Patent attributes
Techniques for designing optical couplers are disclosed. According to one aspect of the optical couplers, different from the prior art couplers, a holding tube (a sub-assembly) for holding an optical lens (e.g., a GRIN lens) and an optical filter (e.g., a thin film filter) is formed by concatenating two single tubes, one for accommodating the optical lens and the other for accommodating the optical filter. The two tubes are not required to have an identical dimension. As a result, inherent flexibilities are provided in the holding tube, especially the optical filter often comes in different sizes. Further, when the sub-assembly is inserted in a sleeve, only either one of the two tubes is secured to the sleeve so as to reduce a risk that, during a thermal condition change, any metal and glass material expansion will not cause the sub-assembly to be under stress that would otherwise be present when both of the tubes are secured to the sleeve. To reduce stress-related optical loss of the optical couplers, an epoxy adhesive is applied onto only a portion of an optical lens and a portion of a tube.
