All-fiber dissipative soliton Raman laser based on phosphosilicate fiber

1.3/1.4 µm dual-wave band dissipative soliton resonance in a passively mode-locked Bi-doped phosphosilicate fiber laser

We report the 1.3/1.4 µm dual-wave band dissipative soliton resonance (DSR) in a passively mode-locked bismuth-doped phosphosilicate fiber (Bi-PSF) laser. The low-water-peak Bi-PSF with two bismuth active centers associated with silicon and phosphorus supports the O+E-band gain. Using a 1239 nm home-made Raman fiber laser as pump source and nonlinear amplifying loop mirror for initiating mode-locking, stable DSR operation at 1343 and 1406 nm is achieved with the spectral bandwidth of 12 and 16 nm. The pulse duration with the pump power increases from 62 to 270 ps with a repetition frequency of 4.069 MHz. The average power is 11.05 mW corresponding to the maximum energy of 2.7 nJ. This is, to the best of our knowledge, the first demonstration of a mode-locked fiber laser in the ∼1.38 µm water absorption band and the O+E dual-wave band operation for applications in all-spectral-band communications, bio-medical imaging, and terahertz difference frequency generation.

Femtosecond optical parametric chirped-pulse amplification in birefringent step-index fiber

We demonstrate an optical parametric chirped-pulse amplifier (OPCPA) that uses birefringence phase matching in a step-index single-mode optical fiber. The OPCPA is pumped with chirped pulses that can be compressed to sub-30-fs duration. The signal (idler) pulses are generated at 905 nm (1270 nm), have 26 nJ (20 nJ) pulse energy, and are compressible to 70 fs duration. The short compressed signal and idler pulse durations are enabled by the broad bandwidth of the pump pulses. Numerical simulations guiding the design are consistent with the experimental results and predict that scaling to higher pulse energies will be possible. Forgoing a photonic crystal fiber for phase-matching offers practical advantages, including allowing energy scaling with mode area.

Synchronously pumped Raman laser for simultaneous degenerate and nondegenerate two-photon microscopy

Two-photon fluorescence microscopy is a nonlinear imaging modality frequently used in deep-tissue imaging applications. A tunable-wavelength multicolor short-pulse source is usually required to excite fluorophores with a wide range of excitation wavelengths. This need is most typically met by solid-state lasers, which are bulky, expensive, and complicated systems. Here, we demonstrate a compact, robust fiber system that generates naturally synchronized femtosecond pulses at 1050 nm and 1200 nm by using a combination of gain-managed and Raman amplification. We image the brain of a mouse and view the blood vessels, neurons, and other cell-like structures using simultaneous degenerate and nondegenerate excitation.

1.3 µm dissipative soliton resonance generation in Bismuth doped fiber laser

In this work, a Figure-9 (F9) bismuth-doped fiber laser (BiDFL) operating in the dissipative soliton resonance (DSR) regime is presented. The 1338 nm laser used a BiDF as the active gain medium, while a nonlinear amplifying loop mirror (NALM) in an F9 configuration was employed to obtain high energy mode-locked pulses. The wave breaking-free rectangular pulse widened significantly in the time domain with the increase of the pump power while maintaining an almost constant peak power of 0.6 W. At the maximum pump power, the mode-locked laser delivered a rectangular-shaped pulse with a duration of 48 ns, repetition rate of 362 kHz and a radio-frequency signal-to-noise ratio of more than 60 dB. The maximum output power was recorded at around 11 mW with a corresponding pulse energy of 30 nJ. This is, to the best of the author's knowledge, the highest mode-locked pulse energy obtained at 1.3 μm as well as the demonstration of an NALM BiDFL in a F9 configuration.

All-fiber 1125 nm spectrally selected subnanosecond source

In this paper, we demonstrate the selection of radiation from the stimulated Raman scattered radiation, while using a spectral filter, based on a high-reflection fiber Bragg grating and an optical circulator. As a result, a stable pulsed signal was obtained at a wavelength of 1125 nm with a repetition rate of 1 MHz. The pulse duration and energy varied from 120 to 173 ps and 9 to 15 nJ, respectively, depending on the operating regimes of the master oscillator and amplifier.

Raman dissipative solitons generator near 1.3 mkm: limiting factors and further perspectives

Raman dissipative solitons (RDS) have been investigated numerically. It was found that the area of stable generation is bounded in terms of pump spectral bandwidth and pulse energy. Existing optimum is strongly affected by the net cavity dispersion. The spectral bandwidth of the generated RDS linearly depends on its energy and reaches more than 50 nm in the 5-meters long cavity. Developed numerical model reproduces all the effects observed experimentally. It predicts ability to generate high-quality pulses with energy up to 6 nJ compressible down to ∼100 fs duration. The work shows that RDS generation technique can produce high-energy ultrashort pulses at wavelengths not covered by typical active mediums.

Design guidelines for normal-dispersion fiber optical parametric chirped-pulse amplifiers

We theoretically investigate methods of controlling pulse generation in normal-dispersion fiber optical parametric chirped-pulse amplifiers. We focus on high-energy, ultrashort pulses at wavelengths widely separated from that of the pump, and find that within this regime, a number of simple properties describe the essential phase and gain dynamics. Of primary importance are the relationships between the chirps of the pump, seed, and parametric gain, which we theoretically predict and then experimentally validate. By properly arranging these parameters, the signal and idler waves can be widely customized to fulfill a remarkable range of application requirements, spanning from narrowband to few-cycle.

Orthogonal beam ballistic backscatter stimulated Raman microscopy

When the axial gain length of a stimulated Raman microscope is less than about 40% of the emission wavelength significant dipole-like ballistic backscatter will occur. Here we analyze a scanning microscope configured with orthogonal water dipping pump and probe objectives that satisfies this criterion. The pump beam focus may be a Gaussian spot or a droplet Bessel beam which minimizes the secondary Bessel beam lobes and provides multiple simultaneous pump focal spot regions. Radial and linearly polarized pump beams enable backscattered polarized signals along both transverse axes of the probe beam. Low level Mie backscatter is the primary photon noise source which should enable rapid sub-wavelength resolution 3-dimensional imaging of label-free Raman contrast for in-vivo pathology, as well as, imaging physiologic concentrations of Raman labelled metabolites and drugs.

Watt-level all-fiber optical parametric chirped-pulse amplifier working at 1300 nm

We report watt-level average output power near 1300 nm from an all-fiber ultrafast optical parametric chirped-pulse amplifier. A compressed output pulse duration of ∼300  fs is achieved. Multiphoton imaging of a variety of samples carried out with this light source shows a good signal-to-noise ratio. With the demonstrated imaging capability, we believe that this high-power ultrafast laser source addresses a key need in deep tissue multiphoton microscopy.