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Scientists significantly extend the frequencies produced by miniature optical rulers

Spectral transformation to create ultra-wideband microcoms. The RW = 1117 nm micro ring resonator is excited by a 282 THz primary pump and a 192 THz synthetic pump. Primary comb generation with low primary pump power near the threshold. The comb spacing is equal to seven free spectral ranges (FSRs) and is reproduced around the synthetic pump and idler, emphasizing the mixing process between the two pumps and the main comb teeth. b As before, the generation of a primary comb at a higher primary pump output where the spectral spacing of the primary part matches the spectral spacing of the synthetic part, as expected by FWM-BS theory. c 2 Soliton state. The characteristic 8FSR modulation of the comb envelope is replicated near the synthesis pump. The inset shows a 2-soliton pulse array calculated by LLE. This will display the simulated comb envelope in red. Respect the FWM-BS phase matching condition and highlight the missing comb teeth in the main part (Δμ = -4). Missing parts of this part are converted into synthetic parts of the comb. d Single soliton state. The effect of the synthesis pump extends the comb bandwidth to 1.6 octaves and creates new DWs at both ends of the spectrum. The spectrum is consistent with the generalized LLE solution (red line) using the dual pump model and significantly exceeds the expected spectrum when only the primary pump is applied (green dashed line). The phase coherent nature of the comb is verified by beat note measurements using a narrow line width laser across the comb spectrum (four insets on the left). The noise floor for each measurement is indicated by a dashed line and is high in the O-band due to the use of an additional RF amplifier. The rightmost inset shows an LLE simulation of expected time domain operation with dual pumps (red) and only primary pumps applied (green). The horizontal bar at the bottom of the graph compares the span achieved here with the octave span DKS from the reference. 3, 32. Note that the low frequency part of the spectrum shows OSA artifacts at 146, 159, and.

Like vocal coaches who extend the octave range of opera singers, researchers at the National Institute of Standards and Technology (NIST) have expanded nearly two-thirds of the frequency range in which chip-scale devices can generate and measure vibrations. did. Exquisitely accurate light waves. The extended range of systems known as microring resonator frequency combs or microcoms can lead to better sensors for greenhouse gases and can also improve global navigation systems.


NIST’s Gregory Moille, including team leader Kartik Srinivasan, and his colleagues, along with collaborators at the Joint Quantum Institute (NIST-University of Maryland Research Partnership) and the University of Maryland, in the December 14, 2021 issue. Nature Communications..

The frequency comb works like an optical version of a ruler. Just as a ruler divided into hundreds of scales separated by a known distance measures objects of unknown length, frequency combs measure hundreds of lights of unknown frequency accurately. It features different ultra-sharp, evenly spaced frequency spikes (the tool is so named because the frequency combs resemble comb teeth).

Over the last two decades, scientists at NIST and other research institutes have used microcombs to build precision optical clocks, calibrate detectors that analyze starlight to search for planets beyond the solar system, and the environment. It has been shown that it can play an important role in the detection of trace gases in.

One type of microcomb that is widely studied at NIST is a small rectangular waveguide that is a channel that traps light waves, coupled to a ring-shaped resonator about 50 micrometers (1 / 1,000,000th of a meter) in diameter. It consists of tubes. The laser beam injected into the waveguide enters the microring resonator and runs around the ring.

Circulating light usually begins to change in amplitude and can form different patterns. However, with careful adjustment of the laser, the light in the microring forms solitons. This is an isolated wave pulse that maintains its shape as it travels around the ring.

NIST researchers have developed a method that nearly doubles the range of frequency combs produced by microring resonators by using two lasers instead of one. Credit: S. Kelley / NIST

Each time the soliton makes one round trip around the microring, a portion of the pulse is split into the waveguide. Immediately, the entire sequence of wave pulses fills the waveguide, and each wave is temporally separated from the adjacent wave at the same constant intervals, that is, the time it takes the soliton to orbit around the microring. .. A series of wave pulses in a waveguide corresponds to a single set of evenly spaced frequencies, forming the teeth of a frequency comb. The number and amplitude of teeth is primarily determined by the size and composition of the ring, as well as the power and frequency of the laser.

Recently, NIST scientists wondered what would happen if two lasers were used to create a microcomb, each producing light of a different frequency than one. They are, Soliton Light circulating in a microring resonator, the second laser is a replica of the original tooth set, but induces two new tooth sets or evenly spaced frequencies shifted to higher and lower frequencies. Did. The lower frequency set is in the infrared part of the spectrum and the other is at very high frequencies near visible light. The comb also retains the original teeth at near infrared frequencies.

The extended range of microcombs allows for numerous applications at different frequencies. The system is the first time researchers have produced a stable microcomb that connects such a wide range of light frequencies, Srinivasan said.

In addition, the team found that by changing the frequency of the second laser, it was easy to shift the new set of teeth to higher or lower frequencies, regardless of the shape or configuration of the microring resonator. This makes the system extremely versatile.

This feat allows a single microcomb to measure the characteristic vibrations of atoms and molecules containing contaminants. These vibrations emit and absorb light over a wide range of frequencies, increasing the sensitivity of the detector.

A wider range may also help subsequent efforts to stabilize Micro comb, Makes the scale remain fixed rather than slightly moved from the original set of colors.Enhanced stability could spur the development of portable opticals Atomic clock It’s accurate enough to be used outside the lab, leading to a more accurate and accurate navigation system, Moille said.


The new design of the “optical ruler” has the potential to revolutionize watches, telescopes and telecommunications.


For more information:
Gregory Moille et al, Ultra Wideband Car Microcomb with Soliton Spectral Transformation, Nature Communications (2021). DOI: 10.1038 / s41467-021-27469-0

Quote: Scientists have obtained a miniature optical ruler (February 23, 2022) from https: //phys.org/news/2022-02-scientists-greatly-frequencies-miniature-optic.html on February 23, 2022. Significantly expands the frequencies produced by (days)

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Scientists significantly extend the frequencies produced by miniature optical rulers

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