Basic research on the optical pulse transmission and nonlinear phenomina in the photonic crystal slab waveguide

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It is well known that two-dimensional (2D) photonic-crystal (PC) slab waveguides (WGs) exhibit the noticeable light propagation characteristics. A typical example is that the light can pass through an abruptly bent corner of those line-defect WGs without any appreciable loss, resulting in being very attractive for ultra-small and low-energy optical integrated circuits (PIC). This is caused by the fact that the PC-slab WG has the advantage of tight light confinement vertically due to total internal reflection and laterally due to photonic band gap (PBG) effect, respectively. Moreover, that the group velocity vg^<WG> is small makes the power inside the WG larger by a factor n_g= (vg^<0>/vg^<WG>), being very advantageous to optical nonlinear (ONL) phenomena. So far, passive PC components have already been successfully developed, active components such as all-optical switch, buffer memory and optical amplifier have seldom been developed except a few cases. One of the best ways to develop u … More ltra-fast active components is to make efficient use of ONL phenomena such as stimulated Raman scattering (SRS) and self-or cross-phase-modulation (SPM or XPM) due to instantaneous optical Kerr effect. AlGaAs-based PC WGs have the advantage over the Si-based ones of avoiding two-photon absorption (TPA). Different from the case of Si, the TPA in the AlGaAs is practically avoided by increasing Al-content, thus increasing the electronic band gap.In this work, we first observed the SPM-induced spectral broadening for PC-slab WGs in a wavelength range from 1,460 to 1,535 nm; the SPM (or a phase shift) due to the nonlinear refractive index n_2 leads to a marked spectral evolution as the input pulse power P_<in> is increased. We have examined the spectrum of the light-pulse transmitted through an Al_<0.26>Ga_<0.74>As-based sample, by varying the power of incident pulse with T_0 (pulse duration) =1.6 ps. As a result, we found that the spectrum gets broader with increase of P_<in>, and on further increasing, develops a double-peak structure, corresponding to a phase shift of 1.3 π. The power required for this shift is estimated to be as small as 〜1.4 W for a 1.0 mm-long sample. The estimated n_2-value is 〜1.3 X 10^<-13>cm^2/W. On the other hand, the SRS has the potential for developing a light amplifier and a compact light source. Until now, however, no experimental work has been reported yet on SRS for the PC-slab WG In this connection we mention that several successful works on SRS have already been reported on GaP-based-and Si-based wire-WGs. So, we performed a pump-probe experiment of SRS amplification of light around 1,550 nm in an Al_<0.26>Ga_<0.74>As-based PhC-slab WG As a result, we observed more than 6 dB signal amplification with pump pulse energy of 22 pJ in an effective sample-length of 〜0.5 mm, which corresponds to a net gain of 〜3 dB. This result encourages us to develop an ultra-fast all-optical switch in future. Less