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lenses and a thermoelectric cooler. The small signal frequency
response of the modules was measured at several bias voltages
from +8 to -8V (Fig. 3). The Tr-EA modulator demonstrated a
small bias-voltage dependence of response, reflecting no accumulation of carriers in the absorption layer. The frequency response for
the PIN-EA modulator degraded radically at the forward-biased
regon due to the increase of junction capacitance as a result of the
large carrier accumulation.
Fig. 4 shows the waveform of the optical output under a
10Gbitk NRZ scheme with PRBS P3- 1. Electrical signals with a
50% cross-point were conducted to modulator modules under a
swing voltage of 3.8VP, and bias voltages (V,) of -1.0, -1.5 and
-2.OV. For the Tr-EA modulator, a clear optical waveform without degradation of timing jitter was obtained at the bias voltages.
The cross-point (X,) of the eye pattern was thus easily controlled
using the bias voltage in which a symmetrical waveform with X, =
50% was realised at V , = -1.5V. The PIN-EA modulator under V , =
-1V showed X, = 50%, but an inappropriate waveform with large
timing jitter in the trailing edges caused by the pattern effect. At a
lower V, of -1.5V, a clear eye opening was observed in which a
symmetrical waveform was not obtained.
In summary, we have proposed and demonstrated a triode EA
modulator using a PINIP junction structure. By suppressing the
pattern effect, the upper limit of the applied voltage was extended
to +8V, or higher. The symmetrical eye pattern was easily
obtained by shifting the applied voltage range to the plus-biased
region without increased timing jitter at the trailing edges.
0 IEE 1998
Electronics Letters Online No: 19980228
K. Yamada,
K. Nakamura
and
26 November 1997
H. Horikawa (Semiconductor
Co., Ltd., 550-5
Technology Laboratory, Oki Electric Industry
Higashiasukawa, Huchioji, Tokyo 193, Japan)
E-mail: yamadak@hlabs.oki.co.jp
References
EDAGAWA, N.,
and
pulse generation up to
20-GHz repetition rate by a sinusoidally driven InGaAsP
electroabsorption modulator’, ZEEE J. Lightwave Technol., 1993,
11, (3), pp. 468473
SUZUKI, M., TANAKA, H., EDAGAWA, N., and MATSUSHIMA, Y . : ‘New
applications of a sinusoidally driven InGaAsP electroabsorption
modulator to in-line optical gates with ASE noise reduction effect’,
ZEEE J. Lightwave Technol., 1992, 10, (12), pp. 1912-1918
DEVAUX, F., BORDES, P., CADIOU, J.F., PENARD, E., GUENA, J., and
LEGAUD, P.: ‘Distribution of millimetre radiowave signals with an
MQW electroabsorption modulator’, Electron. Lett., 1994, 30, (18),
SUZUKI, M.,
TANAKA, H.,
UTAKA, K.,
MATSUSHIMA, Y.:‘Transform-limited optical
pp. 1522-1524
and NESSET, D.: ‘Efficient
harmonic generation using an electroabsorption modulator’, IEEE
Photonics Technol. Lett., 1995, 7, (3), pp. 312-314
DEVAUX, F., CHELLES, s., OUGAZZADEN,A., MIRCEA, A., HUET, F., and
CARRE, M.: ‘10GbiVs operation of polarisation insensitive, strained
InGaAsP/InGaAsP MQW electroabsorption modulator’, Electron.
Lett., 1994, 29, (13), pp. 1201-1203
YAMADA, K., MURAI, H., NAKAMURA, K., MATSUI, Y., and OGAWA, Y.:
‘Low polarisation dependence (< 0.3dB) of an EA modulator using
a polyimide-buried high-mesa ridge structure with an InGaAsP
bulk absorption layer’, Electron. Lett., 1995, 31, (3), pp. 237-238
BERGANO, N.s.,
KERFOOT, F.w., and DAVIDSON, c.R.:
‘Margin
measurement in optical amplifier systems’, ZEEE Photonics
Technol. Lett., 1993, 5 , (3), pp. 304-306
MOODIE, D.G., WAKE, D., WALKER, N.G.,
All-optical oscillator based on the antiparallel connection of two GaAs/AIGaAs
multiple shallow quantum well PINIP diodes
Pin
I l.
0.-K. Kwon, K . 3 . Lee, H.-Y. Chu, E.-H. Lee and
B.-T. Ahn
The authors propose a new scheme for a non-biased all-optical
oscillator based on the anti-parallel connection of two G A S /
AlGaAs multiple shallow-quantum well p-i-n-i-p (PI”) diodes.
Under the illumination of 3mW lasers, the oscillator revealed the
electrical and optical oscillations with a frequency of -43.8MHz.
I
P
The intensity oscillations in the reflected beams from the two
diodes showed a phase difference of E, an o d o f freflection change
of -22%, and a contrast ratio of 2.
c
-
The negative differential resistance (NDR) of resonant tunnelling
diodes (RTDs) and multiquantum well (MQW) p-i-n (PIN) diodes
has attracted much attention due to its applications to ultra-fast
microwave devices [l] and optical bistable devices [2, 31. Contrary
to RTDs based on resonant tunnelling phenomena, the NDR of
MQW PIN diodes was mainly due to the electroabsorption change
in quantum wells. However, for electrical and optical applications,
both devices demanded an external bias voltage and complex circuit interconnections, which caused parasitic R-L-C circuit problems, as well as performance degradation in operation [3, 41.
However, the removal of the external voltage electrically stabilised the diode-circuit and gave rise to many advantages in the
working parameters, such as fast operation time and layout simplification [3, 41. Recently, we have observed electrical and optical
oscillations at the NDR region of reverse-biased GaAs/AIGaAs
multiple shallow quantum well (MSQW) PIN diodes under the
illumination of a high power laser. To achieve all-optical oscillations, the I-Vcurve of the diode must reveal both the peak-photocurrent at a forward-bias voltage and the wide NDR region. In
this Letter, we propose a novel all-optical oscillator based on the
anti-parallel connection of two MSQW p-i-n-i-p(PINIP) diodes
without external bias voltage.
306
I
QWRS
I
a
b
144111
Fig. 1 Illustration of all-optical oscillator based on anti-parallel connection of two PINIP diodes
a Schematic diagram
b Equivalent circuit of
U
In this study, we designed the PINIP diodes to obtain both
large electric field swing and strong light absorption for large optical modulation in an all-optical scheme [3]. The layer structure
was grown by gas-source molecular beam epitaxy. Quarter-wavelength reflector stacks consisting of 14.5 pairs of 72.5nm wide
AMs/ 61.6nm wide AI,,,Ga,,As were grown on the semi-insulating
GaAs substrate, followed by PINIP layers. For p - and n-doping,
Al,,Gq& layers were doped with Be (1 x 1019cm-3)
and Si (5 x
ELECTRONICS LETTERS
5th February 1998
Vol. 34
No. 3
I
101*cm3),
respectively. In each intrinsic region, 20.5 pairs of lOnm
wide GaAsI5nm wide A&,,Ga,,,As MSQWs were sandwiched
between 20 nm wide undoped Al, ,Ga, ,As spacers. The anti-reflection coating was made on the top of the PINIP diode.
Fig. l a and b shows, respectively, the schematic diagram and
the equivalent circuit of the non-biased all-optical oscillator based
on the anti-parallel connection of two PINIP diodes. The areas of
the top and the bottom mesa at each PINIP diode were -40 x 50
and 150 x 75pn2, respectively. The 856nm line of a semiconductor laser diode with a Gaussian beam shape - 1 0 in
~ diameter
was split into two and illuminated on both PINIP diodes. The
energy of the laser was around the transition energy of a heavyhole exciton ground state of an MSQW at room temperature. Pl,,
and PA (and P,) denote the incident and reflected lasers, respectively. We used the HP4145B parameter analyser for I- Vmeasurements. The electrical signal was extracted by a bias-T and
monitored by an oscilloscope and an RF spectrum analyser. The
intensity oscillations in the reflected laser were measured with the
same oscilloscope and fast photodetectors.
-
Under the illumination of the laser, the oscillator showed an Nshape Z- V curve resulting from the current difference between the
forward and the reverse currents in two PINIP diodes, revealing
the NDR feature. When the laser power was low, the I- V curve of
the oscillator at the NDR was smooth with no oscillations. On
increasing the laser power, the N-shape NDR of the oscillator
became larger, and the continuous NDR of each PINIP diode
eventually developed into some current-plateaux, due to either the
bias-circuit-oscillation or the intrinsic oscillation in the diode-circuit 14, 51. Both the position and width of the current-plateaux
also shifted to high reverse bias voltages and became wider with
the laser power. For non-biased all-optical oscillation, the overlap
between the current-plateau regions of the intrinsic oscillations in
two PINIP diodes is essential at OV. This condition was achieved
when the laser power on each diode was > 3mW. The peculiar
shape of the I-V curves around OV resulted from the overlap
between the current-plateaux of two diodes.
The electrical and optical oscillations in an all-optical oscillator
without any external bias are shown in the bottom and top traces
of Fig. 3, respectively. Fig. 3a and b represent the oscillations in
the PINIP diodes A and B, respectively. Both oscillations had a
frequency of 43.8MHz. As the bias voltage changed from - 1.5 to
1.5V in the Z-V measurements, the optical oscillations from A
started to occur at
0.75V with the minimum value of reflectivity oscillations, and disappeared at -0.75V with the maximum
value of reflectivity oscillations, while those from B showed the
opposite behaviour. From the reflectivity measurement of the optical oscillation, we found that the maximum amplitude of oscillation without the external bias covered approximately the whole
voltage width (- 1SV)of the NDR region, although the frequency
and amplitude of oscillations showed a slight dependence on the
bias voltage. Under the illumination of -3mW lasers, the intensity
oscillations in the reflected beam from the two diodes revealed a
phase difference of x, an o d o f f reflection change (AR) of -22%,
and a contrast ratio (CR) of -2. It is emphasised that the present
results of AR and CR are even comparable to the best optical
modulation performance of all-optical bistable devices [3]. Therefore, the proposed device can be useful for all-optical modulation
of lasers and also as an electrical oscillator. The performance of
the present oscillator can be further improved by optimising the
device structure [4].
In summary, we first proposed a novel non-biased all-optical
oscillator, based on the anti-parallel connection of two MSQW
PINIP diodes. Under the illumination of lasers on both PINIP
diodes, the oscillator revealed electrical and optical oscillations
with the same frequency of -43.8MHz. The latter oscillations for
the two diodes showed a phase difference of n,AR of -22%, and a
CR of -2.
-
bias voltage,V
/hlinl
Fig. 2 Measured I- V curve of oscillator
~
Acknowledgment: This work was supported by the Ministry of
Information and Communications, Republic of Korea.
12 November 1997
0 IEE 1998
Electronics Letters Online No: I9980237
0.-K. Kwon, K.-S. Lee, H.-Y. Chu and E.-H. Lee (Basic Research
Laboratory, Electronics and Telecommunications Research Institute, PO
Box 106, Yusong, Taejon 305-600, Korea)
B.-T. Ahn (Department of Materials Science and Engineering, Korea
Advanced Institue of Science and Technology, Tuejon 305-701, Korea)
References
1
SOLLNER, T.C.L.G., GOODHUE, W.D., TANNENWALD, P.E., PARKER, C.D.,
and PECK, D.D.: ‘Resonant tunneling through quantum wells at
frequencies up to 2.5THz’, Appl. Phys. Lett., 1983, 43, pp. 588-590
2
Fig. 3 Oscillation diagrams of diode A and diode B as measured by an
oscilloscope
a Diode A
electrooptic effect device: optoelectronic bistability and oscillation,
and self-linearized modulation’, IEEE J. Quantum Electron., 1985,
QE-21, pp. 1462-1476
b Diode B
Upper traces = optical oscillations; lower traces = electrical oscillations
Scale of x-axis = 20nsidiv; spectral frequency = 43.8MHz
MILLER, D.A.B., CHEMLA, D.S., DAMEN, T.C., WOOD, T.H., BURRUS, C.A.,
GOSSARD, A.c.,
and WIEGMANN, w.: ‘The quantum well self-
3
KWON, o.K., KIM, K., HYUN, K S , LEE, E.H., MEI, x.B., and TU, c.w.:
Fig. 2 displays the I-V curve of the oscillator with and without
laser illumination in the solid and the dotted lines, respectively.
‘A
novel all-optical bistable device in a noninterferometric double p-i
(ESQWs)-n diode structure’, IEEE Photonics Technol. Lett., 1996,
8, pp. 224226
4 KIDNER, c . , MEHDI, I., EAST, J.R., and HADDAD, GI.: ‘Power and
stability limitations of resonant tunneling diodes’, IEEE Trans.
Microw. Theory Techniques, 1990, 38, pp. 864872
ELECTRONICS LETTERS
No. 3
5th February 7998
Vol. 34
307
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