CN214542906U

CN214542906U - Compact high-repetition-frequency full-polarization-maintaining optical fiber mode-locked laser

Info

Publication number: CN214542906U
Application number: CN202120905350.8U
Authority: CN
Inventors: 邹宏新; 张祥
Original assignee: National University of Defense Technology
Current assignee: National University of Defense Technology
Priority date: 2021-04-28
Filing date: 2021-04-28
Publication date: 2021-10-29
Anticipated expiration: 2031-04-28

Abstract

The utility model discloses a compact high repetition frequency fully polarization maintaining optical fiber mode-locked laser, it is based on nonlinear amplification ring mirror mode locking method, has characteristics such as mode locking point is fixed, can long-time stable operation. The use of the phase shifter unit and the wavelength division multiplexing polarization maintaining fiber collimator reduces the requirement on the pump power, thereby reducing the damage to the optical device caused by long-time operation. Compared with the same type of polarization maintaining fiber laser with short cavity length and high repetition frequency, the self-starting mode locking can be realized under higher repetition frequency. The single composite polarization maintaining optical fiber collimator structure solves the problems of difficult processing and manufacturing and higher cost of adjusting devices when a plurality of collimators are used, and improves the reliability of the whole laser system and the yield of industrial mass production. The optical band-pass filter in or out of the laser cavity can effectively compress the relative intensity noise of the output pulse. The use of a beam splitter within a composite polarization maintaining fiber collimator allows the output pulses to have more optional characteristics such as noise, power, spectral width, and contrast.

Description

Compact high-repetition-frequency full-polarization-maintaining optical fiber mode-locked laser

Technical Field

The utility model relates to an ultrashort pulse laser field, concretely relates to high repetition frequency polarization maintaining optical fiber mode-locked laser.

Background

Over the past two and three decades, the theory and experiments of mode-locked lasers have been greatly developed. Pulses generated by the mode-locked laser are applied to more and more scenes, such as ultra-fine laser spectroscopy, timing and synchronization, two-photon spectroscopy, generation of terahertz radiation, research of attosecond dynamics, generation of pure microwaves, ultra-precision machining of materials and the like. Early applications of femtosecond pulses were limited to well-controlled laboratory environments, but more and more applications now require mode-locked lasers to operate under less stable or even harsh conditions, such as in industrial manufacturing plants, vehicles, airplanes, rockets, and even satellites. The polarization-maintaining fiber mode-locked laser can naturally protect a light beam path from being influenced by the environment to a great extent, and has the advantages of simple and compact structure, easiness in packaging, low cost, robustness and the like. Therefore, it can provide reliable femtosecond light source for the applications, and is a promising technology.

Currently, there are three types of mode-locked fiber lasers. The first is to use semiconductor saturable absorber mirror (SESAM), carbon nanotube and graphene etc. saturable absorbing material to realize mode locking. Although such mode-locked lasers can achieve very high repetition rates, the low damage threshold of the material and the potential degradation over time make the laser less stable for long periods of time. The second is to realize Nonlinear Polarization Rotation (NPR) of light in the fiber by fusing the polarization maintaining fiber with a suitable optical axis angle. This mode locking requires a long polarization maintaining fiber to accumulate the nonlinear phase shift, resulting in a low repetition rate of the laser. Therefore, the method is still in a research stage and cannot meet the requirements of practical application. The third is a non-linear amplification ring mirror (NALM) scheme, which is based on the principle that two beams of light transmitted in opposite directions are generated in a polarization-maintaining fiber loop, and are interfered in a beam splitter, and the non-linear phase shift of the two beams of light is utilized to control the transmittance of light with different intensities, so that the saturable absorption characteristic is realized. Because of the all-fiber approach, the problems encountered with the first material mode-locking approach are avoided. However, the polarization maintaining fiber NALM mode locking scheme is difficult to realize high repetition frequency exceeding 250MHz, and the laser with the high repetition frequency has the problems of difficult processing and manufacturing, high manufacturing cost, high pumping power consumption requirement, difficult mode locking, difficult increase of repetition frequency and the like.

Therefore, how to overcome the above-mentioned drawbacks of NALM mode locking has become an important issue to be solved by those skilled in the art.

SUMMERY OF THE UTILITY MODEL

To the not enough of above-mentioned technique, the utility model provides a compact high repetition frequency fully protects polarisation fibre mode-locked laser.

The utility model discloses a realize above-mentioned purpose, adopted following technical scheme:

a compact high-repetition-frequency full polarization-maintaining optical fiber mode-locked laser comprises a first polarization-maintaining single-mode fiber 1, a polarization-maintaining gain fiber 13, a second polarization-maintaining single-mode fiber 14, a pumping source 15, a first composite polarization-maintaining optical fiber collimator 2, a first phase shifter unit 6, a first polarization beam splitter 9, a first 1/4 wave plate 10, a second optical band-pass filter 11, an electro-optical modulator 23, a grating pair 24, a reflector 25 and piezoelectric ceramics 26; the first polarization maintaining single mode fiber 1 is connected with the polarization maintaining gain fiber 13 through a fiber fusion point 12, multiple sections of polarization maintaining single mode fibers and polarization maintaining gain fibers can be added between the first polarization maintaining single mode fiber 1 and the polarization maintaining gain fiber 13, and a loop formed by the first polarization maintaining single mode fiber 1 and the polarization maintaining gain fiber 13 can be replaced by a full polarization maintaining gain fiber loop; piezoelectric ceramics are added to a loop formed by the first polarization maintaining single-mode fiber 1 and the polarization maintaining gain fiber 13; the pumping source 15 is connected with the first composite polarization maintaining fiber collimator 2 through a second polarization maintaining single mode fiber 14; the light output by the first composite polarization maintaining optical fiber collimator 2 passes through the first output window 4 and the second output window 16 and then respectively passes through the first isolator 3 and the third isolator 17 to output pulse laser outwards; the output light of the third output window 18 of the first composite polarization-maintaining fiber collimator 2 sequentially passes through the first phase shifter unit 6, the first polarization beam splitter 9, the first 1/4 wave plate 10, the second optical band-pass filter 11, the electro-optical modulator 23, the grating pair 24 and the reflector 25; the piezoelectric ceramic 26 is fixed with the reflector 25 together to adjust the position of the reflector 25; the first polarization beam splitter 9 has two output directions, light in one direction passes through the third optical band-pass filter 21 and the fourth isolator 22, and light in the other direction passes through the first optical band-pass filter 8 and the second isolator 7; the first polarization beam splitter 9 is a polarization beam splitting cube; the grating pair 24 can be replaced by a prism pair dispersion compensation optical device, and can be removed when dispersion compensation is not needed in the optical path; the electro-optic modulator 23 may be anywhere in the optical cavity; the second optical band-pass filter 11 can be anywhere in the optical cavity; an optical band-pass filter can be added between the second output window 16 and the third isolator 17, and between the first isolator 3 and the first output window 4; the reflector 25 is a total reflector or a partial reflector, the transmission end of the partial reflector is another pulse output port, and an isolator and an optical band-pass filter can be added behind the output port.

Further, the first composite polarization maintaining fiber collimator 2 is composed of a first polarization maintaining single-mode fiber 1, a polarization maintaining gain fiber 13, a second polarization maintaining single-mode fiber 14, a wavelength division multiplexing polarization maintaining fiber collimator 27, a polarization maintaining fiber collimator 28, a beam splitter 29, and a second polarization beam splitter 30; the polarization directions of the two split beams of the second polarization beam splitter 30 are simultaneously aligned with the slow axis or the fast axis of the wavelength division multiplexing polarization-maintaining fiber collimator 27 and the polarization-maintaining fiber collimator 28; linearly polarized light output by the polarization-maintaining optical fiber collimator 28 is divided into two beams on the beam splitter 29, one beam is output through the second output window 16, the other beam passes through the second polarization beam splitter 30 and then passes through the third output window 18 together with linearly polarized light output by the wavelength division multiplexing polarization-maintaining optical fiber collimator 27, conversely, light input from the third output window 18 is divided into two beams through the second polarization beam splitter 30, one beam is input into the wavelength division multiplexing polarization-maintaining optical fiber collimator 27, and the other beam is split on the beam splitter 29 and then respectively enters the polarization-maintaining optical fiber collimator 28 and the first output window 4; the second polarization beam splitter 30 is a polarization beam splitter such as a Wollaston prism, a Rochon prism or a polarization beam splitting cube; the beam splitter 29 can be between the polarization-maintaining optical fiber collimator 28 and the second polarization beam splitter 30, or between the wavelength division multiplexing polarization-maintaining optical fiber collimator 27 and the second polarization beam splitter 30; the polarization maintaining gain fiber 13 and the first polarization maintaining single mode fiber 1 form an optical fiber loop in which an optical fiber coupler can be introduced; the wavelength division multiplexing polarization-maintaining fiber collimator 27 is manufactured by changing the transmission end of a commercial polarization-maintaining fiber wavelength division multiplexer into a collimator structure and changing a single-mode polarization-maintaining fiber at the common end of the wavelength division multiplexer into a polarization-maintaining gain fiber; the alternative structure of the wavelength division multiplexing polarization maintaining fiber collimator 27 is as follows: the tail fiber of the transmission end or the reflection end of the commercial polarization maintaining optical fiber wavelength division multiplexer is connected with the tail fiber of the polarization maintaining optical fiber collimator, and the single-mode polarization maintaining optical fiber of the public end is changed into a polarization maintaining gain optical fiber; the polarization maintaining fiber collimator 28 can be replaced by a wavelength division multiplexing polarization maintaining fiber collimator.

Furthermore, the first phase shifter unit 6 is formed by sequentially arranging the first faraday rotator 5, the second 1/4 wave plate 19 and the first half wave plate 20, and can add a fixed phase difference to the two linearly polarized light beams output by the first composite polarization-maintaining fiber collimator 2 and having mutually perpendicular polarization directions; the positions of the second 1/4 wave plate 19 and the first half wave plate 20 can be interchanged; the first phase shifter element 6 may be replaced by a number of different configurations of a wave plate and faraday rotator combination, and the first phase shifter element 6 may also be replaced by a reflective phase shifter element.

Further, the first composite polarization-maintaining fiber collimator 2 and the first phase shifter unit 6 are replaced by a second composite polarization-maintaining fiber collimator 31, and a second half-wave plate 36 is added between the second composite polarization-maintaining fiber collimator 31 and the first polarization beam splitter 9; the second composite polarization maintaining fiber collimator 31 is formed by adding a second phase shifter unit 35 on the basis of the structure of the first composite polarization maintaining fiber collimator 2; the second phase shifter unit 35 and the beam splitter 29 may be between the polarization maintaining fiber collimator 28 and the second polarization beam splitter 30, or between the wavelength division multiplexing polarization maintaining fiber collimator 27 and the second polarization beam splitter 30; the second phase shifter element 35 is formed by sequentially arranging a second faraday rotator 32, a third 1/4 wave plate 33 and a third faraday rotator 34, and can add a fixed phase difference to linearly polarized light passing in the forward direction and the reverse direction, the second phase shifter element 35 can be replaced by a plurality of different structures of a combination of a wave plate and a faraday rotator, and the second phase shifter element 35 can also be replaced by a reflection-type phase shifter element; the second half-wave plate 36 can be replaced by a directly rotating second composite polarization-maintaining fiber collimator 31 or the first polarization beam splitter 9, and can also be replaced by other types of wave plate combined structures or combined structures of a Faraday rotator and a wave plate; the second polarization beam splitter 30 can be replaced by a beam splitter that does not split beams according to the polarization direction, meanwhile, the polarization directions of the output lights of the wavelength division multiplexing polarization-maintaining fiber collimator 27 and the polarization-maintaining fiber collimator 28 are correspondingly adjusted to be the same, and the components of the second composite polarization-maintaining fiber collimator 31 through which the light output by the third output window 18 passes are adjusted to be the second optical band-pass filter 11, the electro-optical modulator 23, the grating pair 24 and the reflector 25.

Further, the reflecting mirror 25 can be replaced by a saturable absorption mirror or a structure formed by saturable absorption material and reflecting mirror; the second optical band-pass filter 11 can be replaced by a structure formed by a dispersion prism and a diaphragm to tune a wavelength range; the first polarization-preserving single-mode fiber 1, the polarization-preserving gain fiber 13, the first composite polarization-preserving fiber collimator 2 and the second composite polarization-preserving fiber collimator 31 are all fixed on a temperature control device, and the accurate adjustment and stabilization of the repetition frequency or carrier envelope frequency deviation are realized through temperature control.

Compared with the prior art, the utility model, following beneficial effect has:

one, the utility model discloses polarization maintaining fiber laser is based on nonlinear amplification ring mirror mode locking, for traditional saturable absorption material and the rotatory mode locking method of nonlinear polarization, has that the mode locking point is stable, can long-time steady operation and characteristics such as anti environmental disturbance ability reinforce. The use of the wavelength division multiplexing polarization-maintaining fiber collimator maximally improves the asymmetry of a loop, and compared with the common same type of short-cavity long high-repetition-frequency polarization-maintaining fiber laser, the self-starting mode locking under higher repetition frequency can be realized. Simultaneously, for the same repetition frequency's of the same type polarization maintaining fiber laser, the utility model discloses the required pumping power of polarization maintaining fiber laser is lower, has reduced high pumping power to optical device's damage, has increased optical device's life, and has the characteristics of energy-conservation and low-power consumption. Additionally, the utility model discloses optical fiber of optic fibre mode-locked laser all is the polarization maintaining fiber who adopts, can maintain the polarization state of transmission light in the optic fibre better, better resists the instability that arouses because of external environment's change.

The wavelength division multiplexing polarization maintaining optical fiber collimator greatly improves the asymmetry of an optical fiber loop, effectively shortens the cavity length of a laser, solves the problems of difficult processing and manufacturing and high cost caused by using a plurality of collimators and improves the reliability of the whole laser system compared with the same type polarization maintaining optical fiber NALM mode-locked laser. The single composite polarization maintaining optical fiber collimator structure can greatly reduce the coupling difficulty and stability between the collimator and the reflector, and the influence on the coupling efficiency when the piezoelectric ceramic is used for moving the reflector can be greatly reduced, so that the yield of industrial batch production is improved.

And thirdly, the optical band-pass filter can effectively compress the relative intensity noise of the output pulse. The beam splitter enables the utility model discloses the pulse that noise is minimum, power is great, the spectral width is widest and the contrast is higher in the fiber laser output loop.

Drawings

Fig. 1 is a schematic structural diagram of a laser according to a first embodiment of the present invention;

fig. 2 is a schematic structural view of a composite polarization maintaining fiber collimator according to a first embodiment of the present invention;

fig. 3 is a schematic structural diagram of a laser according to a second embodiment of the present invention;

fig. 4 is a schematic structural diagram of a composite polarization maintaining fiber collimator according to the second embodiment of the present invention.

The reference numbers illustrate:

1-a first polarization-preserving single-mode fiber, 2-a first composite polarization-preserving fiber collimator, 3-a first isolator, 4-a first output window, 5-a first Faraday rotator, 6-a first phase shifter unit, 7-a second isolator, 8-a first optical band-pass filter, 9-a first polarization beam splitter, 10-a first 1/4 wave plate, 11-a second optical band-pass filter, 12-a fiber fusion point, 13-a polarization-preserving gain fiber, 14-a second polarization-preserving single-mode fiber, 15-a pump source, 16-a second output window, 17-a third isolator, 18-a third output window, 19-a second 1/4 wave plate, 20-a first half wave plate, 21-a third optical band-pass filter, 22-a fourth isolator, 23-an electro-optical modulator, 24-a grating pair, 25-a reflector, 26-piezoelectric ceramics, 27-a wavelength division multiplexing polarization-maintaining fiber collimator, 28-a polarization-maintaining fiber collimator, 29-a beam splitter, 30-a second polarization beam splitter, 31-a second composite polarization-maintaining fiber collimator, 32-a second Faraday rotator, 33-a third 1/4 wave plate, 34-a third Faraday rotator, 35-a second phase shifter unit and 36-a second half-wave plate.

Detailed Description

The present invention will be described in further detail with reference to the following drawings and examples, which should not be construed as limiting the scope of the present invention.

Example one

Fig. 1 is a schematic structural diagram of a laser according to a first embodiment, and as shown in fig. 1, a compact high-repetition-frequency fully polarization-maintaining fiber mode-locked laser includes a first polarization-maintaining single-mode fiber 1, a polarization-maintaining gain fiber 13, a second polarization-maintaining single-mode fiber 14, a pump source 15, a first composite polarization-maintaining fiber collimator 2, a first phase shifter unit 6, a first polarization beam splitter 9, a first 1/4 wave plate 10, a second optical band-pass filter 11, an electro-optical modulator 23, a grating pair 24, a mirror 25, and a piezoelectric ceramic 26; the first polarization maintaining single mode fiber 1 is connected with the polarization maintaining gain fiber 13 through a fiber fusion point 12, multiple sections of polarization maintaining single mode fibers and polarization maintaining gain fibers can be added between the first polarization maintaining single mode fiber 1 and the polarization maintaining gain fiber 13, and a loop formed by the first polarization maintaining single mode fiber 1 and the polarization maintaining gain fiber 13 can be replaced by a full polarization maintaining gain fiber loop; piezoelectric ceramics are added to a loop formed by the first polarization maintaining single-mode fiber 1 and the polarization maintaining gain fiber 13; the pumping source 15 is connected with the first composite polarization maintaining fiber collimator 2 through a second polarization maintaining single mode fiber 14; the light output by the first composite polarization maintaining optical fiber collimator 2 passes through the first output window 4 and the second output window 16 and then respectively passes through the first isolator 3 and the third isolator 17 to output pulse laser outwards; the output light of the third output window 18 of the first composite polarization-maintaining fiber collimator 2 sequentially passes through the first phase shifter unit 6, the first polarization beam splitter 9, the first 1/4 wave plate 10, the second optical band-pass filter 11, the electro-optical modulator 23, the grating pair 24 and the reflector 25; the piezoelectric ceramic 26 is fixed with the reflector 25 together to adjust the position of the reflector 25; the first polarization beam splitter 9 has two output directions, light in one direction passes through the third optical band-pass filter 21 and the fourth isolator 22, and light in the other direction passes through the first optical band-pass filter 8 and the second isolator 7; the first polarization beam splitter 9 is a polarization beam splitting cube; the grating pair 24 can be replaced by a prism pair dispersion compensation optical device, and can be removed when dispersion compensation is not needed in the optical path; the electro-optic modulator 23 may be anywhere in the optical cavity; the second optical band-pass filter 11 can be anywhere in the optical cavity; an optical band-pass filter can be added between the second output window 16 and the third isolator 17, and between the first isolator 3 and the first output window 4; the reflector 25 is a total reflector or a partial reflector, the transmission end of the partial reflector is another pulse output port, and an isolator and an optical band-pass filter can be added behind the output port; the first phase shifter unit 6 is formed by sequentially arranging a first Faraday rotator 5, a second 1/4 wave plate 19 and a first half wave plate 20, and can add a fixed phase difference to two linearly polarized light beams which are output by the first composite polarization-maintaining fiber collimator 2 and have mutually vertical polarization directions; the positions of the second 1/4 wave plate 19 and the first half wave plate 20 can be interchanged; the first phase shifter element 6 may be replaced by a number of different configurations of a wave plate and faraday rotator combination, and the first phase shifter element 6 may also be replaced by a reflective phase shifter element.

As described above, the working principle of the first embodiment is as follows:

when the optical fiber laser works, the pumping source 15 couples pumping light into the cavity through the first composite polarization maintaining optical fiber collimator 2, and the laser oscillates by increasing the pumping power to be higher than the threshold value of the optical fiber laser; meanwhile, two beams of light which are transmitted in opposite directions by the polarization-maintaining optical fiber in the slow axis or the fast axis are combined after passing through the first composite polarization-maintaining optical fiber collimator 2, and two beams of light which are orthogonal in polarization pass through the first phase shifter unit 6, so that a fixed phase bias is obtained, and the polarization direction is deflected at a certain angle. The polarization direction deflection enables two beams of light with orthogonal polarization to be split on the first polarization beam splitter 9, and the split light with the same polarization component interferes, and the process forms a nonlinear amplification ring mirror. Due to the nonlinear effect of the optical fiber, the light output by interference is subjected to intensity modulation controlled by the accumulated nonlinear phase shift difference of the two beams of light, so that the strong light transmittance is high, the weak light transmittance is low, and the saturated absorption characteristic is realized. The light transmitted back and forth repeatedly passes through the saturable absorption effect to form stable pulse.

Fig. 2 is a schematic structural diagram of a first composite polarization maintaining fiber collimator in the first embodiment, and as shown in fig. 2, the first composite polarization maintaining fiber collimator 2 is composed of a first polarization maintaining single-mode fiber 1, a polarization maintaining gain fiber 13, a second polarization maintaining single-mode fiber 14, a wavelength division multiplexing polarization maintaining fiber collimator 27, a polarization maintaining fiber collimator 28, a beam splitter 29, and a second polarization beam splitter 30; the polarization directions of the two split beams of the second polarization beam splitter 30 are simultaneously aligned with the slow axis or the fast axis of the wavelength division multiplexing polarization-maintaining fiber collimator 27 and the polarization-maintaining fiber collimator 28; linearly polarized light output by the polarization-maintaining optical fiber collimator 28 is divided into two beams on the beam splitter 29, one beam is output through the second output window 16, the other beam passes through the second polarization beam splitter 30 and then passes through the third output window 18 together with linearly polarized light output by the wavelength division multiplexing polarization-maintaining optical fiber collimator 27, conversely, light input from the third output window 18 is divided into two beams through the second polarization beam splitter 30, one beam is input into the wavelength division multiplexing polarization-maintaining optical fiber collimator 27, and the other beam is split on the beam splitter 29 and then respectively enters the polarization-maintaining optical fiber collimator 28 and the first output window 4; the second polarization beam splitter 30 is a Wollaston prism, and can be replaced by a Rochon prism or a polarization beam splitter such as a polarization beam splitting cube; the beam splitter 29 can be between the polarization-maintaining optical fiber collimator 28 and the second polarization beam splitter 30, or between the wavelength division multiplexing polarization-maintaining optical fiber collimator 27 and the second polarization beam splitter 30; the polarization maintaining gain fiber 13 and the first polarization maintaining single mode fiber 1 form an optical fiber loop in which an optical fiber coupler can be introduced; the wavelength division multiplexing polarization-maintaining fiber collimator 27 is manufactured by changing the transmission end of a commercial polarization-maintaining fiber wavelength division multiplexer into a collimator structure and changing a single-mode polarization-maintaining fiber at the common end of the wavelength division multiplexer into a polarization-maintaining gain fiber; the alternative structure of the wavelength division multiplexing polarization maintaining fiber collimator 27 is as follows: the tail fiber of the transmission end or the reflection end of the commercial polarization maintaining optical fiber wavelength division multiplexer is connected with the tail fiber of the polarization maintaining optical fiber collimator, and the single-mode polarization maintaining optical fiber of the public end is changed into a polarization maintaining gain optical fiber; the polarization maintaining fiber collimator 28 can be replaced by a wavelength division multiplexing polarization maintaining fiber collimator.

High repetition rate of the laser can be achieved by shortening the length of the loop fiber or the length of the free space section; the electro-optical modulator 23 and the piezoelectric ceramic 26 are respectively used for fine adjustment and coarse adjustment of the optical path to accurately change the pulse repetition frequency; piezoelectric ceramics are added to a loop formed by the first polarization maintaining single-mode fiber 1 and the polarization maintaining gain fiber 13 and used for adjusting the length of the fiber; the first polarization-preserving single-mode fiber 1, the polarization-preserving gain fiber 13 and the first composite polarization-preserving fiber collimator 2 are all fixed on a temperature control device, and high-precision adjustment and stabilization of the repetition frequency or carrier envelope frequency deviation are realized through temperature control.

The first 1/4 wave plate 10 adjusts the pulse output in the direction from the first polarization beam splitter 9 to the third optical band-pass filter 21 by changing the polarization state of linearly polarized light, so as to play a role in controlling the intra-cavity loss, and further adjust the pulse output in the direction from the first polarization beam splitter 9 to the first optical band-pass filter 8 and in the direction from the first output window 4 to the second output window 16; the intra-and extra-cavity bandpass filters, such as the first optical bandpass filter 8, the second optical bandpass filter 11 and the third optical bandpass filter 21, act to compress the pulse relative intensity noise.

The grating pair 24 is used for compensating the intracavity dispersion, for example, the first polarization-maintaining single-mode fiber 1, the polarization-maintaining gain fiber 13 and other optical devices make the intracavity dispersion have a larger positive value, and the negative dispersion can be compensated by adding the grating pair 24 in the cavity.

The reflector 25 can be replaced by a saturable absorber or a structure formed by saturable absorbing materials and reflectors, and the replaced structure is used for assisting the self-starting mode locking of the compact high-repetition-frequency fully-polarization-maintaining fiber mode-locked laser.

The second optical bandpass filter 11 can be replaced by a structure of a dispersion prism and a diaphragm to tune the wavelength range.

Example two

With respect to the first embodiment, the first composite polarization-maintaining fiber collimator 2 and the first phase shifter unit 6 are replaced by a second composite polarization-maintaining fiber collimator 31, and a second half-wave plate 36 is added between the second composite polarization-maintaining fiber collimator 31 and the first polarization beam splitter 9; the second composite polarization maintaining fiber collimator 31 is formed by adding a second phase shifter unit 35 on the basis of the structure of the first composite polarization maintaining fiber collimator 2; the second phase shifter unit 35 and the beam splitter 29 may be between the polarization maintaining fiber collimator 28 and the second polarization beam splitter 30, or between the wavelength division multiplexing polarization maintaining fiber collimator 27 and the second polarization beam splitter 30; the second half-wave plate 36 can be replaced by the second composite polarization-maintaining fiber collimator 31 or the first polarization beam splitter 9, or can be replaced by other types of wave plate combined structures or a combined structure of a faraday rotator and a wave plate.

Fig. 3 is a schematic structural diagram of a laser provided in the second embodiment, and as shown in fig. 3, a compact high-repetition-frequency fully polarization-maintaining fiber mode-locked laser includes a first polarization-maintaining single-mode fiber 1, a polarization-maintaining gain fiber 13, a second polarization-maintaining single-mode fiber 14, a pump source 15, a second composite polarization-maintaining fiber collimator 31, a second half-wave plate 36, a first polarization beam splitter 9, a first 1/4 wave plate 10, a second optical band-pass filter 11, an electro-optical modulator 23, a grating pair 24, a mirror 25, and a piezoelectric ceramic 26; the first polarization maintaining single mode fiber 1 is connected with the polarization maintaining gain fiber 13 through a fiber fusion point 12, multiple sections of polarization maintaining single mode fibers and polarization maintaining gain fibers can be added between the first polarization maintaining single mode fiber 1 and the polarization maintaining gain fiber 13, and a loop formed by the first polarization maintaining single mode fiber 1 and the polarization maintaining gain fiber 13 can be replaced by a full polarization maintaining gain fiber loop; the pumping source 15 is connected with a second composite polarization-maintaining fiber collimator 31 through a second polarization-maintaining single-mode fiber 14; the light output by the second composite polarization maintaining optical fiber collimator 31 passes through the first output window 4 and the second output window 16 and then respectively passes through the first isolator 3 and the third isolator 17 to output pulse laser outwards; the output light of the third output window 18 of the second composite polarization-maintaining fiber collimator 31 sequentially passes through the second half-wave plate 36, the first polarization beam splitter 9, the first 1/4 wave plate 10, the second optical band-pass filter 11, the electro-optical modulator 23, the grating pair 24 and the reflector 25; the piezoelectric ceramic 26 is fixed with the reflector 25 together to adjust the position of the reflector 25; the first polarization beam splitter 9 has two output directions, light in one direction passes through the third optical band-pass filter 21 and the fourth isolator 22, and light in the other direction passes through the first optical band-pass filter 8 and the second isolator 7; the first polarization beam splitter 9 is a polarization beam splitting cube; the grating pair 24 can be replaced by a prism pair dispersion compensation optical device, and can be removed when dispersion compensation is not needed in the optical path; the electro-optic modulator 23 may be anywhere in the optical cavity; the second optical band-pass filter 11 can be anywhere in the optical cavity; an optical band-pass filter can be added between the second output window 16 and the third isolator 17, and between the first isolator 3 and the first output window 4; the reflector 25 is a total reflector or a partial reflector, the transmission end of the partial reflector is another pulse output port, and an isolator and an optical band-pass filter can be added behind the output port.

As described above, the working principle of the second embodiment is as follows:

when the fiber laser works, the pumping source 15 couples pumping light into the cavity through the second composite polarization maintaining fiber collimator 31, and the laser oscillates by increasing the pumping power to be higher than the threshold value of the fiber laser; meanwhile, two beams of light transmitted in opposite directions of the slow axis or the fast axis of the polarization-maintaining optical fiber are combined after passing through the second composite polarization-maintaining optical fiber collimator 31, and two beams of light orthogonal to each other in polarization obtain a fixed phase bias. Then the two beams of light with orthogonal polarization are deflected by a certain angle through a second half-wave plate 36, so that the two beams of light can be split on the first polarization beam splitter 9, the split beams with the same polarization component interfere with each other, and the process forms a nonlinear amplification ring mirror. Due to the nonlinear effect of the optical fiber, the light output by interference is subjected to intensity modulation controlled by the accumulated nonlinear phase shift difference of the two beams of light, so that the strong light transmittance is high, the weak light transmittance is low, and the saturated absorption characteristic is realized. The light transmitted back and forth repeatedly passes through the saturable absorption effect to form stable pulse.

Fig. 4 is a schematic structural diagram of a second composite polarization maintaining fiber collimator according to a second embodiment, and as shown in fig. 4, the second composite polarization maintaining fiber collimator 31 is composed of a first polarization maintaining single-mode fiber 1, a polarization maintaining gain fiber 13, a second polarization maintaining single-mode fiber 14, a wavelength division multiplexing polarization maintaining fiber collimator 27, a polarization maintaining fiber collimator 28, a second phase shifter unit 35, a beam splitter 29, and a second polarization beam splitter 30; the polarization directions of the two split beams of the second polarization beam splitter 30 are simultaneously aligned with the slow axis or the fast axis of the wavelength division multiplexing polarization-maintaining fiber collimator 27 and the polarization-maintaining fiber collimator 28; linearly polarized light output by the polarization-maintaining fiber collimator 28 is divided into two beams on the beam splitter 29 through the second phase shifter unit 35, one beam is output through the second output window 16, the other beam passes through the second polarization beam splitter 30 and then passes through the third output window 18 together with a linearly polarized light combined beam output by the wavelength division multiplexing polarization-maintaining fiber collimator 27, conversely, light input from the third output window 18 is divided into two beams through the second polarization beam splitter 30, one beam is input into the wavelength division multiplexing polarization-maintaining fiber collimator 27, and the other beam is split on the beam splitter 29 and then respectively enters the polarization-maintaining fiber collimator 28 (through the second phase shifter unit 35) and the first output window 4. The second phase shifter element 35 is formed by arranging the second faraday rotator 32, the third 1/4 wave plate 33, and the third faraday rotator 34 in this order, and can add a fixed phase difference to linearly polarized light passing in the forward and reverse directions, and the second phase shifter element 35 can be replaced by a plurality of different structures of a combination of a wave plate and a faraday rotator, and the second phase shifter element 35 can also be replaced by a reflective phase shifter element. The polarization maintaining gain fiber 13 and the first polarization maintaining single mode fiber 1 form an optical fiber loop in which an optical fiber coupler can be introduced; the wavelength division multiplexing polarization-maintaining fiber collimator 27 is manufactured by changing the transmission end of a commercial polarization-maintaining fiber wavelength division multiplexer into a collimator structure and changing a single-mode polarization-maintaining fiber at the common end of the wavelength division multiplexer into a polarization-maintaining gain fiber; the alternative structure of the wavelength division multiplexing polarization maintaining fiber collimator 27 is as follows: the tail fiber of the transmission end or the reflection end of the commercial polarization maintaining optical fiber wavelength division multiplexer is connected with the tail fiber of the polarization maintaining optical fiber collimator, and the single-mode polarization maintaining optical fiber of the public end is changed into a polarization maintaining gain optical fiber; the polarization maintaining fiber collimator 28 can be replaced by a wavelength division multiplexing polarization maintaining fiber collimator; the second polarization beam splitter 30 can be replaced by a beam splitter which does not split beams according to the polarization direction, meanwhile, the polarization directions of the light output by the wavelength division multiplexing polarization-maintaining fiber collimator 27 and the polarization-maintaining fiber collimator 28 are correspondingly adjusted to be the same, and the components of the light output by the second composite polarization-maintaining fiber collimator 31 through the third output window 18 are adjusted to be the second optical band-pass filter 11, the electro-optical modulator 23, the grating pair 24 and the reflector 25.

High repetition rate of the laser can be achieved by shortening the length of the loop fiber or the length of the free space section; the electro-optical modulator 23 and the piezoelectric ceramic 26 are respectively used for fine adjustment and coarse adjustment of the optical path to accurately change the pulse repetition frequency; piezoelectric ceramics are added to a loop formed by the first polarization maintaining single-mode fiber 1 and the polarization maintaining gain fiber 13 and used for adjusting the length of the fiber; the first polarization-preserving single-mode fiber 1, the polarization-preserving gain fiber 13 and the second composite polarization-preserving fiber collimator 31 are all fixed on a temperature control device, and high-precision adjustment and stabilization of the repetition frequency or carrier envelope frequency deviation are realized through temperature control.

The first 1/4 wave plate 10 adjusts the pulse output in the direction from the first polarization beam splitter 9 to the third optical band-pass filter 21 by changing the polarization state of linearly polarized light, so as to play a role in controlling the intra-cavity loss, and further adjust the pulse output in the direction from the first polarization beam splitter 9 to the first optical band-pass filter 8 and in the direction from the first output window 4 to the second output window 16; the pulse power output by the first output window 4 and the second output window 16 to the first isolator 3 and the third isolator 17, respectively, and the pulse power output by the first polarization beam splitter 9 to the third optical band-pass filter 21 and the first optical band-pass filter 8 can be adjusted by rotating the second half-wave plate 36 or the first polarization beam splitting cube 9 or the second composite polarization-maintaining fiber collimator 31. The intra-and extra-cavity bandpass filters, such as the first optical bandpass filter 8, the second optical bandpass filter 11 and the third optical bandpass filter 21, act to compress the pulse relative intensity noise.

Claims

1. A compact high-repetition-frequency full-polarization-maintaining optical fiber mode-locked laser is characterized by comprising a first polarization-maintaining single-mode fiber (1), a polarization-maintaining gain fiber (13), a second polarization-maintaining single-mode fiber (14), a pumping source (15), a first composite polarization-maintaining optical fiber collimator (2), a first phase shifter unit (6), a first polarization beam splitter (9), a first 1/4 wave plate (10), a second optical band-pass filter (11), an electro-optical modulator (23), a grating pair (24), a reflector (25) and piezoelectric ceramics (26); the first polarization-preserving single-mode fiber (1) is connected with the polarization-preserving gain fiber (13) through a fiber fusion point (12), multiple sections of polarization-preserving single-mode fibers and polarization-preserving gain fibers can be added between the first polarization-preserving single-mode fiber (1) and the polarization-preserving gain fiber (13), and a loop formed by the first polarization-preserving single-mode fiber (1) and the polarization-preserving gain fiber (13) can be replaced by a full polarization-preserving gain fiber loop; piezoelectric ceramics are added to a loop formed by the first polarization-preserving single-mode fiber (1) and the polarization-preserving gain fiber (13); the pumping source (15) is connected with the first composite polarization-maintaining fiber collimator (2) through a second polarization-maintaining single-mode fiber (14); the light output by the first composite polarization-maintaining optical fiber collimator (2) passes through a first output window (4) and a second output window (16) and then respectively passes through a first isolator (3) and a third isolator (17) to output pulse laser outwards; the output light of a third output window (18) of the first composite polarization-maintaining optical fiber collimator (2) sequentially passes through a first phase shifter unit (6), a first polarization beam splitter (9), a first 1/4 wave plate (10), a second optical band-pass filter (11), an electro-optical modulator (23), a grating pair (24) and a reflector (25); the piezoelectric ceramic (26) and the reflector (25) are fixed together to adjust the position of the reflector (25); the first polarization beam splitter (9) has two output directions, light in one direction passes through the third optical band-pass filter (21) and the fourth isolator (22), and light in the other direction passes through the first optical band-pass filter (8) and the second isolator (7); the first polarization beam splitter (9) is a polarization beam splitting cube; the grating pair (24) can be replaced by a prism pair dispersion compensation optics, which is removable in the optical path when no dispersion compensation is required; the electro-optical modulator (23) can be at any position of the optical cavity; the second optical band-pass filter (11) can be at any position of the optical cavity; an optical band-pass filter can be added between the second output window (16) and the third isolator (17) and between the first isolator (3) and the first output window (4); the reflector (25) is a total reflector or a partial reflector, the transmission end of the partial reflector is another pulse output port, and an isolator and an optical band-pass filter can be added behind the output port.

2. The compact high-repetition-frequency fully-polarization-maintaining fiber mode-locked laser according to claim 1, wherein the first composite polarization-maintaining fiber collimator (2) is composed of a first polarization-maintaining single-mode fiber (1), a polarization-maintaining gain fiber (13), a second polarization-maintaining single-mode fiber (14), a wavelength-division multiplexing polarization-maintaining fiber collimator (27), a polarization-maintaining fiber collimator (28), a beam splitter (29) and a second polarization beam splitter (30); the polarization directions of the two split beams of the second polarization beam splitter (30) are simultaneously aligned with the slow axis or the fast axis of the wavelength division multiplexing polarization-maintaining fiber collimator (27) and the polarization-maintaining fiber collimator (28); linearly polarized light output by the polarization-maintaining optical fiber collimator (28) is divided into two beams on a beam splitter (29), one beam is output through a second output window (16), the other beam passes through a second polarization beam splitter (30) and then is combined with linearly polarized light output by a wavelength division multiplexing polarization-maintaining optical fiber collimator (27) and then passes through a third output window (18), conversely, light input from the third output window (18) is divided into two beams through the second polarization beam splitter (30), one beam is input into the wavelength division multiplexing polarization-maintaining optical fiber collimator (27), and the other beam is split on the beam splitter (29) and then is respectively incident to the polarization-maintaining optical fiber collimator (28) and a first output window (4); the second polarization beam splitter (30) is a polarization beam splitter such as a Wollaston prism, a Rochon prism or a polarization beam splitting cube; the beam splitter (29) can be arranged between the polarization-maintaining optical fiber collimator (28) and the second polarization beam splitter (30) or between the wavelength division multiplexing polarization-maintaining optical fiber collimator (27) and the second polarization beam splitter (30); the polarization maintaining gain fiber (13) and the first polarization maintaining single mode fiber (1) form an optical fiber loop in which an optical fiber coupler can be introduced; the wavelength division multiplexing polarization-maintaining optical fiber collimator (27) is manufactured by changing the transmission end of a commercial polarization-maintaining optical fiber wavelength division multiplexer into a collimator structure and changing a single-mode polarization-maintaining optical fiber at the common end of the wavelength division multiplexer into a polarization-maintaining gain optical fiber; the alternative structure of the wavelength division multiplexing polarization-maintaining optical fiber collimator (27) is as follows: the tail fiber of the transmission end or the reflection end of the commercial polarization maintaining optical fiber wavelength division multiplexer is connected with the tail fiber of the polarization maintaining optical fiber collimator, and the single-mode polarization maintaining optical fiber of the public end is changed into a polarization maintaining gain optical fiber; the polarization-maintaining fiber collimator (28) can be replaced by a wavelength division multiplexing polarization-maintaining fiber collimator.

3. The compact high-repetition-frequency full-polarization-maintaining fiber mode-locked laser device as claimed in claim 1, wherein the first phase shifter unit (6) is formed by sequentially arranging a first faraday rotator (5), a second 1/4 wave plate (19) and a first half wave plate (20), and can add a fixed phase difference to two linearly polarized light beams with mutually perpendicular polarization directions output by the first composite polarization-maintaining fiber collimator (2); the positions of the second 1/4 wave plate (19) and the first half wave plate (20) can be interchanged; the first phase shifter element (6) may be replaced by a number of different configurations of a wave plate and faraday rotator combination, and the first phase shifter element (6) may also be replaced by a reflective phase shifter element.

4. A compact high repetition frequency fully polarization maintaining fiber mode locked laser according to claim 1, characterized in that the first compound polarization maintaining fiber collimator (2) and the first phase shifter unit (6) are replaced by a second compound polarization maintaining fiber collimator (31), and a second half wave plate (36) is added between the second compound polarization maintaining fiber collimator (31) and the first polarization beam splitter (9); the second composite polarization-maintaining fiber collimator (31) is formed by adding a second phase shifter unit (35) on the basis of the structure of the first composite polarization-maintaining fiber collimator (2); the second phase shifter unit (35) and the beam splitter (29) may be between the polarization maintaining fiber collimator (28) and the second polarization beam splitter (30), or may be between the wavelength division multiplexing polarization maintaining fiber collimator (27) and the second polarization beam splitter (30); the second phase shifter unit (35) is formed by sequentially arranging a second Faraday rotator (32), a third 1/4 wave plate (33) and a third Faraday rotator (34), can add fixed phase difference to linearly polarized light passing in the forward direction and the reverse direction, can be replaced by a plurality of different structures combining the wave plate and the Faraday rotator, and can also be replaced by a reflection type phase shifter unit (35); the second half-wave plate (36) can be replaced by a second composite polarization-maintaining fiber collimator (31) or a first polarization beam splitter (9) which is directly rotated, and can also be replaced by other types of wave plate combined structures or combined structures of a Faraday rotator and a wave plate; the second polarization beam splitter (30) can be replaced by a beam splitter which does not split beams according to the polarization direction, meanwhile, the polarization directions of the output light of the wavelength division multiplexing polarization-maintaining fiber collimator (27) and the polarization-maintaining fiber collimator (28) are correspondingly adjusted to be the same, and the light output by the second composite polarization-maintaining fiber collimator (31) through the third output window (18) sequentially passes through devices to be adjusted into a second optical band-pass filter (11), an electro-optical modulator (23), a grating pair (24) and a reflector (25).

5. A compact high repetition frequency fully-polarization-maintaining fiber mode-locked laser as claimed in claim 1 or 4, wherein said reflector (25) is replaced by a saturable absorber or a structure of saturable absorber and reflector; the second optical band-pass filter (11) can be replaced by a structure formed by a dispersion prism and a diaphragm to tune a wavelength range; the first polarization-preserving single-mode fiber (1), the polarization-preserving gain fiber (13), the first composite polarization-preserving fiber collimator (2) and the second composite polarization-preserving fiber collimator (31) are all fixed on a temperature control device, and the accurate adjustment and stabilization of the repetition frequency or the carrier envelope frequency deviation are realized through temperature control.