Surface Emitting Second Harmonic Generation in Poled Polymer Waveguides

Abstract

The mixing of counter propagating guided waves to generate second harmonic radiation normal to the surface was initially demonstrated in Ti in-diffused LiNbO3 waveguides over a decade ago.[1] Although the signals were too small to be useful in practice, several applications were demonstrated or proposed, including picosecond signal processing, [2] picosecond optical transient digitizers,[3] and spectrometers.[4] The device potential of this phenomenon for ultra fast signal processing, waveguide division demultiplexing, etc., has attracted attention recently.[5] Since the signal at the harmonic frequency only traverses the waveguide depth, applications to blue and green light source can be realized by using huge resonant nonlinearities which is over 400pm/V. In the last few years, several works in GaAs based waveguides were reported and the conversion efficiency was improved dramatically by using a form of quasi-phase matching in multi layered structures. On the other hand, organic polymers have also been shown to have great potential for second order nonlinear optical applications because they have large nonlinearities and ease of fabrication. Using very large second order nonlinearities in poled polymers, signals are easily detectable with uncooled CCD arrays on a single shot basis and all the device applications become realistic. Here we discuss surface emitting second harmonic generation (SHG) devices in 4-dimethylamino-4′-nitrostilbene (DANS) side-chain polymers.