It is shown that the resonance-like phenomena or the relaxation oscillations in the light output of the directly modulated injection lasers is suppressed by a non-resonant π-type electric circuit connected to the laser diode. Application of this suppressor circuit is not sensitive to the bias current of laser diode and the cut-off frequency of modulation is sufficiently large. It is pointed out that the use of this method at the narrow stripe laser is the most effective.

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 kA・cm^-2. µm^-1 and then the intrinsic lifetime was obtained. Deduced carrier lifetime well agreed with that estimated from relaxation oscillation measurement.

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.

Accelerated life test of AlGaAs-GaAs DH lasers were carried out at ambient temperatures of 70, 90, 100 and 110. The temperature dependence of degradation rates deduced from the experimental results indicated the presence of the activation energy of 0.7-0.9 eV. The median lifetime extrapolated to 25 was 1.310⁶ hrs for the activation energy of 0.7 eV. The degradation of dynamic characteristics of lasers is also demonstrated.

The TJS lasers which have the kink-free behavior and good proportionalities in the outputs between the front mirror and the rear mirror have been tested by cw aging. After 12,000-hour cw againg, a TJS laser has been found to still lase in a single longitudinal mode as well as in the fundamental transverse mode. The life of TJS lasers at 25 is estimated to be at least 80,000 hours on the basis that the laser is still alive after 3,000-hour aging at 60. By considering that the spatial homogeneity in the active region of the TJS laser is maintained for long time cw aging, the reason why the single mode behavior is kept even after the aging can be explained. Here, the spatial homogeneity in the active region of the TJS laser may be due to a small size of the region and to high hole concentration of the region.

Thin-film waveguide Luneburg and geodesic lenses are being developed for near-infrared integrated optics. Considerations which yield a preference for these structures are enumerated, together with specifics, for generalized Luneburg lenses employing Ta₂O₅ (lens) with Corning 7059 (waveguide) on thermally-grown SiO₂ on Si substrates. Spheric geodesic lenses formed with the same waveguide, isolation layer, and substrate materials are included.

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.

We report a performance analysis and experimental results of an optical intensity modulator using a pair of optical gate couplers and conventional electro-optic phase shifters. The modulator involves only three straight waveguides. The optical gate coupler consists of three coupled waveguides. At the input gate coupler, input light is equally divided and fed into parallel arms of the phase shifters. A retardation φ between the two arms of the phase shifters is controlled electro-optically by applied voltage. At the output gate coupler, both lights are re-combined according to the phase shifts. The modulator is fabricated monolithically by diffusing Ti into a z-cut LiNbO₃. Each patterned waveguide is about 6 µm wide and spacing is 2.9 µm at the gate coupler. The lenght of the gate coupler is 6 mm and a pair of electrodes are 7 mm long and the spacing is 12 µm. For E^y₀₀mode (r₁₃) the half-wave voltage is 21 V, the extinction ratio is 11.3 dB and insertion loss is 9.8 dB at 1.15 µm.

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.

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.

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.

Two strip-waveguides, with and without a function of light intensity modulation, have been monolithically integrated with an embedded stripe DH laser. The strip-waveguides are constructed with guide films of high resistivity GaAs_0.9 P_0.1 and surroundings of slightly lower refractive index GaAs_0.85 P_0.15. The intensity of spontaneous light output from the stripe Ga_0.97 Al_0.03 As laser can be modulated by a voltage applied to the waveguide-modulator through an isolated electrode. It is seen that the maximum modulation occurs at a wavelength shorter than the peak wavelength of emission spectrum as a result of the Franz-Keldysh effect.

Practical design of a high-efficiency relief-type waveguide hologram is demonstrated for the future integration of holograms in optical IC. The hologram is recorded in light-sensitive layer on a thin film waveguide. After the exposure and the subsequent etching, one can obtain a waveguide hologram of relief type. It is shown analytically that, when the parameters are optimized, the relief type provides a high efficiency and an aperture size suitable for storing pictorial informations. Waveguide holograms were fabricated by chemical etching technique in amorphous As₂S₃ (recording medium)/sputtered glass film (wave-guiding layer) structure. From the intensity distribution of the diffracted light in the hologram plane, the total diffraction efficiency (the sum of the efficiencies in the air side and in the substrate side) was estimated to be 92%. This result compares favourably with the theoretical prediction, and the efficiency of 92% is remarkably higher value than that of a hologram of coventional type storing a pictorial information. Very little deterioration of the image quality owing to the etching was observed. The applicability of the method to the design of a waveguide hologram to be reconstructed by ir light was also confirmed. The high efficiency would make the waveguide hologram of this type promising also as an advancement of holographic circult couplers.

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.

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.

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.

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.

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.

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.

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.

A method to estimae the coupling length of the fiber in which modes couple each other due to the random bending of fiber axis is given. The coupling length is estimated from the comparison of the measured transfer function to the theoretical one which is derived previously. The coupling length of a graded-index fiber is estimated to be about 0.8 km using this method. Further, the coupling length of recent graded-index fibers is presumed to be about several Km. For step-index fibers, it is estimated to be in the range between 0.5-5 Km.

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.

Semiautomated measurement of the refractive-index profiles of single-mode fibers using the scattering-pattern method developed by the same authors is described. The scattering-pattern method features very high resolution, typically 0.2 µm: hence at present it is the only method suitable for single-mode fibers. The measurement have been performed by using a semiautomated system. This system consists of an automated measuring apparatus of the scattering pattern and softwares for calculating the refractive-index profile. The obtained profiles are compared with those of preforms.

It is very important to choose appropriate fiber parameters such as core and outer diameters and refractive index difference of fiber for obtaining low loss and stable fiber cables for practical use. Several problems related to determine the fiber parameters must be taken into concideration for a design of fiber structures. Many theoretical and experimental studies on the relationship between fiber parameters and transmission characteristics to show fiber parameters dependence on excess loss useful for the design of practical fiber cables. In this paper, we made clear experimentally the relationship between excess losses and fiber parameters for jacketed step-index fibers with various combinations of core and outer diameters, index difference and jacket diameter. As the results, we found that the excess loss caused by winding uniformly on the mandrel is proportional to (a/)^2-3 and is independent of fiber diameter and that the loss due to microbending by external forces remarkably affected by both a/ and the fiber and jacket diameters. The results obtained by the investigations are utilised for manufacturing low loss and stable optical fiber cables.

From theoretical or experimental point of view, graded-index multimode fibers are interesting and promissing transmission lines for future optical communication systems. Their transmission characteristics, however, have not been well recognized so far. Therefore, it is necessary to clarify the characteristics before considering graded-index multimode fibers for practical uses. Among the characteristics, optical loss and pulse dispersion are of paramount importance. This paper presents baseband frequency characteristics of recently produced graded-index multimode fibers in the frequency range from DC to 1.7 GHz. The characteristic dependence of graded-index multimode fibers on wavelength and excitation condition is also studied in comparison with that of a step-index multimode fiber. Wavelength, rather than excitation condition, is shown to be an important factor that determines the characteristics of the fiber. The wavelength dependence of the bandwidth has been found to be critically influenced by the profile of the fiber. In order to understand the detailed characteristics of graded-index multimode fibers, the measurement covering a wide frequency range, e. g., from DC to over 2 GHz, is necessary.

This paper describes the transmission characteristics of a graded-index fiber fabricated by CVD method. First, baseband frequency responses are discussed to be related with local bumps in refractive-index profiles. It is indicated that even a slight local bump causes serious deterioration of frequency response. Second, transmission loss characteristics are discussed as to four types of graded-index fibers. It is concluded that transmission loss is mainly originated from Rayleigh scattering loss and that in order to decrease scattering loss it is needed to reduce the fractional index differences caused by doping oxides. Finally, the transmission characteristics of long-length graded-index fibers are discussed. It is experimentally indicated that the dependency of bandwidth B on length L is nearly expressed as BL^-0.7-0.8 and that bandwidth of 160 MHz and transmission loss of 30 dB over 10 km are achieved.

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%.

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 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.

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.

An initial trial of the optical fiber transmission system in NTT is reported in this paper. In NTT's transmission networks, the shorthaul application appears attractive in the near future. The laboratory test is primarily targeted to 32 Mb/s bit rate and 8 km long repeater spacing. We report here the design philosophy of step-index multimode fibers and repeaters for this trial. Through the design and manufacturing of fibers, the fundamental and common characteristics of fibers are clarified. Stable, compact and low power consuming optical repeaters are realized. Trere is no trouble of optical repeatered line and all repeaters in the line are operating with sufficient optical power margin. Multi-repeatered test has confirmed that experimental results are in good agreement with the design values.