Abstract
Acousto-optic (AO) frequency shifters that utilize single Bragg diffraction all suffer from the undesirable characteristics with the propagation direction of the frequency-shifted light varying with the magnitude of frequency shift.1,2 As a result, the frequency-shifted light will miss the core of a single-mode optical fiber which in turn severely limits the bandwidth of frequency shift, Recently, we proposed a scheme2 involving double AO Bragg diffractions in cascade which enables the propagation direction of the frequency-shifted light to remain unchanged, irrespective of the magnitude of frequency shift. Using this scheme, a guided-wave passband AO frequency shifter operating at the optical wavelength of 0.6328 μm was made2 in a LiNbO, waveguide to demonstrate the aforementioned desirable characteristics. However, in some cases baseband optical frequency shifters with the frequency shift centered at zero frequency (dc) is desired. We have also recently made a baseband AO frequency shifter3 utilizing AO Bragg diffractions in cascade in a LiNbO3 waveguide that operates at the optical wavelength of 0.6328 μm. Since the frequency-shifted light maintains its propagation direction irrespective of the magnitude of frequency shift, such passband and baseband AO frequency shifters, when employed for single-mode fiberoptic systems, can provide very large tunable frequency shift, only limited by the bandwidth of the SAW transducer and/or that of the AO Bragg diffractions involved1.
© 1992 Optical Society of America
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