%0 Journal Article
%T Continuous Operation of a Bragg Diffraction Type Electrooptic Frequency Shifter at 16£¿GHz with 65% Efficiency
%A Shintaro Hisatake
%A Kenji Hattori
%A Tadao Nagatsuma
%J Advances in Optical Technologies
%D 2012
%I Hindawi Publishing Corporation
%R 10.1155/2012/676785
%X We demonstrate for the first time the continuous operation of a Bragg diffraction type electrooptic (EO) frequency shifter using a 16£¿GHz modulation signal. Because frequency shifting is based on the Bragg diffraction from an EO traveling phase grating (ETPG), this device can operate even in the millimeter-wave (>30£¿GHz) range or higher frequency range. The ETPG is generated based on the interaction between a modulation microwave guided by a microstrip line and a copropagating lightwave guided by a planner waveguide in a domain-engineered LiTaO3 EO crystal. In this work, the modulation power efficiency was improved by a factor of 11 compared with that of bulk devices by thinning the substrate so that the modulation electric field in the optical waveguide was enhanced. A shifting efficiency of 65% was achieved at the modulation power of 3£¿W. 1. Introduction Coherent optical frequency conversion based on external modulation is an important technique not only for the optical communication and optical measurement but also for microwave and millimeter-wave photonics because it corresponds to an upconversion from RF to optical domain. Photomixing of two optical modulation sidebands generated by an electrooptic phase modulator (EOM) or a frequency comb generator has been used to generate low phase noise coherent microwaves or millimeter-waves, which are desirable for many applications such as the radar [1], sensing [2¨C4], and wireless communications [5]. The advantages of the external modulation method over other methods such as optical injection locking, optical phase-locked loop, and dual-wavelength laser source are the system¡¯s simplicity, stability, and frequency tunability. However, typical sinusoidal phase modulation is an inherently inefficient method of frequency conversion. At best, the fraction of the power in the first-order sideband generated by normal phase modulation is theoretically , where is a first-order Bessel function of the first kind and is the modulation depth. The conversion efficiency of 34% corresponds to an extra loss of about 5£¿dB. Because the noise figure (NF) of an optical amplifier is relatively poor compared to electronic amplifiers, extra loss due to a low conversion efficiency impacts most key aspects of microwave and millimeter-wave photonics in which low-loss 1550£¿nm components should be used [6, 7]. The lower conversion efficiency results in a lower carrier-to-noise ratio (CNR). The higher conversion efficiency is essential not only for microwave and millimeter-wave photonics applications but also for other photonic
%U http://www.hindawi.com/journals/aot/2012/676785/