Optical filtering device using counterpropagating difference frequency generation

Abstract

Abstract: A high-efficiency optical filter composed of counter-propagating wavelength converter in ZnTe, is demonstrated. The device has a extremely narrow bandwidth 0.5 angstrom, corresponding to pump intensity 1.2MW/cm 2 and length of crystal 1cm, is tunable over several nanometers in bandwidth using combination of device length and pump intensity. The presented scheme is also a candidate of wavelength-dependant switcher. INTRODUCTION Recently, the deployment of multi-wavelength digital optical telecommunication networks and of signal processing based on wavelength division multiplexing (WDM) urges to develop efficient wavelength converting techniques. In particular, in the quest for best operating on signals at bit rates exceeding the tens of Gbps, it is of the utmost importance to explore the possibility of effectively performing all-optical transfer of information content between optical carriers at different wavelengths 1-2 . Several attempts, such as using nearly four-wave mixing in laser diodes or amplifiers and employing difference frequency generation (DFG) in waveguides 3-6 , have been made to convert wavelength 1.5 m (an appealing feature for WDM networks) based on third-order and second-order optical nonlinear effects, respectively. It is also known that the DFG-based wavelength converters are generally classified into two kinds of configurations: classic forward-propagating DFG (FDFG) and counter-propagating DFG (CDFG) configurations, which correspond to second-order wavelength conversion architectures with propagation directions of signal and idler beams being respectively equal or opposite 7 . Moreover, the signal field conversion and amplification in CDFG configurations are more effective compared to that in traditional FDFG configuration. On the other hand, In most communication receives, optical filters are important devices used in the front end during the light focusing. The basic types of optical filters consist of the absorption filter, birefringent filter, and atomic resonance filter. Among these filters, birefringent filter can only achieve bandwidths as low as 10 angstroms. Atomic resonance filter use the atomatic line widths of certain materials to produce passbands on the order of the line width, which require careful control of the input optical wavelength when used as a communication filter. In order to overcome these disadvantages and get more effective optical filters for communication, the realization of optical filters with much narrow bandwidths and high-efficiency has been hot research subject. In this paper, for the first time, we report our results on studies of wavelength converting bandwidth behavior in CDFG-based wavelength converter. It is predicable that CDFG-based wavelength converter is an excellent candidate for narrow-bandwidth optical filter and wavelength-dependant switcher. The novel CDFG-based wavelength converter for bandwidth tunable optical filters, which can be controlled through both the pump intensity and device length, has been presented.