Dual-side waveguide-based wavelength demultiplexer

#The present invention generally relates to the field of demultiplexers and, more particularly, to a demultiplexer that includes a grating assembly formed on a first side thereof and a photodetector assembly formed on a second side thereof which is opposite the first side.

#Various types of demultiplexer designs have been proposed. One common configuration is to have the grating that provides the separation function within an interior location of the demultiplexer, such as within a waveguide that is the optical carrier for the multiplexed or combined optical signal. Gratings of this type require at least some type of crystal regrowth. Crystal regrowth is a complex and difficult process, and the result of any such regrowth may yield a demultiplexer that suffers one or more types of deficiencies in its performance.

#Another common configuration for a demultiplexer provides a demultiplexing function which divides all N wavelengths among N separate detection channels (i.e., the multiplexed signal is split and sent to N separate detection channels). The Mth signal channel thereby rejects the other N−1 wavelengths in its channel and detects only the Mth wavelength. Thus (N−1)/N portion of the original signal is rejected. This has an adverse impact on the power demands for the demultiplexer.

#FIG. 1A is a cross-sectional view of one embodiment of a dual-side demultiplexer.

#FIG. 1B is an enlarged, cross-sectional view of one of the gratings used by the demultiplexer of FIG. 1A.

#FIG. 1C is a side view of another embodiment of a dual-side demultiplexer.

#The present invention will now be described in relation to the accompanying drawings which at least assist in illustrating its various pertinent features.

#One embodiment of a dual-side demultiplexer 40 is illustrated in FIGS. 1A-B. The demultiplexer 40 generally includes a first waveguide 44 through which a multiplexed or combined optical signal (e.g., a signal of a plurality of individual optical signals of particular wavelengths) generally travel through the first waveguide 44 in the direction of the arrow A. Hereafter, this combined or multiplexed optical signal will be discussed as including a plurality of wavelength-specific optical signals. Separation of this multiplexed optical signal into a plurality of individual optical signals is accomplished by a grating assembly 52 that is formed on a surface 48 of the first waveguide. These individual optical signals may be of a very specific wavelength or within a relatively narrow band of wavelengths that is on the order of 1-2 nanometers wide. In any case, these individual optical signals are directed to a second waveguide 72 which functions as an output channel for the plurality of individual optical signals. Control over which particular optical signal is able to pass from the first waveguide 44 to the second waveguide 72 is provided by an index control channel or barrier layer 68. Individual optical signals that are able to pass through the barrier layer 68 and into the second waveguide 72 are “read out” by a photodetector assembly 80 that is formed on a surface 88 of the second waveguide 72.

#The first waveguide 44 again is an optical conduit or confinement for a multiplexed or combined optical signal, and includes the grating assembly 52 that is formed on its surface 48. Surface 48 of the first waveguide 44 is opposite that of a surface 46 of the first waveguide 44 that interfaces with the barrier layer 68. The grating assembly 52 generally includes a plurality of gratings 56 that are spaced in the general direction in which the multiplexed optical signal travels through the first waveguide 44 that is represented by the arrow A in FIGS. 1A-B. Although only three gratings 56 are illustrated in FIG. 1A, it should be appreciated that any number of gratings 56 may be utilized. In one embodiment, the demultiplexer 40 includes about 64 gratings 56. One key feature of the grating assembly 52 is that the gratings 56 are reflective versus transmissive. Using a reflective grating versus a transmissive grating allows the demultiplexer 40 to have reduced power demands, as well as allowing for the manufacture of the demultiplexer 40 using back-side processing techniques versus crystal regrowth. Generally, the combination of material indices of refraction for the first waveguide 44, second waveguide 72, barrier layer 68, and the grating assembly 52, as well as the period and pitch of the gratings 56 of the grating assembly 52, determines if the grating assembly 52 is reflective or transmissive.