Periodic polarization of lithium niobate PPLN and lithium tantalate PPLT

Periodic polarized lithium niobate and periodic polarized lithium tantalate are ferroelectric crystal materials that achieve quasi phase matching through microdomain engineering. The core feature of this structure is the periodic reversal of spontaneous polarization vectors within the crystal, which can effectively compensate for phase mismatch in nonlinear optical frequency conversion processes and significantly improve conversion efficiency.

Structural features:

Both materials have artificially designed periodic domain structures. The polarization directions of domains are alternately arranged with a specific period ∧, forming one-dimensional or two-dimensional polarization reversal gratings. This cycle can be accurately calculated based on the target interaction wavelength through quasi phase matching conditions.

Preparation process:

Prepared using standard electric field polarization method. This process defines periodic electrode patterns on the crystal surface through photolithography technology, and then applies a pulsed electric field higher than the coercive field strength of the crystal to achieve 180 ° polarization reversal of the selected domain in the unprotected area.

Comparison of Material Properties

Key parameter description:

• Quasi phase matching: The inverted lattice vectors provided by periodic domain structures can be used to compensate for the mismatch of wave vectors between interacting light waves, achieving efficient nonlinear optical processes.

• Photorefractive effect: Under short wavelength or high power density illumination, the refractive index of a crystal may undergo unexpected changes. PPLT naturally has stronger anti photorefractive ability.

• Damage threshold: The laser damage threshold of crystals is closely related to wavelength, pulse width, and material quality.

Main application areas

Based on quasi phase matching technology, these two materials are mainly used for the following nonlinear optical processes:

1. Laser frequency conversion

• Second harmonic generation: converting infrared laser into visible light.

• Optical parametric oscillation: Converting pump laser energy into wavelength adjustable signal light and idler light is an important technical approach for generating mid infrared coherent light sources.

• Sum frequency and difference frequency generation: achieve the mixing of lasers with different wavelengths to generate new wavelengths.

  
  

2. Quantum optics

• Entangled photon pair generation: Utilizing spontaneous parametric down conversion process to prepare entangled photon sources for quantum information research.

• Quantum frequency conversion: changing the wavelength of a single photon or entangled photon to adapt to interfaces of different quantum systems.

3.  Integrated Photonics 

• The waveguide type periodic polarization devices prepared on thin film lithium niobate or thin film lithium tantalate platforms provide the core material foundation for realizing miniaturized and low-power nonlinear optical chips.

Selection reference

The selection of PPLN or PPLT should be based on specific application requirements:

• When pursuing the highest nonlinear conversion efficiency and operating in wavelength regions where the optical birefringence effect is not significant, PPLN is the preferred choice.

• When working in the visible or near-infrared wavelength range, or when there is a high demand for long-term stability and maximum suppression of the optical birefringence effect is required, PPLT exhibits better performance stability.