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