Polymeric long-period waveguide grating

Abstract

Long-period Waveguide Grating (LPWG) has become attractive in recent years. It is relatively small in size and has the potential integration with various optical components on the Si substrate. In addition, it can be used in producing useful optical devices applied in the sensor applications. This thesis focuses on the aspect of fabrication, the characterization and the potential sensor application of LPWG. In this project, LPWG is demonstrated as polymeric waveguide fabricated on SiO2/Si substrate. One of the recently developed polymers Epoxy NovoIak Resin (ENR) is used as the waveguide core. The ENR polymer is a negative tone and is more environmentally stable when compared with most of the commercial available polymers like PMMA, and thus it is beneficial to the fabrication of optical waveguide and devices. The fabrication of LPWG device is performed using standard cleanroom processes involving: 1) UV photolithography to pattern the photoresist grating on Si wafer, 2) reactive ion etching (RIE) to transfer the grating pattern onto the surface of the Si wafer, 3) thermal oxidation to form the buffer SiO2 layer, and 4) spin coating and UV photolithography to form the ENR polymeric waveguide. The performance and characteristics of the LPWG are studied in this project. The surface morphologies of the LPWG are investigated by using various techniques such as alpha step profiler, Optical Microscope (OM), Scanning Electronic Microscope (SEM) and Atomic Force Microscope (AFM). The study reveals that the sidewall of the channel and the surface of the device are fairly smooth. In addition, the grating depth and periodicity of the LPWG device can be well controlled during the fabrication processes. Experimental results confirm that the relationship between the transmission peak wavelength and the grating period is linear. Thus, a large variety of LPWG devices with well-controlled characteristics can be obtained based on the phase-matching condition. As a result, the LPWG exhibits that a maximum attenuation of –18dB, a minimum 3dB bandwidth of 6nm, and the grating length can be obtained in LPWG with lcm length. The temperature dependence dΛ/dT of the LPWG is also investigated, and is found to be similar to that of long-period Fiber Grating (LPFG).

Date of Award	15 Jul 2004
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Yue Bun Edwin PUN (Supervisor)