JP2010169625A - Gas detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas detector detecting two or more gases to be detected in a measured atmosphere. <P>SOLUTION: The gas detector includes a wavelength sweep light source 1, which has a semiconductor luminous element 10 emitting wavelength-modulated laser light of a predetermined wavelength width to stride across a line width of an absorption line for distinguishing the detecting object gases and sweep means 11, 12, 13 sweeping the wavelength-modulated laser light, at a sweep speed lower than the modulation speed of wavelength modulation, over a wavelength range containing the absorption lines of detecting object gases and emits the wavelength-modulated laser light into the measured atmosphere 2 containing the detecting object gases; a light-receiving part 3, which receives laser light passing through the measured atmosphere 2 in association with the emission of the laser light from the wavelength sweep light source 1; and a gas detection part 5, which measures the concentration of the detecting object gases in the measured atmosphere 2 using electric signals from the light-receiving part 3 and outputs the measured data. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a gas detection device that performs gas detection using an absorption line of a detection target gas, and more particularly to a gas detection device that can detect a plurality of gases at high speed.

  In recent years, with respect to environmental problems, a technique for detecting a specific gas in the atmosphere is required for reducing greenhouse gas emissions, monitoring air pollutants, and the like.

  The gas molecule has a light absorption characteristic that absorbs light of a specific wavelength according to its type. In general, gas molecules often absorb electromagnetic waves in the infrared region. For example, methane absorbs light having wavelengths of 1.6 μm, 3.3 μm, and 7 μm. Therefore, the presence and concentration of the detection target gas can be detected extremely simply and quickly by emitting laser light having a specific wavelength into the measurement target space and measuring the attenuation state.

  A gas detector using such light absorption characteristics is configured as shown in FIG. 10, for example (see, for example, Patent Document 1).

  In the gas detection device disclosed in Patent Document 1, the light receiving element 131a of the light receiver 131 receives the laser light emitted from the semiconductor laser module 120 and passed through the gas 130 to be measured in the measurement atmosphere to generate a light receiving current. Convert. The gas detector 132 converts the received light current obtained by the light receiver 131 into a voltage signal by the current-voltage converter 133. Further, the gas detection unit 132 detects the detection target gas by the fundamental wave signal detector 134, the second harmonic wave signal detector 135, and the fundamental wave second harmonic wave division unit 136 using the voltage signal, and finally Outputs gas detection signal.

  In order to match the wavelength of the laser light emitted to the gas 130 to be measured with the extremely steep absorption line of the detection target gas, the semiconductor laser module 120 is based on light reception measurement with respect to the reference gas cell in which the detection target gas is sealed. Thus, a laser beam stabilization mechanism that stabilizes the wavelength of the laser beam by adjusting the temperature of the Peltier element is added.

JP 11-326199 A

  However, the conventional gas detection device disclosed in Patent Document 1 can detect only one type of detection target gas because the laser beam stabilization mechanism has only one reference gas cell.

  The present invention has been made to solve such a conventional problem, and an object of the present invention is to provide a gas detection device capable of detecting a plurality of detection target gases contained in a measurement atmosphere. .

  The gas detector of the present invention includes a semiconductor light emitting element that emits laser light that is wavelength-modulated with a predetermined wavelength width so as to straddle the line width of an absorption line for identifying a detection target gas, and the wavelength-modulated laser. Sweeping means for sweeping light at a sweep speed slower than the modulation speed of the wavelength modulation over a wavelength range including an absorption line of a gas to be detected to be measured, and detecting the laser light swept by the wavelength A light source unit that emits into the measurement atmosphere containing the target gas, and a laser beam that passes through the measurement atmosphere as the laser beam is emitted from the light source unit is received as measurement light, and the laser beam that corresponds to the received laser beam A light receiving unit that outputs a signal; and a gas detection unit that measures the concentration of the detection target gas in the measurement atmosphere based on the signal from the light receiving unit and outputs the measurement data. Yes.

  With this configuration, it is possible to detect a plurality of detection target gases contained in the measurement atmosphere.

  The gas detection apparatus of the present invention recognizes the wavelength of the laser light of the semiconductor light emitting element swept by the sweeping means, and outputs a signal corresponding to the recognized wavelength, and the wavelength recognition means When the wavelength recognized by is a wavelength within a predetermined wavelength range for each absorption line, the signal from the light receiving unit is output to the gas detecting unit, and the wavelength recognized by the wavelength recognizing unit is And a signal switch that cuts off the input of the signal to the gas detector when the wavelength is out of the wavelength range.

  With this configuration, even if a large number of gases are mixed in the measurement atmosphere, the type and concentration of each gas in the measurement atmosphere can be easily specified.

  The gas detection apparatus of the present invention recognizes the wavelength of the laser light of the semiconductor light emitting element swept by the sweeping means, and outputs a signal corresponding to the recognized wavelength, and the wavelength recognition means And a storage unit that stores the wavelength recognized by the measurement unit and the measurement data output from the gas detection unit in association with each other.

  With this configuration, it is possible to detect all measured gases included in the wavelength range swept by the sweep means.

  In the gas detection device of the present invention, the light source unit is configured such that the semiconductor light emitting element is formed such that the reflectance of one of the two end surfaces is lower than the reflectance of the other end surface, and the sweep means includes: A diffraction grating that diffracts the light emitted from the one end face of the semiconductor light emitting element, and a rotatable rotating mirror that reflects the light diffracted by the diffraction grating and re-enters the diffraction grating through a reverse optical path. The diffraction grating diffracts the re-incident light and returns it to the one end face of the semiconductor light emitting element, and sweeps the wavelength of the laser light by the rotation of the rotating mirror. The wavelength sweeping light source is used.

  With this configuration, a plurality of detection target gases contained in the measurement atmosphere can be detected by sweeping the wavelength of the laser light emitted in the measurement atmosphere.

  Further, in the gas detection device of the present invention, the light source unit converts the light emitted from the one end face of the semiconductor light emitting element into parallel light, and emits the parallel light to the diffraction grating, and A space sandwiched between a plane extending the reflecting surface of the rotating mirror and a plane extending the diffraction surface of the diffraction grating toward the rotation center position of the rotating mirror, and a predetermined incident position of the diffraction grating and the A fixed mirror disposed at a position between the rotation center position of the rotation mirror and reflecting the parallel light emitted from the collimator lens toward a predetermined incident position of the diffraction grating; An element and the collimating lens are arranged on a space side including the diffraction grating in two spaces separated by a plane obtained by extending a reflection surface of the rotating mirror, and the diffraction grating is connected to the semiconductor light emitting element. The optical path up to the rotation mirror is non-intersecting with respect to the rotation mirror, a distance r from the rotation center position to a predetermined incident position of the diffraction surface of the diffraction grating, and a plane obtained by extending the reflection surface from the rotation center position L2, the optical path length L3 from the effective resonance end face of the semiconductor light emitting element to the fixed mirror, the optical path length L4 from the fixed mirror to a predetermined incident position of the diffraction surface of the diffraction grating, and the diffraction grating to the diffraction grating The relationship of r = (L3 + L4-L2) / sin α is established between the incident angle α and the light incident angle α.

  With this configuration, the configuration of the rotating mirror is simple and the relationship r = (L3 + L4-L2) / sin α is established, so that high-speed continuous wavelength sweeping with respect to the emitted light of the semiconductor light-emitting element is performed without mode hopping. Can do.

  In the gas detection device of the present invention, the light source unit further includes a light emitting element driving unit, and the semiconductor light emitting element includes an active layer on a semiconductor substrate and emits light upon receiving current injection to emit the light. A light emitting region that propagates along the active layer, and a phase adjustment region that includes a waveguide layer optically coupled to the active layer and changes a phase of light emitted by the light emitting region, are arranged in the optical axis direction. The light emitting element driving unit is configured so that a current for emitting light is applied to the light emitting region and a modulation current for modulating the wavelength of the laser light is applied to the phase adjusting region. have.

  With this configuration, since the light intensity of the emitted light from the semiconductor light emitting element does not change depending on the modulation current, modulation distortion can be suppressed and the detection sensitivity of the detection target gas can be improved.

  In the gas detection device of the present invention, the semiconductor light emitting element includes the active layer in which the semiconductor substrate is an n-type semiconductor substrate and the light emitting region is formed on the n-type semiconductor substrate, A first p-type cladding layer stacked on the active layer, wherein the phase adjustment region has an energy gap larger than the energy of the light on the n-type semiconductor substrate, and the light emitting region A waveguide layer optically coupled to the active layer; and a second p-type cladding layer stacked on the waveguide layer, the refractive index of the light from the light emitting region depending on the injection current The doping concentration in the thickness direction of the second p-type cladding layer in contact with the waveguide layer in the phase adjustment region has a maximum value within a predetermined distance from the upper end of the waveguide layer. Having a structure formed as It can have.

  In the gas detection device of the present invention, the range of the predetermined distance may be 25 to 150 nm.

  In the gas detection device of the present invention, a third p-type cladding layer is formed on the first p-type cladding layer in the light emitting region and the second p-type cladding layer in the phase adjustment region, and the third p-type cladding layer includes the third p-type cladding layer. A separation groove having a predetermined width may be formed at a boundary portion between the light emitting region and the phase adjustment region.

In the gas detector of the present invention, the doping concentration at the end point in the thickness direction of the third p-type cladding layer is larger than the doping concentration at the start point in the thickness direction, and 1.0 × 10 ¹⁸ (/ cm ³ ) to It has the structure set to the range of 2.5 * 10 < ¹⁸ > (/ cm < ³ >).

  With this configuration, the waveguide loss can be reduced without increasing the series resistance in the film thickness direction of the light emitting region, and therefore, continuous wavelength sweeping with respect to the emitted light of the semiconductor light emitting element can be performed in a mode hop free manner.

  The present invention provides a gas detection device having an effect of being able to detect a plurality of detection target gases contained in a measurement atmosphere.

The block diagram which shows the structure of the gas detection apparatus of the 1st Embodiment of this invention. Graph showing the light absorption characteristics of the gas to be detected The schematic diagram for demonstrating the conditions for the wavelength sweep light source used for the gas detection apparatus of the 1st Embodiment of this invention to sweep a wavelength continuously. Sectional drawing which shows the semiconductor light-emitting device used for the gas detection apparatus of the 1st Embodiment of this invention The block diagram which shows the structure of the gas detection apparatus of the 2nd Embodiment of this invention. FIG. 4 is an external view, a plan view, and a cross-sectional view showing a semiconductor light emitting element used in a gas detection device of a third embodiment of the present invention Doping concentration distribution diagram of second p-type cladding layer in phase adjustment region Doping concentration distribution diagram of third p-type cladding layer in phase adjustment region The schematic diagram for demonstrating the conditions for the wavelength sweep light source used for the gas detection apparatus of the 4th Embodiment of this invention to sweep a wavelength continuously. Block diagram showing the configuration of a conventional gas detector

Hereinafter, embodiments of a gas detection device according to the present invention will be described with reference to the drawings.
(First embodiment)
FIG. 1 is a block diagram showing a configuration of a first embodiment of a gas detection device according to the present invention.

  That is, as shown in FIG. 1, the gas detection apparatus of the first embodiment emits laser light that is wavelength-modulated with a predetermined wavelength width so as to straddle the line width of the absorption line for identifying the detection target gas. A semiconductor light emitting device 10 that performs wavelength sweeping of the wavelength-modulated laser light at a sweep speed slower than the modulation speed of wavelength modulation over a wavelength range that includes the absorption line of the gas to be detected to be measured (collimating lens 11 , A diffraction grating 12, a rotating mirror 13), and a wavelength swept light source 1 as a light source unit that emits a wavelength swept laser beam into a measurement atmosphere 2 containing a detection target gas. A light receiving unit 3 that receives the laser light passing through the measurement atmosphere 2 as the laser light is emitted as the measurement light, and outputs a current signal corresponding to the received laser light.

  Further, the gas detection device of the present embodiment is configured to change the wavelength of the laser light of the semiconductor light emitting element 10 that has been swept in wavelength by the current voltage converter 4 that converts the current signal output from the light receiving unit 3 into a voltage signal, and the sweep unit. The wavelength detector 6 as a wavelength recognizing means for recognizing and outputting a wavelength information signal corresponding to the recognized wavelength, and the concentration of the detection target gas in the measurement atmosphere 2 using the voltage signal from the current-voltage converter 4 A gas detector 5 that measures and outputs the measurement data.

  And the gas detection apparatus of this embodiment converts into the gas detection part 5 by the current voltage converter 4 when the wavelength detected by the wavelength detection part 6 is a wavelength within the wavelength range predetermined for every absorption line. And a signal switch 7 that outputs the voltage signal thus detected and blocks the input of the voltage signal to the gas detector 5 when the wavelength detected by the wavelength detector 6 is outside the wavelength range.

  For example, the wavelength detector 6 receives a laser beam emitted from the wavelength sweep light source 1 and passes (or attenuates) only a plurality of laser beams of known wavelengths, and the intensity of the output light of the fixed wavelength filter. It is comprised with the light receiving element to detect. An etalon or the like can be used as the fixed wavelength filter. Alternatively, the wavelength detector 6 detects the light intensity of the laser light emitted from the wavelength swept light source 1 by the light receiving element, and performs wavelength sweep based on the wavelength dependence of the laser light intensity of the known wavelength swept light source 1. The wavelength of the laser beam emitted from the light source 1 may be determined.

The signal switch 7 is determined based on the optimum absorption center wavelength λ _{i as} a detection target and the line width of the absorption line for each of the n types (n ≧ 1) of the detection target gases G _i (i = 1 to n). The detection wavelength width Δλ _i is stored. Usually, the detection target gas has a plurality of optimum absorption center wavelengths λ _i (and Δλ _i ), and the signal switch 7 stores them.

As shown in FIG. 2, the absorption center wavelength λ _i has a sufficient distance from the absorption center wavelength λ _j and detection wavelength width Δλ _j (j ≠ i) of other gases including the detection wavelength width Δλ _i. It is necessary to be away. For example, 1653.72 nm and 1 nm may be employed as the absorption center wavelength and detection wavelength width of methane (CH ₄ ), respectively.

  The wavelength swept light source 1 includes a semiconductor light emitting element 10 in which the reflectance of one end face 10a of the two end faces 10a and 10b is lower than the reflectance of the other end face 10b, and one end face 10a of the semiconductor light emitting element 10. A collimating lens 11 that converts the light emitted from the collimating lens 11 into a parallel light, a diffraction grating 12 that diffracts the parallel light emitted from the collimating lens 11, and a diffraction grating that reflects the light diffracted by the diffraction grating 12 in the reverse optical path. And a rotatable mirror 13 that re-enters the light. The diffraction grating 12 diffracts the re-incident light and feeds it back to one end face 10a of the semiconductor light-emitting element 10. It has a structure of a Littman-type external resonance type wavelength sweeping light source that sweeps the wavelength of outgoing light by rotation.

  In the wavelength swept light source having this structure, only a specific wavelength orthogonal to the reflecting surface 13a of the rotating mirror 13 is emitted from the semiconductor light among the wavelength components of the light emitted from the semiconductor light emitting element 10 and diffracted by the diffraction surface 12a of the diffraction grating 12. Return to element 10. As a result, stimulated emission is caused by light of the specific wavelength in the semiconductor light emitting element 10, so that light of the specific wavelength (hereinafter referred to as a resonance wavelength) can be resonated.

  This resonance wavelength is determined by the angle formed by the diffraction surface 12 a of the diffraction grating 12 and the reflection surface 13 a of the rotating mirror 13, the incident angle of the incident light on the diffraction grating 12, the number of engravings of the diffraction grating 12, and the semiconductor light emitting element 10. It is defined by the optical path length from the diffraction grating 12 to the rotating mirror 13, and can be changed by adjusting the angle (or distance) of the reflection surface 13a with respect to the diffraction surface 12a.

Further, the wavelength swept light source 1 includes a light emitting element driving unit 14 that applies a modulation current I _e as a modulation current having a frequency f ₁ for modulating the wavelength of the emitted light to the semiconductor light emitting element 10 described later. The modulation current I _e is a current modulated with the amplitude I _w and the frequency f ₁ (for example, 10 kHz) around the center current value I ₀ .

  Here, as shown in FIG. 3, H1 is a plane obtained by extending the diffraction surface 12a of the diffraction grating 12, H2 is a plane obtained by extending the effective resonance end surface 10c of the semiconductor light emitting element 10, and the reflection surface 13a of the rotating mirror 13 is extended. The obtained plane is designated as H3.

The rotation center position O of the rotation mirror 13 is included in the plane H1 and provided on the diffraction grating 12 side from the position where the plane H1 and the plane H2 intersect. The plane H1 and the plane H3 are provided on the rotation mirror 13. The distance r from the rotation center position O of the rotation mirror 13 to the predetermined incident position P of the light incident on the diffraction grating 12 is set so as to intersect between the rotation center position O and the diffraction grating 12, and the predetermined incidence. The relationship between the effective optical path length L1 from the position P to the semiconductor light emitting element 10, the distance L2 from the rotation center position O of the rotating mirror 13 to the plane H3, and the incident angle α of the light with respect to the diffraction grating 12 satisfies the following expression. By setting each part in this manner, it becomes possible to perform continuous wavelength sweep of the resonance wavelength in a mode-hop-free manner.
r = (L1-L2) / sin α (1)

The gas detection unit 5 includes a fundamental wave signal detector 51 that detects a fundamental wave voltage signal h ₁ that is a signal component of the frequency f ₁ contained in the voltage signal converted by the current-voltage converter 4, and is included in the voltage signal. A second harmonic signal detector 52 for detecting a second harmonic voltage signal h ₂ that is a signal component of the frequency f ₂ that is twice the frequency f ₁ to be detected, and the second harmonic voltage detected by the second harmonic signal detector 52. the concentration of the detection target gas G _i contained a value obtained amplitude of H ₂ signal h ₂ by dividing the fundamental wave signal detector 51 amplitude H ₁ of the fundamental wave voltage signal h ₁ detected by the measurement atmosphere 2 A fundamental second harmonic division unit 53 that outputs the corresponding detection value D _i (= H ₂ / H ₁ ).

  This signal operation (division) is performed because the light received by the light receiving unit 3 causes a level fluctuation to some extent for reasons other than the transmission through the measurement atmosphere 2. This is to perform accurate density detection.

A storage unit 8 that stores the detection value D _i output from the gas detection unit 5 may be provided at the subsequent stage of the gas detection unit 5. The storage unit 8 is also configured to receive the detection wavelength detected by the wavelength detection unit 6, and stores the detection value D _i and the detection wavelength value in association with each other. The data stored in the storage unit 8 can be extracted from the storage unit 8 by an operation signal from an operation unit (not shown), and can be displayed as a detection result on a display unit (not shown).

  Next, the semiconductor light emitting element 10 used in the gas detection device of the present embodiment will be described with reference to the drawings. FIG. 4 is a cross-sectional view of the semiconductor light emitting device 10 cut along the light propagation direction.

  The semiconductor light emitting device 10 includes, for example, an active layer 102 made of InGaAsP (indium, gallium, arsenic, phosphorus) on an n-type semiconductor substrate 101 made of n-type InP (indium / phosphorus). The layer 102 includes an MQW and an SCH layer sandwiching the MQW, a p-type InP cladding layer 103, and a contact layer 104 made of InGaAs (indium gallium arsenide).

  Further, an upper electrode 106 is formed on the contact layer 104, and a lower electrode 105 is deposited on the lower surface of the n-type semiconductor substrate 101.

Next, the operation of the gas detector of the present embodiment configured as described above will be described.
First, by applying a modulation current I _e having a center current value I ₀ , an amplitude I _w , and a frequency f ₁ between the upper electrode 106 and the lower electrode 105 of the semiconductor light emitting element 10 by the light emitting element driving unit 14, The inside of the active layer 102 enters a light emitting state.

The light generated in the active layer 102 propagates along the active layer 102, and in the resonator constituted by the other end face 10 b and the rotating mirror 13, the effective optical path length determined by the refractive index of the active layer 102 and the like. And oscillates at a wavelength λ _e corresponding to the angle formed by the diffraction surface 12 a of the diffraction grating 12 and the reflection surface 13 a of the rotating mirror 13 and the modulation current I _e . Here, the center wavelength λ ₀ of the wavelength λ _e is a resonance wavelength when the center current value I ₀ is applied to the semiconductor light emitting device 10.

As a result, light oscillating with an amplitude λ _w (for example, 10 pm) and a frequency f ₁ around the center wavelength λ ₀ is emitted from the wavelength sweep light source 1 to the measurement atmosphere 2. At this time, as shown in FIG. 1, the 0th-order diffracted light W from the diffraction grating 12 is incident on the wavelength detector 6.

  Note that the light emitted from the wavelength swept light source 1 is distributed into two using a half mirror (not shown), one is emitted to the measurement atmosphere 2, and the other is substituted for the 0th-order diffracted light W of the diffraction grating 12. The light may be incident on the wavelength detector 6.

The light emitted from the wavelength swept light source 1 to the measurement atmosphere 2 is transmitted through the measurement atmosphere 2 and received by the light receiving unit 3 to be converted into a current signal. The current signal converted by the light receiving unit 3 is input to the current-voltage converter 4 and converted into a voltage signal. The voltage signal converted by the current-voltage converter 4 is input to the gas detector 5 via the signal switch 7.
On the other hand, the wavelength of the light emitted from the wavelength swept light source 1 to the wavelength detector 6 is detected by the wavelength detector 6.

Here, a case where the wavelength λ _{e of} the light emitted from the wavelength swept light source 1 is swept from the short wavelength side to the long wavelength side will be described as an example, but the wavelength λ _e is swept from the long wavelength side to the short wavelength side. Needless to say.

When the wavelength λ _i −Δλ _i (i = 1 to n) is detected by the wavelength detector 6, the signal switch 7 is turned on, and the input of the voltage signal to the gas detector 5 is started.

When the wavelength λ _i + Δλ _i is detected by the wavelength detector 6, the signal switch 7 is turned off, and the input of the voltage signal to the gas detector 5 is blocked.

In the period when the signal switch 7 is in the ON state (that is, the period during which the laser beam passes through the wavelength range from λ _i −Δλ _i to λ _i + Δλ _i ) Δt, the voltage signal is the fundamental wave signal detector 51 of the gas detector 5. The fundamental wave voltage signal h ₁ and the second harmonic voltage signal h ₂ are detected.

Then, the fundamental wave the second harmonic divider section 53, a value obtained by dividing the second harmonic amplitude of H ₂ voltage signal h ₂ with an amplitude H ₁ of the fundamental wave voltage signal h ₁ is included in the measurement atmosphere 2 The detection value D _i (= H ₂ / H ₁ ) corresponding to the concentration of the detection target gas G _i is output.

  As described above, the gas detection device of the present embodiment sweeps in the wavelength sweep range including the absorption line of the detection target gas while modulating the wavelength of the emitted light, thereby detecting a plurality of detection targets included in the measurement atmosphere. Gas can be detected.

In addition, since the gas detection device of this embodiment stores in advance a detection wavelength width Δλ _i that differs for each detection target gas, an appropriate processing time is set according to the line width of the absorption line of each detection target gas. be able to.

  Further, the gas detection device of the present embodiment includes a signal switch, so that even if the measurement atmosphere is a mixture of many gases, the type and concentration of each gas in the measurement atmosphere can be easily specified. be able to.

(Second Embodiment)
A second embodiment of the gas detector according to the present invention will be described with reference to the drawings. The description of the same configuration as that of the first embodiment is omitted.

In the first embodiment, gas detection is performed only for n types (n ≧ 1) of detection target gases G _i (i = 1 to n) preset by the signal switch 7. On the other hand, in the second embodiment, all the gases to be measured included in the wavelength range swept by the wavelength sweep light source 1 are detected, and then the presence or absence of the desired gas to be measured is confirmed. Yes.

As shown in FIG. 5, the gas detection device of the second embodiment does not include the signal switch 7 in the first embodiment. Similarly to the first embodiment, the detected value D _{i of the} gas to be measured calculated by the fundamental second harmonic division unit 53 is input to the storage unit 8. Further, the detection wavelength detected by the wavelength detection unit 6 is also input to the storage unit 8.

  In the present embodiment, the storage unit 8 stores the detection results of all the gases to be measured included in the wavelength range swept by the wavelength sweep light source 1 and the detection wavelength values received from the wavelength detection unit 6 in association with each other. For example, the data of the desired gas to be measured can be extracted from the storage unit 8 by an operation signal from the operation unit 9 and displayed as a detection result on a display unit (not shown).

(Third embodiment)
A third embodiment of the gas detector according to the present invention will be described with reference to the drawings. The description of the same configuration as in the first and second embodiments is omitted.

  That is, as shown in FIG. 6, the gas detector of the third embodiment replaces the semiconductor light emitting element 10 and the light emitting element driving unit 14 of the first and second embodiments with two end faces 20 a and 20 b. The semiconductor light emitting element 20 and the light emitting element drive part 44 in which the reflectance of one end surface 20a is lower than the reflectance of the other end surface 20b are provided. 6A is an external view of the semiconductor light emitting element 20, FIG. 6B is a plan view, and FIG. 6C is a cross-sectional view taken along line AA of FIG. 6B.

As shown in FIG. 6C, the light emitting element driving unit 44 applies a current I _e for emitting light to the light emitting region 22 of the semiconductor light emitting element 20 described later, and adjusts the phase of the semiconductor light emitting element 20 described later. A modulation current I _pc for modulating the wavelength of light is applied to the region 23.

The modulation current I _pc is a current modulated with the amplitude I _pcw and the frequency f ₁ (for example, 10 kHz) around the center current value I _pc0 .

The semiconductor light emitting element 20 has an n-type semiconductor substrate 21 made of InP (hereinafter simply referred to as the substrate 21). The substrate 21 has a substantially constant doping concentration (for example, 1 × 10 ¹⁸ / cm ³ ).

  A light emitting region 22 that emits light is formed on one end side (right end side in FIGS. 6B and 6C) on the substrate 21, and the other end side (left end side in FIGS. 6B and 6C). Is formed with a phase adjustment region 23 for changing the phase of light emitted by the light emitting region 22.

  In the light emitting region 22, an active layer 24 made of InGaAsP is formed at a substantially constant width (for example, 5 μm) in the center on the substrate 21, and a first p-type cladding layer 25 made of InP has a predetermined thickness (for example, 250 nm). ). Note that the active layer 24 referred to here includes an MQW and an SCH layer sandwiching the MQW.

  On the other hand, a waveguide layer 26 made of InGaAsP is formed in the center on the substrate 21 on the phase adjustment region 23 side so as to be optically coupled to the active layer 24. Here, the active layer 24 has a gain with respect to light in a certain wavelength range and is formed so as to propagate the light in the length direction, whereas the waveguide layer 26 mainly guides the light. Although it has a wave action, it may have a gain for the light.

When carriers are injected by the application of the modulation current I _pc from the light emitting element driver 44, the effective refractive index of the waveguide layer 26 decreases due to the plasma effect. As a result, the phase of the light transmitted through the waveguide layer 26 changes, so that the wavelength of the laser light emitted from the wavelength sweep light source 1 including the semiconductor light emitting element 20 is modulated.

  The energy gap of the waveguide layer 26 is set to be larger than the energy of the light, and the light is not absorbed by the waveguide layer.

  A second p-type cladding layer 27 is formed on the waveguide layer 26 so as to be continuous with substantially the same thickness as the first p-type cladding layer 25. The connection position of the active layer 24 and the waveguide layer 26 and the connection position of the first p-type cladding layer 25 and the second p-type cladding layer 27 are the same.

  A third p-type cladding layer 28 made of InP is formed on and on the first p-type cladding layer 25 and the second p-type cladding layer 27.

  A buried layer 29 made of p-type InP is formed on the substrate 21 on the side of the active layer 24, and a buried layer 30 made of n-type InP is formed on the buried layer 29. .

  The boundary between the light emitting region 22 and the phase adjusting region 23 of the third p-type cladding layer 28 is a bridge portion 31 where the active layer 24 and the waveguide layer 26 are optically coupled, and regions on the left and right sides thereof. It is comprised from the isolation | separation groove | channels 32 and 33 provided in this. The bridge portion 31 has, for example, a length of 50 μm, a width of 15 μm, and a depth of about 7.5 μm with respect to the size of the semiconductor light emitting element 20 (for example, a length of 1000 μm, a width of 400 μm, and a thickness of 100 μm).

  The separation grooves 32 and 33 are formed not only by the third p-type cladding layer 28 but also by performing an etching process deeper than the interface between the buried layers 29 and 30 and the substrate 21.

  The length of the bridging portion 31 in the element length direction is advantageously longer in order to obtain a high separation resistance. However, when the active region length decreases, the emission intensity decreases or the phase adjustment region length decreases. Since the phase adjustment amount decreases, it is preferable to set the range of 25 μm to 100 μm.

  Further, the narrower the width of the bridging portion 31 is, the higher the separation resistance is. However, it is necessary to provide a margin for the width of the active layer 24 and the waveguide layer 26 (for example, 5 μm), and the light spot size is large. In consideration of the above, it is preferable to set the range of 10 μm to 20 μm. The depth is preferably in the range of 5 μm to 10 μm because etching of holes deeper than the interface between the substrate 21 and the buried layers 29 and 30 can be restricted.

  A contact layer 34 made of InGaAs is formed on the third p-type cladding layer 28 on the light emitting region 22 side with the separation grooves 32 and 33 as a boundary, and on the third p-type cladding layer 28 on the phase adjusting region 23 side. Similarly, a contact layer 35 made of InGaAs is formed, and a first upper electrode 36 made of gold (Au), platinum (Pt), and titanium (Ti) is formed on each contact layer 34, 35. Two upper electrodes 37 are formed by vapor deposition. A lower electrode 38 made of gold (Au), germanium (Ge), and platinum (Pt) is formed on the entire lower surface of the substrate 21 by vapor deposition.

  By the way, in the conventional semiconductor light emitting device having the phase adjustment region, the conduction band discontinuity ΔEc between the waveguide layer and the p-type cladding layer in the phase adjustment region is small. There is a problem that the amount of phase adjustment is limited.

  As a result of conducting various experiments on the semiconductor light emitting device 20 having the above structure, the applicant of the present invention has a characteristic distribution in the doping concentration of the second p-type cladding layer 27 on the waveguide layer 26 in the phase adjustment region 23, that is, a conductive distribution. It has been found that the maximum phase adjustment range can be expanded without flowing useless current by suppressing the overflow in the phase adjustment region 23 by giving a distribution having a maximum within a predetermined distance from the waveguide layer 26.

  FIG. 7 shows this configuration. As a result of various experiments, the doping concentration in the thickness direction of the second p-type cladding layer 27 in contact with the waveguide layer 26 in the phase adjustment region 23 as in the characteristic F is within a predetermined range from the upper end of the waveguide layer 26, particularly 25. By forming so as to have a maximum value within a range of ˜150 nm, the effect of suppressing the overflow of injected carriers in the phase adjustment region 23 is enhanced, and it is not necessary to flow a useless current that does not contribute to the change in the refractive index. It was found that high efficiency of the entire device can be realized. The characteristic F ′ is an example of an actual doping concentration distribution.

  Thus, it has been found that setting the maximum position relatively close to the waveguide layer 26 is effective in blocking carriers (electrons) that diffuse as reactive currents. In particular, improvement in efficiency in the high implantation region was confirmed.

  The doping profile of the third p-type cladding layer 28 is important for determining the series resistance and the waveguide loss.

If the series resistance in the film thickness direction of the light emitting region 22 is high, mode hops are likely to occur. This is a phenomenon that occurs because the refractive index changes due to Joule heat generated by current injection, resulting in a long wave. Although it referred to as a single mode from the mode current difference to change the mode of the next-hop current I _hop in the injected current Fabry-Perot modes, the higher the mode hopping current I _hop, stable operation in one mode This is preferable because the range is wide.

That is, in order to increase the mode hop current I _hop , it is desirable to set the doping concentration high and lower the series resistance. On the other hand, if the doping concentration in the region close to the active layer 24 and the waveguide layer 26 is set high, the loss increases.

  Therefore, the doping profile of the third p-type cladding layer 28 is such that the series resistance of the entire third p-type cladding layer 28 becomes a predetermined value that does not cause mode hops, and the lower layer region close to the active layer 24 and the waveguide layer 26. It is necessary to make it low at (starting point portion in the thickness direction).

The characteristic of one doping profile is shown in FIG. In this characteristic H, the doping concentration is changed from the lower layer region (starting portion in the thickness direction) close to the active layer 24 and the waveguide layer 26 to the active layer 24 and the upper layer region far from the waveguide layer 26 (end portion in the thickness direction). Toward, it is gradually increased to 3.0 × 10 ¹⁷ , 8.5 × 10 ¹⁷ , and 1.8 × 10 ¹⁸ (/ cm ³ ). As a result, the series resistance value of 0.5Ω is obtained. Empirically speaking, the series resistance is preferably 0.7Ω or less. For this purpose, the doping concentration at the end point in the thickness direction is set to 1.0 × 10 ¹⁸ (/ cm ³ ) to 2.5 × 10 ¹⁸ ( / Cm ³ ) has been confirmed.

  Further, by limiting the layer thickness t to the range of 2 μm to 3.2 μm, the loss from the vicinity of the waveguide layer 26 is reduced, and the separation resistance from the light emitting region 22 to the phase adjusting region 23 is set to 1 kΩ. I was able to. If the layer thickness t of the third p-type cladding layer 28 is made smaller, the separation resistance can be further increased, but it becomes smaller than the spot size of the emission end face, increasing the loss and making it impossible to guide the wave. Also, if the layer thickness is larger than 3.2 μm, the resistance of the third p-type cladding layer 28 decreases and the isolation resistance between the regions decreases, so the above-mentioned layer thickness range is preferable.

  In FIG. 8, the doping concentration is increased in three steps. However, the number of change steps may be two or four or more, or may be increased linearly, and the step change and the linear change are changed. You may use together.

Next, the operation of the gas detector of the present embodiment configured as described above will be described.
First, a predetermined current (several hundred mA to 1 A) is applied between the first upper electrode 36 and the lower electrode 38 on the light emitting region 22 side of the semiconductor light emitting element 20 by the light emitting element driving unit 44, whereby the active layer 24. The inside becomes a light emitting state.

The light generated in the active layer 24 propagates along the active layer 24 and the waveguide layer 26, and is guided to the active layer 24 in the resonator constituted by the other end face 20b, the diffraction grating 12, and the rotating mirror 13. It oscillates at a resonance wavelength λ ₀ corresponding to the effective optical path length determined by the refractive index of the waveguide layer 26 and the angle formed by the diffraction surface 12 a of the diffraction grating 12 and the reflection surface 13 a of the rotating mirror 13.

  In the above description, the reflectance of one end surface 20a on the phase adjustment region 23 side is lower than the reflectance of the other end surface 20b on the light emitting region 22 side, but the other end surface 20b on the light emitting region 22 side is used. May be configured to be lower than the reflectance of one end face 20a on the phase adjustment region 23 side, and the diffraction grating 12 and the rotating mirror 13 may be disposed on the light emitting region 22 side.

Next, a modulation current I _pc having a center current value I _pc0 , an amplitude I _pcw , and a frequency f ₁ is applied between the second upper electrode 37 and the lower electrode 38 on the phase adjustment region 23 side by the light emitting element driving unit 44. Is done. By applying the modulation current I _pc , light oscillating with an amplitude λ _w (for example, 10 pm) and a frequency f ₁ is emitted from the wavelength sweep light source 1 to the measurement atmosphere 2.

  Subsequent operations relating to the wavelength detector 6, the light receiver 3, the current-voltage converter 4, and the gas detector 5 are the same as those in the first embodiment, and a description thereof will be omitted.

  As described above, in the gas detection device of this embodiment, since the light intensity of the emitted light of the semiconductor light emitting element does not change depending on the modulation current, it is modulated as compared with the gas detection devices of the first and second embodiments. Distortion can be suppressed and the detection sensitivity of the detection target gas can be improved.

  In addition, since the gas detection device of this embodiment can reduce the waveguide loss without increasing the series resistance in the film thickness direction of the light emitting region, it performs continuous wavelength sweep on the emitted light of the semiconductor light emitting element in a mode hop free manner. be able to.

(Fourth embodiment)
A gas detection device according to a fourth embodiment of the present invention will be described with reference to the drawings. The description of the same configuration as in the first to third embodiments is omitted.

  FIG. 9 shows a configuration of a main part of the wavelength swept light source 40 used in the present embodiment.

  The wavelength swept light source 40 parallels the semiconductor light emitting elements 10 and 20 used in the first to third embodiments and the light emitted from one end face 10a or 20a which is a low reflection end face of the semiconductor light emitting elements 10 or 20. A collimating lens 81 that converts light, a fixed mirror 83 that reflects parallel light emitted from the collimating lens 81 toward a predetermined incident position G of a diffraction surface 82a of a diffraction grating 82, which will be described later, and a light reflected from the fixed mirror 83. A rotating mirror 84 having a diffraction grating 82 for diffracting light and a reflecting plate 85 for reflecting light of only a wavelength component perpendicularly incident on the diffracted light diffracted by the diffraction grating 82 to the diffraction grating 82 through a reverse optical path. It is composed of

  Here, a plane obtained by extending the diffraction surface 82a of the diffraction grating 82 is H1, a plane obtained by extending the effective resonance end faces 10c and 20c in consideration of the refractive index inside the semiconductor light emitting devices 10 and 20 is H2, and the reflection surface of the reflector 85 A plane obtained by extending 85a is defined as H3.

  The fixed mirror 83 is disposed in a space between the plane H3 and the plane H1 and between the rotation center position O and the predetermined incident position G of the diffractive surface 82a. Further, the semiconductor light emitting elements 10 and 20 and the collimating lens 81 are arranged in a space including the diffraction grating 82 out of two spaces defined by the plane H3. Further, the optical path from the semiconductor light emitting elements 10, 20 to the diffraction grating 82 is non-intersecting with respect to the rotating mirror 84.

  The angle of the reflection surface 85a of the reflection plate 85 with respect to the diffraction surface 82a of the diffraction grating 82 is periodically changed within a predetermined angle range by a driving device (not shown) around the rotation center position O, thereby reflecting The wavelength of the light returned to the semiconductor light emitting elements 10 and 20 by the reverse optical path is continuously and periodically changed by the surface 85a. Along with this, the wavelength of the laser light emitted from the wavelength sweep light source 40 also changes continuously and periodically.

  Here, the rotation frequency (corresponding to the wavelength sweep speed) of the reflecting plate 85 is, for example, 700 Hz. The frequency of the modulation current applied to the semiconductor light emitting elements 10 and 20 is, for example, 10 kHz.

9, the optical path length L3 from the effective resonance end faces 10c, 20c of the semiconductor light emitting elements 10 and 20 to the fixed mirror 83, the optical path length L4 from the fixed mirror 83 to the predetermined incident position G, and the reflector of the rotating mirror 84 The relationship between the distance L2 from the rotation center position O to the plane H3, the distance r from the rotation center position O to the predetermined incident position G of the diffraction grating 82, and the incident angle α of light with respect to the diffraction grating 82 is as follows. By setting each part so as to satisfy the following equation, it is possible to perform continuous wavelength sweeping in a mode hop-free manner.
r = (L3 + L4-L2) / sin α (2)

  Further, since light is incident on the diffraction grating 82 via the fixed mirror 83 and the reflecting plate 85 and the optical path do not cross each other, it is not necessary to provide a hole for passing light in the reflecting plate 85, and the rigidity thereof. Deformation due to the reduction does not occur, and a stable and high-speed wavelength sweep can be performed even with a thin plate.

  As described above, the gas detection device of this embodiment can further improve the detection sensitivity of the detection target gas because the wavelength sweep light source can perform mode hop-free, high-speed and stable continuous wavelength sweep. .

1, 40 wavelength swept light source (light source)
2 Measurement atmosphere 3 Light receiving part 5 Gas detection part 6 Wavelength detection part (wavelength recognition means)
7 Signal switch 8 Storage unit 10, 20 Semiconductor light emitting element 10a, 20a One end face 10b, 20b The other end face 10c, 20c Effective resonance end face 11, 81 Collimator lens (sweep means)
12, 82 Diffraction grating (sweep means)
12a, 82a Diffraction surface 13, 84 Rotating mirror (sweep means)
13a Reflecting surface 14, 44 Light emitting element driving unit 21 n-type semiconductor substrate 22 light emitting region 23 phase adjusting region 24 active layer 25 first p-type cladding layer 26 waveguide layer 27 second p-type cladding layer 28 third p-type cladding layer 32, 33 Separation groove 83 Fixed mirror 85 Reflecting plate 85a Reflecting surface

Claims (10)

A semiconductor light emitting element (10, 20) that emits laser light that is wavelength-modulated with a predetermined wavelength width so as to straddle the line width of an absorption line for identifying a detection target gas, and the wavelength-modulated laser light, Sweeping means (11, 12, 13, 81, 82, 84) for sweeping the wavelength at a sweep speed slower than the modulation speed of the wavelength modulation over the wavelength range including the absorption line of the detection target gas to be measured; A light source unit (1, 40) that emits the wavelength-swept laser light into a measurement atmosphere (2) containing the detection target gas;
A light receiving unit (3) that receives, as measurement light, laser light that passes through the measurement atmosphere as the laser light is emitted from the light source unit, and outputs a signal corresponding to the received laser light;
A gas detection device comprising: a gas detection unit (5) that measures the concentration of the detection target gas in the measurement atmosphere based on the signal from the light receiving unit and outputs the measurement data. Wavelength recognition means (6) for recognizing the wavelength of the laser light of the semiconductor light emitting element swept by the sweep means and outputting a signal corresponding to the recognized wavelength;
When the wavelength recognized by the wavelength recognizing unit is a wavelength within a predetermined wavelength range for each absorption line, the signal from the light receiving unit is output to the gas detecting unit and recognized by the wavelength recognizing unit. 2. The gas detection according to claim 1, further comprising: a signal switch (7) that cuts off the input of the signal to the gas detection unit when the measured wavelength is outside the wavelength range. apparatus. Wavelength recognition means (6) for recognizing the wavelength of the laser light of the semiconductor light emitting element swept by the sweep means and outputting a signal corresponding to the recognized wavelength;
The gas detection according to claim 1, further comprising a storage unit (8) for storing the wavelength recognized by the wavelength recognition unit and the measurement data output from the gas detection unit in association with each other. apparatus. The light source unit is
The semiconductor light emitting element is formed such that the reflectance of one of the two end faces (10a, 20a) is lower than the reflectance of the other end face (10b, 20b),
The sweeping means diffracts the light emitted from the one end face of the semiconductor light emitting element (12, 82), and reflects the light diffracted by the diffraction grating to the diffraction grating through a reverse optical path. A rotatable mirror (13, 84) for re-incidence,
The diffraction grating diffracts the re-entered light and feeds it back to the one end face of the semiconductor light emitting element, and comprises a Littman-type wavelength swept light source that sweeps the wavelength of the laser light by rotating the rotating mirror. The gas detection device according to claim 1, wherein the gas detection device is a gas detection device. The light source unit is
A collimating lens (81) for converting light emitted from the one end face of the semiconductor light emitting element into parallel light, and emitting the parallel light to the diffraction grating;
A space sandwiched between a plane extending the reflecting surface of the rotating mirror and a plane extending the diffraction surface of the diffraction grating toward the rotation center position of the rotating mirror, and a predetermined incident position of the diffraction grating and the A fixed mirror (83) arranged at a position between the rotation center position of the rotation mirror and reflecting the parallel light emitted from the collimating lens toward a predetermined incident position of the diffraction grating;
The semiconductor light emitting element and the collimating lens are arranged on the space side including the diffraction grating among two spaces separated by a plane extending the reflection surface of the rotating mirror,
An optical path from the semiconductor light emitting element to the diffraction grating is non-intersecting with respect to the rotating mirror;
A distance r from the rotation center position to a predetermined incident position of the diffraction surface of the diffraction grating, a distance L2 from the rotation center position to a plane extending the reflection surface, and the fixed from the effective resonance end face of the semiconductor light emitting device Between the optical path length L3 to the mirror, the optical path length L4 from the fixed mirror to the predetermined incident position of the diffraction surface of the diffraction grating, and the light incident angle α from the fixed mirror to the diffraction surface of the diffraction grating,
r = (L3 + L4-L2) / sin α
The gas detection device according to claim 4, wherein: The light source unit further includes a light emitting element driving unit (44),
The semiconductor light emitting element is
On the semiconductor substrate (21),
A light emitting region (22) including an active layer (24), emitting light upon receiving current injection and propagating the light along the active layer;
A waveguide layer (26) optically coupled to the active layer, and a phase adjustment region (23) for changing the phase of light emitted by the light emitting region, is formed in the optical axis direction;
A current for emitting light is applied to the light emitting region by the light emitting element driver, and a modulation current for modulating the wavelength of the laser light is applied to the phase adjustment region. The gas detection device according to any one of claims 1 to 5. The semiconductor light emitting element is
The semiconductor substrate is an n-type semiconductor substrate;
The light emitting region includes the active layer formed on the n-type semiconductor substrate, and a first p-type cladding layer (25) stacked on the active layer,
The waveguide layer having an energy gap larger than the energy of the light on the n-type semiconductor substrate and optically coupled to the active layer of the light emitting region; and A second p-type cladding layer (27) laminated thereon, and a refractive index for light from the light emitting region changes according to an injection current,
The second p-type cladding layer in contact with the waveguide layer in the phase adjustment region is formed so that a doping concentration in a thickness direction has a maximum value within a predetermined distance from an upper end of the waveguide layer. The gas detection device according to claim 6.   The gas detection device according to claim 7, wherein the range of the predetermined distance is 25 to 150 nm.   A third p-type cladding layer (28) is formed on the first p-type cladding layer in the light emitting region and the second p-type cladding layer in the phase adjusting region, and the light emitting region and the phase adjusting region in the third p type cladding layer are formed. The gas detection device according to claim 7 or 8, wherein a separation groove (32, 33) having a predetermined width is formed at a boundary portion between the gas detection device and the gas detection device. The doping concentration at the end point in the thickness direction of the third p-type cladding layer is larger than the doping concentration at the start point in the thickness direction, and 1.0 × 10 ¹⁸ (/ cm ³ ) to 2.5 × 10 ¹⁸ (/ cm ^3). The gas detection device according to claim 9, wherein the gas detection device is set within a range.

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