Research And Fabrication Of A UV Curable Polymeric AWG Multiplexer

Human society is entering into an information age powered by rapidly evolving technologies in areas of microelectronics, optoelectronics, computing and communications. However, as the result of the rapid increase of information, continuous requests have been made for the increase of speed, the enlargement of capacity and the decrease of cost of communications, some traditional communication technologies and devices could not fulfill the demands of applications. Therefore, it is imperious demand to enlarge the speed and capacity for the current fiber network. The wavelength division multiplexer (WDM) is an efficient method. The recent and rapid development in demand for optical Internet services and data communication has prompted many research groups to study dense wavelength division multiplexing (DWDM) systems. Specially, array-waveguide grating (AWG) fabricated by using polymeric optical waveguides are attracting considerable interest because of their potential applications in optical communications, optical interconnections, and integrated optics.Key issues in the polymeric waveguide materials include a low propagation loss at 1550nm wavelength, a high thermal stability and small birefringence, easy control of refractive index, large volume and low cost production facilities. These features make polymeric AWG devices apt for employing planar light wave circuit (PLC) technology. In the past few years, the rising polymeric SU-8 2005(MicroChem, MA, USA), a kind of thick negative resist with high aspect ratio, high sidewall quality, high transparency (above 400nm), good self-leveling up capability and dimensional control is playing a key role in micro-electro mechanical systems(MEMS) and micro-optic-electro-mechanical systems (MOEMS). .It is obvious that the advantages of the resist compared to PMMA are a higher sensitivity and chemical stability. Inducting the negative resist for optical waveguide material, it is very significant for optimizing producing process and enhancing optical performances of AWG device.In this paper, an arrayed waveguide grating (AWG) multiplexer can offer some basic functions including multiplexing, demultiplexing, optical add/drop multiplexing (OADM) and optical interconnection. Also, it possesses some advantages, such as easy optical integrating, narrow wavelength spacing, much more signal channels and low crosstalk. Recently, considerable attention and great efforts have been focused on the development of polymeric AWG.The AWG consists of input/output channel waveguides, input/output concave slab waveguides composed of many channel waveguides with a constant path difference between adjacent waveguides. It can work as grating and complete the function of multiplexing and de-multiplexing for light with different wavelength. Difficulty in AWG designing is greatly lowered by computer simulation and by using software to analyze and design AWG. Beam Propagation Method (BPM) is one of the most effective methods in soloving field ditribution in optical waveguide. Brief introduction to BPM is contained in paper, as well as Effective Index Method (EIM) and Weighted Index Method (WIM) both based on BPM.In this paper, a polymeric 41-channel AWG multiplexer was fabricated by simple direct Ultraviolet photolithography process. We try to use a cross-linkable negative photoresist as core material and an optically clear UV curable epoxy as cladding material. Once exposed to Ultraviolet light through a photomask, the polymeric waveguide stripes were obtained upon development. Due to the superiority of UV resist in MEMS, The characteristic of the optical waveguide is better than that fabricated by steam-redissolution technique of polymeric waveguide. The propagation loss is low as 2.03dB/cm at 1550nm wavelength. By Optic (BPM-WDM) software for computer simulation of light propagation, the insertion loss of the multiplexer is 4.75dB to 9.55dB and the crosstalk of the 41 channels is about -20dB. The diffraction loss of the central channel is 6.19dB.The AWG multiplexer has modulated channel spacing of 0.791nm and actual channel spacing of 0.789nm, the center wavelength is close to 1550nm. The new technique will be very well suited for fabricating optical integrated circuits (OICS).