A spectral detector, a spectrometer and a spectral detection method

Abstract

The application discloses a spectrum detector, a spectrum instrument and a spectrum detection method. The spectrum detector comprises a tunable laser, a phase modulator, a 50:50 beam splitter, a first photodiode, a second photodiode, a transimpedance amplifier, a data acquisition module, a control module and a data processing module. The tunable laser is used as a local light source, and the control module and the phase modulator are added, so that the laser beam is coherently coupled with a to-be-detected light signal. The coherently coupled light beams are respectively incident into two similar photodiodes, and a photocurrent difference signal is generated at a series connection node of the two photodiodes. After processing the signal, intensity information of the amplified coherent signal is obtained. Then, the data processing module combines phase scanning information of the laser beam under different wavelengths, and wavelength and spectrum information of the to-be-detected light signal are obtained, so that efficient detection of a weak light beam or a single-photon-level light signal is realized.

Description

Technical Field

[0001] This application belongs to the field of spectral analysis, and specifically relates to a spectral detector, a spectrometer, and a spectral detection method. 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] 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

[0004] To address the aforementioned problems, this application provides a spectral detector, spectrometer, and spectral detection method for detecting weak light or single-photon-level beams. The specific solution is as follows:

[0005] In a first aspect, this application discloses a spectral detector, including a tunable laser, a phase modulator, a 50:50 beam splitter, a first photodiode, a second photodiode, a transimpedance amplifier, a data acquisition module, a control module, and a data processing module.

[0006] The tunable laser is used to output a laser beam to the phase modulator and feed back the laser beam information to the control module; the phase modulator is used to modulate the phase of the laser beam; the output end of the phase modulator is connected to the first incident end of the 50:50 beam splitter; the second incident end of the 50:50 beam splitter is used to input the optical signal to be measured; the 50:50 beam splitter is used to coherently couple the laser beam and the optical signal to be measured; the 50:50 beam splitter includes an upper output end and a lower output end; the first photodiode detects the coherently coupled beam output from the upper output end of the 50:50 beam splitter, and the second photodiode detects the coherently coupled beam output from the lower output end of the 50:50 beam splitter; the first photodiode and the second photodiode are connected in series to form a series node and a photocurrent difference is generated at the series node. The signal; 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; the control module is used to adjust and control the wavelength of the laser beam output by the tunable laser and output the wavelength information of the currently tuned laser beam to the data processing module, and control the phase modulator to perform phase periodic scanning of the laser beam; the data processing module is used to receive the signals output by the data acquisition module and the control module and analyze and process them to obtain the maximum photovoltage signal at each tuned laser beam wavelength and convert the maximum photovoltage signal into light intensity information, and obtain the correspondence between light intensity and wavelength.

[0007] 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. Based on the control of the microcontroller, the modulation drive module adjusts the drive voltage of the phase modulator.

[0008] Preferably, the phase modulator, 50:50 beam splitter, first photodiode, second photodiode, transimpedance amplifier, data acquisition module, control module, and data processing module are fabricated on a chip using a monolithic integration process.

[0009] 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.

[0010] Furthermore, the modulation driving module includes a signal generation circuit, a preamplifier circuit, and a post-amplifier high-voltage operational amplifier circuit. The signal generation circuit is used to generate and output a voltage signal; the preamplifier circuit is used to amplify the voltage signal output by the signal generation circuit; and the post-amplifier high-voltage operational amplifier circuit is used to further amplify the voltage signal output by the preamplifier circuit.

[0011] Preferably, the 50:50 beam splitter is one of an optical fiber beam splitter, a multimode interference coupler, or a directional coupler.

[0012] Preferably, 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.

[0013] Secondly, this application discloses a spectrometer, which includes a display system and a spectral detector disclosed in this application. The display system is used to input control parameters and commands, and to display the phase scanning process and spectral curves.

[0014] Thirdly, this application discloses a spectral detection method, which is applied to the spectral detector disclosed in this application. The spectral detector includes a tunable laser, a phase modulator, a 50:50 beam splitter, a first photodiode, a second photodiode, a transimpedance amplifier, a data acquisition module, a control module, and a data processing module; the method includes:

[0015] The optical signal to be tested is input to the 50:50 beam splitter;

[0016] The control module adjusts and controls the output of the tunable laser with a wavelength of λ1, and at the same time, the tunable laser feeds back the laser beam information to the control module.

[0017] Based on the laser beam with a current wavelength of λ1, the control module controls the phase modulator to perform a phase periodic scan on the laser beam, forming a different phase difference with the optical signal to be measured. The phase periodic scan range is 0-2π.

[0018] The 50:50 beam splitter coherently couples the laser beam with wavelength λ1 and the optical signal to be measured, and the output beam is incident on the first photodiode and the second photodiode respectively, and a photocurrent difference signal is generated at the series node of the first photodiode and the second photodiode.

[0019] The photocurrent difference signal is input to the data processing module after passing through a transimpedance amplifier and a data acquisition module;

[0020] The data processing module receives and analyzes the signals output by the data acquisition module and the control module to obtain the maximum photovoltage signal of the laser beam with wavelength λ1, and converts the maximum photovoltage signal into light intensity information.

[0021] Once the phase periodic scan 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 phase periodic scan of all preset wavelength laser beams is completed.

[0022] The data processing module obtains the maximum photovoltage signal at each preset laser beam wavelength and converts each maximum photovoltage signal into corresponding light intensity information, forming a correspondence between light intensity and wavelength.

[0023] 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; 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 modulation drive module, based on the control of the microcontroller, adjusts the drive voltage of the phase modulator.

[0024] In summary, compared with the prior art, the above-described technical solutions conceived in this application can achieve the following beneficial effects:

[0025] This application provides a spectral detector, a spectrometer, and a spectral detection method. The spectral detector includes a tunable laser, a phase modulator, a 50:50 beam splitter, a first photodiode, a second photodiode, a transimpedance amplifier, a data acquisition module, a control module, and a data processing module. By setting the tunable laser as the local oscillator and adding the control module and phase modulator, the laser beam is coherently coupled to the optical signal to be measured. The coherently coupled beams are incident on two similar photodiodes, generating a photocurrent difference signal at the series junction of the two photodiodes. After processing this signal, the intensity information of the amplified coherent signal is obtained. Then, the data processing module combines the phase scanning information of the laser beam at different wavelengths to obtain the wavelength and spectral information of the optical signal to be measured, achieving efficient detection of weak beams or single-photon level optical signals. In addition, the phase modulator, 50:50 beam splitter, first photodiode, second photodiode, transimpedance amplifier, data acquisition module, control module, and data processing module can be fabricated on a chip using monolithic integration technology, reducing the size of the spectral detector and spectrometer and lowering the cost of spectral detection. Attached Figure Description

[0026] 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.

[0027] Figure 1 This is a schematic diagram of the structure of a spectral detector provided in an embodiment of this application;

[0028] Figure 2 A schematic diagram of the principle of a spectral detector provided in an embodiment of this application;

[0029] Figure 3 This is a schematic diagram of the control module in an embodiment of this application;

[0030] Figure 4 This is a schematic diagram of the current regulation module in an embodiment of this application;

[0031] Figure 5 This is a schematic diagram of the modulation driving module in an embodiment of this application;

[0032] Figure 6 This is a schematic diagram of the structure of a spectrometer provided in an embodiment of this application;

[0033] Figure 7 A flowchart of a spectral detection method provided in an embodiment of this application;

[0034] Figure 8 A flowchart of another spectral detection method provided in an embodiment of this application. Detailed Implementation

[0035] 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.

[0036] 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.

[0037] 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.

[0038] A spectrometer, or spectral detector, 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, 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.

[0039] 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 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 limited 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.

[0040] Based on this, this application provides a spectral detector, specifically, referring to... Figure 1 This is a schematic diagram of the structure of a spectral detector provided in an embodiment of this application. The spectral detector includes a tunable laser, a phase modulator, a 50:50 beam splitter, a first photodiode, a second photodiode, a transimpedance amplifier, a data acquisition module, a control module, and a data processing module.

[0041] The phase modulator, 50:50 beam splitter, first photodiode, second photodiode, transimpedance amplifier, data acquisition module, control module, and data processing module can be fabricated based on discrete devices and PCB circuit boards. More preferably, they are fabricated on a chip using monolithic integration technology to reduce the size of the spectral detector and spectrometer and lower the cost of spectral detection. It should be noted that when the chip material is a III-V group material such as InP or GaAs, the tunable laser can be directly integrated on the chip.

[0042] The tunable laser is used to output a laser beam to the phase modulator and feed back the laser beam information to the control module. This laser beam information includes the wavelength and frequency of the laser beam. The tunable laser can continuously change the output wavelength of the laser beam within a certain range, and the output laser beam serves as a local oscillator source. 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 number of preset scan wavelengths of the laser beam. 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.

[0043] 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.

[0044] The phase modulator is used to modulate the phase of the laser beam output from a tunable laser. Specifically, the phase modulator utilizes the photoelectric effect to modulate the transmitted laser beam. 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 phase modulator 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.

[0045] The output of the phase modulator is connected to the first incident end of the 50:50 beam splitter; the second incident end of the 50:50 beam splitter is used to input the optical signal to be measured; the 50:50 beam splitter is used to coherently couple the laser beam and the optical signal to be measured.

[0046] The 50:50 beam splitter can be one of an optical fiber beam splitter, a multimode interference coupler, or a directional coupler. Those skilled in the art can select different types of 50:50 beam splitters as needed. After the laser beam and the optical signal under test are coupled by interference at the 50:50 beam splitter, two coherent superimposed optical fields are output. In this embodiment, the optical signal under test includes a weak optical signal or an optical signal at the single-photon level.

[0047] The 50:50 beam splitter includes an upper output and a lower output; the first photodiode detects the coherent coupled beam output from the upper output of the 50:50 beam splitter, and the second photodiode detects the coherent coupled beam output from the lower output of the 50:50 beam splitter; 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.

[0048] Here, 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 good stability, which can meet the requirements of low-noise photoelectric detection and are also more conducive to chip integration. After the optical signal under test is coherently coupled to the laser beam at a 50:50 beam splitter, the two coherently coupled beams output are respectively incident on the two similar photodiodes. 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 potential imbalance effect, and can also suppress the common-mode noise of the two beams simultaneously, improving the common-mode rejection ratio.

[0049] The series node is connected to the input terminal of the transimpedance amplifier. 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 the photovoltage difference signal.

[0050] The input terminal of the data acquisition module is connected to the output terminal of the transimpedance amplifier; the output terminal of the data acquisition module is connected to the data processing module. The data acquisition module is used to receive the amplified photovoltage difference signal and perform preliminary processing on this signal.

[0051] 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.

[0052] The control module is used to adjust and control the wavelength of the laser beam output by the tunable laser, while outputting the wavelength information of the currently tuned laser beam to the data processing module, and to control the phase modulator to perform phase periodic scanning of the laser beam.

[0053] The control module simultaneously controls the tunable laser and the phase modulator. 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 phase modulator to perform periodic phase scanning of the laser beam at that wavelength, creating a different phase difference with the optical signal under test. 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 wavelength λ1, the control module controls the phase modulator to perform a phase periodic scan on the laser beam of wavelength λ1. The phase scan range is 0-2π. Therefore, the laser beam of wavelength λ1 forms a different phase difference with the optical signal under test. After the phase scan of the entire cycle is completed, the control module controls the tunable laser to switch to output a laser beam of wavelength λ2. Based on the laser beam of wavelength λ2, the control module controls the phase modulator to perform a phase periodic scan on the laser beam of wavelength λ2. After the phase scan of the entire cycle of the laser beam of wavelength λ2 is completed, the control module switches to the laser beam of wavelength λ3 for phase periodic scan. This process is repeated until the phase periodic scan of wavelength λn is completed.

[0054] The data processing module is used to receive and analyze the signals output by the data acquisition module and the control module, obtain the maximum photovoltage signal at each wavelength of the tuned laser beam, convert the maximum photovoltage signal into light intensity information, and obtain the correspondence between light intensity and wavelength.

[0055] In this embodiment of the invention, by setting a tunable laser as the local oscillator light source and adding a control module and a phase modulator, the laser beam is coherently coupled with the optical signal to be measured to obtain the intensity information of the amplified coherent signal. Then, the data processing module combines the phase scanning information of the laser beam at different wavelengths to obtain the wavelength and spectral information of the optical signal to be measured, thereby achieving efficient detection of the spectrum of weak beams.

[0056] To make this application clearer, the following will be combined with Figure 2 The working principle of the spectral detector is explained in detail.

[0057] For an optical signal whose wavelength differs from that of the laser beam in the light being measured, the output current at the series junction of the first and second photodiodes is:

[0058]

[0059] For an optical signal with the same wavelength as the laser beam in the light being measured, the output current at the series junction of the first photodiode and the second photodiode is:

[0060]

[0061] in The responsivity of the first photodiode and the second photodiode. The intensity of the laser beam. The intensity of the light to be measured is the light with the same wavelength as the laser beam. To determine the phase difference between the light to be measured and the laser beam, the phase difference is adjusted to... hour,

[0062]

[0063] Then the light energy in the light to be measured that has the same spectrum as the laser light It was magnified The power was multiplied and converted into current output, due to... relatively Very small, so approximately equal to Enlarged 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.

[0064] Based on the spectral detector 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 3 As shown.

[0065] 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 modulation drive module, based on the control of the microcontroller, adjusts the drive voltage of the phase modulator.

[0066] 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 a timing signal 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 (PLL) can be designed inside the microcontroller to provide the operating clock for the entire spectrometer, enabling rapid wavelength switching of the tunable laser. Furthermore, based on the locked-down tunable laser beam wavelength, the microcontroller modulates the laser beam phase by controlling the modulation drive module to output different drive voltages. The modulation phase of the laser beam is determined by the drive voltage. By changing the drive voltage, a phase periodic scan at the tunable laser beam wavelength is completed. During this phase scan, a different phase difference is formed between the laser beam and the optical signal under test. As can be seen from the above working principle, when the phase difference between the laser beam and the light signal to be measured is 0, the maximum photovoltage signal at the current wavelength of the tuned laser beam is obtained. The data processing module converts the maximum photovoltage signal at the current wavelength of the tuned laser beam into light intensity information and records it. After all wavelengths of laser beams have completed phase period scanning, the data processing module obtains the maximum photovoltage signal at the wavelength of each tuned laser beam, forming a correspondence between light intensity and wavelength, which is the spectral curve.

[0067] Based on the spectral detector provided in the above embodiments of this application, the current adjustment module further 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, and the output terminal of the amplifier is connected to the input terminal of the tunable laser.

[0068] In one embodiment of the present invention, the current regulation module includes three sets of tuning current circuits, such as... Figure 4As 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.

[0069] Based on the spectral detector provided in the above embodiments of this application, the modulation driving module further includes a signal generation circuit, a preamplifier circuit, and a post-amplifier high-voltage operational amplifier circuit, such as... Figure 5 As shown. The signal generation circuit is used to generate and output a voltage signal, the preamplifier circuit is used to amplify the voltage signal output by the signal generation circuit, and the post-amplifier high-voltage operational amplifier circuit is used to further amplify the voltage signal output by the preamplifier circuit.

[0070] Specifically, the output of the signal generation circuit is connected to the input of the preamplifier circuit, the output of the preamplifier circuit is connected to the input of the post-high voltage operational amplifier circuit, and the output of the post-high voltage operational amplifier circuit is connected to the input of the phase modulator.

[0071] The signal generation circuit can directly synthesize voltage signals using DDS technology, and both the amplitude and frequency of the signal can be adjusted. Specifically, a microcontroller can control the DDS chip to generate a controllable output voltage. By changing the frequency control word of the DDS chip, a corresponding output voltage can be generated, thus achieving output voltage regulation. When a voltage signal is applied to the phase modulator, the phase of the laser beam passing through the phase modulator changes with the voltage.

[0072] Because the initial voltage signal generated by the signal generation circuit is small (millivolt level), it cannot directly drive the phase modulator to work properly. Therefore, the voltage signal needs to be amplified before being applied to the electro-optic crystal inside the phase modulator. Furthermore, since smaller signals often have greater noise, amplifying the small signal can also improve the signal-to-noise ratio. The voltage signal output from the signal generation circuit is input to the preamplifier circuit, which amplifies the millivolt-level initial voltage signal to a volt-level signal. Then, a post-amplifier high-voltage operational amplifier circuit further amplifies the voltage signal from the preamplifier circuit to a hundred-volt level signal, thus meeting the requirements for driving the phase modulator.

[0073] Based on all the spectral detectors provided in the embodiments of this application, the embodiments of this application also provide a spectrometer, such as... Figure 6 As shown, the spectrometer includes a display system and a spectral detector. The display system is used to input control parameters and commands, as well as to display the phase scanning process and spectral curves.

[0074] The display system primarily serves two functions: command input and display. Specifically, it can be used to input control parameters and commands, such as starting detection, setting the scanning wavelength range, and scanning step size. Furthermore, the display system also displays the phase scanning progress and spectral curves, such as showing the relationship between light intensity and wavelength.

[0075] Based on all the spectral detectors provided in the embodiments of this application, the embodiments of this application also provide a corresponding spectral detection method, such as... Figure 7 The diagram shown is a flowchart of a spectral detection method provided in an embodiment of this application.

[0076] The spectral detection method includes:

[0077] S71: The optical signal to be tested is input to the 50:50 beam splitter.

[0078] In this embodiment, the optical signal to be measured includes a weak optical signal or an optical signal at the level of a single photon.

[0079] S72: The control module adjusts and controls the output of the tunable laser with a wavelength of λ1, and at the same time, the tunable laser feeds back the laser beam information to the control module.

[0080] 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.

[0081] S73: Based on the laser beam with a current wavelength of λ1, the control module controls the phase modulator to perform a phase periodic scan on the laser beam, forming a different phase difference with the optical signal to be measured. The phase periodic scan range is 0-2π.

[0082] S74: The 50:50 beam splitter coherently couples a laser beam with wavelength λ1 to the optical signal under test, and outputs the beams to 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.

[0083] S75: The photocurrent difference signal is input to the data processing module after passing through the transimpedance amplifier and the data acquisition module.

[0084] In this embodiment, the transimpedance amplifier converts the photocurrent difference signal into a photovoltage difference signal and amplifies it. The data acquisition module receives the amplified photovoltage difference signal and performs preliminary processing on it, such as converting the photovoltage difference signal into a digital photovoltage difference signal.

[0085] S76: The data processing module receives the signals output by the data acquisition module and the control module and analyzes and processes them to obtain the maximum photovoltage signal of the laser beam with wavelength λ1, and converts the maximum photovoltage signal into light intensity information.

[0086] In this embodiment, the signal transmitted from the data acquisition module to the data processing module includes a digital signal of photovoltage difference, and the signal transmitted from the control module to the data processing module includes laser beam information with wavelength λ1. When the phase difference between the laser beam with wavelength λ1 and the light signal to be measured is 0, the maximum photovoltage signal at the wavelength of the laser beam is obtained, and the data processing module converts the maximum photovoltage signal at the wavelength into light intensity information and records it.

[0087] S77: The phase period scan of the laser beam with wavelength λ1 is completed. The control module adjusts the output of the tunable laser with wavelength λ2 and repeats the above process until the phase period scan of all preset wavelength laser beams is completed.

[0088] S78: The data processing module obtains the maximum photovoltage signal at each preset laser beam wavelength and converts each maximum photovoltage signal into corresponding light intensity information, forming a correspondence between light intensity and wavelength.

[0089] In this embodiment, after all preset wavelength laser beams have completed phase period scanning, the data processing module obtains the maximum photovoltage signal at each preset laser beam wavelength and converts it into corresponding light intensity information, forming a correspondence between light intensity and wavelength, which is a spectral curve.

[0090] In this embodiment, a tunable laser is used as the local oscillator light source, and a control module and a phase modulator are added. The control module controls the tunable laser to output different wavelengths and accurately switches between wavelengths. Based on the laser beam at the current tuned wavelength, the control module controls the phase modulator to perform a periodic phase scan of the laser beam, forming a different phase difference with the optical signal under test.

[0091] Then, the laser beam and the optical signal under test are coherently coupled in a 50:50 beam splitter. The coherently coupled beams are then incident on two similar photodiodes, generating a photocurrent difference signal at the series junction of the two photodiodes. After analysis and processing by a transimpedance amplifier, a data acquisition module, and a data processing module, the intensity information of the amplified coherent signal is obtained. The data processing module then combines the phase scanning information of the laser beam at different wavelengths to obtain the wavelength and spectral information of the optical signal under test, thus achieving efficient detection of weak beams or single-photon level optical signals.

[0092] Based on the spectral detection method provided in the above embodiments of this application, the control module further includes a microcontroller, a current adjustment module, and a modulation drive module. The microcontroller controls the current adjustment module and the modulation drive module. The current adjustment module, based on the control of the microcontroller, adjusts the wavelength and power of the laser beam output by the tunable laser. The modulation drive module, based on the control of the microcontroller, adjusts the drive voltage of the phase modulator. Based on the above, this application provides another spectral detection method, such as... Figure 8 As shown, the spectral detection method includes:

[0093] S81: The optical signal to be tested is input to the 50:50 beam splitter.

[0094] S82: The current regulation module, based on the microcontroller's control, regulates the output laser beam of the tunable laser with a wavelength of λ1, while the tunable laser feeds back the laser beam information to the microcontroller.

[0095] In this embodiment, the current regulation module, based on the control of the microcontroller, adjusts the specific laser beam wavelength output by the tunable laser and accurately switches between wavelengths. At the same time, the microcontroller processes the laser beam information fed back by the tunable laser in real time, processes the laser beam wavelength information with the current wavelength λ1, and outputs it to the data processing module.

[0096] S83: Based on the current laser beam with wavelength λ1, the modulation drive module outputs different drive voltages under the control of the microcontroller to act on the phase modulator. The phase modulator performs a phase periodic scan on the laser beam with wavelength λ1, forming different phase differences with the optical signal under test. The phase periodic scan range is 0-2π.

[0097] In this embodiment, the phase of a laser beam with wavelength λ1 is modulated by controlling the output of different driving voltages from the modulation driving module. The modulation phase of the laser beam is determined by the driving voltage. By changing the driving voltage, the phase periodic scanning of the tuned laser beam wavelength is completed. During the phase scanning of the laser beam, different phase differences between the laser beam and the optical signal under test are formed.

[0098] The S84:50:50 beam splitter coherently couples a laser beam with wavelength λ1 to the optical signal under test, and the output beam is incident on the first photodiode and the second photodiode respectively, and a photocurrent difference signal is generated at the series node of the first photodiode and the second photodiode.

[0099] S85: The photocurrent difference signal is input to the data processing module after passing through the transimpedance amplifier and the data acquisition module.

[0100] S86: The data processing module receives and analyzes the signals output by the data acquisition module and the microcontroller to obtain the maximum photovoltage signal of the laser beam with wavelength λ1, and converts the maximum photovoltage signal into light intensity information.

[0101] S87: The phase period scan of the laser beam with wavelength λ1 is completed. The current adjustment module, based on the control of the microcontroller, adjusts the output laser beam with wavelength λ2 of the tunable laser. The above process is repeated until the phase period scan of all preset wavelength laser beams is completed.

[0102] S88: The data processing module obtains the maximum photovoltage signal at each preset laser beam wavelength and converts each maximum photovoltage signal into corresponding light intensity information, forming a correspondence between light intensity and wavelength.

[0103] 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.

[0104] 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.

[0105] 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 spectral detector, characterized in that, It includes a tunable laser, a phase modulator, a 50:50 beam splitter, a first photodiode, a second photodiode, a transimpedance amplifier, a data acquisition module, a control module, and a data processing module; The tunable laser is used to output a laser beam to the phase modulator and feed back the laser beam information to the control module; the phase modulator is used to modulate the phase of the laser beam; the output end of the phase modulator is connected to the first incident end of the 50:50 beam splitter; the second incident end of the 50:50 beam splitter is used to input the optical signal to be measured; the 50:50 beam splitter is used to coherently couple the laser beam and the optical signal to be measured; the 50:50 beam splitter includes an upper output end and a lower output end; the first photodiode detects the coherently coupled beam output from the upper output end of the 50:50 beam splitter, and the second photodiode detects the coherently coupled beam output from the lower output end of the 50:50 beam splitter; the first photodiode and the second photodiode are connected in series to form a series node and generate a photocurrent difference signal 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; the control module is used to adjust and control the wavelength of the laser beam output by the tunable laser while outputting the wavelength information of the currently tuned laser beam to the data processing module, and to control the phase modulator to perform phase periodic scanning of the laser beam; the data processing module is used to receive the signals output by the data acquisition module and the control module and analyze and process them to obtain the maximum photovoltage signal at each tuned laser beam wavelength and convert the maximum photovoltage signal into light intensity information, thereby obtaining the correspondence between light intensity and wavelength.

2. The spectral detector 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 modulation drive module adjusts the drive voltage of the phase modulator based on the control of the microcontroller.

3. The spectral detector according to claim 1, characterized in that, The phase modulator, 50:50 beam splitter, first photodiode, second photodiode, transimpedance amplifier, data acquisition module, control module, and data processing module are fabricated on a chip using monolithic integration technology.

4. The spectral detector according to claim 2, 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.

5. The spectral detector according to claim 2, characterized in that, The modulation driving module includes a signal generation circuit, a preamplifier circuit, and a post-amplifier high-voltage operational amplifier circuit. The signal generation circuit is used to generate and output a voltage signal; the preamplifier circuit is used to amplify the voltage signal output by the signal generation circuit; and the post-amplifier high-voltage operational amplifier circuit is used to further amplify the voltage signal output by the preamplifier circuit.

6. The spectral detector according to any one of claims 1-5, characterized in that, The 50:50 beam splitter is one of an optical fiber beam splitter, a multimode interference coupler, or a directional coupler.

7. The spectral detector according to any one of claims 1-5, 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. A spectrometer, characterized in that, The spectrometer includes a display system and a spectral detector as described in any one of claims 1-7, wherein the display system is used to input control parameters and commands, and to display the phase scanning process and spectral curves.

9. A spectral detection method, characterized in that, The method is applied to the spectral detector according to any one of claims 1-7, the spectral detector comprising a tunable laser, a phase modulator, a 50:50 beam splitter, a first photodiode, a second photodiode, a transimpedance amplifier, a data acquisition module, a control module, and a data processing module; the method includes: The optical signal to be tested is input to the 50:50 beam splitter; The control module adjusts and controls the output of the tunable laser with a wavelength of λ1, and at the same time, the tunable laser feeds back the laser beam information to the control module. Based on the laser beam with a current wavelength of λ1, the control module controls the phase modulator to perform a phase periodic scan on the laser beam, forming a different phase difference with the optical signal to be measured. The phase periodic scan range is 0-2π. The 50:50 beam splitter coherently couples the laser beam with wavelength λ1 and the optical signal to be measured, and the output beam is incident on the first photodiode and the second photodiode respectively, and a photocurrent difference signal is generated at the series node of the first photodiode and the second photodiode. The photocurrent difference signal is input to the data processing module after passing through a transimpedance amplifier and a data acquisition module; The data processing module receives and analyzes the signals output by the data acquisition module and the control module to obtain the maximum photovoltage signal of the laser beam with wavelength λ1, and converts the maximum photovoltage signal into light intensity information. Once the phase periodic scan 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 phase periodic scan of all preset wavelength laser beams is completed. The data processing module obtains the maximum photovoltage signal at each preset laser beam wavelength and converts each maximum photovoltage signal into corresponding light intensity information, forming a correspondence between light intensity and wavelength.

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