Laser vibrometer-rangefinder based on self-sweeping fiber laser.

A vibrometer-rangefinder based on principles of coherent optical frequency-domain reflectometry (C-OFDR) is experimentally demonstrated. A self-sweeping ytterbium-doped fiber laser, which does not require any spectrally selective elements and drivers for wavelength tuning, with a sweeping range of 1056-1074 nm is used as a tunable source of probe radiation for the C-OFDR measurements. We demonstrate the possibility of measuring target vibrations in the frequency range from 2 Hz to 5 kHz with an amplitude of down to ∼5 nm at a distance of up to ∼13 m. The maximum measurable vibration frequency is limited by the instability of the self-sweeping laser parameters in the time domain and is estimated as ∼7.5 kHz.

Spectral characterization technique of self-organized distributed feedback in a self-sweeping fiber laser.

We report on spectral characterization technique of self-organized dynamical distributed feedback (DDFB) in a self-sweeping Yb-doped fiber laser. The DDFB is originated from gain and refraction index gratings formed (recorded by standing waves) in the laser's active medium and dynamically changes during frequency self-sweeping operation. Dynamic nature of the feedback requires fast characterization (reading) of corresponding reflection spectrum. The reading process can be separated from the recording one in time due to sufficiently long characteristic time of the dynamical gratings. The DDFB spectra are measured during off-state of the self-sweeping laser with a tunable probe radiation near the dynamical grating reflection maximum. The spectra reconstructed in a range of ~1 GHz from a sequence of shorter probe wave scans have narrow sharp peak with width of ~50 MHz and reflectivity of about 0.1%. A good agreement between theory and experimental results is demonstrated.

Random Raman fiber laser based on a twin-core fiber with FBGs inscribed by femtosecond radiation.

Narrowband Raman lasing in a polarization-maintaining two-core fiber (TCF) is demonstrated. Femtosecond point-by-point inscription of fiber Bragg gratings (FBGs) in individual cores produces a half-open cavity with random distributed feedback. The laser linewidth in the cavity with a single FBG inscribed in one core of the TCF reduced by ∼2 times with respect to the cavity with a fiber loop mirror. It is shown that the inscription of two FBGs in different cores leads to the formation of a Michelson-type interferometer, leading to the modulation of generation spectra near threshold. This technique offers new possibilities for spectral filtering or multi-wavelength generation.

Broad-range self-sweeping single-frequency linearly polarized Tm-doped fiber laser.

We experimentally demonstrate a linearly polarized Tm-doped fiber laser with sweeping range up to 26 nm in the region of 1.92 µm. The main feature of the laser is generation of periodic microsecond pulses in which each contains practically only single longitudinal mode radiation. The laser frequency changes from pulse to pulse with high linearity by one intermode beating frequency of the laser ∼8 MHz. The developed source is applied to measure spectrum of water absorption lines in air.

Michelson mode selector for spectral range stabilization in a self-sweeping fiber laser.

We report on spectral range stabilization in a self-sweeping laser by adding a narrowband fiber Bragg grating (FBG) to the output mirror in the Michelson configuration. The effects of FBG reflectivity and optical path difference in the Michelson interferometer on the laser spectral dynamics are investigated. Optimization of the interferometer allows us to demonstrate broadband (over 16 nm) self-sweeping operation and reduction of the start and stop wavelength fluctuations by two orders and one order of magnitude (∼100 and 15 times) for start and stop bounds, respectively (down to several picometers). The proposed approaches significantly improve quality of the spectral dynamics and facilitate application of the self-sweeping lasers.

Raman fiber laser with random distributed feedback based on a twin-core fiber.

An operation of a linearly polarized Raman fiber laser with random distributed feedback based on a polarization-maintaining twin-core fiber (TCF) is demonstrated for the first time, to the best of our knowledge. The results indicate that the TCF allows one to obtain laser generation with a linewidth that is about five times smaller than that for the random laser based on a conventional fiber with similar parameters. The reasons for narrowing include both the weakening of nonlinear effects due to the power density reduction and the spectrally selective properties of the TCF.

All-fiber Brillouin optical spectrum analyzer based on self-sweeping fiber laser.

We proposed and demonstrated an all-fiber scheme for optical spectrum measurement based on stimulated Brillouin scattering and frequency self-sweeping laser without external driver and frequency tunable elements. The resolution and measuring range of proposed analyzer is measured to be 23 MHz and 5 THz respectively. The ways for improvement of the device characteristics are discussed.

Mechanism of mode coupling in multicore fiber lasers.

We present what is believed to be the first experimental demonstration of a new mechanism of mode coupling in multicore fibers (MCFs) based on their indirect interaction inside the fiber via intermediate mode, analogous to the Bragg mode, which is very sensitive to bending of the fiber. Very strong coupling between the core modes regardless of large spacing (approximately 28 microm) between them has been demonstrated in the MCF laser as well as in the probe beam schemes. 70% of power conversion from one core to another with beating length of tens of centimeters in 4-core MCF is measured.