Tadasi Sueta

Optical pulse compression using high-frequency electrooptic phase modulation

An electrooptic method of generating and compressing optical pulses in the picosecond range is described. The method utilizes electrooptic phase modulation together with group delay/velocity dispersion and is applicable to most CW lasers. From the theoretical analysis, it is shown that normal as well as anomalous dispersion is applicable for pulse compression and that nearly transform-limited pulses can be obtained by the optimum choice of group-delay dispersion. In experiments, pulse compression was utilized for a CW Ar laser using a LiTaO/sub 3/ electrooptic phase modulator with a diffraction grating. Almost transform-limited pulses of 2.1 ps were obtained at 9.35-GHz repetition. The possibility of generating subpicosecond pulses down to several tens of femtosecond pulses is also discussed. >

High‐repetition‐rate optical pulse generator using a Fabry‐Perot electro‐optic modulator

A high‐repetition‐rate optical pulse generator which employs a Fabry‐Perot electro‐optic modulator as the output coupler of a laser resonator was constructed. Using this generator with a He–Ne 6328‐A laser tube, 21‐psec optical pulses at a repetition rate of 2.7 × 109 pps were experimentally obtained with an average power level of 0.5 mW. In addition, it is demonstrated that the width of the pulses obtained from this generator can be narrowed without regard to the gain‐linewidth limitation. This kind of pulse generator may be particularly useful for obtaining short optical pulses from low‐gain gas lasers, and it is possible to obtain 1010‐pps picosecond pulses from a He–Ne 6328‐A laser.

Operation mechanism of the single-mode optical-waveguide Y junction.

An explanation of the working mechanism of single-mode optical-waveguide Y junction is presented. Taking into account the contribution of radiation mode, the power conservation at the junction is clearly verified. Also, the analogy between the behavior of the single-mode Y junction and that of a beam splitter is discussed.

Integrated optic pressure sensor on silicon substrate.

A novel integrated optic pressure sensor was constructed with the Mach-Zehnder interferometer structure of glass waveguides on a silicon substrate. Pressure is sensed by detecting the deformation of a thin diaphragm fabricated by using the anisotropic etching of a silicon substrate. The basic design concept of the present sensor was provided by analyzing its operation. The measurable pressure range and the sensitivity can be set by the proper selection of the diaphragm structure. A device was built and its operation performances were tested at 633 nm. For the fabricated device, the measured halfwave pressure was 0.8 x 10(5) Pa and the extinction ratio was 10 dB.

Optical-waveguide hybrid coupler

As a novel guided-wave passive device, the optical-waveguide hybrid coupler is proposed and its first known demonstration is reported. The proposed device consists of symmetric and nonsymmetric branching forks connected at a junction. An explanation of the working mechanism is presented. The feasibility of the device is confirmed by constructing and testing the hybrid coupler with an integrated Mach-Zehnder interferometer composed of a Y junction and phase shifters using a Ti-diffused LiNbO(3) waveguide.

LiNbO 3 traveling-wave light modulator/switch with an etched groove

A Ti dffused lithium niobate traveling-wave interferometric light modulator/switch with a groove excavated at the electrode gap has been fabricated and tested at microwave frequency. The groove suppresses the undesirable light coupling between the two parallel waveguides for the phase shifting section so that the drive voltage is decreased by reducing the separation of the parallel waveguides, or of the electrodes. In addition, the groove decreases the effective index for the modulating wave to reduce the velocity mismatch between light wave and microwave so that the bandwidth is broadened. The modulation experiment was carried out from dc to 15 GHz at 633 nm light wavelength. For the modulator with the electrodes 6 mm long and 10 μm apart, the half-wave or switching voltage was 3 V, the extinction ratio was 18 dB, the 3 dB bandwidth was 12 GHz and a P/\Delta f of 1.5 mW/GHz was obtained.

Integrated optic devices for microwave applications

Integrated optic devices designed for use in microwave applications are reviewed and the prospects for these new technologies are discussed. First, the modulation of light at microwave frequencies is briefly summarized. Then integrated optical circuits containing high-performance modulators are presented. Efficient light modulation at millimeter-wave frequencies is discussed. Finally, possible applications of high-speed light modulators are shown. >

Optical fiber sensors using the method of polarization-rotated reflection

The method of polarization-rotated reflection is applied to sensors with polarization-maintaining optical fibers. By the use of this scheme, stable measurement can be realized because the fluctuation of the light propagation characteristics in the fiber is canceled automatically without any additional active phase compensation techniques. Several kinds of sensors were designed for the measurement of different physical values. A magnetic field sensor and a temperature sensor were built and the performances were tested to confirm their basic features experimentally.

An integrated 1 × 4 high-speed optical switch and its applications to a time demultiplexer

A one-to-four optical switch was fabricated by integrating three interferometric modulators on az-cut LiNbO3substrate. Each of three modulators consists of a symmetric Y-junction and an asymmetric X-junction as 3-dB input and output couplers, respectively, to function as a one-to-two light switching element. They are arranged so that the input light is switched at the first stage into two intermediate guides which are connected to two second stage elements where light signals are further divided into the final four output ports. The measured switching voltages were 6.6 and 13.3 V for the first- and second-stage elements respectively, forTE-mode at a 633-nm wayelength, and the maximum crosstalk ratio was -18 dB. The device was driven by a 1-GHz signal and the transmission characteristics for four output ports were measured. The device performs the function of demultiplexing an optical signal from 4 to 1 Gbit.

Picosecond signal sampling and multiplication by using integrated tandem light modulators

A picosecond signal sampling experiment was performed successfully by using integrated optic technologies. Two interferometric modulators of the traveling-wave and lumped types were integrated in series on a LiNbO 3 crystal surface. The traveling-wave modulator was oprated as a sampling gate activated by an electrical pulse train of 1-GHz repetition from a comb generator, while the lumped one was driven by a 2-GHz CW signal. The aperture time of the gate was estimated about 52 ps from the measurement using the image tube streak camera modified to sinusoidal scan at 1 GHz. Also a signal multiplication experiment was carried out using 100- and 10-MHz CW signals.