A compact, single-fiber optical head requires minimal internal alignment.
This work represents a radical simplification in the design of the optical head needed for high-precision laser ranging applications. The optical head is now a single fiber-optic collimator with dimensions of order of 1×1×2 cm, which can be easily integrated into the system being measured with minimal footprint. Previous heads were significantly larger, with multiple optical elements requiring careful alignment. The new design has only one optical fiber per head, rather than four, making it much easier to multiplex between tens or hundreds of heads. It is capable of subnanometer precision, consistent with the demanding requirements of new missions.
This advance in optical-head design is enabled by the application of pseudo- random noise (PRN) codes to optical metrology systems. This code is used to discriminate between multiple optical returns that have different propagation delays. In this way, the phase of the signal from the reference surface on the optical head can be measured independently of the phase of the signal from the more distant target retro-reflector.
A prototype system has been assembled in the laboratory. The data were recorded on a digital oscilloscope, and the signal processing was applied off-line in software. Future work will include the implementation of the software algorithms in a real-time FPGA-based signal processing system, and the demonstration of different multiplexing schemes.
This work was done by Serge Dubovitsky, Daniel Shaddock, Brent Ware, and Oliver Lay of Caltech for NASA’s Jet Propulsion Laboratory.
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Refer to NPO-45102, volume and number of this NASA Tech Briefs issue, and the page number.
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Range-Gated Metrology With Compact Optical Head (reference NPO-45102) is currently available for download from the TSP library.
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