Nagaatsu Ogasawara

Optical Bistability in a Semiconductor Laser Amplifier

Optical bistability has been observed in a semiconductor laser operating as an amplifier. The bistability arises from the refractive index change due to a decrease in the active-region carrier density accompanied by optical amplification. Output pulsations due to the competition between the free-carrier and thermal effects have also been observed.

A Nonlinear Optical Organic Crystal for Waveguiding SHG Devices: (-)2-(α-Methylbenzylamino)-5-Nitropyridine (MBANP)

A nonlinear optical organic material, (-)2-(α-methylbenzylamino)-5-nitropyridine (MBANP), has been comprehensively investigated with the objective of application to frequency doubling of laser diodes. Its molecular hyperpolarizability is as large as that of p-nitroaniline. MBANP crystallizes with a highly asymmetric molecular arrangement. The largest nonlinear optical coefficient, d22, is measured to be 60 pm/V. The corresponding figure of merit for frequency doubling at 1.064 µm is 3.5 times larger than that for d33 of LiNbO3. Cerenkov-radiation-type, phase-matched second-harmonic generation has been demonstrated utilizing the d22 coefficient by making use of an appropriate waveguiding structure.

Theoretical analysis of Cerenkov-type optical second-harmonic generation in slab waveguides

Optical second-harmonic generation in the Cerenkov-radiation scheme in slab waveguides has been theoretically investigated for all the possible type I configurations. By solving the nonlinear wave equations analytically, a simple general expression for the second-harmonic power has been obtained. Characteristics of the Cerenkov-type second-harmonic generation and optimum conditions for attaining high conversion efficiencies are discussed on the basis of the theoretical analysis. It is shown that, in order to attain high conversion efficiencies, off-diagonal elements of the nonlinear optical coefficient tensor should be utilized taking advantage of birefringence. >

Refractive Indices of 2-Methyl-4-Nitroaniline (MNA)

We report on the results of ellipsometric measurements of refractive indices and their dispersion over the wavelength range 500 nm-1100 nm on a single-crystal thin film of 2-methyl-4-nitroaniline (MNA). The refractive indices show large anisotropy attributable to the orientation of the molecular dipole moment.

Static and Dynamic Properties of Nonlinear Semiconductor Laser Amplifiers

Optical memory, differential amplification and optical limiting have been experimentally achieved in an AlGaAs laser amplifier, demonstrating the feasibility of nonlinear optical signal processing using semiconductor laser amplifiers. The results of the analysis of the dynamic properties of semiconductor laser amplifiers are also presented; subnanosecond and femto-Joule switching, critical slowing down and output spiking due to self-tuning at the onset of light injection have been analyzed.

Linewidth Enhancement Factor in GaAs/AlGaAs Multi-Quantum-Well Lasers

The linewidth enhancement factor α in GaAs/AlGaAs multi-quantum-well (MQW) lasers has been determined from the spontaneous emission spectra below threshold. It is demonstrated that the value of α in MQW lasers is appreciably smaller than that in conventional double heterostructure (DH) lasers because of the enhanced carrier-density-derivative of the optical gain.

Multiple-Reflection Effects in Optical Second-Harmonic Generation

We report the first observation of multiple-reflection effects in optical second-harmonic generation. The observation has been made possible by the use of a single-mode laser diode as a light source. The experimental results agree excellently with a theoretical analysis which takes account of the multiple reflections of both the fundamental and harmonic waves.

An Extended X-Ray-Absorption Fine-Structure Study of Bond Lengths in GaAs1-xPx

Extended X-ray-absorption fine-structure measurements were performed on GaAs1-xPx, a typical III-V-V type semiconductor alloy, with the composition x as a parameter. The results reveal that the Ga-As and Ga-P nearest-neighbor bond lengths differ, showing a tendency to retain their respective bond lengths in the binary compounds. This feature is similar to that found earlier in Ga1-xInxAs, a III-III-V type alloy.

Transient Temperature Variation of Injection Lasers

We have observed the transient temperature variation of the active region of injection lasers. It is found that the heat generated in the active region is only about half the total input power. Analysis on the heat generation mechanisms suggests that the leakage current must be taken into account in buried-heterostructure lasers.

Second Harmonic Generation in an AlGaAs Double-Heterostructure Laser

Second-harmonic radiation emanating from an AlGaAs transverse-mode-stabilized laser diode has been observed under continuous-wave operation at room temperature. The far-field beam width of the second-harmonic radiation has been found to be apprecialy narrower than that of the fundamental laser radiation.