Summary of Key Optical Parameters and Characteristics of Lithium Niobate (LiNbO₃)

1. Refractive Index and Birefringence

Refractive Index:

Ordinary Ray (n₀): ~2.28–2.33 (visible to mid-infrared, wavelength-dependent).

Extraordinary Ray (nₑ): ~2.16–2.21 (varies with wavelength), resulting in significant negative birefringence (n₀ > nₑ).

Birefringence Δn (n₀ - nₑ): ~0.12–0.15 (visible range), tunable via thermal adjustment due to temperature-sensitive refractive indices[3][4].

2. Transmission Range

Transparency Spectrum: UV (~300 nm) to IR (~5 μm), covering visible, near-infrared, and mid-infrared bands, suitable for broadband optical applications[1][4].

3. Nonlinear Optical Susceptibility

Nonlinear Coefficient (d₃₃): ~27 pm/V (below Curie temperature), double that of lithium tantalate (LT), ideal for efficient second-harmonic generation (SHG) and optical parametric oscillation (OPO)[3][5].

4. Electro-Optic Effects

Electro-Optic Coefficient (r₃₃): ~30–35 pm/V (at λ=633 nm), enabling transverse electro-optic modulation (light propagates along Z-axis, electric field applied along X-axis). Widely used in high-speed modulators and Q-switches[2][3].

5. Absorption and Damage Threshold

Absorption Coefficient: Extremely low in visible-near-infrared (nearly transparent), higher in UV.

Optical Damage Threshold: >100 GW/cm², suitable for high-power laser applications[2][3].

6. Other Optical Properties

Spontaneous Polarization: ~0.70 C/m² at room temperature, with a Curie temperature of 1210°C (one of the highest among ferroelectrics)[3].

Photorefractive Effect: Capable of recording dynamic optical patterns for holographic storage and adaptive optics.

Thermo-Optic Coefficient: Negative thermal expansion along the Z-axis, allowing refractive index tuning via temperature changes without mechanical adjustment[3].

Typical Applications

Nonlinear Optics: SHG, OPO, difference frequency generation (e.g., mid-infrared lasers).

Electro-Optic Devices: High-speed modulators, beam deflectors.

Acousto-Optic Devices: High-frequency acousto-optic modulators (leveraging large acousto-optic coefficients).

Optical communication: Integrated optical waveguide filter (based on lithium niobate thin film process)