A method and device for measuring nonlinearity of an electro-optical modulator

Abstract

The present invention discloses a method and device for measuring the nonlinearity of an electro-optical modulator, belonging to the technical field of photoelectric device measurement, and includes the following steps: inputting an optical signal output by a laser source into an electro-optical modulator to be measured; the optical signal passes through an electro-optical modulator to be measured, and outputs a modulated optical signal; the modulated optical signal enters a standard photodetector operating in a linear region, and a large-signal response item of the electro-optical modulator to be measured is obtained at different input electrical signal powers; an electrical signal is output to the electrical signal output end of the electro-optical modulator to be measured via a small-signal disturbance source, and a small-signal response item of the electro-optical modulator to be measured is obtained at different input electrical signal powers. By combining the large-signal response item and the small-signal response item, the complete nonlinear parameters of the electro-optical modulator to be measured at the input electrical signal power are obtained; and further, the complete nonlinear parameters of the electro-optical modulator to be measured at different frequencies are obtained. The present invention can achieve high-precision measurement of the nonlinearity of electro-optical modulators.

Description

Technical Field

[0001] The present invention relates to the technical field of photoelectric device measurement, and in particular to a nonlinear measurement method and device for an electro-optical modulator. Background Art

[0002] Accurately measuring the responses of microwave photonic devices, links, and systems is a crucial prerequisite for achieving technological innovation, overcoming challenges, and improving performance in microwave photonics. The performance of microwave photonic devices, links, and arrays is determined not only by key technical capabilities and design and manufacturing processes, but also by measurement and performance characterization capabilities. Nonlinearity is a fundamental issue facing microwave photonics technology. Key microwave photonic components, such as photodetectors and electro-optical modulators, utilize optoelectronic / electro-optical nonlinearities to achieve cross-domain conversion from lightwave to microwave and vice versa. This conversion process inevitably involves irreversible nonlinearities, and the resulting microwave photonic links and systems also exhibit nonlinearities. Previously, the development of key microwave photonic components, as well as microwave photonic links and systems, was conducted under small-signal conditions, ignoring the nonlinearities of electro-optical and optoelectronic conversion. Measurement and characterization were performed using S-parameters, which describe the characteristics of linear systems, with accuracy barely meeting requirements. However, the continuous improvement of microwave photonic devices, links, and systems in terms of operating frequency range, instantaneous bandwidth, and power handling capacity has forced these devices and systems into increasingly nonlinear operating regions. The spectral mapping of input and output signals has exhibited significant nonlinearity, deviating increasingly from a linear relationship. The shift from small-signal linearity to large-signal nonlinearity inevitably generates harmonics and intermodulation frequency components under the excitation of single-tone and multi-tone signals. The presence of nonlinearity significantly increases the difficulty of accurately measuring and characterizing the frequency response of microwave photonic devices, links, and systems.

[0003] Therefore, it is urgent to establish a microwave photon nonlinear model and a multi-dimensional nonlinear parameter broadband measurement theory, and to develop new nonlinear parameter broadband measurement technology and measurement instruments and equipment.

[0004] Based on this, the present invention designs a method and device for measuring the nonlinearity of an electro-optical modulator to solve the above problems. Summary of the Invention

[0005] In view of the above-mentioned shortcomings of the prior art, the present invention provides a method and device for measuring the nonlinearity of an electro-optical modulator.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solutions:

[0007] A method for measuring the nonlinearity of an electro-optical modulator comprises the following steps:

[0008] Step 1: First, input the optical signal output by the laser source into the electro-optical modulator to be tested;

[0009] Step 2: The output optical signal passes through an electro-optical modulator to be tested. Under the action of the external electric field of the radio frequency signal injected by the microwave source, the optical signal is intensity modulated and a modulated optical signal is output;

[0010] Step 3: The modulated optical signal enters a standard photodetector operating in the linear region to achieve photoelectric linear mapping, and the standard photodetector outputs an electrical signal;

[0011] Analyze the amplitude and phase changes of the DC, fundamental frequency, and intermodulation components corresponding to the output electrical signal of the standard photodetector, sweep the power of the microwave signal output by the microwave source, and obtain the large signal response of the electro-optical modulator under different input electrical signal powers;

[0012] Step 4: Output an electrical signal to the electrical signal output terminal of the electro-optical modulator under test through a small signal disturbance source, simulate the influence of the reflected signal at the electrical signal output terminal of the electro-optical modulator under test on its performance, and output the electrical signal in the link;

[0013] The amplitude and phase information of the DC, fundamental frequency and intermodulation components corresponding to the output electrical signal of the standard photodetector are extracted through the DC component detection module and the microwave amplitude and phase detection module, and the small signal response items of the electro-optical modulator to be tested under different input electrical signal powers are obtained.

[0014] Step 5: Combine the large-signal response item and the small-signal response item of the electro-optical modulator under test in steps 3 and 4 to obtain the complete nonlinear parameters of the electro-optical modulator under the input electrical signal power; scan the frequency of the electrical signal input to the electro-optical modulator under test, and repeat steps 1 to 4 at different frequencies to obtain the complete nonlinear parameters of the electro-optical modulator under test at different frequencies.

[0015] Furthermore, the optical signal output by the laser source is expressed as:

[0016]

[0017] in, is the amplitude of the electric field of the input light wave, is the angular frequency of the laser source output signal.

[0018] Furthermore, in step 2, the modulated optical signal is expressed as:

[0019]

[0020] in, and They are the phase changes caused by each branch in the electro-optic modulator to be tested. Through the action of the external electric field on the two modulation arms of the electro-optic modulator to be tested, the phase shift and Get corresponding changes, so that , then the output modulated optical signal can be simplified as:

[0021]

[0022] in, is the phase difference between the two modulation arm branches, .

[0023] Furthermore, step 1 further includes: inputting two microwave signals with different frequencies and the same power output by the microwave source into the electro-optical modulator to be tested operating at the orthogonal point; the input dual-tone signal is expressed as:

[0024]

[0025] Where m is the amplitude, ω1 and ω2 are the angular frequencies of the two-tone signal, and t is the time variable.

[0026] Furthermore, in step 2, the modulated optical signal is expressed as:

[0027]

[0028] Among them, φ1, φ2, φ3 are phases, j is the imaginary unit, and t is the time variable.

[0029] Furthermore, in step 3, the electrical signal output by the standard photodetector is expressed as:

[0030]

[0031] in, is the amplitude value of the output light intensity.

[0032] Furthermore, in step 3, the electrical signal output by the standard photodetector is expressed as:

[0033] .

[0034] Furthermore, the electrical signal output in step 4 is expressed as:

[0035] .

[0036] Furthermore, the electrical signal output in step 4 is expressed as:

[0037] .

[0038] In order to better achieve the purpose of the present invention, the present invention also provides an electro-optic modulator nonlinear measurement device, comprising:

[0039] A laser source, used to output an optical signal of a fixed frequency;

[0040] A microwave source for generating a modulated signal;

[0041] Standard photodetector, used to detect light signals and linearly map them into electrical signals;

[0042] A small signal disturbance source is used to generate a disturbance signal to simulate a reflected signal at the electrical signal output end of the electro-optical modulator to be tested;

[0043] A DC component detection module, used for detecting the DC component in the signal;

[0044] The microwave amplitude and phase detection module is used to extract the amplitude and phase information of the electrical signal.

[0045] Compared to existing technologies, the present invention offers the following advantages: it enables highly accurate measurement of electro-optic modulator nonlinearity. Electro-optic modulator nonlinearity accounts for a significant portion of link nonlinearity, so characterizing electro-optic modulator nonlinearity can improve link nonlinearity measurement. This invention addresses the limitation of S-parameters, which can only provide a linear description during measurement and characterization, thereby addressing the nonlinear measurement portion. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. Those skilled in the art can also derive other drawings based on these drawings without inventive effort.

[0047] Figure 1 This is a structural block diagram of the electro-optic modulator nonlinear measurement device of the present invention. DETAILED DESCRIPTION

[0048] To make the purpose, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0049] Example 1: In some embodiments, please refer to the accompanying drawings of the specification. Figure 1A nonlinear measurement device for an electro-optical modulator includes a laser source, a microwave source, an electro-optical modulator to be tested, a standard photodetector, a small-signal disturbance source, a DC component detection module, and a microwave amplitude-phase detection module. The laser source is used to output a fixed-frequency optical signal. The microwave source is used to generate a modulated signal. The standard photodetector is used to detect the optical signal and linearly map it into an electrical signal. The small-signal disturbance source is used to generate a disturbance signal to simulate the reflected signal at the electrical signal output end of the electro-optical modulator to be tested. The DC component detection module is used to detect the DC component in the signal. The microwave amplitude-phase detection module is used to extract the amplitude-phase information of the electrical signal.

[0050] Embodiment 2: In some embodiments, a method for measuring nonlinearity of an electro-optic modulator includes the following steps:

[0051] Step 1: First, input the optical signal output by the laser source into the electro-optical modulator to be tested; the optical signal output by the laser source is expressed as:

[0052]

[0053] in, is the amplitude of the electric field of the input light wave, is the angular frequency of the laser source output signal.

[0054] Step 2: The output optical signal passes through an electro-optical modulator to be tested. Under the action of the external electric field injected by the microwave source into the RF signal, the optical signal is intensity modulated and the modulated optical signal is output. The expression is:

[0055]

[0056] in, and They are the phase changes caused by each branch in the electro-optic modulator to be tested. Through the action of the external electric field on the two modulation arms of the electro-optic modulator to be tested, the phase shift and Get corresponding changes, so that , then the output modulated optical signal can be simplified as:

[0057]

[0058] in, is the phase difference between the two modulation arm branches, .

[0059] Step 3: The modulated optical signal enters a standard photodetector operating in the linear region to achieve photoelectric linear mapping. The electrical signal output by the standard photodetector is expressed as:

[0060]

[0061] in, is the amplitude value of the output light intensity.

[0062] The amplitude and phase changes of the DC, fundamental frequency and intermodulation components corresponding to the output electrical signal of the standard photodetector are analyzed, the power of the microwave signal output by the microwave source is swept, and the large signal response items of the electro-optical modulator to be tested under different input electrical signal powers are obtained.

[0063] Step 4: Output an electrical signal to the electrical signal output terminal of the electro-optical modulator under test through a small signal disturbance source to simulate the impact of the reflected signal at the electrical signal output terminal of the electro-optical modulator under test on its performance. Output the electrical signal in the link, which is expressed as:

[0064]

[0065] The amplitude and phase information of the DC, fundamental frequency and intermodulation components corresponding to the output electrical signal of the standard photodetector are extracted through the DC component detection module and the microwave amplitude and phase detection module, and the small signal response items of the electro-optical modulator to be tested under different input electrical signal powers are obtained.

[0066] Step 5: Combine the large-signal response item and the small-signal response item of the electro-optical modulator under test in steps 3 and 4 to obtain the complete nonlinear parameters of the electro-optical modulator under the input electrical signal power; scan the frequency of the electrical signal input to the electro-optical modulator under test, and repeat steps 1 to 4 at different frequencies to obtain the complete nonlinear parameters of the electro-optical modulator under test at different frequencies.

[0067] Embodiment 3: A method for measuring the nonlinearity of an electro-optical modulator, comprising the following steps:

[0068] Step 1: First, input the optical signal output by the laser source into the electro-optical modulator to be tested; the optical signal output by the laser source is expressed as:

[0069]

[0070] in, is the amplitude of the electric field of the input light wave, is the angular frequency of the laser source output signal.

[0071] Two microwave signals with different frequencies and the same power output by the microwave source are input to the electro-optical modulator under test operating at the orthogonal point. The input dual-tone signal is expressed as:

[0072]

[0073] Where m is the amplitude, ω1 and ω2 are the angular frequencies of the two-tone signal, and t is the time variable;

[0074] Step 2: The output optical signal passes through an electro-optical modulator to be tested. Under the action of the external electric field injected by the microwave source into the RF signal, the optical signal is intensity modulated and the modulated optical signal is output. The expression is:

[0075]

[0076] Among them, φ1, φ2, φ3 are phases, j is an imaginary unit, and t is a time variable;

[0077] Step 3: The modulated optical signal enters a standard photodetector operating in the linear region to achieve photoelectric linear mapping. The electrical signal output by the standard photodetector is expressed as:

[0078]

[0079] in:

[0080]

[0081] make , expand the Bessel function to get:

[0082]

[0083] Among them, A is a simplified equivalent, J0, J 2k 、J 2k+1 is the Jacobian determinant of the corresponding order, m is the amplitude, k is an integer, and t is the time variable.

[0084] make , expand the Bessel function to get:

[0085]

[0086] Where B is a simplified equivalent, ω is the angular frequency, l is the cumulative variable, and J 2l+1 is the Jacobian determinant.

[0087] Similarly, Performing Bessel expansion and sorting through trigonometric operations such as product and difference, we can get the relationship between the third-order intermodulation harmonics and the output light intensity as follows:

[0088]

[0089] Among them, ε0, ε1, and ε3 are amplitudes.

[0090] Summarizing the harmonics in the output light wave, the expression is:

[0091]

[0092]

[0093] The expressions for the amplitude coefficients of the 1st, 2nd, and 3rd harmonic components are:

[0094]

[0095]

[0096]

[0097] Among them, J1, J2, and J3 are Jacobian determinants.

[0098] The amplitude and phase changes of the DC, fundamental frequency and intermodulation components corresponding to the output electrical signal of the standard photodetector are analyzed, the power of the microwave signal output by the microwave source is swept, and the large signal response items of the electro-optical modulator to be tested under different input electrical signal powers are obtained.

[0099] Step 4: Output an electrical signal to the electrical signal output terminal of the electro-optical modulator under test through a small signal disturbance source to simulate the impact of the reflected signal at the electrical signal output terminal of the electro-optical modulator under test on its performance. Output the electrical signal in the link, which is expressed as:

[0100]

[0101] The amplitude and phase information of the DC, fundamental frequency and intermodulation components corresponding to the output electrical signal of the standard photodetector are extracted through the DC component detection module and the microwave amplitude and phase detection module, and the small signal response items of the electro-optical modulator to be tested under different input electrical signal powers are obtained.

[0102] Step 5: Combine the large-signal response item and the small-signal response item of the electro-optical modulator under test in steps 3 and 4 to obtain the complete nonlinear parameters of the electro-optical modulator under the input electrical signal power; scan the frequency of the electrical signal input to the electro-optical modulator under test, and repeat steps 1 to 4 at different frequencies to obtain the complete nonlinear parameters of the electro-optical modulator under test at different frequencies.

[0103] The present invention can achieve high-precision measurement of the nonlinearity of the electro-optical modulator. The nonlinearity of the electro-optical modulator accounts for the main part of the nonlinearity of the link. Therefore, the nonlinearity characterization of the electro-optical modulator can improve the nonlinearity measurement of the link.

[0104] The present invention solves the defect that the S parameter can only be described linearly during measurement and characterization, and makes up for the part of nonlinear measurement.

[0105] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements will not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for measuring nonlinearity of an electro-optical modulator, characterized in that: The following steps are involved: Step 1: First, input the optical signal output by the laser source into the electro-optical modulator to be tested; Step 2: The output optical signal passes through an electro-optical modulator to be tested. Under the action of the external electric field of the radio frequency signal injected by the microwave source, the optical signal is intensity modulated and a modulated optical signal is output; Step 3: The modulated optical signal enters a standard photodetector operating in the linear region to achieve photoelectric linear mapping, and the standard photodetector outputs an electrical signal; Analyze the amplitude and phase changes of the DC, fundamental frequency, and intermodulation components corresponding to the output electrical signal of the standard photodetector, sweep the power of the microwave signal output by the microwave source, and obtain the large signal response of the electro-optical modulator under different input electrical signal powers; Step 4: Output an electrical signal to the electrical signal output terminal of the electro-optical modulator under test through a small signal disturbance source, simulate the influence of the reflected signal at the electrical signal output terminal of the electro-optical modulator under test on its performance, and output the electrical signal in the link; The DC component detection module and the microwave amplitude and phase detection module are used to extract the amplitude and phase information of the DC, fundamental frequency and intermodulation components corresponding to the output electrical signal of the standard photodetector, and obtain the small signal response items of the electro-optical modulator under different input electrical signal powers; Step 5: Combine the large-signal response item and the small-signal response item of the electro-optical modulator under test in steps 3 and 4 to obtain the complete nonlinear parameters of the electro-optical modulator under the input electrical signal power; scan the frequency of the electrical signal input to the electro-optical modulator under test, and repeat steps 1 to 4 at different frequencies to obtain the complete nonlinear parameters of the electro-optical modulator under test at different frequencies.

2. The method for measuring nonlinearity of an electro-optical modulator according to claim 1, wherein: The optical signal output by the laser source is expressed as: ， in, is the amplitude of the electric field of the input light wave, is the angular frequency of the laser source output signal.

3. The method for measuring the nonlinearity of an electro-optical modulator according to claim 2, wherein: In step 2, the modulated optical signal is expressed as: ， in, and They are the phase changes caused by each branch in the electro-optic modulator to be tested. Through the action of the external electric field on the two modulation arms of the electro-optic modulator to be tested, the phase shift and Get corresponding changes, so that , then the output modulated optical signal can be simplified as: ， in, is the phase difference between the two modulation arm branches, .

4. The method for measuring nonlinearity of an electro-optical modulator according to claim 2, wherein: Step 1 also includes: inputting two microwave signals with different frequencies and the same power output by the microwave source into the electro-optical modulator to be tested operating at the orthogonal point; the input dual-tone signal is expressed as: ， Where m is the amplitude, ω1 and ω2 are the angular frequencies of the two-tone signal, and t is the time variable.

5. The method for measuring nonlinearity of an electro-optical modulator according to claim 4, wherein: In step 2, the modulated optical signal is expressed as: ， in, 、 、 is the phase, j is the imaginary unit, and t is the time variable.

6. The method for measuring nonlinearity of an electro-optical modulator according to claim 3, wherein: In step 3, the electrical signal output by the standard photodetector is expressed as: ， in, is the amplitude value of the output light intensity.

7. The method for measuring nonlinearity of an electro-optical modulator according to claim 5, wherein: In step 3, the electrical signal output by the standard photodetector is expressed as: 。 8. The method for measuring nonlinearity of an electro-optical modulator according to claim 6, wherein: The output electrical signal expression in step 4 is: 。 9. The method for measuring nonlinearity of an electro-optical modulator according to claim 7, wherein: The output electrical signal expression in step 4 is: ， Among them, ε0 and ε1 are amplitudes.

10. A device for measuring nonlinearity of an electro-optical modulator based on the method according to any one of claims 1 to 9, characterized in that: include: A laser source, used to output an optical signal of a fixed frequency; A microwave source for generating a modulated signal; Standard photodetector, used to detect light signals and linearly map them into electrical signals; A small signal disturbance source is used to generate a disturbance signal to simulate a reflected signal at the electrical signal output end of the electro-optical modulator to be tested; A DC component detection module, used for detecting the DC component in the signal; The microwave amplitude and phase detection module is used to extract the amplitude and phase information of the electrical signal.

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