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CN-121584379-B - O-band harmonic mode-locked laser based on double-pump nonlinear polarization evolution

CN121584379BCN 121584379 BCN121584379 BCN 121584379BCN-121584379-B

Abstract

The invention discloses an O-band harmonic mode-locked laser based on double-pump nonlinear polarization evolution, which comprises a first pump source, a second pump source, a first wavelength division multiplexer, a second wavelength division multiplexer, a gain fiber, a first polarization controller, a polarization related isolator, a second polarization controller and a coupler, and forms a bidirectional pump annular laser resonant cavity. The first polarization controller and the second polarization controller are respectively arranged at two sides of the polarization related isolator to jointly form a nonlinear polarization evolution mode locking structure. By increasing the power of the double pump sources and adjusting the polarization state in the cavity, the switching from fundamental frequency mode locking to multi-order harmonic mode locking can be realized, the highest can reach 33 orders, the upper limit of the repetition frequency of the O-band all-fiber mode-locked laser is broken through, and the optical fiber mode-locked laser has the advantages of compact structure, high damage threshold, low cost and easiness in all-fiber integration, and is suitable for the fields of optical communication and the like.

Inventors

  • LIU KUNYAO
  • WANG JIXU
  • LI NIANQIANG

Assignees

  • 苏州大学

Dates

Publication Date
20260508
Application Date
20260127

Claims (10)

  1. 1. An O-band harmonic mode-locked laser based on double-pump nonlinear polarization evolution, which is characterized by comprising: the system comprises a first pump source, a second pump source, a first wavelength division multiplexer, a second wavelength division multiplexer, a gain fiber, a first polarization controller, a polarization-dependent isolator, a second polarization controller and a coupler; The first pump source is connected with one end of the gain optical fiber through the first wavelength division multiplexer, the second pump source is connected with the other end of the gain optical fiber through the second wavelength division multiplexer to form a bidirectional pumping annular laser resonant cavity, and pump light is injected into the annular laser resonant cavity through the first wavelength division multiplexer and the second wavelength division multiplexer respectively by the first pump source and the second pump source so that the total pump power injected into the annular laser resonant cavity is the sum of the pump powers of the first pump source and the second pump source; The output end of the gain optical fiber is connected with the first polarization controller, the polarization related isolator, the second polarization controller and the coupler, and the output port of the coupler is fed back to the first wavelength division multiplexer to enable the optical path to be closed to form the annular laser resonant cavity; The first polarization controller and the second polarization controller are respectively arranged at two sides of the polarization related isolator; the first polarization controller, the polarization-dependent isolator and the second polarization controller together form a nonlinear polarization evolution mode locking structure.
  2. 2. The O-band harmonic mode-locked laser based on the two-pump nonlinear polarization evolution of claim 1, wherein the operating state switching from fundamental frequency mode locking to multi-order harmonic mode locking is realized by increasing the output power of the first pump source and the second pump source and adjusting the polarization states in the annular laser resonant cavity determined by the first polarization controller and the second polarization controller.
  3. 3. The O-band harmonic mode-locked laser based on double-pump nonlinear polarization evolution according to claim 2, wherein the highest order of the multi-order harmonic mode locking is 33 th order.
  4. 4. The O-band harmonic mode-locked laser based on double-pump nonlinear polarization evolution of claim 1, wherein the first pump source and the second pump source are semiconductor lasers with wavelength of 1240 nanometers.
  5. 5. The O-band harmonic mode-locked laser based on double-pump nonlinear polarization evolution of claim 1, wherein the gain fiber is a bismuth-doped phosphate quartz fiber.
  6. 6. The O-band harmonic mode-locked laser based on double-pump nonlinear polarization evolution according to claim 1, wherein the length of the gain fiber is 50 meters.
  7. 7. The O-band harmonic mode-locked laser based on double-pump nonlinear polarization evolution of claim 1, wherein the first wavelength division multiplexer and the second wavelength division multiplexer are 1240/1310 nm wavelength division multiplexers.
  8. 8. The O-band harmonic mode-locked laser based on the double-pump nonlinear polarization evolution according to claim 1, wherein the split ratio of the coupler is 80:20, 20% of ports are used for laser output, and 80% of ports are fed back into the resonant cavity.
  9. 9. The O-band harmonic mode-locked laser based on double-pump nonlinear polarization evolution of claim 1, wherein a fusion point loss between the gain fiber and the first wavelength division multiplexer is lower than 0.02 dB, and a fusion point loss between the gain fiber and the second wavelength division multiplexer is lower than 0.02 dB.
  10. 10. An optical communication system comprising the O-band harmonic mode-locked laser based on double-pump nonlinear polarization evolution according to any one of claims 1 to 9.

Description

O-band harmonic mode-locked laser based on double-pump nonlinear polarization evolution Technical Field The invention relates to the technical field of fiber lasers, in particular to an O-band harmonic mode-locked laser based on double-pump nonlinear polarization evolution. Background As an important tool of modern photonics, the ultra-fast fiber laser has great application potential in the fields of precision machining, biological imaging, optical communication, basic scientific research and the like. Since the advent of lasers, technological developments have always sought higher peak power, shorter pulse widths, and more stable operation. The traditional solid laser, such as titanium gem laser, can generate femtosecond order pulse, but has complex system, huge volume and high stability requirement, which limits the industrial application. Compared with the prior art, the fiber laser has become an ideal platform for realizing high-power and ultra-fast laser output by virtue of the characteristics of excellent beam quality, high-efficiency heat dissipation capability and easiness in realizing all-fiber integration brought by the waveguide structure. Wherein, the realization of passive mode locking in the cavity by using nonlinear effect is a key technology for generating ultrashort pulse. The O-band (1260 nm-1360 nm) is one of the core windows for optical communications, where single-mode optical fibers have low loss and near-zero dispersion characteristics. However, achieving high performance ultrafast laser sources in this band presents inherent challenges. The traditional rare earth ion (such as erbium ion) doped quartz optical fiber has weak gain in the O band and is difficult to be used as an effective gain medium. This bottleneck was not broken until the advent of bismuth doped phosphate silica fibers, which provided effective luminescence gain for the O-band. However, the gain factor of bismuth doped fibers is relatively low, and longer gain fibers are typically required to achieve adequate laser gain, which results in increased cavity length. In mode-locked lasers, the cavity length directly determines the cycle time of the pulse within the cavity, i.e., the fundamental repetition rate. The longer the cavity length, the lower the fundamental repetition frequency. Therefore, the fundamental frequency repetition frequency of the O-band all-fiber mode-locked laser based on the bismuth-doped fiber is generally low. At present, the highest repetition rate of the O-band all-fiber mode-locked laser is only about 10 MHz. Harmonic mode locking techniques are an effective approach to increasing the repetition frequency, but their stable implementation is highly dependent on the performance of the intracavity saturable absorber. In many mode locking technologies, nonlinear Polarization Evolution (NPE) is an artificial saturable absorber mechanism based on the optical fiber kerr effect, and the working principle is that through accurate regulation and control of the polarization state in a resonant cavity, the peak part and the two wing parts of a pulse experience different losses when passing through a polarization-related element by utilizing nonlinear phase shift dependent on light intensity, so that the narrowing and mode locking of the pulse are realized. The NPE structure is an all-fiber virtual absorber essentially, has the outstanding advantages of no limitation of specific wavelength, high damage threshold, relatively simple and compact structure (usually only few elements such as a polarization controller and a polarization-dependent isolator are needed), and the like, and is very suitable for generating harmonic mode locking pulses with high repetition frequency and high peak power. However, although NPE technology is very mature in the near infrared band (e.g., 1 micron, 1.5 microns), there is a lack of research to apply it to O-band bismuth-doped fiber lasers, particularly for achieving high repetition rate (in the order of hundred megahertz) harmonic mode locking. At present, the technical route for realizing the O-band all-fiber mode locking mainly comprises the adoption of a saturated absorber (such as a carbon nano tube and a semiconductor saturated absorber), a nonlinear amplifying annular mirror, an active mode locking (such as an acousto-optic modulator) and the like. The existing schemes have obvious limitations that the damage threshold of a material type saturable absorber is low, the material type saturable absorber is difficult to stably work under high pumping power to realize high-order harmonic mode locking, the nonlinear amplifying annular mirror is complex in structure and easy to generate messy multi-pulse under high power, and the acousto-optic modulator has the problems of high cost, high insertion loss, difficulty in all-optical fiber fusion integration and the like. These factors together restrict the further increase in the repetition frequency of the O-band all-fiber ultraf