Yoshito Shuto

Optical intensity modulation in a vertically stacked coupler incorporating electro‐optic polymer

A vertically stacked directional coupler incorporating electro‐optic poled polymer was fabricated by spin coating, photolithography, and reactive ion etching processes, based on the fabrication technique used for polymeric single‐mode channel waveguides. Vertically coupled operation at 1.3 μm have been achieved between two stacked channels which were kept 3.5–5 μm apart by a narrow cladding layer. The intensity modulation has been clearly demonstrated in the coupler with electrodes when a voltage is applied at 10 kHz between them.

Reflection measurement technique of electro‐optic coefficients in lithium niobate crystals and poled polymer films

A simple reflection technique proposed by Teng and Man [Appl. Phys. Lett. 56, 1734 (1990)] as well as independently by Schildkraut [Appl. Opt. 29, 2839 (1990)] for measuring the electro‐optic coefficients of poled polymer films is applied to measure the r33 values of both z‐cut lithium niobate crystal and diazo‐dye‐substituted polymer films. The measured r33 value of the lithium niobate crystal is in excellent agreement with the known value, and the observed r33 values of the poled polymer films agree well with those predicted from the second‐harmonic‐generation measurements.

Quasi‐phase‐matched second harmonic generation in a polymer waveguide with a periodic poled structure

Quasi‐phase‐matched (QPM) second harmonic generation in a poled polymer waveguide has been realized. A waveguide with a periodic structure was fabricated by conventional photolithography and reactive ion etching. The waveguide with a QPM structure was composed of poled polymer and UV cured epoxy resin. Phase‐matched second harmonic generation was observed, using laser light with a fundamental wavelength 1.48–1.65 μm. This phase matched condition was dependent on the periodic length. The waveguide had a typical second harmonic generation efficiency of about 4×10−1% W−1 cm−2 around a wavelength of 1.55 μm.

Quasi-phase-matched second-harmonic generation in diazo-dye-substituted polymer channel waveguides

First-order quasi-phase-matched (QPM) second-harmonic generation (SHG) is demonstrated in a poled diazo-dye-substituted polymer channel waveguide. The channel waveguide with a nonlinear grating was fabricated by the serial grafting technique using conventional photolithography and reactive ion etching. The dependence of the conversion efficiency on both the waveguide parameter and the grating structure was derived theoretically. A normalized internal conversion efficiency of 1.1% W/sup -1/ cm/sup -2/ at 1.586 /spl mu/m was obtained in the fabricated waveguide with a phase-matched interaction length of 3.4 mm. The experimentally obtained conversion efficiency is compared with the theoretical value, taking into account the effect of mode-mismatching and propagation loss.

Noncollinearly Phase-Matched Second Harmonic Generation in Stilbene-Dye-Attached Polymer Thin Films

Noncollinearly phase-matched second harmonic generation (SHG) of Nd:YAG-laser light (1.064 µm) has been measured in a thin-film waveguide of stilbene-dye substituted methacrylate polymer on a glass substrate. The second-order nonlinear optical coefficient d33 of the corona-poled film is 1.6×10-8 esu (at 1.064 µm). The phase-matching crossing angle of two guided fundamental beams is about 3.6° in the 1.38±0.02 µm-thick polymer waveguide. The SHG efficiency has been estimated to be about 5×10-5% for the fundamental peak power of about 130 W. The broad angular dependence of SH power has resulted from the short interaction length (0.1~1 mm order) of two fundamental beams.

Plastic module of laser diode and photodiode mounted on planar lightwave circuit for access network

Low-cost plastic packaging of laser diodes and photodiodes mounted on planar lightwave circuit (PLC) platform are developed and its reliability is confirmed under various environmental and endurance tests. The high performance of the module is maintained under reliability tests, such as high-humidity high-temperature tests (85/spl deg/C, 85%RH) and temperature cycling tests (-40/spl deg/C/85/spl deg/C). No laser diodes show any device characteristics change during environmental tests and their stability has very little dependence on current bias. Although the photodiodes show an increase in leakage current under high-temperature high-humidity tests and the rate of leakage current increase is proportional to the square root of bias voltage, the increase is negligible for system use. These plastic modules can be applied to actual access networks and other fiber-optic networks.

Vertically stacked coupler and serially grafted waveguide: Hybrid waveguide structures formed using an electro-optic polymer

Two hybrid waveguide structures formed using an electro-optic polymer are described. They are a vertically stacked coupler and a serially grafted waveguide. These structures were fabricated by spin-coating, photolithographic, and reactive ion etching processes. Directional coupling was successfully demonstrated between the vertically stacked waveguides, and the crosstalk was −15 dB. This waveguide structure was applied to an optical intensity modulator. The serially grafted waveguide allows butt coupling between the functional waveguide and passive waveguides, and the connection loss at a grafting point was as low as 0.005 dB. This waveguide structure was applied to a Mach–Zehnder optical intensity modulator and a quasi-phase-matched second-harmonic generator.

Electrooptic Light Modulation in Poled Azo-Dye-Substituted Polymer Waveguides

The DC electrooptic modulation of 0.633-µm He-Ne laser light has been measured in thin-film waveguides of copolymers containing Disperse Red-1 (DR1) and/or novel dis-azo-dye side chains. The polarized laser light is butt-coupled to the polymer waveguides with propagation length of 4 mm and film thickness of 10-15 µm. The DC linear electrooptic coefficients r33 of the poled DR1- and dis-azo-dye-substituted polymer films are estimated to be 18 pm/V and 27 pm/V at 0.633 µm. Comparison with second-harmonic generation results demonstrates that the DC linear electrooptic effect in the poled azo-dye-substituted polymers is primarily electronic in nature.

Electrooptic light modulation and second-harmonic generation in novel diazo-dye-substituted poled polymers

The nonlinear-optical susceptibilities, x/sup (2)/, of a diazo-dye-substituted polymer poled with high electric fields were determined experimentally and theoretically. The electrooptic modulation of He-Ne laser light in a traveling-wave channel-waveguide modulator using the diazo-dye-substituted poled polymer is reported, and the linear electrooptic coefficient of the poled polymer is estimated from a measured half-wave voltage. The polymer studied is a poly(methyl methacrylate) copolymerized with a methacrylate ester of the dicyanovinyl-terminated diazo dye derivative. This polymer is called 3RDCVXY. The corona-poled 3RDCVXY polymer exhibits a x/sup (2)/ value of 1*10/sup -6/ esu at 1.06 mu m. The thermal stability is excellent even at 80 degrees C. The poled 3RDCVXY polymer film shows a linear electrooptic coefficient as high as 40 pm/V at 0.633 mu m. An electrooptical light modulation in the channel 3RDCVXY polymer waveguides with a half-wave voltage as low as 5 V was obtained.<<ETX>>

Fiber fuse generation in single-mode fiber-optic connectors

The evolution of the fiber fuse phenomenon in a single-mode fiber-optic connector was studied theoretically. A narrow air gap of the order of 1 /spl mu/m was assumed to be formed between the fiber end-faces in the connector as a result of the adhesion of dust to both the ferrule and the fiber end-faces. It was assumed that there was a thin water layer in the gap because condensable water molecules in the air could easily be trapped by the SiOH groups on the silica-glass surface. The water layer exhibited a large absorption coefficient of about 850 cm/sup -1/ at 1.48 /spl mu/m. The temperature distributions near the air gap were numerically calculated by using the explicit finite-difference method. When a high-power laser operating at 1.48 /spl mu/m was input into the connector, the temperature along the fiber-core center increased abruptly at the thin water layer. The air gap was heated above 4/spl times/10/sup 5/ K when the optical power was 2 W and the gap was 1 /spl mu/m. The heat in the air gap gradually diffused into the neighboring optical fiber over time. The temperature of the heated fiber reached over 1/spl times/10/sup 4/ K, which is high enough to initiate the fiber fuse phenomenon.