A monolithic integrated gas detection device based on an anti-symmetric grating

Abstract

The present invention discloses a monolithic integrated gas detection device based on an anti-symmetric grating, which includes an active region, a passive region, and a detector integrally fabricated on an epitaxial wafer; the active region, the passive region, and the detector are sequentially butt-jointed and formed, and the passive region is a single-channel or double-channel structure. The number of active regions is 1 and it is butt-jointed with the passive region. The number of detectors is the same as the number of channels of the passive region and it is butt-jointed with the passive region; the energy band structures of the active region and the detector are consistent, and the band gap size of the energy band of the passive region is different from that of the active region. This device uses a monolithic integrated gas detection chip. Only a broadband light source is required for the light source. Accurate control of the wavelength is achieved through filtering by the passive region. The physical process of the passive region is relatively simple compared with that of the active region, and the wavelength is easier to control. Therefore, the present invention reduces the related costs of the manufacturing process and packaging process of the laser, thereby reducing the cost of the TDLAS method and expanding the application scope.

Description

Technical Field

[0001] The present invention relates to the field of optoelectronic technology, and more specifically to an optical integrated chip, which is mainly applied to the field of gas absorption spectrum detection and can realize a gas detection device with low cost, simple and compact structure. Background Art

[0002] In recent years, measurement technologies have been constantly updated, and among them, optical sensors have developed particularly rapidly. At the same time, the application scenarios of gas detection technologies are increasing, such as biomedical monitoring, industrial process monitoring, atmospheric environment monitoring, etc. People have put forward higher requirements for the sensitivity, responsiveness, and reliability of gas detection technologies. Currently, gas detection mainly includes semiconductor oxide gas sensors, thermal gas sensors, electrochemistry gas sensors, gas chromatographs, spectral absorption sensors, and so on. Among these detection technologies, non-optical methods have a short service life, are prone to poisoning and aging, and cannot be monitored online in many cases. In contrast, laser gas detection has the advantages of high sensitivity, high detection accuracy, good use stability, being less susceptible to external interference, and good environmental adaptability.

[0003] In the optical detection method, tunable diode laser absorption spectroscopy (TDLAS) is one of the mainstream technical solutions for gas detection currently. Its principle is relatively simple. Due to the rotation and vibration of gas molecules, absorption of light with a specific wavelength is formed. By scanning the wavelength with a tunable laser and analyzing the molecular absorption spectrum information, the type and concentration of gas molecules can be judged. Currently, this technology has relatively high requirements for the wavelength characteristics of the laser. At different ambient temperatures, the working wavelength of a semiconductor laser is extremely prone to drift, thus deviating from the gas absorption peak. This results in relatively high costs for TDLAS sensors on the market, so it is somewhat difficult to mass-produce them.

[0004] Therefore, how to provide a gas detection device that can reduce the relevant costs of the manufacturing process and packaging process of the laser, thereby reducing the cost of the TDLAS method and expanding the application range is an urgent problem that needs to be solved by those skilled in the art. Summary of the Invention

[0005] In view of this, the present invention provides a monolithic integrated gas detection device based on an anti-symmetric grating, aiming to solve the above technical problems.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A monolithic integrated gas detection device based on an anti-symmetric grating, comprising an active region, a passive region, and a detector integrally fabricated on an epitaxial wafer; the active region, the passive region, and the detector are sequentially butted and formed, and the passive region is a single-channel or dual-channel structure, the number of active regions is 1 and is butted with the passive region, the number of detectors is the same as the number of channels of the passive region and is butted with the passive region; the energy band structures of the active region and the detector are the same, and the bandgap size of the energy band of the passive region is different from that of the active region.

[0008] Through the above technical solution, this device uses a monolithic integrated gas detection chip. Only a broadband light source is required for the light source. The accurate control of the wavelength is achieved through the filtering of the passive region. The physical process of the passive region is relatively simple compared with that of the active region, and the wavelength is easier to control. Therefore, the present invention reduces the relevant costs of the manufacturing process and packaging process of the laser, thereby reducing the cost of the TDLAS method, expanding the application range, and having great application value in future smart cities, sensor networks, smart homes, etc.

[0009] The integration of the active region, the passive region, and the detector can be achieved through technologies such as butt-joint growth, selective area epitaxy, quantum well offset, and quantum well intermixing. Among them, the most suitable ones are butt-joint growth and quantum well intermixing methods. Butt-joint growth means selectively etching away the waveguide core layer and then regrowing the waveguide core layer with materials of other components. Quantum well intermixing means forming a large number of point defects on the surface layer of the quantum well material and promoting the movement of the point defects towards the quantum well through external excitation, thereby changing the material composition and energy band structure of the quantum well. The advantage of quantum well intermixing is that it can flexibly control the energy band width of the quantum well of the epitaxial wafer with little influence on the waveguide structure.

[0010] Preferably, in the above-mentioned monolithic integrated gas detection device based on an anti-symmetric grating, the waveguide width of the active region needs to be controlled within the range of 2 to 3 μm. The radiation waveguide width of the passive region is within 2 μm to achieve the radiation mode of light. The multimode waveguide width of the passive region is 4 μm to maintain the existence of the first-order mode, thereby achieving hybrid mode resonance.

[0011] Preferably, in the above-mentioned monolithic integrated gas detection device based on an anti-symmetric grating, the active region is a broadband light source near the infrared light wavelength.

[0012] Preferably, in the above-mentioned monolithic integrated gas detection device based on an anti-symmetric grating, the active region is a semiconductor optical amplifier (SOA). A reflective film is coated on the end face of the semiconductor optical amplifier far from the passive region, and the reflectivity is within the range of 95% to 99.99% to increase the output optical power of the SOA.

[0013] Preferably, in the above-mentioned monolithic integrated gas detection device based on an anti-symmetric grating, the passive region includes a radiation waveguide and a multimode waveguide; the multimode waveguide is docked with the detector, the width of the radiation waveguide is smaller than the widths of the active region, the multimode waveguide and the detector, and both ends of the radiation waveguide are transitionally docked between the multimode waveguide and the active region through tapered waveguides.

[0014] Preferably, in the above-mentioned monolithic integrated gas detection device based on an anti-symmetric grating, the multimode waveguide contains a π-phase shift anti-symmetric grating (π-ASBG). By utilizing the hybrid mode resonance of the π-phase shift anti-symmetric grating and the dissipation of the tapered waveguide, the passive region can achieve narrowband transmission of light waves without reflection.

[0015] Preferably, in the above-mentioned monolithic integrated gas detection device based on an anti-symmetric grating, the anti-symmetric grating is equivalently realized by using a sampled Bragg grating method, that is, there is a phase shift in the sampling structure of the grating structure, and the phase shift value is π. Thus, the Bragg wavelength of the grating can be precisely controlled, and low-cost preparation can be achieved.

[0016] Preferably, in the above-mentioned monolithic integrated gas detection device based on an anti-symmetric grating, electrodes are made on the anti-symmetric grating, and the effective refractive index of the passive region is adjusted by injecting current, thereby controlling the Bragg wavelength of the anti-symmetric grating and realizing the selection of the narrowband transmission wavelength of the grating.

[0017] The gas to be measured is introduced into the radiation waveguide of the passive region, and the gas to be measured interacts with the radiation light. An absorption spectrum of the gas to be measured within a certain spectral range can be obtained in front of the π-ASBG. Through the filtering of the π-ASBG, only a certain narrowband light can be transmitted and detected by the detector. By adjusting the current applied to the π-ASBG and changing its transmission wavelength, the formed absorption spectrum can be recorded, and then the gas information can be analyzed.

[0018] Preferably, in the above-mentioned monolithic integrated gas detection device based on an anti-symmetric grating, electrodes are added to both the active region and the passive region, and an electrical isolation region is added between the electrodes to control the injected current separately. The manufacturing method of the electrical isolation region is as follows: the ohmic contact layer InGaAsP and the ridge waveguide layer InP in the corresponding region of the laser are etched off by dry or wet methods, and then an insulating material SiO2 with a thickness in the range of 100 nm to 300 nm is covered, and the width of the isolation region is in the range of 5 μm to 80 μm.

[0019] Preferably, in the above-mentioned monolithic integrated gas detection device based on an anti-symmetric grating, when the passive region is single-channel, the gas to be detected is introduced into one side of the radiation waveguide and interacts with the radiation light of the radiation waveguide; when the passive region is dual-channel, the passive region has a Y-shaped structure, including two groups of the radiation waveguides and the multimode waveguide, and the gas to be detected is introduced between the two groups of the radiation waveguides and interacts with the radiation light of the radiation waveguide, thereby identifying two different components in the gas to be detected.

[0020] The parallel connection of two chips is realized through a Y-branch, so as to simultaneously identify two different components in the mixed gas. The light output from the SOA is divided into two beams by the Y-branch, and then passes through the passive region and the detector respectively, and the simultaneous detection of two different gas components can be realized. Since the design of the anti-symmetric phase-shifted grating and the radiation waveguide has no reflection effect, the two channels will not interfere with each other.

[0021] Preferably, in the above-mentioned monolithic integrated gas detection device based on an anti-symmetric grating, the gases detected by the detector include methane, oxygen, ammonia, hydrogen sulfide, carbon monoxide or carbon dioxide.

[0022] Preferably, in the above-mentioned monolithic integrated gas detection device based on an anti-symmetric grating, the monolithic integrated gas detection chip is used to realize near-infrared laser detection or mid-infrared laser detection.

[0023] As can be seen from the above technical solutions, compared with the prior art, the present invention discloses a monolithic integrated gas detection device based on an anti-symmetric grating, which has the following beneficial effects:

[0024] 1. The gas absorption spectrum can be obtained by this device without relying on an external spectrometer. After the effective refractive index of the anti-symmetric grating is changed by current injection into the passive region and specific wavelength filtering is performed, only a detector is integrated behind the grating to detect the intensity of a certain wavelength, and then the gas absorption spectrum can be obtained by current scanning.

[0025] 2. The narrowband transmission performance of the phase-shifted anti-symmetric grating is better, and the resolution is 0.1 nm, which has a higher resolution compared with other gas detectors.

[0026] 3. Compared with the TDLAS method, the active region of the present invention uses a broadband light source, and there is no need to control the wavelength of the DFB laser, and only the transmission wavelength of the passive region filter needs to be adjusted. The physical process of the passive region is relatively simple compared with the active region, and the wavelength is easier to control. Therefore, this solution reduces the related costs of the manufacturing process and packaging process of the active region. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the accompanying drawings required for the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can be obtained based on the provided drawings.

[0028] Figure 1 The accompanying drawing is a schematic structural diagram of the monolithic integrated gas detection device according to Embodiment 1 provided by the present invention;

[0029] Figure 2 The accompanying drawing is a schematic diagram of the guided mode provided by the present invention;

[0030] Figure 3 The accompanying drawing is a schematic diagram of the radiation mode provided by the present invention;

[0031] Figure 4 The accompanying drawing is a topographical schematic diagram of the anti-symmetric grating provided by the present invention;

[0032] Figure 5 The accompanying drawing is a schematic structural diagram of the monolithic integrated gas detection device according to Embodiment 2 provided by the present invention.

[0033] Wherein:

[0034] 1 - Active region;

[0035] 2 - Passive region;

[0036] 21 - Radiation waveguide; 22 - Multimode waveguide; 23 - Tapered waveguide;

[0037] 3 - Detector;

[0038] 4 - Reflective film;

[0039] 5 - Gas to be measured. Detailed implementation manners

[0040] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0041] See the attached Figure 1 、 45, embodiments of the present invention disclose a monolithic integrated gas detection device based on an anti-symmetric grating, including an active region 1, a passive region 2, and a detector 3 integrally fabricated on an epitaxial wafer; the active region 1, the passive region 2, and the detector 3 are sequentially butt-jointed and formed, and the passive region 2 is a single-path or double-path structure, the number of active regions 1 is 1 and is butt-jointed with the passive region 2, the number of detectors 3 is the same as the number of paths of the passive region 2 and is butt-jointed with the passive region 2; the energy band structures of the active region 1 and the detector 3 are the same, and the bandgap size of the energy band of the passive region 2 is different from that of the active region 1.

[0042] To further optimize the above technical solution, the active region 1 is a broadband light source near the infrared light wavelength.

[0043] To further optimize the above technical solution, the active region 1 is a semiconductor optical amplifier, and a reflective film 4 is coated on the end face of the semiconductor optical amplifier away from the passive region 2.

[0044] To further optimize the above technical solution, the passive region 2 includes a radiation waveguide 21 and a multimode waveguide 22; the multimode waveguide 22 is butt-jointed with the detector 3, the width of the radiation waveguide 21 is smaller than the widths of the active region 1, the multimode waveguide 22, and the detector 3, and both ends of the radiation waveguide 21 are transitionally butt-jointed between the multimode waveguide 22 and the active region 1 through tapered waveguides 23. As Figure 2 and Figure 3 shown, the smaller the waveguide width, the more intense the mode radiation.

[0045] To further optimize the above technical solution, the multimode waveguide 22 contains an anti-symmetric grating with a π phase shift.

[0046] To further optimize the above technical solution, the anti-symmetric grating is equivalently realized by sampling the Bragg grating method.

[0047] To further optimize the above technical solution, electrodes are fabricated on the anti-symmetric grating, and the effective refractive index of the passive region is adjusted by injecting current, thereby controlling the Bragg wavelength of the anti-symmetric grating.

[0048] To further optimize the above technical solution, the gases detected by the detector 3 include methane, oxygen, ammonia, hydrogen sulfide, carbon monoxide, or carbon dioxide.

[0049] To further optimize the above technical solution, the monolithic integrated gas detection chip is used to realize near-infrared laser detection or mid-infrared laser detection.

[0050] The present invention is generally applicable to III-V compound semiconductor materials (such as GaAlAs / GaAs, InGaAs / InGaP, GaAsP / InGaP, InGaAsP / InP, InGaAsP / GaAsP, AlGaInAs, etc.), and can also be applied to II-VI compound semiconductor materials, IV group semiconductor materials, and various ternary and quaternary compound semiconductor materials.

[0051] If the quantum well intermixing technology is used to fabricate the passive region, the specific manufacturing method of the present invention is as follows:

[0052] (a) Perform a first epitaxial growth on an InP substrate, mainly including the growth of the active region 1 and the grating layer;

[0053] (b) After the growth of the active region 1 is completed, perform quantum well intermixing treatment on the passive region 2 part to realize the passivation of this region;

[0054] (c) Fabricate the waveguide Bragg grating on the first epitaxial wafer based on the photolithography method of holographic exposure and contact exposure;

[0055] (d) Grow InP material again on the substrate with the fabricated grating, which is a transitional P-type doping, and fabricate a contact layer material for contacting with the metal and a transitional layer material for lattice matching transition between the InP material and the contact layer material on the surface;

[0056] (e) After the second epitaxial growth, fabricate a ridge waveguide pattern with a width of about 2 μm based on contact photolithography and perform etching to obtain a ridge waveguide structure;

[0057] (f) Perform photolithography on the fabricated ridge waveguide, fabricate an electrical isolation pattern and perform etching, and etch away the highly doped contact layer on the surface, generally etching to about half of the waveguide height;

[0058] (g) Grow an insulating layer material, generally silicon dioxide, on the surface of the ridge waveguide to isolate between the metal electrode and the device and protect other positions on the device surface from oxidation;

[0059] (h) Perform a window opening process based on contact photolithography and insulating layer etching to form electrical contact between the device in the specified area and the electrode;

[0060] (i) Based on contact photolithography and metal lift-off process, fabricate the front electrode pattern by metal sputtering deposition;

[0061] (j) Grind and thin the back of the sample and polish it, and then fabricate the back electrode by metal sputtering deposition.

[0062] The passive region 2 can also be realized by butt-joint growth technology, making the wavelength corresponding to the bandgap of the epitaxial material more than 100 nm shorter than that of the gain region. The epitaxy of the detector 3 can be the same as that of the laser epitaxial structure, or it can also be butt-joint grown and designed and fabricated separately. The epitaxial material structure is the same as that of the traditional gas-facing detector.

[0063] The SOA region in the chip of the present invention can be used for multiple bands, specifically such as the 1310 band, the 1550 band, and the 1650 band, which are specifically determined according to the absorption peak of the gas to be detected. The value of the grating period and the quantum well material in the gain region need to be designed according to the specific lasing wavelength required.

[0064] Grating Bragg wavelength:

[0065] The gain spectrum wavelength range of the SOA needs to be consistent with the absorption spectrum of the gas to be detected. The gain spectrum can be adjusted by quantum wells. If it is near-infrared, it is generally the result of multi-quantum well materials. If it is mid-infrared, it is generally a quantum cascade structure. The transmission wavelength of the anti-symmetric grating in the passive region is adjusted by the grating period, and its grating Bragg wavelength λ=(n eff0 +n eff1 )Λ. Where n eff0 is the effective refractive index of the waveguide fundamental mode, n eff1 is the effective refractive index of the waveguide first-order mode, and Λ is the grating period. Since the waveguide refractive index is related to the carrier concentration, the grating Bragg wavelength can be adjusted by applying an external current, thereby adjusting the wavelength of the transmitted light.

[0066] Grating narrowband transmission:

[0067] The narrowband transmission performance of the π-ASBG is guaranteed by the hybrid mode resonance in its grating. There is a mutual conversion between the fundamental transverse mode TE0 and the first-order transverse mode TE1 in the anti-symmetric grating, which is called hybrid mode resonance. Adding a phase shift in the anti-symmetric grating can achieve narrowband transmission. The stronger the hybrid mode resonance, the narrower its transmission bandwidth. And the resonance intensity is related to the coupling coefficient κ of the grating, and its empirical formula is κ = πΔn / λ, which is proportional to the refractive index difference between the convex and concave parts of the grating. Therefore, the greater the grating etching depth, the better the narrowband transmission performance. If the grating structure is equivalently realized by sampling, the +1st order of the grating is used, and its coupling coefficient is 1 / π of the 0th order grating, so the grating requires a greater etching depth.

[0068] Example 1:

[0069] See the appendix Figure 1 , in this embodiment, the passive region 2 is single-channel, and the gas 5 to be detected is introduced into one side of the radiation waveguide 21 and reacts with the radiation light of the radiation waveguide 21.

[0070] The gas to be measured 5 is introduced into the radiation waveguide 21 in the passive region 2, and the gas to be measured 5 is allowed to interact with the radiation light. An absorption spectrum of the gas to be measured 5 within a certain spectral range can be obtained in front of the π-ASBG. Through the filtering of the π-ASBG, only a narrowband light can be transmitted and detected by the detector 3. By adjusting the current applied to the π-ASBG and changing its transmission wavelength, the formed absorption spectrum can be recorded, and then the information of the gas can be analyzed.

[0071] Embodiment 2:

[0072] See the appendix Figure 5 In this embodiment, when the passive region 2 is a two-way structure, the passive region 2 has a Y-shaped structure, including two sets of radiation waveguides 21 and multimode waveguides 22. The gas to be measured 5 is introduced between the two sets of radiation waveguides 21 and interacts with the radiation light of the radiation waveguides 21, thereby identifying two different components in the gas to be measured 5.

[0073] The parallel connection of two chips is realized through the Y-branch, so as to simultaneously identify two different components in the mixed gas. The light output from the SOA is divided into two beams by the Y-branch, and then passes through the passive region 2 and the detector 3 respectively, so as to realize the simultaneous detection of two different gas components. Since the design of the anti-symmetric grating and the radiation waveguide 21 has no reflection effect, the two channels will not interfere with each other.

[0074] In this specification, the various embodiments are described in a progressive manner. The key point of each embodiment is to illustrate the differences from other embodiments. The same or similar parts among the various embodiments can be referred to each other. For the devices disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple, and the relevant parts can be referred to the description of the method part.

[0075] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but will be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A monolithic integrated gas detection device based on an anti-symmetric grating, characterized in that It includes an active region (1), a passive region (2), and a detector (3) integrally fabricated on an epitaxial wafer; the active region (1), the passive region (2), and the detector (3) are butt-jointed and formed in sequence, and the passive region (2) is of a single-channel or dual-channel structure. The number of the active regions (1) is 1, which is butt-jointed with the passive region (2). The number of the detectors (3) is the same as the number of channels of the passive region (2), and is butt-jointed with the passive region (2); the energy band structures of the active region (1) and the detector (3) are the same, and the bandgap size of the energy band of the passive region (2) is different from that of the active region (1). The passive region (2) includes a radiation waveguide (21) and a multimode waveguide (22); the multimode waveguide (22) is butt-jointed with the detector (3). The width of the radiation waveguide (21) is smaller than the widths of the active region (1), the multimode waveguide (22), and the detector (3). Both ends of the radiation waveguide (21) are transitionally butt-jointed between the multimode waveguide (22) and the active region (1) through tapered waveguides (23). The multimode waveguide (22) contains an antisymmetric grating with a π-phase shift.

2. The monolithic integrated gas detection device based on an anti-symmetric grating according to claim 1, characterized in that, The active region (1) is a broadband light source near the infrared light wavelength.

3. The monolithic integrated gas detection device based on an anti-symmetric grating according to claim 1, wherein The active region (1) is a semiconductor optical amplifier, and a reflective film (4) is coated on the end face of the semiconductor optical amplifier away from the passive region (2).

4. The monolithic integrated gas detection device based on an anti-symmetric grating according to claim 1, characterized in that, The antisymmetric grating is equivalently realized by means of a sampled Bragg grating.

5. The monolithic integrated gas detection device based on an anti-symmetric grating according to claim 4, characterized in that The antisymmetric grating is provided with electrodes, and the effective refractive index of the passive region is adjusted by injecting current, thereby controlling the Bragg wavelength of the antisymmetric grating.

6. The monolithic integrated gas detection device based on an anti-symmetric grating according to claim 1, wherein, When the passive region (2) is of a single channel, the gas to be measured (5) is introduced into one side of the radiation waveguide (21) and reacts with the radiation light of the radiation waveguide (21); when the passive region (2) is of a dual channel, the passive region (2) is of a Y-shaped structure, including two sets of the radiation waveguides (21) and the multimode waveguides (22). The gas to be measured (5) is introduced between the two sets of the radiation waveguides (21) and reacts with the radiation light of the radiation waveguide (21), thereby identifying two different components in the gas to be measured (5).

7. A monolithic integrated gas detection device based on an anti-symmetric grating according to any one of claims 1-6, characterized in that The monolithic integrated gas detection device is used to realize near-infrared laser detection or mid-infrared laser detection.

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