Researchers make major dissipative Kerr soliton breakthrough

New research may lead to highly precise, power-efficient light measurement tools, driving advancements in various technology fields.
Christopher McFadden
This discovery could improve things like atomic clocks.

N. Phillips/NIST/Wikimedia Commons  

Researchers have discovered a way to improve optical frequency combs to measure light waves with much higher precision than previously accomplished. This could lead to the development and improvement of devices that require such precision, like atomic clocks. The researchers showed that dissipative Kerr solitons (DKSs) can create chip-based optical frequency combs with enough output power for use in optical atomic clocks and other practical applications.

More precise clocks

"Frequency combs are ubiquitous in metrology -- just like a ruler measures length, they let us measure optical frequency with great precision," explains Grégory Moille from the Joint Quantum Institute at NIST/University of Maryland. "Making them on chip helps us greatly reduce their power consumption, but also reduces the power in each comb tooth. This makes it hard to interface on-chip combs with another system like atomic frequency standards. We show that by simply carefully injecting another weak laser in the comb device; it lets us tune the system and therefore optimize the power in several comb teeth power by more than an order of magnitude," he added.

Optical frequency combs emit a continuous stream of short, closely spaced light pulses that contain millions of colors. These can be utilized to measure light waves as if they were radio waves. With this technology, atomic clocks, computers, and communications can be linked with optical waves that oscillate at frequencies 10,000 times higher than those found in electronics.

Typically, optical frequency combs are produced with mode-locked lasers, which are often limited to use in advanced scientific labs. However, there have been recent efforts to create optical frequency combs with compact microresonators based on DKSs. DKSs are "packets of lights" that depend on a double balance of nonlinearity and dispersion, along with dissipation and gain. While DKS-based combs require minimal energy, they have not, until now, generated sufficient output power for practical use.

To overcome this, the researchers in the new study utilized the recently proposed Kerr-induced synchronization of "Kerr solitons" with an external stable laser reference to generate optical frequency combs with greater power. This, they found out, leads to a significant boost of power on the opposite end of the comb spectrum in comparison to the reference laser.

To this end, the new research shows through both theoretical and experimental methods, that using an external reference pump at 193 THz can adjust the repetition rate of a comb that spans an octave. This adjustment allows for tuning of the phase-matching condition of the comb tooth at the dispersive wave, which optimizes its power. Additionally, they manage to observe a self-balancing effect, which is connected to the DKS's core robustness property. As a result, they were able to increase the power of the 388 THz comb tooth by more than 15 times.

Scratching the surface

"We are just scratching the surface of what optimization can be performed," explains Moille. "We have not reached the power limit of this optimization and hope to reach a power level compatible with interfacing our comb directly with other systems," he added.

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