Optical Grade Lithium Niobate, Lithium Tantalate

Lithium Niobate and TantalateThe 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
Curie temperature

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

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

 

Refractive index measurement point
refractive index

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

E-O Coefficients

r(10-12) mV-1 at 632.8nm

Optical grade lithium niobate
Optical grade lithium tantalate
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