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The main advantage of this new structure is the relatively
simple fabrication process. To our knowledge this is the first
DESIGN AND FABRICATION OF
MONOLITHICALLY INTEGRATED DFB
LASER-WAVELENGTH DUPLEXER
TRANSCEIVERS FOR TPON/BPON ACCESS
LINKS
Indexinv terms: Optical communication, Optoelectronics
2
The fabrication and characterisation of monolithically integrated OEIC transceivers for use in optical subscriber access
links are reported. A design incorporating DFB lasers, wavelength duplexers and a monitor photodiode, specific to the
TPONJBPON passive optical network configuration is presented.
3
E. 1
Introduction: Optoelectronic integrated circuit (OEIC) tech-
I
0
0
25
50
75
I,mA
100
Fig. 2 Output power against current ofITG-DFB-BCRW laser
CW T = 0°C
Inset: correspondingemission spectrum at I = 90mA
quasi-index-guided DFB laser with a contacted surface
grating and the first I = 1.55pm InGaAsP DFB laser which
could be realised by a single LPE growth step without corrugation overgrowth. The period of the surface grating can be
precisely designed from photoluminescence and layer thickness measurements of all epitaxial layers. Because of the
BCRW structure no oxide insulation is necessary. The coupling coefficient is mainly determined by the design of the ITG,
which allows an effective coupling in spite of the large distance
between the active layer and the surface grating. This new
structure is especially interesting for laser devices with
I50cm-’, because with decreasing coupling coefficient the
absorption losses caused by the contact metallisation are
decreasing, too. A further optimisation of the contact metallisation will additionally reduce the absorption losses of these
lasers and hence lower the threshold currents.
nology offers a very attractive route to the implementation of
optical subscriber access links. Complex optical terminal functions should be realisable at low cost through the benefits of
an integrated circuit approach. Other advantages are in size,
testing and design flexibility compared to discrete or hybrid
approaches. We describe the monolithic integration of DFB
lasers, 3 dB couplers, wavelength duplexers and monitor
photodiodes, in a circuit designed for use in optical subscriber
access links within the proposed telephony/broadband passive
optical network (TPON/BPON) systems.’.* Here, two different signal wavelengths are used, 1300nm for telephony-only
traffc and 1530nm for broadband distributive signals. We
believe the work described here represents the first time that
an OEIC has been designed to meet the demands of such a
specific system function. The key requirements for the integration scheme are high yield, versatile integration technology
and process tolerant device designs.
Design and fabrication: A schematic diagram and photograph
insert of the integrated chip described here are shown in Fig.
1. The device consists of a 1300nm DFB laser integrated with
TPON
130Gnm DFB laser
Acknowledgments: The authors wish to thank Prof. Dr. W.
Harth and Dr. H. Grothe for their encouragement and H.
Michel (Siemens AG Munich) for the preparation of the first
order surface gratings. Financial support from the Deutsche
Forschungsgemeinschaft is gratefully acknowledged.
dup
A. RAST
A. ZACH
20th February 1991
Lehrstuhl fur Allgemeine Elektrotechnik und Angewandte Elektronik
Technische Universitiit Miinchen
Arcisstr. 21, D-8000 Miinchen 2, Germany
References
1
2
3
4
5
6
s.: ‘Next generation undersea lightwave systems’.
Conf.Optical Fiber Comm., OFC ’90, January 1990, WCl, 22-26
‘A novel InGaAsPflnP distributed feedback laser with a
AEU, 1989, 43, pp.
contacted surface grating for 1 = 1.55”.
388-389
SUEMATSU, Y., and KISHINO, K.: ‘Coupling coefficient in strongly
coupled dielectric waveguides’, Radio Science, 1977, 12, pp.
587-592
MiiLLER, G., HARTL, E., and HONSBWG,
M.: ‘Low-threshold InGaAsP
ridge-waveguide laser fabricated by new contacting system’, Electron. Lett., 1986, 22, pp. 526-527
RAST, A., and ZACH, A.: ‘InGaAsPflnP-BCRW-DFB-laser with a
contacted surface grating for 1 = 135p”, to be published in
AEO, 1991
HARTL, E., and M ~ ~ L L E R
G.:
, ‘Transition from gain guiding to index
guiding and characterisation of 1.55pm bridgeantacted ridgewaveguide lasers’, IEE Proc. J , 1987,134, pp. 22-26
BERGANO, N.
RAST, A.:
ELECTRONICS LETTERS 9th May 1991 Vol. 27 No. 10
input 1530nm
BPON
network port
Fig. 1 Schematic diagram with photograph insert of monolithically inregrated DFB laser-wavelength duplexer transceiver OEIC for use in
TPONJBPON access links
a strip loaded waveguide, 3 dB coupler and an interferometric
(Mach-Zehnder) wavelength d ~ p l e x e r The
. ~ chip dimensions
are 3.65”
long, 0.6“
wide and 0.12”
thick. The 3dB
passive waveguide splitter immediately following the laser
serves to separate upstream and downstream telephony channels within the 126C1340nm wavelength band. The duplexer,
consisting of a further pair of similar splitters separated by a
waveguide phase-shift region, separates the 1300nm bidirectional interactive data from the downstream broadband
signals near 1530nm. It is designed to do so ideally without
loss. A further DFB laser structure on the otherwise unused
remaining waveguide arm from the 3dB splitter has been
included as a monitor photodiode. This component may also
be used in laser drive mode to assist in active fibre alignment
at the TPON receive port. Integration is achieved by a buttcoupled selfaligned approach using two-stage selective area
MOVPE g r ~ w t h over
~ . ~ either LPE or MOVPE DFB laser
source wafers. The 3 dB splitters within the structure are of a
809
novel design which gives substantial insensitivity to polarisation and waveguide parameters. The wavelength duplexer
consists of two such couplers forming a Mach-Zehnder interferometer. These are connected via concentrically curved
waveguides providing an inbuilt, high precision nA/2 path
difference aimed at minimising the 1300nm local laser crosstalk.
Device results: Fig. 2 shows light/current characteristics for a
TPON/BPON OEIC recorded for the rear, cleaved facet of
the laser and for the network port of the duplexer, respectively. Output powers from the duplexer network port of
1300nm state as measured by the power ratio of light in the
two duplexer output arms.
Fig. 3 shows the output wavelength spectrum from the laser
which exhibits singlemode operation and better than 30dB
sidemode suppression. A similar response was observed for
the monitor diode when driven in lasing mode. Monitor operation has also been demonstrated. Linear tracking between
the monitor diode current and the laser rear cleaved facet
output was achieved with IOpA/mW responsivity.
Conclusion: The fabrication of DFB lasers monolithically integrated with couplers and wavelength duplexers to form transceiver chips suitable for meeting the requirements of
TPON/BPON optical access links has been described. Laser,
duplexer and monitor photodiode operation have all been
achieved on single OEIC chips for the first time.
Acknowledgments: This work was supported by GEC Plessey
Telecommunications; the OEIC process used being derived
from work carried out under the EC RACE programme,
project R1012. The authors wish to thank C. Wilkins, J.
Thompson, N. Maung, D. Reid and N. Forbes for material
growth and grating fabrication, and H. Hiams for assistance
with device processing.
0
20
40
laser drive
60
P. J. WILLIAMS
R. G. WALKER
80
21st February 1991
P. M. CHARLES
current,mA
R. OGDEN
A. K. WOOD
Q
N. CARR
A. C. CARTER
Plessey Research Caswell
Caswell, Towcester, Northants “ 1 2
8EQ, United Kingdom
References
laser drive current ,mA
b
1247121
FE. 2 Lightlcurrent characteristicsfor the rear, cleaved loser facet and
duplexer network port of TPONIBPON OEIC
a Rear, cleaved laser facet
b Duplexer network port
0-5mW were observed. Threshold currents were typically 1
s
20mA. A direct measure of the loss has not yet been carried
out but assuming symmetry of the laser output, total losses
from the laser to network port of the duplexer of approximately 11dB may be inferred, including the 3 dB splitter for
the TPON circuits and the laser to waveguide butt join.
However, some asymmetry of the laser output may be
expected which could suggest a higher internal loss. Duplexer
directionalities of 10 :1 were observed in the bar (through)
HOPPIIT, c . E. and CWK& D. E. A.: ‘The provision of telephony
over passive optical networks’, Br. Telecom. Technol. J., April
1989,7, pp. l W 1 1 4
FAULKNER, D. w., and m m m , D. I.: ‘Broadband systems on
passive optical networks’, Br. Tefecom. Technol. J., April 1989, 7,
pp. 115-122
WALKER, R. G., URQUHART, I., BENNION, I., and CARTER, A. c.: ‘1.3/
1.53pm Mach-Zehnder wavelength duplexers for integrated
optoelectronictransceiver modules’, IEE Pruc. J., 137,pp. 33-38
WILLIAMS, P. I., CHARLES P., o m ,I., CDNSIDINE, L., and CARTEX,
A. c . : ‘High performance buried ridge DFB lasers monolithically
integrated with butt coupled strip loaded passive waveguides for
OEIC, Electron. Lett., 1990.26. pp. 142-143
WILLIAMS, P.I., WALKER, R. G, CHARLES P. M., WOOD, A. K., CARR, N.,
TAYLOR, R. I., and CARTEX, A. c.: ‘Optoelectronicintegrated circuits
for telephony/broadband passive optical (TPON/BPON) networks: design and experimental results’. Cont Dig., 12th IEEE
Int. Semiconductor Laser Conf., Davos, 1990, pp. 161165
THREE-GUIDE DIRECTIONAL COUPLER AS
POLARISATION INDEPENDENT OPTICAL
SWITCH
Indexina toms: Directional couvlers. Outical switching
~~~~~~
The polarisation independent directional coupler switch with
three coupled waveguides is demonstrated. The device
exhibits improved voltage tolerance over existing designs.
128
130
132
wavelength .pm
Fig. 3 Wowlength lasing spectrum taken fromrear, cleaned laser facet
of TPONlBPON OEIC
SO mA CW drive
a10
Introduction: Because the cost effective way of implementing
optical communication systems is based on a singlemode fibre
rather than the polarisation maintaining fibre, the optical
switch has to be polarisation independent. So far, many types
of polarisation independent optical switches have been proposed and demonstrated. Among them, the directional
coupler type optical switch shows the best performance.’
ELECTRONICS LETTERS 9th May 1991 Vol. 27 No. 10
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