A method for testing frequency response of a photodetector

Abstract

The application discloses a kind of photoelectric detector frequency response test methods, laser output optical signal is modulated by first signal source and second signal source output signal respectively after electro-optic harmonic excitation module, and the modulated optical signal of electro-optic harmonic excitation module is sent into the photoelectric detector to be measured to generate photoelectric current signal;Control and data processing module controls first signal source to be respectively in the state of opening and closing, under this condition, the amplitude information of specific frequency signal in the output optical signal of the photoelectric detector to be measured is obtained using spectrum analysis module, and the modulation coefficient test of electro-optic modulator in electro-optic harmonic excitation module can be realized by using control and data processing module analysis and calculation;In the state that first signal source is opened, the amplitude information of specific frequency signal in the output optical signal of the photoelectric detector to be measured is obtained using spectrum analysis module, and the modulation coefficient of electro-optic harmonic excitation module is measured, and the test of the frequency response of the photoelectric detector to be measured is realized by analysis and calculation.

Description

Technical Field

[0001] This invention belongs to the field of optoelectronic devices, and particularly relates to the field of frequency response testing of optoelectronic devices, specifically a method for testing the frequency response of a photodetector. Background Technology

[0002] As a fundamental core component in fiber optic communication systems and microwave photonics systems, the main function of photodetectors is to demodulate the envelope modulation signal on an optical signal into the electrical domain, realizing optical-to-electrical conversion. With the development of fiber optic communication systems, the operating speed and bandwidth of these systems are increasing, and the bandwidth requirements for photodetectors are also growing. To accurately evaluate the operating speed and bandwidth of a fiber optic communication system, the frequency response of various components within the system should be characterized, especially the frequency response of the photodetector, which typically reflects the system's operating capability at high frequencies.

[0003] Frequency response testing methods for photodetectors are generally divided into two categories: The first is the all-optical excitation method, such as the optical heterodyne method, the optical intensity noise method, and the optical pulse method. The optical heterodyne method uses the output optical signal of one or more tunable lasers to beat with the output optical signal of another fixed-wavelength laser in the photodetector under test. The frequency response of the photodetector under test can be extracted from the AC signal generated by the beating. This method can achieve ultra-wide frequency response testing of photodetectors, but it has extremely high requirements for the performance of the tunable laser, requiring precise tuning of the laser output wavelength and highly stable output optical power. Another all-optical excitation method is the optical noise beating method. This method uses the amplified spontaneous emission noise in a semiconductor optical amplifier to generate an ultra-wide spectrum optical signal. This optical signal is input to the photodetector under test for photoelectric conversion. The frequency response of the photodetector under test can be extracted using a spectrum analyzer. However, this method has lower testing accuracy and a smaller dynamic range. The second category is the electro-optic excitation method, including the electro-optic sweep frequency method, the secondary modulation method, the two-tone modulation method, and the optical sampling method. Electro-optic frequency sweeping uses a microwave network analyzer to perform frequency sweeping tests on the cascaded network of an electro-optic intensity modulator and the photodetector under test. The obtained frequency response is the cascaded response of the two types of devices. Additional calibration of the electro-optic modulator's frequency response or the use of an electro-optic modulator with a known frequency response is required to obtain the frequency response of the photodetector under test. Two-tone modulation (DTMC) uses two-tone signals with similar frequencies to drive the electro-optic modulator. The sum and difference frequencies of the two-tone modulation frequencies are measured in the photocurrent signal output by the photodetector under test, and the frequency response of the photodetector under test can be calculated. Optical sampling utilizes the rich spectral resources of sampled optical pulses to upconvert the low-frequency modulation signal of the electro-optic modulator to the required test range. Then, frequency configuration is used to eliminate the optical pulse spectral response and the electro-optic modulator's frequency response, thus achieving the test of the photodetector's frequency response. Currently, there is a need for a frequency response testing method for photodetectors with scalable frequency capabilities. Summary of the Invention

[0004] The purpose of this invention is to provide a testing method suitable for photodetectors, which features low cost, expandable measurement frequency range, high resolution, and electro-optical response pre-calibration.

[0005] A method for testing the frequency response of a photodetector, characterized by comprising the following steps: Step 1: Construct a photodetector frequency response testing device, including a laser, an electro-optic harmonic excitation module, an electro-optic detector under test, a spectrum analysis module, a control and data processing module, a first signal source, and a second signal source; the laser, the electro-optic harmonic excitation module, and the photodetector under test are sequentially optically connected; the first and second signal sources are electrically connected to the electro-optic harmonic excitation module; the photodetector under test is electrically connected to the spectrum analysis module; and the control and data processing module is data connected to the first signal source, the second signal source, and the spectrum analysis module. Step 2: The optical signal output by the laser passes through the electro-optic harmonic excitation module and is modulated by the output signals of the first signal source and the second signal source respectively. The output modulated optical signal is sent to the photodetector under test for photoelectric conversion to generate a photocurrent signal. The photocurrent signal is collected and analyzed by the spectrum analysis module. Step 3: Turn off the first signal source and set the output frequency of the second signal source to f. b A sinusoidal signal with constant power is used to extract the frequency kf from the photocurrent signal output by the photodetector using a spectrum analysis module. b The amplitude is denoted as A(kf) b ;0;m b (f b )); Step 4: Keep the second signal source set, turn on the first signal source and output a frequency of f. m The sinusoidal signal was used to extract the frequency kf from the output photocurrent of the photodetector using a spectrum analysis module. b nf m ±kf b The signal amplitude is denoted as A(kf) b ;m(f m );m b (f b )), A(nf m ±kf b ;m(f m );m b (f b ), where k and n are both natural numbers; Step 5: Using the data measured in Steps 3 and 4, calculate according to the following formula to obtain the value of the electro-optic modulator in the electro-optic harmonic excitation module at a modulation frequency of f. mmodulation coefficient m(f) m ): Among them, J0(m(f) m ()) is a zeroth-order Bessel function of the first kind; Step 6: Use the modulation coefficient m(f) calculated in Step 5 m The frequency response of the photodetector under test can be calculated using the following formula: Step 7: Using the control and data processing module to control the first signal source and the spectrum analysis module, repeating steps 3, 4, 5, and 6 will yield the nf values ​​of the photodetector under test at different frequencies. m ±kf b Frequency response at that location.

[0006] Compared with the prior art, the present invention has the following beneficial effects: I. This invention employs a swept-frequency microwave source and a fixed-frequency signal source to jointly drive the electro-optic harmonic excitation module, thereby achieving pre-calibration of the electro-optic harmonic excitation module; Second, this invention uses a swept-frequency microwave source to achieve photodetector frequency response testing within an n-fold swept-frequency range, which greatly reduces testing costs. Attached Figure Description

[0007] Figure 1 This is a schematic diagram of the device of the present invention.

[0008] Figure 2 This is a test result diagram of the present invention. Detailed Implementation

[0009] The following is a further description of the present invention in conjunction with the accompanying drawings and embodiments. It should be noted that the scope of protection claimed by the present invention is not limited to the scope described in the embodiments, and should not be construed as limiting the scope of protection of the present invention.

[0010] like Figure 1 As shown, a laser emits a beam of light signal, which is then fed into the electro-optic harmonic excitation module and is respectively controlled by the output signal f from the first signal source. m With the output signal f of the second signal source b Modulation occurs when the modulated optical signal is sent to the photodetector under test for photoelectric conversion, generating a photocurrent signal. The control and data processing module keeps the first signal source off and uses the spectrum analysis module to obtain the frequency kf in the output optical signal of the photodetector under test. b The amplitude information A(kf) of the signal b ;0;m b (f bThe control and data processing module controls the first signal source to be in the on state, and uses the spectrum analysis module to obtain the frequency kf in the output optical signal of the photodetector under test. b nf m ±kf b The amplitude information A(kf) of the signal b ;m(f m );m b (f b )), A(nf m ±kf b ;m(f m );m b (f b The frequency response of the photodetector is obtained by analyzing and calculating using the control and data processing module; by changing the output frequency of the first signal source through the control and data processing module and repeating the above steps, the photodetector can be tested at different frequencies.

[0011] To better explain the technical invention, the measurement principle of the present invention will be briefly introduced below using a single-drive Mach-Zehnder modulator as an electro-optic harmonic excitation module.

[0012] The optical signal output from the laser, after passing through a single-drive Mach-Zehnder modulator, is represented as: Where E0 and f0 are the amplitude and frequency of the optical signal, respectively; γ is the splitting ratio of the upper and lower arms of the single-drive Mach-Zehnder modulator. This is the bias phase of a single-drive Mach-Zehnder modulator.

[0013] The output optical signal of the single-drive Mach-Zehnder modulator enters the photodetector for photoelectric conversion, generating a beat frequency electrical signal, which is then expanded by the Jacobi-Anger modulator as follows: Where R is the frequency responsivity of the photodetector, J n (·) is the nth order Bessel function of the first kind.

[0014] As can be seen from formula (2), when the first signal source is turned off, the frequency of the beat frequency signal output by the photodetector is kf. b The frequency component amplitude is

[0015] When the first signal source is activated, the photodetector outputs a beat frequency signal with a frequency of kf. b The frequency component amplitude is

[0016] Formulas (3) and (4) can be used to obtain the calculation formulas for the modulation coefficients of a single-drive Mach-Zehnder modulator.

[0017] It can be seen from formula (2) that the frequency component nf m ±kf b The amplitude can be expressed as

[0018] The modulation coefficient m(f) calculated using formula (5) m Combining this with formula (6), the frequency response of the photodetector can be obtained as follows: Example

[0019] The block diagram of the testing device of this invention is as follows: Figure 1 As shown, the optical signal with a laser output frequency of f0 = 193.1 THz is fed into a Mach-Zehnder electro-optic intensity modulator, and is modulated by the first signal source output frequency f... m =0.05~25GHz swept microwave signal and second signal source output frequency f b A 1MHz sinusoidal signal is used to modulate and generate a modulated optical signal. The modulated optical signal is sent to a photodetector for photoelectric conversion, and the generated photocurrent signal is recorded and analyzed by a spectrum analysis module.

[0020] The control and data processing module shuts down the first signal source, and the control spectrum analysis module extracts and records the photocurrent signal with a frequency of 2MHz (2f). b The amplitude information A(2f) b ;0;m b (f b The control and data processing module is used to turn on the first signal source, and the spectrum analysis module is used to extract and record the photocurrent signal with a frequency of 2MHz (2f). b The amplitude information A(2f) b ;m(f m );m b (f b )) and 0.1~50GHz (2f m The amplitude information A(2f) m ;m(f m );m b (f b The modulation coefficients of the Mach-Zehnder electro-optic intensity modulator in the range of 0.05–25 GHz can be calculated using formula (5). Figure 2 As shown by the dashed line; then, the frequency response of the photodetector under test in the range of 0.1 to 50 GHz is calculated using formula (7), as follows. Figure 2 As shown by the solid line in the middle.

Claims

1. A method for testing the frequency response of a photodetector, characterized in that... Includes the following steps: Step 1: Construct a photodetector frequency response testing device, including a laser, an electro-optic harmonic excitation module, an electro-optic detector under test, a spectrum analysis module, a control and data processing module, a first signal source, and a second signal source; the laser, the electro-optic harmonic excitation module, and the photodetector under test are sequentially optically connected; the first and second signal sources are electrically connected to the electro-optic harmonic excitation module; the photodetector under test is electrically connected to the spectrum analysis module; and the control and data processing module is data connected to the first signal source, the second signal source, and the spectrum analysis module. Step 2: The optical signal output by the laser passes through the electro-optic harmonic excitation module and is modulated by the output signals of the first signal source and the second signal source respectively. The output modulated optical signal is sent to the photodetector under test for photoelectric conversion to generate a photocurrent signal. The photocurrent signal is collected and analyzed by the spectrum analysis module. Step 3: Turn off the first signal source and set the output frequency of the second signal source to f. b A sinusoidal signal with constant power is used to extract the frequency kf from the photocurrent signal output by the photodetector using a spectrum analysis module. b The amplitude is denoted as A(kf) b ;0;m b (f b )); Step 4: Keep the second signal source set, turn on the first signal source and output a frequency of f. m The sinusoidal signal was used to extract the frequency kf from the output photocurrent of the photodetector using a spectrum analysis module. b nf m ±kf b The signal amplitude is denoted as A(kf). b ;m(f m );m b (f b )), A(nf m ±kf b ;m(f m );m b (f b ), where k and n are both natural numbers; Step 5: Using the data measured in Steps 3 and 4, calculate according to the following formula to obtain the value of the electro-optic modulator in the electro-optic harmonic excitation module at a modulation frequency of f. m modulation coefficient m(f) m ): Among them, J0(m(f) m ()) is a zeroth-order Bessel function of the first kind; Step 6: Use the modulation coefficient m(f) calculated in Step 5 m The frequency response of the photodetector under test can be calculated using the following formula: Step 7: Using the control and data processing module to control the first signal source and the spectrum analysis module, repeating steps 3, 4, 5, and 6 will yield the nf values ​​of the photodetector under test at different frequencies. m ±kf b Frequency response at that location.

2. The method for testing the frequency response of a photodetector according to claim 1, characterized in that: The electro-optic harmonic excitation module is a Mach-Zehnder interferometer structure. It can operate in interference mode to form a Mach-Zehnder electro-optic intensity modulator, or it can operate in heterodyne mode to form a Mach-Zehnder heterodyne interferometer for use as heterodyne interferometer.

3. The method for testing the frequency response of a photodetector according to claim 1, characterized in that: The modulation coefficient of the electro-optic harmonic excitation module is used as a parameter to calculate the frequency response of the photodetector under test.

4. The method for testing the frequency response of a photodetector according to claim 1, characterized in that: The frequency response measurement range of the photodetector under test can be extended to the output frequency f of the first signal source. m n times.

5. The method for testing the frequency response of a photodetector according to claim 1, characterized in that: When the electro-optic harmonic excitation module is a Mach-Zehnder electro-optic intensity modulator, the formula in step 5 is expressed as follows:

Images