The conditions to obtain noise-like pulses (NLPs) from a figure-eight fiber laser (F8L) and their application for supercontinuum (SC) generation in the anomalous dispersion regime are reported. The F8L is designed to remove the undesired low-intensity background radiation from pulse emission, generating NLPs with a 3-dB spectral bandwidth of 17.43 nm at the fundamental repetition frequency of 0.8 MHz. After amplification, NLPs reach a maximum average power of 9.2 mW and 123.32 nm spectral bandwidth. By controlling the amplifier pump power, flat SC generation is demonstrated through both a 800-m long spool of SMF-28 fiber and a piece of 5-m long highly nonlinear optical fiber. The results demonstrate a satisfactory flatness of 3-dB over a bandwidth of 1000 nm in the range from 1261 to 2261 nm, achieving to the best of our knowledge, one of the flattest SC generated from noise-like pulses.
Active mode-locking of an all-fiber ring laser by transmittance modulation of an in-fiber acousto-optic tunable bandpass filter (AOTBF) is reported. Cavity loss modulation is achieved by full acousto-optic mode re-coupling cycle induced by standing flexural acoustic waves. The modulator permits the implementation of 28 dB of nonresonant light suppression, 1.4 nm of modulation bandwidth, 74% of modulation depth and 4.11 dB of optical loss in a 72.5 cm-long all-fiber configuration. The effects of the modulated AOTBF on the laser performance are investigated. Transform-limited optical pulses of 8.8 ps temporal width and 6.0 W peak power were obtained at 4.87 MHz repetition rate.
The present manuscript experimentally demonstrates multi-wavelength generation from a thulium-doped all-fiber laser by implementing a multi-cavity Fabry-Perot filter. The filter, with a composition that relies of several silica-air and air-silica interfaces, provide a spectral reflection response that allows the laser to be operated in single-, dual-or triple-wavelength emissions by simple and clear adjustment of the polarization state. In this way, the fiber laser is capable to operate over a broad range of wavelengths extending from 1844 to 1928 nm. In addition, dual-wavelength operations are also feasible in the 1844 and 1928 nm regions, exhibiting a mode spacing of 4.41 nm and 1.62 nm, respectively. Beside this, the laser is able to switch to a sextuple-wavelength operation regime in the 1885 nm region, maintaining a minimum wavelength spacing of 1.53 nm. The laser demonstrates high wavelength stability, with variations below 60 pm at all analyzed wavelengths, and a minimum peak power fluctuation of ±2.77 dB.
Q-switched and mode-locked (QML) pulse generation from an all-fiber ring laser based on intermodal acousto-optic bandpass modulation is reported. The modulator relies on full-acoustooptic mode re-coupling cycle induced by a standing flexural acoustic wave, with a transmission response that is controlled by amplitude modulation of the acoustic wave signal. The Q factor of the cavity is controlled by a rectangular pulse wave with variable frequency and duty cycle, whereas mode locking is achieved by amplitude modulation derived from a standing flexural acoustic wave. The best QML pulses were obtained at 0.5 kHz repetition rate, with a pump power of 549.2 mW, at the optical wavelength of 1568.2 nm. A maximum overall energy of 2.14 J at an average output power of 1.07 mW was achieved, corresponding to a burst of mode-locked sub-pulses of 100 ps pulse duration within a QML envelope of 3.5 s.
A long-cavity passively mode-locked thulium-doped allfiber laser is reported incorporating a tapered acoustooptic tunable bandpass filter (AOTBF). The operation of the AOTBF relies on the intermodal coupling between core and cladding modes when a flexural acoustic wave propagates along an 80-m tapered fiber. The filter works in transmission and exhibits a 3-dB bandwidth of 9.02 nm with an insertion loss of 3.4 dB. The laser supports ultrashort pulse generation at a low repetition rate of 784.93 kHz. Optical pulses with 2.43 nm of optical bandwidth and 2.1 ps pulse duration were obtained in a broad tuning range from 1824.77 to 1905.16 nm.
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