Tuning and temperature compensation of the air-gap etalon for dense wavelength-division multiplexing application
AssigneeOplink Communications, Inc.
InventorShijie Gu
Life of this patent
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Abstract
An etalon includes a tuning plate in the air-gap between the etalon mirrors. The method of tuning includes selecting a tuning plate that makes the optical length of the etalon slightly less than required for ITU and then rotating the tuning plate through a small angle until tuning is complete. The tuning plate material is selected to provide dispersion compensation and to compensate for thermal expansion of the mirror spacers.
Claims15
A method for tuning an etalon, the etalon comprising an air-gap between two parallel mirrors, the method comprising:
- measuring the free spectral range (FSR) of the etalon;
- calculating the thickness of an ideal tuning plate that would bring the etalon exactly into tune;
- selecting and installing a thinner tuning plate that is thinner than the ideal tuning plate in the air-gap in the etalon so that the FSR of the etalon is slightly greater than the design FSR;
- rotating the tuning plate until the FSR of the etalon coincides with the design FSR to within a required precision.
A tuned etalon comprising:
- a spacer;
- a first mirror;
- a second mirror, wherein the spacer spaces the second mirror apart from and parallel to the first mirror with an air-gap between the first mirror and the second mirror;
- and
- a tuning plate located between the first mirror and the second mirror, the tuning plate being rotated about an axis that is parallel to the mirrors so as to increase the effective thickness of the tuning plate and thereby bring the etalon into tune;
- wherein the tuning plate is a glass plate made of glass that has a negative temperature coefficient of refractive index.
The etalon of claim 9 wherein the glass is selected from the group of optical glasses that includes S-FPL51 and S-PHM52.
A tuned etalon comprising:
- a spacer;
- a first mirror;
- a second mirror, wherein the spacer spaces the second mirror apart from and parallel to the first mirror with an air-gap between the first mirror and the second mirror;
- and
- a tuning plate located between the first mirror and the second mirror, the tuning plate being rotated about an axis that is parallel to the mirrors so as to increase the effective thickness of the tuning plate and thereby bring the etalon into tune;
- wherein the tuning plate is made from a material that has a negative value of the effective coefficient of thermal expansion over the temperature range of 0° to 65° C., wherein the effective coefficient of thermal expansion is defined as (n−1)αh+βh where n is the index of refraction, αh is the thermal expansion coefficient, and βh is the temperature coefficient of the refractive index.
Dependencies are inferred from the claim text.