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
355nm 406nm 532nm 633nm 1064nm
Lithium Niobate 25°C 2.40179 2.32631 2.23622 2.20351 2.15714
50°C 2.40343 2.32807 2.23765 2.20458 2.15757
75°C 2.40722 2.33080 2.23940 2.20607 2.15884
Magnesium Doped Lithium Niobate 25°C 2.38482 2.31248 2.22530 2.19323 2.14757
50°C 2.38778 2.31441 2.22644 2.19424 2.14861
75°C 2.39152 2.31718 2.22819 2.19567 2.14966
Lithium Tantalate 25°C 2.34263 2.28411 2.21086 2.18288 2.14174
50°C 2.34574 2.28625 2.21208 2.18386 2.14250
75°C 2.34971 2.28877 2.21335 2.18485 2.14333
SolGel 25°C 2.27829 2.27014 2.19138 2.15536 2.09486
50°C 2.27985 2.27211 2.19278 2.15641 2.09524
75°C 2.28344 2.27452 2.19450 2.157869 2.09647
Sellmeier Coefficients

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

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

Curie temperature measurement point

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.

Inside each Wafer Total Wafer
LiNbO3 within ±1×10-4 within ±2×10-4
LiTaO3 within ±2×10-4 within ±2×10-4

Refractive index measurement point

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 ne 2.2030 2.1821 2.1936
no 2.2880 2.1787 2.2831
Birefingence no– ne 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
Optical grade lithium niobate Optical grade lithium tantalate
E-O Coefficients
r(10-12) mV-1 at 632.8nm
rT22 6.8
rT33 32.2 30.5
rT51 32
rS13 11 7
rS22 3.4 1
rS33 36.7 30.3
rS51 18.2 20

Nonlinear Optical Coefficients

at 1.06μm (d31=d15)

d22/d36KDP 6.5 4.4
d31/d36KDP -12.3 -2.7
d33/d36KDP -86 -41
Transmission Spectra

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) ne1 no1
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, no : TE mode ne : TM mode

Properties Optical grade LiTaO3
Curie Temperature Crystal Density Refractive Index
Tc (° C) ρ (kg/m3)  ne1 no1
602.5 7462.2 2.1821 2.1787

(1) Prism coupler method – 24°C at 632.8nm, no : TE mode ne : 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

Reproduced by kind permission of Yamaju Ceramics Co., Ltd.
© Yamaju 2004 Specifications subject to change without notice. All rights reserved.

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