Synchronous pumping and medium infrared picosecond optical parametric oscillator of harmonic mode-locked fiber laser

Abstract

The invention discloses a harmonic mode-locked fiber laser synchronous pumping and medium-red picosecond optical parametric oscillator, which comprises a pumping source, a quarter-wave plate, a half-wave plate and a polarization beam splitter for controlling pumping power, which are arranged on the same horizontal line, the polarization beam splitter and the high reflective mirror are arranged on the same vertical straight line, and the high reflective mirror, the first plano-convex lens, the first plano-concave lens, the MgO: PPLN crystal, the second plano-concave lens, the second plano-convex lens, the reflective mirror and the spectroscope are arranged on the same horizontal line. The harmonic mode-locked fiber laser synchronous pump comprises a pump source, and the pump source comprises a harmonic mode-locked erbium-doped fiber laser and an MOPA amplifier. According to the invention, low average dispersion and high average nonlinearity are realized in the fiber laser, harmonic mode-locked laser output with high signal-to-noise ratio and high stability can be realized, and the technical prejudice of non-uniform pulse intensity and low signal-to-noise ratio output by an intermediate infrared tunable ultrafast laser realized by a traditional mode is overcome.

Description

Technical Field

[0001] The invention relates to a pump and an oscillator, in particular to a harmonic mode-locked fiber laser synchronous pump and a mid-infrared picosecond optical parametric oscillator. Background Art

[0002] Ultrafast mid-infrared lasers are widely needed in the fields of spectroscopy, remote sensing, and biomedicine. In particular, high-repetition-rate ultrafast mid-infrared lasers are important tools in the fields of nonlinear optics, pump-detection, and biophotonics. Optical parametric oscillator (OPO) is the most effective way to generate ultrafast mid-infrared lasers. It has the advantages of extremely wide spectral coverage and tuning range, high power output, and good stability. At present, the main methods for generating high-repetition-rate ultrafast mid-infrared lasers are synchronously pumped OPO by titanium sapphire lasers, harmonic pumped OPOs, and Vernier effect pumped OPOs. Although these methods have achieved certain results, they all have their inevitable shortcomings. Titanium sapphire lasers usually require large water cooling systems and pumping systems, and are very expensive, which greatly limits their practical applications. For harmonic pumping and Vernier effect pumping, since the signal light circulates N times in the cavity before encountering the next pump light and thus being amplified, the pulse amplitude of the signal light output is very uneven, which affects the uniformity of the pulse energy and peak power of the generated mid-infrared laser, and also causes the signal-to-noise ratio of the generated mid-infrared pulse to be extremely low. In addition, since only the signal light oscillates, the repetition frequency of the output idler light is not improved. These shortcomings have greatly limited its application and need to be solved urgently.

[0003] In summary, the problems and defects of the prior art are as follows:

[0004] (1) The amplitude of the pulses output by existing high-repetition-rate mid-infrared ultrafast lasers is very uneven, and the peak power and pulse energy are also uneven, and the stability is poor;

[0005] (2) The signal-to-noise ratio of existing high-repetition-rate mid-infrared ultrafast lasers is low;

[0006] (3) The repetition rate of the idler light output by existing high-repetition-rate mid-infrared ultrafast lasers has not been improved. Summary of the invention

[0007] Purpose of the invention: In order to overcome the deficiencies in the prior art, the purpose of the present invention is to provide a harmonic mode-locked fiber laser synchronous pumping with good stability, high repetition rate, high output power and easy operation. Another purpose of the present invention is to provide a high repetition rate, high signal-to-noise ratio and tunable mid-infrared picosecond optical parametric oscillator.

[0008] Technical solution: The synchronous pumping of a harmonic mode-locked fiber laser described in the present invention comprises a pump source, the pump source comprises a harmonic mode-locked erbium-doped fiber laser and a MOPA amplifier, the harmonic mode-locked erbium-doped fiber laser comprises a first laser, a first wavelength division multiplexer, a first erbium-doped gain fiber, a mode matcher, a highly nonlinear fiber, a first polarization controller, a polarization-dependent optical isolator, a second polarization controller, an output coupler, a first polarization-independent optical isolator, the first wavelength division multiplexer, the first erbium-doped gain fiber, the mode matcher, the highly nonlinear fiber, the first polarization controller, the polarization-dependent optical isolator, the second polarization controller, and the output coupler form a ring cavity, the wavelength division multiplexer is connected to the first laser, and the output coupler is connected to the first laser. One end near the first wavelength division multiplexer is also connected to the first polarization-independent optical isolator; the MOPA amplifier includes a second erbium-doped gain fiber, a second wavelength division multiplexer, a second polarization-independent optical isolator, a second laser, a cladding light stripper, an erbium-ytterbium co-doped fiber, a beam combiner, a high-power optical isolator, a third laser, and a collimator. The first polarization-independent optical isolator, the second erbium-doped gain fiber, the second wavelength division multiplexer, the second polarization-independent optical isolator, the cladding light stripper, the erbium-ytterbium co-doped fiber, the beam combiner, the high-power optical isolator, and the collimator are connected in sequence, and one end of the second wavelength division multiplexer near the second polarization-independent optical isolator is also connected to the second laser, and one end of the beam combiner near the high-power optical isolator is also connected to the third laser.

[0009] For the first time, the use of harmonic mode-locked fiber lasers to synchronously pump optical parametric oscillators has been realized. The mid-infrared ultrafast pulses output by the optical parametric oscillator not only have a very uniform pulse intensity and signal-to-noise ratio while maintaining a high repetition rate, but also have a very compact structure and work very stably, filling the gap in the difficulty of achieving high repetition rate and high signal-to-noise ratio ultrafast tunable lasers in the mid-infrared band. The pump source structure and type of the optical parametric oscillator have been optimized, and harmonic mode locking and MOPA amplifiers have been used for synchronous pumping, which has incomparable advantages such as low cost, good stability, full fiberization and high signal-to-noise ratio.

[0010] Furthermore, the first laser and the second laser are both 976nm single-mode semiconductor lasers.

[0011] Furthermore, the third laser is a 976nm multi-mode semiconductor laser.

[0012] Furthermore, the ratio of the intracavity circulating oscillation to the power output of the output coupler is 95:5.

[0013] Furthermore, the first wavelength division multiplexer and the second wavelength division multiplexer are both 980 / 1550nm wavelength division multiplexers.

[0014] Furthermore, the length of the first erbium-doped gain optical fiber and the second erbium-doped gain optical fiber is 2-3 m, and the dispersion is -20 ps / nm / km.

[0015] A mid-infrared picosecond optical parametric oscillator described in the present invention includes a pump source, a quarter wave plate, a half wave plate, and a polarization beam splitter for controlling the pump power, which are arranged on the same horizontal line. The polarization beam splitter and the high-reflection mirror are arranged on the same vertical line. The high-reflection mirror, a first plano-convex lens, a first plano-concave mirror, an MgO:PPLN crystal, a second plano-concave mirror, a second plano-convex mirror, a reflector, and a beam splitter are arranged on the same horizontal line.

[0016] Further, the pump source is used to excite the optical parametric oscillation process, including a harmonically locked erbium-doped fiber laser and a MOPA amplifier, the harmonically locked erbium-doped fiber laser includes a first laser, a first wavelength division multiplexer, a first erbium-doped gain fiber, a mode matcher, a highly nonlinear fiber, a first polarization controller, a polarization-dependent optical isolator, a second polarization controller, an output coupler, a first polarization-independent optical isolator, the first wavelength division multiplexer, the first erbium-doped gain fiber, the mode matcher, the highly nonlinear fiber, the first polarization controller, the polarization-dependent optical isolator, the second polarization controller, and the output coupler form a ring cavity, the wavelength division multiplexer is connected to the first laser, and the output coupler is close to the first wavelength division multiplexer One end of the MOPA amplifier is also connected to the first polarization-independent optical isolator; the MOPA amplifier includes a second erbium-doped gain fiber, a second wavelength division multiplexer, a second polarization-independent optical isolator, a second laser, a cladding light stripper, an erbium-ytterbium co-doped fiber, a beam combiner, a high-power optical isolator, a third laser, and a collimator. The first polarization-independent optical isolator, the second erbium-doped gain fiber, the second wavelength division multiplexer, the second polarization-independent optical isolator, the cladding light stripper, the erbium-ytterbium co-doped fiber, the beam combiner, the high-power optical isolator, and the collimator are connected in sequence, and one end of the second wavelength division multiplexer close to the second polarization-independent optical isolator is also connected to the second laser, and one end of the beam combiner close to the high-power optical isolator is also connected to the third laser.

[0017] Furthermore, the reflector can separate the pump light and the idler light.

[0018] Furthermore, the beam splitter can separate the signal light and the idler light.

[0019] Furthermore, the high reflective mirror is a 1550nm high reflective mirror.

[0020] Working principle: The pump light is input from the input mirror and becomes signal light and idler light after passing through the crystal. The signal light is reflected by the plano-concave mirror and continues to oscillate in the cavity. The residual pump light and idler light are directly output. The structure for achieving harmonic mode-locked operation is to use nonlinear polarization rotation technology in a low-dispersion and high-nonlinear cavity to achieve 51-order (800MHz) harmonic mode-locked output. Harmonic mode-locked laser output can be easily achieved by properly adjusting the PC. A polarization-independent optical isolator (PI-ISO 1) is used in the connection part with the seed source to prevent return light. The prepared MOPA amplifier part is connected to the harmonic mode-locked seed source to achieve high-power pulsed laser output, which can be used as a pump source for an optical parametric oscillator. The quarter wave plate, half wave plate and polarization beam splitter are used to control the pump power. The 1550nm high-reflection mirror is used to change the propagation direction of the pump light. The plano-convex lens is used to focus the pump light to 100 microns to achieve cavity mode matching. The MgO:PPLN nonlinear crystal is used as a frequency conversion crystal. The plano-concave mirror is used for high reflection of the signal light and for anti-reflection of the pump light and idler light, and together with the MgO:PPLN nonlinear crystal, it forms a resonant cavity.

[0021] Beneficial effects: Compared with the prior art, the present invention has the following significant features:

[0022] 1. Low average dispersion and high average nonlinearity are achieved in fiber lasers, so it is very easy to achieve high signal-to-noise ratio and high stability harmonic mode-locked laser output, overcoming the technical bias of uneven pulse intensity and low signal-to-noise ratio of mid-infrared tunable ultrafast laser output achieved by traditional methods;

[0023] 2. The MOPA amplifier used is an all-fiber structure and adopts reverse pumping. It has high amplification efficiency and output power, and has the advantages of good heat dissipation, high efficiency, high stability and easy operation;

[0024] 3. The harmonic mode-locked synchronously pumped optical parametric oscillator is used to achieve high repetition rate and high signal-to-noise ratio picosecond tunable mid-infrared laser output. The output mid-infrared ultrafast laser has very uniform pulse intensity and high power stability.

[0025] 4. The mid-infrared picosecond optical parametric oscillator has a high repetition frequency and signal-to-noise ratio, a very uniform output pulse intensity, good power stability, all-fiber pumping, a very compact structure and good tunability. It has high long-term working stability. The output signal light and idler light have a high repetition frequency. While maintaining a repetition frequency of up to 800MHz, it has a signal-to-noise ratio of up to 52dB. The output pulse width is only 6.8ps. When the maximum pump power is running, the RMS of the signal light and idler light is only 0.8% and 1.1%;

[0026] 5. The pulse sequence has a very uniform intensity distribution, and the peak power and pulse energy are also very uniform. The tuning ranges of the signal light and the idler light are 2.3-2.46 microns and 4.18-4.74 microns respectively, and 120mW of idler light power can be provided at 4.18 microns;

[0027] 6. It can be used as a mid-infrared ultrafast pulse and high-energy pulse laser light source in the fields of ultrafast laser and micro-nano material interaction, medical processing, space laser communication, ablation cooling material removal and optical frequency comb. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic diagram of the structure of the pump source 1 of the present invention;

[0029] Figure 2 It is a schematic structural diagram of the mid-infrared picosecond optical parametric oscillator of the present invention;

[0030] Figure 3 is a pulse sequence diagram of the harmonic mode-locked output of the present invention;

[0031] Figure 4 is a spectrum diagram of the harmonic mode-locked output of the present invention;

[0032] Figure 5 is a radio frequency spectrum diagram of the harmonic mode-locked output of the present invention;

[0033] Figure 6 is a graph of the autocorrelation pulse width of the harmonic mode-locked output of the present invention;

[0034] Figure 7 This is the power diagram of the harmonic mode locking of the present invention as a seed source after prevention;

[0035] Figure 8 It is the main amplified power diagram of the present invention;

[0036] Fig. 9 It is the seed source, prevention and main amplification output spectrum of the present invention;

[0037] Fig.10 This is a pulse sequence diagram of the 2.3 micron signal light output of the present invention;

[0038] Fig.11 is a radio frequency spectrum diagram of a 2.3 micron signal light output pulse of the present invention;

[0039] Fig.12 It is a power variation diagram of output signal light and idler light when the crystal planning period is 29.84 microns of the present invention;

[0040] Fig.13 is a pulse width measurement diagram of a 2.3 micron signal light output pulse of the present invention;

[0041] Fig.14 1. It is the output spectrum diagram of the signal light and the idler light at different periods of the present invention;

[0042] Fig.15 1 is a diagram of the maximum output power of signal light and idler light at different wavelengths of the present invention, a is the idler light, b is the signal light;

[0043] Fig.16 It is a graph of the stability of the signal light and idler light output powers of the present invention. DETAILED DESCRIPTION

[0044] Example 1

[0045] like Figure 1, the pump source 1 includes a harmonically locked erbium-doped fiber laser and a MOPA amplifier, which is seeded by the harmonically locked erbium-doped fiber laser and amplified by the MOPA amplifier in two stages, and the seed source is passively soliton harmonic mode-locked by nonlinear polarization rotation technology. The harmonically locked erbium-doped fiber laser has the advantages of easy operation, full fiberization, high signal-to-noise ratio and stability. The harmonically locked erbium-doped fiber laser includes a first laser 101, a first wavelength division multiplexer 102, a first erbium-doped gain fiber 103, a mode matcher 104, a highly nonlinear fiber 105, a first polarization controller 106, a polarization-dependent optical isolator 107, a second polarization controller 108, an output coupler 109, and a first polarization-independent optical isolator 110. The first wavelength division multiplexer 102, the first erbium-doped gain fiber 103, the mode matcher 104, the highly nonlinear fiber 105, the first polarization controller 106, the polarization-dependent optical isolator 107, the second polarization controller 108, and the output coupler 109 are connected by a fiber fusion splicer to form a ring cavity by fusing the single-mode optical fiber. The wavelength division multiplexer 102 is connected to the first laser 101, and the end of the output coupler 109 close to the first wavelength division multiplexer 102 is also connected to the first polarization-independent optical isolator 110. The MOPA amplifier has the advantages of high amplification efficiency, stability and good heat dissipation. The MOPA amplifier includes a pre-amplification part and a main amplifier part, both of which use reverse pumping. The pre-amplification part includes a second erbium-doped gain fiber 111, a second wavelength division multiplexer 112, a second polarization-independent optical isolator 113, and a second laser 114; the main amplification part includes a cladding light stripper 115, an erbium-ytterbium co-doped fiber 116, a combiner 117, a high-power optical isolator 118, a third laser 119, and a collimator 120. The first polarization-independent optical isolator 110, the second erbium-doped gain fiber 111, the second wavelength division multiplexer 112, the second polarization-independent optical isolator 113, the cladding light stripper 115, the erbium-ytterbium co-doped fiber 116, the combiner 117, the high-power optical isolator 118, and the collimator 120 are connected in sequence, and the end of the second wavelength division multiplexer 112 close to the second polarization-independent optical isolator 113 is also connected to the second laser 114, and the end of the combiner 117 close to the high-power optical isolator 118 is also connected to the third laser 119.

[0046] The first laser 101 (Pump 1) and the second laser 114 are both 976nm single-mode semiconductor lasers, the third laser 119 is a 976nm multi-mode semiconductor laser, and the ratio of the intracavity circulating oscillation to the power output of the output coupler 109 is 95:5. The first wavelength division multiplexer 102 and the second wavelength division multiplexer 112 are both 980 / 1550nm wavelength division multiplexers. The length and dispersion of the first erbium-doped gain fiber 103 and the second erbium-doped gain fiber 111 are 2m and D=-18.5ps / nm / km respectively. The length, dispersion and nonlinear coefficient of the high nonlinear fiber 105 are 7m, 0±1ps / nm / km and 14W respectively.-1 km -1 The length of the single-mode fiber (SMF-28e) is 4.1 m, and the dispersion is D = 17 ps / nm / km. The length and total dispersion of the ring cavity are 13.1 m and 0.044 ps, respectively. 2 , the average cavity dispersion and nonlinearity are -3.3ps respectively. 2 km -1 and 7.5W -1 km -1 Such low dispersion and high nonlinearity are very beneficial to the generation of harmonic mode-locking operation. The Er-Yb co-doped fiber 116 is 3 meters long. The first wavelength division multiplexer 102 and the second wavelength division multiplexer 112 are both 980 / 1550nm wavelength division multiplexers, which can combine 980nm and 1550nm light into one beam and transmit it in one optical fiber.

[0047] The preparation method of synchronous pumping of harmonic mode-locked fiber laser comprises the following steps:

[0048] A. Preparation of harmonic mode-locked fiber laser:

[0049] A1. Prepare the nonlinear polarization rotation part: Take a polarization-dependent optical isolator 107 (PS-ISO), install the first polarization controller 106 (PC) and the second polarization controller 108 (PC) to the two ends of the optical fiber pigtail of the polarization-dependent optical isolator, and finally fix them on the optical breadboard.

[0050] A2. The harmonic mode-locked fiber laser has lower average dispersion and higher average nonlinearity. The entire ring cavity is composed of the first wavelength division multiplexer 102 (WDM), the first erbium-doped gain fiber 103 (DEF1), the mode matcher 104 (MFA), the high nonlinear fiber 105 (HNLF), the nonlinear polarization rotation part (PS-ISO and PC) and the 95:5 output coupler 109 (OC). The above devices are sequentially fused by a fiber fusion splicer to form a ring cavity. By properly adjusting the first polarization controller 106 and the second polarization controller 108, harmonic mode-locked laser output can be easily achieved.

[0051] B. Preparation of MOPA amplifier part:

[0052] B1. Preparation of the pre-amplifier part: The pre-amplifier part adopts reverse pumping, with a second laser 114 (Pump 2) as a pump source, and is composed of a second wavelength division multiplexer 112 and a second erbium-doped gain fiber 111. The part connected to the seed source uses a first polarization-independent optical isolator 110 (PI-ISO 1) to prevent return light.

[0053] B2. Preparation of the main amplifier part: The main amplifier part also adopts reverse pumping, with the third laser 119 (Pump 3) as the pump source, and is composed of a cladding light stripper 115 (CPS), erbium ytterbium co-doped fiber 116 (EYDF), a combiner 117 (Combiner), a high-power optical isolator 118 (PI-ISO 3) and a collimator 120. The second polarization-independent optical isolator 113 (PI-ISO 2) is used to prevent return light in the pre-amplification connection part.

[0054] C. Connect the prepared MOPA amplifier part to the seed source of the harmonic mode-locked fiber laser to achieve high-power pulsed laser output and obtain synchronous pumping of the harmonic mode-locked fiber laser.

[0055] Example 2

[0056] like Figure 2 The pump source 1 of Example 1 is used as the pump source 1 of the mid-infrared picosecond optical parametric oscillator to excite the optical parametric oscillation process. The pump source 1, the quarter wave plate 2, the half wave plate 3, and the polarization beam splitter 4 for controlling the pump power are arranged on the same horizontal line, the polarization beam splitter 4 and the high reflective mirror 5 are arranged on the same vertical line, and the high reflective mirror 5, the first plano-convex lens 6, the first plano-concave mirror 7, the MgO:PPLN crystal 8, the second plano-concave mirror 9, the second plano-convex mirror 10, the reflector 11, and the beam splitter 12 are arranged on the same horizontal line. The high reflective mirror 5 is a 1550nm high reflective mirror. The quarter wave plate 2, the half wave plate 3 and the polarization beam splitter 4 are used to control the pump power, the high reflective mirror 5 is used to change the propagation direction of the pump light, the first plano-convex lens 6 and the second plano-convex mirror 10 are used to converge the pump light to 100 microns to achieve cavity mode matching, the MgO:PPLN crystal 8 is used as a frequency conversion crystal, the first plano-concave mirror 7 and the second plano-concave mirror 9 are used for high reflection of signal light, pump light and idle light, and together with the MgO:PPLN crystal 8, they form a resonant cavity, and the beam splitter 12 is used to separate the residual pump light, signal light and idle light. The distance between the first plano-concave mirror 7 and the second plano-concave mirror 9 is 160 mm. The mid-infrared picosecond optical parametric oscillator has a high repetition frequency, a high signal-to-noise ratio, a more uniform pulse intensity, a smaller size and good stability.

[0057] Due to the lower dispersion and higher nonlinearity in the cavity, harmonic mode-locking operation can be easily achieved by properly adjusting the first polarization controller 106 and the second polarization controller 108 . Figure 3-6 The output characteristics of the 51st harmonic mode-locking operation are shown when the pump power is 800 MW by adjusting the first polarization controller 106 and the second polarization controller 108. The pulse sequence output by the harmonic mode-locking is as follows: Figure 3As shown, the pulse time interval is 1.25ns, corresponding to a repetition frequency of about 800MHz, and the pulse amplitude presents a relatively uniform pattern, indicating good stability.

[0058] Figure 4 This is the spectrum of harmonic mode locking, with a central wavelength of 1550.6nm. The Kelly sidebands on both sides also prove that it works in the soliton state. The output RF spectrum was measured for further evaluation, such as Figure 5 As shown, under the conditions of a span of 2 GHz and a resolution bandwidth of 10 kHz, a repetition rate of 800.7 MHz and an excellent signal-to-noise ratio of up to 60 dB are displayed, further proving the good stability of the harmonic mode-locked laser. The laser cavity length of 13.1 m corresponds to a fundamental repetition rate of 15.7 MHz, and a repetition rate of 800.7 MHz corresponds to 51-order harmonic mode-locked operation. Figure 6 The autocorrelation trace of the harmonic mode-locked pulse is shown using sech 2 The pulse width obtained after fitting the function is 6ps.

[0059] When the pump power is 800 mW, the power output by the harmonic mode-locked seed source is 15 mW. The maximum pump power that the pump source of the preamplifier part (the second laser 114) can provide is 414 mW. At this time, the maximum output power of 120 mW is obtained, and the corresponding optical conversion efficiency is 29%. Figure 7 The pump source of the main amplifier part (third laser 119) can provide a maximum pump power of 27W. In order to suppress the nonlinear effect in the amplification process as much as possible, the maximum pump power is set to 13.3W. At this time, the maximum output power obtained is 4W, and the corresponding optical conversion efficiency is 30%, as shown in FIG. Figure 8 The output spectrum at different powers is shown in Fig. 9 As shown, it can be seen that after amplification, the spectrum does not undergo obvious deformation and broadening, indicating that the amplification effect is good.

[0060] Fig.10 The pulse sequence of the measured signal light is shown. It can be seen that the amplitude of the output pulse is relatively uniform, and the pulse interval is 1.25ns, corresponding to a repetition frequency of 800MHz. The inset is the output pulse sequence with a time span of 180ns. The pulses are also relatively uniform under large time spans, indicating good working stability.

[0061] Fig.11 The corresponding RF spectrum is shown, with a signal-to-noise ratio of up to 52dB under the conditions of a span and resolution bandwidth of 1.5GHz and 100HZ respectively, further demonstrating the excellent stability of the output pulse. At a repetition frequency of up to 800.7MHz, the signal light still maintains a high signal-to-noise ratio and good pulse amplitude uniformity, which are far better than previously reported.

[0062] Under the condition of crystal period of 29.84 microns, the threshold of optical parametric oscillator is 3.8W. Fig.12 The corresponding signal light and idler light output power changes are shown when the pump power range is 3.8-4W. When the pump power is 4W, the maximum output power of the signal light (2302.8nm) is 7mW, and the maximum output power of the idler light (4746.9nm) is 20mW. Since the absorption rate of the MgO:PPLN crystal 8 increases above the 4.5 micron band, and the range of the anti-reflection film at both ends of the crystal is only 2.2-4.5 microns, the threshold of the optical parametric oscillator will increase and the output power will decrease when the idler light output wavelength is greater than 4.5 microns.

[0063] The pulse width of the signal light was measured using the cross-correlation method. The results are as follows: Fig.13 As shown. By using MgO:PPLN crystal to make the pump light and the signal light sum frequency, the relationship between the optical path difference between the two beams and the sum frequency light intensity can be observed, and the pulse width of the signal light can be calculated. The measurement results show that the half-height width of the sum frequency light intensity is 2.9mm, and the pulse width of the signal light (2302.8nm) can be calculated to be about 6.8ps.

[0064] In order to characterize the wavelength tunability of the optical parametric oscillator, the output performance of the signal light and idler light in the six channels of the crystal was measured. The crystal temperature was fixed at 26.85℃, and the output spectra of the signal light and idler light in the six channels with polarization periods of 29.87, 30.28, 30.72, 31.16, 31.60 and 32.14 μm were as follows: Fig.14 As shown, the corresponding signal light center wavelengths are 2302.8, 2330.3, 2357.9, 2385.4, 2418.4 and 2462.5nm, and the idler light center wavelengths are 4746.9, 4634, 4528.9, 4430.7, 4321.1 and 4187.2nm, respectively. The center wavelengths of the signal light and the idler light are basically consistent with the results calculated by the Sellmeier equation. The tuning range of the signal light is 2.3-2.46 microns, with a span of 169nm. The tuning range of the idler light is 4.18-4.74 microns, with a span of 560nm.

[0065] In addition, under the six channels with polarization periods of 29.87-32.14 μm, the thresholds of SPOPO are 3.8, 3.6, 3.4, 3.2, 3.3, and 3 W, respectively, and the corresponding maximum output powers are as follows Fig.15As shown in the figure, the maximum power of signal light and idler light output is obtained when the period is 32.14 microns. The maximum signal light power is 15mW (2462.5nm), and the maximum idler light power is 120mW (4187.2nm). Since the signal light output coupling ratio of the optical parametric oscillator cavity is only 0.2%, the signal light output power is low. The output power of SPOPO can be increased by increasing the output coupling ratio and increasing the pump power (further increasing the amplification level of MOPA).

[0066] Finally, we measured the stability of the maximum output power of the signal light and the idler light when the polarization period was 32.14 μm. The results are as follows: Fig.16 As shown, the corresponding RMS values ​​within 8 hours of operation are 1.1% (4187.2nm) and 0.8% (2462.5nm), respectively. SPOPO has good power stability.

[0067] Application Example 1

[0068] The high-performance mid-infrared picosecond optical parametric oscillator of Example 2 is used as a laser light source to successfully achieve fine processing, repair and treatment of high-end micro-nano materials. The high-performance mid-infrared picosecond optical parametric oscillator of the present invention can be used as an optical frequency comb as a laser light source to achieve precise laser ranging, and can also realize coherent optical communication and optical atomic clocks. It can also be used as a practical laser light source in the medical field and life science field.

Claims

1. A harmonic mode-locked fiber laser synchronous pumping, characterized in that: The invention comprises a pump source (1), wherein the pump source (1) comprises a harmonically mode-locked erbium-doped fiber laser and a MOPA amplifier, wherein the harmonically mode-locked erbium-doped fiber laser comprises a first laser (101), a first wavelength division multiplexer (102), a first erbium-doped gain fiber (103), a mode matcher (104), a highly nonlinear fiber (105), a first polarization controller (106), a polarization-dependent optical isolator (107), a second polarization controller (108), an output coupler (109), a first polarization-independent optical isolator (109), and a second polarization controller (109). (110), the first wavelength division multiplexer (102), the first erbium-doped gain fiber (103), the mode matcher (104), the highly nonlinear fiber (105), the first polarization controller (106), the polarization-dependent optical isolator (107), the second polarization controller (108), and the output coupler (109) form a ring cavity, the wavelength division multiplexer (102) is connected to the first laser (101), and the end of the output coupler (109) close to the first wavelength division multiplexer (102) is also independent of the first polarization. The MOPA amplifier comprises a second erbium-doped gain fiber (111), a second wavelength division multiplexer (112), a second polarization-independent optical isolator (113), a second laser (114), a cladding light stripper (115), an erbium-ytterbium co-doped fiber (116), a beam combiner (117), a high-power optical isolator (118), a third laser (119), and a collimator (120). The first polarization-independent optical isolator (110), the second erbium-doped gain fiber (111), the second wavelength division multiplexer (112), a second polarization-independent optical isolator (113), a second laser (114), a cladding light stripper (115), an erbium-ytterbium co-doped fiber (116), a beam combiner (117), a high-power optical isolator (118), a third laser (119), and a collimator (120). A wavelength division multiplexer (112), a second polarization-independent optical isolator (113), a cladding light stripper (115), an erbium-ytterbium co-doped optical fiber (116), a beam combiner (117), a high-power optical isolator (118), and a collimator (120) are connected in sequence; an end of the second wavelength division multiplexer (112) close to the second polarization-independent optical isolator (113) is also connected to a second laser (114); an end of the beam combiner (117) close to the high-power optical isolator (118) is also connected to a third laser (119).

2. The synchronous pumping of a harmonic mode-locked fiber laser according to claim 1, characterized in that: The first laser (101) and the second laser (114) are both 976nm single-mode semiconductor lasers.

3. The synchronous pumping of a harmonic mode-locked fiber laser according to claim 1, characterized in that: The third laser (119) is a 976nm multi-mode semiconductor laser.

4. The synchronous pumping of a harmonic mode-locked fiber laser according to claim 1, characterized in that: The ratio of intracavity circulating oscillation to power output of the output coupler (109) is 95:

5.

5. The synchronous pumping of a harmonic mode-locked fiber laser according to claim 1, characterized in that: The first wavelength division multiplexer (102) and the second wavelength division multiplexer (112) are both 980 / 1550nm wavelength division multiplexers.

6. The synchronous pumping of a harmonic mode-locked fiber laser according to claim 1, characterized in that: The length of the first erbium-doped gain optical fiber (103) and the second erbium-doped gain optical fiber (111) is 2-3 m, and the dispersion is -20 ps / nm / km.

7. A mid-infrared picosecond optical parametric oscillator, characterized in that: The invention comprises a pump source (1), a quarter wave plate (2), a half wave plate (3), and a polarization beam splitter (4) for controlling pump power, which are arranged on the same horizontal line; the polarization beam splitter (4) and a high reflective mirror (5) are arranged on the same vertical straight line; and the high reflective mirror (5), a first plano-convex lens (6), a first plano-concave mirror (7), a MgO:PPLN crystal (8), a second plano-concave mirror (9), a second plano-convex mirror (10), a reflector (11), and a beam splitter (12) are arranged on the same horizontal line.

8. A mid-infrared picosecond optical parametric oscillator according to claim 7, characterized in that: The pump source (1) comprises a harmonically mode-locked erbium-doped fiber laser and a MOPA amplifier. The harmonically mode-locked erbium-doped fiber laser comprises a first laser (101), a first wavelength division multiplexer (102), a first erbium-doped gain fiber (103), a mode matcher (104), a highly nonlinear fiber (105), a first polarization controller (106), a polarization-dependent optical isolator (107), a second polarization controller (108), an output coupler (109), and a first polarization-independent optical isolator (110). The first wavelength division multiplexer (102), the first erbium-doped gain fiber (103), the mode matcher (104), the highly nonlinear fiber (105), the first polarization controller (106), the polarization-dependent optical isolator (107), the second polarization controller (108), and the output coupler (109) form a ring cavity. The wavelength division multiplexer (102) is connected to the first laser (101), and one end of the output coupler (109) close to the first wavelength division multiplexer (102) is also connected to the first polarization-independent optical isolator ( 110); the MOPA amplifier comprises a second erbium-doped gain fiber (111), a second wavelength division multiplexer (112), a second polarization-independent optical isolator (113), a second laser (114), a cladding light stripper (115), an erbium-ytterbium co-doped fiber (116), a beam combiner (117), a high-power optical isolator (118), a third laser (119), and a collimator (120); the first polarization-independent optical isolator (110), the second erbium-doped gain fiber (111), the second wavelength division multiplexer (112), a second polarization-independent optical isolator (113), a second laser (114), a cladding light stripper (115), an erbium-ytterbium co-doped fiber (116), a beam combiner (117), a high-power optical isolator (118), a third laser (119), and a collimator (120). A multiplexer (112), a second polarization-independent optical isolator (113), a cladding light stripper (115), an erbium-ytterbium co-doped optical fiber (116), a beam combiner (117), a high-power optical isolator (118), and a collimator (120) are connected in sequence; an end of the second wavelength division multiplexer (112) close to the second polarization-independent optical isolator (113) is also connected to a second laser (114); an end of the beam combiner (117) close to the high-power optical isolator (118) is also connected to a third laser (119).

9. The mid-infrared picosecond optical parametric oscillator according to claim 7, characterized in that: The reflector (11) is capable of separating pump light and idler light.

10. The mid-infrared picosecond optical parametric oscillator according to claim 7, characterized in that: The beam splitter (12) is capable of separating signal light and idler light.

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