| 摘要 |
PURPOSE:To enable correction of magnification error caused by variance of oscillation wavelength of a semiconductor laser by providing a clock signal generating means for generating a clock signal and transmitting it to a modulation signal outputting means and a means for changing frequency of a clock signal and correcting magnification errors. CONSTITUTION:Oscillators 15-17 generate clock signals having various different typesof frequency, and a multiplexer 18 selects the clock signals from the oscillators 15-17 in accordance with the signal from a changeover switch and transmits them to a phase locked circuit 2. Reference oscillation wavelength of a semiconductor laser 3 is set to 790nm. When its oscillation wavelength is of a segment ''1'', the multiplexer 18 switches the changeover switch so that the clock signal of 1.874mHz from the oscillator 15 can be selected. In the same manner the multiplexer 18 switches the changeover switch so that the clock sigal of 1.890mHz and that of 1.906mHz can be selected in case of a segment II and in case of a segment III, respectively. Thus when three types of clock frequency are used, magnification errors can be reduced to 1/3 compared with the use of only one clock frequency.
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