CN117405242A - Optical frequency demodulation system and optical frequency demodulation method - Google Patents
Optical frequency demodulation system and optical frequency demodulation method Download PDFInfo
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- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
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Abstract
The application discloses an optical frequency demodulation system and an optical frequency demodulation method, which solve the technical problem of low accuracy of optical frequency detected by the prior art. The optical frequency demodulation system comprises an optical intensity modulator, a polarization state modulation unit, a beam splitter and combiner, a first reflecting mirror, a delay device, a second reflecting mirror, a beam splitter, a photoelectric detector and a controller, wherein the optical intensity modulator is coupled and connected with the polarization state modulation unit, the reflecting mirror is used for reflecting the split beam back to the beam splitter and combiner, and the delay device is coupled and connected with the beam splitter and combiner; the light splitter splits the combined light into a third light split and a fourth light split, and the third light split and the fourth light split are output by two second light output ends of the light splitter, two photoelectric detectors are arranged, and the two photoelectric detectors are respectively coupled and connected to the two second light output ends of the light splitter; the controller is used for calculating the optical frequency of the optical signal to be measured according to the measured characterization values of the transmitted light with different light intensities and different polarization states and the demodulation expression of the optical phase delay angle, which are measured by the photoelectric detector. The invention realizes high-precision demodulation of the optical frequency.
Description
Technical Field
The application belongs to the technical field of optical frequency demodulation, and particularly relates to an optical frequency demodulation system and an optical frequency demodulation method.
Background
In the laser frequency control and analysis, and fiber grating detection and demodulation processes, it is very important to accurately measure or obtain high-resolution optical frequency information.
Spectroscopic analysis is a method currently in common use for measuring optical frequency information, including dispersive elements using diffraction gratings, using FP cavity resonators or fiber gratings, using interferometric demodulation, and the like. In the measuring process, the optical frequency information is usually reflected by measuring the light intensity information of the grating under different wavelengths, or the resolution of the optical frequency is improved by selecting the grating with larger slope, but the accuracy of the detected optical frequency is low.
Disclosure of Invention
In order to solve the technical problem of low accuracy of current optical frequency detection, the application provides an optical frequency demodulation system and an optical frequency demodulation method.
In a first aspect of the present application, there is provided an optical frequency demodulation system, comprising:
the light intensity modulator is used for coupling and connecting with the light signal to be detected so as to modulate the light signal to be detected into first transmission light with different light intensities;
a polarization state modulation unit coupled to the light intensity modulator to modulate the first transmitted light into a second transmitted light of a different polarization state;
The light splitting and combining device is provided with a first light input end, a first light output end, a first light splitting end and a second light splitting end, wherein the first light input end is coupled and connected with the polarization state modulation unit so as to split the second transmission light into a first light splitting and a second light splitting, and the first light splitting end and the second light splitting end are respectively used for outputting the second transmission light, and the light splitting and combining device is used for combining two reflected lights entering from the first light splitting end and the second light splitting end into combined light;
the first reflector is used for reflecting the first light beam back to the first light splitting end of the light splitting and combining device;
the delayer is coupled and connected to the second light splitting end of the light splitting and combining device;
the second reflector is used for reflecting the second light splitting transmitted by the delayer back to the delayer;
the optical splitter is provided with a second optical input end and two second optical output ends, the second optical input end is coupled and connected with the first optical output end of the optical splitter and combiner so as to split the combined light into a third light splitter and a fourth light splitter, the third light splitter and the fourth light splitter are output by the two second optical output ends of the optical splitter, and the optical splitter is parallel to the optical axis of the first optical output end of the optical splitter and the fourth light splitter;
the two photoelectric detectors are respectively coupled and connected to the two second light output ends of the light splitter;
And the controller is used for calculating the optical frequency of the optical signal to be measured according to the measured characterization values of the transmitted light with different light intensities and different polarization states and the demodulation expression of the optical phase delay angle, which are measured by the photoelectric detector.
In some embodiments, a quarter wave plate is further disposed between the beam splitter and the beam splitter, and the quarter wave plate is parallel to the optical axis of the first light output end of the beam splitter and the optical axis of the beam splitter.
In some embodiments, the first mirror and the second mirror are both faraday mirrors.
In some embodiments, a first dual-fiber collimator is arranged between the beam splitter and the photoelectric detector, and the first dual-fiber collimator is provided with two collimating input ends respectively coupled with two second light output ends of the beam splitter and two collimating output ends respectively coupled with the two photoelectric detectors; when the delay device is an optical fiber delay line, the optical frequency demodulation system further comprises a first single optical fiber collimator positioned between the beam splitter and the delay device.
In some embodiments, the polarization state modulation unit includes a first optical switch, a second dual-fiber collimator and a first polarizer sequentially disposed along an optical path, where the first optical switch is provided with a third optical input end and two third optical output ends, the third optical input end of the first optical switch is coupled to the optical intensity modulator, the two alignment input ends of the second dual-fiber collimator are respectively connected to the two third optical output ends of the first optical switch, the two alignment input ends of the first polarizer are coupled to the two alignment output ends of the second dual-fiber collimator, and the alignment output end of the first polarizer is coupled to the first optical input end of the optical splitter and the optical axis is 45 °.
In some embodiments, the light intensity modulator is provided with two modulation output ends, the polarization state modulation unit comprises a first 0 ° polarizer, a 90 ° polarizer and a second optical switch, the second optical switch is provided with a fourth optical output end and two fourth optical input ends, the two fourth optical input ends are respectively coupled to the first 0 ° polarizer and the 90 ° polarizer, and the fourth optical output end is coupled to the first optical input end of the beam splitter; the first 0-degree polarizer and the 90-degree polarizer are 45 degrees with the optical axis of the first light input end of the light splitting and combining device.
In some embodiments, the polarization state modulation unit includes a second 0 ° polarizer and an adjustable 90 ° polarizer sequentially disposed between the light intensity modulator and the beam splitter/combiner along an optical path; the second 0-degree polarizer and the first optical input end of the beam splitter-combiner form an optical axis of 45 degrees.
In some embodiments, the polarization state modulation unit includes a third 0 ° polarizer, a third optical switch, a first 90 ° faraday rotator, and a 2*1 coupler, where the third 0 ° polarizer is coupled to the light intensity modulator, the third optical switch is provided with a fifth optical input end and two fifth optical output ends, the fifth optical input end is coupled to the third 0 ° polarizer, one of the fifth optical output ends of the third optical switch is coupled to one of the coupling input ends of the coupler, two ends of the first 90 ° faraday rotator are coupled to the other of the fifth optical output ends of the third optical switch and the other coupling input end of the coupler, and the coupling output end of the coupler is coupled to the first optical input end of the light splitting/combining device; the third 0-degree polarizer forms 45 degrees with the optical axis of the first light input end of the light splitting and combining device.
In some embodiments, the polarization state modulation unit includes:
a fourth 0 degree polarizer coupled to the light intensity modulator;
the fourth optical switch is provided with a sixth optical input end and two sixth optical output ends, and the sixth optical input end is coupled and connected with the fourth 0-degree polarizer;
a second 90 ° faraday rotator coupled to one of said sixth light output ends;
the two collimating input ends of the third double-fiber collimator are respectively coupled and connected with the other sixth light output end and the second 90-degree Faraday rotator;
and the two light combining input ends of the light combining device are coupled and connected with the two collimation output ends of the third double-fiber collimator one by one, and the light combining output end of the light combining device is coupled and connected with the first light input end of the light splitting and combining device.
When the light combiner selects PBS, the second 0-degree polarizer is parallel to the output shafts of the light combiner and the fourth optical switch, and the other one is 90 degrees.
In a second aspect of the present application, there is provided an optical frequency demodulation method, which is applicable to the optical frequency demodulation system of the first aspect, and the optical frequency demodulation method includes:
the testing steps are as follows: coupling the light intensity modulator of the optical frequency demodulation device with the optical signal to be detected, so that each photoelectric detector outputs measurement characterization values under the first light intensity and the second light intensity in the 90-degree polarization state and measurement characterization values under the first light intensity and the second light intensity in the 0-degree polarization state;
The calculation steps are as follows: substituting the eight measurement characterization values into a demodulation expression of the optical phase delay angle, and calculating the optical frequency of the light source to be measured.
In some embodiments, the demodulation expression of the optical phase retardation angle is:
or alternatively, the first and second heat exchangers may be,
wherein: deltaU 11M Is the difference value of the measurement characterization value of the first light intensity and the second light intensity of a photoelectric detector in the 90 DEG polarization state, delta U 12M For the difference of the measured characterization values of the first light intensity and the second light intensity of the other photodetector in the 90 DEG polarization state, deltaU 21M Is the difference value of the measurement characterization value of the first light intensity and the second light intensity of a photoelectric detector in the 0 DEG polarization state, delta U 22M For another photoelectric detectionThe difference between the measured characterization values for the first and second light intensities at 0 polarization.
The optical frequency demodulation system provided by the embodiment of the application comprises an optical intensity modulator, a polarization state modulation unit, a light splitting and combining device, a first reflecting mirror, a time delay device, a second reflecting mirror, a light splitting device, a photoelectric detector and a controller. The light intensity modulator may modulate the light signal to be measured into first transmission light with different light intensities, for example, the light intensity modulator modulates the light signal to be measured into first transmission light with the first light intensity and first transmission light with the second light intensity, where the intensities of the first light intensity and the second light intensity are different. The polarization state modulation unit is coupled to the light intensity modulator, and can modulate the first transmission light into second transmission light with different polarization states, for example, the polarization state modulation unit modulates the first transmission light into second transmission light with 90 ° polarization states and 0 ° polarization states, and the coupling connection of the light intensity modulator and the polarization state modulation unit enables the polarization state modulation unit to output the following four types of second transmission light respectively: (1) the light intensity is a first light intensity, a 90 degree polarization state; (2) the light intensity is the second light intensity, 90 degree polarization state; (3) the light intensity is the first light intensity, 0 degree polarization state; (4) the light intensity is the second light intensity, 0 degree polarization state.
The beam splitter and combiner can be a Polarization Beam Splitter (PBS), has beam splitting and beam combining functions, and can divide the second transmission light into a first beam splitter and a second beam splitter, wherein the first beam splitter and the second beam splitter are mutually orthogonal linear polarized light, and the two mutually orthogonal linear polarized light are respectively output from a first beam splitting end and a second beam splitting end; the light splitter and combiner can also process the reflected light entering from the first light splitting end and the second light splitting end respectively to form combined light, and the combined light is emitted through the first light output end. The delay device is arranged to enable the second light beam to generate delay relative to the first light beam after passing through the delay device, and also enable the reflected light reflected by the second reflecting mirror to generate delay after passing through the delay device for the second time. The delay may be a fiber optic delay line, a group phase delay (DGD) or other birefringent crystal. The first beam splitter and the second beam splitter rotate 90 degrees under the action of the Faraday reflector and return according to the original path. The beam splitter can split the combined light emitted by the first light output of the beam splitter into two beams of light, and the two beams of light are respectively output to the two photoelectric detectors. The two photodetectors are respectively coupled to the two second light output ends of the beam splitter to convert the optical signals of the two mutually orthogonal polarized lights into electrical signals and output the electrical signals in the form of characterization values.
According to the method, an optical signal to be detected is demodulated into four kinds of second output light in sequence through the light intensity modulator and the polarization state modulation unit which are connected in a coupling mode, each kind of second output light is divided into a first light splitting mode and a second light splitting mode through the light splitting device, the first light splitting mode rotates by 90 degrees under the action of the first reflecting mirror and returns to the first light splitting end according to an original path, the second light splitting end delays through the time delay device, then rotates by 90 degrees under the action of the second reflecting mirror and returns to the time delay device for the second time according to the original path, then returns to the second light splitting end, the two linearly polarized reflected lights with the phase delay difference of theta, which are returned through the first light splitting end and the second light splitting end, are combined into combined lights, the combined lights are divided into two polarized lights which are mutually orthogonal through the light splitting device, and the characterization value is output through the photoelectric detector.
The types of the second output light are four, and each second output light can respectively output a characterization value by two photodetectors. If the signal to be measured is sequentially adjusted to four second output lights, each photoelectric detector can output four characterization values, and eight characterization values are output in total. The controller is used for calculating the optical phase delay angle according to the eight characterization values and the expression of the optical phase delay angle, and calculating and obtaining the optical frequency of the optical signal to be measured according to the optical phase delay angle.
Because the optical frequency demodulation is carried out by the signal processing method of the dual-optical-path polarization analysis, the influence of no optical bias voltage, optical path loss and light source fluctuation is eliminated by means of the coefficient matching of the dual-optical-path optical frequency demodulation system, and the high-precision demodulation of the optical frequency is realized.
Drawings
Fig. 1 shows a schematic diagram of an optical frequency demodulation system in one or more embodiments of the present application.
Fig. 2 shows a schematic structural diagram of an optical frequency demodulation system in one or more embodiments of the present application.
Fig. 3 shows a schematic structural diagram of an optical frequency demodulation system in one or more embodiments of the present application.
Fig. 4 shows a schematic structural diagram of an optical frequency demodulation system in one or more embodiments of the present application.
Fig. 5 shows a schematic structural diagram of an optical frequency demodulation system in one or more embodiments of the present application.
Fig. 6 shows a schematic structural diagram of an optical frequency demodulation system in one or more embodiments of the present application.
Reference numerals illustrate:
100-light intensity modulator.
200-polarization state modulation unit, 211-first optical switch, 212-second dual-fiber collimator, 213-first polarizer;
221-first 0-degree polarizer, 222-90-degree polarizer, 223-second optical switch, 224-second single fiber collimator;
231-a second 0-degree polarizer, 232-an adjustable 90-degree polarizer, 233-a third single-fiber collimator;
241-third 0 ° polarizer, 242-third optical switch, 243-first 90 ° faraday rotator, 244-coupler, 245-fourth single fiber collimator;
251-fourth 0 degree polarizer, 252-fourth optical switch, 253-second 90 degree Faraday rotator, 254-third dual fiber collimator, 255-combiner.
300-beam splitter-combiner, 410-first reflector, 420-second reflector, 510-fiber delay line, 520-first single-fiber collimator, 600-quarter wave plate, 700-beam splitter, 800-first double-fiber collimator, 900-photodetector, 910-first photodetector, 920-second photodetector.
Detailed Description
In order to make the present application more clearly understood by those skilled in the art, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application, and it is apparent that the described embodiments are only some embodiments of the present application, not all embodiments. All other embodiments, which can be made by one of ordinary skill in the art without undue burden from the present disclosure, are within the scope of the present disclosure.
According to the first aspect of the embodiment of the application, the optical frequency demodulation system is provided, optical frequency information can be demodulated, and the accuracy and resolution of the optical frequency information are high.
Referring to fig. 1, the optical frequency demodulation system provided in the embodiment of the present application includes an optical intensity modulator 100, a polarization state modulation unit, a beam splitter 300, a first mirror 410, a delay device, a second mirror 420, a beam splitter 700, a photodetector 900, and a controller. The light intensity modulator 100 is coupled to the optical signal to be measured to modulate the optical signal to be measured into first transmission light with different light intensities; the polarization state modulation unit is coupled to the light intensity modulator 100 to modulate the first transmission light into a second transmission light with a different polarization state; the beam splitter/combiner 300 is provided with a first optical input end, a first optical output end, a first beam splitting end and a second beam splitting end, the first optical input end is coupled to the polarization state modulation unit so as to split the second transmission light into a first beam splitting light and a second beam splitting light, and the first beam splitting light and the second beam splitting light are respectively output from the first beam splitting end and the second beam splitting end, and the beam splitter/combiner 300 is used for combining two reflected light beams entering from the first beam splitting end and the second beam splitting end into combined light; the first reflecting mirror 410 is configured to reflect the first light beam back to the first light splitting end of the light splitter/combiner 300; the delay device is coupled to the second beam splitting end of the beam splitter/combiner 300; the second mirror 420 is used for reflecting the second light beam transmitted by the retarder back to the retarder; the optical splitter 700 is provided with a second optical input end and two second optical output ends, wherein the second optical input end is coupled to the first optical output end of the optical splitter-combiner 300 so as to split the combined light into a third optical splitter and a fourth optical splitter, and the third optical splitter and the fourth optical splitter are output by the two second optical output ends of the optical splitter 700; the two photodetectors 900 are provided, and the two photodetectors 900 are respectively coupled to two second light output ends of the beam splitter 700; the controller is configured to calculate an optical frequency of the optical signal to be measured according to the measured characterization values of the transmitted light with different light intensities and different polarization states and the demodulation expression of the optical phase delay angle, which are measured by the photodetector 900.
The light intensity modulator 100 may modulate the light signal to be measured into first transmission light of different light intensities, for example, the light intensity modulator 100 modulates the light signal to be measured into first transmission light of a first light intensity and first transmission light of a second light intensity, which are different in intensity. The light intensity modulator 100 may select a light attenuator (VOA) or a 1*N optical switch to modulate the intensity of the light to be measured, and when the light intensity modulator 100 selects the light attenuator, a square wave signal is externally connected to modulate the light signal to be measured into an optical signal with a variable intensity.
The polarization state modulation unit is coupled to the light intensity modulator 100, and can modulate the first transmission light into second transmission light with different polarization states, for example, the polarization state modulation unit modulates the first transmission light into second transmission light with 90 ° polarization states and 0 ° polarization states, and the coupling connection of the light intensity modulator 100 and the polarization state modulation unit enables the polarization state modulation unit to output the following four types of second transmission light respectively: (1) the light intensity is a first light intensity, a 90 degree polarization state; (2) the light intensity is the second light intensity, 90 degree polarization state; (3) the light intensity is the first light intensity, 0 degree polarization state; (4) the light intensity is the second light intensity, 0 degree polarization state.
The beam splitter 300 may be a Polarizing Beam Splitter (PBS), and has beam splitting and beam combining functions, so as to split the second transmission light into a first beam splitter and a second beam splitter, where the first beam splitter and the second beam splitter are mutually orthogonal linear polarized lights, and the two mutually orthogonal linear polarized lights are output from the first beam splitter end and the second beam splitter end respectively; the light splitter 300 may further process the reflected light entering from the first light splitting end and the second light splitting end respectively to form combined light, and emit the combined light through the first light output end.
The delay device is arranged to delay the second light beam passing through the delay device relative to the first light beam, and delay the reflected light beam reflected by the second reflecting mirror 420 passing through the delay device for the second time. The delay may be a fiber delay line 510, a group phase delay (DGD) or other birefringent crystal.
The first mirror 410 and the second mirror 420 may be faraday mirrors, and the first beam splitter and the second beam splitter rotate 90 ° under the effect of the faraday mirrors and return in the original path.
The beam splitter 700 may divide the combined light emitted by the first optical output of the beam splitter/combiner 300 into two beams of light, and output the two beams of light to the two photodetectors 900 respectively, where the beam splitter 700 may be a wollaston prism, and plays a role in polarization analysis. The beam splitter 700 may also be a PBS.
The two photodetectors 900 are respectively coupled to two second optical output ends of the optical splitter 700, so as to convert optical signals of two mutually orthogonal polarized lights into electrical signals and output the electrical signals in the form of a representation value.
The application demodulates the optical signal to be measured into four kinds of second output light sequentially through the light intensity modulator 100 and the polarization state modulation unit which are connected in a coupling way, each kind of second output light is divided into a first beam splitter and a second beam splitter through the beam splitter-combiner 300, the first beam splitter rotates 90 degrees under the action of the first reflecting mirror 410 and returns to the first beam splitter end according to the original path, the second beam splitter end delays through the delayer, then rotates 90 degrees under the action of the second reflecting mirror 420 and returns to the delayer for secondary delay according to the original path, the second beam splitter end returns the value, the two beams of linear polarized reflected light with the phase delay difference of theta returned through the first beam splitter end and the second beam splitter end are recombined into a combined light, the combined light is divided into two beams of polarized light which are mutually orthogonal through the beam splitter 700, and the characterization value is output through the photoelectric detector 900.
Four types of second output light are provided, and each second output light may output a characterization value from the two photodetectors 900. If the signal to be measured is sequentially adjusted to four second output lights, each photodetector 900 can output four characterization values, and a total of eight characterization values are output. The controller is used for calculating the optical phase delay angle according to the eight characterization values and the expression of the optical phase delay angle, and calculating and obtaining the optical frequency of the optical signal to be measured according to the optical phase delay angle.
In some embodiments, referring to fig. 1, a quarter wave plate 600 is further disposed between the beam splitter 300 and the beam splitter 700, and the quarter wave plate 600 is parallel to the optical axis of the first optical output end of the beam splitter 300 and the optical axis of the beam splitter 700. The quarter wave plate 600 is provided to delay the optical phase of the combined light returned to the beam splitter/combiner 300 by 90 °, thereby improving the sensitivity of the optical frequency calculation result.
In some embodiments, referring to fig. 1, a first dual-fiber collimator 800 is disposed between the optical splitter 700 and the photodetector 900, the first dual-fiber collimator 800 is provided with two collimating input ends and two collimating output ends, the two collimating input ends of the first dual-fiber collimator 800 are respectively coupled to the two second light output ends of the optical splitter 700, and the two collimating output ends of the first dual-fiber collimator 800 are respectively coupled to the two photodetectors 900. The first dual-fiber collimator 800 is formed by precisely positioning a pigtail and a self-focusing lens, and can convert two mutually orthogonal polarized lights split by the beam splitter 700 into collimated light (parallel light), so as to reduce transmission loss and ensure that optical signals with enough energy are transmitted to the photodetector 900.
In some embodiments, referring to fig. 1, when the delay device is a fiber delay line 510, in order to improve the light transmission efficiency, the optical frequency demodulation system further includes a first single fiber collimator 520 located between the optical splitter 300 and the delay device. The first single fiber collimator 520 may convert the second split light into collimated light to reduce transmission loss. The optical fiber delay line 510 may be a fixed optical fiber delay line or a tunable optical fiber delay line.
In some embodiments, referring to fig. 2, the polarization modulation unit includes a first optical switch 211, a second dual-fiber collimator 212, and a first polarizer 213 sequentially disposed along an optical path, where the first optical switch 211 is provided with a third optical input end and two third optical output ends, the third optical input end of the first optical switch 211 is coupled to the optical intensity modulator 100, the two collimating input ends of the second dual-fiber collimator 212 are respectively connected to the two third optical output ends of the first optical switch 211, the two polarizing input ends of the first polarizer 213 are coupled to the two collimating output ends of the second dual-fiber collimator 212, and the polarizing output end of the first polarizer 213 is coupled to the first optical input end of the optical splitter-combiner 300, and the optical axis is 45 °.
The first optical switch 211 may be configured to form two optical paths, where the first optical switch 211 may control the two third optical output ends to be turned on alternately, and when one of the third optical output ends is turned on, the first optical path is turned on, and the first transmission light of the first light intensity/the second light intensity sequentially passes through the corresponding third optical output end, the collimating input end of the corresponding second dual-fiber collimator 212, and the first polarizer 213; when the other third light output end is turned on, the second light path is turned on, and the first transmission light of the first light intensity/the second light intensity sequentially passes through the corresponding third light output end, the collimating input end of the corresponding second dual fiber collimator 212, and the first polarizer 213.
The two polarized inputs of the first polarizer 213 are respectively a 90 ° polarized input and a 0 ° polarized input, and the optical signals output from the two collimating outputs of the second dual-fiber collimator 212 are aligned with the two optical axes of the first polarizer 213, respectively, so that the optical signal entering the 90 ° polarized input is polarized by the first polarizer 213 to be 90 ° polarized, and the optical signal entering the 0 ° polarized input is polarized by the first polarizer 213 to be 0 °.
In some embodiments, the first polarizer 213 may be a Wollaston prism, and in other embodiments, the first polarizer 213 may be a polarizing beam splitter, i.e., a PBS+ mirror.
In some embodiments, referring to fig. 3, the light intensity modulator 100 is provided with two modulation output ends, the polarization state modulation unit includes a first 0 ° polarizer 221, a 90 ° polarizer 222, and a second optical switch 223, the second optical switch 223 is provided with a fourth optical output end and two fourth optical input ends, the two fourth optical input ends are respectively coupled to the first 0 ° polarizer 221 and the 90 ° polarizer 222, and the fourth optical output end is coupled to the first optical input end of the beam splitter 300; the first 0 ° polarizer 221 and the 90 ° polarizer 222 are each 45 ° with respect to the optical axis of the first light input end of the beam splitter 300.
The first 0 ° polarizer 221 may convert the first transmission light output from the modulation output terminal of the corresponding light intensity modulator 100 into 0 ° linear polarized light, and transmit the light to the first light input terminal of the light splitter-combiner 300 through the second optical switch 223.
The 90 ° polarizer 222 converts the first transmission light outputted from the modulation output end of the corresponding light intensity modulator 100 into 90 ° linear polarized light, and transmits the light to the first light input end of the beam splitter/combiner 300 through the second optical switch 223.
The first 0 ° polarizer 221 and the 90 ° polarizer 222 may be a polarizer, a nicol, or the like.
In order to improve the light transmission efficiency, in some embodiments, referring to fig. 3, a second single fiber collimator 224 is disposed between the fourth light output end of the second optical switch 223 and the first light input end of the beam splitter/combiner 300, so as to maximize the light beam transmitted by the optical fiber into the space transmission device.
In some embodiments, referring to fig. 4, the polarization modulation unit includes a second 0 ° polarizer 231 and an adjustable 90 ° polarizer 232 sequentially disposed between the light intensity modulator 100 and the beam splitter/combiner 300 along the optical path; the second 0 deg. polarizer 231 is 45 deg. to the optical axis of the first light input end of the beam splitter 300.
In some embodiments, the second 0 ° polarizer 231 is a polarizer plate for polarizing the incoming first transmitted light to 0 ° linearly polarized light. In some embodiments, the adjustable 90 ° polarizer 232 is an electronically controlled adjustable 90 ° faraday rotator having two operating positions, a 0 ° operating position and a 90 ° operating position, respectively, that is, when the adjustable 90 ° polarizer 232 is in the 0 ° operating position, it does not polarize the light passing through itself, i.e., outputs 0 ° linearly polarized light to the first light input end of the beam splitter/combiner 300; when the adjustable 90 polarizer 232 is in the 90 operating position, the light passing through itself is polarized by 90 to transmit 90 linearly polarized light to the first light input of the beam splitter/combiner 300.
In some embodiments, referring to fig. 4, a third single fiber collimator 233 is disposed between the tunable 90 ° polarizer 232 and the first optical input end of the beam splitter 300.
In some embodiments, referring to fig. 5, the polarization modulating unit includes a third 0 ° polarizer 241, a third optical switch 242, a first 90 ° faraday rotator 243, and a coupler 244, where the third 0 ° polarizer 241 is coupled to the light intensity modulator 100, the third optical switch 242 is provided with a fifth optical input end and two fifth optical output ends, the fifth optical input end is coupled to the third 0 ° polarizer 241, one of the fifth optical output ends of the third optical switch 242 is coupled to one of the coupling input ends of the coupler 244, two ends of the first 90 ° faraday rotator 243 are coupled to the other of the fifth optical output ends of the third optical switch 242 and the other coupling input end of the coupler 244, and the coupling output end of the coupler 244 is coupled to the first optical input end of the beam splitter 300; the third 0 deg. polarizer 241 is at 45 deg. to the first light input end optical axis of the beam splitter/combiner 300. The coupler 244 may be a 2*1 coupler, a 3*1 coupler, or the like, and is not limited thereto.
The third 0 ° polarizer 241 may be a polarizing plate that polarizes the light beam passing through itself to output 0 ° linearly polarized light, which 0 ° linearly polarized light passes through from one of the fifth light output ends (the other fifth light output end is turned off) to the coupler 244 by the third light switch 242, and enters the first light input end of the beam splitter/combiner 300; at the other fifth light output end of the third light switch 242, which is turned on (one fifth light output end is turned off), the output 0 ° linearly polarized light is transmitted to the first 90 ° faraday rotator 243 along the other fifth light output end of the third light switch 242, so that the 0 ° linearly polarized light is rotated by 90 ° to 90 ° linearly polarized light, and enters the first light input end of the beam splitter/combiner 300 through the coupler 244.
In some embodiments, a fourth single fiber collimator 245 is disposed between the coupling-out end of the coupler 244 and the first optical input end of the beam splitter-combiner 300.
In some embodiments, referring to fig. 6, the polarization modulation unit includes a fourth 0 ° polarizer 251, a fourth optical switch 252, a second 90 ° faraday rotator 253, a third dual fiber collimator 254, and a combiner 255, where the second 0 ° polarizer 231 is coupled to the light intensity modulator 100; the fourth optical switch 252 is provided with a sixth optical input end and two sixth optical output ends, and the sixth optical input end is coupled to the fourth 0 ° polarizer 251; a second 90 faraday rotator 253 is coupled to one of the sixth light outputs; the two collimation input ends of the third dual-fiber collimator 254 are respectively coupled to the other sixth light output end and the second 90 ° faraday rotator 253; the two light combining input ends of the light combiner 255 are coupled to the two collimating output ends of the third dual-fiber collimator 254, and the light combining output end of the light combiner 255 is coupled to the first light input end of the light splitter-combiner 300.
In some embodiments, the combiner 255 may be a non-polarizing beam splitter (NPBS). In some embodiments, the light combiner 255 may further use a Polarizing Beam Splitter (PBS), where the light combiner 255 uses a Polarizing Beam Splitter (PBS), the second 0 ° polarizer 231 is parallel to the optical axis of one interface of the PBS and the output axis of the fourth optical switch 252, and the second 0 ° polarizer 231 is 90 ° to the optical axis of the other interface of the PBS.
In some embodiments, the first optical switch 211, the second optical switch 223, the adjustable 90 ° polarizer 222, the third optical switch 242, and the fourth optical switch 252 are all electrically connected to a controller to control the opening and closing of two optical paths corresponding to the optical switches, and the adjustable 90 ° polarizer 222 is switched between the 0 ° working position and the 90 ° working position, and the controller can control the adjustable 90 ° polarizer 222 to be automatically switched between the 0 ° working position and the 90 ° working position within a set interval time, and the set interval time can be set as required, and the set interval time is not limited in particular.
An embodiment of a second aspect of the present application provides an optical frequency demodulation method, which is applicable to the optical frequency demodulation system of the first aspect, where accuracy of optical frequency information demodulated by the demodulation method is high, and resolution is high.
The optical frequency demodulation method provided by the embodiment of the application comprises the following steps:
Test procedure: coupling the light intensity modulator 100 of the optical frequency demodulation device with the optical signal to be measured, so that each photoelectric detector 900 outputs measurement characterization values under the first light intensity and the second light intensity in the 90-degree polarization state and measurement characterization values under the first light intensity and the second light intensity in the 0-degree polarization state;
calculation step: substituting the eight measurement characterization values into a demodulation expression of the optical phase delay angle, and calculating the optical frequency of the light source to be measured.
In some embodiments, the demodulation expression for the optical phase delay angle is:
or alternatively, the first and second heat exchangers may be,
wherein: deltaU 11M Is the difference between the measured characterization values of the first and second intensities of light for a photodetector 900 at 90 polarization, deltaU 12M For the difference in measured characterization values for the first and second intensities of light for the other photodetector 900 at a 90 polarization state, deltaU 21M Is the difference between the measured characterization values of the first and second light intensities of a photodetector 900 at 0 polarization, deltaU 22M Is the difference between the measured characterization values for the first and second intensities of light for the other photodetector 900 at 0 polarization.
The demodulation expression of the optical phase retardation angle can be obtained by the following method:
taking an optical frequency adjusting device (without a quarter wave plate 600) including an optical intensity modulator 100, a polarization state modulating unit 200, a beam splitter 300, a first reflecting mirror 410, a second reflecting mirror 420, a retarder, a beam splitter 700 and a photodetector 900 as an example, a numerical analysis model of the dual-optical-path optical frequency demodulation system is constructed by using a jones matrix.
First, define the incident light Jones vector as E in Normalizing the intensity of the light signal to be measured, i.e. E, without taking into account any defects x ＝E y =1. The jones matrix of the first transmitted light outputting the second transmitted light of two different polarization states through the polarization state modulation unit can be expressed as:
for detailed analysis, one polarization state is taken as an example, and the optical splitter/combiner 300, the delay device, the reflecting mirrors (the first reflecting mirror 410 and the second reflecting mirror 420) and the optical splitter 700 in the optical frequency demodulation system can be expressed as follows:
θ＝2πfτ (7)
wherein J is P Jones matrix, J, of the beam splitter 300 F Jones matrix, J, being a delay FM Jones matrix, J, for first mirror 410 and second mirror 420 W In order to form the optical system matrix of the beam splitter 700, θ is an optical phase delay angle generated when the first beam splitter and the second beam splitter split by the beam splitter 300 are reflected by the first mirror 410 and the second mirror 420, respectively, and τ is a delay time generated when the first beam splitter and the second beam splitter split by the beam splitter 300 are reflected by the first mirror 410 and the second mirror 420, respectively, and f is an optical frequency of an optical signal to be measured.
The total output of the optical propagation path of the optical signal to be measured is:
Note that inThe light intensity coefficient is synthesized for the light beam passing through the beam splitter-combiner 300 for the second time, that is, the light intensity coefficient is synthesized for the light beam when the two reflected light beams enter the beam splitter-combiner 300.
The characterization values detected by the two photodetectors 900 are respectively:
in the method, in the process of the invention,and->Are respectively->Is>And->Are respectively->And->Is a complex matrix of the matrix.
Similarly, after the polarization state modulation unit works, the total output of the optical propagation path of the optical signal to be measured in the other polarization state is as follows:
the characterization values detected by the two photodetectors 900 are respectively:
as can be seen from (9), (10), (12) and (13), the expression of the characterization value detected by the photodetector 900 is:
or->
Wherein,is the optical path loss coefficient under ideal condition, and in practical application, the optical path loss coefficient is +.>And the representation of the characterization value detected by photodetector 900 also takes into account the absence of a bias voltage. Thus, the expression of the characterization value detected by photodetector 900 is actually:
P out ＝△V(T 1 ) +P (1.+ -. Cos θ) or
Taking the representation value as a voltage representation value U as an example, the expression of the voltage representation value U detected by the photodetector 900 is as follows:
U＝△V(T 1 ) +P (1.+ -. Cos θ) or
Wherein DeltaV (T) 1 ) Is thatNo bias voltage exists, P is the optical path loss coefficient when the transmission optical path is conducted,
P 0 For the output light intensity of the light signal to be measured, P is the light intensity of the first light intensity, the second light intensity, the 90 degree polarization state and the 0 degree polarization state 0 All are unchanged.
Alpha is the light intensity loss coefficient of the light intensity modulator 100, and the light intensity attenuation coefficient at the first light intensity is alpha 1 The attenuation coefficient of the light intensity at the second light intensity is alpha 2 。
Beta is the light intensity loss coefficient when the light passes through the polarization state modulation unit, and when the second transmitted light is in 90 DEG polarization state, the light intensity loss coefficient is beta 1 The light intensity loss coefficient is beta when the second transmitted light is in 0 degree polarization state 2 。
Gamma is the loss coefficient of the light intensity of the second transmitted light transmitted to the photodetector 900 after entering the beam splitter/combiner 300, and is respectively gamma 1 (first photodetector 910) and γ 2 (second photodetector 920).
G is the gain of the photodetector 900 to convert the optical signal into an electrical signal, and the first photodetector 910 is G 1 The second photodetector 920 is G 2 。
Two photodetectors 900 are illustrated as a first photodetector 910 and a second photodetector 920, respectively:
the expressions of the first and second characterization values of the first and second light intensities of the first photodetector 910 in the 90 ° polarization state are:
the expressions of the third characterization value and the fourth characterization value of the first light intensity and the second light intensity of the second photodetector 920 in the 90 ° polarization state are respectively:
/>
The expressions of the fifth characterization value and the sixth characterization value for the first light intensity and the second light intensity when the first photodetector 910 is in the 0 ° polarization state are respectively:
the seventh calibration characteristic value and the eighth calibration characteristic value of the second photodetector 920 under the first light intensity and the second light intensity in the 0 ° polarization state have the following expressions:
subtracting the formula (17) and the formula (18) to obtain:
subtracting the formula (19) and the formula (20) to obtain:
subtracting the formula (21) and the formula (22) to obtain:
subtracting the formula (23) and the formula (24) to obtain:
the following treatments (25), (26), (27) and (28) were performed:
positive values in the results are obtained (positive values are all taken in subsequent calculations):
the following other treatments (25), (26), (27) and (28) were performed:
the demodulation expression of the optical phase retardation angle thus obtained is:
equation (29) and equation (31) are solutions of two demodulation expressions of the optical phase delay angle, and one of them may be selected according to the need, which is not limited in this application.
Due to the optical frequency of the optical signal to be measuredThereby, the optical frequency of the optical signal to be measured can be demodulated.
After the optical frequency of the optical signal to be measured in the first environment is known, the optical frequency of the optical signal to be measured in the second environment can be calculated by adopting the steps, so that the optical frequency variation of the optical signal to be measured in the first environment and the second environment can be demodulated; the optical phase delay angle difference of the optical signal to be measured in the first environment and the second environment can be demodulated.
The first environment and the second environment may be any one of different temperatures, different vibration frequencies, different vibration intensities, and different atmospheric pressures, or may be a combination of a plurality of kinds.
In some embodiments, when the optical frequency demodulation system includes the quarter wave plate 600, the demodulation expression of the optical phase retardation angle is:
or->
The optical frequency demodulation system and the optical frequency demodulation method provided by the invention have at least the following advantages:
(1) The optical frequency demodulation system demodulates the measured light into two beams of first transmission light with different light intensities through the light intensity modulator 100, then makes the first transmission light polarized through the polarization state modulation unit, divides the polarized first transmission light into two beams of orthogonal polarized light through the beam splitter-combiner 300, makes the two beams of orthogonal polarized light after being transmitted through different optical paths under the action of the delayer, and then respectively reflects the two beams of orthogonal polarized light through the Faraday reflector, then passes through the beam splitter-combiner 300 again, finally splits the beams through the beam splitter 700, and the signals are respectively collected by the two photodetectors 900. According to the method, the optical frequency demodulation is carried out through the signal processing method of the dual-optical-path polarization analysis, and due to the fact that the second transmission optical polarization state is different, the voltage signals detected by the photoelectric detectors are also different, the influence of no optical bias voltage, optical path loss and light source fluctuation is eliminated by means of coefficient matching of the dual-optical-path optical frequency demodulation system, so that dynamic balance of two paths of photoelectric signals is achieved, and high-precision demodulation of optical frequency is guaranteed.
(2) The optical frequency demodulation system is provided with the quarter wave plate 600, so that the sensitivity of optical frequency detection is improved.
(3) The optical frequency demodulation system can be used for accurately measuring the change of the optical frequency of the light to be measured caused by the change of the external environment (such as temperature, strain, vibration and the like), and has the characteristics of accurate error compensation and simple algorithm.
In this application, unless expressly stated or limited otherwise, a first feature "above" or "below" a second feature may include both the first and second features being in direct contact, and may also include the first and second features not being in direct contact but being in contact with each other by way of additional features therebetween. Moreover, a first feature being "above," "over" and "on" a second feature includes the first feature being directly above and obliquely above the second feature, or simply indicating that the first feature is higher in level than the second feature. The first feature being "under", "below" and "beneath" the second feature includes the first feature being directly under and obliquely below the second feature, or simply means that the first feature is less level than the second feature.
In the description of the present application, it should be understood that the terms "center," "longitudinal," "transverse," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise" indicate or positional relationships are based on the positional relationships shown in the drawings, merely for convenience of description and to simplify the description, and do not indicate or imply that the devices or elements referred to must have a specific orientation, be configured and operated in a specific orientation, and therefore should not be construed as limiting the present application.
In the present application, unless explicitly specified and limited otherwise, the terms "coupled," "secured," and the like are to be construed broadly, and for example, "secured" may be either permanently attached or removably attached, or integrally formed; can be mechanically or electrically connected; can be directly connected or indirectly connected through an intermediate medium, and can be communicated with the inside of two elements or the interaction relationship of the two elements. The specific meaning of the terms in this application will be understood by those of ordinary skill in the art as the case may be.
In addition, descriptions such as those related to "first," "second," and the like, are provided for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated in this application. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include one or more features. In the description of the present application, the meaning of "a plurality" is two or more, unless explicitly defined otherwise.
While embodiments of the present application have been shown and described, it will be understood by those of ordinary skill in the art that: many changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the application, the scope of which is defined by the claims and their equivalents.
Claims (10)
1. An optical frequency demodulation system, comprising:
the light intensity modulator is used for coupling and connecting with the light signal to be detected so as to modulate the light signal to be detected into first transmission light with different light intensities;
a polarization state modulation unit coupled to the light intensity modulator to modulate the first transmitted light into a second transmitted light of a different polarization state;
the light splitting and combining device is provided with a first light input end, a first light output end, a first light splitting end and a second light splitting end, wherein the first light input end is coupled and connected with the polarization state modulation unit so as to split the second transmission light into a first light splitting and a second light splitting, and the first light splitting end and the second light splitting end are respectively used for outputting the second transmission light, and the light splitting and combining device is used for combining two reflected lights entering from the first light splitting end and the second light splitting end into combined light;
the first reflector is used for reflecting the first light beam back to the first light splitting end of the light splitting and combining device;
the delayer is coupled and connected to the second light splitting end of the light splitting and combining device;
the second reflector is used for reflecting the second light splitting transmitted by the delayer back to the delayer;
the optical splitter is provided with a second optical input end and two second optical output ends, the second optical input end is coupled and connected with the first optical output end of the optical splitter and combiner so as to split the combined light into a third light splitter and a fourth light splitter, the third light splitter and the fourth light splitter are output by the two second optical output ends of the optical splitter, and the optical splitter is parallel to the optical axis of the first optical output end of the optical splitter and the fourth light splitter;
The two photoelectric detectors are respectively coupled and connected to the two second light output ends of the light splitter;
and the controller is electrically connected with the photoelectric detector and is used for calculating the optical frequency of the optical signal to be detected according to the measured characterization values of the transmitted light with different light intensities and different polarization states and the demodulation expression of the optical phase delay angle, which are measured by the photoelectric detector.
2. The optical frequency demodulating system according to claim 1, wherein a quarter wave plate is further provided between the beam splitter and the beam splitter, and the quarter wave plate is parallel to the optical axis of the first optical output end of the beam splitter and the optical axis of the beam splitter.
3. The optical frequency demodulation system according to any one of claims 1-2, wherein a first dual-fiber collimator is arranged between the optical splitter and the photo-detector, and the first dual-fiber collimator is provided with two collimating input ends respectively coupled to two second optical output ends of the optical splitter and two collimating output ends respectively coupled to two photo-detectors; when the delay device is an optical fiber delay line, the optical frequency demodulation system further comprises a first single optical fiber collimator positioned between the beam splitter and the delay device.
4. The optical frequency demodulation system according to any one of claims 1-2, wherein the polarization state modulation unit comprises a first optical switch, a second dual-fiber collimator and a first polarizer, which are sequentially arranged along an optical path, the first optical switch is provided with a third optical input end and two third optical output ends, the third optical input end of the first optical switch is coupled to the optical intensity modulator, the two collimating input ends of the second dual-fiber collimator are respectively connected to the two third optical output ends of the first optical switch, the two polarizing input ends of the first polarizer are coupled to the two collimating output ends of the second dual-fiber collimator, and the polarizing output end of the first polarizer is coupled to the first optical input end of the optical splitter and the optical axis is 45 °.
5. The optical frequency demodulation system according to any one of claims 1-2, wherein the optical intensity modulator is provided with two modulation output terminals, the polarization state modulation unit comprises a first 0 ° polarizer, a 90 ° polarizer and a second optical switch, the second optical switch is provided with a fourth optical output terminal and two fourth optical input terminals, the two fourth optical input terminals are respectively coupled to the first 0 ° polarizer and the 90 ° polarizer, and the fourth optical output terminal is coupled to the first optical input terminal of the beam splitter; the first 0-degree polarizer and the 90-degree polarizer are 45 degrees with the optical axis of the first light input end of the light splitting and combining device.
6. The optical frequency demodulating system according to any one of claims 1-2, wherein the polarization state modulating unit includes a second 0 ° polarizer and an adjustable 90 ° polarizer sequentially disposed between the light intensity modulator and the beam splitter-combiner along an optical path; the second 0-degree polarizer and the first optical input end of the beam splitter-combiner form an optical axis of 45 degrees.
7. The optical frequency demodulation system according to any one of claims 1-2, wherein the polarization state modulation unit comprises a third 0 ° polarizer, a third optical switch, a first 90 ° faraday rotator, and a coupler, the third 0 ° polarizer is coupled to the optical intensity modulator, the third optical switch is provided with a fifth optical input end and two fifth optical output ends, the fifth optical input end is coupled to the third 0 ° polarizer, one of the fifth optical output ends of the third optical switch is coupled to one of the coupling input ends of the coupler, two ends of the first 90 ° faraday rotator are coupled to the other of the fifth optical output ends of the third optical switch and the other coupling input end of the coupler, and the coupling output end of the coupler is coupled to the first optical input end of the light splitting/combining device; the third 0-degree polarizer forms 45 degrees with the optical axis of the first light input end of the light splitting and combining device.
8. An optical frequency demodulation system according to any one of claims 1-2, wherein the polarization state modulation unit comprises:
a fourth 0 degree polarizer coupled to the light intensity modulator;
the fourth optical switch is provided with a sixth optical input end and two sixth optical output ends, and the sixth optical input end is coupled and connected with the fourth 0-degree polarizer;
a second 90 ° faraday rotator coupled to one of said sixth light output ends;
the two collimating input ends of the third double-fiber collimator are respectively coupled and connected with the other sixth light output end and the second 90-degree Faraday rotator;
and the two light combining input ends of the light combining device are coupled and connected with the two collimation output ends of the third double-fiber collimator one by one, and the light combining output end of the light combining device is coupled and connected with the first light input end of the light splitting and combining device.
9. An optical frequency demodulation method suitable for use in an optical frequency demodulation system according to any one of claims 1-8, the optical frequency demodulation method comprising:
the testing steps are as follows: coupling the light intensity modulator of the optical frequency demodulation device with the optical signal to be detected, so that each photoelectric detector outputs measurement characterization values under the first light intensity and the second light intensity in the 90-degree polarization state and measurement characterization values under the first light intensity and the second light intensity in the 0-degree polarization state;
The calculation steps are as follows: substituting the eight measurement characterization values into a demodulation expression of the optical phase delay angle, and calculating the optical frequency of the light source to be measured.
10. The optical frequency demodulating method according to claim 9, wherein the demodulation expression of the optical phase delay angle is:
or alternatively, the first and second heat exchangers may be,
wherein: deltaU 11M Is the difference value of the measurement characterization value of the first light intensity and the second light intensity of a photoelectric detector in the 90 DEG polarization state, delta U 12M For the difference of the measured characterization values of the first light intensity and the second light intensity of the other photodetector in the 90 DEG polarization state, deltaU 21M Is the difference value of the measurement characterization value of the first light intensity and the second light intensity of a photoelectric detector in the 0 DEG polarization state, delta U 22M For the difference in measured characterization values of the first and second light intensities of the other photodetector at 0 deg. polarization.
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