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We demonstrate a hybrid-structure fiber laser composed of single-mode fiber (SMF) and four-mode fiber (FMF), capable of delivering stable near-chirp-free soliton with the bandwidth of 75 pm. Ascribed to the spectral-domain intermodal interference, the SMF-FMF cavity serves not only as a ring resonator but also as an intrinsic spectral filter. The wavelength of the narrowband soliton is tunable within 10 nm by a polarization controller. Simulation results validate the experimental observations, revealing that the filtering effect simultaneously balances the self-phase modulation induced spectral broadening and saturable absorption induced temporal compression. The narrowband fiber laser is attractive for spectroscopy, quantum optics, and material processing, and offers a promising platform to study the evolution dynamics of few-mode solitons. [ABSTRACT FROM AUTHOR]

A multi-switchable generation between dissipative solitons (DSs) and noise-like pulses (NLPs) in a fiber laser is demonstrated. A 45° tilted fiber grating is applied as an effective in-line all-fiber polarizer to realize the nonlinear polarization rotation (NPR) mechanism. With the fixed orientations of polarization controllers, the operation regimes of the fiber laser can be alternatively switched between DS and NLP by monotonically increasing pump power only. We observed five switching stages between DS/NLP regimes with the pump power elevating from 200 to 660 mW. Remarkably, the whole procedure could be precisely controlled forwardly and backwardly. This multi-shuttle behavior between the two distinct types of output pulse can be attributed to the transmission of NPR mechanism together with the gain filtering effect. To the best of our knowledge, this is the first report on the multi-shuttle behavior between DS and NLP in a fiber laser under monotonic change of pump power. Our findings may contribute to in-depth understanding of nonlinear dynamics and laser physics. [ABSTRACT FROM AUTHOR]

Here, an efficient dissipative soliton mode-locked fiber laser in the L-band using nonlinear polarization rotation technology is demonstrated. With a maximum pump power of 495.3 mW and polarization state optimization, the fiber laser delivers a maximum output power of 68.6 mW with an 11.16 MHz repetition rate and corresponding single pulse energy of 6.15 nJ. The dissipative soliton spectrum is centered at 1599.6 nm with a 3 dB bandwidth of 47.8 nm. The full width at half maximum of the compressed pulse is 156 fs. To the best of our knowledge, this is the highest single pulse energy reported so far for an L-band passively mode-locked all-fiber laser. [ABSTRACT FROM AUTHOR]

We investigated nonlinear optical characteristics of Tungsten disulfide (WS2) films and experimentally demonstrated their high potential for application as nonlinear saturable absorbers in passively mode-locked fiber lasers. Side polished fiber (SPF) was fabricated and WS2 film was overlaid to provide an efficient evanescent field interaction. The WS2 film was prepared using two methods: liquid phase exfoliation to form few-layer nano-sheets, and chemical vapor deposition (CVD) to grow uniform multilayer WS2 on a SiO2 substrate. Two SPF saturable absorbers were prepared by either spin coating WS2 solution or lifting off the multilayer CVD WS2 on SPF. An all-fiber ring cavity was built and the WS2 film overlaid on SPF was employed as a mode locker along with Er-doped fiber as a gain medium. Using the spin-coated WS2 SPF, stable soliton-like pulses were generated with a spectral width of 5.6 nm and 467 fs pulse duration. The fiber laser cavity containing CVD WS2 SPF generated a transform-limited soliton pulse train with a spectral width of 8.23 nm and a pulse duration of 332 fs. Our study confirmed a high potential of WS2 film as a novel 2-D nonlinear optical material for laser applications. [ABSTRACT FROM PUBLISHER]

We show analytically and experimentally that direct photodetection of a temporally-stretched and chirped optical pulse-train together with its time-delayed replica can be exploited to realize the generation of tunable continuous-wave microwave signals. The proposed scheme utilizes the chromatic dispersion of the standard single-mode-fiber (SMF) to temporally-stretch and chirp an optical pulse-train in such a way that the pulses overlap with each other. The temporally-stretched pulse-train is then sent to a Mach-Zehnder Interferometer (MZI) where it first splits and then recombines with a time-delayed replica of itself at the output. Proper management of both the dispersion in the system as well as the relative time-delay of the two arms of the MZI enables one to tune the frequency of the generated microwave signal to any integer multiple of the pulse source's repetition frequency which is within the bandwidth of the photodetector. Based on the proposed scheme, using an initial 2 GHz pulse-train, we demonstrate generation of tunable continuous-wave microwave signals from 4 GHz to 14 GHz. [ABSTRACT FROM PUBLISHER]

The current status of fiber based optical parametric oscillators is presented with a focus on pulsed systems employing microstructure fibers. It is shown based on standard expressions for parametric processes in optical fibers that systems employing short (less than a few cm) optical fibers lead to superior performance in terms of wavelength tunability and output power. Practical guidelines for realizing a working system are given. These devices are now practical as ultrafast pulsed-light sources and for extending the wavelengths of operation of existing mode-locked fiber lasers. [ABSTRACT FROM PUBLISHER]

Chirped radio-frequency (RF) pulse generation based on optical spectral shaping and nonlinear wavelength-to-time mapping in a nonlinearly chirped fiber Bragg grating (NLCFBG) is investigated. In the proposed approach, the spectrum of a femtosecond pulse generated by a mode-locked fiber laser is shaped by an optical filter that has a sinusoidal frequency response. The spectrum-shaped optical pulse is sent to the NLCFBG, to implement nonlinear wavelength-to-time mapping. A chirped electrical pulse with the central frequency and chirp rate determined respectively by the first- and second-order dispersions of the NLCFBG is then obtained at the output of a high-speed photodetector. An approximate model that describes the chirped RF pulse generation is derived, which is verified by numerical simulations. Chirped pulse generation with a pulse compression ratio as high as 450 is demonstrated. The key device in the chirped RF pulse generation system is the NLCFBG, which is investigated in detail with an emphasis on the influence of its group delay ripples on the performance of the pulse generation system. Techniques to design and fabricate the NLCFBG are also discussed. The proposed approach provides a potential solution for the generation of chirped RF pulse with a high central frequency and large chirp rate for applications in pulse compression radar systems. [ABSTRACT FROM PUBLISHER]

The authors experimentally investigate the phenomena of the pulse-shape distortion due to the drift of cavity length or modulation frequency in a harmonically mode-locked semiconductor fiber ring laser (SFRL). Also, it is experimentally demonstrated that the optical pulse shaping by cross-phase modulation (XPM) can be applied to enhance the robustness of a harmonic mode-locked semiconductor ring laser to the environmental factors, e.g., the modulation-frequency drift and/or the cavity-length drift. The mechanism of pulse-shape distortion due to the modulation-frequency drift or cavity-length drift is explained and experimentally verified. As the locking condition of the SFRL goes to the rational harmonic mode-locking (RHML) regime, the pulse-shape distortion becomes dominant. To validate the explanation, a simple equation for estimating and comparing the amount of cavity-length detuning in terms of frequency is proposed for comparison, which is called the equivalent frequency detuning (EFD). The distortion mostly appeared in the trailing edge of the pulse. By selectively filtering the XPM-induced red-chirped wavelength components in the rising edge of the pulse, the mode-locked pulse train with large pulse-shape distortion can be reshaped to regenerate a mode-locked pulse train with less pulse-shape distortion than the pulse train without the proposed scheme. This method can be used to reduce the pulse-shape distortion effectively, maintaining the pulse repetition rate under the large modulation-frequency detuning, or equivalently, large cavity-length detuning. The proposed scheme is able to generate the pulse-trains robust to the modulation-frequency drift and/or cavity-length drift of the mode-locked SFRL [ABSTRACT FROM PUBLISHER]

This paper compares two approaches for evaluating the amplitude and timing jitters of an Er-fiber laser mode-locked at 10 GHz. Using a low-noise oscillator as the clock drive for the mode-locking, relative amplitude jitter was measured as low as 0.0384% and timing jitter as low as 0.0153% (Δf=100 Hz-40 MHz). Applying the mode-locked pulse train in a photonic sampling experiment at 10 Gsample/s, a spurious free dynamic range (SFDR) of ∼48.5 dB (over the Nyquist bandwidth of 5 GHz) for multiple analog inputs at L band (1-2.6 GHz). These results correspond to an analog-to-digital conversion resolution of ∼8 SFDR bits at 10 Gsample/s. Finally, the use of "instantaneous companding" is demonstrated to correct for third-order distortions generated by a Mach-Zehnder modulator used in the photonic sampling link. [ABSTRACT FROM PUBLISHER]

The propagation of strongly chirped pulses in an amplified fiber-optic communications system is experimentally investigated. Spectral narrowing of the pulses is observed. The narrowing is attributed to interplay between the initial chirp and the nonlinearity in the transmission line. Four-wave mixing (FWM) between wavelength channels is found to be similar to that for unchirped nonreturn-to-zero (NRZ) pulses. Low error rate transmission over 720 km is achieved using these chirped pulses, which are generated by a transmitter based on a mode-locked fiber laser [ABSTRACT FROM PUBLISHER]