are composed of multiple waveguides arranged in the conducting direction, and the duty cycle of the segmented waveguides (11, 12, …, 1n) decreases in the conducting direction.

3. The high-efficiency optical waveguide chip-fiber coupler of claim 1, wherein: The polarization-insensitive mode multiplexer / demultiplexer (3) is composed of a low-contrast multimode bus waveguide (301), a transverse high-order mode coupler (H) and a longitudinal high-order mode coupler (V) connected in sequence in the conducting direction, one end of the transverse high-order mode coupler (H) is connected to the low-contrast multimode waveguide (2) through the low-contrast multimode bus waveguide (301), the other end is connected to one end of the longitudinal high-order mode coupler (V), and the other end of the longitudinal high-order mode coupler (V) outputs n ports and is connected to n low-contrast single-mode waveguides (41, 42, …, 4n) respectively.

4. A high efficiency optical waveguide chip-fiber coupler according to claim 3, wherein: The polarization-insensitive mode multiplexer / demultiplexer (3) is a 1*3 multiplexer / demultiplexer, specifically: The transverse high-order mode coupler (H) is composed of a transverse bus waveguide (302), a transverse access waveguide (303), a transverse S-shaped bending waveguide (304) and an inclined angle height conversion waveguide (305), the input end of the transverse bus waveguide (302) is connected to the output end of the low-contrast multimode bus waveguide (301), the output end of the transverse bus waveguide (302) is connected to the input end of the inclined angle mode rotating waveguide (306) of the longitudinal high-order mode coupler (V); the transverse bus waveguide (302) is provided with parallel and coupled transverse access waveguides (303) beside; the output end of the transverse access waveguide (303) is connected to one end of the transverse S-shaped bending waveguide (304), the other end of the transverse S-shaped bending waveguide (304) is connected to the input end of the inclined angle height conversion waveguide (305), and the output end of the inclined angle height conversion waveguide (305) is connected to the input end of a corresponding low-contrast single-mode output waveguide (311); The longitudinal high-order mode coupler (V) is composed of an inclined angle mode rotating waveguide (306), a longitudinal bus waveguide (307), a longitudinal access waveguide (308) and a longitudinal S-shaped bending waveguide (309), the output end of the inclined angle mode rotating waveguide (306) is connected to the input end of the longitudinal bus waveguide (307), the output end of the longitudinal bus waveguide (307) is connected to the input end of a corresponding low-contrast single-mode output waveguide (312); the longitudinal bus waveguide (307) is provided with parallel and coupled longitudinal access waveguides (308) beside; the output end of the longitudinal access waveguide (308) is connected to one end of the longitudinal S-shaped bending waveguide (309), the other end of the longitudinal S-shaped bending waveguide (309) is connected to the input end of a corresponding low-contrast single-mode output waveguide (313); The output end of each low-reflective-index-difference single-mode output waveguide (311, 312, 313) is connected with a corresponding low-reflective-index-difference single-mode waveguide (41, 42, 43), and the output end of each low-reflective-index-difference single-mode waveguide (41, 42, 43) is used as the output end of the low-reflective-index-difference conversion chip (ii).

5. A high efficiency optical waveguide chip-fiber coupler according to claim 4, wherein: The arrangement relationship between the transverse bus waveguide (302) and the transverse access waveguide (303) and the arrangement relationship between the longitudinal bus waveguide (307) and the longitudinal access waveguide (308) are the same, and are that the width of the bus waveguide gradually decreases and the width of the access waveguide gradually increases along the transmission direction, and the bus waveguide and the access waveguide are arranged in parallel with each other on the same side, and the other side of each is arranged as a side slope with a respective tapering slope.

6. A high efficiency optical waveguide chip-fiber coupler according to claim 4, wherein: The oblique-angle height conversion waveguide (305) and the oblique-angle mode rotation waveguide (306) have the same structure, and are divided into two waveguide sections of an input section and an output section connected in sequence along the transmission direction, the input section and the output section are connected in a vertical arrangement and are connected by an oblique end surface inclined to the transmission direction, the width of the input section gradually decreases along the transmission direction, the width of the output section gradually increases along the transmission direction, and the thickness of the input section is greater than the thickness of the output section.

7. A high efficiency optical waveguide chip-fiber coupler as set forth in claim 1, characterized by: The low-high-reflective-index-difference waveguide mode spot conversion module (c) is composed of n single-mode end surface couplers (51, 52,..., 5n) arranged side by side, the input end of each single-mode end surface coupler (51, 52,..., 5n) is flush with the end surface of the high-reflective-index-difference chip (iii), the input end of each single-mode end surface coupler (51, 52,..., 5n) is coaxially arranged with a corresponding low-reflective-index-difference single-mode waveguide (41, 42,..., 4n), the input end of each low-reflective-index-difference single-mode output waveguide (311, 312,..., 31n) in the high-reflective-index-difference chip (iii) is connected with a corresponding low-reflective-index-difference single-mode waveguide (41, 42,..., 4n), and the output ends of the n single-mode end surface couplers (51, 52,..., 5n) are respectively connected with n high-reflective-index-difference single-mode waveguides (61, 62,..., 6n).

8. A high efficiency optical waveguide-few mode fiber coupler according to claim 1, wherein: The single-mode end surface coupler (51, 52,..., 5n) has an inverted taper structure, a double-layer structure or a trident structure.

9. A high efficiency optical waveguide chip-fiber coupler as set forth in claim 1, characterized by: The polarization control device (71, 72,..., 7n) is a polarization beam splitter or a polarization beam splitter rotator.

10. A high efficiency optical waveguide chip-fiber coupler as set forth in claim 1, characterized by: The few-mode fiber (i) receives 2n linearly polarized mode optical signals and emits them to the multi-mode end surface coupler (1), the 2n linearly polarized mode optical signals are coupled into the low-reflective-index-difference multi-mode waveguide (2) through the multi-mode end surface coupler (1), the 2n linearly polarized mode optical signals are transmitted to the polarization-insensitive mode multiplexer / demultiplexer (3) through the low-reflective-index-difference multi-mode waveguide (2), the 2n linearly polarized mode optical signals are demultiplexed into n base mode optical signals through the polarization-insensitive mode multiplexer / demultiplexer (3), and the n base mode optical signals are respectively output from n low-reflective-index-difference single-mode waveguides (41, 42,..., 4n), each base mode optical signal is a transverse electric base mode, a transverse magnetic base mode or a coexisting transverse electric base mode and transverse magnetic base mode mode pair optical signal. Subsequently, the mode field matching conversion refractive index difference is carried out through the single-mode end face coupler (51, 52, …, 5n), and then coupled into n high refractive index difference single-mode waveguides (61, 62, …, 6n) respectively, conducted to n polarization control devices (71, 72, …, 7n) through the n high refractive index difference single-mode waveguides (61, 62, …, 6n) respectively, and separated into different linear polarization mode optical signals by the polarization control devices (71, 72, …, 7n), finally, the 2n linear polarization mode optical signals are input into 2n high refractive index difference single-mode waveguides (801, 802, …, 8n1, 8n2) respectively to realize the signal coupling.

Images