Optical module with high reflection isolation and compact size

An optical apparatus comprising:

• a first lens with a first side and a second side, the first side being perpendicular to an optical axis of the lens, and the second side being made slightly slanted or perpendicular to the optical axis of the lens;
• a fiber with a facet towards the second side of the first lens, the facet of the fiber being so slanted that the facet of the fiber and the second side of first the lens are non-congruent with respect to the optical axis of the lens;
• a second lens disposed coaxially with the first lens;
• a first optical filter disposed between the first lens and the second lens and towards the first side of the lens;
• and
• a second optical filter disposed towards the second side of the first lens and covering only a portion of the second side of the first lens such that a light beam coming from the fiber is coupled to the first lens without having to go through the second optical filter while a reflected light beam from the first optical filter impinges right into the second filter, wherein the first optical filter and the second optical filter are conjugate in respective spectrum responses, and wherein the second filter is provided to block possible residuals in a signal from the first optical filter to achieve a high degree of isolation.