Periodically Poled Lithium Niobate (PPLN) Crystal is a type of non-linear optical crystal with distinguished high conversion efficiencies and a wide transparent spectrum of 0.4-5μm. The periodic domain structures of the PPLN crystals are patterned through a process of inverting the crystal dipole moment using a high-voltage electric field. The introduction of MgO dopants is achieved through controlled thermal diffusion or ion implantation, ensuring uniform distribution within the crystal lattice. The 5% MgO doping in LiNbO3 improves the damage threshold of the PPLN to a significant extent and broadens its phase-matching bandwidth. MgO: PPLN crystals exhibit a unique quasi-phase-matching (QPM) phenomenon, which allows the utilization of a higher nonlinear coefficient than in the case of birefringent phase matching (In the case of LiNbO3, where birefringent phase matching often utilizes the coefficient d31=4.35 pm/V, whereas QPM often uses the higher d33=27 pm/V, which results in 17 pm/V taking into account of other influential factor. The use of d33 has a considerable advantage in circumstances where high optical intensities can not be obtained). Other important merits of QPM also include convenient temperature environment, the absence of spatial walk-off, and the attenuated possibility of photorefractive issues.  PPLN are excellent for a diverse range of nonlinear interactions such as Second Harmonic Generation (SHG), Sum Frequency Generation (SFG), etc. through precise engineering of the crystal's domain structure.

An optical waveguide is an inhomogeneous structure for guiding light, i.e. for restricting the spatial region in which light can propagate. PPLN crystals can be combined with waveguide structures to enhance the conversion process. North Optics offers both MgO:PPLN bulk crystal chips and MgO:PPLN waveguides. As a general principle, PPLN bulk crystal chips are straightforward to handle and can withstand higher power levels (Watts), whereas PPLN waveguides excel in conversion efficiency but present greater challenges in light coupling. 

Magnesium-doped PPLN demonstrates superior properties in innovative laser applications owing to its elevated effective nonlinear coefficient, enabling frequency conversion across diverse mechanisms with high efficiencies. Shanghai North Optics offers a series of standard and custom MgO:PPLN crystal chips and MgO:PPLN waveguides. Standard input wavelengths include 976nm, 1029nm,1064nm, 1545nm, 1550nm, 1560nm, 2100nm, etc. to deliver an output wavelength coverage ranging from the visible to mid-infrared spectral region, whereas other custom wavelengths are also available. Facilities of forefront technologies are equipped for the production of PPLN crystals. During the fabrication process, using a mask, the electrode patterns are defined on the wafer, and the metal will be deposited after a lithographic process. The application of a high-voltage electric field will switch the position of the lithium ion and niobate ion within a defined domain, forming periodically flipped dipole orientations. After the whole electric field poling procedure is done, the LiNbO3 wafer is diced into miniature chips and then further processed with high altitudes of precision control. With unparalleled advantages of high conversion efficiencies, high damage threshold, exceptional optical transmittance, and thermal characteristics, our MgO:PPLN crystals and waveguides are attractive candidates for various frequency conversion processes including up-conversion (SHG/SFG) and down-conversion (DFG/OPA/OPG/OPO), being able to withstand high power intensities. Besides, miscellaneous QPM structures are all procurable in North Optics.

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