A method and system for calibrating electro-optical tuning efficiency of a lithium niobate microcavity modulator

Abstract

The application discloses a kind of lithium niobate microcavity modulator electro-optic tuning efficiency calibration method and system, to solve the problem of serious direct current drift interference, poor reliability of measurement results, low repeatability in prior art.It includes:1) scanning the wavelength of the microcavity to be measured, collecting static transmission spectrum and fitting, extracting resonance wavelength, optical full width at half maximum and quality factor;2) adjust the narrow linewidth laser to the resonance wavelength, build the optical power feedback closed loop, suppress the resonance point drift caused by environmental disturbance;3) generate high-frequency periodic linear scan voltage and load to the modulation electrode, make the transmission power change periodically with the transmission peak of tuning;4) collect time-domain transmission voltage signal and store synchronously with scan voltage signal;5) combine transmission voltage waveform, optical full width at half maximum and scan voltage electrical characteristics, obtain electro-optic tuning efficiency.The application can effectively suppress interference, improve calibration accuracy and repeatability, suitable for lithium niobate microcavity modulator performance test.

Description

Technical Field

[0001] This invention belongs to the field of optoelectronic device technology, and further relates to electro-optic modulator technology. Specifically, it is a method and system for calibrating the electro-optic tuning efficiency of a lithium niobate microcavity modulator, which can be used in the fields of optical communication and photonic integration. Background Technology

[0002] Lithium niobate (LiNbO3, LN) has become a core material platform in integrated photonics due to its excellent electro-optic (EO) properties, wide-band transparency, and mature nanofabrication technology. In particular, the emergence of lithium niobate-on-insulator (LNOI) technology has made it possible to fabricate micro / nano photonic devices with subwavelength optical field confinement and ultra-high quality factor (Q). Microcavity-enhanced electro-optic modulators (such as photonic crystal nanobeam cavities (PCNBC) and microring resonators (MRR)) utilize the strong optical field and matter interaction within a high-Q cavity to significantly improve electro-optic modulation efficiency, achieving device miniaturization, low power consumption, and high speed. They have irreplaceable application value in 5G / 6G optical communication, microwave photonics, quantum information processing, and optical sensing. Electro-optic tuning efficiency (the resonant wavelength shift per unit voltage, measured in pm / V) is the most critical performance parameter of microcavity electro-optic modulators, directly determining key indicators such as the π phase shift voltage, voltage-length product, and 3dB modulation voltage. Accurate measurement of this parameter is a prerequisite for device design optimization, performance evaluation, and industrial application.

[0003] The widely used method in the industry for measuring the electro-optic tuning efficiency of lithium niobate microcavities is the quasi-static DC voltage scanning method. First, the microcavity device under test is fixed on a coupling stage, and optical and electrical measurement systems are connected. The wavelength of a narrow-linewidth laser is scanned to obtain the microcavity transmission spectrum under zero bias voltage, determining the initial resonant wavelength. Then, a series of discrete static bias voltages are applied sequentially. At each voltage point, the voltage is kept stable, and the laser wavelength is scanned to obtain the transmission spectrum under that voltage. The resonant wavelength is extracted using Lorentz fitting. Finally, a curve is plotted with the applied voltage as the abscissa and the resonant wavelength as the ordinate. The slope of the curve, i.e., the electro-optic tuning efficiency, is obtained through linear fitting. However, this method has fatal flaws in the measurement of high-Q lithium niobate microcavities, including: 1) severe DC drift interference; under continuous electric field, lithium niobate materials undergo charge redistribution, surface charge shielding, and buffer layer relaxation, causing the resonant wavelength to drift over time (i.e., DC drift). The characteristic relaxation time of this drift is typically on the order of milliseconds to seconds. 2) Measurement results are unreliable and have poor repeatability; the optical linewidth of high-Q lithium niobate microcavities can be as narrow as nanometers or even picometers. Even tiny drifts can be confused with the true electro-optic response, leading to a systematic overestimation or underestimation of tuning efficiency measurements. Furthermore, the measurement results are highly dependent on the voltage scan speed and the dwell time at each voltage point. Results obtained under different measurement conditions vary significantly and cannot be used as a reliable standard for evaluating device performance. 3) Measurement efficiency is low, making industrial applications difficult; to obtain a complete spectrum, wavelength scanning is required at each voltage point, and the entire measurement process is time-consuming, further exacerbating the impact of drift.

[0004] Although existing research has focused on the DC drift problem of lithium niobate modulators, it has mainly concentrated on drift suppression of Mach-Zehnder interferometer (MZI) type devices, such as using special packaging, material modification or feedback control circuits. However, these techniques cannot be directly applied to the tuning efficiency measurement of high-Q microcavities, and there is an urgent need to propose an effective measurement scheme for high-Q microcavities. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by proposing a calibration method and system for the electro-optic tuning efficiency of lithium niobate microcavity modulators. This addresses the problems of severe DC drift interference, unreliable measurement results, poor repeatability, and low efficiency in the traditional quasi-static DC voltage scanning method for measuring the electro-optic tuning efficiency of high-Q lithium niobate microcavities. This invention, for the first time, proposes a technique that utilizes the time scale difference between the Pockels effect (femtosecond response) and DC drift (millisecond to second response) to achieve complete decoupling of the electro-optic response and drift term through high-frequency dynamic voltage driving. This technique can thoroughly separate the true electro-optic response from the drift-induced error, achieving high-precision and highly repeatable measurement of the electro-optic tuning efficiency.

[0006] To achieve the above objectives, the technical solution of the present invention includes the following:

[0007] A method for calibrating the electro-optic tuning efficiency of a lithium niobate microcavity modulator includes the following steps:

[0008] (1) Wavelength scanning was performed on the lithium niobate microcavity under test using a tunable narrow linewidth laser, and the transmitted light power of the microcavity was collected using an optical power meter to obtain the static transmission spectrum; and the static transmission spectrum was fitted by a function to extract the resonant wavelength λ0 and the full width at half maximum (FWHM) Δλ of the microcavity under zero bias. opt and the corresponding optical quality factor Q;

[0009] (2) The output wavelength of the narrow linewidth laser is pre-tuned to near the resonant wavelength λ0 of the microcavity to construct a transmission power feedback closed loop, and the transmission power fluctuation of the microcavity is monitored in real time. The resonant point drift caused by environmental disturbance is suppressed by adjusting the driving current of the laser or the piezoelectric ceramic feedback.

[0010] (3) Generate a periodic linear scanning voltage signal with a frequency higher than the DC drift response speed of the lithium niobate microcavity, and apply the voltage signal to the modulation electrode of the lithium niobate microcavity under test, so that the transmitted light power of the microcavity generates a periodic transmission peak change with the tuning synchronization of the linear scanning voltage signal, and outputs a modulated light signal.

[0011] (4) Acquire the time-domain transmission voltage signal converted from the modulated optical signal, and store the waveforms of the signal and the linear scanning voltage signal simultaneously in the data processing unit;

[0012] (5) Based on the waveform of the time-domain transmitted voltage signal, extract the time point corresponding to the voltage drop to half of the peak value, and calculate the full width at half maximum (FWHM) of the time domain. Combined with the optical full width at half maximum (FWHM) obtained in step (1) Based on the electrical characteristics of the linear scanning voltage signal in step (3), the electro-optic tuning efficiency of the microcavity modulator under test is calculated. .

[0013] Meanwhile, this invention also proposes a calibration system for the electro-optic tuning efficiency of a lithium niobate microcavity modulator, comprising an optical unit, an electrical unit, and a data processing unit connected in sequence via communication. The optical unit includes a narrow-linewidth tunable semiconductor laser, a fiber polarization controller, a fiber-to-chip coupler, a fiber beam splitter, an optical power meter, an erbium-doped fiber amplifier, a bandpass filter, and a high-speed photodetector, used to perform static optical characterization of the microcavity under test, laser wavelength locking, and transmitted light signal acquisition and transmission. The electrical unit includes a dual-channel arbitrary waveform function generator, a DC biaser, a high-bandwidth microwave probe, and a high-bandwidth digital oscilloscope, used to perform dynamic high-frequency voltage driving and synchronous acquisition of time-domain signals. The data processing unit is used to perform data processing and tuning efficiency calculation.

[0014] Furthermore, the aforementioned data processing unit is a computer that communicates with a high-bandwidth digital oscilloscope, and the computer has a built-in dedicated data processing module for performing automated calculations of Lorentz spectral fitting, time-domain waveform averaging, linewidth parameter extraction, and electro-optic tuning efficiency.

[0015] Compared with the prior art, the present invention has the following advantages:

[0016] First, this invention uses a periodic linear scanning voltage signal with a frequency higher than the DC drift response speed of the lithium niobate microcavity to drive the device under test. It fully utilizes the inherent time scale difference between the femtosecond-level instantaneous response of the Pockels effect and the millisecond to second-level relaxation response of the DC drift, completely decoupling the intrinsic electro-optic response of the device from the quasi-static DC drift term. This fundamentally solves the fatal defect in the traditional quasi-static DC scanning method, which is caused by the confusion between the resonant wavelength drift and the true electro-optic response due to the effects of charge redistribution, surface charge shielding, and buffer layer relaxation of lithium niobate material, resulting in a systematic overestimation or underestimation of the tuning efficiency measurement value. It completely eliminates the interference of DC drift on the measurement results.

[0017] Secondly, because this invention employs a technique of constructing a drift-free optical reference by fitting static transmission spectra under zero bias voltage, and combining synchronously acquired time-domain transmission waveforms and driving voltage signals, the intrinsic tuning efficiency is calculated through the correspondence between the time-domain full width at half maximum (FWHM) and the static optical linewidth; this eliminates the drawbacks of traditional methods where measurement results are highly dependent on human testing conditions such as voltage scan speed and voltage point dwell time; and through actual testing on 31 groups of devices with different electrode structures, the relative deviation of the measurement results of this invention is less than 3%, achieving high-precision and high-repeatability quantitative calibration of electro-optic tuning efficiency. The measurement results can be directly used as a standardized and highly reliable basis for evaluating device performance.

[0018] Third, this invention employs a technique that locks the wavelength of a narrow-linewidth laser to the resonant wavelength of the microcavity and constructs a closed-loop transmission power feedback to maintain a stable resonant state between the laser and the microcavity. This completely replaces the full-wavelength scanning operation that needs to be performed at each discrete voltage point in the traditional method, reducing the time of a single complete measurement from 5-10 minutes in the traditional method to a few seconds, thus improving the measurement efficiency by tens of times. At the same time, it significantly shortens the measurement window and significantly reduces the cumulative effects of environmental disturbances and slow drift, which can fully meet the needs of rapid and high-throughput characterization of batch samples in the mass production stage of devices.

[0019] Fourth, because this invention uses a high-frequency dynamic voltage-driven device greater than 1kHz, it can directly measure the dynamic electro-optic response of the device at the actual operating frequency, rather than the quasi-static low-frequency response that traditional methods can only measure. This breaks the limitation of traditional methods that can only complete static performance characterization. The measurement results are more consistent with the actual working state of the device in scenarios such as 5G / 6G optical communication, microwave photonics, and quantum information processing, providing more practical parameter basis for device high-frequency performance optimization and system integration.

[0020] Fifth, this invention is based on the core inventive concept of "decoupling electro-optic response and drift by utilizing time scale differences." The solution architecture does not depend on specific microcavity structures, driving waveforms, or data processing methods, and has extremely strong scalability: In terms of device adaptation, this solution is compatible with various high-Q electro-optic microcavities with optical quality factors Q≥1000, such as microring resonators, photonic crystal nanobeam cavities, and two-dimensional photonic crystal microcavities. It can also be extended to other electro-optic tuning devices with DC drift problems, such as aluminum nitride, lithium tantalate, lead zirconate titanate, and silicon-based carrier dispersive devices. In terms of solution compatibility, it can adapt to various driving waveforms such as triangular waves, sawtooth waves, and nonlinearly corrected sine waves, as well as various laser locking methods such as resonant peak locking and half-high point locking, and various data processing schemes such as Lorentz fitting and frequency domain transformation. It completely solves the limitation of traditional methods that are only applicable to low-Q or drift-free devices, and has extremely strong scene adaptability and solution scalability.

[0021] Sixth, this invention is equipped with a dedicated calibration system that links the optical unit, electrical unit, and data processing unit. Through the built-in dedicated data processing module, it can efficiently complete the entire closed-loop operation of static spectrum fitting, laser wavelength locking, dynamic voltage driving, synchronous acquisition of time-domain signals, and automated calculation of tuning efficiency. This avoids human error caused by manual point-by-point operation and manual fitting calculation in traditional methods. It can form a standardized and reproducible test process, which is convenient for promotion and application as a standard characterization method in the industry, and provides standardized test support for the industrialization of integrated photonic devices. Attached Figure Description

[0022] Figure 1 : Overall implementation flowchart of the method of this invention;

[0023] Figure 2 : A schematic diagram of the process for calculating electro-optic tuning efficiency using a triangular wave voltage signal in the method of this invention;

[0024] Figure 3 : A schematic diagram of the process for calculating electro-optic tuning efficiency using a sawtooth wave voltage signal in the method of this invention;

[0025] Figure 4 : A schematic diagram illustrating the implementation principle of the method of this invention;

[0026] Figure 5 : A schematic diagram of the LNOI PCNBC electro-optic modulator structure provided in this embodiment of the invention;

[0027] Figure 6 A partial schematic diagram of the electro-optic modulation device provided in this embodiment of the invention;

[0028] Figure 7 : A schematic diagram of the overall architecture of the system of this invention;

[0029] Figure 8 The static transmission spectrum of a typical PCNBC device provided in this embodiment of the invention;

[0030] Figure 9 Comparison chart of calibration results obtained using traditional methods and the method of this invention. Detailed Implementation

[0031] The present invention will now be further described with reference to the accompanying drawings.

[0032] Example 1: Refer to Appendix Figure 1 The present invention proposes a method for calibrating the electro-optic tuning efficiency of a lithium niobate microcavity modulator, which specifically includes the following steps:

[0033] Step 1) A tunable narrow-linewidth laser is used to perform wavelength scanning on the lithium niobate microcavity under test. The transmitted light power of the microcavity is collected using an optical power meter to obtain the static transmission spectrum. Then, a function is fitted to the static transmission spectrum to extract the resonant wavelength of the microcavity under zero bias. Optical half-height full width And the corresponding optical quality factor Q. In this embodiment, the lithium niobate microcavity to be tested is a high-Q optical microcavity with a narrow spectral line transmission spectrum, including a microring resonator, a photonic crystal nanobeam cavity, and a two-dimensional photonic crystal microcavity; the waveguide structure of the microcavity includes electro-optic material-based homogeneous waveguides and heterogeneous integrated waveguides, and the optical quality factor Q ≥ 1000.

[0034] Step 2) Pre-tune the output wavelength of the narrow-linewidth laser to the resonant wavelength of the microcavity. Nearby, a closed-loop transmission power feedback system is constructed to monitor the transmission power fluctuations of the microcavity in real time. By adjusting the laser's drive current or piezoelectric ceramic feedback, the resonant point drift caused by environmental disturbances is suppressed. In this embodiment, step 2) can also be performed by locking the laser wavelength to the half-maximum of the microcavity resonant curve, so that the transmission power changes linearly with the resonant wavelength shift. The electro-optic tuning efficiency is then calculated in subsequent steps by measuring the magnitude of the transmission power change.

[0035] Step 3) Generate a periodic linear scanning voltage signal with a frequency higher than the DC drift response speed of the lithium niobate microcavity, and apply this voltage signal to the modulation electrode of the lithium niobate microcavity under test. This causes the transmitted light power of the microcavity to change periodically with the tuning of the linear scanning voltage signal, and outputs a modulated light signal. In this embodiment, the aforementioned periodic linear scanning voltage signal is a triangular wave voltage signal or a sawtooth wave voltage signal with a frequency greater than 1 kHz. Applying this voltage signal to the modulation electrode of the lithium niobate microcavity under test specifically involves superimposing a static bias voltage through a DC biaser and then applying it to the modulation electrode of the lithium niobate microcavity under test through a high-bandwidth microwave probe, so that the modulation range is located at the target bias point.

[0036] Step 4) Acquire the time-domain transmission voltage signal converted from the modulated optical signal, and simultaneously store the waveforms of this signal and the linear scanning voltage signal in the data processing unit. In this embodiment, the modulated optical signal is amplified by an erbium-doped fiber amplifier, filtered by a bandpass filter, and then converted into a time-domain transmission voltage signal by a high-speed photodetector, which is input to port 1 of a high-bandwidth digital oscilloscope; at the same time, the linear scanning voltage signal is input to port 2 of the high-bandwidth digital oscilloscope, completing the synchronous acquisition of the two types of time-domain signals.

[0037] Step 5) Based on the waveform of the time-domain transmitted voltage signal, extract the time point corresponding to the voltage drop to half of its peak value, and calculate the full width at half maximum (FWHM) of the time domain. Combined with the optical full width at half maximum (FWHM) obtained in step 1), Based on the electrical characteristics of the linear scanning voltage signal in step 3), the electro-optic tuning efficiency of the microcavity modulator under test is calculated. In this embodiment, for the two periodic linear scanning voltage signals mentioned in step 3), the following two methods for calculating the electro-optic tuning efficiency are given respectively. Specific steps:

[0038] See attached document Figure 2 When the periodic linear scanning voltage signal is a triangular wave voltage signal, the peak-to-peak voltage of the triangular wave voltage signal is denoted as... Electro-optic tuning efficiency Calculate according to the following steps:

[0039] (5a1) Based on the frequency f1 and peak-to-peak voltage V of the triangular wave voltage signal pp1 Calculate the rate of voltage change:

[0040] ;

[0041] (5a2) Set the current time domain half-width to full width at half-height. Convert to full width at half maximum (FWHM) of the current voltage domain:

[0042] ;

[0043] (5a3) Calculate the electro-optic tuning efficiency according to the following formula. :

[0044] .

[0045] See attached document Figure 3 When the periodic linear scanning voltage signal is a sawtooth wave voltage signal, the peak-to-peak voltage of the sawtooth wave voltage signal is denoted as... Electro-optic tuning efficiency Calculate according to the following steps:

[0046] (5b1) Based on the frequency of the sawtooth wave voltage signal Peak-to-peak voltage Calculate the rate of voltage change:

[0047] ;

[0048] (5b2) Set the current time domain half-height and full width to 6000. Convert to full width at half maximum (FWHM) of the current voltage domain:

[0049] ;

[0050] (5b3) Calculate the electro-optic tuning efficiency according to the following formula. :

[0051] .

[0052] In addition to the two driving waveforms (triangular wave and sawtooth wave) in the above embodiments, this invention can also use a sine wave for driving. However, since the voltage change rate of a sine wave is nonlinear, it is necessary to convert the time-domain waveform into a linear response through nonlinear correction, resulting in slightly lower measurement accuracy, but still suppressing drift. If the periodic linear scanning voltage signal in step 3) is replaced with a sine wave voltage signal, then in the current step 5) data processing, the time-domain transmission waveform driven by the sine wave is first nonlinearly corrected, and then the linewidth parameter is extracted to calculate the electro-optic tuning efficiency. In step 5) above, in addition to directly measuring the full width at half maximum (FWHM) of the time domain, the time-domain transmission waveform can also be fitted with a Lorentz function to extract more accurate linewidth parameters, further improving measurement accuracy; or the time-domain signal can be converted into a frequency-domain signal through Fourier transform to extract the change in resonant frequency, and finally complete the calculation of the electro-optic tuning efficiency. This method can be extended to the tuning efficiency calibration of electro-optic tuned microcavity devices including aluminum nitride, lithium tantalate, lead zirconate titanate, and silicon-based carrier dispersive type.

[0053] Example 2: Refer to Appendix Figure 7This invention proposes a calibration system for the electro-optic tuning efficiency of a lithium niobate microcavity modulator, used to execute the method described in Example 1. The system includes an optical unit, an electrical unit, and a data processing unit connected in sequence via communication; wherein:

[0054] The first part, the optical unit, includes a narrow-linewidth tunable semiconductor laser, a fiber polarization controller, a fiber-to-chip coupler, a fiber beam splitter, an optical power meter, an erbium-doped fiber amplifier (EDFA), a bandpass filter (BPF), and a high-speed photodetector. These components are used for static optical characterization of the microcavity under test, laser wavelength locking, and the acquisition and transmission of transmitted light signals. In this embodiment, a high-precision thermoelectric cooler (TEC) temperature control station and a 90:10 fiber beam splitter are preferably used as components to implement this unit.

[0055] Part Two: Electrical Unit, consisting of a dual-channel arbitrary waveform function generator, a high-bandwidth microwave probe, a DC biaser, and a high-bandwidth digital oscilloscope; used to complete dynamic high-frequency voltage drive and synchronous acquisition of time-domain signals.

[0056] Part Three: Data Processing Unit, used to perform data processing and tuning efficiency calculations. This embodiment preferably uses a computer connected to a high-bandwidth digital oscilloscope, and this computer has a built-in dedicated data processing module for automatically calculating Lorentz spectral fitting, time-domain waveform averaging, linewidth parameter extraction, and electro-optic tuning efficiency.

[0057] Example 3: The overall implementation steps of the calibration method proposed in this example are the same as in Example 1. A specific example is given below to further illustrate the detailed process of calibration using the method of this invention:

[0058] Step 1: Static optical characterization

[0059] With the electric drive system off, the wavelength of the narrow-linewidth continuous-wave laser is scanned to obtain the static transmission spectrum of the lithium niobate microcavity under test (e.g., ...). Figure 8 (As shown). In this embodiment, the transmission spectrum is fitted using the Lorentz function to extract the intrinsic parameters of the microcavity: the resonant wavelength at zero bias. Optical half-width linewidth It provides a drift-free static optical reference for subsequent dynamic calibration, eliminating systematic errors during dynamic measurement.

[0060] Step 2: Laser wavelength locking

[0061] Precisely lock the laser wavelength to the resonant wavelength of the microcavity. At this location, the transmitted light power is monitored in real time using an optical power meter to ensure that the laser and the microcavity maintain a resonant state.

[0062] Step 3: Dynamic triangular wave voltage drive

[0063] A periodic triangular wave voltage signal with a frequency much higher than the DC drift characteristic frequency (typically >10kHz, preferably 10kHz~1MHz) is generated using a dual-channel (function generator channel 1 and function generator channel 2) arbitrary waveform function generator. The peak-to-peak voltage of the triangular wave... The system is configured to offset the total wavelength of the microcavity resonant wavelength by 1 to 2 times the optical linewidth, ensuring complete sampling of the Lorentz line shape without introducing nonlinear optical effects. A voltage signal is applied to the modulation electrode of the microcavity under test via a DC biaser and a high-bandwidth microwave probe. A static bias voltage can be superimposed on the DC biaser, allowing the modulation range to be positioned at any bias point.

[0064] Step 4: Synchronous acquisition of time-domain signals

[0065] The transmitted light signal from the microcavity is amplified by an erbium-doped fiber amplifier (EDFA) and filtered by a bandpass filter (BPF). It is then converted into an electrical signal by a high-speed photodetector and input into a high-bandwidth digital oscilloscope. The function generator channel 2 outputs a reference voltage signal that is completely synchronized with the drive signal and inputs it into oscilloscope channel 2 (set to high impedance input mode) to accurately calibrate the voltage amplitude actually applied to the device electrodes.

[0066] Step 5: Data Processing and Tuning Efficiency Calculation

[0067] First, the averaged time-domain transmission waveform is analyzed, and the full width at half maximum (FWHM) of the Lorentz-shaped transmission pulse is measured. Then, based on the frequency f of the triangular wave and the peak-to-peak voltage... Calculate the rate of change of voltage: Then convert the time-domain full width at half maximum (FWHM) to the voltage-domain full width at half maximum (FWHM): Finally, the intrinsic electro-optic tuning efficiency is calculated using the core formula. :

[0068] .

[0069] The invention has been validated on a lithium niobate electro-optic modulator, and the device is characterized by an optical quality factor higher than 1000.

[0070] The above simulation analysis proves the correctness and effectiveness of the method proposed in this invention.

[0071] The precise characterization method provided by this invention can accelerate device design optimization and performance improvement in the field of optical communication, promoting its large-scale application in data centers, telecommunications networks, and consumer electronics; it can also drive the development of microwave photonics technology towards higher frequencies, larger bandwidths, and lower power consumption, enhancing the technological level of my country's national defense and civilian communication systems; in the field of quantum information processing, it can ensure the performance consistency of quantum devices, providing important support for the practical application of quantum information processing technology; at the same time, it can be used in the integrated photonics industry, significantly improving device R&D efficiency, shortening product launch cycles, and reducing production costs; it can promote the maturity and development of my country's integrated photonics industry chain and enhance my country's competitiveness in the global photonics industry.

[0072] The parts of this invention not described in detail are common knowledge to those skilled in the art. The above description is only a preferred embodiment of the present invention and is not intended to limit the invention. Obviously, those skilled in the art, after understanding the content and principle of the present invention, may make various modifications and changes in form and detail without departing from the principle and structure of the present invention, including: replacing the driving waveform, replacing the laser locking method, replacing the data processing method, and expanding the device type. In addition to locking to the resonant peak, the laser can also be locked to the half-maximum of the resonant curve. At this time, the transmitted light power changes approximately linearly with the resonant wavelength shift. The tuning efficiency can be calculated by measuring the change in transmitted light power, but additional linearity calibration is required. In addition to directly measuring the full width at half maximum (FWHM) in the time domain, the time domain transmitted waveform can be fitted with a Lorentz function or the time domain signal can be converted into a frequency domain signal through Fourier transform to extract the change in resonant frequency. Moreover, this method is not only applicable to polymer-loaded LNOI PCNBC, but can also be extended to other electro-optic microcavity devices with DC drift problems, such as etched LNOI microcavities, silicon-lithium niobate heterogeneous integrated microcavities, and aluminum nitride microcavities. However, these modifications and alterations based on the ideas of this invention are still within the scope of protection of the claims of this invention.

Claims

1. A method for calibrating the electro-optic tuning efficiency of a lithium niobate microcavity modulator, characterized in that, Includes the following steps: (1) Wavelength scanning was performed on the lithium niobate microcavity under test using a tunable narrow linewidth laser, and the transmitted light power of the microcavity was collected using an optical power meter to obtain the static transmission spectrum; then, the static transmission spectrum was fitted by a function to extract the resonant wavelength of the microcavity under zero bias. Optical half-height full width and the corresponding optical quality factor Q; (2) Pre-tuning the output wavelength of the narrow linewidth laser to the resonant wavelength of the microcavity. Nearby, a closed loop of transmitted light power feedback is constructed to monitor the fluctuation of transmitted light power in the microcavity in real time. By adjusting the driving current of the laser or the piezoelectric ceramic feedback, the resonant point drift caused by environmental disturbances is suppressed. (3) Generate a periodic linear scanning voltage signal with a frequency higher than the DC drift response speed of the lithium niobate microcavity, and apply the voltage signal to the modulation electrode of the lithium niobate microcavity under test, so that the transmitted light power of the microcavity generates a periodic transmission peak change with the tuning synchronization of the linear scanning voltage signal, and outputs a modulated light signal. (4) Acquire the time-domain transmission voltage signal converted from the modulated optical signal, and store the waveforms of the signal and the linear scanning voltage signal simultaneously in the data processing unit; (5) Based on the waveform of the time-domain transmitted voltage signal, extract the time point corresponding to the voltage drop to half of the peak value, and calculate the full width at half maximum (FWHM) of the time domain. Combined with the optical full width at half maximum (FWHM) obtained in step (1) Based on the electrical characteristics of the linear scanning voltage signal in step (3), the electro-optic tuning efficiency of the microcavity modulator under test is calculated. .

2. The method according to claim 1, characterized in that: The lithium niobate microcavity to be tested in step (1) is a high-Q optical microcavity with a narrow transmission spectrum, including a microring resonator, a photonic crystal nanobeam cavity, and a two-dimensional photonic crystal microcavity; the waveguide structure of the microcavity includes electro-optic material-based homogeneous waveguides and heterogeneous integrated waveguides, and the optical quality factor Q≥1000.

3. The method according to claim 1, characterized in that: The periodic linear scanning voltage signal mentioned in step (3) is a triangular wave voltage signal or a sawtooth wave voltage signal with a frequency greater than 1kHz; the voltage signal is applied to the modulation electrode of the lithium niobate microcavity under test by superimposing a static bias voltage through a DC biaser and then applying it to the modulation electrode of the lithium niobate microcavity under test through a high-bandwidth microwave probe so that the modulation range is located at the target bias point.

4. The method according to claim 3, characterized in that: When the periodic linear scanning voltage signal is a triangular wave voltage signal, the peak-to-peak voltage of the triangular wave voltage signal is denoted as... The electro-optic tuning efficiency described in step (5) The specific calculation is based on the following steps: (5a1) Based on the frequency of the triangular wave voltage signal Peak-to-peak voltage Calculate the rate of voltage change: ； (5a2) Set the current time domain half-width to full width at half-height. Convert to full width at half maximum (FWHM) of the current voltage domain: ； (5a3) Calculate the electro-optic tuning efficiency according to the following formula. : 。 5. The method according to claim 3, characterized in that: When the periodic linear scanning voltage signal is a sawtooth wave voltage signal, the peak-to-peak voltage of the sawtooth wave voltage signal is denoted as... The electro-optic tuning efficiency described in step (5) The specific calculation is based on the following steps: (5b1) Based on the frequency of the sawtooth wave voltage signal Peak-to-peak voltage Calculate the rate of voltage change: ； (5b2) Set the current time domain half-height and full width to 6000. Convert to full width at half maximum (FWHM) of the current voltage domain: ； (5b3) Calculate the electro-optic tuning efficiency η according to the following formula: 。 6. The method according to claim 1, characterized in that: The modulated optical signal described in step (4) is amplified by an erbium-doped fiber amplifier and filtered by a bandpass filter. It is then converted into a time-domain transmission voltage signal by a high-speed photodetector and input to port 1 of a high-bandwidth digital oscilloscope. At the same time, a linear scanning voltage signal is input to port 2 of the high-bandwidth digital oscilloscope to complete the synchronous acquisition of the two types of time-domain signals.

7. The method according to claim 1, characterized in that: Calibration can be achieved using any one or more of the following substitution methods: Method 1. In step (3), the periodic linear scanning voltage signal is replaced with a sinusoidal voltage signal. Then, in the data processing step (5), the time-domain transmission waveform driven by the sinusoidal wave is first nonlinearly corrected, and then the linewidth parameter is extracted to calculate the electro-optic tuning efficiency. Method 2. In step (2), the wavelength of the laser is locked to the half-maximum of the microcavity resonance curve, so that the transmitted light power changes linearly with the resonant wavelength shift, and the electro-optic tuning efficiency is calculated by measuring the change amplitude of the transmitted light power. Method 3. In step (5), the time-domain transmission waveform is fitted with the Lorentz function to extract the time-domain linewidth parameter, or the time-domain signal is converted into a frequency-domain signal by Fourier transform to extract the resonant frequency change, thereby completing the calculation of the electro-optic tuning efficiency.

8. The calibration method according to any one of claims 1-7, characterized in that: The method is extended to the calibration of tuning efficiency for electro-optic tunable microcavity devices, including those based on aluminum nitride, lithium tantalate, lead zirconate titanate, and silicon-based carrier dispersive electro-optic tunable microcavity devices.

9. A calibration system for the electro-optic tuning efficiency of a lithium niobate microcavity modulator, characterized in that: For performing the calibration method according to any one of claims 1-7, the system comprises an optical unit, an electrical unit, and a data processing unit that are sequentially and communicatively connected. The optical unit includes a narrow-linewidth tunable semiconductor laser, a fiber polarization controller, a fiber-to-chip coupler, a fiber beam splitter, an optical power meter, an erbium-doped fiber amplifier, a bandpass filter, and a high-speed photodetector, used to perform static optical characterization of the microcavity under test, laser wavelength locking, and transmission of transmitted light signals; the electrical unit includes a dual-channel arbitrary waveform function generator, a DC biaser, a high-bandwidth microwave probe, and a high-bandwidth digital oscilloscope, used to perform dynamic high-frequency voltage driving and synchronous acquisition of time-domain signals; the data processing unit is used to perform data processing and tuning efficiency calculations.

10. The system according to claim 9, characterized in that: The data processing unit is a computer that communicates with a high-bandwidth digital oscilloscope, and the computer has a built-in dedicated data processing module for performing automated calculations of Lorentz spectral fitting, time-domain waveform averaging, linewidth parameter extraction, and electro-optic tuning efficiency.

Images