Dmitriy Panasenko

Time-domain waveform processing by chromatic dispersion for temporal shaping of optical pulses

We describe a novel method for subpicosecond pulse shaping based on longitudinal spectral decomposition in dispersive media. The entire system is created with standard telecommunications equipment allowing for integration with optical communication networks. The technique has the potential for time–bandwidth products ⩾104 due to exclusive reliance on time-domain processing. We introduce the principle of operation and subsequently support it with results from our experimental system. Both theory and experiments suggest third-order dispersion as the principle limitation to realizing a large number of resolvable spots. Chirped fiber Bragg gratings offer a route to increase the time–bandwidth product for high-speed signal processing applications.

Er-Yb femtosecond ring fiber oscillator with 1.1-W average power and GHz repetition rates

We report an all-fiber passively mode-locked femtosecond laser oscillator based on the heavily doped Er-Yb phosphate-glass active fiber. Only 20 cm of the gain fiber is sufficient to produce as much as 1.1 W of average output power at 1.5 /spl mu/m directly from the oscillator. The laser can be harmonically mode-locked at repetition rates ranging from 1.7 to 7.2 GHz by adjusting the polarization bias in the cavity. The pulsewidth varies from 300 to 570 fs at the lowest and the highest repetition rate, respectively, and the maximum peak pulse power exceeds 1 kW.

All-Fiber Picosecond Laser System at 1.5

Amplification of ultrashort pulses in doped fibers is limited by an onset of nonlinear effects in the fiber. At the 1.5-mum wavelength, single-mode fibers typically have anomalous dispersion. The self-phase modulation combined with dispersion leads to instability of multinanojoule pulses in such fibers. Various techniques developed to amplify pulses beyond the nonlinearity limit typically rely on a delicate balance between dispersive and nonlinear effects in different parts of the laser system. We report a simple all-fiber alternative to these complex techniques that utilizes a rapid amplification of pulses in a short and heavily doped phosphate-glass active fiber. In our preliminary experiments, picosecond pulses at 1.5 mum generated by a passively mode-locked fiber oscillator at a repetition rate of 70 MHz are amplified in a 15-cm-long heavily Er-Yb codoped fiber amplifier to the average output power of 1.425 W. The pulse energy and peak power reach 20.4 nJ and 16.6 kW, respectively, while the pulse distortion is minimal in both temporal and spectral domains. Further power up-scaling is possible by using active phosphate fiber with a large mode area, in the amplifier stage

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We report on a passively mode-locked all-fiber laser oscillator at 1.5 microm based on heavily doped phosphate-glass active fiber. An active fiber only 20 cm long is sufficient to produce as much as 2.4 W of average output power directly from the oscillator. The width of the mode-locked pulses varies from 8 ps at the lowest output power in the mode-locked state to 44 ps at the highest power. Our picosecond laser oscillator features a high repetition rate of 95 MHz and high peak pulse power of approximately 540 W. The oscillator combines the convenience of all-fiber construction with power performance that was previously achievable only with mode-locked bulk-optic laser oscillators or more complex systems involving fiber amplifiers.

m Based on Amplification in Short and Heavily Doped Phosphate-Glass Fiber

Microstructured and multi-core fiber lasers were fabricated that have produced more than 1.3 W/cm at 1.5 mum. Near 2 W single frequency, single-transverse-mode output was demonstrated

All-fiber passively mode-locked laser oscillator at 1.5 μm with watts-level average output power and high repetition rate

We report using short, heavily-doped active phosphate fiber for generation of picosecond pulses at 1.5 mum, with the peak power of 19 kW which results in a record-high aerial power density of 24 GW/cm2 in the fiber core.

Microstructured and multicore fibers and fiber lasers

We report passive harmonic mode locking of Er/Yr doped phosphate fiber ring laser. The laser can be mode-locked at repetition rates from 1.7 to 7.2 GHz producing pulses with durations from 300 fs to 570 fs and 1.1 W of average power.

All-fiber source of high-power picosecond pulses at 1.5μm using short heavily-doped phosphate-fiber amplifier

We describe novel methods for waveform synthesis and detection relying on longitudinal spectral decomposition of subpicosecond optical pulses. Optical processing is performed in both all-fiber and mixed fiber/free-space systems. Demonstrated applications include ultrafast optical waveform synthesis, microwave spectrum analysis, and high-speed electrical arbitrary waveform generation. The techniques have the potential for time bandwidth products ≥104 due to exclusive reliance on time-domain processing. We introduce the principles of operation and subsequently support these with results from our experimental systems. Both theory and experiments suggest third order dispersion as the principle limitation to large time-bandwidth products. Chirped fiber Bragg gratings offer a route to increasing the number of resolvable spots for use in high speed signal processing applications.

High average power harmonically mode locked ring laser based on phosphate glass fiber

Heavily doped active fibers based on the soft phosphate glass offer an attractive gain medium for compact and high-power laser oscillators. We report a passively modelocked fiber oscillator at 1.5μm based on such active fiber. The standing-wave laser cavity consists of a 20cm-long piece of the side-pumped active phosphate fiber which is heavily co-doped with Er and Yb ions, and a low-ratio fused coupler. The length of the all-fiber laser cavity is 65cm. The modelocked operation of the oscillator is started and sustained by a Semiconductor Saturable Absorber Mirror (SESAM), and no additional pulse narrowing mechanism is used. In order to avoid a premature over-saturation of the SESAM, the fiber end which is butt-coupled to the SESAM is adiabatically tapered which expands the propagating fiber mode and decreases the power density incident on the absorber substantially. The stable modelocked operation of the laser oscillator occurs in the range between 0.65W and 2.3W of the average output power, which is limited by the maximum available pump power at 975nm. The peak pulse power is limited by the saturated SESAM at ~450W, and the pulse width grows from 11psec to 35psec as the pump power is increased. At the pulse repetition rate of 160MHz, the pulse energy reaches 14.4nJ. Our laser oscillator combines the convenience of the all-fiber construction with the power performance previously achievable only with the modelocked bulk-optic laser oscillators or more complex systems involving fiber amplifiers.

Information processing with spectral decomposition of ultrafast pulses in the time-domain

R optical fiber sources of ultrashort pulses hold promise for replacing their bulky and expensive counterparts, and bringing ultrafast technology from the research lab into the real world. Potential applications include material processing, nonlinear optics, biomedical imaging, remote sensing and optical frequency metrology. The main obstacle to reaching this goal is nonlinearity in the gain fiber: Light propagating in a single-mode fiber is tightly confined in the fiber core, and amplification of ultra-short pulses in conventional meters-long doped fibers is limited by the onset of self-phase modulation and stimulated Raman scattering. The various techniques that have been developed to beat the nonlinearity with 1.1 1020 ions/cm3 of Er+3 and 8.6 1020 ions/cm3 of Yb+3 ions. These concentrations are higher than those possible in fused silica, a common fiber material, by at least an order of magnitude. The short-pulse operation of the oscillator is initiated by the semiconductor saturable absorber mirror (SESAM), which serves as one of the reflectors in the standing-wave laser cavity. The other is a highly chirped fiber Bragg grating. The oscillator produces picosecond pulses at a repetition rate of 70 MHz with average power of 60 mW. This optical signal is amplified in a short phosphate-fiber amplifier to the average power of 1.5 W. The peak pulse power of the pulses reaches 17 kW. The corresponding aerial power density in the fiber core at the output of the system is 21 GW/cm2, which is the highest among all ultrafast fiber-laser systems at 1.5 m that have been reported previously. In spite of such high power density, both temporal and spectral distortion of the pulses is minimal, as indicated by the nonlinear autocorrelation of the pulses and optical spectrum before and after amplification (see figure graphs). Further power up-scaling is clearly possible by using a large-mode area fiber in the amplifier stage.