A group of researchers from the Russian Quantum Center (RQC), the Moscow Institute of Physics and Technology (MIPT), Lomonosov Moscow State University (MSU), and Samsung R&D Institute Russia have developed a method for drastically narrowing the emission spectrum of an ordinary diode laser, like that in a laser pointer. This makes their device a useful replacement for the more complex and expensive single-frequency lasers.

Now  not any laser can be used to pump optical frequency combs in a microresonator. The laser needs to be both powerful and monochromatic. The latter means that the light it emits has to fall into a very narrow frequency band. The most common and cheap lasers nowadays are diode lasers. Although they are compact and convenient, in spectroscopy they fall short of more complex and expensive devices. The reason is that diode lasers are not sufficiently monochromatic: the radiation they emit is “smeared” across a 10-nanometer band.

The researchers made laser light more monochromatic, they used the very microresonators that generate optical frequency combs. That way they managed to retain nearly the same laser power and size — the microresonator is mere millimeters across – while also increasing monochromaticity by a factor of almost 1 billion. That is, the transmission band is narrowed down to attometers – billionths of a billionth of a meter – and an optical frequency comb is generated, if required.

Now compact and inexpensive diode lasers are available for almost the entire optical spectrum, but their natural linewidth and stability are insufficient for many prospective tasks. However according to this research that it is possible to effectively narrow down the wide spectrum of powerful multifrequency diode lasers, at almost no cost to power. The technique the scientists employ involves using a microresonator as an external resonator to lock the laser diode frequency. In this system, the microresonator can both narrow the linewidth and generate the optical frequency comb.

Where is the money?

In 2017, the global market for diode lasers reached $ 7 billion and the total laser diode market is expected to reach USD 11.94 Billion by 2020, at a CAGR of about 13.0%. Optical storage and communication are the largest segments, accounting for the majority of the global share. Region-wise, Asia-Pacific represents one of the leading market. Specifically this invention has many possible applications. Except eye surgery, laser sights, and fiber optic communication, one of the key uses of lasers is spectroscopy, which measures the precise chemical composition of virtually anything. Due to the compactness of new technology it could be integrated into smartphones or watches. Also is in telecommunications, where it would considerably improve the bandwidth of fiber optic networks by increasing the number of channels. Another sphere that would benefit is the design of sensors, such as reflectometers used as the basis of security and monitoring systems. For example, if a fiber optic cable runs along a bridge or an oil pipeline, the light in the cable will respond to the slightest disturbances or variations in the geometry of the object, pinpointing potential problems. Laser frequency combs can also be used for satellite navigation systems, in lidars, or optical radars, which are installed on self-driving cars, and even in astrophysics — to search for exoplanets using the radial velocity method.

The techer: Michael Gorodetsky

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