L. E. Nelson

77-fs pulse generation from a stretched-pulse mode-locked all-fiber ring laser.

By incorporating a section of large positive-dispersion fiber in an all-fiber erbium ring laser, we obtain high-energy pulses with spectral widths of 56 nm. The chirp on these pulses is highly linear and can be compensated for with dispersion in the output coupling fiber lead. The result is a fully self-starting source of 77-fs pulse with 90 pJ of energy and greater than 1 kW of peak power at a 45-MHz repetition rate.

Stretched-pulse additive pulse mode-locking in fiber ring lasers: theory and experiment

additive pulse mode-locking uses segments of fiber of large positive and large negative group velocity dispersion (GVD) in the cavity. The changes in pulse width per pass due to the varying GVD can be an order of magnitude or more. A theory is developed based on the master equation that covers this case of large pulse changes in one transit. The general predictions of the theory are verified by experimental results.

Broadly tunable sub‐500 fs pulses from an additive‐pulse mode‐locked thulium‐doped fiber ring laser

We report an additive‐pulse mode‐locked (APM) thulium‐doped fiber ring laser producing 350–500 fs pulses tunable from 1798 to 1902 nm. The laser operates in the soliton regime, where periodic perturbations cause predictable sidebands and modulation in the optical spectrum.

Soliton versus nonsoliton operation of fiber ring lasers

To date most passively mode‐locked erbium‐doped fiber laser systems have employed solitons for short pulse generation, and ultrashort high energy pulses have been difficult to achieve. We show that by reducing the system nonlinearity via pulse stretching and employing net positive dispersion cavities, pulses of sub‐100‐fs duration and ≳100 pJ energy are readily generated. Data are presented for varying net dispersion in a fiber ring.

Technique for obtaining high-energy ultrashort pulses from an additive-pulse mode-locked erbium-doped fiber ring laser

We report a self-starting stretched-pulse polarization additive-pulse mode-locked erbium-doped fiber ring laser with high output power. By using the light normally absorbed by the intracavity polarizer as the output, we obtained pulses with energies greater than 0.5 nJ at a repetition rate of 48 MHz. External chirp compensation was used to shorten the highly chirped output pulses to durations of less than 100 fs. The power levels suggest that erbium-doped fiber lasers may replace bulk solid-state lasers, such as the color-center laser, for some applications.

Efficient frequency doubling of a femtosecond fiber laser

We report optimization of a stretched-pulse erbium-doped fiber laser for second-harmonic generation and the evaluation of several nonlinear crystals for this application. With compressed fundamental pulse energies of 2.7 nJ at 31.8 MHz, we achieved 10% conversion efficiency and 86-fs, 771-nm pulses with energies of 270 pJ. Frequency-resolved optical gating was used to analyze both the fundamental and the frequencydoubled pulses.

Effect of third-order dispersion on passive mode locking

The effect of third-order dispersion on the width of mode-locked pulses is investigated analytically and numerically. The pulse width increases monotonically with increasing third-order dispersion as a consequence of the symmetric chirp introduced by it. The chirp broadens the bandwidth and lowers the gain. Computer simulations show the appearance of a resonant sideband that also taxes the gain. Reducing the filter bandwidth partially suppresses the sideband and narrows the pulse.

Diode-pumped environmentally stable stretched-pulse fiber laser

We present results obtained with a stretched-pulse polarization additive pulse mode-locked (P-APM) fiber laser using an environmentally stable cavity design. With 980-nm diode-pumping levels of 200-mW 1.2-nJ pulses with 50 nm of spectrum are obtained. These pulses can be externally compressed to sub-100 fs. The effects of high output coupling (>80%) and pumping configuration on output performance an d intracavity pulse dynamics are studied.

Ultrafast Fiber Lasers

Erbium-doped fibers are making it possible to develop compact, diode-pumped sources of ultrashort pulses for a variety of applications. Operating principles of these devices are reviewed and recent experimental progress in our laboratory on soliton and stretched-pulse lasers is described.

Additive pulse limiting

Actively modelocked lasers are convenient sources of transform-limited pulses which are synchronized to a master clock in optical communications. A convenient source for communications is the erbium fiber laser, which generally has a cavity length 1 m or greater. To achieve a high bit-rate, 1 Gbit/s or greater, with such a long-cavity laser, the modelocking may be done at a harmonic of the laser roundtrip frequency with multiple pulses in the pulse. It has been found in such cases that the pulse energies may fluctuate from pulse to pulse. This is due to the fact that the relaxation time of the gain medium is much longer than the laser roundtrip time, and thus the saturation of the gain medium cannot stabilize against such fluctuations.<<ETX>>