Annular external cavity interband cascade laser and method of making the same

Abstract

The application provides a kind of annular external cavity interband cascade laser and its preparation method, comprising: interband cascade laser;A layer of anti-reflection film is plated on the front cavity side of interband cascade laser;The front cavity side and the rear cavity side of interband cascade laser are respectively provided with front cavity straight lens and rear cavity straight lens;Blazed grating is arranged on the front cavity side of front cavity straight lens;Gold-coated mirror group includes first gold-coated mirror, second gold-coated mirror and third gold-coated mirror arranged along the exit light path of blazed grating;Wherein, front cavity straight lens, blazed grating, first gold-coated mirror, second gold-coated mirror, third gold-coated mirror and rear cavity straight lens form annular light path cavity;Light signal is emitted from the front cavity side of interband cascade laser, and after passing through annular light path cavity, it is incident again to interband cascade laser from the rear cavity side.The device can obtain wider spectral tuning range and larger output power than zero-order diffraction light output Littrow external cavity.

Description

Technical Field

[0001] This invention relates to the fields of mid-infrared semiconductor optoelectronic device technology and laser spectrometer technology, specifically to a ring external cavity interband cascaded laser and its fabrication method. Background Technology

[0002] Interband cascade lasers (ICLs) are semiconductor lasers that combine the advantages of long upper level lifetime of quantum well lasers and high internal quantum efficiency of quantum cascade lasers with emission spectra in the mid-infrared band. Their dominant operating wavelength is 3–4 μm, perfectly filling the band gap between the near-infrared (below 3 μm) band of quantum well lasers and the mid-infrared (above 4 μm) band of quantum cascade lasers (QCLs). They have advantages such as small size, tunable wavelength, and lower power consumption than quantum cascade lasers.

[0003] The 3–5 μm band, as the first atmospheric window in the mid-infrared band, contains a large number of molecular absorption lines of gases, and each molecule corresponds to a specific spectral line, hence it is known as the "fingerprint" band of gas molecules. Spectroscopic research in the mid- and far-infrared bands has enormous potential in atmospheric detection, monitoring of explosive gas leaks, and medical diagnosis. High-precision gas detection demands high single-mode performance, which can be effectively addressed by integrating distributed feedback (DFB) lasers. However, practical applications often require the detection of multiple gases. Since the spectra of molecular absorption lines do not overlap and the tuning range of DFB lasers is relatively small, multiple single-mode lasers are often needed to cover a large spectral range, causing inconvenience in fabrication and device layout. To address this, a laser is combined with a blazed grating to form an external cavity (EC) laser. The grating serves as the wavelength selection element in the external cavity, providing a highly portable and tunable laser source for spectral analysis.

[0004] The Littrow EC structure with zero-order diffraction output, as the most commonly used external cavity structure, has been combined with an ICL to expand the tuning range. To further improve the spectral linewidth, a Littman-Metcalf structure, which has one more plane mirror than the Littrow structure, can be used. By combining a mirror after the blazed grating, the secondary frequency selection through the mirror increases the external cavity length and wavelength selectivity of the EC-QCL, resulting in a very narrow spectral linewidth. However, the light incident on the mirror and returning along the same path does not satisfy the Littrow angle, and the low diffraction efficiency actually narrows the tuning range. Therefore, a structure is needed that can combine the advantages of both EC structures—broadening the spectrum and reducing linewidth—while also improving output power to some extent.

[0005] Furthermore, the diffracted light energy of a blazed grating is mostly concentrated in the first-order diffracted light. Using the zeroth-order diffracted light as the output light limits the device's output power, typically to less than 10% of the amplification power. Using a ring cavity resonator with two counter-propagating rings has been proven to achieve higher power through bidirectional light coupling. Moreover, a ring cavity resonator with two counter-propagating traveling waves can significantly reduce the spatial hole burning (SHB) effect associated with standing waves, greatly improving spectral stability. Currently, traditional external cavity lasers heavily rely on the performance of the ICL used. Lasers with generally low output power and spectral tuning performance cannot continue to achieve higher power or further expand the tuning range using traditional external cavity structures. Summary of the Invention

[0006] (a) Technical problems to be solved

[0007] To address the aforementioned shortcomings, the main objective of this invention is to provide a ring external cavity interband cascaded laser and its fabrication method, thereby achieving better linewidth quality, output power, and tuning range than traditional external cavities when using the same ICL.

[0008] (II) Technical Solution

[0009] To achieve the above objectives, in a first aspect, the present invention provides a ring-shaped external cavity interband cascaded laser, comprising: an interband cascaded laser; an antireflection coating deposited on the front cavity surface of the interband cascaded laser; a front cavity surface straight lens and a rear cavity surface straight lens respectively disposed on the front cavity surface and the rear cavity surface of the interband cascaded laser; a blazed grating disposed on the front cavity surface of the front cavity surface straight lens; and a gold-plated mirror assembly comprising a first gold-plated mirror, a second gold-plated mirror, and a third gold-plated mirror disposed along the output optical path of the blazed grating; wherein the front cavity surface straight lens, the blazed grating, the first gold-plated mirror, the second gold-plated mirror, the third gold-plated mirror, and the rear cavity surface straight lens form a ring-shaped optical path cavity; the front cavity surface of the interband cascaded laser emits an optical signal, which exits clockwise through the ring-shaped optical path cavity and then re-enters the interband cascaded laser from the rear cavity surface.

[0010] In the above scheme, the cavity of the interband cascaded laser is a Fabry-Perot structure and can operate continuously at room temperature.

[0011] In the above scheme, the blazed grating is fixed on a grating frame, and the grating frame is set in the direction of the light path emitted from the front cavity straight lens.

[0012] In the above scheme, the front cavity straight lens and the rear cavity straight lens are fixed on the copper plate of the optical lifting platform.

[0013] In the above scheme, the optical signal is emitted from the rear cavity side of the inter-band cascaded laser. After the optical signal exits counterclockwise through the annular optical path cavity, it is re-injected into the inter-band cascaded laser from the front cavity side (1).

[0014] The above scheme also includes a pyroelectric power meter; wherein, the optical signal that has completed clockwise propagation and the optical signal that has completed counterclockwise propagation are directionally coupled in an interband cascaded laser; after directional coupling, only the zero-order diffracted light incident in the clockwise direction and emitted after passing through the blazed grating will be detected; the pyroelectric power meter is used to detect the zero-order diffracted light.

[0015] In a second aspect, the present invention provides a method for fabricating a ring-shaped external cavity interband cascaded laser, comprising: step S1, providing an interband cascaded laser and depositing an antireflection coating on the front cavity surface of the interband cascaded laser; step S2, providing a front cavity surface straight lens and a rear cavity surface straight lens, respectively disposed on the front cavity surface and the rear cavity surface of the interband cascaded laser; step S3, providing a blazed grating disposed on the front cavity surface of the front cavity surface straight lens; and step S4, a gold-plated mirror assembly, comprising a first gold-plated mirror, a second gold-plated mirror, and a third gold-plated mirror disposed along the output light path of the blazed grating. Gold-plated reflector; Step S5: The front cavity straight lens, blazed grating, first gold-plated reflector, second gold-plated reflector, third gold-plated reflector, and rear cavity straight lens form a ring optical path cavity; Step S6: The front cavity side of the inter-band cascaded laser emits a light signal, which exits clockwise through the ring optical path cavity and then re-enters the inter-band cascaded laser from the rear cavity side; Step S7: The clockwise-propagating light signal and the counterclockwise-propagating light signal are directionally coupled in the inter-band cascaded laser; After directional coupling, only the zeroth-order diffracted light incident clockwise and exiting after passing through the blazed grating will be detected.

[0016] In the above scheme, step S3 includes: fixing the blazed grating to the grating frame, which can be rotated by a traveling wave reducer.

[0017] In the above scheme, step S1 specifically includes: flip-soldering the interband cascaded laser onto the aluminum nitride heat sink layer, and then sintering it onto the indium heat sink layer; wherein, the cavity of the interband cascaded laser has the same width as the aluminum nitride heat sink layer and the indium heat sink layer; the indium heat sink layer is provided with screw holes; and fixing the sintered interband cascaded laser onto the optical lifting platform.

[0018] In the above scheme, step S4 specifically includes: using an infrared detection card and a diode laser to sequentially adjust the position and angle of the first gold-plated reflector, the second gold-plated reflector, and the third gold-plated reflector.

[0019] (III) Beneficial Effects

[0020] The technical solutions of the embodiments of the present invention have at least the following beneficial effects:

[0021] (1) By introducing multiple mirrors, the cavity length can be increased several times compared to the ordinary EC cavity length, which helps to extend the photon lifetime and obtain a narrower external cavity spectral linewidth;

[0022] (2) After directional coupling, CW (clockwise) and CCW (counterclockwise) light enter the ICL through the ring cavity, resulting in greater light intensity in the laser chip. Therefore, the ICL can easily obtain a wider tuning range than the traditional external cavity.

[0023] (3) After the CW (clockwise) and CCW (counterclockwise) light are directionally coupled, they enter the ICL through the ring cavity, and the light intensity fed back to the laser chip is greater, which enhances the power emitted after diffraction by the blazed grating.

[0024] (4) CW (clockwise) and CCW (counterclockwise) light are traveling waves in the ring cavity, which can significantly reduce the spatial hole burning (SHB) effect associated with standing waves and greatly improve spectral stability. Attached Figure Description

[0025] Figure 1 A schematic diagram of a ring-shaped external cavity interband cascaded laser according to an embodiment of the present invention is shown.

[0026] Figure 2 A flowchart illustrating a method for fabricating a ring-shaped external cavity interband cascaded laser according to an embodiment of the present invention is shown.

[0027] Figure 3 The diagram illustrates the propagation of light emitted after passing through a blazed grating according to an embodiment of the present invention.

[0028] Figure 4 The spectrum of a ring external cavity interband cascaded laser according to an embodiment of the present invention is schematically shown.

[0029] [Explanation of reference numerals in the attached figures]

[0030] 1-Inter-band cascaded laser; 2-Antireflective coating; 3-Front cavity surface straight lens;

[0031] 4-Rear cavity straight lens; 5-Blazed grating; 6-First gold-plated reflector;

[0032] 7-Second gold-plated reflector; 8-Third gold-plated reflector; 9-Pyroelectric power meter. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0034] Please refer to the following for details. Figure 1 , Figure 1A schematic diagram of a ring-shaped external cavity interband cascaded laser according to an embodiment of the present invention is shown.

[0035] like Figure 1 As shown, this embodiment of the invention provides a ring-shaped external cavity inter-band cascaded laser, comprising: an inter-band cascaded laser 1; an anti-reflection coating 2 deposited on the front cavity surface of the inter-band cascaded laser 1; a front cavity surface straight lens 3 and a rear cavity surface straight lens 4 respectively disposed on the front cavity surface and rear cavity surface of the inter-band cascaded laser 1; a blazed grating 5 disposed on the front cavity surface of the front cavity surface straight lens 3; and a gold-plated mirror assembly comprising a first gold-plated mirror 6, a second gold-plated mirror 7, and a third gold-plated mirror 8 disposed along the output optical path of the blazed grating 5; wherein the front cavity surface straight lens 3, the blazed grating 5, the first gold-plated mirror 6, the second gold-plated mirror 7, the third gold-plated mirror 8, and the rear cavity surface straight lens 4 form a ring optical path cavity; the front cavity surface of the inter-band cascaded laser 1 emits an optical signal, which exits clockwise through the ring optical path cavity and then re-enters the inter-band cascaded laser 1 from the rear cavity surface.

[0036] Among them, the cavity of the interband cascaded laser 1 is a Fabry-Perot structure and can operate continuously at room temperature; it can form non-reciprocal losses in both CW (clockwise) and CCW (counterclockwise) directions, thereby improving output power and suppressing the FP (Fabry-Perot) mode in ICL.

[0037] For example, for an ICL with a center wavelength of 3.3 micrometers, the front cavity surface coating material is Al2O3 / Ge (300 / 30nm).

[0038] In this embodiment, the front cavity straight lens 3 and the rear cavity straight lens 4 are fixed on the copper plate of the optical lifting platform.

[0039] The front cavity collimating lens 3 is located outside the front cavity surface of the ICL, and the rear cavity collimating lens 4 is located outside the rear cavity surface of the ICL. They are fixed to the copper plate of the lifting platform on which the ICL is placed by UV adhesive. Both collimating lenses have high numerical apertures (NA = 0.85), which can collimate the divergent light emitted from the front and rear cavity surfaces of the ICL into a parallel beam.

[0040] In this embodiment, the blazed grating 5 is fixed on a grating frame, which is positioned in the direction of the light path emitted from the front cavity straight lens 3.

[0041] The grating frame can be rotated using a traveling wave reducer to provide wavelength-selective optical feedback. The laser chip is mounted with its epitaxial direction perpendicular to the groove direction of the blazed grating.

[0042] For example, the blazed grating can be designed with a wavelength of 3.5 μm, a grating gradation of 300 g / mm, and is coated with an anti-reflection coating. The grating diffraction efficiency in the direction perpendicular to the gradation is >80%.

[0043] In this embodiment, the optical signal is emitted from the rear cavity side of the inter-band cascaded laser 1. After exiting counterclockwise through the annular optical path cavity, the optical signal is re-injected into the inter-band cascaded laser 1 from the front cavity side.

[0044] In this embodiment, the optical signal that has completed clockwise propagation and the optical signal that has completed counterclockwise propagation are directionally coupled in the interband cascaded laser 1; after directional coupling, only the zero-order diffracted light incident in the clockwise direction and emitted after passing through the blazed grating 5 will be detected; the pyroelectric power meter 9 is used to detect the zero-order diffracted light.

[0045] In summary, a ring-shaped external cavity interband cascaded laser utilizes a blazed grating and three gold-plated mirrors to redirect light emitted from the front cavity surface of a FP interband cascaded laser with an antireflection coating on the front cavity surface back to the rear cavity surface after optical path adjustment. This creates traveling-wave light in two directions: clockwise from the front cavity surface and counterclockwise from the rear cavity surface. Due to the non-reciprocal loss introduced by the antireflection coating on the front cavity surface in both directions, directional coupling occurs in the clockwise direction. The directionally coupled light is then reflected by the blazed grating in its zero-order reflection direction to obtain the output light. This scheme, by introducing multiple mirrors, allows the cavity length to be several times larger than that of a conventional EC cavity, which helps to extend photon lifetime and obtain a narrower external cavity spectral linewidth. Furthermore, the traveling-wave nature significantly reduces spatial aperture burn-off associated with standing waves, improving spectral stability. Furthermore, after directional coupling, clockwise and counterclockwise light enter the ICL through the ring cavity, resulting in greater light intensity in the laser chip. Therefore, it is easier to obtain a wider tuning range and higher output power than the traditional external cavity structure with zero-order diffraction light output.

[0046] Figure 2 A flowchart illustrating a method for fabricating a ring-shaped external cavity interband cascaded laser according to an embodiment of the present invention is shown.

[0047] Please refer to the following for details. Figure 2 The specific process of the method for fabricating a ring external cavity interband cascaded laser according to an embodiment of the present invention includes steps S1 to S7.

[0048] In operation S1, an interband cascaded laser 1 is provided, and an antireflection coating 2 is deposited on the front cavity surface side of the interband cascaded laser 1.

[0049] In operation S2, a front cavity surface straight lens 3 and a rear cavity surface straight lens 4 are provided, and the front cavity surface straight lens 3 and the rear cavity surface straight lens 4 are respectively provided on the front cavity surface side and the rear cavity surface side of the interband cascaded laser 1.

[0050] In operation S3, a blazed grating 5 is provided and disposed on the front cavity side of the front cavity straight lens 3;

[0051] In operation S4, the gold-plated reflector group includes a first gold-plated reflector 6, a second gold-plated reflector 7, and a third gold-plated reflector 8 arranged along the outgoing light path of the blazed grating 5.

[0052] In operation S5, the front cavity straight lens 3, the blazed grating 5, the first gold-plated reflector 6, the second gold-plated reflector 7, the third gold-plated reflector 8, and the rear cavity straight lens 4 form an annular optical path cavity.

[0053] During operation S6, the inter-band cascaded laser 1 emits a light signal from the front cavity side, and after the light signal is emitted clockwise through the annular optical path cavity, it is re-injected into the inter-band cascaded laser 1 from the rear cavity side.

[0054] When operating S7, the clockwise emitted optical signal and the counterclockwise emitted optical signal are directionally coupled in the interband cascaded laser 1; after directional coupling, only the zeroth-order diffracted light incident in the clockwise direction and emitted after passing through the blazed grating 5 will be detected.

[0055] Specifically, the interband cascaded laser 1 is flip-welded onto the aluminum nitride heat sink layer and then sintered onto the indium heat sink layer; wherein, the cavity of the interband cascaded laser 1 has the same width as the aluminum nitride heat sink layer and the indium heat sink layer; the indium heat sink layer is provided with screw holes; the sintered interband cascaded laser 1 is fixed on the optical lifting platform.

[0056] After placing the optical equipment, the positions and angles of the first gold-plated reflector 6, the second gold-plated reflector 7, and the third gold-plated reflector 8 were adjusted sequentially using an infrared detection card and a diode laser, carefully aligning the optical path. Two reverse propagation modes, clockwise and counterclockwise, formed a closed loop within the annular outer cavity. The entire annular resonant cavity is over 1 meter long.

[0057] Figure 3 The diagram illustrates the propagation of light emitted after passing through a blazed grating according to an embodiment of the present invention.

[0058] In this example, the operating state of the ring external cavity interband cascaded laser can be as follows: the ICL of the ring external cavity interband cascaded laser is placed on a temperature controller (TEC), and the operating temperature of the ICL is fixed near room temperature by a three-stage water cooling device.

[0059] In this embodiment, the ring external cavity interband cascaded laser achieves directional propagation in the CW (clockwise) direction after the optical signal is directionally coupled and the injection current is adjusted.

[0060] Please refer to the following for details. Figure 3 Once directional propagation occurs, only the zero-order diffracted light incident in the CW (clockwise) direction and emitted after passing through the blazed grating will be detected. This zero-order diffracted light serves as the output light of the entire annular external cavity interband cascaded laser and is detected by the pyroelectric power meter 9.

[0061] Among them, the zeroth-order diffracted light incident counterclockwise and emitted after passing through the blazed grating is undetectable.

[0062] The optical signal propagating in the annular optical path cavity is the first-order diffracted light. The optical signal emitted by the interband cascaded laser exits the annular optical path cavity in a clockwise (counterclockwise) manner and then re-enters the interband cascaded laser.

[0063] Figure 4 The spectrum of a ring external cavity interband cascaded laser according to an embodiment of the present invention is schematically shown.

[0064] Please refer to the following for details. Figure 4 In this embodiment, for example, using the same ICL at room temperature and operating under continuous wave conditions, the tuning range of the conventional Littrow external cavity can be obtained as a tuning range of 80 cm for the laser wavelength. -1 In this invention, the tuning range of the annular outer cavity exceeds 150cm. -1 This demonstrates that the annular external cavity achieves a larger spectral tuning range than the traditional Littrow external cavity, approximately twice the tuning range of the Littrow external cavity.

[0065] The annular external cavity interband cascaded laser in this embodiment forms a closed annular optical path using a diffraction grating and a mirror. Light emitted from the front and rear cavity surfaces of the ICL propagates in two directions within the annular cavity: CW (clockwise) and CCW (counterclockwise). Due to the difference in reflectivity of the coatings on the front and rear cavity surfaces, non-reciprocal loss is introduced, resulting in a difference in optical power in the two directions. This induces the ICL to form an orientation in the CW (clockwise) direction, which has lower loss and higher power, under certain conditions. The zero-order diffracted light incident on the blazed grating from the front cavity surface in the CW (clockwise) direction is used as the output light, resulting in a higher output power compared to the commonly used Littrow external cavity structure with zero-order diffracted light output. Simultaneously, the annular external cavity arrangement increases the cavity length, effectively lowering the threshold and increasing the intensity of light fed back into the laser, allowing the same ICL to achieve a wider spectral range than traditional external cavities.

[0066] Those skilled in the art will understand that although the invention has been shown and described with reference to specific exemplary embodiments thereof, they should understand that various changes in form and detail may be made to the invention without departing from the spirit and scope of the invention as defined by the appended claims and their equivalents. Therefore, the scope of the invention should not be limited to the above embodiments, but should be determined not only by the appended claims, but also by their equivalents.

[0067] Similarly, it should be understood that, in order to simplify the invention and aid in understanding one or more of the various disclosed aspects, features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof in the foregoing description of exemplary embodiments of the invention. However, this method of disclosure should not be construed as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as reflected in the preceding claims, the disclosed aspects consist of fewer than all features of a single previously disclosed embodiment. Therefore, the claims following the detailed description are hereby expressly incorporated into that detailed description, wherein each claim itself is a separate embodiment of the invention.

[0068] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A ring-shaped external cavity interband cascaded laser, comprising: Interband cascaded laser (1); An antireflection coating (2) is deposited on the front cavity surface of the interband cascaded laser (1); The front cavity surface of the inter-band cascaded laser (1) is provided with a front cavity surface straight lens (3) and a rear cavity surface straight lens (4). A blazed grating (5) is disposed on the front cavity side of the front cavity straight lens (3); The gold-plated reflector assembly includes a first gold-plated reflector (6), a second gold-plated reflector (7), and a third gold-plated reflector (8) disposed along the outgoing light path of the blazed grating (5); The front cavity straight lens (3), the blazed grating (5), the first gold-plated reflector (6), the second gold-plated reflector (7), the third gold-plated reflector (8), and the rear cavity straight lens (4) form an annular optical path cavity. The inter-band cascaded laser (1) emits an optical signal from the front cavity side. After the optical signal exits clockwise through the annular optical path cavity, it is re-injected into the inter-band cascaded laser (1) from the rear cavity side.

2. The annular external cavity interband cascaded laser according to claim 1, characterized in that, The cavity of the interband cascaded laser (1) is a Fabry-Perot structure and can operate continuously at room temperature.

3. The annular external cavity interband cascaded laser according to claim 1, characterized in that, The blazed grating (5) is fixed on a grating frame, which is positioned in the direction of the light path emitted by the front cavity straight lens (3).

4. The annular external cavity interband cascaded laser according to claim 3, characterized in that, The front cavity straight lens (3) and the rear cavity straight lens (4) are fixed on the copper plate of the optical lifting platform.

5. The annular external cavity interband cascaded laser according to claim 1, characterized in that, The inter-band cascaded laser (1) emits an optical signal from the rear cavity side. After the optical signal exits counterclockwise through the annular optical path cavity, it is re-injected into the inter-band cascaded laser (1) from the front cavity side.

6. The annular external cavity interband cascaded laser according to claim 5, characterized in that, It also includes a pyroelectric power meter (9); The optical signal that completes the clockwise outward propagation and the optical signal that completes the counterclockwise outward propagation will be directionally coupled in the interband cascaded laser (1); After the directional coupling, only the zeroth-order diffracted light incident in the clockwise direction and emitted after passing through the blazed grating (5) will be detected; The pyroelectric power meter (9) is used to detect the zero-order diffracted light.

7. A method for fabricating a ring-shaped external cavity interband cascaded laser as described in any one of claims 1 to 6, characterized in that, include: Step S1, provide an interband cascaded laser (1), and deposit an anti-reflection film (2) on the front cavity surface side of the interband cascaded laser (1); Step S2, a front cavity surface straight lens (3) and a rear cavity surface straight lens (4) are provided, and the front cavity surface straight lens (3) and the rear cavity surface straight lens (4) are respectively provided on the front cavity surface side and the rear cavity surface side of the interband cascaded laser (1); Step S3, a blazed grating (5) is provided and disposed on the front cavity side of the front cavity straight lens (3); Step S4, gold-plated reflector group, including a first gold-plated reflector (6), a second gold-plated reflector (7) and a third gold-plated reflector (8) arranged along the outgoing light path of the blazed grating (5); Step S5, the front cavity straight lens (3), the blazed grating (5), the first gold-plated reflector (6), the second gold-plated reflector (7), the third gold-plated reflector (8) and the rear cavity straight lens (4) form an annular optical path cavity; Step S6: The front cavity side of the inter-band cascaded laser (1) emits an optical signal, which is then emitted clockwise through the annular optical path cavity and then re-injected into the inter-band cascaded laser (1) from the rear cavity side. Step S7: The clockwise emitted optical signal and the counterclockwise emitted optical signal are directionally coupled in the interband cascaded laser (1); After the directional coupling, only the zero-order diffracted light incident in the clockwise direction and emitted after passing through the blazed grating (5) will be detected.

8. The preparation method according to claim 7, characterized in that, Step S3 includes fixing the blazed grating (5) to the grating frame, which can be rotated by a traveling wave reducer.

9. The preparation method according to claim 7, characterized in that, Step S1 specifically includes: The interband cascaded laser (1) was flip-welded onto the aluminum nitride heat sink and then sintered onto the indium heat sink. The cavity of the interband cascaded laser (1) has the same width as the aluminum nitride heat sink and the indium heat sink; the indium heat sink is provided with screw holes; The sintered interband cascaded laser (1) is fixed on the optical lifting platform.

10. The preparation method according to claim 7, characterized in that, Step S4 specifically includes: using an infrared detection card and a diode laser to sequentially adjust the position and angle of the first gold-plated reflector (6), the second gold-plated reflector (7), and the third gold-plated reflector (8).

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