Optical waveguides – With optical coupler – Input/output coupler
Reexamination Certificate
2001-08-06
2003-04-15
Ullah, Akm E. (Department: 2874)
Optical waveguides
With optical coupler
Input/output coupler
C385S024000, C385S011000, C359S199200
Reexamination Certificate
active
06549708
ABSTRACT:
FIELD OF THE INVENTION
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.
BACKGROUND OF THE INVENTION
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 M
th
signal channel thereby rejects the other N−1 wavelengths in its channel and detects only the M
th
wavelength. Thus (N−1)/N portion of the original signal is rejected. This has an adverse impact on the power demands for the demultiplexer.
BRIEF SUMMARY OF THE INVENTION
A first aspect of the present invention is embodied by a particular demultiplexer design. This demultiplexer includes first and second waveguides that may be viewed as being in a stacked configuration, with the second waveguide being disposed a higher elevation in the stack than the first waveguide. “Stacked” does not necessarily mean that the second waveguide is directly above the first waveguide or vice versa, although this typically will be the case. A grating assembly is disposed on either the upper or the lower surface of the stack, but nonetheless on the first waveguide.
Various refinements exist of the features noted in relation to the first aspect of the present invention. Further features may also be incorporated in the first aspect of the present invention as well. These refinements and additional features may exist individually or in any combination. Both the first and second waveguides are optical conduits of sorts. Multiplexed or combined optical signals may be directed into the first waveguide for demultiplexing by the grating assembly, such that the first waveguide may be characterized as an input channel. These individual demultiplexed optical signals (e.g., of individual wavelengths) may be directed into the second waveguide for a readout of the same, such that the second waveguide may be characterized as a plurality of output channels. Each of these output channels may be associated with a single individual wavelength or a relatively narrow band of wavelengths that is on the order of 1-2 nanometers wide. Hereafter, any discussion of “individual wavelengths” progressing to the second waveguide for readout encompasses both individual wavelengths and this relatively narrow wavelength band on the order of 1-2 nanometers wide.
Definition of these plurality of output channels in the second waveguide may be accomplished by having the second waveguide actually be in the form of a plurality of second waveguide sections that are spaced in a direction in which the combined optical signal progresses through the first waveguide. A photodetector may be attached to/formed on/in each of these second waveguide sections for actually accomplishing this readout. A photodetector may be part of its corresponding second waveguide section (i.e., a given photodetector may be smaller than its corresponding second waveguide section), or may in fact define the entirety of its corresponding second waveguide section. It may be possible to utilize a continuous second waveguide with a plurality of photodetectors that are spaced in the direction in which the combined optical signal is progressing through the first waveguide for other applications of the structure associated with the first aspect, although there may be difficulties with this configuration for the subject demultiplexing application. Preferably, a photodetector assembly is integrally formed in association with the second waveguide, including defining the entirety of the second waveguide (e.g., a given photodetector may define the entirety of its corresponding second waveguide section) and defining only a portion of the second waveguide in which case the photodetector would be disposed on/extend within the second waveguide. As such, a photodetector assembly is effectively disposed on one side of the stack, and the grating assembly is disposed on the opposite side of the stack to provide a dual-side demultiplexer.
What may be characterized as a barrier layer or index control channel may be and preferably is disposed between the first and second waveguides in the case of the first aspect. In the case where the second waveguide is continuous, the barrier layer would be continuous. Where the second waveguide is in the form of a plurality of spaced second waveguide sections, the barrier layer would typically be in the form of a plurality of spaced barrier layer sections (e.g., such that a barrier layer section is disposed between each second waveguide section and the first waveguide), although it could still be a continuous structure as well. Selective coupling of the first and second waveguides effectively is the function of the barrier layer. Functionally, the barrier layer allows only certain light to pass from the first waveguide into the second waveguide in a particular region of the second waveguide. The remainder of the light is thereby prohibited from progressing from the first waveguide into this region of the second waveguide. Consider the case where the second waveguide is in the form of a plurality of spaced second waveguide sections, and where the barrier layer is similarly in the form of a plurality of spaced barrier layer sections. Light of a certain wavelength may be directed from the grating assembly associated with the first waveguide toward a particular barrier layer section and its overlying second waveguide section. This particular barrier layer section allows this certain wavelength light to progress through the barrier layer section and into its overlying second waveguide section. All other light is prohibited from passing through this barrier layer section into its overlying second waveguide section. One may view the grating assembly as not only separating out a particular wavelength from a combined or multiplexed optical signal, but “processing” this particular wavelength of light into a form which will allow the same to pass from the first waveguide, through the barrier layer, and into its overlying second waveguide section.
The first and second waveguides may be characterized as being asynchronous in the first aspect. Furthermore, the first and second waveguides may and typically will have different refractive indices, may and typically will have different thicknesses, or both. As noted above, the second waveguide may be a continuous structure or may be in the form of a plurality of second waveguide sections that are spaced in a direction in which a multiplexed or combined optical signal is progressing through the first waveguide.
The function of the grating assembly is to somehow separate out the individual optical signals from a combined or multiplexed signal in the case of the first aspect. Preferably this is done by principles of reflection versus transmission. That is, preferably the grating assembly of the first aspect is a reflective grating versus a transmissive grating. The grating assembly may include a plurality of grating subassemblies that are spaced in a direction in which a multiplexed or combined optical signal is progressing through the first waveguide. Each grating subassembly may be wavelength specific (or specific to a given bandwidth as noted). Furthermore, each grating subassembly may account for both polaritie
Liu Feng
Wood Lance A.
Worchesky Terrance L.
Connelly-Cushwa Michelle R.
Lockheed Martin Corporation
Marsh & Fischmann & Breyfogle LLP
Ullah Akm E.
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