A wide temperature range laser methane detection device and method based on DBR laser

Abstract

This invention relates to the field of laser methane gas detection technology, and discloses a wide-temperature-range laser methane detection device and method based on a DBR laser. The device employs a DBR laser with a wide wavelength tuning range, and adjusts the laser wavelength by controlling the current injected into the Bragg reflector to compensate for the center wavelength drift caused by ambient temperature. Combined with a reference gas chamber, a methane gas chamber to be detected, and a photodetector assembly, accurate detection of methane gas is achieved. By dynamically adjusting the current injected into the Bragg reflector to compensate for wavelength drift, the center wavelength of the laser is ensured to always be aligned with the methane absorption peak, thereby calculating the methane concentration. This device eliminates the need for traditional temperature control devices such as TECs and thermistors, and has a wide temperature range, fast response speed, and low cost.

Description

Technical Field

[0001] This invention relates to the field of laser methane gas detection technology, and discloses a wide-temperature-range laser methane detection device and method based on a DBR laser. Background Technology

[0002] Tunable Semiconductor Laser Absorption Spectroscopy (TDLAS) is a commonly used and effective gas analysis technique, particularly suitable for methane concentration detection. This technique uses a single-mode laser emitted from a semiconductor laser chip to scan a specific spectral line of the gas being tested. By measuring the change in laser intensity caused by the characteristic absorption of the incident light by the laser after passing through the gas, the concentration and other characteristics of the gas can be accurately determined. However, a key to successful TDLAS measurement is locking the center wavelength of the semiconductor laser chip to the specific absorption line of methane. The wavelength of a semiconductor laser chip is highly sensitive to temperature. Typically, for every 1°C increase in the operating temperature of the laser chip, the center wavelength of the semiconductor laser chip shifts approximately 0.1 nm towards longer wavelengths; conversely, for every 1°C decrease in temperature, the center wavelength shifts approximately 0.1 nm towards shorter wavelengths. In existing technologies, to ensure that the center wavelength of a semiconductor laser chip remains constant despite changes in ambient temperature, a combination of a thermoelectric cooler (TEC) and a thermistor is used to control the operating temperature of the laser chip. This keeps the operating temperature of the laser chip at a specific level, thus preventing the center wavelength from drifting due to ambient temperature variations. However, the method of introducing a TEC and thermistor not only increases costs but also complicates the semiconductor laser packaging process. Furthermore, when the ambient temperature deviates significantly from the set temperature, the current and voltage of the TEC become very large, potentially causing the power supply to be overloaded, leading to TEC malfunction and wavelength control failure. Using a TEC to control the center wavelength through temperature also suffers from tracking errors, which can also cause errors in center wavelength control.

[0003] To reduce costs, a method has emerged that uses a heating resistor instead of a thermocouple (TEC). This method uses a combination of a thin-film resistor and a thermistor integrated on the laser chip's heat sink to control the laser chip's operating temperature, ensuring that the laser chip's operating temperature remains at a specific level and preventing center wavelength drift. However, since the resistor can only heat and does not pump heat, the laser chip's operating temperature must be set at a point far above room temperature, and the laser can only operate in environments below this temperature. Because the laser must always operate at temperatures far above room temperature, this is detrimental to its lifespan. Furthermore, since the resistor only has a heating function, when the ambient temperature rises, the laser chip's operating temperature can only be adjusted to the set point by cutting off the current to the heating resistor and allowing natural heat dissipation. This process is time-consuming and difficult to stably control the laser chip at the set temperature, leading to instability in the laser's center wavelength. Additionally, this method of controlling the laser chip's operating temperature using a combination of heating resistors and thermistors has a very limited range of ambient temperatures it can handle. Summary of the Invention

[0004] To address the aforementioned technical shortcomings, the purpose of this invention is to provide a wide-temperature-range laser methane detection device and method based on a DBR laser, solving the problems of high cost, slow response, temperature control error, unstable temperature control, and small temperature adaptability caused by the existing methods of using TEC or heating resistors to stabilize the center wavelength of the laser chip.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] In a first aspect, a wide-temperature-range laser methane detection device based on a DBR laser includes:

[0007] A DBR laser is used to emit laser light, and the laser wavelength is adjusted by controlling the current injected into the Bragg reflector region of the DBR laser.

[0008] A beam splitter is used to split the laser output from a DBR laser into two paths.

[0009] The reference chamber is used to seal methane gas at a preset concentration and is set in one of the laser beam splitting paths;

[0010] The methane chamber is used to introduce the methane gas to be tested and is located in another laser beam splitting path.

[0011] The first photodetector is used to receive one of the laser beams that has passed through the reference gas cell;

[0012] The second photodetector is used to receive another laser beam that has passed through the methane chamber;

[0013] The control unit receives detection signals from the first photodetector and the second photodetector, calculates the offset of the laser center wavelength caused by changes in ambient temperature using the detection signal from the first photodetector, compensates for the offset of the laser center wavelength, and calculates the concentration of the methane gas to be measured using the detection signal from the second photodetector.

[0014] DBR lasers can be constructed using a simple three-section structure, consisting of an active region, a phase control region, and a Bragg reflection region.

[0015] The active region, as the core of light generation, emits laser light by injecting current through the positive and negative electrodes. The main component of the active region is a multi-quantum well layer sandwiched between the upper and lower confinement layers. The upper and lower confinement layers are separated by a cladding layer between the p-contact layer and the n-InP substrate.

[0016] The phase control region and the Bragg reflection region adjust the laser wavelength through current injection. In the Bragg reflection region, there is a grating with a periodically changing refractive index inside, which reflects a specific Bragg wavelength to control the lasing wavelength. The grating is etched on the main core layer, which is sandwiched between the upper and lower cladding layers. There are reflective and antireflective coatings on the two end faces of the DBR laser, respectively.

[0017] The present invention improves the design of the above-mentioned DBR laser chip by means of the following measures to increase its wavelength tuning range.

[0018] The formula for the wavelength of laser emitted by a DBR laser chip is:

[0019]

[0020] In formula (1) For the grating period, This represents the effective refractive index of the Bragg reflection region.

[0021] The wavelength of the laser emitted by the DBR laser chip can be changed by altering the effective refractive index. This is achieved by increasing the current injected into the Bragg reflector. Due to the plasma effect of charge carriers, the refractive index of the Bragg reflector decreases, resulting in a decrease in the effective refractive index of the Bragg reflector and a shift of the DBR laser wavelength towards shorter wavelengths. Conversely, when the current injected into the Bragg reflector decreases, the DBR laser wavelength shifts towards longer wavelengths.

[0022] Variation of refractive index of the bulk core layer in the Bragg reflector region based on carrier plasma effect This can be expressed as:

[0023]

[0024] In formula (2) The amount of electron charge. The wavelength of the laser. At the speed of light, The vacuum permittivity, For the refractive index of the material, and These represent the changes in electron and hole densities, respectively. and These are the effective masses of electrons and holes, respectively.

[0025] The greater the variable, The greater the variation, the wider the wavelength tuning range of the DBR laser. Because... Much larger ,so right Their contribution is even greater.

[0026] Preferably, in one possible implementation of the first aspect, the core layer of the Bragg reflection region in the DBR laser is made of InGaAlAs material.

[0027] In the Bragg reflector region, the core layer is made of InGaAlAs material to reduce the effective electron mass. In this way, in the same There will be a larger [opportunity] below. This means a large wavelength variation. Meanwhile, the active region's multi-quantum-well structure also uses InGaAlAs, which is necessary for the docking of the active and passive regions, and also because InGaAlAs multi-quantum-wells have high differential gain.

[0028] Preferably, in one possible implementation of the first aspect, a carrier confinement layer is provided between the core layer and the cladding layer of the Bragg reflection region in the DBR laser;

[0029] The carrier confinement layer is made of InAlAs material, and a potential barrier is established through the energy level difference between the main core layer and the carrier confinement layer.

[0030] A carrier confinement layer with a larger bandgap difference is placed between the main core layer and the upper and lower cladding layers to prevent carrier overflow and improve the efficiency of carrier confinement under the same injection current. This results in a larger [result] when injecting the same number of electrons. This refers to a large wavelength variation.

[0031] Since the interfaces between the p-InP cladding, n-InP cladding, and the main core layer do not have a sufficiently high barrier to block electrons and holes, electrons can easily cross over. The potential barrier overflows into the cladding. Holes, like electrons, can easily escape the main core layer, thus reducing the potential barrier. and .

[0032] A very thin InAlAs confinement layer is inserted between the main core layer and the p-InP and n-InP cladding layers. A p-side carrier blocking layer is added between the p-InP cladding layer and the main core layer, and an n-side carrier blocking layer is added between the n-InP cladding layer and the main core layer. Both the p-side and n-side carrier blocking layers are confinement layers made of InAlAs. Due to the large band gap difference between the InAlAs confinement layer and the main core layer, electrons and holes at the interface of the confinement layer collide with a very high barrier wall and are bounced back to the main core layer. This high barrier effectively traps electrons and holes in the main core layer, thereby increasing the energy density. and .

[0033] Preferably, in one possible implementation of the first aspect, the DBR laser is fabricated using a BH structure, and the carriers in the main core layer are limited by adjusting the width of the main core layer of the Bragg reflection region in the DBR laser.

[0034] The DBR laser chip is fabricated using a BH structure to prevent injected current from flowing out laterally and to limit the width of the core layer. This also improves performance under the same circuit injection conditions. Value. This can be improved by reducing the volume of the main core layer and confining the injected carriers within the main core layer to prevent overflow. The length of the core layer is related to the coupling coefficient of the grating and cannot be adjusted arbitrarily. The thickness of the core layer is consistent with the waveguide layer of the active region and cannot be adjusted arbitrarily either. Only the width of the core layer can be reduced. Therefore, in DBR laser chips fabricated using a BH structure, an InP current blocking layer is used between the p-contact layer and the n-InP substrate. This layer confines the injected current within a narrow, buried strip, preventing lateral current diffusion. It also limits the width of the core layer, thus improving both electron injection efficiency and... .

[0035] The aforementioned design improvements can significantly enhance the wavelength tuning range of DBR laser chips. Existing chips have a wavelength tuning range of 1.3... A three-segment DBR laser chip in the Bragg reflector region, after adding a 10nm InAlAs confinement layer between the main core layer and the upper and lower cladding layers, achieves a tunable range exceeding 5nm. Based on the formula for the refractive index change of the main core layer in the Bragg reflector region, the refractive index change in the Bragg reflector region... And directly proportional to Therefore, in the 1650nm band, which is the band where methane has a strong absorption peak, the tunable range of the DBR laser chip designed above can be greater than 8nm.

[0036] The wavelength of the laser emitted by the DBR laser chip changes 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 0.1nm towards the longer wavelength direction; when the ambient temperature decreases by 1°C, the wavelength of the laser emitted by the DBR laser chip shifts by 0.1nm towards the shorter wavelength direction.

[0037] When the current injected into the Bragg reflector increases, the effective refractive index of the Bragg reflector decreases due to the plasma effect of charge carriers, causing the DBR laser wavelength to shift towards shorter wavelengths. Conversely, when the current injected into the Bragg reflector decreases, the DBR laser wavelength shifts towards longer wavelengths. Therefore, the change in the emitted laser wavelength of the DBR laser chip caused by changes in ambient temperature can be corrected by adjusting the current injected into the Bragg reflector. This ensures that the center wavelength of the DBR laser chip's output remains locked at a specific absorption peak of the methane gas being measured.

[0038] Because the tunable range of the DBR laser chip, improved through the above design, can exceed 8nm in the 1650nm band, the wavelength drift caused by the ±40℃ change in ambient temperature can be directly compensated by adjusting the current injected into the Bragg reflector 203 of the DBR laser chip. Therefore, using the improved DBR laser chip, temperature control using a TEC and thermistor can be completely eliminated over a wide temperature range to maintain the laser's center wavelength consistent with the absorption peak of methane gas in the 1650nm band at different ambient temperatures.

[0039] Preferably, in one possible implementation of the first aspect, the Bragg reflection region of the DBR laser further includes a grating, and 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 center wavelength of the laser emitted by the DBR laser chip is consistent with the absorption peak wavelength of methane gas.

[0040] Preferably, in one possible implementation of the first aspect, the DBR laser can adopt a TO56 package structure since it does not require TEC for temperature control, and the DBR laser chip is mounted on the TO56 socket boss.

[0041] Preferably, in one possible implementation of the first aspect, the reference gas chamber and the first photodetector are integrated into a single device, and a preset concentration of methane gas is enclosed within the single device.

[0042] Secondly, a wide-temperature-range laser methane detection method based on a DBR laser, which is implemented based on the aforementioned wide-temperature-range laser methane detection device based on a DBR laser, includes the following steps:

[0043] After the output laser of the DBR laser is split, one part is incident into a reference gas chamber sealed with methane gas of a preset concentration, and the other part is incident into a methane gas chamber in which the methane gas to be tested is introduced.

[0044] The first photodetector receives the laser signal transmitted through the reference gas cell, and the second photodetector receives the laser signal transmitted through the methane gas cell.

[0045] The control unit analyzes the laser signal received by the first photodetector and transmitted through the reference gas cell, and adjusts the recombination 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.

[0046] The composite current is used to adjust the center wavelength of the laser emitted by the DBR laser so that it is aligned with the absorption peak of methane gas when the ambient temperature changes.

[0047] 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 methane gas when the temperature is 25°C, the injected current in the Bragg reflection region is the middle value of the tuning current range, and the center wavelength of the laser emitted by the DBR laser is still deviated from the methane absorption peak.

[0048] The concentration of the methane gas to be measured is calculated by analyzing the laser signal transmitted through the methane gas chamber received by the second photodetector through the control unit.

[0049] Preferably, in one possible implementation of the second aspect, the composite current includes a DC component and a symmetrical scanning current superimposed thereon;

[0050] The symmetrical scanning current is a ramp-type scanning current centered on the DC component;

[0051] The output photocurrent intensity of the first photodetector varies with the ramp-type scanning current;

[0052] The center point of the ramp-shaped scanning current corresponds to an absorption peak of methane gas, causing the photocurrent intensity output by the first photodetector to reach a minimum at the center point of the scanning current.

[0053] When changes in ambient temperature cause the center wavelength of the laser emitted by the DBR laser to drift, the position of the minimum value of the photocurrent intensity shifts away from the center point of the ramp-type scanning current.

[0054] The current value of the DC component is adjusted based on the offset to align the center wavelength of the DBR laser with the absorption peak wavelength of methane gas.

[0055] By properly designing the Bragg zone grating, the center wavelength of the emitted laser from the DBR laser at room temperature (25°C) will match the wavelength of the methane absorption peak when the DC current component injected into the Bragg reflection zone is at the midpoint of the Bragg zone's tuning current range. If, due to various errors, the DC current component injected into the Bragg zone of the DBR laser is at the midpoint of the Bragg zone's tuning current range, but the center wavelength of the emitted laser still slightly deviates from the methane absorption peak wavelength, the current injected into the phase zone can be adjusted to compensate for this, ensuring that the center wavelength of the emitted laser is completely consistent with the methane absorption peak wavelength.

[0056] The beneficial effects of this invention are as follows: by improving the design based on the DBR laser, and proposing a method to control the center wavelength of the laser by adjusting the current in the Bragg reflection region and the phase region current of the DBR laser, the laser can be precisely locked at the absorption peak of methane gas in the 1650nm band within the ambient temperature range of -15℃ to +65℃, thus eliminating the dependence of the laser methane detector on TEC and thermistor.

[0057] Since the current-injected tuned laser wavelength only requires nanoseconds to microseconds, which is lower than the microsecond response of TEC temperature control, the present invention significantly accelerates the compensation response speed for wavelength drift caused by changes in ambient temperature, and also solves the tracking error problem of existing technologies, ensuring fast and accurate wavelength locking.

[0058] In addition, the present invention is applicable to a wide temperature range and can significantly reduce power consumption because the current used for tuning the wavelength is in the milliampere range, which is much smaller than the ampere-level requirement of TEC, thus reducing the power supply load and improving energy efficiency.

[0059] In addition, it has a significant cost advantage, eliminating the need for TEC and thermistors to simplify packaging and reduce manufacturing complexity.

[0060] Furthermore, this method improves detection accuracy and stability by monitoring wavelength drift in real time and dynamically adjusting it through a reference gas cell. Attached Figure Description

[0061] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0062] Figure 1 This application provides a structural diagram of a wide-temperature-range laser methane detection device based on a DBR laser.

[0063] Figure 2This application provides a schematic diagram of the structure of a three-segment DBR laser.

[0064] Figure 3 This application provides a schematic diagram of the interface band structure without a limiting layer.

[0065] Figure 4 A schematic diagram of the interface band structure with a constraint layer is provided for this application.

[0066] Figure 5 This application provides a schematic diagram of the BH structure of a DBR laser.

[0067] Figure 6 This application provides a schematic diagram showing that the light intensity received by the first photodetector has a minimum value at the center point of the injected scanning current in the Bragg reflection region.

[0068] Figure 7 This application provides a flowchart of a wide-temperature-range laser methane detection method based on a DBR laser.

[0069] Figure 8 This application provides an improved wide-temperature-range laser methane detection device.

[0070] Figure 9 A schematic diagram of an integrated device in which a reference gas cell and a first photodetector are integrated is provided for this application.

[0071] Figure 10 This application provides a schematic diagram of a DBR laser chip mounted on a TO56 tube socket boss.

[0072] Explanation of reference numerals in the attached figures:

[0073] 11-DBR laser, 12-beam splitter, 13-reference gas cell, 14-methane gas cell, 15-first photodetector, 16-second photodetector, 17-control unit;

[0074] 201-Active region, 202-Phase control region, 203-Bragg reflection region, 204-P contact layer, 205-Positive electrode, 206-Negative electrode, 207-Grate, 208-Multiple quantum well layer, 209-Upper confinement layer, 210-Lower confinement layer, 211-Main core layer, 212-n-InP substrate, 213-Reflective coating, 214-Antireflective coating;

[0075] 31-p-InP cladding, 32-n-InP cladding, 33-p-side carrier blocking layer, 34-n-side carrier blocking layer, 35-InP current blocking layer;

[0076] 41- An integrated device combining the reference gas cell and the first photodetector;

[0077] 51-TO46 socket, 52-PD chip, 53-TO46 cap;

[0078] 61-DBR laser chip, 62-chip heat sink, 63-TO56 socket. Detailed Implementation

[0079] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0080] Example 1: As Figure 1 As shown, the present invention provides a wide-temperature-range laser methane detection device based on a DBR laser, including a DBR laser 11, a beam splitter 12, a reference gas chamber 13, a methane gas chamber 14, a first photodetector 15, a second photodetector 16, and a control unit 17.

[0081] A DBR laser 11 is used to emit laser light, and the laser wavelength is adjusted by controlling the current injected into the Bragg reflector 203 of the DBR laser 11; a beam splitter 12 is used to split the laser light output from the DBR laser 11 into two paths; a reference gas chamber 13 is used to seal methane gas of a preset concentration and is set in one of the laser beam splitting paths; a methane gas chamber 14 is used to introduce the methane gas to be tested and is set in the other laser beam splitting path; a first photodetector 15 is used to receive one of the laser lights transmitted through the reference gas chamber 13; a second photodetector 16 is used to receive the other laser light transmitted through the methane gas chamber 14; a control unit 17 receives the detection signals output by the first photodetector 15 and the second photodetector 16, analyzes the detection signal output by the first photodetector 15, calculates the offset of the laser center wavelength caused by changes in ambient temperature, adjusts the injection current of the Bragg reflector 203 of the DBR laser 11 to compensate for the offset of the laser center wavelength, and calculates the concentration of the methane gas to be tested based on the detection signal output by the second photodetector 16.

[0082] like Figure 2 As shown, the DBR laser 11 adopts a three-segment 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 the upper confinement layer 209 and the lower confinement layer 210. The upper confinement layer 209 and the lower confinement layer 210 are separated by a cladding layer between the p-contact layer 204 and the n-InP substrate 212.

[0083] The phase control region 202 and the Bragg reflection region 203 adjust the laser wavelength by current injection. In the Bragg reflection region 203, there is a grating 207 with a periodically changing refractive index inside, which reflects a specific Bragg wavelength to 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. There are a reflective film 213 and an antireflective film 214 on the two end faces of the DBR laser, respectively.

[0084] This embodiment improves the design of the DBR laser 11 and increases its wavelength tuning range through the following measures.

[0085] As mentioned above, the wavelength of the laser emitted by the DBR laser 11 can be obtained by formula (1).

[0086] The wavelength of the laser emitted by the DBR laser 11 is changed by altering the effective refractive index. This is achieved by increasing the current injected into the Bragg reflector 203. Due to the plasma effect of charge carriers, the refractive index of the Bragg reflection decreases, which in turn causes the effective refractive index of the Bragg reflector to decrease, and the Bragg wavelength to shift towards shorter wavelengths. Conversely, when the current injected into the Bragg reflector 203 decreases, the DBR laser wavelength will shift towards longer wavelengths.

[0087] As mentioned earlier, the variation in refractive index of the core layer of the Bragg reflector region based on the carrier plasma effect... It can be represented by formula (2).

[0088] The greater the variable, The greater the variation, the wider the wavelength tuning range of the DBR laser 11. Because... Much larger ,so right Their contribution is even greater.

[0089] Specifically, the design improvements in this embodiment that increase the wavelength tuning range of the DBR laser 11 include:

[0090] 1. In the Bragg reflector region 203, the main core layer 211 is made of InGaAlAs material to reduce the effective electron mass. In this way, in the same There will be a larger [opportunity] below. This means a large wavelength variation. Meanwhile, the active region 201 also uses InGaAlAs for its multi-quantum-well structure. This is necessary for the docking of the active and passive regions, and also because InGaAlAs multi-quantum-wells have high differential gain.

[0091] 2. A carrier confinement layer with a larger bandgap difference is provided between the main core layer 211 and the upper and lower cladding layers to prevent carrier overflow and improve the efficiency of carrier injection under the same circuit conditions. This results in a larger number of electrons being injected. This refers to a large wavelength variation.

[0092] Figure 3 This is a schematic diagram of the interface energy bands when the core layer 211 without a confinement layer is directly sandwiched between the p-InP cladding layer 31 and the n-InP cladding layer 32. In the diagram, e represents electrons and h represents holes. Due to the conduction band difference, and because the interfaces between the p-InP cladding 31, n-InP cladding 32, and the main core layer 211 do not have a sufficiently high barrier to block electrons and holes, as shown by the arrows, electrons can easily cross over. The potential barrier overflows into the cladding. Holes, like electrons, can easily escape the main core layer, thus reducing the potential barrier. and .

[0093] Figure 4 This is a schematic diagram of the interface band structure with a very thin InAlAs confinement layer inserted between the main core layer 211 and the p-InP cladding layers 31 and n-InP cladding layers 32. A p-side carrier blocking layer 33 is added between the p-InP cladding layer 31 and the main core layer 211, and an 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 confinement layers made of InAlAs. In the diagram, e represents electrons and h represents holes. Due to the large energy gap difference between the InAlAs confinement layer and the main core layer 211, electrons and holes collide with a high barrier wall at the interface of the confinement layer and are bounced back to the main core layer 211. In this way, the high barrier layer effectively traps electrons and holes in the main core layer 211, thereby increasing the energy density. and .

[0094] 3. The chip side of the DBR laser 11 is fabricated using a BH structure to prevent the injected current from flowing out laterally and to limit the width of the main core layer 211. This also improves performance under the same circuit injection conditions. value. Figure 5 This is a structural diagram of the BH structure of the DBR laser 11. Specifically, in this embodiment, by reducing the volume of the main core layer 211, the carriers in the main core layer 211 are confined, thereby improving... The length of the core layer 211 is related to the coupling coefficient of the grating and cannot be adjusted arbitrarily. The thickness of the core layer 211 is consistent with the waveguide layer of the active region 201 and cannot be adjusted arbitrarily. Only the width of the core layer can be reduced. Therefore, in the DBR laser 11 fabricated using a BH (buried heterostructure) structure, an InP current blocking layer 35 is used between the p-contact layer 204 and the n-InP substrate 212. This confines the injected current within a narrow, buried strip to prevent lateral current diffusion and also limits the width of the core layer 211, thereby improving both electron injection efficiency and... .

[0095] The aforementioned design improvements can significantly enhance the wavelength tuning range of the DBR laser 11. The existing range is 1.3... The three-segment DBR laser 11 in the band, after adding a 10nm InAlAs confinement layer between the main core layer 211 and the upper and lower cladding layers of the Bragg reflector 203, has a tunable range of over 5nm. According to the carrier plasma effect formula (2) of the DBR laser 11, the emissivity change of the Bragg reflector 203... Proportional to Therefore, in the 1650nm band, which is the band where methane has a strong absorption peak, the tunable range of the DBR laser 11 designed above is greater than 8nm.

[0096] 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 shifts to a longer 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 shifts to a shorter wavelength direction by 0.1 nm.

[0097] When the current injected into the Bragg reflector 203 increases, the effective refractive index of the Bragg reflection decreases due to the plasma effect of charge carriers, causing the Bragg wavelength to shift towards shorter wavelengths. Therefore, the change in the wavelength of the laser emitted by the DBR laser 11 caused by changes in ambient temperature can be corrected by adjusting the current injected into the Bragg reflector 203. This ensures that the center wavelength of the output of the DBR laser 11 remains locked at a constant wavelength at a specific absorption peak of the methane gas being measured.

[0098] In the 1650nm wavelength band, the tunable range of the DBR laser 11 in this embodiment is greater than or equal to 8nm. Specifically, the wavelength drift caused by the ±40℃ change in ambient temperature can be directly compensated by adjusting the current injected into the Bragg reflector 203 of the DBR laser 11. Therefore, in the wide-temperature-range laser methane detection device using the improved DBR laser 11 in this embodiment, it is not necessary to use TEC and thermistors to control the temperature and maintain the laser center wavelength consistent with the absorption peak of methane gas in the 1650nm wavelength band at different ambient temperatures.

[0099] In this embodiment, the control unit 17 outputs a current to the DBR laser 11 to control the output optical power of the DBR laser 11. The recombination current of the injected Bragg reflector 203 at wavelength 11 of the DBR laser is controlled. Auxiliary regulation current of the current in phase control region 202 Composite current It consists of two parts, one of which is the DC section. It is used to control the center wavelength of the DBR laser 11, aligning it with the absorption peak of methane gas. Secondly, it is superimposed on... above A ramp-type scanning current symmetrical to the center value When the ambient temperature changes, the control unit 17 can adjust the settings in a timely manner by analyzing the signal received by the first photodetector 15. and Ensure that the center wavelength of the DBR laser 11 is aligned with the absorption peak of methane gas, and yes The center value. Current injected into phase control region 202. It is used to assist in adjusting the wavelength of the DBR laser.

[0100] The period of the grating 207 is designed appropriately for the Bragg reflector 203. This allows the DBR laser 11 to achieve the desired current value when injected into the Bragg reflector 203 at room temperature (25°C). When the current is at the midpoint of the entire Bragg tuned current range, the center wavelength of the DBR laser 11 coincides with an absorption peak of methane gas (e.g., 1653.7 nm).

[0101] Thus, the current injected into the Bragg reflector 203 can be adjusted up or down by 40°C around 25°C throughout the entire tuning range. That is, by tuning the current injected into the Bragg reflector 203, the wavelength can be adjusted within a temperature range of -15°C to +65°C. Due to design errors and other reasons, at room temperature, when the current injected into the Bragg reflector 203... When the tuning current is at its median value, the auxiliary tuning current of the phase control region 202 can only be adjusted if the center wavelength of the DBR laser 11 still deviates slightly from the methane absorption peak. To compensate, when the current value injected into the Bragg reflector 203 is at the midpoint of the entire tuning current range at room temperature (25°C), the center wavelength of the DBR laser 11 coincides with an absorption peak of methane gas.

[0102] After collimation, a portion of the DBR laser output is split and directed into a reference gas cell 13 containing a certain concentration of methane gas. The intensity of the transmitted light is measured using a first photodetector 15. Then, the injection current of the Bragg reflector 203 is symmetrically scanned near the absorption peak. The output photocurrent intensity of the first photodetector 15 then varies with the scanning current injected into the Bragg reflector 203. Due to the symmetrical scanning, the intensity varies at the center point of the scanning current. This corresponds to the absorption peak of methane, meaning the output photocurrent intensity of the first photodetector 15 has a minimum value at the center point of the scanning current, such as... Figure 6 As shown, when the ambient temperature changes, the center wavelength of the DBR laser 11 shifts, and the location of the aforementioned minimum photocurrent intensity also shifts from the center of the scanning current. The direction and magnitude of this wavelength shift can be determined based on the magnitude and direction of this shift.

[0103] Having determined the direction and magnitude of the wavelength drift of the DBR laser 11, the center value (average value) of the DBR scanning current is adjusted to pull the center wavelength of the DBR laser 11 back to an absorption peak of methane gas (e.g., 1653.7 nm). In this way, the center wavelength of the DBR laser 11 is precisely locked to an absorption peak of methane gas over the entire temperature range.

[0104] The second photodetector 16 is used to receive the DBR laser signal passing through the methane chamber 14 containing the methane gas to be tested, and the control unit 17 analyzes and calculates the concentration of the methane gas to be tested.

[0105] Example 2: Figure 7 As shown, this invention provides a wide-temperature-range laser methane detection method based on a DBR laser. This method employs a wide-temperature-range laser methane detection device based on a DBR laser as described in Example 1, comprising:

[0106] After the output laser beam of the DBR laser 11 is split, one part is incident on the reference gas chamber 13 containing methane gas, and the other part is incident on the methane gas chamber 14 through which the methane gas to be tested is introduced. The laser signal transmitted through the reference gas chamber 13 is received by the first photodetector 15, and the laser signal transmitted through the methane gas chamber 14 is received by the second photodetector 16.

[0107] 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. This concentration is then transmitted to the host system via the control unit 17.

[0108] The control unit 17 analyzes the laser signal received by the first photodetector 15 that has passed through the reference gas cell 13, and injects a composite current into the Bragg reflection region 203 of the DBR laser 11. This composite current is used to control the center wavelength of the laser emitted by the DBR laser 11 when the ambient temperature changes, so that it is aligned with the absorption peak of the methane gas.

[0109] Control unit 17 outputs current to DBR laser 11 to control the output optical power of DBR laser 11. and the current controlling the wavelength of the DBR laser 11, including the composite current. and auxiliary regulating current Composite current It consists of two parts, one of which is the DC component. This is used to control the center wavelength of the DBR laser 11, aligning it with the absorption peak of methane gas. Secondly, it is superimposed on the DC component. above Symmetrical ramp-type scanning current with center value When the ambient temperature changes, the control unit 17 can adjust the DC component in a timely manner by analyzing the signal received by the second photodetector 16. and ramp-type scanning current Ensure that the center wavelength of the DBR laser 11 is aligned with the absorption peak of methane gas, and that the DC component... It is an auxiliary regulating current. The central value of .

[0110] Specifically, the injection current of the Bragg reflector 203 is symmetrically scanned near the absorption peak. The output photocurrent intensity of the first photodetector 15 then varies with the scanning current injected into the Bragg reflector 203. Due to the symmetrical scanning, the absorption peak of methane corresponds to the center point of the scanning current; that is, the output photocurrent intensity of the first photodetector 15 has a minimum at the center point of the scanning current. When the ambient temperature changes, the center wavelength of the DBR laser 11 drifts, and the position of the current intensity minimum shifts away from the center of the scanning current. The direction and magnitude of the wavelength drift of the DBR laser 11 can be determined based on the magnitude and direction of this shift.

[0111] By determining the direction and magnitude of the wavelength drift of the DBR laser 11, and adjusting the center value of the scanning current of the DBR laser 11, the center wavelength of the DBR laser 11 is pulled 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 throughout the entire temperature range.

[0112] Auxiliary regulating current This is used to adjust the correction so that the center wavelength of the laser emitted by the DBR laser 11 is consistent with the wavelength of the methane gas absorption peak when the injected current in the Bragg reflector 203 is at the middle value of the tuning current range at a temperature of 25°C.

[0113] Specifically, the auxiliary regulating current injected into the phase control region 202 This is used to assist in adjusting the center wavelength of the laser emitted by the DBR laser 11. At room temperature, when the injected current into the Bragg reflector 203 is at the median value of the tuning current, if the center wavelength of the DBR laser still deviates from the methane absorption peak, then adjustment is needed. To make corrections.

[0114] The control unit 17 analyzes the laser signal received by the second photodetector 16 that has passed through the methane gas chamber 14, and calculates the concentration of the methane gas to be measured.

[0115] Example 3: Figure 8 As shown, this invention provides an improved wide-temperature-range laser methane detection device based on a DBR laser. This device improves upon the laser methane detection device in Embodiment 3 and includes a DBR laser 11, a beam splitter 12, an integrated device 41 combining a reference gas cell and a first photodetector, a methane gas cell 14, a second photodetector 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 controlling the wavelength of the DBR laser 11 includes a composite current. and auxiliary regulating current The improved wide-temperature-range laser methane detection device has a more compact structure, is easier to assemble, and is also less expensive.

[0116] Figure 9 This is a schematic diagram of an integrated device combining a reference gas chamber 13 and a first photodetector 15. A certain concentration of methane gas is sealed within a TO46 socket 51 and a TO46 cap 53, and combined with a PD chip 52 to form a functional device integrating a reference gas chamber 13 and a first photodetector 15.

[0117] In this embodiment, since the DBR laser 11 does not require TEC temperature control, the DBR laser chip can be packaged in a TO56, which greatly reduces the cost of the DBR laser 11. Figure 10 As shown, the four gold wires connect the positive and negative terminals of the active region 201 and the DC portion of the composite current, respectively. and auxiliary regulating current Since no TEC is needed, the DBR laser chip 61 is directly mounted on the bump of the TO56 socket 63 via the chip heat sink 62, making the packaging very simple.

[0118] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A wide-temperature-range laser methane detection device based on a DBR laser, characterized in that, include: A DBR laser is used to emit laser light, and the laser wavelength is adjusted by controlling the current injected into the Bragg reflector region of the DBR laser. A beam splitter is used to split the laser output from a DBR laser into two paths. The reference chamber is used to seal in methane gas of a preset concentration and is placed in one of the laser beam splitting paths; The methane chamber is used to introduce the methane gas to be tested and is located in another laser beam splitting path. The first photodetector is used to receive one of the laser beams that has passed through the reference gas cell; The second photodetector is used to receive another laser beam that has passed through the methane chamber; The control unit receives detection signals from the first photodetector and the second photodetector, calculates the offset of the laser center wavelength caused by changes in ambient temperature using the detection signal from the first photodetector, compensates for the offset of the laser center wavelength, and calculates the concentration of the methane gas to be measured using the detection signal from the second photodetector. A wide-temperature-range laser methane detection method based on a DBR laser includes the following steps: After the output laser of the DBR laser is split, one part is incident into a reference gas chamber sealed with methane gas of a preset concentration, and the other part is incident into a methane gas chamber in which the methane gas to be tested is introduced. The first photodetector receives the laser signal transmitted through the reference gas cell, and the second photodetector receives the laser signal transmitted through the methane gas cell. The control unit analyzes the laser signal received by the first photodetector and transmitted through the reference gas cell, and adjusts the recombination 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 composite current is used to adjust the center wavelength of the laser emitted by the DBR laser so that it is aligned with the absorption peak of methane gas when the ambient temperature changes. 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 varies with the ramp-type scanning current; The center point of the ramp-shaped scanning current corresponds to an absorption peak of methane gas, causing the photocurrent intensity output by the first photodetector to reach a minimum at the center point of the scanning current. When changes in ambient temperature cause the center wavelength of the laser emitted by the DBR laser to drift, the position of the minimum value of the photocurrent intensity shifts away from 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 center wavelength of the DBR laser with the absorption peak wavelength of 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 methane gas when the temperature is 25°C, the injected current in the Bragg reflection region is the middle value of the tuning current range, and the center wavelength of the laser emitted by the DBR laser is still deviated from the methane absorption peak. The concentration of the methane gas to be measured is calculated by analyzing the laser signal transmitted through the methane gas chamber received by the second photodetector through the control unit.

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

3. The wide-temperature-range laser methane detection device based on a DBR laser according to claim 2, characterized in that, In the DBR laser, a carrier confinement layer is provided between the core layer and the cladding layer of the Bragg reflection region; The carrier confinement layer is made of InAlAs material, and a potential barrier is established through 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 a DBR laser according to claim 1, characterized in that, The DBR laser is fabricated using a BH structure, and the carriers in the main core layer are limited by adjusting the width of the main core layer of the Bragg reflection region in the DBR laser.

5. The wide-temperature-range laser methane detection device based on a 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 center 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 a DBR laser according to claim 1, characterized in that, The DBR laser adopts a TO56 package structure, and the DBR laser chip is mounted on the TO56 socket boss.

7. The wide-temperature-range laser methane detection device based on a DBR laser according to claim 1, characterized in that, The reference gas chamber and the first photodetector are integrated into a single device, and a preset concentration of methane gas is enclosed within this single device.

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