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channel as was described in previous work.1 In the present
work the same Si 3 N 4 mask that was used during epitaxy is
also used to define the edge of the lateral zinc diffusion
window (Fig. 2). This original Si 3 N 4 mask has also been
designed to be used for microcleavage.2 Thus the critical fabrication steps for this laser are self aligned. The gold-germanium
and gold-zinc electrodes were applied in the conventional way.
The complete laser is shown schematically in Fig. 2.
10
pulsed
operation
L=300urf>
Conclusions: Three-channel lasers operating at 1-51 fim wavelength have been described. These lasers are obtained by a
simple fabrication process involving one LPE growth step and
a self aligned zinc diffusion process. The use of semi-insulating
InP substrate leads to good current confinement resulting in
low-threshold currents. Other advantages are the low parasitic
capacitance and high immunity to short-circuit defects that
are inherent to the present structure. This is due to the lateral
separation of the laser electrodes which are located at different
places on the insulating substrate.
U. KOREN
S. ARAI
P. K. TIEN
Nth January 1984
Bell Laboratories
Holmdel, NJ 07733, USA
75
References
1
YU, K. L., KOREN, u., CHEN, T. R., CHEN, P. c , and YARIV, A.: 'Groove
GalnAsP laser on semi-insulating InP', Electron. Lett., 1981, 17,
pp. 790-792
2
KOREN, U., HASSON, A., YU, K. L., CHEN, T. R., MARGALIT, S., a n d
YARIV, A.: 'Low threshold InGaAsP/InP lasers with microcleaved
mirrors suitable for monolithic integration', Appl. Phys. Lett.,
1982, 41, pp. 791-793
CW operation
T=15°C
3
ARAI,
s., SUEMATSU,
Y., and
ITAGA,
Y.: ' 1 1 1 - 1 6 7
nm
(100)
GalnAsP/InP injection lasers prepared by liquid phase epitaxy',
IEEE J. Quantum Electron., 1980, QE-16, pp. 197-204
2-5
20
40
60
current , mA
80
CHLORINE CONCENTRATION PROFILES IN
SILICA FIBRES
100
|6O7/3|
Fig. 3 Light/current characteristics of three-channel buried-crescent
laser
Results: Light/current characteristics of the laser operating at
1-51 /zm wavelength are shown in Fig. 3. Differential quantum
efficiency for both facets is 30-40% for pulsed operation with
10 mW/facet power output. CW light/current characteristics
are also shown. Threshold currents as low as 16 mA for a
laser length of 300 pm and channel width of 2-3 nm were
observed. Mostly, single transverse mode operation was
obtained for lasers with channel widths of 2-3 jim. Far-field
patterns are shown in Fig. 4. Half-intensity angles of 17
and 31° were observed for the parallel and perpendicular
angles, respectively.
lOr
.£0-5
-20 -10
0
10 20
9...deg
Indexing terms: Optical fibres, Optical materials
Chlorine concentration profiles in silica fibres were studied
by X-ray microanalysis and consideration of the chemical
reactions concerned with chlorine in the fibre fabrication
process. The chlorine content was proportional to the doped
element contents. The Cl/Ge content ratio was larger than
the Cl/Si or Cl/P content ratio.
Introduction: Silica fibres contain a very small amount of
chlorine, since chlorides are used for raw materials and chlorine gas is used for a dehydrating agent in a fibre fabrication
process, such as VAD and MCVD methods. An impurity
influence on fibre characteristics has been sufficiently examined for various transition metal ions and a hydroxyl group.
The reduction in these impurities led to the development of
low-loss optical fibres.12 However, the chlorine influence is
not clear.3
This letter reports chlorine concentration profiles in silica
fibres measured by X-ray microanalysis. The profiles are discussed through consideration on chemical reactions concerned
with chlorine in the fibre fabrication process.
30
•s 10
0/
.Z 0 5
-30
-20 -10
0
deg
10
20
0
1607/41
Fig. 4 Far-field patterns at I = 21lh
a Parallel to junction plane
b Perpendicular to junction plane
178
Fig. 1 Line-analysis results in cross-section of a VAD fibre
ELECTRONICS LETTERS
16th February 1984
Vol. 20 No. 4
Measurement: An elementary analysis on silica fibres was performed with an electron probe X-ray microanalyser. Silica
fibres were fabricated by the VAD or MCVD process. The
distribution of each element in silica fibres was measured by
the line analysis in the fibre's cross-section. The concentration
at each point in the fibre's cross-section was determined from
the point-by-point analysis results corrected by the Bence and
Albee method. 4
Table 1 ENTHALPY DIFFERENCES BY
CHEMICAL STATE CHANGE
M
P
Si
Ge
= M — OH--+=M—Cl
+ 48- 3
+ 35-1
= M—C\-*. M - O A
-14- 2
+ 0-4
Change
—16-5
0-20
are substituted for by chlorine. The enthalpy differences from
a hydroxidised state to a chlorinated state of positive ions
composing silica fibres are shown in Table 1. Since its value to
germanium is smaller than that to silicon, it is considered that
chlorine binds to germanium with higher probability than to
silicon in silica fibres.
In the preform synthesis process of the MCVD method,
chlorides for raw materials react with oxygen and become
oxides. Chlorine in fibres fabricated by the MCVD process is
presumed to remain in the above process. The enthalpy difference for germanium from a chlorinated state to an oxidised
state is larger than those for silicon and phosphorus, as shown
in Table 1. This fact leads to the presumption that the Cl/Ge
content ratio is larger than others in silica fibres.
(622/21
Conclusions: Chlorine concentration profiles in silica fibres
were measured by the X-ray microanalysis. The chlorine
content was proportional to the doped element contents. The
Cl/Ge content ratio was larger than the Cl/Si or Cl/P content
ratio. This result can be explained by consideration on chemical reactions concerned with chlorine in the fibre fabrication
process.
SUGe
Fig. 2 Relationship between chlorine and germanium contents of a VAD
fibre
Line analysis results for a VAD fibre are shown in Fig. 1.
Chlorine was distributed with a plateau shape in the core part
of a fibre. The nearer the centre of the core part, the higher
was chlorine content. In a pure silica fibre, the chlorine concentration profile was fiat. The relationship between the chlorine and germanium contents measured by the X-ray
microanalysis is shown in Fig. 2. The chlorine content was
found to increase linearly with the germanium content. The
content ratios for Cl/Si and Cl/Ge calculated by the leastsquares method were 0094 and 0-73 atom%, respectively.
These results were obtained for fibres gone through the dehydration process in the VAD method. Fibres without the
dehydration process contained very little chlorine.
Acknowledgment: The authors would like to express their
sincere thanks to N. Inagaki for his encouragement.
H. HANAFUSA
Y. TAJIMA
16th January 1984
Ibaraki Electrical Communication Laboratory
Nippon Telegraph & Telephone Public Corporation
Tokai, Ibaraki-ken 319-11, Japan
References
1
MIYA, T., TERUNUMA, Y., HOSAKA, T., a n d MIYASHITA, T.: ' U l t i m a t e d
low-loss single-mode fibre at 1-55 j<m\ Electron. Lett., 1979, 15,
pp. 106-108
2
HANAWA, H., SUDO, s., KAWACHI, M., and NAKAHARA, M.: 'Fabrica-
tion of completely OH-free VAD fibre', ibid., 1980, 16, pp. 699-700
3
HETHERINGTON, c , JACK, K. H., and KENNEDY, j . c : 'The viscosity of
vitreous silica', Phys. Chem. Glasses, 1964, 5, pp. 130-136
4 BENCE, A. E., and ALBEE, A. L. : 'Empirical correction factors for the
electron microanalysis of silicates and oxides', J. Geology, 1968,
76, pp. 382-403
ANALYTICAL FORMULAS FOR COPLANAR
LINES IN HYBRID AND MONOLITHIC MICs
|62Z/31
Fig. 3 Line-analysis results in cross-section of an MCVD fibre, except
for silicon and oxygen
Indexing terms: Integrated circuits, Microwave circuits and
systems
Fig. 3 shows line-analysis results for an MCVD fibre. Germanium and phosphorus were doped in the core part and
phosphorus and boron were doped in the cladding layer. The
chlorine concentration profiles were like the figures for the
doped elements. The chlorine to the doped element content
ratios obtained by solving simultaneous equations of the first
degree, were 0018, 1-7 and 0018 atom% for Si, Ge and P,
respectively.
Discussion: Since there was very little chlorine in fibres fabricated without the dehydration process in the VAD method,
chlorine is presumed to be mixed at the dehydration process.
In the above process, hydroxyl groups are adsorbed chemically on the surface of oxide particles in a porous preform and
ELECTRONICS LETTERS 16th February 1984
Vol. 20
Some analytical formulas for the parameters of coplanar
lines are discussed and validated; a chart is given for the
design of coplanar waveguides on GaAs. The formulas discussed here, together with those presented previously by us
(1983) represent a suitable set for the design of coplanar lines
for hybrid and monolithic MICs (microwave integrated
circuits).
Owing to the increasing popularity of coplanar waveguides
(CPW, Fig. 1) and coplanar striplines (CPS, Fig. 3) for the
design of hybrid and monolithic microwave integrated circuits,
it is important to have a set of reliable analytical formulas for
their quasi-TEM electrical parameters (characteristic impedance Z^ and effective dielectric constant e e / / ). While exact
No. 4
179
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