This optical chip can convert light pulses into digital signals faster and more efficiently than existing technology. (Ryan Scott, UC Davis photo)
A new device invented by engineers at UC Davis could make it much faster to convert pulses of light into electronic signals and back again. The technology could be applied to ultrafast, high-capacity communications, imaging of the Earth’s surface and for encrypting secure messages.
“We have found a way to measure a very high capacity waveform with a combination of standard electronics and optics,” said S.J. Ben Yoo, professor of electrical and computer engineering at UC Davis. A paper describing the technology was published Feb. 28 in the journal Nature Photonics.
The device is up to 10,000 times faster than existing technologies for measuring light pulses, Yoo said. It overcomes the limitations of existing approaches, by measuring both the amplitude (intensity) and the phase of a pulse at the same time, and can measure information capacity into the 100 terahertz range in real time. Current electronics are limited to information capacity in tens of gigahertz bandwidth.
The development of a real-time optical waveform measurement technique with quantum-limited sensitivity, unlimited record lengths and an instantaneous bandwidth scalable to terahertz frequencies would be beneficial in the investigation of many ultrafast optical phenomena. Currently, full-field (amplitude and phase) optical measurements with a bandwidth greater than 100 GHz require repetitive signals to facilitate equivalent-time sampling methods or are single-shot in nature with limited time records. Here, we demonstrate a bandwidth- and time-record scalable measurement that performs parallel coherent detection on spectral slices of arbitrary optical waveforms in the 1.55 µm telecommunications band. External balanced photodetection and high-speed digitizers record the in-phase and quadrature-phase components of each demodulated spectral slice, and digital signal processing reconstructs the signal waveform. The approach is passive, extendable to other regions of the optical spectrum, and can be implemented as a single silicon photonic integrated circuit.
Higher-frequency pulses can pack more information into a given length of time. By making it possible to take a complex waveform and quickly decode it into a digital electronic signal, the device would make it possible to pack more data into optical signals.
Operated in reverse, the same kind of device could be used to generate optical signals from electronics.
The device — developed by Yoo’s UC Davis research group, including graduate student Nicolas Fontaine; postdoctoral researchers Ryan Scott, Linjie Zhou and Francisco Soares; and Professor Jonathan Heritage — divides the incoming signal into slices of frequency spectrum, processes the slices in parallel and then integrates them.
The technology could be used in ultra-high-speed communications and also in LiDAR (light detection and ranging) systems. LiDAR uses pulses of laser light to rapidly scan the landscape and produce highly detailed, three-dimensional images of the Earth’s surface.
The next step is to work on putting the whole device into a small silicon chip, Yoo said.
Silicon photonics: A chip-scale one-way valve for light
Being able to isolate optical signals on-chip is a great challenge for integrated photonics, and is crucial to the success of large-scale photonic integrated circuits. Photonic integration has the potential to reduce power consumption, size and cost while improving reliability and performance.