Integrated Photonics for Communications
by Dom Siriani
Written by Dom Siriani
Much like yesterday, today my FiO/LS presentation selection seemed to have a theme. This time it was integrated photonics for the use in optical communications. It seems natural to have a large focus in this area, since it repeatedly is shown how the energy and cost per bit/sec must be reduced in order to keep up with consumer demand. It’s really remarkable how quickly user consumption on the internet has increased over a relatively short amount of time (think of how prominent video on demand has become in just a few years), and this poses significant challenges for developing the next generation of photonic devices and data transmission methodologies.
A great deal of this information was contained in the first talk of the “Integrated Photonics for High-Capacity Communications” session by Radhakrishnan Nagarajan. He highlighted how today long-haul communications are dominated by InP technologies, as well as how the continued increase in communication speeds is requiring new transmission and receiving methods. In particular, an area of intense focus is integrating as many capabilities as possible on a single monolithic chip to reduce cost and power consumption. Additionally, coherent transmission and detection schemes, such as quadrature phase shift keying (QPSK), are being used to go beyond the data rates provided by wavelength division multiplexing (WDM). In essence, data transmission capacity over fiber is dictated by the spectrum bandwidth, the channel density over that bandwidth, and the spectral efficiency in bits/sec/Hz. Assuming there are bandwidth limits, the challenge is to increase the channel density and spectral efficiency, which can be done with a combination of WDM and QPSK. I won’t go into any further detail here, but he provided further information on monolithic and integrated InP transmitters and receivers for >1 Tb/sec data rates.
In addition to this talk, I saw several others with a similar theme. There was a very nice presentation on frequency combs using ring resonators. By integrating the desired nonlinearity with the ring, greater mode locking stability was achieved by decreasing the loop length of the system. There was also further work on integrating devices in InP, particularly some advanced passive switches with broad bandwidth. And finally, I also saw work on making injection-locked, mode-locked quantum dot lasers. The presenter showed how the injection locking to an external, high-Q resonator significantly improved the stability and decreased both the RF and optical linewidths.
And now it’s about time for the post-deadline presentations. So much information and so little time!
Disclaimer: Opinions, interpretations, conclusions, and recommendations are those of the author and are not necessarily endorsed by the United States Government and MIT Lincoln Laboratory.
Posted: 18 Oct 2012 by Dom Siriani