Multi-Channel Coherent PM-QPSK InP Transmitter ... - Infinera

Multi-Channel Coherent PM-QPSK InP Transmitter
Photonic Integrated Circuit (PIC) Operating At 112 Gb/s
Per Wavelength
P. Evans, M. Fisher, R. Malendevich, A. James, P. Studenkov, G. Goldfarb, T. Vallaitis, M. Kato, P. Samra,
S. Corzine, E. Strzelecka, R. Salvatore, F. Sedgwick, M. Kuntz, V. Lal, D. Lambert, A. Dentai, D. Pavinski,
J. Zhang, B. Behnia, J. Bostak, V. Dominic, A. Nilsson, B. Taylor, J. Rahn, S. Sanders, H. Sun, K.-T. Wu,
J. Pleumeekers, R. Muthiah, M. Missey, R. Schneider, J. Stewart, M. Reffle, T. Butrie, R. Nagarajan,
C. Joyner, M. Ziari, F. Kish, and D. Welch
Infinera Corporation, 169 Java Drive, Sunnyvale, CA 94089 USA
e-mail: pevans@infinera.com
1. Introduction
Abstract: A 10-wavelength, polarization-multiplexed, monolithically integrated InP transmitter
PIC is demonstrated for the first time to operate at 112 Gb/s per wavelength with a coherent
receiver PIC.
OCIS codes: (250.5300) Photonic integrated circuits; (060.5060) Phase modulation; (060.1660) Coherent communications;
Photonic integration is critical to realizing large-scale, high-efficiency, phase-sensitive modulation schemes based
on coherent detection. We have previously reported transmitter PIC operation at 40 Gb/s DQPSK at 20 Gbaud [1]
and later with polarization multiplexing at 10 Gbaud [2]. In this paper, we describe the first demonstration of a
coherent PM-QPSK, 10-wavelength transmitter PIC. This architecture is enabled by integration of 10 narrow
linewidth tunable lasers. We report on operation of a packaged module pair at 57 Gb/s per wavelength and a chip at
112 Gb/s per wavelength.
2. PIC Design
The transmitter PIC integrates 10 DFB lasers with an array of 2-stage nested Mach-Zehnder modulators (MZM) and
in two different optical paths functionally labeled TE and TM in Fig. 1 [2]. The PIC uses a single TE polarization on
chip (the TE/TM labels refer to the data paths). The 10-wavelength chip operates at 200 GHz channel spacing and
covers half of the C-band. The PIC chip has 20 super-MZM paths and 40 sub-MZM paths. DC elements are used
as shown to balance the modulators. Variable optical attenuators (VOA) are used to enable power equalization for
each wavelength and polarization. The modulator path outputs for the 10 wavelengths of each polarization path are
multiplexed using an arrayed waveguide grating (AWG). The AWG outputs are fiber-coupled and multiplexed offchip
with a polarization beam combiner (PBC).
PBC
DC
DC
DC
DC
RF
RF
RF
RF
DC
DC
Fig. 1. Schematic of PIC (center). The insert on the right is a picture of the active areas of the PIC. The functional blocks of the
modulator section consisting of a nested Mach-Zehnder-Modulator for each polarization is shown on the left.
3. Performance
The DC performance of the sub-MZMs is characterized by scanning the RF electrode biases along the RF path and
measuring the power transfer function. Excellent uniformity is demonstrated in Fig. 2 where we show the
superimposed power transfer functions of all 40 sub-MZMs on one PIC. A V π of 2.5V and DC extinction ratios (as

defined in Fig. 2a) in excess of 30dB across all sub-MZMs is achieved. These high extinction ratios imply a power
imbalance between MZ arms of

Fig. 4. Polarization-multiplexed, 14.25 Gbaud constellation diagrams for all channels and polarizations of the 10×57 Gb/s
transmitter PIC.
The RF performance of a standalone transmitter PIC was characterized for 112 Gb/sec operation using a new
PIC design wherein the MZM design was improved to operate at 28 Gbaud. In this experiment, the two RF data
streams were constructed using a 28 Gb/s pattern generator with a 2 15 -1 PRBS pattern and applied to the chip using
multiple ground-signal-signal-ground RF probes. The RF signal was applied first to the TE and then the TM
polarization. The optical receiver used to characterize the device was a 10-channel receiver PIC module [3]. For
each polarization, the optical signal was split, delayed and recombined to generate polarization-multiplexed inputs to
the receiver module. Figure 5 shows the back-to-back constellation diagram for four data streams at 28 Gbaud per
stream, or 112 Gb/s per wavelength across half of the C-band. Again, operation better than the FEC limit was
demonstrated.
Fig. 5. 28 Gbaud constellation diagrams for each polarization of wavelengths 1 and 10 of a 10 wavelength transmitter PIC.
3. Conclusion
We report the first demonstration of a 10-wavelength PM-QPSK transmitter PIC running at 57 Gb/s per wavelength
in a packaged module. We also demonstrate the operation of a standalone transmitter PIC chip at 112 Gb/s per
wavelength in conjunction with a packaged receiver PIC. This 112 Gb/s operation demonstrates the viability of 10-
wavelength InP PICs to scale to a Terabit /chip capacity and beyond.
4. References
[1] S. Corzine et al., “10-Channel x 40Gb/s per channel DQPSK monolithically integrated InP-based transmitter PIC,” presented at the OFC
2008, Feb. 2008, Paper PDP18.
[2] S. Corzine, et al., “Large-Scale InP Transmitter PICs for PM-DQPSK Fiber Transmission Systems,” IEEE PTL, Vol. 22, No. 14, p.1015, July
2010.
[3] R. Nagarajan et al., “10 Channel, 100Gbit/s per Channel, Dual Polarization, Coherent QPSK, Monolithic InP Receiver Photonic Integrated
Circuit,” presented at the OFC 2011, Mar. 2011.