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Fig. 2 shows the differential phase shift of the computeroptimised dual-depth £-plane corrugated square waveguide
polariser. Between 11-2 and 14-8 GHz the phase deviation is
only ±1° from the desired 90° value. Without matching sections the return losses are about 26 dB for the TE 01 -wave and
20 dB for the TE 10 -wave. With linear taper sections these
values may be reduced to 40 dB, as has been proved by suitable calculations. The slight reduction of the absolute phase
difference value in this case may be compensated for by slightly increasing the corrugation depths.
Acknowledgment: The authors gratefully acknowledge a
number of helpful discussions with Dr. Fasold, the head of the
antenna laboratory of MBB Erno Raumfahrt GmbH.,
Miinchen, W. Germany, who has called our attention to this
6th April 1984
InGaAsP/InP MQW lasers. 34 In this letter an InGaAs/
InGaAlAs/InAlAs/InP SCH-MQW laser diode is proposed.
This laser has been grown by molecular-beam epitaxy (MBE),
and room-temperature pulsed operation at 1-57 /xm has been
The InGaAs/lnGaAIAs/lnAIAs/lnP SCH-MQW lasers are
composed of InGaAs well layers, InGaAlAs quaternary
barrier layers and InAlAs and InP cladding layers, as shown
in Fig. 1. The barrier layer thickness (Lbl) of the first and last
InGaAlAs barrier layers between the InGaAs well layer and
InAlAs cladding layer is larger than that (Lb2) of other barriers.
n-lnAI As
Microwave Department
University of Bremen
Kufsteiner Strasse, NW I, D-2800 Bremen 33, W. Germany
n-InP sub
1 TOYAMA, N.: 'A cross-shaped horn and a square waveguide polarizer for a circularly polarized shaped beam antenna for a broadcasting satellite'. 1980 IEEE MTT-S Int. Microwave Symp. Digest,
Washington D.C., pp. 299-301
2 FASOLD, D., and LIEKE, M.: 'A circularly polarised offset reflector
antenna for direct broadcasting satellites'. Proc. 13th European
Microwave Conf., Nurnberg, 1983, pp. 896-901
3 SIMMONS, A. J.: 'Phase shift by periodic loading of waveguide and
its application to broad-band circular polarization', IRE Trans.,
1955, MTT-3, pp. 18-21
ADATIA, N., KEEN, K., WATSON, B. K., CRONE, C , a n d DANG, N.: 'Study
of an antenna system for an experimental TV satellite'. ESA Contract Report 3285/77/NL/AK(SC), ERA Report RFTC 420877,
March 1979
BALDWIN, R., and MCINNES, P. A.: 'Corrugated rectangular horns for
use as microwave feeds', Proc. IEE, 1975, 122, pp. 465-469
AL-HARIRI, A. M. B., OLVER, A. D., and CLARRICOATS, P. J. B.: ' L o w -
attenuation properties of corrugated rectangular waveguide', Electron. Lett., 1974, 10, pp. 304-305
SRIDHAR, N., and SRIVASTAVA, G. P.: 'Theoretical analysis of hybrid
modes in a dual-depth corrugated waveguide feed', ibid., 1982, 18,
pp. 793-794
PATZELT, H., and ARNDT, F. : 'Double-plane steps in rectangular
waveguides and their application for transformers, irises, and
filters', IEEE Trans., 1982, MTT-30, pp. 771-776
SCHMIEDEL, H.: 'Anwendung der Evolutionsoptimierung bei Mikrowellenschaltungen', Frequenz, 1981, 35, pp. 306-310
InGaAs/lnGaAIAs/lnAIAs/lnP SCH-MQW
Indexing terms: Laser and laser applications, Semiconductor
lasers. Molecular-beam epitaxy
InGaAs/lnGaAIAs/lnAIAs/lnP separate-confinement heterostructure-multiquantum-well (SCH-MQW) laser diodes have
been fabricated by molecular-beam epitaxy (MBE), and
room-temperature pulsed operation at 1 -57 //m has been
achieved. This SCH-MQW laser is composed of InGaAs well
layers, InGaAlAs quaternary barrier layers, and InAlAs and
InP cladding layers.
Semiconductor lasers operating in the 1-3—1 -6 /im-wavelength
region are very important for low-loss optical fibre communication systems, and InGaAsP/InP DH lasers have been most
extensively studied by liquid-phase epitaxy (LPE). Recently,
multiquantum-well (MQW) lasers operating in this wavelength region have been in several systems, such as InGaAs/
InAlAs MQW lasers,' InGaAs/InP MQW lasers2 and
ELECTRONICS LETTERS 24th May 1984 Vol.20
No. 11
Fig. 1 Structure of InGaAs/InGaAlAs/InAlAs/lnP
grown by MBE
AlAs mole fraction y in InGaAlAs barrier layers is 0-2
This structure has several advantages compared with
InGaAs/InAlAs MQW lasers and InGaAs(P)/InP MQW
lasers. First, by using the InGaAs/InGaAlAs/InAlAs
SCH-MQW structure, higher carrier injection efficiency and
higher carrier and optical confinement can be obtained. The
InGaAs/InGaAlAs system, which can be grown by MBE, is
very suitable for the fabrication of SCH-MQW lasers because
the conduction-band discontinuity A£c(0-5 eV) in the InGaAs/
InAlAs system5 is larger than that (0-22 eV) in the InGaAs/
InP system,6 and A£ c can be varied by using InGaAlAs
quaternary barrier layers. Secondly, compared with InGaAs/
InAlAs MQW lasers with InAlAs cladding layers, improved
thermal dissipation due to the replacement of the most part of
InAlAs cladding layers by InP layers having lower thermal
resistance can be expected. This SCH-MQW laser was grown
in an MBE system7 with two Ga cells as well as In and Al
cells as the group III beam sources.
The InGaAs/lnGaAIAs/lnAIAs/lnP SCH-MQW wafer
grown on Sn-doped (100) InP substrates is composed of: (i) a
0-8 /im-thick Si-doped InP cladding layer (n = 5 x
1017 cm" 3 ); (ii) a 0-2 ^m-thick Si-doped InAlAs cladding layer
(1-5 x 1018 cm" 3 ); (iii) a 0-14 ^m-thick Be-doped InGaAs/
InGaAlAs SCH-MQW active layer (p = 5 x 10 17 cm" 3 ); (iv)
a 0-2 ^im-thick Be-doped InAlAs cladding layer (1-2 x
1018 cm" 3 ); (v) a 1-5 ^m-thick Be-doped InP cladding layer
(5 x 1017 cm" 3 ); (vi) a 0-3 //m-thick Be-doped InGaAs cap
layer (1-2 x 10 18 cm" 3 ). The active layer is composed of 12
InGaAs wells (well thickness Lz ~ 100 A) and 13 InGaAlAs
barriers (barrier thickness Lbl =* 90 A, Lb2 =* 30 A). The AlAs
mole fraction y in the InGaAlAs barrier layer is 0-20. This
corresponds to A£c of 018 eV, assuming that the A£ c between
InGaAs and InGaAlAs is 70% of A£ 9 (energy gap difference)
similar to the A£ c between InGaAs and InAlAs.5 The
SCH-MQW lasers were grown at a substrate temperature of
53O°C, and InP layers were grown at 480°C. The growth rate
of the SCH-MQW layers was 0-25 /im/h, while InP layers
were grown at 0-8 jum/h.
To confirm the formation of quantum levels in the InGaAs
well layers, photoluminescence (PL) measurement was carried
out on the InGaAs/lnGaAIAs/lnAIAs/lnP SCH-MQW wafer
at room temperature. Fig. 2 shows the PL spectra at 300 K
for the SCH-MQW wafer and an InGaAs/InAlAs DH wafer
(active layer thickness cz 800 A) grown by MBE. Active layers
are doped with Be in both wafers {p = 5 x 10 17 cm" 3 ). The
PL wavelength (1-57 jim) of the SCH-MQW wafer is shorter
than that (1-68 /^m) of the DH wafer, and the PL halfwidth
(1170 A, 59 meV) of the SCH-MQW wafer is narrower than
that (1600 A, 70 meV) of the DH wafer. The observed PL
peak energy of the SCH-MQW wafer is close to the calculated
value using a finite-depth potential well model. These results
indicate that quantum levels are formed in the InGaAs well
layers of the InGaAs/InGaAlAs^ = 0-2)/InAlAs/InP SCHMQW wafer.
DH laser diodes grown by MBE in this study. Further
reduction in the threshold current density will be expected, for
example, by optimising the barrier height, barrier layer thickness and well layer numbers, as well as the growth conditions.
In summary, InGaAs/InGaAlAs/InAlAs/InP SCH-MQW
laser diodes have been fabricated by MBE. The barrier layers
were composed of InGaAlAs (y = 0-2) layers, and the cladding
layers were composed of InAlAs and InP layers. Roomtemperature pulsed operation at 1-57 /im was achieved in
these InGaAs/InGaAlAs {y = 0-2)/InAlAs/InP SCH-MQW
laser diodes.
The authors are'grateful to H. Nagai and K. Kuroiwa for
valuable discussions. They also thank M. Fujimoto, T.
Ikegami and K. Kurumada for their continuous encouragement.
28th March 1984
Atsugi Electrical Communication Lab.
Nippon Telegraph & Telephone Public Corporation
Atsugi-shi, Kanagawa 243-01, Japan
Fig. 2 Photoluminescence spectra at room temperature of InGaAs/
InGaAlAs (y = 0-2)/InAlAs SCH-MQW wafer and InGaAs/InAlAs
DH wafer
Using this SCH-MQW wafer, metal stripe laser diodes
(stripe width cz 70 fan, length ^ 200 /im) were fabricated.
These laser diodes were mounted p-side-up on TO-5 stems by
thermocompression bonding. Fig. 3 shows the lasing spectrum
of the SCH-MQW laser diode in pulse operation at room
temperature. The emission wavelength is about 1-57 /mi,
which is close to the calculated value using a finite potential
well model. This is the first investigation of the SCH-MQW
laser diodes operating in the 1-5 /zm wavelength region. At
present, the threshold current density and To value of the
SCH-MQW laser diodes is similar to that of the InGaAs/InP
1 = 1-11th
K., and LANG, R.: '1-3 nm InGaAsP/InP multiquantum well lasers
grown by vapour-phase epitaxy', Electron. Lett., 1983, 19, pp.
REZEK, E. A., HOLONYAK, N., JUN., and FULLER, B. K.: 'Temperature
dependence of threshold current for coupled multiple quantumwell In1_A.Ga;<.P1_TAs,-InP heterostructure laser diodes', J. Appl.
Phys., 1980, 51, pp." 2402-2405
PEOPLE, R., WECHT, K. w., ALAVI, K., and CHO, A. Y.: 'Measurement
of the conduction-band discontinuity of molecular beam epitaxial
grown In 0 . 52 Al 0 . 48 As/In 0 . 53 Ga 0 . 47 As N-n heterojunction by C-V
profiling', Appl. Phys. Lett., 1983, 43, pp. 118-120
6 FORREST, s. R., and KIM, o. K.: 'An n-In o . 53 Ga O47 As/N-InP rectifier', J. Appl. Phys., 1981, 52, pp. 5838-5842
22 °C
TEMK1N, H., ALAVI, K., WAGNER, W. R., PEARSALL, T. P., a n d CHO, A.
Y.: '1-5-1-6 fim Ga 0 . 47 In 0 . 53 As/Al 0 . 48 In 0 . 52 As multiquantum well
lasers grown by MBE', Appl. Phys. Lett., 1983, 42, pp. 845-847
2 TSANG, w. T.: 'Ga o . 47 In o . 53 As/InP multiquantum well heterostructure lasers grown by MBE operating at 1 -53 /mi', ibid., 1984,
44, pp. 288-290
ASAHI, H., KAWAMURA, Y., and NAGAI, H.: 'Molecular beam epitaxial
growth of InGaAlP visible laser diodes operating at 0-66-0-68 /<m
at room temperature', ibid., 1983, 54, pp. 6958-6963
Indexing terms: Waveguides, Groove guide, Directional couplers
An approximate closed-form expression for the calculation of
the coupling properties of groove-guide directional couplers
is deduced from an exact analysis and confirmed by measurements.
1 57
1 58
1 59
Fig. 3 Lasing spectrum at room temperature of InGaAs/'InGaAlAs
(y = 0-2)/InAlAs/InP SCH-MQW laser diodes
Jlh = 35kA/cm 2 ; To = 55 K
Introduction: In a recent publication 1 an analysis of the coupling of two uniformly coupled groove guides has been proposed using an exact mode-matching technique. However, for
the design of groove-guide directional couplers as characterised by Fig. 1 this theory is complicated and further insufficient by neglecting the influence of the curved sections.
Consequently this letter presents an extension of the rigorous
theory resulting in a simple design formula which has been
used to construct some directional couplers specified for the
millimetre-wave region. Measurement results are also included
to confirm the validity of the approximate formula.
Method: As is well known by Miller's paper, 2 a system of two
coupled waveguides exhibits a cyclic power transfer between
the guides which may be explained as interference of the even
(index V) and odd (index 'o') modes. In this sense the exact
Vol. 20 No. 11
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