C. R. Doerr

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.

Additive-pulse limiting.

When lasers with a long gain-relaxation time are actively mode locked at a harmonic of the round-trip frequency, the energy fluctuates from pulse to pulse unless stabilized. We report a new principle for pulse energy stabilization in harmonically mode-locked lasers.

Soliton fiber ring laser stabilization and tuning with a broad intracavity filter

The periodic perturbations to the soliton in passively mode-locked fiber soliton lasers cause dispersive wave shedding, which lead to sharp spectral sidebands that limit pulse duration. By using a broad intracavity birefringent plate filter, the side-bands are greatly reduced, and the pulse duration is shortened. The filter also allows wavelength tuning, and a 43 nm continuous tuning range is demonstrated for pulses of 311-357 is duration in a fully self-starting diode pumped system.<<ETX>>

Asynchronous soliton mode locking

We report a harmonically mode-locked erbium-doped fiber ring laser with short solitons. A phase modulator running asynchronously with the pulses provides pulse start-up, continuous background cleanup, and a new form of pulse timing stabilization. Steady-state operation of picosecond solitons at a repetition rate of 1 GHz was obtained with no need for modulator drive frequency stabilization.

Sub-shot-noise measurement with fiber-squeezed optical pulses.

A novel scheme employing two pulses separated by a short time delay is used to cancel the phase noise from guided-acoustic-wave Brillouin scattering in a fiber ring interferometer. The dual-pulse-excited fiber ring is used to generate squeezed vacuum that, when injected into a measuring Mach–Zehnder interferometer, improves its sensitivity by 3 dB beyond the shot-noise limit.

Additive-pulse mode-locking/limiting storage ring.

A pulse-storage ring is an optical device capable of memorizing a pulse sequence of 0s and ls. The soliton ring of Nakazawa et al. [Electron. Lett. 29, 729 (1993)] with nearly unlimited transmission distance is such a device. We propose and experimentally demonstrate a different type of pulse-storage ring that uses intensity-dependent interferometric action to create a stronger intracavity transmission differential between the 0s and the ls.

Orthogonal polarization fiber gyroscope with increased stability and resolution

The orthogonal polarization fiber gyroscope (OPFG) is an interferometric fiber gyroscope design that requires no phase bias in the fiber ring and is insensitive to light-source intensity noise. However, in the original OPFG [Hitachi Rev. 33, 215 (1984)], environmental changes caused first-order false rotation signals. We propose and experimentally verify modifications that eliminate the first-order sensitivity to environmental changes and that improve the gyroscopes resolution as well. We believe that this modified OPFG is the first interferometric fiber gyroscope capable of stable, high-sensitivity measurement that contains only reciprocal optical elements.

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>>

Dispersion of pulsed squeezing for reduction of sensor nonlinearity

In applications of pulsed squeezed light in sensors, the high peak intensity of the light used in the squeezer will also cause nonlinearity in the sensor, destroying some of the quantum noise reduction. A dispersive element inserted between the squeezer and the sensor reduces the sensor nonlinearity, leaving the squeezing unaffected.

Quantum Noise Reduction Using a Nonlinear Sagnac Loop with Positive Dispersion

Recent experiments at MIT using light from a mode-locked Nd:YLF laser at 1.3µm in a fiber Sagnac loop have achieved noise levels 5.1dB below shot noise. In these experiments, squeezing is limited by the gaussian shape of the pump pulses. We show that by operating the interferometer away from 1.3µm that limitation can be overcome. For these wavelengths the group velocity dispersion of silica fibers creates negative correlations between the noise on different parts of the pump.