CN118263768A - Automatic frequency stabilization method of semiconductor laser - Google Patents
Automatic frequency stabilization method of semiconductor laser Download PDFInfo
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- 239000004065 semiconductor Substances 0.000 title claims abstract description 111
- 230000006641 stabilisation Effects 0.000 title claims abstract description 66
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- 238000000034 method Methods 0.000 title claims abstract description 44
- 238000000862 absorption spectrum Methods 0.000 claims abstract description 39
- 150000001340 alkali metals Chemical group 0.000 claims abstract description 38
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- 230000007704 transition Effects 0.000 claims abstract description 18
- 229910052783 alkali metal Inorganic materials 0.000 claims abstract description 17
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- 238000002834 transmittance Methods 0.000 claims description 4
- ZLMJMSJWJFRBEC-UHFFFAOYSA-N Potassium Chemical group [K] ZLMJMSJWJFRBEC-UHFFFAOYSA-N 0.000 claims description 3
- TVFDJXOCXUVLDH-UHFFFAOYSA-N caesium atom Chemical group [Cs] TVFDJXOCXUVLDH-UHFFFAOYSA-N 0.000 claims description 3
- 238000004364 calculation method Methods 0.000 claims description 3
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- 125000004436 sodium atom Chemical group 0.000 claims description 3
- 238000006243 chemical reaction Methods 0.000 claims description 2
- 229910052708 sodium Inorganic materials 0.000 claims description 2
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Abstract
The application discloses an automatic frequency stabilization method of a semiconductor laser, which is used for automatically stabilizing the output laser frequency of the semiconductor laser locked at any alkali metal atom transition frequency, and comprises the following steps: responding to a frequency locking instruction input by a user, acquiring a target locking point in the frequency locking instruction, extracting a feedback voltage signal and a frequency discrimination signal of the target locking point according to the pre-acquired locking point information, and feeding back the feedback voltage signal to a modulation port of the semiconductor laser; adjusting a feedback voltage signal according to the frequency discrimination signal of the target locking point to perform feedback control on the laser frequency, so as to realize closed-loop locking of the laser frequency and further realize automatic frequency stabilization; the locking point information is obtained through first-order and second-order differential data of saturated absorption spectrum signals of alkali metal atoms to laser. The application can rapidly realize frequency locking of one of a plurality of optional locking points.
Description
Technical Field
The application belongs to the technical field of optical frequency stabilization, and particularly relates to an automatic frequency stabilization method of a semiconductor laser.
Background
The laser frequency stabilization technology has wide application in the fields of quantum mechanics, precision measurement, laser spectroscopy, gravitational wave detection and the like, and in the application fields, the frequency of laser output by a semiconductor laser is often required to be flexibly adjusted in order to facilitate the rapid switching and adjustment of different experimental parameters.
At present, a laser frequency stabilization method for a semiconductor laser generally adopts a laser frequency stabilization device designed in an analog circuit and digital control mode, and the principle of realizing frequency stabilization is as follows: by adjusting the scanning voltage injected into the modulation port of the semiconductor laser, observing a plurality of frequency discrimination signals obtained after modulation and demodulation by an analog circuit, the frequency discrimination signals can reflect the change of the frequency required by locking and the actual output frequency of the semiconductor laser; then repeatedly coarsely and finely regulating the scanning voltage to a proper position, so that the system only comprises one frequency discrimination signal required by a target locking point; and then closing scanning, obtaining a scanning voltage value corresponding to the zero crossing point position of the frequency discrimination signal, and outputting the voltage as a feedback voltage to a modulation port to realize closed-loop control. However, the laser frequency stabilization method needs to reset the scanning voltage each time to acquire the feedback voltage required by the target locking point for frequency closed-loop locking, has low efficiency, and cannot quickly realize frequency locking of one of a plurality of optional locking points.
Therefore, how to quickly implement frequency locking of one of the optional lock points is a need to be addressed.
Disclosure of Invention
Aiming at the defects of the prior art, the application aims to provide an automatic frequency stabilization method of a semiconductor laser, which aims to solve the problem that the traditional laser frequency stabilization technology can not quickly realize frequency locking of one of a plurality of optional locking points.
To achieve the above object, in a first aspect, the present application provides an automatic frequency stabilization method of a semiconductor laser for automatic stabilization of an output laser frequency of the semiconductor laser locked at any one of transition frequencies of alkali metal atoms, comprising the steps of:
S30, responding to a frequency locking instruction input by a user, acquiring a target locking point in the frequency locking instruction, extracting a feedback voltage signal and a frequency discrimination signal of the target locking point according to the pre-acquired locking point information, and outputting the feedback voltage signal to a modulation port of the semiconductor laser;
s40, adjusting a feedback voltage signal according to the frequency discrimination signal of the target locking point to perform feedback control on the laser frequency, so as to realize closed-loop locking of the laser frequency and further realize automatic frequency stabilization;
The locking point information comprises feedback voltage signals and frequency discrimination signals of a plurality of locking points, and the locking point information acquisition method comprises the following steps:
s10, injecting a scanning voltage signal into a modulation port, and scanning the laser frequency by adjusting the scanning voltage signal until the complete alkali metal atom transition frequency is scanned;
S20, acquiring a saturated absorption spectrum signal of laser output by the semiconductor laser through corresponding alkali metal atoms by scanning voltage, synchronously performing first-order and second-order differential processing on the saturated absorption spectrum signal, acquiring a plurality of locking points according to the minimum value of second-order differential data, then extracting scanning voltage corresponding to each locking point as a feedback voltage signal of each locking point, and simultaneously extracting first-order differential data of data points near each locking point as a frequency discrimination signal of each locking point.
The automatic frequency stabilization method of the semiconductor laser provided by the application utilizes the characteristic of laser interaction output by the semiconductor laser by the alkali metal atoms, and the feedback voltage signals and the frequency discrimination signals of all locking points are obtained in advance through the first-order and second-order differential data of the saturated absorption spectrum signals of the alkali metal atoms to the laser, when any locking point is subjected to frequency locking, the frequency locking can be carried out by extracting selected locking point information from the information obtained in advance, and compared with the traditional method of locking when the locking point is adjusted to the rest one locking point every time, the automatic frequency stabilization method of the semiconductor laser does not need to lock a plurality of points one by one in the process of adjusting scanning voltage for many times, and can rapidly realize the frequency locking of one of the plurality of locking points.
As a further preference, after step S30, the following steps are further included:
S50, judging whether the frequency of the semiconductor laser is unlocked according to the first-order differential data and the variation of the feedback voltage signal, if so, executing the step S60, and if not, executing the step S40;
s60, after closing feedback control, executing step S10, updating the feedback voltage signals and the frequency discrimination signals of all the locking points, and extracting the feedback voltage signals and the frequency discrimination signals of the updated target locking points;
S70, comparing the slope correlation threshold value of the updated frequency discrimination signal of the target locking point and the frequency discrimination signal of the target locking point extracted for the first time with a set value, executing step S80 when the slope correlation threshold value is larger than the set value, and executing step S60 when the slope correlation threshold value is smaller than or equal to the set value;
S80, judging that the locking point before the frequency unlocking of the semiconductor laser is found again, finishing automatic unlocking after unlocking, closing scanning, outputting a feedback voltage signal of the updated target locking point to a modulation port of the semiconductor laser, and executing the step S40;
S90, after receiving an end instruction input by a user, ending the feedback control.
As a further preferred aspect, the slope correlation thresholdThe calculation formula of (2) is as follows:
wherein x is the frequency discrimination signal of the target locking point extracted for the first time in the step S70; x i is the data point in the frequency discrimination signal x, i=1, 2, 3, … n; Is the average value of n data points in the frequency discrimination signal x; y is the frequency discrimination signal of the target locking point updated in step S70, y i is the data point in the frequency discrimination signal y, i=1, 2,3, … n; Is the average of n data points in the frequency discrimination signal y.
As a further preferred option, in step S10, the sweep voltage signal is adjusted to adjust the bias and amplitude of the sweep voltage signal.
As a further preferred aspect, the scan voltage signal is a triangular wave signal.
As a further preferred aspect, the alkali metal atom is a sodium atom, a potassium atom, a rubidium atom or a cesium atom, and the semiconductor laser is an external cavity semiconductor laser or a distributed feedback laser.
In a second aspect, the present application provides an automatic frequency stabilization system for a semiconductor laser for automatic stabilization of an output laser frequency of the semiconductor laser locked at any one of alkali metal atom transition frequencies, comprising:
The locking point information acquisition module is used for injecting a scanning voltage signal into a modulation port of the semiconductor laser, and scanning the laser frequency output by the semiconductor laser by adjusting the scanning voltage signal until the complete alkali metal atom transition frequency is scanned; then acquiring a saturated absorption spectrum signal of the output laser of the semiconductor laser through corresponding alkali metal atoms by scanning voltage, synchronously performing first-order and second-order differential processing on the saturated absorption spectrum signal, acquiring a plurality of locking points according to the minimum value of the second-order differential data, then extracting the scanning voltage corresponding to each locking point as a feedback voltage signal of each locking point, and simultaneously extracting first-order differential data of data points near each locking point as a frequency discrimination signal of each locking point;
The response and extraction module is used for responding to the frequency locking instruction input by a user, acquiring target locking points in the frequency locking instruction, extracting feedback voltage signals and frequency discrimination signals of the target locking points according to the feedback voltage signals and the frequency discrimination signals of the locking points acquired by the locking point information acquisition module, and outputting the feedback voltage signals to a modulation port of the semiconductor laser;
And the feedback control module is used for adjusting the feedback voltage signal according to the frequency discrimination signal of the target locking point so as to perform feedback control on the laser frequency, realize automatic frequency stabilization of the laser frequency and further realize automatic frequency stabilization.
In a third aspect, the present application provides an automatic frequency stabilization device for a semiconductor laser, comprising a spectrum generating and detecting assembly, a digital-to-analog converter, an analog-to-digital converter, and a signal processor, the semiconductor laser being provided with a controller;
The spectrum generating and detecting assembly comprises an absorption air chamber filled with alkali metal particles and is used for generating and detecting saturated absorption spectrum signals of alkali metal atoms for outputting laser light to the semiconductor laser;
The signal processor is used for sending a temperature and current adjusting instruction to the controller, stabilizing the temperature and current of the semiconductor laser at set values, and is also used for the automatic frequency stabilization method of the semiconductor laser; the signal processor acquires the saturated absorption spectrum signal through an analog-to-digital converter, and outputs a feedback voltage signal or a scanning voltage signal to a modulation port of the semiconductor laser through the digital-to-analog converter.
As a further preferred aspect, the spectrum generation and detection assembly comprises:
The light adjusting component is used for adjusting the power of the laser output by the semiconductor laser;
the high-transmittance low-reflection mirror is used for dividing the laser after power adjustment into first reflected light and first transmitted light, and enabling the first reflected light to pass through the absorption air chamber;
The reflection assembly comprises a reflection mirror and a half-transmission half-reflection mirror, the reflection mirror is used for reflecting first transmitted light into second reflected light, the half-transmission half-reflection mirror is used for reflecting the second reflected light into third reflected light, the third reflected light is used as pumping light to pass through the absorption air chamber, the propagation direction of the pumping light in the absorption air chamber is collinear with the propagation direction of the first reflected light which is used as detection light in the absorption air chamber, and meanwhile the half-transmission half-reflection mirror is also used for transmitting the detection light which passes through the absorption air chamber to the photoelectric detector;
And the photoelectric detector is used for detecting saturated absorption spectrum signals of the detection light.
As a further preferred aspect, the light adjustment assembly comprises:
The photoelectric isolator is used for preventing the output laser of the semiconductor laser from reversely passing;
The optical conversion assembly comprises an optical fiber coupler and a polarization maintaining optical fiber and is used for converting laser in the form of optical fiber light into space light;
And the power adjusting component comprises a half-wave plate and a polarization beam splitter prism and is used for adjusting the power of the space light.
It will be appreciated that the advantages of the second and third aspects may be found in the relevant description of the first aspect and are not described in detail herein.
Drawings
FIG. 1 is a graph of a set of Rb atomic versus laser light saturation absorption spectra and scan voltage signals measured according to the present application at frequencies near the Rb atomic D2 line transition resonance frequency;
FIG. 2 is a first order differential curve (a) and a second order differential curve (b) of the saturated absorption spectrum of Rb atoms to laser light provided by the present application;
FIG. 3 is a flow chart of an automatic frequency stabilization method of a semiconductor laser provided by the application;
FIG. 4 is a flow chart of a method for implementing a relock after unlocking provided by the application;
FIG. 5 is a schematic diagram of an automatic frequency stabilization system for a semiconductor laser according to the present application;
Fig. 6 is a schematic structural diagram of an automatic frequency stabilizing device of a semiconductor laser provided by the application;
FIG. 7 is a schematic diagram of a spectrum generating and detecting assembly according to an embodiment of the present application;
Fig. 8 is a schematic diagram of an operation of a signal processor according to an embodiment of the present application for executing an automatic frequency stabilization method.
Detailed Description
The present application will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present application more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the application.
It is to be understood that in the description of the application, the terms "plurality" and "a plurality" mean at least one, such as one, two, etc., unless explicitly specified otherwise; the term "plurality" means two or more, unless specifically defined otherwise; the terms "first" and "second" and the like are used to distinguish between different objects and are not used to describe a particular order of objects; the term "and/or" includes any and all combinations of one or more of the associated listed items.
The automatic frequency stabilization method of the semiconductor laser provided by the application can be applied to a signal processor in a laser frequency stabilization device designed based on a digital control mode, the signal processor can be an upper computer, and the corresponding relation between the output laser frequency of the semiconductor laser and the scanning voltage injected by a modulation port of the semiconductor laser is determined by utilizing the interaction characteristic of alkali metal atoms and the output laser of the semiconductor laser, so that the automatic stabilization of the laser frequency locked at the transition frequency of any one of the alkali metal atoms D1 line or D2 line is realized.
It should be noted that the alkali metal atoms provided by the present application may contain sodium atoms, potassium atoms, rubidium (Rubidium, rb) atoms, and cesium atoms, and only one electron is present in the outermost layer of these alkali metal atoms, so that they are similar in properties, in particular, in properties similar to those of laser interaction. Semiconductor lasers provided by the present application include, but are not limited to, external cavity semiconductor lasers (External Cavity Diode Laser, ECDL) and distributed feedback lasers (Distributed Feedback Laser, DFB).
The principle of the automatic frequency stabilization method provided by the application is mainly described below by the characteristic of interaction between Rb atoms and ECDL output laser:
the application is found through research: for ECDL, the scan voltage injected at its modulation port varies When the piezoelectric ceramic changes with it, the ECDL diffraction grating angle is changed, so that the output laser frequency is changed, corresponding to the changed frequencyCan be expressed as:
（1）
In the formula (1), the components are as follows, The frequency change coefficients of temperature, current and sweep voltage of ECDL, respectively; the variations of temperature, current and scan voltage of ECDL, respectively.
In the formula (1), the ECDL temperature and current are controlled at proper positions, and then the result is obtainedChanging the sweep voltage of the ECDL piezo can change the frequency of the output laser almost linearly.
For ECDL, it is generally equipped with a controller to control the operation temperature of ECDL, injection current, and sweep voltage of piezo-ceramic. PN junction in semiconductor is very sensitive to temperature, and adjusting temperature affects stability of laser frequency, temperature tuning rate can reach 10 GHz/°c magnitude, but adjusting temperature response is slow, and the temperature is generally fixed to be a proper value. The current tuning rate of the laser frequency can reach 1 GHz/mA, the laser frequency can quickly respond to current change, but the laser is easy to jump mode during adjustment. The scanning voltage of the piezoelectric ceramic is finely adjusted, so that the ECDL can be precisely tuned and frequency stabilized in a mode-jump-free range.
Therefore, the scanning voltage is input to the modulation port of the controller, so that the adjustment of the piezoelectric ceramics of the ECDL can be realized, and the scanning of the emergent laser frequency of the ECDL can be realized. If the method is used for scanning 780 nm ECDL the frequency of the output laser and decomposing the output laser into strong and weak two beams of laser, the Rb atoms in the absorption air chamber are pumped by the stronger laser and detected by the weaker laser, so that the saturated absorption spectrum of the Rb atoms to the laser can be detected.
Fig. 1 is a graph of a set of saturated absorption spectrum signals and scanning voltage signals of Rb atoms measured in the present application for laser light having a frequency near the Rb atom D2 line transition resonance frequency, in which triangular waves (frequency: 5 Hz; bias: 3.5V; amplitude: 2V) shown by broken lines are input as scanning voltages to a piezoceramic modulation port of an ECDL, and solid lines in the graph are detected saturated absorption spectrum signals.
As can be seen from fig. 1, the piezoelectric ceramic scanning voltage has a one-to-one correspondence with 6 saturation absorption peaks. When the scanning voltage is scanned from 3.5V to 7.5V, the scanning voltage of 780 and nm ECDL injected into the piezoelectric ceramic is linearly increased to obtain the Rb atom D2 line ground stateTransition excited stateThe saturation absorption spectrum signals of (a) respectively correspond to the saturation absorption peaks from left to rightA kind of electronic deviceCross line、Cross lineAndTransition lineAndA kind of electronic deviceCross line、Cross lineAndTransition line。
Fig. 2 shows a first-order differential curve (a) and a second-order differential curve (b) of an Rb atom to laser saturation absorption spectrum, where as can be seen from fig. 2, the first-order differential curve has a wide linear region of zero-crossing points, which is helpful for improving the long-term locking capability of a laser frequency stabilization device, and the signal has a dispersion-like linear shape and can be used as a frequency discrimination signal; the second-order differential curve is not zero at the center of the spectral line, positive and negative cannot be distinguished, the laser frequency deviation direction cannot be reflected, the second-order differential curve cannot be used as a frequency discrimination signal, but the minimum value is prominent, and the second-order differential curve can be used for acquiring a feedback voltage signal.
In the laser frequency stabilization device of the saturated absorption spectrum, the optical power during frequency stabilization is less in change in a period of time, but in the long-term frequency stabilization process, the condition of stable frequency and power drift possibly exists, so that a rough locking point cannot be obtained through first-order differentiation of the saturated absorption spectrum signal, and the aim of automatic re-locking after unlocking cannot be achieved. However, the second differential curve of the saturated absorption spectrum has a large difference in value at 6 locking points and is almost zero at other points, so that the initial value of the feedback voltage can be obtained through the second differential curve of the saturated absorption spectrum as a rough locking point.
Based on the above analysis, the present application provides an automatic frequency stabilization method for a semiconductor laser, as shown in fig. 3, comprising the following steps:
S30, responding to a frequency locking instruction input by a user, acquiring a target locking point in the frequency locking instruction, extracting a feedback voltage signal and a frequency discrimination signal of the target locking point according to the pre-acquired locking point information (feedback voltage signals and frequency discrimination signals of a plurality of locking points), and outputting the feedback voltage signals to a modulation port of the semiconductor laser.
In step S30, when the alkali metal atom is an Rb atom, the target lock point is any one of the Rb atom D2 line transition frequencies (corresponding to the 6 saturation absorption peaks in fig. 1).
And S40, adjusting a feedback voltage signal according to the frequency discrimination signal of the target locking point so as to perform feedback control on the laser frequency, thereby realizing closed-loop locking of the laser frequency and further realizing automatic frequency stabilization.
In step S40, the lock point information includes feedback voltage signals of a plurality of lock points, that is, rough feedback voltages of a plurality of lock points, and frequency discrimination signals of the respective lock points.
Note that, the lock point information may be acquired when a lock point information acquisition instruction is received, or may be acquired when a frequency locking instruction is received.
In the application, the acquisition method of the locking point information comprises the following steps:
S10, injecting a scanning voltage signal into the modulation port, and scanning the output laser frequency of the semiconductor laser by adjusting the scanning voltage signal until the complete transition frequency of the D1 line or the D2 line of the alkali metal atoms is scanned, namely, all saturated absorption peaks in the saturated absorption spectrum signal are scanned, for example, when Rb atoms are adopted by the alkali metal atoms, 6 saturated absorption peaks in the graph 1 are required to be scanned.
In step S10, the scan voltage signal may be a triangular wave signal, and adjusting the scan voltage signal may be performed by adjusting the bias and amplitude of the triangular wave signal.
S20, acquiring a saturated absorption spectrum signal of laser output by the semiconductor laser through corresponding alkali metal atoms by scanning voltage, synchronously performing first-order and second-order differential processing on the saturated absorption spectrum signal, acquiring a plurality of locking points according to the minimum value of second-order differential data, then extracting scanning voltage corresponding to each locking point as a feedback voltage signal of each locking point, and simultaneously extracting first-order differential data of data points near each locking point as a frequency discrimination signal of each locking point.
In step S20, since the front and rear data points of the differential processing are invalid, effective data interception is performed on the first-order and second-order differential data, i.e. the front and rear data points in the data are removed; and then determining transition frequency of a D1 line or a D2 line of an alkali metal atom as a plurality of locking points through minimum value points in the second-order differential data, extracting scanning voltage corresponding to each minimum value point, taking the scanning voltage of each locking point as a feedback voltage signal of each locking point, and simultaneously extracting first-order differential data of data points near each locking point as frequency discrimination signals of each locking point.
According to the automatic frequency stabilization method of the semiconductor laser, provided by the application, the characteristic of laser interaction output by the semiconductor laser is utilized, the first-order differential data and the second-order differential data of the laser saturation absorption spectrum signals are obtained in advance through the alkali metal atoms, the feedback voltage signals and the frequency discrimination signals of all locking points are obtained in advance, when any locking point is subjected to frequency locking, the frequency locking can be carried out by extracting the information of the target locking point from the information of the locking point obtained in advance, and compared with the traditional locking which is carried out by adjusting to the remaining locking point each time, the frequency stabilization method of the semiconductor laser does not need to lock a plurality of points one by one in the process of adjusting scanning voltage for many times, and can be used for rapidly realizing the frequency locking of one of the plurality of locking points.
Considering that the output laser frequency of the semiconductor laser can cause frequency unlocking due to vibration, shielding, long drift and other reasons in the frequency stabilization process (feedback control link), in order to realize unlocking and then re-locking, the application can use the frequency discrimination signals of all locking points obtained in the step S30 as the threshold judgment condition of automatic re-locking, namely in the feedback control link, after the frequency unlocking is found, the feedback control is closed, scanning is started, namely the step S10 is shifted, the frequency discrimination signals of the target locking points are obtained again, the slope correlation threshold of the frequency discrimination signals of the target locking points obtained for the first time is matched, and the locking points are found again when the requirement is met, so that the re-locking after the unlocking is completed.
Specifically, as shown in fig. 4, the method for implementing the re-locking after the unlocking includes the following steps:
s50, judging whether the frequency unlocking of the semiconductor laser occurs according to the first-order differential data and the variation of the feedback voltage signal, if so, executing the step S60, and if not, executing the step S40.
In step S50, when the frequency of the laser light output from the semiconductor laser changes due to shielding or vibration, the saturated absorption spectrum of the laser light by the alkali metal atoms changes accordingly, and the first-order differential data of the saturated absorption spectrum changes greatly. In addition, when the frequency of the output laser of the semiconductor laser changes due to long-term drift, the feedback voltage signals of the front and back two times generate larger changes. When the first-order differential signal or the feedback voltage of the front and the back is too large in change, the frequency of the first-order differential signal is judged to be unlocked.
And S60, after the feedback control is closed, executing the step S10, updating the feedback voltage signals and the frequency discrimination signals of all the locking points, and extracting the updated feedback voltage signals and frequency discrimination signals of the target locking points.
And S70, comparing the slope correlation threshold value of the updated frequency discrimination signal of the target locking point and the frequency discrimination signal of the target locking point extracted for the first time with a set value, executing step S80 when the slope correlation threshold value is larger than the set value, and executing step S60 when the slope correlation threshold value is smaller than or equal to the set value.
In step S70, a slope correlation thresholdThe calculation formula of (2) is as follows:
（2）
In the formula (2), x is the frequency discrimination signal of the target locking point extracted for the first time in the step S70; x i is the data point in the frequency discrimination signal x, i=1, 2, 3, … n; Is the average value of n data points in the frequency discrimination signal x; y is the frequency discrimination signal of the target locking point updated in step S70, y i is the data point in the frequency discrimination signal y, i=1, 2,3, … n; Is the average of n data points in the frequency discrimination signal y. Slope correlation threshold Only the slope and not the amplitude.
And S80, judging that the locking point before the frequency unlocking of the semiconductor laser is found again, finishing automatic unlocking after unlocking, closing scanning, outputting a feedback voltage signal of the updated target locking point to a modulation port of the semiconductor laser, and executing the step S40.
S90, after receiving an end instruction input by a user, ending the feedback control.
According to the automatic frequency stabilization method of the semiconductor laser, when the semiconductor laser is unlocked in a long-term operation process, feedback control is automatically closed, scanning is opened, the rescanned frequency discrimination signal is matched with the slope correlation threshold value of the frequency discrimination signal scanned last time, and when the requirement is met, the locking point is judged to be found again, so that automatic re-locking after unlocking is completed.
In addition, the application also provides an automatic frequency stabilization system of the semiconductor laser and an automatic frequency stabilization device of the semiconductor laser.
The automatic frequency stabilization system of the semiconductor laser provided by the application is used for automatically stabilizing the output laser frequency of the semiconductor laser locked at any alkali metal atom transition frequency, as shown in fig. 5, and comprises the following components:
The locking point information acquisition module 10 is used for injecting a scanning voltage signal into a modulation port of the semiconductor laser, and scanning the output laser frequency of the semiconductor laser by adjusting the scanning voltage signal until the complete alkali metal atom transition frequency is scanned; and then acquiring a saturated absorption spectrum signal of the output laser of the semiconductor laser by corresponding alkali metal atoms through the scanning voltage, synchronously performing first-order and second-order differential processing on the saturated absorption spectrum signal, acquiring a plurality of locking points according to the minimum value of the second-order differential data, then extracting the scanning voltage corresponding to each locking point as a feedback voltage signal of each locking point, and simultaneously extracting first-order differential data of data points near each locking point as a frequency discrimination signal of each locking point.
The response and extraction module 20 is configured to respond to a frequency locking instruction input by a user, obtain target locking points in the frequency locking instruction, extract feedback voltage signals and frequency discrimination signals of the target locking points according to the feedback voltage signals and the frequency discrimination signals of the plurality of locking points obtained by the locking point information obtaining module, and output the feedback voltage signals to a modulation port of the semiconductor laser.
The feedback control module 30 is configured to adjust a feedback voltage signal according to the frequency discrimination signal of the target locking point, so as to perform feedback control on the laser frequency, realize closed-loop locking of the laser frequency, and further realize automatic frequency stabilization.
As shown in fig. 6, the automatic frequency stabilization device of the semiconductor laser provided by the application comprises a spectrum generating and detecting assembly 40, a digital-to-analog converter 60, an analog-to-digital converter 70 and a signal processor 50, and the semiconductor laser is provided with a controller 80. Further, a temperature control module (not shown) may be included.
The spectrum generating and detecting unit 40 includes an absorption gas chamber filled with alkali metal particles, and is used for generating and detecting a saturated absorption spectrum signal of alkali metal atoms for outputting laser light to the semiconductor laser 90.
Specifically, as shown in fig. 7, the spectrum generating and detecting assembly 40 provided in this embodiment may include a light adjusting assembly 41 (a photo-isolator 411, a fiber coupler 412, a polarization maintaining fiber 413, a half-wave plate 414 and a polarization splitting prism 415), a high-transmittance low-reflection mirror 42, an absorption air chamber 44, a reflection mirror 43, a half-transmission half-reflection mirror 45 and a photo-detector 46.
In the present embodiment, the photo-isolator 411 is used to prevent the reverse passage of the laser light output from the semiconductor laser 90 from affecting the frequency stability. The optical fiber coupler 412 and the polarization maintaining fiber 413 are used to convert the laser light in the form of optical fiber light emitted from the semiconductor laser 90 into spatial light. The half wave plate 414 and the polarization splitting prism 415 are used to adjust the power ratio of the spatial light. The absorption cell 44 is filled with only Rb metal particles of natural abundance. The high-transmittance low-reflection mirror 42 is used for decomposing the space light after power adjustment into stronger transmitted light and weaker reflected light, and the reflected light passes through the absorption air chamber 44 as detection light. The reflecting mirror 43 and the half mirror 45 are used for changing the direction of the transmitted light so that the transmitted light passes through the absorption air chamber 44 as pump light, and the propagation direction of the pump light in the absorption air chamber is collinear with the propagation direction of the probe light in the absorption air chamber 44, while the half mirror 45 is also used for transmitting the probe light passing through the absorption air chamber 44 to the photodetector 46. The photodetector 46 is used to detect the saturated absorption spectrum signal of the detection light.
The signal processor 50 is used for sending temperature and current regulation instructions to the controller 80 to stabilize the temperature and current of the semiconductor laser 90 at set values; and is also used to send temperature control adjustment instructions to the temperature control module by which the temperature of the absorption air chamber 44 is controlled. In addition, the signal processor 50 acquires the saturated absorption spectrum signal detected by the photodetector 46 through the analog-to-digital converter 70, and outputs a feedback voltage signal or a scan voltage signal to the modulation port of the semiconductor laser through the digital-to-analog converter 60.
Specifically, taking the automatic stabilization of the output laser of the semiconductor laser locked at any Rb atom D2 line transition frequency as an example, the principle of implementing automatic frequency stabilization by the signal processor 50 provided in this embodiment is described, as shown in fig. 8, the implementation of automatic frequency stabilization by the signal processor 50 provided in this embodiment is mainly divided into two processes, namely, a locking point information acquisition process and an automatic frequency locking process.
Locking point information acquisition process: responding to a locking point information acquisition instruction input by a user, outputting scanning voltage to a modulation port of the semiconductor laser, and scanning the output laser frequency of the semiconductor laser by adjusting the scanning voltage until 6 complete Rb atomic saturation absorption peaks are scanned; at this time, the saturated absorption spectrum signals obtained by the analog-to-digital converter are subjected to first-order and second-order differential processing synchronously, and as the front data point and the rear data point of the differential processing are invalid, the first-order and second-order differential signals are intercepted first, so that the subsequent processing is convenient; then carrying out smoothing filtering on the first-order differential data to reduce noise so as to facilitate the subsequent acquisition of a required frequency discrimination signal from the data; meanwhile, the minimum value is obtained through second order differential data to serve as 6 locking points, and as the position of the minimum value has a one-to-one correspondence with the scanning voltage, the corresponding scanning voltage is extracted through the position of each minimum value, and feedback voltage signals serving as 6 locking points are obtained; because the point near the minimum value of the second-order differential signal has a corresponding relation with the zero crossing point frequency discrimination signal of the first-order differential curve, the frequency discrimination signal of each locking point can be extracted through the relation, and the frequency discrimination signal is used as the judgment condition of the subsequent automatic frequency stabilization. The above manner acquires 6 feedback voltage signals and 6 frequency discrimination signals.
Automatic frequency locking process: extracting a feedback voltage signal and a frequency discrimination signal of the target locking point according to target locking points in a frequency locking instruction input by a user, closing scanning at the moment, opening feedback control, and adjusting the feedback voltage signal according to the frequency discrimination signal of the target locking point so as to perform PID feedback control on the laser frequency and realize closed loop locking of the laser frequency; when the frequency of the semiconductor laser is possibly unlocked due to vibration, shielding, long drift and the like, the feedback control is closed, the scanning is opened, when the slope threshold value of the frequency discrimination signal scanned again and the frequency discrimination signal acquired for the first time is larger than a set value, the frequency discrimination signal is considered to be scanned again to a locking point, the feedback voltage signal and the frequency discrimination signal are automatically updated, and then the updated frequency discrimination signal is used as a threshold value judgment condition after the next unlocking.
It will be readily understood by those skilled in the art that the foregoing description is merely a preferred embodiment of the application and is not intended to limit the application, but any modifications, equivalents, improvements or modifications made within the spirit and principles of the application are intended to be included within the scope of the application.
Claims (10)
1. An automatic frequency stabilization method of a semiconductor laser, characterized in that the automatic frequency stabilization method is used for automatically stabilizing the output laser frequency of the semiconductor laser locked at any alkali metal atom transition frequency, and comprises the following steps:
S30, responding to a frequency locking instruction input by a user, acquiring a target locking point in the frequency locking instruction, extracting a feedback voltage signal and a frequency discrimination signal of the target locking point according to the pre-acquired locking point information, and outputting the feedback voltage signal to a modulation port of the semiconductor laser;
s40, adjusting a feedback voltage signal according to the frequency discrimination signal of the target locking point to perform feedback control on the laser frequency, so as to realize closed-loop locking of the laser frequency and further realize automatic frequency stabilization;
The locking point information comprises feedback voltage signals and frequency discrimination signals of a plurality of locking points, and the locking point information acquisition method comprises the following steps:
s10, injecting a scanning voltage signal into a modulation port, and scanning the laser frequency by adjusting the scanning voltage signal until the complete alkali metal atom transition frequency is scanned;
S20, acquiring a saturated absorption spectrum signal of laser output by the semiconductor laser through corresponding alkali metal atoms by scanning voltage, synchronously performing first-order and second-order differential processing on the saturated absorption spectrum signal, acquiring a plurality of locking points according to the minimum value of second-order differential data, then extracting scanning voltage corresponding to each locking point as a feedback voltage signal of each locking point, and simultaneously extracting first-order differential data of data points near each locking point as a frequency discrimination signal of each locking point.
2. The method for automatic frequency stabilization of a semiconductor laser as claimed in claim 1, further comprising, after the step S30, the steps of:
S50, judging whether the frequency of the semiconductor laser is unlocked according to the first-order differential data and the variation of the feedback voltage signal, if so, executing the step S60, and if not, executing the step S40;
s60, after closing feedback control, executing step S10, updating the feedback voltage signals and the frequency discrimination signals of all the locking points, and extracting the feedback voltage signals and the frequency discrimination signals of the updated target locking points;
S70, comparing the slope correlation threshold value of the updated frequency discrimination signal of the target locking point and the frequency discrimination signal of the target locking point extracted for the first time with a set value, executing step S80 when the slope correlation threshold value is larger than the set value, and executing step S60 when the slope correlation threshold value is smaller than or equal to the set value;
S80, judging that the locking point before the frequency unlocking of the semiconductor laser is found again, finishing automatic unlocking after unlocking, closing scanning, outputting a feedback voltage signal of the updated target locking point to a modulation port of the semiconductor laser, and executing the step S40;
S90, after receiving an end instruction input by a user, ending the feedback control.
3. The method for automatic frequency stabilization of a semiconductor laser as claimed in claim 2, wherein the slope correlation threshold valueThe calculation formula of (2) is as follows:
Wherein x is the frequency discrimination signal of the target locking point extracted for the first time in the step S70; x i is the data point in the frequency discrimination signal x, i=1, 2,3, … n; Is the average value of n data points in the frequency discrimination signal x; y is the frequency discrimination signal of the target locking point updated in step S70, y i is the data point in the frequency discrimination signal y, i=1, 2, 3, … n; Is the average of n data points in the frequency discrimination signal y.
4. The method of automatic frequency stabilization of a semiconductor laser as claimed in claim 1, wherein in step S10, the scan voltage signal is adjusted to adjust the bias and amplitude of the scan voltage signal.
5. The method of automatic frequency stabilization of a semiconductor laser of claim 1, wherein the sweep voltage signal is a triangular wave signal.
6. The method of automatic frequency stabilization of a semiconductor laser according to claim 1, wherein the alkali metal atom is a sodium atom, a potassium atom, a rubidium atom or a cesium atom, and the semiconductor laser is an external cavity semiconductor laser or a distributed feedback laser.
7. An automatic frequency stabilization system for a semiconductor laser, the automatic frequency stabilization system being used for automatic stabilization of an output laser frequency of the semiconductor laser locked at any one of alkali metal atom transition frequencies, comprising:
The locking point information acquisition module is used for injecting a scanning voltage signal into a modulation port of the semiconductor laser, and scanning the laser frequency output by the semiconductor laser by adjusting the scanning voltage signal until the complete alkali metal atom transition frequency is scanned; then acquiring a saturated absorption spectrum signal of the output laser of the semiconductor laser through corresponding alkali metal atoms by scanning voltage, synchronously performing first-order and second-order differential processing on the saturated absorption spectrum signal, acquiring a plurality of locking points according to the minimum value of the second-order differential data, then extracting the scanning voltage corresponding to each locking point as a feedback voltage signal of each locking point, and simultaneously extracting first-order differential data of data points near each locking point as a frequency discrimination signal of each locking point;
The response and extraction module is used for responding to the frequency locking instruction input by a user, acquiring target locking points in the frequency locking instruction, extracting feedback voltage signals and frequency discrimination signals of the target locking points according to the feedback voltage signals and the frequency discrimination signals of the locking points acquired by the locking point information acquisition module, and outputting the feedback voltage signals to a modulation port of the semiconductor laser;
And the feedback control module is used for adjusting the feedback voltage signal according to the frequency discrimination signal of the target locking point so as to perform feedback control on the laser frequency, realize automatic frequency stabilization of the laser frequency and further realize automatic frequency stabilization.
8. An automatic frequency stabilizing device of a semiconductor laser is characterized by comprising a spectrum generating and detecting assembly, a digital-to-analog converter, an analog-to-digital converter and a signal processor, wherein the semiconductor laser is provided with a controller;
The spectrum generating and detecting assembly comprises an absorption air chamber filled with alkali metal particles and is used for generating and detecting saturated absorption spectrum signals of alkali metal atoms for outputting laser light to the semiconductor laser;
The signal processor is used for sending a temperature and current adjusting instruction to the controller, stabilizing the temperature and current of the semiconductor laser at set values, and also used for executing the automatic frequency stabilization method of the semiconductor laser according to any one of claims 1 to 6; the signal processor acquires the saturated absorption spectrum signal through an analog-to-digital converter, and outputs a feedback voltage signal or a scanning voltage signal to a modulation port of the semiconductor laser through the digital-to-analog converter.
9. An automatic frequency stabilization apparatus for a semiconductor laser as defined in claim 8, wherein the spectrum generating and detecting assembly comprises:
The light adjusting component is used for adjusting the power of the laser output by the semiconductor laser;
the high-transmittance low-reflection mirror is used for dividing the laser after power adjustment into first reflected light and first transmitted light, and enabling the first reflected light to pass through the absorption air chamber;
The reflection assembly comprises a reflection mirror and a half-transmission half-reflection mirror, the reflection mirror is used for reflecting first transmitted light into second reflected light, the half-transmission half-reflection mirror is used for reflecting the second reflected light into third reflected light, the third reflected light is used as pumping light to pass through the absorption air chamber, the propagation direction of the pumping light in the absorption air chamber is collinear with the propagation direction of the first reflected light which is used as detection light in the absorption air chamber, and meanwhile the half-transmission half-reflection mirror is also used for transmitting the detection light which passes through the absorption air chamber to the photoelectric detector;
And the photoelectric detector is used for detecting saturated absorption spectrum signals of the detection light.
10. An automatic frequency stabilization apparatus for a semiconductor laser as defined in claim 9, wherein the light conditioning assembly comprises:
The photoelectric isolator is used for preventing the output laser of the semiconductor laser from reversely passing;
The optical conversion assembly comprises an optical fiber coupler and a polarization maintaining optical fiber and is used for converting laser in the form of optical fiber light into space light;
And the power adjusting component comprises a half-wave plate and a polarization beam splitter prism and is used for adjusting the power of the space light.
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