M. Shirasaki

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.

Squeezing in a fiber interferometer with a gigahertz pump

We report 5.1 dB of squeezing from a fiber interferometer pumped with a 1-GHz pulse source that successfully eliminates guided-acoustic-wave Brillouin scattering in significant frequency regimes. The pulse source is a diode-pumped Nd:YLF laser actively mode locked at 1.314 microm. The squeezing results are consistent with the limits imposed by the Gaussian pulse shape and the detection quantum efficiency.

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.

Analysis and measurement of GAWBS spectrum in a nonlinear fiber ring

The spectral density of the phase noise of an optical pulse in a fiber produced by guided acoustic wave Brillouin scattering (GAWBS) is derived from first principles. The predictions are in good agreement with the experimental results in a fiber interferometer. The experiments show that the lower limit on the quantum noise reduction is set by GAWBS. The GAWBS are of sufficiently low level to permit 5 dB squeezing.

Reduction of guided-acoustic-wave Brillouin scattering noise in a squeezer.

A new scheme for interferometric measurements that uses squeezed light produced in an optical fiber ring is proposed. Guided-acoustic-wave Brillouin scattering noise is suppressed by cancellation of the phase fluctuations caused by this scattering in two consecutive pulses that are pi phase shifted with respect to each other.

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.

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.

Squeezing with fiber Sagnac loop and sub-shot-noise measurement

Squeezed states of light are minimum uncertainty states for which the mean square fluctuations in phase and in quadrature with respect to a reference signal are unequal. Among other interesting properties, they provide improved sensitivity of optical interferometric phase measurements. To understand this potential, one must note that quantum theory imposes measurement uncertainty only on a pair of noncommuting variables; the measurement of any one quantum observable could be done with no uncertainty.<<ETX>>