This paper presents a novel 60 GHz-band photonic-integrated array-antenna and module for radio-over-fiber (RoF)-based beam forming. An integrated photonic array-antennas (IPA), where eight photodiodes and 4×2 arrayed patch-antenna are integrated in a single board, is actually fabricated, and 3.5-Gbit/s QPSK digital signal transmission with beam forming of the IPA is experimentally demonstrated. In addition, a novel 60-GHz compact antenna module is proposed and fabricated for increasing the number of antenna elements and flexibility creating various beam patterns. The feasibility of beam forming operation for the proposed antenna module is confirmed by a 60-GHz RoF transmission experiment. The capability of detecting the mobile terminal direction, which is one of the indispensable functions for actual environment, is also studied. The obtained results in this paper will be useful for designing future radio access networks based on RoF transmission technology.

We present our recent work on monolithically integrated devices comprising a variety of functional elements such as high speed optical transmitters and receivers, electro-absorption modulators integrated with tunable dispersion compensators and fast-tunable wavelength converters.

A newly developed hybrid-integrated Symmetric Mach-Zehnder (HI-SMZ) all-optical switch is reported. For integration, we chose the Symmetric Mach-Zehnder (SMZ) structure rather than the Polarization-Discriminating Symmetric Mach-Zehnder (PD-SMZ) structure which is similar to SMZ but more often used in experiments using discrete optical components. We discuss advantages and disadvantages of SMZ and PD-SMZ to show that SMZ is more suitable for integration. We also discuss about the use of SOAs as nonlinear elements for all-optical switches. We conclude that, although the ultrafast switching capability of SMZ is limited by the gain compression of SOAs, the very low switching energy is more important for practical devices. We then describe the HI-SMZ all-optical switch. This integration scheme has advantages which include low loss, low dispersion silica waveguides for high speed operation and ease in large scale integration of many SMZs with other optical, electrical, and opto-electrical devices. We show that a very high dynamic extinction ratio is possible with HI-SMZ. We also examine HI-SMZ with 1 ps pulses to show its ultrafast capability. Finally, we describe a 168 to 10.5 Gbps error-free demultiplexing experiment which is to our best knowledge the fastest experiment with an integrated device.

The hybrid electrical/optical multi-chip integration technique for optical modules for optical network system has been developed. Employing the technique, a 44 broadcast-and-select type optical matrix switch module has been realized. The module consists of four sets of silica waveguide 1 : 4 splitters/4 : 1 combiners, four 4-channel arrays of polarization insensitive semiconductor optical amplifiers with spot-size converters as optical gates, printed wiring chips for electrical wiring and single mode fibers for optical signal interface on planar waveguide platform fabricated by atmospheric pressure chemical vapor deposition. All the gates and the wiring chips were mounted precisely onto the platform at once in flip-chip manner by self-align technique using AuSn solder bumps. Coupling loss between the waveguide and the SOA gate was estimated to be 4.5 dB. Averaged fiber-to-fiber signal gain, on-off ratio and polarization dependent loss for each of the signal paths was 7 dB 2 dB, more than 40 dB and 0.5 dB, respectively. High speed 10 Gb/s photonic cell switching as short as 2 nsec has been successfully achieved.

The hybrid electrical/optical multi-chip integration technique for optical modules for optical network system has been developed. Employing the technique, a 44 broadcast-and-select type optical matrix switch module has been realized. The module consists of four sets of silica waveguide 1 : 4 splitters/4 : 1 combiners, four 4-channel arrays of polarization insensitive semiconductor optical amplifiers with spot-size converters as optical gates, printed wiring chips for electrical wiring and single mode fibers for optical signal interface on planar waveguide platform fabricated by atmospheric pressure chemical vapor deposition. All the gates and the wiring chips were mounted precisely onto the platform at once in flip-chip manner by self-align technique using AuSn solder bumps. Coupling loss between the waveguide and the SOA gate was estimated to be 4.5 dB. Averaged fiber-to-fiber signal gain, on-off ratio and polarization dependent loss for each of the signal paths was 7 dB 2 dB, more than 40 dB and 0.5 dB, respectively. High speed 10 Gb/s photonic cell switching as short as 2 nsec has been successfully achieved.

Extremely compact multi-mode interference (MMI) devices using central wide-angle coupling of input and output waveguides are proposed. It is shown that MMI can be used to change the propagation direction of light without the need for corner mirrors or bent waveguides. The concept can also be used for very compact power splitters which are even smaller than conventional MMI power splitters. Coupling between waveguides at wide angles is discussed and a number of regularities are found. The results can be useful for the design of more compact integrated circuits by a reduction of the number of bent waveguides which usually take up the largest part of the area of a photonic integrated circuit.

Butt-joint waveguide couplings are fabricated for use in InP-based photonic integration, and characterized by scanning electron microscopy and optical transmission measurements. Several parameters have been optimized in the characterization study: size and shape of the mask protecting the first waveguide layer during butt-joint regrowth, and the crystallographic direction of the butt-joint interface. The studies show that high-quality butt-joints having negligible optical loss can be made with good fabrication tolerance. Using the optimized butt-joint, DBR-type, gain-clamped SOAs have been fabricated which are free of internal excess reflections. A constant optical gain of 21 dB is obtained up to a signal output power of 25 mW. The devices show CATV grade linearity in a 77 channel CATV linearity test at a distortion level of -55 dB below carrier.