The first laser based on the wave physics phenomenon called bound states in the continuum (BIC) has been developed. The technology could revolutionize the development of surface lasers, making them more compact and energy-efficient for communications and computing applications. The BIC lasers could also be developed as high-power lasers for industrial and defense applications.

BICs are waves that remain perfectly confined, or bound, in an open system. Conventional waves in an open system escape, but BICs defy this norm and stay localized; they do not escape despite having open pathways to do so. Previous research at UCSD demonstrated, at microwave frequencies, that BICs could be used to efficiently trap and store light to enable strong light-matter interaction.

Schematic of the BIC laser: a high-frequency laser beam (blue) powers the membrane to emit a laser beam at telecommunication frequency (red). (Kanté group/UC San Diego)

BIC lasers can be readily tuned to emit beams of different wavelengths — a useful feature for medical lasers made to precisely target cancer cells without damaging normal tissue. The lasers can also be made to emit beams with specially engineered shapes (spiral, donut, or bell curve), called vector beams, that could enable increasingly powerful computers and optical communication systems that can carry up to 10 times more information than existing ones.

Light sources are key components of optical data communications technology in cellphones, computers, and astronomy. The new kind of light source is more efficient than what is available today in terms of power consumption and speed.

The BIC laser is constructed from a thin semiconductor membrane made of indium, gallium, arsenic, and phosphorus. The membrane is structured as an array of nano-sized cylinders suspended in air. The cylinders are interconnected by a network of supporting bridges that provide mechanical stability to the device. By powering the membrane with a high-frequency laser beam, the BIC system was able to emit its own lower-frequency laser beam (at telecommunication frequency).

Surface lasing occurred with arrays as small as 8 × 8 particles. In comparison, the surface lasers that are widely used in data communications and high-precision sensing, called VCSELs (vertical-cavity surface-emitting lasers), need much larger (100 times) arrays and more power to achieve lasing. The VCSEL may one day be replaced by the BICSEL, or bound state in the continuum surface-emitting laser, which could lead to smaller devices that consume less power.

The array can also be scaled up in size to create high-power lasers for industrial and defense applications. The next step is to make BIC lasers that are electrically powered, rather than optically powered by another lase, enabling them to run off of a conventional battery.

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