Long period polymer waveguide gratings device

Abstract

Long Period Gratings (LPGs) in optical fibers are useful and versatile devices. Many applications have been demonstrated. An UV irradiation is required to create modulation gratings inside the fiber core. Because the fiber geometry is normally round in shape and made of silica, the structural flexibility of the final device is limited. To circumvent the geometry and material constraint of an optical fiber, long period gratings can be implemented in polymer waveguide, and LPGs can be integrated with other optical circuits to form new functional devices. Long period waveguide grating (LPWG) was demonstrated in a low-loss negative tone UV sensitive epoxy novolak resin (ENR) polymer. The grating structure was fabricated on top of the waveguide using standard UV lithography process, and no other subsequent process is required after the development step. In comparison with the conventional UV photolithography followed RIE techniques for the fabrication of grating structure, our method has the advantage of greatly simplifying the fabrication process, yet avoiding the complexity of multi-layer polymer processing and relaxing the fabrication difficulties thereby reducing the error generated in the process. Experimental results indicate that with an appropriate design of structure a transmission peak at desired wavelength can be achieved. The LPWG exhibits an attenuation peak of -18dB at 1300nm using a grating length of 17mm. This spectral characteristic is similar to that of the conventional long period fiber grating (LPFG). Apart from this, analysis by heating the LPWG reveals that the peak wavelength shifted with temperature due to the refractive index of polymer is sensitive to temperature. The temperature sensitivity of the LPWG is linear and is found to be ~0.89nm/°C. This value is similar to those reported using air-clad fibers. Red shift of the transmission peak wavelength was also observed and discussed. On the other hand, experiment result also indicates that the position of the transmission peak wavelength depends on the grating period. The grating depth has a significant influence on the attenuation of the transmission peak wavelength. Such LPWG may lead to wide range of integrated-optics devices and sensors.

Date of Award	4 Oct 2004
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Yue Bun Edwin PUN (Supervisor)