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of CFRP-tube and -joint, and the reflector is composed of thin
CFRP shells supported by a CFRP-tube truss as shown in
Fig. 3.
satellite'. AIAA 10th commun. satellite syst. conf., Orlando, AIAA84-681, 19-22 March 1984, pp. 181-187
YAMADA, Y., and KAGOSHIMA, K. : 'Design of sidelobe characteristics
of offset parabolic reflector antenna with cluster feed by receiving
mode analysis'. 1984 internat. IEEE APS symp., Boston, MA, June
1984, pp.498-501
BIRD, T. s., and BOOMARS, j . L.: 'Evaluation of focal fields and
radiation characteristics of a dual-offset reflector antenna', IEE
Proc. H, Microwaves, Opt. & Antennas, 1980,127, pp. 209-218
-0 5
0
0-5
azimuth angle, degree
1 OdB LOW-LOSS COUPLING OF LASER
DIODE TO SINGLE-MODE FIBRE USING A
PLANOCONVEX GRADED-INDEX ROD LENS
1
Indexing terms: Optics, Optoelectronics, Optical couplers
Marked low-loss coupling between a laser diode and a
single-mode fibre has been realised, utilising a planoconvex,
high-numerical-aperture graded-index rod lens with greatly
improved small wavefront aberration.
Introduction: Efficient coupling circuits between semiconductor laser diodes (LDs) and single-mode fibres (SMFs) are
the key devices for use in optical fibre communication
systems. Many coupling methods, utilising a fibre lens or
microlens, have been demonstrated.1'2 Among them, a coupling circuit using graded-index-rod (GRIN-rod) lenses fabricated by the ion-exchange technique3 is a promising way to
realise low-loss coupling and stable operation.4
This letter reports extremely low-loss LD-to-SMF coupling
by utilising a planoconvex, high-numerical-aperture (NA)
GRIN-rod lens. 10dB low-loss coupling, which improved the
coupling loss by more than 2dB compared with previous
results,4 has been attained by realising an extremely small
wavefront aberration.
-05
-0-5
0
0-5
azimuth angle,degree
10
1283/;
Fig. 2 Radiation patterns of 2-5 m reflector
a Calculated (29-5 GHz)
b Measured (29-5 GHz)
Lens design: The rod lens has a spherical input facet to
increase the effective NA for the lens.56 To minimise LD-toSMF coupling loss, wavefront aberration was minimised by
adjusting the radius of the spherical input facet and the lens
length in addition to the optimisation of the refractive-index
distribution. Considering the LD radiation angle, the effective
lens NA was assumed to be 0-4. Furthermore, considering
practical package dimensions, the distance between the LD
and the rod lens was fixed at 0-7 mm. Spot-size magnification
was assumed to be about four to match the focused beam size
to the SMF spot size. Measured refractive-index distribution
parameters were used in this design.
Fig. 3 Deployed configuration of antenna structural model
The reflector surface roughness of less than 017 mm RMS
is achieved for the 2-5 m reflector. The total weight of the
antenna module is about 150 kg, including two main reflectors, two subreflectors, two grids and four cluster feeds for
K-band, an S-band feed, a 20GHz/S-band frequency-selective
surface and a tower. The 3-5 m main reflector for the 20GHz
band is used for the 2-6/2-5 GHz bands (S-band) as well. The
S-band system is for mobile communication with five beams.
Acknowledgments: The authors wish to thank Dr. T. Yasaka
and Dr. K. Kagoshima for valuable discussions.
Experiments: The coupling loss measurement set-up is shown
in Fig. 1. The LD was a 1 -3 /im-wavelength DC-PBH LD
AZ
DC-PBH-LD
urn
planoconvex
rod lens
Fig. 1 Laser diode to single-mode fibre coupling configuration
Coupling loss (dB) = - 1 0 log {PJP0) + 015
I. OHTOMO
H. KUMAZAWA
Y. YAMADA
M. MINOMO
2nd September 1986
NTT Electrical Communication Laboratories
Yokosuka-shi 238-03, Japan
References
MIYAUCHI, K., YAMAMOTO, H., and KONDO, K.: 'Communication
equipment technologies of Japanese domestic communication
1122
(double-channel planar buried-heterostructure laser diode).
The SMF had a 10/xm core diameter and a 1-2/mi cutoff
wavelength. The rod lens facets and the SMF ends were
coated with an antireflection film, to suppress light reflection
back to the LD.
Coupling loss was evaluated by the ratio PJP0, where Po is
the LD output power and Px the SMF output power. In this
experiment the 015dB reflection loss is added to the coupling
loss, because the output end of the SMF, used for the usual
LD-SMF module, is not antireflection-coated.
ELECTRONICS LETTERS 9th October 1986
Vol. 22 No. 21
Characteristics: LD-SMF coupling losses for the different LD
radiation angles are shown in Fig. 2. An ultra-low coupling
loss of 10 dB was attained for the 27° x 21° (FWHM) radi-
27x21
33x28
i
•V I
IV
Conclusion: A marked low coupling loss of 10dB between a
laser diode and a single-mode fibre has been realised, utilising
a planoconvex, high-numerical-aperture GRIN-rod lens with
greatly reduced lens wavefront aberration. The coupling loss
has improved by more than 2 dB, compared with the previous
results.
Acknowledgments: The authors would like to thank I. Kitano,
K. Koizumi, M. Toyama and N. Akazawa of Nippon Sheet
Glass Co. Ltd., and F. Saito, M. Sakaguchi, A. Ueki, K.
Washio and K. Minemura of NEC Corporation for their
encouragement and stimulating discussions during the course
of this work. The authors are also grateful to their colleagues
for supplying laser diodes and for fruitful discussions.
35x33
500
1000
product of LD radiation angles 6X x6,
(FWHM )# arbitrary unit
Fig. 2 LD-SMF
angles
H. HONMOU
|27 7 / ? |
1st September 1986
R. ISHIKAWA
Opto-Electronics Research Laboratories
NEC Corporation
4-1-1, Miyazaki
Miyamae-Ku, Kawasaki City 213, Japan
coupling losses for different laser diode radiation
ation angle. Even for the 35° x 33° (FWHM) radiation angle,
the coupling loss increased only up to l-2dB. These values
represent more than 2dB loss reduction from the previously
achieved planoconvex rod lens coupling.4 These low coupling
losses have been obtained by improving the lens wavefront
aberration. Fig. 3 shows the wavefront aberration for a rod
H. UENO
Central Research Laboratory
Nippon Sheet Glass Co. Ltd.
1, Kaidoshita
Konoike, Itami City 664, Japan
M. KOBAYASHI
Fibre Optics and Fine Glass Division
Nippon Sheet Glass Co. Ltd.
5-8-1, Nishihashimoto
Sagamihara City 229, Japan
References
1
previous
work
this work
2
Fig. 3 Wavefront aberration of planoconvex rod lens
3
MINOWA, j . , SARUWATARI, M., and SUZUKI, N. : 'Optical componentry
utilized in field trial of single-mode fiber long-haul transmission',
IEEE J. Quantum Electron., 1982, QE-18, pp. 705-717
KHOE, G. D. : 'Advanced passive componentry for optical fiber communication systems'. IOOC '83, Tokyo, 1983, 29C3-3
UCHIDA, T., FURUKAWA, M., KITANO, I., KOIZUMI, K., a n d MATSU-
MURA, H.: 'Optical characteristics of a light-focusing fiber guide
and its applications', IEEE J. Quantum Electron., 1970, QE-6, pp.
606-612
lens, measured with a Fizeau interferometer. The wavefront
aberration for the previous lens is shown for comparison. The
measured relation between the LD-SMF coupling loss and the
RMS wavefront aberration is shown in Fig. 4. The RMS
4
ISHIKAWA, R., SHIKADA, M., YAMAGISHI, T., and FUJII, K.: 'LD-fibre
coupling circuit using high numerical aperture graded-index rod
lens'. 1983 natl. conf. rec. IECE Japan, 1983, No. 293
5
ODAGIRI, Y., SEKI, M., and KOBAYASHI, K.: 'LD-SMF spherical ended
SELFOC lens coupling circuit'. 1982 natl. conv. rec. IECE Japan,
1982, No. 866
6
YAMAGISHI, T., FUJII, K., and KITANO, i.: 'New GRIN lens with high
N.A.'. CLEO '82, Phoenix, 1982, WN3
7
KUWAHARA, H., SASAKI, M., and TOKOYO, N. : 'Efficient coupling from
semiconductor lasers into single-mode fibers with tapered hemispherical ends', Appl. Opt., 1980,19, pp. 2578-2583
RMS
HIGH-FREQUENCY PERFORMANCE OF
LATTICE-STRAINED HETEROJUNCTION
GalnAs/GaAs BIPOLAR TRANSISTORS
002
004
0 06
008
0 10
012xA
wavefront aberration (at A = 6 33 nm),waves
Indexing terms: Semiconductor devices and materials, Bipolar
transistors
Fig. 4 Wavefront aberration dependence of LD-SMF coupling loss
wavefront aberration was reduced to as low as 004,1
(X = 633 nm).
Tolerances for misalignment between rod lens and the SMF
were measured for the 0-5 dB loss increment, as an example.
The tolerances in lateral direction (AX), optical axial direction
(AZ) and angular direction (Ad) for the rod lens were
±3-4^m, 100/im and ±2-3°, respectively. Those for the SMF
were ±2/mi, 84 fim and +1-8°. This result indicates that a
stable LD-SMF module can be constructed, compared with
the other coupling methods such as tapered hemispherical end
fibre coupling.7
ELECTRONICS LETTERS 9th October 1986
The performance of bipolar devices and circuits in the novel
lattice-strained GalnAs/GaAs materials system show an
improving trend with increased In composition in the base.
An fT of 8 GHz has been measured using an 8 fim emitter
stripe width and 8% In. A small-signal model is presented.
Introduction: Heterojunction bipolar transistors using a
strained GalnAs base layer sandwiched between a GaAs
emitter and collector layers may offer certain advantages as
compared to the more conventional AlGaAs/GaAs system.
Lower contact resistances are possible, as are lower emitter
Vol. 22 No. 21
1123
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