High-resolution integrated optic holographic wavelength division multiplexer

A high resolution Integrated Optical Wavelength Division Multiplexer (WDM) has been successfully developed to increase optical fiber communication capacity through wavelength multiplexing/demultiplexing. The Integrated Optical WDM uses multiple gratings to deflect different wavelengths from one multiple wavelength optical input into many different directions. Each pre-recorded grating deflects one and only one wavelength to an arbitrary but pre-determined angle. The planar optical waveguide with a holographic grating was fabricated monolithically through the standard ion-exchange process. A layer of holographic material (DCG) was then spun on top of the planar waveguide. Finally a phase grating was created by interfering two Argon laser beams on the substrate''s surface. The angle (23) between the two Argon beams and the glass substrate orientation angle (4) completely determines the wavelength selection characteristic. An optical signal interacts with the holographic gratings evanescently when light is propagating in the waveguide. Due to the device geometry the light-hologram interaction length can be made very long. The long interaction length ( coupled with the large index modulation depth of DCG (En 1) will dramatically increase the wavelength selection resolution and deflection angle resolution. Presently a 7 channel WDM with 6nm channel separation and 6 angular separation has been achieved. Theoretical studies showed that hundreds of channels with extremely narrow wavelength selectivity resolution (mm) and deflection angle resolution (0. 2) are achievable with a 1mm interaction length. With an even longer interaction both number of channels and resolution can be increased by another order of magnitude.