CN111327366A - System and method for quickly locking minimum bias point of electro-optic intensity modulator - Google Patents
System and method for quickly locking minimum bias point of electro-optic intensity modulator Download PDFInfo
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- CN111327366A CN111327366A CN202010306364.8A CN202010306364A CN111327366A CN 111327366 A CN111327366 A CN 111327366A CN 202010306364 A CN202010306364 A CN 202010306364A CN 111327366 A CN111327366 A CN 111327366A
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- 238000000034 method Methods 0.000 title claims abstract description 13
- 230000005540 biological transmission Effects 0.000 claims abstract description 14
- 230000008033 biological extinction Effects 0.000 claims abstract description 13
- 239000013307 optical fiber Substances 0.000 claims description 24
- 230000010287 polarization Effects 0.000 claims description 9
- 238000001914 filtration Methods 0.000 claims description 4
- 230000010354 integration Effects 0.000 claims description 3
- 230000035945 sensitivity Effects 0.000 claims description 3
- 238000004891 communication Methods 0.000 abstract description 6
- 230000003287 optical effect Effects 0.000 abstract description 6
- 238000013461 design Methods 0.000 abstract description 2
- 238000011160 research Methods 0.000 description 4
- 238000010586 diagram Methods 0.000 description 3
- 230000032683 aging Effects 0.000 description 2
- 239000013078 crystal Substances 0.000 description 2
- 230000007613 environmental effect Effects 0.000 description 2
- 239000000835 fiber Substances 0.000 description 2
- 238000005259 measurement Methods 0.000 description 2
- 230000005693 optoelectronics Effects 0.000 description 2
- 238000012545 processing Methods 0.000 description 2
- 238000001514 detection method Methods 0.000 description 1
- GQYHUHYESMUTHG-UHFFFAOYSA-N lithium niobate Chemical compound [Li+].[O-][Nb](=O)=O GQYHUHYESMUTHG-UHFFFAOYSA-N 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/50—Transmitters
- H04B10/501—Structural aspects
- H04B10/503—Laser transmitters
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/50—Transmitters
- H04B10/516—Details of coding or modulation
- H04B10/54—Intensity modulation
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/70—Photonic quantum communication
Abstract
The invention discloses a system and a method for quickly locking a minimum bias point of an electro-optic intensity modulator. The method of the invention utilizes an electric light intensity modulator to periodically modulate the distribution probability of single photon signals and demodulate corresponding TTL signals with the same frequency to obtain error signals corresponding to a transmission curve, uses the error signals to continuously tune offset voltage to lock the minimum offset point of the transmission curve in real time, and obtains long-time high extinction ratio single photon pulse output. The invention solves the problem that the minimum bias point of the electro-optic intensity modulator can not be directly locked at the single photon intensity. The invention has reasonable design, simple locking system, high locking precision and high stability, and can be applied to the fields of quantum communication, optical sensing and the like.
Description
Technical Field
The invention relates to the technical field of quantum communication, optical sensing and the like, in particular to a system and a method for quickly locking a minimum offset point of an electro-optical intensity modulator.
Background
The high extinction ratio single photon pulse has important application in the fields of quantum communication, optical sensing and the like, in the field of quantum communication, the higher the extinction ratio of the single photon pulse is, the higher the interference visibility is, and the lower the corresponding communication error rate is, in the field of optical sensing, the higher the extinction ratio of the single photon pulse is, the smaller the measurement error is, and the higher the corresponding measurement accuracy is, so that how to obtain the high extinction ratio single photon pulse is widely concerned by people. The electro-optical intensity modulator is a device for realizing laser intensity modulation based on a crystal electro-optical effect, usually a bias point of the electro-optical intensity modulator is set at a minimum transmission point, and an electric pulse signal is loaded at a radio frequency end, so that an input continuous single photon signal can be modulated into a single photon pulse with a high extinction ratio. However, the bias point shifts due to external mechanical vibration, environmental temperature changes, instrument aging, and the like. At this time, the pulsed light substrate will separate a part of energy, which causes the extinction ratio of the single photon pulse to decrease, so the minimum bias point of the electro-optical intensity modulator needs to be locked to output the single photon pulse with high extinction ratio. The traditional locking method is based on classical strong light for locking and can not directly lock single photon intensity.
Disclosure of Invention
In order to solve the problem that the minimum offset point of the electro-optic intensity modulator cannot be directly locked at the single-photon intensity in the prior art, the invention aims to provide a system and a method for rapidly locking the minimum offset point of the electro-optic intensity modulator, the minimum offset point can be automatically locked at the single-photon intensity in real time, so that single-photon pulses with long-time high extinction ratio are output, and the locking system is simple, high in locking precision and high in stability.
The invention is realized by adopting the following technical scheme:
a system for rapidly locking the minimum bias point of an electro-optic intensity modulator comprises a laser, an attenuator, the electro-optic intensity modulator, an optical fiber coupler, a single photon detector, a phase-locked amplifier, a signal generator, a first adder, an analog proportional-integral-derivative controller, a second adder and a digital delay pulse generator.
The laser output line polarization laser signal passes through the attenuator and then enters the electro-optic intensity modulator, the output end of the electro-optic intensity modulator is connected with the input end of the optical fiber coupler, the first output end of the optical fiber coupler is used as a signal output end (used for scientific research), the second output end of the optical fiber coupler is connected with the input end of the single photon detector, the output end of the single photon detector is connected with the input end of the phase-locked amplifier, the output end of the phase-locked amplifier is connected with the input end of the analog proportional-integral-derivative controller, the output end of the signal generator is connected with the first input end of the first adder, the output end of the analog proportional-integral-derivative controller is connected with the second input end of the first adder, the output end of the first adder is connected with the offset end of the electro-optic intensity modulator, and the modulation output end of the phase-locked amplifier is connected, and a first output end of the digital delay pulse generator is connected with a second input end of a second adder, an output end of the second adder is connected with a radio frequency end of the electro-optical intensity modulator, and a second output end of the digital delay pulse generator is connected with a trigger end of the single photon detector.
The method for rapidly locking the minimum bias point of the electro-optic intensity modulator by using the system comprises the following steps:
the laser outputs a linear polarization laser signal transmitted along the slow axis of the polarization-maintaining optical fiber, the laser signal enters the attenuator to reduce the intensity to a single photon magnitude, and then the single photon signal is transmitted along the slow axis of the polarization-maintaining optical fiber to enter the electro-optic intensity modulator for modulation.
The signal generator outputs a triangular wave scanning signal which is loaded to a bias end of electro-optic intensity modulation through a first adder so as to perform linear scanning near a minimum bias point, a modulation end of a lock-in amplifier outputs a high-frequency sine wave signal which is loaded to a radio frequency end of the electro-optic intensity modulator through a second adder so as to rapidly modulate the distribution probability of a single photon signal, a digital delay pulse generator outputs a path of TTL pulse which is also loaded to the radio frequency end of the electro-optic intensity modulator through the second adder so as to chop continuous light into single photon pulse light, the modulated single photon pulse is transmitted along a slow axis of a polarization maintaining fiber and enters a fiber coupler to be divided into two beams, one single photon pulse is used for scientific research, the other single photon pulse is detected by a single photon detector, the digital delay pulse generator outputs the other path of TTL pulse to be used as a trigger clock of the single photon detector, and the time interval of the two paths of TTL, the single photon detector converts the single photon pulse light into TTL signals to be input into the lock-in amplifier.
The phase-locked amplifier demodulates the modulated TTL signal, namely the TTL signal and the same-frequency modulation signal are subjected to frequency mixing processing and low-pass filtering to obtain an error signal for locking a minimum offset point, the integration time, the sensitivity, the filtering slope and the phase of the modulation signal of the phase-locked amplifier are adjusted to enable the signal-to-noise ratio of the error signal to be maximum, the central position of the error signal corresponds to the minimum offset point of a transmission curve, and the error signal is used for tracking and locking the minimum offset point in real time.
The error signal is optimized by the analog proportional-integral-derivative controller and then loaded to the offset end of the electro-optic intensity modulator through the first adder, the triangular wave scanning signal output by the signal generator is switched into direct-current voltage, the voltage amplitude and the parameters of the analog proportional-integral-derivative controller are adjusted, the amplitude of the error signal is enabled to be minimum, the error signal realizes real-time locking of the minimum offset point of the electro-optic intensity modulator through continuous tuning of offset voltage, and long-time high extinction ratio single photon pulse output is obtained.
The invention utilizes the electric light intensity modulator to modulate the single photon signal through the periodic intensity and demodulate the photoelectric converted TTL signal at the same frequency to obtain an error signal corresponding to the transmission curve, and continuously tunes the bias voltage by using the error signal to lock the minimum bias point of the transmission curve in real time. The method solves the problem that the minimum bias point of the electro-optic intensity modulator cannot be directly locked at the single photon intensity.
The invention has reasonable design and good practical application value.
Drawings
Fig. 1 shows a schematic connection diagram of the system of the invention (the dashed lines represent optical signals transmitted by polarization-maintaining optical fibers and the solid lines represent electrical signals).
Fig. 2 shows a transmission diagram of an electro-optical intensity modulator.
Fig. 3 shows an error signal for locking the minimum bias point.
In the figure: the system comprises a 1-laser, a 2-attenuator, a 3-electro-optic intensity modulator, a 4-optical fiber coupler, a 5-single photon detector, a 6-phase-locked amplifier, a 7-signal generator, an 8-first adder, a 9-analog proportional-integral-derivative controller, a 10-second adder and a 11-digital delay pulse generator.
Detailed Description
The following detailed description of specific embodiments of the invention refers to the accompanying drawings.
A system for rapidly locking the minimum bias point of an electro-optic intensity modulator is shown in FIG. 1 and comprises a laser 1 (orbit Lightwave, ETH), an attenuator 2, an electro-optic intensity modulator 3, an optical fiber coupler 4 (THORLABS, PN1550R5A 1), a single photon detector 5 (Quantum, QCD 300), a phase-locked amplifier 6 (SRS, SR 830), a signal generator 7 (Tektronix, AFG 3102), a first adder 8, an analog proportional-integral-derivative controller 9 (SRS, SIM 960), a second adder 10 and a digital delay pulse generator 11 (SRS, DG 645).
As shown in figure 1, a classical linear polarization laser signal output by a laser 1 passes through an attenuator 2 and then enters an electro-optical intensity modulator 3, the output end of the electro-optical intensity modulator 3 is connected with the input end of an optical fiber coupler 4, a first output end of the optical fiber coupler 4 outputs a signal for scientific research, a second output end of the optical fiber coupler 4 is connected with the input end of a single photon detector 5, the output end of the single photon detector 5 is connected with the input end of a phase-locked amplifier 6, the output end of the phase-locked amplifier 6 is connected with the input end of an analog proportional integral derivative controller 9, the output end of a signal generator 7 is connected with a first input end of a first adder 8, the output end of the analog proportional integral derivative controller 9 is connected with a second input end of the first adder 8, the output end of the first adder 8 is connected with a bias end of the electro-optical intensity modulator 3, the modulation output end of the phase-locked amplifier 6, the first output end of the digital delay pulse generator 11 is connected with the second input end of the second adder 10, the output end of the second adder 10 is connected with the radio frequency end of the electro-optical intensity modulator 3, and the second output end of the digital delay pulse generator 11 is connected with the trigger end of the single photon detector 5.
The electro-optical intensity modulator used in the embodiment of the invention is an intensity modulator with a Mach-Zehnder interferometer structure, and laser intensity modulation is realized by changing external voltage to adjust the relative phase of two waveguide arms based on the electro-optical effect of the lithium niobate crystal. Under classical light intensity, corresponding transmission light intensity of the electro-optic intensity modulator under different bias voltages is measured in sequence by using a direct-current power supply and a photoelectric detector to obtain a transmission curve diagram of the electro-optic intensity modulator, as shown in fig. 2, the transmission curve is subjected to random drift due to factors such as environmental disturbance and instrument aging, and therefore the minimum bias point needs to be locked in real time.
The method for rapidly locking the minimum bias point of the electro-optic intensity modulator by using the system comprises the following steps:
the laser 1 outputs a 1550nm linear polarization classical laser signal transmitted along a slow axis of the polarization-maintaining optical fiber, the laser signal enters the attenuator 2 to reduce the intensity to a single photon magnitude, namely the average photon number in each detection gate corresponding to the single photon detector 5 is about 0.1, and then the single photon signal is transmitted along the slow axis of the polarization-maintaining optical fiber to enter the electro-optic intensity modulator 3 for modulation.
A signal generator 7 outputs a 10Hz triangular wave scanning signal to be loaded to a bias end of an electro-optic intensity modulator 3 through a first adder 8 so as to perform linear scanning near a minimum bias point, a modulation end of a phase-locked amplifier 6 outputs an 8kHz sine wave signal to be loaded to a radio frequency end of the electro-optic intensity modulator 3 through a second adder 10 so as to rapidly modulate the single photon signal distribution probability, a digital delay pulse generator 11 outputs a TTL pulse with a frequency of 4MHz and is also loaded to the radio frequency end of the electro-optic intensity modulator 3 through the second adder 10 so as to chop continuous light into 4MHz single photon pulse light, the modulated single photon pulse is transmitted along a polarization maintaining optical fiber slow axis and enters an optical fiber coupler 4 (a splitting ratio of 50: 50) to be divided into two single photon pulses with equal intensity, one single photon pulse is used for scientific research, the other single photon pulse is detected by a single photon detector 5, the digital delay pulse generator 11 outputs another path of TTL pulse with a frequency of 4MHz as a trigger clock of the single-photon detector 5, and adjusts the time interval of the two paths of TTL pulses to align the single-photon pulse with the sampling gate of the single-photon detector 5, so that the single-photon detector 5 has the highest collection efficiency, and the single-photon detector 5 converts the single-photon pulse light into a TTL signal to be input to the lock-in amplifier 6.
The phase-locked amplifier 6 demodulates the modulated TTL signal, that is, the TTL signal and the same-frequency modulated signal are subjected to frequency mixing processing and low-pass filtering to obtain an error signal for locking the minimum offset point, adjusts the integration time of the phase-locked amplifier 6 to 3ms, the sensitivity to 50mV, and the filter slope to 12dB, and changes the phase of the sine wave modulated signal so that the signal-to-noise ratio of the error signal is at most 39, as shown in fig. 3, the center position of the error signal corresponds to the minimum offset point of the transmission curve, and the error signal is used for tracking and locking the minimum offset point in real time.
The error signal is optimized by an analog proportional integral derivative controller 9 and then loaded to the offset end of the electro-optic intensity modulator 3 by a first adder 8, the triangular wave scanning signal output by a signal generator 7 is switched into direct current voltage, the voltage amplitude and the parameter of the analog proportional integral derivative controller 9 are adjusted, the amplitude of the error signal is minimum, the error signal realizes real-time locking of the minimum offset point of the electro-optic intensity modulator 3 through continuous tuning of offset voltage, and the extinction ratio of the output single photon pulse within 1000s is larger than 27 dB.
According to the embodiment of the invention, the photoelectric intensity modulator is used for periodically modulating the single photon signal distribution probability and demodulating the corresponding TTL signal at the same frequency to obtain the error signal corresponding to the transmission curve, the error signal is used for continuously tuning the offset voltage to lock the minimum offset point of the transmission curve in real time, and the long-time high extinction ratio single photon pulse output is obtained.
In a word, the invention provides a new system and a new method for directly and quickly locking the minimum offset point of an electro-optic intensity modulator at single photon intensity, obtains long-time high-extinction-ratio single photon pulse output, has simple locking system, high locking precision and high stability, and can be applied to the fields of quantum communication, optical sensing and the like.
It should be noted that modifications and applications may occur to those skilled in the art without departing from the spirit and scope of the invention as defined by the appended claims.
Claims (2)
1. A system for fast locking the minimum bias point of an electro-optic intensity modulator, characterized by: the device comprises a laser (1), an attenuator (2), an electro-optic intensity modulator (3), an optical fiber coupler (4), a single photon detector (5), a phase-locked amplifier (6), a signal generator (7), a first adder (8), an analog proportional-integral-derivative controller (9), a second adder (10) and a digital delay pulse generator (11);
an output line polarization laser signal of the laser (1) passes through the attenuator (2) and then enters the electro-optical intensity modulator (3), the output end of the electro-optical intensity modulator (3) is connected with the input end of the optical fiber coupler (4), the first output end of the optical fiber coupler (4) serves as a signal output end, the second output end of the optical fiber coupler (4) is connected with the input end of the single photon detector (5), the output end of the single photon detector (5) is connected with the input end of the phase-locked amplifier (6), the output end of the phase-locked amplifier (6) is connected with the input end of the analog proportional-integral-derivative controller (9), the output end of the signal generator (7) is connected with the first input end of the first adder (8), and the output end of the analog proportional-integral-derivative controller (9) is connected with the second input end of the first adder (8), the output end of the first adder (8) is connected with the offset end of the electro-optic intensity modulator (3), the modulation output end of the phase-locked amplifier (6) is connected with the first input end of the second adder (10), the first output end of the digital delay pulse generator (11) is connected with the second input end of the second adder (10), the output end of the second adder (10) is connected with the radio frequency end of the electro-optic intensity modulator (3), and the second output end of the digital delay pulse generator (11) is connected with the trigger end of the single photon detector (5).
2. A method for rapidly locking a minimum bias point of an electro-optic intensity modulator, comprising: the method is realized based on the system for rapidly locking the minimum bias point of the electro-optical intensity modulator in claim 1;
the laser (1) outputs a linear polarization laser signal transmitted along the slow axis of the polarization-maintaining optical fiber, the laser signal enters the attenuator (2) to reduce the intensity to a single photon magnitude, and the single photon signal is transmitted along the slow axis of the polarization-maintaining optical fiber and enters the electro-optic intensity modulator (3) for modulation;
the signal generator (7) outputs a triangular wave scanning signal which is loaded to the offset end of the electro-optical intensity modulator (3) through a first adder (8); the modulation end of the phase-locked amplifier (6) outputs a high-frequency sine wave signal which is loaded to the radio frequency end of the electro-optical intensity modulator (3) through a second adder (10); a digital time delay pulse generator (11) outputs one path of TTL pulse, the TTL pulse is loaded to a radio frequency end of an electro-optic intensity modulator (3) through a second adder (10) and is used for chopping continuous light into single photon pulse light, the modulated single photon pulse is transmitted along a polarization maintaining optical fiber slow axis and enters an optical fiber coupler (4) to be divided into two beams, one beam of single photon pulse is output, the other beam of single photon pulse is detected by a single photon detector (5), the digital time delay pulse generator (11) outputs the other path of TTL pulse to serve as a trigger clock of the single photon detector (5), the time interval of the two paths of TTL pulses is adjusted to enable the photon counting collected by the single photon detector (5) to be maximum, and the single photon detector (5) converts the single photon pulse light into TTL;
the phase-locked amplifier (6) demodulates the modulated TTL signal to obtain an error signal for locking the minimum offset point, and the integration time, the sensitivity, the filtering slope and the phase of the modulation signal of the phase-locked amplifier (6) are adjusted to maximize the signal-to-noise ratio of the error signal, wherein the central position of the error signal corresponds to the minimum offset point of a transmission curve, and the error signal is used for tracking and locking the minimum offset point in real time;
the error signal is optimized by an analog proportional integral derivative controller (9) and then loaded to a bias end of the electro-optic intensity modulator (3) through a first adder (8), a triangular wave scanning signal output by a signal generator (7) is switched into direct current voltage, the voltage amplitude and parameters of the analog proportional integral derivative controller (9) are adjusted, the amplitude of the error signal is enabled to be minimum, the error signal realizes real-time locking of the minimum bias point of the electro-optic intensity modulator (3) through continuous tuning of bias voltage, and high extinction ratio single photon pulse output is obtained.
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| US20050058460A1 (en) * | 2003-09-16 | 2005-03-17 | Xiangzhong Wang | Optical transmission controller |
| US9496962B1 (en) * | 2013-06-27 | 2016-11-15 | Clariphy Communications, Inc. | Systems and methods for biasing optical modulating devices |
| CN109193323A (en) * | 2018-11-16 | 2019-01-11 | 忻州师范学院 | Lock the device and method of optical communicating waveband twin-laser frequency |
| CN110146162A (en) * | 2019-06-21 | 2019-08-20 | 忻州师范学院 | The device and method of real-time lock single photon intensity |
| CN211579977U (en) * | 2020-04-17 | 2020-09-25 | 忻州师范学院 | System for fast locking minimum bias point of electro-optical intensity modulator |
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Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US20050058460A1 (en) * | 2003-09-16 | 2005-03-17 | Xiangzhong Wang | Optical transmission controller |
| US9496962B1 (en) * | 2013-06-27 | 2016-11-15 | Clariphy Communications, Inc. | Systems and methods for biasing optical modulating devices |
| CN109193323A (en) * | 2018-11-16 | 2019-01-11 | 忻州师范学院 | Lock the device and method of optical communicating waveband twin-laser frequency |
| CN110146162A (en) * | 2019-06-21 | 2019-08-20 | 忻州师范学院 | The device and method of real-time lock single photon intensity |
| CN211579977U (en) * | 2020-04-17 | 2020-09-25 | 忻州师范学院 | System for fast locking minimum bias point of electro-optical intensity modulator |
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