A two-dimensional receiver OEIC array having an address selector for highly parallel interprocessor networks has been realized. The receiver OEIC array consists of two-dimensionally arranged 1616 (256) optical receiver cells with switching transistors, address selectors (decoders), and a comparator. Each optical receiver comprises a pin PD and a transimpedance-type HBT amplifier. The HBT has an InP passivation structure to suppress the emitter-size effect, which results in the improvement of current gains, especially at low collector current densities. The receiver OEIC array was fabricated on a 3-inch diameter InP substrate with pin/HBT integration technology. Due to the function of address selection, only one cell is activated and the other cells are mute, so the receiver OEIC array shows low crosstalk and low power consumption characteristics. The array also shows a 266-Mb/s data transmission capability. This receiver OEIC array is a most complex InP-based OEIC ever reported. The realization of the two-dimensional receiver OEIC array promises the future interprocessor networks with highly parallel optical interconnections.

Narrow-beam and low threshold current characteristics have been realized for a 1.3 µm FS-BH (Facet Selective growth Buried Heterostructure) laser diode monolithically integrated with a tapered waveguide lens by a selective area epitaxial growth technique. The beam divergences in the perpendicular and horizontal directions have been reduced down to about 12. By the introduction of the strained quantum well structure and the optimized cavity structure, the threshold current has been kept as low as 6 mA which is comparable to the conventional Fabry-Perot laser diodes. Even at high temperature as high as 85, the threshold current and the operation current (P=10 mW) have been suppressed to as low as 23 mA and 63 mA, respectively. Furthermore error-floor-free characteristics for 622 Mbps-50 km transmission have been confirmed under severe optical feedback condition.

This paper describes the technological issues in achieving a low-cost hybrid WDM module for access network systems. The problems which should be resolved in developing a low-cost module are clarified from the viewpoint of the module assembly in mass production. A design concept for a low-cost module suitable for mass production is indicated, which simplifies the alignment between a laser diode and a waveguide, and reduces the number of the components such as lenses and mirrors. The low-cost module is achieved by employing a flip-chip bonding method with passive alignment using a spot-size converter integrated laser diode (SS-LD) and p-i-n waveguide photodiodes (WGPDs) on a planar lightwave circuit (PLC) platform. We confirm that the SS-LD and the WGPD provide high coupling efficiency with a large tolerance for passive alignment. To achieve a high-sensitivity receiver, the module is designed to employ an asymmetric PLC Y-splitter that prefers a PD responsivity to an LD output power because of the high-coupling efficiency of the LD, and to employ a bare preamplifier mounting to reduce the parasitic capacitance into a preamplifier. We also demonstrate the dynamic performance for a 50-Mb/s burst signal, such as a high sensitivity, an instantaneous AGC response, and a small APC deviation of the transceiver.

We propose an InGaAlAs waveguide p-i-n photodiode (WG-PD) with a thick symmetric double-core for surface-hybrid integration onto optical platforms, which can be applied to low cost optical modules for access networks. The waveguide structure is designed to efficiently couple to flat-ended single mode fibers while maintaining low-voltage (less than 2 V) operation. Crystal growth conditions and a passivation technique are also investigated for obtaining high responsivity, low dark current and highly reliable operation. Fiber-coupled responsivity as high as 0.95 A/W, at a 1.3-µm wavelength, and vertical coupling tolerance as wide as 2.6 µm are demonstrated for a dispersion-shifted fiber (DSF) coupling at an operating voltage of 2 V. Dark current is as low as 300 pA at 25 and 12 nA at 100. A temperature accelerated aging test is performed to show the feasibility of using the WG-PD in long-term practical applications.

Laser module fabricated with silicon platform technology is very attractive for low-cost modules. The technology enables passive optical alignment of an LD to an optical fiber. Our marker design for passive alignment allows positioning accuracy within 1 µm of LD. However, coupling efficiency is a key issue because that by conventional butt coupling scheme is low with about 10 dB coupling loss. We investigated optical coupling characteristics in various types of coupling scheme: conventional flat end fibers, cone fibers, integrated GRIN rod lenses on the platform and the coupling with new-type LDs integrated with spot size transformer. Improvement of coupling efficiency with 3 dB and 7.5 dB compared to flat-end fiber is achieved by using the cone fiber and the GRIN rod lens, respectively, although 1-dB coupling tolerances for alignment deteriorated with these schemes. We obtained high efficient coupling with 3.5 dB coupling loss and wide alignment tolerance of 2.3 µm simultaneously with a new-type LD integrated with spot size transformer owing to its expanded spot size characteristics.

A low dark current CCD linear image sensor with pixels consisting of a photodiode and a storage area has been developed. In order to suppress the dark current, the wafer process has been improved. An impurity profile of a photodiode was modified to minimize depletion width, which was monitored by the photodiode potential. Surface states under the storage gate were decreased by hydrogen annealing with plasma-deposited silicon nitride as an inter metal dielectric film. As the isolation dose decreased, the dark current both in the photodiode and in the storage region were effectively suppressed. Finally, low dark currents of 5 pA/cm2 at photodiode and 120 pA/cm2 at storage area were obtained.

The multichannel distortions of direct modulated laser diode were studied from the view point of rate equations. A novel technique for compensating the composite second order distortion (CSO) was proposed. Meanwhile, the related calibration procedures were indicated. After the compensation, 10 dB improvement in CSO was obtained

Current-voltage characteristics of triple-barrier resonant tunneling diodes are theoretically analyzed taking phase breaking into account. The peak current in predicted using conventional theories is much smaller, typically by a factor of 1/3000 for a coherent length of 100 nm, than that measured because the incoherent tunneling process is neglected. We take both the coherent and the incoherent tunneling processes into account in the analysis and show that the product of the peak current and the voltage width at half maximum of the peak current is almost constant even when the phase coherent length varies between 50 and 1000 nm. The peak current density increases by two orders of magnitude in the model developed here.

The resistive-fuse network for early vision was studied using circuit simulation to clarify the potential of implementation with resonant tunneling diodes (RTDs). To over-come the fundamental problem of the RTD network, i.e., the RTDs cannot perform simulated annealing (SA), pseudo SAs were proposed. These methods are based on the time-variation of the input signal strength, and are found to be effective in restoring images. A resistive-fuse network is shown to be one of the most promising applications of RTDs.

We proposed a new marker design for passive alignment of a laser to a fiber on a silicon waferboard. Our fiducial marker is simple form and easy to fabricate. With a unique marker design, high accurate positioning of the laser chip is easily achieved using a conventional flip-chip bonder. We have successfully fabricated laser modules with uniform coupling, within 1 dB for a flat end single-mode fiber and within 2 dB for a hemispherical end fiber. This assembly method offers the potential for low-cost optical module packaging.

Precise direct mounting of laser diode (LD) and photodiode (PD) chips on silica planar lightwave circuits (PLCs) has been investigated for application to transceiver modules. To achieve submicron optical alignment, self-aligned index marks on the PLCs and LDs were directly detected by transmission infrared light. The repeatability of the positioning was measured to be within 0.125 µm. The output power of the resultant module was 0.2 mW at 80 mA. A waveguide-type PD was also mounted in the same way, and module sensitivity of 0.25 A/W was demonstrated.

We have proposed a multiplexed fiber-optic sensor system using an optical loop with a frequency shifter. The measured output power spectrum of the system has shown that the multiprexed signals superimpose upon a noise pedestal which is like a series of hill peaks. In this paper, the output power spectrum is theoretically analyzed from the output intensity autocor-relation function. It displays that the noise pedestal originates from the laser phase-induced intensity noise. The noise level depends on the coherence time of the laser source. The positions of peaks are decided by the working frequency of the frequency shifter in the optical loop. The sensitivity of the system are related to the bandwidth B, the coherence time Tc, the sensor number n to be multiplexed, the loop loss α, and the fiber coupler parameters. Properly choosing these parameters is beneficial to improve the sensitivity of system.

This paper describes the performance of a predistorter implementation to a superluminescent diode (SLD) in fiber-optic wireless systems under the optical reflection. SLD intensity noise and 3rd-order intermodulation distortion (IM3) are experimentally compared with those of DFB-and FP-LD. It is observed that the IM3 of SLD has ideal 3rd characteristics and output noise remains unchanged against the number of optical connectors. It is also found that the predistorter reduces IM3 by 8 dB. Receiver sensitivity of the system is discussed from the view point of overall design. the BER performance of an SLD with predistorter using a π/4-QPSK signal as a subcarrier is also described theoretically and experimentally.

A GaAs defferential oscillator IC with on-chip LC resonator has been developed for suppressing the relative intensity noise (RIN) of a laser diode. The relationship between the Q-factor and minimum supply voltage for oscillation is fully described. In view of reducing the present LC resonator, we made use of BST (Barium Strontium Titanate) capacitor to make the resonator without increasing the chip area. The oscillation frequency is stable since it's determined by the geometry of the resonator. The experimentally fabricated oscillator IC achieved the output power of 12 dBm at the frequency of 600 MHz with voltage/current conditions of 2 V/20 mA. The present IC keeps quite stable RIN value less than -138 dB/Hz under the light-feedback condition up to 10%.

The intermodulation distortion (IMD) due to laser diode (LD) nonlinearity of an asynchronous direct-sequence code division multiple access (DS/CDMA) system in optical transmission is analyzed. A third-order polynomial without memory is used to present LD nonlinearity. In DS/CDMA systems, only one harmonic of the third-order inter-modulation term falls on the signal frequency band and influences the system performance. The average distortion is derived with only the information of autocorrelation functions. The results are useful for CDMA system design and performance analysis. With LD nonlinearity it is necessary to select an optimal modulation index that provides a maximum signal-to-noise ratio (SNR). The analytical method is applicable to other general nonlinearities in CDMA systems.

Coupling optics for a monolithic array LD module has been developed. High efficient and small sized confocal optics with aspheric lenses based on hyperbolic surfaces has been designed to achieve the uniformity of coupling loss. A small sized (7.2 cc) 4 channel array LD module with this optics was fabricated. This module has low (4.2 dB) and uniform (0.5 dB) coupling loss.

We propose and demonstrate an excellent linearly frequency-swept laser diode (LD) for sensing system utilizing frequency-moduleted continuous-wave (FMCW) technique. In order to linearly sweep the optical frequency, we adopt a reference interferometer and an electric phase comparator. The interference beat signal of the reference interferometer is phase-compared with an external reference rectangular signal having a fixed frequency near the interference beat signal frequency by a lock-in amplifier. The error signal from the lock-in amplifier is fed back to the modulating signal of the injection current of the LD. Thus, a phase-locked loop composed of optical and electric circuits can be established, and the beat signal frequency is locked to the frequency of the reference signal. The optical frequency of the LD is, therefore, excellently linearly swept in time. In order to experimentally confirm the linearlity of the proposed method, we apply this light source to the FMCW reflectometry. Resultingly, the improvement of the linearity is estimated to be about 10 dB. And the theoretically limited spatial resolution of the FMCW reflectometry is achieved.

A numerical method is introduced which is suitable for mode analysis in an optical resonator with complicated refractive-index variations such as vertical cavity surface emitting lasers (VCSELs). In this method, the optical field of a laser mode is expressed as a linear combination of component fields with their coefficents to be determined. After a hypothetical boundary is set surrounding the region to be analyzed, the component fields are obtained by numerically integrating the wave equation in the inside region using the conditions on part of the boundary as the initial values of the integration. The total field, which is a linear combination of these fields, satisfies the equation and the selected part of the boundary conditions regardless of the coefficients. The conditions imposed on the total field on the rest of the boundary lead to a matrix eigenvalue problem, from which the optical frequency and the coefficients are obtained. The matrix expresses only boundary conditions and, therefore, its size is much smaller than that of a matrix expressing bulk conditions, as appears in the finite element method or the finite difference method. At the same time, this method has the advantage of adaptability for graded-index problems in contrast to conventional boundary formalisms such as the boundary element method and the mode matching method, because in the present method the component fields (or base functions) are calculated for individual index distributions while in these methods an inflexible set of base functions is used. As an example of the application of the method, mode properties in gain-guided VCSELs are analyzed using this method based on a two-dimensional model. This is the first model that takes into account the effects of standing-wave formation in the resonator and of the incident angle- and polarization-dependence of reflectivity. The ability to treat these effects makes the present method suitable for VCSELs equipped with a thin active layer and with multi-layer reflectors. Basic properties including polarization, threshold gain, oscillation wavelegths, and deflection of far-field patterns have been predicted for various cavity sizes and for various gradients in gain distributions. The major results of the analysis are: TE modes have lower thresholds than TM modes; the laser beam can be steered by tailoring the gain distribution as with edge-emitting lasers.

A design of a high power laser structure is presented which is based on an increase of the cavity length as well as a maximization of the stripe width. This requires a low value for the modal attenuation coefficent and a low optical confinement factor. A model is presented from which the modal gain, the confinement factor, the active region thickness, the stripe width, the length and the reflection coefficients can be calculated. A variant for all design parameters needed to reach 1 W emission in the fundamental lateral mode is given. These values are used to design the epitaxial structure.

Electrical and optical properties of organic multilayer structure have been investigated. Two types of current-voltage characteristics have been found for thin multilayer structure of organic films. Optical property and its application for electroluminescent diode have been presented. The diode characteristics have been discussed in terms of energy band scheme.