X. L. Tian

High-energy laser pulse with a submegahertz repetition rate from a passively mode-locked fiber laser

We demonstrate an ultralong cavity, all-fiber, all-normal-dispersion Yb-doped fiber laser that is passively mode locked by a semiconductor saturable absorber mirror (SESAM). Without any discrete dispersion-compensation components or conventional spectral filters, the SESAM works together with the strongly chirped pulse and the nonlinearity induced spectrum broadening to perform a filtering-equivalent function, thus stabilizing the mode locking. The laser generates 4.3 nJ stable mode-locked pulses with a 397 kHz fundamental repetition rate at a 1068 nm central wavelength.

High-energy wave-breaking-free pulse from all-fiber mode-locked laser system.

We demonstrated an all-fiber mode-locked laser system which generated high-energy wave-breaking-free pulses with low repetition rate. The system included a passively mode-locked fiber laser which acted as a master oscillator and an Yb-doped fiber amplifier. By increasing the cavity length of the laser, pulse energy could be significantly increased. According to different cavity length, wave-breaking-free pulse with 2.9 nJ-6.9 nJ pulse energy and 870 kHz-187 kHz repetition rate has been achieved from the master oscillator. Over 4 microJ pulse can be obtained after amplification.

Single-frequency 1060 nm semiconductor-optical-amplifier-based fiber laser with 40 nm tuning range

A compact single-frequency 1060 nm fiber laser based on a high-power semiconductor optical amplifier (SOA) has been proposed and demonstrated with over 40 nm wavelength tuning range. The inhomogeneous gain-broadening feature of the SOA and the unpumped ytterbium-doped fiber-based saturable absorber contribute to the single longitudinal mode lasing of the fiber laser. The maximum 3 dBm output power can be obtained with the optical signal to noise ratio larger than 50 dB. Stable single-frequency operation can be maintained more than 1 h with negligible power fluctuations and low relative intensity noise.

Wavelength-Tunable High-Energy All-Normal-Dispersion Yb-Doped Mode-Locked All-Fiber Laser With a HiBi Fiber Sagnac Loop Filter

We experimentally demonstrate a broadly wavelength-tunable high-energy Yb-doped mode-locked fiber laser without any dispersion compensation. Wide tunability and filtering effect are simultaneously obtained using a fiber Sagnac loop filter in an all-fiber laser mode-locked by a semiconductor saturable absorber mirror. The Sagnac loop filter is constructed with a segment of a high birefringence (HiBi) fiber, a 3-dB coupler, and a polarization controller. By optimizing the HiBi fiber length and adjusting the polarization controller within the loop, the wavelength of the output pulse with 3 nJ pulse energy could be continuously tuned over the range from 1032 to 1052 nm. The heating of the HiBi fiber also led to wavelength shifting of the output pulse with a sensitivity of approximately -0.3-nm°C.

Four-wave mixing assisted self-stable 4×10 GHz actively mode-locked Erbium fiber ring laser

We proposed and developed a self-stable multiwavelength (4 cbannels) 10-GHz actively mode-locked Erbium-doped fiber ring laser with 0.8 nm wavelength spacing. A 1-km highly nonlinear fiber is incorporated in the laser cavity to eliminate the strong gain competitions in the homogeneously broadened EDF by multiple parametric four-wave mixing processes. The fiber nonlinearity is also helpful to provide phase locking and stabilize the output pulse. Stable laser pulses at 1556.55, 1557.36, 1558.17, and 1558.98 nm are successfully obtained simultaneously with supermode noise suppression ratio greater than 50 dB. The corresponding time-bandwidth products of four channels are 0.39 ∼ 0.41.

Investigation on optimized launch power in the distributed Brillouin fiber sensor design

Distributed sensors, based on Brillouin effect in the optical fiber, provide an excellent method for measuring temperature and strain over long distances. There are two types of such sensors. The first type is based on spontaneous Brillouin scattering, and is called Brillouin optical time domain reflectometer (BOTDR). It measures the Brillouin frequency shift or Brillouin power or Brillouin gain bandwidth to get the temperature and strain information. The second type of sensor is based on stimulated Brillouin amplification. It is called Brillouin optical time domain analyzer(BOTDA). Normally, it uses one laser at each fiber ends, one as pump and the other as a probe light. The probe light will experience Brillouin amplification. Through the analysis of Brillouin gain spectrum (BGS), we can get the temperature and strain information. Both the two types of sensors are attracting attention all over the world, and temperature resolution of less than 1 degree and strain resolution up to 5 με was reported. The fiber distances of up to 150km was presented while other papers reported a spatial resolution of the order of 1cm with frequency domain techniques or correlation techniques. We proposed and analyzed our design, it is an improvement of BOTDA with a single end laser, which make it easy to implement in field. Through simulations, optimized launch power has been found for a certain design.

Repetition rate switching in a passively mode-locked fibre laser

Here we demonstrated a dispersion stretched passively mode-locked fiber laser. The laser was mode-locked by nonlinear polarization rotation (NPR) technical. Both dispersion managed soliton and noise-like pulses were observed in the experiment. Harmonic mode-locked noise-like pulses were observed. By changing the pump power or rotating the waveplates, noise-like pulse could split and always form equally spaced pulse train, thus the repetition rate of the output pulse could be switched among different orders of harmonic frequency. The experiment results were analyzed. We found that peak power clamping caused by NPR module led to pulse splitting, the pulse interaction through the Raman light drives the pulse to space equally.

Comb Spectrum Shaping Effect of a Fiber Sagnac Loop on an All-Normal-Dispersion Yb-Doped Mode-Locked Fiber Laser

In this letter, a high birefringence fiber (HBF) Sagnac loop is adopted in an all-normal-dispersion (ANDi) Ytterbium-doped (Yb-doped) passively mode-locked fiber laser. The HBF Sagnac loop acting as a comb spectrum filter has properties of controllable wavelength spacing and tunable transmission wavelength in the laser. With these properties of the HBF Sagnac loop filter, the laser offers a wide range of lasing performance. In the experiment, by changing the HBF length and adjusting the polarization within the loop, obviously different spectral profiles are observed, and broad wavelength tunability is also achieved.

Passively mode-locked fiber ring laser with large normal net dispersion

Here we experimentally demonstrated a passively mode-locked fiber laser (PMFL) with large normal net dispersion. Stable mode-locked pulse output was achieved at two different central wavelengths respectively, proved that small net dispersion is not a critical requirement for mode-locking. The output pulse had much larger pulse duration compared to other results had ever been achieved in PMFL. The pulse could be easily compressed by single mode fiber (SMF).

Tunable single polarization Yb 3+ -doped fiber ring laser by using 45° tilted fiber Bragg grating filter

A tunable single polarization Yb3+-doped fiber laser using tilted fiber Bragg grating was demonstrated. It generates high DOP (> 99.8%) 1.06 mum laser with 25 nm tuning range.