A proof-of-concept technique has been developed for measuring and controlling the individual phases of array elements. Electro-optic steering and beam-forming of laser beams is an emerging field with devices such as optical phased arrays that are capable of steering with significantly reduced noise floors and that are faster by orders of magnitude.
One of the most difficult aspects of realizing an optical phased array is the phasing of the individual elements that make up the array. The path length of each individual element must be controlled with accuracy on the order of a nanometer. For a multi-element array, this becomes increasingly complex and bulky as the size of the array increases.
Digitally enhanced interferometry (DI) achieves phase measurement and control of each array element using a single detector. Instead of individually sensing the phase of each element on a separate detector, DI separates out each of the element phases digitally by employing pseudo-random codes to separate the elements. In this way, the complexity is shifted from the optical and mechanical hardware to the digital software processing domain where the main limitation is computing capability.
This work was done by Glenn de Vine and Danielle M. Wuchenich of Caltech, and Daniel A. Shaddock for NASA’s Jet Propulsion Laboratory. NPO-49135
This Brief includes a Technical Support Package (TSP).
Optical Phased Array with Digitally Enhanced Interferometry
(reference NPO-49135) is currently available for download from the TSP library.
Don't have an account?
Overview
The document discusses advancements in Optical Phased Arrays (OPAs) with a focus on the integration of Digitally Enhanced Interferometry (DI) for laser beam steering and shaping. Unlike traditional microwave phased arrays, OPAs have primarily been confined to research settings due to challenges in aligning the phases of array elements at much shorter wavelengths. The introduction of DI has addressed these challenges, enabling robust and scalable metrology for OPA technology.
The research conducted at NASA's Jet Propulsion Laboratory (JPL) aimed to enhance the capabilities of electro-optically controlled laser systems. In initial demonstrations, a linear array of three elements achieved open-loop beam steering of over 1 milliradian, surpassing theoretical expectations. This capability is significant for various applications, particularly in Earth Science and Astrophysics, where precise laser measurements are crucial.
The document highlights the advantages of the OPA design, which includes reduced risk, size, and mass while improving performance. Key benefits include the absence of mechanical actuation, high open-loop bandwidth (tens of GHz), and the ability to perform sub-picometer metrology. These features make OPAs ideal for missions requiring laser beam pointing and measurements, such as LiDAR, optical communications, and inter-spacecraft optical metrology.
One notable application mentioned is the GRACE-2 mission, where the initial beam steering capabilities of the OPA exceed the mission's requirements by a factor of three. This demonstrates the potential of OPAs to meet the dynamic range steering needs for future all-optical missions.
Furthermore, the document cites DARPA's recognition of OPAs as enabling technology for a wide range of applications, including surveillance, 3D imaging, precision targeting, and low probability of intercept communication. The compatibility of the OPA approach with high-power beam forming opens avenues for directed-energy applications, such as space debris de-orbiting.
In summary, the document outlines the transformative potential of OPAs with DI in advancing laser technology, emphasizing their application in scientific missions and various technological fields. The research at JPL represents a significant step toward practical implementation, promising to enhance the capabilities of future aerospace instruments and systems.
