DARPA Making Progress on Miniaturized Atomic Clocks for Future PNT Applications

Estimated reading time: 5 minutes

To date, the miniaturization of trapped-atom sensors has been stymied by bulk optical elements - such as lenses and mirrors—that traditionally compose the necessary optical system. The precision atomic sensors the Honeywell team has developed rely on a magneto-optic trap (MOT), which requires a three-dimensional arrangement of laser beams coming from different directions, precisely crossing at a point. To achieve this precise configuration without the use of lenses or mirrors, the researchers developed an integrated photonic chip that guides light around an “optical circuit”—which is analogous to the guiding of electrical signals in traditional computer chips. The photonic chip emits three large collimated beams of light in the proper three-dimensional arrangement to make a MOT. By combining these intersecting laser beams with a specialized set of compact magnetic field coils, Honeywell used this light source to trap rubidium atoms, and realize an advanced, miniature atomic clock.

Honeywell’s integrated photonic chip technology not only reduces the size, weight, and power of laser delivery systems, but also allows for batch fabrication of complex optical systems with reduced manufacturing cost.

Figure 2: Silicon chip with waveguides and gratings to create a 3D laser beam pattern. In the photo, the light-guiding channels glow from the light they are directing, and the invisible 3D beams coming out of the chip are indicated by a computer-rendered overlay. Source: Honeywell

Finally, a team from NASA’s Jet Propulsion Laboratory (JPL), with support from researchers at SRI International; University of California, Davis; and University of Illinois Urbana-Champaign, has demonstrated an experimental atomic clock capable of meeting ACES’ target metrics, while proving immune to temperature and environmental issues. Building off research that created the Deep Space Atomic Clock (DSAC), the team developed an ion-based approach to atom cooling that relies on ionized mercury and ultraviolet lamps instead of lasers. The JPL atomic clock showed an immunity of less than 1 part in 14 decimal places for 1 degree Celsius change. To put that in perspective, that is about 100x better than current CSACs. The use of mercury ions also provides more stability while making the technology less sensitive to magnetic fields and temperature changes.

Figure 3: This photo is of the ACES 10 cc package developed by researchers from NASA’s JPL. Source: NASA Jet Propulsion Laboratory

As evidenced by the NIST and Honeywell research, progress on the ACES program is generating new means of fabricating atomic clock technologies at wafer scale, which makes continued exploration more cost effective and less reliant on massive engineering endeavors. “Today, we are dealing with complicated optical systems that require massive amounts of engineering whenever you want to iterate on a design. The early progress made on ACES shows that there are viable options in development for doing this same thing without the massive engineering manpower or hefty costs associated with current approaches,” noted Burke.

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