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