High-linearity silicon light modulator and control method thereof

Abstract

The invention relates to a high-linearity silicon optical modulator which comprises an input waveguide, the input waveguide is connected with a first multi-mode interference device, the first multi-mode interference device is connected with a second multi-mode interference device through two first waveguide arms, and the second multi-mode interference device is connected with one end of an upper waveguide arm and one end of a lower waveguide arm. The other end of the upper waveguide arm and the other end of the lower waveguide arm are jointly connected with a third multi-mode interference device. The other end of the third multimode interference device is connected with the output waveguide; the upper waveguide arm is connected with an adjustable micro-ring through coupling, and the upper waveguide arm and the lower waveguide arm are respectively provided with a thermal phase shifter. A thermal phase shifter is embedded in an arm where two multimode interference devices are connected to change the phase. By applying direct-current voltage to the thermal phase shifter, the optical phase on the arm can be changed, so that the splitting ratio of the MMI can be accurately controlled.

Description

Technical Field

[0001] This invention relates to the field of modulator technology, and more specifically to a high linearity silicon optical modulator. Background Technology

[0002] Optical modulators, as core components of optical communication, optical interconnects, and microwave photonic systems, play a crucial role in efficiently and accurately loading electrical signals onto optical carriers. Their performance, including modulation rate, insertion loss, power consumption, size, and, most importantly, linearity, directly determines the transmission capacity, distance, signal quality, and cost of the entire optoelectronic system.

[0003] Among numerous performance metrics, linearity is of uncompromising importance for many cutting-edge applications. Linearity essentially describes how linearly the modulator's output optical power changes with the input drive voltage. An ideal linear modulator should have a first-order transfer function. Nonlinearities present in real-world devices can cause severe signal distortion, primarily in the form of harmonic distortion (a single frequency input generates higher harmonics that are integer multiples of its own, such as 2f and 3f) and intermodulation distortion (multiple frequency inputs generate new sum or difference frequency components, such as 2f1-f2). These distortions directly degrade core performance metrics such as spurious-free dynamic range (SFDR, characterizing the system's ability to simultaneously process large and small signals against a noisy background) and the output third-order intercept (OIP3, the output power point where the fundamental signal power equals the power of the third-order intermodulation products). The lack of linearity has serious consequences in critical applications: in microwave photonic links (such as radar and satellite communications), intermodulation distortion can generate false signals, leading to target recognition failures.

[0004] Existing technical solution: Patent application number: CN201911330998.0. This design is a silicon microring coupling modulation structure with voltage-adjustable coupling efficiency, including a microring waveguide structure, a 2×2 3dBMI at the input end, a 1×2 MMI at the output end, and an unbalanced MZ phase modulation structure. One end of the microring waveguide structure is connected to the input port of the 2×2 3dBMI, and the other end is connected to the output port of the 1×2 3dBMI. One end of the unbalanced MZ phase modulation structure is connected to the output port of the 2×2 3dBMI, and the other end is connected to the input port of the 1×2 3dBMI. By controlling the voltage of the thermal phase shifter to introduce a phase difference, combined with two directional couplers with fixed coupling coefficients, the coupling efficiency can be precisely achieved to the desired value. The study only considered the effect of the difference in coupling coefficient between the micro-ring and the MZI coupling region on linearity, without considering the effect of the MMI splitting ratio on the modulator operation. In reality, due to process errors, the MMI cannot achieve accurate splitting. Summary of the Invention

[0005] To achieve the objectives of this invention, the technical solution adopted is as follows: a high linearity silicon photonic modulator, comprising: an input waveguide, wherein the input waveguide is connected to a first multimode interferometer, the first multimode interferometer is connected to a second multimode interferometer via two first waveguide arms, the second multimode interferometer is connected to one end of an upper waveguide arm and a lower waveguide arm, the other ends of the upper and lower waveguide arms are connected to a third multimode interferometer; the other end of the third multimode interferometer is connected to an output waveguide; the upper waveguide arm is coupled to an adjustable microring, and both the upper and lower waveguide arms are provided with thermal phase shifters.

[0006] Preferably, an adjustable coupling region is provided between the adjustable microring and the upper waveguide arm.

[0007] Preferably, the adjustable coupling region includes: two directional couplers connected in series on the upper waveguide arm and a thermal phase shifter disposed between the two directional couplers, wherein the thermal phase shifter is disposed on the upper waveguide arm.

[0008] Preferably, the adjustable microring is a microring modulator with a modulation region.

[0009] Preferably, a control method for the high linearity silicon photonic modulator includes:

[0010] S1: Light enters the first multimode interferometer through the input waveguide;

[0011] S2: After beam splitting, it enters the second multimode interferometer through the first waveguide arm;

[0012] S3: The splitting ratio is changed by using a second multimode interferometer;

[0013] S4: The light from the upper waveguide arm and the lower waveguide arm passing through the adjustable micro-ring is combined by the third multimode interferometer and finally output through the output waveguide.

[0014] Compared with the prior art, the beneficial effects of the present invention are:

[0015] This invention embeds a thermal phase shifter on one arm of a two-mode multimode interferometer (MMI) to change the phase. By applying a DC voltage to the thermal phase shifter, the phase of the light on that arm can be changed, thereby achieving precise control of the MMI splitting ratio. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the overall structure of the high linearity silicon optical modulator in this invention.

[0017] Figure 2 This is a detailed structural diagram of the high linearity silicon optical modulator in this invention.

[0018] Figure 3This is a detailed structural diagram of the tunable coupling region of the high linearity silicon optical modulator in this invention;

[0019] Figure 4 This is a simulation diagram of the coupling coefficient of the adjustable coupling region of the high linearity silicon optical modulator in this invention;

[0020] Figure 5 This is a graph showing the power of the upper and lower waveguide arms of the high linearity silicon optical modulator in this invention as a function of the thermal phase shifter.

[0021] In the figure: 101, First multimode interferometer; 102, Second multimode interferometer; 103, Adjustable coupling region; 104, Micro-ring modulator; 105, First thermal phase shifter; 106, Second thermal phase shifter; 107, Third thermal phase shifter; 108, Third multimode interferometer. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] Example:

[0024] like Figure 1 As shown, the present invention provides a technical solution: a high linearity silicon optical modulator, comprising: an input waveguide, wherein a first multimode interferometer 101 is connected to the input waveguide, and the first multimode interferometer 101 is connected to a second multimode interferometer 102 via two first waveguide arms. A first thermal phase shifter 105 is fixedly connected to any one of the first waveguide arms.

[0025] The second multimode interferometer 102 is connected to one end of the upper waveguide arm and the lower waveguide arm. The other ends of the upper waveguide arm and the lower waveguide arm are connected to the third multimode interferometer 108. The other end of the third multimode interferometer 108 is connected to the output waveguide. The upper waveguide arm is coupled to an adjustable microring. Both the upper waveguide arm and the lower waveguide arm are equipped with thermal phase shifters.

[0026] An adjustable coupling region 103 is provided between the adjustable microring and the upper waveguide arm. The adjustable coupling region 103 includes: two directional couplers connected in series on the upper waveguide arm and a second thermal phase shifter 106 disposed between the two directional couplers, the second thermal phase shifter 106 being disposed on the upper waveguide arm.

[0027] The tunable microring has a microring modulator 104 with a modulation region. The superlinear phase modulation of the microring modulator 104 complements the sinusoidal nonlinear modulation of MZI to obtain a more ideal transmission spectrum.

[0028] By appropriately setting the operating point of the device, the phase difference between the two arms of the MZI modulator, and the coupling coefficient of the micro-ring modulator 104, a high-linearity micro-ring assisted MZI modulator can be obtained. Combining a thermal phase shifter and an adjustable coupling region 103 allows the modulator to be maintained at its optimal operating point.

[0029] A control method for a high linearity silicon optical modulator includes:

[0030] S1: Light enters the first multimode interferometer 101 through the input waveguide;

[0031] S2: After 50:50 beam splitting, it enters the second multimode interferometer 102 through the first waveguide arm;

[0032] Among them, the 1×2 first multimode interferometer 101 and the 2×2 second multimode interferometer 102 perform beam splitting, which has high wavelength insensitivity and wider bandwidth, and works with the first thermal phase shifter 105 to accurately achieve the required beam splitting ratio.

[0033] S3: The splitting ratio is changed by the second multimode interferometer 102;

[0034] like Figure 2 As shown, the input light Ein enters the 1×2 first multimode interferometer 1 (101) through a straight waveguide. This first multimode interferometer is a 50:50 equal power multimode interferometer, meaning that the two output beams have equal power and a phase difference. at this time

[0035]

[0036] Where j represents an imaginary number, we have

[0037]

[0038] E2 undergoes a phase shifter, resulting in a phase change. Let the phase change be Δφ, i.e.

[0039]

[0040] At this time, E1 and E′2 serve as the inputs to the 2×2 second multimode interferometer 102, and the transfer matrix of the 2×2 second multimode interferometer 102 has...

[0041]

[0042] Performing matrix operations has

[0043]

[0044] but

[0045]

[0046] The spectrophotometric ratio is:

[0047] P out1 ;P out2 =(1+cosΔφ): (1-cosΔφ);

[0048] When the first thermal phase shifter 105 is not working, i.e., Δφ = 0, the splitting ratio is 1:0, meaning all light is coupled into the upper waveguide arm. When the first thermal phase shifter 105 is working and changes the phase by 90 degrees, i.e. At this point, the splitting ratio is 1:1, and this structure can be regarded as a coupler with a 50:50 splitting ratio, with equal output power in the upper and lower arms.

[0049] Therefore, by simply adjusting the phase of the first thermal phase shifter 105, the splitting ratio of the MMI structure can be changed, thus achieving precise control.

[0050] S4: The light from the upper waveguide arm and the lower waveguide arm passing through the adjustable micro-ring is combined by the third multimode interferometer 108 and finally output through the output waveguide.

[0051] The adjustable coupling region 103 is composed of two directional couplers with fixed coupling efficiencies combined with the second thermal phase shifter 106. By changing the DC voltage of the second thermal phase shifter 106, the phase difference can be caused, which can effectively change the coupling coefficient of the micro-ring to ensure that the coupling coefficient of the micro-ring is 0.963 (coupling efficiency is 0.926).

[0052] The adjustable coupling region 103 can be divided into three parts: a directional coupler with a coupling efficiency of 0.5, a straight waveguide transmission region, and a directional coupler with a coupling efficiency of 0.5.

[0053] like Figure 3 As shown, light enters from port a1. According to the transmission matrix theory, the optical field components of the upper and lower waveguides can be expressed in the following matrix form:

[0054]

[0055] Where τ and κ are the transmission coefficient and coupling coefficient, respectively, and τ and κ satisfy:

[0056] τ 2 +κ 2 =1;

[0057] The parameter structures of the two directional couplers are exactly the same, that is...

[0058]

[0059] Between the two directional couplers, the upper waveguide arm is a straight waveguide, and its phase change is negligible. The lower waveguide arm integrates a third thermal phase shifter 107 to change the phase. Assuming the phase change is Δφ, then:

[0060]

[0061] The three parts of the transmission matrix are summarized as follows:

[0062]

[0063] By τ 2 =κ 2 =0.5, so we know that Substituting the transfer matrix and rearranging, we can obtain

[0064]

[0065] Therefore, the overall coupling efficiency When the third thermal phase shifter 107 is not working, Δφ=0, All light is coupled into the micro-ring. When the third thermal phase shifter 107 is working and Δφ = π, All light is output from the through-hole, with no light coupling into the micro-ring.

[0066] By controlling the phase shift of the third thermal phase shifter 107, the coupling efficiency of the entire coupling region can be arbitrarily changed from 0 to 1, realizing the adjustable coupling function.

[0067] The superlinear phase modulation of the microring structure 104 is complementary to the sinusoidal nonlinear modulation of the MZI, resulting in a more ideal transmission spectrum. By reasonably setting the operating point of the device, the phase difference between the two arms of the MZI, and the coupling coefficient of the microring modulator, a high linearity microring-assisted MZI modulator can be obtained.

[0068] The combination of the second thermal phase shifter 106 and the adjustable coupling region 103 can keep the modulator at its optimal operating point.

[0069] The transfer function of the micro-ring assisted MZI modulator is:

[0070]

[0071] Where Δφ is the phase difference between the upper and lower arms, which is caused by the third thermal phase shifter 107. At this point, the microring will undergo Fano resonance. The microring modulator operates in a region far from the resonance peak, which is beneficial to linearity. At this time, the transfer function of the microring modulator is T(θ)≈1, and α1 and α2 are the loss factors of the upper and lower waveguide arms, respectively. This is the phase response of the micro-ring modulator 104.

[0072]

[0073] Where α r Since the loss factor is α1 = α2 = α1 / α2, the waveguide loss is negligible. r =1, the transfer function of the micro-ring assisted MZI modulator can be simplified to

[0074]

[0075] Work location selection By adjusting the micro-loop modulation voltage, the maximum SFDR (spurious-free dynamic range) operating point can be obtained.

[0076] The first thermal phase shifter 105 and the adjustable coupling region 103 are the core areas of the design. By applying voltage to the first thermal phase shifter 105, the splitting ratio of the MMI and the coupling coefficient of the micro-ring can be changed respectively. This avoids errors in the splitting ratio and coupling coefficient caused by process errors, which would prevent the device from failing to meet the expected requirements and thus deteriorating the device performance. Through the adjustable structure, the parameters that have deteriorated due to process errors can be readjusted to the parameters we want, such as a 50:50 splitting ratio and a coupling efficiency of 0.926. This allows us to find the highest point of the modulator's SFDR, reduce the impact of process errors on the device, and make the device more stable.

[0077] The embodiments disclosed herein are preferred embodiments, but are not limited thereto. Those skilled in the art can readily grasp the spirit of the present invention based on the above embodiments and make different extensions and variations, but as long as they do not depart from the spirit of the present invention, they are all within the protection scope of the present invention.

Claims

1. A high linearity silicon optical modulator, characterized in that, include: An input waveguide is provided, which is connected to a first multimode interferometer. The first multimode interferometer is connected to a second multimode interferometer via two first waveguide arms. The second multimode interferometer is connected to one end of an upper waveguide arm and a lower waveguide arm. The other ends of the upper and lower waveguide arms are connected to a third multimode interferometer. The other end of the third multimode interferometer is connected to an output waveguide. An adjustable microring is coupled to the upper waveguide arm. Both the upper and lower waveguide arms are equipped with thermal phase shifters.

2. The high linearity silicon optical modulator according to claim 1, characterized in that, An adjustable coupling region is provided between the adjustable microring and the upper waveguide arm.

3. The high linearity silicon optical modulator according to claim 2, characterized in that, The adjustable coupling region includes: two directional couplers connected in series on the upper waveguide arm and a thermal phase shifter disposed between the two directional couplers, wherein the thermal phase shifter is disposed on the upper waveguide arm.

4. The high linearity silicon optical modulator according to claim 1, characterized in that, The adjustable microring is equipped with a microring modulator with a modulation region.

5. A control method for the high linearity silicon optical modulator according to any one of claims 1 to 4, characterized in that, include: S1: Light enters the first multimode interferometer through the input waveguide; S2: After beam splitting, it enters the second multimode interferometer through the first waveguide arm; S3: The splitting ratio is changed by using a second multimode interferometer; S4: The light from the upper waveguide arm and the lower waveguide arm passing through the adjustable micro-ring is combined by the third multimode interferometer and finally output through the output waveguide.

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