Theory of design parameters for quasi-phase-matched waveguides andapplication to frequency doubling in polymer waveguides

摘要

A theory of dispersion in single-mode symmetric waveguides isnpresented for phase-matching second harmonic generation (SHG) of thenfundamental modes, based on the approximate analytical waveguide theorynof Botez. The theory is used to derive new equations for the maximumnphase-matching distance allowed when there are random fluctuations innwaveguide thicknesses, under critical and noncritical phase-matchingnconditions. The theory is also used to calculate the overlap integral asna function of the waveguide parameters VΩ andnV2Ω. A new expression is derived for the efficiency ofnSHG in waveguides in terms of waveguide parameters that can be used tonoptimize SHG. Theoretical results are presented for typical LiNbO3n and polymer waveguides. Quasi-phase-matched (QPM) waveguides arenfabricated from nonlinear optical (NLO) polymers using the techniques ofnperiodic poling and bleaching, and channel waveguides are printed by thenbleaching of the NLO polymers. The NLO polymers are characterized forntheir refractive indexes, optical loss, NLO coefficients, and bleachingncharacteristics. Phase-matched SHG results are presented for thendifferent fabrication methods over a distance of 0.5 cm, and annassessment is given of the relative strengths and weaknesses of thendifferent fabrication approaches