Sang-Yung Shin

Design of corrugated waveguide filters by the Gel’fand–Levitan–Marchenko inverse-scattering method

A rigorous design rule of corrugated waveguide filters is developed by employing the Gel’fand–Levitan–Marchenko inverse-scattering method for the two-component coupled-wave equations of the Zakharov–Shabat type. In the course of developing the design method, the coupled Gel’fand–Levitan–Marchenko integral equations for the Zakharov–Shabat system having no discrete spectrum are shown to be reducible to a set of linear simultaneous equations amenable to simple numerical calculations when the reflection coefficient is a rational function.

Optical implementation of the Hopfield model for two-dimensional associative memory

Optical implementation of Hopfields neural network model [Proc. Natl. Acad. Sci. USA 79, 2554 (1982)] for two-dimensional associative memory is discussed. Two-state neuron elements are represented by a twisted nematic liquid-crystal optical switch array, and three-dimensional holographic interconnections are realized with these elements. Unipolar connections, created by adding a constant to bipolar interconnections and compensating them with an input-dependent thresholding operation, are realized. The 16- (4 x 4) neuron system model acts as a content-addressable associative memory with error-correction capability.

Dynamic gain and output power control in a gain-flattened erbium-doped fiber amplifier

We demonstrate an erbium-doped fiber amplifier (EDFA) that has a flat-gain spectrum over an 18-nm band and a constant per-channel output power regardless of the input powers and the number of channels. The gain flatness and the constant output are obtained by changing the laser diode pump power and the attenuation of the voltage-controlled attenuator (VCA) dynamically. The response times of pump control circuit and attenuator control circuit are 650 ns and 9 ms, respectively. The power excursion of surviving channel in an EDFA with fast control circuit is /spl sim/1% of that without fast control circuit when channels are added or dropped.

Mode-order converter in a multimode waveguide

A novel device that converts the order of modes in an integrated-optic multimode waveguide was proposed and fabricated. The device consists of two mode splitters and tapered waveguides. Its operation at a wavelength of 1.55 microm was confirmed by observation of the output mode profiles. The cross talk measured by an indirect method was >10.2 dB. The excess loss with reference to a straight multimode waveguide was 1.5 dB, compared with the propagation loss of a straight multimode waveguide.

Fabrication of polymeric large-core waveguides for optical interconnects using a rubber molding process

Polymeric large-core (47 /spl mu/m/spl times/41 /spl mu/m) optical waveguides for optical interconnects have been fabricated by using a rubber molding process. For low-cost low-loss large-core waveguides, our newly developed thick-photoresist patterning process is used for a master fabrication. Also a low-loss thermocurable polymer, perfluorocyclobutane (PFCB), is used in fabricating optical waveguides by rubber molding for the first time. The propagation loss is measured to be 0.4 dB/cm at the wavelength of 1.3 /spl mu/m, and 0.7 dB/cm at the wavelength of 1.55 /spl mu/m.

Tunable polymer waveguide notch filter using a thermooptic long-period grating

The feasibility of a polymer waveguide notch filter using a thermooptic long-period grating is demonstrated experimentally. It consists of a channel waveguide, a cladding surrounding the channel, and buffer layers sandwiching the cladding. Periodic heaters, placed on the filter surface, induce thermooptically a long-period grating. The attenuation of the filter is controlled by adjusting the power applied to the periodic heaters. The filter is made of thermocurable polymers by using conventional processes. For transverse-electric mode, its attenuation increases from 0 to 27 dB as the power applied to the periodic heaters increases from 0 to 851 mW. For the maximum attenuation spectrum, the 3-dB bandwidth of the attenuation band is 16 nm.

Fabrication of ridge waveguides by UV embossing and stamping of sol-gel hybrid materials

Multimode large core (45/spl times/35 /spl mu/m/sup 2/) optical ridge waveguides are fabricated in the room temperature by ultraviolet (UV) imprinting of soft rubber template with the organic-inorganic sol-gel hybrid materials. The fabrication processes may be either well-known UV embossing or stamping. A new sol-gel hybrid material that is thermally stable has been developed for the fabrication of low-loss optical waveguides. The UV curable methacrylic sol-gel hybrid material is used for the core layer and fluorinated methacrylic sol-gel hybrid material is used for the cladding layer. The optical propagation loss of fabricated waveguide measured by the cutback method is 0.36 dB/cm at 850 nm and the surface roughness of waveguide is about 5 /spl Aring/ root mean square.

Poling-induced waveguide polarizers in electrooptic polymers

In order to demonstrate polymeric waveguide polarizers, photobleached polymer waveguides supporting both TE and TM modes are integrated with poling induced polymer waveguides that support either TE or TM modes. Fabrication parameters like UV exposures and poling voltages are controlled to reduce excess losses due to the mode profile mismatch between the connected waveguides. A TM-pass polarizer is realized by poling the polymer in the vertical direction. For TE-pass polarizer the polymer is poled horizontally by using four poling electrodes which enhance the uniformity of the poling field direction. The measured excess loss is less than 0.5 dB, and polarization extinction ratios for TM-pass and TE-pass polarizers are 20.7 dB and 17.1 dB, respectively.

Lithium niobate integrated-optic voltage sensor with variable sensing ranges

A lithium niobate integrated-optic voltage sensor with variable sensing ranges is realized, which consists of a Mach-Zehnder interferometric wave-guide with an array of buried electrodes. The buried electrodes are fabricated by wet etching of proton-exchanged lithium niobate. In this sensor, the sensing range is almost linearly controlled by simply changing the electrode gap and length. Thus the whole sensing range is effectively extended by integrating a number of electrodes which give different sensing ranges. A sensor with three variable sensing ranges is fabricated and its overall sensing range covers 7 mV to 400 V.

0.1-nm narrow bandwidth transmission of a 2.5-Gb/s spectrum-sliced incoherent light channel using an all-optical bandwidth expansion technique at the receiver

We introduce a new all-optical technique to transmit a spectrum-sliced incoherent channel with its optical bandwidth smaller than the conventional limit. As a demonstration, we reduce the optical bandwidth to only 0.1 nm for the 2.5-Gb/s incoherent channel transmission. Even though the signal-to-noise ratio (SNR) is poor during the transmission, sufficient SNR can be obtained through the intrachannel four-wave mixing at the receiver. With this slim bandwidth transmission technique, the maximum number of spectrum-sliced wavelength-division-multiplexed channels can be increased greatly and the dispersion penalty can be reduced simultaneously.