Thin-film interference filter with quarter-wavelength unit sub-layers arranged in a generalized pattern
AssigneeSemrock, Inc.
InventorsLigang Wang, Turan Erdogan
Life of this patent
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Abstract
Thin-film interference filters are constructed with a generalized pattern of layers differing in both thickness and refractive index to produce spectral responses appropriate for adjusting optical power among a plurality of different wavelength channels. Each of the layers is composed of unit sub-layers having thicknesses equal to a quarter-wavelength thickness of a monitoring beam. Interference fluctuations of the monitoring beam associated with the deposition of the unit sub-layers enable a gain-flattening filter to achieve greater manufacturing accuracy by exploiting self-correcting effects of “turning point monitoring” techniques.
Claims46
A gain-flattening interference filter that adjusts relative power among a plurality of different wavelength channels conveyed through the filter comprising:
- a plurality of layers formed from at least two different refractive index materials;
- each of the layers being composed of an integer multiple number of unit sub-layers having physical thicknesses corresponding to a quarter-wavelength travel of a monitoring light beam as transmitted through the unit sub-layers;
- the at least two different refractive index materials including high and low refractive index materials arranged in the unit sub-layers having physical thicknesses that differ in inverse relation to their refractive indices;
- and
- the high and low index unit sub-layers being arranged in a substantially non-repeating pattern for producing different attenuating effects among the different wavelength channels conveyed through the filter.
A method of making a gain-flattening interference filter for relatively adjusting optical power among a plurality of different wavelength channels conveyed through the filter comprising steps of:
- determining relative optical power adjustments among the plurality of different wavelength channels;
- choosing at least two different refractive index materials capable of being separately deposited as high and low refractive index layers;
- choosing a wavelength of a monitoring light beam;
- depositing the high and low refractive index layers as integer multiples of unit sub-layers having physical thicknesses corresponding to quarter-wavelength travels of the monitoring light beam as transmitted through the sub-layers;
- and
- arranging the unit sub-layers of the high and low refractive index layers in a substantially non-repeating pattern for producing different attenuating effects among the different wavelength channels conveyed through the filter.
A method of designing a gain-flattening interference filter for adjusting optical power among a plurality of different wavelength channels comprising steps of:
- determining relative optical power adjustments among the plurality of different wavelength channels;
- choosing at least two different refractive index materials capable of functioning as high and low refractive index layers;
- dividing the high and low refractive index layers into high and low index sub-layers having unit thicknesses;
- organizing combinations of the high and low index sub-layers into a set of base permutations including alternatives that vary in both number and order of the high and low index sub-layers;
- assembling the high and low index layers into a number of levels;
- filling each of the levels with one of the alternatives from the set of base permutations;
- evaluating optical performance characteristics of the levels filled by alternatives from the set of base permutations;
- comparing the optical performance characteristics of the filled levels to the determined relative optical power adjustments among the plurality of different wavelength channels;
- and
- refilling the levels with different alternatives from the set of base permutations based on the results of the comparison for better matching the optical performance characteristics of the selected number of levels with the determined optical power adjustments among the plurality of different wavelength channels.
An interference filter assembled from a succession of layers having variable thicknesses regulatable by a turning point monitoring technique for variably attenuating a working range of wavelengths comprising:
- the succession of variable-thickness layers being formed from at least two different refractive index materials;
- each of the variable-thickness layers within an uninterrupted portion of the succession being composed of an integer multiple number of unit sub-layers having physical thicknesses corresponding to a quarter-wavelength travel of a monitoring light beam as transmitted through the unit sub-layers;
- some of the unit sub-layers of quarter-wavelength thickness being formed from one of the refractive index materials and other of the unit sub-layers of quarter-wavelength thickness being formed from other of the refractive index materials;
- the different index unit sub-layers being arranged in a substantially non-repeating pattern;
- and
- the monitoring light beam wavelength from which the quarter-wavelength travel is derived being longer than the working range of wavelengths attenuated by the interference filter.
Dependencies are inferred from the claim text.