Nonlinear measurement method and device for electro-optical modulator

Abstract

The invention discloses an electrooptical modulator nonlinear measurement method and device, and belongs to the technical field of photoelectric device measurement, and the method comprises the following steps: inputting an optical signal outputted by a laser source into a to-be-measured electrooptical modulator; the optical signal passes through an electro-optical modulator to be measured, and a modulated optical signal is output; the modulation optical signal enters a standard photoelectric detector working in a linear region to obtain a large signal response item of the electro-optical modulator to be detected under different input electric signal powers; and outputting an electric signal to an electric signal output end of the electro-optical modulator to be tested through the small signal disturbance source to obtain small signal response items of the electro-optical modulator to be tested under different input electric signal powers. The large signal response item and the small signal response item are combined to obtain a complete nonlinear parameter of the electro-optical modulator to be tested under the input electric signal power; and thus, complete nonlinear parameters of the electro-optical modulator to be measured under different frequencies are obtained. According to the invention, high-precision measurement of nonlinear measurement of the electro-optical modulator can be realized.

Description

Technical Field

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

[0002] Accurate measurement of microwave photonic devices, links and system responses is an important prerequisite for achieving innovation in microwave photonic technology, breakthroughs in difficult problems and performance improvements. The level of microwave photonic devices, links and arrays is not only determined by key technical capabilities and design and manufacturing processes, but also depends on measurement and performance characterization capabilities. Nonlinearity is the essential problem facing microwave photonic technology. Microwave photonic key devices represented by photodetectors and electro-optic modulators use optoelectronic / electro-optical nonlinearity to achieve cross-domain conversion from light waves to microwaves / microwaves to light waves. There must be nonlinearities that cannot be eliminated during the conversion process, and the microwave photonic links and systems constructed therefrom also have nonlinearities. Previously, both the development of microwave photonic key devices and the research and development of microwave photonic links and systems were carried out under small signal conditions, ignoring the nonlinearity of electro-optical and optoelectronic conversions, and using S parameters that describe the characteristics of linear systems for measurement and characterization, with accuracy that could only barely meet the requirements. However, with the continuous improvement of the operating frequency range, instantaneous bandwidth, and carrying power of microwave photonic devices, links, and systems, the devices and systems are forced to enter an increasingly nonlinear working area. The spectrum mapping of input and output signals has shown obvious nonlinearity, and the difference from the linear relationship is getting bigger and bigger. The change from small signal linearity to large signal nonlinearity will inevitably generate harmonics and intermodulation frequency components under the stimulation of single-tone and multi-tone signals. The existence of nonlinearity greatly 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 microwave photon nonlinear models and multi-dimensional nonlinear parameter broadband measurement theories, and to develop new nonlinear parameter broadband measurement technologies and measurement instruments.

[0004] Based on this, the present invention designs a nonlinear measurement method and device for an electro-optic 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-optic modulator.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solutions: A method for measuring the nonlinearity of an electro-optic modulator comprises the following steps: Step 1: First, input the optical signal output by the laser source into the electro-optic 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 a linear region to achieve photoelectric linear mapping, and the standard photodetector outputs an electrical signal; Analyze the amplitude and phase changes of the DC, baseband and intermodulation components corresponding to the output electrical signal of the standard photodetector, scan the power of the microwave signal output by the microwave source, and obtain the large signal response items of the electro-optic modulator to be tested under different input electrical signal powers; Step 4: output an electrical signal to the electrical signal output terminal of the electro-optical modulator to be tested through a small signal disturbance source, simulate the influence of the reflected signal at the electrical signal output terminal of the electro-optical modulator to be tested on its performance, and output the electrical signal in the link; The amplitude and phase information of the DC, baseband 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-optic modulator to be tested under different input electrical signal powers are obtained.

[0007] Step 5, combining the large signal response item and the small signal response item of the electro-optic modulator to be tested in step 3 and step 4, obtaining the complete nonlinear parameters of the electro-optic modulator to be tested under the input electrical signal power; scanning the frequency of the electrical signal input to the electro-optic modulator to be tested, repeating steps 1 to 4 at different frequencies, and obtaining the complete nonlinear parameters of the electro-optic modulator to be tested at different frequencies.

[0008] Furthermore, the optical signal output by the laser source is expressed as:

[0009] in, is the amplitude of the electric field of the input light wave, is the angular frequency of the laser source output signal.

[0010] Furthermore, in step 2, the modulated optical signal is expressed as:

[0011] in, and They are the phase changes caused by each branch in the electro-optic modulator to be tested. The external electric field acts on the two modulation arms of the electro-optic modulator to be tested, causing the phase shift and Get the corresponding changes, so that , then the output modulated optical signal can be simplified as:

[0012] in, is the phase difference between the two modulation arm branches, .

[0013] 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 working at the orthogonal point; the input dual-tone signal is expressed as:

[0014] Among them, m is the amplitude, ω1 and ω2 are the angular frequencies of the two-tone signal, and t is the time variable.

[0015] Furthermore, in step 2, the modulated optical signal is expressed as:

[0016] Among them, φ1, φ2, φ3 are phases, j is an imaginary unit, and t is a time variable.

[0017] Furthermore, in step 3, the electrical signal output by the standard photodetector is expressed as:

[0018] in, is the amplitude value of the output light intensity.

[0019] Furthermore, in step 3, the electrical signal output by the standard photodetector is expressed as: .

[0020] Furthermore, the electrical signal output in step 4 is expressed as: .

[0021] Furthermore, the electrical signal output in step 4 is expressed as: .

[0022] In order to better achieve the purpose of the present invention, the present invention also provides an electro-optic modulator nonlinear measurement device, comprising: 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 reflection signal at the electrical signal output end of the electro-optic 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.

[0023] Compared with the prior art, the present invention has the following beneficial effects: the present invention can realize high-precision measurement of nonlinear measurement of electro-optic modulator. The nonlinearity of electro-optic modulator accounts for the main part of link nonlinearity, so the nonlinear characterization of electro-optic modulator can improve the nonlinear measurement of link. The present invention solves the defect that S parameters can only be described linearly when measuring and characterizing, and makes up for the part of nonlinear measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the prior art descriptions are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0025] Figure 1 It is a structural block diagram of the nonlinear measurement device of the electro-optic modulator of the present invention. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are 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 creative work are within the scope of protection of the present invention.

[0027] Embodiment 1: In some embodiments, please refer to the drawings of the specification Figure 1 A nonlinear measurement device for an electro-optic modulator comprises a laser source, a microwave source, an electro-optic modulator to be tested, a standard photodetector, a small signal disturbance source, a DC component detection module and a microwave amplitude and phase detection module; wherein the laser source is used to output a light signal of a fixed frequency; the microwave source is used to generate a modulated signal; the standard photodetector is used to detect the light signal and linearly map 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-optic modulator to be tested; the DC component detection module is used to detect the DC component in the signal; and the microwave amplitude and phase detection module is used to extract the amplitude and phase information of the electrical signal.

[0028] Embodiment 2: In some embodiments, a method for measuring nonlinearity of an electro-optic modulator comprises the following steps: Step 1: First, input the optical signal output by the laser source into the electro-optic modulator to be tested; the optical signal output by the laser source is expressed as:

[0029] in, is the amplitude of the electric field of the input light wave, is the angular frequency of the laser source output signal.

[0030] Step 2: The output optical signal passes through an electro-optic modulator to be tested. Under the action of the external electric field of the RF signal injected by the microwave source, the optical signal is intensity modulated and the modulated optical signal is output. The expression is:

[0031] in, and They are the phase changes caused by each branch in the electro-optic modulator to be tested. The external electric field acts on the two modulation arms of the electro-optic modulator to be tested, causing the phase shift and Get the corresponding changes, so that , then the output modulated optical signal can be simplified as:

[0032] in, is the phase difference between the two modulation arm branches, .

[0033] 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:

[0034] in, is the amplitude value of the output light intensity.

[0035] 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 scanned, and the large signal response items of the electro-optic modulator to be tested under different input electrical signal powers are obtained.

[0036] Step 4: Output an electrical signal to the electrical signal output terminal of the electro-optic modulator to be tested through a small signal disturbance source, simulate the influence of the reflected signal at the electrical signal output terminal of the electro-optic modulator to be tested on its performance, and output the electrical signal in the link, which is expressed as:

[0037] The amplitude and phase information of the DC, baseband 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-optic modulator to be tested under different input electrical signal powers are obtained.

[0038] Step 5, combining the large signal response item and the small signal response item of the electro-optic modulator to be tested in step 3 and step 4, obtaining the complete nonlinear parameters of the electro-optic modulator to be tested under the input electrical signal power; scanning the frequency of the electrical signal input to the electro-optic modulator to be tested, repeating steps 1 to 4 at different frequencies, and obtaining the complete nonlinear parameters of the electro-optic modulator to be tested at different frequencies.

[0039] Embodiment 3: A method for measuring nonlinearity of an electro-optic modulator, comprising the following steps: Step 1: First, input the optical signal output by the laser source into the electro-optic modulator to be tested; the optical signal output by the laser source is expressed as:

[0040] in, is the amplitude of the electric field of the input light wave, is the angular frequency of the laser source output signal.

[0041] Two microwave signals with different frequencies and the same power output by the microwave source are input to the electro-optic modulator under test working at the orthogonal point; the input dual-tone signal is expressed as:

[0042] Where m is the amplitude, ω1, ω2 are the angular frequencies of the two-tone signal, and t is the time variable; Step 2: The output optical signal passes through an electro-optic modulator to be tested. Under the action of the external electric field of the RF signal injected by the microwave source, the optical signal is intensity modulated and the modulated optical signal is output. The expression is:

[0043] Among them, φ1, φ2, φ3 are phases, j is an imaginary unit, and t is a time variable; 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:

[0044] in:

[0045] make , expand the Bessel function to get:

[0046] 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.

[0047] make , expand the Bessel function to get:

[0048] Among them, B is a simplified equivalent, ω is the angular frequency, l is the accumulated variable, and J 2l+1 is the Jacobian determinant.

[0049] Similarly, After Bessel expansion and trigonometric operations such as product and difference, the relationship between the third-order intermodulation harmonic wave and the output light intensity can be obtained as follows:

[0050] Among them, ε0, ε1, ε3 are amplitudes.

[0051] Summarizing the harmonics in the output light wave, the expression is:

[0052]

[0053] The amplitude coefficient expressions of the 1st, 2nd and 3rd harmonic components are:

[0054]

[0055]

[0056] Among them, J1, J2, and J3 are Jacobian determinants.

[0057] 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 scanned, and the large signal response items of the electro-optic modulator to be tested under different input electrical signal powers are obtained.

[0058] Step 4: Output an electrical signal to the electrical signal output terminal of the electro-optic modulator to be tested through a small signal disturbance source, simulate the influence of the reflected signal at the electrical signal output terminal of the electro-optic modulator to be tested on its performance, and output the electrical signal in the link, which is expressed as:

[0059] The amplitude and phase information of the DC, baseband 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-optic modulator to be tested under different input electrical signal powers are obtained.

[0060] Step 5, combining the large signal response item and the small signal response item of the electro-optic modulator to be tested in step 3 and step 4, obtaining the complete nonlinear parameters of the electro-optic modulator to be tested under the input electrical signal power; scanning the frequency of the electrical signal input to the electro-optic modulator to be tested, repeating steps 1 to 4 at different frequencies, and obtaining the complete nonlinear parameters of the electro-optic modulator to be tested at different frequencies.

[0061] The present invention can realize high-precision measurement of nonlinearity of electro-optic modulator. The nonlinearity of electro-optic modulator accounts for the main part of link nonlinearity, therefore, characterizing the nonlinearity of electro-optic modulator can improve the nonlinearity measurement of link.

[0062] 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.

[0063] 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 the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such 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 embodiments of the present invention.

Claims

1. A method for measuring nonlinearity of an electro-optic modulator, characterized in that: The following steps are involved: Step 1: First, input the optical signal output by the laser source into the electro-optic 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 a linear region to achieve photoelectric linear mapping, and the standard photodetector outputs an electrical signal; Analyze the amplitude and phase changes of the DC, baseband and intermodulation components corresponding to the output electrical signal of the standard photodetector, scan the power of the microwave signal output by the microwave source, and obtain the large signal response items of the electro-optic modulator to be tested under different input electrical signal powers; Step 4: output an electrical signal to the electrical signal output terminal of the electro-optical modulator to be tested through a small signal disturbance source, simulate the influence of the reflected signal at the electrical signal output terminal of the electro-optical modulator to be tested on its performance, and output the electrical signal in the link; The amplitude and phase information of the DC, baseband 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-optic modulator to be tested under different input electrical signal powers are obtained; Step 5, combining the large signal response item and the small signal response item of the electro-optic modulator to be tested in step 3 and step 4, obtaining the complete nonlinear parameters of the electro-optic modulator to be tested under the input electrical signal power; scanning the frequency of the electrical signal input to the electro-optic modulator to be tested, repeating steps 1 to 4 at different frequencies, and obtaining the complete nonlinear parameters of the electro-optic modulator to be tested at different frequencies.

2. The method for measuring the nonlinearity of an electro-optic modulator according to claim 1, characterized in that: 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 nonlinearity of an electro-optic modulator according to claim 2, characterized in that: 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. The external electric field acts on the two modulation arms of the electro-optic modulator to be tested, causing the phase shift and Get the 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 the nonlinearity of an electro-optic modulator according to claim 2, characterized in that: Step 1 also includes: inputting two microwave signals with different frequencies and the same power output by the microwave source into the electro-optic modulator to be tested working at the orthogonal point; the input dual-tone signal is expressed as: Among them, 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-optic modulator according to claim 4, characterized in that: In step 2, the modulated optical signal is expressed as: Among them, φ1, φ2, φ3 are phases, j is an imaginary unit, and t is a time variable.

6. The method for measuring the nonlinearity of an electro-optic modulator according to claim 3, characterized in that: 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-optic modulator according to claim 5, characterized in that: In step 3, the electrical signal output by the standard photodetector is expressed as: 。 8. The method for measuring the nonlinearity of an electro-optic modulator according to claim 6, characterized in that: The output electrical signal expression in step 4 is: 。 9. The method for measuring the nonlinearity of an electro-optic modulator according to claim 7, characterized in that: The output electrical signal expression in step 4 is: 。 10. A nonlinear measurement device for an electro-optic modulator, 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 reflection signal at the electrical signal output end of the electro-optic 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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