High-speed PAM-4 and QAM Complex Waveform Modulation for Increasing Data Capacity in Optical Communication
Abstract
The increasing demand of power-hungry applications in high performance computing and data centers has driven the development of the high-speed optical interconnects. Massive data centers capable of housing exabytes of information have become the primary market for many industries. In datacom applications, optical interconnects based on 850 nm oxide-confined Vertical-Cavity-Surface-Emitting-Lasers (VCSELs) have become widely deployed for short reach applications because of the low power consumption and small footprint. Since 2015, Prof. Milton Feng and his research group (High-speed Integrated-Circuit, HSIC) became the world leader in VCSELs by demonstrating a record performance of 57 Gb/s back-to-back (BTB) error-free transmission at 25 ¡C in 2016 OFC. Furthermore, we have presented the record VCSEL performance NRZ 50 Gb/s error free data transmission at room temperature and 44 Gb/s at 85 ¡C over 100-meter OM4 fibers in 20191. However, the development of VCSEL has been reached a bottleneck where the bandwidth is capped at around 30 GHz. With conventional non-return-tozero on-off keying (NRZ-OOK), it can only support up to 60 Gb/s NRZ data transmission without using forward-error-correction (FEC) in receivers. Apart from the remarkable VCSEL performance of 30 GHz, Professor FengÕs research group has recently achieved the breakthrough of VCSEL with modulation bandwidth > 100 GHz at ~ 82K. This breakthrough unveils the potential of using directly modulated VCSEL for 200 Gb/s NRZ data transmission per channel and thus opens a new frontier in VCSEL-based optical link with energy efficiency < 0.1 pJ/bit. Due to limited bandwidth of VCSEL (< 30 GHz), the industry has recently adopted complex modulation schemes such as four-level pulse-amplitude modulation (PAM-4) and quadrature-amplitude-modulation (QAM) for increasing data rate/channel in optical link. These novel techniques set the key to IEEE Ethernet standard to deliver next generation 800 G data transmission. By taking advantage of these modulation techniques, the symbol rate of 100 GBaud/s per channel in the optical links can be translated to 200 Gb/s (PAM-4) or even 400 Gb/s (QAM-16). To achieve the industry modulation standards, we require the capability to perform PAM-4, PAM-8, QAM-4, QAM-8 and QAM-16 analysis. Besides, equipment capable of performing 400 Gb/s data transmission is necessary in order to characterize our 100 GHz VCSEL precisely, which can only be realized by aforementioned modulation schemes. With a rich background in high-speed optoelectronic device research established from UIUC pioneers like Prof. Nick. Holonyak, Jr. semiconductor laser (QW laser, high power DFB laser, oxide-confined VCSEL and transistor laser) and Prof. G. E Stillman semiconductor detector (PIN and APD), Prof. Feng group is among the top contenders in the field of high-speed semiconductor laser (VCSEL, edge-emitting QW transistor laser, vertical cavity transistor laser), photodetector (PIN, APD and single photon detector) for optical links, signal integrity and lidar. Our current measurement setup relies on MUX/DEMUX to provide 120 Gb/s data rate. To improve the test capability in high-speed data transmission with NRZ, PAM and QAM from 120 Gb/s to 400 Gb/s per channel with our record SOA VCSEL bandwidth > 100 GHz, we would like to propose to purchase one Keysight M8194A arbitrary waveform generator (AWG), two SHF 65 Hz bias-tees and two Totoku 67GHz microwave cables. With the assistance of these proposed equipment, we have confidence in pushing the VCSEL development to the next level. And with careful operation and maintenance, the estimated useful life of the equipment will be > 10 years.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jan 04, 2021
- Source ID
- W911NF2110022
Entities
People
- Milton Feng
Organizations
- Army Contracting Command
- United States Army
- University of Illinois Urbana–Champaign