More on: IBM approaches 100Gbit/s all CMOS optical transceivers

IBM has revealed more about its 100Gbit/s CMOS optical transmitter, reported at the Conference on Lasers and Electro Optics in San Jose last week.

Using its sub-100nm CMOS9WG silicon-on-insulator process, it has implemented Mach-Zehnder modulators (MZMs) and a compatible 50Ω CMOS driver.

Unlike the 16Gbit/s drivers it reported recently, which were voltage-mode, these run up to 32Gbit/s and are current-mode.

“We present a monolithic CMOS transmitter with a link sensitivity comparable to a 25Gbit/s commercial reference transmitter, exhibiting a 5.2dB extinction ratio, 4.9dB insertion loss, and error free operation up to 32Gbit/s,” said IBM in its paper ‘Demonstration of error free operation up to 32Gb/s from a CMOS integrated monolithic nano-photonic transmitter’.

The firm is aiming to make optical CMOS transceivers for medium-range links (up to a few km) in data centres. These will include opto-mechanical interfaces for single-mode fibres. The chip reported in San Jose has four modulators – 100Gbit/s aggregate when run at the 25Gbit/s design speed – but does not have the optical filters and combiner necessary to get all the data into one fibre.

Fed from an external laser, the transmitter used ~135mW, which is 5.4pJ/bit at 25Gbit/s.

According to the IBM, process refinements have been identified that should give ~1.3dB of loss improvements.