System Bits: Dec. 31

Low signal loss waveguides
With the potential to enable a leap ahead in size reduction and performance, DARPA-funded researchers at UCSB and CalTech have developed new methods to integrate long coils of waveguides with low signal loss onto microchips—potentially enabling a leap ahead in size reduction and performance.

Long coils of optical waveguides—any structure that can guide light, like conventional optical fiber—can be used to create a time delay in the transmission of light. These delays are useful in military application ranging from small navigation sensors to wideband phased array radar and communication antennas and although optical fiber has extremely low signal loss, an advantage that enables the backbone of the global Internet, it is limited in certain photonic delay applications. Connecting fiber optics with microchip-scale photonic systems requires sensitive, labor-intensive assembly and a system with a large number of connections suffers from signal loss.

DARPA’s integrated Photonic Delay program created a new class of photonic waveguides with losses approaching that of optical fiber, built onto microchips and include up to 50 meters of coiled material that is used to delay light. Conventional fiber optic coils of the same length would be about the size of a small juice glass. These waveguides also employ modern silicon processing to achieve submicron precision and more efficient manufacturing. The result is a new component that is smaller and more precise than anything before in its class.

The ultra-low loss, true-time delay chip developed at UCSB is composed of silicon nitride. Selecting this material may allow for integration with a variety of devices and materials thereby reducing size, weight and power requirements of an overall system. UCSB researchers also demonstrated 3D waveguide stacking, enabling more waveguide length, and thus, longer photonic delays.

Researchers at CalTech had a different approach for a chip-scale waveguide using silicon oxide to construct the waveguide and demonstrated low loss over 27 meters.

Ultra-low loss, true-time delay chip developed at the University of California, Santa Barbara with four different delay lines. (Source: UCSB)

The results are firsts for optical waveguides with performance that is equal or superior to larger, fiber optic-based devices, the researchers asserted. Chip-scale waveguides, with smaller sizes and new integration possibilities promise advanced, compact military systems such as tactical gyroscopes that significantly outperform state-of-the-art MEMS devices with the same footprint.

Toward microrobots
The fluid movement of eukaryotic flagella is a highly sought-after capability in small-scale devices, such as microrobots but scientists have struggled to build a simple, controllable model that can recreate it, until now. Brandies University researchers have built the first viable computer model to generate flagella-like movement with man-made structures.

The model simplifies the motion of complex flagella using spherical self-propelled particles called colloids in a structure resembling a string of beads. The colloids exert pressure on themselves, causing the filament to beat. To make the model viable, the researchers had to figure out the proper strength of the colloids’ attachment. If the connections were too tight, the string would be stiff and unmoving; too loose, and it would be floppy and ineffective. Then they determined the length of the filament required for motion — too short or too long and it wouldn’t be able to propel anything.

After determining the strength and length of the filament, the team anchored one end of it, as if to a cell wall, and observed those graceful, beating motions on their computer model. They explained that because this system is so simple, and its construction so different from that of flagella, they should be able to elucidate the most fundamental features of flagella that give rise to and control motion. These features can be understood without having to unravel all 650 moving parts of a flagellum.

The research may pave the way to develop flagella-like microrobots to carry drugs to targeted cells or to create microfluidic devices that could pump and circulate fluid.