CN116299506A - Optical comb absolute distance measurement system - Google Patents

Optical comb absolute distance measurement system Download PDF

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Publication number
CN116299506A
CN116299506A CN202310150661.1A CN202310150661A CN116299506A CN 116299506 A CN116299506 A CN 116299506A CN 202310150661 A CN202310150661 A CN 202310150661A CN 116299506 A CN116299506 A CN 116299506A
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polarization
optical comb
power amplification
optical
sampling
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Chinese (zh)
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胡明列
刘润民
宋有建
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Tianjin University
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Tianjin University
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
    • G01S17/02—Systems using the reflection of electromagnetic waves other than radio waves
    • G01S17/06—Systems determining position data of a target
    • G01S17/08—Systems determining position data of a target for measuring distance only
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
    • G01S7/483—Details of pulse systems
    • G01S7/484—Transmitters
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
    • G01S7/483—Details of pulse systems
    • G01S7/486—Receivers
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A90/00—Technologies having an indirect contribution to adaptation to climate change
    • Y02A90/10—Information and communication technologies [ICT] supporting adaptation to climate change, e.g. for weather forecasting or climate simulation

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • General Physics & Mathematics (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Remote Sensing (AREA)
  • Electromagnetism (AREA)
  • Lasers (AREA)

Abstract

The invention discloses an optical comb absolute distance measurement system, which comprises: the device comprises a double optical comb generating module, a power amplifying module, an asynchronous optical sampling module and a measurement control unit, wherein the double optical comb generating module is used for generating double-wavelength double optical comb mode locking pulses; the power amplification module is used for carrying out power amplification and narrow-band spectral filtering on the dual-wavelength dual-optical comb mode-locked pulse, and the dual-wavelength dual-optical comb mode-locked pulse is output in two paths through a power amplification first output end and a power amplification second output end; the asynchronous optical sampling module is used for sampling the dual-wavelength dual-optical comb mode locking pulse after power amplification and narrow-band spectrum filtering to generate an interference signal or a cross-correlation signal with distance information; the measurement control unit is used for calculating a distance measurement value carried in an interference signal or a cross-correlation signal based on the repetition frequency of the local oscillation sampling pulse output by the second power amplification output end, and is also used for correcting the working state of the double optical comb generating module based on the interference signal or the cross-correlation signal output by the output end of the asynchronous optical sampling module.

Description

Optical comb absolute distance measurement system
Technical Field
The invention relates to the technical field of laser ranging, in particular to an optical comb absolute ranging system.
Background
The double optical comb system is a Fourier transform spectrum tool which does not need a mechanical delay line and generates interference signals similar to cross correlation by pulse sequences of two optical combs with slightly different repetition frequencies in the time domain; whereas in the frequency domain, two optical combs with different longitudinal mode spacing, by multi-heterodyne interference, convert the two optical combs of hundred THz down to a single radio frequency comb of MHz. Therefore, the method is widely applied to the fields of high-resolution spectroscopy, femtosecond laser ranging, three-dimensional imaging and the like.
At present, an absolute distance measurement system based on a single-cavity double-optical comb generally adopts a material-saturable absorber as a mode locking device of a double-optical-comb light source. The dual-optical comb light source is provided by a single-cavity dual-output mode-locked laser, however, phase-locked control is still needed by piezoelectric ceramics, and the balanced cross-correlation structure is quite complex, so that the whole system is too huge. In addition, a pair of optical combs with offset repetition frequencies are generated in a single resonant cavity, and the common material saturable absorber has the defects of deliquescence, low damage threshold, long relaxation time and the like. Moreover, such double optical combs are difficult to ensure short-term or long-term stability, and dual wavelength mode locking is difficult to start, which seriously affects applications in the fields of absolute distance measurement and the like.
Disclosure of Invention
The invention provides an optical comb absolute ranging system which can feed back and adjust the polarization state of an electric control polarization element in a double optical comb generating module in real time so as to adjust generated mode locking pulse in real time, ensure the correct and stable state of the double optical comb mode locking pulse, accelerate the starting speed of the ranging system and improve the measuring precision.
In order to achieve the above object, an embodiment of the present invention provides an optical comb absolute ranging system, including:
the double optical comb generating module is used for generating double-wavelength double optical comb mode locking pulses;
the power amplification module comprises a power amplification input end, a power amplification first output end and a power amplification second output end, wherein the power amplification input end is connected with the output end of the double-optical comb generating module and is used for carrying out power amplification and narrow-band spectral filtering on the double-wavelength double-optical comb mode-locking pulse and outputting the double-wavelength double-optical comb mode-locking pulse in two ways through the power amplification first output end and the power amplification second output end;
the asynchronous optical sampling module comprises a local oscillation sampling end and a sampling end to be detected, wherein the local oscillation sampling end is connected with the power amplification second output end, the sampling end to be detected is connected with the power amplification first output end, and is used for sampling the dual-wavelength dual-optical comb mode locking pulse after power amplification and narrow-band spectrum filtering to generate an interference signal or a cross-correlation signal with distance information;
and the measurement control unit is respectively connected with the double optical comb generating module, the power amplification second output end and the output end of the asynchronous optical sampling module, and is used for calculating the distance measurement value carried in the interference signal or the cross-correlation signal based on the repetition frequency of the local oscillation sampling pulse output by the power amplification second output end and correcting the working state of the double optical comb generating module based on the interference signal or the cross-correlation signal output by the output end of the asynchronous optical sampling module.
Optionally, the dual optical comb generating module includes:
the device comprises a first pumping source, a first wavelength division multiplexer, a first gain optical fiber, a first electric control polarization element, a polarization-dependent isolator, a second electric control polarization element, a polarization maintaining optical fiber and an output coupler which are sequentially connected; the input end of the output coupler is connected with the signal injection end of the first wavelength division multiplexer, the first output end of the output coupler is connected with the polarization maintaining optical fiber, and the second output end of the output coupler is connected with the power amplification input end.
Optionally, the second electrically controlled polarizing element and the polarization maintaining fiber form a filter of the dual optical comb generating module, and the filter bandwidth of the filter meets the following requirements:
Δλ＝λ 2 /(Δn·L PMF ) Wherein Deltan is the birefringence of the polarization maintaining fiber, L PMF And lambda is 1550nm, and delta lambda is the filter bandwidth for the length of the polarization maintaining optical fiber.
Optionally, the power amplification module includes:
the input end of the filter is connected with the output end of the double optical comb generating module, and the output end of the filter is respectively connected with the input end of the first power amplifying assembly and the input end of the second power amplifying assembly;
the first power amplifying assembly and the second power amplifying assembly each include: the optical fiber Bragg grating, the second pumping source, the polarization uncorrelated isolator, the second wavelength division multiplexer, the second gain optical fiber and the three-port circulator are sequentially connected; the first end of the three-port circulator is connected with the second gain optical fiber, the second end of the three-port circulator is connected with the sampling end to be detected or the local oscillator sampling end, and the third end of the three-port circulator is connected with the optical fiber Bragg grating.
Optionally, the parameters of the fiber bragg gratings in the first power amplification component and the second power amplification component are the same.
Optionally, the asynchronous optical sampling module comprises: a local oscillation sampling unit and a sampling unit to be tested;
wherein, the sampling unit to be tested includes: a first collimator, a first quarter wave plate, a first polarizing beam splitter, a reference mirror, a second quarter wave plate, and a target mirror;
the first mode locking pulse output by the power amplification first output end is divided into a first polarization mode locking pulse and a second polarization mode locking pulse through the first collimator and the first quarter wave plate, the first polarization mode locking pulse is reflected to the first quarter wave plate through the first polarization beam splitter and then reaches the reference reflector, and the second polarization mode locking pulse is transmitted through the first polarization beam splitter and then reaches the target reflector through the second quarter wave plate; the first polarization mode locking pulse reflected by the reference reflector and the second polarization mode locking pulse reflected by the target reflector are combined through the first polarization beam splitter and then are incident to the local oscillation sampling unit through the second half wave plate;
the local oscillation sampling unit comprises: a second collimator, a second half-wave plate, a third half-wave plate, a second polarizing beam splitter, an avalanche diode, and an interference signal generating unit or a cross-correlation signal generating unit;
and the second mode locking pulse output by the second power amplification output end passes through the second collimator, the second half wave plate and the second polarization beam splitter, then is converged with the combined beam of the first polarization mode locking pulse and the second polarization mode locking pulse, and then passes through the interference signal generating unit or the cross-correlation signal generating unit, and then reaches the avalanche diode, and the avalanche diode is used for sampling.
Optionally, the interference signal generating unit includes a fourth half-wave plate and a third polarizing beam splitter.
Optionally, the cross-correlation signal generating unit includes a focusing lens and a sum frequency crystal.
Optionally, the control end of the measurement control unit is connected with the first electric control polarizing element and the second electric control polarizing element respectively, and the input end of the measurement control unit is connected with the output end of the asynchronous optical sampling module; the measurement control unit generates a voltage signal based on the interference signal or the cross-correlation signal output by the asynchronous optical sampling module and outputs the voltage signal to the first electric control polarizing element and the second electric control polarizing element.
Optionally, the first electrically controlled polarization element and the second electrically controlled polarization element are electrically controlled polarization controllers or electrically controlled wave plates, and the electrically controlled polarization controllers or the electrically controlled wave plates each include 8 voltage input pins to form four direct-current voltage channel drives.
In summary, the optical comb absolute ranging system according to the embodiment of the present invention includes: the device comprises a double optical comb generating module, a power amplifying module, an asynchronous optical sampling module and a measurement control unit, wherein the double optical comb generating module is used for generating double-wavelength double optical comb mode locking pulses; the power amplification module is used for carrying out power amplification and narrow-band spectral filtering on the dual-wavelength dual-optical comb mode-locked pulse, and the dual-wavelength dual-optical comb mode-locked pulse is output in two paths through a power amplification first output end and a power amplification second output end; the asynchronous optical sampling module is used for sampling the dual-wavelength dual-optical comb mode locking pulse after power amplification and narrow-band spectrum filtering to generate an interference signal or a cross-correlation signal with distance information; the measurement control unit is used for calculating a distance measurement value carried in an interference signal or a cross-correlation signal based on the repetition frequency of the local oscillation sampling pulse output by the second power amplification output end, and is also used for correcting the working state of the double optical comb generating module based on the interference signal or the cross-correlation signal output by the output end of the asynchronous optical sampling module. Therefore, the ranging system can feed back and adjust the polarization state of the electric control polarization element in the double optical comb generating module in real time so as to adjust the generated mode locking pulse in real time, ensure the correct and stable state of the double optical comb mode locking pulse, accelerate the starting speed of the ranging system and improve the measuring precision.
It should be understood that the description in this section is not intended to identify key or critical features of the embodiments of the invention or to delineate the scope of the invention. Other features of the present invention will become apparent from the description that follows.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for the description of the embodiments will be briefly described below, and it is apparent that the drawings in the following description are only some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic diagram of an absolute distance measurement system of an optical comb according to an embodiment of the present invention;
FIG. 2 is a spectral diagram of a stabilized dual wavelength mode-locked pulse provided by an embodiment of the present invention;
FIG. 3 is a schematic diagram of interferometry ranging according to an embodiment of the present invention;
fig. 4 is a schematic diagram of a cross-correlation ranging principle according to an embodiment of the present invention.
Detailed Description
In order that those skilled in the art will better understand the present invention, a technical solution in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in which it is apparent that the described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the present invention without making any inventive effort, shall fall within the scope of the present invention.
It should be noted that the terms "first," "second," and the like in the description and the claims of the present invention and the above figures are used for distinguishing between similar objects and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used may be interchanged where appropriate such that the embodiments of the invention described herein may be implemented in sequences other than those illustrated or otherwise described herein. Furthermore, the terms "comprise" and "have," as well as any variations thereof, are intended to cover a non-exclusive inclusion.
Fig. 1 is a schematic structural diagram of an optical comb absolute ranging system according to an embodiment of the present invention. As shown in fig. 1, the ranging system 100 includes: a dual optical comb generation module 110, a power amplification module 120, an asynchronous optical sampling module 130, and a measurement control unit 140.
The dual optical comb generating module 110 is configured to generate dual-wavelength dual optical comb mode-locking pulses; the power amplification module 120 includes a power amplification input end, a power amplification first output end and a power amplification second output end, where the power amplification input end is connected with the output end of the dual-optical comb generating module 110 and is used for performing power amplification and narrow-band spectral filtering on dual-wavelength dual-optical comb mode-locked pulses, and outputs the dual-wavelength dual-optical comb mode-locked pulses in two ways through the power amplification first output end and the power amplification second output end; the asynchronous optical sampling module 130 comprises a local oscillation sampling end and a sampling end to be detected, wherein the local oscillation sampling end is connected with the second output end of the power amplification, and the sampling end to be detected is connected with the first output end of the power amplification and is used for sampling the dual-wavelength dual-optical comb mode locking pulse after power amplification and narrow-band spectrum filtering to generate an interference signal or a cross-correlation signal with distance information; the measurement control unit 140 is respectively connected to the dual optical comb generating module 110, the power amplifying second output end, and the output end of the asynchronous optical sampling module 130, and is configured to calculate a distance measurement value carried in the interference signal or the cross-correlation signal based on the repetition frequency of the local oscillation sampling pulse output by the power amplifying second output end, and further configured to correct the working state of the dual optical comb generating module 110 based on the interference signal or the cross-correlation signal output by the output end of the asynchronous optical sampling module 130.
It should be noted that, the dual optical comb generating module 110 generates dual optical comb mode-locking pulses, the power amplifying module 120 amplifies and filters the dual optical comb mode-locking pulses, and outputs the dual optical comb mode-locking pulses in two paths, the asynchronous optical sampling module 130 samples the filtered and power amplified dual optical comb mode-locking pulses respectively, outputs an electrical signal including distance information, and the measurement control unit 140 may adjust the dual optical comb generating module 110 according to whether the electrical signal output by the asynchronous optical sampling module 130 is abnormal, so that the dual optical comb generating module 110 generates stable and correct dual optical comb mode-locking pulses. In addition, when the electrical signal output by the asynchronous optical sampling module 130 is normal, the measurement control unit 140 may calculate the distance information carried by the electrical signal according to the electrical signal output by the asynchronous optical sampling module 130.
The measurement control unit 140 may pre-store normal electrical signals and record the number of signals (pulse envelope/interference fringes) in one down-sampling period, and then compare the number of electrical signals in one period output by the asynchronous optical sampling module 130 with the pre-stored normal electrical signals to determine whether the electrical signals output by the asynchronous optical sampling module 130 are abnormal. For example, the number of electrical signals in one period in a normal state is usually 2, and the other cases are abnormal states, so that fine adjustment of the voltage applied to the electrically controlled polarization element in the double optical comb generating module 110 is required.
Therefore, the ranging system can feed back and adjust the mode locking pulse generated by the double optical comb generating module in real time, so that the correct and stable state of the double optical comb mode locking pulse is ensured, the starting speed of the ranging system is accelerated, and the measuring precision is improved.
Optionally, as shown in fig. 1, the dual optical comb generating module 110 includes:
the device comprises a first pump source 1, a first wavelength division multiplexer 2, a first gain optical fiber 3, a first electric control polarization element 4, a polarization-dependent isolator 5, a second electric control polarization element 6, a polarization maintaining optical fiber 7 and an output coupler 8 which are sequentially connected; the input end of the output coupler 8 is connected with the signal injection end of the first wavelength division multiplexer 2, the first output end of the output coupler 8 is connected with the polarization maintaining fiber 7, and the second output end of the output coupler 8 is connected with the power amplification input end.
The first pump source 1, the first wavelength division multiplexer 2, the first gain optical fiber 3, the first electric control polarization element 4, the polarization-dependent isolator 5, the second electric control polarization element 6, the polarization maintaining optical fiber 7 and the output coupler 8 are welded by adopting single-mode optical fibers. The output end of the first pump source 1 is connected with the pump input end of the first wavelength division multiplexer 2, the output end of the first wavelength division multiplexer 2 is connected with the first end of the first gain optical fiber 3, the second end of the first gain optical fiber 3 is connected with the first end of the first electric control polarization element 4, the second end of the first electric control polarization element 4 is connected with the first end of the polarization dependent isolator 5, the second end of the polarization dependent isolator 5 is connected with the first end of the second electric control polarization element 6, the second end of the second electric control polarization element 6 is connected with the first end of the polarization maintaining optical fiber 7, the second end of the polarization maintaining optical fiber 7 is connected with the first output end of the output coupler 8, the input end of the output coupler 8 is connected with the signal injection end of the first wavelength division multiplexer 2, and the second output end of the output coupler 8 outputs dual-wavelength mode locking pulses.
It should be noted that, the first gain optical fiber 3 may be one of an ytterbium-doped optical fiber, an erbium-ytterbium co-doped optical fiber, or a thulium-doped optical fiber, and may be selected according to the requirement of a specific band. It should be noted that the types of the first gain fiber 3 include, but are not limited to, the above examples, and those skilled in the art may select according to the actual situation. The first pump source 1 comprises a semiconductor laser with a central wavelength of 976nm. It should be noted that the type and the center wavelength of the first pump source 1 are not particularly limited in this embodiment, and those skilled in the art may select the type and the corresponding center wavelength of the first pump source 1 according to practical situations. The operating wavelength of the first wavelength division multiplexer 2 comprises 980/1550nm. The annular cavity of the double optical comb generating module 110 has a cavity length of 19.8m. The cavity length of the annular cavity of the double optical comb generating module 110 is not limited to 19.8m, and may be set according to the actual situation by those skilled in the art. The spectral diagram of the dual-wavelength mode-locked pulse generated by the dual-optical comb generating module 110 is shown in fig. 2. The repetition frequencies of the two peaks in FIG. 2 are 10.1222MHz and 10.1232MHz, respectively, corresponding to a 1kHz repetition frequency difference.
It will be appreciated that the gain spectrum of the dual optical comb generating module 110 is provided by the first pump source 1 pumping the first gain fiber 3 through the first wavelength division multiplexer 2. The first electrically controlled polarization element 4, the polarization dependent isolator 5 (PD-ISO) and the second electrically controlled polarization element 6, for example an electrically controlled polarization controller (EPC), together constitute an artificially saturable absorber as a passive mode-locking device. Among other things, this mode locking approach is also known as Nonlinear Polarization Evolution (NPE) mode locking.
The first electrically controlled polarizing element 4 and the second electrically controlled polarizing element 6 are electrically controlled polarizing controllers or electrically controlled wave plates, so as to reduce the influence of environmental and mechanical vibration on stability. The electric control polarization controller or the electric control wave plate comprises 8 voltage input pins to form four direct-current voltage channel drives.
In addition, in this embodiment, the second electrically controlled polarizing element 6 and the polarization maintaining fiber 7 form a Lyot filter structure, so that the gain spectrum has two or more gain peaks, and the corresponding filter bandwidth can be adjusted by selecting the lengths of different polarization maintaining fibers. That is, the first electrically controlled polarizer 4, the polarization-dependent isolator 5, the second electrically controlled polarizer 6 and the polarization maintaining fiber 7 in this embodiment form a passive mode locking device and a filtering structure, and simultaneously perform the dual functions of an artificially saturable absorber and comb filtering, so that the laser generates stable dual-wavelength mode locking pulses in a proper polarization state.
In this embodiment, the second electrically controlled polarizing element 6 and the polarization maintaining fiber 7 form a filter of the dual optical comb generating module 110, and the filtering bandwidth of the filter satisfies:
Δλ＝λ 2 /(Δn·L PMF ) Wherein Deltan is the birefringence of the polarization maintaining fiber, L PMF For the length of the polarization maintaining fiber, lambda is 1550nm, and delta lambda is the filter bandwidth. That is, the length of the polarization maintaining fiber 7 corresponds to the combThe bandwidth of the linear filter is determined by the above formula, and the length of the polarization maintaining fiber 7 is 15cm, which corresponds to a filter bandwidth of 34nm, wherein the filtering position and the modulation depth are adjusted by the second electrically controlled polarization element 6.
In addition, in the present embodiment, the output coupler 8 outputs a part of light with a fixed proportion to the power amplifying module 120 (not described here), and the rest of light continues to circulate in the resonant cavity. Wherein, the output proportion is selected according to the need.
Illustratively, the first pump source employs a 976nm semiconductor laser and pump light through 980/1550nm first wavelength division multiplexer 2 to pump the erbium doped fiber (first gain fiber 3). The output coupler has a split ratio of 1:9, i.e. 10% of the light output, and the remaining 90% of the light is coupled into the wavelength division multiplexer to form a ring cavity. The polarization dependent isolator allows signal light to run only one way within the annular cavity. The signal light generated by stimulated radiation at the erbium-doped fiber sequentially passes through a composite structure formed by a polarization-dependent isolator 4, a polarization maintaining fiber 5 and an electric control polarization controller (an electric control polarization element 6), and returns to the first wavelength division multiplexer 2 from 90% end of the output coupler, so that the laser generates stable dual-wavelength mode locking pulse under a proper polarization state due to the dual effects of nonlinear polarization evolution mode locking effect and comb filtering. Wherein the laser ring cavity has a cavity length of 19.8m. The length of the polarization maintaining fiber 5 corresponds to the bandwidth of comb filtering, and is defined by Δλ=λ 2 /(Δn·L PMF ) And determining, wherein Deltan is the birefringence of the polarization-maintaining optical fiber 5, LPMF is the length of the polarization-maintaining optical fiber 5, the length of the polarization-maintaining optical fiber 5 used in the embodiment is 15cm, lambda is 1550nm, deltan is a filtering interval, and the filtering bandwidth, the filtering position and the modulation depth corresponding to 34nm are adjusted by an electric control polarization controller. Through the 4 direct current voltage channels of algorithm control automatically controlled polarization controller, can carry out global search to all possible polarization states on poincare sphere, find a set of voltage value that can realize the dual wavelength mode locking, when this set of voltage value is fixed, mode locking state also keeps unchanged, therefore has very high stability, and the voltage value that the mode locking corresponds varies because of the laser.
Thus, the dual optical comb generation module 110 employs a ring cavity structure based on a nonlinear polarization rotating artificially saturable absorber, which has lower quantum noise than the material maintainable and absorber, which is advantageous for higher measurement accuracy in, for example, laser ranging applications.
In addition, the control end of the measurement control unit 140 is respectively connected with the first electric control polarizing element 4 and the second electric control polarizing element 6, and the input end of the measurement control unit 140 is connected with the output end of the asynchronous optical sampling module 130; wherein the measurement control unit 140 generates a voltage signal based on the interference signal or the cross correlation signal output from the asynchronous optical sampling module 130 and outputs the voltage signal to the first and second electrically controlled polarization elements 4 and 6.
It should be noted that, after the measurement control unit 140 processes the interference signal or the cross-correlation signal output by the asynchronous optical sampling module 130 through an algorithm, a set of new voltage values is obtained, and the set of voltage values is added to the electronically controlled polarization element in the cavity, so as to form feedback control; wherein the algorithm comprises: genetic algorithm, rosenberg search algorithm, greedy algorithm, etc.; in addition, feedback control may be accomplished in an on-line or off-line manner. For example, the number of signals at the output end of the asynchronous optical sampling module 130 may be compared with the number of pre-stored signals, and if the signals do not match, the voltage on the electronically controlled polarizing element may be adjusted so that the number of signals at the output end of the asynchronous optical sampling module 130 finally matches the number of pre-stored signals.
Furthermore, by setting four direct-current voltage channels for driving, the first electric control polarizing element 4 and the second electric control polarizing element 6 can generate all possible polarization states on the poincare sphere, and a common polarization controller cannot achieve full coverage, so that the two electric control polarizing elements can sweep the whole polarization space in the laser cavity, and the driving voltage of the electric control polarizing elements is controlled through an algorithm, so that the polarization states corresponding to the dual-wavelength mode locking can be realized and stabilized, and the starting speed is greatly improved. Compared with the prior art, in the embodiment, the measurement control unit 140 is adopted to control the electric control polarization element, so that the polarization state of the mode locking pulse free running in the resonant cavity is effectively controlled, the double optical comb is stabilized, and the short-term stability and the long-term stability of the free running double light source are greatly improved; meanwhile, the polarizing element in the embodiment is an electric control polarizing element, and the voltage of the electric control polarizing element can be controlled by a program to automatically generate a desired pulse without manual operation or adjustment by a professional, so that the electric control polarizing element is convenient and practical. And the polarization state is changed by controlling the voltage applied to the electric control polarization element, so that the traditional mechanical polarization control element is replaced, and the influence of vibration on the polarization state of the laser cavity can be better avoided, and the instability of the mode locking state is further caused.
Optionally, with continued reference to fig. 1, the power amplification module 120 includes:
the input end of the filter 9 is connected with the output end of the double optical comb generating module 110, and the output end of the filter 9 is respectively connected with the input end of the first power amplifying component and the input end of the second power amplifying component;
the first power amplifying assembly and the second power amplifying assembly each comprise: the optical fiber Bragg grating, the second pumping source, the polarization uncorrelated isolator, the second wavelength division multiplexer, the second gain optical fiber and the three-port circulator are sequentially connected; the first end of the three-port circulator is connected with the second gain optical fiber, the second end of the three-port circulator is connected with the sampling end to be tested or the local oscillation sampling end, and the third end of the three-port circulator is connected with the fiber Bragg grating.
That is, the power amplification module 120 includes: a first polarization uncorrelated isolator 10, a second polarization uncorrelated isolator 16, a second wavelength division multiplexer 12, a third wavelength division multiplexer 18, a second gain fiber 13, a third gain fiber 19, a second pump source 11, a third pump source 17, a first three-port circulator 14, a second three-port circulator 20, a first fiber bragg grating 15 and a second fiber bragg grating 21; the parameters of the first fiber Bragg grating 15 and the second fiber Bragg grating 21 are the same; the input end of the filter 9 is connected with the second output end of the output coupler 8, the first output end of the filter 9 is connected with the input end of the first polarization uncorrelated isolator 10, the output end of the first polarization uncorrelated isolator 10 is connected with the signal injection end of the second wavelength division multiplexer 12, the pump input end of the second wavelength division multiplexer 12 is connected with the second pump source 11, the output end of the second wavelength division multiplexer 12 is connected with the first end of the second gain optical fiber 13, the second end of the second gain optical fiber 13 is connected with the first end of the first three-end circulator 14, and the second end of the first three-end circulator 14 is connected with the first fiber Bragg grating 15; the second output end of the filter 9 is connected with the input end of the second polarization uncorrelated isolator 16, the output end of the second polarization uncorrelated isolator 16 is connected with the signal injection end of the third wavelength division multiplexer 18, the pump input end of the third wavelength division multiplexer 18 is connected with the third pump source 17, the output end of the third wavelength division multiplexer 18 is connected with the first end of the third gain optical fiber 19, the second end of the third gain optical fiber 19 is connected with the first end of the second three-end circulator 20, and the second end of the second three-end circulator 20 is connected with the second fiber bragg grating 21; the third terminal of the first three-terminal circulator 14 and the third terminal of the second three-terminal circulator 20 output a double optical comb.
The types of the second gain optical fiber 13 and the third gain optical fiber 19 are the same as those of the first gain optical fiber 3.
The devices are welded sequentially in a single-mode welding mode, wherein an a port of a first three-port circulator 14 is welded with the output end of a second gain optical fiber 13, and a b port of the first three-port circulator 14 is welded with a first fiber Bragg grating 15; the a-port of the second three-port circulator 20 is fused to the output of the third gain fiber 19, and the b-port of the second three-port circulator 20 is fused to the second fiber bragg grating 21.
In the power amplification module 120 according to the embodiment of the present invention, the filter 9 divides the dual-wavelength mode-locked pulse output by the output coupler 8 into two paths according to wavelengths, and the filtering position is determined according to a specific dual-wavelength position. The two single optical combs separated into two paths by the filter 9 are respectively subjected to power amplification through the second gain optical fiber 13 and the third gain optical fiber 19, so that the two optical combs have a certain overlapping part in the spectrum range, wherein the types of the second gain optical fiber 13 and the third gain optical fiber 19 used are determined by the spectrum range of the laser output by the resonant cavity. The two power amplified pulses pass through two identical first and second fiber bragg gratings 15 and 21 through a three-port circulator (first and second three-port circulators 14 and 20), and the filtering positions of the first and second fiber bragg gratings 15 and 21 are the spectral overlapping portions of the two optical combs, and the corresponding filtering bandwidths are typically only a few nanometers to prevent frequency aliasing.
The dual-frequency pulse output from the second output end (10% end) of the output coupler 7 passes through a filter 9, and the double combs with the central wavelengths of 1532.78nm and 1566.72nm are divided into two paths, and are respectively amplified in a nonlinear manner by the erbium-doped optical fiber, so that the spectra of the two optical combs have a certain overlapping portion. The two paths of light enter the two identical fiber Bragg gratings through the circulator and are respectively output at the second port of the circulator, and the filtering bandwidth is 1nm.
Optionally, with continued reference to fig. 1, the asynchronous optical sampling mode 130 includes: a local oscillation sampling unit and a sampling unit to be tested;
wherein, the sampling unit that awaits measuring includes: a first collimator 22, a first quarter wave plate 24, a first quarter wave plate 26, a first polarizing beam splitter 25, a reference mirror 28, a second quarter wave plate 27 and a target mirror 29; the first mode locking pulse output by the power amplification first output end is divided into a first polarization mode locking pulse and a second polarization mode locking pulse through the first collimator 22 and the first half wave plate 24, the first polarization mode locking pulse is reflected to the first quarter wave plate 26 through the first polarization beam splitter 25 and then reaches the reference mirror 28, and the second polarization mode locking pulse is transmitted through the first polarization beam splitter 25 and then reaches the target mirror 29 through the second quarter wave plate 27; the first polarization mode locking pulse reflected by the reference mirror 28 and the second polarization mode locking pulse reflected by the target mirror 29 are combined through the first polarization beam splitter 25 and then are incident to the local oscillation sampling unit through the second half wave plate 30;
the local oscillation sampling unit comprises: a second collimator 23, a second half wave plate 30, a third half wave plate 31, a second polarizing beam splitter 32, an avalanche diode 35, and an interference signal generating unit 33 or a cross correlation signal generating unit 34; the second mode-locked pulse output by the second output end of the power amplification passes through the second collimator 23, the second half wave plate 30 and the second polarization beam splitter 32, then is converged with the combined beam of the first polarization mode-locked pulse and the second polarization mode-locked pulse, and then passes through the interference signal generating unit 33 or the cross-correlation signal generating unit 34, and then reaches the avalanche diode 35, and the avalanche diode 35 is used for sampling. The interference signal generating unit 33 includes a fourth half wave plate and a third polarizing beam splitter. The cross-correlation signal generating unit 34 includes a focusing lens and a sum frequency crystal.
That is, the signal light comb output by the power amplifying module 120 outputs spatial light through the first collimator 22, and after passing through the first half wave plate 24, the spatial light is split into two paths of reflected vertical polarized light and transmitted horizontal polarized light at the first polarizing beam splitter 25, wherein the reflected light will be used as a reference light comb, the transmitted light will be used as a target light comb, the reference light comb returns to the first polarizing beam splitter 25 through the first quarter wave plate 26 and the reference mirror 28 for transmission, the target light comb returns to the first polarizing beam splitter 25 through the second quarter wave plate 27 and the target mirror 29 for reflection, and then, two beams of light with mutually perpendicular polarizations are incident on the second polarizing beam splitter 32 after passing through the second half wave plate 30.
The local oscillation optical comb output by the power amplification module 120 outputs space light through the second collimator 23, and the space light enters the second polarization beam splitter 32 after passing through the third half wave plate 31, and the second half wave plate 30 and the third half wave plate 31 are adjusted to make the power of the local oscillation optical comb and the power of the signal optical comb after passing through the second polarization beam splitter 32 equal. The interference signal needs a fourth half wave plate and a third polarization beam splitter 33, so that the signal optical comb and the local oscillation optical comb have the same polarization component, and the interference signal is obtained in an avalanche diode 35; the cross-correlation signal replaces the fourth half wave plate and the third polarization beam splitter 33 with a focusing lens and a sum frequency crystal 34, and after the signal optical comb and the local oscillator optical comb with mutually perpendicular polarization directions are focused by the focusing lens, a sum frequency cross-correlation is generated in the sum frequency crystal (PPKTP crystal is selected here), and the avalanche diode 35 measures the cross-correlation signal.
Fig. 3 is a schematic diagram of interferometry ranging according to an embodiment of the present invention. Only the asynchronous optical sampling process of the target optical comb and the local oscillator optical comb is shown in the figure, and the downsampled interference signal of the target optical comb is obtained.
Fig. 4 is a schematic diagram of a cross-correlation ranging principle according to an embodiment of the present invention. Local oscillation optical combs perpendicular to the polarization direction of the signal optical comb can be generated due to different repetition frequencies (f r1 ≠f r2 ) Downsampling is carried out on a target optical comb and a reference optical comb, cross-correlation signals are generated through PPKTP crystals, and the distance between two downsampled electric pulse signals, namely the time difference Td of two electric pulses of a target reflecting mirror and a reference reflecting mirror, is that the distance L between the two reflecting mirrors is:
Figure BDA0004090649930000141
wherein L is a ＝c/(2n g ·f r ) The non-fuzzy range of the measuring system is obtained through rough measurement.
Finally, the measurement control unit 140 measures the repetition frequency f of the real-time local oscillation optical comb mainly by frequency counting r2 The method comprises the steps of carrying out a first treatment on the surface of the The time sequence electric signals are collected, the envelopes of the interference signals are extracted by utilizing Hilbert transformation for interferometry ranging, and then the time difference Td of two electric pulses of the target reflecting mirror and the reference reflecting mirror is calculated; for the distance measurement of the cross-correlation method, td is directly calculated; finally, the electric signal with distance information is used for feedback control of the electric control polarization element in the double optical comb generating module 110 so as to ensure the correct and stable state of the output double optical comb, for example, the abnormality of the double optical comb pulse can be immediately found in the electric signal acquired from the avalanche diode 35, which is difficult to find in the double optical comb pulse sampling process, and then the electric control polarization element in the double optical comb generating module 110 is used for restoring to the normal locking state.
Therefore, the two optical comb generating modules in the embodiment are different from two independent mode locking lasers with slightly different repetition rates, the two independent mode locking lasers need complex phase locking loops, and asynchronous pulse sequences generated in a single resonant cavity have inherent mutual coherence, so that additional phase locking is not needed, and the cost control and miniaturization are facilitated. The polarization state of the mode locking pulse which runs freely in the resonant cavity is effectively controlled through an on-line/off-line algorithm by adopting an electric control polarization controller or an electric control wave plate as a polarization element, so that the short-term stability and the long-term stability of the free-running double optical comb are greatly improved; in addition, the invention adopts a single resonant cavity to generate an all-optical fiber structure of the double-optical comb, and a single double-optical comb light source replaces two independent single-optical comb light sources, thereby greatly simplifying the complexity of the system, reducing the cost and being beneficial to modularization and instrumentation of the double-optical comb light source; meanwhile, the invention does not need a huge phase-locked system to lock the repetition frequency and the carrier envelope offset frequency, thereby reducing the number of auxiliary equipment and the volume of the light source system; in addition, the feedback of the ranging signal to the polarizing element in the light source is introduced, so that the stability and reliability of the double-optical-comb ranging are further improved, and the double-optical-comb ranging device has the capability of continuous measurement for a long time.
In summary, the optical comb absolute ranging system according to the embodiment of the present invention includes: the device comprises a double optical comb generating module, a power amplifying module, an asynchronous optical sampling module and a measurement control unit, wherein the double optical comb generating module is used for generating double-wavelength double optical comb mode locking pulses; the power amplification module is used for carrying out power amplification and narrow-band spectral filtering on the dual-wavelength dual-optical comb mode-locked pulse, and the dual-wavelength dual-optical comb mode-locked pulse is output in two paths through a power amplification first output end and a power amplification second output end; the asynchronous optical sampling module is used for sampling the dual-wavelength dual-optical comb mode locking pulse after power amplification and narrow-band spectrum filtering to generate an interference signal or a cross-correlation signal with distance information; the measurement control unit is used for calculating a distance measurement value carried in an interference signal or a cross-correlation signal based on the repetition frequency of the local oscillation sampling pulse output by the second power amplification output end, and is also used for correcting the working state of the double optical comb generating module based on the interference signal or the cross-correlation signal output by the output end of the asynchronous optical sampling module. Therefore, the ranging system can feed back and adjust the polarization state of the electric control polarization element in the double optical comb generating module in real time so as to adjust the generated mode locking pulse in real time, ensure the correct and stable state of the double optical comb mode locking pulse, accelerate the starting speed of the ranging system and improve the measuring precision.
The above embodiments do not limit the scope of the present invention. It will be apparent to those skilled in the art that various modifications, combinations, sub-combinations and alternatives are possible, depending on design requirements and other factors. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of the present invention.

Claims (10)

1. An optical comb absolute ranging system, comprising:
the double optical comb generating module is used for generating double-wavelength double optical comb mode locking pulses;
the power amplification module comprises a power amplification input end, a power amplification first output end and a power amplification second output end, wherein the power amplification input end is connected with the output end of the double-optical comb generating module and is used for carrying out power amplification and narrow-band spectral filtering on the double-wavelength double-optical comb mode-locking pulse and outputting the double-wavelength double-optical comb mode-locking pulse in two ways through the power amplification first output end and the power amplification second output end;
the asynchronous optical sampling module comprises a local oscillation sampling end and a sampling end to be detected, wherein the local oscillation sampling end is connected with the power amplification second output end, the sampling end to be detected is connected with the power amplification first output end, and is used for sampling the dual-wavelength dual-optical comb mode locking pulse after power amplification and narrow-band spectrum filtering to generate an interference signal or a cross-correlation signal with distance information;
and the measurement control unit is respectively connected with the double optical comb generating module, the power amplification second output end and the output end of the asynchronous optical sampling module, and is used for calculating the distance measurement value carried in the interference signal or the cross-correlation signal based on the repetition frequency of the local oscillation sampling pulse output by the power amplification second output end and correcting the working state of the double optical comb generating module based on the interference signal or the cross-correlation signal output by the output end of the asynchronous optical sampling module.
2. The optical comb absolute ranging system of claim 1, wherein the dual optical comb generating module comprises:
the device comprises a first pumping source, a first wavelength division multiplexer, a first gain optical fiber, a first electric control polarization element, a polarization-dependent isolator, a second electric control polarization element, a polarization maintaining optical fiber and an output coupler which are sequentially connected; the input end of the output coupler is connected with the signal injection end of the first wavelength division multiplexer, the first output end of the output coupler is connected with the polarization maintaining optical fiber, and the second output end of the output coupler is connected with the power amplification input end.
3. The optical comb absolute distance measurement system according to claim 2, wherein the second electrically controlled polarization element and the polarization maintaining fiber form a filter of the double optical comb generating module, and a filtering bandwidth of the filter satisfies:
Δλ＝λ 2 /(Δn·L PMF ) Wherein Deltan is the birefringence of the polarization maintaining fiber, L PMF And lambda is 1550nm, and delta lambda is the filter bandwidth for the length of the polarization maintaining optical fiber.
4. The optical comb absolute ranging system of claim 1, wherein the power amplification module comprises:
the input end of the filter is connected with the output end of the double optical comb generating module, and the output end of the filter is respectively connected with the input end of the first power amplifying assembly and the input end of the second power amplifying assembly;
the first power amplifying assembly and the second power amplifying assembly each include: the optical fiber Bragg grating, the second pumping source, the polarization uncorrelated isolator, the second wavelength division multiplexer, the second gain optical fiber and the three-port circulator are sequentially connected; the first end of the three-port circulator is connected with the second gain optical fiber, the second end of the three-port circulator is connected with the sampling end to be detected or the local oscillator sampling end, and the third end of the three-port circulator is connected with the optical fiber Bragg grating.
5. The optical comb absolute distance measurement system of claim 1, wherein parameters of the fiber bragg gratings in the first power amplification component and the second power amplification component are the same.
6. The optical comb absolute ranging system of claim 1, wherein the asynchronous optical sampling module comprises: a local oscillation sampling unit and a sampling unit to be tested;
wherein, the sampling unit to be tested includes: a first collimator, a first quarter wave plate, a first polarizing beam splitter, a reference mirror, a second quarter wave plate, and a target mirror;
the first mode locking pulse output by the power amplification first output end is divided into a first polarization mode locking pulse and a second polarization mode locking pulse through the first collimator and the first quarter wave plate, the first polarization mode locking pulse is reflected to the first quarter wave plate through the first polarization beam splitter and then reaches the reference reflector, and the second polarization mode locking pulse is transmitted through the first polarization beam splitter and then reaches the target reflector through the second quarter wave plate; the first polarization mode locking pulse reflected by the reference reflector and the second polarization mode locking pulse reflected by the target reflector are combined through the first polarization beam splitter and then are incident to the local oscillation sampling unit through the second half wave plate;
the local oscillation sampling unit comprises: a second collimator, a second half-wave plate, a third half-wave plate, a second polarizing beam splitter, an avalanche diode, and an interference signal generating unit or a cross-correlation signal generating unit;
and the second mode locking pulse output by the second power amplification output end passes through the second collimator, the second half wave plate and the second polarization beam splitter, then is converged with the combined beam of the first polarization mode locking pulse and the second polarization mode locking pulse, and then passes through the interference signal generating unit or the cross-correlation signal generating unit, and then reaches the avalanche diode, and the avalanche diode is used for sampling.
7. The optical comb absolute ranging system of claim 6, wherein the interference signal generating unit comprises a fourth half wave plate and a third polarizing beam splitter.
8. The optical comb absolute distance measurement system according to claim 6, wherein the cross-correlation signal generating unit comprises a focusing lens and a sum frequency crystal.
9. The optical comb absolute distance measurement system according to claim 2, wherein a control end of the measurement control unit is connected with the first and second electric control polarization elements respectively, and an input end of the measurement control unit is connected with an output end of the asynchronous optical sampling module; the measurement control unit generates a voltage signal based on the interference signal or the cross-correlation signal output by the asynchronous optical sampling module and outputs the voltage signal to the first electric control polarizing element and the second electric control polarizing element.
10. The optical comb absolute distance measurement system according to claim 9, wherein the first electrically controlled polarization element and the second electrically controlled polarization element are electrically controlled polarization controllers or electrically controlled wave plates, and the electrically controlled polarization controllers or the electrically controlled wave plates comprise 8 voltage input pins, so that four direct-current voltage channel drives are formed.
CN202310150661.1A 2023-02-22 2023-02-22 Optical comb absolute distance measurement system Pending CN116299506A (en)

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