An optical circuit switch, comprising: a fiber hole array including an array of receptacles shaped to accept respective optical fibers; a plurality of internal optical fibers enclosed within the optical circuit switch, with one end of each fiber disposed within a respective receptacle of the fiber hole array; a collimating lens array positioned adjacent to the fiber hole array and including a plurality of collimators, wherein each collimator optically couples light into or out of a corresponding one of the internal optical fibers; a MEMS mirror array; and a first reflective surface (130, 560), wherein, the fiber hole array, the collimator, the MEMS mirror array, and the first reflective surface are positioned relative to one another such that light exiting each of the internal optical fibers passes through its corresponding collimator and is redirected by a first mirror within the MEMS array towards the first reflective surface, which directs the light back towards a second mirror of the MEMS mirror array, which in turn redirects the light towards a second internal optical fiber; characterised in that the optical circuit switch additionally comprises: a second reflective surface (120, 530) positioned within the optical path between the collimating lens array and the MEMS mirror array, wherein the first and second reflective surfaces are configured to reflect light of at least a first wavelength and to be substantially transmissive with respect to a light of a second wavelength, and a light source configured to direct light of the second wavelength through the second reflective surface and towards the MEMS mirror array; and a light detector configured to detect light of the second wavelength emitted by the light source that has passed through the second reflective surface, off of the mirror array, and through the first reflective surface. a fiber hole array including an array of receptacles shaped to accept respective optical fibers; a plurality of internal optical fibers enclosed within the optical circuit switch, with one end of each fiber disposed within a respective receptacle of the fiber hole array; a collimating lens array positioned adjacent to the fiber hole array and including a plurality of collimators, wherein each collimator optically couples light into or out of a corresponding one of the internal optical fibers; a MEMS mirror array; and a first reflective surface (130, 560), wherein, the fiber hole array, the collimator, the MEMS mirror array, and the first reflective surface are positioned relative to one another such that light exiting each of the internal optical fibers passes through its corresponding collimator and is redirected by a first mirror within the MEMS array towards the first reflective surface, which directs the light back towards a second mirror of the MEMS mirror array, which in turn redirects the light towards a second internal optical fiber; characterised in that the optical circuit switch additionally comprises: a second reflective surface (120, 530) positioned within the optical path between the collimating lens array and the MEMS mirror array, wherein the first and second reflective surfaces are configured to reflect light of at least a first wavelength and to be substantially transmissive with respect to a light of a second wavelength, and a light source configured to direct light of the second wavelength through the second reflective surface and towards the MEMS mirror array; and a light detector configured to detect light of the second wavelength emitted by the light source that has passed through the second reflective surface, off of the mirror array, and through the first reflective surface. a second reflective surface (120, 530) positioned within the optical path between the collimating lens array and the MEMS mirror array, wherein the first and second reflective surfaces are configured to reflect light of at least a first wavelength and to be substantially transmissive with respect to a light of a second wavelength, and a light source configured to direct light of the second wavelength through the second reflective surface and towards the MEMS mirror array; and a light detector configured to detect light of the second wavelength emitted by the light source that has passed through the second reflective surface, off of the mirror array, and through the first reflective surface.