Last week’s CLEO conference was a revelation: a virtual conference, and free to attend (though presenters were charged a $100 fee). Everything worked very smoothly; well done to the OSA and the organising committees.

Particularly exciting was the volume of papers, posters, and presentations concerning optical combs including the two Plenary Sessions on Tuesday (12th May).

The first plenary talk (“Intelligent Optical Synthesizer”) given by Professor Kaoru Minoshima, Professor from The University of Electro-Communications in Japan, showed the growing range of applications enabled by optical combs; everything from optical rulers to adaptive sensing and 3D imaging. The second plenary, given by Prof. John Bowers, Director of the Institute for Energy Efficiency at UCSB, highlighted the need for parallelisation in optical networks and how many of the projects featured, among them DODOS and PIPES, included optical combs and multiwavelength sources. Optical combs were also featured in three of the meeting’s post-deadline papers.

Far from solely being an interesting scientific tool or device, we are now seeing increasing interest in optical combs for industrial applications.

Within the communications industry it is becoming increasingly challenging to increase the symbol rate on a single wavelength. Vendors in this space recognise that a move to parallelism will be necessary to continue to increase the per-channel capacities needed by their customers.

A single optical comb can replace an array of independent lasers leading to cost, footprint and power consumption savings. Frequency locking of the channels allows intra-channel guard bands to be minimized or eliminated, while simplifying control by reducing the degrees of freedom. Coherence between comb lines in a multi-wavelength transmission system also offers potential for improved non-linear impairment compensation.

Optical combs have applications that optimise gas sensing, fiber sensing, LiDAR, atomic clock generation and others. However, for optical combs to become mainstream in high-volume applications they need to offer comparable performance to today’s semiconductor laser diodes in terms of cost, footprint, stability, reliability, power consumption, output power, and linewidth. Combs based on mode-locked laser diodes, micro-ring resonators, and electro-optic modulators all have attractive features.

Pilot Photonics’ gain switched optical combs offer an excellent balance of the key features, particularly low linewidth, good output power per line, and high stability. They also offer excellent flexibility, with the ability to set the comb spacing with sub-kHz precision and sweep it continuously at MHz sweep rates. Recent demonstrations of gain switched comb expansion using discrete components is now being translated on-chip, with a goal of creating an 800GHz bandwidth gain switched comb with high output power per line. This development, coupled with our on-chip demultiplexer and integrated modulator development promise a powerful and versatile light and information source for the communications, automotive, medical and energy industries for many years to come.

While physical attendance at conferences and trade-shows has definite advantages (beer, food, meeting colleagues), CLEO did a wonderful job of making it feel like the real thing. I am sure we will see many more virtual conferences taking place in the coming months, and I look forward to following the further development and growth of optical combs as they push towards the mainstream.