An optical fiber ring resonator based electro-optic modulator parameter measurement device

Abstract

The application relates to the technical field of optical measurement, and discloses an electro-optic modulator parameter measuring device based on a fiber ring resonant cavity, which comprises an optical signal modulation system, a fiber ring resonant cavity system and a signal acquisition system which are connected in sequence through optical fibers; the optical signal modulation system comprises an electro-optic modulator to be measured, which modulates optical signals and outputs the modulated signals; the fiber ring resonant cavity system comprises a fiber coupler and a linear piezoelectric ceramic fiber stretcher; the fiber coupler is used for forming a ring-shaped optical fiber, and a plurality of reciprocating optical signal loops are formed in the ring-shaped optical fiber; the linear piezoelectric ceramic fiber stretcher is used for changing the length of the ring-shaped optical fiber; and the signal acquisition system acquires signals and calculates parameters. Compared with the prior art, the resolution during measurement is improved.

Description

Technical Field

[0001] This invention relates to the field of optical measurement technology, and more specifically to a device for measuring the parameters of an electro-optic modulator based on a fiber optic ring resonator. Background Technology

[0002] An electro-optic phase modulator is a key device that modulates an electrical signal to the phase of an optical signal, and it is widely used in microwave photonics systems, high-speed fiber optic communication, and coherent optical communication. Its basic working principle utilizes the electro-optic effect to change the phase of a light wave through an electromodulation signal, thereby achieving electro-optic signal conversion. The performance of an electro-optic phase modulator is typically characterized by two key parameters: modulation bandwidth and half-wave voltage. Modulation bandwidth represents the range of electrical signal frequencies that the modulator can effectively respond to, and is an important indicator of its high-speed modulation capability; half-wave voltage refers to the modulation voltage required to induce a π-phase shift in the output light wave, and is directly related to the modulator's driving efficiency. Therefore, before practical application, the above parameters of the electro-optic phase modulator must be accurately measured and calibrated.

[0003] Currently, common methods for testing key parameters of electro-optic phase modulators include: spectrometer method, Sagnac loop interferometry, two-tone heterodyne method, and scanning Fabry-Perot (FP) interferometer method. Among these, the spectrometer method relies on spectral analysis of the modulation sideband and carrier wave, and its accuracy is limited by the light source linewidth and spectrometer resolution, resulting in low measurement resolution. Although the Sagnac loop interferometry can achieve intensity modulation conversion of the phase modulation signal through coherent interference, it is only applicable to weak modulation conditions, and the uneven response of the detector needs to be calibrated before measurement. The two-tone heterodyne method and the scanning FP interferometer method both involve complex system setup and unstable spatial optical paths. Once the system is set up, it is difficult to move, and it is easily affected by environmental disturbances during the measurement process, resulting in poor repeatability. Summary of the Invention

[0004] To overcome the shortcomings of the prior art, such as low measurement resolution and complex and difficult-to-move system, the present invention provides an electro-optic modulator parameter measurement device based on an optical fiber ring resonator.

[0005] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0006] An electro-optic modulator parameter measurement device based on an optical fiber ring resonator includes an optical signal modulation system, an optical fiber ring resonator system, and a signal acquisition system connected sequentially by optical fibers.

[0007] The optical signal modulation system includes an optical signal generator and a measurand electro-optic modulator connected in sequence via optical fibers. The measurand electro-optic modulator modulates the optical signal and outputs the modulated signal.

[0008] The fiber optic ring resonant cavity system includes a fiber optic coupler and a linear piezoelectric ceramic fiber stretcher. The fiber optic coupler includes a first input port, a second input port, a first output port, and a second output port. The first input port is connected to the output of the optical signal modulation system, and the first output port is connected to the input of the signal acquisition system. The second input port is connected to the second output port via a ring optical fiber, and multiple reciprocating optical signal loops are formed within the ring optical fiber. The linear piezoelectric ceramic fiber stretcher is connected to the ring optical fiber and is used to change the length of the ring optical fiber.

[0009] The signal acquisition system includes a photodetector and an acquisition device connected in sequence via optical fibers. The input end of the photodetector is connected to the output end of the optical fiber ring resonant cavity system. The acquisition device acquires the voltage signal output by the photodetector.

[0010] By changing the driving frequency or driving voltage of the optical signal generator and the length of the ring optical fiber, the modulation sideband is found in the spectrum of the voltage signal. The modulation coefficient is calculated based on the modulation sideband, and the parameters of the electro-optic modulator to be measured are calculated based on the relationship between the modulation coefficient and the driving frequency or driving voltage.

[0011] This invention also proposes a method for measuring the parameters of an electro-optic modulator based on a fiber optic ring resonator, applied to a parameter measurement device for an electro-optic modulator based on a fiber optic ring resonator. The method includes:

[0012] The optical signal modulation system modulates the optical signal, changes the driving frequency or driving voltage of the optical signal generator, and changes the length of the ring optical fiber;

[0013] The voltage signal output by the photodetector is acquired by the acquisition device. The spectrum of the voltage signal includes multiple carriers with equal spacing, and the spacing between the carriers is used as the free spectral range.

[0014] Search for modulation sidebands within the free spectral range;

[0015] The modulation coefficient is calculated based on the modulation sideband, and the parameters of the electro-optic modulator to be measured are calculated based on the relationship between the modulation coefficient and the driving frequency or driving voltage.

[0016] Compared with the prior art, the beneficial effects of the technical solution of the present invention are as follows:

[0017] This invention utilizes fiber optic loops and linear piezoelectric ceramic fiber stretching. By controlling the length of the loop fiber, the optical path can be actively changed to adjust the resonance conditions, thereby obtaining multiple order sideband signals. The acquisition of multiple sidebands expands the system's dynamic range, enabling it to cover a wider range of parameter variations, while avoiding measurement blind zones and response dead zones. This improves the sensitivity and accuracy of the measurement system and significantly increases the range of parameter measurements. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of an electro-optic modulator parameter measurement device based on an optical fiber ring resonator, as described in Example 1.

[0019] Figure 2 This is a structural diagram of the linear piezoelectric ceramic fiber stretcher in Example 1;

[0020] Figure 3 The waveform diagram of the signal acquired by the acquisition device in Example 3;

[0021] Figure 4 The modulation bandwidth measurement results are from Example 4;

[0022] Figure 5 The results of the half-wave voltage measurement in Example 4;

[0023] Figure 6 The time-domain plot of the electro-optic phase modulator power from -6dBm to 24dBm in Example 4 is shown.

[0024] Among them, 1-continuous light laser, 2-coupler, 3-waveform generator, 4-input port of electro-optic phase modulator, 5-electro-optic modulator under test, 6-modulation end of electro-optic modulator under test, 7-output port of electro-optic modulator under test, 8-fiber polarization controller, 9-polarization maintaining fiber, 10-first input port, 11-fiber coupler, 12-second input port, 13-linear piezoelectric ceramic fiber stretcher, 14-second output port, 15-fiber loop, 16-first output port, 17-photodetector, 18-acquisition device, 19-signal line. Detailed Implementation

[0025] The accompanying drawings are for illustrative purposes only and should not be construed as limiting the scope of this patent.

[0026] To better illustrate this embodiment, some parts in the accompanying drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions;

[0027] It will be understood by those skilled in the art that certain well-known structures and their descriptions may be omitted in the accompanying drawings.

[0028] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0029] Example 1

[0030] This embodiment proposes a parameter measurement device for an electro-optic modulator based on a fiber optic ring resonator, such as... Figure 1 The diagram shown is a schematic of the electro-optic modulator parameter measurement device based on an optical fiber ring resonator in this embodiment.

[0031] An electro-optic modulator parameter measurement device based on an optical fiber ring resonator includes an optical signal modulation system, an optical fiber ring resonator system, and a signal acquisition system connected in sequence by optical fibers.

[0032] The optical signal modulation system includes an optical signal generator and a measurand 5 connected in sequence by optical fiber. The measurand 5 modulates the optical signal and outputs the modulated signal.

[0033] The fiber optic ring 15 resonant cavity system includes a fiber optic coupler 11 and a linear piezoelectric ceramic fiber stretcher 13. The fiber optic coupler 11 includes a first input port 10, a second input port 12, a first output port 16, and a second output port 14. The first input port 10 is connected to the output of the optical signal modulation system, and the first output port 16 is connected to the input of the signal acquisition system. The second input port 12 is connected to the second output port 14 through a ring optical fiber, and multiple reciprocating optical signal loops are formed within the ring optical fiber. The linear piezoelectric ceramic fiber stretcher 13 is connected to the ring optical fiber and is used to change the length of the ring optical fiber.

[0034] The signal acquisition system includes a photodetector 17 and an acquisition device 18 connected in sequence via optical fibers. The input end of the photodetector 17 is connected to the output end of the resonant cavity system of the optical fiber ring 15. The acquisition device 18 acquires the voltage signal output by the photodetector 17.

[0035] By changing the driving frequency or driving voltage of the optical signal generator and changing the length of the ring optical fiber, the modulation sideband is found in the spectrum of the voltage signal. The modulation coefficient is calculated based on the modulation sideband. The parameters of the electro-optic modulator 5 to be measured are calculated based on the relationship between the modulation coefficient and the driving frequency or driving voltage.

[0036] In an optional embodiment, the optical signal generator includes a continuous laser and a waveform generator 3. The continuous laser 1 is connected to the electro-optic modulator 5 to be measured via a coupler. The waveform generator 3 is connected to the modulation port of the electro-optic modulator 5 to provide a driving voltage and a driving frequency.

[0037] In one alternative embodiment, the continuous laser operates at a wavelength of 1064 nm.

[0038] In an optional embodiment, an optical fiber polarization controller 8 is further provided between the optical signal modulation system and the optical fiber ring 15 resonant cavity system. The optical fiber polarization controller 8 is used to adjust the polarization state of the output optical signal of the optical signal modulation system.

[0039] In one optional embodiment, the parameters include modulation bandwidth and half-wave voltage; when measuring the modulation bandwidth, the driving voltage of the optical signal generator is fixed, the driving frequency of the optical signal generator is changed, the relationship between the modulation coefficient and the driving frequency is obtained, and the modulation bandwidth is calculated; when measuring the half-wave voltage, the driving frequency of the optical signal generator is fixed, the driving voltage of the optical signal generator is changed, the relationship between the modulation coefficient and the driving voltage is obtained, and the half-wave voltage is calculated.

[0040] In an optional embodiment, when the driving voltage or driving frequency of the optical signal generator changes, the length of the ring optical fiber is changed by the linear piezoelectric ceramic fiber stretcher 13, and the stretching length is greater than one carrier wavelength.

[0041] In an optional embodiment, the step of calculating the modulation coefficient based on the modulation sideband includes: calculating the modulation parameters based on the voltage amplitude of the multi-order sidebands, the calculation formula of which is as follows:

[0042]

[0043] Where m is the modulation coefficient. It is an nth-order Bessel function of the first kind. Let be the voltage amplitude of the nth sideband.

[0044] In an optional embodiment, the optical signal modulation system, the fiber optic ring 15 resonant cavity system, and the signal acquisition system are connected by polarization-maintaining fiber 9.

[0045] like Figure 2 The diagram shown is a structural diagram of the linear piezoelectric ceramic fiber stretcher 13.

[0046] Example 2

[0047] This embodiment proposes a method for measuring the parameters of an electro-optic modulator based on a fiber optic ring resonator, which is applied to the electro-optic modulator parameter measurement device based on a fiber optic ring resonator proposed in Embodiment 1. The method includes:

[0048] The optical signal modulation system modulates the optical signal, changes the driving frequency or driving voltage of the optical signal generator, and changes the length of the ring optical fiber;

[0049] The voltage signal output by the photodetector 17 is acquired by the acquisition device 18. The spectrum of the voltage signal includes multiple carriers with equal spacing, and the spacing between the carriers is used as the free spectral range.

[0050] Search for modulation sidebands within the free spectral range;

[0051] The modulation coefficient is calculated based on the modulation sideband, and the parameters of the electro-optic modulator 5 to be measured are calculated based on the relationship between the modulation coefficient and the driving frequency or driving voltage.

[0052] In an alternative embodiment, before measurement, the beam splitting ratio of the resonant cavity system of the fiber ring 15 is adjusted by the fiber polarization controller 8 to achieve optimal coupling.

[0053] In this embodiment, by adjusting the coupling ratio through the fiber polarization controller 8 to achieve the optimal coupling state, the coupling efficiency, signal-to-noise ratio, and stability of the fiber ring 15 resonant cavity system can be significantly improved, thereby enhancing its signal response capability and improving measurement sensitivity and accuracy.

[0054] Example 3

[0055] This embodiment provides a principle explanation of this application.

[0056] Phase modulation relies on the linear electro-optic effect of the crystal in the electro-optic phase modulator, meaning the refractive index of the crystal is linearly related to the applied electric field. The electric field expression for the phase-modulated wave after the beam passes through the electro-optic phase modulator is:

[0057] (1)

[0058] in For modulation signal, This is called the phase modulation coefficient, also known as the modulation factor. For electric field strength, The initial phase of the signal. The angular frequency of the light emitted by the continuous-wave laser. The waveform generator 3 generates the signal frequency for the waveform. For time, Let be the amplitude of the signal. Further, the phase-modulated wave can be obtained by expanding the Bessel function:

[0059]

[0060] (2)

[0061] in yes m of n The first-order Bessel function of the first kind, where m is the phase modulation coefficient. In single-frequency sinusoidal wave modulation, the spectrum of its angle-modulated wave is composed of an infinite number of sidebands symmetrically distributed on both sides of the optical carrier frequency, as shown in Figure 3.

[0062] Based on the properties of Bessel functions, we have:

[0063] (3) Where V is the value obtained by photodetector 17 Figure 3 The voltage amplitude of each modulation sideband in the middle.

[0064] The relationship between the phase modulation coefficient and the half-wave voltage and driving voltage can be further obtained:

[0065] (4)

[0066] in, The parameter is the half-wave voltage of the electro-optic phase modulator. The amplitude of the modulation signal provided to waveform generator 3.

[0067] The following section introduces the basic working principle of the fiber optic ring 15-shaped resonant cavity.

[0068] According to the law of conservation of energy, the output light intensities at each port of the fiber optic ring-shaped resonant cavity are:

[0069] (5)

[0070] in (i=10,12,14,16) represents Figure 1 The electric field strength at ports 10, 12, 14, and 16. This represents the insertion loss of the coupler.

[0071] According to coupled-mode theory Figure 1 The output electric fields of ports 14 and 16 shown can be expressed as:

[0072] (6)

[0073] (7)

[0074] j is the imaginary unit. This represents the coupling coefficient. Further... and The relation is:

[0075] (8)

[0076] in Where L is the fiber attenuation coefficient, and L is the length of the fiber optic ring-shaped resonant cavity. The refractive index of the optical fiber. For light frequency, It is the speed of light.

[0077] Substitute equation (8) into equation (6), and let:

[0078] (9)

[0079] From equations (6), (7), and (8), the output intensity of this cycle can be obtained as follows:

[0080] (10)

[0081] (11)

[0082] That is, the light intensity output from the two output ports of the fiber optic ring 15-shaped resonant cavity will form an infinite number of equally spaced resonant peaks (carrier waves) as shown in Figure 3, where in equation (11) The signal detected by photodetector 17.

[0083] Two conditions for resonance of a fiber optic ring-shaped resonant cavity:

[0084] (12)

[0085] (13)

[0086] That is, under ideal circumstances, Figure 1 All the light input at port 10 enters the fiber optic ring 15-shaped resonant cavity for circulation. That is, the optimal resonant coupling coefficient.

[0087] The free spectral range (FSR) of a fiber optic loop 15-type resonant cavity is similar to that of a scanning FP cavity:

[0088] (14)

[0089] A specific free spectral path can be obtained by adjusting the length of the fusion splice fiber ring 15.

[0090] The linewidth of the resonance peak is The precision is then:

[0091] (15)

[0092] The modulation sidebands of an electro-optic phase modulator are detected by using a scanning fiber ring 15-shaped resonant cavity. A piezoelectric fiber stretcher is used for scanning, and the length of the fiber ring 15 is adjusted. When the modulation sidebands meet the resonance conditions of the fiber ring 15-shaped resonant cavity during the scanning process, they can be detected, and modulation sideband information within the free spectral path range can be obtained.

[0093] Finally, by acquiring the signal from photodetector 17 using the acquisition card, a spectrum diagram as shown in Figure 4 can be obtained.

[0094] For waveform generator 3, by fixing the driving voltage and scanning the driving frequency, the relationship between the modulation coefficient and the driving frequency can be obtained according to equation (3), and the bandwidth can be further obtained; by fixing the driving frequency and scanning the driving voltage, the relationship between the modulation coefficient and the driving voltage can be obtained according to equation (4), and the half-wave voltage can be obtained according to the slope.

[0095] Example 4

[0096] This embodiment uses the electro-optic modulator parameter measurement device based on an optical fiber ring resonator proposed in Embodiment 1 and the electro-optic modulator parameter measurement method based on an optical fiber ring resonator proposed in Embodiment 2 to measure the parameters of the electro-optic phase modulator and compares them with the prior art.

[0097] like Figure 4 The figure shows the modulation bandwidth measurement results; red represents the measurement results of this application, and blue represents the measurement results of the Fabry-Perot interferometer. It can be seen that, compared with the prior art, this application maintains the same modulation ratio at high frequencies, but the lower limit of the measured low frequency is much lower than that of the Fabry-Perot interferometer, demonstrating an improvement in resolution. More importantly, compared with the prior art, this application has a simpler and more portable device structure, does not involve complex spatial optical paths, and has greater advantages in field applications of electro-optic phase modulators, such as environmental simulation testing.

[0098] like Figure 5 The figure shows the half-wave voltage measurement results; red represents the measurement results of this application, and blue represents the measurement results of the Fabry-Perot interferometer. It can be seen that this application maintains the same half-wave voltage measurement results as the prior art.

[0099] like Figure 6 The figure shows the output time domain diagram of the fiber optic ring resonator device when the power of the electro-optic phase modulator ranges from -6dBm to 24dBm.

[0100] The same or similar labels correspond to the same or similar parts;

[0101] The terms used to describe positional relationships in the accompanying drawings are for illustrative purposes only and should not be construed as limiting this patent.

[0102] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A parameter measurement device for an electro-optic modulator based on a fiber optic ring resonator, characterized in that, This includes an optical signal modulation system, an optical fiber ring resonator system, and a signal acquisition system, which are connected sequentially via optical fibers. The optical signal modulation system includes an optical signal generator and a measurand electro-optic modulator connected in sequence via optical fibers. The measurand electro-optic modulator modulates the optical signal and outputs the modulated signal. The fiber optic ring resonant cavity system includes a fiber optic coupler and a linear piezoelectric ceramic fiber stretcher. The fiber optic coupler includes a first input port, a second input port, a first output port, and a second output port. The first input port is connected to the output of the optical signal modulation system, and the first output port is connected to the input of the signal acquisition system. The second input port is connected to the second output port via a ring optical fiber, and multiple reciprocating optical signal loops are formed within the ring optical fiber. The linear piezoelectric ceramic fiber stretcher is connected to the ring optical fiber and is used to change the length of the ring optical fiber. The signal acquisition system includes a photodetector and an acquisition device connected in sequence via optical fibers. The input end of the photodetector is connected to the output end of the optical fiber ring resonant cavity system. The acquisition device acquires the voltage signal output by the photodetector. By changing the driving frequency or driving voltage of the optical signal generator and the length of the ring optical fiber, the modulation sideband is found in the spectrum of the voltage signal. The modulation coefficient is calculated based on the modulation sideband, and the parameters of the electro-optic modulator to be measured are calculated based on the relationship between the modulation coefficient and the driving frequency or driving voltage.

2. The electro-optic modulator parameter measurement device based on an optical fiber ring resonator according to claim 1, characterized in that, The optical signal generator includes a continuous laser and a waveform generator. The continuous laser is connected to the electro-optic modulator under test via a coupler. The waveform generator is connected to the modulation port of the electro-optic modulator under test and is used to provide driving voltage and driving frequency.

3. The electro-optic modulator parameter measurement device based on an optical fiber ring resonator according to claim 2, characterized in that, The operating wavelength of the continuous laser is 1064 nm.

4. The electro-optic modulator parameter measurement device based on an optical fiber ring resonator according to claim 1, characterized in that, An optical fiber polarization controller is also provided between the optical signal modulation system and the optical fiber ring resonator system. The optical fiber polarization controller is used to adjust the polarization state of the output optical signal of the optical signal modulation system.

5. A parameter measurement device for an electro-optic modulator based on a fiber optic ring resonator according to any one of claims 1 to 4, characterized in that, The parameters include modulation bandwidth and half-wave voltage. When measuring the modulation bandwidth, the driving voltage of the optical signal generator is fixed, the driving frequency of the optical signal generator is changed, the relationship between the modulation coefficient and the driving frequency is obtained, and the modulation bandwidth is calculated. When measuring the half-wave voltage, the driving frequency of the optical signal generator is fixed, the driving voltage of the optical signal generator is changed, the relationship between the modulation coefficient and the driving voltage is obtained, and the half-wave voltage is calculated.

6. The electro-optic modulator parameter measurement device based on an optical fiber ring resonator according to claim 5, characterized in that, When the driving voltage or driving frequency of the optical signal generator changes, the length of the ring fiber is changed by the linear piezoelectric ceramic fiber stretcher, and the stretching length is greater than one carrier wavelength.

7. The electro-optic modulator parameter measurement device based on an optical fiber ring resonator according to claim 5, characterized in that, The step of calculating the modulation coefficient based on the modulation sidebands includes: calculating the modulation parameters based on the voltage amplitude of the multi-order sidebands, the calculation formula of which is as follows: in, m The modulation coefficient, It is an nth-order Bessel function of the first kind. V The voltage amplitude of each sideband is denoted as .

8. The electro-optic modulator parameter measurement device based on an optical fiber ring resonator according to claim 1, characterized in that, The optical signal modulation system, the fiber optic ring resonator system, and the signal acquisition system are connected by polarization-maintaining optical fibers.

9. A method for measuring the parameters of an electro-optic modulator based on a fiber optic ring resonator, characterized in that, The method of measuring parameters of an electro-optic modulator based on a fiber optic ring resonator as described in any one of claims 1 to 8 includes: The optical signal modulation system modulates the optical signal, changes the driving frequency or driving voltage of the optical signal generator, and changes the length of the ring optical fiber; The voltage signal output by the photodetector is acquired by the acquisition device. The spectrum of the voltage signal includes multiple carriers with equal spacing, and the spacing between the carriers is used as the free spectral range. Search for modulation sidebands within the free spectral range; The modulation coefficient is calculated based on the modulation sideband, and the parameters of the electro-optic modulator to be measured are calculated based on the relationship between the modulation coefficient and the driving frequency or driving voltage.

10. The method for measuring the parameters of an electro-optic modulator based on a fiber optic ring resonator according to claim 9, characterized in that, Before measurement, the beam splitting ratio of the fiber optic ring resonator system is adjusted to achieve optimal coupling by using a fiber polarization controller.

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