A terahertz quantum cascade laser dual optical comb control system

Abstract

This invention relates to a dual-comb control system for a terahertz quantum cascade laser, comprising a first terahertz quantum cascade laser, a second terahertz quantum cascade laser, a first T-type biaser, and a second T-type biaser. The first terahertz quantum cascade laser operates in optical frequency comb mode, while the second terahertz quantum cascade laser operates above a threshold current. The first and second terahertz quantum cascade lasers emit terahertz light from each other. The first terahertz quantum cascade laser also functions as a detector to detect a mixing signal. The state of the mixing signal is switched by changing the power of the radio frequency signal generated by the radio frequency source. This invention enables the switching of the mixing signal between chaotic, unstable, and dual-comb states under high drive current, significantly improving the spectral width and application scenarios of the dual-comb system based on the quantum cascade laser.

Description

Technical Field

[0001] This invention relates to the field of semiconductor optoelectronic device application technology, and in particular to a dual optical comb control system for a terahertz quantum cascade laser. Background Technology

[0002] An optical frequency comb is composed of a series of equally spaced, narrow-linewidth, and stable-phase frequency modes, characterized by high frequency stability and low phase noise. It is widely used in high-precision measurement fields such as atomic clocks, astronomical observation, distance measurement, optical sensing, frequency calibration, and molecular spectroscopy. The terahertz (THz) wave energy scale corresponds precisely to ultrafast processes such as the evolution of biological macromolecular structures and charge carrier dynamics. These characteristics allow terahertz optical frequency combs to discover physical processes that conventional techniques cannot reveal in biomedicine and non-destructive testing. Developing THz-band optical frequency comb technology is an effective way to expand its high-precision applications. A quantum cascade laser (QCL) is an electrically pumped semiconductor laser based on inter-subband electron transitions. It features short gain recovery time, high output power, and good far-field characteristics, making it an ideal light source for generating chip-scale optical frequency combs within the 1-5 THz range.

[0003] Dual-comb spectroscopy is a direct application of terahertz optical frequency combs in high-precision measurements. Two optical frequency combs with similar repetition frequencies are mixed to generate multiheterodyne spectra at lower frequencies. When the two optical frequency combs have sufficient stability, the multiheterodyne spectral signal obtained by mixing presents as a dual-comb signal. A dual-comb spectroscopy system formed by the beat frequency of two THz optical frequency combs can completely overcome the problem of traditional THz spectrometers (such as Fourier transform spectrometers and time-domain spectrometers) requiring mechanical scanning and thus unable to achieve high-speed spectral detection, achieving truly real-time, high-precision THz spectral detection and imaging. Currently, there is no mature mixer in the 2-5 THz band that can achieve high-speed, broadband mixing. However, the unique laser self-probing mechanism of THz QCLs allows the QCL to replace the mixer in a dual-comb system. A single THz QCL can act as a laser source and simultaneously function as a mixer and detector to detect the mixed signal of two THz waves, thus greatly simplifying the equipment and eliminating the dependence on high-sensitivity broadband detectors and high-frequency, high-speed mixers.

[0004] Common dual-comb control frequency stabilization technology requires the mixing signal to be in the state of dual-comb before it can be applied. However, under high drive current, lasers often have large phase noise, and the frequency modes of dual-combs cannot be distinguished from the mixing signal. Therefore, traditional phase-locked loop technology cannot be used to improve the stability of dual-combs. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a dual optical comb control system for a terahertz quantum cascade laser that can change the coherence of the laser.

[0006] The technical solution adopted by this invention to solve its technical problem is as follows: a dual-comb control system for a terahertz quantum cascade laser is provided, including a first terahertz quantum cascade laser, a second terahertz quantum cascade laser, a first T-type biaser, and a second T-type biaser. The mixing port of the first T-type biaser is connected to the first terahertz quantum cascade laser, the AC port is connected to a signal processing module, and the DC port is connected to a power supply. The mixing port of the second T-type biaser is connected to the second terahertz quantum cascade laser, the AC port is connected to an RF source, and the DC port is connected to a power supply.

[0007] The first terahertz quantum cascade laser operates in optical frequency comb mode, and the second terahertz quantum cascade laser operates above the threshold current. The first terahertz quantum cascade laser and the second terahertz quantum cascade laser emit terahertz light to each other. The first terahertz quantum cascade laser also acts as a detector to detect the mixing signal. The state of the mixing signal is switched by changing the power of the radio frequency signal generated by the radio frequency source.

[0008] The output of the signal processing module is also connected to a spectrum analyzer, which is used to detect and record the mixing signal in real time.

[0009] The signal processing module includes an amplifier and a bandpass filter connected in sequence. The amplifier is used to amplify the mixed signal, and the bandpass filter is used to filter out noise signals.

[0010] The bandwidth of the amplifier is greater than the signal bandwidth when the mixing signal is in dual optical comb mode; the operating bandwidth of the bandpass filter covers the bandwidth of the mixing signal.

[0011] The amplifier is a microwave low-noise amplifier.

[0012] The frequency of the radio frequency signal generated by the radio frequency source is equal to the repetition frequency of the mixing signal in dual optical comb mode.

[0013] Beneficial effects

[0014] Due to the adoption of the above technical solution, the present invention has the following advantages and positive effects compared with the prior art: The present invention uses radio frequency injection technology to change the coherence of the laser by adjusting the power of the radio frequency signal, so that the laser does not need to work under the optical frequency comb condition, and can switch between three states: chaotic, unstable and dual optical comb. Attached Figure Description

[0015] Figure 1This is a schematic diagram of the dual optical comb system of the terahertz quantum cascade laser according to an embodiment of the present invention;

[0016] Figure 2 This is a schematic diagram of the structure of the terahertz quantum cascade laser dual optical comb system according to an embodiment of the present invention;

[0017] Figure 3 This is a schematic diagram of the mixing signal generated by the dual optical comb system of the terahertz quantum cascade laser according to an embodiment of the present invention. Detailed Implementation

[0018] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0019] The embodiments of the present invention relate to a dual-comb control system for a terahertz quantum cascade laser. The control system employs two terahertz quantum cascade lasers (THz QCLs), which achieve self-probing based on the picosecond-level relaxation time of the THz QCLs. One THz QCL is regulated by radio frequency injection, while the other THz QCL simultaneously acts as a mixer to detect the mixing signals of the two QCLs. By adjusting the power of the injected radio frequency signal, the mixing signal is controlled, enabling it to switch between chaotic, unstable, and dual-comb states under high drive current.

[0020] The principle of this implementation method is as follows: Figure 1 As shown, the THz band optical frequency comb has two adjacent modes (f m and f m+1 The spacing is f. rep According to the phase matching condition, its wave vector should satisfy k. m+1 =k m +k rep By adjusting the signal strength injected via radio frequency, the phase mismatch of the THz QCL can be controlled, thereby achieving control of the THz QCL.

[0021] like Figure 2As shown, the dual-comb control system for the terahertz quantum cascade laser in this embodiment includes a first terahertz quantum cascade laser 1, a second terahertz quantum cascade laser 2, a first T-type bias 3, and a second T-type bias 4. The mixing port of the first T-type bias 3 is connected to the first terahertz quantum cascade laser 1, the AC port is connected to the signal processing module, and the DC port is connected to the power supply. The mixing port of the second T-type bias 4 is connected to the second terahertz quantum cascade laser 2, the AC port is connected to the radio frequency source 5, and the DC port is connected to the power supply.

[0022] In this embodiment, the first terahertz quantum cascade laser 1 operates in optical frequency comb mode, and the second terahertz quantum cascade laser 2 operates above the threshold current. The radio frequency source 5 injects a radio frequency signal into the second terahertz quantum cascade laser 2. The terahertz light emitted by the second terahertz quantum cascade laser 2 directly illuminates the first terahertz quantum cascade laser 1, mixing with the terahertz light emitted by the first terahertz quantum cascade laser 1. This mixed signal is detected by the first terahertz quantum cascade laser 1, which also acts as a detector. The detected mixed signal is processed by the signal processing module after passing through the first T-type bias circuit 3, and then the spectrum analyzer 6 detects and records the mixed signal in real time.

[0023] In this embodiment, the radio frequency source 5 can generate radio frequency signals of different power and frequency, which are transmitted to the second terahertz quantum cascade laser 2 through the AC port of the second T-type biaser 4, thereby controlling the state of the second terahertz quantum cascade laser 2. In this embodiment, the frequency of the radio frequency signal needs to be equal to the repetition frequency f when the mixing signal is in the dual-comb state. rep The power of the radio frequency signal is adjusted according to the state of the required mixing signal. By adjusting the power of the radio frequency signal, the mixing signal can be converted in chaotic, unstable and dual-comb states under high drive current.

[0024] The signal processing module in this embodiment includes an amplifier 7 and a bandpass filter 8 connected in sequence. The amplifier 7 amplifies the mixed signal, and the bandpass filter 8 filters out noise signals. The amplifier 7 in this embodiment can be a microwave low-noise amplifier, with its input connected to the AC port of the first T-type biaser 3 and its output connected to the bandpass filter 8. It amplifies the mixed signal obtained from the self-detection of the first terahertz quantum cascade laser 1, providing a signal gain of 30dB. Its bandwidth should be greater than the signal bandwidth when the mixed signal is in a dual-comb state, thus achieving overall amplification of the dual-comb signal and meeting the signal strength detection requirements of the subsequent spectrum analyzer. The operating bandwidth of the bandpass filter in this embodiment covers the bandwidth of the mixed signal, thereby filtering out noise signals and ensuring the extraction of the mixed signal.

[0025] The method for adjusting the coherence of the dual optical comb signal using the above control system is as follows:

[0026] Step S1: In this embodiment, the lasers are all terahertz quantum cascade lasers. The lasing spectrum of the two terahertz quantum cascade lasers is 3.4–3.8 THz, and the carrier frequency of the mixing signal of the two terahertz quantum cascade lasers is 5.5 GHz. The two terahertz quantum cascade lasers are placed face-to-face to ensure that the terahertz light emitted by the second terahertz quantum cascade laser can illuminate the first terahertz quantum cascade laser.

[0027] Step S2: Provide two T-type biasers, both operating in the DC-18GHz range. The AC port of the second T-type biaser is connected to an RF source for RF signal transmission, the DC port is connected to a power supply for powering the second terahertz quantum cascade laser, and the hybrid port is directly connected to the second terahertz quantum cascade laser. The AC port of the first T-type biaser is connected to an amplifier, the DC port is connected to a power supply, and the hybrid port is directly connected to the first terahertz quantum cascade laser.

[0028] Step S3: Provide an RF source with an output frequency equal to the round-trip frequency of the laser cavity and a maximum power of 26 dBm. Connect the output port of the RF source to the AC port of the second T-type bias, thereby realizing RF injection into the second terahertz quantum cascade laser. The injected RF signal can be directly adjusted in power and frequency by the RF source.

[0029] Step S4: Provide a bandpass filter with a working bandwidth that covers the bandwidth of the mixing signals from the two lasers to extract the mixing signal. The bandpass filter is connected to the amplifier via a high-frequency coaxial cable.

[0030] Step S5: Provide a microwave low-noise amplifier for amplifying the signal. It can provide a gain of 30dB and operate in the range of 1-18GHz. The low-noise amplifier is connected to the first T-type bias via a high-frequency coaxial cable.

[0031] Step S6: Provide a spectrum analyzer with an operating range of 2Hz-26.5GHz for detecting terahertz mixing signals. This analyzer can record and analyze the state of the mixing signal under different injected RF signal powers. The spectrum analyzer is connected to a bandpass filter via a high-frequency coaxial cable.

[0032] Step S7: Under different conditions such as laser drive current and operating temperature, adjust the power of the injected radio frequency signal to convert the mixing signal from an unstable and chaotic state to a dual-comb state. For example... Figure 3As shown, when the power of the radio frequency signal is 6.5 dBm, there is no coherence between the laser modes, and the mixing signal is in a chaotic state; when the power of the radio frequency signal is 12.5 dBm, there is weak coherence between the laser modes, and the mixing signal is in an unstable state; when the power of the radio frequency signal is 8.5 dBm, the coherence between the laser modes is greatly improved, and the mixing signal is in a dual-comb state.

[0033] It is easy to see that this invention improves the coherence of the dual optical comb of the terahertz quantum cascade laser by radio frequency injection, thereby controlling the state of the mixing signal and realizing the switching between chaos, instability and dual optical comb. This can greatly improve the spectral width and application scenarios of the dual optical comb system based on the quantum cascade laser, and has important applications in high-precision terahertz spectral detection.

Claims

1. A dual-comb control system for a terahertz quantum cascade laser, characterized in that, It includes a first terahertz quantum cascade laser, a second terahertz quantum cascade laser, a first T-type biaser, and a second T-type biaser. The mixing port of the first T-type biaser is connected to the first terahertz quantum cascade laser, the AC port is connected to the signal processing module, and the DC port is connected to the power supply. The mixing port of the second T-type biaser is connected to the second terahertz quantum cascade laser, the AC port is connected to the radio frequency source, and the DC port is connected to the power supply. The first terahertz quantum cascade laser operates in optical frequency comb mode, and the second terahertz quantum cascade laser operates above the threshold current. The first and second terahertz quantum cascade lasers emit terahertz light from each other. The terahertz light emitted by the second terahertz quantum cascade laser directly illuminates the first terahertz quantum cascade laser, mixing with the terahertz light emitted by the first terahertz quantum cascade laser. The first terahertz quantum cascade laser also acts as a detector to detect the mixed signal. The chaotic state, unstable state, and dual-grating state of the mixed signal are switched by changing the power of the radio frequency signal generated by the radio frequency source. The frequency of the radio frequency signal generated by the radio frequency source is equal to the repetition frequency of the mixed signal in dual-frequency comb mode.

2. The dual-comb control system for a terahertz quantum cascade laser according to claim 1, characterized in that, The output of the signal processing module is also connected to a spectrum analyzer, which is used to detect and record the mixing signal in real time.

3. The dual-comb control system for a terahertz quantum cascade laser according to claim 1, characterized in that, The signal processing module includes an amplifier and a bandpass filter connected in sequence, wherein the amplifier is used to amplify the mixing signal; The bandpass filter is used to filter out noise signals.

4. The dual-comb control system for a terahertz quantum cascade laser according to claim 3, characterized in that, The bandwidth of the amplifier is greater than the signal bandwidth when the mixing signal is in dual optical comb mode; the operating bandwidth of the bandpass filter covers the bandwidth of the mixing signal.

5. The dual-comb control system for a terahertz quantum cascade laser according to claim 3, characterized in that, The amplifier is a microwave low-noise amplifier.

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