Method and system for measuring the frequency response of an electro-optic modulator based on a spectrum analyzer

Abstract

This invention discloses a method and system for measuring the frequency response of an electro-optic modulator based on a spectral analyzer. The system includes a laser, a 95:5 single-mode fiber splitter, an optical power meter, an electro-optic modulator, a control power supply, an RF signal generator, and a spectral analyzer. The measurement method includes the following steps: calculating a calibration factor to correct optical power drift through optical path splitting, driving the modulator by applying several discrete single-frequency RF points, and measuring the carrier power P0(f) using the spectral analyzer. i ) and the first-order sideband power P1(f i ), and determined by the power ratio R(f) i )=10 (P1‑P0) / 10 Combining the Jacobi–Anger expansion / Bessel function relation, the phase modulation index β(f) is solved by inverse solution. i Then, the phase transfer function H(f) at each frequency point is calculated and fitted. i The continuous frequency response S of the modulator is obtained. 21 This invention simplifies the testing process, reduces reliance on high-speed photodetectors and vector network analyzers, and enables high-precision electro-optic response testing of electro-optic modulators at high frequencies.

Description

Technical Field

[0001] This invention belongs to the field of microwave photonics technology, specifically relating to a method and system for measuring the frequency response of an electro-optic modulator based on a spectral analyzer. Background Technology

[0002] The frequency response S21 of an electro-optic modulator is a key indicator of its high-speed performance. A common measurement method involves applying a sweep drive to the modulator, performing photoelectric conversion using a high-speed photodetector, and then measuring the response using a vector network analyzer / spectrum analyzer. However, this "electrical measurement" method is highly dependent on the bandwidth and linearity of the photodetector, and the insertion loss and reflections of the RF link require complex de-embedding. This typically leads to limitations in high-frequency testing of electro-optic modulators due to detector and RF link constraints, resulting in increased testing complexity and decreased accuracy.

[0003] Spectral analyzers can directly acquire the spectral distribution of the output light from electro-optic modulators, accurately measuring the power and frequency positions of the carrier wave and several sidebands. Based on the Jacobi-Anger expansion and Bessel function relationship of phase modulation, the modulation index can be obtained from the carrier-to-sideband power ratio, thus promising to complete the testing of electro-optic frequency response in the optical domain. Therefore, research and application of spectral analyzers in the characterization of the frequency response of electro-optic modulators will help simplify the testing process, reduce dependence on high-speed photodetectors, and significantly improve the accuracy and repeatability of high-frequency response measurements. Summary of the Invention

[0004] The purpose of this invention is to provide a method and system for measuring the frequency response of an electro-optic modulator based on a spectral analyzer. The method involves directly measuring the carrier and sideband power output by the modulator using a spectral analyzer and calculating and fitting the result to obtain its frequency response.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] On the one hand, a method for measuring the frequency response of an electro-optic modulator based on a spectral analyzer is provided, including the following steps:

[0007] (1) The optical signal output from the laser source is split into an electro-optic modulator and an optical power meter at an intensity ratio of 95:5;

[0008] (2) The electro-optic modulator receives light from the laser and generates corresponding optical sidebands under radio frequency drive, and sends them to the spectrometer;

[0009] (3) The spectrometer detects the optical signal after passing through the electro-optic modulator, measures the output spectrum, and extracts the carrier power P0(f). i ) and the first-order sideband power P1(f i );

[0010] (4) First, record the optical power meter reading P when there is no radio frequency drive. OPM With the spectrometer reading P OSA Therefore, the calibration factor C=P is calculated. OPM / P OSA This calibration factor is applied to the power at any frequency point measured by the spectral analyzer to recover the true optical power and reduce the impact of optical source and system instability on S. 21 The impact of characterization accuracy;

[0011] Secondly, the power ratio R(f) at each frequency was measured using a spectral analyzer. i )=10 (P1-P0) / 10 Inverse phase modulation index β(f) i );

[0012] Next, calculate the voltage-to-phase transfer function H(f) i )=φ(f i )=β(f i ) / V pp (f i );

[0013] Finally, for each discrete point {(f i ,φ(f i The continuous frequency response S of the electro-optic modulator was obtained by smooth fitting. 21 .

[0014] On the other hand, a system for measuring the frequency response of an electro-optic modulator based on a spectral analyzer is also provided.

[0015] Lasers are used to provide stable, low-phase-noise optical carriers;

[0016] A single-mode fiber optic splitter is used to split laser light into an electro-optic modulator and an optical power meter at an intensity ratio of 95:5.

[0017] Optical power meter, used to measure the split power of a laser;

[0018] An electro-optic modulator is a device under test that receives light from a laser and generates corresponding optical sidebands under radio frequency drive.

[0019] The control power supply is used to provide a bias voltage to the electro-optic modulator, keeping it at the quadrature bias point;

[0020] A signal generator is used to provide several peak-to-peak values ​​(Vo) for the electro-optic modulator. pp Discrete radio frequency point f of 4V i The single-frequency radio frequency drive signal;

[0021] A spectrometer is used to detect optical signals after passing through an electro-optic modulator, measure the output spectrum, and extract the carrier power P0(f). i ) and the first-order sideband power P1(f i ).

[0022] Preferably, the laser is a narrow linewidth distribution feedback semiconductor laser with a center wavelength of 1550 nm and a linewidth of <500 kHz.

[0023] Preferably, the optical power meter has a dynamic range of -60 dBm to +27 dBm and a calibration accuracy of ±2.5% in the 1550 nm band, and is used to measure the shunt power P of a laser. OPM .

[0024] Preferably, the electro-optic modulator is a Mach-Zehnder modulator fabricated using a thin-film lithium niobate process.

[0025] Preferably, the signal generator is a low-noise radio frequency signal source in the test frequency band of 100 MHz to 40 GHz, used to provide the electro-optic modulator with a peak-to-peak Vo of 10 GHz to 40 GHz. pp Discrete radio frequency point f of 4 V i The single-frequency radio frequency drive signal.

[0026] Preferably, the spectrometer has a narrow resolution bandwidth of ≤ 0.01 nm and a high dynamic range of 60 dB.

[0027] Compared with the prior art, the present invention has the following advantages:

[0028] 1. This invention directly measures the carrier and sideband power output by the modulator using a spectral analyzer and calculates and fits the frequency response to achieve characterization of the electro-optic frequency response in the optical domain, resulting in more direct and accurate measurement results. Furthermore, the introduction of an optical power calibration mechanism effectively compensates for system errors caused by the instability of the light source and system, further ensuring the consistency and repeatability of the measurement results.

[0029] 2. The measurement system of this invention mainly consists of a light source, a spectrum analyzer, and a basic radio frequency source, eliminating the need for high-speed photodetectors, broadband vector network analyzers, and complex radio frequency cable connections required in traditional links, thus greatly simplifying the hardware configuration. At the same time, this method avoids the cumbersome de-embedding calibration steps caused by radio frequency link insertion loss and reflection in traditional "electrical measurement" methods, reducing the complexity of test operations and dependence on high-value instruments and equipment.

[0030] 3. In the measurement system, the spectral analyzer can intuitively display the modulated carrier and each order of sidebands, making the test process and results clear at a glance, which is convenient for fault diagnosis and result verification. Moreover, since optical signals are not sensitive to electromagnetic interference during transmission, this method has stronger anti-interference ability compared with electrical measurement, and can obtain stable and reliable test data in complex laboratory or production environments. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the system for measuring the frequency response of an electro-optic modulator based on a spectral analyzer, according to the present invention.

[0032] Figure 2 It is the output spectrum of the spectrometer (carrier + upper / lower sideband).

[0033] Figure 3 It is the carrier and first-order sideband interception when a 10 GHz radio frequency signal is input.

[0034] Figure 4 It is the carrier and first-order sideband interception when a 20 GHz radio frequency signal is input.

[0035] Figure 5 It is the carrier and first-order sideband interception when a 30 GHz radio frequency signal is input.

[0036] Figure 6 It is the carrier and first-order sideband interception when a 40 GHz radio frequency signal is input.

[0037] Figure 7 The S21 curve (10~40 GHz) of the modulator under test is obtained by fitting. Detailed Implementation

[0038] To make the objectives and advantages of the present invention clearer, the present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0039] This invention relates to a method for measuring the frequency response of an electro-optic modulator based on a spectral analyzer, comprising the following steps:

[0040] (1) The optical signal output from the laser source is split into an electro-optic modulator and an optical power meter at an intensity ratio of 95:5;

[0041] (2) The electro-optic modulator receives light from the laser and generates corresponding optical sidebands under radio frequency drive, and sends them to the spectrometer;

[0042] (3) The spectrometer detects the optical signal after passing through the electro-optic modulator, measures the output spectrum, and extracts the carrier power P0(f). i ) and the first-order sideband power P1(f i );

[0043] (4) First, record the optical power meter reading P when there is no radio frequency drive. OPM With the spectrometer reading P OSA Therefore, the calibration factor C=P is calculated. OPM / P OSA This calibration factor is applied to the power at any frequency point measured by the spectral analyzer to recover the true optical power and reduce the impact of optical source and system instability on S. 21 The impact of characterization accuracy;

[0044] Secondly, the power ratio R(f) at each frequency was measured using a spectral analyzer. i )=10 (P1-P0) / 10 Inverse phase modulation index β(f) i );

[0045] Next, calculate the voltage-to-phase transfer function H(f) i )=φ(f i )=β(f i ) / V pp (f i );

[0046] Finally, for each discrete point {(f i ,φ(f i The continuous frequency response S of the electro-optic modulator was obtained by smooth fitting. 21 .

[0047] like Figure 1 As shown, this invention discloses a system for measuring the frequency response of an electro-optic modulator based on a spectrum analyzer. The process is calibration-testing-calculation. The system includes a laser, a single-mode fiber splitter, an optical power meter, an electro-optic modulator, a control power supply, a signal generator, and a spectrum analyzer. Solid lines in the figure represent the optical path, and dashed lines represent the circuit. Optical path: First, the laser generates a stable optical signal. This signal is split into two paths by the single-mode fiber splitter. One path enters the electro-optic modulator, and the modulated signal is output to the spectrum analyzer for spectral analysis. The other path enters the optical power meter for power measurement. Circuit: The signal generator generates a modulated electrical signal, which is input to the electro-optic modulator. The electro-optic modulator modulates the optical signal according to the electrical signal. The control power supply provides the necessary bias voltage to the electro-optic modulator.

[0048] To compensate for system errors introduced by laser output and light intensity drift due to time or bias after passing through the electro-optic modulator, a single-mode fiber optic splitter is used in this system to simultaneously introduce the test light into both the optical power meter and the spectrum analyzer. The optical power meter reading P is recorded separately when there is no RF drive. OPM With the spectrometer reading P OSA Therefore, the calibration factor C=P is calculated.OPM / P OSA This calibration factor is applied to the power at any frequency point measured by the spectrometer to recover the true optical power and reduce the impact of optical source and system instability on S. 21 The influence of characterization accuracy was then considered. The power ratio R(f) at each frequency was then measured using a spectral analyzer. i )=10 (P1-P0) / 10 Inverse phase modulation index β(f) i Then, the voltage-to-phase transfer function H(f) is calculated. i )=φ(f i )=β(f i ) / V pp (f i Finally, for each discrete point {(f)} i ,φ(f i The continuous frequency response S of the electro-optic modulator was obtained by smooth fitting. 21 .

[0049] Specifically, in this system,

[0050] The laser is a narrow-linewidth distributed feedback semiconductor laser with a center wavelength of 1550 nm and a linewidth of <500 kHz, used to provide a high-stability, low-phase-noise optical carrier.

[0051] The single-mode fiber optic splitter has a splitting ratio of 95:5, which is used to split the laser beam into the electro-optic modulator and the optical power meter at an intensity ratio of 95:5.

[0052] The optical power meter has a dynamic range of -60 dBm to +27 dBm and a calibration accuracy of ±2.5% in the 1550 nm band. It is used to measure the shunt power P of a laser. OPM .

[0053] The electro-optic modulator is a Mach-Zehnder modulator fabricated using a thin-film lithium niobate process. It is the device under test in this embodiment, which receives light from a laser and generates corresponding optical sidebands under the drive of a radio frequency signal.

[0054] A control power supply is used to provide a bias voltage to the electro-optic modulator 4, so that it is located at the quadrature bias point.

[0055] The signal generator is a low-noise RF signal source in the test band from 100 MHz to 40 GHz, used to provide the electro-optic modulator with a peak-to-peak Vo from 10 GHz to 40 GHz. pp Discrete radio frequency point f of 4 V i The single-frequency radio frequency drive signal.

[0056] The spectrometer features a narrow resolution bandwidth of ≤ 0.01 nm and a high dynamic range of 60 dB, used to detect optical signals after modulation, measure the output spectrum, and extract the carrier power P0(f). i ) and the first-order sideband power P1(f i ).

[0057] The following are the relevant parameters obtained by measuring and calculating using this method:

[0058] Figure 2 shows the modulation output spectrum obtained by the spectrum analyzer 7 under the driving condition of a 10 GHz RF signal source input. The carrier, first-order sideband, and second-order sideband can be clearly observed in the figure. The carrier power is the highest, followed by the first-order sideband, and the amplitude of the second-order sideband further decreases, showing typical modulation spectrum distribution characteristics.

[0059] Figure 3 When a 10 GHz radio frequency signal is input, the carrier and first-order sideband are obtained through the spectrum analyzer 7. The carrier power is 2.99 dBm, and the first-order sideband power is -14.27 dBm.

[0060] Figure 4 When a 20 GHz radio frequency signal is input, the carrier and first-order sideband are obtained through the spectrum analyzer 7. The carrier power is -1.13 dBm, and the first-order sideband power is -19.75 dBm.

[0061] Figure 5 When a 30 GHz radio frequency signal is input, the carrier and first-order sideband are obtained through the spectrum analyzer 7. The carrier power is 2.99 dBm, and the first-order sideband power is -20.50 dBm.

[0062] Figure 6 When a 40 GHz radio frequency signal is input, the carrier and first-order sideband are obtained through the spectrum analyzer 7. The carrier power is -1.37 dBm, and the first-order sideband power is -30.53 dBm.

[0063] The calculation results of the above calibrated data are shown in Table 1:

[0064] Table 1-1 Data results calculated at each discrete frequency point

[0065]

[0066] Figure 7 The S of the electro-optic modulator obtained by fitting the above discrete frequency points is... 21 curve.

[0067] As can be seen from the above, the method and system for measuring the frequency response of an electro-optic modulator based on a spectral analyzer proposed in this embodiment corrects optical power drift by calculating a calibration factor through optical path splitting, decomposes the phase modulation index using the carrier and first-order sideband power, and obtains the voltage-phase transfer function. Finally, it performs smooth fitting on discrete points to obtain a continuous S21 curve. This method is low in equipment cost, easy to operate, and has good test stability and repeatability, making it an effective method for characterizing the frequency response of electro-optic modulators.

[0068] The above embodiments are merely specific examples to further illustrate the purpose, technical solution, and beneficial effects of the present invention, and the present invention is not limited thereto. Any modifications, equivalent substitutions, improvements, etc., made within the scope of the disclosure of the present invention are included within the protection scope of the present invention.

Claims

1. A method for measuring the frequency response of an electro-optic modulator based on a spectral analyzer, characterized in that, Includes the following steps: (1) The optical signal output from the laser source is split into an electro-optic modulator and an optical power meter at an intensity ratio of 95:5; (2) The electro-optic modulator receives light from the laser and generates corresponding optical sidebands under radio frequency drive, and sends them to the spectrometer; (3) The spectrometer detects the optical signal after passing through the electro-optic modulator, measures the output spectrum, and extracts the carrier power P0(f). i ) and the first-order sideband power P1(f i ); (4) First, record the optical power meter reading P when there is no radio frequency drive. OPM With the spectrometer reading P OSA Therefore, the calibration factor C=P is calculated. OPM / P OSA ; This calibration factor is applied to the power at any frequency point measured by the spectral analyzer to recover the true optical power and reduce the impact of optical source and system instability on S. 21 The impact of characterization accuracy; Secondly, the power ratio R(f) at each frequency was measured using a spectral analyzer. i )=10 (P1-P0) / 10 Inverse phase modulation index β(f) i ); Next, calculate the voltage-to-phase transfer function H(f) i )=φ(f i )=β(f i ) / V pp (f i ); Finally, for each discrete point {(f i ,φ(f i The continuous frequency response S of the electro-optic modulator was obtained by smooth fitting. 21 .

2. A system for measuring the frequency response of an electro-optic modulator based on a spectral analyzer, using the method described in claim 1, characterized in that: Lasers are used to provide stable, low-phase-noise optical carriers; A single-mode fiber optic splitter is used to split laser light into an electro-optic modulator and an optical power meter at an intensity ratio of 95:

5. Optical power meter, used to measure the split power of a laser; An electro-optic modulator is a device under test that receives light from a laser and generates corresponding optical sidebands under radio frequency drive. The control power supply is used to provide a bias voltage to the electro-optic modulator, keeping it at the quadrature bias point; A signal generator is used to provide several peak-to-peak values ​​(Vo) for the electro-optic modulator. pp Discrete radio frequency point f of 4V i The single-frequency radio frequency drive signal; A spectrometer is used to detect optical signals after passing through an electro-optic modulator, measure the output spectrum, and extract the carrier power P0(f). i ) and the first-order sideband power P1(f i ).

3. The system for measuring the frequency response of an electro-optic modulator based on a spectral analyzer according to claim 2, characterized in that: The laser is a narrow linewidth distributed feedback semiconductor laser with a center wavelength of 1550 nm and a linewidth of <500 kHz.

4. The system for measuring the frequency response of an electro-optic modulator based on a spectral analyzer according to claim 2, characterized in that: The optical power meter has a dynamic range of -60 dBm to +27 dBm and a calibration accuracy of ±2.5% in the 1550 nm band. It is used to measure the split power P of a laser. OPM .

5. The system for measuring the frequency response of an electro-optic modulator based on a spectral analyzer according to claim 2, characterized in that: The electro-optic modulator is a Mach-Zehnder modulator fabricated using a thin-film lithium niobate process.

6. The system for measuring the frequency response of an electro-optic modulator based on a spectral analyzer according to claim 2, characterized in that: The signal generator is a low-noise radio frequency signal source in the test frequency band of 100 MHz to 40 GHz, used to provide the electro-optic modulator with a peak-to-peak Vo of 10 GHz to 40 GHz. pp Discrete radio frequency point f of 4 V i The single-frequency radio frequency drive signal.

7. The system for measuring the frequency response of an electro-optic modulator based on a spectral analyzer according to claim 2, characterized in that: The spectrometer has a narrow resolution bandwidth of ≤ 0.01 nm and a high dynamic range of 60 dB.

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