Infrared light source and gas detection device

Abstract

The invention discloses an infrared light source and a gas detection device, and belongs to the technical field of optoelectronic integration. The infrared light source comprises a laser emitter, wherein the output end of the laser emitter is used for outputting pump light; the input end of the nonlinear optical device is connected with the output end of the laser transmitter, and the nonlinear optical device is used for converting the pump light into signal light and idler frequency light with the first target wavelength; the Bragg grating comprises a first Bragg grating and a second Bragg grating, the first Bragg grating is arranged between the laser transmitter and the nonlinear optical device, the second Bragg grating is arranged at the output end of the nonlinear optical device, and the signal light is reflected between the first Bragg grating and the second Bragg grating; the idler frequency light is output through the second Bragg grating to form infrared light of a second target wavelength, and the second target wavelength ranges from 2.5 micrometers to 20 micrometers. The integration level of the infrared light source can be remarkably improved, and the overall stability of the infrared light source can be enhanced.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of optoelectronic integration, and particularly relates to an infrared light source and a gas detection device. BACKGROUND

[0002] The middle infrared light region contains the strongest absorption bands of many important gas molecules and functional groups, which is crucial for spectral sensing and environmental monitoring. A middle infrared light source is a necessary condition for realizing middle infrared sensing. At present, the mainstream method for preparing a middle infrared light source is a nonlinear frequency conversion technology. In the nonlinear frequency conversion technology, pump light is converted into signal light and idler light. For middle infrared wavelength conversion, low-frequency idler light is generally needed without signal light.

[0003] At present, a cavity mirror is usually formed by coating to confine the signal light. However, the coating process is difficult to be performed inside the device, which reduces the integration degree of the device. In addition, the coating process has poor film uniformity, which weakens the stability of the device. SUMMARY

[0004] The present application aims to at least solve one of the technical problems existing in the prior art. To this end, the present application provides an infrared light source and a gas detection device, which can significantly improve the integration degree of the infrared light source and enhance the overall stability of the infrared light source.

[0005] In a first aspect, the present application provides an infrared light source, comprising: a laser emitter, an output end of the laser emitter being configured to output pump light; a nonlinear optical device, an input end of the nonlinear optical device being connected with the output end of the laser emitter, the nonlinear optical device being configured to convert the pump light into signal light and idler light of a first target wavelength; a Bragg grating, comprising a first Bragg grating and a second Bragg grating, the first Bragg grating being arranged between the laser emitter and the nonlinear optical device, the second Bragg grating being arranged at an output end of the nonlinear optical device, the signal light being reflected between the first Bragg grating and the second Bragg grating, the idler light being output via the second Bragg grating to form infrared light of a second target wavelength, the second target wavelength being between 2.5 microns and 20 microns.

[0006] The infrared light source according to the present application converts the pump light into signal light and idler light through the nonlinear frequency conversion characteristics of the nonlinear optical device, the first Bragg grating and the second Bragg grating are arranged on the two sides of the nonlinear optical device respectively, the first Bragg grating and the second Bragg grating form a Bragg reflector, when the Bragg condition is met, the signal light reciprocally oscillates in the Bragg reflector, and the low-frequency idler light is transmitted out to form the mid-infrared light. The Bragg grating replaces the traditional reflector relying on external coating process, so that the infrared light source does not need to be coated inside, the Bragg grating can be micro-processed on the chip, which can significantly improve the integration, and the Bragg grating has excellent wavelength selectivity and process repeatability, good film uniformity and high thermal stability, thereby enhancing the overall stability of the infrared light source.

[0007] According to an embodiment of the present application, the infrared light source further comprises: a temperature adjusting assembly connected with the nonlinear optical device, the temperature adjusting assembly being used for adjusting the temperature of the nonlinear optical device to adjust the first target wavelength of the idler light, so as to adjust the second target wavelength of the infrared light.

[0008] According to an embodiment of the present application, the laser emitter, the first Bragg grating, the nonlinear optical device and the second Bragg grating form a first optical path structure, and the infrared light source further comprises an optical integration device, an input end of the optical integration device being connected with output ends of a plurality of the first optical path structures, so as to aggregate the infrared light output by each of the first optical path structures to form infrared light of a third target wavelength.

[0009] According to an embodiment of the present application, a heat insulation structure is arranged between each of the first optical path structures.

[0010] According to an embodiment of the present application, the wavelengths of the pump light output by the laser emitters in each of the first optical path structures are different.

[0011] According to an embodiment of the present application, the optical integration device comprises a Y-shaped waveguide.

[0012] According to an embodiment of the present application, the infrared light source further comprises: a tapered waveguide, an input end of the tapered waveguide being connected with an output end of the laser emitter, and an output end of the tapered waveguide being connected with an input end of the nonlinear optical device, the tapered waveguide being used for expanding the pump light output by the laser emitter.

[0013] According to an embodiment of the present application, the input end of the tapered waveguide is connected with the output end of the laser emitter through optical wire bonding.

[0014] According to one embodiment of the present application, the nonlinear optical device is made of a periodically poled lithium niobate material.

[0015] In a second aspect, the present application provides a gas detection device, comprising: The infrared light source according to the first aspect.

[0016] According to the gas detection device of the present application, the pump light is converted into signal light and idler light through the nonlinear frequency conversion characteristics of the nonlinear optical device, the first Bragg grating and the second Bragg grating are arranged on the two sides of the nonlinear optical device respectively, the first Bragg grating and the second Bragg grating form a Bragg reflector, when the Bragg condition is met, the signal light reciprocally oscillates in the Bragg reflector, and the low-frequency idler light is transmitted out to form a mid-infrared light. The Bragg grating replaces the traditional reflector relying on external coating process, so that the infrared light source does not need to be coated with complex film inside, the Bragg grating can be micro-processed on the chip, which can significantly improve the integration, at the same time, the Bragg grating has excellent wavelength selectivity and process repeatability, good film uniformity and high thermal stability, so as to enhance the overall stability of the infrared light source.

[0017] Additional aspects and advantages of the present application will be in part apparent and in part pointed out hereinafter. BRIEF DESCRIPTION OF DRAWINGS

[0018] The above and / or additional aspects and advantages of the present application will become apparent and be readily appreciated from the following description, including the appended drawings, wherein: Figure 1 is one of the structural schematic diagrams of the infrared light source provided by the embodiments of the present application; Figure 2 is the second structural schematic diagram of the infrared light source provided by the embodiments of the present application; Figure 3 is the third structural schematic diagram of the infrared light source provided by the embodiments of the present application; Figure 4 is the fourth structural schematic diagram of the infrared light source provided by the embodiments of the present application; Figure 5 is the fifth structural schematic diagram of the infrared light source provided by the embodiments of the present application; Figure 6 is the sixth structural schematic diagram of the infrared light source provided by the embodiments of the present application.

[0019] Reference signs: Infrared light source 100, laser emitter 1, temperature adjustment assembly 2, polymer waveguide 3, tapered waveguide 4, Bragg grating 5, first Bragg grating 51, second Bragg grating 52, nonlinear optical device 6. 7. Y-shaped waveguide; 8. Platform; 9. Thermal insulation structure; 10. Carrier. Detailed Implementation

[0020] The technical solutions of the embodiments of this application will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application are within the scope of protection of this application.

[0021] The terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and not to describe a specific order or sequence. It should be understood that such use of data can be interchanged where appropriate so that embodiments of this application can be implemented in orders other than those illustrated or described herein, and the objects distinguished by "first," "second," etc., are generally of the same class and the number of objects is not limited; for example, a first object can be one or more. Furthermore, in the specification and claims, "and / or" indicates at least one of the connected objects, and the character " / " generally indicates that the preceding and following objects are in an "or" relationship.

[0022] The infrared light source 100 and gas detection device provided in this application will be described in detail below with reference to the accompanying drawings, through specific embodiments and application scenarios.

[0023] like Figure 1 As shown, the infrared light source 100 provided in this embodiment includes a laser emitter 1, a nonlinear optical device 6, and a Bragg grating 5.

[0024] In this embodiment, the output of laser emitter 1 is used to output pump light.

[0025] Among them, laser emitter 1 is a device that generates and emits a laser beam, and pump light is a specific wavelength light used to excite particles in the laser medium to a high energy level in order to achieve population inversion.

[0026] The output of laser emitter 1 outputs pump light by controlling the drive current and selecting a specific wavelength.

[0027] In this embodiment, the input end of the nonlinear optical device 6 is connected to the output end of the laser emitter 1. The nonlinear optical device 6 is used to convert the pump light into signal light and idler light of the first target wavelength.

[0028] Among them, nonlinear optical device 6 is a device that can realize optical frequency conversion by utilizing the nonlinear optical effect of materials.

[0029] The signal light is a light wave that is amplified or generated in a nonlinear process, while the idler light is another wavelength light wave that is automatically generated under the conditions of energy conservation and phase matching. The wavelength of the idler light is determined by the wavelength difference between the pump light and the signal light.

[0030] The first target wavelength is the wavelength that the desired idler light will reach. The first target wavelength can be adjusted by adjusting the wavelength of the pump light or by adjusting the phase matching condition of the nonlinear optical device 6.

[0031] The nonlinear optical device 6 transfers the energy of the pump light to the signal light and idler light through the principles of phase matching and energy conservation, thereby amplifying the signal light and generating the idler light.

[0032] In this embodiment, the Bragg grating 5 includes a first Bragg grating 51 and a second Bragg grating 52. The first Bragg grating 51 is disposed between the laser emitter 1 and the nonlinear optical device 6, and the second Bragg grating 52 is disposed at the output end of the nonlinear optical device 6. The signal light is reflected between the first Bragg grating 51 and the second Bragg grating 52, and the idler light is output through the second Bragg grating 52 to form infrared light of the second target wavelength, which is between 2.5 micrometers and 20 micrometers.

[0033] Among them, the Bragg grating 5 is an optical element with a periodic refractive index variation structure etched in an optical material, which can selectively reflect light of a specific wavelength, that is, light that satisfies the Bragg condition is reflected while light of other wavelengths can be transmitted.

[0034] The first Bragg grating 51 and the second Bragg grating 52 together form a resonant cavity for the signal light, which confines the signal light within the resonant cavity and reflects it multiple times. The idler light can be transmitted through the second Bragg grating 52, thus separating the signal light and the idler light, and forming infrared light from the idler light.

[0035] The second target wavelength is between 2.5 micrometers and 20 micrometers, and the resulting infrared light is mid-infrared light. The specific data of the second target wavelength can be determined based on the wavelength of the idler light selected for transmission by the second Bragg grating 52.

[0036] In this embodiment, the output terminal of the laser emitter 1 outputs pump light to the nonlinear optical device 6. The nonlinear optical device 6 converts the pump light into signal light and idler light of the first target wavelength. The signal light reaches the second Bragg grating 52 and is reflected by the second Bragg grating 52 to the first Bragg grating 51. The first Bragg grating 51 also reflects the signal light. The signal light is reflected between the first Bragg grating 51 and the second Bragg grating 52. The idler light reaches the second Bragg grating 52 and is transmitted out from the second Bragg grating 52, outputting infrared light of the second target wavelength.

[0037] In related technologies, a coating is typically used to form a cavity mirror to confine the signal light. However, this coating process is difficult to perform inside the device, which reduces the device's integration level. In addition, the coating process has poor film uniformity, resulting in weak device stability.

[0038] According to the infrared light source 100 provided in the embodiments of this application, the pump light is converted into signal light and idler light through the nonlinear frequency conversion characteristics of the nonlinear optical device 6. A first Bragg grating 51 and a second Bragg grating 52 are respectively arranged on both sides of the nonlinear optical device 6. The first Bragg grating 51 and the second Bragg grating 52 form a Bragg reflector. When the Bragg condition is met, the signal light oscillates back and forth in the Bragg reflector, while the low-frequency idler light is transmitted out to form mid-infrared light. The Bragg grating 5 replaces the traditional reflector that relies on external coating process, so that the infrared light source 100 does not need to be coated internally. The Bragg grating 5 can be micro-fabricated on the chip, which can significantly improve the integration. At the same time, the Bragg grating 5 has excellent wavelength selectivity and process repeatability, good film uniformity and high thermal stability, thereby enhancing the overall stability of the infrared light source 100.

[0039] In some embodiments, the infrared light source 100 further includes a temperature regulation component 2.

[0040] Temperature adjustment component 2 is connected to nonlinear optical device 6. Temperature adjustment component 2 is used to adjust the temperature of nonlinear optical device 6 to adjust the first target wavelength of idler light, thereby adjusting the second target wavelength of infrared light.

[0041] Among them, the temperature regulation component 2 is a component that regulates the temperature of the nonlinear optical device 6 through active temperature control technologies such as heating and cooling.

[0042] In this embodiment, the temperature adjustment component 2 changes the refractive index of the nonlinear optical device 6 by adjusting the temperature of the nonlinear optical device 6, thereby changing the wavelength matching condition of the nonlinear effect of the nonlinear optical device 6. That is, after the refractive index of the nonlinear optical device 6 changes with the temperature, the original phase matching relationship of the pump light, signal light and idler light changes, the wavelength of the idler light is spontaneously adjusted, the first target wavelength of the idler light changes with the temperature, and thus indirectly changes the second target wavelength of the infrared light.

[0043] In this embodiment, by introducing the temperature regulation component 2, the temperature of the nonlinear optical device 6 can be precisely controlled. The refractive index of the nonlinear optical device 6 changes with temperature. Temperature regulation can directly affect the generation process of idler light, thereby changing the wavelength of the output infrared light. This makes the output wavelength of the infrared light source adjustable, which can adapt to different application requirements and improve the flexibility and applicability of the light source.

[0044] In some embodiments, the laser emitter 1, the first Bragg grating 51, the nonlinear optical device 6 and the second Bragg grating 52 form a first optical path structure, and the infrared light source 100 further comprises an optical integration device, an input end of the optical integration device is connected with output ends of a plurality of first optical path structures, so that infrared lights output by the first optical path structures are aggregated to form infrared light of a third target wavelength.

[0045] In some embodiments, the optical integration device is a device that aggregates infrared lights from different first optical path structures to form infrared light of a single third target wavelength.

[0046] In this embodiment, the infrared light source 100 comprises a plurality of first optical path structures, each first optical path structure comprises a laser emitter 1, a first Bragg grating 51, a nonlinear optical device 6 and a second Bragg grating 52 arranged in sequence, and an output end of each first optical path structure outputs infrared light, and the infrared light is input to the optical integration device for aggregation to form infrared light of a third target wavelength.

[0047] In this embodiment, by using a plurality of first optical path structures and using the optical integration device to aggregate the infrared light output by the optical path structures, the synthesis of multi-wavelength infrared light can be realized, the output power of the infrared light source can be increased, and a wider wavelength adjustment range can be provided.

[0048] In some embodiments, a heat insulation structure 9 is arranged between each first optical path structure.

[0049] In some embodiments, the heat insulation structure 9 is a structure that can isolate heat transfer, and can be a heat insulation groove.

[0050] In this embodiment, the heat insulation structure 9 is arranged between each first optical path structure, which can reduce the mutual influence of heat between each first optical path structure.

[0051] In some embodiments, the wavelengths of the pump light output by the laser emitters 1 in each first optical path structure are different.

[0052] In this embodiment, the wavelengths of the pump light output by the laser emitters 1 in each first optical path structure are different, and accordingly, each first optical path structure can output mid-infrared light of different wavelengths, and the optical integration device can aggregate the mid-infrared light of different wavelengths to flexibly tune the third target wavelength of the output mid-infrared light, thereby obtaining a broadband mid-infrared light source.

[0053] In some embodiments, the optical integration device comprises a Y-type waveguide 7.

[0054] In some embodiments, the Y-type waveguide 7 is an optical device that can combine two input light signals into a common output end.

[0055] In this embodiment, the number of Y-type waveguides 7 can be determined according to the number of first light path structures, for example, the infrared light source 100 includes four first light path structures, the output ends of the first light path structure a and the first light path structure b are respectively connected to the two input ends of the No. 1 Y-type waveguide 7, the output ends of the first light path structure c and the first light path structure d are respectively connected to the two input ends of the No. 2 Y-type waveguide 7, the output ends of the No. 1 Y-type waveguide 7 and the No. 2 Y-type waveguide 7 are respectively connected to the two input ends of the No. 3 Y-type waveguide 7, and the output end of the No. 3 Y-type waveguide 7 outputs the mid-infrared light of the third target wavelength.

[0056] In this embodiment, the Y-type waveguide 7 is used as an optical integrated device, which can effectively couple and transmit the infrared light output by the plurality of first light path structures. The Y-type waveguide 7 has the advantages of simple structure, low loss, easy manufacturing, etc., which can ensure the efficiency and stability of the infrared light in the transmission process and improve the overall performance of the light source.

[0057] In some embodiments, the infrared light source 100 further includes a tapered waveguide 4.

[0058] In this embodiment, the input end of the tapered waveguide 4 is connected to the output end of the laser emitter 1, and the output end of the tapered waveguide 4 is connected to the input end of the nonlinear optical device 6. The tapered waveguide 4 is used to expand the beam of the pump light output by the laser emitter 1.

[0059] The tapered waveguide 4 is a waveguide with a cross-sectional width that gradually changes along the propagation direction, which is used to achieve efficient matching, expansion or coupling of optical modes.

[0060] The tapered waveguide 4 performs mode matching and beam expansion on the pump light output by the laser emitter 1 through the gradually widening structure, reduces the optical power density, reduces the risk of nonlinear effects or damage, and improves the coupling efficiency of the pump light and the nonlinear optical device 6.

[0061] In some embodiments, the input end of the tapered waveguide 4 is connected to the output end of the laser emitter 1 through optical wire bonding.

[0062] The optical wire bonding is a micro-assembly technology that connects optical fibers or waveguides to the optical ports of optical devices such as lasers through precise alignment and fixation methods such as soldering or bonding, to achieve efficient and stable optical signal transmission.

[0063] In this embodiment, the input end of the tapered waveguide 4 is connected to the output end of the laser emitter 1 through optical wire bonding, which can achieve precise alignment and efficient optical coupling between the tapered waveguide 4 and the laser emitter 1, while ensuring thermal stability and mechanical reliability.

[0064] In some embodiments, the nonlinear optical device 6 is made of periodically poled lithium niobate material.

[0065] In the embodiment, the nonlinear optical device 6 made of lithium niobate material utilizes its excellent nonlinear optical coefficient and electro-optic characteristics to achieve quasi-phase matching through a periodic polarization structure, and efficiently converts pump light into idler light of a specific wavelength.

[0066] In the embodiment, the nonlinear optical device 6 made of lithium niobate material utilizes its excellent nonlinear optical coefficient and electro-optic characteristics to achieve quasi-phase matching through a periodic polarization structure, and efficiently converts pump light into idler light of a specific wavelength.

[0067] A specific embodiment of the infrared light source 100 is described below.

[0068] In the embodiment, the infrared light source 100 includes four first optical path structures, as shown in FIG. 1. Figure 2 FIG. 2 shows a three-dimensional structural schematic diagram of the infrared light source 100, as shown in FIG. 1. Figure 3 FIG. 3 shows a top view of the infrared light source 100, as shown in FIG. 1. Figure 4 FIG. 4 shows a front view of the infrared light source 100, as shown in FIG. 1. Figure 5 FIG. 5 shows a left view of the infrared light source 100, as shown in FIG. 1. Figure 6 FIG. 6 shows a right view of the infrared light source 100, as shown in FIG. 1.

[0069] The infrared light source 100 provided in the embodiment integrates the laser emitter 1, the tapered waveguide 4, the Bragg grating 5, the nonlinear optical device 6, and the Y-type waveguide 7. The nonlinear optical device 6 can be a periodically poled lithium niobate (PPLN).

[0070] First, the thin-film lithium niobate used to make the PPLN part is periodically poled. The tapered waveguide 4, the Bragg grating 5, and the Y-type waveguide 7 do not need to be periodically poled. Using mature photolithography and etching processes, photoresist is coated on a lithium niobate-on-insulator (LNOI) platform 8, and then exposure, development, etching, and photoresist removal are performed in sequence, thereby obtaining a structure in which the tapered waveguide 4, the Bragg grating 5, the PPLN, and the Y-type waveguide 7 are integrated together.

[0071] In the embodiment, four first optical path structures are integrated together to obtain greater mid-infrared bandwidth tuning, and the Y-type waveguide 7 is used for combining and outputting. To avoid mutual influence during temperature tuning, heat isolation is constructed again by etching in the middle of adjacent first optical path structures.

[0072] The output end of the laser emitter 1 is connected to the input end of the tapered waveguide 4 through photonic wire bonding (PWB) technology. The connection method is flexible, alignment-free, efficient, and low-loss, avoids the use of lenses, and can improve the integration of the device.

[0073] The taper waveguide 4 slowly expands the spot of the pump light output by the laser emitter 1 from the narrow waveguide to the wide waveguide, and keeps single mode all the time, which is beneficial to the subsequent nonlinear frequency conversion process.

[0074] The nonlinear frequency conversion characteristics of the PPLN are used to convert the pump light into signal light and idler light, and the Bragg grating 5 forms a Bragg reflector, which effectively confines the signal light and only allows the idler light to be output.

[0075] The infrared light source 100 provided by the embodiment of the present application can realize large bandwidth tuning, improve the integration of the device, and is suitable for mid-infrared gas sensing applications.

[0076] The principle of realizing the technical effect of the infrared light source 100 provided by the embodiment of the present application is introduced below.

[0077] Firstly, for nonlinear frequency conversion and large bandwidth tuning, the polarization process of the PPLN is realized by inducing ferroelectric domain reversal through an external electric field, and the core is to convert the original spontaneous polarization single domain structure in the lithium niobate crystal into a periodically alternating reverse domain structure. The periodically polarized PPLN satisfies the quasi-phase matching (QPM) condition, and the optical parametric oscillator (OPO) based on the PPLN satisfies the energy conservation

[0078] wherein is the frequency of the pump light, and are the frequency of the signal light and the frequency of the idler light after the nonlinear frequency conversion of the PPLN respectively, h is the Planck constant, and the above formula can also be changed to

[0079] wherein is the wavelength of the pump light, and are the wavelength of the signal light and the wavelength of the idler light after the nonlinear frequency conversion of the PPLN respectively.

[0080] The methane gas has a strong absorption peak at the mid-infrared wavelength of 4.6 µm, and when the pump wavelength is 1.31 µm, if the idler light of 4.6 µm is to be realized, then the signal light should be 1.83161 µm, and when designing the polarization period of lithium niobate, the polarization after the design can satisfy the nonlinear frequency conversion of the pump light of 1.31 µm into the signal light of 1.83161 µm and the idler light of 4.6 µm.

[0081] The OPO wavelength of the PPLN has a temperature sensitivity of about 1 nm / °C, so when the temperature changes by 50°C, the OPO wavelength can be tuned in a range of 50 nm. When the four laser emitters 1 work simultaneously, the OPO wavelength can be tuned in a large bandwidth of 200 nm by tuning the temperature by 50°C.

[0082] For the Bragg grating 5 resonator design, the Bragg grating 5 can produce strong selective reflection on the Bragg wavelength, while allowing other wavelengths of light to pass almost losslessly. The Bragg wavelength can be expressed as

[0083] wherein, is the effective refractive index of the Bragg grating 5, and Λ is the grating period. In addition, in order to realize large bandwidth tuning of the idler light while suppressing the output of the signal light, the reflection bandwidth of the Bragg grating 5 should also be large. The reflection bandwidth of the Bragg grating 5 can be expressed as

[0084] wherein, is the length of the Bragg grating 5, represents the coupling coefficient of the Bragg grating 5, which depends on the refractive index modulation and can be expressed by the following formula

[0085] wherein, is the overlap factor of the forward light field and the backward light field propagation mode with the grating, which generally takes a value between 0 and 1. For a uniform Bragg grating 5, can be taken as 1.

[0086] The reflectivity of the Bragg grating 5 can be expressed as

[0087] It can be seen that the reflectivity of the Bragg grating 5 is mainly affected by and Increasing and can improve the reflectivity, thereby enhancing the reflection of the Bragg grating 5.

[0088] When the laser emitter 1 works, the tuning range of the idler light is 50 nm, and the corresponding tuning range of the signal light is about 8 nm. For example, when the pump light emitted by the laser emitter 1 is 1.31 µm, the tuning range of the idler light is 4.55 µm-4.6 µm, and the tuning range of the signal light is 1.83966 µm-1.83161 µm, about 8 nm. In addition, the temperature sensitivity of the Thin-Film Lithium Niobate (TFLN) Bragg grating 5 is about 20 pm / ℃-30 pm / ℃, which is much smaller than the temperature sensitivity of the PPLN, 1 nm / ℃. When the temperature changes by 50℃, the drift of the Bragg wavelength is about 1 nm-1.5 nm. When the temperature changes by 50℃, in order to meet the continuous reflection of the signal light in the Bragg grating 5 resonant cavity without output, the reflection bandwidth of the Bragg grating 5 should be kept at more than 20 nm, and the length L and the coupling coefficient of the Bragg grating 5 are adjusted The Bragg reflection bandwidth can be effectively adjusted .

[0089] The manufacturing method of the infrared light source 100 provided in the embodiments of the present application is introduced below.

[0090] Step one, periodic polarization, a periodic metal electrode pattern is made on the surface of the LNOI platform 8 after cleaning and polishing by using the Electron Beam Lithography (EBL) technology at a specified position. Then, a series of short and strong high-voltage pulses are applied on the periodic electrode to generate a strong local electric field. The strong electric field drives the directional reversal of the ferroelectric domain in the TFLN, so as to finally achieve the goal of periodic polarization.

[0091] Step two, lithography, the LNOI after periodic polarization is spin-coated with photoresist, and then the EBL is used to expose the photoresist surface to a pre-designed pattern. The exposed LNOI is developed in a developing solution to obtain a two-dimensional surface pattern of the pre-designed pattern.

[0092] Step three, etching, the developed LNOI is etched by using the Inductively Coupled Plasma (ICP) technology, and the preliminary three-dimensional pre-designed structure is obtained after etching.

[0093] Step four, lithography and etching, after completing steps one to three, lithography and etching are needed again to obtain a thermal isolation groove between adjacent two structures of the same type, so as to play a heat insulation role.

[0094] Step five, the structure obtained after etching is integrated with the laser, PWB technology is used to connect the output end of the laser with the input end of the tapered waveguide 4 through the polymer waveguide 3, and this low-loss connection mode can ensure that the pump light is well coupled into the tapered waveguide 4.

[0095] In this embodiment, the materials of the tapered waveguide 4, the Bragg grating 5, the PPLN and the Y-type waveguide 7 are all lithium niobate, the first optical path structure formed by the laser emitter 1, the tapered waveguide 4, the Bragg grating 5 and the PPLN can have four groups, and the adjacent first optical path structures are separated by the heat insulation structure 9 to avoid mutual influence when the temperature adjusting assembly 2 is temperature-controlled, and the temperature adjusting assembly 2 can be a thermoelectric cooler (TEC).

[0096] The polymer waveguide 3 is manufactured by PWB technology, and the purpose is to integrate the laser emitter 1 with the tapered waveguide 4 and ensure that the pump light is coupled into the tapered waveguide 4 in the form of low-loss single mode.

[0097] The tapered waveguide 4 can gradually expand the narrow light spot of the laser emitter 1 to a wide light spot for the nonlinear frequency conversion process at the wide waveguide.

[0098] The Bragg grating 5 is used for enhanced reflection and bound signal light, and the parameters such as etching depth, period and length of the Bragg grating 5 are designed to ensure that the Bragg wavelength is the signal light wavelength required by the design scheme and the reflection bandwidth is greater than 20 nm.

[0099] The PPLN converts the pump light into signal light and idler light that can be used for mid-infrared gas sensing through nonlinear frequency conversion, and the polarization period of the PPLN is designed to meet the requirements of the design scheme.

[0100] One Y-type waveguide 7 can combine two groups of output light, and three Y-type waveguides 7 can realize the combination of four groups of output light.

[0101] The TEC is the temperature adjusting assembly 2, which is used for individual temperature control of the laser emitter 1 and the PPLN, and there is a TEC below each laser and PPLN, and the design of the heat insulation groove can avoid the mutual influence of the TEC when controlling the temperature of the PPLN.

[0102] The carrier 10 is used to provide a carrier for the infrared light source 100.

[0103] The working process of the infrared light source 100 provided in the embodiments of the present application is described below.

[0104] First, the TEC controls the temperature of the laser emitter 1 and the PPLN separately, so that they are maintained at a constant temperature. Then, the pump light of the laser emitter 1 is coupled into the tapered waveguide 4 in the form of low loss through the polymer waveguide. The pump light is gradually expanded into the wide TFLN waveguide in the form of single mode. Subsequently, through the nonlinear frequency conversion characteristics of the PPLN, the pump light is converted into signal light and idler light. The signal light is reflected in the resonant cavity of the Bragg grating 5 and is not output, and only the idler light is output. The output idler light is output through the Y-shaped waveguide 7.

[0105] When the TEC temperature of the PPLN changes, the wavelength of the idler light also changes, realizing the function of mid-infrared wavelength tuning. If the TEC temperature of the PPLN changes by 50 ℃, the wavelength of the idler light will change by about 50 nm. When the pump wavelengths of the four groups of laser emitters 1 are different, the TEC of the four groups of PPLN is changed by 50 ℃ separately. Then, the final mid-infrared wavelength after the combination of the Y-shaped waveguide 7 realizes a large bandwidth tuning of 200 nm.

[0106] The infrared light source 100 provided in the embodiment of the present application highly integrates the laser emitter 1, the tapered waveguide 4, the Bragg grating 5, the PPLN and the Y-shaped waveguide 7, and can improve the tuning bandwidth and performance of the mid-infrared light source.

[0107] The infrared light source 100 provided in the embodiment of the present application is manufactured by using the periodic polarization, photolithography, etching and PWB process to integrate the laser emitter 1, the polymer waveguide 3, the tapered waveguide 4, the Bragg grating 5, the PPLN and the Y-shaped waveguide 7, thereby improving the bandwidth of the mid-infrared light source, avoiding the complex process flow of coating, and reducing the manufacturing cost.

[0108] Compared with the PPLN mid-infrared light source design scheme based on an optical parametric oscillator (OPO) in the related art, the infrared light source 100 provided in the embodiment of the present application connects the output end of the laser emitter 1 and the input end of the tapered waveguide 4 through the PWB technology. This design method is flexible, alignment-free, efficient and low-loss, avoids the use of lenses, and improves the integration of the device. The design of the tapered waveguide 4 gradually expands the spot of the pump light of the laser emitter 1 from the narrow waveguide to the wide waveguide, and always maintains single mode, which is beneficial to the subsequent nonlinear frequency conversion process. The Bragg grating 5 constitutes a Bragg reflector, effectively confines the signal light, and finally only the idler light is output, thereby avoiding the process flow of coating and reducing the manufacturing cost. The embodiment can realize a large-bandwidth tunable mid-infrared light source, improve the integration of the device, and is suitable for mid-infrared gas sensing applications.

[0109] Photonics integration technology is a technology for integrating multiple optical elements, such as laser emitters 1, modulators, waveguides, filters, etc., onto a single chip. The miniaturization and integration characteristics of photonics integration technology greatly improve the performance and reliability of optical systems. Currently, platforms supporting photonics integration technology include indium phosphide (InP), silicon photonics (SiPh), silicon nitride (SiN), lithium niobate (LiNbO3), etc. The InP platform has the advantage of supporting active devices such as lasers, detectors, etc., and has good applications in high-speed optical communication, coherent transceiver, etc. The SiPh platform has the advantages of high CMOS process compatibility, high integration, and low cost, and has typical applications in data center interconnection. The SiN platform can achieve ultra-low loss of 0.1 dB / cm and has great potential in quantum optics and high-precision sensing. The LiNbO3 platform can achieve high-speed electro-optic modulation (>100 GHz) and has broad application prospects in microwave photonics and quantum communication.

[0110] A Bragg grating is a special grating structure whose core principle is mode coupling and Bragg reflection condition (phase matching condition). A Bragg grating uses periodic modulation of refractive index to achieve strong selective reflection of specific wavelengths. When the phase difference between the forward wave and the reflected wave in the grating region is an integer multiple of the grating period, i.e., it satisfies the phase matching condition (Bragg condition). The wavelength that satisfies the Bragg condition and has the strongest reflection is called the Bragg wavelength. A Bragg grating is like a wavelength-selective mirror, only light with a wavelength very close to the Bragg wavelength will be reflected, while light with a wavelength deviating from the Bragg wavelength will be transmitted and almost not reflected.

[0111] Lithium niobate is an irreplaceable material in the field of optoelectronics. However, traditional lithium niobate has large volume and low integration, which seriously limits its development in the field of photonics integration. In recent years, with the rapid development of micro-nano manufacturing technology, thin-film lithium niobate (TFLN) has been successfully manufactured. TFLN is expected to become a core material platform in the fields of high-speed optical communication, quantum computing, laser radar, optical sensing, etc. due to its small volume and high integration.

[0112] Mid-infrared light sources occupy an irreplaceable position in modern science and technology. Because the two key atmospheric transmission windows (3-5 µm and 8-12 µm) cover the absorption bands of most important gas molecules, and in this mid-infrared waveband, mid-infrared light can propagate with lower loss. Therefore, mid-infrared light sources have become the ideal choice for trace gas detection and are the core technology of high-precision gas sensing. However, the current mid-infrared laser sources such as quantum cascade lasers and interband cascade lasers face the challenges of large size and high cost, which limit their development in the future of small photonic integrated sensing.

[0113] The infrared light source 100 provided by the embodiment of the present application is based on a periodically poled lithium niobate (PPLN) platform 8, which utilizes the nonlinear frequency conversion characteristics of PPLN and combines the strong reflection characteristics of the Bragg grating 5, and can effectively realize the large-bandwidth conversion of near-infrared light to mid-infrared light. When multiple laser emitters 1 are used as pump light sources, the large-bandwidth tuning of the output mid-infrared light can be realized, which improves the integration and performance of the infrared light source 100 and reduces the manufacturing cost of the infrared light source 100.

[0114] The mid-infrared region of 3 µm-5 µm contains the strongest absorption bands of many important gas molecules and functional groups, which is crucial for spectral sensing and environmental monitoring. Mid-infrared light sources are necessary for mid-infrared sensing. Currently, the mainstream methods for preparing mid-infrared light sources include nonlinear frequency conversion, quantum cascade lasers, doped gain medium lasers, and on-chip integration technology. Among them, the nonlinear frequency conversion technology can provide a wider spectral coverage, a wider tuning range, and lower frequency noise.

[0115] The strong electro-optic effect and nonlinear effect of TFLN make it one of the preferred platforms for nonlinear frequency conversion. TFLN frequency conversion can be divided into two categories according to its phase matching method: PPLN devices based on quasi-phase matching (QPM) and TFLN waveguide devices based on mode phase matching. The former can easily complete the phase matching process by adjusting the polarization period and can obtain higher nonlinear conversion efficiency, so it is the most commonly used frequency conversion method. QPM nonlinear devices can be extended to the mid-infrared region, and the wide transparent wavelength range of lithium niobate can completely cover the above-mentioned mid-infrared waveband.

[0116] At present, PPLN generally needs to use optical parametric oscillation (OPO) technology to improve the conversion efficiency. The pump light can be converted into signal light and idler light through OPO. For mid-infrared wavelength conversion, low-frequency idler light is generally needed without signal light. Therefore, a coating is used to form a cavity mirror to confine the signal light, but such a coating process is difficult to perform inside the device, reducing the degree of integration. In addition, the coating process has poor film uniformity and weak stability. Therefore, using the coating process to build a resonant cavity still faces many challenges.

[0117] The infrared light source 100 provided by the embodiment of the present application uses a Bragg grating 5 structure to replace the coating to form a resonant cavity. When the Bragg condition is met, the signal light will oscillate back and forth in the Bragg grating 5 mirror, and the low-frequency idler light will be transmitted out. This improves the nonlinear conversion efficiency and improves the device performance.

[0118] For large bandwidth tunable problems, in the related art, due to the strong nonlinear frequency conversion capability of PPLN, the optical parametric oscillator based on TFLN has been widely studied. The traditional tuning method is to tune the OPO wavelength (including signal light and idler light) by tuning the pump wavelength and temperature, that is, the temperature of the pump laser is changed by using a temperature control device, so that the pump wavelength changes, thereby changing the OPO wavelength. However, the tuning bandwidth range realized by this tuning method is relatively narrow, and it is generally tuned in the visible light and near-infrared light wavelength band range. A typical wavelength conversion is that the pump wavelength is 775 nm, and the OPO wavelength after conversion by PPLN is 1550 nm. By tuning the pump wavelength of the laser through temperature, the change range of the pump wavelength in this tuning method is small, and therefore, the tuning range of the OPO wavelength is also relatively small. In addition, this tuning method is more inclined to near-infrared band tuning, and there are few reports on mid-infrared band tuning in the range of 3µm-5µm.

[0119] In the embodiment of the present application, starting from the PPLN, the PPLN is temperature-controlled by using the advantage that the PPLN is more affected by temperature than the laser emitter 1, so as to realize greater idler light bandwidth tuning. Through reasonable structural design, the design scheme can realize large bandwidth mid-infrared wavelength tuning, and has excellent application prospect in the field of gas sensing.

[0120] For the resonant cavity design problem, in the related art, the OPO does not perform the resonant cavity design, so the signal light and the idler light can be simultaneously detected at the output end, but the power is weak, the wavelength of the signal light is less than that of the idler light, so it is easier to convert the idler light to the mid-infrared waveband through the PPLN. In gas sensing, in order to improve the output light power and avoid the influence of other wavelengths, the output of the signal light needs to be suppressed, and only the idler light is allowed to output. In order to achieve the above goal, in the related art, film coating is performed on both ends of the PPLN. The purpose of film coating is to confine the signal light in the cavity, so that it oscillates back and forth without output, and only the pump light input and the idler light output are allowed. First, the PPLN is cleaved, and then film coating is performed on both ends of the PPLN. This is a simple process of film coating. The laser needs to use a lens to couple the pump light into the PPLN waveguide. The output idler light also needs to be collected through a lens. Although film coating can achieve the above goal, this way reduces the integration of the device, and the uniformity and stability of the end face film coating are uncertain and have errors, which may affect the performance of the device, and the price is expensive.

[0121] In the embodiments of the present application, the Bragg grating 5 is used instead of film coating, and the Bragg condition (phase matching condition) is used to achieve the purpose of confining the signal light, improve the integration of the device, and reduce the size of the device, and the manufacturing cost is low.

[0122] The infrared light source 100 provided by the embodiments of the present application improves the bandwidth of the mid-infrared light source. When four laser emitters 1 work simultaneously, the temperature of the four PPLNs is tuned by 50℃ respectively, the output idler light can achieve a large bandwidth tuning of 200nm, if more groups of laser emitters 1 and PPLNs are integrated, a larger bandwidth of the mid-infrared light source is expected to be obtained; the integration is improved, the PWB technology and the Y-shaped waveguide 7 are used instead of the lens coupling, the integration of the whole device is improved, and the size of the device is also reduced; the precision is improved and the cost is reduced, the Bragg grating 5 is used instead of the film coating to form the resonant cavity, the error caused by the non-uniformity of the film coating is avoided, and the high cost caused by the film coating process is also avoided.

[0123] The embodiments of the present application also provide a gas detection device.

[0124] The gas detection device includes the above-mentioned infrared light source 100.

[0125] According to the gas detection device provided by the embodiment of the present application, the nonlinear frequency conversion characteristics of the nonlinear optical device 6 are used to convert the pump light into signal light and idler light, the first Bragg grating 51 and the second Bragg grating 52 are arranged on the two sides of the nonlinear optical device 6 respectively, the first Bragg grating 51 and the second Bragg grating 52 form a Bragg reflector, when the Bragg condition is met, the signal light reciprocally oscillates in the Bragg reflector, and the low-frequency idler light is transmitted out to form the mid-infrared light, the Bragg grating 5 replaces the traditional reflector relying on an external coating process, so that the infrared light source 100 does not need to be coated in the internal part, the Bragg grating 5 can be micro-processed on the chip, the integration level can be significantly improved, meanwhile, the Bragg grating 5 has excellent wavelength selectivity and process repeatability, good film uniformity and high thermal stability, so that the overall stability of the infrared light source 100 can be enhanced.

[0126] In the description of the present application, it should be understood that the orientations or positional relationships indicated by the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like are based on the orientations or positional relationships shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation of the present application.

[0127] In the description of the present application, "the first feature" and "the second feature" can include one or more features.

[0128] In the description of the present application, "a plurality of" means two or more.

[0129] In the description of the present application, "above", "over" and "on" of the first feature to the second feature can include that the first and second features are in direct contact, or that the first and second features are not in direct contact but are in contact through another feature between them.

[0130] In the description of the present application, "above", "over" and "on" of the first feature to the second feature include that the first feature is directly above and obliquely above the second feature, or only means that the first feature is higher than the second feature in horizontal height.

[0131] Other configurations of … according to the embodiments of the present application are known to those skilled in the art without departing from the spirit of the present application, and thus will not be described here in detail. It is to be noted that the terms "comprising", "including", or any other variants are intended to cover non-exclusive inclusion, so that processes, methods, articles, or apparatuses including a series of elements include not only those elements but also other elements not explicitly listed, or other elements inherent to such processes, methods, articles, or apparatuses. Without more limitations, an element defined by the statement "including a …" does not exclude the presence of additional identical elements in the process, method, article, or apparatus including the element. In addition, it is to be noted that the scope of the methods and apparatuses in the embodiments of the present application is not limited to performing functions in the order shown or discussed, but can also include performing functions in a substantially simultaneous manner or in reverse order, for example, the described methods can be performed in an order different from that described, and various steps can be added, omitted, or combined. In addition, features described with reference to certain examples can be combined in other examples.

[0132] The embodiments of the present application are described above with reference to the accompanying drawings, but the present application is not limited to the above-described specific embodiments, which are merely illustrative rather than restrictive, and a person of ordinary skill in the art can make many forms under the inspiration of the present application without departing from the purpose of the present application and the scope protected by the claims.

[0133] In the description of the present specification, the description of the terms "one embodiment", "some embodiments", "exemplary embodiment", "example", "specific example", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the exemplary description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0134] Although the embodiments of the present application have been shown and described, those skilled in the art can understand that various changes, modifications, replacements, and variations can be made to the embodiments without departing from the principles and purposes of the present application, and the scope of the present application is defined by the claims and their equivalents.

Claims

1. An infrared light source, characterized by The infrared light source comprises: a laser emitter, an output end of the laser emitter being configured to output pump light; a nonlinear optical device, an input end of the nonlinear optical device being connected with the output end of the laser emitter, the nonlinear optical device being configured to convert the pump light into signal light and idler light of a first target wavelength; a Bragg grating, the Bragg grating comprising a first Bragg grating and a second Bragg grating, the first Bragg grating being arranged between the laser emitter and the nonlinear optical device, the second Bragg grating being arranged at an output end of the nonlinear optical device, the signal light being reflected between the first Bragg grating and the second Bragg grating, the idler light being output via the second Bragg grating to form infrared light of a second target wavelength, the second target wavelength being between 2.5 microns and 20 microns.

2. The infrared light source of claim 1, wherein, Further comprising: a temperature adjusting assembly, the temperature adjusting assembly being connected with the nonlinear optical device, the temperature adjusting assembly being configured to adjust a temperature of the nonlinear optical device to adjust the first target wavelength of the idler light, so as to adjust the second target wavelength of the infrared light.

3. The infrared light source of claim 1, wherein, The laser emitter, the first Bragg grating, the nonlinear optical device and the second Bragg grating form a first optical path structure, and the infrared light source further comprises an optical integration device, an input end of the optical integration device being connected with output ends of a plurality of the first optical path structures, so as to aggregate the infrared light output by each of the first optical path structures to form infrared light of a third target wavelength.

4. The infrared light source of claim 3, wherein, A heat insulation structure is arranged between each of the first optical path structures.

5. The infrared light source of claim 3, wherein, The laser emitter outputs pump light of different wavelengths in each of the first optical path structures.

6. The infrared light source of claim 3, wherein, The optical integration device comprises a Y-shaped waveguide.

7. The infrared light source according to any one of claims 1 to 6, characterized in that Further comprising: a tapered waveguide, an input end of the tapered waveguide being connected with an output end of the laser emitter, an output end of the tapered waveguide being connected with an input end of the nonlinear optical device, the tapered waveguide being configured to expand the pump light output by the laser emitter.

8. The infrared light source of claim 7, wherein, The input end of the tapered waveguide is connected with the output end of the laser emitter through optical wire bonding.

9. The infrared light source according to any one of claims 1-6, characterized in that, The nonlinear optical device is made of periodically poled lithium niobate material.

10. A gas detection device, characterized by The infrared light source according to any one of claims 1-9. The infrared light source according to any one of claims 1-9.

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