Abstract: A multi-pass optical filter using two identical filters provides narrower band filtering by double filtering an optical signal passing therethrough. Although passing a beam of light at an optical filter having a substantially thick optical thickness is known to have significant coupling losses due to angular misalignment of the output beam and the receiving optical fibre, it has been found that twice filtering in the conventional manner by serially coupling two same filters increases coupling losses. However, this invention provides a coupling arrangement wherein losses are significantly lessened by offsetting the axes of the lensed filters such that the beam exiting the first filter couples into the second filter as it would be reflected backward into the first filter.