attributes of chg for photonics applications transmission ... · attributes of chg for photonics...
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Photonics applications I
Attributes of ChG for photonics applications
Transmission window
IR transmitting lens
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Useful attributes for photonics
High refractive index over wavelengths useful in photonics and
optical communications
Low phonon energy for reducing multiphonon relaxation of
excited state of doped ions
Wide optical transmission window extended to mid IR
Strong photosensitivity: photoinduced changes in n and ,
photoinduced (vectorial) dichroism, photoinduced volume
expansion and fluidity, photodissolution of Ag, photoinduced
differential etching, and so on
High third order optical susceptibility for nonlinear optical
applications
Large acousto-optic effect
Low processing temperatures compared to other conventional
glasses
2
- Important
- Condensed summary
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Photonics applications: classification
Passive applications; IR transmission, waveguide IR transmitting window, lenses, fibers…
Photoinduced optical waveguides, Ag-photodissolved
waveguides, photoetched waveguides…
Bragg diffraction gratings, polarization gratings, holographic
recordings, photonic crystals (3D Bragg gratings)…
Active applications; undoped or doped Optical amplifiers and lasers; RE-activated, SRS, SBS…
Optical devices; all-optical ultrafast nonresonant-type
optical switches
Photoresists for photolithography
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- Important
- Condensed summary
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Infrared transmission
Aggarwal and Sanghera, J. Optolectron. Adv. Mater. 4 (2002) 665. 4
- Important
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IR-side absorption
Due to the combination of
vibrations and higher harmonics
(multiphonon absorption) of the
short-range order units.
Essentially continuous phonon
spectrum toward longer
wavelengths due to the structural
disorder.
ChGs consist of relatively heavy
elements and the chemical
bonds are usually weaker than
oxide glasses.
Feltz book, p. 373.
- Important
- Needs understanding
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Transmission window
Feltz book, p. 370.
- For information
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Effects of impurities
Feltz book, p. 375.
- Important
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8Lezal et al, Chalcogenide Letters, 1 (2004) 11.
Sundaram et al, Lezal et al, Pacific Northwest National Lab.
- For information
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Some IT transmitting materials
Feltz book, p. 430.
- For information
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1010
Some IR transmitting ChGs
Lezal et al, Chalcogenide Letters, 1 (2004) 11.
Feltz book, p. 429.
Ge-Sb-Se
Ge-As-Se
- For information
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1111
UV-side absorption
Electronic transitions between the
valence and conduction bands;
absorption edge, optical band gap
The Tauc edge (@ > 104 cm-1)
Transitions from delocalized
states in the valence band to
delocalized states of the
conduction band.
On the assumption that the
energy dependence of the DOS
is parabolic,
Feltz book, p. 380.
- Important
- Needs understanding
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12Feltz book, p. 381.
- Important
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131313
UV-side absorption
The Urbach edge
The exponential section of
the absorption edge;
Probably caused by a freezing
of potential fluctuations in the
glass transition region and/or
thermal fluctuations of the
energy of the optical band gap.
Feltz book, p. 382.
Nahass et al, J. Optoelectron. Adv. Mater. 8
(2006) 1817.
- Important
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14141414
UV-side absorption
Feltz book, p. 383.
* Wood and Tauc, Phys. Rev. B, 5 (1972) 3144.
The Weak absorption tail
Another exponential
dependence for the low
absorption region ( < 1 cm-1);
Probably due to the additional
band gap states, which are
formed from electronic impurities
such as transition metal elements
or defects such as valence
alternation pairs and dangling
bonds.*
- Important
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Large refractive indices between 2 to greater than 3.
In As2S3 glass, n increases as sulfur is replaced by the more polarisable
selenium and tellurium.
The high n is advantageous for strong optical field confinement which
allows small waveguide bend radii (leading to compact circuit designs)
and enhanced optical intensities (for efficient nonlinear interactions).
In addition, the large index contrast relative to air can potentially provide
a complete band-gap for photonic crystals.
Refractive index and dispersion
Ta’eed et al, Opt. Express, 15 (2007) 9205.
- Important
As2S3
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The zero dispersion wavelength for chalcogenide glasses (material
dispersion) lies well in the mid IR (e.g. 5 μm for As2S3).
At communication wavelengths around 1.55 μm these materials exhibit
strong normal dispersion (i.e. not anomalous).
This is not necessarily detrimental to performance as typical device
lengths are short, of the order of centimeters.
Furthermore, there is the possibility of using waveguide dispersion to
engineer the chromatic dispersion, similar to what has been achieved in
silica.
Refractive index and dispersion
S. O. Kasap, Optoelectronics and Photonics, Prentice-Hall, 2001.
- For information
- Advanced
silica
silica
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17Yayama et al, J. Non-Cryst. Solids, 239 (1998) 187.
- For information
- Advanced
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18Yayama et al, J. Non-Cryst. Solids, 239 (1998) 187.
- For information
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Refractive index and dispersion
Feltz book, p. 390.
The Abbe number V of a material is defined
as
where nd, nF and nC are the refractive
indices of the material at the wavelengths of
the Fraunhofer d-, F- and C- spectral lines
(587.6 nm, 486.1 nm and 656.3 nm
respectively). Low dispersion (low chromatic
aberration) materials have high values of V.
http://en.wikipedia.org/wiki/Abbe_number
- For information
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IR-transmitting lens
Zhang et al, J. Optoelectronics and Advanced Materials, 5 (2003) 1327.
- For information
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2121
IR-transmitting lens
Material Innovations, 2006.
- For information
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22Kvisteroy et al, 11th International Forum on Advanced Microsystems for Automotive Applications, 2007.
- For information
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23Kvisteroy et al, 11th International Forum on Advanced Microsystems for Automotive Applications, 2007.
- For information
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24Kvisteroy et al, 11th International Forum on Advanced Microsystems for Automotive Applications, 2007.
- For information
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25Cantronic’s catalog
- For information
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26LightPath’s caatlog.
- For information
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27OptoCrystal’s catalog
- For information