Picosecond square wave amplification system based on photonic crystal fiber

Abstract

The utility model discloses a picosecond square wave amplification system based on a photonic crystal fiber, which is characterized by comprising an oscillator used for outputting a laser pulse; the isolator is used for preventing the seed light from being fed back into the oscillator; the stretcher is coupled to the oscillator and is used for expanding the pulse width of the laser pulse output by the oscillator; the pulse shaping device is used for processing the laser pulse, the pre-amplifier is used for amplifying the average power of the laser pulse processed by the stretcher, the pulse shaping device comprises a 4f amplitude modulation system based on a liquid crystal spatial light modulator (SLM), and the 4f amplitude modulation system comprises a grating G1, a grating G2, a concave mirror M1, a concave mirror M2 and the liquid crystal spatial light modulator. The utility model relates to the technical field of laser amplification systems, and the system can realize real-time and controllable pulse amplitude shaping of ultrashort laser pulses through a liquid crystal spatial light modulator so as to obtain pulses with specific shapes, such as square wave pulses.

Description

Technical Field

[0001] The utility model relates to the technical field of laser amplification systems, and in particular to a picosecond square wave amplification system based on photonic crystal optical fibers. Background Art

[0002] With the continuous development and widespread application of ultrashort laser pulse technology, people are pursuing narrow pulses while increasingly demanding pulse shape and phase control. Among them, the technology of ultrashort laser pulse shaping has had a strong impact on disciplines such as ultrafast spectroscopy, nonlinear fiber optics and strong field physics. In pulse shaping technology, nanosecond or picosecond square wave pulses have high application value in the study of light-matter interaction due to their steep edges.

[0003] Current ultrashort pulse shaping technology mainly uses passive technology, which is usually based on grating pairs, prism pairs, chirped mirrors, or a combination of them. The physical and optical properties of these components are fixed, and the phases of different orders are independent of each other. Therefore, the ability of each component to perform pulse compensation is limited, and it is difficult to achieve complete compensation for any phase and amplitude distribution.

[0004] The utility model proposes an active technology, which can realize arbitrary and directional compensation of pulses, a pulse shaping system of an acousto-optic programmable dispersion filter or a mechanical deformable mirror, which realizes pulse shaping through computer program control, has the advantages of good optical modulation characteristics, high spatial resolution, low power consumption, fast response speed, simple interface, parallel real-time processing, etc., and can be applied to the shape and phase control of femtosecond laser pulses. Utility Model Content

[0005] The utility model provides a picosecond square wave amplification system based on photonic crystal fiber, which can realize real-time and controllable pulse amplitude shaping of ultrashort laser pulses through a liquid crystal spatial light modulator to obtain pulses of specific shapes, such as square wave pulses.

[0006] A picosecond square wave amplification system based on photonic crystal fiber, characterized by comprising: an oscillator for outputting laser pulses;

[0007] an isolator for preventing seed light from feeding back into the oscillator;

[0008] A stretcher, coupled to the oscillator, for expanding the pulse width of the laser pulse output by the oscillator;

[0009] A pre-amplifier, used to amplify the average power of the laser pulse processed by the stretcher;

[0010] A pulse shaping device, used for pre-compensating the laser pulse after amplification by the pre-amplifier, the pulse shaping device comprising a 4f amplitude modulation system based on a liquid crystal spatial light modulator, the 4f amplitude modulation system comprising a grating G1, a grating G2, a concave mirror M1, a concave mirror M2 and a liquid crystal spatial light modulator SLM, used for modulating the spectrum of the output pulse after pre-amplification to form a pulse with a specific shape;

[0011] A main amplifier is used to amplify the energy of the laser pulse processed by the pulse shaping device and output a square wave pulse with energy gain.

[0012] As a further limitation of the present technical solution, the oscillator is a fiber mode-locked laser, which achieves mode locking by using nonlinear polarization rotation.

[0013] As a further limitation of the present technical solution, the grating G1 and the grating G2 and the concave mirrors M1 and M2 are completely symmetrically arranged with respect to the liquid crystal spatial light modulator SLM to form a 4f structure, and the pulse shaping device also includes a reflector S1, a reflector S2, a polarizer P1 and a polarizer P2, and the reflector S1 and the reflector S2 and the polarizers P1 and P2 are completely symmetrically arranged with respect to the liquid crystal spatial light modulator SLM, the reflector S1 reflects the light of the grating G1 onto the concave mirror M1, and the reflector S2 reflects the light of the grating G2 onto the concave mirror M2.

[0014] As a further limitation of the technical solution, the main amplifier includes a fiber amplifier, a high reflector HR, an aspheric mirror AL1, an aspheric mirror AL2, an aspheric mirror AL3, a λ / 2 lens, a dichroic mirror DM1, a dichroic mirror DM2 and a dichroic mirror DM3, wherein the gain fiber of the fiber amplifier is a photonic crystal fiber PCF;

[0015] Wherein, the optical fiber amplifier uses a laser diode LD as a pumping source to generate pumping light, and the pumping light is output through a pigtail;

[0016] The aspheric mirror AL1, the aspheric mirror AL2 and the aspheric mirror AL3 are used to couple the pump light into the photonic crystal fiber PCF;

[0017] The dichroic mirror DM1, the dichroic mirror DM2 and the dichroic mirror DM3 are used for filtering light;

[0018] The λ / 2 lens is used to isolate residual light.

[0019] As a further limitation of the present technical solution, the grating G1, the grating G2, the concave mirror M1 and the concave mirror M2 are used for light path shaping.

[0020] As a further limitation of the present technical solution, by controlling the voltage value of each pixel on the liquid crystal spatial light modulator SLM, square wave modulation is performed on the spectrum of the pre-amplified output pulse to generate a square wave spectrum.

[0021] Compared with the prior art, the advantages and positive effects of the utility model are:

[0022] 1. In the photonic crystal fiber femtosecond laser amplification system, the electro-optic modulation characteristics of the liquid crystal spatial light modulator are used to achieve real-time and controllable pulse amplitude shaping of ultrashort laser pulses, and a square wave pulse with a central wavelength of 1064nm, a spectral width of 13nm, and a pulse width of 15ps is obtained;

[0023] 2. The spectral evolution characteristics of the amplified square wave pulse were analyzed to quantitatively control the modulation function of the spatial light modulator and finally obtain a square wave pulse with energy gain.

[0024] 3. It can overcome the change of spectrum shape caused by uneven gain of PCF amplifier and realize pulse broadband amplification by using 4f amplitude modulation system based on SLM, which is a new way to generate arbitrary waveform. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. Obviously, the drawings described below are only some embodiments of the present utility model. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work. In the drawings:

[0026] Figure 1 It is a schematic diagram of the device of the utility model;

[0027] Figure 2 It is the pre-amplification output spectrum diagram of the utility model;

[0028] Figure 3 It is a schematic diagram of a pulse shaping device of the utility model;

[0029] Figure 4 It is the spectrum diagram of the utility model;

[0030] Figure 5 is the autocorrelation curve of the utility model;

[0031] Figure 6 The amplifier power of the utility model is 1.58W, the output power is 262mW, and the spectrum diagram before and after the amplifier is not pre-compensated. The dotted line in the figure is the spectrum diagram before the main amplifier when pre-compensation is not performed, and the solid line is the spectrum shape after being amplified by the main amplifier;

[0032] Figure 7 The amplifier power of the utility model is 1.58W, the output power is 262mW, and the spectrum diagram of the amplifier before and after pre-compensation is performed. The dotted line in the figure is the spectrum diagram after pre-compensation, and the solid line is the spectrum shape after amplification by the main amplifier;

[0033] Figure 8 It is the pulse time domain shape restored by the picaso time domain restoration algorithm of the utility model. The dotted line is the pulse time domain shape after pre-compensation, and the solid line is the time domain pulse shape after the main amplifier after pre-compensation. DETAILED DESCRIPTION

[0034] The following is combined with Figure 1-Figure 8 The utility model is further described with implementation modes.

[0035] A picosecond square wave amplification system based on photonic crystal fiber, comprising: an oscillator for outputting laser pulses with a central wavelength of 1034 nm, a bandwidth of 20 nm, and an average power of 57 mW;

[0036] In this embodiment, a fiber mode-locked laser with a central wavelength of 1034 nm is selected as the oscillator. The laser can output laser pulses with an average power of 57 mW at a repetition frequency of 36 MHz. Stable mode-locked operation is achieved by adjusting the nonlinear polarization rotation parameters of the laser.

[0037] an isolator for preventing seed light from feeding back into the oscillator;

[0038] A stretcher, coupled to the oscillator, for extending the pulse width of the laser pulse output by the oscillator to 15 ps, with an average power of 10.4 mW;

[0039] A pre-amplifier, used to amplify the average power of the laser pulse processed by the stretcher to 700 mW;

[0040] In this embodiment, the pre-amplifier amplifies the average power of the laser pulse to 700 mW, providing sufficient energy for subsequent laser pulse shaping;

[0041] A pulse shaping device, used for pre-compensating the laser pulse after amplification by the pre-amplifier, the pulse shaping device comprising a 4f amplitude modulation system based on a liquid crystal spatial light modulator, the 4f amplitude modulation system comprising a grating G1, a grating G2, a concave mirror M1, a concave mirror M2 and a liquid crystal spatial light modulator SLM, used for modulating the spectrum of the output pulse after pre-amplification to form a pulse with a specific shape;

[0042] In this embodiment, the grating G1 and the grating G2 use 1200 lines / mm, the radius of the concave mirror M1 and the concave mirror M2 is 350 mm, and the liquid crystal spatial light modulator SLM uses SLM640 / 12 produced by JenopOptik of Germany, which is composed of 640 liquid crystal nematics, each of which has a width of 97 and a gap of 3. For a laser pulse with a central wavelength of 1040 nm, the adjustable maximum phase value is 4, and the frequency resolution of the liquid crystal pixel is 0.2 nm;

[0043] In this embodiment, the grating G1 diffracts the incident light to disperse the frequency components of the incident pulse. After the converging effect of the concave mirror M1, the light is focused into a small diffraction-limited light spot on its rear focal plane, so that the frequency components are spatially separated in one dimension. The liquid crystal spatial light modulator SLM is placed on the rear focal plane of the concave mirror M1 to perform amplitude modulation on the spectral components after dispersion. The grating G2 and the concave mirror M2 converge and output the dispersed frequency components to eliminate spatial dispersion.

[0044] The optical path between the grating G1 and the concave mirror M1 and the optical path between the concave mirror M1 and the liquid crystal spatial light modulator SLM are both f. The entire system is completely symmetrical about the liquid crystal spatial light modulator SLM, forming a 4f structure. By precisely controlling the voltage of each pixel on the liquid crystal spatial light modulator SLM, square wave modulation of the pulse spectrum can be achieved, thereby forming a rectangular pulse in the time domain.

[0045] A main amplifier is used to amplify the energy of the laser pulse processed by the pulse shaping device and output a square wave pulse with energy gain.

[0046] The oscillator is a fiber mode-locked laser, which realizes mode locking by nonlinear polarization rotation.

[0047] The stretcher includes an aspherical mirror AL2, which is used to stretch the pulse output by the oscillator.

[0048] The grating G1 and the grating G2 and the concave mirrors M1 and M2 are completely symmetrically arranged with respect to the liquid crystal spatial light modulator SLM to form a 4f structure. The pulse shaping device further comprises a reflector S1, a reflector S2, a polarizer P1 and a polarizer P2. The reflector S1 and the reflector S2 and the polarizers P1 and P2 are completely symmetrically arranged with respect to the liquid crystal spatial light modulator SLM. The reflector S1 reflects the light of the grating G1 onto the concave mirror M1, and the reflector S2 reflects the light of the grating G2 onto the concave mirror M2.

[0049] In this embodiment, the reflector S1 and the reflector S2 are used to guide the light beam to the pulse shaping device, and the polarizer P1 and the polarizer P2 are used to ensure that the light beam has a correct polarization state when entering the liquid crystal spatial light modulator SLM, so as to ensure that the laser pulse can efficiently pass through the system and achieve the expected shaping effect;

[0050] The main amplifier comprises a photonic crystal fiber PCF, a high reflector HR, an aspheric mirror AL1, an aspheric mirror AL2, an aspheric mirror AL3, a λ / 2 lens, a dichroic mirror DM1, a dichroic mirror DM2 and a dichroic mirror DM3, wherein the gain fiber of the optical fiber amplifier is a photonic crystal fiber PCF;

[0051] Wherein, the optical fiber amplifier uses a laser diode LD as a pumping source to generate pumping light, and the pumping light is output through a pigtail;

[0052] The three aspherical mirrors AL are used to couple the pump light into the photonic crystal fiber PCF;

[0053] The dichroic mirror DM1, the dichroic mirror DM2 and the dichroic mirror DM3 are used for filtering light;

[0054] The λ / 2 lens is used to isolate residual light.

[0055] The main amplifier comprises a fiber amplifier, a high reflector HR, an aspheric mirror AL1, an aspheric mirror AL2, an aspheric mirror AL3, a λ / 2 lens, a dichroic mirror DM1, a dichroic mirror DM2 and a dichroic mirror DM3, wherein the gain fiber of the fiber amplifier is a photonic crystal fiber PCF, and the gain fiber has a polarization-maintaining structure;

[0056] The optical fiber amplifier PCF uses a high-power laser diode LD with a wavelength of 976 nm as a pumping source to generate pumping light, and the pumping light is output through a pigtail and coupled to a gain optical fiber with a polarization-maintaining structure through the aspheric mirror AL;

[0057] The diameter of the pigtail is 200 and the numerical aperture is 0.22;

[0058] The three aspherical mirrors AL are used to couple the pump light into the photonic crystal fiber PCF (gain fiber);

[0059] The dichroic mirrors DM1, DM2 and DM3 are used for filtering light, and are highly transparent to light with a wavelength of 976 nm and highly reflective to light with a wavelength of 1040 nm;

[0060] The λ / 2 mirror is used to isolate residual light in the pump light.

[0061] The grating G1, grating G2, concave mirror M1 and concave mirror M2 are used for light path shaping.

[0062] In this embodiment, the laser pulse is shaped by the pulse shaping device and then enters the main amplifier for energy amplification. In the main amplifier, the fiber amplifier is used as a pumping source to generate pumping light. The pumping light passes through a high reflector HR, and is filtered by dichroic mirrors DM1, DM2 and DM3. A λ / 2 lens isolates residual light. Three aspherical mirrors AL couple the pumping light into the photonic crystal fiber PCF of the fiber amplifier for pre-compensation. The high reflector HR reflects the light, so that the system outputs picosecond square wave laser pulses.

[0063] In this embodiment, the dichroic mirrors DM1, DM2 and DM3 are used to isolate the residual pumping light to ensure that only the light with a wavelength of 1040 nm is amplified.

[0064] By controlling the voltage value of each pixel on the liquid crystal spatial light modulator SLM, square wave modulation is performed on the spectrum of the pre-amplified output pulse to generate a square wave spectrum with a central wavelength of 1031 nm and a bandwidth of 13 nm.

[0065] In this embodiment, in order to verify the performance of the system, the amplified pulses were measured using a spectrometer and an autocorrelator. The measurement results are shown in FIG. Figure 2 , Figure 4-Figure 7 As shown, based on the spectral data and its autocorrelation curve, the pulse time domain shape restored by the Picaso time domain restoration algorithm is as follows Figure 8 As shown, it can be seen that the leading and trailing edges of the pulse are relatively steep, and the top of the formed square wave is relatively flat. The test results show that the system can output a square wave spectrum with a central wavelength of 1031nm and a bandwidth of 13nm, and the leading and trailing edges of the pulse are steep and the top is flat, which meets the expected design goals.

[0066] The above embodiments demonstrate the technical solution of the utility model, which realizes the precise shaping and amplification of ultrashort laser pulses.

[0067] In this embodiment, an oscillator is used to output laser pulses; the pulse width is extended to 15ps by a stretcher; the pulse is amplified by a pre-amplifier; the pulse is amplitude modulated by a pulse shaping device to form a rectangular pulse; the modulated pulse is energy amplified by a main amplifier to output a square wave pulse with energy gain.

[0068] The above description is only an embodiment of the present invention, and does not limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made by using the contents of the specification and drawings of the present invention, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A picosecond square wave amplification system based on photonic crystal fiber, characterized in that: include: An oscillator, used to output laser pulses; an isolator for preventing seed light from feeding back into the oscillator; A stretcher, coupled to the oscillator, for expanding the pulse width of the laser pulse output by the oscillator; A pre-amplifier, used to amplify the average power of the laser pulse processed by the stretcher; A pulse shaping device, used for pre-compensating the laser pulse after amplification by the pre-amplifier, the pulse shaping device comprising a 4f amplitude modulation system based on a liquid crystal spatial light modulator, the 4f amplitude modulation system comprising a grating G1, a grating G2, a concave mirror M1, a concave mirror M2 and a liquid crystal spatial light modulator SLM, used for modulating the spectrum of the output pulse after pre-amplification to form a pulse with a specific shape; A main amplifier is used to amplify the energy of the laser pulse processed by the pulse shaping device and output a square wave pulse with energy gain.

2. The picosecond square wave amplification system based on photonic crystal fiber according to claim 1, characterized in that: The oscillator is a fiber mode-locked laser, which realizes mode locking by nonlinear polarization rotation.

3. The picosecond square wave amplification system based on photonic crystal fiber according to claim 1, characterized in that: The grating G1 and grating G2 as well as the concave mirrors M1 and concave mirrors M2 are completely symmetrically arranged with respect to the liquid crystal spatial light modulator SLM to form a 4f structure. The pulse shaping device also includes a reflector S1, a reflector S2, a polarizer P1 and a polarizer P2. The reflector S1 and the reflector S2 as well as the polarizers P1 and the polarizer P2 are completely symmetrically arranged with respect to the liquid crystal spatial light modulator SLM. The reflector S1 reflects the light of the grating G1 onto the concave mirror M1, and the reflector S2 reflects the light of the grating G2 onto the concave mirror M2.

4. The picosecond square wave amplification system based on photonic crystal fiber according to claim 3 is characterized in that: The main amplifier comprises a fiber amplifier, two high-reflection mirrors HR, three aspherical mirrors AL, a λ / 2 lens, a dichroic mirror DM1, a dichroic mirror DM2 and a dichroic mirror DM3, wherein the gain fiber of the fiber amplifier is a photonic crystal fiber PCF; Wherein, the optical fiber amplifier uses a laser diode LD as a pumping source to generate pumping light, and the pumping light is output through a pigtail; The three aspherical mirrors AL are used to couple the pump light into the photonic crystal fiber PCF; The dichroic mirror DM1, the dichroic mirror DM2 and the dichroic mirror DM3 are used for filtering light; The λ / 2 lens is used to isolate residual light.

5. The picosecond square wave amplification system based on photonic crystal fiber according to claim 4, characterized in that: The grating G1, grating G2, concave mirror M1 and concave mirror M2 are used for light path shaping.

6. The picosecond square wave amplification system based on photonic crystal fiber according to claim 5, characterized in that: By controlling the voltage value of each pixel on the liquid crystal spatial light modulator SLM, the spectrum of the pre-amplified output pulse is modulated into a square wave to generate a square wave spectrum.

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