Integrated waveguide gratings for wavelength-demultiplexing of free space waves from guided waves.

Optical waveguide demultiplexer was designed and fabricated by integration of two types of gratings, namely, guided-mode-selective focusing grating couplers (GMS-FGCs) and different-guided-mode-coupling distributed Bragg reflectors (DGM-DBRs) in a slab waveguide for constructing a wavelength-division-multiplexing chip-to-chip optical interconnecting board. In the waveguide demultiplexer, guided signal waves were separated wavelength-selectively by DGM-DBRs, and coupled out by GMS-FGCs to focused free space waves. Two-channel demultiplexing with 5-nm-wavelength spacing was demonstrated at around 850-nm wavelength.

Free-space-wave drop demultiplexing waveguide device fabricated by use of the interference exposure method.

Integration of free-space-wave add-drop multiplexers that consist of focusing grating couplers (FGCs) and distributed Bragg reflectors (DBRs) in thin-film waveguides have been investigated for construction of an intraboard wavelength-division-multiplexing optical interconnection. Compact optics of a Lloyd mirror configuration and a contact-type mask aligner were combined as an interference exposure system for fabrication of DBRs of 300 microm coupling length. DBRs were integrated with FGCs on a thin-film waveguide on a glass substrate for two-channel wavelength-drop demultiplexing from guided waves to free-space waves. Measured outcoupled wavelengths of two free-space waves from two pairs of a FGC and a DBR agreed with the design values of 845 and 849 nm.