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NRL develops nonmechanical laser steering

20 Nov 2018

Chip-based SEEOR beam technology offers alternative to “inefficient” mechanical scanners.

Scientists at the U.S. Naval Research Laboratory have demonstrated a nonmechanical, chip-based beam steering technology that offers an alternative to mechanical gimbal-style laser scanners, which the team says are “costly, cumbersome and often unreliable and inefficient”.

The chip, known as a steerable electro-evanescent optical refractor, or SEEOR, takes laser light in the mid-wavelength infrared (MWIR) as an input and directs the beam in two dimensions at the output without the need for mechanical devices — demonstrating improved steering capability and higher scan speed rates than conventional methods.

Further details of this research is published in the December 2018 edition of the Journal of the Optical Society of America.

“Given the low size, weight and power consumption and continuous steering capability, this technology represents a promising path forward for MWIR beam-steering technologies,” said Jesse Frantz, research physicist, NRL Optical Sciences Division. “Mapping in the MWIR spectral range demonstrates useful potential in a variety of applications, such as chemical sensing and monitoring emissions from waste sites, refineries, and other industrial facilities.”

Optical waveguide

The SEEOR is based on an optical waveguide, which confines light in a set of thin layers with a total thickness of less than 10µm. Laser light enters through one facet and moves into the core of the waveguide. Once in the waveguide, a portion of the light is located in a liquid crystal (LC) layer on top of the core. A voltage applied to the LC through a series of electrodes changes the refractive index in portions of the waveguide, making it act as a variable prism. This refractive index change enables high-speed and continuous steering of the photon beam in two dimensions.

SEEORs were originally developed to manipulate shortwave infrared light and have found applications in guidance systems for self-driving cars. "Making a SEEOR that works in the MWIR was a major challenge," said Frantz said. "Most common optical materials do not transmit MWIR light or are incompatible with the waveguide architecture, so developing these devices required a tour de force of materials engineering.”

To achieve this, the NRL researchers designed new waveguide structures and LCs that are transparent in the MWIR, as well as new ways to pattern these materials and induce alignment in the LCs without their absorbing too much light.

This development combined efforts across multiple NRL divisions including the Optical Sciences Division for MWIR materials, waveguide design and fabrication, and the Center for Bio/Molecular Science and Engineering for synthetic chemistry and liquid crystal technology. The resulting SEEORs can steer MWIR light through an angular range of 14° x 0.6°. The researchers are now working on ways to increase this angular range and to extend the portion of the optical spectrum where SEEORs work even further.

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