Passively Stabilized Doubly-Resonant Brillouin Fiber Lasers

We consider ultra narrow-line lasers based on doubly-resonant fiber cavities, describe experimental techniques, and present two methods for passive stabilization of single-frequency fiber Brillouin lasers. In the first approach, Brillouin fiber laser is passively stabilized at the pump resonance frequency by employing the self-injection locking phenomenon. We have demonstrated that this locking phenomenon delivers a significant narrowing of the pump laser linewidth and generates the Stokes wave with linewidth of about 0.5 kHz. In the second methodology, the fiber laser is stabilized with an adaptive dynamical grating self-organized in un-pumped Er-doped optical fiber. The laser radiates a single-frequency Stokes wave with a linewidth narrower than 100 Hz. The ring resonators of both presented lasers are simultaneously resonant for the pump and the Stokes radiations. For adjusting the double resonance at any preselected pump laser wavelength, we offer a procedure that provides a good accuracy of the final resonance peak location with ordinary measurement and cutting errors. The stable regime for both Brillouin lasers is observed during some intervals, which are interrupted by short-time jumping-intervals. The lasers’ stability can be improved by utilizing polarization-maintaining (PM) fiber configuration and a cavity protection system

Two-photon photochemical long-period grating fabrication in hydrogenated photonic crystal fiber

We report on the photochemical fabrication of a long-period grating in photonic crystal fiber. The characteristic fluence value for inscription is an order of magnitude less than that for standard telecom fiber

Fiber Laser for Phase-Sensitive Optical Time-Domain Reflectometry

We have designed a new fiber laser configuration with an injection-locked DFB laser applicable for phase-sensitive optical time-domain reflectometry. A low-loss fiber optical ring resonator (FORR) is used as a high finesse filter for the self-injection locking of the DFB (IL-DFB) laser. By varying the FORR fidelity, we have compared the DFB laser locking with FORR operating in the under-coupled, critically coupled, and over-coupled regimes. The critical coupling provides better frequency locking and superior narrowing of the laser linewidth. We have demonstrated that the locked DFB laser generates a single-frequency radiation with a linewidth less than 2.5 kHz if the FORR operates in the critically coupled regime. We have employed new IL-DFB laser configuration operating in the critical coupling regime for detection and localization of the perturbations in phase-sensitive OTDR system. The locked DFB laser with a narrow linewidth provides reliable long-distance monitoring of the perturbations measured through the moving differential processing algorithm. The IL-DFB laser delivers accurate localization of the vibrations with a frequency as low as ~50 Hz at a distance of 9270 m providing the same signal-to-noise ratio that is achievable with an expensive ultra-narrow linewidth OEwaves laser (OE4020–155000-PA-00)

Fine repetition rate tuning of harmonically mode-locked fiber laser using continuous wave injection

peer reviewedWe report on an optical injection as a new technique enabling fine one-by-one tuning of the pulse repetition rate (PRR) of a soliton harmonically mode-locked (HML) fiber laser built on the nonlinear polarization evolution (NPE)

Brillouin-like amplification in rare-earth-doped optical fibers

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Spectral compression in ring similariton fiber laser

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Double harmonic mode-locking in soliton fiber ring laser acquired through the resonant optoacoustic coupling

peer reviewedPassive harmonic mode-locking of a soliton fiber laser locked to optoacoustic resonance (OAR) in the cavity fiber ensures high-frequency laser operation, high pulse stability, and low timing jitter. However, the pulse repetition rate (PRR) of such lasers is limited to ∼1 GHz for standard fibers due to the available acoustic modes. Here, we address these limitations by demonstrating a soliton fiber laser built from standard fiber components and subjected to double harmonic mode-locking (DHML). As an example, the laser adjusted to operate at the 15th harmonic of its cavity matching the OAR at ∼199 MHz could be driven to operate at a high harmonic of this particular OAR frequency, thus reaching ∼12 GHz. This breakthrough is made possible through controllable optoacoustic interactions in a short, 50 cm segment of unjacketed cavity fiber. We propose that the precise alignment of the laser cavity harmonic and fiber acoustic modes leads to a long-lived narrow-band acoustic vibration. This vibration sets the pace for the pulses circulating in the cavity by suppressing modes that do not conform to the Vernier principle. The surviving modes, equally spaced by the OAR frequency, in cooperation with the gain depletion and recovery mechanism, facilitate the formation of stable high-frequency pulse sequences, enabling DHML. In this process, the OAR rather than the laser cavity defines the elementary step for laser PRR tuning. Throughout the entire PRR tuning range, the soliton fiber laser exhibits enhanced stability, demonstrating supermode suppression levels better than ∼40 dB and picosecond pulse timing jitter

Modeling of Brillouin-like amplification in rare-earth-doped optical fibers

editorial reviewedWe present a theoretical formalism to describe the amplification of two monochromatic waves counter-propagating in a rare-earth-doped optical fiber amplifier. Interaction of the waves through a dynamical population inversion grating inscribed in the active fiber by the waves during their amplification results in a strong power transfer from one wave to another providing a preferable amplification of one wave at the expense of another. In this sense, the effect is similar to stimulated Brillouin scattering and is expected to be observed with both pumped and unpumped rare-earth-doped fibers possessing a finite polarizability difference between the excited and ground states