A. A. Sysoliatin

DDF-Based All-Fiber Optical Source of Femtosecond Pulses Smoothly Tuned in the Telecommunication Range

The possibility of the creation of an optical source of femtosecond pulses that are smoothly tuned in the telecommunication range using a dispersion-decreasing fiber is demonstrated. The smooth tuning is based on the Raman frequency conversion of ultrashort pulses, which can be effectively tuned due to the compression mechanism for maintaining of a relatively high pulse intensity in the medium with a monotonically decreasing anomalous dispersion. The generation of a 90-fs soliton pulse whose spectrum is smoothly tuned in the wavelength range 1.6–1.8 μm is experimentally demonstrated.

Experimental demonstration of spectral broadening in an all-silica Bragg fiber

We present the first report on experimental observation of nonlinear spectral broadening in an all-solid photonic band gap Bragg fiber of relatively large mode area approximately 62 microm(2). The theoretically designed Bragg fiber for this specific application was fabricated by the well known MCVD technique. Nonlinear spectral broadening was observed by launching high power femtosecond pulses of 1067 nm pump wavelength. These first results indicate that fabrication of such Bragg fibers, once perfected, should potentially serve as an alternative route for realization of supercontinuum light.

Widely-wavelength-tunable few-cycle optical pulse generation from an all-fiber erbium-doped laser system

A scheme for the construction of fiber laser systems for the generation of tunable ultrashort optical pulses is proposed. The scheme is based on the self-Raman shift of the soliton frequency in dispersion-decreasing fibers with the subsequent spectral broadening owing to the supercontinuum generation in a short highly nonlinear fiber and the compression in the corresponding fiber compressor. An all-fiber laser system for the generation of ultrashort laser pulses in the wavelength range 1.6–2.0 μm is experimentally demonstrated. In particular, the shortest pulses with a duration of 24 fs are generated at wavelengths of 1.8–1.9 μm, which corresponds to less than four optical cycles.

Generation of Optical Soliton Pulses Smoothly Tunable in a Wide Frequency Range in Silica Fibers with Variable Dispersion

The possibility of the efficient conversion of the frequency of an optical soliton pulse in fibers with length-variable dispersion is physically analyzed and experimentally investigated. The effect is based on the Raman transformation of the frequency of an ultrashort pulse, which can be varied with high efficiency due to the compression mechanism of maintaining a high intensity of the pulse in a medium with monotonically decreasing anomalous dispersion. A smooth rearrangement of the spectrum of the soliton pulse 90 fs in duration in the range 1.58–1.75 μm is demonstrated.

Wavelength-tunable few-cycle optical pulses directly from an all-fiber Er-doped laser setup

A simple design, which we believe to be the first of its kind, of an all-fiber-based optical source is proposed for the generation of widely tunable few-cycle pulses as short as 20-25 fs duration in the range of 1.6-2.1 microm. Few-cycle pulses are obtained by compression of femtosecond pulses from the erbium-doped fiber laser in a three-stage scheme that uses (i) the effects of the soliton compression and the Raman frequency tuning in the dispersion decreasing fiber, as well as (ii) supercontinuum generation in a high-nonlinear silica fiber, and (iii) subsequent compression in a short conventional fiber.

Highly Nonlinear Dispersion Increasing Fiber for Femtosecond Pulse Generation

The optical pulse evolution in a highly nonlinear normal dispersion-increasing fiber has been considered, both experimentally and theoretically. It was found that large spectral broadening in tapered waveguides could occur without temporal instabilities and impose the linear frequency modulation, i.e., chirp, required for high-quality pulse compression. The pedestal-free pulses have been demonstrated after dechirping in a standard single-mode fiber.

Amplification of chirped pulses in inhomogeneous three-level active optical fibers

The possibility of efficient amplification of self-similar frequency-modulated wave packets in amplifiers inhomogeneous along their length is investigated. Special features of the amplification dynamics in erbium fiber amplifiers that operate according to the three-level scheme are analyzed. It is shown that active optical fibers with a specially designed profile of the normal group-velocity dispersion allow amplifying subpicosecond pulses with high efficiency.

Trigger effect of infrared femtosecond laser irradiation on neoplasm in experimental cervical cancer

The present work discusses effect of infrared (IR) femtosecond laser irradiation on neoplasm of white mice with experimental cervical cancer- 5 (CC-5 on the 20th and 30th days after tumor transplantation). Tumor tissue was irradiated by femtosecond erbium doped fiber laser: the wavelength is 1.55 μm, average and peak powers are1,25 mW and 6kW, respectively, irradiation trials n=10. The average energy density (energy dose) on a tissue for two groups of animals was 0,24 J/cm2 and 0,36 J/cm2 for a single trial. Irradiation was followed by biochemical determination of LPO AOS parameters (“Lipid peroxidation-antioxidants” system): malondialdehyde (MDA), activity of superoxide dismutase (SOD), catalase and glutathione-reductase (GR), glutathione-S-transferase (GST). A subsequent morphological study of tumor tissue was performed. Mathematical analysis of data demonstrates a weak dependence of the studied parameters on energy dose. The latter implies the trigger effect of IR femtosecond laser irradiation on redox-dependent processes in neoplasm at experimental cervical cancer.

A multistage fiber amplifier with a decreased rate of frequency modulation of amplified pulses

We propose a new all-fiber cascade picosecond pulse amplification scheme based on optical fibers with varying normal group velocity dispersion (GVD). Amplification is performed in the fiber sections with exponential growth of the normal dispersion. Amplification sections are altered by the sections of passive fibers with the decreasing normal GVD. The pulse chirp in dispersion decreasing fibers can be adjusted by the increment of dispersion variation, enabling control of the pulse spectral width to keep it within an amplification band. To illustrate this concept numerical simulations are performed.

Wavelength-tunable few-cycle optical pulse generation from an all-fiber erbium-doped laser system

In this work, to create widely wavelength-tunable few-cycle pulses, we propose to use the following three-stage scheme for nonlinear transformation of femtosecond pulses from the conventional modelocked erbium-doped setup. A silica fiber with slowly decreasing dispersion (DDF) is used for preliminary pulse compression and central wavelength tuning over a broad range at the first stage. At the second stage, the highly nonlinear dispersion-shifted fiber with a small normal dispersion is spliced to the DDF for supercontinuum generation, which is then compressed (third stage) to the few-cycle pulse in the fiber compressor.