Testing method for measuring half-wave voltage of thin-film lithium niobate modulator under high frequency based on low-frequency signal

Abstract

The invention relates to the technical field of thin-film lithium niobate modulators, in particular to a test method for measuring the half-wave voltage of a thin-film lithium niobate modulator under high frequency based on low-frequency signals, which comprises the following steps of: inputting sawtooth waves at the radio frequency end of the thin-film lithium niobate modulator to be tested through a signal generator, and amplifying an oscillogram of an oscilloscope; by adjusting the amplitude and the bias point of the input sawtooth wave, the rising edge of the waveform output by the detector is divided into a half-cycle sine wave, and at the moment, the difference value of the voltages of the sawtooth wave corresponding to the wave crest and the wave trough of the sine wave is the half-wave voltage of the modulator. According to the method, the half-wave voltage of the thin-film lithium niobate modulator at the high frequency can be measured by inputting the low-frequency sawtooth wave, and the frequency corresponding to the half-wave voltage can be calculated according to the period of the sine wave. The problems of low precision, long test time and high requirement on a test instrument in the process of measuring the high-frequency half-wave voltage by the existing conventional test method are solved.

Description

Technical Field

[0001] The invention relates to the technical field of thin film lithium niobate modulators, and in particular to a test method for measuring a high frequency lower half-wave voltage of a thin film lithium niobate modulator based on a low frequency signal. Background Art

[0002] In recent years, thin-film lithium niobate electro-optic modulators have developed rapidly. Among them, the half-wave voltage of the modulator is an important parameter to measure the electro-optic effect. The electrode voltage provided by the modulator when the waveguide phase changes by π is the half-wave voltage.

[0003] At present, the half-wave voltage of the modulator is mainly measured by inputting a triangular wave signal. By adjusting the amplitude and bias of the input triangular wave, the modulator outputs multiple signals in the form of cut sine waves. By selecting a sine signal in one cycle and calculating the voltage difference between the corresponding points of the triangular wave at the peak and trough, the half-wave voltage of the thin-film lithium niobate modulator can be obtained. The frequency corresponding to the half-wave voltage is the frequency of the input triangular wave signal.

[0004] This method can conveniently measure the half-wave voltage of the thin-film lithium niobate modulator. Testing the half-wave voltage at high frequency using this method requires the use of a high-frequency signal generator and an oscilloscope with a high-frequency range. With the development of thin-film lithium niobate modulators, the amount of modulator testing is also increasing. Therefore, there is an urgent need for a modulator high-frequency half-wave voltage test method with high test efficiency, low repetition error, and low test instrument requirements. Summary of the invention

[0005] The purpose of the present invention is to provide a test method for measuring the half-wave voltage of a thin-film lithium niobate modulator at high frequency based on a low-frequency signal. The method measures the half-wave voltage of a thin-film lithium niobate modulator at high frequency by inputting a low-frequency sawtooth wave, thereby solving the technical problems of low accuracy, long test time and high requirements on test instruments in measuring the half-wave voltage at high frequency in the existing conventional test methods.

[0006] To achieve the above object, the present invention provides a test method for measuring the high-frequency lower half-wave voltage of a thin-film lithium niobate modulator based on a low-frequency signal, comprising the following steps:

[0007] Build a test platform;

[0008] The sawtooth wave signal is divided into two paths through a power divider and input into a thin-film lithium niobate electro-optic modulator and an oscilloscope respectively;

[0009] Adjust the input wave amplitude and offset so that the modulator output waveform presents a periodic sine wave shape at the rising edge of the sawtooth wave;

[0010] Record the modulator output waveform peak time T 2and trough moment T 1 The voltage value V(T 2 ) and V(T 1 ), calculate the voltage difference dV;

[0011] The power divider is used to calibrate the calculation result, and the half-wave voltage V of the modulator is calculated. π ;

[0012] The frequency corresponding to the half-wave voltage is calculated.

[0013] When the test platform is constructed, the test instruments required are composed of a laser, a signal generator, a power divider, a photodetector, an oscilloscope and an electro-optic modulator of the lithium niobate to be tested.

[0014] The laser, the electro-optic modulator, the photodetector and the oscilloscope are connected in sequence, and the power divider is connected to the electro-optic modulator, the oscilloscope and the signal generator respectively.

[0015] Among them, when the input sawtooth wave signal is fully modulated by the modulator, the modulator output waveform presents a periodic sine wave waveform at the rising edge of the sawtooth wave, and at this time it satisfies:

[0016] dV=V(T 2 )-V(T 1 ) (1)

[0017] Vπ=k(V(T 2 )-V(T 1 )) (2)

[0018] Among them, V π Represents the half-wave voltage of the modulator under test, T 1 Indicates the trough moment of the modulator output waveform, T 2 Indicates the peak moment of the modulator output waveform. The sawtooth voltage values ​​corresponding to the two moments are V(T 1 ) and V(T 2 ), k represents the output waveform voltage amplitude V at both ends of the power divider after calibration. A and V B The proportionality factor.

[0019] Wherein, the calibration steps of the power divider are:

[0020] The test instruments only include signal generator, oscilloscope and power divider;

[0021] The signal generator is divided into two paths by a power divider, and the two paths are input to the two ports of the oscilloscope respectively, and then the sawtooth wave with the same parameters when testing the thin film lithium niobate electro-optic modulator is input to the two ports of the oscilloscope;

[0022] Calculating a ratio k of sawtooth wave amplitudes of two ports of the oscilloscope;

[0023] The modulator half-wave voltage V is calculated by formula (2): π .

[0024] Among them, in the calculation method of the frequency corresponding to the half-wave voltage, the period T of a single sinusoidal wave signal is:

[0025] T=2|T 2 -T 1 | (3)

[0026] The half-wave voltage V π The corresponding frequency f satisfies:

[0027]

[0028] Where f represents the high frequency corresponding to the measured modulator half-wave voltage, T 1 Indicates the trough moment of the modulator output waveform, T 2 Indicates the peak moment of the modulator output waveform.

[0029] The sawtooth wave signal is output by the signal generator, and the sawtooth wave signal is a 500 Hz sawtooth wave signal.

[0030] The present invention discloses a test method for measuring the half-wave voltage of a thin-film lithium niobate modulator at high frequency based on a low-frequency signal. A sawtooth wave is input at the radio frequency end of the thin-film lithium niobate modulator to be tested through a signal generator, and the waveform diagram of the oscilloscope is amplified. By adjusting the amplitude and bias point of the input sawtooth wave, a sine wave with a divided half cycle appears on the rising edge of the waveform output by the detector. At this time, the difference between the voltages corresponding to the sawtooth wave at the peak and the trough of the sine wave is the half-wave voltage of the modulator. The frequency corresponding to the half-wave voltage can be calculated through the period of the sine wave. The method measures the half-wave voltage of the thin-film lithium niobate modulator at high frequency by inputting a low-frequency sawtooth wave, thereby solving the problems of low precision, long test time and high requirements on test instruments in the existing conventional test methods in measuring the half-wave voltage at high frequency. In addition, the method can effectively improve the precision of the half-wave voltage test of the thin-film lithium niobate modulator, improve the test efficiency, and has the advantages of low repetition error, which has important guiding significance for experimental testing of thin-film lithium niobate modulators. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art are briefly introduced below.

[0032] Figure 1 It is a schematic diagram of the experimental configuration of the test method for measuring the high-frequency lower half-wave voltage of a thin-film lithium niobate modulator based on a low-frequency signal according to the first embodiment of the present invention.

[0033] Figure 2 1 is a waveform diagram of an input sawtooth wave signal and an output waveform of a thin-film lithium niobate modulator according to the first embodiment of the present invention.

[0034] Figure 3 4 is a waveform diagram of the rising edge of the sawtooth wave according to the first embodiment of the present invention.

[0035] Figure 4 It is a connection diagram of a power divider calibration instrument according to the first embodiment of the present invention.

[0036] Figure 5 It is a flowchart of a test method for measuring the high-frequency lower half-wave voltage of a thin-film lithium niobate modulator based on a low-frequency signal according to the first embodiment of the present invention.

[0037] Figure 6 This is a waveform diagram of the input triangle wave signal and the measured waveform of the thin-film lithium niobate electro-optic modulator according to the first embodiment of the present invention. DETAILED DESCRIPTION

[0038] Embodiments of the present invention are described in detail below. Examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, but should not be construed as limiting the present invention.

[0039] First embodiment:

[0040] See also Figures 1 to 6 The present invention provides a test method for measuring the high-frequency lower half-wave voltage of a thin-film lithium niobate modulator based on a low-frequency signal, comprising the following steps:

[0041] S101. Build a test platform.

[0042] Specifically, when the test platform is constructed, the required test instruments are configured to consist of a laser, a signal generator, a power divider, a photodetector, an oscilloscope, and an electro-optic modulator of the lithium niobate to be tested. The laser, the electro-optic modulator, the photodetector, and the oscilloscope are connected in sequence, and the power divider is respectively connected to the electro-optic modulator, the oscilloscope, and the signal generator.

[0043] S102, splitting the sawtooth wave signal into two paths through a power divider, and inputting the two paths into a thin film lithium niobate electro-optic modulator and an oscilloscope respectively.

[0044] Specifically, first power on the chip of the electro-optic modulator of the thin-film lithium niobate to be tested and other test instruments and equipment, wait for 5 minutes to make it in a stable working state, set the signal generator to output a sawtooth wave signal of more than 5Vpp, and the signal generator loads the output sawtooth wave signal on the radio frequency end of the thin-film lithium niobate modulator. The sawtooth wave signal is divided into two paths AB by the power divider and respectively input into the electro-optic modulator of the lithium niobate to be tested and directly input into the oscilloscope. At the same time, adjust the oscilloscope to the automatic sampling mode, and the output light of the electro-optic modulator is also input into the oscilloscope after being photoelectrically converted by the photoelectric detector. The output signal waveform of the electro-optic modulator changes with the sawtooth wave signal voltage. At this time, the sawtooth wave signal output by the signal generator corresponds to the waveform output by the electro-optic modulator as shown in FIG. Figure 2 shown.

[0045] S103, adjusting the input wave amplitude and bias so that the modulator output waveform presents a waveform in the shape of a sine wave with one cycle at the rising edge of the sawtooth wave.

[0046] Specifically, the waveform image at the rising edge of the sawtooth wave is amplified by the oscilloscope, the amplitude and offset of the output end of the signal generator are adjusted, and the output signal waveform of the electro-optic modulator at the corresponding position of the rising edge of the sawtooth wave is observed at the same time, until the output signal curve of the electro-optic modulator is observed on the oscilloscope to present a single-cycle sine wave signal. At this time, a cut-off sine wave signal of one cycle can be observed at this position, and its shape is as follows: Figure 3 As shown, this means that the input signal is now fully modulated by the thin film lithium niobate optoelectronic modulator.

[0047] S104, record the modulator output waveform peak time T 2 and trough moment T 1 The voltage value V(T 2 ) and V(T 1 ), calculate the voltage difference dV.

[0048] Specifically, two curves at this time are selected, and the horizontal coordinate corresponding to the valley in the signal output by the electro-optic modulator is read by the oscilloscope cursor, and the point is recorded as the time T 1 Similarly, the horizontal coordinate corresponding to the peak of the recorded signal is the time T 2 , then, the peak time T 2 and trough moment T 1 Corresponding to the voltage value V(T 2 ) and V(T 1 ), at this time, record the peak time T 2 and trough moment T 1The voltage value V(T 2 ) and V(T 1 ), and record the original signal emitted by the signal generator and the modulated signal detected by the detector, compare the two curves, and record the voltage difference dV required for the output light intensity of the electro-optic modulator to go from maximum to minimum:

[0049] dV=V(T 2 )-V(T 1 ) (1)

[0050] S105, calibrating the calculation result using the power divider to calculate the half-wave voltage V of the modulator π .

[0051] Specifically, reconnect the test instrument, remove the laser, the electro-optic modulator and the photodetector, and only keep the signal generator, the oscilloscope and the power divider, and input the two signals AB at the output end of the power divider into the oscilloscope at the same time, such as Figure 4 As shown in the figure, the sawtooth wave amplitudes at both ends of A and B are V A and V B The measured voltage difference dv is calibrated, and the modulator half-wave voltage V π for:

[0052] Vπ=k(V(T 2 )-V(T 1 )) (2)

[0053] Wherein, the calibration steps of the power divider are:

[0054] The test instruments only include signal generator, oscilloscope and power divider;

[0055] The signal generator is divided into two paths by a power divider, and the two paths are input to the two ports of the oscilloscope respectively, and then the sawtooth wave with the same parameters when testing the thin film lithium niobate electro-optic modulator is input to the two ports of the oscilloscope;

[0056] Calculating a ratio k of sawtooth wave amplitudes of two ports of the oscilloscope;

[0057] The modulator half-wave voltage V is calculated by formula (2): π .

[0058] S106: Calculate the frequency corresponding to the half-wave voltage.

[0059] Specifically, in the method for calculating the frequency corresponding to the half-wave voltage, the period T of the single sinusoidal wave signal is:

[0060] T=2|T 2 -T1 | (3)

[0061] The half-wave voltage V π The corresponding frequency f satisfies:

[0062]

[0063] Where f represents the high frequency corresponding to the measured modulator half-wave voltage, T 1 Indicates the trough moment of the modulator output waveform, T 2 Indicates the peak moment of the modulator output waveform.

[0064] When using a test method of this embodiment for measuring the high-frequency lower half-wave voltage of a thin-film lithium niobate modulator based on a low-frequency signal, the instruments required for the test include: a laser, an oscilloscope, a power divider, a photoelectric detector, and a low-frequency signal generator.

[0065] This embodiment tests a low half-wave voltage thin-film lithium niobate electro-optic modulator. This embodiment builds a test platform according to the above steps and tests the half-wave voltage of the thin-film lithium niobate modulator to be tested. The signal input by the signal generator is a 500Hz sawtooth wave, and the test results displayed by the oscilloscope are as follows: Figure 4 and Figure 5 As shown, Figure 4 It is a waveform diagram of the signal source input signal and the output signal of the thin film lithium niobate electro-optic modulator according to an embodiment of the present invention. Figure 5 This is the waveform diagram of the input sawtooth signal and the amplified output signal of the thin-film lithium niobate electro-optic modulator when the input signal is fully modulated. Figure 5 It can be seen that the peak time T 2 =1.34us and trough time T 1 =-1.74us, from formula (3) we can get the frequency f = 162.33kHz; the voltage V(T 2 )=-1.03V,V(T 1 )=583.33mV, voltage difference dV=1.61V. After calibrating the voltage difference result, we can get the output V of the power divider at both ends. A / V B =1:1, the half-wave voltage V can be obtained π =1.61 V. In summary, the half-wave voltage of the thin-film lithium niobate electro-optic modulator measured at 162.33 kHz is 1.61 V using the method of the present invention.

[0066] In order to verify the accuracy of this method, the half-wave voltage of the same thin-film lithium niobate electro-optic modulator was tested using the commonly used method of triangle wave measurement. Figure 1Similarly, change the input signal of the signal generator to a 162.33kHz triangle wave signal. By adjusting the amplitude and offset of the input triangle wave, the modulator outputs multiple discontinuous cut sine wave signals, such as Figure 6 As shown. Take the peak and trough of the signal in one cycle, and their corresponding moments are T 3 = -940.00ns and T 4 =860.00ns, voltage V(T 3 )=-958.33mV,V(T 4 )=652.78mV, then from the test results we can know that the half-wave voltage V of the modulator at 162.33kHz π =1.61 V. By comparison, the results of the two test methods are the same, which verifies the accuracy of the proposed method, which can accurately measure the half-wave voltage of the thin-film lithium niobate electro-optic modulator at high frequencies through low-frequency signals.

[0067] This method has important guiding significance for the testing of thin film lithium niobate electro-optic modulators.

[0068] What is disclosed above is only one or more preferred embodiments of the present application, and cannot be used to limit the scope of rights of the present application. Ordinary technicians in this field can understand that all or part of the processes of implementing the above embodiments and equivalent changes made according to the claims of the present application are still within the scope covered by the present application.

Claims

1. A test method for measuring the high-frequency lower half-wave voltage of a thin-film lithium niobate modulator based on a low-frequency signal, characterized in that: The following steps are involved: Build a test platform; The sawtooth wave signal is divided into two paths through a power divider and input into a thin-film lithium niobate electro-optic modulator and an oscilloscope respectively; Adjust the input wave amplitude and offset so that the modulator output waveform presents a periodic sine wave shape at the rising edge of the sawtooth wave; Record the peak time T2 and the trough time T1 of the modulator output waveform, which correspond to the voltage values ​​V(T2) and V(T1) output by the signal source, respectively, and calculate the voltage difference dV; The power divider is used to calibrate the calculation result, and the half-wave voltage V of the modulator is calculated. π ; The frequency corresponding to the half-wave voltage is calculated.

2. The test method for measuring the high-frequency lower half-wave voltage of a thin-film lithium niobate modulator based on a low-frequency signal as claimed in claim 1, characterized in that: When the test platform is constructed, the required test instruments are composed of a laser, a signal generator, a power divider, a photoelectric detector, an oscilloscope, and an electro-optic modulator of the lithium niobate to be tested.

3. The test method for measuring the high-frequency lower half-wave voltage of a thin-film lithium niobate modulator based on a low-frequency signal as claimed in claim 2, characterized in that: The laser, the electro-optic modulator, the photodetector and the oscilloscope are connected in sequence, and the power divider is connected to the electro-optic modulator, the oscilloscope and the signal generator respectively.

4. The test method for measuring the high-frequency lower half-wave voltage of a thin-film lithium niobate modulator based on a low-frequency signal as claimed in claim 3, characterized in that: When the input sawtooth wave signal is fully modulated by the modulator, the modulator output waveform presents a periodic sine wave waveform at the rising edge of the sawtooth wave, and at this time it satisfies: dV=V(T2)-V(T1) (1) Vπ=k(V(T2)-V(T1)) (2) Among them, V π represents the half-wave voltage of the modulator to be tested, T1 represents the trough moment of the modulator output waveform, T2 represents the peak moment of the modulator output waveform, and the sawtooth voltage values ​​corresponding to the two moments are V(T1) and V(T2), respectively. k represents the output waveform voltage amplitude V at both ends of the power divider after calibration. A and V B The proportionality factor.

5. The test method for measuring the high-frequency lower half-wave voltage of a thin-film lithium niobate modulator based on a low-frequency signal as claimed in claim 4, characterized in that: The calibration steps of the power divider are: The test instruments only include signal generator, oscilloscope and power divider; The signal generator is divided into two paths by a power divider, and the two paths are input to the two ports of the oscilloscope respectively, and then the sawtooth wave with the same parameters when testing the thin film lithium niobate electro-optic modulator is input to the two ports of the oscilloscope; Calculating a ratio k of sawtooth wave amplitudes of two ports of the oscilloscope; The modulator half-wave voltage V is calculated by formula (2): π .

6. The test method for measuring the high-frequency lower half-wave voltage of a thin-film lithium niobate modulator based on a low-frequency signal as claimed in claim 1, characterized in that: In the calculation method of the frequency corresponding to the half-wave voltage, the period T of a single sinusoidal wave signal is: T=2|T2-T1| (3) The half-wave voltage V π The corresponding frequency f satisfies: Among them, f represents the high frequency corresponding to the measured half-wave voltage of the modulator, T1 represents the trough moment of the modulator output waveform, and T2 represents the peak moment of the modulator output waveform.

7. The test method for measuring the high-frequency lower half-wave voltage of a thin-film lithium niobate modulator based on a low-frequency signal as claimed in claim 1, characterized in that: The sawtooth wave signal is output by the signal generator, and the sawtooth wave signal is a 500 Hz sawtooth wave signal.

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