A spectrum analyzer and spectrum detection method based on zero beat detection

Abstract

The application discloses a spectrum analyzer and a spectrum detection method based on homodyne detection. The spectrum analyzer comprises a tunable laser, two 50:50 beam splitters, a fixed phase modulation module, a controller, a data processing module and two homodyne detection modules. The laser beam output by the tunable laser is a local oscillation light. The two 50:50 beam splitters correspondingly split a to-be-detected light and the laser beam. A group of to-be-detected split light beams and a group of laser light pulses are directly input into one homodyne detection module. Another group of to-be-detected split light beams and a group of laser light pulses modulated by the fixed phase modulation module are input into another homodyne detection module. The fixed phase modulation module makes the phase difference between the input laser light pulses and the output laser light pulses be pi / 2 or 3pi / 2. The two groups of homodyne detection modules respectively coherently detect the laser light pulses and the to-be-detected split light beams input thereon and amplify the detection signals. Finally, the to-be-detected light intensity corresponding to each tunable laser beam wavelength is obtained.

Description

Technical Field

[0001] This application belongs to the field of spectral analysis, and specifically relates to a spectrometer and spectral detection method based on zero-pace detection. Background Technology

[0002] A spectrometer, or simply spectrometer, is a scientific instrument that decomposes complex composite light into spectral lines for measurement and calculation. It is widely used in radiometric analysis, color measurement, and chemical composition analysis, and plays a vital role in industries such as metallurgy, geology, hydrology, medicine, petrochemicals, environmental protection, and space exploration. In the lighting industry, spectrometers are commonly used to measure the color parameters of light sources.

[0003] Balanced homodyne detectors (BHDs) are a technique used for measuring the amplitude and phase of optical signals. They have important applications in quantum random number generation, quantum noise analysis, heterodyne detection, and weak signal detection. In weak signal detection, BHDs can be used to detect quantum noise. The key to this measurement is using a balanced homodyne detector to extract and amplify the AC noise signal loaded onto the light wave. This detector should possess low noise and high sensitivity, enabling effective detection of shot noise while ensuring its own electronic noise is significantly lower than the shot noise (typically, the shot noise spectrum is more than 10 dB higher than the electronic noise spectrum), thus avoiding overwhelming the shot noise. Simultaneously, to make the shot noise spectrum the dominant output spectrum, the detector needs to detect milliwatt-level optical fields, thus requiring sufficiently high gain saturation characteristics.

[0004] Currently, most spectrometers on the market are based on spatial optical grating structures to analyze and detect the wavelength of incident light waves. This type of method can generally only perform spectral analysis on relatively strong light beams (on the order of microwatts). At the same time, due to the large optical loss of the system and the detection intensity range of ordinary optical detectors, the system cannot perform effective spectral analysis on weak light or light beams on the order of single photons, which limits its practical application and application scenarios. Summary of the Invention

[0005] To address the aforementioned problems, this application provides a spectrometer and spectral detection method for detecting weak light or single-photon level beams. It employs two sets of zero-beat detection modules to couple and amplify the local oscillator laser beam with the signal light to be measured, and then analyzes and processes the data to obtain the intensity of the signal light. The specific scheme is as follows:

[0006] In the first aspect, this application discloses a spectrometer based on zero-beat detection, including a tunable laser, a first 50:50 beam splitter, a second 50:50 beam splitter, a fixed phase modulation module, a control module, a data processing module, and two zero-beat detection modules.

[0007] The output end of the tunable laser is connected to the input end of the first 50:50 beam splitter, and is used to output a laser beam and feed back the laser beam information to the control module.

[0008] Both the first and second 50:50 beam splitters include an upper output and a lower output. The upper output of the first 50:50 beam splitter is connected to one of the zero-beat detection modules, and the lower output of the first 50:50 beam splitter is connected to the input of the fixed-phase modulation module. The output of the fixed-phase modulation module is connected to another zero-beat detection module. The first 50:50 beam splitter is used to split the input laser beam into two sets of laser pulses with the same energy. One set of laser pulses is directly input to one zero-beat detection module, and the other set of laser pulses is transmitted to another zero-beat detection module through the fixed-phase modulation module. The fixed-phase modulation module is used to perform phase modulation on the input laser pulses so that the phase difference between the input laser pulse and the output laser pulse is π / 2 or 3π / 2.

[0009] The second 50:50 beam splitter is used to split the input test light into two sets of test beams with the same energy. One set of test beams is input to one zero-beat detection module, and the other set of test beams is input to another zero-beat detection module.

[0010] The output of the zero-beat detection module is connected to the data processing module and is used to coherently detect the input laser light pulse and the beam to be tested and amplify the detection signal.

[0011] The control module is used to adjust the wavelength of the laser beam output by the tunable laser and feed back the wavelength information of the currently tuned laser beam to the data processing module, as well as control the phase modulation of the laser pulse by the fixed phase modulation module.

[0012] The data processing module is used to receive and analyze the signals output by the control module and the two sets of zero-beat detection modules to obtain the light intensity information of the light to be measured corresponding to the wavelength of each tuned laser beam and to form the correspondence between the light intensity to be measured and the wavelength of the laser beam.

[0013] Furthermore, the zero-shot detection module includes a third 50:50 beam splitter, a first photodiode, a second photodiode, a transimpedance amplifier, and a data acquisition module. The third 50:50 beam splitter includes an upper output and a lower output for coherent coupling of the input laser pulse and the beam to be tested. The upper output of the third 50:50 beam splitter is connected to the optical path of the first photodiode, and the lower output of the third 50:50 beam splitter is connected to the optical path of the second photodiode. The first photodiode and the second photodiode are connected in series to form a series node, and a photocurrent difference signal is generated at the series node. The series node is connected to the input terminal of the transimpedance amplifier. The input terminal of the data acquisition module is connected to the output terminal of the transimpedance amplifier. The transimpedance amplifier is used to convert the photocurrent difference signal into a photovoltage difference signal and amplify the photovoltage difference signal. The output terminal of the data acquisition module is connected to the data processing module for acquiring the photovoltage difference signal output by the transimpedance amplifier and performing signal conversion.

[0014] Furthermore, the control module includes a microcontroller, a current regulation module, and a modulation drive module. The microcontroller controls the current regulation module and the modulation drive module. Based on the control of the microcontroller, the current regulation module adjusts the wavelength and power of the laser beam output by the tunable laser. The tunable laser feeds back the laser beam wavelength and power information to the microcontroller. Based on the control of the microcontroller, the modulation drive module adjusts the drive voltage of the fixed-phase modulation module so that the phase difference between the input laser pulse and the output laser pulse is π / 2 or 3π / 2.

[0015] Preferably, the fixed phase modulation module, the first 50:50 beam splitter, the second 50:50 beam splitter, the zero-beat detection module, the control module, and the data processing module are fabricated on a chip using a monolithic integration process.

[0016] Furthermore, the current regulation module includes at least three sets of tuning current circuits, each tuning current circuit including a digital-to-analog converter and an amplifier. The input terminal of the digital-to-analog converter is connected to the output terminal of the microcontroller, the input terminal of the amplifier is connected to the output terminal of the digital-to-analog converter, and the output terminal of the amplifier is connected to the input terminal of the tunable laser.

[0017] Preferably, the first 50:50 beam splitter and the second 50:50 beam splitter are one of an optical fiber beam splitter, a multimode interference coupler, or a directional coupler.

[0018] Furthermore, the data acquisition module includes an analog-to-digital converter (ADC) for converting the amplified photovoltage difference signal into a digital photovoltage difference signal. The input terminal of the ADC is connected to the output terminal of the transimpedance amplifier, and the output terminal of the ADC is connected to the input terminal of the data processing module.

[0019] Furthermore, the spectrometer also includes a display system, which is connected to the data processing module and the control module, and is used to input control parameters and commands, locate and position phase adjustment parameters, and display the correspondence between the intensity of the light to be measured and the wavelength of the laser beam.

[0020] Secondly, this application discloses a spectral detection method based on zero-beat detection, which is applied to the aforementioned spectrometer. The spectrometer includes a tunable laser, a first 50:50 beam splitter, a second 50:50 beam splitter, a fixed phase modulation module, a control module, a data processing module, and two zero-beat detection modules. The method includes:

[0021] The light to be tested is input to the second 50:50 beam splitter;

[0022] The second 50:50 beam splitter splits the input beam under test into two sets of beams with the same energy. One set of beams under test is input to one zero-beat detection module, and the other set of beams under test is input to another zero-beat detection module.

[0023] The control module adjusts the output laser beam of the tunable laser to a wavelength of λ1 and transmits it to the first 50:50 beam splitter. At the same time, the tunable laser feeds back the laser beam information to the control module.

[0024] The first 50:50 beam splitter splits the input laser beam with wavelength λ1 into two sets of laser pulses with the same energy. One set of laser pulses is directly input to a zero-beat detection module, and the other set of laser pulses is input to a fixed phase modulation module.

[0025] Based on the laser beam with a current wavelength of λ1, the control module controls the fixed phase modulation module to perform phase modulation on the input laser light pulse, so that the phase difference between the input laser light pulse and the output laser light pulse is π / 2 or 3π / 2.

[0026] The phase-modulated laser pulse is input to another zero-beat detection module;

[0027] Two sets of zero-beat detection modules coherently detect the input laser light pulse and the beam to be tested, and amplify the detection signal;

[0028] The data processing module receives the detection signals output by the two sets of zero-beat detection modules and analyzes and processes them to obtain the light intensity information of the laser beam with wavelength λ1.

[0029] Once the detection of the laser beam with wavelength λ1 is completed, the control module adjusts the output of the tunable laser to a laser beam with wavelength λ2, and repeats the above process until the detection of all preset wavelength laser beams is completed.

[0030] The data processing module obtains the light intensity information corresponding to the wavelength of each tuned laser beam and forms the correspondence between the light intensity and the wavelength of the laser beam.

[0031] Furthermore, when the zero-beat detection module includes a third 50:50 beam splitter, a first photodiode, a second photodiode, a transimpedance amplifier, and a data acquisition module, the two sets of zero-beat detection modules coherently detect and amplify the input laser light pulse and the beam to be measured from the split beam, including:

[0032] The third 50:50 beam splitter coherently couples a laser light pulse with wavelength λ1 to the beam to be tested, and the output beam is incident on the first photodiode and the second photodiode respectively, and generates a photocurrent difference signal at the series node of the first photodiode and the second photodiode.

[0033] The transimpedance amplifier converts the photocurrent difference signal into a photovoltage difference signal and amplifies the photovoltage difference signal;

[0034] The data acquisition module acquires the amplified photovoltage difference signal and performs signal conversion before transmitting it to the data processing module.

[0035] Overall, compared with the prior art, the above-described technical solutions conceived in this application can achieve the following beneficial effects:

[0036] This application provides a spectrometer and a spectroscopic detection method based on zero-beat detection. The spectrometer includes a tunable laser, a first 50:50 beam splitter, a second 50:50 beam splitter, a fixed phase modulation module, a control module, a data processing module, and two zero-beat detection modules. The laser beam output from the tunable laser is used as the local oscillator. Two 50:50 beam splitters are used to split the test beam and the laser beam into two beams respectively. One set of the test beam is input to one zero-beat detection module, and the other set is input to the other zero-beat detection module. One set of laser pulses is directly input to one zero-beat detection module, and the other set of laser pulses is modulated by a fixed-phase modulation module and then input to the other zero-beat detection module. The fixed-phase modulation module makes the phase difference between the input laser pulse and the output laser pulse π / 2 or 3π / 2. The two sets of zero-beat detection modules coherently detect and amplify the detection signals of the laser pulses and the test beams, and finally obtain the test light intensity information corresponding to the wavelength of each tunable laser beam and form the correspondence between the test light intensity and the laser beam wavelength. In this application, a laser beam is used as the local oscillator light, and the intensity of the light under test is amplified after coherent detection by two sets of zero-beat detection modules. This obtains the intensity information of the light under test corresponding to the wavelength of each tuned laser beam, achieving efficient detection of weak beams or single-photon-level optical signals. Furthermore, the fixed-phase modulation module, the first 50:50 beam splitter, the second 50:50 beam splitter, the zero-beat detection module, the control module, and the data processing module can be fabricated on a single chip using monolithic integration technology, reducing the size of the spectrometer and lowering the cost of spectral detection. Attached Figure Description

[0037] To more clearly illustrate the technical solutions in this embodiment or the prior art, the drawings used in the description of the embodiment or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0038] Figure 1 A schematic diagram of a spectrometer based on zero-pace detection provided in an embodiment of this application;

[0039] Figure 2 This is a schematic diagram of the zero-shot detection module provided in the embodiments of this application;

[0040] Figure 3 A schematic diagram of a spectrometer based on zero-pace detection is provided for another embodiment of this application;

[0041] Figure 4 A schematic diagram of the principle of a spectrometer based on zero-pace detection provided for an embodiment of this application;

[0042] Figure 5 This is a schematic diagram of the control module in an embodiment of this application;

[0043] Figure 6 This is a schematic diagram of the current regulation module in an embodiment of this application;

[0044] Figure 7 A schematic diagram of a spectrometer based on zero-pace detection is provided for another embodiment of this application;

[0045] Figure 8 A flowchart of a spectral detection method based on zero-pace detection is provided for an embodiment of this application;

[0046] Figure 9 This is a flowchart of the detection method of the zero-shot detection module in the embodiments of this application. Detailed Implementation

[0047] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the embodiments of this application will be further described in detail below with reference to the accompanying drawings and specific implementation methods. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0048] Many specific details are set forth in the following description in order to provide a full understanding of this application. However, this application may also be implemented in other ways different from those described herein. Those skilled in the art can make similar extensions without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0049] To facilitate understanding and explanation of the technical solutions provided in the embodiments of this application, the background technology of this application will be described first.

[0050] A spectrometer is a scientific analytical instrument that decomposes complex composite light into spectral lines for measurement and calculation. It is widely used in radiometric analysis, color measurement, and chemical composition analysis, playing a vital role in industries such as metallurgy, geology, hydrology, medicine, petrochemicals, environmental protection, and space exploration. Currently, most spectrometers or spectrometers on the market are based on spatial optical grating structures to analyze and detect the wavelength of incident light waves. This method generally can only perform spectral analysis on relatively strong light beams (on the microwatt scale). Furthermore, due to significant optical losses and the limited detection intensity range of ordinary optical detectors, this system cannot effectively perform spectral analysis on weak light or single-photon level beams, thus limiting its practical applications and application scenarios.

[0051] Balanced bouncing detection is a technique used for measuring the amplitude and phase of optical signals. It has important applications in quantum random number generation, quantum noise analysis, heterodyne detection, and weak signal detection. In weak signal detection, balanced bouncing detection can be used to detect quantum noise. The key to this measurement is using a balanced bouncing detector to extract and amplify the AC noise signal loaded onto the light wave. This detector should have low noise and high sensitivity, so that it can not only effectively detect shot noise but also keep its own electronic noise far below the shot noise, avoiding overwhelming the shot noise. Simultaneously, in order for the shot noise spectrum to become the dominant output spectrum, the detector needs to detect a milliwatt-level optical field, thus possessing sufficiently high gain saturation characteristics.

[0052] Based on this, this application provides a spectrometer based on zero-pace detection, specifically, referring to... Figure 1 The present application provides a schematic diagram of the structure of a spectrometer based on zero-beat detection. The spectrometer includes a tunable laser, a first 50:50 beam splitter, a second 50:50 beam splitter, a fixed phase modulation module, a control module, a data processing module, and two zero-beat detection modules.

[0053] The first 50:50 beam splitter, the second 50:50 beam splitter, the fixed-phase modulation module, the control module, the data processing module, and the two zero-beat detection modules can be fabricated based on discrete devices and PCB circuit boards. More preferably, they can be fabricated on a chip using monolithic integration technology to reduce the size of the spectrometer and lower the cost of spectral detection. It should be noted that when the chip material is a group III-V material such as InP or GaAs, the tunable laser can be directly integrated on the chip.

[0054] The output of the tunable laser is connected to the input of the first 50:50 beam splitter, and is used to output a laser beam and feed back the laser beam information to the control module.

[0055] The laser beam information here includes the wavelength and frequency of the laser beam. A tunable laser can continuously change the output wavelength of the laser beam within a certain range, and the output laser beam serves as the local oscillator. It should be noted that one or more tunable lasers can be used. The number can be determined by considering multiple factors, such as the frequency range or expected frequency range of the light source or signal source under test, the spectral detection accuracy, and the preset number of laser beams with different wavelengths. This application does not specify a particular number of tunable lasers. When multiple tunable lasers are used, they are connected in parallel and uniformly controlled by the control module. Each tunable laser outputs a laser beam sequentially according to a timing signal.

[0056] Narrow-linewidth tunable lasers are preferred. The narrower the linewidth of the tunable laser, the longer its coherence length, enabling ultra-high precision, ultra-long distance, and ultra-high sensitivity detection of weak light signals, thus improving the resolution of spectral detection.

[0057] Both the first and second 50:50 beam splitters include an upper output and a lower output. The upper output of the first 50:50 beam splitter is connected to one of the zero-beat detection modules, and the lower output of the first 50:50 beam splitter is connected to the input of the fixed-phase modulation module. The output of the fixed-phase modulation module is connected to another zero-beat detection module. The first 50:50 beam splitter is used to split the input laser beam into two sets of laser pulses with the same energy. One set of laser pulses is directly input to one zero-beat detection module, and the other set of laser pulses is transmitted to another zero-beat detection module through the fixed-phase modulation module. The fixed-phase modulation module is used to perform phase modulation on the input laser pulses so that the phase difference between the input laser pulse and the output laser pulse is π / 2 or 3π / 2.

[0058] The second 50:50 beam splitter is used to split the input test light into two sets of test beams with the same energy. One set of test beams is input to a zero-beat detection module, and the other set of test beams is input to another zero-beat detection module.

[0059] For better explanation and understanding, the two zero-shot detection modules are named the first zero-shot detection module and the second zero-shot detection module, respectively.

[0060] Specifically, the first 50:50 beam splitter splits the input laser beam into two beams. One set of laser pulses is directly input to the first zero-beat detection module, while the other set of laser pulses is transmitted to the second zero-beat detection module via a fixed-phase modulation module. The fixed-phase modulation module modulates the phase of the input laser pulses, ensuring that the phase difference between the input and output laser pulses is π / 2 or 3π / 2. Similarly, the second 50:50 beam splitter splits the input beam under test into two beams. One set of the split beam is input to the first zero-beat detection module, while the other set is input to the second zero-beat detection module.

[0061] Here, the first 50:50 beam splitter and the second 50:50 beam splitter are one of the following: fiber optic beam splitter, multimode interference coupler, or directional coupler. Those skilled in the art can choose different types of products as needed.

[0062] The fixed-phase modulation module in this application modulates a transmitted laser beam using the photoelectric effect. By controlling the driving voltage to change the refractive index or birefringence of the photoelectric crystal, the phase of the output laser beam is altered. The fixed-phase modulation module does not change the polarization state of the light, only its phase. The phase difference generated by the transverse photoelectric effect of the electro-optic crystal is proportional to the driving voltage. The modulation phase of the laser beam is determined by the voltage, and the phase of the laser beam is modulated by changing the driving voltage. Here, the fixed-phase modulation module modulates a set of laser light pulses input to it. By changing the driving voltage, the phase difference between the input and output laser light pulses is made to be π / 2 or 3π / 2. Specifically, the fixed-phase modulation module can be one of a lithium niobate electro-optic phase modulator, a gallium arsenide electro-optic phase modulator, or a lithium tantalate electro-optic phase modulator.

[0063] The output of the zero-shot detection module is connected to the data processing module and is used to coherently detect the input laser pulse and the beam to be tested and amplify the detection signal.

[0064] The first zero-step detection module performs coherent detection on a set of input beams to be tested and a set of laser pulses directly input to them, and amplifies the detection signals. The second zero-step detection module performs coherent detection on a set of input beams to be tested and a set of modulated laser pulses, and amplifies the detection signals. Both sets of detection signals are transmitted to the data processing module.

[0065] The control module is used to adjust the wavelength of the laser beam output by the tunable laser and feed back the wavelength information of the currently tuned laser beam to the data processing module, as well as control the phase modulation of the laser pulse by the fixed phase modulation module.

[0066] The control module simultaneously controls the tunable laser and the fixed-phase modulation module. Specifically, the control module controls the tunable laser to output a specific wavelength and accurately switch between wavelengths. When there are multiple tunable lasers, the control module outputs a timing signal to control the order in which each tunable laser outputs its laser beam. Furthermore, based on wavelength locking of the tunable laser beam, the control module controls the fixed-phase modulation module to modulate the laser pulse at that wavelength, ensuring that the phase difference between the input and output laser pulses is π / 2 or 3π / 2. A preset tunable laser can output several laser beams with different wavelengths, namely wavelength λ1, wavelength λ2, wavelength λ3...wavelength λn. The control module controls the tunable laser to output a laser beam of wavelength λ1 and locks it. Based on the laser beam of this wavelength, the first 50:50 beam splitter splits it into two beams. The control module then controls the fixed phase modulation module to perform phase modulation on a group of laser light pulses of wavelength λ1. After the phase modulation and corresponding detection of the laser light pulses of wavelength λ1 are completed, the control module controls the tunable laser to switch to output a laser beam of wavelength λ2. Based on the laser beam of this wavelength, the control module controls the fixed phase modulation module to perform phase modulation on a group of laser light pulses of wavelength λ2. After the phase modulation and corresponding detection of the laser light pulses of wavelength λ2 are completed, the control module switches to the laser beam of wavelength λ3 to complete the above process. This process is repeated until the phase modulation and detection of wavelength λn are completed.

[0067] The data processing module is used to receive and analyze the signals output by the control module and the two sets of zero-beat detection modules to obtain the light intensity information of the light to be measured corresponding to the wavelength of each tuned laser beam and to form the correspondence between the light intensity to be measured and the wavelength of the laser beam.

[0068] In this application, the intensity of the light under test is amplified by coherent detection of the laser beam as the local oscillator light and the light under test through two sets of zero-beat detection modules. The intensity information of the light under test corresponding to the wavelength of each tuned laser beam is obtained by analysis and processing, so as to achieve efficient detection of weak beams or single-photon level optical signals.

[0069] Specifically, in embodiments of the present invention, the zero-beat detection module includes a third 50:50 beam splitter, a first photodiode, a second photodiode, a transimpedance amplifier, and a data acquisition module, such as... Figure 2As shown, the third 50:50 beam splitter includes an upper output and a lower output for coherent coupling of the input laser pulse and the beam to be split. The upper output of the third 50:50 beam splitter is connected to the optical path of the first photodiode, and the lower output of the third 50:50 beam splitter is connected to the optical path of the second photodiode. The first photodiode and the second photodiode are connected in series to form a series node, and a photocurrent difference signal is generated at the series node. The series node is connected to the input of the transimpedance amplifier. The input of the data acquisition module is connected to the output of the transimpedance amplifier. The transimpedance amplifier is used to convert the photocurrent difference signal into a photovoltage difference signal and amplify the photovoltage difference signal. The output of the data acquisition module is connected to the data processing module for acquiring the photovoltage difference signal output by the transimpedance amplifier and performing signal conversion.

[0070] In this embodiment, the third 50:50 beam splitter coherently couples the input laser pulse and the beam to be measured to form a superimposed optical field. The coherently coupled beam is split into two and incident on the first and second photodiodes, respectively. The first and second photodiodes are two similar photodiodes. Photodiodes have advantages such as simple structure, low dark current, low bias voltage, good dynamic characteristics and stability, which can meet the requirements of low-noise photoelectric detection and are more conducive to chip integration. The two photodiodes are connected in series. The received photocurrent signals are subtracted at the series node, and the resulting difference signal can reflect the relevant information of the optical signal. This setting avoids the complex operation of subtracting and the possible imbalance effect, and can also suppress the common-mode noise of the two beams simultaneously, improving the common-mode rejection ratio. The photocurrent difference signal generated at the series node is input to the transimpedance amplifier, which converts the photocurrent difference signal into a photovoltage difference signal and amplifies it. The data acquisition module performs preliminary processing on the amplified photovoltage difference signal.

[0071] In one embodiment of the present invention, the data acquisition module includes an analog-to-digital converter for converting the amplified photovoltage difference signal into a photovoltage difference digital signal. The input terminal of the analog-to-digital converter is connected to the output terminal of the transimpedance amplifier, and the output terminal of the analog-to-digital converter is connected to the input terminal of the data processing module.

[0072] based on Figure 1 and Figure 2 This application provides a spectrometer based on zero-pace detection, such as... Figure 3As shown, the spectrometer specifically includes a tunable laser, a first 50:50 beam splitter, a second 50:50 beam splitter, a fixed-phase modulation module, a control module, a data processing module, two third 50:50 beam splitters, two first photodiodes, two second photodiodes, two transimpedance amplifiers, and two data acquisition modules. Furthermore, the first 50:50 beam splitter, the second 50:50 beam splitter, the fixed-phase modulation module, the control module, the data processing module, the two third 50:50 beam splitters, the two first photodiodes, the two second photodiodes, the two transimpedance amplifiers, and the two data acquisition modules are fabricated on a single chip using a monolithic integrated circuit process.

[0073] To make this application clearer, the following will be combined with Figure 4 The working principle of the spectrometer is explained in detail.

[0074] For the zero-beat detection module, when the wavelength of the light signal to be measured is different from that of the laser beam, the output current of the first photodiode and the second photodiode at the series node is:

[0075]

[0076] For a light signal with the same wavelength as the laser beam in the light to be measured, the output current of the first photodiode and the second photodiode at the series node in the first zero-beat detection module is:

[0077]

[0078] in The responsivity of the first photodiode and the second photodiode. The intensity of the laser beam output by the tunable laser. The intensity of the light to be measured is the light with the same wavelength as the laser beam. The phase difference between the light to be measured and the laser beam is denoted as .

[0079] Compared to the first zero-beat detection module, the second zero-beat detection module, after beam splitting, generates laser pulses that, after modulation by a fixed-phase modulation module, have a fixed phase difference of π / 2 or 3π / 2 between the output laser pulse and the input laser pulse. Therefore, in the second zero-beat detection module, when modulated to a fixed phase difference of π / 2, the output current of the first photodiode and the second photodiode at the series junction is:

[0080] =

[0081] When modulated with a fixed phase difference of 3π / 2, the output current of the first and second photodiodes in the second zero-beat detection module at the series node is:

[0082] =

[0083] The current output from the first and second zero-beat detection modules is transmitted to the data processing module through a transimpedance amplifier and a data acquisition module. The voltage signal obtained after the data processing module performs a sum-of-squares operation is as follows:

[0084]

[0085] in The amplification factor of the transimpedance amplifier is given by the formula above, which indicates that the intensity of the light to be measured with the same wavelength as the laser beam is... Proportional to The output detection signal of the zero-beat detection module is further amplified by the sum-of-squares operation of the data processing module, resulting in a light intensity of the same wavelength as the laser beam. It was magnified This makes it theoretically possible to increase by a factor of two. The intensity of the laser beam can be used to measure weak light energy or light energy at the level of a single photon. However, light signals with wavelengths different from the laser beam will not be detected.

[0086] Based on the spectrometer provided in the above embodiments of this application, the control module further includes a microcontroller, a current regulation module, and a modulation drive module, such as... Figure 5 As shown. The microcontroller controls the current regulation module and the modulation drive module; the current regulation module, based on the control of the microcontroller, adjusts the wavelength and power of the laser beam output by the tunable laser; the tunable laser feeds back the laser beam wavelength and power information to the microcontroller; the modulation drive module, based on the control of the microcontroller, adjusts the drive voltage of the fixed-phase modulation module so that the phase difference between the input laser pulse and the output laser pulse is π / 2 or 3π / 2.

[0087] The microcontroller is the core of the entire control module. It not only controls the tunable laser to output a specific laser beam wavelength and accurately switches between wavelengths, but also processes the laser beam information fed back from the tunable laser in real time. Simultaneously, it processes the currently tuned laser beam wavelength information and outputs it to the data processing module. When there are multiple tunable lasers, the microcontroller outputs timing signals to control the order in which each tunable laser outputs its laser beam. To ensure high current control accuracy in the current regulation module, a phase-locked loop can be designed inside the microcontroller to provide the operating clock for the entire spectrometer, enabling rapid wavelength switching of the tunable laser.

[0088] Furthermore, based on the locked wavelength of the tuned laser beam, the microcontroller controls the modulation drive module to output different drive voltages, enabling the fixed-phase modulation module to perform phase modulation of the laser pulse at the current tuned wavelength. For each tuned laser beam wavelength, a lookup table can be used to locate the adjustment parameters required to modulate the corresponding wavelength laser pulse phase difference to π / 2 or 3π / 2. Different adjustment parameters generate corresponding drive voltage signals, and the modulation drive module adjusts the fixed-phase modulation module accordingly. This lookup table can be built into the microcontroller or installed on a display system or host computer. For tuned laser beams of different wavelengths, phase modulation of each tuned laser beam is achieved by changing the drive voltage, resulting in a modulation phase difference of π / 2 or 3π / 2.

[0089] Specifically, the current regulation module includes at least three sets of tuning current circuits, each tuning current circuit including a digital-to-analog converter and an amplifier. The input terminal of the digital-to-analog converter is connected to the output terminal of the microcontroller, the input terminal of the amplifier is connected to the output terminal of the digital-to-analog converter, and the output terminal of the amplifier is connected to the input terminal of the tunable laser.

[0090] In one embodiment of the present invention, the current regulation module includes three sets of tuning current circuits, such as... Figure 6 As shown. Of course, four or more groups of tuner current circuits can be set; this application does not limit the number of groups of tuner current circuits. The tuner current circuit, based on microcontroller control, adjusts the wavelength of the tunable laser. A data table of the tuner current and the output wavelength of the tunable laser is pre-generated and stored in the microcontroller. When the three groups of tuner current circuits simultaneously switch to the target current combination, the tunable laser outputs a specific laser beam wavelength. That is, the microcontroller controls the digital-to-analog converter (DAC) to tune the corresponding tuner current circuit for current output control, thereby adjusting the laser beam wavelength. The three groups of tuner currents are output through the DAC. To achieve high current control accuracy, a 14-bit resolution or higher resolution parallel data transmission DAC can be selected. The microcontroller outputs the wavelength switching information in parallel to the DAC, amplifies the signal through an amplifier, and outputs the corresponding current to the tunable laser, thus adjusting the laser beam wavelength.

[0091] In another embodiment of this application, the spectrometer further includes a display system, such as... Figure 7 As shown, the display system is connected to the data processing module and the control module, and is used to input control parameters and commands, search for positioning phase adjustment parameters, and display the correspondence between the light intensity to be measured and the wavelength of the laser beam.

[0092] The display system primarily functions in two ways: command input and display. Specifically, it can be used to input control parameters and commands, such as starting detection, setting the laser beam wavelength range, and the detection period for each wavelength. Furthermore, the display system can have a built-in lookup table to locate the corresponding phase adjustment parameters based on the user-input laser beam wavelength and the required phase difference, and then output these parameters to the control module. The display system can also show the correspondence between the measured light intensity and the laser beam wavelength.

[0093] Based on all the spectrometers provided in the embodiments of this application, the embodiments of this application also provide a corresponding spectral detection method based on zero-pace detection, such as... Figure 8 The diagram shown is a flowchart of a spectral detection method based on zero-pace detection provided in an embodiment of this application.

[0094] The spectral detection method includes:

[0095] S11: The light to be tested is input to the second 50:50 beam splitter.

[0096] In this embodiment, the light to be measured includes weak light signals or light signals at the level of a single photon.

[0097] S12: The second 50:50 beam splitter splits the input beam under test into two sets of beams with the same energy. One set of beams under test is input to one zero-beat detection module, and the other set of beams under test is input to another zero-beat detection module.

[0098] In this embodiment, the two zero-beat detection modules are the first zero-beat detection module and the second zero-beat detection module. The second 50:50 beam splitter splits the input light to be tested into two sets of beams of equal energy. One set of beams is input to the first zero-beat detection module, and the other set is input to the second zero-beat detection module.

[0099] S13: The control module adjusts the output laser beam of the tunable laser with wavelength λ1 and transmits it to the first 50:50 beam splitter. At the same time, the tunable laser feeds back the laser beam information to the control module.

[0100] In this embodiment, a preset tunable laser can output several laser beams with different wavelengths, namely wavelength λ1, wavelength λ2, wavelength λ3...wavelength λn. The control module controls the tunable laser to output a laser beam with wavelength λ1 and locks it in place. Simultaneously, the tunable laser transmits this laser beam information to the control module. This laser beam information includes information such as the wavelength and optical frequency of the laser beam. The control module receives the laser beam information and outputs it to the data processing module.

[0101] S14: The first 50:50 beam splitter splits the input laser beam with wavelength λ1 into two sets of laser pulses with the same energy. One set of laser pulses is directly input to a zero-beat detection module, and the other set of laser pulses is input to a fixed phase modulation module.

[0102] In this embodiment, the first 50:50 beam splitter divides the input laser beam with wavelength λ1 into two sets of laser pulses with the same energy. One set of laser pulses is directly input to the first zero-beat detection module, and the other set of laser pulses is input to the fixed phase modulation module.

[0103] S15: Based on the current laser beam with wavelength λ1, the control module controls the fixed phase modulation module to perform phase modulation on the input laser light pulse, so that the phase difference between the input laser light pulse and the output laser light pulse is π / 2 or 3π / 2.

[0104] In this embodiment, the phase of a laser pulse with wavelength λ1 is modulated by controlling the modulation drive module to output different drive voltages, so that the phase difference between the input and output laser pulses is π / 2 or 3π / 2. The modulation phase of the laser pulse is determined by the drive voltage. For each tuned laser beam wavelength, the adjustment parameter required to modulate the corresponding wavelength laser pulse phase difference of π / 2 or 3π / 2 can be located by looking up a table, and different adjustment parameters generate corresponding drive voltage signals.

[0105] S16: The phase-modulated laser pulse is input to another zero-beat detection module.

[0106] In this embodiment, a laser light pulse modulated with a fixed phase is input to the second zero-beat detection module.

[0107] S17: Two sets of zero-beat detection modules coherently detect the input laser light pulse and the beam to be tested, and amplify the detection signal.

[0108] In this embodiment, the first zero-beat detection module performs coherent detection on a set of input beams to be tested and a set of laser pulses directly input to them, and amplifies the detection signals. The second zero-beat detection module performs coherent detection on a set of input beams to be tested and a set of laser pulses modulated with a fixed phase, and amplifies the detection signals. Both sets of detection signals are transmitted to the data processing module.

[0109] S18: The data processing module receives the detection signals output by the two sets of zero-beat detection modules and analyzes and processes them to obtain the light intensity information of the laser beam with wavelength λ1.

[0110] As can be seen from the above explanation of the working principle, the data processing module further amplifies the light intensity to be measured by performing a sum of squares operation on the two sets of received detection signals, and finally obtains the light intensity to be measured corresponding to the laser beam with wavelength λ1 by reverse calculation.

[0111] S19: The detection of the laser beam with wavelength λ1 is completed. The control module adjusts the output of the tunable laser to a laser beam with wavelength λ2. The above process is repeated until the detection of all preset wavelength laser beams is completed.

[0112] S110: The data processing module obtains the light intensity information corresponding to the wavelength of each tuned laser beam and forms the correspondence between the light intensity to be measured and the wavelength of the laser beam.

[0113] In this embodiment, after all tuned laser beams of preset wavelengths have been detected, the data processing module obtains the light intensity information corresponding to the wavelength of each tuned laser beam, forming a correspondence between light intensity and wavelength, i.e., a spectrum. The spectrum can be displayed through a display system.

[0114] In this embodiment, the laser beam output by the tunable laser is used as the local oscillator. Two 50:50 beam splitters are used to split the beam to be tested and the laser beam into two beams respectively. One set of the beam to be tested is input to the first zero-beat detection module, and the other set of the beam to be tested is input to the second zero-beat detection module. One set of laser light pulses is directly input to the first zero-beat detection module, and the other set of laser light pulses is modulated by a fixed phase modulation module and then input to the second zero-beat detection module. The control module controls the tunable laser to output different wavelengths and accurately switch between wavelengths. Based on the laser beam of the current tuning wavelength, the control module controls the fixed phase modulation module to perform phase modulation on a group of laser light pulses after the laser beam is split, so that the phase difference between the input laser light pulse and the output laser light pulse is π / 2 or 3π / 2. Two sets of zero-beat detection modules coherently detect the laser light pulses input to them and the beam to be measured and amplify the detection signal. Finally, the light intensity information of the light to be measured corresponding to the wavelength of each tuned laser beam is obtained, and the correspondence between the light intensity to be measured and the wavelength of the laser beam is formed, realizing efficient detection of weak beams or single-photon level optical signals.

[0115] Based on the spectral detection method provided in the above embodiments of this application, when the zero-beat detection module includes a third 50:50 beam splitter, a first photodiode, a second photodiode, a transimpedance amplifier, and a data acquisition module, such as Figure 9 The flowchart shown illustrates the following steps for the two sets of zero-beat detection modules to coherently detect and amplify the input laser pulse and the beam to be tested:

[0116] S21: The third 50:50 beam splitter coherently couples the laser light pulse with wavelength λ1 and the beam to be tested, and the output beam is incident on the first photodiode and the second photodiode respectively, and generates a photocurrent difference signal at the series node of the first photodiode and the second photodiode.

[0117] It is important to note that the laser pulses with wavelength λ1 received by the third 50:50 beam splitter in the two sets of zero-beat detection modules are different. The laser pulses received by the third 50:50 beam splitter in one set of zero-beat detection modules are unmodulated, while the laser pulses received by the third 50:50 beam splitter in the other set of zero-beat detection modules are pulse signals modulated by a fixed-phase modulation module.

[0118] S22: The transimpedance amplifier converts the photocurrent difference signal into a photovoltage difference signal and amplifies the photovoltage difference signal.

[0119] S23: The data acquisition module acquires the amplified photovoltage difference signal and performs signal conversion before transmitting it to the data processing module.

[0120] The various embodiments in this specification are described in a progressive, parallel, or combined manner. Each embodiment focuses on the differences from other embodiments, and the same or similar parts between the embodiments can be referred to each other.

[0121] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that an article or apparatus comprising a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such an article or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the article or apparatus that includes the aforementioned element.

[0122] The above description of the disclosed embodiments enables those skilled in the art to make or use this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A spectrometer based on zero-pace detection, characterized in that, It includes a tunable laser, a first 50:50 beam splitter, a second 50:50 beam splitter, a fixed phase modulation module, a control module, a data processing module, and two zero-beat detection modules; The output end of the tunable laser is connected to the input end of the first 50:50 beam splitter, and is used to output a laser beam and feed back the laser beam information to the control module. Both the first and second 50:50 beam splitters include an upper output and a lower output. The upper output of the first 50:50 beam splitter is connected to one of the zero-beat detection modules, and the lower output of the first 50:50 beam splitter is connected to the input of the fixed-phase modulation module. The output of the fixed-phase modulation module is connected to another zero-beat detection module. The first 50:50 beam splitter is used to split the input laser beam into two sets of laser pulses with the same energy. One set of laser pulses is directly input to one zero-beat detection module, and the other set of laser pulses is transmitted to another zero-beat detection module through the fixed-phase modulation module. The fixed-phase modulation module is used to perform phase modulation on the input laser pulses so that the phase difference between the input laser pulse and the output laser pulse is π / 2 or 3π / 2. The second 50:50 beam splitter is used to split the input test light into two sets of test beams with the same energy. One set of test beams is input to one zero-beat detection module, and the other set of test beams is input to another zero-beat detection module. The output of the zero-beat detection module is connected to the data processing module and is used to coherently detect the input laser light pulse and the beam to be tested and amplify the detection signal. The control module is used to adjust the wavelength of the laser beam output by the tunable laser and feed back the wavelength information of the currently tuned laser beam to the data processing module, as well as control the phase modulation of the laser pulse by the fixed phase modulation module. The data processing module is used to receive and analyze the signals output by the control module and the two sets of zero-beat detection modules to obtain the light intensity information of the light to be measured corresponding to the wavelength of each tuned laser beam and to form the correspondence between the light intensity to be measured and the wavelength of the laser beam.

2. The spectrometer based on zero-beat detection according to claim 1, characterized in that, The zero-shot detection module includes a third 50:50 beam splitter, a first photodiode, a second photodiode, a transimpedance amplifier, and a data acquisition module. The third 50:50 beam splitter includes an upper output and a lower output for coherent coupling of the input laser pulse and the beam to be tested. The upper output of the third 50:50 beam splitter is connected to the optical path of the first photodiode, and the lower output of the third 50:50 beam splitter is connected to the optical path of the second photodiode. The first photodiode and the second photodiode are connected in series to form a series node, and a photocurrent difference signal is generated at the series node. The series node is connected to the input of the transimpedance amplifier. The input of the data acquisition module is connected to the output of the transimpedance amplifier. The transimpedance amplifier is used to convert the photocurrent difference signal into a photovoltage difference signal and amplify the photovoltage difference signal. The output of the data acquisition module is connected to the data processing module for acquiring the photovoltage difference signal output by the transimpedance amplifier and performing signal conversion.

3. The spectrometer based on zero-beat detection according to claim 1, characterized in that, The control module includes a microcontroller, a current regulation module, and a modulation drive module. The microcontroller controls the current regulation module and the modulation drive module. Based on the control of the microcontroller, the current regulation module adjusts the wavelength and power of the laser beam output by the tunable laser. The tunable laser feeds back the laser beam wavelength and power information to the microcontroller; the modulation drive module, based on the control of the microcontroller, adjusts the drive voltage of the fixed phase modulation module so that the phase difference between the input laser pulse and the output laser pulse is π / 2 or 3π / 2.

4. The spectrometer based on zero-beat detection according to claim 1, characterized in that, The fixed phase modulation module, the first 50:50 beam splitter, the second 50:50 beam splitter, the zero-beat detection module, the control module, and the data processing module are fabricated on a chip using a monolithic integration process.

5. The spectrometer based on zero-beat detection according to claim 3, characterized in that, The current regulation module includes at least three sets of tuning current circuits. Each tuning current circuit includes a digital-to-analog converter and an amplifier. The input terminal of the digital-to-analog converter is connected to the output terminal of the microcontroller. The input terminal of the amplifier is connected to the output terminal of the digital-to-analog converter. The output terminal of the amplifier is connected to the input terminal of the tunable laser.

6. The spectrometer based on zero-beat detection according to any one of claims 1-5, characterized in that, The first 50:50 beam splitter and the second 50:50 beam splitter are one of the following: fiber optic beam splitter, multimode interference coupler, or directional coupler.

7. The spectrometer based on zero-beat detection according to claim 2, characterized in that, The data acquisition module includes an analog-to-digital converter (ADC) for converting the amplified photovoltage difference signal into a digital photovoltage difference signal. The input terminal of the ADC is connected to the output terminal of the transimpedance amplifier, and the output terminal of the ADC is connected to the input terminal of the data processing module.

8. The spectrometer based on zero-beat detection according to any one of claims 1-5, characterized in that, The spectrometer also includes a display system, which is connected to the data processing module and the control module. The display system is used to input control parameters and commands, locate and position phase adjustment parameters, and display the correspondence between the intensity of the light to be measured and the wavelength of the laser beam.

9. A spectral detection method based on zero-beat detection, characterized in that, The method is applied to the spectrometer according to any one of claims 1-8, the spectrometer comprising a tunable laser, a first 50:50 beam splitter, a second 50:50 beam splitter, a fixed phase modulation module, a control module, a data processing module, and two zero-beat detection modules; the method includes: The light to be tested is input to the second 50:50 beam splitter; The second 50:50 beam splitter splits the input beam under test into two sets of beams with the same energy. One set of beams under test is input to one zero-beat detection module, and the other set of beams under test is input to another zero-beat detection module. The control module adjusts the output laser beam of the tunable laser to a wavelength of λ1 and transmits it to the first 50:50 beam splitter. At the same time, the tunable laser feeds back the laser beam information to the control module. The first 50:50 beam splitter splits the input laser beam with wavelength λ1 into two sets of laser pulses with the same energy. One set of laser pulses is directly input to a zero-beat detection module, and the other set of laser pulses is input to a fixed phase modulation module. Based on the laser beam with a current wavelength of λ1, the control module controls the fixed phase modulation module to perform phase modulation on the input laser light pulse, so that the phase difference between the input laser light pulse and the output laser light pulse is π / 2 or 3π / 2. The phase-modulated laser pulse is input to another zero-beat detection module; Two sets of zero-beat detection modules coherently detect the input laser light pulse and the beam to be tested, and amplify the detection signal; The data processing module receives the detection signals output by the two sets of zero-beat detection modules and analyzes and processes them to obtain the light intensity information of the laser beam with wavelength λ1. Once the detection of the laser beam with wavelength λ1 is completed, the control module adjusts the output of the tunable laser to a laser beam with wavelength λ2, and repeats the above process until the detection of all preset wavelength laser beams is completed. The data processing module obtains the light intensity information corresponding to the wavelength of each tuned laser beam and forms the correspondence between the light intensity and the wavelength of the laser beam.

10. The spectral detection method based on zero-beat detection according to claim 9, characterized in that, When the zero-beat detection module includes a third 50:50 beam splitter, a first photodiode, a second photodiode, a transimpedance amplifier, and a data acquisition module, the two sets of zero-beat detection modules coherently detect and amplify the input laser light pulse and the beam to be tested beam, including: The third 50:50 beam splitter coherently couples a laser light pulse with wavelength λ1 to the beam to be tested, and the output beam is incident on the first photodiode and the second photodiode respectively, and generates a photocurrent difference signal at the series node of the first photodiode and the second photodiode. The transimpedance amplifier converts the photocurrent difference signal into a photovoltage difference signal and amplifies the photovoltage difference signal; The data acquisition module acquires the amplified photovoltage difference signal and performs signal conversion before transmitting it to the data processing module.

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