Katsuhiko Hirabayashi

Tunable liquid-crystal Fabry-Perot interferometer filter for wavelength-division multiplexing communication systems

We explain how to obtain the bandwidth and tunable range required for wavelength-division multiplexing communication systems and how to design tunable liquid-crystal Fabry-Perot interferometer filters. The main factors determining the performance are liquid-crystal loss, mirror loss, surface roughness, and parallelism, as well as mirror reflectivity and cavity gap. Experimental results closely agree with the designed performance. Temperature dependence, response time, acceptable input power, and reliability are investigated. Pigtailed polarization-independent filter modules with a Peltier controller are made and are shown to have low polarization dependence ( >

Optical-fiber variable-attenuator arrays using polymer-network liquid crystal

This paper describes compact variable optical attenuator arrays made by using fiber splicers and polymer-network liquid crystal. Fibers are inserted into the splicers and the gaps between the ends of the fibers are filled with the polymer-network liquid crystal. The residual loss for each array element is low (about 0.8 dB), the attenuation of 1.55-/spl mu/m light is about 8 dB and the driving voltage is 20 V/sub rms/. The polarization dependence is <2 dB. The power consumption is also very low (30 nW/ch). They are used for channel power equalizers for WDM systems.

Free-space optical interconnections with liquid-crystal microprism arrays

Liquid-crystal microprism arrays are shown to be useful for providing electrically controlled alignment of optical beams and fixed various free-space optical interconnections. They can deflect closely spaced micro-optical beams individually to any position with high transmittance (95%), high deflection angle (~10°), and low voltage (<2.8 V(rms)). Various fixed optical interconnections can be made simply by changes in the voltages applied to the microprism.

Tunable wavelength filter using nano-sized droplets of liquid crystal

An electrically tunable optical filter has been developed that uses a polymer containing fine droplets of nematic liquid crystal as the active cavity in a Fabry-Perot interferometer (FPI). This FPI filter, whose finesse was 62, had a free spectral range of 37 nm in the 1.55-/spl mu/m range with a full-width at half maximum of 0.6 nm and a transmission loss of 2.4 dB. The polarization dependent loss was smaller than 0.17 dB. The transmitted peak wavelength decreased with an electric field. This resulted in a tuning range of 10 nm at 300 V. The switching time was about 370 /spl mu/s.

Liquid crystal devices for optical communication and information processing systems

Abstract This paper reviews liquid crystal optical devices including tunable filters, photonic switches and spatial light modulators, and examines their application to optical communication and information processing systems. Optical processing has three major advantages: massive parallelism, high speed and broad wavebands. Compared with typical optical materials including silica, semiconductors and inorganic electrooptic crystals used in communication systems, a liquid crystal has a number of outstanding features including its large refractive index change and large polarization rotation power at a low voltage. These features make it possible to develop new optical components.

Narrow-band tunable wavelength-selective filters of Fabry-Perot interferometers with a liquid crystal intracavity

Optimum designs for tunable wavelength-selective filters of Fabry-Perot interferometers with a liquid crystal intracavity are described. A nematic liquid crystal with index numbers 1.5506 and 1.4771 was used. Methods of aligning liquid crystal molecules were studied. The filters provide high finesse (150-410), high transmittance (20-70%), narrow transmission peak (FWHM: 0.17-0.35 nm), and a large shift (>50 nm) at a wavelength of 1.5 mu m. These filters have a potential to select over 50 channels in WDM.<<ETX>>

Liquid crystal variable optical attenuators integrated on planar lightwave circuits

Variable optical attenuators using polymer-network liquid crystal have been integrated with the pitch of 250 /spl mu/m on planar lightwave circuits. Trenches are cut in the direction perpendicular to the parallel light waveguides into planar lightwave circuits, a transparent electrode is deposited inside the trenches, and the trenches are filled with polymer-network liquid crystal. The typical attenuation range is 18 dB when the driving voltage is <20 Vrms at 1.55-/spl mu/m wavelength. The power consumption is estimated to be very low (200 nW/ch).

Optical beam direction compensating system for board-to-board free space optical interconnection in high-capacity ATM switch

In interconnections between bookshelf-assembled asynchronous transfer mode (ATM) switch boards, a large number of micro-optical signal beams can be optically interconnected by a beam direction compensating system using a vertical cavity surface emitting laser, an x-y beam positioning sensor and a beam deflector made of an adjustable liquid prism. This beam direction compensating system can suppress the decrease in coupling efficiency between transmitters and receivers to no more than 15%, even if boards are inserted and extracted repeatedly, and are shocked repeatedly at a high intensity of 100 G. The compensation is very fast (20 ms). Furthermore, various optical interconnections necessary for ATM switching networks can be achieved by beam deflectors of a liquid crystal microprism array. In this preliminary study, we fabricate no more than eight-channel optical interconnections. However, since one surface emitting laser diode can have many channels in a small area (64 channels per 4 mm/sup 2/) and the aperture of this adjustable liquid prism is wide (28 mm in diameter) and uniform, a huge number of optical interconnection channels is possible using this system.

ZnS:Mn Electroluminescent Device Prepared by Metal-Organic Chemical Vapor Deposition

AC thin-film ZnS:Mn electroluminescent devices were fabricated by metal-organic chemical vapor deposition, using dimethylzinc and H2S as source gases and tri-carbonyl-methyl-cyclopentadienyl-Mn as the dopant gas. Tri-carbonyl-methyl-cyclopentadienyl-Mn was decomposed by heating at 580°C at the entrance of the reactor, enabling the ZnS film to be doped homogeneously with the optimum concentration of Mn. The brightness of metal/insulator/semiconductor electroluminescent devices made with the resulting ZnS:Mn film was more than 5000 cd/m2 (5 kHz, 130 V), while metal/insulator/semiconductor/insulator electroluminescent devices had a brightness of more than 6000 cd/m2 (5 kHz, 160 V) and exhibited hysteresis in their brightness-voltage characteristics.

Color Electroluminescent Devices Prepared by Metal Organic Chemical Vapor Deposition

This paper discusses the preparation of AC thin film ZnS:Tb (green), Sm (red) and Tm (blue) color electroluminescent devices by metal organic chemical vapor deposition, using dimethylzinc and H2S as source gases. A new doping method for luminescent centers was used. This was accomplished by evaporating TbF3, SmF3 SmCl3 and TmF3 after they had been heated to their melting points during the growth of ZnS in a MOCVD reactor. The maximum brightnesses of ZnS:TbF3, ZnS:SmCl3 and ZnS:TmF3 are 5000, 1000 and 10 cd/m2. The ZnS:SmCl3 EL devices showed a deeper red chromaticity than the ZnS:SmF3 EL ones.