In this paper we report on amplitude and group delay distorsion in optical fibres. Theoretical results are derived from the ray optics calculations. We show how we modified our frequency domain equipment previously designed for amplitude and phase vs frequency recording: experimental datas on step index fibres are given in 5-45 MHz frequency range. Final broadband remote operation system is discussed.

A directional coupler type light modulator connected to a single mode optical fiber, was fabricated using Ti-diffused LiNbO3 waveguides. Two 8 µm wide parallel waveguides separated by 5 µm with 15 mm interaction length were used. Modulation characteristics at the infrared wavelength of 1.15 µm were as follows; 4.0 V modulation voltage, 1.0 GHz 3 dB bandwidth, 17.6 dB extinction ratio and 8.2 dB optical insertion loss.

Ultimate limit of the bandwidth of the multimode optical fiber with the index profile consisting of α-power and the fourth-order terms of radius is derived, rejecting the effects of the cladding and compensating the material dispersion. The 3 dB-bandwidth can be increased up to 1.9 GHz at 10 km length.

Step index fibers having borosilicate cladding and phosphorilicate core are fabricated by drawing the preform prepared by a modified CVD method. These are 0.17 in N.A., 150 µm in fiber diameter, 15 µm in cladding thickness and 60 µm in core diameter. The influences of drawing temperature, speed and tension upon transmission losses of fibers are investigated, the following results are obtained; (1) the Rayleigh scattering coefficient does not vary with drawing conditions, but (2) the loss due to imperfections of waveguides is increased by drawing under improper tensions and (3) an excess loss in short wavelengths are induced by drawing at high temperature. From the measurement of residual strain, it is found extensive strain in cores of fibers having the excess loss. It is concluded that an increase of the loss vesults from imperfections in the core-cladding interface caused by drawing under improper tensions, and that the excess in short wavelenghts is induced when the preform is drawn under such conditions to cause the extensive residual strain in a core. It is a phenomenon similar to the rupture of Si-O bond.

We have developed a flat type multi-fibers cable which is intended to use in data bus. As the broad-band characteristics is not necessarily required in such systems, we adopted the silicone cladding pure silica core fiber for the constitution unit of the flat type cable which has 10 optical fibers. The flat type cable is 5 mm wide and 0.5 mm thick and 1 km long. Core diameter and cladding diameter of silicone clad optical fiber is 150 µm and 360 µm respectively and refractive index difference between core and cladding is approximately 3.6%. In order to prevent silicone clad fiber from optical and mechanical damages due to handling and enviromental forces, they are jacketed with polyester elastomer of 0.5 mm in diameter. Mean value of the transmission losses of 10 fibers of the flat cable is 3.6 dB/km and the standard deviation of losses is 0.3 dB/km at 0.82 µm. This flat cable could be advantageous in solving the problems of inductive disturbance from electrical equipment and cable congestion in comparison with the usual cable with copper conductor. As the results of many optical and mechanical tests on the cable, we found it possible that the cable can be used pratically.

Spontaneous carrier lifetimes in InGaAsP/InP double heterostructure lasers emitting at1.3µm were experimentally determined from lasing delay time measarement. Various step-current superposed on bias current was applied to a laser diode with 20 µm-stripe geometry. The carrier lifetime apparently decreased with increasing bias current from 4-5 ns at non-biased state to2 ns at well biased state. This change in the measured lifetime was explained by considering the effect of junction capacitance. It was shown that the effect was almost removed by the application of bias current of more than1 kAcm-2. µm-1 and then the intrinsic lifetime was obtained. Deduced carrier lifetime well agreed with that estimated from relaxation oscillation measurement.

Spectra of the stimulated Raman scattering in silica glass and benzene filled capillary fibers have been observed. No antistokes bands have been seen in glass and weak anomalously shifted antistokes band have been seen in benzene capillar. The localization of stokes band has been determined by the cascade scattering on two normal vibrations of silicate and phosphate tetrahedra in glass and those of benzene molecules in liquid.

The fabrication of strong optical fibers by drawing methods with CO2 laser and with oxyhydrogen flame as the heat sources have been reported. On the other hand, it is well known that a drawing method with furnace is superior in massproduction and in stability of temperature. It is generally considered that the fracture of a glass fiber occurs from the flaws existing on the fiber. To eliminate these flaws, we have developed a drawing machine having a furnace with a carbon resistance heater, and studied the fiber drawing conditions with the newly developed machine. We have obtained optical fibers with high tensile strength in the optimum condition. The average tensile strength of the fibers is 4.7 GN/m2, and the Weibull plot is almost linear and steep. In the proof test, no failure was observed at 1.1 GN/m2 over 1 km long.

Experimental and theoretical studies have been carried out on propagation in curved single-mode optical fibres. Mode conversion at the start of a bend produces a transition region which affects the bend loss, transverse energy distribution and gives rise to ray emission. It is shown that the modes of a curved multimode fibre can be conveniently and simply described using parabolic cylindrical co-ordinaces.

The Blodgett-Langmuir molecular film technique has been used to deposit an organic, crystalline, birefringent film on a fused quartz substrate with very accurate control on thickness (1). Modes excited with a prism-film coupler permit the determination of the film's permittivity tensor and thickness by correlating the experimental data with theory.

We describe the use of integrated optical waveguides for the study of locally illuminated superconductors. The creation of optically controlled Josephson junctions is discussed.

DH lasers are believed to be one of the most suitable light sources for optical fiber transmission. However, the light output of DH lasers has usually such detrimental effects as a relaxation oscillation and a spectral broadening during pulse response. For high bit rate and long-distance fiber transmission, lasers need to have a high performance pulse responce and a narrow spectral width. We examined the dynamic characteristics of GaAs/GaAlAs DH lasers, which had an internally striped planar (ISP) structure using sulfur diffusion, by changing the stripe width. By narrowing the stripe width to the range of 5 to 7 µm of ISP lasers with an undoped active region and the cavity length of about 150 µm, significant improvement was achieved in frequency response, pulse response and spectral behavior as well. The frequency response was flat up to 2 GHz without a resonant-like peak. The relaxation oscillation was suppressed up to 10-mW light output. The spectral width at 400-Mb/s modulation was controlled within 20 without degradation of extinction ratio. Threshold currents were in the range of 55 to 70 mA. The light output increased linearly up to 10 mW without a kink. The external differential quantum efficiency was about 60 %. These lasers are operating stably after more than 1,000 hours at 70 under 3-mW light output. A narrow stripe-geometry ISP laser has a promising feature in that it can be used in high bit rate and long-distance fiber transmission.

Optical waveguiding phenomena at 10.6 µm have been observed in evaporated amorphous Se films with Au-cladding. The far-field analysis has shown that the fundamental TE0 mode is most dominantly confined. The results show that amorphous Se can be used to form planar waveguides for the 10.6 µm radiation of a CO2 laser. It has been also observed that the attenuation of TM modes is much larger than that of TE modes in accordance with the theory of the metal-clad optical waveguides. As an application, a photoelastic modulator utilizing a piezoelectric resonance of the Au-clad amorphous Se waveguide has been fabricated. The PZT piezoelectric ceramics is used as the substrate to excite mechanical vibration. The modulator is operated around its fundamental length-expanding resonance of 211.2 kHz. The band-width and the half-wave voltage are determined to be 5.4 kHz and 55 V, respectively.

The accuracy of the formulas for calculating the refractive index profile from its tansverse interference pattern is investigated in detail by computer simulations. The principle error is confirmed to be about 10-3% of the index difference between the core and the cladding. Te transverse interference patterns from a multimode graded index fiber and a thin fiber of which core diameter is several microns are obtained by using an interferometer microscope and their refractive index profiles were practically determined with the help of these formulas. Their α parameters were obtained.

Steady-state lossed of optical fibers have been obtained by launching beams of different numerical apertures and by measuring the losses and the corresponding radiation patterns at both ends of the fiber. The steady-state losses are associated with that radiation pattern whose distribution remains essentially unchanged. Other information obtainable from NA-dependent loss measurements include, for example, the excess scattering losses in graded-index fibers due to the increased concentration fluctuations near the fiber axis, and the influence of a central index dip on fiber losses. The NA-dependent spectral-loss characteristics of a plastic-clad silica fiber, and of 0.22 and 0.34 NA Ge-B-doped fibers are presented as examples.

A recently developed asymptotic theory of inhomogeneous waves has been successfully aplied to the study of guided modes in a class of planar ducts and fibers. In the present note, the theory is extended to provide results for other cylindrical profiles.

This method can reduce the measuring time considerably and can improve spatial resolution by using a Q (quasi)-fiber in comparison with an usual fiber-polishing method. The overall measuring error was less than 0.03% for the case of index difference1%.

The sides of strip waveguides create TE-TM coupling which has so far been neglected in published analyses. For all TM" modes and for higher TE" modes on strip waveguides under suitable conditions, this coupling produces interesting new effects, such as leakage and resonance, which have implications for device performance.

High strength fiber optical waveguides have been prepared by hermetically coating the pristine fiber surface with a metallic jacket. The static fatigue characteristics of these fibers at high stress levels have been observed to be orders of magnitude superior to plastic jacketed fibers.