We have demonstrated for the first time, to the best of our knowledge, the successful direct amplification of a cylindrical-vector beams with axially symmetric polarization and doughnut-shaped intensity profile in picosecond MOPA system based on a double-clad ytterbium-doped spun tapered fiber with a ring-shaped active core. The output radially polarized beam with absolute contrast between bright and dark zones carries 10 ps pulses at 1030 nm with a 14.5 W average power level, 91 kW peak power and 0.97 μJ pulse energy.
In this study we demonstrate high power master oscillator power amplifier (MOPA) laser system delivering 50 ps pulses and capable to work in wide range of repetition rates. The gain-switched (GS) fiber coupled diode is used as a seed source to provide microwatt power level pulses at 1039.5 nm with FWHM 50 ps duration at a repetition rate in the range of 1 to 20 MHz. The maximum achieved amplified average power at 20 MHz repetition rate was measured to be 513 W corresponding to 481.9 kW of peak power and 25.7 µJ pulse energy. The gain of high-power amplifier reached over 44 dB with around 69% slope efficiency. Almost all optical power (<97%) was enclosed in the pulsed signal. In contrast, with repetition rate decreasing, the part of the optical power contained in the pulsed signal began to decrease, which directly follows from the spectra. The fraction of signal radiation decreased to about 50 % at maximum achieved power of 338.9 W at a repetition rate of 1 MHz. The peak power and the pulse energy in this case may be estimated as 3.2 MW and 169.5 µJ (in the limits of signal spectral bandwidth) respectively and corresponds to over 52 dB of gain with 60 % slope efficiency. The pulse duration changed insignificantly during amplification. Herewith advantages of polarization maintaining tapered double-clad optical fiber (PM-T-DCF) having near single mode input core diameters were allowed to maintain modal content during amplification and preserve near single mode output without significant deterioration
We developed ytterbium-doped double-clad large mode area (MFD = 30 μm) spun tapered fibers with low internal birefringence and perfect beam quality (M2 < 1.2). Picosecond MOPA system (95ps/100 MHz, 1064 nm) based on proposed active tapered fiber with output average power of 64 W (gain 32 dB) is demonstrated.
We present a single-mode narrow band linear-polarized picosecond green fiber source delivered up to 146.4 kW of peak power. The laser architecture is composed of frequency-doubled all-fiber MOPA system operating at 1064 nm. The commercially available gain-switched semiconductor laser diode was used as a seed source delivered 77 ps pulses with the repetition rate between 100 kHz - 80 MHz. Two stages of pre-amplifiers based on the single-mode Yb-doped fibers were designed to amplify microwatt pulsed signal up to milliwatt level. A high-power amplification cascade comprised a double-clad polarization-maintaining tapered Yb3+-doped fiber as a gain medium. The frequency doubling was realized in a single-pass scheme with LBO crystal. The MOPA design with the active tapered fiber enabled to amplify effectively a narrowband picosecond IR radiation with relatively small spectral broadening. We obtained stable laser radiation with 77 ps pulses at repetition rate of 1 MHz, 290 pm spectral bandwidth with a central wavelength of 532 nm, the average power of 12 W corresponding to 12 μJ of pulse energy and 146.4 kW of peak power. The overall efficiency of secondharmonic generation reached 37 % in a single pass scheme. The obtained results showed advantages of the MOPA system based on a tapered amplifier in comparison with already published picosecond green laser systems exploited standard amplifiers based on cylindrical fixed-core fibers. The single-mode green laser with high peak power and narrow line are in high demand for a wide range of Raman spectroscopy applications.
This paper presents a solution to one of the major problems of plasmonic fiber Bragg grating sensors concerning their high sensitivity to changes in the polarization state of light propagating through optical fiber. For the first time these kind of sensors have been produced using polarization maintaining fibers, thereby stabilization has been achieved using mechanical action and bending the supplied fiber. Comparative experiments have demonstrated that the sensor readings stability is at least an order of magnitude higher relative to other sensors, which record in a standard fiber with an isotropic structure.
An optical scheme for polarization encoding BB84 protocol is described. Fiber electro-optical LiNbO3 phase modulators based on Pockels cells provide both polarization states generation for Alice and basis choosing for Bob at high frequency, requiring low operation voltages (Vπ < 5V). Proposed scheme uses only one laser source, which guarantee the indistinguishability of the pulses and active basis choosing allows the system to have two single photon detectors in contrast to the four in the standard polarization encoding schemes. Two phase modulators compensate each others’ polarization mode dispersion, caused by the natural birefringence of the lithium niobate crystal. The system consists of standard components and has simple configuration. The principle of operation is experimentally demonstrated.
We have experimentally investigated fundamental mode propagation in few-meter-long adiabatic step-index tapers with high numerical aperture, core diameter up to 117μm (V=38), and tapering ratio up to 18. We confirmed single fundamental mode guiding in tapers with uniform core index profile by several experiments. We observed an annular near field distribution and degraded beam quality for large output core diameters, found to occur due to intrinsic mechanical stress in the fibers. We expect that eliminating the stress would prevent the mode deformation and allow constructing single-mode, diffraction-limited tapered large-mode-area amplifiers with a good beam shape.
We present a comparative theoretical and experimental study of different schemes of fiber lasers with tapered doubleclad
fiber (T-DCF) as an active medium. We have developed a theoretical model for obtaining the distribution of power
and power density inside the fiber for the considered laser schemes with different longitudinal shapes of T-DCFs. The
slope efficiencies, spectral characteristics, and beam quality deterioration associated with the mode conversion in the TDCF
were also studied experimentally for different laser schemes. In addition, a spontaneous transition to a self-pulsing
regime under certain conditions, and the associated problems have been investigated. Characteristics of T-DCF lasers
constructed in co- and counter-propagating schemes are discussed and compared to those of regular fiber lasers,
equivalent in active volume or in brightness.
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