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Polarization insensitive second harmonic generation (SHG) is proposed in an electro-optic (EO) tunable periodically poled Lithium Niobate (PPLN). The PPLN consists of four sections. External electric fields could be selectively applied to them to induce polarization rotation between the ordinary and extraordinary waves. If the domain structure is well-designed, the fundamental wave with an arbitrary polarization state can be frequency doubled efficiently in this special PPLN.

We propose a scheme to realize arbitrarily polarized light optical parametric amplification in a periodically poled Lithium Niobate using quasi-phase matching. The domain structure should be well-designed with suitable electric field applied on selected sections.

Optical parametric amplification (OPA) of arbitrarily polarized light is proposed in a multi-section periodically poled Lithium Niobate (PPLN). External electric field is applied on selected sections to induce the polarization rotation of involved lights, thus the quasi-phase matched optical parametric processes exhibit polarization insensitivity under suitable voltage. In addition to the amplified signal wave, an idler wave with the same polarization is generated simultaneously. As an example, a ~10 times OPA showing polarization independency is simulated. Applications of this technology are also discussed.

Electromagnetically induced transparency — Like spectrum with tunable group delay is observed in a periodically poled LiNbO 3 with a central defect when an electric field is applied. A low voltage bulk phase shifter is obtained.

Polarization independent sum frequency generation (SFG) is proposed in an electro-optic (EO) tunable periodically poled Lithium Niobate (PPLN). The PPLN consists of four sections. External electric field could be selectively applied to them to induce polarization rotation between the ordinary and extraordinary waves. If the domain structure is well designed, the signal wave with an arbitrary polarization state could realize efficient frequency up-conversion as long as a z-polarized pump wave is selected. The applications in single photon detection and optical communications are discussed.

Polarization independent sum frequency generation (SFG) is proposed in an electro-optic (EO) tunable periodically poled Lithium Niobate (PPLN). The PPLN consists of four sections. External electric field could be selectively applied to them to induce polarization rotation between the ordinary and extraordinary waves. If the domain structure is well designed, the signal wave with an arbitrary polarization state could realize efficient frequency up-conversion as long as a z polarized pump wave is selected. The applications in single photon detection and optical communications are discussed.

Periodically poled Lithium Niobate (PPLN) is a promising material for wavelength conversion and switching in an all optical network. However, current PPLN based network elements are normally polarization sensitive, which is not convenient for telecom applications. We proposed a polarization insensitive frequency conversion approach in a PPLN. The second harmonic generation (SHG) studied as an example. The PPLN consists of four sections. External electric fields could be selectively applied to them to induce polarization rotation between the ordinary and extraordinary waves. If the domain structure is well designed, the fundamental wave with an arbitrary polarization state can be frequency doubled efficiently in this special PPLN.

Electromagnetically induced transparency (EIT)-like transmission is observed in an electro-optic (EO) tunable periodically poled lithium niobate (PPLN) with a central defect. When an electric field is applied, light satisfying the phase matching condition keeps its original polarization, although it experiences polarization rotation then turns back. Therefore the corresponding light always may pass though freely but with an EO tunable phase and dispersion. On the other hand, light with a neighboring wavelength is blocked. An EIT-like spectrum is thus obtained with tunable group delay. A low-voltage bulk phase shifter with over two orders of magnitude larger index change is obtained.

In recent years, photonic crystal fibre based modal interferometers have been widely investigated. Owing to the nature of Mach-Zenhder-like interference, the sensing range is limited by the sinusoidal spectrum's period. A splicing approach is proposed and demonstrated to achieve unique four-beam interference so that quadrupled sensing range is obtained without reduction in detection limit, which would be much desired in wide range refractive index, pressure and temperature sensing. As an example, a high-temperature sensor ranging from 28 to 484°C is demonstrated.

We theoretically propose a broadband optical isolator based on second-harmonic generation in a one-dimensional quadratic nonlinear photonic crystal (NPC) with an embedded defect. An external electric field along the z axis is applied to modulate the NPC refractive index periodically. Complete optical isolation always could be reached with the help of an external field. Influences of the defect position and thickness are discussed. The spectral and power tolerances of the isolator also have been investigated and show high contrast within a wide wavelength range at different power levels.