CN112146755A - Device and method for generating ultra-broadband terahertz dual-optical comb based on non-resonant radio frequency injection - Google Patents

Abstract

The invention relates to an ultra-wideband terahertz double optical comb device based on non-resonant radio frequency injection, comprising a first terahertz quantum cascade laser and a second terahertz quantum cascade laser in a vacuum environment, wherein the first terahertz quantum cascade laser The terahertz quantum cascade laser and the second terahertz quantum cascade laser are placed at the same height with a certain distance between them, and the light of the first terahertz quantum cascade laser enters the second terahertz quantum level through a parabolic mirror A cascaded laser, and optical coupling is performed in the resonant cavity of the second terahertz quantum cascade laser. The invention also relates to a method for generating an ultra-wideband terahertz double optical comb based on non-resonant radio frequency injection. The present invention enables the resulting dual-comb spectrum to be wider.

Description

Device and method for generating ultra-broadband terahertz dual-optical comb based on non-resonant radio frequency injection

technical field

The invention relates to the technical field of semiconductor optoelectronic device applications, in particular to a device and method for generating ultra-wideband terahertz double optical combs based on non-resonant radio frequency injection.

Background technique

Broadband dual-comb light sources with equally spaced and low phase noise frequency lines are important for high-resolution spectroscopy and metrology. In the terahertz frequency range, electrically pumped Quantum Cascade Lasers (QCLs) with high output power, good far-field beam quality and wide frequency coverage can generate optical frequency combs. However, due to the group velocity dispersion, free-running THz QCLs (Terahertz QCLs, THz QCLs) generally show a limited dual-comb bandwidth of optical frequency combs, which is much smaller than the gain bandwidth of the laser. At present, although resonant RF injection locking at the laser round-trip frequency has been widely used for emission spectrum broadening of THz QCLs, due to the large phase noise and non-ideal microwave circuits caused by resonant injection (the injection frequency is equal to the round-trip frequency of the resonator), It is still difficult to significantly broaden the bandwidth of optical frequency combs and dual optical combs.

Compared with traditional Fourier Transform Infrared (FTIR) spectroscopy and time-domain spectroscopy (Time-domain Spectroscopy), dual-comb spectroscopy (i.e., multi-heterodyne spectroscopy using two THz QCLs) Analysis in the THz band is transferred to the RF band for better signal resolution and processing. In addition, the dual-comb heterodyne spectroscopy system can achieve fast and high-resolution spectroscopy without any moving parts due to its compact system structure, and its noise characteristics are superior to FTIR spectroscopy and time-domain spectroscopy. wider spectral range.

In the prior art, the THz QCL dual-comb spectrum that has been realized includes an on-chip dual-comb and a compact split dual-comb. For the on-chip dual-comb system, both lasers are fabricated on the same substrate. It is precisely because of this structure that the THz QCLs are optically coupled through the substrate or the laser medium, which makes this system unable to meet the spectral detection requirements. For the compact split dual-comb system, although the two THz QCLs do not share the same substrate, due to the close distance between the two, it is difficult to perform rapid detection with large volumes or complex samples.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to provide a device and method for generating an ultra-wideband terahertz double-comb based on non-resonant radio frequency injection, so that the spectrum of the generated double-comb is wider.

The technical solution adopted by the present invention to solve the technical problem is: to provide an ultra-wideband terahertz double-comb device based on non-resonant radio frequency injection, including a first terahertz quantum cascade laser and a second terahertz quantum cascade laser in a vacuum environment Quantum cascade laser, the first terahertz quantum cascade laser and the second terahertz quantum cascade laser work independently, the first terahertz quantum cascade laser is connected to the first T-type biaser, the first terahertz quantum cascade laser A T-type biaser is connected to the first radio frequency source, the first terahertz quantum cascade laser and the first T-type biaser are respectively connected to the first DC source; the second terahertz quantum cascade laser connected with a second T-type biaser, the second T-type biaser is respectively connected with a second radio frequency source and a spectrum analyzer, the second terahertz quantum cascade laser and the second T-type biaser are respectively Connected to the second DC source, the first terahertz quantum cascade laser and the second terahertz quantum cascade laser are placed at the same height with a certain distance between them, wherein the first terahertz quantum cascade laser The light enters the second terahertz quantum cascade laser through a parabolic mirror, and is optically coupled in the resonant cavity of the second terahertz quantum cascade laser; the first terahertz quantum cascade laser and the second terahertz quantum cascade laser The DC bias currents of the quantum cascade lasers are different, and the emission spectra of the first and second terahertz quantum cascade lasers overlap but their frequencies are different.

The distance between the first terahertz quantum cascade laser and the second terahertz quantum cascade laser is 15-30 cm.

A first microstrip line for impedance matching is placed at a position of 2 to 5 mm on the rear face of the first terahertz quantum cascade laser; and a position of 2 to 5 mm on the rear face of the second terahertz quantum cascade laser is placed for impedance matching. matching the second microstrip line.

The upper electrodes of the first terahertz quantum cascade laser are respectively bonded to the ceramic sheet through gold wire leads, the ceramic sheet is connected to the positive end of the first DC source, and the first terahertz quantum cascade The lower electrode of the laser is connected to the negative electrode of the first DC source; the upper electrode of the second terahertz quantum cascade laser is bonded to the ceramic sheet through a gold wire lead, and the ceramic sheet is connected to the positive electrode of the second DC source One end is connected, and the lower electrode of the second terahertz quantum cascade laser is connected to the negative electrode of the second DC source.

The upper electrode of the first terahertz quantum cascade laser is respectively bonded to the first microstrip line through the gold wire lead; the upper electrode of the second terahertz quantum cascade laser is connected to the second microstrip line through the gold wire lead. Bond.

The first T-type biaser has a DC bias port, a radio frequency port and a mixed radio frequency and DC port, the DC bias port is connected to the first DC source, and the radio frequency port is connected to the The first radio frequency source is connected, and the hybrid port is connected to the first terahertz quantum cascade laser through a first high frequency coaxial cable; the second T-type biaser has a DC bias port, a radio frequency port and a radio frequency and DC hybrid port, the DC bias port is connected to the second DC source, the radio frequency port is respectively connected to the second radio frequency source and the spectrum analyzer, the hybrid port is connected to the Two high-frequency coaxial cables are connected to the second terahertz quantum cascade laser.

The technical solution adopted by the present invention to solve the technical problem is to provide a method for generating an ultra-wideband terahertz dual optical comb based on non-resonant radio frequency injection, and adopting the above-mentioned device for generating an ultra-wideband terahertz dual optical comb based on non-resonant radio frequency injection, comprising: The following steps:

(1) The two DC sources supply power to the first terahertz quantum cascade laser and the second terahertz quantum cascade laser respectively at the same time;

(2) The first radio frequency source injects a radio frequency signal into the first terahertz quantum cascade laser, and the frequency of the injected radio frequency signal is close to the intra-cavity round-trip frequency of the first terahertz quantum cascade laser. The second terahertz quantum cascade laser does not perform radio frequency injection, and a down-conversion spectrum is observed on the spectrum analyzer;

(3) Gradually increase the power of the injected radio frequency signal, and at the same time change the frequency of the injected radio frequency signal according to the change of the dual-comb spectrum on the spectrum analyzer, resulting in a wider dual-comb spectrum than the case of resonance injection;

(4) The radio frequency signal injected by the second radio frequency source into the second terahertz quantum cascade laser, the injected radio frequency signal is close to the intra-cavity round-trip frequency of the second terahertz quantum cascade laser, at this time the first terahertz quantum cascade laser THz quantum cascade lasers do not perform RF injection, and gradually increase the power and frequency of the injected RF signal, which also produces a wider dual-comb spectrum than in the case of resonant injection.

beneficial effect

Compared with the prior art, the present invention has the following advantages and positive effects due to the adoption of the above-mentioned technical solution: the present invention generates down-conversion double-light by optical coupling beat frequency between two terahertz quantum cascade lasers that are far apart. Comb spectroscopy, and generate a wider dual-comb spectral bandwidth by off-resonant RF injection. Moreover, two THz QCLs can act as lasers and detectors, respectively, to perform non-resonant RF injection to achieve ultra-broadband dual-comb spectroscopy. Compared with the traditional Fourier transform infrared spectrometer, the invention has the characteristics of high speed, high efficiency and high resolution, and can also be applied to the fast and precise terahertz spectrum measurement of substances.

Description of drawings

Fig. 1 is the structural representation of the present invention;

FIG. 2 is a spectrogram of the beat signal under the corresponding conditions of the present invention.

Detailed ways

The present invention will be further described below in conjunction with specific embodiments. It should be understood that these examples are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of the present application.

Embodiments of the present invention relate to an ultra-broadband terahertz double-comb device based on non-resonant radio frequency injection, as shown in FIG. 1 , including a first terahertz quantum cascade laser 1 and a second terahertz quantum laser in a vacuum environment Cascade laser 2, the first terahertz quantum cascade laser 1 and the second terahertz quantum cascade laser 2 work independently, and the first terahertz quantum cascade laser 1 passes through the first high-frequency coaxial cable 3 is connected to the first T-type biaser 4, the first T-type biaser 4 is connected to the first radio frequency source 5, the first terahertz quantum cascade laser 1 and the first T-type biaser 4 They are respectively connected to the first DC source 6; the second terahertz quantum cascade laser 2 is connected to the second T-type biaser 8 through the second high-frequency coaxial cable 7, and the second T-type biaser The setter 8 is connected to the second radio frequency source (not shown in the figure), the second T-type biaser 8 is also connected to the spectrum analyzer 10 through the low noise amplifier 9, and the second terahertz quantum cascade laser 2 and the second T-bias device 8 are respectively connected to the second DC source 11 . Wherein, the first terahertz quantum cascade laser 1 and the second terahertz quantum cascade laser 2 are placed at the same height, and there is a certain distance between them, wherein the light of the first terahertz quantum cascade laser 1 Enter the second terahertz quantum cascade laser 2 through the parabolic mirror 12, and perform optical coupling in the resonant cavity of the second terahertz quantum cascade laser 2; the first terahertz quantum cascade laser 1 and the second The DC bias currents of the terahertz quantum cascade laser 2 are different, and the emission spectra of the first terahertz quantum cascade laser 1 and the second terahertz quantum cascade laser 2 overlap but their frequencies are different.

In this embodiment, the distance between the first terahertz quantum cascade laser 1 and the second terahertz quantum cascade laser 2 is 15-30 cm. A first microstrip line for impedance matching is placed at a position of 2 to 5 mm on the rear face of the first terahertz quantum cascade laser 1; A second microstrip line for impedance matching.

The upper electrodes of the first terahertz quantum cascade laser 1 are respectively bonded to ceramic sheets through gold wire leads, and the ceramic sheets are connected to the positive end of the first direct current source 6, and the first terahertz quantum The lower electrode of the cascade laser 1 is connected to the negative electrode of the first DC source 6; the upper electrode of the second terahertz quantum cascade laser 2 is bonded to the ceramic sheet through gold wire leads, and the ceramic sheet is connected to the second terahertz quantum cascade laser 2. The positive terminals of the two DC sources 11 are connected to one end, and the lower electrodes of the second terahertz quantum cascade laser 2 are connected to the negative terminals of the second DC sources 11 .

The upper electrodes of the first terahertz quantum cascade laser 1 are respectively bonded to the first microstrip line through gold wire leads, and the first high-frequency coaxial cable 3 is connected to the first T-bias device 4; The upper electrode of the second terahertz quantum cascade laser 2 is bonded to the second microstrip line through a gold wire lead, and the second high-frequency coaxial cable 7 is connected to the second T-type biaser 8 .

The first T-type biaser 4 has a DC bias port, a radio frequency port and a mixed radio frequency and DC port, the DC bias port is connected to the first DC source 6, and the radio frequency port is connected to the first DC source 6. The first radio frequency source 5 is connected, and the hybrid port is connected to the first terahertz quantum cascade laser 1 through the first high frequency coaxial cable 3; the second T-type biaser 8 has a DC A bias port, a radio frequency port and a radio frequency and DC hybrid port, the DC bias port is connected to the second DC source 11, the radio frequency port is connected to the spectrum analyzer 10 through the low noise amplifier 9, so The hybrid port is connected to the second terahertz quantum cascade laser 2 through the second high-frequency coaxial cable 7 .

The method for realizing ultra-broadband dual-optical comb spectroscopy using the above device adopts non-resonant radio frequency injection modulation, including:

Step S1 : providing the first terahertz quantum cascade laser 1 and the second terahertz quantum cascade laser 2 . The first terahertz quantum cascade laser 1 and the second terahertz quantum cascade laser 2 are placed in two refrigerators, separated by 15-30 cm, and their low-temperature operation is controlled by liquid helium. The first microstrip line and the second microstrip line for impedance matching are provided at the rear face positions of the first terahertz quantum cascade laser 1 and the second terahertz quantum cascade laser 2, the first microstrip line and the The two microstrip lines are respectively connected with the upper electrodes of the respective terahertz quantum cascade lasers through gold wires, and the whole device is in a vacuum and closed environment;

Step S2 : providing a first DC source 6 , a first T-bias device 4 and a first radio frequency source 5 . The first DC source 6 is connected to the DC bias port of the first T-bias device 4, the first RF source 5 is connected to the RF port of the first T-bias device 4, and the first T-bias device 4 The hybrid port is connected with the first microstrip line at the rear end of the first terahertz quantum cascade laser 1 through a first high-frequency coaxial cable 3 .

Step S3 : providing a second DC source 11 , a second T-bias device 8 , a second radio frequency source, a low noise amplifier 9 and a spectrum analyzer 10 . The second DC source 11 is connected to the DC bias port of the second T-bias device 8, the spectrum analyzer 10 is connected to the radio frequency port of the second T-type bias device 8 through the low noise amplifier 9, and the second T-type bias device 8 is connected. The radio frequency port of the setter 8 is also connected to a second radio frequency source, and the hybrid port of the second T-bias device 8 is connected to the microstrip line at the rear end of the second terahertz quantum cascade laser 2 through a second high frequency coaxial cable 7 .

Step S4: The first DC source and the second DC source supply power to the first terahertz quantum cascade laser 1 and the second terahertz quantum cascade laser 2 at the same time, respectively. The DC bias currents of the first terahertz quantum cascade laser 1 and the second terahertz quantum cascade laser 2 are not exactly the same, and the first terahertz quantum cascade laser 1 and the second terahertz quantum cascade laser 2 The emission spectrum overlaps but its frequencies are not identical;

Step S5: The first radio frequency source 5 injects a low-power radio frequency signal into the first terahertz quantum cascade laser 1 (at this time, the second terahertz quantum cascade laser 2 does not perform radio frequency injection), and the frequency of the injected radio frequency signal is close to the first terahertz quantum cascade laser. The intra-cavity round-trip frequency (resonant injection) of a terahertz quantum cascade laser 1 will generate a down-conversion spectrum at this time.

Step S6: Gradually increase the power of the injected radio frequency signal, and at the same time change the frequency of the injected radio frequency signal according to the change of the dual-comb spectrum on the spectrum analyzer 10, resulting in a wider dual-comb spectrum than the case of resonance injection (see FIG. 2).

Step S7: The second radio frequency source injects a lower power radio frequency signal into the second terahertz quantum cascade laser 2 (at this time, the first terahertz quantum cascade laser 1 does not perform radio frequency injection), and the injected radio frequency signal is close to the second terahertz quantum cascade laser. The intracavity round-trip frequency (resonant injection) of the Hertz quantum cascade laser 2, gradually increasing the power and frequency of the injected RF signal, also shows a wider dual-comb spectrum than in the case of resonant injection (see Figure 2).

Step S8: Provide the sample to be tested, and place it in the middle of the two parabolic mirrors for fast sample detection.

It is not difficult to find that the present invention generates a down-conversion dual-comb spectrum by optical coupling beat frequency of two terahertz quantum cascade lasers far apart, and generates a wider dual-comb spectrum bandwidth through non-resonant radio frequency injection. Moreover, the two THzQCLs can act as lasers and detectors, respectively, to perform non-resonant RF injection to achieve ultra-broadband dual-comb spectroscopy. Compared with the traditional Fourier transform infrared spectrometer, the invention has the characteristics of high speed, high efficiency and high resolution, and can also be applied to the fast and precise terahertz spectrum measurement of substances.

Claims (7)

1. The device comprises a first terahertz quantum cascade laser and a second terahertz quantum cascade laser which are positioned in a vacuum environment and work independently, wherein the first terahertz quantum cascade laser is connected with a first T-shaped bias device, the first T-shaped bias device is connected with a first radio frequency source, and the first terahertz quantum cascade laser and the first T-shaped bias device are respectively connected with the first direct current source; the terahertz quantum cascade laser is characterized in that the first terahertz quantum cascade laser and the second terahertz quantum cascade laser are placed at the same height and have a certain distance therebetween, wherein light of the first terahertz quantum cascade laser enters the second terahertz quantum cascade laser through a parabolic mirror and is optically coupled in a resonant cavity of the second terahertz quantum cascade laser; the direct current bias currents of the first terahertz quantum cascade laser and the second terahertz quantum cascade laser are different, and the emission spectrums of the first terahertz quantum cascade laser and the second terahertz quantum cascade laser are overlapped but the frequencies of the first terahertz quantum cascade laser and the second terahertz quantum cascade laser are different.

2. The non-resonant radio frequency injection based ultra-wideband terahertz double-optical comb device as claimed in claim 1, wherein the distance between the first terahertz quantum cascade laser and the second terahertz quantum cascade laser is 15-30 cm.

3. The non-resonant radio frequency injection based ultra-wideband terahertz double-optical comb device as claimed in claim 1, wherein a first microstrip line for impedance matching is placed at a position 2-5 mm from the rear end face of the first terahertz quantum cascade laser; and a second microstrip line for impedance matching is placed at the position of 2-5 mm on the rear end face of the second terahertz quantum cascade laser.

4. The device for generating the ultra-wideband terahertz double-optical comb based on the off-resonance radio frequency injection as claimed in claim 1, wherein the upper electrode of the first terahertz quantum cascade laser is respectively bonded with a ceramic piece through a gold wire lead, the ceramic piece is connected with one end of the positive electrode of the first direct current source, and the lower electrode of the first terahertz quantum cascade laser is connected with the negative electrode of the first direct current source; an upper electrode of the second terahertz quantum cascade laser is bonded with a ceramic chip through a gold wire lead, the ceramic chip is connected with one end of a positive electrode of the second direct current source, and a lower electrode of the second terahertz quantum cascade laser is connected with a negative electrode of the second direct current source.

5. The non-resonant radio frequency injection-based ultra-wideband terahertz dual optical comb device as claimed in claim 3, wherein the upper electrode of the first terahertz quantum cascade laser is bonded to the first microstrip line through gold wire leads, respectively; and the upper electrode of the second terahertz quantum cascade laser is bonded with the second microstrip line through a gold wire lead.

6. The non-resonant radio frequency injection based ultra-wideband terahertz double-optical comb device according to claim 1, wherein the first T-shaped biaser has a dc bias port, a radio frequency port and a mixed radio frequency and dc port, the dc bias port is connected to the first dc source, the radio frequency port is connected to the first rf source, and the mixed port is connected to the first terahertz quantum cascade laser through a first high frequency coaxial cable; the second T-shaped bias device is provided with a direct current bias port, a radio frequency port and a radio frequency and direct current mixed port, the direct current bias port is connected with the second direct current source, the radio frequency port is respectively connected with the second radio frequency source and the spectrum analyzer, and the mixed port is connected with the second terahertz quantum cascade laser through a second high-frequency coaxial cable.

7. The method for generating the ultra-wideband terahertz double-optical comb based on the non-resonance radio frequency injection is characterized in that the device for generating the ultra-wideband terahertz double-optical comb based on the non-resonance radio frequency injection as claimed in any one of claims 1 to 6 is adopted, and comprises the following steps:

(1) two direct current sources respectively and simultaneously supply power to the first terahertz quantum cascade laser and the second terahertz quantum cascade laser;

(2) injecting a radio frequency signal into the first terahertz quantum cascade laser by the first radio frequency source, wherein the frequency of the injected radio frequency signal is close to the intracavity round-trip frequency of the first terahertz quantum cascade laser, and at the moment, the second terahertz quantum cascade laser does not perform radio frequency injection, and a down-conversion spectrum is observed on the spectrum analyzer;

(3) gradually increasing the power of the injected radio frequency signal, and simultaneously changing the frequency of the injected radio frequency signal according to the change of the double-optical comb spectrum on the spectrum analyzer to generate a wider double-optical comb spectrum than under the resonance injection condition;

(4) and the second radio frequency source injects radio frequency signals into the second terahertz quantum cascade laser, the injected radio frequency signals are close to the intracavity round-trip frequency of the second terahertz quantum cascade laser, at the moment, the first terahertz quantum cascade laser does not inject radio frequency, the power and the frequency of the injected radio frequency signals are gradually increased, and a double optical comb spectrum which is wider than that under the resonance injection condition is also generated.

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