This week’s blog post is provided by featured author, Dr. Simon Poole.
I recently had the opportunity to visit a number of universities and research institutes in Scotland and Ireland working in the photonics space. Whilst many of these groups were using our WaveShaper family of LCoS-based Programmable Optical Processors in their research (in some cases several of them!) it was very interesting to see other applications of LCoS in their research.
In many of the places I visited, LCoS were being used as a critical part of experimental tools called Optical Tweezers which are used for trapping and manipulating nanometer and micrometer-sized particles. In these, a laser beam is focused by sending it through a microscope objective and, at the narrowest point of the focused beam the particles (which must be a dielectric, not a conductor) are attracted to the region of strongest electric field at the center of the beam. The LCoS is used to control the intensity distribution of the impinging laser beam and thereby control both the number and position of the optical traps generated. The example below (from David Grier’s group at New York University) shows a typical experimental arrangement for an LCoS-based optical tweezers experimental system.
A really cute video showing Optical Tweezers to play a game of Tetris can be seen here. More practical applications included medical research, where the ability to hold and manipulate individual cells and, in some instances, individual proteins, offers a unique capability to study both inter- and intra-cellular interactions with exquisite control.
In a similar vein, a particularly impressive experiment I was able to see in action was at St Andrews (and no, I didn’t get in a round of golf – despite it being perfect golfing weather with temperatures of 5°C and horizontal rain) where Tomáš Čižmár and Kishan Dolakia are doing some beautiful work on image reconstruction through multimode fibres using an LCoS spatial light modulator. More details of the experimental technique, and the results obtained, can be found here.
One final LCoS application, this time from Heriot-Watt University in Edinburgh, used an LCoS spatial light modulator to control the intensity profile of a high-power laser for laser machining applications. The LCoS allowed Prof Duncan Hand and his team to optimise the spatial intensity profile to be more ‘top-hat’-like, compared to the usual Gaussian beam, and thus provide improved performance in laser marking and drilling applications.
I also had a chance to meet Gordon Povey, CEO of PureVLC, a company set up to commercialize the optical Li-Fi technique developed at Edinburgh University. Li-Fi exploits the fact that even LEDs used for room lighting can be modulated at high speeds (up to 20 MHz) and so can be used for broadcasting information at high speeds. By using OFDM techniques, the researchers at Edinburgh University have demonstrated data rates of over 120 Mbit/sec (a spectral efficiency of >6 bits/sec/Hz) using ‘off the shelf’ lighting LEDs. The company is at an early stage of product development, but there is a lot of interest in the technology as an adjunct to existing Wi-Fi networks in applications including localised ‘hot-spots’ for high-speed downloads, as well as in content distribution systems for in-flight entertainment in aircraft. Li-Fi is not something that will challenge optical fibres as a transmission medium, but is a very interesting alternative for the ‘last meter’ connection to a users’ mobile device.