A stable mode-locked fiber laser employing graphene as a saturable absorber is presented. One
monolayer graphene can obtain mode-locking when the cavity is around 12m, but when the cavity
decreases to 6m, no stable pulses can be formed. In order to solve this problem, cascade of two
monolayer graphenes is used and stable mode locked pulses with a frequency of 44.53MHz, a
bandwidth of 2.4nm, a pulse width of 43.89ps and an average power of 19.10mW have been directly
obtained from the laser. Our results show the atomic-layer graphene may be a promising satrurable
absorber for stable pulses formation of fiber laser.
We have proposed and demonstrated a nanosecond square-wave fiber laser working in the 1060nm band. The passively
mode-locked fiber laser based on the nonlinear optical loop mirror has a peak power clamping effect which leads to the
generation of nanosecond square-wave pulses. To investigate the spectrum width of the nanosecond square-wave pulse
laser, we added couplers with different coupling ratio to the bidirectional ring of the figure-8 fiber laser and analyzed the
laser output. The results show that a higher output coupling ratio leads to stronger peak power clamping effect, and the
peak power of the square-wave pulse gets lower and the corresponding spectrum band width is narrower.
A passively mode-locked ytterbium-doped all fiber laser has been demonstrated based on the nonlinear polarization
rotation technique in a all normal dispersion cavity. By optimizing the coupling ratio and position of the output coupler,
stable mode-locked pulses is generated with an average power of 200 mW at a repetition rate of 3.3 MHz, and
corresponding to single pulse energy of 60 nJ. The slope efficiency of power is as high as 68%.
We have demonstrated a passively mode-locked fiber laser with a composite cavity structure for repetition rate control.
An optical delay line is used to control the length so that the lengths of the main cavity and the sub-ring cavity are
accurately co-prime. Using this method we have obtained 46th harmonic pulses with a fundamental repetition of
17.39MHz. The fundamental mode-locking is substantially suppressed. The SNR of rf spectrum is higher than 45 dB.
Stable 800MHz repetition rate mode-locked pulses in duration of 14.27 ps are generated. The detuning phenomenon
appears when two cavity’s lengths are not matched. A larger pump power is required to maintain the oscillation.
This paper designs and implements one kind of automatic mode-locked system. It can adjust a passively mode-locked
fiber laser to keep steady mode-locked states automatically. So the unsteadiness of traditional passively mode-locked
fiber laser can be avoided. The system transforms optical signals into electrical pulse signals and sends them into MCU
after processing. MCU calculates the frequency of the signals and judges the state of the output based on a quick
judgment algorithm. A high-speed comparator is used to check the signals and the comparison voltage can be adjusted to
improve the measuring accuracy. Then by controlling two polarization controllers at an angle of 45degrees to each other,
MCU extrudes the optical fibers to change the polarization until it gets proper mode-locked output. So the system can
continuously monitor the output signal and get it back to mode-locked states quickly and automatically. States of the
system can be displayed on the LCD and PC. The parameters of the steady mode-locked states can be stored into an
EEPROM so that the system will get into mode-locked states immediately next time. Actual experiments showed that,
for a 6.238MHz passively mode-locked fiber lasers, the system can get into steady mode-locked states automatically in
less than 90s after starting the system. The expected lock time can be reduced to less than 20s after follow up
We have demonstrated an all-fiber passively mode-locked ytterbium fiber laser operating with a
rectangular spectrum profile. Mode-locking is achieved by adopting nonlinear polarization rotation
(NPR) in an all fiber ring cavity with normal dispersion. The 3 dB bandwidth of the spectrum is 8.6
nm, the signal-to-noise ratio (SNR) is more than 40 dB, and the rising and falling band edges are very
steep. The mode-locking pulse train is stable and has a repetition of 13.4 MHz. We believe that the
laser is operating in the gain-guided soliton state, which means soliton formation is induced purely by
the existence of gain and gain dispersion. This kind of mode-locked fiber laser with the rectangular
spectrum has potential applications in optical-based ultra-high-speed signal collection system, optical
frequency combs generation and supercontinuum light source.