Ryoji Inaba

Two-dimensional mode size transformation by /spl Delta/n-controlled polymer waveguides

We report a new type of polymer waveguide for two-dimensional (2-D) mode size transformation in which /spl Delta/n (refractive index difference between core and cladding) is properly controlled along the waveguide axis while the core cross section is kept uniform. The beam diameter in the /spl Delta/n-controlled waveguide where the core diameter is 3.7 /spl mu/m and /spl Delta/n changes from 0.0027 to 0.0009 toward one end in the 5 mm-gradient /spl Delta/n, region, is about twice as large as that in a normal waveguide where /spl Delta/n is 0.0027. The optical loss accompanied by mode size transformation is calculated to be less than 2.5% based on beam propagation methods (BPMs).

Improved coupling efficiency using /spl Delta/n-controlled polymer waveguides with two-dimensional spot-size transformation

A new type of polymer waveguide for two-dimensional spot-size transformation is reported, with which coupling efficiency of waveguides with 4- and 8-/spl mu/m core diameters was reduced by /spl ap/1.6 dB. The length needed for spot-size transformation was less than 1 mm along the direction of propagation. In this polymer waveguide, refractive index difference between core and cladding (/spl Delta/n) is properly controlled along the direction of propagation while the core cross section is kept uniform.

Studies on CO/sub 2/ laser drilling: formation mechanism of residual thin materials at the bottom of laser via

Formation mechanism of residual thin materials at the bottom of a microvia processed with CO/sub 2/ laser is studied with a bromine (Br)-containing epoxy film designed for sequential build-up printed wiring boards. By observing Br content distribution in a cross section of the epoxy film after laser processing, it is estimated that the film around the via is heated up to 1600 K and that the residual thin film at the bottom of the via is heated up to 2000 K upon laser irradiation. Based on heat transfer simulations for epoxy and copper layer structures, the epoxy film within a 0.1-/spl mu/m distance from the copper surface is unable to be removed by laser irradiation because the temperature of this region cannot be heated above the decomposition temperature of /spl ap/2500 K due to a large heat flow from the epoxy layer to the copper.

Spot-size Transformation By An-controlled Polymer Waveguides

waveguides connected together by waveguide arrays of different lengths. The input light is demultiplexed into the various wavelength and fed into five optical gates connected to the wavelength router. The optical gate is a 7 mm long MachZehnder type switch. At the end of the optical gates, a mirror is formed to reflect the selected light back to the wavelength router, which then works as a multiplexer. The total number of arrayed waveguides is 32. The difference in length between adjacent waveguides is 2 pm. The curved waveguides have a 60 mm radius of curvature. The total length of the device is 50 mm. The device was fabricated in z-cut LiNbO,. Titanium 70 nm thick and 7 km wide was diffused at 1050°C for 9 hours to obtain a single mode waveguide. Measured characteristics of the device are shown in Fig. 2(a) and (b). Fig. 2(a) shows the filter response of the device under zero bias voltage. Fig. 2(b) shows the filter response of a single channel. Switching voltage was 35 V for the TE mode and the worst case crosstalk was -12 dB. The insertion loss was about 13 dB including the 3 dB loss at the coupler. A reflective arrayed structure; with optical gates located at the same side of the slab waveguide as the input and output ports, can be used to halve the device length. The device length then becomes short enough to be integrated onto one chip even when using a large difference in length between arrayed waveguides to cope with high WDM density. A proton exchanged waveguide or some other type of fabrication process may be introduced to attain a curved waveguide with a small radius in order to shorten the device length. In conclusion, we demonstrated a wavelength filter using a wavelength router and optical gate fabricated in LiNbO,.