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Optical Grade Lithium Niobate, Lithium Tantalate

The next generation of optical materials include single crystals of Lithium Niobate and Lithium Tantalate . The main target of development has been the production of larger diameter wafers (6 inch) to meet optical device manufacturers' requirements.

This has been achieved by :

Reducing the impurity level using highly selected raw material
Control of single crystal composition by Curie temperature measurement
Manipulation of growth in a temperature controlled environment

This has resulted in successful production of 6 inch diameter wafers.

Variation of Refractive Index with Temperature

Sellmeier Coefficients

Optical Grade Lithium Niobate	Lithium Tantalate , 5 and 6 inch

Evaluation and Quality Control for Optical Wafers

1 Evaluation Using Curie Temperature - Related to the composition of LiNbO3 / LiTaO3

Quality Control level of Curie temperature

Curie temperature measurement point

	Inside each wafer	Total Wafer
LiNbO3	within 1°C	within 2 °C
LiTaO3	within 1°C	within 1°C

2 Evaluation Using Refractive Index- Related to the composition of LiNbO3 / LiTaO3

There is significant correlation between refractive index and composition. For quality control purposes, these figures are a measurement to achieve high quality as standard

Quality Control level of refractive index

Refractive index measurement point

	Inside each wafer	Total Wafer
LiNbO3	within ±1x10^-4	within ±2x10^-4
LiTaO3	within ±2x10^-4	within ±2x10^-4

$LiNbO3 Refractive Index Measurement$

3 X-Ray Topography

This is a very simple way to control the crystal quality to determine whether whether Optical or Saw grade. To improve the quality of optical grade, we aim to achieve sub-grain boundary free wafer.

Magnesium Doped Lithium Niobate for PPLN

(Periodically Poled Lithium Niobate)

It is well known that applying a short wavelength (blue or green) laser to lithium niobate causes "optical damage" through the photo-refrective effect, and also refractive index fluctuations. To control these phenomena, high optical damage threshold materials have been developed, using magnesium as a dopant. The characteristics of Magnesium doped lithium niobate are resistance to optical damage, low absorption loss and no refractive index fluctuation within the crystal.

In general, the main requirement for MgO:LN for optical applications is a stable and homogeneous refractive index;( Erbium doping is also available). At shorter wavelengths, for example with blue lasers, the photorefractive effect must also be considered – here we can see local changes in the refractive index in areas under laser illumination which lead to optical damage.

Development and manufacture of MgO:LN has taken place since 1985. Over this time the focus has been on optimising growth conditions and improving raw material purity (to avoid impurities such as Fe) with the result that sub-grainboundary free material is now readily available with excellent transmission characeristics.

With high optical damage resistance and homogeneity, MgO:LN wafers (upto 4 inches in diameter) are now being used in new applications in the optical network, blue laser and other markets.

Properties of Optical Grade Lithium Niobate, Tantalate, Magnesium doped Lithium Niobate
		Optical grade lithium niobate	Optical grade lithium tantalate	Magnesium Doped lithium niobate
Composition		48.5mol% Li	48.5mol% Li	48.5% Li, 5mol%MgO
Curie point ° C		1133 ±2	603±2	1209±3
Impurities level ppm		Fe<1.0, Cu< 0.1 Mn<0.05, Ni<0.1 Cr<0.1,Mo<0.1	Fe<1.0, Cu< 0.5 Mn<0.2, Ni<0.1 Cr<0.5,Mo<0.1	Fe<1.0, Cu< 0.5 Mn<0.05, Ni<0.1 Cr<0.1,Mo<0.1
Crystal density (kg/m³)		4647.022	7462.2	4642.814
Lattice constants c(Å)		13.8658		13.8704
Refractive index at 633nm	n_e	2.2030	2.1821	2.1936
Refractive index at 633nm	n_o	2.2880	2.1787	2.2831
Birefingence n_o- n_e		0.0850	-0.0034	0.0895
Transparent wavelength (nm)		310-5500	270-5500	300-5500
Optical damage thresholds at 488nm At-ion laser (kW/cm²)		~10	~10	>1700

Electro-Optic Coefficients, Nonlinear Optical Coefficients
E-O Coefficients r(10^-12) mV^-1 at 632.8nm		Optical grade lithium niobate	Optical grade lithium tantalate
	r^T₁₃	10	8.4
	r^T₂₂	6.8
	r^T₃₃	32.2	30.5
	r^T₅₁	32

	r^S₁₃	11	7
	r^S₂₂	3.4	1
	r^S₃₃	36.7	30.3
	r^S₅₁	18.2	20
Nonlinear Optical Coefficients at 1.06μm (d₃₁=d₁₅)	d₂₂/d₃₆^KDP	6.5	4.4
	d₃₁/d₃₆^KDP	-12.3	-2.7
	d₃₃/d₃₆^KDP	-86	-41

Transmission Spectra

Transmission Spectra Comparisons

	Photoabsorption : LiNbO3 MgO Doped	Photoabsorption : LiTaO3 Optical Grade

Equipment	Hitachi U-3500 Spectrometer
Sample Thickness	0.5 mm	0.5 mm
Scan Speed	15 nm/min	60 nm/min
Scan Area	280~500 nm	250~500 nm
Sampling	0.1 nm	0.1 nm

Properties LiNbO3 (MgO doped)

MgO	Curie Temperature	Crystal Density	Lattice Constants	Refractive Index
(mol %)	Tc (° C)	ρ (kg/m³)	c(Å)	n_e¹	n_o¹
0	1130.7	4647.022	13.8658	2.2031	2.2879
3	1197.7	4644.132	13.8679	2.1953	2.2848
5	1210.2	4642.814	13.8704	2.1936	2.2831
7	1204.1	4636.706	13.8762	2.1921	2.2743

(1) Prism coupler method - 24°C at 632.8nm, n_o : TE mode n_e : TM mode

Properties Optical grade LiTaO3

Curie Temperature	Crystal Density	Refractive Index
Tc (° C)	ρ (kg/m³)	n_e¹	n_o¹
602.5	7462.2	2.1821	2.1787

(1) Prism coupler method - 24°C at 632.8nm, n_o : TE mode n_e : TM mode

General Specification

Material	Cut Angle	Size	Surface Finish
			Front	Back
LiNbO3	Z-Cut Y-Cut X-Cut	3" φ x 0.5 mm T	mirror	FO#1200
			mirror	mirror
		3" φ x 1.0 mm T	mirror	FO#1200
			mirror	mirror
	Z-Cut Y-Cut X-Cut	4" φ x 0.5 mm T	mirror	FO#1200
			mirror	mirror
		4" φ x 1.0 mm T	mirror	FO#1200
			mirror	mirror
	Z-Cut	5" φ x 1.0 mm T	mirror	mirror
MgO:LiNbO3 (MgO 5 mol% )	Z-Cut	3" φ x 0.5 mm T	mirror	mirror
	X-Cut	3" φ x 1.0 mm T
LiTaO3	Z-Cut	2" φ x 0.5 mm T	mirror	mirror

Note : Fe content is less that 1ppm, all wafers

Other specifications can be provided upon request: Please state

Cut angle accuracy
Wafer thickness
Orientation Flat length
Wafer Flatness