We present first results archived with a widely-tunable discrete-cavity diode-pumped solid-state laser, at around 1.55 μm wavelength, for phase-sensitive optical time domain reflectometer (Φ-OTDR).

This paper reviews the method of semiconductor laser diode frequency stabilization by phase modulation. Also parameters are identified that affect the quality of stabilization and the estimation of Allan deviation is obtained. The pilot setup has been put together and it consists of: a semiconductor distributed feedback laser diode, a fiber phase modulator, an electrical signal generator, an acetylene-13 isotope cuvette, a photodetector, a lock-in amplifier and personal computer for measurement processing. Modulated laser diode radiation passed through a gas cell provides information about the position of radiation spectral line relative to the center of gas spectral line. Gas molecular spectral lines provide frequency standard with low sensitivity to external effects. When using the reference signal, one can get an error signal in a lock-in amplifier that changes the laser diode temperature and, as a result, its wavelength. Allan deviation was estimated based on measured frequency data. Long-term stability can be improved in the time range between 0.1 s and 100 s up to 1∙10-8 (Allan deviation). This method of stabilization is useful for the development of compact high reliable optical frequency standards for space applications.

We report investigation of frequency response of the He-Ne laser stabilized over methane line on temperature fluctuations. Stabilization technic is based on saturated dispersion resonance registration in two-mode laser with orthogonal polarizations. Anisotropic elements of the laser cavity are sensitive to temperature fluctuations that lead to laser frequency drift for averaging time more than 10 s. We developed temperature stabilization system with 10 mK stability in the range from 20 to 45 degrees C. That makes possible to shift temperature working point and measure temperature coefficient of the stabilized frequency (TCF) for this type of optical standard.

A novel laser for phase-sensitive optical time-domain reflectometry (Φ-OTDR) is presented. The advantages of a compact solid-state laser are listed, current problems are shown. Experiments with a microchip single-optical-element laser, from setup construction to usage in Φ-OTDR system, are presented. New laser scheme with two-photon intracavity absorber is suggested and its advantages are described.

We propose a novel scheme for laser phase noise measurements with minimized sensitivity to external fluctuations including interferometer vibration, temperature instability, other low-frequency noise, and relative intensity noise. In order to minimize the effect of these external fluctuations, we employ simultaneous measurement of two spectrally separated channels in the scheme. We present an algorithm for selection of the desired signal to extract the phase noise. Experimental results demonstrate potential of the suggested scheme for a wide range of technological applications.

We demonstrate the generation of stable 127 fs self-similar pulses at a central wavelength of 1560 nm with 7.14 mW average output power. Similariton lasers have low repetition rate deviation in the averaging time interval 1-1·10 3 s, a low relative intensity noise -125 dBc/Hz, a narrow single comb line width of 32 kHz, and high reliability. Thus, such lasers are highly promising for further development of the stabilized combs.

Цифровой частотный детектор для метанового мобильного стандарта частоты Д. А. Шелестов 1 , Д. А. Тюриков 2 , А

We report on the experiments related to the Er-Yb microchip laser setup with fiber diode pumping. The main goal is a new radiation source for the use in the phase-sensitive optical time domain reflectometry (φ-OTDR) development.

Ultrashort pulse (USP) fiber lasers have become one of the most important instruments in various fields of science and industry during two past decades. A number of applications requires stability of pulse duration, repetition rate and low intensity noise of an USP source. For example, stabilization of this parameters is in great demand in frequency metrology field, dual comb spectroscopy, THz pulse spectroscopy and etc. It should be noted, that hybrid Mode-locking (ML) for USP generation have attracted a great attention due to their capabilities of enhancing pulse quality and providing reliable ML startup by taking advantage of a co-action of two saturable absorbers (SA) - a slow SA such as SESAM, carbon nanostructures or graphene, and a fast absorber based on nonlinear polarization evolution (NPE) effect. Recently Carbon:Boron Nitride Single-Walled Nanotubes(C:BNNTs) SA is proved to be reliable absorber with excellent saturation parameters for erbium-doped fiber laser ML. In this paper we have obtained and measured stability of stretch pulse generation in the hybrid ML erbium-doped all-fiber ring laser by using C:BNNTs SA in the co-action with NPE effect. We have managed to realize two different types of stable single-pulse, self-starting stretch pulse generation at a repetition frequency of 42.2MHz with S/N ratio ~ 63 dB. Note, that the total intracavity group velocity dispersion β 2 was -0.021 ps 2 at 1550 nm. Obtained sech 2 -type spectrum has a FWHM of ≈ 4nm at the output average power of 16.7mW and the Gauss-type spectra has a FWHM of ≈ 56 nm at the same output power. Pulse width measured by intensity autocorrelator is 650 fs for both USP generation regimes. Note, that the time-bandwidth product for the sech 2 pulse is TBP=Δv × τ min ≈ 0.322 and for the Gauss pulse TBP ≈ 4.45 (typical TBP for a Gauss pulse ≈ 0.44). Thus, the obtained sech 2 pulse is close to the bandwidth-limit (TBP ≈ 0.315 for a classical soliton). It should be noted, that minimal Gauss pulse width (up to sub-100 fs duration) can be achieved simply by proper fiber length control at the laser output.

In present paper we demonstrated an improved technique for characterization of ultra-short pulse duration (PD) based on second harmonic generation (SHG). We utilized Yb- doped fiber laser with picosecond duration of pulses as implementation of proposed technique and for estimating the accuracy of pulse duration measurement. KTiOPO4 crystal was used for the purpose of second harmonic generation. We determined the duration of laser pulses by analysing the combination of signal intensities on input and output of SHG crystal. We observed experimentally error of pulse duration measurement less then 2%. We showed strong dependence between the average power of SHG and the duration of picosecond pulses.

A system based on coherent optical time domain reflectometry (OTDR) for subsea pipeline monitoring is described. The fiber sensor length is increased using erbium-doped fiber amplifier (EDFA) cascades. The sampling frequency is increased by dividing the fiber sensor into separate sensitive areas, with parallel scanning. The calculation of the erbium amplifier cascade spontaneous noise influence on the signal-to-noise ratio (SNR) is carried out.

The mid-IR cw tunable solid state two-mode Cr2+:ZnSe laser with intracavity methane cryocell was developed. The laser was applied for sub-Doppler spectroscopy of (υ1+υ4) vibrational-rotational band of methane and observation of narrow resonances of saturated dispersion at λ = 2.36 μm. The new technique of low pressure methane gas cooling was used instead of liquid nitrogen “jacket” design applied in our previous work. Parameters of saturated dispersion resonances were estimated in 77-300 K temperature range. The experiments confirmed that laser with the new “dry cooled” methane cell has prospectives for reaching a short-term frequency stability at the level of 10-15-0-16 and can be used as a compact device.

An optically pumped cw laser on a Cr2+:ZnSe crystal with a tunable (in the range of 2.3-2.6 mu m) wavelength, operating with generation of two axial modes, has been developed. It is shown that the minimum laser frequency-noise spectral density does not exceed 0.03 Hz Hz(-1/2). Application of this laser in problems of Doppler and Doppler-free spectroscopy makes it possible to detect spectral absorption lines of gases with sensitivities of 5 x 10(-12) and 2 x 10(-10) cm(-1), respectively (averaging time tau = 1 s). Having stabilised this laser with respect to the Doppler-free resonances of saturated dispersion of methane molecule, one can obtain a short-term frequency stability of 10(-15)-10(-16) (tau = 1 s).