Half-wave voltage testing method and system suitable for broadband intensity modulator

Abstract

The invention discloses an intensity modulator half-wave voltage testing method and system suitable for a wide frequency band. The method comprises the steps that an intensity modulator to be tested is connected with a continuous light source, an optical power meter, a voltage source and a signal generator; the voltage source carries out direct current bias voltage scanning on the intensity modulator to be measured, the output optical power measured by the optical power meter is recorded, and the bias voltage VB corresponding to the minimum point of the output optical power is equal to V0; the signal generator generates a sinusoidal signal and injects the sinusoidal signal into the to-be-measured intensity modulator; the voltage source performs direct current bias voltage scanning on the intensity modulator to be measured, records the output average optical power measured by the optical power meter, and judges that the output average optical power is a maximum value / minimum value when VB is equal to V0; changing the peak-to-peak value of the sinusoidal signal, and measuring the peak-to-peak value VPP-T of the sinusoidal signal when the output average optical power of the intensity modulator to be measured is converted from the minimum value to the maximum value when VB is equal to V0; and calculating the half-wave voltage of the to-be-measured intensity modulator according to the peak-to-peak value VPP-T of the sinusoidal signal. The half-wave voltage testing device is suitable for half-wave voltage testing of all frequencies within the bandwidth range of the intensity modulator.

Description

Technical Field

[0001] The present invention relates to a method and system for testing a half-wave voltage of an intensity modulator, and in particular to a method and system for testing a half-wave voltage of an intensity modulator applicable to a wide frequency band. Background Art

[0002] An optical intensity modulator (OIM) is an optoelectronic device that modulates the intensity of an optical carrier wave using acousto-optic, electro-optic, or thermo-optic effects. Mach-Zehnder intensity modulators based on electro-optic crystals such as lithium niobate are the most widely used. These devices have important applications in fiber-optic communications, optical sensing, quantum optics, and other fields. Half-wave voltage is a key performance metric for modulators, determining their modulation efficiency. The smaller the half-wave voltage, the higher the modulation efficiency. Determining the magnitude of the half-wave voltage is crucial. Performance evaluation is essential for both manufacturers and customers. Furthermore, when designing a system, knowing the specific half-wave voltage is crucial for correctly configuring the driver circuit, ensuring optimal modulator operation, and avoiding nonlinear distortion.

[0003] Existing methods for testing the half-wave voltage of an intensity modulator primarily include the triangle wave method and the spectral method. At a relatively low frequency, the DC bias is adjusted to operate the intensity modulator at its Q point. A triangle wave is then injected into the intensity modulator's RF modulation port for modulation. The output optical signal undergoes photoelectric conversion and is then received by an oscilloscope. The half-wave voltage of the intensity modulator under test can be derived from the time difference between adjacent peaks and valleys on the oscilloscope, the frequency of the triangle wave signal, and the peak-to-peak value of the triangle wave. This method offers the advantage of high accuracy, but is generally only used to test the half-wave voltage at relatively low frequencies. Testing high-frequency half-wave voltages requires a high-speed oscilloscope and AWG, which are expensive and difficult to implement in practice. The spectral method modulates the intensity modulator with a sinusoidal RF signal and directly observes the modulated optical signal output by the intensity modulator using a spectrometer. The RF signal power is continuously increased until the optical carrier is completely suppressed, at which point the peak-to-peak value of the RF signal is 2.44 times the half-wave voltage. This method can be used to test the high-frequency half-wave voltage of an intensity modulator. However, it requires very high RF signal power, with the peak-to-peak value needing to be 2.44 times the half-wave voltage. It also requires a high resolution spectrometer. Furthermore, for low-frequency signals, it is difficult to clearly observe the carrier and sidebands on a spectrometer, so only high-frequency half-wave voltage can be tested.

[0004] In view of the technical shortcomings of the above testing methods, it is necessary to develop better testing methods. Summary of the Invention

[0005] Purpose of the invention: The purpose of the present invention is to provide a half-wave voltage testing method and system for an intensity modulator applicable to a wide frequency band, which can measure the half-wave voltage of all frequencies within the bandwidth range of the intensity modulator and has a wide range of applications.

[0006] Technical solution: The present invention comprises the following steps:

[0007] Step S1, connecting the intensity modulator to be measured with a continuous light source, an optical power meter, a voltage source and a signal generator;

[0008] Step S2: Control the voltage source to scan the DC bias voltage of the intensity modulator to be measured, and record the output optical power measured by the optical power meter, and the bias voltage V corresponding to the minimum output optical power point. B =V0;

[0009] Step S3, control the signal generator to generate a peak-to-peak value of V PP-1 , a sinusoidal signal with a frequency of the frequency to be measured f is injected into the intensity modulator to be measured;

[0010] Step S4, control the voltage source again to scan the DC bias voltage of the intensity modulator to be measured, and record the output optical power measured by the optical power meter to determine V B = V0 when the average optical power output is the maximum or minimum point;

[0011] Step S5, change the peak-to-peak value of the sinusoidal signal to measure the intensity modulator V B = V0 when the output optical power changes from the minimum value to the maximum value of the sinusoidal signal peak-to-peak value V PP-T ;

[0012] Step S6: According to the peak-to-peak value V of the sinusoidal signal PP-T Calculate the half-wave voltage of the intensity modulator under test.

[0013] The half-wave voltage V of the intensity modulator to be measured π =V π =V PP-T 1.53.

[0014] In step S4, if V B = V0 when the average optical power output is at its minimum. Then increase the peak-to-peak value of the RF signal. If V B =V0, the output average optical power reaches its maximum value, which reduces the peak-to-peak value of the RF signal.

[0015] In step S4, when 0<V PP <1.53V π When the average optical power output by the intensity modulator is V B = V0 has a minimum value; when 1.53V π <V PP <3.51V π When the average optical power output by the intensity modulator is V B =V0 has a maximum value, where V PPis the peak-to-peak value.

[0016] A system for testing a half-wave voltage of a wide-band intensity modulator includes a continuous light source, an intensity modulator, a voltage source, a signal generator, and an optical power meter. The intensity modulator is connected to the continuous light source, the optical power meter, the voltage source, and the signal generator.

[0017] The signal generator is a sinusoidal signal generator, and the required sinusoidal signal peak-to-peak value is 1.53 times the half-wave voltage of the intensity modulator to be measured.

[0018] The light input port of the intensity modulator is connected to a continuous light source, the light output port is connected to an optical power meter, the DC bias electrode is connected to a voltage source, and the RF modulation port is connected to a signal generator.

[0019] The intensity modulator is one of a Mach-Zehnder electro-optical bias intensity modulator and a thermo-optical bias intensity modulator.

[0020] The optical power meter is a low-bandwidth instrument, and the measurement result is the average optical power output by the intensity modulator to be measured.

[0021] The voltage source is a DC adjustable voltage source.

[0022] Beneficial effects: The present invention can measure the half-wave voltage of all frequencies within the bandwidth of the intensity modulator with an accuracy of up to 0.01V, and has a wide range of applications. In addition, the instruments and equipment used in the intensity modulator half-wave voltage test method disclosed in the present invention are all commonly used equipment, and do not require expensive instruments and equipment such as high-speed oscilloscopes, high-frequency AWGs, and high-resolution spectrometers. The cost is low, and the power requirement for the signal generator is only that the peak-to-peak value of the generated sinusoidal signal reaches the half-wave voltage V of the intensity modulator to be measured. π It is 1.53 times that of the original data, which is suitable for scenarios such as manufacturer production testing. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a system block diagram of the present invention;

[0024] Figure 2 A curve showing the variation of the transfer function of the electro-optical intensity modulator with the bias voltage and a schematic diagram of the operating point disclosed in an embodiment of the present invention;

[0025] Figure 3 Schematic diagram of the first type of 0th-order Bessel function and its first two positive zeros disclosed in an embodiment of the present invention;

[0026] Figure 4 Different sinusoidal signals V disclosed in the embodiments of the present invention PP The curve of the average output optical power of the Mach-Zehnder electro-optical bias intensity modulator as a function of the bias voltage is shown below;

[0027] Figure 5 This is a flow chart of a method and system for testing half-wave voltage of an intensity modulator applicable to a wide frequency band disclosed in an embodiment of the present invention;

[0028] Figure 6 This is a comparison chart of the intensity modulator half-wave voltage obtained by testing the half-wave voltage testing method disclosed in an embodiment of the present invention and the data provided by the manufacturer. DETAILED DESCRIPTION

[0029] The present invention will be further described below with reference to the accompanying drawings.

[0030] Example 1

[0031] like Figure 5 As shown, the half-wave voltage test method of the intensity modulator applicable to a wide frequency band of the present invention can realize the half-wave voltage test of all frequencies within the bandwidth range of the intensity modulator, and specifically includes the following steps:

[0032] Step S1, press Figure 1 As shown, a test link is constructed. Connect the optical input port of the intensity modulator (2) under test to a continuous light source (CLS) 1, its optical output port to an optical power meter (5), a DC bias electrode to a voltage source (3), and its RF modulation port to a signal generator (4). Turn on the CLS 1. The optical signal output by CLS 1 enters the optical input port of the intensity modulator (2) as a carrier. The output signal is received by the optical power meter (5), which measures its average optical power in real time. The sampling frequency of the optical power meter (5) should be less than the frequency of the sinusoidal signal. The voltage source (3) provides a DC bias voltage to the intensity modulator (2), shifting its operating point. The sinusoidal signal generated by the signal generator (4) is injected into the RF modulation port of the intensity modulator (2), modulating the optical signal.

[0033] Step S2: Control the voltage source 3 to scan the DC bias electrode of the intensity modulator 2. At the same time, use the optical power meter 5 to measure the output optical power and record it, and obtain the curve of the output optical power of the intensity modulator to be measured versus the DC bias voltage. B The bias voltage corresponding to the point where the output optical power is the smallest is V B =V0;

[0034] Step S3, turn on the signal generator 4, generate a frequency of f and a peak-to-peak value of V PP-1 A sinusoidal signal is injected into the RF modulation port of the intensity modulator 2 to be measured;

[0035] Step S4, control the voltage source 3 again to scan the voltage of the DC bias electrode of the intensity modulator 2 and record the output average optical power to determine V B = V0, the output average optical power is the minimum or maximum point. If V B= V0 when the average optical power output is at its minimum. Then increase the peak-to-peak value of the RF signal. If V B =V0, the output average optical power reaches its maximum value, which reduces the peak-to-peak value of the RF signal.

[0036] Step S5, repeat step S4 until the V B = V0, the peak-to-peak value of the sinusoidal signal V when the average optical power output by the intensity modulator to be measured changes from the minimum value to the maximum value PP-T ;

[0037] Step S6: According to the peak-to-peak value of the sinusoidal signal V PP-T Calculate the half-wave voltage of the intensity modulator 2 to be tested at frequency f, the calculation formula is V π =V PP-T 1.53.

[0038] The intensity modulator of this embodiment uses a Mach-Zehnder electro-optical bias intensity modulator, and its transfer function can be expressed as:

[0039]

[0040] Among them, V B Indicates the DC bias voltage, V π represents the intensity modulator half-wave voltage, v RF represents a sinusoidal modulated signal, Indicates the initial phase. For the convenience of calculation, it is assumed that the initial phase is 0. When no sinusoidal signal is applied, the curve and operating point of the transfer function are shown as follows: Figure 2 shown.

[0041] When the RF modulation port of the intensity modulator 2 is injected with an amplitude of V RF , when the angular frequency is a sinusoidal signal of ω, the transfer function of the intensity modulator can be expressed as:

[0042]

[0043] Formula (2) can be expressed as:

[0044]

[0045] Among them, J n (x) represents the nth-order Bessel function of the first kind.

[0046] In this embodiment, the optical power meter 5 used is a low-bandwidth instrument and cannot detect high-frequency modulated signals. Therefore, the optical power meter 5 receives the average optical power, which does not contain high-frequency components. Therefore, formula (3) can be simplified as follows:

[0047]

[0048] From formula (4), it can be seen that the curve of the transfer function of the intensity modulator 2 changing with the bias voltage is related to the amplitude of the injected sinusoidal signal. The curve of the first type 0th order Bessel function J0(x) is as follows: Figure 3 As shown, the first two zero points greater than 0 are 2.405 and 5.520 respectively. Therefore, the amplitude of the sinusoidal signal V RF The size of determines the change trend of the intensity modulator 2 transfer function. When 0<πV RF / V π <2.405, that is, 0<V RF <0.7655V π When the average optical power output by intensity modulator 2 is V B =V π It has a minimum value at 2.405<πV RF / V π <5.520, i.e. 0.7655V π <V RF <1.757V π When the average optical power output by intensity modulator 2 is V B =V π Has a maximum value. Figure 4 Shows V PP =2V RF =V π / 2,V π , 3V π / 2, 2V π Schematic diagram of the average output optical power of the intensity modulator 2 changing with the DC bias voltage.

[0049] In the actual test, the initial phase of the intensity modulator 2 is not 0 and is random. When no sinusoidal signal is applied, the bias voltage corresponding to the point where the output optical power is the smallest is V B =V0, peak-to-peak value V PP To express the amplitude of the sinusoidal signal, the above conclusion can be rewritten as: when 0<V PP <1.53V π When the average optical power output by intensity modulator 2 is V B = V0 has a minimum value; when 1.53V π <V PP <3.51V π When the average optical power output by intensity modulator 2 is V B = V0 has a maximum value. Therefore, the intensity modulator 2 can output the optical power at V B = V0 when the sinusoidal signal V changes from the minimum value to the maximum value PP To determine the half-wave voltage of the intensity modulator 2.

[0050] Assume that the half-wave voltage of intensity modulator 2 is 3V to 3.5V and the required accuracy is 0.01V. Let V PP-1 is 4V, this DC bias sweep V B = V0 when the output optical power has the minimum value, V PP-2 is 6V, this DC bias sweep V B = V0 when the output optical power reaches its maximum value. PP-T In the range of 4V to 6V, the peak-to-peak value of the sinusoidal RF signal is determined by the dichotomy method. PP-T The possible range is:

[0051] L=2*0.5 n-2 =0.5 n-3 ,n>2 (5)

[0052] To achieve an accuracy of 0.01V, L < 0.01 must be satisfied, i.e.

[0053] 0.5 n-3 <0.01 (6)

[0054] It can be solved that n>9.64, that is, a maximum of 10 repeated operations are required to obtain the half-wave voltage of the intensity modulator 2, and the error is less than 0.01 V. In the automated test of actual engineering production, this is a very fast process.

[0055] Through the above steps, the test of the half-wave voltage of the intensity modulator is realized. This method does not require expensive instruments such as high-speed oscilloscopes. The required equipment are all conventional instruments. The power requirement for the signal generator is only that the peak-to-peak value of the sinusoidal signal reaches 1.53 times the half-wave voltage of the intensity modulator to be tested. The half-wave voltage of all frequencies within the bandwidth range of the intensity modulator can be measured, which is suitable for scenarios such as industrial production testing. Figure 6 The half-wave voltage data of the intensity modulator tested by the method described in this embodiment is shown. As can be seen from the figure, the half-wave voltage tested by the method described in the present invention is consistent with the half-wave voltage data provided by the manufacturer.

[0056] Example 2

[0057] like Figure 1 As shown, the half-wave voltage test system of the intensity modulator suitable for a wide frequency band of this embodiment includes a continuous light source 1, an intensity modulator 2, a voltage source 3, a signal generator 4 and an optical power meter 5; the optical input port of the intensity modulator 2 is connected to the continuous light source 1, the optical output port is connected to the optical power meter 5, the DC bias electrode is connected to the voltage source 3, and the RF modulation port is connected to the signal generator 4.

[0058] Signal generator 4 is a sinusoidal signal generator. The required sinusoidal signal peak-to-peak value should reach 1.53 times the half-wave voltage of the intensity modulator to be measured. Continuous light source 1, voltage source 3, and optical power meter 5 are all commonly used devices. Voltage source 3 is a DC adjustable voltage source. Intensity modulator 2 is either a Mach-Zehnder electro-optical biased intensity modulator or a thermo-optical biased intensity modulator.

[0059] The testing method of the half-wave voltage testing system for an intensity modulator applicable to a wide frequency band in this embodiment is similar to that in the first embodiment and will not be described in detail.

Claims

1. A method for testing half-wave voltage of an intensity modulator applicable to a wide frequency band, characterized in that: The following steps are involved: Step S1, connecting the intensity modulator to be measured with a continuous light source, an optical power meter, a voltage source and a signal generator; Step S2: Control the voltage source to scan the DC bias voltage of the intensity modulator to be measured, and record the output optical power measured by the optical power meter, and the bias voltage V corresponding to the minimum output optical power point. B =V0; Step S3, control the signal generator to generate a peak-to-peak value of V PP-1 , a sinusoidal signal with a frequency of the frequency to be measured f is injected into the intensity modulator to be measured; Step S4, control the voltage source again to scan the DC bias voltage of the intensity modulator to be measured, and record the output average optical power measured by the optical power meter to determine V B = V0 when the average optical power output is the maximum or minimum point; Step S5, change the peak-to-peak value of the sinusoidal signal to measure the intensity modulator V B = V0 when the output average optical power changes from the minimum value to the maximum value of the sinusoidal signal peak-to-peak value V PP-T ; Step S6: According to the peak-to-peak value V of the sinusoidal signal PP-T Calculate the half-wave voltage of the intensity modulator under test.

2. The method for testing half-wave voltage of an intensity modulator applicable to a wide frequency band according to claim 1, characterized in that: The half-wave voltage V of the intensity modulator to be measured π =V π =V PP-T / 1.

53.

3. The method for testing half-wave voltage of an intensity modulator applicable to a wide frequency band according to claim 1, characterized in that: In step S4, if V B = V0 when the output average optical power is the minimum point, then increase the peak-to-peak value of the sinusoidal signal. If V B =V0, the output average optical power reaches its maximum value, which reduces the peak-to-peak value of the sinusoidal signal.

4. The method for testing half-wave voltage of an intensity modulator applicable to a wide frequency band according to claim 3, characterized in that: In step S4, when 0<V PP <1.53V π When the average optical power output by the intensity modulator is V B = V0 has a minimum value; when 1.53V π <V PP <3.51V π When the average optical power output by the intensity modulator is V B =V0 has a maximum value, where V PP is the peak-to-peak value of the sinusoidal signal.

5. A system applicable to the wide-band intensity modulator half-wave voltage testing method according to any one of claims 1 to 4, characterized in that: include: A continuous light source, an intensity modulator, a voltage source, a signal generator and an optical power meter are provided, wherein the intensity modulator is connected with the continuous light source, the optical power meter, the voltage source and the signal generator.

6. The half-wave voltage test system for an intensity modulator applicable to a wide frequency band according to claim 5, characterized in that: The signal generator is a sinusoidal signal generator, and the required sinusoidal signal peak-to-peak value is 1.53 times the half-wave voltage of the intensity modulator to be measured.

7. The half-wave voltage test system for an intensity modulator applicable to a wide frequency band according to claim 5, characterized in that: The light input port of the intensity modulator is connected to a continuous light source, the light output port is connected to an optical power meter, the DC bias electrode is connected to a voltage source, and the RF modulation port is connected to a signal generator.

8. The half-wave voltage test system for an intensity modulator applicable to a wide frequency band according to claim 7, characterized in that: The intensity modulator is one of a Mach-Zehnder electro-optical bias intensity modulator and a thermo-optical bias intensity modulator.

9. The half-wave voltage test system for an intensity modulator applicable to a wide frequency band according to claim 5, characterized in that: The optical power meter is a low-bandwidth instrument, and the measurement result is the average optical power output by the intensity modulator to be measured.

10. The half-wave voltage test system for an intensity modulator applicable to a wide frequency band according to claim 5, characterized in that: The voltage source is a DC adjustable voltage source.

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