This paper first shows the basic idea about the mass production technology of AlGaAs laser diodes using Molecular Beam Epitaxy (MBE) technique. 'GaAs passivation technique' is the key to realize the stable mass production of self-aligned structure laser diodes. This paper, then, describes the designing concept and performance of a novel laser diode for short-haul optical data communications which we have recently developed. It has a high relaxation oscillation frequency, around 3 GHz, which is favorable to transmit data at a rate of 600 to 1200 Mbps. The lifetime (MTTF) is above 100,000 hours under 3 mW cw operation at 60 degree(s)C.
It is important to control a polarization anisotropy, thus, a molecular
alignment in obtaining such a crystal that can exhibit optimized phase-matchable
second harmonic generation ( SHG ). Along with this view, we designed a novel
dihedral rigid molecule which has two nitroaniline moieties rigidly connected each
other through two adjacent sp3 carbons. We synthesized the molecules so designed and
examined their crystals in SHG activities and phase-matching characteristics by a
convenient powder method with a Nd:YAG laser. It has been found that one of
crystals, namely, 3,9-dinitro-5a,6, ha, 12-tetrahydro[1,4]benzoxadino[3 ,2-bJ][1,4]-
benzoxadine ( DNBB ) crystal manifests larger phase-matchable SHG than
N-(4-nitrophenyl)-L-prolinol ( NPP ) crystal so far known as the typical efficient
phase-matchable organic crystal. DNBB crystal has been shown to possess much
improved material properties ; high thermal stability, distinguished hardness,
insolubility to water, no sublimation, and high registivity to optical damage, for
device applications in comparison with the crystals of p-nitroaniline derivatives
reported so far.
The benzylidene-aniline derivative with an electron-donating group at 4-position
and an electron-accepting group at 4'-position has been suggested by MO calculation,
to have a small molecular dipole moment but a large second-order hyperpolarizability
in comparison with those of p-nitroaniline analogous molecules, hence, to be a
promising molecule on searching for a new organic crystal with large second-order
optical nonlinearity.
Chemical modification of the molecule suggested led to a discovery of a series
of crystals having high activities in second harmonic generation ( SHG ) ; one of
which, 4'-nitrobenzylidene-3-acetamino-4-methoxyaniline ( MNBA ) crystal in
monodinic Cc with four molecules per unit cell showed larger powder SHG than
2-methyl-4-mtroaniline ( MNA ) crystal in a preliminary powder SHG experiment. A
strongly polarized non-centrosymmetric molecular packing has been achieved in this
crystal by the presence of intermolecular hydrogen bond between neighboring acetainino
groups.
Calculation by an oriented gas model with the use of the detailed structural
data from X-ray analysis for the MNBA crystal predicted that the crystal may have up
to ca. 2.9 times larger macroscopic optical nonlinearity than MNA crystal. This has
been experimentally proven by measuring the d for SHG by Maker fringe method. The
largest d coefficient was found to be dii , and the value obtained was 454 pm/V which
is 1.8 times larger than d11 of MNA crystal and 13 times larger than of lithium
mobate ( ) crystal.
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