Effects of the taper-joining of two single-mode fibers, where the fibers are first spliced by fusion, and are then heated and stretched to form the taper-joint, are analyzed and discussed. Due to reductions both in the lateral and angular offsets in the process of forming the taper, the loss can be reduced by one tenth, which is much smaller than that in the case where fibers are spliced after the formation of the taper. It is also pointed out that the joint must be kept straight to avoid the radiation loss due to curving of the joint. Finally, it is ascertained experimentally that the taper joint can be obtained by the arc-discharge method in both the splicing and the stretching processes.

In order to find the optimum index profile of the single-mode optical fiber with respect to the cabling loss due to the random bends with the Gaussian correlation function, the relation between the random-bend loss and the index profile is investigated. The formula of the random-bend loss is derived for arbitrary index profile. In the derivation, the loss is calculated as the power of dipole radiation due to the equivalent refractive index perturbation in contrast with the conventional mode coupling analysis. Using this formula, random-bend losses are calculated for four types of index profiles; the convex, parabolic, step, and concave type of index profiles, under the condition that connection losses are same for all types of profiles. As results of the comparison, the random-bend loss is minimum in the case of the convex type of profile and it is decreased down to 40% of that in the case of the step profile.

It was shown experimentally that the noise, which is estimated to be due to mode hopping among modes composed of a laser mirror and an external reflection point, was suppressed in distributed-Bragg-reflector(DBR) single mode lasers biased above a certain level. This tendency agree with our theoretical prediction.

An electron-wave device consisting of a hot electron transistor structure with a transversal potential grating in a base region is proposed. A reduced transit time and extremely small charging times provide significant potential for high-speed operation.

Mass transport was first employed in an OMVPE system for 1.55 µm GaInAsP/InP laser. The wafers grown by OMVPE were treated at 700 under cracked PH3 and H2+N2 atmosphere for 1 hr, resulting in buried structure and the BH laser showed low threshold current of 50 mA (pulsed) without optimization.

For the dynamic single mode (DSM) laser, the condition for suppression of the noise caused by the mode hopping among composite resonator modes induced by an external reflection is derived theoretically. The gain suppression effect in the laser media suppresses the mode hopping noise under the appropriate laser parameters and the operating conditions. Theoretical results were verified by experiment of noise measurement of BIG-DBR type DSM lasers.