CN111562005A - Fluid control CRDS technology for inhibiting influence of current starting wavelength repeated scanning - Google Patents
Fluid control CRDS technology for inhibiting influence of current starting wavelength repeated scanning Download PDFInfo
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Abstract
The invention discloses a flow control CRDS technology for inhibiting the influence of current turn-on wavelength repeated scanning, which comprises a drive circuit module and a Central Processing Unit (CPU), wherein the drive circuit module is integrated with a temperature control module, a drive current source module, a threshold circuit, a DFB laser and a PD signal control circuit. The threshold circuit in the driving circuit module drives the current source to rapidly close the input current of the laser so as to achieve the effect of chopping the laser and further generate a cavity ring-down signal. When the current source of the threshold circuit driving the laser is turned on again, the detector signal control circuit is triggered to turn off the output signal of the detector in a short time, so that errors caused by repeated scanning of laser wavelength in cavity ring-down detection are avoided. The invention provides a new solution to the problem of repeated scanning of the laser wavelength in current chopping.
Description
Technical Field
The invention relates to the technical field of laser spectrums, in particular to a flow control CRDS technology for inhibiting influence of repeated scanning of current starting wavelength.
Background
From the problem of atmospheric pollution threatening the safe survival of human beings, the development of modern industry and agriculture for improving the living standard of human beings, the scale production of advanced manufacturing industries such as semiconductors and chips, and finally the fields of deep sea, Tibet plateau scientific investigation, polar region detection, large wind tunnel, basic science research and the like, the detection of trace gases, particularly ultra-sensitive trace gases, plays a key role and greatly influences the rapid development of the fields. The laser absorption spectrum technology is that when the frequency of laser resonates with the energy level of target molecules, the laser can be absorbed by the molecules, the particle number concentration of the molecules can be determined by utilizing the size of the absorption amount, and the laser absorption spectrum technology is widely applied to the field of trace gas detection due to the advantages of high sensitivity and high resolution. However, due to the limitation of noise, the detection sensitivity of direct absorption is limited by the detection noise of the system, and the sensitivity is low. There are many laser spectrum techniques for measuring gas developed on the basis of the laser direct absorption spectrum technique, and the cavity ring-down spectroscopy method utilizes a high-fineness optical cavity, the effective absorption length can reach dozens of kilometers, and the measurement is not affected by the laser power fluctuation, so that the detection sensitivity is very high.
Over the past 20 years, various CRDS (cavity ring-down spectroscopy) schemes have been proposed and applied, which are distinctive and complementary. For example, CRDS (cavity ring-down spectroscopy) can be divided into two types, pulse and continuous wave, depending on the type of laser source selected. Among them, the cw cavity ring-down spectroscopy has a higher spectral resolution, a stronger cavity output optical power, and can be applied to a semiconductor laser commonly used in the communication field as a light source, so that it is a preferred solution for the current internationally commercialized high-precision gas analyzers (such as Tiger Optics and picaro series products).
In the conventional CRDS (cavity ring-down spectroscopy), laser emitted from a laser enters a high-fineness ring-down cavity through an acousto-optic modulator (AOM), and then a transmission signal is detected by a photodetector, wherein the detected signal is divided into two paths, and one path enters a threshold circuit to drive the AOM to turn off the laser, so that a cavity ring-down signal is generated. And the other path enters a control circuit to carry out ring-down signal acquisition and data processing. Due to the defects of high price, complex device, large volume, large heat productivity of a driving power amplifier and the like of the AOM, the integration of the cavity ring-down spectrum detection system is limited.
Disclosure of Invention
In order to solve the defects of the prior art, a current control CRDS technology for inhibiting the influence of current starting wavelength repeated scanning is provided, and a new solution is provided for the problem of laser wavelength repeated scanning in current chopping.
The invention provides a flow control CRDS technology for inhibiting the influence of current-on wavelength repeated scanning, which comprises a driving circuit module and a Central Processing Unit (CPU), wherein the driving circuit module is integrated with a temperature control module, a driving current source module, a threshold circuit, a DFB laser and a PD signal control circuit, the driving circuit module drives the DFB laser to emit laser to an optical beam splitter, and the laser is divided into two parts through the optical beam splitter: one part enters the ring-down cavity through the matched lens and the optical isolator, and the signal of the part is detected by the photoelectric detector; the other part enters an analog-digital converter after passing through a wavelength calibration module, wherein detection signals of the photoelectric detector are also divided into two paths: one path of the feedback is fed back to a threshold circuit part in the driving circuit module, a driving current source module in the driving circuit module is driven, the input current of the DFB laser is quickly closed, an acousto-optic modulator is replaced to achieve the effect of chopping the laser, and then a ring-down cavity signal is generated; the other path enters an analog-to-digital converter, and is sent to a computer together with a signal passing through a wavelength calibration module for wavelength calibration, ring-down signal acquisition and data processing, the signal of a Central Processing Unit (CPU) is divided into three paths, and the first path outputs a triangular wave signal for scanning laser wavelength to a driving current source module in a driving circuit module; the second path generates a trigger signal to carry out data acquisition on the analog-to-digital converter; the third path generates four step waves, and controls the high-voltage amplifier to drive PZT of the ring-down cavity to periodically change the cavity length.
As a further improvement of the above scheme, when the threshold circuit in the driving circuit module acts on the driving current source module to turn on again, the signal control circuit of the photodetector is triggered to turn off the output signal of the photodetector in a short time, so as to avoid the error caused by the repeated scanning of the laser wavelength in the ring-down cavity detection.
As a further improvement of the above solution, the driving circuit module monitors the intensity of the laser in the ring-down cavity through the photodetector by using a threshold circuit, when the intensity of the laser in the ring-down cavity reaches a set threshold, the driving current source module in the driving circuit module is triggered to rapidly turn off the current of the DFB laser, so that the intensity of the laser in the ring-down cavity is freely attenuated over time, when the attenuation is completed, the rising edge of the threshold circuit signal controls the driving current source module to turn on the DFB laser, because when the DFB laser is turned on again, the current of the driving current source module changes, the laser wavelength does not reach a stable state before chopping in a short time, the laser wavelength overshoots, the wavelength rescanning effect is generated, and then an interference cavity mode occurs, and the interference cavity mode may trigger the threshold circuit to chop the laser in the unstable state of the laser, therefore, the rising edge of the threshold circuit can be utilized to generate a trigger signal while controlling the driving current source to be switched on, the signal control circuit of the photoelectric detector is triggered to switch off the signal output by the photoelectric detector in a short time, and the output signal of the photoelectric detector is switched off, so that the interference cavity mode can be filtered by the photoelectric detector in the unstable laser state process, and the influence of the instability of the laser wavelength on the detection system is eliminated.
As a further improvement of the above scheme, the transmission signal of the ring-down cavity is focused on a photodetector, and the signal of the photodetector is also divided into two paths: the first path is fed back to a threshold circuit part in the driving circuit module, when the laser and the ring-down cavity resonate, the amplitude of a signal detected at a transmission end of the ring-down cavity is increased, when the amplitude of the signal reaches a threshold value set by a threshold value adjusting knob, the threshold circuit can trigger a current driving module of the ring-down cavity to rapidly turn off the laser by cutting off the injection current of the current driving module, the laser is reflected back and forth in the ring-down cavity, the intensity of the transmitted light is continuously weakened due to absorption loss in the cavity, the intensity change of the transmitted light is detected after the cavity, a ring-down signal with the continuously weakened laser intensity along with the time can be obtained, the turn-off time can be controlled by the threshold value pulse width adjusting knob, after the attenuation process of the laser intensity in the ring-down cavity is ensured, two trigger signals are generated, the first signal controls a driving current source module of the driving circuit module to, within 5ms after the laser is started, the photoelectric detector responds to the interference cavity mode signal to inhibit the repeated scanning of the wavelength, meanwhile, the second path of signal gives a ring-down signal to the analog-to-digital converter for sampling the photoelectric detector, the second path of laser passing through the optical beam splitter calibrates the scanned laser wavelength through the wavelength calibration module, and the etalon signal of the calibrated laser wavelength and the ring-down signal enter the analog-to-digital converter together.
As a further improvement of the scheme, the volume of the driving circuit module is 80mm x 40mm, a temperature control module is integrated on the driving circuit module, a temperature adjusting knob is arranged on the driving circuit module, and the temperature range of the DFB laser can be adjusted to 15-35 ℃; the threshold circuit is provided with a threshold adjusting knob, and the adjustable trigger threshold is 0, 1V-4, 5V; and the threshold pulse width adjusting knob can adjust the pulse width to be 1-20ms, and the time adjusting knob for switching off the PD signal control circuit can adjust the time to be 1-15 ms, wherein the working range of the current for driving the DFB laser is 0-110 mA.
As a further improvement of the scheme, the cavity body of the ring-down cavity is made of invar material with ultralow thermal expansion coefficient, and the thermal expansion coefficient of the invar material is less than 10-7The cavity length is 25cm, the free spectral region FSR is approximately equal to 600MHz, high-reflection-rate cavity mirrors plated at two ends of the cavity of the ring-down cavity by the ultra-low loss ion sputtering coating technology are fixed on two end faces of the cavity by optical vacuum glue, and meanwhile, in order to enable the cavity length to be tuned, a high-performance piezoelectric ceramic push-pull cavity mirror is bonded in front of one cavity mirror to change the position of a longitudinal mode of the cavity, so that the spectral resolution is increased.
The invention has the beneficial effects that:
1. the invention adopts the control of the output current of the driving current source on the driving circuit module to further control the chopping and the starting of the laser power of the DFB laser, and the starting and chopping time reaches ns magnitude;
2. the invention utilizes the fact that when the wavelength is unstable, the response of the photoelectric detector to the cavity mode signal is closed, and the repeated scanning of the laser wavelength generated by cutting off the laser by current is inhibited;
3. according to the invention, the temperature control module, the driving current source module, the threshold circuit module and the DFB laser mounting base are integrated on the circuit board with the size of 80mm x 40mm, so that the system cost is saved, the system volume is reduced, and conditions are provided for engineering and portability;
4. compared with other types of ring-down cavity spectrum technical schemes, the current control system has the advantages of few devices, high signal-to-noise ratio, high spectral resolution, excellent anti-seismic performance and the like.
Drawings
The following detailed description of embodiments of the invention is provided in conjunction with the appended drawings, in which:
FIG. 1 is a diagram of a ring-down cavity spectral detection arrangement that suppresses the wavelength rescanning effect that results from current chopping;
FIG. 2 is an experimentally measured effect of repeated scanning of the laser wavelength at the location of the gas absorption line due to current chopping; in the figure, a concave curve is the position of laser in direct gas absorption, and a square wave signal is laser wavelength overshoot which appears after the laser is chopped at the position of an absorption line by using current modulation;
FIG. 3 is a schematic diagram of suppression wavelength rescanning: wherein, (a) is the main cavity mode and the interference cavity mode signal detected by the photoelectric detector when the wavelength is unstable due to current chopping; (b) under the condition that an interference cavity mode exists, the threshold circuit responds to the disconnection of the laser; (c) ring-down signals including a main cavity mode and an interference cavity mode are detected by the photoelectric detector; (d) in order to trigger the PD signal control circuit by using the rising edge of the threshold circuit, t existing in the interference cavity modefThe response of the photoelectric detector to the cavity mode signal is turned off within time, and then the interference of the cavity mode is suppressed; (e) after the interference cavity mode is filtered, laser induced by a threshold circuit is switched off; (f) detecting a main cavity mode signal required by spectrum detection detected by a photoelectric detector after filtering an interference cavity mode;
the optical fiber coupling device comprises a driving circuit module 1, an optical beam splitter 2, a matching lens 3, an optical isolator 4, a ring-down cavity 5, a photoelectric detector 6, a wavelength calibration module 7, an analog-to-digital converter 8, a computer 9, a high-voltage amplifier 10 and a central processing unit CPU 11.
Detailed Description
As shown in fig. 1, a central processing unit CPU generates a 5Hz triangular wave scanning signal, scans a driving current source in a driving circuit module, and generates laser light which is divided into two parts after passing through a beam splitter: one part of the main cavity mode enters the ring-down cavity after passing through the matched lens and the optical isolator, and the main cavity mode (shown in figure 3) with the interference cavity mode filtered out is completely converted into a ring-down signal by a threshold circuit and a PD signal control circuit in the driving circuit module after interaction of gas, and is detected by a photoelectric detector and sent to an analog-to-digital converter; and the other part enters a wavelength calibration module after passing through a collimator, records etalon amplitude of each ring-down trigger moment and simultaneously sends the etalon amplitude to an analog-to-digital converter. Triggering an analog-to-digital converter to acquire photoelectric detector signals of 5 triangular wave periods by using a 1Hz square wave signal generated by a Central Processing Unit (CPU), fitting each ring-down signal through a computer to obtain ring-down time, recording etalon amplitude corresponding to the ring-down time, and determining a relative wavelength value according to a polynomial obtained in a calibration mode. The CPU simultaneously generates four step waves with the repetition frequency of 0.25Hz synchronous with 1Hz, and the PZT of the ring-down cavity is driven by the high-voltage amplifier to periodically change the cavity length. And the computer performs box-dividing average combination on the relative wavelength values under the four step cavity lengths and the ring-down time corresponding to the relative wavelength values to obtain a spectrum signal. And fitting the spectral line type by adopting a Lorentzian function to determine the gas concentration.
The driving circuit module monitors the intensity of laser in the ring-down cavity through the photoelectric detector by using the threshold circuit, when the intensity of the laser in the ring-down cavity reaches a set threshold, the driving current source module in the driving circuit module is triggered to rapidly turn off the current of the DFB laser, so that the intensity of the laser in the ring-down cavity is freely attenuated along with time, when attenuation is completed, the rising edge of a threshold circuit signal controls the driving current source module to turn on the DFB laser, and when the DFB laser is turned on again, the current of the driving current source module changes, so that the laser wavelength cannot reach a stable state before chopping in a short time, laser wavelength overshoot occurs, a wavelength repeated scanning effect (shown in figure 2) is generated, and then an interference cavity mode occurs, and the interference cavity mode can trigger the threshold circuit to chop the laser in the unstable laser section. Therefore, the rising edge of the threshold circuit is utilized to generate a trigger signal when the laser is turned on again, and the signal control circuit of the photoelectric detector is triggered to cut off the signal output by the photoelectric detector in a short time. Since the output signal of the photodetector is turned off, the interference cavity mode occurred during the unstable state of the laser is filtered by the photodetector, and the influence of the instability of the laser wavelength on the detection system is eliminated (as shown in fig. 3). It can be seen from fig. 2 that the chopping of the laser is very rapid, but when the laser is turned on, the laser wavelength overshoots due to the increase of the current of the driving current source from zero. From fig. 2, it is shown that the maximum time required for the laser to turn on to recover to a stable state is about 5ms, and the time from turning on to recovering to a stable state of wavelength of DFB lasers varies from one DFB laser to another. The experiment of fig. 2 shows that the repeated scanning time of the laser wavelength is about 5ms, and the wavelength repeated time of different DFB lasers is different due to different performance parameters. Therefore, the turn-off time is set in the drive circuit module and can be adjusted to be within the range of 1ms-15ms, and the requirements of different DFB lasers are met. In CRDS (cavity ring-down spectroscopy), the process of turning off the laser is required to be very rapid in order to accurately measure the lifetime of photons within the ring-down cavity. The laser chopping speed of the actually measured driving circuit module is about 200ns, the laser opening speed is about 100ns, and the laser cutting speed is far shorter than the cavity time of the ring-down. The device is simple, convenient to operate and low in cost, and interference signals generated by current chopping are eliminated, so that the current-controlled optical switch can replace an acousto-optic modulator and serve as an optical switch controlled by current. And secondly, the current of the DFB laser can be tuned by using a driving current source module in the driving circuit module, so that laser wavelength scanning is realized, and absorption spectrum measurement or concentration detection of the gaseous medium in the ring-down cavity is realized.
Meanwhile, we add the following components to a drive circuit module with the volume of 80mm by 40 mm: the temperature control module is provided with a temperature adjusting knob and can adjust the temperature range of the DFB laser to 15-35 ℃; the threshold circuit is provided with a threshold adjusting knob, and the adjustable trigger threshold is 0.1V-4.5V; the threshold value pulse width adjusting knob can adjust the pulse width to be 1-20ms, and the time adjusting knob is turned off by the PD signal control circuit and can adjust the time to be 1-15 ms. Wherein the current working range for driving the DFB laser is 0-110 mA.
The DFB laser used in this example was a tunable distributed feedback laser, a 1578nm hydrogen sulfide DFB laser manufactured by NEL corporation of japan as a light source. The DFB laser works under the drive of temperature control and current, and the laser emitted by the DFB laser is divided into 1: 1 into two parts. The first part enters a matching lens and an optical isolator to carry out mode matching, when the longitudinal mode position of the ring-down cavity coincides with the laser frequency, laser is coupled into the ring-down cavity filled with the gas to be detected, and stable resonance is formed in the cavity.
In the example, we build a ring down cavity as follows: the main body of the cavity is made of invar steel with ultralow thermal expansion coefficient, and the thermal expansion coefficient is less than 10-7/° c, the cavity length is 25cm, and the free spectral range FSR ≈ 600 MHz. The two ends of the cavity body adopt high-reflection-rate cavity mirrors plated by an ultra-low-loss ion sputtering coating technology (the fineness of the cavity is about 10 ten thousand), and then the cavity body is fixed on the two end faces of the cavity body by optical vacuum glue. Meanwhile, in order to enable the cavity length to be tuned, a high-performance piezoelectric ceramic push-pull cavity mirror is bonded in front of one cavity mirror to change the position of a longitudinal mode of the cavity, so that the spectral resolution is increased.
The transmission signal of the ring-down cavity is focused on the photoelectric detector, and the signal of the photoelectric detector is also divided into two paths. The first path is fed back to a threshold circuit part in the driving circuit module, when the laser and the ring-down cavity resonate, the amplitude of a signal detected at a transmission end of the ring-down cavity is increased, and when the amplitude of the signal reaches a threshold set by a threshold adjusting knob, the threshold circuit triggers the current driving module of the ring-down cavity to rapidly cut off the laser by cutting off the injection current of the current driving module. The laser is reflected back and forth in the ring-down cavity, the intensity of the transmitted light is continuously weakened due to absorption loss in the cavity, the change of the intensity of the transmitted light is detected behind the cavity, and a ring-down signal that the intensity of the laser is continuously weakened along with the time can be obtained. The turn-off time can be controlled by a threshold pulse width adjusting knob, after the attenuation process of ensuring the laser intensity in the ring-down cavity is finished, two trigger signals are generated, a drive current source module of a first signal control drive circuit module starts the injection current of the drive current source module to rapidly open a light path, and a second trigger PD signal control circuit switches off the response of a photoelectric detector to interference cavity mode signals within 5ms after the laser is started, so that the wavelength repeated scanning effect is inhibited. Meanwhile, the second path of signal gives a ring-down signal to the analog-to-digital converter sampling photoelectric detector.
The second path of laser passing through the optical beam splitter scales the scanned laser wavelength through the wavelength calibration module, and an etalon signal of the scaled laser wavelength and the ring-down signal enter the analog-to-digital converter together.
The central processing unit is a self-made ARM chip and has the functions of:
(1) outputting a triangular wave signal of the scanning laser wavelength to a driving current source module in a driving circuit module;
(2) generating a square wave trigger signal synchronous with the step (1) into an analog-to-digital converter, triggering the analog-to-digital converter, a high-speed data acquisition card and a computer to acquire an etalon signal and a ring-down signal;
(3) and (3) generating four step waves synchronous with the step (2), driving the piezoelectric ceramics on the ring-down cavity through a high-voltage amplifier, and periodically changing the cavity length by the piezoelectric ceramics, so that the position of the cavity mode is changed, the point number of the spectral signal is increased, and the spectral resolution is increased.
And the computer calculates and combines the ring-down signal and the etalon signal which are sampled at 4 cavity lengths corresponding to the step waves to obtain a spectrum signal, and then fits the spectrum line type to determine the gas concentration.
The above embodiments are not limited to the technical solutions of the embodiments themselves, and the embodiments may be combined with each other into a new embodiment. The above embodiments are only for illustrating the technical solutions of the present invention and are not limited thereto, and any modification or equivalent replacement without departing from the spirit and scope of the present invention should be covered within the technical solutions of the present invention.
Claims (6)
1. A current control CRDS technology for inhibiting the influence of current-on wavelength repeated scanning is characterized in that: the drive circuit module is integrated with a temperature control module, a drive current source module, a threshold circuit, a DFB laser and a PD signal control circuit, the drive circuit module drives the DFB laser to emit laser to a light beam splitter, and the laser is divided into two parts through the light beam splitter: one part enters the ring-down cavity through the matched lens and the optical isolator, and the signal of the part is detected by the photoelectric detector; the other part enters an analog-digital converter after passing through a wavelength calibration module, wherein detection signals of the photoelectric detector are also divided into two paths: one path of the feedback is fed back to a threshold circuit part in the driving circuit module, a driving current source module in the driving circuit module is driven, the input current of the DFB laser is quickly closed, an acousto-optic modulator is replaced to achieve the effect of chopping the laser, and then a ring-down cavity signal is generated; the other path enters an analog-to-digital converter, and is sent to a computer together with a signal passing through a wavelength calibration module for wavelength calibration, ring-down signal acquisition and data processing, the signal of a Central Processing Unit (CPU) is divided into three paths, and the first path outputs a triangular wave signal for scanning laser wavelength to a driving current source module in a driving circuit module; the second path generates a trigger signal to carry out data acquisition on the analog-to-digital converter; the third path generates four step waves, and controls the high-voltage amplifier to drive PZT of the ring-down cavity to periodically change the cavity length.
2. The technique of claim 1 for suppressing the effects of current-initiated wavelength rescanning as defined by the following claims, wherein: when the threshold circuit in the driving circuit module acts on the driving current source module to be started again, the photoelectric detector signal control circuit is triggered, the output signal of the photoelectric detector is cut off in a short time, and therefore errors caused by repeated scanning of laser wavelength in ring-down cavity detection are avoided.
3. The technique of claim 2 for suppressing the effects of current-initiated wavelength rescanning as defined by the following claims, wherein: the driving circuit module utilizes a threshold circuit to monitor the laser intensity in the ring-down cavity through a photoelectric detector, when the laser intensity in the ring-down cavity reaches a set threshold, a driving current source module in the driving circuit module is triggered to rapidly cut off the current of the DFB laser, so that the laser intensity in the ring-down cavity is freely attenuated along with time, when the attenuation is completed, the rising edge of a threshold circuit signal controls the driving current source module to turn on the DFB laser, and because when the DFB laser is turned on again, the current of the driving current source module changes, the laser wavelength can not reach a stable state before the ring-down in a short time, laser wavelength overshoot occurs, a wavelength repeated scanning effect is generated, and then an interference cavity mode occurs, and the interference cavity mode can also trigger the threshold circuit to ring-down the laser in the unstable state of the laser, therefore, the rising edge of the threshold circuit can be utilized, the driving current source is controlled to be started, meanwhile, a trigger signal is generated, the signal control circuit of the photoelectric detector is triggered to cut off a signal output by the photoelectric detector in a short time, and the output signal of the photoelectric detector is cut off, so that an interference cavity mode can be filtered by the photoelectric detector in the unstable laser state process, and the influence of instability of laser wavelength on a detection system is further inhibited.
4. The technique of claim 1 for suppressing the effects of current-initiated wavelength rescanning as defined by the following claims, wherein: the transmission signal of the ring-down cavity is focused on a photoelectric detector, and the signal of the photoelectric detector is also divided into two paths: the first path is fed back to a threshold circuit part in the driving circuit module, when the laser and the ring-down cavity resonate, the amplitude of a signal detected at a transmission end of the ring-down cavity is increased, when the amplitude of the signal reaches a threshold value set by a threshold value adjusting knob, the threshold circuit can trigger a current driving module of the ring-down cavity to rapidly turn off the laser by cutting off the injection current of the current driving module, the laser is reflected back and forth in the ring-down cavity, the intensity of the transmitted light is continuously weakened due to absorption loss in the cavity, the intensity change of the transmitted light is detected after the cavity, a ring-down signal with the continuously weakened laser intensity along with the time can be obtained, the turn-off time can be controlled by the threshold value pulse width adjusting knob, after the attenuation process of the laser intensity in the ring-down cavity is ensured, two trigger signals are generated, the first signal controls a driving current source module of the driving circuit module to, within 5ms after the laser is started, the photoelectric detector responds to the interference cavity mode signal to inhibit the wavelength repeated scanning effect, meanwhile, the second path of signal gives a ring-down signal to the analog-to-digital converter for sampling the photoelectric detector, the second path of laser passing through the optical beam splitter calibrates the scanned laser wavelength through the wavelength calibration module, and the etalon signal of the calibrated laser wavelength and the ring-down signal enter the analog-to-digital converter together.
5. The technique of claim 1 for suppressing the effects of current-initiated wavelength rescanning as defined by the following claims, wherein: the volume of the driving circuit module is 80mm x 40mm, a temperature control module and a temperature adjusting knob are integrated on the driving circuit module, and the temperature range of the DFB laser can be adjusted to 15-35 ℃; the threshold circuit is provided with a threshold adjusting knob, and the adjustable trigger threshold is 0, 1V-4, 5V; and the threshold pulse width adjusting knob can adjust the pulse width to be 1-20ms, and the time adjusting knob for switching off the PD signal control circuit can adjust the time to be 1-15 ms, wherein the working range of the current for driving the DFB laser is 0-110 mA.
6. The technique of claim 1 for suppressing the effects of current-initiated wavelength rescanning as defined by the following claims, wherein: the cavity body of the ring-down cavity is made of invar material with ultralow thermal expansion coefficient, and the thermal expansion coefficient of the invar material is less than 10-7The cavity length is 25cm, the free spectral region FSR is approximately equal to 600MHz, high-reflection-rate cavity mirrors plated at two ends of the cavity of the ring-down cavity by the ultra-low loss ion sputtering coating technology are fixed on two end faces of the cavity by optical vacuum glue, and meanwhile, in order to enable the cavity length to be tuned, a high-performance piezoelectric ceramic push-pull cavity mirror is bonded in front of one cavity mirror to change the position of a longitudinal mode of the cavity, so that the spectral resolution is increased.
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Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102053007A (en) * | 2009-10-29 | 2011-05-11 | 龙兴武 | Absolute measuring method for intramembranous loss parameter of high-reflectivity membrane |
| CN105938094A (en) * | 2016-05-26 | 2016-09-14 | 中国人民解放军国防科学技术大学 | Method for eliminating ripple effect in folded cavity ring-down and cavity enhanced absorption spectrum system |
| CN107941467A (en) * | 2017-12-08 | 2018-04-20 | 山西大学 | The method for directly acquiring distributed feedback semiconductor lasing light emitter current-modulation wavelength response |
| CN207457884U (en) * | 2017-11-24 | 2018-06-05 | 内蒙古光能科技有限公司 | A kind of laser current control voltage source of CRDS gas concentration detectors |
| CN109115252A (en) * | 2018-09-21 | 2019-01-01 | 太原理工大学 | A kind of Grating examinations device based on fiber annular cavity-type BPM |
| CN110470622A (en) * | 2019-08-28 | 2019-11-19 | 中国科学院长春光学精密机械与物理研究所 | Gas concentration detection method, apparatus and system |
-
2020
- 2020-05-15 CN CN202010414966.5A patent/CN111562005B/en active Active
Patent Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102053007A (en) * | 2009-10-29 | 2011-05-11 | 龙兴武 | Absolute measuring method for intramembranous loss parameter of high-reflectivity membrane |
| CN105938094A (en) * | 2016-05-26 | 2016-09-14 | 中国人民解放军国防科学技术大学 | Method for eliminating ripple effect in folded cavity ring-down and cavity enhanced absorption spectrum system |
| CN207457884U (en) * | 2017-11-24 | 2018-06-05 | 内蒙古光能科技有限公司 | A kind of laser current control voltage source of CRDS gas concentration detectors |
| CN107941467A (en) * | 2017-12-08 | 2018-04-20 | 山西大学 | The method for directly acquiring distributed feedback semiconductor lasing light emitter current-modulation wavelength response |
| CN109115252A (en) * | 2018-09-21 | 2019-01-01 | 太原理工大学 | A kind of Grating examinations device based on fiber annular cavity-type BPM |
| CN110470622A (en) * | 2019-08-28 | 2019-11-19 | 中国科学院长春光学精密机械与物理研究所 | Gas concentration detection method, apparatus and system |
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