Target wave band output structure, laser output light source and gas detection system

Abstract

The invention provides a target wave band output structure, a laser output light source and a gas detection system, and relates to the technical field of photoelectricity, and the target wave band output structure comprises a substrate, a periodically polarized waveguide, a reflecting film and a first directional coupler. Wherein the periodically polarized waveguide is arranged on the substrate, and a first optical signal and a second optical signal are transmitted in the periodically polarized waveguide; the reflecting films are arranged at two ends of the periodically polarized waveguide along a first direction and reflect a first optical signal; the first directional coupler comprises a first coupling waveguide and a first Bragg grating embedded in the first coupling waveguide. According to the scheme, pump light is converted into a first optical signal and a second optical signal by utilizing a periodically polarized waveguide, the first optical signal is limited in the waveguide through a reflecting film, and meanwhile, the second optical signal is efficiently coupled and output from the periodically polarized waveguide by utilizing a first directional coupler embedded with a first Bragg grating; therefore, the separation of dual-band light is realized, and the process complexity is reduced while the integration level is improved.

Description

Technical Field

[0001] This application relates to the field of optoelectronic technology, and in particular to a target band output structure, a laser output light source, and a gas detection system. Background Technology

[0002] Because many gases exhibit unique and strong absorption fingerprint peaks in the mid-infrared band (2.5–25 μm), mid-infrared light sources have become an ideal choice for trace gas detection and a core technology for high-precision gas sensing. However, directly generating efficient and wide-range tunable mid-infrared laser sources in this band still faces significant challenges.

[0003] Currently, the nonlinear frequency conversion characteristics of periodically polarized lithium niobate (PPLN) can be used to convert pump light into signal light and idler light, with the idler light serving as the desired mid-infrared light source. However, outputting the idler light from the PPLN requires dual-wavelength coating at its output end, a complex and costly process. To avoid dual-wavelength coating, although directional couplers can be used to couple the idler light from the main waveguide to the output waveguide, the coupling effect of traditional directional couplers is relatively weak. Summary of the Invention

[0004] This application provides a target band output structure, a laser output source, and a gas detection system. The aim is to use a periodically polarized waveguide to convert pump light into a first optical signal and a second optical signal, confine the first optical signal within the waveguide through a reflective film, and simultaneously use a first directional coupler embedded with a first Bragg grating to efficiently couple the second optical signal out from the periodically polarized waveguide, thereby achieving separation of the two bands of light, improving integration while reducing process complexity.

[0005] To achieve the above objectives, the embodiments of this application adopt the following technical solutions: In one aspect, a target band output structure is provided, including a substrate, a periodically polarized waveguide, a reflective film, and a first directional coupler.

[0006] A periodically polarized waveguide is disposed on a substrate. A first optical signal and a second optical signal are transmitted in the periodically polarized waveguide, the wavelengths of the first and second optical signals being different. The periodically polarized waveguide extends along a first direction, which is parallel to the substrate. A reflective film is disposed at both ends of the periodically polarized waveguide along the first direction, and the reflective film reflects the first optical signal. A first directional coupler is disposed on the substrate, and the first directional coupler includes a first coupling waveguide and a first Bragg grating embedded in the first coupling waveguide. The first directional coupler is located on one side of the periodically polarized waveguide along a second direction and is coupled to the periodically polarized waveguide. The second direction is parallel to the substrate and perpendicular to the first direction. The second optical signal is coupled from the periodically polarized waveguide to the first directional coupler.

[0007] Specifically, the first optical signal can refer to the signal light, and the second optical signal can refer to the idler light (i.e., the mid-infrared light source).

[0008] In the target band output structure provided in this application embodiment, the input pump light is efficiently converted into a first optical signal and a second optical signal by utilizing the nonlinear frequency conversion characteristics of the periodically polarized waveguide. A reflective film that only reflects the first optical signal is prepared at both ends of the periodically polarized waveguide along the first direction, confining the first optical signal within the periodically polarized waveguide. At the same time, a first directional coupler with a first Bragg grating is provided on one side of the periodically polarized waveguide to efficiently couple the second optical signal (i.e., the mid-infrared light source) in the periodically polarized waveguide into the first coupling waveguide. Thus, wavelength conversion and mid-infrared light source output are realized simultaneously on a single substrate, improving the integration of the target band output structure and avoiding the traditional dual-wavelength coating process, thereby reducing the manufacturing cost and complexity.

[0009] In some embodiments, a periodically polarized waveguide includes a first sub-waveguide and two second sub-waveguides located at both ends of the first sub-waveguide. The first sub-waveguide has a periodic polarization structure, and the second sub-waveguides are in an aperiodic polarization state.

[0010] The reflective film is disposed at two mutually distant ends of the two second sub-waveguides; the first directional coupler is disposed on one side of one of the second sub-waveguides along the second direction.

[0011] In some embodiments, the first directional coupler has an output terminal, and the second optical signal is output from the output terminal of the first directional coupler.

[0012] The target band output structure also includes an anti-reflection coating, which is disposed on the output end of the first directional coupler.

[0013] In some embodiments, the first coupling waveguide includes a first sub-section and two second sub-sections disposed at both ends of the first sub-section; a first Bragg grating is embedded in the first sub-section, one of the two second sub-sections serves as the output end of the first directional coupler, and the other is bent.

[0014] In some embodiments, the target band output structure further includes a second directional coupler disposed on a substrate. The second directional coupler includes a second coupling waveguide and a second Bragg grating embedded in the second coupling waveguide. The second directional coupler is located on one side of the periodic polarized waveguide along a second direction and is coupled to the periodic polarized waveguide.

[0015] The first directional coupler and the second directional coupler are located at the two ends of the periodically polarized waveguide, respectively.

[0016] In some embodiments, the second directional coupler has an input terminal for receiving a light source input.

[0017] The target band output structure also includes an interface waveguide and a cladding. The interface waveguide is disposed on the substrate and connected to the input of the second directional coupler; the area of ​​the interface waveguide's cross-section perpendicular to the substrate is gradually varied. The cladding surrounds the interface waveguide.

[0018] In some embodiments, a thin-film resistor is further included, which is disposed on one side of the periodically polarized waveguide along a second direction, and / or disposed on the side of the first Bragg grating away from the periodically polarized waveguide along the second direction.

[0019] In some embodiments, the wavelength of the light output by the first directional coupler is 2.5 μm to 25 μm.

[0020] In a second aspect, a laser output light source is provided, including a laser and a target band output structure provided in any embodiment of the first aspect.

[0021] The laser is coupled to the input end of the target band output structure.

[0022] The technical effects of the gas detection system in the second aspect can be seen in the technical effects of the design of the target band output structure in the first aspect, which will not be repeated here.

[0023] Thirdly, a gas detection system is provided, including a detection chamber and a laser output light source provided in the second aspect. The detection chamber is used to introduce the gas to be detected, and at least a portion of the laser output light source is located within the detection chamber.

[0024] The technical effects of the gas detection system in the third aspect can be seen in the technical effects of the laser output light source design in the second aspect, which will not be repeated here. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in this application, the accompanying drawings used in some embodiments of this application will be briefly described below. Obviously, the drawings described below are only drawings of some embodiments of this application, and those skilled in the art can obtain other drawings based on these drawings. In addition, the drawings described below can be regarded as schematic diagrams and are not the actual dimensions of the products or the actual flow of the methods involved in the embodiments of this application.

[0026] Figure 1 A schematic diagram of the target band output structure provided in an embodiment of this application; Figure 2 A top view of the target band output structure provided in the embodiments of this application; Figure 3 A front view of the target band output structure provided in the embodiments of this application; Figure 4 A rear view of the target band output structure provided in an embodiment of this application; Figure 5 A side view of the target band output structure provided in an embodiment of this application; Figure 6 Another side view of the target band output structure provided in the embodiments of this application; Figure 7 A schematic diagram of a laser output light source provided in an embodiment of this application; Figure 8 This is a schematic diagram of a gas detection system provided in an embodiment of this application. Detailed Implementation

[0027] The technical solutions in some embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments provided in this application are within the scope of protection of this application.

[0028] In the description of this application, it should be understood that the terms "center", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0029] Unless the context otherwise requires, throughout the specification and claims, the term "comprising" is interpreted as open-ended and encompassing, meaning "including, but not limited to." In the description of the specification, terms such as "one embodiment," "some embodiments," "exemplary embodiment," "exemplary," or "some examples," etc., are intended to indicate that a particular feature, structure, material, or characteristic associated with that embodiment or example is included in at least one embodiment or example of this application. The illustrative representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the aforementioned particular features, structures, materials, or characteristics may be included in any suitable manner in any one or more embodiments or examples.

[0030] The terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the embodiments of this application, unless otherwise stated, "multiple" means two or more.

[0031] Connection or link: can refer to a mechanical or physical connection relationship, that is, A and B are connected or linked. It can mean that there are fastened components (such as screws, bolts, rivets, etc.) between A and B, or that A and B are in contact with each other and are difficult to separate. A and B can be fixed, detachable, or integrated; they can be directly connected or indirectly connected through an intermediate medium.

[0032] Coupling can be understood as direct coupling and / or indirect coupling. "Coupled connection" can be understood as a direct coupling connection and / or indirect coupling connection. Direct coupling, also known as "electrical connection," refers to components being in direct or indirect physical contact and electrically conductive. For example, in circuit construction, different components are connected through physical lines that can transmit electrical signals, such as copper foil or wires on a printed circuit board (PCB). "Indirect coupling" can be understood as two conductors conducting electricity through a gap or without contact. In one embodiment, indirect coupling can also be called capacitive coupling, for example, using the coupling between two conductive parts to form an equivalent capacitance to achieve signal transmission.

[0033] As used herein, “parallel,” “perpendicular,” and “equal” include the described situation and situations that are similar to the described situation, within an acceptable deviation range, which is determined by those skilled in the art taking into account the measurement under discussion and the errors associated with the measurement of a particular quantity (i.e., the limitations of the measurement system). For example, “parallel” includes absolute parallelism and approximate parallelism, where an acceptable deviation range for approximate parallelism may be, for example, within 5°; “perpendicular” includes absolute perpendicularity and approximate perpendicularity, where an acceptable deviation range for approximate perpendicularity may also be, for example, within 5°; “equal” includes absolute equality and approximate equality, where an acceptable deviation range for approximate equality may be, for example, a difference between the two equals being less than or equal to 5% of either one.

[0034] This document describes exemplary embodiments with reference to sectional views and / or plan views, which are idealized exemplary drawings. In the drawings, the thickness of layers and regions is enlarged for clarity. Therefore, variations in shape relative to the drawings are contemplated due to, for example, manufacturing techniques and / or tolerances. Therefore, exemplary embodiments should not be construed as limited to the shapes of the regions shown herein, but rather include shape deviations due to, for example, manufacturing processes. Thus, the regions shown in the drawings are schematic in nature, and their shapes are not intended to show the actual shapes of the regions of the device, nor are they intended to limit the scope of the exemplary embodiments.

[0035] Furthermore, the scenarios described in the embodiments of this application are for the purpose of more clearly illustrating the technical solutions of the embodiments of this application, and do not constitute a limitation on the technical solutions provided in the embodiments of this application. As those skilled in the art will know, with the emergence of new scenarios, the technical solutions provided in the embodiments of this application are also applicable to similar technical problems.

[0036] This application provides a target band output structure 100.

[0037] Figure 1This is a schematic diagram of a target band output structure 100 provided in an embodiment of this application.

[0038] Figure 2 This is a top view of the target band output structure 100 provided in an embodiment of this application.

[0039] Figure 3 A front view of the target band output structure 100 provided in the embodiments of this application.

[0040] Figure 4 This is a rear view of the target band output structure 100 provided in an embodiment of this application.

[0041] Figure 5 A side view of the target band output structure 100 provided in an embodiment of this application.

[0042] Figure 6 Another side view of the target band output structure 100 provided in the embodiments of this application.

[0043] In some embodiments, see Figure 1 and Figure 2 The target band output structure 100 includes a substrate 1, a periodically polarized waveguide 2, a reflective film 3, and a first directional coupler 4.

[0044] For example, substrate 1 may be a lithium niobate structure on an insulator, which typically includes, from top to bottom, a lithium niobate thin film layer, an insulating layer (e.g., silicon dioxide) and a mechanical support substrate (e.g., silicon, lithium niobate bulk material, etc.).

[0045] See Figure 1 and Figure 2 A periodically polarized waveguide 2 is disposed on a substrate 1; a first optical signal and a second optical signal are transmitted in the periodically polarized waveguide 2, the wavelength of the first optical signal is different from the wavelength of the second optical signal; the periodically polarized waveguide extends along a first direction X, the first direction X is parallel to the substrate 1.

[0046] For example, the material of the periodically polarized waveguide 2 can be periodically polarized lithium niobate (PPLN) or periodically polarized lithium tantalate (PPLT).

[0047] For example, when the material of the periodically polarized waveguide 2 is lithium niobate, its fabrication can be achieved by inducing ferroelectric domain inversion through an applied electric field. That is, the spontaneously polarized single-domain structure within the lithium niobate crystal is transformed into a periodically alternating reverse domain structure, thereby obtaining periodically polarized lithium niobate (i.e., periodically polarized waveguide 2). The periodically polarized waveguide 2 possesses quasi-phase matching (QPM) characteristics, which can effectively compensate for phase mismatch during nonlinear frequency conversion.

[0048] Based on the aforementioned QPM characteristics, this periodically polarized waveguide 2 can be used for nonlinear processes such as difference frequency generation (DFG). To further improve conversion efficiency, it can be combined with optical parametric oscillator (OPO) technology. During OPO operation, the incident pump light (e.g., a 1.55μm near-infrared source) can be converted into signal light and idler light under nonlinear interaction.

[0049] The OPO process based on periodically polarized waveguide 2 satisfies energy conservation. Let the pump light frequency be ω1, ω2 and ω3 be the signal light frequency and idler light frequency after nonlinear frequency conversion, respectively, and their wavelengths be λ1, λ2 and λ3, respectively. Let h be Planck's constant, then we have:

[0050] Or an equivalent wavelength relation:

[0051] For example, methane gas has a characteristic absorption peak around 4.6 µm. When the pump light wavelength λ1 is 1.31 µm, to obtain the idler light λ3 at 4.6 µm, the corresponding signal light λ2 can be calculated to be 1.83161 µm according to the above relationship. Therefore, when designing the periodically polarized waveguide 2, the polarization period of the periodically polarized waveguide 2 needs to be adjusted to meet the quasi-phase matching condition for converting the nonlinear frequency of the 1.31 µm pump light into the 1.83161 µm signal light and the 4.6 µm idler light. In the above process, the generated idler light is located in the mid-infrared band with a longer wavelength, while the signal light is in a shorter wavelength range.

[0052] For example, the first optical signal can be the aforementioned signal light (with a shorter wavelength), and the second optical signal can be the aforementioned idler light. The second optical signal is located in the mid-infrared band (e.g., 3-5 μm or longer), which has strong characteristic absorption lines for many gas molecules (e.g., CH4, CO2, CO, etc.), making it suitable for high-sensitivity, high-selectivity mid-infrared gas sensing. By adjusting the pump light wavelength or the polarization period of the periodically polarized waveguide 2, the wavelength of the second optical signal can be flexibly tuned to align with the absorption peak of a specific gas, thus making it suitable for multi-component gas sensing or spectral analysis.

[0053] See Figure 1 and Figure 2 The reflective film 3 is disposed at both ends of the periodically polarized waveguide 2 along the first direction, and the reflective film 3 reflects the first optical signal.

[0054] For example, for mid-infrared wavelength conversion applications, idler light (i.e., the second optical signal) located in the mid-infrared band is typically required, while signal light (i.e., the first optical signal) is not needed. In this embodiment, by fabricating reflective films 3 at both ends of the waveguide to form cavity reflectors, the first optical signal is confined within the cavity, preventing it from escaping to the outside of the periodically polarized waveguide 2 and interfering with the extraction and utilization of the second optical signal, thereby improving system efficiency and stability.

[0055] See Figure 1 and Figure 2 A first directional coupler 4 is disposed on the substrate 1. The first directional coupler 4 includes a first coupling waveguide 41 and a first Bragg grating 42 embedded in the first coupling waveguide 41. The first directional coupler 4 is located on one side of the periodically polarized waveguide 2 along the second direction Y and is coupled to the periodically polarized waveguide 2. The second direction Y is parallel to the substrate 1 and perpendicular to the first direction X. The second optical signal is coupled from the periodically polarized waveguide 2 to the first directional coupler 4.

[0056] For example, the first Bragg grating 42 can be a uniform Bragg grating, capable of producing strong selective reflection of a specific Bragg wavelength while allowing light of other wavelengths to pass through with low loss. The Bragg wavelength can be expressed as:

[0057] in, Λ is the effective refractive index of the grating, and Λ is the grating period.

[0058] Based on the principle of phase matching:

[0059] Wherein, β1 and β2 are the propagation constants of the second optical signal in the waveguide mode of the first Bragg grating 42 and the waveguide mode of the periodically polarized waveguide 2, respectively. Under the above conditions, the second optical signal can be efficiently directionally coupled from the periodically polarized waveguide 2 to the first Bragg grating 42. The key parameters of the first Bragg grating 42, such as its etching depth, period, and length, need to be precisely designed according to the design scheme to ensure that its Bragg wavelength strictly matches the wavelength of the target pump light or the second optical signal. If the two waveguide modes themselves are mismatched, the phase matching condition can be satisfied by designing the grating parameters (especially the period), thereby achieving efficient coupling between the periodically polarized waveguide 2 and the first directional coupler 4.

[0060] Furthermore, the first Bragg grating 42 can also adopt a chirped grating structure. By adjusting the distribution of the grating period along the propagation direction, the operating bandwidth can be increased while maintaining high reflection efficiency.

[0061] In the target band output structure 100 provided in this application embodiment, the nonlinear frequency conversion characteristics of the periodic polarized waveguide 2 are utilized to efficiently convert the input pump light into a first optical signal and a second optical signal. A reflective film 3 that only reflects the first optical signal is prepared at both ends of the periodic polarized waveguide 2 along the first direction X, thus confining the first optical signal within the periodic polarized waveguide 2. At the same time, a first directional coupler 4 with a first Bragg grating 42 embedded is provided on one side of the periodic polarized waveguide 2 to efficiently couple the second optical signal (i.e., the mid-infrared light source) in the periodic polarized waveguide 2 into the first coupling waveguide 41. Thus, wavelength conversion and mid-infrared light source output are realized simultaneously on a single substrate 1, improving the integration of the target band output structure 100 and avoiding the traditional dual-wavelength coating process, thereby reducing the manufacturing cost and complexity.

[0062] In some embodiments, see Figure 1 and Figure 2 The periodically polarized waveguide 2 includes a first sub-waveguide 21 and two second sub-waveguides 22 located at both ends of the first sub-waveguide 21. The first sub-waveguide 21 has a periodic polarization structure, and the second sub-waveguides 22 are in an aperiodic polarization state. (See also...) Figure 5 and Figure 6 The reflective film 3 is disposed on the two mutually distant ends of the two second sub-waveguides 22; the first directional coupler 4 is disposed on one side of one of the second sub-waveguides 22 along the second direction Y.

[0063] For example, see Figure 2Pump light can be input from the second sub-waveguide 22 without the first directional coupler 4 on the side, and transmitted with low loss into the first sub-waveguide 21. Here, nonlinear frequency conversion is performed to convert the pump light into a first optical signal (signal light) and a second optical signal (idle light). The first optical signal is reflected by the reflective films 3 coated on the two far apart end faces of the two second sub-waveguides 22, and oscillates back and forth in the resonant cavity formed by the two second sub-waveguides 22 and the middle first sub-waveguide 21, making full use of energy and preventing outward output. At the same time, the second optical signal is coupled out efficiently and selectively through the first directional coupler 4 set on the side of one of the second sub-waveguides 22, due to the wavelength selectivity of the first Bragg grating 42 embedded inside, becoming a usable mid-infrared light source.

[0064] Understandably, in the above process, the first sub-waveguide 21 with a periodic polarization structure can focus on nonlinear frequency conversion without having to consider mode matching and transmission loss, thus improving conversion efficiency. Meanwhile, the aperiodic second sub-waveguides 22 at both ends maintain a uniform, domain-free structure, enabling low-loss transmission. Furthermore, the reflective film 3, deposited on the end face of the second sub-waveguide 22, allows the first optical signal to oscillate within the low-loss uniform waveguide, improving the quality factor of the resonant cavity and enhancing the oscillation intensity. In addition, the first directional coupler 4 extracts the second optical signal from the side of the second sub-waveguide 22, reducing the difficulty of simultaneously achieving efficient conversion and low-loss output in the same area. Through clear functional partitioning, the performance of the target band output structure 100 is improved while also reducing fabrication difficulty.

[0065] In some embodiments, see Figure 1 , Figure 2 and Figure 3 The first directional coupler 4 has an output terminal A, and the second optical signal is output from the output terminal A of the first directional coupler 4. The target band output structure 100 also includes an anti-reflection coating 5, which is disposed on the output terminal A of the first directional coupler 4.

[0066] For example, the antireflection film 5 can reduce the Fresnel reflection loss of the second optical signal at the interface between the first coupling waveguide 41 and the air of the first directional coupler 4, thereby increasing the output power of the second optical signal and enabling more mid-infrared light energy to be effectively utilized. Furthermore, the antireflection film 5 placed at the output end A can directly reduce back reflection, preventing stray light from feeding back into the first coupling waveguide 41 or the resonant cavity, thereby improving the signal-to-noise ratio of the target band output structure 100 and enhancing the long-term stability of the light source output.

[0067] In some embodiments, see Figure 1 and Figure 2The first coupling waveguide 41 includes a first sub-section 411 and two second sub-sections 412 disposed at both ends of the first sub-section 411; the first Bragg grating 42 is embedded in the first sub-section 411, and one of the two second sub-sections 412 serves as the output end A of the first directional coupler 4, while the other is bent.

[0068] For example, see Figure 2 The second sub-part 412 at the right end of the first sub-part 411 serves as the output terminal A, and the second sub-part 412 at its left end is bent.

[0069] For example, the curved second sub-section 412 can effectively suppress end-face reflection. Its curved structure disrupts the vertical reflective surface of the end face of the first coupling waveguide 41, causing the reflected light that may be generated to deviate from the original incident light path and fail to couple back to the waveguide core transmission mode. This reduces the noise and crosstalk caused by reflection within the first coupling waveguide 41, and improves the working stability and signal-to-noise ratio of the target band output structure 100.

[0070] For example, the convex surface of the curved second sub-section 412 can be oriented towards the periodically polarized waveguide 2, causing the optical path transmitted through it to naturally deflect away from the periodically polarized waveguide 2. In terms of spatial layout, this orientation optimizes the optical path wiring on the substrate 1, reserving sufficient and regular space for the periodically polarized waveguide 2 and its surrounding functional areas, avoiding intersections and mutual interference between different optical paths, and facilitating the realization of higher-density photonic integration.

[0071] For example, see Figure 2 The second sub-section 412, serving as output terminal A, may further include a bent waveguide 4121 and a straight waveguide 4122. The bent waveguide 4121 is connected to one end of the first sub-section 411, acting as an optical path deflector; the straight waveguide 4122 is connected to the end of the bent waveguide 4121, serving as the final output port for the second optical signal and providing a stable optical field output. This structure, in conjunction with the bent second sub-section 412 on the other side, achieves efficient and flexible directional output while maintaining consistency in manufacturing processes and design.

[0072] For example, based on the aforementioned structure of the periodically polarized waveguide 2 including a first sub-waveguide 21 with a periodically polarized structure and two non-periodicly polarized second sub-waveguides 22 located at its two ends, the design of the output end A of the first directional coupler 4 including an anti-reflection film 5 can be combined to further significantly reduce the Fresnel reflection loss of the output end A and improve the output power of the second optical signal and the system conversion efficiency, based on the efficient generation and separation of signal light and idler light by utilizing the reflective film 3 and the periodically polarized structure.

[0073] Alternatively, based on the aforementioned structure of the periodically polarized waveguide 2, which includes a first sub-waveguide 21 with a periodically polarized structure and two non-periodicly polarized second sub-waveguides 22 located at its two ends, the first directional coupler 4 can be combined with a design that includes a first sub-section 411 with an embedded first Bragg grating 42, a second sub-section 412 as an output end A, and another second sub-section 412 in a curved arrangement. This achieves efficient nonlinear conversion and optical path separation while using the curved second sub-section 412 to suppress end-face reflection, optimize the internal optical path of the device, and make the overall layout more compact, reducing crosstalk between different functional areas.

[0074] Furthermore, based on the above structure, an antireflection coating 5 can be deposited on the output end A. (See also...) Figure 2 For example, an antireflective coating 5 can be deposited at the end of 4122 to reduce surface reflection and achieve low-loss output. This will further improve the output power of the second optical signal while achieving efficient nonlinear conversion and optical path separation and suppressing end-face reflection, so that more mid-infrared light energy can be effectively utilized.

[0075] In some embodiments, see Figure 1 and Figure 2 The target band output structure 100 further includes a second directional coupler 6, which is disposed on the substrate 1. The second directional coupler 6 includes a second coupling waveguide 61 and a second Bragg grating 62 embedded in the second coupling waveguide 61. The second directional coupler 6 is located on one side of the periodic polarized waveguide 2 along the second direction Y and is coupled to the periodic polarized waveguide 2. The first directional coupler 4 and the second directional coupler 6 are located at opposite ends of the periodic polarized waveguide 2.

[0076] For example, the second directional coupler 6 can utilize the wavelength selectivity of its second Bragg grating 62 to efficiently couple externally input pump light from the second coupling waveguide 61 to the periodically polarized waveguide 2, providing the required pump light for subsequent nonlinear frequency conversion.

[0077] For example, see Figure 2 The first directional coupler 4 and the second directional coupler 6 can be located on one side of the two second sub-waveguides 22, and on different sides of the periodically polarized waveguide 2 along its length direction (i.e., the first direction X). Their specific implementation is not limited to a single layout; for example, they can be arranged symmetrically or asymmetrically. This split design allows the input of the pump light to be spatially separated from the output of the second optical signal (i.e., the mid-infrared light source), thereby achieving decoupling between the input and output and avoiding mutual interference.

[0078] For example, the aforementioned periodically polarized waveguide 2 can be based on a structure including a first sub-waveguide 21 with a periodically polarized structure and two aperiodically polarized second sub-waveguides 22 located at its two ends, or combined with an antireflection film 5 included at the output end A of the first directional coupler 4, or further employing a structure in which the first directional coupler 4 includes a first sub-section 411 with an embedded first Bragg grating 42, a second sub-section 412 as the output end A, and another second sub-section 412 is bent. The above embodiments can be implemented individually or in combination, not only efficiently achieving nonlinear frequency conversion and selective output of the second optical signal (i.e., mid-infrared light source), but also, through combination, further reducing insertion loss, suppressing stray reflections, and optimizing the optical path layout, thereby improving conversion efficiency and output performance while enhancing the overall integration and reliability of the target band output structure 100.

[0079] In some embodiments, see Figure 1 and Figure 2 The second directional coupler 6 has an input terminal B, which is used for light source input. The target band output structure 100 further includes an interface waveguide 7 and a cladding 8. The interface waveguide 7 is disposed on the substrate 1 and connected to the input terminal B of the second directional coupler 6; the area of ​​the cross-section of the interface waveguide 7 perpendicular to the substrate 1 is gradually varied; the cladding 8 surrounds the interface waveguide 7.

[0080] For example, the cross-sectional area of ​​the interface waveguide 7 perpendicular to the substrate 1 is set in a gradient. Through the gradual transition of the cross-sectional size, the pump light with a large mode size output by the external laser 200 can be gradually converted into a small mode supported by the interface waveguide 7 and the second coupling waveguide 61 under adiabatic conditions. This smoothly adapts to the mode field distribution between the external optical field and the waveguide, thereby reducing the coupling insertion loss of the pump light at the input end B and achieving efficient mode field matching.

[0081] For example, the interface waveguide 7 can be made of lithium niobate, and its cross-sectional shape and size can be obtained by using mature photolithography and etching processes.

[0082] For example, the cladding 8 has a lower refractive index than the interface waveguide 7, which can effectively confine the optical field inside the interface waveguide 7 for transmission, prevent optical energy leakage, and ensure that the pump light is guided to the second directional coupler 6 in a low-loss manner.

[0083] Specifically, the interface waveguide 7 and the cladding 8 together form a low-loss, high-reliability optical input channel. The interface waveguide 7 performs mode field conversion and matching, while the cladding 8 ensures lateral optical field confinement. The two work together to optimize the overall input efficiency and transmission stability of the pump light from the external light source to the second directional coupler 6.

[0084] In addition, see Figure 1 and Figure 2 The second directional coupler 6 can adopt a structure similar to that of the first directional coupler 4. For example, the second coupling waveguide 61 can also include multiple sub-sections, such as a middle sub-section for embedding the second Bragg grating 62, a sub-section serving as an input end B for receiving pump light, and a curved sub-section. This curved sub-section can effectively suppress end-face reflections and optimize spatial layout, thereby achieving efficient pump light input and low-loss output of the second optical signal (i.e., the mid-infrared light source) when used in conjunction with the first directional coupler 4.

[0085] In some embodiments, see Figure 1 and Figure 2 The target band output structure 100 also includes a thin film resistor 9, which is disposed on one side of the periodically polarized waveguide 2 along the second direction Y, and / or disposed on the side of the first Bragg grating 42 away from the periodically polarized waveguide 2 along the second direction Y.

[0086] For example, the thin-film resistor 9 can be used as a temperature control device to independently control the temperature of the first Bragg grating 42 and the periodically polarized waveguide 2. Since the center wavelength of the Bragg grating and the quasi-phase matching condition of the periodically polarized waveguide 2 are both temperature sensitive, by applying local and precise thermal regulation through the thin-film resistor 9, precise compensation can be made for the thermal sensitivity characteristics of different structures, such as stabilizing the quasi-phase matching condition and the Bragg wavelength, thereby stabilizing the nonlinear conversion efficiency and the output light wavelength, reducing the influence of thermal crosstalk and environmental fluctuations, and improving the output stability and operational controllability of the target band output structure 100.

[0087] In some embodiments, the wavelength of the light output by the first directional coupler 4 is 2.5 μm to 25 μm.

[0088] It is worth noting that the 2.5μm~25μm band belongs to the mid-infrared band. The energy of mid-infrared photons matches the energy level transitions of various gas molecules, thus having a significant advantage in gas detection. Within the mid-infrared band, the absorption spectrum of gases is dense and has distinctive absorption peaks. Different molecular functional groups exhibit strong and specific absorption behaviors. For example, CH or OH bond vibrations typically form absorption around 2.7μm, while absorption by C=O or N=O bonds mostly occurs in the 4.5μm to 4.7μm range.

[0089] In addition, different gases exhibit strong absorption of specific wavelengths of laser light. For example, CO2 shows significant absorption in the 4.2~4.3μm band, and CH4 also has a distinct absorption peak near 3.3μm.

[0090] For example, by adjusting the polarization period and pump light wavelength of the periodically polarized waveguide 2 of the target band output structure 100, it can output specific mid-infrared wavelengths such as 2.7μm, 4.2μm, and 4.7μm, which can cover the characteristic absorption spectra of various gases such as water (H2O), methane (CH4), carbon monoxide (CO), carbon dioxide (CO2), and nitrogen dioxide (NO2). Thus, the target band output structure 100 can detect multi-component gases through multi-wavelength laser output.

[0091] For example, the interface waveguide 7, the first directional coupler 4, the second directional coupler 6, and the periodically polarized waveguide 2 can all be made of lithium niobate. Integrating them based on the same material ensures good process compatibility between the components, while fully leveraging the advantages of lithium niobate, such as its wide transmittance, high nonlinear coefficient, and excellent electro-optic tuning characteristics.

[0092] Exemplarily, the fabrication of a mid-infrared light source involves the following steps: Periodic metal electrode patterns (i.e., the periodically polarized portions in the periodically polarized waveguide 2) are fabricated at designated locations on a cleaned and polished substrate 1 (i.e., a lithium niobate structure on an insulator) using techniques such as electron beam lithography (EBL), metal electrode deposition, and metal electrode lift-off. Subsequently, a series of short, strong high-voltage pulses are applied to the periodic electrodes to generate a sufficiently strong local electric field. This strong electric field drives the directional reversal of ferroelectric domains in the thin-film lithium niobate, thereby ultimately achieving the goal of periodic polarization. The metal electrodes are then removed. Next, photoresist is spin-coated onto the periodically polarized substrate 1, followed by exposure of a pre-designed pattern on the photoresist surface using EBL. The exposed substrate 1 is then developed in a developer to obtain a two-dimensional surface pattern of the pre-designed pattern. Further, inductively coupled plasma (ICP) etching is used to etch the developed substrate 1, resulting in a preliminary three-dimensional pre-designed structure. In addition, a certain thickness of silicon dioxide (SiO2) is deposited on the interface waveguide 7 to form the cladding 8.

[0093] Figure 7 This is a schematic diagram of a laser output light source 1001 provided in an embodiment of this application.

[0094] This application also provides a laser output light source 1001, see reference. Figure 7 This includes a laser 200 and a target band output structure 100. The output end of the laser 200 is coupled to the input end of the target band output structure 100. For details on the specific structure of the target band output structure 100, please refer to [reference needed]. Figure 1 and Figure 2 As shown.

[0095] For example, see Figure 1 and Figure 2 Laser 200 couples pump light into interface waveguide 7 and cladding 8 via docking. Interface waveguide 7 is connected to input B of second directional coupler 6, and pump light is coupled into second directional coupler 6 under adiabatic conditions. Next, pump light is transmitted to second Bragg grating 62, and phase matching is used to directionally couple pump light from second Bragg grating 62 into aperiodic polarized second sub-waveguide 22. Subsequently, pump light is transmitted to periodically polarized first sub-waveguide 21, where, under the action of nonlinear frequency conversion characteristics, it is converted into signal light (i.e., the first optical signal) and mid-infrared idler light (i.e., the second optical signal). The first optical signal oscillates back and forth between periodically polarized waveguides 2 coated with high-reflectivity film 3 without output. Phase matching is again used to directionally couple mid-infrared second optical signal into first Bragg grating 42, and output through output A of first directional coupler 4.

[0096] For example, the laser 200 can be used to output pump light. For instance, its wavelength can be in the near-infrared band (e.g., around 1 μm). After being coupled into the periodically polarized waveguide 2, the pump light can generate a second optical signal (i.e., idler light) with a wavelength in the mid-infrared band through a nonlinear frequency conversion process, thereby realizing wavelength conversion from near-infrared to mid-infrared.

[0097] For example, the laser 200 can serve as an external pump source, and optical coupling between it and the interface waveguide 7 and the cladding 8 can be achieved through docking coupling; alternatively, optical coupling can also be achieved using lenses, optical wire bonding, or other methods. For instance, a polymer waveguide can be 3D printed using photonic wire bonding (PWB) technology, with its two ends connected to the output end of the laser 200 and the input end of the interface waveguide 7, respectively, thereby enabling pump light to be efficiently coupled from the laser 200 into the interface waveguide 7.

[0098] For example, the laser output source 1001, based on a stable and tunable mid-infrared laser output from the target band output structure 100, can be widely used in the field of trace gas sensing. By adjusting the pump light wavelength of the laser 200 or the polarization period of the periodically polarized waveguide 2, the wavelength of the second optical signal can be precisely matched to the characteristic absorption peak of a specific gas (such as CH4, CO2, NO2, etc.).

[0099] It is understood that the characteristics and effects of each component in the target band output structure 100 can be referred to the description of each component and corresponding effects of the target band output structure 100 in any of the foregoing embodiments, and will not be repeated here.

[0100] Figure 8 This is a schematic diagram of a gas detection system 1000 provided in an embodiment of this application.

[0101] This application also provides a gas detection system 1000, see reference. Figure 8 It includes a detection chamber 1002 and a laser output source 1001. The detection chamber 1002 is used to introduce the gas to be detected, and the target band output structure of the laser output source 1001 is at least partially located within the detection chamber 1002.

[0102] For example, the target band output structure 100 included in the laser output light source 1001 can be placed inside the detection chamber 1002, or the first directional coupler 4 included in the target band output structure 100 can be placed inside the detection chamber 1002, so that the mid-infrared light source output by it can detect the detection gas located in the detection chamber 1002.

[0103] By placing at least a portion of the laser output light source 1001 within the detection chamber 1002, thus fully exposing it to the gas environment to be tested, the gas to be tested is introduced into or exists in the detection chamber 1002, thereby constructing a controllable gas detection environment. This enables highly sensitive and selective quantitative detection of multiple gas components, making it suitable for various application scenarios such as environmental monitoring, industrial process control, medical diagnosis, and safety early warning.

[0104] For example, the gas detection system 1000 operates based on optical absorption spectroscopy. When the laser output light source 1001 outputs light of a specific wavelength, it interacts with gas molecules in the detection chamber 1002. The gas molecules absorb the light energy of their characteristic wavelength, causing the intensity of the output light signal to attenuate. By detecting this attenuation, the gas concentration can be analyzed. Thus, the gas detection function of the gas detection system 1000 is realized.

[0105] For example, the internal space of the detection chamber 1002 must match the physical dimensions and shape of the laser output light source 1001 to ensure stable fixation. Furthermore, the detection chamber 1002 needs to be airtight, or at least have a controllable gas flow path, to prevent external ambient gases from interfering with the measurement results and to ensure uniform internal gas concentration. The connection between the detection chamber 1002 and the optical interface of the laser output light source 1001 needs to maintain a good seal, allowing the optical path to remain unobstructed while ensuring that gas does not leak from these interfaces, thereby maintaining the stability of the detection conditions and the accuracy of the measurement.

[0106] It is understood that the characteristics and effects of each component in the laser output light source 1001 can be referred to the description of each component and corresponding effects of the laser output light source 1001 in the foregoing embodiments, and will not be repeated here.

[0107] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions conceived by those skilled in the art within the scope of the technology disclosed herein should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A target band output structure, characterized in that, include: Substrate; A periodically polarized waveguide is disposed on the substrate; a first optical signal and a second optical signal are transmitted in the periodically polarized waveguide, the wavelengths of the first optical signal and the second optical signal being different; the periodically polarized waveguide extends along a first direction, the first direction being parallel to the substrate; A reflective film is disposed at both ends of the periodically polarized waveguide along the first direction, and the reflective film reflects the first optical signal; A first directional coupler is disposed on the substrate. The first directional coupler includes a first coupling waveguide and a first Bragg grating embedded in the first coupling waveguide. The first directional coupler is located on one side of the periodically polarized waveguide along a second direction and is coupled to the periodically polarized waveguide. The second direction is parallel to the substrate and perpendicular to the first direction. The second optical signal is coupled to the first directional coupler by the periodically polarized waveguide.

2. The target band output structure according to claim 1, characterized in that, The periodic polarized waveguide includes a first sub-waveguide and two second sub-waveguides located at both ends of the first sub-waveguide. The first sub-waveguide has a periodic polarization structure, and the second sub-waveguides are in an aperiodic polarization state. The reflective film is disposed on two mutually distant ends of the two second sub-waveguides; the first directional coupler is disposed on one side of one of the second sub-waveguides along the second direction.

3. The target band output structure according to claim 1, characterized in that, The first directional coupler has an output terminal, and the second optical signal is output from the output terminal of the first directional coupler; The target band output structure further includes: An antireflection membrane is disposed on the output end of the first directional coupler.

4. The target band output structure according to claim 1, characterized in that, The first coupling waveguide includes a first sub-section and two second sub-sections disposed at both ends of the first sub-section; the first Bragg grating is embedded in the first sub-section, and one of the two second sub-sections serves as the output end of the first directional coupler, while the other is bent.

5. The target band output structure according to claim 1, characterized in that, Also includes: A second directional coupler is disposed on the substrate. The second directional coupler includes a second coupling waveguide and a second Bragg grating embedded in the second coupling waveguide. The second directional coupler is located on one side of the periodic polarized waveguide along a second direction and is coupled to the periodic polarized waveguide. The first directional coupler and the second directional coupler are located at the two ends of the periodic polarized waveguide, respectively.

6. The target band output structure according to claim 5, characterized in that, The second directional coupler has an input terminal for receiving a light source input; The target band output structure further includes: An interface waveguide is disposed on the substrate and connected to the input terminal of the second directional coupler; the area of ​​the interface waveguide's cross-section perpendicular to the substrate is gradually varied. The cladding is arranged around the interface waveguide.

7. The target band output structure according to claim 1, characterized in that, Also includes: A thin-film resistor is disposed on one side of the periodically polarized waveguide along the second direction, and / or disposed on the side of the first Bragg grating away from the periodically polarized waveguide along the second direction.

8. The target band output structure according to claim 1, characterized in that, The wavelength of the light output by the first directional coupler is 2.5μm~25μm.

9. A laser output light source, characterized in that, include: Target band output structure as described in any one of claims 1 to 8; The laser is coupled to the input end of the target band output structure.

10. A gas detection system, characterized in that, include: The laser output light source as described in claim 9; A detection chamber for introducing the gas to be detected, wherein at least a portion of the laser output light source is located within the detection chamber.

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