Abstract: An optical assembly comprises an optical device (103); an enclosure (101) for containing the optical device (103), the enclosure (101) including a transparent section (107) to allow passage of a light beam (104) to or from the optical device (103); and means for measuring the attenuation of a test light beam (212) through the transparent section(107). Preferably, the optical assembly also comprises means for compensating for the measured amount of attenuation by adjusting a measurement or a characteristic of the optical device (103) or a related optical device to compensate for the measured amount of attenuation.

Abstract: The optical filter (1) receives a dense wavelength division multiplexed signal (2) as an input. The filter (1) is adapted to output a single channel (3) of less than 1 nm bandwidth. The filter (1) has a plurality of cavities (4) which are each optically connected to an adjacent cavity (4) by means of a coupling layer (8) one or more) cavities (4) include a spacer (5) of thickness greater than 7 ?m. Each spacer (5) defines two opposed surfaces (6) each having a plurality of thin layers 7 disposed thereon. Preferably the total number of thin layers (7) per cavity (4) is less than 35. Also disclosed are optical interleavers.