A recent breakthrough is promising to drive the development of next-generation long-haul telecommunications systems while making optical communications more widely accessible. Together with Fujikura Ltd., researchers from Singapore’s A*STAR Institute of Microelectronics (IME) have debuted 40- to 60-Gb/s silicon-based optical modulators. The modulators boast advanced multilevel modulation formats for high-speed, long-haul data transmission. In doing so, they bring the industry closer to attaining low-cost, ultra-high-bandwidth and small-footprint optical communications on silicon.
Each modulator consists of a set of silicon phase shifters, which are integrated in a nested Mach-Zehnder configuration. In terms of multilevel modulations, the modulators rely on simple quadrature-phase-shift-keying (QPSK) and differential-QPSK (DQPSK) formats. The result is increased information capacity, which creates more data-communication throughput for a given optical channel.
The modulators have demonstrated communication speeds of more than 40 and 60 Gb/s for DQPSK and QPSK, respectively. For channel grid spacing of 50 GHz, for example, 40G DQPSK results in a spectral efficiency that is 2X that of 20G with conventional on-off keying (OOK) format (which is widely used commercially). These new modulators are smaller than conventional lithium-niobate modulators. Being CMOS-compatible, they also are less expensive to fabricate.
