The time delay unit also includes a reflecting element for reflecting the optical signal back to the dispersive element along an optical path {TAIL ~ whose length} is {HEAD ~ a function} of the angle 
The time delay unit also includes a reflecting element for reflecting the optical signal back to the dispersive element along an optical path { TAIL ~ whose length } is { HEAD ~ a function } of the angle
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH