A comparison of free space and fiber mixer performances in a heterodyne laser radar

The author compares the signal-to-noise ratio at the IF stage of a heterodyne laser radar receiver using the traditional free space mixer with the IF CNR from a heterodyne laser radar receiver using a fiber mixer stage. The comparison indicates the fiber mixer will generally under-perform the free space mixer unless the f-numbers of the receiver optics and the single-mode fiber are approximate matches. In this case, the fiber mixer performs as well as the free space-mixer and can even out-perform it for some optics designs