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We demonstrated stable 160 GHz clock signal generation, by using a reciprocating optical modulator with uniform fiber Bragg gratings having narrow passbands adjacent to reflection bands, which enables effective generation of high-order sideband components.

We demonstrated millimeter-wave generation by using reciprocating optical modulation. A light-wave modulated by V-band millimeter-waves was obtained from a micro-wave signal, and was also modulated by a baseband signal, using an optical phase modulator.

We propose a novel photo-electronic oscillator for frequency comb generation. Asymmetric-filtered deeply phase-modulated signal is fed back to a modulation electrode. By self-oscillating operation of the photo-electronic oscillator, optical frequency comb signal is generated.

We proposed a novel technique for generation of micro- or millimeter-wave pulses using optical frequency-shift-keying (FSK) modulation. FSK signals were obtained by an integrated four optical phase modulators.

We propose a novel optical modulation format conversion technique using double-sideband suppressed-carrier modulation. An optical 10 Gbps frequency-shift-keying signal was directly converted into a phase-shift-keying signal.

We proposed high carrier suppression double sideband modulation using a Mach-Zehnder optical modulator with active trimming technique. The modulator has a pair of trimmers in the arms of the Mach-Zehnder structure. The trimmers can compensate amplitude imbalance in the Mach-Zehnder structure due to fabrication error, where the imbalance generates residual carrier in double sideband suppressed carrier (DSB-SC) modulation. We demonstrated high carrier suppression ration of 50dB in DSB-SC modulation at 10.5GHz, by using an integrated Mach Zehnder LiNbO 3 modulator, where each arm has an intensity trimmer consisting of a sub Mach-Zehnder interferometer.

By using an integrated optical frequency-shift-keying (FSK) modulator, we demonstrate 10 Gbit/s optical FSK transmission over a 130 km single mode fiber. Fiber dispersion was compensated by a balanced photodetector with an optical delay.

We propose a novel scheme for continuous-phase frequency-shift-keying (CP-FSK) optical modulation. By synchronizing the baseband signal with the clock for sideband generation, external CP-FSK modulation is demonstrated at 10 Gbit/s for the first time.

We propose and demonstrate a reciprocating optical modulator having a phase-shifted fiber Bragg grating, a tunable fiber Bragg grating, and a resonant-type optical modulator. It enables effective generation of high-order double sideband components.

We demonstrated OOK/FSK simultaneous modulation in a WDM system, where optical labels for payloads in OOK signals can be in FSK format. 1 Gbps FSK signal was added to 4×10 Gbps OOK signals, by an FSK modulator. (2 pages)

A reciprocating optical modulator (ROM) effectively generates harmonic components of modulation signal. We propose a novel optoelectronic oscillator (OEO) consisting of the ROM. By single-mode self-oscillating operation of the OEO, millimeter-wave-band radio-on-fiber signal is generated.

We propose and demonstrate optical frequency comb generation with good spectral flatness, using a conventional Mach-Zehnder modulator asymmetrically dual-driven by large-amplitude sinusoidal signals with different amplitudes. 120-GHz bandwidth, 10-GHz spacing frequency comb was experimentally generated. (2 pages)

In our former report, we have proposed a resonant-electrode-type optoelectronic oscillator (RE-OEO). An optical modulator used in the RE-OEO has a resonant electrode, over which standing wave arises around the frequency of the resonance. The frequency components out of the resonant frequency are highly suppressed, so that single-mode oscillation in microwave frequency is easily achieved. In addition, the RE-OEO oscillates with lower input threshold power since modulation efficiency can be improved at the resonant condition. We experimentally investigate, in this paper, the characteristics of injection locking for the RE-OEO when microwave near the oscillation frequency is launched on it.

We demonstrated high extinction ratio optical intensity switching by an integrated Mach-Zehnder LiNbO3 modulator, where each arm has a small Mach-Zehnder interferometer for compensation of amplitude mismatching in the arms. The extinction ratio was 50 dB. (2 pages)

We demonstrated optical frequency sweep using optical single sideband modulation technique, where the frequency shift range was 2 GHz-10 GHz. Undesired sidebands due to electric phase errors can be compensated by synchronized bias control. (2 pages)

We propose a high-speed external modulation method for optical minimum-shift keying (MSK), where initial phase control together with FSK modulation enables externally continuous-phase modulation with arbitrary frequency deviation. 10-Gb/s MSK modulation spectrum was experimentally obtained. (2 pages)

We propose a high-speed versatile lightwave modulator which can generate on-off-keying, phase-shift-keying and frequency-shift-keying signals. 40 Gbit/s optical FSK modulation was demonstrated by using the modulator consisting of four phase modulators, where frequency deviation was 80 GHz. (2 pages)

We propose a novel optoelectronic oscillator (OHO) made of a push-pull Mach-Zehnder modulator biased at null point, oscillating at half the frequency of feedback signal. Optical two-tone signal with 10.5-GHz frequency difference is experimentally generated.

We investigated stability of millimetre-waves generated by using an integrated reciprocating optical modulator consisting of two optical filters and an optical modulator. The amplitude fluctuation was less than 1% without using feedback stabilization techniques.

We demonstrate high-speed optical FSK transmission over a 95 km SMF at 10 Gbit/s using an integrated LiNbO/sub 3/ optical FSK modulator consisting of four phase modulators. FSK signal was demodulated by an optical interleaver.

In this paper, we experimentally demonstrate simultaneous multichannel wavelength multicasting (MWM) and exclusive-OR logic gate multicasting (XOR-LGM) for three 10Gbps non-return-to-zero differential phase-shift-keying (NRZ-DPSK) signals in quantum-dot semiconductor optical amplifier (QD-SOA) by exploiting the four-wave mixing (FWM) process. No additional pump is needed in the scheme. Through the interaction of the input three 10Gbps DPSK signal lights in QD-SOA, each channel is successfully multicasted to three wavelengths (1-to-3 for each), totally 3-to-9 MWM, and at the same time, three-output XOR-LGM is obtained at three different wavelengths. All the new generated channels are with a power penalty less than 1.2dB at a BER of 10(-9). Degenerate and non-degenerate FWM components are fully used in the experiment for data and logic multicasting.

In this paper, we propose and investigate an optical multiplexing technique, called orthogonal time-frequency domain multiplexing (OTFDM) with multilevel signaling, that enables ultrafast, high-spectral-efficiency transmission. On the transmitter side, optical rectangular combs generated from electro-optic modulators are data modulated and multiplexed into the time-frequency domain. On the receiver side, the OTFDM signal is demultiplexed and coherently demodulated by coherent matched detection in which multi-frequency homodyne mixing with a locally generated comb down-converts a target OTFDM tributary channel into baseband frequencies. These multiplexing and demultiplexing processes are fully performed in the optical domain using optoelectronic devices, without the use of fast Fourier transform circuits or optical channel selection filters. It is analytically and numerically proved that multilevel signals such as nPSK and nQAM can be OTFDM-multiplexed and demultiplexed while retaining orthogonality between tributaries. The spectral efficiency of this method reaches as high as 1 Baud/Hz per single polarization, i.e., the Nyquist limit, enabling high-bandwidth operation unrestricted by an electronic response in the transmitter or receiver.

The generation of a 40-Gb/s 16-QAM radio-over-fiber (RoF) signal and its demodulation of the wireless signal transmitted over free space of 30 mm in W-band (75-110 GHz) is demonstrated. The 16-QAM signal is generated by a coherent polarization synthesis method using a dual-polarization QPSK modulator. A combination of the simple RoF generation and the versatile digital receiver technique is suitable for the proposed coherent optical/wireless seamless network.

A monolithically-integrated quad-parallel Mach-Zehnder optical modulator has been fabricated. 3 and 6 dB electro-optical bandwidths of Mach-Zehnder structures embedded in the modulator were evaluated as 22 and 36 GHz, respectively. By using the monolithic optical modulator, a 10 Gbaud 16-level quadrature amplitude modulation (QAM) signal was successfully obtained.

The broadband wavelength tunability of femtosecond pulse generation using a Mach-Zehnder-modulator-based flat-comb generator (MZ-FCG) and a dispersion-flattened dispersion-decreasing fiber (DF-DDF) was demonstrated. Near-Fourier-transform-limit picosecond pulses generated from the MZ-FCG were compressed into femtosecond pulses by adiabatic soliton compression. By tuning the wavelength of the input cw light, 200 fs, 10 GHz pulses were generated in the wavelength range of 1,535 to 1,570 nm. Such wide-range wavelength tunability was realized by both the independence of a comb-flattening condition from the inputted wavelength and the dispersion flatness of the DF-DDF.

Optical quadrature amplitude modulation (QAM) attracts considerable attention in the enhancement of communications capacity, due to its high spectral efficiency. However, this modulation format is more sensitive to signal distortion than conventional formats, making it more difficult to create, transmit, and detect signals. In this paper, we propose an adaptive scheme for demodulation of the distorted optical signals with paying attention to use of DSP-technology. The scheme is based on the adjustment of the thresholds against the signal distortion. Successful demodulation of optical QAM signals is demonstrated with a sufficiently low bit-error rate.

This Letter reports on picosecond pulse generation at a repetition of 10 GHz by using a single-stage electro-optic LiNbO(3) Mach-Zehnder modulator, stressing the simplicity of its setup. It is analytically and experimentally proved that dual-arm modulation with in-phase sinusoidal signals having slightly different amplitudes generated a highly coherent optical comb with a great spectral flatness and a parabolic phase relationship in its spectrum. The generated comb was Fourier synthesized and shaped into an ultrashort pulse train with an optical bandpass filter and a dispersive fiber. The pulse source was highly stable, exhibiting an ultralow timing jitter of less than 130 fs.

An optoelectronic oscillator that employs a reciprocating optical modulator is demonstrated. By giving positive optoelectronic feedback to the modulator, the reciprocating modulation in the modulator effectively multiplies the fundamental oscillation frequency by several times. A 52.8 GHz millimetre-wave signal is generated by self-oscillation.

Wavelength-tunable ultra-flat optical frequency comb generation is demonstrated using only a conventional Mach-Zehnder modulator that is asymmetrically dual-driven by large-amplitude sinusoidal signals with different amplitudes. A 10 GHz-spaced frequency comb with a 10 dB bandwidth of 230 GHz was experimentally generated. In addition, 50 nm widely wavelength tunable operation was achieved.

Ultrafast and precise optical frequency sweep for fine spectral measurement has been demonstrated by using single-sideband modulation, where the theoretical limit of resolution owing to the uncertainty between time and frequency was almost achieved.

We describe the use of two-photon absorption in submicron silicon wire waveguides for all-optical switching by cross-absorption modulation. Optical pulses of 3.2 ps were successfully converted from high power pump to low power continuous-wave signal with a fast recovery time. High speed operation was based on the induced optical absorption from non-degenerate two-photon absorption inside the waveguides.

We propose an optical initial phase control technique for external modulation in the format of minimum-shift keying (MSK). In this scheme, the optical phase discontinuities inherent to external frequencyshift- keying (FSK) modulation are compensated by use of an initial phase controller in conjunction with a FSK modulator. We present the principle of the control method and then numerically and experimentally prove that the signal has a modulation spectrum more compact than that of conventional binary phase-shift keying. 10-Gbit/s external modulation in MSK format was experimentally demonstrated.

A reciprocating optical modulator consisting of two optical filters and an optical phase modulator that has a resonant electrode to enhance modulation efficiency at a particular frequency is proposed. Lightwave reciprocates in the modulator, where the optical phase modulator placed between the two optical filters acts both on forward and backward lightwaves.

We have realized a novel optical modulation format conversion using double-sideband suppressed-carrier modulation. An optical wideband frequency-shift-keying (FSK) signal, generated by an external FSK modulator, can be directly converted into an optical phase-shift-keying (PSK) signal, where the FSK signal having two spectral components was fed to an optical intensity modulator followed by an optical bandpass filter. Optical frequency of the FSK signal was mapped into optical phase of the bandpass filter output whose phase deviation depends on a chirp of the FSK signal. We demonstrated modulation format conversion from FSK to PSK at 10 Gbps, by using a high-speed optical FSK modulator and a dual electrode Mach-Zehnder intensity modulator.

A novel optoelectronic oscillator (OEO) made from a LiNbO3 intensity modulator with a resonant electrode in double-stub structure is proposed and demonstrated. The OEO can generate an optical clock or subcarrier signal with self-oscillation. The resonant electrode makes it possible for the OEO to oscillate at a single frequency and with high efficiency. 6.9 GHz singlemode oscillation was achieved with an optical input threshold power of 0.01 mW.

An optical frequency-shift-keying (FSK) modulator with a pair of Mach-Zehnder structures that can switch optical frequency is developed. The operation is demonstrated at a 10 Gbit/s FSK transmission conducted on a standard single-mode fibre of 60 km, where the FSK signal is demodulated by a fibre Bragg grating.

Using the cascade of the second-harmonic generation and the difference frequency mixing in a 30 mm-long quasi-phase matched LiNbO3 waveguide device, all-optical time-division demultiplexing of a 160 Gbit/s signal into 10 Gbit/s channels is demonstrated. The power penalty is as small as 2.5 dB at the bit error rate of 10−9, which is attributed to crosstalk of the switch.

We propose a pump-linewidth-tolerant wavelength conversion scheme with coherent two-tone pump, and demonstrate high quality wavelength conversion of 64QAM signals with

We proposed a novel scheme for the fourth order harmonic generation with two Mach-Zehnder (MZ) optical modulators. High extinction ratio intensity modulation technique with active trimmers is used for high spurious suppression ratio. Each modulator has a pair of trimmers in the arms of the MZ structure. The trimmers can compensate amplitude imbalance in the MZ structure, and suppress residual carrier in double sideband suppressed carrier (DSB-SC) modulation. A photonic local signal of 42GHz was generated from a 10.5GHz modulating signal, where spurious component intensity was 41.8dBc without using any optical or electric filters for spurious suppression. The upper limit of modulating frequency in the state-of-the-art is about 50GHz. Thus, we can generate high-purity stable 200GHz photonic local signals by using this technique, which would be useful for large scale millimeter wave antenna arrays.

We present a newly developed 32-pixel high-speed 2D photodetector array operated at up to 39 Gbaud, and its application for WDM FSO communications. 4-WDM 25-Gbaud FSO parallel beams could be directly detected by the 2D-PDA.

We studied a 10-GHz 32-pixel two-dimensional photodetector array for advanced optical fiber communications and LIDAR applications. Electromagnetic field simulation revealed the RF crosstalk problem between pixels. A fabricated high-speed photodetector array will be discussed.