Berkeley Lab Develops Laser/Anti-Laser Device

Researchers at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) have developed a single device that acts both as a laser and an anti-laser. The scientists demonstrated both the laser and anti-laser functions at a frequency within the telecommunications band.

They reported their findings in a paper in the journal Nature Photonics. The findings may lay the groundwork for developing a new type of integrated device that can operate as a laser, a modulator, an amplifier, and an absorber or detector.

A coherent perfect absorber (CPA) or anti-laser reverses what a laser does. So, instead of strongly amplifying a beam of light, an anti-laser can completely absorb incoming coherent light beams.

Applications for anti-lasers, which Yale researchers first demonstrated five years ago, are still being explored. The researchers at Berkeley Lab speculate that because anti-laser can pick up weak coherent signals while in a “noisy” incoherent background, an anti-laser could be used as an extremely sensitive chemical or biological detector.

Also, the researchers said that a device that can incorporate both lasing and anti-lasing capabilities could become valuable in constructing photonic integrated circuits.

Nanofabrication technology produced the 824 repeating pairs of gain and loss materials that of the device, which measured just 200 micrometers long and 1.5 micrometers wide. In comparison, a single strand of human hair measures about 100 micrometers in diameter.

The gain material was fabricated with indium gallium arsenide phosphide (InGaAsP), a well-known amplifier material used in optical communications. The loss medium paired chromium with germanium. The repeating pattern formed a resonant system in which light bounces back and forth while building up the amplification or absorption magnitude.

Schematics show light input (green) entering opposite sides of a single device. When the phase of light input 1 is faster than that of input 2 (left panel), the gain medium dominates, resulting in lasing mode. When the phase of light input 1 is slower than input 2 (right panel) this results in anti-lasing mode. (Credit: Zi Jing Wong/UC Berkeley)

Schematics show light input (green) entering opposite sides of a single device. When the phase of light input 1 is faster than that of input 2 (left panel), the gain medium dominates, resulting in lasing mode. When the phase of light input 1 is slower than input 2 (right panel) this results in anti-lasing mode. (Credit: Zi Jing Wong/UC Berkeley)

The scientists noted that such a system requires parity-time symmetry for any net gain (light amplification) or net loss (light absorption) to occur.

Co-author Liang Feng, former postdoctoral researcher in Zhang’s Lab, and now an assistant professor of electrical engineering at the University at Buffalo stated, “The successful attainment of both lasing and anti-lasing within a single integrated device is a significant step towards the ultimate light control limit.”