WA3.2 (Contributed) 1:45 PM 2:00 PM -
High-Power Heterogeneously Integrated Waveguide-Coupled Balanced Photodiodes on Silicon-on-Insulator Xiaojun Xie"', Qiugui Zhou', Erik Norberg2, Matt Jacob-Mitos2, Zhanyu Yang', Yaojia Chen', Anand Ramaswamy2, Gregory Fish2, Joe C. Campbell', and Andreas Beling' I Electrical
and Computer Engineering Department, University ofYirginia, Charlottesville, VA 22904 2 Aurrion Inc., 130 Robin Hill Rd. #300, Goleta, CA 93117 *
[email protected]
Abstract- We demonstrate InP-based modified uni-traveling
plasma-activated and bonded on the SOl waveguide layer at
carrier balanced photodiodes integrated on silicon-on-insulator
room temperature [8]. The III-V mesas were formed by dry
(SOl)
waveguides with an internal responsivity of 0.78 A/W, 14
GHz
bandwidth,
and >20 dB common-mode rejection ratio
(CMRR). T he unsaturated RF output power reaches 15.2 dBm at 20 GHz.
etching and gold contacts were plated on both the p and n
mesas. In order to reduce RF loss originating from the low resistivity Si substrate, RF probe pads were deposited on a
3-J.lm-thick SU8 layer and connected to the contacts by
Index Terms- High power photodiode,
silicon photonics,
air-bridges.
microwave photonics
I.
INT RODUCTION
High-power balanced photodiodes are critical components for analog photonic links that employ heterodyne detection owing to their capability to suppress laser relative intensity noise and amplified spontaneous emission noise from erbium-doped fiber amplifiers [1]. Various approaches including normal-incidence [1, 2], waveguide photodiodes [3, 4], and velocity-matched distributed configurations [5] have been employed to fabricate high-power
monolithic
balanced
photodiodes.
Waveguide
photodiodes can achieve high bandwidth-efficiency products and, by their nature, have become key devices in photonic integrated circuits. We recently demonstrated high-power and high-speed waveguide photodiodes on SOl with 12 dBm output power at 40 GHz using a heterogeneous integration technology [6]. In this work, we extend this technology and demonstrate InP-based balanced photodiodes heterogeneously integrated with SOl waveguides. A 25-J.lm long balanced photodiode (PD)
Figure I Photodiode layer structure. Doping concentrations in cm·3
achieved 0.78 AlW internal responsivity, 14 GHz bandwidth,
III.
17.2 dBm output power at 10 GHz and 15.2 dBm output power at 20 GHz.
EXPERIMENT A L RESULTS
The balanced photodetector has a pair of PDs each with an II.
active area of 14x25 J.lm2. The PDs were independently biased DEVICE DESIGN AND FABRICA TION
through a custom designed microwave probe that allowed the
A schematic cross section of the balanced PD epitaxial layer
photocurrents to be monitored separately. A lensed fiber array
structure is shown in Figure 1. Compared to the wafer structure
with approximately 2-J.lm-diameter spot size and 250-J.lm pitch
in
was used to couple light into the two input waveguides. Based
[7], thin bandgap-graded InGaAsP layers were added
between the InGaAs absorber and the InP matching layer to
on coupling loss measurement [6], the internal responsivity is
smooth the abrupt heterojunction barrier and prevent carrier
estimated to be 0.78 A/W at 1550 nm wavelength for a 25 J.lm
pile-up. In addition, the thickness of the InP matching layer was
long device. The PD pair exhibited
o
25
30 dB at low
E � � :t 0 Il. u..
III
12
0
15
3
10
2.5
0
1.5
Q.
-5
iii' � c
0 Vi III �
Q.
E
o
-10
0.5
-15
o
10
Figure 5. Output RF power of 14x25 �m2 PD at +/-6 V bias voltage and AC compression at 10 GHz and 20 GHz vs. average photocurrent.
24
-30
3.5
Photocurrent (rnA)
:::l
-
--------�� 4 D Balanced PO at 10 GHz (62.8mA., 17.2 dBm)
20
-20
"5 -S--18 o
Photocurrent (rnA)
II:
Osingle PO 1 (15 GHz) Osingle PO 2 (14 GHz) .balanced PO (14 GHz) +common mode
-12
100
2
'5 0
1-6 �
10
5
'5
6
m :E.
-0.5
1
under
photodetector
observed.
E
E o
Figure 4. Output RF power of 14x25 �m2 PD at +/-6 V bias voltage and AC compression at 10 GHz vs. average photocurrent.
20 dB at the 3 dB cut off frequency were
�
Q.
-15 ·20
c 0
Vi III
0.5
result of the symmetry provided by monolithic integration, high frequency and
iD 2.5�
·10
demonstrated a bandwidth of 14 GHz in differential mode. As a common mode reject ratios (CMRRs) of
Single PO 1 Cofll)feSSion x Single PO 2 Co�ession
-5
were used to control the RF phase and relative input powers, respectively. As shown in Figure 3, the individual photodiodes
Balanced PO Co�esslon al10 GHz
•
10
i
1.E-12
5
+
10
o
IV.
-+-
+-+-
20
30
40
onto
Frequency (GHz) Figure 3. Frequency responses measured at +/-5 bias voltage and 10 mA photocurrent per PD.
As expected,
for the balanced detectors operating in
differential mode, the combined photocurrents of the two PDs exhibited
�
Figure 4 shows the RF output power at lO GHz versus average photocurrent at room temperature and +/-6V bias voltage
measured with 50 Q external load. The maximum RF output power levels of the individual photodiodes were 11.5 dBm at 32.6 rnA photocurrent and 11.1 dBm at 31.1 mA photocurrent. In differential mode the balanced detector exhibited 62.8 rnA total photocurrent and 17.2 dBm output RF power. At 20 GHz,
SOl
Devices
waveguides were fabricated and characterized.
with
14x25
J.!m2
photodiodes
have
an
internal
responsivity of 0.78 A/W and a bandwidth of 14 GHz. The RF output power reaches 17.2 dBm at 10 GHz and 15.2 dBm at 20 GHz.
6 dB higher output RF power than the output RF
power from a single PD with the same per-diode-photocurrent.
the maximum RF power was 15.2 dBm (Figure.5).
SUMMARY
InP-based balanced photodiodes heterogeneously integrated
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6.
X. Xie, et aI, Optical Fiber Communication Conference (OFC), Th5B. 7, 2015.
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