A polarization-independent electro-optical switch

Abstract

The present invention discloses a large bandwidth, low loss, high-speed switching, polarization-insensitive electro-optical switch, comprising: an input waveguide for receiving light including TE polarization and TM polarization components or one of the components from an optical fiber, a laser or other optoelectronic device; an input-end power beam splitter connected to the input waveguide; a modulation zone unit connected to the power beam splitter; an output-end power combiner connected to the output end of the modulation zone unit; and an electric field for applying voltage to control the phase difference; the modulation zone unit comprises: a TM waveguide branch (i.e., a modulation zone waveguide branch), the TM waveguide branch being arranged on the electric field; and a TE waveguide branch connected in parallel with the TM waveguide branch. The present invention realizes polarization-independent waveguides, power combiners, and power splitters based on a special waveguide structure design. The polarization-dependent characteristics of modulation efficiency are utilized to introduce light of two polarization states into different modulation paths, so as to realize different modulation zone lengths of different polarization states.

Description

Technical Field

[0001] The invention relates to the field of semiconductor technology, and in particular to a polarization-independent electro-optical switch. Background Art

[0002] In recent years, with the rapid development of communication networks, the amount of Internet communication data has increased rapidly at a rate of 50%-60% per year, and users' requirements for bandwidth and transmission rate have continued to increase. In data exchange networks, the development of electrical switches has gradually encountered bottlenecks: the backhaul delay index of 5G networks has put forward more stringent requirements on the performance of switching nodes; the power consumption of electrical switching equipment at network nodes is as high as 10,000 watts, and the power consumption is close to the permitted limit. 80% of the power consumption comes from optoelectronic / electro-optical conversion and electrical switching switches. Therefore, the advantages of optical switching technology such as large bandwidth, low power consumption and low latency are becoming increasingly prominent, which will provide new ways and solutions to meet the growing communication needs.

[0003] As a key component in optical communication networks, optical switches are mainly used in large data exchange centers and supercomputers. Optical switches are usually required to have characteristics such as large bandwidth, low loss and polarization independence. In addition, in the data packet switching type, the switching speed of the optical switch needs to reach the nanosecond level to avoid data packet loss. However, it is difficult for traditional silicon-based optical switches with plasma dispersion effect PIN structure to achieve polarization independence and low loss and high switching speed performance at the same time. First, carrier injection introduces additional light absorption loss, and the loss is relatively large in actual use. Second, the polarization-independent waveguide conditions of thin-film silicon materials are harsh and the process is difficult to achieve.

[0004] Therefore, achieving large bandwidth, low loss, high switching speed and polarization independence at the same time is an urgent problem that needs to be solved in optical switches. Summary of the invention

[0005] The purpose of the present invention is to propose a large bandwidth, low loss, high-speed switching, polarization-insensitive electro-optical switch, which realizes the switching effect for transverse electric mode (TE) and transverse magnetic mode (TM) signals simultaneously in the C-band through electro-optical modulation based on a Mach-Zehnder interferometer (MZI) structure, solves the technical problem of polarization-independent characteristics that are difficult to achieve with silicon waveguides or other materials, and solves the technical problem of introducing large additional losses during electro-optical modulation.

[0006] The specific technical solution adopted by the present invention is:

[0007] A polarization-independent optical switch, comprising:

[0008] An input waveguide for receiving light including TE polarization and TM polarization components or one of the polarization components from an optical fiber, a laser or other optoelectronic device;

[0009] The input end connected to the input waveguide includes a power distribution device such as a multimode interference coupler;

[0010] a modulation zone unit connected to the power beam splitter;

[0011] The output end connected to the output end of the modulation zone unit includes a power beam combining device such as a multi-mode interference coupler;

[0012] and an electric field for applying voltage to achieve modulation such as phase control;

[0013] The modulation zone unit comprises:

[0014] A TM waveguide branch, wherein the TM waveguide branch is arranged on the electric field;

[0015] A TE waveguide branch is connected in parallel with the TM waveguide branch, and the TE waveguide branch is arranged on the electric field.

[0016] The modulation zone unit also includes:

[0017] A modulation zone waveguide main path connected to the input end power splitter;

[0018] A polarization beam splitter connected to the modulation zone waveguide main path, wherein the output end of the polarization beam splitter is connected to the TM waveguide branch and the TE waveguide branch;

[0019] A polarization beam combiner is connected to the TM waveguide branch and the TE waveguide branch, and the output end of the polarization beam combiner is connected to the output end power beam combiner.

[0020] The modulation zone waveguide main path, TM waveguide branch, and TE waveguide branch are all made of lithium niobate or other materials with different modulation efficiencies for TE polarized light and TM polarized light in waveguides.

[0021] The electric field comprises: a plurality of spaced metal electrodes, the modulation zone waveguide main path is arranged between adjacent metal electrodes, and the TM waveguide branch path is also arranged between adjacent metal electrodes.

[0022] The input waveguide includes a first input waveguide and a second input waveguide.

[0023] The input-end multimode interference coupler is a polarization-insensitive power beam splitter (such as a multimode interference coupler MMI).

[0024] There are two modulation area units.

[0025] The output end power combiner is a polarization insensitive power combiner (such as a multi-mode interference coupler MMI).

[0026] The present invention comprises a first input waveguide, a second input waveguide, a polarization-insensitive power beam splitter (such as a 2×2 multimode interference coupler MMI), a polarization beam splitter, a TE waveguide, a polarization beam combiner, a metal electrode, a modulation area waveguide main path, a first output waveguide and a second output waveguide. External polarized light input light is input into the device through the first input waveguide or the second input waveguide, and the power is equally divided into two modulation arms (i.e., two modulation area units) through the polarization-insensitive power beam splitter (such as a 2×2 MMI). Both modulation arms have a polarization beam splitter and a polarization beam combiner. Light containing a TE polarization component and a TM polarization component or one of the polarization components is separated from the TE or TM light and then beam combined back to the modulation area waveguide main path through a section of unmodulated TE or TM waveguide branch, so that different modulation area lengths of different polarization states are achieved. After combining, the light fields of the two modulation arms are interfered and output on a polarization-insensitive power combiner (such as a 2×2 MMI). By applying voltage to the metal electrodes to control the phase difference between the two modulation arms, the optical signal can be output from the first output waveguide or the second output waveguide.

[0027] The input and output waveguides have polarization-insensitive characteristics and can transmit TE and TM polarized light simultaneously.

[0028] The power beam splitter has the characteristic of being polarization-insensitive, and can equally split the input light into two modulation arms for either TE or TM polarized light.

[0029] The polarization beam splitter can separate the TE or TM component in the input light, and the polarization beam splitter exists in both modulation arms. The TE light or TM light after polarization beam splitting passes through the waveguide branch and then through the polarization beam combiner to return to the main waveguide of the modulation area, while the other polarized light that does not enter the waveguide branch is always transmitted in the main waveguide of the modulation area and the waveguide branch of the modulation area. The combined light passes through the power beam combiner again, and the difference in the modulation effect of TE and TM in the modulation area can be reduced or eliminated through the difference in the length of the modulation arm of the TE or TM component, so as to achieve polarization insensitivity of the output spectrum.

[0030] The existing polarization-insensitive optical switch technology is based on the invention of the Mach-Zehnder interferometer optical switch, the structure of the polarization rotator, and the separate processing of the split polarized light in the switch modulation arm for switch path selection.

[0031] The modulation area waveguide main path, TM waveguide branch (i.e., modulation area waveguide branch), and TE waveguide branch all use materials with different TE and TM modulation efficiencies, such as lithium niobate materials. The present invention, if based on a thin film lithium niobate platform, can achieve a sub-nanosecond switching speed. Polarization-independent waveguides, power beam splitters, and power combiners are realized based on a special waveguide structure design. The polarization-dependent characteristics of modulation efficiency are utilized to introduce light in two polarization states into different modulation paths, so that different modulation area lengths of different polarization states are realized.

[0032] Compared with the prior art, the present invention has the following advantages:

[0033] 1. The device of the present invention can process input optical signals of any polarization state, and can simultaneously process input optical signals of different wavelengths and different polarization states, without the need for structural changes in the device. Compared with the active polarization control device that can only process a single input polarization state based on the prior detection of the input light polarization state, the use of a polarization separation rotator to separate and rotate the polarized light, and then interference beam combining to convert all input light into a single polarization state, this solution is more flexible and free to use.

[0034] 2. Easy-to-integrate optical path design: This design only requires one electrical signal to realize the optical switch function in a single optical switch. Compared with the structure of polarization diversity scheme that first performs polarization splitting and rotation, and then processes the two optical switches separately and then polarization rotates and combines the beams, the optical path design is greatly simplified, which is more compact and easier to integrate.

[0035] 3. Ultra-high switching speed polarization-independent optical switch: The switching speed of silicon waveguide thermal optical switch is in the microsecond (μs) level, while in the data packet switching type, the switching speed of the optical switch needs to reach the nanosecond level to avoid data packet loss. The present invention can use lithium niobate or other waveguide materials with different modulation efficiencies for TE polarized light and TM polarized light in a high-speed device platform to achieve a sub-nanosecond switching speed.

[0036] 4. Low-loss polarization-independent optical switch: Existing electro-optical switch technology is based on silicon-based plasma dispersion effect PIN structure or phase change material, which will introduce additional light absorption loss, and the loss is relatively large in actual use. The present invention can realize polarization-independent optical switch based on thin-film lithium niobate, using lithium niobate or other low-loss device platform with different modulation efficiency of TE polarized light and TM polarized light in waveguide, and can realize on-chip ultra-low loss waveguide with loss less than 0.1dB / cm, and no additional light absorption loss is introduced during modulation. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 A schematic diagram of the structure of the polarization-independent electro-optical switch of the present invention;

[0038] Reference numerals: first input waveguide-1, second input waveguide-2, polarization-insensitive power beam splitter (e.g., 2×2 multimode interference coupler MMI)-3, polarization beam splitter-4, TE or TM waveguide branch-5, polarization beam combiner-6, metal electrode-7, modulation area waveguide main path-8, first output waveguide-9 and second output waveguide-10;

[0039] Figure 2It is a schematic structural diagram of the polarization-insensitive power beam splitter (for example, a 2×2 multi-mode interference coupler MMI) of the present invention;

[0040] Figure 3 The simulated transmission spectra of the polarization-insensitive power beam splitter (for example, a 2×2 multimode interference coupler MMI) of the present invention in two polarization states;

[0041] Figure 4 It is a schematic diagram of the structure of the polarization beam splitter of the present invention. DETAILED DESCRIPTION

[0042] Currently, common high-speed optical switches are usually implemented using silicon-based plasma dispersion effects. Ion doping is introduced into silicon waveguides, and the effective refractive index of the waveguide mode is changed by applying electrical signals to achieve the purpose of phase shift. The injection of carriers not only causes additional phase shift, but also brings additional losses. At the same time, the polarization-independent conditions of thin-film silicon waveguides are harsh. High-speed optical switches implemented using silicon-based plasma dispersion effects are difficult to achieve polarization-independence, which is a technical problem existing in current silicon-based high-speed optical switches.

[0043] In addition to the silicon-based plasma dispersion effect, the common use of phase change materials to achieve high-speed optical switches also has the problems of high loss, polarization dependence and difficulty in heterogeneous integration. The embodiments of the present invention provide a polarization-independent optical switch structure with low loss and high switching speed, which solves the technical problem that the polarization-independent characteristics of silicon waveguides or other materials are difficult to achieve, and at the same time solves the technical problem of introducing large additional losses during electro-optical modulation.

[0044] The polarization-insensitive optical switch proposed according to the embodiments of the present invention will be described below with reference to the accompanying drawings.

[0045] Figure 1The schematic diagram of the structure of the polarization-independent electro-optical switch of the present invention is shown in FIG. A polarization-independent electro-optical switch includes: an input waveguide (a first input waveguide 1 and a second input waveguide 2) for receiving external input light including TE polarization and TM polarization components or one of the polarization components; an input-end multimode interference coupler connected to the input waveguide; a modulation zone unit connected to the input-end multimode interference coupler; an output-end multimode interference coupler connected to the output end of the modulation zone unit; and an electric field for applying voltage to control the phase difference; there are two modulation zone units, each of which includes: a TM waveguide branch (i.e., a modulation zone waveguide branch), the TM waveguide branch being arranged on the electric field; and a TE single-mode waveguide branch 5 (i.e., a TE single-mode waveguide) connected in parallel with the TM waveguide branch. The modulation area unit further includes: a modulation area waveguide main path 8 connected to the input end multimode interference coupler; a polarization beam splitter 4 connected to the modulation area waveguide main path 8, the output end of the polarization beam splitter 4 is connected to the TM waveguide branch and the TE single-mode waveguide branch 5; a polarization beam combiner 6 connecting the TM waveguide branch and the TE single-mode waveguide branch 5, the output end of the polarization beam combiner 6 is connected to the output end multimode interference coupler 3. The electric field includes: a plurality of spaced metal electrodes 7, the modulation area waveguide main path 8 is arranged between adjacent metal electrodes 7, and the TM waveguide branch is also arranged between adjacent metal electrodes 7.

[0046] The present invention includes a first input waveguide 1, a second input waveguide 2, a polarization-insensitive 2×2 multimode interference coupler (MMI) 3 (input-end multimode interference coupler, output-end multimode interference coupler), a polarization beam splitter 4, a TE single-mode waveguide branch 5, a polarization combiner 6, a metal electrode 7, a modulation zone waveguide main path 8, a first output waveguide 9 and a second output waveguide 10.

[0047] The laser inputs TE or TM polarized light into the device through the first input waveguide 1 or the second input waveguide 2, and the power is equally divided into two modulation arms (i.e., two modulation area units) through the polarization-insensitive 2×2MMI3. Both modulation arms have a polarization beam splitter 4 and a polarization beam combiner 6. After the TE light is separated, it passes through a TE single-mode waveguide branch 5 and then beam combines back to the modulation area waveguide main road 8, so that the modulation areas with different polarization states have different lengths. After beam combining, the light fields of the two modulation arms are outputted through interference on the polarization-insensitive 2×2MMI3. By applying a voltage to the metal electrode 7 to control the phase difference of the two modulation arms, the optical signal can be output from the first output waveguide 9 or the second output waveguide 10.

[0048] The input and output waveguides (the first input waveguide 1, the second input waveguide 2, the first output waveguide 9 and the second output waveguide 10) can transmit TE and TM polarized light simultaneously. Figure 2 is a schematic diagram of the structure of the polarization-insensitive 2×2 multimode interference coupler of the present invention, and as shown Figure 3The polarization-insensitive 2×2 multimode interference coupler (MMI) 3 shown has the characteristic of polarization insensitivity, and the simulated transmission spectra in two polarization states are similar, and the input light can be equally divided into two modulation arms (8) for TE or TM polarized light. Figure 4 This is a schematic diagram of the structure of the polarization beam splitter of the present invention. The polarization beam splitter 4 can separate the TE component in the input light, and the polarization beam splitter exists in both modulation arms. The TE light after polarization beam splitting passes through the TE single-mode waveguide branch 5 and then through the polarization beam combiner 6 to return to the modulation area waveguide main road 8, while the TM light is always transmitted in the modulation area waveguide main road 8 and the modulation area waveguide branch (i.e., TM waveguide branch). The combined light passes through the 2×2MMI again, which can achieve polarization insensitivity of the output spectrum.

[0049] In the present invention, the modulation area waveguide main path, the TM waveguide branch (i.e., the modulation area waveguide branch), and the TE single-mode waveguide branch all use lithium niobate. Since lithium niobate is an anisotropic medium, its refractive index can be written in tensor form:

[0050]

[0051] Among them, n o is the refractive index of lithium niobate material in the x and y directions, n e is the refractive index of lithium niobate material in the z direction.

[0052] Because lithium niobate is a 3M point group crystal with the characteristics of secondary rotation axis and mirror symmetry, its electro-optic tensor matrix can be written as:

[0053]

[0054] Where γ is the electro-optic tensor matrix, and the matrix element γ ij is the linear electro-optic coefficient of the crystal.

[0055] Therefore, under the action of the electric field in the Z direction, the TE and TM polarization states have different refractive index changes, which can be written as:

[0056]

[0057] The measured value of the linear electro-optic coefficient of lithium niobate crystal is: γ 13 ≈9.6pm / V, γ 33 ≈30.9pm / V, the ratio of TE to TM modulation efficiency is 1:3.19, that is, within the same optical path and at the same voltage, the phase change of TE polarized light is 3.19φ, while the phase change of TM polarized light is φ. φ is the phase change.

[0058] The present invention separates the TE light through a polarization beam splitter 4, passes through a TE single-mode waveguide branch 5, and then combines the light back to the modulation area waveguide main path 8, so as to achieve different modulation area lengths for different polarization states. By adjusting the lengths of several modulation area waveguides, the TE and TM phase changes are nearly 1:1, thereby achieving the purpose of polarization insensitivity.

[0059] Compared with the existing structure that first performs polarization splitting and then processes it separately in two optical switches, which requires 1 polarization beam splitter, 1 polarization beam combiner, 4 multimode interferometers, and 2 sets of electrodes, the present invention innovatively places the polarization beam splitting part in the modulation area, requiring only 1 polarization beam splitter, 1 polarization beam combiner, 2 multimode interferometers, and 1 set of electrodes, which is equivalent to reducing the optical path to half of the original, greatly reducing the device size and loss. In addition, in a single optical switch, the present invention only requires one electrical signal to achieve path selection, avoiding the isolation and synchronization circuits required for the two sets of electrical signals, and greatly reducing the complexity and power consumption of the circuit part.

[0060] Compared with the existing structure based on polarization rotator, it is necessary to know in advance whether the input light mode is TE or TM. If the light mode is unclear, the phase difference between the two modes cannot be accurately controlled. The polarization beam splitter used in the present invention can process mixed polarization optical signals and has a wider application range.

Claims

1. A polarization-independent optical switch, characterized in that: include: An input waveguide for receiving light including TE polarization and TM polarization components or one of the polarization components from an optical fiber, a laser or other optoelectronic device; The input end connected to the input waveguide includes a multimode interference coupler, which is a power distribution device; A modulation zone unit connected to the power distribution device; The output end connected to the output end of the modulation zone unit includes a multimode interference coupler, and the multimode interference coupler is a power beam combining device; and an electric field for applying a voltage to achieve phase control modulation; The modulation zone unit comprises: A TM waveguide branch, wherein the TM waveguide branch is arranged on the electric field; a TE waveguide branch connected in parallel with the TM waveguide branch, wherein the TE waveguide branch is arranged on the electric field; A modulation zone waveguide main path connected to the power distribution device at the input end; A polarization beam splitter connected to the modulation zone waveguide main path, wherein the output end of the polarization beam splitter is connected to the TM waveguide branch and the TE waveguide branch; A polarization beam combiner is connected to the TM waveguide branch and the TE waveguide branch, wherein the output end of the polarization beam combiner is connected to the power beam combining device at the output end; the polarization beam splitter separates the TE and TM light, and the separated TE light and TM light respectively pass through different waveguide branches; The modulation arms of the TM waveguide branch and the TE waveguide branch have different lengths.

2. The polarization-independent electro-optical switch according to claim 1, characterized in that: The modulation zone waveguide main path, TM waveguide branch, and TE waveguide branch are all made of lithium niobate or other materials with different modulation efficiencies for TE polarized light and TM polarized light in the waveguide.

3. The polarization-independent optical switch according to claim 1, characterized in that: The electric field structure includes: a plurality of spaced metal electrodes, the modulation zone waveguide main path is arranged between adjacent metal electrodes, and the TM waveguide branch path is also arranged between adjacent metal electrodes.

4. The polarization-independent electro-optical switch according to claim 1, characterized in that: The input waveguide includes a first input waveguide and a second input waveguide.

5. The polarization-independent electro-optical switch according to claim 1, characterized in that: The power distribution device at the input end is a polarization insensitive power divider.

6. The polarization-independent electro-optical switch according to claim 1, characterized in that: There are two modulation area units.

7. The polarization-independent electro-optical switch according to claim 1, characterized in that: The power beam combining device at the output end is a polarization insensitive power beam combiner.

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