Researchers boost cheap diode laser for precise measurements

November 07, 2018 // By Nick Flaherty
Researchers in Russia have developed a method for drastically narrowing the emission spectrum of an ordinary diode laser so that it can replace single-frequency lasers in compact test and monitoring equipment.

The study by researchers from the Russian Quantum Center (RQC), the Moscow Institute of Physics and Technology (MIPT), Lomonosov Moscow State University (MSU) and the Samsung R&D Institute Russia.

"This work has two main results," said the paper's lead author RQC Scientific Director Michael Gorodetsky, who is also an MSU professor. "First, it serves to show that you can make a cheap narrow-linewidth laser, which would be single-frequency yet highly efficient and compact. Secondly, the same system with virtually no modifications can be used for generating optical frequency combs. It can thus be the core component of a spectroscopic chemical analyzer."

The optical frequency comb technique underlies laser-based spectroscopy, generating optical radiation at a million extremely stable frequencies. It turned out that there is an easier way to generate frequency combs, which relies on optical microresonators. These are ring- or disk-shaped transparent components that use non-linear materials to transform laser radiation into a frequency comb, also referred to as a microcomb.

"Optical microresonators with whispering gallery modes were first proposed at MSU's Faculty of Physics in 1989. They offer a unique combination of submillimeter size and an immensely high quality factor," said MIPT doctoral student Nikolay Pavlov. "Microresonators open the way toward generating optical combs in a compact space and without using up much energy. Compact and inexpensive diode lasers are available for almost the entire optical spectrum. However, their natural linewidth and stability are insufficient for many prospective tasks. In this paper, we show that it is possible to effectively narrow down the wide spectrum of powerful multifrequency diode lasers, at almost no cost to power. The technique we 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."

The proposed design has many possible applications. One of them is in telecommunications, wh ere it would considerably improve the bandwidth of

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