[0029] All the features disclosed in this specification, except for mutually exclusive features and/or steps, can be combined in any manner.
[0030] Combine below Figure 1 ~ Figure 2 The present invention will be described in detail.
[0031] Such as Figure 1 ~ Figure 2 As shown, the dual-wavelength thulium-doped fiber laser capable of coexisting noise-like and high-frequency harmonic mode-locking provided by the present invention includes a laser diode 1. The laser diode 1 is connected with end-to-end pump beam combiners 2, and thulium-doped fiber lasers. Fiber 3, single-mode fiber 4, dispersion compensation fiber 5, coupler 6, polarization-maintaining fiber 7, and polarization-dependent isolation controller; the polarization-dependent isolation controller is the polarization controller 8 connected to the polarization-maintaining fiber 7 in turn Isolator 9 and polarization controller two 10. That is equivalent to pump combiner 2, thulium-doped fiber 3, single-mode fiber 4, dispersion compensation fiber 5, coupler 6, polarization maintaining fiber 7, polarization controller one 8, polarization dependent isolator 9, and polarization controller two 10 constitutes a cycle, and the laser diode 1 is connected to the pump beam combiner 2. Among them, the pump combiner 2 is a (N+1)×1 pump combiner, and N is a natural number greater than or equal to zero.
[0032] The pump light source of this scheme uses a 793nm laser diode. The pump light source generated by the pump light source enters the thulium-doped fiber 3 through the (2+1)×1 beam combiner 2, and the (2+1)×1 beam combiner 2 The function is to couple the pump light and the laser after being transmitted in the cavity for a week into the thulium-doped fiber 3. The thulium-doped fiber 3 is used as a gain fiber to provide an energy level structure for the generation of 2μm laser. After absorbing 793nm pump light, a 2μm laser is produced through energy level transition.
[0033] The coupler 6 divides the generated 2μm laser into two parts, which account for 10% and 90% of the input light respectively. The 10% output port outputs 10% of the 2μm laser and is output through the output fiber, and the 90% output port outputs 90% of the 2μm laser. And the polarization-maintaining fiber 7 (Polarization-maintaining fiber) continues to transmit in the laser cavity, and the polarization-maintaining fiber 7 is used to realize the comb filtering effect, so as to realize the dual-wavelength output of the laser.
[0034] At the same time, to prevent the laser from propagating backward in the cavity, a polarization-dependent isolator 9 needs to be inserted in the cavity. When the laser passes in the forward direction, the loss is extremely low, and when the laser passes in the reverse direction, the loss is extremely high. This principle is used to block the reverse laser At the same time, since the polarization-dependent isolator 9 (PDISO) is used to generate the NPE effect, combining the polarization controller 8 and the polarization controller 10 before and after it realizes mode locking, and realizes mode competition suppression and realizes the generation of dual wavelengths.
[0035] The thulium-doped fiber 3 used in this patent is a section of double-clad thulium-doped fiber, and the double-clad thulium-doped fiber is an octagonal inner-clad thulium-doped fiber. Choosing an appropriate length of dispersion compensation fiber 5 can help achieve near-zero dispersion in the cavity Select the appropriate length of the single-mode fiber 4 to adjust the total cavity length of the laser so that the laser cavity length is within the range that can generate noise-like pulses and harmonic mode-locked pulses, so that the laser can simultaneously output noise-like pulses and pulses. Harmonic mode locking pulse. The polarization-maintaining fiber 7 is used as a comb filter in the cavity to generate dual-wavelength output.
[0036] Among them, polarization-maintaining fiber 7 (PMF) is used to generate a comb filtering effect to achieve dual-wavelength output. Another necessary condition for dual-wavelength mode locking is the suppression of mode competition between wavelengths. Therefore, we use polarization-dependent isolator 9 to produce NPE effect and form wavelength-dependent loss, thereby achieving suppression of mode competition and achieving dual-wavelength locking. It can also ensure the one-way transmission of light in the cavity. Two PCs (Polarization Controller One 8 and Polarization Controller Two 10) are used to optimize mode locking. At the same time, the thulium-doped fiber and single-mode fiber in this structure have a large negative dispersion value, and the large negative dispersion is not easy to produce soliton splitting, and it is not easy to achieve high-frequency harmonic mode locking, so the structure has a positive dispersion value The compensation of DCF to ensure that the laser finally works in the near-zero dispersion region, so that the splitting threshold of the soliton is low, which is conducive to the generation of high-frequency harmonic mode locking. In a mode-locked fiber laser, we know that when the cavity length is short, only harmonic mode-locked pulses are output; when the cavity length is long, only noise-like pulses are output. Therefore, it is possible to output only in the transition region with a suitable cavity length Harmonic mode-locked pulses may also output noise-like pulses. Therefore, we plan to select the appropriate length of single-mode fiber and dispersion compensation fiber to ensure that the laser is working near the zero-dispersion region, while keeping the laser cavity length in the transition region that can output both harmonic mode-locked and noise-like pulses. , So as to achieve the coexistence of noise-like and harmonic mode locking. The laser of this structure finally outputs 10% of the laser to the laser through a 10/90 optical coupler at the output end for observation.
[0037] This is a schematic diagram of the cavity length affecting the laser output pulse type. When the cavity length is short, only harmonic mode-locked pulses are output, and when the cavity length is long, only noise-like pulses are output. Only in the transition region with a suitable cavity length, it is possible to output harmonics. Wave mode-locked pulses may also output noise-like pulses. The type of pulse generated in the transition region is determined by the phase delay of the laser. The phase delay of a mode-locked laser mode-locked fiber laser can be expressed as:
[0038] Dj=Dj PC +Dj NL +Dj birefringence;
[0039] Where Dj PC , Dj NL And Dj birefringence Refers to the phase delay caused by the polarization controller, the nonlinear effect caused by the high pulse peak, and the nonlinear effect caused by the birefringent fiber. Where Dj PC And Dj birefringence The values of are all related to the wavelength.
[0040] Therefore, at different wavelengths, the phase delay of the laser will also be different. In this way, in a fiber laser with a cavity length in the transition region, by adjusting the polarization controller (polarization controller one 8 and polarization controller two 10), The dual-wavelength output of harmonic mode-locked pulse and noise-like pulse can appear at the same time.
[0041] In this design, we adjust the polarization controller to adjust the pump power within the required range to achieve dual-wavelength output of noise-like pulses and harmonic mode-locked pulses.
[0042] The parts of the present invention that are not described in detail belong to the well-known technology in the art. Based on the existing description, those skilled in the art have been able to implement it without creative work, and therefore will not be repeated.
