Optical waveguides – With optical coupler – Particular coupling structure
Reexamination Certificate
1999-06-18
2001-07-10
Healy, Brian (Department: 2874)
Optical waveguides
With optical coupler
Particular coupling structure
C385S031000, C385S036000, C385S037000, C385S049000, C385S052000, C385S129000, C385S130000, C385S131000, C359S199200, C359S199200, C359S199200, C430S056000, C430S057500, C430S127000
Reexamination Certificate
active
06259841
ABSTRACT:
TECHNICAL FIELD
The invention makes a contribution to the field of optical communications, especially to couplings with optical devices that separate the wavelengths.
BACKGROUND
Inputs and outputs are generally coupled to ends of planar waveguides in alignment with a direction of light propagation through the waveguides. For example, optical fiber inputs and outputs are generally coupled by aligning a core layer of each fiber with a core layer of the planar waveguide. Cladding layers surrounding the fiber cores separate the cores along the ends of the waveguides. The number of fibers that can be coupled to an end of a waveguide is limited by the diameters of the fibers.
Despite the further miniaturization of features within planar waveguides, waveguide dimensions are often significantly increased to provide sufficient room for coupling the input and output fibers. Fiber diameters, which typically measure around 125 microns, can be reduced to only about 70 to 75 microns without significantly deteriorating in structure or function. Similar problems are apparent with other types of inputs and outputs such as laser light sources and photodetectors—each of which is generally larger in transverse dimension (e.g., diameter) than optical fibers.
This problem is particularly apparent in planar waveguide multiplexer/demultiplexer devices that route optical signals between individual and common inputs or outputs (e.g., optical fibers). Within many of these planar waveguides, a dispersing mechanism, such as a diffraction grating, angularly distinguishes different wavelength signals and a focusing mechanism, such as a lens, converts the angularly distinguished signals into spatially distinguished signals. An array of inputs or outputs is aligned with the spatially distinguished signals along an end of the planar waveguide.
Even a tight grouping of the inputs or outputs requires a much larger planar waveguide than would otherwise be required to accomplish its function. Either the dispersing and focusing mechanisms must be increased in size to spatially separate the signals to match the spacing between the inputs or outputs or an intermediate coupling must be added to otherwise expand the signal separation to match the input or output spacing. The intermediate coupling adds length to the planar waveguide and reduces coupling efficiencies.
Planar waveguides have also been coupled to each other and to external devices, such as lasers and photodetectors, using out-of-plane mirrors that reflect light normal to the direction of light propagation through the planar waveguides. For example, U.S. Pat. No. 4,750,799 to Kawachi et al. mounts a micro-reflecting mirror between guides of a planar waveguide for folding light through a right angle to an external device mounted on top of the planar waveguide. The micro-reflecting mirror is separately manufactured from coated glass or plastic and is mounted between the guides so that the mirror's reflective surface is oriented at 45 degrees to the direction of light propagation.
U.S. Pat. No. 5,182,787 to Blonder et al. and U.S. Pat. No. 5,263,111 to Nurse et al. teach the fabrication of similar out-of-plane mirrors as integral structures of planar waveguides. Both involve etching cavities in planar waveguides and coating an inclined side wall of the cavity with a reflective material. Blonder et al. etch the opposite side wall nearly perpendicular to minimize refraction of light emitted into the cavity. Nurse et al. coat portions of a cavity floor and shelf in addition to an inclined side wall for improving uniformity of the reflective surface.
However, none of the proposed arrangements for coupling external devices or other planar waveguides to top or bottom surfaces of planar waveguides entail any suggestions for reducing spacing requirements of multiple inputs or outputs.
SUMMARY OF INVENTION
My invention is particularly useful for reducing dimensions of optical devices that involve coupling signals or signal portions distinguished by wavelength. Without changing the outer dimensions of inputs or outputs to such devices, the inputs or outputs are effectively positioned closer together to reduce requirements for spatial dispersion of the wavelengths within the devices.
The same coupling elements can often function as either inputs or outputs depending on the direction of light travel through optical devices. Since my invention is concerned with improving multiple wavelength couplings regardless of the direction of light travel, the term “input/output” is used to refer to such elements that might function as inputs, outputs, or both.
One example of my invention includes a wavelength separator within a waveguide for directing different wavelengths through separate foci along a focal line that lies in a plane of propagation through the waveguide. Reflective surfaces also located within the waveguide fold the wavelengths out of the plane of propagation and into alignment with an array of input/outputs. At least some of the reflective surfaces are offset from the focal line so that the input/outputs can be spaced closer together in a dimension along the focal line.
Preferably the reflective surfaces are located along a centerline that intersects the focal line at an angle. The input/outputs are arranged along a corresponding centerline and can be mounted as a group on a surface of the waveguide. The spacing between the input/outputs along the centerline is limited by the outer dimensions of the input/outputs, but their effective spacing along the focal line is reduced by a factor of the cosine of the angle between the centerline and the focal line.
The focal depth through which the different wavelengths are focused is preferably at least as large as the amount the reflective surfaces are offset from the focal line—so the offset has little effect on mode field dimensions of the focused wavelengths or on the resulting coupling efficiencies. However, larger offsets can be accommodated by shaping the reflective surfaces to refocus the wavelengths within desired dimensions. Also, each of the reflective surfaces can be individually inclined to their common centerline to enhance coupling efficiencies.
The reflective surfaces can be made in a variety of ways, including variations for accommodating integrated, hybrid, and bulk designs. For example, the reflective surfaces can be integrated within a planar waveguide by etching a cavity having side walls inclined through a common angle with the plane of propagation. The cavity can be left empty for supporting total internal reflection from one of the inclined side walls, or the other of the side walls can be coated with a reflective surface and the cavity can be filled with an index-matching material for supporting external reflections from the coated side wall.
A more conventional cavity can also be formed in a planar waveguide and filled with a different material for forming the reflective surface. For example, the cavity can be filled with an organic material that can be ablated by ultraviolet irradiation, leaving an inclined surface. A photosensitive material can also be used to fill the cavity. Selective exposure of the photosensitive material and subsequent development can be used to produce a similar inclined surface. Other photosensitive material together with interfering light beams can be used to produce a holographic grating within the cavity composed of a plurality of partially reflective surfaces. The holographic grating functions as an interference filter having a pass band that reflects the desired wavelengths.
The reflective surfaces can also be separately formed as one or more reflective optics and inserted into cavities or troughs formed in planar waveguides. For example, a thin optical fiber having triangular cross section can be mounted in a trough formed in the waveguide. One of the side surfaces of the fiber can be coated to form a continuous reflective surface oriented for folding wavelengths out of the plane of propagation and into alignment with respective input/outputs. A similar fiber coul
Agon Juliana
Corning Incorporated
Greener William
Healy Brian
Ryan Thomas
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