Mode-locked Femtosecond Fiber Laser Research Articles

Femtosecond mode-locked holmium fiber laser pumped by semiconductor disk laser

We report on a 2085 nm holmium-doped silica fiber laser passively mode-locked by semiconductor saturable absorber mirror and carbon nanotube absorber. The laser, pumped by a 1.16 μm semiconductor disk laser, produces 890 femtosecond pulses with the average power of 46 mW and the repetition rate of 15.7 MHz.

Phase-coherent repetition rate multiplication of a mode-locked laser from 40 MHz to 1 GHz by injection locking

We have used injection locking to multiply the repetition rate of a passively mode-locked femtosecond fiber laser from 40 MHz to 1 GHz while preserving optical phase coherence between the master laser and the slave output. The system is implemented almost completely in fiber and incorporates gain and passive saturable absorption. The slave repetition rate is set to a rational harmonic of the master repetition rate, inducing pulse formation at the least common multiple of the master and slave repetition rates.

高功率被动锁模2.0 μm掺铥飞秒脉冲光纤激光器

高功率被动锁模2.0 μm掺铥飞秒脉冲光纤激光器

Precision spectroscopy of Rb atoms using single comb-line selected from fiber optical frequency comb

We demonstrated the selection of a single comb-line from an optical frequency comb (OFC) of a mode-locked femtosecond fiber laser with a 250 MHz pulse repetition rate, and applied for precision spectroscopy of Rb atoms at 1529 nm. The single comb-line was selected from the fiber-OFC with a 1.5 GHz mode-spacing using spectral-mode-filtering and femtosecond laser injection-locking. When the repetition rate of the mode-locked femtosecond fiber laser was scanned over the range of 382.6 Hz at 250 MHz, we observed the double-resonance optical pumping spectra of the 5S(1/2)-5P(3/2)-4D(3/2) transition of Rb atoms using the selected comb-line of an OFC scanned over the range of 300 MHz at 196,037,213.8 MHz.

Highly efficient femtosecond pulse stretching by tailoring cavity dispersion in erbium fiber lasers with an intracavity short-pass edge filter

We demonstrate highly efficient pulse stretching in Er(3+)-doped femtosecond mode-locked fiber lasers by tailoring cavity dispersion using an intracavity short-pass edge filter. The cavity dispersion is preset at around zero to obtain the shortest pulsewidth. When the cutoff wavelength of the short-pass edge filter is thermo-optically tuned to overlap the constituting spectral components of mode-locked pulses, large negative waveguide dispersion is introduced by the steep cutoff slope and the total cavity dispersion is moved to normal dispersion regime to broaden the pulsewidth. The time-bandwidth product of the mode-locked pulse increases with the decreasing temperature at the optical liquid surrounding the short-pass edge filter. Pulse stretch ratio of 3.53 (623.8 fs/176.8 fs) can be efficiently achieved under a temperature variation of 4 °C.

Passive Harmonically Mode-Locked Yb$^{3 +}$-Doped Fiber Laser Free From Anomalous Dispersion

We report on an all normal dispersion harmonically mode-locked ytterbium-doped femtosecond fiber laser. The mode-locking mechanism of the laser is based on nonlinear polarization evolution with strong pulse shaping. Bandpass filtering is achieved with a cascaded long-period fiber grating, forming highly chirped pulses. The laser generates stable 2.5-ps duration pulses at a repetition rate of 125.39 MHz that could be dechirped externally to 310 fs with a maximum pulse energy of 0.36 nJ.

18 wavelengths 839Gs/s optical sampling clock for photonic A/D converters

In this paper, a simple approach to generate the time-wavelength interleaved sampling clock for photonic A/D converters is proposed using commercially available mode-locked femtosecond fiber laser and optical wavelength/time division multiplexing (WDM/OTDM) techniques with low cost passive optical components. A time and wavelength mapping module is configured using specially designed wavelength division multiplexer and mechanical tunable fiber stretchers. OTDM modules with low optical insertion loss and flexibly configurable multiple factor are implemented with the fused-biconical optical fiber couplers. Experiment is carried out using 18 WDM channels and 128 times OTDM to demonstrate the generation of 83.9Gs/s time-wavelength interleaved sampling clock.

Wavelength-Tunable Er$^{3+}$-Doped fs Mode-Locked Fiber Laser Using Short-Pass Edge Filters

We demonstrate a wavelength-tunable Er <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> -doped femtosecond mode-locked soliton fiber laser by incorporating a short-pass edge filter into a ring cavity. When the filter is thermo-optically tuned toward shorter wavelengths to strongly attenuate the wavelengths longer than the cutoff, the constituting wavelengths of the mode-locked fiber laser move to shorter wavelengths and the laser center wavelength can be tuned over 1539.7 ~ 1560 nm. The cavity dispersion is preset in the deep soliton region to keep small fluctuations of laser pulsewidth when the laser wavelength is tuned.

Self-stabilization of a mode-locked femtosecond fiber laser using a photonic bandgap fiber

We demonstrate a self-stabilization mechanism of a semiconductor saturable absorber mode-locked linear-cavity Yb-doped fiber laser using an intracavity photonic bandgap fiber. This mechanism relies on the spectral shift of the laser pulses to a spectral range of higher anomalous dispersion and higher loss of the photonic bandgap fiber, as a reaction to the intracavity power buildup. This, in particular, results in a smaller cavity loss for the stably mode-locked laser, as opposed to the Q-switched mode-locking scenario. The laser provides stable 39-49 pJ pulses of around 230 fs duration at 29 MHz repetition rate.

Femtosecond mode-locked fiber laser employing a hollow optical fiber filled with carbon nanotube dispersion as saturable absorber

We propose a novel in-line saturable absorber incorporating a hollow optical fiber (HOF) filled with single-walled carbon nanotube (SWCNT) dispersion. The evanescent field of the propagating light in the ring core interacts with the SWCNT/polymer composite distributed over the whole length of the HOF. The proposed saturable absorber with all-fiber format offers the robust and long nonlinear interaction along the waveguide direction expecting the increase of the threshold for optical and thermal damages with simple fabrication process. Low concentration SWCNT/polymer composite exhibiting very broadband resonant absorption around 1.5 microm with low scattering loss is prepared and based on this, we successfully demonstrate the passively mode-locked fiber laser including the SWCNT-filled HOF where the spectral bandwidth and the pulse duration of the laser output are 5.5 nm and 490 fs, respectively, with a repetition rate of 18.5 MHz.

Ultrafast ranging lidar based on real-time Fourier transformation

Real-time Fourier-transformation-based ranging lidar using a mode-locked femtosecond fiber laser is demonstrated. The object signal and the reference signal are guided from a fiber Mach-Zehnder interferometer into a dispersive element. The two optical pulses extend and overlap with each other temporally, which yields a microwave pulse on the photodetector with its frequency proportional to the time delay between the two signals. The temporal interferograms are transformed from the time domain into the frequency domain using a time-to-frequency conversion function obtained in the calibration process. The Fourier transform is used in the data processing. A range resolution of 334 nm at a sampling rate of 48.6 MHz over a distance of 16 cm is demonstrated in the laboratory.

Properties and stability limits of an optimized mode-locked Yb-doped femtosecond fiber laser

Stable mode-locked operation in a simple normal-cavity-dispersion laser oscillator that consists of only Yb-doped fiber and saturable absorber is studied. The Yb-doped fiber design parameters: group velocity dispersion (GVD), nonlinearity coefficient, bandwidth (Yb-BW), length and gain are considered to be the controlling parameters of the laser cavity. The pulse characteristics such as the temporal width, spectrum and pulse energy as a function of these elements are reported here. A pulse spectrum transition from M-like to Pi-like and then to parabolic-like shape is observed with different values of the controlling parameters which are similar to that has been observed before in a solid-state laser. The stability limits in the domain of the Yb-BW and length are studied. The stability dependence on GVD, nonlinearity coefficient and gain of the Yb-doped fiber are elucidated. Moreover, the pulse instability dyn ics beyond stability limits are found to be similar to that reported before for similariton.

A passively mode-locked femtosecond soliton fiber laser at 15 μm with a CNT-doped polycarbonate saturable absorber

We report a new 1.5 mum femtosecond fiber soliton laser incorporating a polymer saturable absorber that consists of polycarbonate (PC) with carbon nanotubes (CNTs). We installed the polymer in a fiber laser with a cavity length of 5.1 m, in which an erbium-doped fiber was used as the gain medium. Stable passive mode-locking was achieved for a pump power of 303 mW at 39 MHz, and a pulse width of 115 fs with an average output power of 3.4 mW was obtained.

High repetition rate passively mode-locked erbium-doped fiber laser

We report a passively mode-locked high repetition rate erbium-doped femtosecond fiber laser via nonlinear polarization rotation, with a fundamental repetition rate of 101.94 MHz. The output power is 34 mW when pumped by a single mode fiber coupled laser diode at 370 mW. The spectral width is 25 nm, corresponding to a transform limited pulse width of 105 fs.

Synchronization of mode-locked femtosecond lasers through a fiber link

Two mode-locked femtosecond fiber lasers, connected via a 7 km fiber link, are synchronized to an rms timing jitter of 19 fs, observed over the entire Nyquist bandwidth (half of the 93 MHz repetition frequency). This result is achieved in two steps. First, active cancellation of the fiber-transmission noise reduces timing jitter caused by path length fluctuations to a record level of 16 fs. Second, using a wide bandwidth interactivity actuator, the slave laser is synchronized to the incoming stable pulse train from the reference laser to within 10 fs. These results are confirmed by an optical cross-correlation measurement performed independently of the feedback loop operated in the microwave domain.

Colliding-pulse passive harmonic mode-locking in a femtosecond Yb-doped fiber laser with a semiconductor saturable absorber

We demonstrate a passive harmonic mode-locked femtosecond Yb-doped fiber laser employing a semiconductor saturable absorber in a colliding-pulse configuration. 380-fs pulses at 605 MHz repetition rate with >60 dB supermode suppression is achieved.

Synchronously pumped optical parametric oscillator driven by a femtosecond mode-locked fiber laser

A femtosecond all-fiber laser source incorporating a cw mode-locked Yb-doped silica fiber oscillator and amplifier has been used to synchronously pump an optical parametric oscillator based on periodically poled lithium niobate. The signal output, consisting of 330-fs pulses at a 54-MHz repetition rate and average powers up to 90 mW, was tuned from 1.55 to 1.95microm , with a corresponding idler range of 2.30-3.31microm .

High repetition rate femtosecond WDM pulse generation using direct space-to-time pulse shapers and arrayed waveguide gratings

For the application of high repetition rate wavelength division multiplexed (WDM) pulse train generation from a femtosecond modelocked fiber laser, the direct space-to-time pulse shaper and a properly designed arrayed waveguide grating (AWG) are equivalent. The analogy between the bulk optics and integrated configuration is explored for this application. The critical design parameters of the AWG are the free spectral range and the pathlength difference between adjacent guides in the array.

Broad-band high-repetition-rate source for spectrally sliced WDM

A uniform 35-nm-wide spectrum is generated by broadening the output from a 2.5-GHz mode-locked femtosecond fiber laser in dispersion shifted fiber. The obtained spectrum is suitable for spectral slicing and wavelength-division-multiplexed applications. The spectral broadening in dispersion shifted fiber is optimized as a function of the launched pulse chirp parameter.

Compact system of wavelength-tunable femtosecond soliton pulse generation using optical fibers

Using passively mode-locked femtosecond (fs) fiber laser and polarization maintaining fibers, the compact system of wavelength-tunable femtosecond (fs) fundamental soliton pulse generation is realized. The monocolored soliton pulse, not multicolored ones, with the ideal sech <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> shape is generated, and its wavelength can be linearly shifted by varying merely the fiber-input power in the wide wavelength region of 1.56-1.78 μm for a 75-m fiber. The soliton pulses of less than 200 fs are generated with the high conversion efficiency of 75%-85%. This system can be widely used as a portable and practical wavelength-tunable fs optical pulse sources.