CN117269111A - Optical cavity ring-down spectroscopy system based on dual-optical-path PDH mode locking technology - Google Patents
Optical cavity ring-down spectroscopy system based on dual-optical-path PDH mode locking technology Download PDFInfo
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- G—PHYSICS
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Abstract
The invention discloses an optical cavity ring-down spectrum system based on a double-light-path PDH mode locking technology, which comprises a laser frequency feedback control module, a laser phase polarization modulation module and a beam splitting modulation module. The laser frequency feedback control module utilizes an integrated laser frequency stabilizer to adjust the laser frequency output by the external cavity diode laser. The laser phase polarization modulation module realizes polarization and phase modulation through a Mach-Zehnder modulator and an integrated laser frequency stabilizer. The beam splitting modulation module realizes the generation of two light beams with perpendicular polarization through devices such as an optical fiber beam splitter, a half wave plate, a Faraday rotator, a polarizer and the like, and keeps the real-time locking of the laser frequency. One beam is PDH light and is used for modulating the laser emission frequency; the other beam is probe light for actual measurement. The fast switch ensures that the input of probe light is cut off when a ring down event occurs, thereby reducing interference and improving signal to noise ratio. The invention has higher speed and precision, and improves the efficiency and reliability of spectrum analysis.
Description
Technical Field
The invention relates to an optical cavity ring-down spectroscopy system based on a dual-light path PDH mode locking technology, and belongs to the field of laser spectroscopy.
Background
Cavity Ring-down spectroscopy CRDS (Cavity Ring-Down Spectroscopy) is a high-precision, ultrasensitive spectroscopic measurement technique used to study the light absorption and scattering processes of gas and liquid samples. The basic principle of CRDS is to obtain relevant parameters such as absorption coefficient or scattering coefficient of a sample by measuring exponential decay of light intensity in the sample. In CRDS, light is reflected multiple times within the cavity to form a back and forth propagating beam. As light passes through the sample or solution, it is absorbed or scattered, resulting in a decay in light intensity over time. The CRDS calculates the absorption or scattering characteristics of the sample by mathematical analysis using the decay rate of the light intensity in the decay cavity over time.
In CRDS technology, the frequency stability of the laser is very important for the accuracy and repeatability of the measurement results. Any frequency offset or fluctuation may lead to the introduction of measurement errors. Conventional CRDS techniques have certain limitations in terms of light source frequency stability.
Disclosure of Invention
The invention provides an optical cavity ring-down spectrum system based on a double-light-path PDH mode locking technology, which solves the problems disclosed in the background technology.
In order to solve the technical problems, the invention adopts the following technical scheme: an optical cavity ring-down spectroscopy system based on a dual-light path PDH mode locking technology is characterized in that: the system comprises a laser frequency feedback control module, a laser phase polarization modulation module and a light splitting modulation module;
the laser frequency feedback control module comprises an external cavity diode laser, an optical fiber coupler and an integrated laser frequency stabilizer; the external cavity diode laser is used as a light source, laser light with specific frequency is emitted into the optical fiber coupler, and the optical fiber coupler is used for carrying out optical fiber coupling on the laser;
the laser phase polarization modulation module comprises a Mach-Zehnder modulator, and laser coupled by an optical fiber of an optical fiber coupler is transmitted to the Mach-Zehnder modulator and is subjected to phase and polarization modulation under an integrated laser frequency stabilizer; the laser lock box of the integrated laser frequency stabilizer integrates a waveform generator, a mixer, a low-pass filter and a double-cascade PID controller for PDH locking;
the beam splitting modulation module comprises an optical fiber deconcentrator and a ring-down cavity, the modulated laser enters the optical fiber deconcentrator, and the optical fiber deconcentrator is used for dividing the modulated laser into two parts to form PDH light rays (solid lines in the figure) and detection light rays (broken lines in the figure); after being injected into the ring-down cavity, the PDH light forms an optical signal through reflection, the optical signal is processed and converted by an integrated laser frequency stabilizer, and finally the external cavity diode laser is driven by the generated electric signal;
the probe light enters the ring down cavity where it reflects an infinite number of times to trigger a ring down event.
Further, the beam splitting modulation module further comprises a first half-wave plate, and the first half-wave plate is used for rotating the PDH light polarization modulation by 180 degrees so that the PDH light polarization modulation is perpendicular to the detection light.
Further, the beam splitting modulation module further comprises a first polarization beam splitter, a second half-wave plate, a Faraday rotator and a second polarization beam splitter; after the PDH light polarization is rotated 180 degrees, the PDH light polarization is sequentially input into the ring-down cavity through the first polarization beam splitter, the second half-wave plate, the Faraday rotator and the second polarization beam splitter.
Further, the device also comprises a first photoelectric detector, PDH light is reflected to form an optical signal after being input into the ring-down cavity, the optical signal is reflected into the first photoelectric detector by a reflecting mirror after passing through the second polarization beam splitter, the Faraday rotator, the second half wave plate and the first polarization beam splitter in sequence, the optical signal is received by the first photoelectric detector, and then the first photoelectric detector inputs the optical signal into the integrated laser frequency stabilizer.
Further, the probe light is transmitted into the ring down cavity through a second polarizing beamsplitter.
Further, the fast switch and the second photoelectric detector are further included, when a ring-down event occurs, the fast switch immediately cuts off incidence of detection light, and the second photoelectric detector is used for detecting attenuation of the detection light in the cavity in real time so as to acquire ring-down spectrum data of the optical cavity.
The invention has the beneficial effects that:
1. the invention selects an ECDL external cavity diode laser as a light source, which is a semiconductor laser for controlling the output light frequency by using an external cavity tuning technology, has narrow linewidth, high stability and tuning performance, and becomes an ideal light source selection in the CRDS technology. These characteristics enable ECDL external cavity diode lasers to provide high precision, reliable and flexible light sources for accurate spectroscopic analysis and measurement of CRDS technology. The precision and stability of the device are improved;
2. in the PDH technology section, the invention uses a double-light path PDH technology which is different from the common PDH technology, and divides PDH mode-locked light into two light beams: detecting light and mode locking light. Mode-locked light and probe light enter the ring-down cavity simultaneously in an orthogonal polarization mode, so that ring-down time can be acquired quickly without interrupting PDH locking.
3. The invention uses the optical fiber Mach-Zehnder modulator MZM to replace an acousto-optic modulator, the MZM is used for carrying out frequency movement exceeding 1 gigahertz, the precision can reach millihertz level, and the driving radio frequency signal of the MZM can be cut off by using a fast switch, so that the ring-down event is triggered within 20 nanoseconds. This is a significant improvement over conventionally used acousto-optic modulators where poor attenuation ratio and switching bandwidth can degrade the quality of ring-down measurements.
Drawings
Fig. 1 is a schematic view of a structural light path of the present invention.
Description of the embodiments
The invention is further described below with reference to the accompanying drawings. The following examples are only for more clearly illustrating the technical aspects of the present invention, and are not intended to limit the scope of the present invention.
Noun interpretation: ECDL (external cavity diode laser), MZM (Mach-Zehnder modulator), and integral laser frequency stabilizer
As shown in FIG. 1, the invention discloses an optical cavity ring-down spectrum system based on a dual-optical-path PDH mode locking technology, which consists of a laser frequency feedback control module, a laser phase polarization modulation module and a beam-splitting modulation module, and is mainly implemented by a frequency locking detection system consisting of an ECDL external cavity diode laser, an optical fiber coupler, an MZM Mach-Zehnder modulator, an integrated laser frequency stabilizer, an optical fiber deconcentrator, a half wave plate, a Faraday rotator, a polarization beam splitter, a photoelectric detector and a ring-down cavity. The function of each device and its interrelationship will be described in detail below.
Firstly, an ECDL external cavity diode laser is selected as a light source, which is a semiconductor laser for controlling the output light frequency by using an external cavity tuning technology, and has narrow linewidth, high stability and tuning performance, so that the ECDL external cavity diode laser becomes an ideal light source selection in CRDS technology. These characteristics enable ECDL lasers to provide high precision, reliable and flexible light sources for accurate spectroscopic analysis and measurement of CRDS technology.
The function of the fiber coupler is to perform fiber coupling on the laser light emitted by the ECDL external cavity diode laser and then convey the laser light to the MZM Mach-Zehnder modulator. The optical fiber coupler not only improves the stability of the system, but also ensures that the laser light source can efficiently transmit.
The laser signal is then input to an MZM mach-zehnder modulator and modulated in phase and polarization with an integrated laser frequency stabilizer. The laser lock box of the integrated laser frequency stabilizer integrates a waveform generator, a mixer, a low-pass filter and a two-stage cascade PID controller for locking the PDH, complex electronic equipment required in the traditional PDH technology is integrated together, and the simplicity and the speed of building a system are greatly improved. The MZM mach-zehnder modulator is particularly selected to replace the electro-optic modulator and the acousto-optic modulator used in the conventional PDH technology because the MZM mach-zehnder modulator has high-speed performance, broadband characteristics and low power consumption, can realize very high modulation speed, and is suitable for the requirements of various optical communication systems and different transmission rates. In addition, the MZM mach-zehnder modulator introduces lower distortion due to the phase modulation, maintaining high quality of the optical signal and lower nonlinear distortion. The optical fiber has the characteristics of high stability and easy integration, has small influence of output on environmental factors, and can be easily integrated with other optical components. In combination, the use of MZM Mach-Zehnder modulators provides high quality, high efficiency optical signal transmission, leading to better performance and reliability for PDH technology.
Next, an optical fiber deconcentrator is provided, which functions to divide the modulated laser light into two, forming a PDH light and a probe light, thereby forming a dual optical path system. In fig. 1, two light beams are marked by virtual and real lines, wherein one light beam represents PDH light, the light beam is marked by a solid line, the light beam firstly passes through a first half wave plate, the polarization of the light beam is rotated by 180 degrees, the light beam is perpendicular to the other light beam, and then the PDH light beam is input into a ring-down cavity in a polarization state perpendicular to the other light beam through a second half wave plate, a faraday rotator and the cooperation of a first polarization beam splitter and a second polarization beam splitter, so that the two light beams are not interfered with each other in the detection of an actual ring-down event.
After being injected into the ring-down cavity, PDH light forms an optical signal through reflection, the optical signal is reflected into the first photoelectric detector through a reflecting mirror after passing through a second polarization beam splitter, a Faraday rotator, a second half-wave plate, a first polarization beam splitter and other devices, the optical signal is received by the first photoelectric detector, then is processed and converted through an integrated laser frequency stabilizer, and finally drives an ECDL external cavity diode laser through the generated electric signal, and the emergent laser is subjected to corresponding phase and frequency modulation so as to achieve stable output frequency. The modulation of the ECDL external cavity diode laser by the partially integrated laser frequency stabilizer is high speed.
The other beam in the dual path is the probe light, marked by a dashed line, which is transmitted through the second polarizing beamsplitter into the ring down cavity where it is reflected an infinite number of times to trigger a ring down event. When a ring-down event occurs, the fast switch will immediately intercept the incidence of the probe light and use the second photodetector to detect the attenuation of the probe light in the cavity in real time to obtain the data required by the CRDS.
In this system, the probe light and the PDH light are incident into the cavity simultaneously before the ring-down event occurs, and when the ring-down event occurs, the system only cuts off the incidence of the probe light, while the PDH light remains incident, in order to enable the PDH light to ensure the locking of the laser outgoing laser frequency to the cavity mode in real time, the method can reduce the time required to re-lock the laser mode between the two detections, which can approach the theoretical limit; meanwhile, in the ring-down event and measurement process, the influence of PDH light on detection light is not worried about, and 4000 is arranged between the PDH light and the detection light due to the perpendicular relation of polarization of the PDH light and the detection light in the actual test: a spectral ratio of 1, which means that there is perfect isolation between the PDH light and the probe light signal.
In summary, the workflow of the overall system is as follows: the ECDL external cavity diode laser emits laser with specific frequency, and the laser is input to the MZM Mach-Zehnder modulator through the optical fiber coupler, and then the modulation of phase and polarization is carried out under the control of the signal generator. The modulated laser is divided into PDH light and detection light through the optical fiber deconcentrator, wherein the PDH light is processed to form an electric signal capable of driving the ECDL external cavity diode laser to modulate, and the detection light is reflected and ring-down through the ring-down cavity, so that the incident is triggered and then converted into the acquired data through the second photoelectric detector.
Although the process of manufacturing and operating the complete system requires extremely fine design and strict implementation, the innovation and practicality of this patent is significant. The system can realize the rapid locking of the cavity resonance mode through the design, which clearly improves the convenience and accuracy of experiments greatly.
The PDH technology can rapidly detect the change of the laser frequency by monitoring interference signals in the optical cavity in real time and perform feedback adjustment on the laser in real time so as to keep the frequency stable. By means of the real-time frequency stability and the self-adaptive adjustment capability of the PDH mode locking technology, the CRDS measuring system can offset fluctuation and offset of laser frequency, and therefore accuracy and repeatability of measuring results are improved. By combining the advantages of the CRDS spectrum and the PDH mode locking technology, the high sensitivity and high resolution characteristics of the CRDS can be fully utilized, and meanwhile, the laser frequency is stabilized and regulated in real time by the PDH mode locking technology, so that the frequency stability of the CRDS measuring system is obviously improved. The innovative combination can help to expand the application field of CRDS technology and provide a more accurate and reliable measurement means for the fields of optical analysis, environmental monitoring, chemical research and the like. Therefore, the combination of CRDS spectrum and PDH mode locking technology has important significance for improving the accuracy and reliability of CRDS measurement.
The foregoing is merely a preferred embodiment of the present invention, and it should be noted that modifications and variations could be made by those skilled in the art without departing from the technical principles of the present invention, and such modifications and variations should also be regarded as being within the scope of the invention.
Claims (6)
1. An optical cavity ring-down spectroscopy system based on a dual-light path PDH mode locking technology is characterized in that: the system comprises a laser frequency feedback control module, a laser phase polarization modulation module and a light splitting modulation module;
the laser frequency feedback control module comprises an external cavity diode laser, an optical fiber coupler and an integrated laser frequency stabilizer; the external cavity diode laser is used as a light source, laser light with specific frequency is emitted into the optical fiber coupler, and the optical fiber coupler is used for carrying out optical fiber coupling on the laser;
the laser phase polarization modulation module comprises a Mach-Zehnder modulator, and laser coupled by an optical fiber of an optical fiber coupler is transmitted to the Mach-Zehnder modulator and is subjected to phase and polarization modulation under an integrated laser frequency stabilizer; the laser lock box of the integrated laser frequency stabilizer integrates a waveform generator, a mixer, a low-pass filter and a double-cascade PID controller for PDH locking;
the beam splitting modulation module comprises an optical fiber deconcentrator and a ring-down cavity, the modulated laser enters the optical fiber deconcentrator, and the optical fiber deconcentrator is used for dividing the modulated laser into two parts to form PDH light and detection light; after being injected into the ring-down cavity, the PDH light forms an optical signal through reflection, the optical signal is processed and converted by an integrated laser frequency stabilizer, and finally the external cavity diode laser is driven by the generated electric signal;
the probe light enters the ring down cavity where it reflects an infinite number of times to trigger a ring down event.
2. The dual path PDH mode-locked optical cavity ring-down spectroscopy system according to claim 1, wherein: the beam splitting modulation module further comprises a first half-wave plate, and the first half-wave plate is used for rotating PDH light polarization modulation by 180 degrees to enable the PDH light polarization modulation to be perpendicular to detection light.
3. The dual path PDH mode-locked optical cavity ring-down spectroscopy system according to claim 2, wherein: the light splitting modulation module further comprises a first polarization light splitter, a second half-wave plate, a Faraday rotator and a second polarization light splitter; after the PDH light polarization is rotated 180 degrees, the PDH light polarization is sequentially input into the ring-down cavity through the first polarization beam splitter, the second half-wave plate, the Faraday rotator and the second polarization beam splitter.
4. The dual path PDH mode-locked optical cavity ring-down spectroscopy system according to claim 3, wherein: the PDH light beam is reflected to form an optical signal after being input into the ring-down cavity, the optical signal is reflected into the first photoelectric detector by a reflecting mirror after passing through the second polarization beam splitter, the Faraday rotator, the second half-wave plate and the first polarization beam splitter in sequence, the optical signal is received by the first photoelectric detector, and then the first photoelectric detector inputs the optical signal into the integrated laser frequency stabilizer.
5. The dual path PDH mode-locked optical cavity ring-down spectroscopy system according to claim 3, wherein: the probe light is transmitted into the ring down cavity through the second polarizing beamsplitter.
6. The dual path PDH mode-locked optical cavity ring-down spectroscopy system according to claim 1, wherein: the fast switch immediately cuts off incidence of the detection light when a ring-down event occurs, and the second photoelectric detector is used for detecting attenuation of the detection light in the cavity in real time so as to acquire ring-down spectrum data of the optical cavity.
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