Hiroshi Haga

Guided‐wave optical wavelength demultiplexer using an asymmetric Y junction

An optical wavelength demultiplexer using an asymmetric Y junction is numerically analyzed and the experimental results are reported. This demultiplexer utilizes both the mode splitting characteristic of an asymmetric Y junction and the waveguide dispersion of channel waveguides. Analysis shows that the device with step‐index profile has more than 20 dB isolation for wavelengths with 6.5% separation from the center wavelength. The fabricated device composed of two‐step ion exchanged soda‐lime glass waveguides coated asymmetrically with Corning 7059 glass thin film separated the lights of 0.63 and 0.84 μm wavelengths.

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.

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.

ELECTRIC FIELD RESPONSE OF SECOND ORDER OPTICAL NONLINEARITY IN DYE DOPED POLED POLYMER

The optical nonlinearity induced by electrical poling decays gradually in poled polymers. This suggests that the molecular alignment can be reoriented in the polymer matrix at room temperature by the external electric field. We measured the frequency responses and the temperature characteristics of second‐harmonic generation (SHG) in a dye doped polymer in order to clarify the electric field dependence of the nonlinearity. The experimental results show that there is a slow response of the SHG coefficient variation due to the reorientation of nonlinear molecules and another fast response. This characteristic can be applied to develop a new type of nonlinear optical devices by dynamically controlling the nonlinearity of the material by the external electric field.

Integrated optic error detecting circuit using Ti:LiNbO 3 interferometric light modulators

An electrooptic error detecting circuit is proposed and demonstrated which is constructed by integrating an array of waveguide interferometers with multielectrodes. When the electric signals corresponding to the error detecting codes are applied to the present device, the error detection signals are obtained as optical signals from the waveguide outputs. From these optical outputs it is found whether the input signals include errors or not, and which bit, if there is any error, is an error bit. The performance is confirmed by using an experimental device for seven-bit Hamming codes.

Electrically tunable guided-wave optical frequency converter using dye-doped polymers

We propose a new technique of tuning the phase-matching condition for guided-wave optical frequency converter, and analyze the basic performances theoretically. Quasi-phase matching (QPM) method is the basis of our proposed tunable device. The QPM grating is divided into some segments, and tuning is performed by selecting the optimum phase of each segment. We can adjust the phase of the segment by using the controllability of the optical nonlinearity of dye-doped polymers with poling electric field. This tuning technique is the first proposal in which the characteristic of dye-doped polymers is effectively utilized in guided-wave optical frequency conversion devices.

Precise control of phase constant of optical guided-wave devices by loading Langmuir-Blodgett films

A Langmuir-Blodgett film is used as a cover layer of single mode waveguide to precisely control the phase constant of the guided-mode. The change of phase constant caused by the cover layer is evaluated by measuring the retardation between the two arms of the ion-exchanged glass waveguide Mach-Zehnder interferometer, a part of which is loaded by Langmuir-Blodgett films. A monolayer of cadmium stearate has varied the phase constant on the order of 10/sup -6/. This method can be used to adjust the phase difference or shift to tune the performance of guided-wave devices such as directional couplers and modulators. >

Ultrafast Traveling-Wave Light Modulators with Reduced Velocity Mismatch

Since the concept of optical guided-wave devices was introduced, remarkable progress has been made in the characteristics of opto-electronic devices. One of the most important features of waveguide-type components is the possibility of realizing higher performances compared with the bulk type counterpart. It is of great interest in applications like ultrafast signal processing, communication, and sensors.

Effect of plasticization of dye doped polymer on second‐order optical nonlinearity induced by electric field

The nonlinear molecules dispersed in the polymer with low glass transition temperature (Tg) can be easily reoriented. The plasticizer is utilized in order to lower the Tg of the polymer matrix. We measured the frequency responses of second‐harmonic generation in a dye doped plasticized polymer to clarify the electric field dependence of the second‐order optical nonlinearity. We utilize poly(methyl methacrylate) doped with 2‐methyl‐4‐nitroaniline as the dye doped polymer. di(ethyl‐2 hexyl) phthalate is used as the plasticizer. The experimental results show that the rotational mobility was enhanced up to ten times by a DOP dose of 13.5 wt% in comparison with a dose of 0 wt% at 20°C. Therefore, this method is useful to increase the controllability of the optical nonlinearity by the electric field at room temperature.