FREQUENCY CONVERTER

PURPOSE:To attain high speed frequency conversion to an input signal having frequency fin being any frequency within a broad frequency range into a frequency within a required frequency band independently of the frequency of the said input signal. CONSTITUTION:A mixer 1 is used to convert an input signal having an unknown frequency (=2nd frequency) into a frequency (=3rd frequency) within a required frequency band. A radiating light of a semiconductor laser 7 allowing to a light modulated by the frequency of the said input signal and having one side wave to radiate as a means controlling a local oscillating frequency (=1st frequency) mixed with the input signal is transmitted through an optical element etalon 9, its transmitted luminous intensity is detected by a photodetector 1, and the frequency of the input signal is estimated by a frequency identifier 11 with required accuracy depending on the relation between the light intensity and the frequency of the said input signal and the signal with a frequency in the vicinity of the estimated value is generated. A required local oscillating frequency fL0 is quickly selected and the time required to convert the 2nd frequency into the 3rd frequency is reduced.