AU2021102321A4 - Double-longitudinal-mode Laser Interlocking Method and Device Based on Thermal Frequency Stabilization and Acousto-optic Frequency Shift - Google Patents
Double-longitudinal-mode Laser Interlocking Method and Device Based on Thermal Frequency Stabilization and Acousto-optic Frequency Shift Download PDFInfo
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- 230000003287 optical effect Effects 0.000 claims abstract description 11
- 239000013307 optical fiber Substances 0.000 claims description 22
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- 230000035559 beat frequency Effects 0.000 claims description 5
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- 239000000835 fiber Substances 0.000 claims description 3
- 238000005516 engineering process Methods 0.000 abstract description 7
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- 238000004556 laser interferometry Methods 0.000 abstract 1
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
- H01S3/13—Stabilisation of laser output parameters, e.g. frequency or amplitude
- H01S3/1304—Stabilisation of laser output parameters, e.g. frequency or amplitude by using an active reference, e.g. second laser, klystron or other standard frequency source
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/11—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on acousto-optical elements, e.g. using variable diffraction by sound or like mechanical waves
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
- H01S3/13—Stabilisation of laser output parameters, e.g. frequency or amplitude
- H01S3/131—Stabilisation of laser output parameters, e.g. frequency or amplitude by controlling the active medium, e.g. by controlling the processes or apparatus for excitation
- H01S3/1317—Stabilisation of laser output parameters, e.g. frequency or amplitude by controlling the active medium, e.g. by controlling the processes or apparatus for excitation by controlling the temperature
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- General Physics & Mathematics (AREA)
- Lasers (AREA)
Abstract
The invention provides a double-longitudinal-mode laser interlocking method and
device based on thermal frequency stabilization and acousto-optic frequency shift, and
belongs to the technical field of laser application. By using the acousto-optic frequency
shift technology, the output laser frequencies of multiple double-longitudinal-mode
lasers based on thermal frequency stabilization are locked to the optical frequency of
the same reference double-longitudinal-mode frequency stabilized laser, and
therefore, the laser output by all these lasers can have the unified frequency value.
The aims of this invention is to overcome the defect the poor consistency of
frequencies between traditional frequency stabilized lasers and to provide a novel
laser source for ultra-precision laser interferometry.
2/2
0 +Frequencle/ Laser
stabilization Electric heater Laser tube
_"r control module
Long itudinal 8
mode power pTwo-quad rant
differenceoptoelectroni |
detector
Fig. 4
21 1516
adjustn module frequency shfter 10 Laser(v) sp i ter
v, + f,
v+f-vmearm uemodule photoelctric Polarizer Ocal ier
20 118 17
Fig. 5
Description
2/2
0 +Frequencle/ Laser stabilization Electric heater Laser tube _"r control module Long itudinal 8 mode power pTwo-quad rant differenceoptoelectroni | detector
Fig. 4
21 1516
adjustn module frequency shfter 10 Laser(v) sp i ter v, + f, v+f-vmearmuemodule photoelctric Polarizer Ocal ier
20 118 17
Fig. 5
Double-longitudinal-mode Laser Interlocking Method and Device
Based on Thermal Frequency Stabilization and Acousto-optic Frequency
Shift
The invention belongs to the technical field of laser application, in particular
to a double-longitudinal-mode laser interlocking method and device based on
thermal frequency stabilization and acousto-optic frequency shift.
In recent years, the ultra-precision measurement and processing
technology represented by lithography machines and CNC machine tools has
developed in the direction of large-scale, high-precision, and synchronous
measurement of multi degree of freedom. Total laser power consumption of a
laser interferometric system has increased dramatically and far exceed output
laser power of a single frequency stabilization laser, it is necessary to use
multiple frequency stabilization lasers. However, different frequency
stabilization lasers have difference in relative frequency stability, laser
wavelength value, wavelength drift direction, etc., which will bring about the
inconsistency of measurement accuracy, wavelength reference and spatial
coordinate of different degrees of freedom and will affect the overall
measurement accuracy of the laser interferometric system. To ensure the
overall measurement accuracy of the system, the frequency consistency of
multiple frequency stabilization lasers is required to reach 10-8. Therefore, the
frequency consistency among the frequency stabilization lasers has become an urgent need for the development of ultra-precision measurement and processing technology.
At present, the frequency stabilization lasers used in the laser
interferometric system mainly include the double-longitudinal-mode frequency
stabilization laser, the transverse Zeeman frequency stabilization laser and the
longitudinal Zeeman frequency stabilization laser, which use center frequency
of a laser gain curve as a reference of frequency stabilization control, but the
center frequency of the laser gain curve changes along with gas pressure and
discharge conditions. As a result of inconsistency of physical parameters, the
multiple frequency stabilization lasers have different references of frequency
stabilization control, and therefore, laser output by the multiple frequency
stabilization lasers is lower in frequency consistency, which only can be 10-6 to
-7.
In order to solve the problem of poor frequency consistency of the
frequency stabilization lasers, Harbin Institute of Technology proposed a
double-longitudinal-mode laser based on offset frequency locking method
(Chinese patent application numbers being CN200910072517,
CN200910072518, CN200910072519 and CN200910072523), which uses the
optical frequency output by an iodine frequency stabilization laser or a double
longitudinal-mode laser as reference, and locks the rest double-longitudinal
mode lasers with a certain value offset from the reference frequency, so that
the output laser of the multiple double-longitudinal-mode lasers have the same
wavelength (frequency). However, to realize frequency locking, this method
needs to adjust the internal working parameters of the lasers, which has two
shortcomings. On one hand, the system response speed is relatively low due to an indirect adjustment, on the other hand, due to the change of the internal working parameters, the laser frequency stability might be deteriorated or the lasers are possibly out of stabilization.
In order to overcome the defects in the prior art, the invention discloses a
double-longitudinal-mode laser interlocking method based on thermal
frequency stabilization and acousto-optic frequency shift, which aims to provide
a laser source with excellent wavelength consistency for the ultra-precision
measurement and processing technology. The invention further provides a
double-longitudinal-mode laser interlocking device based on thermal frequency
stabilization and acousto-optic frequency shift.
The objective of the invention is realized by the following technical scheme:
A double-longitudinal-mode laser interlocking method based on thermal
frequency stabilization and acousto-optic frequency shift includes the following
steps:
(1) turning on a power of the reference double-longitudinal-mode
frequency stabilization laser, after preheating and frequency stabilization, the
output laser contains two orthogonally-polarized longitudinal-mode beams,
utilizing a polarization beam splitter to separate one of the longitudinal-mode
beams as the output light, with optical frequency recorded asvr, an fiber splitter
separates the output light into n parts of beam (n being greater than or equal to
1), which are recorded as Xi (i being equal to 1, 2, .... n) and used as the
reference beams respectively for frequency locking of the double-longitudinal
mode lasers Li (i being equal to 1, 2, .... n);
(2) turning on power of the double-longitudinal-mode lasers Li (i being
equal to 1, 2, .... n) to enter the preheating process, measuring the current
temperature of the environment, setting a preheating target temperature Tset
which is higher than the ambient temperature, utilizing an electric heater to heat
laser tubes inside the lasers, making the temperatures of the laser tubes trend
to the preset temperature Tset and reach a thermal balance state, finely
adjusting a working current of the electric heater according to a preheating
algorithm to make the laser emitted from the main and secondary output ends
of the laser tubes include two orthogonally-polarized longitudinal-mode beams;
(3) after the preheating process is ended, the double-longitudinal-mode
lasers Li (i being equal to 1, 2, .... n) enter a frequency stabilization control
process, a Wollaston prism is utilized to separate the two orthogonally-polarized
longitudinal-mode beams at the secondary output ends of the laser tubes, with
optical power being Pi and P2 (i being equal to 1, 2, .... n), which are detected
by a two-quadrant optoelectronic detector, the frequency stabilization control
module calculates the power difference AP=Pi-2 (i being equal to 1, 2, ....
n) of the two longitudinal-mode beams, and then regulates the current of the
electric heater according to the value of AP (i being equal to 1, 2, .... n) to make
AP trend to 0, thereby make the laser frequency trend to a stable value;
(4) utilizing the polarization beam splitter to separate one of longitudinal
mode beams from the main output ends of the laser tubes, recording it as Ti (i
being equal to 1, 2, .... n) with frequency as vi (i being equal to 1, 2,.. n),
which enters an acousto-optic frequency shifter Si (i being equal to 1, 2,.. n)
with working frequency fi, (i being equal to 1, 2, .... n), and then the
correspondingly output laser has a frequency of vi+fi (i being equal to 1, 2, ....
n), splitting the output laser into two parts with an intensity ratio being 9:1,
wherein the part with greater intensity is recorded as Zi (i being equal to 1, 2, ....
n), which is used as output laser of the double-longitudinal-mode laser Li (i
being equal to 1, 2, .... n), and the part with smaller intensity is recorded as Yi
(i being equal to 1, 2, .... n);
(5) mixing the light beam Xi (i being equal to 1, 2, .... n) with the light beam
Yi (i being equal to 1, 2, .... n) to form an optical beat frequency signal, utilizing
an photoelectric detector to convert the beat frequency signal into an electric
signal with a frequency as AVi=Vi+fi-r (i being equal to 1, 2, .... n) which is
measured by a frequency measuring module, calculating a frequency
difference value vr-vi=fi-Avi (i being equal to 1, 2, .... n) between the beam Xi
(i being equal to 1, 2, .... n) and the beam Yi (i being equal to 1, 2, .... n),
adjusting working frequency fi(i being equal to 1, 2, .... n) of the acousto-optic
frequency shifter Si (i being equal to 1, 2, .... n) to be vr-vi (i being equal to 1,
2, .... n), thereby making frequency of the beam Zi (i being equal to 1, 2,.. n)
output by the double-longitudinal-mode lasers Li (i being equal to 1, 2,.. n)
equal to frequency of the reference beam Xi (i being equal to 1, 2, .... n), namely
v+fi=vr (i being equal to 1, 2, .... n);
(6) repeating the steps (4) and (5), making frequency of the output light
beam Zi (i being equal to 1, 2, .... n) of the double-longitudinal-mode lasers Li
(i being equal to 1, 2, .... n) to be always locked at the same frequency value vr
by adjusting working frequency fi (i being equal to 1, 2, .... n) of the acousto
optic frequency shifter Si (i being equal to 1, 2, .... n).
A double-longitudinal-mode laser interlocking device based on thermal
frequency stabilization and acousto-optic frequency shift includes a laser power source A (1), a frequency stabilization state indicator lamp (2), a reference double-longitudinal-mode frequency stabilization laser (3), a polarizing beam splitter A (4) and an optical fiber splitter (5), and further includes n (n being greater than or equal to 1) double-longitudinal-mode lasers Li (i being equal to
1, 2, .... n) which are the same in structure and are in parallel-connection
relationship, wherein both the laser power source A (1) and the frequency
stabilization state indicator lamp (2) are connected to the reference double
longitudinal-mode frequency stabilization laser (3); the polarizing beam splitter
A (4) is arranged between the output end of the reference double-longitudinal
mode frequency stabilization laser (3) and the input end of the optical fiber
splitter (5); the assembly structure of each double-longitudinal-mode laser Li (i
being equal to 1, 2, .... n) is as follows: a laser power source B (13) is connected
to a laser tube (6), an electric heater (11) is wound on the outer wall of the laser
tube (6), the input end of the electric heater (11) is connected to a frequency
stabilization control module (9), a laser tube temperature sensor (10) is
attached onto the outer wall of the laser tube (6), the output end of the laser
tube temperature sensor (10) is connected to the frequency stabilization control
module (9), an ambient temperature sensor (12) is connected to the frequency
stabilization control module (9), a Wollaston prism (7) is placed behind the
secondary output end of the laser tube (6), a two-quadrant optoelectronic
detector (8) is placed behind the Wollaston prism (7), the output end of the two
quadrant optoelectronic detector (8) is connected to the frequency stabilization
control module (9); a polarizing beam splitter B (14) is placed in front of the
main output end of the laser tube (6) , an acousto-optic frequency shifter (15)
is placed behind the polarizing beam splitter B (14); a beam splitter (16) is placed between the acousto-optic frequency shifter (15) and an optical fiber combiner (17); another input end of the optical fiber combiner (17) is connected to the output end of the optical fiber splitter (5); a polarizer (18) is placed between the output end of the optical fiber combiner (17) and a high-speed photoelectric detector (19); the high-speed photoelectric detector (19), a frequency measuring module (20), a frequency adjusting module (21) and the acousto-optic frequency shifter (15) are sequentially connected; and a frequency locking state indicator lamp (22) is connected to the frequency adjusting module (21).
The invention has the following characteristics and good effects:
(1) The invention uses the acousto-optic frequency shifterto realize parallel
frequency locking on multiple double-longitudinal-mode lasers, the output laser
of all double-longitudinal-mode lasers has a uniform frequency value. Due to
the extremely high frequency adjustment resolution of the acousto-optic
frequency shifter, the frequency consistency of each laser can be as high as
-9, which is one to two orders of magnitude higher than that in the existing
method, which is the first innovation point different from the existing technology.
(2) The invention uses an acousto-optic frequency shifter to realize parallel
frequency locking on multiple double-longitudinal-mode lasers. Due to the
higher frequency adjustment response speed of the acousto-optic frequency
shifter, the laser wavelength drift and jump caused by external interference
factors can be effectively suppressed to improve the stability and environmental
applicability of the light source, which is the second innovation point that is
different from the existing technology.
(3) The present invention uses an acousto-optic frequency shifter to realize
parallel frequency locking on the multiple double-longitudinal-mode lasers. Due
to the fact that the frequency adjusting method for the final output laser belongs
to an external adjusting method for the laser tubes, adverse effects on a
frequency stabilization control system of the laser tubes are not generated, so
that the stability of the system and the accuracy of frequency stabilization are
favorably improved. This is the third innovation point that is different from the
existing technology.
Fig. 1 is a schematic diagram showing the principle of a device of the
invention.
Fig. 2 is a schematic diagram showing frequency stabilization structures of
double-longitudinal-mode frequency stabilization lasers in a device of the
invention.
Fig. 3 is a functional block diagram showing closed loop control of a
preheating process of double-longitudinal-mode frequency stabilization lasers
in a device of the invention.
Fig. 4 is a functional block diagram showing closed loop control of a
frequency stabilization process of double-longitudinal-mode frequency
stabilization lasers in a device of the invention.
Fig. 5 is a functional block diagram showing closed loop control of a
frequency locking process of double-longitudinal-mode frequency stabilization
lasers in a device of the invention.
Wherein, 1. Laser power source A; 2. frequency stabilization state indicator
lamp; 3. reference double-longitudinal-mode frequency stabilization laser; 4.
polarizing beam splitter A; 5. optical fiber splitter; 6. laser tube; 7. Wollaston prism; 8. two-quadrant optoelectronic detector; 9. frequency stabilization control module; 10. laser tube temperature sensor; 11. electric heater; 12.
environment temperature sensor; 13. Laser power source B; 14. polarizing
beam splitter B; 15. acousto-optic frequency shifter; 16. beam splitter; 17.
optical fiber combiner; 18. polarizer; 19. High-speed photoelectric detector; 20.
frequency measuring module; 21. frequency adjusting module; and 22.
frequency locking state indicator lamp.
The implementation examples of the invention will be described in detail
below with reference to the accompanying drawings.
As shown in Fig. 1 and Fig. 2, a double-longitudinal-mode laser interlocking
device based on thermal frequency stabilization and acousto-optic frequency
shift includes a Laser power source A 1, a frequency stabilization state indicator
lamp 2, a reference double-longitudinal-mode frequency stabilization laser 3, a
polarizing beam splitter A4 and an optical fiber splitter 5, and further includes n
(n being greater than or equal to 1) double-longitudinal-mode lasers Li (i being
equal to 1, 2, .... n) which are the same in structure and are in parallel
connection relationship, wherein both the Laser power source A 1 and the
frequency stabilization state indicator lamp 2 are connected to the reference
double-longitudinal-mode frequency stabilization laser 3; the polarizing beam
splitter A 4 is arranged between the output end of the reference double
longitudinal-mode frequency stabilization laser 3 and the input end of the optical
fiber splitter 5; the assembly structure of each double-longitudinal-mode laser
Li (i being equal to 1, 2, .... n) is as follows: a laser power source B 13 is
connected to a laser tube 6, an electric heater 11 is wound on the outer wall of the laser tube 6, the input end of the electric heater 11 is connected to a frequency stabilization control module 9, a laser tube temperature sensor 10 is attached onto the outer wall of the laser tube 6, the output end of the laser tube temperature sensor 10 is connected to the frequency stabilization control module 9, an ambient temperature sensor 12 is connected to the frequency stabilization control module 9, a Wollaston prism 7 is placed behind the secondary output end of the laser tube 6 and then is placed on a two-quadrant optoelectronic detector 8, the output end of the two-quadrant optoelectronic detector 8 is connected to the frequency stabilization control module 9; a polarizing beam splitter B14 is placed in front of the main output end of the laser tube 6 and then is placed on an acousto-optic frequency shifter15; a beam splitter16 is placed between the acousto-optic frequency shifter15 and an optical fiber combiner 17; another input end of the optical fiber combiner 17 is connected to the output end of the optical fiber splitter 5; a polarizer 18 is placed between the output end of the optical fiber combiner 17 and a high-speed photoelectric detector 19; the high-speed photoelectric detector 19, a frequency measuring module 20, a frequency adjusting module 21 and the acousto-optic frequency shifter 15 are sequentially connected; and a frequency locking state indicator lamp 22 is connected to the frequency adjusting module 21.
In view of the fact that the device includes multiple double-longitudinal
mode frequency stabilized lasers L1, L2, . . , Ln with the same structure and the
completely consistent working process, the following only describes the
working process of the double-longitudinal-mode frequency stabilized laser Li.
These descriptions are also applicable to other similar double-longitudinal
mode frequency stabilized lasers in the device.
When work starts, the laser power source A 1 is turned on for making the
reference double-longitudinal-mode frequency stabilized laser 3 enter the
preheating and frequency stabilization process. When the above process is
completed, the frequency stabilization state indicator lamp 2 is enabled,
indicating that the reference double-longitudinal-mode frequency stabilized
laser 3 enters a stable working state, and its output laser includes two
longitudinal-mode light beams with polarization directions orthogonal to each
other; one longitudinal-mode light beam is taken as output light by the polarizing
beam splitter A4, is coupled into the optical fiber splitter 5 and is separated into
n frequency datum light beams recorded as X1, X2,..., Xn, and its frequency is
recorded as Vr, which is reference frequency for locking frequency of the
double- longitudinal-mode lasers Li, L2, . . and Ln.
When the frequency stabilization state indicator lamp 2 is enabled, the
laser power source B 13 is turned on for making the double-longitudinal-mode
frequency stabilization laser Li enter the preheating process. The frequency
stabilization control module 9 sets the preheating target temperature Tset ,
higher than the ambient temperature, according to the ambient temperature
value measured by the ambient temperature sensor 12, and uses Tset as an
reference input variable of a preheating closed loop control system as shown
in Fig. 3, and takes a practical temperature Treal, measured by the laser tube
temperature sensor 10, of the laser tube 6 as a feedback signal; the frequency
stabilization control module 9 calculates a difference value of the two, and
adjusts the size of working current of the electric heater 11 according to the size
of the difference value for heating the laser tube 6, so the temperature trends
to a preset target temperature Tset; and based on this, laser at the main output end and the secondary output end of the laser tube comprises two orthogonally popularized longitudinal-mode light beams by finely adjusting the working current value of the electric heater according to the preheating algorithm.
After the preheating process is completed, the frequency stabilization
control module 9 switches the double-longitudinal-mode frequency stabilization
laser Li to enter the frequency stabilization control process After the two
longitudinal-mode light beams output from the secondary output end of the
laser tube 6 are separated by the Wollaston prism7, optical power P11 and P12
is measured by the two-quadrant photoelectric detector 8, wherein the power
difference AP-P11-P12 of the two longitudinal-mode light beams is taken as a
feedback input variable of a frequency stabilization closed loop control system
as shown in Fig. 4, and the reference input variable is set to be 0; the frequency
stabilization control module 9 calculates the difference value between the
reference input variable and the feedback input variable, and adjusts the
working current value of the wound electric heater 11 according to the
frequency stabilization control algorithm, so that the temperature and the
resonant cavity length of the laser tube 6 are adjusted for making the power of
the two longitudinal-mode light beams meet P11= P12, and also trend to a stable
value.
After the frequency stabilization process is ended, the laser Li enters the
frequency locking process, the double-mode laser beam output from the main
output end of the laser tube 6 is separated by the polarizing beam splitter B14
to separate one longitudinal-mode light beam as input light, with frequency
recorded as vi, of the acousto-optic frequency shifter 15 with working frequency
recorded as fi. Due to the acousto-optic interaction, the frequency of the laser beam output from the acousto-optic frequency shifter 15 is vi+fi, and this beam passes through the beam splitter 16 to split into two parts of light with an intensity ratio of 9:1, where the light with greater intensity is recorded as Zi and is used as output laser of the double-longitudinal-mode laser L1, the light with smaller intensity is recorded as a light beam Y1 which is coupled by the optical fiber combiner 17 and enters an optical fiber for being synthesized into a coaxial light beam with the light beam Xi; after passing through the polarizer 18, the coaxial light beam forms an optical beat frequency signal, which has a frequency value Ayi=v1+ fi-v, measured by the frequency measuring module r20 after being subjected to photoelectric conversion through a high-speed photoelectric detector 19, and is used as a feedback input variable of a frequency locking closed loop control system as shown in Fig. 5, and a reference input variable is set to be 0; the frequency adjusting module 21 calculates a frequency difference value vr-vi=fi-Ay1 between the light beam
X1 and the light beam Y1 according to a difference value Ayi of the two, and
adjusts drive frequency fi of the acousto-optic frequency shifter 15 to be vr-vi,
so that the frequency of the light beam Zi output from the laser Li is equal to
frequency vr of a reference light beam X1 (the frequency of light beams Zi and
Y1 being the same). After the frequency locking process is accomplished, the
frequency locking state indicator lamp 22 is enabled by the frequency adjusting
module 21.
When the external environment changes or other factors cause the
frequency of the laser output from the reference dual-longitudinal-mode
frequency stabilization laser 3 or the double-longitudinal-mode laser Li to
change, the above-mentioned frequency stabilization locking process is automatically cycled, and the frequency vi of the laser output from the double longitudinal-mode laser Li is always locked to the reference frequency Vr by adjusting the working frequency f1 of the acousto-optic frequency shifter 15.
Similarly, the frequency V2, V3, ... , Vn of the laser output from the double
longitudinal-mode lasers L2, L3,..., L is also always locked at the reference
frequency Vr.
Claims (2)
1. A double-longitudinal-mode laser interlocking device based on thermal
frequency stabilization and acousto-optic frequency shift includes a laser power
source A (1), a frequency stabilization state indicator lamp (2), a reference
double-longitudinal-mode frequency stabilization laser (3), a polarizing beam
splitter A (4) and an optical fiber splitter (5), and further includes n (n being
greater than or equal to 1) double-longitudinal-mode lasers Li (i being equal to
1, 2, .... n) which are the same in structure and are in parallel-connection
relationship, wherein both the laser power source A (1) and the frequency
stabilization state indicator lamp (2) are connected to the reference double
longitudinal-mode frequency stabilization laser (3); the polarizing beam splitter
A (4) is arranged between the output end of the reference double-longitudinal
mode frequency stabilization laser (3) and the input end of the optical fiber
splitter (5); the assembly structure of each double-longitudinal-mode laser Li (i
being equal to 1, 2, .... n) is as follows: a laser power source B (13) is connected
to a laser tube (6), an electric heater (11) is wound on the outer wall of the laser
tube (6), the input end of the electric heater (11) is connected to a frequency
stabilization control module (9), a laser tube temperature sensor (10) is
attached onto the outer wall of the laser tube (6), the output end of the laser
tube temperature sensor (10) is connected to the frequency stabilization control
module (9), an ambient temperature sensor (12) is connected to the frequency
stabilization control module (9), a Wollaston prism (7) is placed behind the
secondary output end of the laser tube (6), a two-quadrant optoelectronic
detector (8) is placed behind the Wollaston prism (7), the output end of the two
quadrant optoelectronic detector (8) is connected to the frequency stabilization control module (9); a polarizing beam splitter B (14) is placed in front of the main output end of the laser tube (6) , an acousto-optic frequency shifter (15) is placed behind the polarizing beam splitter B (14); a beam splitter (16) is placed between the acousto-optic frequency shifter (15) and an optical fiber combiner (17); another input end of the optical fiber combiner (17) is connected to the output end of the optical fiber splitter (5); a polarizer (18) is placed between the output end of the optical fiber combiner (17) and a high-speed photoelectric detector (19); the high-speed photoelectric detector (19), a frequency measuring module (20), a frequency adjusting module (21) and the acousto-optic frequency shifter (15) are sequentially connected; and a frequency locking state indicator lamp (22) is connected to the frequency adjusting module (21).
2. A double-longitudinal-mode laser interlocking method based on thermal
frequency stabilization and acousto-optic frequency shift, comprising the
following steps:
(1) turning on a power of the reference double-longitudinal-mode
frequency stabilization laser, after preheating and frequency stabilization, the
output laser contains two orthogonally-polarized longitudinal-mode beams,
utilizing a polarization beam splitter to separate one of the longitudinal-mode
beams as the output light, with optical frequency recorded as vr, an fiber splitter
separates the output light into n parts of beam (n being greater than or equal to
1), which are recorded as Xi (i being equal to 1, 2, .... n) and used as the
reference beams respectively for frequency locking of the double-longitudinal
mode lasers Li (i being equal to 1, 2, .... n);
(2) turning on power of the double-longitudinal-mode lasers Li (i being
equal to 1, 2, .... n) to enter the preheating process, measuring the current
temperature of the environment, setting a preheating target temperature Tset
which is higher than the ambient temperature, utilizing an electric heater to heat
laser tubes inside the lasers, making the temperatures of the laser tubes trend
to the preset temperature Tset and reach a thermal balance state, finely
adjusting a working current of the electric heater according to a preheating
algorithm to make the laser emitted from the main and secondary output ends
of the laser tubes include two orthogonally-polarized longitudinal-mode beams;
(3) after the preheating process is ended, the double-longitudinal-mode
lasers Li (i being equal to 1, 2, .... n) enter a frequency stabilization control
process, a Wollaston prism is utilized to separate the two orthogonally-polarized
longitudinal-mode beams at the secondary output ends of the laser tubes, with
optical power being Pi and P2 (i being equal to 1, 2, .... n), which are detected
by a two-quadrant optoelectronic detector, the frequency stabilization control
module calculates the power difference AP=Pi-2 (i being equal to 1, 2, ....
n) of the two longitudinal-mode beams, and then regulates the current of the
electric heater according to the value of AP (i being equal to 1, 2, .... n) to make
AP trend to 0, thereby make the laser frequency trend to a stable value;
(4) utilizing the polarization beam splitter to separate one of longitudinal
mode beams from the main output ends of the laser tubes, recording it as Ti (i
being equal to 1, 2, .... n) with frequency as vi (i being equal to 1, 2,.. n),
which enters an acousto-optic frequency shifter Si (i being equal to 1, 2,.. n)
with working frequency fi, (i being equal to 1, 2, .... n), and then the
correspondingly output laser has a frequency of vi+fi (i being equal to 1, 2, ....
n), splitting the output laser into two parts with an intensity ratio being 9:1,
wherein the part with greater intensity is recorded as Zi (i being equal to 1, 2, ....
n), which is used as output laser of the double-longitudinal-mode laser Li (i
being equal to 1, 2, .... n), and the part with smaller intensity is recorded as Yi
(i being equal to 1, 2, .... n);
(5) mixing the light beam Xi (i being equal to 1, 2, .... n) with the light beam
Yi (i being equal to 1, 2, .... n) to form an optical beat frequency signal, utilizing
an photoelectric detector to convert the beat frequency signal into an electric
signal with a frequency as AVi=Vi+fi-r (i being equal to 1, 2, .... n) which is
measured by a frequency measuring module, calculating a frequency
difference value vr-vi=fi-Avi (i being equal to 1, 2, .... n) between the beam Xi
(i being equal to 1, 2, .... n) and the beam Yi (i being equal to 1, 2, .... n),
adjusting working frequency fi(i being equal to 1, 2, .... n) of the acousto-optic
frequency shifter Si (i being equal to 1, 2, .... n) to be vr-vi (i being equal to 1,
2, .... n), thereby making frequency of the beam Zi (i being equal to 1, 2,.. n)
output by the double-longitudinal-mode lasers Li (i being equal to 1, 2,.. n)
equal to frequency of the reference beam Xi (i being equal to 1, 2, .... n), namely
v+fi=vr (i being equal to 1, 2, .... n);
(6) repeating the steps (4) and (5), making frequency of the output light
beam Zi (i being equal to 1, 2, .... n) of the double-longitudinal-mode lasers Li
(i being equal to 1, 2, .... n) to be always locked at the same frequency value vr
by adjusting working frequency fi (i being equal to 1, 2, .... n) of the acousto
optic frequency shifter Si (i being equal to 1, 2, .... n).
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