Michiyuki Amano

Low-loss passive polymer optical waveguides with high environmental stability

Deuterated polysiloxane with high transparency and high thermal stability was newly synthesized for use as optical waveguide material. Single-mode channel waveguides using the polymer were fabricated by conventional photolithography and dry etching. The propagation loss of the channel waveguides was measured and found to be 0.17 dB/cm at 1.31 /spl mu/m and 0.43 dB/cm at 1.55 /spl mu/m. The thermal and environmental stability of the waveguides was demonstrated by the fact that the propagation loss remained unchanged after tests at 200/spl deg/C for 30 min, at 120/spl deg/C for 1000 h, and at 75/spl deg/C and 90% RH for 1000 h.

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.

Second‐order nonlinearity of a novel diazo‐dye‐attached polymer

Second‐order nonlinear optical properties of a newly synthesized dye‐attached polymer (3R) were investigated. The dye has a conjugated diazo structure, and the βμg (β: second‐order molecular hyperpolarizability, μg: dipole moment in the ground state) is larger than five times that of a monoazo dye (2R). The second‐order nonlinear coefficient (χ(2)) of a 3R polymer is also greater than that of a 2R polymer throughout the fundamental wavelength of 1.06 μm and between from 1.50 to 1.70 μm when the polymers are electrically poled. For both polymers, the χ(2) dependence on the fundamental wavelength corresponds to the absorption spectrum, which is explained by two‐photon resonance near the absorption maxima. The attainable χ(2) of the polymers deviates from the theoretical linear relationship with the dye content when it is high. This indicates that the dipolar interaction increases as the dye content rises.

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.

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>>