Design of an Optical Clock Repetition Rate Multiplier
N. Khan, N. Abas and A. Kalair
We report the design of a cost effective, high power, multiple wavelengths tunable pulse repetition rate DFB laser. The high repetition rate feature is based on time interleaved multiplication of 166MHz Q-switched and mode-locked Nd:Yag laser. The Nd:Yag laser output consists of 10 pulses envelope each 6ps duration and 6.14ns apart from one another. The pump pulses are later split and added using ten stages of beam splitters, delay lines and mirrors so as to shorten inter-pulse period in the first stage by half of the original 6.14ns. The repetition rate of resultant output after ten frequency multiplier stages becomes 166GHz. The signal was multiplied two times after each pass and the resultant optical pulses had repetition rate 1000 times the original signal. Three pairs of above pulses are used to pump solution of Rh6G in ethanol to produce nine different wavelengths pulse trains leading to 9x166GHz=1.494THz repetition rate pulses. It produced an array of 90 multiple colors pulses when pumped by 6.14ns delayed ten pulse and 900 when pumped by pulses multiplied pump source. This could not be increased further due to 6ps inter-pulse periods between the 6ps pulses, however, the principle may be extended to higher order arrays and repetition rates if the pulse size is accordingly femtosecond to attosecond duration with appropriate inter-pulse period. The technique is very simple, but the multiplication or inter-pulse period shortening is limited by the laser pulse duration beyond which pulse intensity amplification is likely to occur due to constructive interferences of time delayed laser pulses within its coherence length. A simple cost effective method for MHz to THz repetition rate multiplier is reported.
Keywords: Repetition rate multiplier, frequency multiplier, Multicolor DFB lasers, Terahertz.