Novel grating-frustrated wavelength division multiplexer using polymer waveguides with inverted-ridge structure

Abstract

A set of grating-frustrated directional couplers is proposed here for wavelength division multiplexer (WDM). Instead of using optical fiber, integrated polymer waveguides with inverted-ridge structure was used in this design. This device is composed of two cascaded directional couplers. Each of the directional coupler is made up of two waveguides with the index of one of the waveguides being a periodic function of z which is the direction of propagation. The average index of the grated waveguide should be equal to that of the un-graded waveguide. According to the coupled wave theory, only the light with a specific wavelength will pass through the waveguide without grating while all other light will be coupled to the grated waveguide when the mixed light is initially input at the un-grated waveguide. This phenomenon is call Bragg reflection and the specific wavelength is called Bragg wavelength. The Bragg wavelength is proportional to the period of the index grating. Therefore, this device is capable of selecting at least three different wavelengths. A detailed analysis of this design is also included in this paper.