I think a really big point that gets missed in what the optical interposer platform provides industry. That is the ability to “mix and match”. This term is starting to be used by POET and is such a good description of what this platform offers.

When we look at the wide range of optical applications there are many trade-offs that are required in terms of device selection. For example an optical engine that can operate at very high speeds for data communications versus something that is required for wide spectral sensitivity for sensing require a different set of devices. And size does matter. Not just for footprint considerations but for high speed applications smaller is better. POET’s optical interposer platform is going to use the best combinations of devices to build application specific optical engines.

One of the devices POET is using from the silicon world is the Mach-Zehnder Interferometer (MZI) Modulator. There has been a long history of work that has taken place to reduce the power consumption of the silicon MZI Modulator which is the modulator of choice for large spectral width and reliable thermal performance. I was just watching the following video by Graham Reed, professor and deputy director of the Optoelectronics and Research Centre at the University of Southampton, giving a keynote address at the Spring 2017 AIM Photonics Roadmap Meeting, "Silicon MZI Modulators: History and Future." https://www.youtube.com/watch?v=5gCsUt7KfIc    

Interestingly Andrew Rickman of Rockley was one of Graham Reed’s first students. Rockley has been working on the optoASIC and interestingly Rockley uses very large silicon waveguides which allows for great wavelength accuracy for waveguide dimensional deviation.  But they take up a lot of real estate and large waveguide devices tend to be slower which is maybe why Rockley is said to be focusing more toward sensing applications now? The other part if my memory serves me correctly is that Rockley uses wirebonding which as I recall they list as a strength instead of a weakness. Wire bonding is an old technology that creates longer distances for electrical connections so electrical transmission speeds become limited. But it is claimed as strength because design changes are much easier to facilitate.

But back to something I was talking about recently with regards to wafer level testing of the optical circuits and how silicon photonics uses surface gratings which are very leaky devices for connecting fiber to the chip. Graham Reed has been working with others to creating an erasable grating coupler at the surface of the wafer using germanium implants.

Laser erasable implanted gratings for integrated silicon photonics

Grating couplers are used to efficiently couple light from an optical fibre to a silicon waveguide as they allow light to be coupled into or out from any location on the device without the need for cleaving. However, using the typical surface relief grating fabrication method reduces surface planarity and hence makes further processing more difficult. The ability to manufacture high quality material layers on top of a grating coupler allows multiple active optical layers to be realized for multi-layer integrated optical circuits, and may enable monolithic integration of optical and electronic circuits on separate layers. Furthermore, the nature of the refractive index change may enable removal via rapid thermal annealing for wafer scale testing applications. We demonstrate for the first time a coupling device utilising a refractive index change introduced by lattice disorder. Simulations show 44% of the power can be extracted from the waveguide by using uniform implanted gratings, which is not dissimilar to the performance of typical uniform surface relief gratings currently used. Losses determined empirically, of 5.5dB per coupler have been demonstrated.

My summary:

As most of you will recognize by now the numbers above are very inferior to  what POET has achieved.

But the point that we should recognize. What POET has done in creating the temporary loopback waveguide is a very simple approach to achieve a complete end to end test of all electrical and optical devices and circuits in one step.

The mix and match capability of the optical interposer design will allow POET to use the best available active devices within the ecosystem as they become available to industry.  Our new president sees future applications using off the shelf devices that have been built to mix and match for a range of POET application specific optical engines.    

The thing is, as industry builds faster more energy efficient devices the old devices will become obsolete and the manufactures will have to continue to jockey for position and introduce new and improve devices.  That to me is the beauty of the optical interposer platform. It will remain relevant and if things work out then the builders of new devices will all want to supply POET and compete for the market that POET serves.