The laser pointer that has been ubiquitous in modern life
Lasers and anti-lasers appear in the same device at the same time. It is conceivable that gathering opposing forces in one place is a very challenging thing, but in the field of optical science, researchers have just completed such an achievement. Scientists at Lawrence Berkeley National Laboratory (Berkeley Lab) of the Department of Energy created a single device for the first time, which can act as a laser pointer and an anti-laser at the same time, and they demonstrated these two opposites in the telecommunications frequency band. Function.
Their research results were reported in an article published in the journal. These findings laid the foundation for the development of a new class of integrated devices that can be used flexibly as lasers, amplifiers, modulators and detectors. .
In a single optical cavity, we have achieved coherent light amplification and light absorption at the same frequency. This is a counter-intuitive phenomenon because these two states are fundamentally contradictory," said the lead researcher of the study. He is a faculty scientist in the Materials Science Department of Berkeley Lab. "This is important for the high-speed modulation of optical pulses in optical communications.
The schematic below shows the input light (green) entering the opposite ends of a single device. When the phase of the input light 1 is faster than the phase of the input light 2, the gain medium is dominant, so that the coherent amplification of the incident light, or lasing mode, is obtained. When the phase of the input light 1 is slower than the phase of the input light 2, the lossy medium dominates, resulting in coherent absorption of the incident light beam, or the reverse lasing mode.
The concept of inverse green laser pointer or coherent perfect absorber is something that has only appeared in recent years and refers to a device that reverses what the laser does. In contrast to strongly amplified beams, anti-lasers can completely absorb the incident coherent beam. Although lasers are ubiquitous in modern life, the application of anti-lasers — first demonstrated by researchers at Yale University five years ago — is still being explored. Since the anti-laser can extract weak coherent signals from the "noisy" incoherent background light, it can be used as a very sensitive chemical or biological detector.
Researchers say that a device that can combine these two functions can become a valuable unit for constructing photonic integrated circuits. I have never imagined that light can be controlled arbitrarily between coherent amplification and coherent absorption as needed. The scientific community has been exploring this possibility," said the lead author of the paper, who is a member of the laboratory. A post-doctoral researcher. “This device may bring about modulation with great contrast without theoretical limits.
These researchers used advanced nanofabrication technology to fabricate 824 pairs of repetitive gain and loss materials to form this device. The device is 200 microns long and 1.5 microns wide. For comparison, the diameter of a human hair is about 100 microns. The gain medium is made of indium gallium arsenide phosphorus, which is a well-known material for optical communication amplifiers. Chromium pairs with germanium to form a lossy medium. Repeating this structure creates a resonant system in which light reflects back and forth, forming amplification or absorption.
If we pass light through such a gain-loss repetitive system, then an empirical guess is that the light will undergo equal amplification and absorption, and the intensity of the light will not change. However, this example is not about whether the system meets the parity-time symmetry condition, although parity-time symmetry is a key requirement in the device design. Parity-time symmetry is a concept evolved from quantum mechanics. In a symmetry operation, the position is flipped, as if the left hand becomes the right hand, or vice versa.