Investigation Of Quasi-Phase Matching Technology And Its Applications

The phase-dismatching among interacting light waves can be efficiently compensated by use of the quasi-phase matching(QPM) technology,thus it is used in many areas.In this dissertation,the optical parametric amplification (OPA) and optical wavelength conversion(OWC) based on QPM technology is investigated theoretically and numerically.The main contents are as follows:1.The principle and development of the QPM technology,especially its use in the area of optical parametric amplification and optical wavelength conversion are summarized.The characteristics and types of the periodically poled crystals are discussed.The schemes applied to convert the pole of the domain are summarized.2.The effects of grating period and noncollinear geometry on the broadly tunable bandwidth of optical parametric amplification are investigated theoretically and numerically for quasi-phase-matched crystal. For ultra-short pulse OPA,the concept of maximum grating period is proposed to achieve the phase matching and group-velocity matching simultaneously in a wide range.By employing the maximum grating period, geometryâ… is recommended due to the much wider signal tunable range compared with geometryâ…¡.An expression is proposed to calculate the maximum grating period for congruent periodically poled LiNbO₃(PPLN) with 800nm pump wave.A feasible scheme is presented to determine the working temperature and noncollinear angleα,maximize the tunable range and simplify the tuning by rotating angleθonly.This scheme can also be used for other QPM crystals and other pump waves.For nanosecond pulse OPA,the optimal grating period and noncollinear geometry are presented to obtain the maximum tunable bandwidth.3.The parametric bandwidth of PPLN based optical parametric amplification with different noncollinear geometries is investigated by expanding the wave-vector mismatch in a Taylor series and retaining terms through second order and by use of the definition directly.The parametric bandwidth can be enhanced in different signal wavelength range by employing suitable geometry or by tuning the grating period.For ultra-short pulses,the enhancement of parametric bandwidth by utilizing suitable geometry is better than that of tuning grating period.But for nanosecond pulses,suitable grating period and noncollinear angleθare more important. The methods of achiving parametric bandwidth by expanding the wave-vector mismatch in a Taylor series or by use of the definition directly are compared.4.The gain bandwidth and gain of PPLN based OPA are studied.On the conditions of phase matching and group velocity matching satisfied simultaneously,an expression is obtained by expanding the wave-vector mismatch in a Taylor series.The effect of grating period and noncollinear geometry on the gain bandwidth is analysised,the difference between parametric bandwidth and gain bandwidth is discussed too.Compared with increasing pump intensity,the gain can be effectively improved by increasing crystal's length,while the grating period and the noncollinear amplification geometry almost have no effect on the gain.5.Three types of non-absolute noncollinear OPA based on PPLN are proposed.The difference between absolute noncollinear OPA and non-absolute noncollinear OPA is discussed.The parametric bandwidth and the signal tunable bandwidth are studied for two types of non-absolute noncollinear OPA which are used often.6.The conversion bandwidth and conversion efficiency of difference frequency generation(DFG)-based,single-pass/double-pass cascaded second-harmonic generation(SHG)+DFG interactions-based and single-pass/double-pass cascaded sum frequency generation(SFG)+DFG interactions-based wavelength conversion in an aperiodic optical superlattice lithium niobate crystal are studied theoretically and numerically.Compared with uniform grating,the conversion bandwidth and stability of the signal and pump wave can be enhanced by optimizing the aperiodic grating,on the presupposition of achiving the same conversion efficiency.Systemcally considered the conversion efficiency,conversion bandwidth and the manufacture of PPLN,two-segment PPLN is recommended to be used in wavelength converter.