R. S. Grant

Two‐photon absorption and self‐phase modulation in InGaAsP/InP multi‐quantum‐well waveguides

We report the first measurement of two‐photon absorption (TPA) and self‐phase modulation in an InGaAsP/InP multi‐quantum‐well waveguide. The TPA coefficient, β2, was found to be 60±10 cm/GW at 1.55 μm. Despite operating at 200 nm from the band edge, self‐phase modulation as high as 8±2 rad was observed for 30‐ps optical pulses at 3.8‐W peak input power. A theoretical calculation indicates that this enhanced phase modulation is primarily due to bandfilling in the quantum wells and the free‐carrier plasma effect.

Passive coupled-cavity mode-locked color-center lasers

Stable, self-starting operation of a coupled-cavity mode-locked KCl:T1(0)(1) color-center laser has been achieved by incorporating a semiconductor diode optical amplifier into the control cavity. By adjustment of the amplifier drive current, nonlinearity in the regimes of either saturable gain or saturable absorption has been exploited to generate subpicosecond pulses. Under conditions of saturable gain, pulse durations as short as 280 fs were obtained. Self-starting has also been demonstrated for a coupled-cavity mode-locked NaCl:OH(-) color-center laser by using the same technique.

All‐optical modulation with ultrafast recovery at low pump energies in passive InGaAs/InGaAsP multiquantum well waveguides

We report on the observation of ultrafast (<1 ps) recovery of all‐optical modulation based on below band gap, optically induced excess absorption using pump pulse energies of less than 4 pJ. At higher pump pulse energies, the hot carriers produced by two‐photon absorption significantly reduce the recovery rate. The increase in absorption recovery times at the higher densities of hot carriers is consistent with a contribution to the nonlinear absorption change from hot electron assisted absorption. The measured hot electron assisted absorption cross section of 2×10−20 m2 is in good agreement with the theoretical value.

Polarization and field dependent two-photon absorption in GaAs/AlGaAs multiquantum well waveguides in the half-band gap spectral region

We report the observation of two photon absorption which is strongly dependent on the applied electric field and the optical polarization. At 1.55 μm wavelength, the two‐photon absorption coefficient of the GaAs/AlGaAs multiquantum well (MQW) waveguides for transverse‐magnetic light is about seven times lower than for transverse‐electric polarized light and changes by a factor of approximately 4 for a change in applied direct‐current electric field of ∼140 kV/cm. Ultrafast nonlinear refraction causing phase changes of over π radians without appreciable excess loss is observed. These measurements demonstrate that GaAs/AlGaAs MQW waveguides could be successfully used for subpicosecond all‐optical switching near half‐band gap, at wavelengths corresponding to the 1.55 μm optical communications band.

Amplitude noise reduction of a coupled-cavity mode-locked NaCl:OH- color-center laser by active synchronization.

Stable noise-free operation of a coupled-cavity mode-locked NaCl:OH− color-center laser was obtained by synchronizing it to the mode-locked Nd:YAG pump laser. This stabilization technique, based on active cavity-length control of the color-center laser, eliminated the amplitude modulation of the output power arising from the beating of the pump laser pulse train with the color-center laser pulse train.

Self-mode-locked NaCl:OH- color-center laser

We have demonstrated self-mode locking of an NaCl:OH,(-) color-center laser by exploiting the Kerr effect in a rod of high-nonlinearity glass placed within the laser cavity. The mode-locking process was initiated by a regenerative acousto-optic modulation, and sub-100-fs pulses were produced at wavelengths of ~1575 nm.

Coupled-cavity mode locking with passive semiconductor waveguides

Coupled-cavity mode locking of a KCI:TI color-center laser has been achieved with passive waveguides fabricated in the AlGaAs material system. The ultrafast refractive nonlinearity at the half-band gap is exploited by the laser to produce pulses as short as 230 fs at operating wavelengths of ∼1520 nm.