A novel integrated optical planar waveguide platform for
absorption-based biosensing is demonstrated. The platform integrates surface ion-exchanged channel waveguides with one-step UV patterned sol-gel structures to define the probing regions. Cytochrome c protein was utilized to characterize the device performance. Spectroscopically specific attenuation of approximately 2 dB in the guided signal occurred at 532nm for 1.4 cm long probing region. The estimated level of detection is about 1 pmol/cm2 of surface adsorbed cytochrome c. The proposed structure enables environmentally stable, compact, and inexpensive sensing devices that can be applied to a wide range of biological and chemical species.
Fabrication of optical waveguides by a simple patterning process using photosensitive polyimide (PSPI) is described. Light waveguide based on PSPI was fabricated by photolithographic processing without use of dry etching process. The PSPI varnish is comprised of polyamic acid (PAA) which was made from fluorinated diamine and fluorinated tetracarboxylic dianhydride, and photosensitizer. The PSPI has the following characteristics: glass transition temperature (Tg) of 330 °C, coefficient of thermal expansion of 40 ppm/K. Moreover the PSPI is colorless, and posses low absorption at 1 .3 and 1 .55im. The sidewalls and the surfaces ofthe fabricated waveguide are very smooth, which is essential for the low loss optical mode propagation and lower scattering of the mode due to the imperfections. Single and multimode buried ridge waveguides on quartz glass substrate were fabricated and tested. Optical propagation losses were measured by standard cut back method and found to be as low as 0.4 dB/cm @ 1.55 jim. This fabrication process would be expected to contribute to low cost production for high performance opto-electronic devices.