Semiconductor laser generates a single wavelength at any power

The researchers used a perforated semiconductor membrane as a scalable

laser resonator. A plate with evenly spaced holes of the same size emits a single wavelength.

Engineers took as the basis of the devicea 200 nm thick indium gallium arsenide phosphide membrane. This semiconductor is used in fiber optics and telecommunication devices. Scientists engraved on the plate using lithography many holes of a fixed size and shape, located at the same distance from each other.

Photograph of the resonator surface. Source: Kante group, Berkeley Engineering

Unique properties of the created resonatorare based on the location and size of the holes, the researchers explain. The perforation is done in such a way as to create Dirac points. The phase of light propagating from one point to another is equal to the refractive index times the distance traveled. Since the refractive index is zero at the Dirac point, the light emitted from different parts of the semiconductor is exactly in phase and therefore optically the same.

“There were about 3,000 holes in the membrane in our study, but theoretically there could be a million or a billion, the result would be the same,” says study co-author Walid Redjem.

The singularity of the Dirac points forms a single-frequency beam. Source: Kante group, Berkeley Engineering

The researchers note that the increase in size andsingle-frequency laser power has been a problem in optics. Coherent directional light with a single wavelength begins to break down as the size of the laser cavity increases. The standard solution is to use external mechanisms, such as waveguides to amplify the beam. However, this approach increases the size of the instrument.

The new device does not require additional modifications. The authors of the development believe that it will find wide application in optical communications, technology and medicine.

Cover image: Kante group, Berkeley Engineering

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