CN109936043B - Tunable ultrashort pulse laser based on annular cavity - Google Patents
Tunable ultrashort pulse laser based on annular cavity Download PDFInfo
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- CN109936043B CN109936043B CN201910364725.1A CN201910364725A CN109936043B CN 109936043 B CN109936043 B CN 109936043B CN 201910364725 A CN201910364725 A CN 201910364725A CN 109936043 B CN109936043 B CN 109936043B
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Abstract
The invention discloses a tunable ultrashort pulse laser based on an annular cavity, wherein a seed laser is connected with one input end of a coupler, a photoelectric detector is connected with one output end of the coupler, and the other input end and the other output end of the coupler are connected through an optical fiber to form an annular feedback cavity; connecting the acousto-optic frequency shifter, the optical fiber amplifier and the optical fiber delay in a ring-shaped feedback cavity; the seed laser switching power supply controls the on and off of the seed laser; when the device works, the seed laser switch power supply is started first, and the coupler outputs continuous light; when pulse laser needs to be generated, the seed laser switch power supply is turned off, and the coupler outputs pulse laser. The device has simple structure and low cost, and the system has multiple pulse tuning functions of a single device.
Description
Technical Field
The invention belongs to the technical field of laser, and particularly relates to a tunable ultrashort pulse laser based on an annular cavity.
Background
The ultra-short pulse laser is a laser with wide application, and is mainly characterized in that the peak power of the output laser is very high, and the pulse width is very narrow (usually in picoseconds and femtoseconds). Currently, main technologies capable of generating ultrashort pulse laser include a mode-locked laser technology, a gain-switched semiconductor laser technology, and a laser intensity modulation technology. The mode-locked laser technology is the most common method for obtaining ultrashort pulse laser output, and various methods for realizing mode locking can be used, but generally the mode-locked laser technology can be divided into two categories: namely active mode locking and passive mode locking. Active mode locking means that the gain or loss of the laser is periodically changed by providing a modulation signal to the laser from the outside, so as to achieve the purpose of mode locking; passive mode locking utilizes nonlinear absorption or nonlinear phase change characteristics of materials to generate laser ultrashort pulses. The mode locking technique is to lock the phase of each longitudinal mode in the laser cavity, thereby obtaining a pulse output with an extremely narrow width. However, the mode locking technique cannot realize the tuning function of various pulses.
Disclosure of Invention
In view of this, the invention provides a tunable ultrashort pulse laser based on a ring cavity, the device has a simple structure and low cost, and the system has multiple pulse tuning functions of a single device.
Furthermore, by utilizing the frequency selection characteristic of the annular feedback cavity and the frequency shift characteristic of the acousto-optic frequency shifter, the ultra-short pulse laser with adjustable output peak power, adjustable pulse width, adjustable repetition frequency and adjustable pulse number can be effectively realized.
A tunable ultrashort pulse laser based on an annular cavity comprises a seed laser, a seed laser switching power supply, a coupler, an acousto-optic frequency shifter, an optical fiber amplifier, an optical fiber delayer and a photoelectric detector;
the seed laser is connected with one input end of the coupler, the photoelectric detector is connected with one output end of the coupler, and the other input end and the other output end of the coupler are connected through optical fibers to form an annular feedback cavity; connecting the acousto-optic frequency shifter, the optical fiber amplifier and the optical fiber delay in a ring-shaped feedback cavity;
the optical fiber amplifier is used for providing gain to compensate the loss of the annular feedback cavity;
the optical fiber delayer is used for adjusting the length of the optical fiber in the annular feedback cavity by adjusting the delay time;
the acousto-optic frequency shifter is used for shifting the frequency of the laser which passes through the annular feedback cavity repeatedly;
the photoelectric detector performs photoelectric conversion on the optical signal output from the coupler and then outputs the optical signal;
the seed laser switching power supply controls the on and off of the seed laser; when the device works, the seed laser switch power supply is started first, and the coupler outputs continuous light; when pulse laser needs to be generated, the seed laser switch power supply is turned off, and the coupler outputs pulse laser.
The peak power and the pulse width of the pulse laser are adjusted by adjusting the gain generated by the optical fiber amplifier;
adjusting the repetition frequency of the pulse laser by adjusting the delay time of the optical fiber delayer;
the pulse number of the pulse laser is changed by adjusting the modulation frequency of the acousto-optic frequency shifter.
Has the advantages that:
(1) the tunable ultrashort pulse laser based on the annular cavity designed by the invention utilizes the frequency selection characteristic of the annular feedback cavity and the frequency shift characteristic of the acousto-optic frequency shifter to generate tunable ultrashort pulse laser, and provides a feasible scheme for the generation of ultrashort pulse laser.
(2) The invention can realize the adjustable output peak power, pulse width, repetition frequency and pulse number of the ultrashort pulse laser.
(3) The invention relates to standardized optical fiber devices, which have the advantages of simple structure, convenient realization and low cost.
Drawings
Fig. 1 is a schematic structural diagram of a tunable ultrashort pulse laser based on a ring cavity according to the present invention.
Detailed Description
The invention provides a tunable ultrashort pulse laser based on a ring cavity, and the working principle of the tunable ultrashort pulse laser is shown in figure 1.
The device comprises a seed laser 1, a seed laser switch power supply 2, a 2 multiplied by 2 coupler 3, an acousto-optic frequency shifter 4, an optical fiber amplifier 5, an optical fiber delayer 6, a photoelectric detector 7 and an oscilloscope 8.
In this embodiment, the 2 × 2 coupler 3 has four ports, which are divided into two input ends and two output ends, the seed laser 1 is connected to one input end of the 2 × 2 coupler 3, the photodetector 7 is connected to one output end of the 2 × 2 coupler 3, and the other input end and the other output end of the 2 × 2 coupler 3 are connected through an optical fiber to form a ring-shaped feedback cavity. In the ring-shaped feedback cavity, an acousto-optic frequency shifter 4, an optical fiber amplifier 5 and an optical fiber delay 6 are connected. The position of the acousto-optic frequency shifter 4, the optical fiber amplifier 5 and the optical fiber delayer 6 in the annular feedback cavity is adjustable. In this embodiment, the three sequences are the acousto-optic frequency shifter 4, the optical fiber amplifier 5 and the optical fiber delay 6.
Wherein the fiber amplifier is used to provide gain to compensate for the loss of the ring feedback cavity.
The optical fiber delayer is used for adjusting the length of the optical fiber in the annular feedback cavity by adjusting the delay time.
The acousto-optic frequency shifter is used for shifting the frequency of the laser which passes through the annular feedback cavity repeatedly.
The photodetector photoelectrically converts the optical signal output from the coupler and outputs the converted optical signal.
Firstly, a seed laser switch power supply 2 is started to enable a seed laser 1 to work, the seed laser 1 generates single-frequency continuous laser, the single-frequency continuous laser is input into a 2 multiplied by 2 coupler 3, and a device in an annular feedback cavity starts to work.
The single-frequency continuous laser output by the 2 x 2 coupler 3 is frequency-shifted by the acousto-optic frequency shifter 4 to generate frequency-shifted laser. The acousto-optic frequency shifter 4 uses acousto-optic interaction (mainly Bragg diffraction) to obtain the frequency shift of light. The laser is diffracted by the ultrasonic grating through the acousto-optic medium, and the propagation direction and the laser frequency of the laser are changed. The frequency of the diffracted light is superimposed with an ultrasonic frequency at the original input laser frequency, and the amount of change in optical frequency is equal to the frequency of the applied radio frequency signal.
The single frequency continuous laser light then passes through a fiber amplifier 5. The fiber amplifier 5 provides gain, and the loss of the ring feedback cavity is compensated by the provided gain.
Then, the single-frequency continuous laser passes through the optical fiber delay device 6, and the length of the optical fiber is controlled by adjusting the delay time of the optical fiber delay device 6, so as to realize different delay times.
In the annular feedback cavity, the positions of the acousto-optic frequency shifter 4, the optical fiber amplifier 5 and the optical fiber delayer 6 are adjustable, so that single-frequency continuous laser can pass through any device.
When all devices are operating steadily, the coupler now outputs continuous light to the photodetector. When pulse laser needs to be generated, the seed laser switch power supply 2 is turned off. At this time, the process of the present invention,the inside balanced state that reaches gain and loss rapidly of annular feedback chamber, annular feedback chamber frequency selection simultaneously satisfies that n lambda is L's laser wavelength can the initial oscillation (wherein, L is the length of optic fibre in the annular feedback chamber, lambda is single-frequency continuous laser wavelength, n is the integer), and the corresponding laser longitudinal mode interval of initial oscillation laser
(where Δ f is the laser vertical and horizontal spacing, and c is the speed of light).
Due to the frequency shift characteristic of the acousto-optic frequency shifter 4, when the laser longitudinal mode interval and the modulation frequency of the acousto-optic frequency shifter 4 satisfy fAN · Δ f (wherein f)AIs the modulation frequency of the acousto-optic frequency shifter, and n is an integer), the acousto-optic frequency shifter is matched with the laser longitudinal mode to lock the frequency and the phase of each longitudinal mode, thereby achieving the effect of stabilizing the mode-locked laser. Finally, stable ultrashort pulse laser is obtained, and the coupler outputs the pulse laser at the moment.
When the laser longitudinal mode interval and the modulation frequency of the acousto-optic frequency shifter 4 meet
The acousto-optic frequency shifter is equivalent to frequency shift
At this time, the double-pulse laser is output. By adjusting the modulation frequency of the acousto-optic frequency shifter 4, the relationship between the modulation frequency of the acousto-optic frequency shifter 4 and the laser longitudinal mode interval is changed, and different pulse numbers of laser can be realized.
The output peak power of the pulse laser is determined by the loss in the annular feedback cavity and the gain generated by the optical fiber amplifier 5, and when the loss in the annular feedback cavity is fixed, the output power of the optical fiber amplifier 5 is increased, so that the gain in the annular feedback cavity is increased, the output laser power is increased, and finally the adjustment of the output power is realized. As the output laser power increases, the gain produced gradually decreases and reaches a state of equilibrium with the loss by adjusting the output power of the optical fiber amplifier 5.
The pulse width of the pulse laser is adjusted by changing the gain generated by the optical fiber amplifier 5, and as the gain is increased, the longitudinal modes capable of starting oscillation in the annular feedback cavity are increased, so that the time domain pulse width is narrowed, and the adjustment of the pulse width is realized.
The repetition frequency of the pulse laser is adjustable by changing the length of the optical fiber in the annular feedback cavity, namely, by changing the delay time of the optical fiber delay 6. According to the frequency selection characteristic of the annular feedback cavity, the repetition frequency of the output laser is a function of the length of the optical fiber in the annular feedback cavity, and the repetition frequency of the output laser can be effectively changed by adjusting the delay time of the optical fiber delayer and changing the length of the optical fiber in the annular feedback.
The invention realizes stable output of ultrashort pulse by using an optical method, an annular feedback cavity constructed by optical fiber and the frequency shift characteristic of an acousto-optic frequency shifter and the frequency selection characteristic of the annular feedback cavity. The ultra-short pulse laser with adjustable output peak power, pulse width, repetition frequency and pulse number is realized by adjusting the length of the annular feedback cavity, the modulation frequency of the acousto-optic frequency shifter and the gain of the optical fiber amplifier. The optical fiber device is a standardized optical fiber device, and is convenient to implement, simple in structure and low in cost.
In summary, the above description is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (1)
1. A tunable ultrashort pulse laser based on a ring cavity is characterized by comprising a seed laser (1), a seed laser switch power supply (2), a coupler (3), an acousto-optic frequency shifter (4), an optical fiber amplifier (5), an optical fiber delayer (6) and a photoelectric detector (7);
the seed laser (1) is connected with one input end of the coupler (3), the photoelectric detector (7) is connected with one output end of the coupler (3), and the other input end and the other output end of the coupler (3) are connected through optical fibers to form an annular feedback cavity; -connecting the acousto-optic frequency shifter (4), the optical fiber amplifier (5) and the optical fiber delay (6) in a ring-shaped feedback cavity;
the optical fiber amplifier (5) is used for providing gain to compensate the loss of the annular feedback cavity;
the optical fiber delayer (6) is used for adjusting the length of the optical fiber in the annular feedback cavity by adjusting the delay time;
the acousto-optic frequency shifter (4) is used for shifting the frequency of the laser which passes through the annular feedback cavity repeatedly;
the photoelectric detector (7) performs photoelectric conversion on the optical signal output from the coupler (3) and outputs the optical signal;
the seed laser switch power supply (2) controls the on and off of the seed laser (1); when the single-frequency continuous laser coupler works, the seed laser switching power supply (2) is started firstly, so that the seed laser (1) works, the seed laser generates single-frequency continuous laser, and the single-frequency continuous laser is input into the coupler (3); when all the devices work stably, the coupler (3) outputs continuous light to the photoelectric detector (7); when pulse laser needs to be generated, the seed laser switch power supply (2) is turned off, and the coupler (3) outputs the pulse laser;
the peak power and the pulse width of the pulse laser are adjusted by adjusting the gain generated by the optical fiber amplifier (5);
adjusting the repetition frequency of the pulse laser by adjusting the delay time of the optical fiber delayer;
the pulse number of the pulse laser is changed by adjusting the modulation frequency of the acousto-optic frequency shifter (4).
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Citations (4)
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| US20020106142A1 (en) * | 2000-06-09 | 2002-08-08 | Shouhua Huang | Acceleration-insensitive opto-electronic oscillators |
| US7006542B2 (en) * | 2003-03-11 | 2006-02-28 | The Boeing Company | System and method for stabilizing a laser output frequency |
| CN103633537A (en) * | 2013-11-13 | 2014-03-12 | 中国科学院物理研究所 | Low noise fiber laser frequency combs device with controllable carrier envelope phase shift frequency |
| CN107093837A (en) * | 2017-06-22 | 2017-08-25 | 北京理工大学 | A kind of radio-frequency modulations pulse laser generation device based on frequency shift feedback loop |
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Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US20020106142A1 (en) * | 2000-06-09 | 2002-08-08 | Shouhua Huang | Acceleration-insensitive opto-electronic oscillators |
| US7006542B2 (en) * | 2003-03-11 | 2006-02-28 | The Boeing Company | System and method for stabilizing a laser output frequency |
| CN103633537A (en) * | 2013-11-13 | 2014-03-12 | 中国科学院物理研究所 | Low noise fiber laser frequency combs device with controllable carrier envelope phase shift frequency |
| CN107093837A (en) * | 2017-06-22 | 2017-08-25 | 北京理工大学 | A kind of radio-frequency modulations pulse laser generation device based on frequency shift feedback loop |
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