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Photorefraction is an effect of refractive index variation in the material exposed to the light. This property makes it possible to create spatial distribution of refractive index in the crystal and can be used in wide variety of devices including spatial light modulators, optical memory, holography, phase conjugation etc.
Most popular photorefractive materials are crystals of Sillenite structure Bi12MO20 (M = Si, Ge, Ti). These crystals have fortunate combination of photorefractive, electrooptic and other properties making it promising materials for optoelectronics.
Sillenite photorefractive monocrystals Bi12SiO20 (BSO) and Bi12GeO20 (BGO) display unique combination of different physical properties.
Sillenite Crystals BSO and BGO are very efficient photoconductors with low dark conductivity. Strong spectral dependence of the photoconductivity allows to produce a wide range of optical device and systems.
Combination of electro-optical and photoconductive properties display photorefractive effect (PR) in the crystals.
Sillenite BSO crystals are used like photoconductor in optically-addressed spatial light modulators (OASLM) and liquid crystal light valves (LCLV) with electro-optical modulation into liquid crystal medium.
Both crystals BSO and BGO are used like electro-optic and photoconductive mediums for construction of PROM, PRIZ spatial modulators. Sillenite crystals are applied in dynamic real-time hologram recording devices, optical correlators, and optical laser systems for adaptive correction of ultra short light pulses.
Production of sillenite thin-film crystal structures by different technologies permits the development of a long list of devices including optical waveguides, integrated optical devices.
The use of waveguide optical structures based on sillenite crystals allows achieving uniform writing illumination in a wide spectral range. Crystals BSO and BGO are used in optical fiber electric/magnetic fields sensors.
| Properties |
| Crystal |
Bi12SiO20 (BSO) |
Bi12GeO20 (BGO) |
| Crystal Structure |
cubic |
cubic |
| Lattice Parameters, A |
10.10 |
10.15 |
| Transmission Range, mkm |
0.4 – 6 |
0.4 – 7 |
| Refractive Index at 633nm |
2.54 |
2.55 |
| Electro-Optic Coefficient r41, pm/V |
5.0 |
3.5 |
| Optical Activity, deg/mm at 633 nm |
20.5 |
20.4 |
| Density, g/cm3 |
9.15 |
9.2 |
| Mohs Hardness |
5 |
5 |
| Melting Point, C |
890 |
920 |
| Dielectric Constant |
56 |
40 |
| Crystal material |
optical grade undoped Czochralski grown monocrystals Bi12GeO20 ( BGO)
and Bi12SiO20( BSO) |
| Bubbles/inclusions |
none large than 100 microns diameter, no 100 mm3 are shall have a total bubble/inclusion volume exceeding the volume
equivalent to a single 100 micron bubble |
| Striae |
none visible with shadowgraph |
| Homogeneity |
H1 (+/- 20 parts per million) |
| Available dimensions |
up to diameter 46 mm X 180 mm length |
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