Content: 1Recent progresses in weak light nonlinear optics1.1 Introduction1.2 Ultraviolet photorefractivity in lithium niobate crystals1.3 Nonlinear optics with incoherent light and discrete spatial solitons1.4 Nonlinear optical properties of novel carbon-based materials1.5 Nonlinear optics from metallic plasmonics1.6 Summary 2Polarization-coupling of light in periodically poled lithium niobate based on electro-optics effect2.1 Introduction2.2 Polarization-coupling of light in periodically poled lithium niobate2.3 Cascaded polarization-coupling process and induced large nonlinear phase2.4 Precise control of parameters of laser based on polarization-coupling 2.5 Photonics application of polarization-coupling effect in PPLN 3 Ultrafast nonlinear optics3.1 Introduction3.2 Ultrashort pulse collapse in quadratic media3.3 Femtosecond laser induced filamentation3.4 Nonlinear interaction of intense ultrashort filaments3.5 Ultrafast optical gating by molecular alignment3.6 Application and prospect 4 Wave coupling theory of linear electrooptical effect and its generalization and applications4.1 Introduction to linear electrooptical effect4.2 Wave coupling theory of linear electrooptical effect in bulk transparent media 4.3 Wave coupling theory of linear electrooptical effect in bulk absorbing media4.4 United wave coupling theory of electrooptical-rotooptical-magnetooptical effects4.5 Wave coupling theory of quasi-phase-matched linear electrooptical effect