A Mach-Zehnder interference structure-based electro-optic phase modulator half-wave voltage test system

Abstract

The utility model belongs to photoelectric device performance test field discloses a kind of electro-optic phase modulator half-wave voltage test system based on Mach-Zehnder interference structure, the system includes: laser light source, optical beam splitter, phase modulator to be measured, optical beam combiner, optical detector, oscilloscope;Wherein, another road connection between optical beam splitter and optical beam combiner still includes adjustable optical attenuator and adjustable optical delay line, adjustable optical attenuator, adjustable optical delay line and phase modulator to be measured constitute parallel structure, respectively located in Mach-Zehnder interference structure's interference arm X road and Y road;Signal generator and phase modulator to be measured adopt standard coaxial cable and form electrical connection, and carry out voltage drive to phase modulator to be measured by the triangular wave signal generated;Optical detector and oscilloscope are connected by cable between them.The utility model is related to and the phase modulator half-wave voltage test system has the advantages such as simple structure, accurate measurement, weak environmental disturbance factor.

Description

Technical Field

[0001] This utility model belongs to the field of optoelectronic device performance testing, specifically relating to a half-wave voltage testing system for an electro-optic phase modulator based on a Mach-Zehnder interference structure. Background Technology

[0002] The half-wave voltage of an electro-optic phase modulator is one of the key parameters of the device, indicating the efficiency of the applied radio frequency signal in modulating the optical phase during operation. For intensity modulators, the half-wave voltage can be tested by directly detecting the amplitude change of the output optical signal, making system setup relatively simple. However, the phase signal output by a phase modulator is difficult to detect directly, and measuring the half-wave voltage often requires a more complex system and components. Common testing methods include sideband analysis, fiber interferometry, and optical phased array methods. These existing measurement techniques avoid directly building a fiber MZM interferometer structure because building an MZM interferometer structure through fiber will introduce centimeter-level arm length differences. Tiny random disturbances such as environmental temperature changes, stress changes, and mechanical perturbations, superimposed on the centimeter-level optical path difference, will cause very severe phase noise, almost completely masking the phase signal generated by modulation. Summary of the Invention

[0003] To address the problems existing in the prior art, this utility model provides a half-wave voltage testing system for electro-optic phase modulators based on a Mach-Zehnder interferometer structure. By constructing a Mach-Zehnder optical interferometer structure, the phase signal to be measured is converted into an intensity signal and then converted into an electrical signal by a photodetector, thereby realizing the measurement of the half-wave voltage of the electro-optic phase modulator.

[0004] To achieve the above objectives, this utility model provides the following solution:

[0005] A half-wave voltage testing system for an electro-optic phase modulator based on a Mach-Zehnder interferometer structure, the system comprising: a laser source, an optical beam splitter, a phase modulator under test, an optical beam combiner, a photodetector, and an oscilloscope;

[0006] The laser source and the optical beam splitter are connected by optical fiber.

[0007] Another connection between the optical beam splitter and the optical beam combiner includes an adjustable optical attenuator and an adjustable optical delay line. The adjustable optical attenuator, the adjustable optical delay line and the phase modulator under test form a parallel structure, located in the X and Y paths of the interferometer arms of the Mach-Zehnder interferometer structure, respectively.

[0008] The signal generator and the phase modulator under test are electrically connected by a standard coaxial cable, and the generated triangular wave signal drives the phase modulator under test with voltage.

[0009] The optical combiner and the photodetector are connected via optical fiber;

[0010] The photodetector and the oscilloscope are connected by a cable.

[0011] Preferably, the laser source outputs light with a wavelength of 1310nm, 1550nm, or other wavelengths in the communication band to be tested. The optical signal is transmitted through a standard polarization-maintaining single-mode fiber, and the output optical interface is an APC / FC connector. The fiber-to-fiber connection is made with the optical beam splitter through a flange.

[0012] Preferably, the optical beam splitter is a 1*2 port device, wherein the input port transmits optical signals through standard polarization-maintaining single-mode fiber, and the input optical interface is an APC / FC connector, which is connected to the output fiber of the laser source via a flange in a fiber-to-fiber manner; the two output ports of the optical beam splitter transmit optical signals through standard polarization-maintaining single-mode fiber, and the input optical interface is an APC / FC connector, which is connected to the single-mode fibers of the APC / FC connectors of the X and Y paths respectively via flanges.

[0013] Preferably, the phase modulator under test in the X-channel is a packaged device with a housing. The housing structure has an RF connector, a DC PIN interface, an input optical port, and an output optical port. The input optical port is connected to the polarization-maintaining beam splitter via polarization-maintaining fiber, an APC / FC connector, and a flange, using a standard fiber-to-fiber connection. The output optical port is connected to the optical combiner via polarization-maintaining fiber, an APC / FC connector, and a flange, also using a standard fiber-to-fiber connection. The RF connector is a 2.92mm, 1.85mm, or GPPO type female RF interface, connected to the output port of the signal generator via a coaxial cable. The coaxial cable is connected to the phase modulator under test via a 2.92mm, 1.85mm, or GPPO type male RF interface, with the same aperture as the RF connector of the modulator under test.

[0014] Preferably, the Y-channel tunable optical attenuator is a packaged device with an interface including a power line, an input optical port, and an output optical port. Both the input and output optical ports are polarization-maintaining optical fibers and APC / FC connectors. The input optical port connector is connected to the optical fiber connector of the optical beam splitter via a flange, and the output optical port is connected to the input optical port of the adjustable optical delay line via a flange. The adjustable optical delay line is also a packaged device with an interface including a power line, an input optical port, and an output optical port. All optical ports are polarization-maintaining optical fibers and APC / FC connectors. Its output optical port is connected to the input optical port of the optical combiner via a flange for fiber-to-fiber connection.

[0015] Preferably, the optical beam combiner and the optical beam splitter have the same structure, both being 1*2 port devices. The difference is that port 1 of the optical beam splitter is an input port, and ports 2 and 3 are output ports, while port 1 of the optical beam combiner is an output port, and ports 2 and 3 are input ports. The two input ports 2 and 3 of the optical beam combiner are connected to the polarization-maintaining fiber ports of the X and Y paths, respectively. The connectors are all APC / FC connectors, and fiber-to-fiber connections are made through flanges. The output port 1 of the optical beam combiner is connected to a photodetector.

[0016] Preferably, the photodetector is a packaged device with an interface including a power line, an RF output port, and an input optical port. The input optical port of the photodetector is connected to the output optical port of the optical combiner. The connection method is to directly insert the APC / FC connector of the polarization-maintaining fiber output of the optical combiner into the input optical port of the photodetector. The RF output port of the photodetector is connected to the input port of the oscilloscope through a 2.92mm coaxial cable.

[0017] Preferably, the oscilloscope includes 2-4 RF input ports.

[0018] Compared with the prior art, the beneficial effects of this utility model are as follows:

[0019] This invention constructs an optical fiber MZM interferometer structure to measure the half-wave voltage of a phase modulator. It introduces an adjustable optical delay line and an adjustable optical attenuator placed on the reference arm of the MZM interferometer structure to significantly suppress the influence of ambient wavebands on the stability of the measurement system, thereby achieving accurate testing of the half-wave voltage of the phase modulator.

[0020] This invention has the advantages of simple structure, accurate measurement, and weak susceptibility to environmental disturbances. Attached Figure Description

[0021] To more clearly illustrate the technical solution of this utility model, the drawings used in the embodiments are briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram of a half-wave voltage testing system for an electro-optic phase modulator based on a Mach-Zehnder interferometer structure, according to an embodiment of this utility model. Detailed Implementation

[0023] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.

[0024] To make the above-mentioned objectives, features and advantages of this utility model more apparent and understandable, the utility model will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0025] Example 1

[0026] like Figure 1 As shown, this utility model provides a half-wave voltage testing system for an electro-optic phase modulator based on a Mach-Zehnder interferometer structure. The system includes: a laser source, an optical beam splitter, a phase modulator under test, an optical beam combiner, a photodetector, and an oscilloscope.

[0027] The laser source and the optical beam splitter are connected by optical fiber.

[0028] Another connection between the optical beam splitter and the optical beam combiner includes an adjustable optical attenuator and an adjustable optical delay line. The adjustable optical attenuator, the adjustable optical delay line and the phase modulator under test form a parallel structure, located in the X and Y paths of the interferometer arms of the Mach-Zehnder interferometer structure, respectively.

[0029] The signal generator and the phase modulator under test are electrically connected by a standard coaxial cable, and the generated triangular wave signal drives the phase modulator under test with voltage.

[0030] The optical combiner and the photodetector are connected via optical fiber;

[0031] The photodetector and the oscilloscope are connected by a cable.

[0032] In this embodiment, the laser source outputs light with a wavelength of 1310nm, 1550nm, or other wavelengths in the communication band to be tested. The optical signal is transmitted through a standard polarization-maintaining single-mode fiber, and the output optical interface is an APC / FC connector. The fiber-to-fiber connection is made with the optical beam splitter through a flange.

[0033] In this embodiment, the optical beam splitter is a 1*2 port device. The input port transmits optical signals through standard polarization-maintaining single-mode fiber, and the input optical interface is an APC / FC connector. It is connected to the output fiber of the laser source via a flange in a fiber-to-fiber manner. The two output ports of the optical beam splitter transmit optical signals through standard polarization-maintaining single-mode fiber, and the input optical interface is an APC / FC connector. They are connected to the single-mode fibers of the APC / FC connectors of the X and Y paths respectively via flanges.

[0034] In this embodiment, the phase modulator under test in the X-channel is a packaged device with a housing. The housing structure has an RF connector, a DC PIN interface, an input optical port, and an output optical port. The input optical port is connected to the polarization-maintaining beam splitter via a polarization-maintaining fiber, an APC / FC connector, and a flange, using a standard fiber-to-fiber connection. The output optical port is connected to the optical combiner via a polarization-maintaining fiber, an APC / FC connector, and a flange, also using a standard fiber-to-fiber connection. The RF connector is a 2.92mm, 1.85mm, or GPPO type female RF interface, connected to the output port of the signal generator via a coaxial cable. The coaxial cable is connected to the phase modulator under test via a 2.92mm, 1.85mm, or GPPO type male RF interface, with the same aperture as the RF connector of the modulator under test.

[0035] In this embodiment, the Y-channel tunable optical attenuator is a packaged device with an interface including a power line, an input optical port, and an output optical port. Both the input and output optical ports are polarization-maintaining optical fibers and APC / FC connectors. The input optical port connector is connected to the optical fiber connector of the optical beam splitter via a flange, and the output optical port is connected to the input optical port of the adjustable optical delay line via a flange. The adjustable optical delay line is also a packaged device with an interface including a power line, an input optical port, and an output optical port. All optical ports are polarization-maintaining optical fibers and APC / FC connectors. Its output optical port is connected to the input optical port of the optical combiner via a flange for fiber-to-fiber connection.

[0036] In this embodiment, the optical beam combiner and the optical beam splitter have identical structures, both being 1*2 port devices. The difference lies in that port 1 of the optical beam splitter is an input port, and ports 2 and 3 are output ports, while port 1 of the optical beam combiner is an output port, and ports 2 and 3 are input ports. The two input ports 2 and 3 of the optical beam combiner are connected to the polarization-maintaining fiber ports of the X and Y paths, respectively. The connectors are both APC / FC connectors, and fiber-to-fiber connections are made via flanges. The output port 1 of the optical beam combiner is connected to a photodetector.

[0037] In this embodiment, the photodetector is a packaged device with an interface including a power line, an RF output port, and an input optical port. The input optical port of the photodetector is connected to the output optical port of the optical combiner. The connection method is to directly insert the APC / FC connector of the polarization-maintaining fiber output of the optical combiner into the input optical port of the photodetector. The RF output port of the photodetector is connected to the input port of the oscilloscope through a 2.92mm coaxial cable.

[0038] In this embodiment, the oscilloscope includes 2-4 RF input ports.

[0039] The basic working principle of the system is that the signal generator drives the phase modulator under test through a triangular wave signal, causing the optical signal passing through it to generate phase modulation. The adjustable optical attenuator in the Mach-Zehnder structure is used to compensate for the optical loss of the phase modulator, and the adjustable optical delay line is used to compensate for the additional phase shift of the phase modulator and the phase difference between the two arms of the entire interference structure. Finally, the optical intensity signal after interference is converted into an electrical signal by a photodetector, and its waveform signal is recorded by an oscilloscope and the half-wave voltage value under test is calculated through data processing.

[0040] The light field of the light source signal is E0e jωt After passing through the optical beam splitter and the X and Y paths of the MZM, the optical powers before beam combining are as follows:

[0041]

[0042] Wherein, Φ1 and Φ2 are the total phase shifts of the X and Y paths, respectively. The phase shift Φ1 of the X path includes three parts: the fixed phase shift of the phase modulator under test, the modulation phase shift, and the phase shift generated by the optical fiber. The phase shift Φ2 of the Y path includes three parts: the fixed phase shift of the adjustable optical delay line and optical attenuator, the working phase shift of the optical delay line, and the phase shift generated by the optical fiber. β1 and β2 are the optical field attenuation factors of the X-path phase modulator under test and the Y-path adjustable optical attenuator and adjustable optical delay line, respectively. This attenuation is caused by device losses. E X and E Y E0e represents the optical field before beam combining in the X and Y paths, respectively. jωt Represents the light field of the light source signal;

[0043] Through the interference structure, the optical field after beam combining is:

[0044]

[0045] Optical power is:

[0046]

[0047] Where P0 is the input optical signal power, Let be the conjugate vector of the combined optical field; let the attenuation ratio of the Y and X optical fields be η = β2 / β1, then the output optical power is:

[0048]

[0049] According to formula (5), the two parameters that most significantly affect optical power are the optical field attenuation amplitude ratio η and the phase difference ΔΦ between the two arms. One of the key innovations of this invention is that the adjustable optical attenuator and the adjustable optical delay line are placed in the Y-path of the interference structure to respectively control the two core parameters η and ΔΦ, thereby achieving power compensation and phase balance, significantly enhancing the system's resistance to environmental interference. The specific details are as follows:

[0050] The function of the tunable optical attenuator: The tunable optical attenuator is to control the optical loss of the two arms X and Y of the interference structure. The optical power passing through the two arms X and Y is denoted as P, respectively. X and P Y They satisfy the following relationship:

[0051] P Y =P X ·η 2 (6)

[0052] The MZM structure interference visibility is:

[0053]

[0054] If an adjustable optical attenuator is not used to compensate for the insertion loss of the phase modulator, the interference visibility V will be significantly reduced under power imbalance between the two arms. For example, if the phase modulator loss is 5dB, corresponding to η = 0.562, the visibility V will drop from the theoretical maximum of 1 to 0.85, resulting in a decrease in the half-wave voltage V0. π The calibration error increases.

[0055] The function of an adjustable optical delay line: The function of an adjustable optical delay line is to control the phase of the transmitted optical signal. The delay of a conventional optical delay line can reach more than 330 ps, ​​corresponding to an optical path difference of more than 100 mm. It can completely compensate for the inherent optical path difference between the X and Y arms of the interference structure caused by fiber length error, device phase shift, etc., so that the MZM interference structure is tuned to a symmetrical state with nearly equivalent arm lengths, thereby improving the system's anti-environment interference capability. The phase difference ΔΦ of the interference structure in formula (5) usually includes three parts: inherent phase difference, modulation phase difference, and phase noise. Among them, the phase noise ΔΦ u The phase noise ΔΦ typically originates from environmental disturbances such as stress, mechanical vibration, and temperature in the X and Y paths. This Δn is a random phase difference generated under the cumulative effect of the arm length difference ΔL between the two arms, and it interferes with the measurement. When the fiber optic cables and components of the measurement system are in a fixed, vibration-isolated environment, the rate of change of Δn introduced by environmental factors such as stress and mechanical vibration over time is negligible. In this case, the phase noise ΔΦ... uMainly affected by temperature disturbances, the thermo-optical coefficient through the optical fiber (β~1×10) -5 / ℃), coefficient of thermal expansion (α~0.55×10 -5 The phase noise, which is generated by ( / ℃), can be simplified as follows:

[0056]

[0057] Where ΔT represents the environmental stability disturbance. Without a tunable optical delay line, the ΔL of the fiber interference structure typically exceeds 20 mm. Taking the operating wavelength λ0 = 1.55 μm, the fiber refractive index n = 1.45, and the temperature disturbance dΔT / dt = 0.1 °C / s, the calculated rate of change of phase noise over time is ΔΦ. u =0.15 rad / s; It should be noted that the ambient temperature disturbance dΔT / dt has a large degree of randomness, which depends on the actual working environment. Therefore, the actual phase noise ΔΦ u It will exhibit random fluctuation characteristics. When observing the modulated waveform with an oscilloscope, this phase noise will cause the waveform to exhibit severe fluctuations and distortions along the axial direction, making it difficult to accurately determine the half-wave voltage V. π Calibration is performed. When an adjustable optical delay line is introduced, the optical delay of the Y-path can be adjusted to compensate for the difference in equivalent arm length ΔL between the two arms, reducing it to near zero. At this point, phase noise is significantly suppressed, resulting in a more stable waveform monitored by the oscilloscope and a significant enhancement in the environmental anti-interference capability of the test system.

[0058] Specifically: The continuous optical signal generated by the laser source is split into two optical signals with an energy ratio of 50:50 in an optical beamsplitter, and then enters the X and Y paths of the Mach-Zehnder interferometer arms. The X path optical signal enters the phase modulator under test (DUT) and undergoes electro-optic phase modulation via a triangular wave signal generated by a signal generator. The Y path optical signal enters the interferometer arm sequentially through an adjustable optical attenuator and an adjustable optical delay line to correct the intensity and phase of the optical signal. After the two optical signals are combined by an optical beam combiner, they are input to a photodetector, converted into electrical signals, and then connected to an oscilloscope for sampling and recording. In the measurement system, the triangular wave voltage signal generated by the signal generator is input to the DUT to generate the electro-optic phase modulation process.

[0059] The phase modulator half-wave voltage testing system involved in this utility model has the advantages of simple structure, accurate measurement, and weak susceptibility to environmental disturbances.

[0060] The embodiments described above are merely preferred embodiments of the present utility model and are not intended to limit the scope of the present utility model. Any modifications and improvements made to the technical solutions of the present utility model by those skilled in the art without departing from the spirit of the present utility model should fall within the protection scope defined by the claims of the present utility model.

Claims

1. A half-wave voltage testing system for an electro-optic phase modulator based on a Mach-Zehnder interferometer structure, characterized in that, The system includes: a laser source, an optical beam splitter, a phase modulator under test, an optical beam combiner, a photodetector, and an oscilloscope; The laser source and the optical beam splitter are connected by optical fiber. Another connection between the optical beam splitter and the optical beam combiner includes an adjustable optical attenuator and an adjustable optical delay line. The adjustable optical attenuator, the adjustable optical delay line and the phase modulator under test form a parallel structure, located in the X and Y paths of the interferometer arms of the Mach-Zehnder interferometer structure, respectively. The signal generator and the phase modulator under test are electrically connected by a standard coaxial cable, and the generated triangular wave signal drives the phase modulator under test with voltage. The optical combiner and the photodetector are connected via optical fiber; The photodetector and the oscilloscope are connected by a cable.

2. The system according to claim 1, characterized in that, The laser source outputs light with wavelengths of 1310nm, 1550nm, or other wavelengths in the communication band to be tested. The optical signal is transmitted through a standard polarization-maintaining single-mode fiber. The output optical interface is an APC / FC connector, and it is connected to the optical beam splitter via a flange in a fiber-to-fiber manner.

3. The system according to claim 1, characterized in that, The optical beam splitter is a 1*2 port device. The input port transmits optical signals through standard polarization-maintaining single-mode fiber, and the input optical interface is an APC / FC connector. It is connected to the output fiber of the laser source via a flange in a fiber-to-fiber manner. The two output ports of the optical beam splitter transmit optical signals through standard polarization-maintaining single-mode fiber, and the input optical interface is an APC / FC connector. They are connected to the single-mode fibers of the APC / FC connectors of the X and Y paths respectively via flanges.

4. The system according to claim 3, characterized in that, The phase modulator under test (DUT) in the X-channel is a packaged device with a housing containing an RF connector, a DC PIN interface, an input optical port, and an output optical port. The input optical port is connected to the polarization-maintaining beam splitter via polarization-maintaining fiber, an APC / FC connector, and a flange, using a standard fiber-to-fiber connection. The output optical port is connected to the optical combiner via the same polarization-maintaining fiber, APC / FC connector, and flange, again using a standard fiber-to-fiber connection. The RF connector is a 2.92mm, 1.85mm, or GPPO type female RF interface, connected to the signal generator's output port via a coaxial cable. The coaxial cable connects to the DUT via a 2.92mm, 1.85mm, or GPPO type male RF interface, with the same aperture as the DUT's RF connector.

5. The system according to claim 3, characterized in that, The Y-channel tunable optical attenuator is a packaged device with interfaces including a power line, an input optical port, and an output optical port. Both the input and output optical ports use polarization-maintaining fiber and APC / FC connectors. The input optical port connector is connected to the fiber optic connector of the optical beam splitter via a flange. The output optical port is connected to the input optical port of the tunable optical delay line via a flange. The tunable optical delay line is also a packaged device with interfaces including a power line, an input optical port, and an output optical port. All optical ports use polarization-maintaining fiber and APC / FC connectors. Its output optical port is connected to the input optical port of the optical combiner via a flange for fiber-to-fiber connection.

6. The system according to claim 1, characterized in that, The optical beam combiner and the optical beam splitter have the same structure, both being 1*2 port devices. The difference is that port 1 of the optical beam splitter is the input port, and ports 2 and 3 are the output ports, while port 1 of the optical beam combiner is the output port, and ports 2 and 3 are the input ports. The two input ports 2 and 3 of the optical beam combiner are connected to the polarization-maintaining fiber ports of the X and Y paths, respectively. The connectors are both APC / FC connectors, and fiber-to-fiber connections are made through flanges. The output port 1 of the optical beam combiner is connected to the photodetector.

7. The system according to claim 1, characterized in that, The photodetector is a packaged device with an interface including a power line, an RF output port, and an input optical port. The input optical port of the photodetector is connected to the output optical port of the optical combiner. The connection method is to directly insert the APC / FC connector of the polarization-maintaining fiber output of the optical combiner into the input optical port of the photodetector. The RF output port of the photodetector is connected to the input port of the oscilloscope through a 2.92mm coaxial cable.

8. The system according to claim 1, characterized in that, The oscilloscope contains 2-4 RF input ports.

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