Dr. Rainer Martini – Director of the Ultrafast Laser Spectroscopy and Communication Laboratory and Associate Professor of Physics and Engineering Physics at Stevens Institute of Technology – has developed technology for frequency and amplitude modulation in laser light that results in clear, ultrafast optical free space communications. Not limited by a physical conductor, a high speed optical system that is stable enough would allow satellites to one day convert to laser technology, resulting in a more mobile military and super-sensitive scanners, as well as faster Internet for the masses.
A laser's beam must be optically modulated in order to transmit large amounts of data, and Stevens researchers realized optically-induced amplitude modulation (AM) of mid-infrared lasers a few years ago. Now, Dr. Martini and other Stevens researchers have developed a technique to optically-induced for frequency modulations (FM) of the beam as well, resulting in a signal that is disrupted significantly less by environmental factors like dust and fog. The new research stands to revolutionize communications, rendering environmental barriers meaningless and allowing mobile units not tied to fiber optic cable to communicate in the range of 100 GHz and beyond – the equivalent of 100 gigabytes of data per second.
Electronic modulation of middle infrared quantum cascade laser is limited to 10 GHz, and optical modulation of frequency and amplitude offers a viable alternative. Last year, Dr. Martini and his team developed a method to optically induce fast amplitude modulation in a quantum cascade laser – a process that allows them to control the laser's intensity. Their amplitude modulation system employed a second laser to modulate the amplitude of the middle infrared laser – in essence using light to control light. But the team still faced the problem of reliability, so they turned to optical frequency modulation.
"FM transmitted data is not affected by the environmental elements that affect AM data," Dr. Martini said.
The recent success allows modulating specifically the emission frequency of the laser, allowing a much more reliable transmission. This optical approach has a number of applications, including frequency modulation in a middle infrared free space communications system, wavelength conversion that will transform a near infrared signal directly into a middle infrared signal, and frequency modulation spectroscopy.
"Dr. Martini's creativity and persistence have yielded great advances in laser optics," said Dr. Michael Bruno, Dean of the Schaefer School of Engineering and Science at Stevens. "As the first person to explore amplitude and frequency modulation, he opened the doors to faster, clearer, free space communications. Today, he continues to advance a field he created."
As pioneers into the evolving world of free-space optical communications, Dr. Martini and his team continue to search for new solutions in translating research into every-day reality. One area of focus could take the lasers below ground by integrating the system into existing fiber optics networks, enabling high speed laser communications both above and below ground. The team is also developing a phase control detector to complement their recently-created phase control emitter, which will create an entirely phase-controlled system and enable researchers to manage every aspect of the system. Such a control is well know from radar and radio systems – yet unprecedented in optical systems. This could open a whole new world of possibilities including enhanced chemical and biological detection by up to 1,000,000 times, and facilitate integration into products.
For Dr. Martini, it is all a matter of perseverance as he explores this new frontier.
"There is proof of concept that we can do it. The question now is what limitations are there,” he said.