Bin Cai

Fabrication of DAST Channel Optical Waveguides

In order to use the large, electro-optic coefficient of a nonlinear optical ionic crystal, 4-(p-dimethylaminostyryl)-1-methylpyridinium tosylate (DAST), a channel optical waveguide structure is needed. We successfully fabricated a waveguide using two methods: by a dry-etching technique and by photo-bleaching. Because DAST has a large optical loss, parts of the waveguide should be composed of a transparent polymer. We used photolithography and a reactive ion etching method to fabricate a serially grafted (conjunct) waveguide of DAST with a transparent polymer waveguide. The waveguide was also fabricated by photobleaching, whereby the refractive indices of the crystal’s a- and b-axes were decreased by degrading the crystal. The cladding part of the DAST waveguide was photobleached by irradiating with UV light. The under- and over-cladding layers of these channel waveguides were composed of a UV-cured resin that did not dissolve the DAST crystal. The loss of the crystal waveguide for the crystal b-direction was around 10 dB/cm, due to the scattering loss of the DAST single crystal.

Refractive index control and Rayleigh scattering properties of transparent TiO2 nanohybrid polymer.

The surface of TiO2 nanoparticles (NPs) was modified by a coupling agent of 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane to render them highly compatible with organic monomer mixtures avoiding aggregation. Such TiO2 NPs were then chemically attached with a prepolymer. The refractive index of hybrid TiO2 NPs-polymer was increased dramatically in comparison with that of pure polymer, and it can be controlled by adjusting the content of TiO2 NPs. The Rayleigh scattering of hybrid TiO2 NPs-polymer was size-dependent and increased with the increase of the TiO2 NPs content. When Rayleigh scattering of the hybrid material prepared with a milling and centrifuge process was significantly lowered, one can obtain a transparent sample, which is good for optical devices.

A Novel Preparation of High-Refractive-Index and Highly Transparent Polymer Nanohybrid Composites

In an attempt to fabricate a high-refractive-index (RI) as well as a highly transparent polymer nanohybrid composite, a combination of a polymer matrix, nanoparticles, and nanoparticle-surface coupling agent was tailored systematically. We developed an effective and versatile hybridizing process for further increasing the RI of the nanohybrid composites. By using various indispensable steps, we achieved the highest RI of n (594 nm) ≈2 and a highly transparent (transmittance ≈93% at 460 nm) polymer nanohybrid composite.

Serially grafted polymer optical waveguides fabricated by light-induced self-written waveguide technique

Serially grafted polymer optical waveguides were fabricated by the light-induced self-written (LISW) waveguide technique for the first time to our knowledge. To realize functional waveguide cores by the LISW technique, transparent materials at the writing wavelength were selected. By inserting thin transparent partitions, a serial-graft structure consisting of passive and active waveguides without any misalignment was realized automatically. This technique is advantageous for its extremely easy process over conventional fabrication techniques.

Refractive Index Control and Grating Fabrication of 4′-N,N-dimethylamino-N-methyl-4-stilbazolium Tosylate Crystal

The refractive index of nonlinear optical ionic crystal 4-N,N-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST) was controlled by a photobleaching technique. The ellipticity of the DAST refractive index ellipsoid decreased after the irradiation of a 532 nm laser. By means of the photobleaching effect we fabricated a grating on DAST single crystals by two-beam interference. The calculation based on the diffraction efficiency indicates that the depth of refractive index change can be extended to 5.75–7.38 µm by 2.08 W/cm2 irradiation power. This result is promising for the fabrication of DAST waveguides by photobleaching.

A three-dimensional polymeric optical circuit fabrication using a femtosecond laser-assisted self-written waveguide technique

We demonstrated a femtosecond pulse laser-assisted self-written waveguide technique that can fabricate three-dimensional (3D) optical waveguides in a photopolymerizing resin. A 488nm Ar+ laser and an 800nm pulse laser were used in this technique. Using the femtosecond laser scanning technique, two optical fibers were connected three dimensionally by a waveguide. The alignment-free aspect of the light-induced self-written waveguide-fabrication technique and the possibilities of 3D waveguide creation inherent in the femtosecond laser polymerization technique were combined to yield a highly versatile technique for the fabrication of 3D waveguides.

Near-infrared luminescent polymer waveguide with a 20dB small-signal gain

Near-infrared optical gain in luminescent polymeric slab asymmetric waveguides has been investigated by use of amplified spontaneous emission. Upon nanosecond photopumping, the waveguides have shown a small-signal gain coefficient of 37.2±2.1cm−1 at 820nm for a pump fluence of 1.57mJ∕cm2 (314kW∕cm2). The loss coefficient and transparency fluence have been found to be 7.3±1.0cm−1 at 820nm and 0.14mJ∕cm2 (28kW∕cm2), respectively. Furthermore, we show that a small-signal gain of 19.7±2.3dB is achievable in a 1.2-mm-long waveguide.

Enhancement of luminescent intensity of calixarene-oxetane polymer doped with europium complex

Calixarene molecules are originally known as inclusion compounds in host-guest chemistry, which can bind various metal ions and organic molecules. We investigated the binding property of calixarene polymer against trivalent europium (Eu3+) complex which possesses excellent luminescent characteristics. An interaction, i.e. coordination structure, is established between calixarene polymer and Eu3+ complex, which results in an effective suppression of concentration quenching of Eu3+ complex and enhancement of luminescent intensity in high concentration.

Fabrication of Inverse Opal TiO2 Waveguide Structure

Inverse opal waveguide structure has been fabricated on patterned polysilane waveguide structure. Embedded inverse opal into patterned polysilane waveguide structure was made up by self assembly of polystyrene template, infiltrated TiO2 dielectric material and finally calcinated at 400 °C. The proposed fabrication method has successfully created inverse opal TiO2 on the patterned polysilane waveguide structure.

Refractive index control and waveguide fabrication of DAST crystals by photobleaching technique

We report on the optical waveguide fabrication of organic ionic crystal, 4-(4-dimethylaminostyryl)-1-methylpyridinium tosylate (DAST), a promising material for electro-optic devices. A photobleaching technique was used to control the refractive index of DAST crystals. The change of refractive index as well as photobleached depth were evaluated by a prism-coupler and the values were compared with the results calculated from diffraction efficiency of refractive index grating. We fabricated a multimode waveguide using a Xe lamp with a mask covered on the crystal and the propagation loss of the waveguide was evaluated at 1.3 μm wavelength.