Micro-transfer printing InP C-band SOAs on advanced silicon photonics platform for lossless MZI switch fabrics and high-speed integrated transmitters.

We present an approach for the heterogeneous integration of InP semiconductor optical amplifiers (SOAs) and lasers on an advanced silicon photonics (SiPh) platform by using micro-transfer-printing (µTP). After the introduction of the µTP concept, the focus of this paper shifts to the demonstration of two C-band III-V/Si photonic integrated circuits (PICs) that are important in data-communication networks: an optical switch and a high-speed optical transmitter. First, a C-band lossless and high-speed Si Mach-Zehnder interferometer (MZI) switch is demonstrated by co-integrating a set of InP SOAs with the Si MZI switch. The micro-transfer-printed SOAs provide 10 dB small-signal gain around 1560 nm with a 3 dB bandwidth of 30 nm. Secondly, an integrated transmitter combining an on-chip widely tunable laser and a doped-Si Mach-Zehnder modulator (MZM) is demonstrated. The laser has a continuous tuning range over 40 nm and the transmitter is capable of 40 Gbps non-return-to-zero (NRZ) back-to-back transmission at wavelengths ranging from 1539 to 1573 nm. These demonstrations pave the way for the realization of complex and fully integrated photonic systems-on-chip with integrated III-V-on-Si components, and this technique is transferable to other material films and devices that can be released from their native substrate.

50 GBd PAM4 transmitter with a 55nm SiGe BiCMOS driver and silicon photonic segmented MZM.

We demonstrate an optical transmitter consisting of a limiting SiGe BiCMOS driver co-designed and co-packaged with a silicon photonic segmented traveling-wave Mach-Zehnder modulator (MZM). The MZM is split into two traveling-wave segments to increase the bandwidth and to allow a 2-bit DAC functionality. Two limiting driver channels are used to drive these segments, allowing both NRZ and PAM4 signal generation in the optical domain. The voltage swing as well as the peaking of the driver output are tunable, hence the PAM4 signal levels can be tuned and possible bandwidth limitations of the MZM segments can be partially alleviated. Generation of 50 Gbaud and 53 Gbaud PAM4 yields a TDECQ of 2.8 and 3.8 dB with a power efficiency of 3.9 and 3.6 pJ/bit, respectively; this is the best reported efficiency for co-packaged silicon transmitters for short-reach datacenter interconnects at these data rates. With this work, we show the potential of limiting drivers and segmented traveling-wave modulators in 400G capable short-reach optical interconnects.

Point-to-point overlay of a 100Gb/s DP-QPSK channel in LR-PONs for urban and rural areas.

The continuing growth in information demand from fixed and mobile end-users, coupled with the need to deliver this content in an economically viable manner, is driving new innovations in access networks. In particular, it is becoming increasingly important to find new ways to enable the coexistence of heterogeneous services types which may require different signal modulation formats over the same fiber infrastructure. For example, the same physical layer can potentially be used to deliver shared 10Gb/s services to residential customers, dedicated point-to-point (P2P) 100Gb/s services to business customers, and wireless fronthaul, in a highly cost-effective manner. In this converged scenario, the performance of phase modulated signals can be heavily affected by nonlinear crosstalk from co-propagating on-off-keying (OOK) channels. In this paper, the overlay of a 100G P2P dual-polarization quadrature phase-shift keying (DP-QPSK) channel in a long-reach passive optical network (LR-PON) in the presence of co-propagating 10Gb/s OOK neighboring channels is studied for two different PON topologies. The first LR-PON topology is particularly suited for densely populated areas while the second is aimed at rural, sparsely populated areas. The experimental results indicate that with an emulated load of 40 channels the urban architecture can support up to 100km span and 512 users, while the rural architecture can support up to 120km span and 1024 users. Finally, a system model is developed to predict the system performance and system margins for configurations different from the experimental setups and to carry out design optimization that could in principle lead to even more efficient and robust schemes.

Optimization of PAM-4 transmitters based on lumped silicon photonic MZMs for high-speed short-reach optical links.

We demonstrate how to optimize the performance of PAM-4 transmitters based on lumped Silicon Photonic Mach-Zehnder Modulators (MZMs) for short-reach optical links. Firstly, we analyze the trade-off that occurs between extinction ratio and modulation loss when driving an MZM with a voltage swing less than the MZM's Vπ. This is important when driver circuits are realized in deep submicron CMOS process nodes. Next, a driving scheme based upon a switched capacitor approach is proposed to maximize the achievable bandwidth of the combined lumped MZM and CMOS driver chip. This scheme allows the use of lumped MZM for high speed optical links with reduced RF driver power consumption compared to the conventional approach of driving MZMs (with transmission line based electrodes) with a power amplifier. This is critical for upcoming short-reach link standards such as 400Gb/s 802.3 Ethernet. The driver chip was fabricated using a 65nm CMOS technology and flip-chipped on top of the Silicon Photonic chip (fabricated using IMEC's ISIPP25G technology) that contains the MZM. Open eyes with 4dB extinction ratio for a 36Gb/s (18Gbaud) PAM-4 signal are experimentally demonstrated. The electronic driver chip has a core area of only 0.11mm2 and consumes 236mW from 1.2V and 2.4V supply voltages. This corresponds to an energy efficiency of 6.55pJ/bit including Gray encoder and retiming, or 5.37pJ/bit for the driver circuit only.

Demonstration of error-free 25Gb/s duobinary transmission using a colourless reflective integrated modulator.

To realise novel, low-cost, photonic technologies that can support 100Gb/s Ethernet in next-generation dense wavelength-division-multiplexed metro transport networks, we are developing arrayed photonic integrated circuits that leverage colourless reflective modulators. Here, we demonstrate a single-channel, hybrid reflective electroabsorption modulator-based device, showing error-free 25.3Gb/s duobinary transmission with bit-error rates less than 1 × 10(-12) over 35km of standard single-mode fibre. We further confirm the modulator's colourless operation over the ITU C-band, with a 1.2dB variation in required optical signal-to-noise ratio over this wavelength range.

An upstream reach-extender for 10Gb/s PON applications based on an optimized semiconductor amplifier cascade.

We present a reach-extender for the upstream transmission path of 10Gb/s passive optical networks based on an optimised cascade of two semiconductor optical amplifiers (SOAs). Through careful optimisation of the bias current of the second stage SOA, over 19dB input dynamic range and up to 12dB compression of the output dynamic range were achieved without any dynamic control. A reach of 70km and split up to 32 were demonstrated experimentally using an ac-coupled, continuous-mode receiver with a reduced 56ns ac-coupling constant.

Optimisation of SOA-REAMs for hybrid DWDM-TDMA PON applications.

We demonstrate how loss-optimised, gain-saturated SOA-REAM based reflective modulators can reduce the burst to burst power variations due to differential access loss in the upstream path in carrier distributed passive optical networks by 18 dB compared to fixed linear gain modulators. We also show that the loss optimised device has a high tolerance to input power variations and can operate in deep saturation with minimal patterning penalties. Finally, we demonstrate that an optimised device can operate across the C-Band and also over a transmission distance of 80 km.

A 10G linear burst-mode receiver supporting electronic dispersion compensation for extended-reach optical links.

We present a novel 10G linear burst-mode receiver (LBMRx). Equipped with a PIN photodiode, a high sensitivity of -22.7 dBm (bit-error rate: 1.1x10(-3)) was achieved when handling bursts with a dynamic range of 22.7 dB (each -22.7 dBm burst was preceded by a 0 dBm burst). The LBMRx requires a 150 ns preamble for fast gain adjustment at the start of each burst and can handle bursts separated by a guard time as short as 25.6 ns. With electronic dispersion compensation, 3400 ps/nm (200 km) chromatic dispersion can be tolerated at 2dB penalty in ASE-impaired links using C-band electro-absorption modulators.