Femtosecond pulsed lasers, which emit light in ultrafast bursts lasting a millionth of a billionth of a second, are powerful tools used in a variety of applications. Lasers are typically expensive table-top systems which limit their use in applications that have size and power consumption restrictions.
New applications in quantum and optical computing, astronomy, optical communications and beyond would be unlocked by an on- chip pulse source. It's been a challenge to integrate the lasers onto the chip.
The Harvard John A. Paulson School of Engineering and Applied Sciences has developed a high-performance, on-chip femtosecond pulse source using a tool that seems straight out of a science fiction novel.
Nature publishes the research.
The senior author of the study said that pulse lasers have remained large.
To make these sources more practical, we decided to shrink a well known approach, used to realize conventional and large-femtosecond sources, using a state of the art integrated photonics platform that we have developed. Microfabrication techniques like those used to make computer chips ensure not only reduced cost and size, but also improved performance and reliability of our sources.
It's possible to bend the rays of light coming from different directions by changing the phase of the lens.
Light beams can bebend in similar ways, but they change the phase of light beams in time. Different colors of light that travel at different speeds are re- timed so that they hit the focal plane at the same time.
A car race in which each color of light is a different car. The leave time of each car is staggered by the time lens, so that they reach the finish line at the same time.
Lonar's lab pioneered the use of optical gratings, which are used in the team's device.
The team starts by passing a continuous-wave, single-color laser beam through an amplifier that controls the amount of light going through the time-lens. The light travels through the bendy part of the lens, where a comb of different colors is created. The phase modulator creates and releases different colored cars at different times.
The last part of the laser is a fishbone grating. The grating changes the speed of the light to bring them all in line with each other, neck and neck, so that they hit the finish line at the same time.
Because the device controls how fast different wavelengths travel and when they hit the focal plane, it effectively transforms the continuous, single color laser beam into a broadband, high-intensity pulse source.
The device is integrated onto a 2 cm by 4 cm chip and requires less power than a table top product.
According to the first author of the study, integrated photonics offers simultaneous improvements in energy use and size.
At the same time, you save energy and space. As the device becomes smaller and more integrated, you get better performance. Imagine if in the future we could carry around pulse lasers in our pockets to sense how fresh fruit is or track our well-being in real time, or in our cars to do distance measurement
The team wants to explore some of the applications for both the laser itself and the time lens technology, including in lensing systems, ultrafast signal processing and quantum networking.
There is more information on the Integrated femtosecond pulse generator.
Journal information: Nature
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