In this paper, we describe the design, optimization and fabrication of high-speed InP/InGaAs heterojunction bipolar phototransistors (photo-HBTs) with both optical cut-off frequency (Fc) and optical gain (Gopt) higher than 100 GHz and 30 dB, respectively. Small- and large-signal models of the photo-HBT have been developed in order to design optoelectronic monolithically integrated circuits (OEIC) using this device. Integrated circuits such as optoelectronic narrow-band amplifiers at 28 GHz with a transimpedance gain of 50 dBΩ and optoelectronic upconverting mixers at 28 and 42 GHz with a mixer conversion gain of 17.8 dB and 9.2 dB respectively, were fabricated. The performances of the mixer circuits were superior to those of individual photo-HBT mixer. These optoelectronic integrated circuits based on InP photo-HBTs are attractive building blocks for realizing compact and cost-effective photoreceivers for millimeter-wave radio-over-fiber links.

We developed compact high-power photonic millimeter-wave emitter (PME) modules for 60-GHz fiber radio links. The PME chip is a monolithic integration of a uni-traveling-carrier photodiode (UTC-PD) and an antenna. One module was fabricated by attaching the chip and a plastic housing to a metal substrate, and the equivalent-isotropic radiated power (EIRP) of over 8 dBm was obtained with weak directivity of the radiated pattern. This module is suitable for point-to-multi-point communication. It is very compact, 29 24 6 mm. A module whose antenna gain was increased by attaching a dielectric lens to it was also fabricated, and the estimated EIRP of 18 dBm was obtained. This type of module is suitable for point-to-point communication and it too is compact, 29 24 17.5 mm. We achieved high-speed error-free data transmission of 1.25- and 2.5-Gbit/s phase-shift keyed (PSK) signal. The maximum distances of free-space propagation were estimated to be 18.2 and 8.9 m at bit rates of 1.25 and 2.5 Gbit/s, respectively.

We present theoretical and experimental results for a microwave photonic oscillator (MPO) that provides a microwave signal and a modulated optical wave simultaneously. Among the different techniques currently in use for optically generating a microwave signal, we have chosen a ring configuration based on an electro-optical Mach-Zehnder modulator (EOM) driven by a 1.55 µm DFB laser diode. An accurate modelling of EOM and the contributions from all noise sources in the oscillation loop allows us to predict performances of our designated MPO in a very good agreement with the measured oscillation power (up to 22 dBm, depending on the DC bias voltage) and phase noise spectral density (-130 dBc/Hz @ 10 kHz away from the carrier). We propose this hybrid microwave photonic source to be used as a local oscillator for a coherent laser radar operating at 1550 nm. A good compromise between a very high tunability range (1-8 GHz) and a high spectral purity (> -120 dBc/Hz @ 10 kHz) is obtained through a dual-loop configuration for the MPO.

An optical FM system using an optical FM LD (laser diode) and an optical frequency discriminator (OFD), in which a nonlinear compensation scheme based on the interaction between its nonlinearities can minimize intermodulation distortion. This paper theoretically investigates the minimization influence for 3rd plus 5th order intermodulation distortion power for an optical FM radio-on-fiber system. The carrier to noise-plus-distortion power ratio (CNDR) is theoretically analyzed in employing the OFD whose transmission characteristic is controlled by a phase shifter. The results show that the designed receiver can achieve higher CNDR in the application of multicarrier transmission.

The dense wavelength division multiplexing (DWDM) technique is very attractive for effectively increasing the channel capability, even for access networks. Some DWDM radio-on-fiber (ROF) systems have been studied recently. In those systems, fiber Bragg gratings (FBG) or arrayed waveguide gratings (AWG) were used to demultiplex DWDM ROF signals. In this report, an alternative channel-selection scheme of DWDM millimeter-wave-band ROF signals by optical heterodyne detection with dual-mode local light is newly proposed. Error-free demultiplexing and transmission over a 25-km-long SMF of the DWDM signal, which consists of two 60-GHz-band, 155-Mb/s-DPSK ROF signals, are demonstrated.

In this paper, an optical signal processing beam forming network (BFN) for two-dimensional (2-D) beam steering is proposed and experimentally demonstrated. Two lightwaves, called the signal and reference, are both Fourier transformed, combined, and then down-converted into RF signals using an optical heterodyne technique. A simple combination of orthogonal one-dimensional position scannings of the signal and reference lightwaves generates RF signals with phase distributions for 2-D beam steering. The system operation and optical losses are theoretically analyzed. Using graded index fiber (GIF) lensed single mode fibers (SMFs), total optical loss of the sampling fiber array is evaluated to be 4.5 dB from the fiber to fiber loss measurements. Using an experimental optical signal processing BFN at 25 GHz, 2-D beam steering is demonstrated at 0, 10, 20, and 30through the measured amplitudes and phases of RF signals for 16 position sets of the signal and reference fibers. The proposed method has the potential to provide ultra-fast beam scanning by utilizing optical switching technologies.

This paper describes the experimental approach of the Direct Optical Switching (DOS) CDM Radio-on-Fiber (RoF) system. Improved carrier-to-interference ratio (CIR) performance by using an Optical Polarity Reversing Correlator (OPRC) in comparison to using a single switch decoder is experimentally obtained. In addition, CIR performance deterioration due to degradation of the extinction ratio of the optical switch decoder is clarified from the theoretical and experimental viewpoints. Finally, we confirmed that CIR performance is improved more by using an M-sequence whose weight is even numbered than by using an odd numbered one.

The conservative mode and the greedy mode scheduling algorithms for OBS switch with shared buffer are presented and discussed. Their performance is evaluated by computer simulations, as well as that of the greedy mode with void-filling algorithm. Simulation results show that the conservative mode and the greedy mode have different characteristics under different input load. The greedy mode and the conservative mode are more applicable in a real system than that with void-filling, owing to their lower computational complexity and FIFO characteristic. Finally, a composite algorithm integrated by the conservative mode and the greedy mode is proposed, which is adapted to the input load with the help of an input load monitor. The simulation results reveal that it has favorable performance under different load.

This paper discusses direct optical injection locking of a millimeter-wave oscillator using an InP/InGaAs heterojunction phototransistor (HPT) and its applications. Previously reported optically injection-locked oscillators (OILOs) are reviewed first. In particular, the features of a direct OILO (DOILO), where synchronization can be achieved by illuminating the active oscillator device itself, are discussed in comparison with the indirect OILO. DOILOs with excellent characteristics require high-performance transistors having both a high maximum oscillation frequency and fast photoresponse. We have developed high-performance opto-microwave-compatible InP/InGaAs HPTs whose layer and fabrication process are fully compatible with ultrahigh-speed heterojunction bipolar transistors. The paper discusses the photocoupling structure, and it is shown that the back-illuminated structure with the aid of InP subcollector enables one to achieve a 100-GHz-class DOILO. The configuration and performance of the 100-GHz-class DOILO are then presented; in particular, injection locking from optical signals with a modulation or beat frequency of around the fundamental (96 GHz) or second harmonic (192 GHz) is successfully demonstrated. To our knowledge, 96 GHz is the highest optically injection-locked frequency and 192 GHz is the highest inputmodulation frequency reported for OILOs. The HPT oscillator IC promises compact, low-power-consumption remote local oscillators for 100-GHz-class wireless systems and 100-Gbit/s-class optoelectronic clock recovery circuits. In addition, when the HPT oscillator is used as a modulator, we can attain cost-effective millimeter-wave systems compatible with conventional optical fiber networks transmitting digitally modulated baseband signals.

We experimentally demonstrated a remote antenna system based on a millimeter-wave (MMW) over fiber scheme for 622-Mbps broadband fixed wireless access systems. In this system, the format of the RF signal is based on a four-carrier signal in which each carrier is modulated by using 64-QAM, to reduce the complexity of the RF system in comparison with the single-carrier QAM system using many more signal-points than 64. The remote antenna system based on the IF-over-fiber scheme was also experimentally demonstrated, as well as the MMW over fiber scheme for comparison. From the experimental results, we found that the remote antenna system based on the MMW over fiber scheme is effective not only from the viewpoints of miniaturization of the remote antenna station and ability to provide a stable millimeter-wave frequency, but also from the viewpoint of link performances such as allowable dynamic range and power penalty, even though the scheme's E/O and O/E devices have a higher cost.

Binary and ternary 5-bit programmable dispersion matrix, based on fiber Bragg reflectors, is built to control a two-channel receive/transmit beamformer at 1550 nm. RF phase measurements for the 32/31 delay configurations are presented. The programmable dispersion matrix is fully demonstrated and characterized for RF signals from 0.2 to 1 GHz.

A simple configuration for millimeter-wave fiber-wireless transmission, with remote local-oscillator (LO) delivery from the central office, both for the uplink and for the downlink, and a simple, cost-effective, base-station solution is proposed. Under the assumption of using commercially available components and a conventional single-mode fiber (with dispersion of 17 ps/nm/km at 1.55 µm), our numerical results show that, with a laser linewidth of 150 MHz, a laser power of 0 dBm and an optical gain of only 6 dB, it is possible to transmit, without repeaters, data rates of 622 Mbit/s across about 18 km at a bit-error-rate of 10-9. By increasing the optical gain to 24 dB, the link length can be increased to approximately 67 km for a laser linewidth of 75 MHz and to 78 km for a laser linewidth 1 MHz.

Correct and quick generation of a membership function is the key point when we implement a real-time fuzzy logic controller. In this Letter, we presented two efficient VLSI architectures, one to generate triangle-shaped and the other to generate trapezoid-shaped membership functions. Simulation results show that our designs require lower hardware cost but achieve faster working rate.

The interrupting characteristics of low voltage current limiting circuit breakers have directly relationship with the magnitude and distribution of magnetic field produced by contact system and splitter plates. In order to analyze the influence of configuration of contact system on current limiting characteristics, 3D magnetic field of arc chamber (including contact system, arc, splitter plates) is calculated. Furthermore, the electromagnetic repulsion force of movable contact is also calculated. The results can be used to improve configuration of arc quenching chamber. The cooperation between operating mechanism and electromagnetic repulsion force is also analyzed in this paper.

An optical fiber line testing system is essential for reducing maintenance costs and improving service reliability in optical access networks. NTT has already developed such a system called AURORA (AUtomatic optical fibeR opeRAtions support system). As we already use the 1310 and 1550nm wavelengths for communication, we use the 1650nm wavelength for maintenance testing in accordance with ITU-T recommendation L.41. Recently, a long wavelength band (L-band) that extends to 1625nm has begun to be used for WDM transmission. With a view to monitoring optical fiber cables transmitting L-band communication light, an attractive way of separating the U-band wavelength of the test lights from the L-band wavelength of the communication light is to use a chirped fiber Bragg grating (FBG) filter because of its steep optical spectrum. However, it is difficult to measure fiber characteristics with an optical time-domain reflectometer (OTDR), because multi-reflections appear in the OTDR trace when FBG filters are installed at both ends of an optical fiber line. In this paper, we consider this problem and show that the reflection loss at the port of a test access module (TAM) must be more than 36.6dB. We also describe the system design for an extended optical fiber line testing system using an L/U-band optical coupler, which has two chirped FBGs between two 4-port circulators for L-band WDM transmission. In this system, the reflection loss at a TAM port was 38.1dB, and we confirmed that there was no degradation in the OTDR trace caused by multi-reflections at the optical filters.

We have exploited a high-power-tolerant variable optical attenuator (VOA) based on the fused fiber coupler in the all-fiber structure. A newly designed VOA employs the external modulation by forcing an axial stress in the tapered region of the fused fiber coupler. In the tapered region, the axial stress changes the refractive index of silica glasses resulting in a change in the coupling coefficient of the coupler. In this paper, we explain the principle of the novel device, VOA, and the optimized fabrication of the fused fiber coupler for the attenuation. The changes of the transmission spectrum for the coupler and the optical power spectrum for pump laser diode (LD), whose center wavelength is 1.47µm, versus the axial displacement were verified by experiment. The possibility of the wavelength uniformity less than 1dB over the range of 1460-1500nm was also obtained by another coupler under a different fabrication condition. The polarization-dependent loss (PDL) at 1.47µm wavelength was 0.65dB for a maximum displacement of 150µm. The designed device has an attractive feature of another output port of the coupler available as a monitoring tap. The device showed a high attenuation above 34dB and an insertion loss below 0.15dB. The all-fiber structure can provide less alignment, which in turn provides a high power tolerance. This novel design, moreover, has a simple and cost-effective structure.

We demonstrate a mode-locked fiber laser (MLFL) method for measuring the chromatic dispersion of long transmission fiber. In this method, device under test (DUT) is inserted in the laser cavity, and the chromatic dispersion is measured by the shift of mode-locking frequency when the lasing wavelength is changed. The experimental results of the MLFL method for a 5km-long single-mode fiber had good agreement with the conventional phase-shift method.

It is found that the supercontinuum spectrum is generated from cross-phase modulated soliton pulses which are propagated through a dispersion-flattened/decreasing fiber with low birefringence. The cross-phase modulation is achieved by exciting two orthogonally polarized modes in a birefringent fiber and the effect of input azimuth of linearly polarized pulses is discussed theoretically and numerically.

The rapid spread of the Internet has led to the construction of broadband networks and the steady installation of optical fiber to the home. The air blowing cable system makes it possible to construct optical fiber networks efficiently and economically when the service demand is unpredictable. We have installed this system for intra-building applications. In this paper, we report ways of applying the air blowing system to aerial distribution using access networks. We showed that certain problems must be overcome before the system can be used for aerial applications. We describe these problems, which include those related to installation distance and environmental conditions and also the system components. In particular, the characteristics at high temperature were degraded because of a reduction in the flux. However, we were able to improve these characteristics by adopting the flexibility of the optical fiber unit.

Consider an undirected graph G=(V,E) with n (=|V|) vertices and m (=|E|) edges. It is well-known that the problem of computing the sequence Nn-1,Nn,...,Nm is #P-complete (see e.g.,[3]), where Ni denotes the number of connected spanning subgraphs with i (n-1!im) edges in G. In this paper, by proving new inequalities on the sequence Nn-1,Nn,...,Nm, we show an interesting and stronger property that the sequence γn-1,γn,...,γm, where γi denotes the average number of spanning trees in the connected spanning subgraphs with i edges, is a convex sequence as well as a monotonically increasing sequence, although this property does not hold for the sequence Nn-1,Nn,...,Nm.