Wide-temperature-range laser methane detection device and method based on DBR laser

Abstract

The invention relates to the technical field of laser methane gas detection, and discloses a wide-temperature-range laser methane detection device and method based on a DBR laser. According to the device, a DBR laser with a wide wavelength tuning range is adopted, and central wavelength drift caused by laser wavelength compensation environment temperature is adjusted by controlling current injected into a Bragg reflection region. The methane gas is accurately detected by combining a reference gas chamber, a methane gas chamber to be detected and a light detector assembly. The wavelength drift is compensated by dynamically adjusting the current injected into the Bragg reflection region to ensure that the laser center wavelength is always aligned with the methane absorption peak, so that the methane concentration is calculated. The device omits traditional temperature control devices such as a TEC and a thermistor, and is wide in adaptive temperature range, high in response speed and low in cost.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of laser methane gas detection, and discloses a wide-temperature-range laser methane detection device and method based on a DBR laser. BACKGROUND

[0002] Tunable diode laser absorption spectroscopy (TDLAS) technology is a very common and effective gas analysis technology, and is very suitable for methane concentration detection. The technology is to use a single-mode laser emitted by a semiconductor laser chip to scan a specific spectral line of a measured gas, and the concentration and other characteristics of the measured gas are accurately obtained by measuring the change in laser intensity caused by the characteristic absorption of the incident light after the laser passes through the measured gas. However, a key to realizing TDLAS measurement is to lock the center wavelength of the semiconductor laser chip at the wavelength of the specific absorption spectral line of the methane gas. The wavelength of the semiconductor laser chip is very sensitive to temperature. Generally, when the working temperature of the laser chip increases by 1 DEG C, the center wavelength of the semiconductor laser chip will drift by about 0.1 nm towards the long wavelength direction, and vice versa. In the prior art, in order to keep the center wavelength of the semiconductor laser chip unchanged when the ambient temperature changes, a combination of a semiconductor cooler (TEC, Thermal Electric Cooler) and a thermistor is specially introduced to control the working temperature of the laser chip, so that the working temperature of the laser chip is always maintained at a specific temperature, thereby preventing the center wavelength from drifting due to changes in the ambient temperature. However, the introduction of TEC and thermistor not only increases the cost but also complicates the packaging process of the semiconductor laser. In addition, when the ambient temperature deviates from the set temperature by a large margin, the current and voltage of the TEC will become very large, and even the power supply will be unable to withstand the excessive load, causing the TEC to lose control and the wavelength control to lose control. There is also a tracking error problem in controlling the center wavelength by using the TEC to control the temperature, which will also cause errors in the control of the center wavelength.

[0003] In order to reduce the cost, a method of using a heating resistor to replace the TEC is presented. The method uses a combination of a thin film resistor and a thermistor integrated on the heat sink of the laser chip to control the operating temperature of the laser chip, so that the operating temperature of the laser chip is always maintained at a certain temperature, and the central wavelength of the laser chip is not shifted. However, since the resistor can only heat and has no pumping heat function, the set point of the operating temperature of the laser chip must be set at a temperature point much higher than room temperature, and the laser can only work in an environment lower than this temperature point. Since the laser always works at a temperature much higher than room temperature, it is very harmful to the service life of the laser. Moreover, since the resistor only has the function of heating, when the ambient temperature rises, the operating temperature of the laser chip can only be adjusted to the set temperature point by cutting off the current of the heating resistor and natural heat dissipation, but this process takes a long time and it is difficult to stably control the laser chip at the set temperature point, thereby causing the instability of the central wavelength of the laser. In addition, the method of using a combination of a heating resistor and a thermistor to control the operating temperature of the laser chip can only adapt to a very limited range of ambient temperature. SUMMARY

[0004] In view of the above technical problems, the present application provides a DBR laser-based wide-temperature-range laser methane detection device and method, which solves the problems of high cost, slow response, temperature control error, unstable temperature control and small temperature adaptation range caused by the method of using TEC or heating resistor to control the temperature of the laser chip to stabilize the central wavelength of the laser chip.

[0005] To solve the above technical problems, the present application adopts the following technical solutions: In a first aspect, a DBR laser-based wide-temperature-range laser methane detection device comprises: a DBR laser for emitting laser and adjusting the laser wavelength by controlling the current injected into the Bragg reflection region of the DBR laser; a beam splitter for splitting the laser output by the DBR laser into two paths; a reference gas chamber for storing methane gas of a predetermined concentration and being arranged in one of the laser beam splitting paths; a methane gas chamber for introducing the methane gas to be measured and being arranged in the other of the laser beam splitting paths; a first photodetector for receiving the laser transmitted through the reference gas chamber; a second photodetector for receiving the laser transmitted through the methane gas chamber; The control unit receives the detection signals output by the first light detector and the second light detector, calculates the shift of the laser center wavelength caused by the change of the ambient temperature through the detection signal output by the first light detector, compensates the shift of the laser center wavelength, and calculates the concentration of the methane gas to be measured through the detection signal output by the second light detector.

[0006] The DBR laser can have the simplest structure of three sections, including an active region, a phase control region and a Bragg reflection region.

[0007] The active region, as the core of light generation, emits laser by injecting current through the positive electrode and the negative electrode, and the main component of the active region is a multi-quantum well layer sandwiched between an upper separate confinement layer and a lower separate confinement layer. The upper separate confinement layer and the lower separate confinement layer are separated from the p-contact layer and the n-InP substrate by the cladding layer.

[0008] The phase control region and the Bragg reflection region adjust the laser wavelength by current injection. In the Bragg reflection region, there is a grating with a periodically varying refractive index inside, which reflects a specific Bragg wavelength to control the lasing wavelength. The grating is etched on the main core layer, and the main core layer is sandwiched between the upper and lower cladding layers. The DBR laser chip has a reflective film and an anti-reflection film on the two end faces respectively.

[0009] The present application improves the design of the above-mentioned DBR laser chip to increase its wavelength tuning range by the following measures.

[0010] The wavelength formula of the DBR laser chip emitting laser is:

[0011] In formula (1) is the grating period, is the effective refractive index of the Bragg reflection region.

[0012] The wavelength of the DBR laser chip emitting laser can be changed by changing the effective refractive index When the current injected into the Bragg reflection region increases, the refractive index of the Bragg reflection region will decrease due to the plasma effect of the carriers, thereby causing the effective refractive index of the Bragg reflection region to decrease, and the DBR laser wavelength shifts to the short wavelength direction. Conversely, when the current injected into the Bragg reflection region decreases, it will cause the DBR laser wavelength to shift to the long wavelength direction.

[0013] The change of the refractive index of the Bragg reflection region main core layer based on the plasma effect of the carriers can be expressed as:

[0014] In formula (2) is the electronic charge, λ0 is the laser wavelength, c is the speed of light, ε0 is the vacuum permittivity, n is the material refractive index, and Δn and Δp are the electron and hole density change, and m and m* are the electron and hole effective mass.

[0015] The greater the changeable amount is, the greater the change is, so the wavelength tuning range of the DBR laser is also greater. Since Δn » Δp, the contribution of Δn is greater.

[0016] Preferably, in a possible implementation of the first aspect, the host core layer of the Bragg reflection region in the DBR laser adopts InGaAlAs material.

[0017] In the Bragg reflection region, the host core layer adopts InGaAlAs material, which is used to reduce the electron effective mass so that there is a greater under the same , i.e. greater wavelength change. At the same time, the multi-quantum well structure of the active region also adopts InGaAlAs, which is required for the butt joint of the active region and the passive region, and also because the InGaAlAs multi-quantum well has a higher differential gain.

[0018] Preferably, in a possible implementation of the first aspect, a carrier confinement layer is arranged between the host core layer and the cladding layer of the Bragg reflection region in the DBR laser. The carrier confinement layer adopts InAlAs material, and a potential barrier is established by the energy level difference between the host core layer and the carrier confinement layer.

[0019] The carrier confinement layer with a greater energy gap difference between the host core layer and the upper and lower cladding layers is used to prevent the overflow of carriers, so as to improve under the same injected current. So there is a greater under the same number of injected electrons, i.e. greater wavelength change.

[0020] Since there is not a high enough potential barrier at the interface between the p-InP cladding layer, the n-InP cladding layer and the host core layer to block the electrons and holes, the electrons can easily overflow to the cladding layer by the potential barrier, and the holes are the same as the electrons, so the holes and the electrons can easily escape from the host core layer, thereby reducing and . ​

[0021] A very thin InAlAs confinement layer is inserted between the body core layer and the p-InP cladding layer and the n-InP cladding layer, a p-side carrier blocking layer is added between the p-InP cladding layer and the body core layer, an n-side carrier blocking layer is added between the n-InP cladding layer and the body core layer, the p-side carrier blocking layer and the n-side carrier blocking layer are confinement layers made of InAlAs. Since the energy gap difference between the InAlAs confinement layer and the body core layer is very large, the electrons and holes at the interface of the confinement layer hit a very high potential barrier wall and are bounced back to the body core layer, so that the electrons and holes are effectively trapped in the body core layer, thereby improving the and .

[0022] Preferably, in a possible implementation of the first aspect, the DBR laser is made in a BH structure, and the carriers in the body core layer are confined by adjusting the width of the body core layer in the Bragg reflection region of the DBR laser.

[0023] The DBR laser chip is made in a BH structure, which is used to prevent the injected current from flowing laterally and to limit the width of the body core layer, thereby improving the value under the same current injection. By reducing the volume of the body core layer and confining the injected carriers in the body core layer, the value can be improved. The length of the body core layer is related to the coupling coefficient of the grating and cannot be adjusted at will, the thickness of the body core layer is consistent with the waveguide layer of the active region and cannot be adjusted at will, and only the width of the body core layer can be reduced. Therefore, the DBR laser chip made in a BH structure uses an InP current blocking layer between the p-contact layer and the n-InP substrate, which prevents the lateral diffusion of the injected current and limits the width of the body core layer, thereby improving the efficiency of electron injection and the .

[0024] The wavelength tuning range of the DBR laser chip can be greatly improved by the above design improvement. The existing three-section DBR laser chip in the 1.3 μm band has an InAlAs confinement layer of 10 nm between the body core layer of the Bragg reflection region and the upper and lower cladding layers, and the tunable range of the DBR laser chip is more than 5 nm. According to the formula for the change of the refractive index of the body core layer of the Bragg reflection region, the change of the refractive index of the Bragg reflection region is proportional to Therefore, the tunable range of the DBR laser chip designed above can be greater than 8 nm in the 1.65 μm band, i.e., in the band with a strong absorption peak of methane.

[0025] The wavelength of the laser emitted by the DBR laser chip varies with the ambient temperature: when the ambient temperature increases by 1 °C, the wavelength of the laser emitted by the DBR laser chip shifts by 0.1 nm towards the long wavelength direction; when the ambient temperature decreases by 1 °C, the wavelength of the laser emitted by the DBR laser chip shifts by 0.1 nm towards the short wavelength direction.

[0026] When the current injected into the Bragg reflection region increases, the effective refractive index of the Bragg reflection region decreases due to the plasma effect of the carriers, thereby causing the DBR laser wavelength to shift towards the short wavelength direction; conversely, when the current injected into the Bragg reflection region decreases, the DBR laser wavelength shifts towards the long wavelength direction. Therefore, when the ambient temperature changes, the wavelength of the laser emitted by the DBR laser chip changes, which can be corrected by adjusting the current injected into the Bragg reflection region of the DBR laser chip, thereby ensuring that the center wavelength of the output of the DBR laser chip is always locked at the wavelength of a certain absorption peak of the methane gas to be detected.

[0027] Because the tuning range of the DBR laser chip improved by the above design can be greater than 8 nm at the 1650 nm band, the wavelength shift caused by a change of ±40 °C in the ambient temperature can be directly compensated by adjusting the current injected into the Bragg reflection region 203 of the DBR laser chip. Therefore, the improved DBR laser chip can be used in a wide temperature range without using a TEC and a thermistor to control the temperature to maintain the center wavelength of the laser consistent with the absorption peak of the methane gas at the 1650 nm band at different ambient temperatures.

[0028] Preferably, in a possible implementation form of the first aspect, the Bragg reflection region of the DBR laser further comprises a grating, by changing the grating period, the center wavelength of the laser emitted by the DBR laser chip is consistent with the absorption peak wavelength of the methane gas when the DBR laser chip is at room temperature and the current value injected into the Bragg reflection region is at the middle value of the tuning current range.

[0029] Preferably, in a possible implementation form of the first aspect, the DBR laser can adopt a TO56 package structure because it does not need a TEC to control the temperature, and the DBR laser chip is attached to the boss of the TO56 package.

[0030] Preferably, in a possible implementation form of the first aspect, the reference gas chamber and the first light detector are integrated into an integrated device, and the methane gas with a preset concentration is enclosed in the integrated device.

[0031] The second aspect is a wide-temperature-range laser methane detection method based on a DBR laser, which is implemented based on the above-described wide-temperature-range laser methane detection device based on a DBR laser, and comprises the following steps: The output laser of the DBR laser is split into two parts, one part is incident on a reference gas chamber containing methane gas with a preset concentration, and the other part is incident on a methane gas chamber connected to the methane gas to be measured; The first light detector receives the laser signal transmitted through the reference gas chamber, and the second light detector receives the laser signal transmitted through the methane gas chamber; The control unit analyzes the laser signal transmitted through the reference gas chamber received by the first light detector, and adjusts the complex current injected into the Bragg reflection region of the DBR laser and the auxiliary adjustment current injected into the phase control region of the DBR laser; The complex current is used to adjust the center wavelength of the laser emitted by the DBR laser when the ambient temperature changes, so that it aligns with the absorption peak of the methane gas; The auxiliary adjustment current is used to adjust the current so that the center wavelength of the laser emitted by the DBR laser is consistent with the absorption peak wavelength of the methane gas when the Bragg reflection region injection current is the middle value of the tuning current range and the center wavelength of the laser emitted by the DBR laser still deviates from the methane absorption peak at a temperature of 25°C; The control unit analyzes the laser signal transmitted through the methane gas chamber received by the second light detector, and calculates the concentration of the methane gas to be measured.

[0032] Preferably, in one possible implementation of the second aspect, the complex current includes a direct current component and a symmetric scanning current superimposed thereon; The symmetric scanning current is a ramp-type scanning current centered on the direct current component; The output photocurrent intensity of the first light detector changes with the change of the ramp-type scanning current; The center point of the ramp-type scanning current corresponds to an absorption peak of the methane gas, so that the photocurrent intensity output by the first light detector has a minimum value at the center point of the scanning current; When the ambient temperature changes cause the center wavelength of the laser emitted by the DBR laser to drift, the position of the photocurrent intensity minimum value deviates from the center point of the ramp-type scanning current; Based on the deviation, the current value of the direct current component is adjusted to align the center wavelength of the DBR laser with the absorption peak wavelength of the methane gas.

[0033] The Bragg region grating is properly designed so that the DBR laser emits laser light at a center wavelength identical to the methane absorption peak wavelength when the DC current component injected into the Bragg region is at the middle of the tuning current range of the Bragg region at room temperature (25℃). If the center wavelength of the laser light emitted by the DBR laser is slightly deviated from the methane absorption peak wavelength due to errors at room temperature, the current injected into the phase region can be adjusted to correct the deviation so that the center wavelength of the laser light emitted by the DBR laser is completely identical to the methane absorption peak wavelength.

[0034] The present application has the advantages that: by improving the design of the DBR laser and adjusting the current of the Bragg region and the current of the phase region to control the center wavelength of the laser, the center wavelength of the laser is accurately locked on the absorption peak of the methane gas at the wavelength of 1650 nm within the temperature range of-15℃ to +65℃, and the dependence of the laser methane detector on the TEC and the thermistor is eliminated.

[0035] Since the current injection for tuning the laser wavelength only needs nanoseconds to microseconds, which is lower than the response of the TEC temperature control at the level of hundreds of microseconds, the response speed of the present application to the wavelength drift caused by the change of the ambient temperature is greatly accelerated, and the tracking error of the prior art is also solved, thereby ensuring the fast and accurate wavelength locking.

[0036] In addition, the present application has a wide temperature range and can significantly reduce power consumption, because the current for tuning the wavelength is at the level of milliamperes, which is much smaller than the requirement of the TEC at the level of amperes, thereby reducing the power supply load and improving the energy efficiency.

[0037] In addition, the present application has a cost advantage, and the TEC and the thermistor are omitted to simplify the packaging and reduce the manufacturing complexity.

[0038] Furthermore, the method can improve the detection accuracy and stability by monitoring the wavelength drift in real time and dynamically adjusting the wavelength. BRIEF DESCRIPTION OF DRAWINGS

[0039] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the following embodiment or prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0040] Figure 1 A structure diagram of a wide-temperature-range laser methane detection device based on a DBR laser is provided.

[0041] Figure 2A three-section DBR laser structure diagram is provided for the present application.

[0042] Figure 3 An interface band diagram without a confinement layer is provided for the present application.

[0043] Figure 4 An interface band diagram with a confinement layer is provided for the present application.

[0044] Figure 5 A BH structure diagram of a DBR laser is provided for the present application.

[0045] Figure 6 A diagram showing that the light intensity received by the first light detector has a minimum value at the center point of the Bragg reflection region is provided for the present application.

[0046] Figure 7 A flow chart of a wide temperature range laser methane detection method based on a DBR laser is provided for the present application.

[0047] Figure 8 An improved wide temperature range laser methane detection device diagram is provided for the present application.

[0048] Figure 9 A diagram of an integrated device of a reference gas chamber and a first light detector is provided for the present application.

[0049] Figure 10 A diagram showing that a DBR laser chip is mounted on the boss of a TO56 tube base is provided for the present application.

[0050] BRIEF DESCRIPTION OF DRAWINGS 11-DBR laser, 12-splitting sheet, 13-reference gas chamber, 14-methane gas chamber, 15-first light detector, 16-second light detector, 17-control unit; 201-active region, 202-phase control region, 203-Bragg reflection region, 204-p contact layer, 205-positive electrode, 206-negative electrode, 207-grating, 208-multiquantum well layer, 209-upper separate confinement layer, 210-lower separate confinement layer, 211-main core layer, 212-n-InP substrate, 213-reflective film, 214-anti-reflection film; 31-p-InP cladding layer, 32-n-InP cladding layer, 33-p-side carrier blocking layer, 34-n-side carrier blocking layer, 35-InP current blocking layer; 41-integrated device of a reference gas chamber and a first light detector; 51-TO46 tube base, 52-PD chip, 53-TO46 tube cap; 61-DBR laser chip, 62-chip heat sink, 63-TO56 tube socket. DETAILED DESCRIPTION

[0051] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0052] Example 1: Figure 1 As shown, the present invention provides a wide temperature range laser methane detection device based on DBR laser, including a DBR laser 11, a beam splitter 12, a reference gas chamber 13, a methane gas chamber 14, a first light detector 15, a second light detector 16 and a control unit 17.

[0053] The DBR laser 11 is configured to emit laser light and adjust the laser wavelength by controlling the current injected into the Bragg reflection region 203 of the DBR laser 11. The beam splitter 12 is configured to split the laser light outputted by the DBR laser 11 into two paths. The reference gas chamber 13 is configured to seal methane gas of a preset concentration and is disposed in one of the laser beam splitting paths. The methane gas chamber 14 is configured to allow the methane gas to be measured to pass through and is disposed in the other of the laser beam splitting paths. The first photodetector 15 is configured to receive one of the laser beams transmitted through the reference gas chamber 13. The second photodetector 16 is configured to receive the other laser beam transmitted through the methane gas chamber 14. The control unit 17 receives detection signals outputted by the first and second photodetectors 15, 16, analyzes the detection signals outputted by the first photodetector 15, calculates the offset of the laser center wavelength caused by changes in ambient temperature, adjusts the injection current into the Bragg reflection region 203 of the DBR laser 11, compensates for the offset of the laser center wavelength, and calculates the methane gas concentration to be measured based on the detection signal outputted by the second photodetector 16.

[0054] like Figure 2 As shown, the DBR laser 11 adopts a three-section structure: an active region 201, a phase control region 202, and a Bragg reflection region 203. The active region 201, as the core of light generation, emits laser light by injecting current through the positive electrode 205 and the negative electrode 206. The main component of the active region 201 is a multi-quantum well layer 208 sandwiched between an upper and lower confinement layer 209 and a lower confinement layer 210. The upper and lower confinement layers 209 and 210 are interposed between a p-contact layer 204 and an n-InP substrate 212 through a cladding layer.

[0055] The phase control region 202 and the Bragg reflection region 203 are adjusted by current injection to control the laser wavelength. In the Bragg reflection region 203, there is a grating 207 with a periodically changed refractive index to reflect the Bragg wavelength and control the lasing wavelength. The grating 207 is etched on the main core layer 211, which is sandwiched between the upper and lower cladding layers. The DBR laser has a reflective film 213 and an anti-reflection film 214 on the two end faces respectively.

[0056] The embodiment improves the design of the DBR laser 11 to increase the wavelength tuning range by the following measures.

[0057] As mentioned above, the wavelength of the laser emitted by the DBR laser 11 can be obtained by formula (1).

[0058] The wavelength of the laser emitted by the DBR laser 11 is changed by changing the effective refractive index of the Bragg reflection region 203. When the current injected into the Bragg reflection region 203 is increased, the refractive index of the Bragg reflection is reduced due to the plasma effect of the carriers, thereby causing the effective refractive index of the Bragg reflection region to be reduced, the Bragg wavelength to be shifted to the short wavelength direction, and vice versa. When the current injected into the Bragg reflection region 203 is reduced, the DBR laser wavelength is shifted to the long wavelength direction.

[0059] As mentioned above, the change of the refractive index of the main core layer of the Bragg reflection region based on the plasma effect of the carriers can be represented by formula (2).

[0060] The greater the changeable amount is, the greater the change is, and thus the greater the wavelength tuning range of the DBR laser 11 is. Since is much greater than , the contribution of to is greater.

[0061] Specifically, the design improvement for increasing the wavelength tuning range of the DBR laser 11 in the embodiment includes: 1. In the Bragg reflection region 203, the main core layer 211 is made of InGaAlAs material to reduce the effective mass of electrons , so that there is a greater under the same , that is, a greater wavelength change. Meanwhile, the multi-quantum well structure of the active region 201 is also made of InGaAlAs, which is required for the interface of the active region 201 and the passive region, and also because the InGaAlAs multi-quantum well has a higher differential gain.

[0062] 2、The carrier confinement layer with a larger energy gap difference is arranged between the main core layer 211 and the upper and lower cladding layers, which is used to prevent the overflow of carriers, so as to improve the , so that there is a larger , that is, a larger wavelength change.

[0063] Figure 3 is the schematic diagram of the interface energy band when the main core layer 211 without the confinement layer is directly sandwiched between the p-InP cladding layer 31 and the n-InP cladding layer 32, in which e represents an electron, and h represents a hole, is the conduction band energy band difference. Since the interface between the p-InP cladding layer 31, the n-InP cladding layer 32 and the main core layer 211 does not have a high enough potential barrier to block the electrons and holes, as shown by the arrows, the electrons can easily cross the potential barrier and overflow to the cladding layer, and the holes are the same as the electrons. Therefore, the electrons and holes can easily escape from the main core layer 211, thereby reducing the and .

[0064] Figure 4 is the schematic diagram of the interface energy band when a very thin InAlAs confinement layer is inserted between the main core layer 211 and the p-InP cladding layer 31 and the n-InP cladding layer 32. The p-side carrier blocking layer 33 is added between the p-InP cladding layer 31 and the main core layer 211, and the n-side carrier blocking layer 34 is added between the n-InP cladding layer 32 and the main core layer 211. The p-side carrier blocking layer 33 and the n-side carrier blocking layer 34 are the confinement layers made of InAlAs. In the figure, e represents an electron, and h represents a hole. Since the energy gap difference between the InAlAs confinement layer and the main core layer 211 is large, the electrons and holes collide with a high potential barrier wall at the interface of the confinement layer and are bounced back to the main core layer 211. In this way, with the high-potential barrier blocking layer, the electrons and holes are effectively trapped in the main core layer 211, thereby improving the and .

[0065] 3、The chip side of the DBR laser 11 is made of the BH structure, which is used to prevent the injected current from flowing out laterally and limit the width of the main core layer 211, and is also used to improve the value under the same current injection. Figure 5 is the structure diagram of the BH of the DBR laser 11. Specifically, in the embodiment, the carriers in the main core layer 211 are limited by reducing the volume of the main core layer 211, thereby improving the The length of the body core layer 211 is related to the coupling coefficient of the grating and cannot be adjusted at will. The thickness of the body core layer 211 is consistent with the waveguide layer of the active region 201 and cannot be adjusted at will. Only the width of the body core layer can be reduced. Therefore, the DBR laser 11 made of the BH (buried hetero-structure) structure uses an InP current blocking layer 35 between the p-contact layer 204 and the n-InP substrate 212. On the one hand, the current injection is limited in a narrow strip to prevent the lateral diffusion of the current. On the other hand, the width of the body core layer 211 is limited, which improves the efficiency of the electron injection and also improves the .

[0066] The above design improvement can greatly improve the wavelength tuning range of the DBR laser 11. The existing three-section DBR laser 11 in the 1.3 μm band has an InAlAs limiting layer of 10 nm between the body core layer 211 of the Bragg reflection region 203 and the upper and lower cladding layers. The tunable range of the DBR laser 11 can reach more than 5 nm. According to the carrier plasma effect formula (2) of the DBR laser 11, the refractive index change of the Bragg reflection region 203 is proportional to . Therefore, the tunable range of the DBR laser 11 designed above is greater than 8 nm in the 1.65 μm band, that is, in the band with a strong absorption peak of methane.

[0067] The wavelength of the laser emitted by the DBR laser 11 changes with the ambient temperature. When the ambient temperature increases by 1 °C, the wavelength of the laser emitted by the DBR laser 11 drifts to the long wavelength direction by 0.1 nm. When the ambient temperature decreases by 1 °C, the wavelength of the laser emitted by the DBR laser 11 drifts to the short wavelength direction by 0.1 nm.

[0068] When the current injected into the Bragg reflection region 203 increases, the effective refractive index of the Bragg reflection will decrease due to the plasma effect of the carriers, thereby causing the Bragg wavelength to shift to the short wavelength direction. Therefore, when the ambient temperature changes, the wavelength of the laser emitted by the DBR laser 11 changes. The wavelength of the laser emitted by the DBR laser 11 caused by the change of the ambient temperature can be corrected by adjusting the current injected into the Bragg reflection region 203, thereby ensuring that the center wavelength of the output of the DBR laser 11 is always locked at the wavelength of a certain absorption peak of the methane gas to be measured.

[0069] The DBR laser 11 in this embodiment has a tuning range of 8 nm or more at the 1650 nm band. Specifically, the wavelength shift caused by a change of ±40°C in the ambient temperature can be directly compensated by adjusting the current injected into the Bragg reflection region 203 of the DBR laser 11. Therefore, in a wide-temperature-range laser methane detection device using the improved DBR laser 11 in this embodiment, the TEC and thermistor can be completely dispensed with to maintain the central wavelength of the laser in conformity with the absorption peak of the methane gas at the 1650 nm band at different ambient temperatures.

[0070] In this embodiment, the control unit 17 outputs to the DBR laser 11 a current for controlling the optical power output by the DBR laser 11 a composite current for controlling the wavelength of the DBR laser 11 injected into the Bragg reflection region 203 and an auxiliary adjustment current for the current of the phase control region 202 The composite current is composed of two parts, one being a direct-current part for controlling the central wavelength of the DBR laser 11 to align with the absorption peak of the methane gas, and the other being a ramp-type scanning current symmetrically centered at When the ambient temperature changes, the control unit 17 can adjust and in time through analysis of the signal received by the first photodetector 15, to ensure that the central wavelength of the DBR laser 11 aligns with the absorption peak of the methane gas, and is the center value of The current injected into the phase control region 202 is used to assist in adjusting the wavelength of the DBR laser 11.

[0071] The period of the grating 207 of the Bragg reflection region 203 is designed so that when the current value injected into the Bragg reflection region 203 is at the middle value of the full range of the Bragg region tuning current, the central wavelength of the DBR laser 11 aligns with one absorption peak (e.g., 1653.7 nm) of the methane gas at room temperature (25°C).

[0072] Thus, the current injected into the Bragg reflection region 203 can be adjusted by 40°C up and down from the center value of 25°C within the full range of the tuning, i.e., the temperature range for wavelength adjustment is -15°C to +65°C. Due to design errors and other reasons, when the Bragg reflection region 203 is injected with a current To tune the median value of the current, the center wavelength of the DBR laser 11 is still slightly deviated from the methane absorption peak, and the auxiliary adjusting current of the phase control region 202 is adjusted to correct it, so that at room temperature (25°C), when the current value injected into the Bragg reflection region 203 is at the median value of the full range of the tuning current, the center wavelength of the DBR laser 11 is consistent with one absorption peak of the methane gas.

[0073] After the DBR laser output is collimated, part of the light is incident into a reference gas chamber 13 sealed with a certain concentration of methane gas, and the intensity of the transmitted light is measured by a first light detector 15. Then the injection current of the Bragg reflection region 203 is symmetrically scanned near the absorption peak. At this time, the output photocurrent intensity of the first light detector 15 will change with the scanning current injected into the Bragg reflection region 203. Due to the symmetric scanning, the output photocurrent intensity of the first light detector 15 has a minimum value at the center point of the scanning current corresponding to the absorption peak of the methane, as shown in Figure 6 When the ambient temperature changes, the center wavelength of the DBR laser 11 drifts, and at this time the position of the above-mentioned minimum value of the photocurrent intensity also deviates from the center of the scanning current. According to the size and direction of the deviation, the direction and size of the wavelength drift of the DBR laser 11 can be determined.

[0074] After the direction and size of the wavelength drift of the DBR laser 11 are determined, the center value (average value) of the DBR scanning current is adjusted to pull the center wavelength of the DBR laser 11 back to one absorption peak (such as 1653.7 nm) of the methane gas, and by this method the center wavelength of the DBR laser 11 is accurately locked to one absorption peak of the methane gas in the entire temperature range.

[0075] The second light detector 16 is used to receive the DBR laser signal passing through the methane gas chamber 14 storing the methane gas to be measured, and the concentration of the methane gas to be measured is analyzed and calculated by the control unit 17.

[0076] Example 2: As shown in Figure 7 , the present application provides a wide temperature range laser methane detection method based on a DBR laser, which uses a wide temperature range laser methane detection device based on a DBR laser in Example 1, comprising: After the output laser of the DBR laser 11 is split, part of it is incident into the reference gas chamber 13 sealed with the methane gas, and the other part is incident into the methane gas chamber 14 into which the methane gas to be measured is introduced. The laser signal transmitted through the reference gas chamber 13 is received by the first light detector 15, and the laser signal transmitted through the methane gas chamber 14 is received by the second light detector 16.

[0077] The outputs of the two photodetectors are sent to the control unit 17 for analysis and processing to derive the concentration of the methane gas being measured, which is transmitted to the upper system by the control unit 17.

[0078] The control unit 17 analyzes the laser signal transmitted through the reference gas chamber 13 received by the first photodetector 15, and injects a complex current into the Bragg reflection region 203 of the DBR laser 11, which is used to control the center wavelength of the laser emitted by the DBR laser 11 to align with the absorption peak of the methane gas when the ambient temperature changes.

[0079] The control unit 17 outputs to the DBR laser 11 a current for controlling the optical power output of the DBR laser 11 and a current for controlling the wavelength of the DBR laser 11, which includes a complex current and an auxiliary adjustment current . The complex current is composed of two parts, a direct current component for controlling the center wavelength of the DBR laser 11 to align with the absorption peak of the methane gas, and a symmetric ramp scanning current with a center value of superimposed on the direct current component . When the ambient temperature changes, the control unit 17 can adjust the direct current component and the ramp scanning current in time through analysis of the signal received by the second photodetector 16, to ensure that the center wavelength of the DBR laser 11 aligns with the absorption peak of the methane gas, and the direct current component is the center value of the auxiliary adjustment current .

[0080] Specifically, the injection current of the Bragg reflection region 203 is symmetrically scanned around the absorption peak. At this time, the output photocurrent intensity of the first photodetector 15 will change with the scanning current injected into the Bragg reflection region 203. Since it is a symmetric scan, the absorption peak of methane corresponds to the center point of the scanning current, i.e. the output photocurrent intensity of the first photodetector 15 has a minimum value at the center point of the scanning current. When the ambient temperature changes, the center wavelength of the DBR laser 11 drifts, and at this time the position of the current intensity minimum value deviates from the center of the scanning current. According to the size and direction of this deviation, the direction and size of the wavelength drift of the DBR laser 11 can be determined.

[0081] After determining the direction and magnitude of the wavelength drift of the DBR laser 11, the center value of the scanning current of the DBR laser 11 is adjusted to bring the center wavelength of the DBR laser 11 back to the absorption peak of methane gas (1653.7 nm). In this way, the center wavelength of the DBR laser 11 is locked to the absorption peak of methane gas over the entire temperature range.

[0082] Auxiliary regulation current It is used to adjust and correct the center wavelength of the laser emitted by the DBR laser 11 to be consistent with the wavelength of the absorption peak of methane gas when the temperature is 25°C and the injection current of the Bragg reflection area 203 is the middle value of the tuning current range and the center wavelength of the laser emitted by the DBR laser 11 still deviates from the methane absorption peak.

[0083] Specifically, the auxiliary regulating current injected into the phase control region 202 It is used to assist in adjusting the central wavelength of the laser emitted by the DBR laser 11. At room temperature, when the current injected into the Bragg reflection region 203 is the median value of the tuning current, the central wavelength of the DBR laser still deviates from the methane absorption peak. To correct it.

[0084] The control unit 17 analyzes the laser signal transmitted through the methane gas chamber 14 and received by the second light detector 16 to calculate the methane gas concentration to be measured.

[0085] Example 3: Figure 8 As shown, the present invention provides an improved wide-temperature range laser methane detection device based on a DBR laser. The device improves the laser methane detection device in Example 3 and includes a DBR laser 11, a beam splitter 12, an integrated device 41 integrating a reference gas chamber and a first light detector, a methane gas chamber 14, a second light detector 16, and a control unit 17. In the figure, the control unit 17 outputs a current to the DBR laser 11 to control the output optical power of the DBR laser 11 and a current to control the wavelength of the DBR laser 11. The current to control the wavelength of the DBR laser 11 includes a composite current. and auxiliary regulation current The improved wide-temperature range laser methane detection device has a more compact structure, is easier to assemble, and has a lower cost.

[0086] Figure 9 This is a schematic diagram of an integrated device integrating the reference gas chamber 13 and the first light detector 15. A certain concentration of methane gas is enclosed in a TO46 tube socket 51 and a TO46 tube cap 53, and combined with a PD chip 52 to form a functional device integrating the reference gas chamber 13 and the first light detector 15.

[0087] In this embodiment, since the DBR laser 11 does not need a TEC for temperature control, the DBR laser chip can be packaged in a TO56, which greatly reduces the cost of the DBR laser 11. As shown in Fig. 4, four gold wires respectively connect the positive and negative electrodes of the active region 201 and the DC part of the composite current and the auxiliary adjusting current to the pins of the tube base. Since a TEC is not needed, the DBR laser chip 61 is directly attached to the boss of the TO56 tube base 63 through a chip heat sink 62, and the packaging is very simple. Figure 10

[0088] Obviously, various modifications and changes can be made to the present application by those skilled in the art without departing from the spirit and scope of the present application. Thus, it is intended that the present application cover the modifications and changes as long as they come within the scope of the claims and their equivalents.​​​

Claims

1. A wide temperature range laser methane detection device based on DBR laser, characterized in that: include: DBR laser, used for emitting laser light and adjusting the laser wavelength by controlling the current injected into the Bragg reflection region of the DBR laser; A beam splitter is used to split the laser output from the DBR laser into two paths; A reference gas chamber, used to seal a preset concentration of methane gas and disposed in one of the laser beam splitting paths; A methane gas chamber is used to introduce the methane gas to be measured and is arranged in another laser beam splitting path; A first light detector is used to receive one path of the laser light transmitted through the reference gas chamber; a second light detector, configured to receive the other path of the laser light transmitted through the methane gas chamber; The control unit receives the detection signals output by the first light detector and the second light detector, calculates the offset of the laser center wavelength caused by the change in ambient temperature based on the detection signal output by the first light detector, compensates for the offset of the laser center wavelength, and calculates the methane gas concentration to be measured based on the detection signal output by the second light detector.

2. The wide temperature range laser methane detection device based on DBR laser according to claim 1, characterized in that: The main core layer of the Bragg reflection zone in the DBR laser is made of InGaAlAs material.

3. The wide temperature range laser methane detection device based on DBR laser according to claim 2, characterized in that: A carrier confinement layer is provided between the main core layer and the cladding layer of the Bragg reflection region in the DBR laser; The carrier confinement layer is made of InAlAs material, and a potential barrier is established by the energy level difference between the main core layer and the carrier confinement layer.

4. The wide temperature range laser methane detection device based on DBR laser according to claim 1, characterized in that: The DBR laser is manufactured using a BH structure, and the carriers in the main core layer are limited by adjusting the width of the main core layer in the Bragg reflection area of ​​the DBR laser.

5. The wide temperature range laser methane detection device based on DBR laser according to claim 1, characterized in that: The Bragg reflection region of the DBR laser also includes a grating. By changing the grating period, when the DBR laser chip is at room temperature and the current value injected into the Bragg reflection region is at the middle value of the tuning current range, the central wavelength of the laser emitted by the DBR laser chip is consistent with the absorption peak wavelength of methane gas.

6. The wide temperature range laser methane detection device based on DBR laser according to claim 1, characterized in that: The DBR laser adopts a TO56 packaging structure, and the DBR laser chip is mounted on the TO56 tube seat boss.

7. The wide temperature range laser methane detection device based on DBR laser according to claim 1, characterized in that: The reference gas chamber and the first light detector are integrated into an integrated device, and methane gas with a preset concentration is enclosed in the integrated device.

8. A wide temperature range laser methane detection method based on DBR laser, characterized in that: The method is implemented based on a wide temperature range laser methane detection device based on a DBR laser as described in claims 1 to 7, and includes the following steps: After the output laser beam of the DBR laser is split, one part is incident on the reference gas chamber filled with methane gas of a preset concentration, and the other part is incident on the methane gas chamber filled with the methane gas to be measured; The first light detector receives the laser signal transmitted through the reference gas chamber, and the second light detector receives the laser signal transmitted through the methane gas chamber; The control unit analyzes the laser signal transmitted through the reference gas chamber and received by the first light detector, and adjusts the composite current injected into the Bragg reflection area of ​​the DBR laser and the auxiliary adjustment current injected into the phase control area of ​​the DBR laser; The composite current is used to adjust the central wavelength of the laser emitted by the DBR laser to align it with the absorption peak of methane gas when the ambient temperature changes; The auxiliary adjustment current is used to adjust the current so that the central wavelength of the laser emitted by the DBR laser is consistent with the absorption peak wavelength of methane gas when the injection current in the Bragg reflection region is at the middle value of the tuning current range and the central wavelength of the laser emitted by the DBR laser still deviates from the methane absorption peak at a temperature of 25°C; The control unit analyzes the laser signal transmitted through the methane gas chamber and received by the second light detector to calculate the concentration of the methane gas to be measured.

9. The wide temperature range laser methane detection method based on DBR laser according to claim 8, characterized in that: The composite current includes a DC component and a symmetrical scanning current superimposed thereon; The symmetrical scanning current is a ramp-type scanning current centered on the DC component; The output photocurrent intensity of the first photodetector changes with the change of the ramp-type scanning current; The center point of the ramp-type scanning current corresponds to an absorption peak of methane gas, so that the photocurrent intensity output by the first photodetector reaches a minimum value at the center point of the scanning current; When the ambient temperature changes and causes the central wavelength of the DBR laser to drift, the position of the minimum value of the photocurrent intensity shifts to the center point of the ramp-type scanning current; The current value of the DC component is adjusted based on the offset to align the central wavelength of the DBR laser with the absorption peak wavelength of methane gas.

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