The present disclosure provides systems and methods for preventing or minimizing optical crosstalk in an optical circuit switch (“OCS”). The OCS may include a collimator lens assembly. The collimator lens assembly may include a lens array defined by a plurality of ports. Each port may include a lenslet and a spacer paired with each lenslet. Crosstalk may occur when light from other ports enter the target port's optical fiber. The collimator lens assembly may include an insert positioned relative to the lenslet. The insert may define an aperture that allows light from the target port to pass through. The insert may prevent a portion of light from adjacent ports from passing through the aperture. The insert may be located between the lenslet and spacer, on the curved surface of the lenslet, or on a plate located at a distance from the front of the lenslet.