All-fiber Dual Repetition Frequency Mode-locked Lasers From A Single Cavity

Dual-comb mode-locked laser from a single resonant cavity is a new type of light source developed in recent years.It can produce two sets of pulse sequences with slightly different repetition frequencies in the same resonant cavity.Dual-comb modelocked laser from a single resonant cavity is widely used in spectral measurement,laser ranging,laser gyroscope,asynchronous optical sampling,fiber bragg grating sensing and other fields,for the reason that the two sets of mode-locked pulse sequences experience the same environment in the laser and have low common-mode noise.Compared with the dual-comb mode-locked laser from a single resonant cavity with spatial structure,all-fiber dual-comb mode-locked laser from a single resonant cavity has the advantages of simple and compact structure,good beam quality,good heat dissipation and stability,which has attracted the attention of the maj ority of researchers.Although great progress has been made in recent years,the construction method of allfiber dual-comb mode-locked laser from a single resonant cavity is relatively simple due to its late start.At present,most of them are built based on two-dimensional saturable absorbers,such as carbon nanotubes and tungsten disulfide.These saturable absorbers generally have the disadvantages of high cost,difficult fabrication and low damage threshold,which seriously hinder the practicability of dual-comb mode-locked laser.In order to solve this problem,this paper aims to develop a novel highperformance all-fiber dual-comb mode-locked laser from a single resonant cavity.Through the systematic study of comb filter,cavity loss,all-fiber saturable absorber and nonlinear amplification loop mirror,we have built a variety of all-fiber dual-comb mode-locked lasers with compact structure,low cost and high damage threshold,from a single resonant cavity.The main research results are as follows:1.A compact all-fiber dual-wavelength mode-locked laser is realized.In order to solve the problem of complex laser structure caused by the separation of comb filter and saturable absorber,a nonlinear optical loop mirror saturable absorber with good filtering performance is designed and fabricated.A compact all-fiber dualwavelength mode-locked laser is built,and the dual-wavelength asynchronous pulse sequences with central wavelengths of 1029 nm and 1046 nm are obtained.2.All-fiber dual-wavelength mode-locked laser with fixed central wavelength is realized.In order to solve the problem that the positions of the two central wavelengths output by the dual-wavelength laser are difficult to be fixed,an allfiber dual-wavelength mode-locked laser based on the intracavity loss is built by adjusting the intracavity loss and combined with the emission spectrum characteristics of erbium-doped fiber.The dual-wavelength asynchronous pulses with fixed positions and central wavelengths of 1558 nm and 1532 nm are obtained.3.All-fiber bidirectional mode-locked laser based on nonlinear multimode interference is realized.In view of the single mode-locked technology of bidirectional mode-locked laser,all-fiber saturable absorber is proposed to build a bidirectional mode-locked laser.The bidirectional asynchronous pulse output with a center wavelength of 1566 nm and repetition rate difference of 7 Hz is successfully realized,which provides a new technical way to realize a compact,low-cost and high-power all-fiber dual-comb mode-locked laser from a single resonant cavity in the future.4.All polarization-maintaining polarization-multiplexing bidirectional mode-locked laser is realized.In order to improve the anti-interference performance of dualcomb mode-locked laser from a single resonant cavity,an isolator related to the fast and slow axis direction of polarization-maintaining fiber is developed.Using this isolator,an all-polarization-maintaining polarization-multiplexing bidirectional mode-locked laser based on nonlinear amplification ring mirror is built.Asynchronous pulses with orthogonal polarization states with center wavelengths of 1577 nm and 1576 nm and repetition frequency difference of 322 Hz are obtained.It paves the way for the realization of anti-interference and lowcost all-fiber dual-comb mode-locked laser from a single.The main innovations are as follows:1.A novel all-fiber saturable absorber is fabricated by tapering technology.Dualwavelength mode-locked laser based on the saturable absorber and cavity loss is demonstrated,and a dual-wavelength asynchronous pulse with fixed wavelength position is obtained.In addition,switchable single-wavelength also can be realized.2.All-fiber bidirectional mode-locked laser based on nonlinear multimode interference is proposed and demonstrated,and the bidirectional asynchronous pulse output is realized.The experiment proves the feasibility of applying a new all-fiber saturable absorber with low cost,easy fabrication and high damage threshold to the bidirectional mode-locked laser,which is expected to provide a new technical way for a novel high-power all-fiber dual-comb mode-locked laser from a single resonant cavity in the future.3.An isolator related to the axial direction of polarization-maintaining fiber is developed,and all polarization-maintaining polarization multiplexing bidirectional mode-locked laser based on nonlinear amplifying ring mirror is built by using the isolator.The asynchronous pulse sequence with orthogonal polarization state is obtained,which lays a foundation for a novel all polarization-maintaining dualcomb mode-locked laser with anti-interference and high performance.