Polymer optical circuits for multimode optical fiber systems

Photochemical Study of Tris(benzotriazol-1-yl)methane

Photodecomposition of tris(benzotrizol-1-yl)methane (1) in benzene gives [1-benzotryazol-1-yl-methylidene]-biphenyl-2-ylamine (2) resulting from the loss of the benzotriazolyl radical and nitrogen followed by addition of benzene. Elimination of the second benzotriazolyl radical from 2 provides the biphenyl-2-ylmethyleneamine radical, which affords phenantridine (3) after ring closure. In contrast, the photolysis of 1 in methanol gives a high yield of benzotriazole (4).

Optimized design of polarization-independent and temperature-insensitive broadband optical waveguide coupler by use of fluorinated polyimide

A statistically optimized design method suitable for a polariation-independent and temperature-insensitive broadband waveguide coupler is proposed. By use of this method, a fluorinated polyimide waveguide 3-dB waveguide coupler for 1490 to approximately 1610 nm application is designed by optimizing polarization and temperature fluctuation. The validity of the design is verified through simulation based on the three-dimensional beam propagation method (3D-BPM), which revealed a coupling ratio of 50 +/- 0.8% in a 120-nm bandwidth in the temperature range -10 to 40 degrees C for both orthogonal polarizations.

Optimized design of fluorinated polyimide based interleaver

Statistical optimization method for the design of a fluorinated polyimide wavelength division element for optical communication is proposed. The opitimized device is an interleaver element suitable for dividing over 40 wavelengths in the 1550 nm band. Optimization considers the inherent polarization dependence of fluorinated polyimide based on measurements of the dispersion characteristics and birefringence of fluorinated polyimide film. A 40-wavelength device is designed by use of the proposed technique for a working wavelength of 1550 nm and a wavelength interval of 0.8 nm. The device exhibited a 1-dB passband of 0.5 nm and a 3-dB passband of 0.8 nm, and output wavelength fluctuation due to polarization effects of less than 0.08 nm.

Stable, low-loss optical waveguides and micromirrors fabricated in acrylate polymers

Acrylate-based optical waveguides have been fabricated with optical loss of 0.5 dB/cm at 1300 nm by means of a new material system that ensures stable optical and mechanical properties over a wide temperature range. No increase in loss was measured after 500 h at temperatures up to 150 degrees C, and there was no significant increase in loss during short (<5 min) temperature excursions to 300 degrees C for bonding. Single-mode waveguides were fabricated with refractive indices for core and clad of 1.505 and 1.500, respectively, so that the mode field is very similar to that of single-mode silica fiber. Guides were fabricated on both planar and structured substrates of Si and GaAs as well as on substrates coated with metals and dielectrics. Fabrication involved spin coating and UV exposure to cross-link the polymer, but the substrate temperature did not exceed 180 degrees C. With this method guides could be fabricated on a range of substrates up to 125 cm in diameter, including those with multilayer metallization for multichip modules, providing optical interconnect capability. Microprism reflecting surfaces were fabricated in the waveguides to couple light out normal to the substrate. All the processing was compatible with normal semiconductor fabrication.

Single-mode optical waveguides fabricated from fluorinated polyimides

Buried channel optical waveguides were fabricated from fluorinated polyimides. They operated in single mode and showed an optical loss of less than 0.3 and 0.7 dB/cm for TE and TM polarizations, respectively, at a wavelength of 1.3 mum. Moreover, these waveguides had high heat and moisture resistance; the optical loss did not significantly change after heating at 380 degrees C for 1 h or after exposure to 85% relative humidity at 85 degrees C for over 200 h.

Design Approaches for VCSEL's and VCSEL-Based Smart Pixels Toward Parallel Optoelectronic Processing Systems

The technical issues involved in applying vertical-cavitysurface-emitting lasers (VCSEL's) to parallel opticalinterconnection systems are discussed from the viewpoint of theirapplication to asynchronous transfer mode switching and parallelcomputer systems. We also discuss approaches to designing a VCSELarray structure for high-speed modulation and the effect ofpixel-performance homogeneity on the transmission bandwidth and powerconsumption. We review monolithic and hybrid integrationtechnologies for VCSEL-based smart-pixel arrays, and we estimate themaximum pixel number and input-output throughput allowed in a chip, considering the power consumption and pixel homogeneity. We showthat a one-chip optoelectronic parallel processing system comprisingmore than 1000 processor elements is possible when smart-pixel arraysare fabricated under the 0.25-mum complementary metal-oxide semiconductor design rule.

Multimode polymeric Y junctions for star couplers in backplane optical interconnect

Three different multimode polymeric Y junctions with 50:50 splitting ratios were designed and their performance analyzed with ray tracing and measurements. There is agreement between measurements and modeling. The best performance is found for a Y junction in which the waveguide is split to S bends with 50% widths.

Experimental studies of electro-optic polymer modulators and waveguides

The results of an experimental study of electro-optic modulators and waveguides based on polymeric materials are presented. Included are the design, fabrication, and testing of integrated Mach-Zehnder modulators, which are based on polymer films that contain a novel, nonlinear electro-optic chromophore. Studies also show the efficacy of photolithography or photobleaching by the use of this chromophore to form passive, branching waveguides, which are operated at the 1300-nm wavelength.

Channel-optical-waveguide fabrication based on electron-beam irradiation of polyimides

A new-channel-waveguide-fabrication process for use with polyimide is described. The new technique uses an electron-beam-induced effect to alter the refractive index of the polyimides directly. Channel waveguides with an 8-µm-wide, 8-µm-deep core have been fabricated on a polyimide film by the use of electron-beam irradiation. Only one kind of polyimide (6FDA/TFDB) was used in this waveguide. The difference in refractive index between the core and the cladding was approximately 0.30% for both TEand TM-polarized incident light when the dose was 1500 µC/cm(2), which was sufficient to produce waveguides. The optical properties of the waveguide are also demonstrated.

Low excess losses in a Y-branching plastic optical waveguide formed through injection molding

We have demonstrated low excess losses (1.9 dB at 660-nm wavelength) in a Y-branching plastic optical waveguide (POWG) that was fabricated using an injection-molding method. The waveguide had an amorphous vinyl polymer as the core and transparent polyolefin as the cladding. We then studied a method for isolating the excess loss in the Y-branching POWG, and with that method we estimated the lower limit of the loss to be 1.41 dB at 660 nm. The sample had a heat-resistant plastic optical fiber (POF) with a core composed of crosslinked poly (methyl methacrylate) (PMMA) copolymer, and a cladding composed of poly (tetrafluoroethylene-co-hexafluoropropylene). The POWG has sufficient reliability for ordinary uses below 100 °C. A model for a bidirectional wavelength-division multiplexing opticalcommunication system with the developed Y-branching POWG and the POF was also demonstrated.

Photogeneration of refractive-index patterns in doped polyimide films

A photosensitive benzophenone tetracarboxylic dianhyride-alkylated diamine polyimide formulation has been evaluated for application in an optical interconnection area. The refractive-index patterns in this material were optically recorded by UV-assisted photodoping of sensitizers. The polyimide films were selectively doped with benzoin-type photosensitizers such as benzildimethylketal and benzoin ethyl ether, which cause a decrease in the refractive index. High-dose UV irradiation that causes cross linking of the polyimide chains was also employed for augmenting the refractive-index difference to 0.017 between the doped and undoped regions. Refractive-index variations and lightguiding properties were investigated as a function of doping concentrations and other processing conditions. The author utilized this technique for the fabrication of embedded polyimide channel waveguides. The two photosensitizers have different effects on the waveguiding characteristics of the polyimide films. Losses for benzoin ethyl ether remained low whereas doping with benzildimethylketal caused significant increase in the waveguiding loss at high doping concentrations. Near-field imaging of the output from such waveguides shows good confinement of 815-nm light.

Storage limit of two-photon-based three-dimensional memories with parallel access

For systems that use parallel access by simultaneous writing or reading of bits located in an entire common plane, diffraction sets a limit to the storage density that is far smaller than that for sequential operation. Comparable densities can be achieved by using a three-dimensional waveguiding structure.

Polyimide optical waveguides fabricated with electron beam lithography

Fabrication of PMMA clad polyimide waveguides by electron beam lithography creates very smooth sidewalls allowing production of narrow low loss waveguides on planar substrates.

Evaluating polyimides as lightguide materials

Lightguides were fabricated from three commercial polyimides of which one contains one and the others contain two hexafluoroisopropylidene (6F) groups. The latter are isomers using either the para or the meta isomer of the same diamine. As the number of 6F groups increases the optical losses of the corresponding lightguides decreases. In thick lightguides of the two 6F groups containing polyimides, loss values below 0.1 dB/cm can be realized using optimized conditions. Two mechanisms-ordering with or without charge transfer complex formation and voids or pinholes-are seen to be responsible for optical losses. The second type of losses can be reduced by cure optimization. Where ordering is possible annealing leads to increased optical losses. Geometrical restraint of the ordering, however, leads to loss reduction in otherwise identical conditions. Losses observed in the bulk are always higher than in the top and bottom layers of the polyimide films.

Polymer waveguide star coupler

A polymer waveguide star coupler formed by the selective photopolymerization method is described. This polymer waveguide star coupler has low insertion loss independent of the core and cladding dimensions of the optical fiber. The six-port star coupler obtained, with input and output fiber arrays, had an insertion loss of 2.6 dB and a loss variation across the six ports of 1.2 dB at 0.84 microm.