Method and apparatus for implementing a multi-channel tunable filter
View Patent ↗The present invention provides a multi-channel tunable filter and methods for making such a filter. In one embodiment, the filter comprises a bank of gratings or a continuously varying filter frequency imprinted into a filter material, such as Lithium Niobate or glass or polymer. An optical read-head comprising a pair of lenses is configured to pass light from within an optical fiber carrying multiple wavelengths through an appropriate grating to extract or drop a specific wavelength. To ensure continuous data transmission, the filter is tuned to a wavelength by configuring the read-head to move in a hitless manner. In one embodiment, the gratings are recorded by the interference of two beams. A first plane wave reflects off a first mirror stack and a second plane wave reflects off a second mirror stack. In another embodiment, the gratings are recorded by a phase masking method.
1. A multi-channel tunable filter comprising:
a three-dimensional filter material; and
a continuously varying grating recorded into said three-dimensional filter material utilizing at least one continuously varying mirror stack wherein any portion of said grating is configured to reflect a given wavelength of a light wave.
2. The filter of claim 1 wherein said three-dimensional filter material is a holographic material.
3. The filter of claim 2 wherein the holographic material is Lithium Niobate.
4. The filter of claim 2 wherein the holographic material is glass.
5. The filter of claim 2 wherein the holographic material is a polymer material.
6. The filter of claim 2 wherein the holographic material is disposed to one or more lasers to stabilize the spectral emission of the one or more lasers.
7. The filter of claim 6 wherein the holographic material is disposed adjacent the emission facet of the laser.
8. The filter of claim 7 further including a collimating element disposed between the emission facet and the holographic material.
9. A method for recording a continuously varying grating comprising: reflecting a first beam off a first continuously varying mirror stack; reflecting a second beam off a continuously varying mirror stack; and producing an interference between reflection of said first beam and reflection of said second beam wherein said interference writes a continuously varying grating period in a recording material to form said grating.
10. The method of claim 9 wherein the two interfering beams are first incident onto two separate blocks of optically transparent material between which is a holographic material.
11. The method of claim 10 further wherein the holographic material is inserted with an index matching liquid that approximately matches the index of the holographic material and the blocks of optically transparent material.
12. The method of claim 11 wherein the holographic material is Lithium Niobate.
13. The method of claim 11 wherein the holographic material is glass.
14. The method of claim 11 wherein the holographic material is a polymer material.
15. The method of claim 9 wherein the first and second mirror stacks are planar mirrors.
16. The method of claim 9 wherein the first and second mirror stacks are cylindrical mirrors.