On-chip integrated dual-mode bidirectional switchable up-down multiplexer and preparation method thereof

Abstract

The invention provides an on-chip integrated dual-mode bidirectional switchable up-down multiplexer and a preparation method thereof. The multiplexer comprises a silicon-based substrate, a buried oxide layer, a silicon waveguide layer and an upper cladding, a reverse mode conversion unit and a bidirectional mode coupler are arranged in the silicon waveguide layer, and routing is performed through an optical switch. According to the multiplexer provided by the invention, a bidirectional switchable function of dual modes (TE0 and TE1 as well as TE0 and TE2) is realized, and efficient optical mode multiplexing and signal transmission can be realized; moreover, the packaging size is small, the loss is low, the crosstalk is low, the manufacturing is simple, and the cost is low. The silicon-on-insulator (SOI) platform processing technology is utilized, miniaturization and integration are achieved, and the wide application prospect in the field of integrated photonics is shown.

Description

Technical Field

[0001] The invention relates to the technical field of integrated photonics, in particular to an on-chip integrated dual-mode bidirectional switchable add / drop multiplexer and a preparation method thereof. Background Art

[0002] With the rapid development of information technology, the demand for optical communication systems is growing, and higher requirements are placed on the key components in optical communication systems - multiplexers. Multiplexers are an important component in optical communication networks, which are used to integrate multiple optical signals into the same optical fiber for transmission to improve the transmission efficiency and bandwidth utilization of optical fibers. Although traditional single-mode multiplexers have met the needs of early optical communication systems to a certain extent, their transmission capacity and flexibility have gradually shown their shortcomings in the face of growing data transmission volume. In order to overcome these problems, researchers began to explore dual-mode or multi-mode multiplexing technology in order to improve the overall performance of the system by increasing the number of transmission modes.

[0003] However, existing mode multiplexers have some obvious limitations. First, traditional multiplexers usually only support one-way transmission and cannot achieve two-way communication, which limits their application in full-duplex communication systems. Secondly, most mode multiplexers have weak mode switching capabilities and it is difficult to flexibly switch between different modes, resulting in poor adaptability of the system in dealing with different application scenarios. In addition, the existing multiplexers are large in size and low in integration, which is not conducive to the realization of miniaturized and low-cost optical communication systems. Finally, traditional multiplexers have high losses and large crosstalk, which affects the quality of signal transmission and the stability of the system. Summary of the invention

[0004] The purpose of the present invention is to provide an on-chip integrated dual-mode bidirectional switchable add / drop multiplexer and a preparation method thereof, the multiplexer can support bidirectional transmission and can flexibly switch between different modes, and has the advantages of small package size, low loss, low crosstalk, low manufacturing difficulty, and large process tolerance.

[0005] The present invention is achieved in that:

[0006] An on-chip integrated dual-mode bidirectional switchable add / drop multiplexer comprises a silicon-based substrate, a buried oxide layer arranged on the silicon-based substrate, a silicon waveguide layer arranged on the buried oxide layer, and an upper cladding layer covering the buried oxide layer and wrapping the silicon waveguide layer; the buried oxide layer and the upper cladding layer are both made of SiO2 material;

[0007] The core design of the silicon waveguide layer is the reverse mode conversion unit placed in the center of the bus waveguide. In addition, bidirectional mode couplers are symmetrically arranged on both sides of the bus waveguide, and both ends of each bidirectional mode coupler are connected to curved waveguides, which are further connected to corresponding optical switches.

[0008] Furthermore, the silicon waveguide layer includes a bus waveguide, which is a long straight waveguide structure; a reverse mode conversion unit is arranged at the central area of ​​the bus waveguide, and the reverse mode conversion unit is composed of two rows of gratings along the direction of the bus waveguide, and the two rows of gratings are offset by half a period; the grating period first increases linearly and then remains uniform, and then decreases linearly; the grating size first increases linearly and then remains uniform, and then decreases linearly; two bidirectional mode couplers are symmetrically arranged on the same side of the bus waveguide, each of which is a long straight waveguide structure, and the bidirectional mode coupler is parallel to and arranged in parallel with the bus waveguide; the two bidirectional mode couplers correspond to the bus waveguides at both ends of the reverse mode conversion unit respectively; the two ends of each bidirectional mode coupler are respectively connected to a curved waveguide, and the curved waveguide is connected to an optical switch; the materials of the bus waveguide, the bidirectional mode coupler, the curved waveguide and the optical switch are all silicon; and the reverse mode conversion unit is made of SiO2 material.

[0009] Preferably, in the above solution, the width of the bus waveguide should be greater than the bidirectional mode couplers on both sides.

[0010] Preferably, in the above solution, the bus waveguide width is 0.8-1.5 μm.

[0011] Preferably, in the above solution, the width of the bidirectional mode couplers on both sides is 0.4-0.55 μm.

[0012] Preferably, in the above solution, the spacing between the bus waveguide and the bidirectional mode coupler is 100-200 nm.

[0013] Preferably, in the above solution, the heights of the bus waveguide, the bidirectional mode coupler, the bent waveguide, the reverse mode conversion unit and the optical switch are all 220 nm.

[0014] Preferably, in the above solution, the bus waveguide, the bidirectional mode coupler, the bent waveguide, the reverse mode conversion unit and the optical switch are manufactured at one time.

[0015] Preferably, in the above scheme, the grating period of the reverse mode conversion unit adopts a chirped design, and its period first increases linearly, then remains uniform, and finally decreases linearly.

[0016] Preferably, in the above scheme, the grating size of the reverse mode conversion unit is designed by apodization, and its length first increases linearly, then remains uniform, and finally decreases linearly.

[0017] Preferably, in the above solution, the grating duty cycle of the reverse mode conversion unit is 0.5.

[0018] Preferably, in the above solution, all waveguides are made of silicon-on-insulator material.

[0019] Preferably, in the above solution, SiO2 material is filled in the reverse mode conversion unit when manufacturing the upper cladding layer.

[0020] Preferably, in the above solution, the optical switch can be formed using the principle of Mach-Zehnder Interferometer (MZI).

[0021] Preferably, in the above solution, the four curved waveguides are all bent in a direction away from the bus waveguide.

[0022] In the above scheme, the preparation method of the on-chip integrated dual-mode bidirectional switchable add / drop multiplexer comprises the following steps:

[0023] a. Preparing a buried oxide layer of SiO2 material on a silicon-based substrate;

[0024] b. Setting a mask on the buried oxide layer, wherein a specific pattern is designed on the mask;

[0025] c. preparing a silicon waveguide layer at a position corresponding to the mask on the buried oxide layer;

[0026] d. Remove the mask and prepare an upper cladding layer of SiO2 material on the buried oxide layer, wherein the upper cladding layer wraps the silicon waveguide layer, thereby forming an on-chip integrated dual-mode bidirectional switchable add / drop multiplexer.

[0027] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0028] 1. More complete functionality: Under the auxiliary control of the reverse mode conversion unit and the optical switch, the present invention better realizes the new function of the dual-mode bidirectional switchable add / drop multiplexer. Compared with many previous designs, it has more flexibility and improves the on-chip integration.

[0029] 2. Easy manufacturing and enhanced reliability. The waveguide structures used in the present invention, including bus waveguides, bidirectional mode couplers and curved waveguides, have characteristic dimensions at the micron or submicron level, which effectively reduces the requirements for equipment accuracy in the manufacturing process of photonic devices, thereby simplifying the manufacturing process and improving the reliability and stability of the device.

[0030] 3. Excellent design flexibility, easy operation and strong scalability. Its input / output ports can be flexibly arranged on both sides of the four curved waveguides and the bus waveguide, which not only improves the degree of freedom in layout, but also achieves efficient conversion between multiple modes including TE0 to TE1, TE0 to TE2, etc. by finely adjusting the specific parameters of the reverse mode conversion unit and the optical switch. This design greatly enriches the system functions and significantly improves its ability to cope with the needs of different application scenarios, showing excellent versatility and adaptability.

[0031] 4. Compact structure, easy preparation and significant cost-effectiveness. The present invention utilizes SOI (silicon on insulator) materials with high refractive index difference to achieve miniaturization and integration of devices. In addition, based on cheap and mature CMOS processing technology, it not only simplifies the production process, but also greatly reduces the production cost, showing broad application prospects in the field of integrated photonics.

[0032] 5. Multifunctionality. The present invention is not only applicable to the multiplexing of multiple modes (TE0 and TE1 / TE0 and TE2), but also can realize the multiplexing function of polarization states under the same structure, thereby greatly enriching its application potential in various optical communication systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 3 is a schematic diagram of the planar (top view) structure of the silicon waveguide layer in an embodiment of the present invention.

[0034] Figure 2 yes Figure 1 Schematic diagram of the structure of the reverse mode conversion unit.

[0035] Figure 3 It is the transmission spectrum of the embodiment of the present invention in the wavelength range of 1500 to 1600nm. Specifically, when the TE0 or TE1 mode is input through the bus waveguide, (a) and (b) respectively present the transmission spectrum observed at the download end (Port A / B). When the TE0 mode is input through different ports (Port a / b) of the optical switch, (c) presents the transmission spectrum observed at the upload end (right side of the bus waveguide).

[0036] Figure 4 1 is the field evolution of the embodiment of the present invention when the wavelength is set to 1550 nm, where (a) and (b) correspond to the downloading situation, and (c) and (d) correspond to the uploading situation.

[0037] In the figure: 1. Bus waveguide; 2. Bidirectional mode coupler; 3. Bend waveguide; 4. Reverse mode conversion unit; 5. Optical switch. DETAILED DESCRIPTION

[0038] The present invention relates to an on-chip integrated dual-mode bidirectional switchable add / drop multiplexer, which is designed to process TE0 and TE1 mode optical signals. The system supports bidirectional transmission and mode conversion of TE0 and TE1 mode optical signals input from the left side of the bus waveguide and TE0 mode optical signals input from Port 2. This silicon-based multiplexer not only has excellent technical performance, but also demonstrates great potential in practical applications. Through careful design, the multiplexer achieves bidirectional input capability and supports the effective transmission of optical signals in two directions; at the same time, it also has a powerful multi-mode multiplexing function, which makes it possible to simultaneously process optical signals of different modes, thereby greatly improving the flexibility and efficiency of the system. In addition, the present invention takes into account the lower manufacturing difficulty and higher process tolerance, which lays a solid foundation for large-scale production and practical deployment.

[0039] The working principle and features of the present invention are described in detail below in conjunction with the accompanying drawings. The embodiments given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0040] like Figure 1 As shown, the present invention provides an on-chip integrated dual-mode bidirectional switchable up / down multiplexer. The design key point of the multiplexer structure lies in the silicon waveguide layer, and the specific structure of the silicon waveguide layer is as follows: a reverse mode conversion unit 4 is set in the central area of ​​the bus waveguide 1, and bidirectional mode couplers 2 are arranged at both ends of the same side of the bus waveguide 1, and both ends of each bidirectional mode coupler 2 are connected to a curved waveguide 3, and the curved waveguide 3 is further connected to the corresponding optical switch 5. The bus waveguide 1, the reverse mode conversion unit 4, the bidirectional mode coupler 2, the curved waveguide 3 and the optical switch 5 together constitute the silicon waveguide layer. Below the silicon waveguide layer is a buried oxide layer, above it is an upper cladding layer, and below the buried oxide layer is a silicon-based substrate. The buried oxide layer and the upper cladding layer are both SiO2 materials.

[0041] The bus waveguide 1 is a long straight waveguide structure, and the reverse mode conversion unit 4 is composed of two rows of hole-shaped gratings arranged side by side in the central area of ​​the bus waveguide 1 along the direction of the bus waveguide 1. The bidirectional mode coupler 2 is also a long straight waveguide structure, and the bidirectional mode coupler 2 is parallel to the bus waveguide 1. The bidirectional mode coupler close to the input end of the bus waveguide 1 is recorded as the first bidirectional mode coupler, and the bidirectional mode coupler close to the output end of the bus waveguide 1 is recorded as the second bidirectional mode coupler. The four curved waveguides are all bent in the direction away from the bus waveguide 1. The curved waveguide is a curved waveguide similar to a 90° arc. After the first bidirectional mode coupler is connected to the curved waveguides at both ends, it corresponds to the part between the input end of the bus waveguide 1 and the reverse mode conversion unit 4; after the second bidirectional mode coupler is connected to the curved waveguides at both ends, it corresponds to the part between the output end of the bus waveguide 1 and the reverse mode conversion unit 4.

[0042] The two rows of hole-shaped grating structures of the reverse mode conversion unit 4 are as follows Figure 2 As shown. The two rows of gratings are offset by half a period, that is, the hole-shaped gratings on one row of gratings correspond to the blank area between two adjacent gratings on the other row of gratings. The grating period adopts a chirped design, and its period first increases linearly, then remains uniform, and finally decreases linearly. The grating shape can be a circular hole or a square hole structure. Figure 2 The grating is a rectangular hole structure, and the direction of the long side of the rectangle is the direction of the bus waveguide 1. The grating length size in each row of gratings is designed with a cut-off, and its length first increases linearly, then remains uniform, and finally decreases linearly. The width of the grating remains unchanged. The grating duty cycle is 0.5.

[0043] The bus waveguide 1, the bidirectional mode coupler 2, the bending waveguide 3 and the optical switch 5 are all made of silicon-on-insulator materials, while the reverse mode conversion unit 4 is made of SiO2 material.

[0044] It should be noted that the bus waveguide 1, the bidirectional mode coupler 2, the curved waveguide 3, the reverse mode conversion unit 4 and the optical switch 5 are manufactured at one time, so when manufacturing the mask, it is necessary to set a specific pattern in the corresponding position in advance. Figure 1 For the structure, when making the silicon waveguide layer, the mask plate has a blocking part at the grating position corresponding to the reverse mode conversion unit 4, and Si is not formed in the blocking part. When the upper cladding layer is subsequently made, SiO2 material is filled in this area, thereby forming a reverse mode conversion unit of SiO2 material.

[0045] In the embodiment of the present invention, the height of the silicon waveguide layer is 220 nm, that is, the heights of the bus waveguide 1, the bidirectional mode coupler 2, the bent waveguide 3, the reverse mode conversion unit 4 and the optical switch 5 are all 220 nm.

[0046] In the embodiment of the present invention, the width of the bus waveguide 1 is 0.8-1.5 μm, and the width of the bidirectional mode coupler 2 and the curved waveguide 3 is 0.4-0.55 μm. Such a design can better achieve mode coupling. The spacing between the bus waveguide 1 and the bidirectional mode coupler 2 is 100-200 nm. The optical switch 5 can be formed using the principle of Mach-Zehnder interferometer (MZI).

[0047] In the embodiment of the present invention, the input optical signal is TE0 or TE1, and its wavelength range is 1500nm-1600nm.

[0048] The simulation results of this embodiment are as follows Figure 3 As shown. Figure 3The simulation results (a) and (b) show that the transmission spectra of the two modes in the download end (Port A / B) are obtained by selecting TE0 or TE1 input in bus waveguide 1. And (c) shows that by inputting TE0 in curved waveguide 3 (Port a / b), the corresponding transmission spectra are obtained at the upload end (right side of bus waveguide 1).

[0049] Figure 4 The field evolution characteristics of the TE0 and TE1 mode optical signals input from both sides of the bus waveguide at a wavelength of 1550nm are shown in this embodiment. Specifically, the transmission characteristics of the optical signal in this embodiment mainly include the following two situations:

[0050] 1. When the TE0 or TE1 mode optical signal is input into the bus waveguide 1 from the left, the TE0 mode optical signal first enters the reverse mode conversion unit 4, where reverse coupling occurs and converts it into the TE1 mode. Subsequently, the TE1 mode optical signal continues to propagate to the bidirectional mode coupler 2 region, where mode coupling occurs, coupling the TE1 mode in the bus waveguide 1 to the lower waveguide and converting it into the TE0 mode. This TE0 mode optical signal is then transmitted through the curved waveguide 3 and finally arrives at Port A. On the other hand, for the directly input TE1 mode optical signal, it is directly coupled to the lower waveguide in the bidirectional mode coupler 2 region, and is also converted into the TE0 mode, and then transmitted through the curved waveguide 3 and finally arrives at Port B. Whether it is the TE0 mode optical signal output from Port A or Port B, it will be further guided to the optical switch 5 and finally arrive at Port 1.

[0051] 2. When the TE0 mode optical signal is input from Port 2 to the optical switch 5, it will be selectively routed to Port a or Port b for output, and then enter the curved waveguide 3. If the TE0 mode optical signal is input from Port a to the curved waveguide 3, it will then be directly coupled to the bus waveguide 1 through the bidirectional mode coupler 2 region, converted to the TE1 mode, and then reach the reverse mode conversion unit 4, where reverse coupling occurs, converting it back to the TE0 mode, and finally output from the right side of the bus waveguide 1. On the other hand, when the TE0 mode optical signal is input from Port b to the curved waveguide 3, it will also be directly coupled to the bus waveguide through the bidirectional mode coupler 2 region to form the TE1 mode, but it does not need to be converted by the reverse mode conversion unit 4, and is directly output from the right side of the bus waveguide 1.

[0052] The grating design of the reverse mode conversion unit 4 in this embodiment meets the phase matching condition in the coupled mode theory, and its phase matching formula can be given by the following formula:

[0053]

[0054] In formula (1), β 前 and β 后 are the propagation constants of the forward mode and the backward mode respectively, m is the order and is generally 1, and Λ is the period.

[0055] The above content introduces in detail the implementation method of the on-chip integrated dual-mode bidirectional switchable up and down multiplexer. The reverse mode conversion unit used in the present invention includes a highly flexible Bragg grating. This design allows the conversion from TE2 mode to TE0 mode to be achieved by appropriately adjusting the grating structure (period and size) while keeping the overall system architecture basically unchanged, thereby constructing a function that can support TE2 and TE0 dual-mode bidirectional switchable up and down multiplexing. Compared with the mode multiplexer in the prior art, the solution of the present invention shows significantly better scalability.

[0056] The waveguide coupler provided by the present invention exhibits excellent multiplexing, and has the advantages of small package size, low loss, low crosstalk, low manufacturing difficulty, large process tolerance, etc., and can be flexibly applied to the fields of optical communication and integrated photonics. The technical solution of the present invention and the obtained optical signal transmission characteristics are significantly better than the existing related devices.

[0057] The contents described in the embodiments of this specification are merely an enumeration of the implementation forms of the inventive concept. The protection scope of the present invention should not be regarded as limited to the specific forms described in the embodiments. The protection scope of the present invention also extends to equivalent technical means that can be conceived by those skilled in the art based on the inventive concept.

Claims

1. An on-chip integrated dual-mode bidirectional switchable add / drop multiplexer, comprising a silicon-based substrate, a buried oxide layer disposed on the silicon-based substrate, a silicon waveguide layer disposed on the buried oxide layer, and an upper cladding layer covering the buried oxide layer and wrapping the silicon waveguide layer; the buried oxide layer and the upper cladding layer are both made of SiO2 material; wherein: The silicon waveguide layer includes a bus waveguide, which is a long straight waveguide structure; a reverse mode conversion unit is arranged at the central area of ​​the bus waveguide, and the reverse mode conversion unit is composed of two rows of gratings along the direction of the bus waveguide, and the two rows of gratings are offset by half a period; the grating period first increases linearly and then remains uniform, and then decreases linearly; the grating size first increases linearly and then remains uniform, and then decreases linearly; two bidirectional mode couplers are symmetrically arranged on the same side of the bus waveguide, each of which is a long straight waveguide structure, and the bidirectional mode coupler is parallel to and arranged in parallel with the bus waveguide; the two bidirectional mode couplers correspond to the bus waveguides at both ends of the reverse mode conversion unit respectively; the two ends of each bidirectional mode coupler are respectively connected to a curved waveguide, and the curved waveguide is connected to an optical switch; the materials of the bus waveguide, the bidirectional mode coupler, the curved waveguide and the optical switch are all silicon; and the reverse mode conversion unit is made of SiO2 material.

2. The on-chip integrated dual-mode bidirectional switchable add / drop multiplexer according to claim 1, characterized in that: The width of the bus waveguide is greater than the width of the bidirectional mode coupler.

3. The on-chip integrated dual-mode bidirectional switchable add / drop multiplexer according to claim 2, characterized in that: The bus waveguide width is 0.8-1.5μm, and the bidirectional mode coupler width is 0.4-0.55μm.

4. The on-chip integrated dual-mode bidirectional switchable add / drop multiplexer according to claim 1, characterized in that: The spacing between the bus waveguide and the bidirectional mode coupler is 100-200nm.

5. The on-chip integrated dual-mode bidirectional switchable add / drop multiplexer according to claim 1, characterized in that: The height of the bus waveguide, bidirectional mode coupler, curved waveguide, reverse mode conversion unit and optical switch are all 220nm.

6. The on-chip integrated dual-mode bidirectional switchable add / drop multiplexer according to claim 1, characterized in that: The grating duty cycle of the reverse mode conversion unit is 0.

5.

7. The on-chip integrated dual-mode bidirectional switchable add / drop multiplexer according to claim 1, characterized in that: The optical switch is formed using the principle of Mach-Zehnder interferometer.

8. The on-chip integrated dual-mode bidirectional switchable add / drop multiplexer according to claim 1, characterized in that: Bus waveguides, bidirectional mode couplers, curved waveguides, reverse mode conversion units, and optical switches are fabricated at one time.

9. The on-chip integrated dual-mode bidirectional switchable add / drop multiplexer according to claim 1, characterized in that: The four curved waveguides are all bent in a direction away from the bus waveguide.

10. A method for preparing the on-chip integrated dual-mode bidirectional switchable add / drop multiplexer according to any one of claims 1 to 9, characterized in that: The steps include: a. Preparing a buried oxide layer of SiO2 material on a silicon-based substrate; b. Setting a mask on the buried oxide layer, wherein a specific pattern is designed on the mask; c. preparing a silicon waveguide layer at a position corresponding to the mask on the buried oxide layer; d. Remove the mask and prepare an upper cladding layer of SiO2 material on the buried oxide layer, wherein the upper cladding layer wraps the silicon waveguide layer, thereby forming an on-chip integrated dual-mode bidirectional switchable add / drop multiplexer.

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