Ultrahigh-speed all-optical label processing method is proposed and experimentally demonstrated. This processing method dramatically increases the label processing capability. Optical packet switch (OPS) systems and networks based on OPS nodes are applications of optical processing technologies. For the experiment, we constructed the world's first 40 Gbit/s/port OPS prototype with an all-optical label processor, optical switch, optical buffer, and electronic scheduler. Three-hop optical packet routing using OPS nodes was experimentally demonstrated with it, verifying the feasibility of OPS networks.

We demonstrate the wide-band (> 25-nm) long-distance (> 1000-km) chromatic dispersion compensation by midway spectral inversion (MSI) using a periodically-polled LiNbO₃ device. In order to achieve a flat zero net dispersion, the fourth order dispersion of the single-mode fibers is canceled by MSI, while the third order dispersion is compensated for by the negative slope dispersion compensation fiber (NS-DCF). The second order dispersion is canceled out by both. The long distance propagation is realized by a double recirculation-loop system. A very flat zero dispersion is measured for the first time for over 1000-km single-mode fiber propagation with MSI dispersion compensation.

We have developed the tunable dispersion compensator based on two twin linearly chirped fiber Bragg gratings with various temperature gradients. Controlling the temperature gradient over one of the twin fiber Bragg gratings by Peltier elements, the dispersion and the dispersion slope were changed independently and continuously. The dispersion and dispersion slope compensator has a large bandwidth of 8 nm and low group-delay ripple of < 4 ps in its chirped fiber Bragg gratings. We experimentally demonstrated a precise controllability of the dispersion and the dispersion slope using linear and parabolic temperature gradient. The dispersion and the dispersion slope changes were achieved continuously with -0.67 ps/nm/ and -0.14 ps/nm²/. The transmission characteristics of the dispersion slope compensation were examined using ultra short pulses in the fiber link. When the total dispersion was zero, the distorted pulse was restored back and the tail was significantly suppressed. 160 Gbit/s signals were also demonstrated over 140 km within 1 dB power penalty by using the dispersion slope compensator.

All optical regenerations or wavelength conversions using SOA-based polarization discriminated switch injected by an assist light were investigated. First of all, cross gain modulation (XGM) and cross phase modulation (XPM) in a SOA injected by an external assist light were quantitatively analyzed. A simple measurement technique of XGM and XPM was shown to confirm that the injection of assist light could reduce a gain recovery time with some sacrifice for XGM and XPM efficiency. All-optical 3R regeneration using two-stage SOA-based polarization discriminated switch at 40 Gbit/s and its tolerances for some degradation against intensity deviation and optical signal-to-noise ratio (OSNR) were also shown. Finally, regeneration capability was evaluated through a dispersion shifted fiber (DSF)-based re-circulating loop transmission experiment. Those results indicate that the SOA-based polarization discriminated switch is a promising candidate for all-optical regenerator from the practical point of view.

The configuration and operation of an all-optical 3R-regenerator for high-speed data transmission are described. An all-optical 3R-regenerator using a fiber-based optical switch is proposed and successfully demonstrated in a 160 Gbit/s 3R-regenerating transmission experiment.

Symmetric Mach-Zehnder (SMZ) type all-optical swit-ches are discussed. The SMZ type all-optical switches feature the so-called differential phase modulation scheme to achieve a speed unrestricted by efficient, thus usually slow nonlinearities. In these switches, semiconductor optical amplifiers (SOAs) are often used to realize low optical power switching. We discussed SOAs from a view point of all-optical switch applications, rather than amplifier applications. Finally, all-optical signal processing experiments are discussed with the SMZ type all-optical switches. These include ultrafast demultiplexing of 336 Gb/s signal pulses and random operations at 42 Gb/s for all-optical logic operation and wavelength conversion.

We describe the characteristics of all-optical switching schemes based on semiconductor optical amplifiers (SOAs), with particular emphasis on the role of the fast carrier dynamics. The SOA response to a single short pulse as well as to a data-modulated pulse train is investigated and the properties of schemes relying on cross-gain as well as cross-phase modulation are discussed. The possible benefits of using SOAs with quantum dot active regions are theoretically analyzed. The bandfilling characteristics and the presence of fast capture processes may allow to reach bitrates in excess of 100 Gb/s even for simple cross-gain modulation schemes.

In this report we present all-optical switches and modulators based on the intersubband transition in semiconductor quantum wells. The use of InGaAs/AlAsSb coupled double quantum well structures is proposed to facilitate intersubband transitions in the optical-communication band, and to reduce the intersubband absorption recovery time from several picoseconds to a few hundred femtoseconds by utilizing enhanced electron-phonon scattering. Subpicosecond all-optical gating and modulation in coupled double quantum wells are observed using pump-probe experiments at optical-communication wavelengths. The results indicate that the intersubband transition in this structure is very useful for ultrafast all-optical switching devices.

An all-optical switch based on a single photonic crystal defect with an air-bridge configuration and two-photon absorption was proposed, fabricated and characterized. In optical measurements, we obtained a sharp defect mode with a quality factor higher than 600 at 1.55 µm. More importantly, we observed its nonlinear response to the excitation of ultrashort pulses by utilizing two-photon absorption. Nonliner refractive index change of about -410^-3 was achieved at a pumping power density of 3.610⁹ W/cm².

Ultrafast all optical switching using pulse trapping by 100 fs ultrashort soliton pulse across zero dispersion wavelength is investigated. The characteristics of pulse trapping are analyzed both experimentally and numerically. Using the pulse trapping, 1 THz ultrafast all optical switching is demonstrated experimentally. Arbitral one pulse is picked off from pulse train. Pulse trapping for CW signal is also demonstrated and ultrashort pulse is generated by pulse trapping. From these investigation, it is shown that ultrafast all optical switching up to 2 THz can be demonstrated using pulse trapping.

Simultaneous wavelength conversion utilizing four-wave mixing in optically-pumped GaN/AlN intersubband optical amplifiers has been investigated by means of a finite-difference time-domain (FDTD) model. The conversion efficiencies at a pump power of +7-+10 dBm were predicted to be -9-+6 dB depending on the frequency detuning (0.3-10.9 THz). The difference in efficiency among 18 channels of WDM signals with 100-GHz spacing was within about 3 dB.

Using ultrafast nonlinear-optical response of organic dye films, a train of picosecond optical pulses can be converted into a space pattern of a mm scale. As applications of this technique we demonstrate a single-shot multichannel optical switching for 1 Tbit/s pulse trains, and a timing jitter suppression of pulse trains using a control system with femtoseconds time resolution.

The oscillation characteristics of a 40 GHz, 1-3 ps regeneratively and harmonically mode-locked erbium-doped fiber laser have been investigated in detail with respect to stability, linewidth, and mode hopping. We show that because the Q value of the microwave filter in the feedback loop is limited to around 1000, which is almost the same as that in a 10 GHz laser, the cavity length should not be greatly increased as this would result in as much as a fourfold increase in the number of longitudinal beat signals. We undertook a detailed stability analysis by using three cavity lengths, 60, 80, and 230 m. The 80 m long cavity greatly improved the long-term stability of the laser because the supermode noise was suppressed and there were not too many longitudinal modes. We measured the linewidth of the longitudinal mode of the laser using a heterodyne method, and it was less than 1 kHz. We also point out that there is a longitudinal mode hopping effect with time that is induced by very small changes in temperature.

A compact and stable optical sampling measurement system with a temporal resolution of 2 ps has been developed. External-cavity mode-locked laser-diode (EC-MLLD) modules, which directly generate coherent 2-ps optical pulses, were used as the optical sampling pulse sources. Real-time measurement of the recovery dynamics in semiconductor saturable absorber devices has been achieved by optical sampling combined with the pump-probe method. An EC-MLLD module was also utilized for simple sub-harmonic all-optical clock recovery based on the synchronization of the mode-locking operation by optical-pulse injection. Optical sampling measurement of 160-Gbit/s return-to-zero signals incorporating all-optical clock recovery has been demonstrated.

Timing noise of 160 GHz optical pulses has been evaluated over nine decades of Fourier frequency using the optoelectronic harmonic mixing technique. For down-converting the 160 GHz pulse intensity into a low-frequency IF signal, the fourth order modulation sidebands produced by a Mach-Zehnder intensity modulator have been employed. Phase noise power spectral density and timing jitter for 155.552-GHz optical time-division multiplexed pulses and 160.640-GHz passively mode-locked pulses are measured using the time domain demodulation and time interval analysis techniques, respectively.

We have developed a novel basic technology for terahertz (THz) imaging, which allows detection and identification of chemicals by introducing the component spatial pattern analysis. The spatial distributions of the chemicals were obtained from terahertz multispectral transillumination images, using absorption spectra previously measured with a widely tunable THz-wave parametric oscillator. We have also separated the component spatial patterns of frequency-dependent absorptions in chemicals and frequency-independent components such as plastic, paper and measurement noise in THz spectroscopic images. Further we have applied this technique to the detection and identification of illicit drugs concealed in envelopes.

This paper proposes a new on-chip linearizer self-adapting to the input power and its implementation to high linear monolithic microwave integrated circuit (MMIC) power amplifier for 1.95 GHz wide-band code division multiple-access (W-CDMA) system. The linearizer consists of InGaP/GaAs heterojunction bipolar transistor (HBT) active bias circuit and reverse biased junction diode of which dynamic admittance to input power level functions adaptively to control the bias to the amplifier. The proposed linearizer has little insertion power loss, and more importantly, it consumes no additional die area and DC power. The HBT MMIC power amplifier with the integrated linearizer exhibits a maximum output power of 30.3 dBm, a power gain of 27.5 dB, a power added efficiency of 42% at the maximum output power under an operation voltage of 3.4 V, and adjacent channel leakage power ratio of -38 dBc at 27 dBm of output power.

We developed a new millimeter-wave plastic chip size package (CSP) to operate up to 100 GHz by using a thin-film substrate. It has a flip-chip distributed amplifier with inverted microstrip lines and the amplifier has a bandwidth of beyond 110 GHz. The transmission line on the substrate consists of grounded coplanar waveguides that yield low insertion loss and high isolation characteristics in coupled lines even in mold resin in comparison with conventional microstrip lines. The CSP amplifier achieved a gain of 7.8 dB, a 3-dB bandwidth of 97 GHz, and operated up to 100 GHz. To the best of our knowledge, this value is the highest operating frequency reported to date for a distributed amplifier sealed in a plastic CSP. We also investigated the transmission characteristics of lead-free solder bumps through experiments by assemblying CSPs on printed circuit boards and modeling them so that we could design the packages accurately.

Low-voltage programmed levels are hard to achieve in multilevel Flash memory using staircase CHEI (channel hot electron injection) programming. The reasons are that low-level programming marginally deviates from the linear relation between threshold voltage V_TH and control gate voltage V_CG . Forward bias enhancement of CHEI is proposed to overcome this drawback. It is demonstrated that the new technique creates a linear relation between V_TH and V_CG , validated down to a critical V_CG that is at least 1 V lower than traditional CHEI. Through extensive measurements, it is further argued that the most suitable magnitude of forward bias is 0.5 V since (i) it produces the lowest program level of 1.4 V; and (ii) higher biases cause not only large current consumption but also worsened drain disturb performance in NOR array configuration. The corresponding linear relation with the unity slope is maintained after 10⁵ program/erase cycling.

A new CMOS positive charge pump (NCP-1) is proposed and compared with the conventional pump in this paper. The comparison indicates that this NCP-1 scheme delivers 1.6 times larger output current into the load with roughly 10% area penalty than the conventional pump. To alleviate the area overhead of NCP-1, another new NCP-2 is proposed, where its current drivability is slightly lower than NCP-1 by as small as 5% but it achieves much smaller layout penalty as small as 2-3% compared with the conventional pump. The effectiveness of NCP-1 is verified experimentally in this paper by using 0.35-µm n-well process technology. These NCP-1 and NCP-2 are useful to DRAMs and NOR-type flash memories with sub-1-V V_DD, where their large-output-current nature is favorable.