Optical Frequency Combs (2023)

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What do optical frequency combs do?

Optical frequency combs are specialized lasers that act like a ruler for light. They measure exact frequencies of light — from the invisible infrared and ultraviolet to visible red, yellow, green and blue light — quickly and accurately.

These Nobel Prize-winning devices fill an important technological gap. Optical frequency combs allow scientists to measure and control light waves as if they were radio waves. With optical frequency combs, technologies that employ radio and microwave frequencies — such as clocks, computers and communications — are now seamlessly connected to optical waves that oscillate at 10,000 times higher frequencies.

Optical frequency combs began as part of NIST scientists’ vision for better optical atomic clocks in the late 1990s. Today, NIST scientists are at the forefront of advancing these tools, and they have found uses beyond just timekeeping.

Optical Frequency Combs (1)

What a Comb Can Do

How are optical frequency combs used?

Timekeeping

Optical frequency combs have been revolutionary for atomic clocks and timekeeping. Optical atomic clocks mark the passage of time by counting the natural oscillation of atoms in the same way a grandfather clock counts the swings of a pendulum. These atoms oscillate about 500,000 billion times a second — a much higher frequency than standard microwave-based atomic clocks. The current electronic systems that are used to measure frequency for microwave-based atomic clocks simply can’t count the optical “ticks.”

Because the teeth of an optical frequency comb are evenly spaced and precise, the comb acts like the gears of a clock, taking the faster optical frequencies and dividing them down to the lower-frequency microwave signals used by electronics and current atomic clocks. This lets scientists link optical atomic clocks’ higher-frequency “ticks” to microwave-based clocks’ lower-frequency “ticks” and electronics used by present day computers and communications systems.

Optical Frequency Combs (2)

How frequency combs unite the EMF spectrum

With these “gears” carrying accurate signals between electronics, microwave-based tools and optical atomic clocks, scientists can use these powerful new clocks for faster, more accurate timekeeping systems. Optical atomic clocks may eventually redefine the second.

In order for these new clocks to be used for national and global timekeeping, scientists need to be able to compare signals from clocks across distances. Optical frequency combs can help achieve that too. NIST and JILA, a joint research institute of NIST and CU Boulder, used lidar to send time signals through the air, comparing two different kinds of atomic clocks.

(Video) Laser spectroscopy, part 7 – Optical frequency combs

Improved timekeeping systems are crucial in many technological applications, from stock trading to navigation. Global Positioning System (GPS) satellites and receivers send radio signals back and forth and use the timing of those signals to pinpoint a user’s location. GPS uses military time, and those clocks check their timing periodically with civilian clocks, like NIST’s optical atomic clocks and others like them around the world. Scientists hope to have optical atomic clocks on navigation satellites in the future, making the system even more precise and allowing GPS to pinpoint locations within centimeters.

Optical atomic clocks are also useful in the pursuit of quantum physics. By dividing time into incredibly small slices, scientists can use these clocks to measure previously undetectable changes, such as the gravitational red shift over short distance scales, the effect of gravity on the passage of time.

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Astronomy and cosmology

Advanced optical atomic clocks also allow scientists to study the constants of nature beyond our own planet. For example, with the help of optical frequency combs, NIST scientists are using these improved clocks to search for elusive dark matter.

Optical frequency combs also are helping scientists search for exoplanets around distant stars. By tracking the exact colors of light from these stars, they can look for a wobble in the motion of a star that would indicate the presence of an Earth-like planet orbiting the star.

Precise distance measurement

Optical frequency combs work over long distances. In 2013, NIST patented lidar, a light detecting and ranging system that utilizes optical frequency combs to measure the distance to an object by analyzing light reflected from it.

This is already being used in a few research applications. NIST’s fire research laboratory has used frequency combs to “see” through flames and identify melting objects. Frequency comb-based lidar has also been used to create 3D maps. Eventually, lidar using optical frequency combs could keep satellites and other space instruments flying in tight formations, acting as a single instrument.

Atmospheric science and greenhouse gases

Atoms and molecules can be identified by which frequencies of light they absorb. Since optical frequency combs generate millions of frequencies in short pulses, they can be used to quickly and efficiently study the quantity, structure and dynamics of various molecules and atoms.

This has many potential applications and is already being used to study pollution. Using optical frequency combs, scientists at JILA have studied short-lived molecules that link burning fossil fuels to air pollution. The structure and dynamics of large and complex molecules can also be probed by frequency combs.

Scientists are also working on using optical frequency combs to detect trace amounts of various molecules in gases. In 2019, scientists and engineers from NIST, University of Colorado Boulder, and LongPath Technologies developed a dual-comb, portable spectroscopy system to detect minute methane emissions from oil and gas fields.

Optical Frequency Combs (4)

Medical diagnostics

The optical frequency comb may have applications in medicine as well. Just as it can be used in chemistry applications, the comb could be used to detect trace molecular indicators of disease. Scientists at JILA have been experimenting with combs to create breathalyzers that detect disease.

How do optical frequency combs work?

Frequency combs measure an unknown optical frequency by measuring the repetition rate of a continuous train of light pulses — which lies in the larger, easy-to-measure radio frequency range.

Light encompasses a broad spectrum of colors, which travel in waves. Each of those colors of light — from the invisible infrared and ultraviolet to red, blue or yellow visible light — has a corresponding frequency, or the number of wave peaks that pass a fixed point every second.

Radio waves and microwaves also travel at the speed of light, but their peaks are much farther apart, allowing modern electronics to count and track them easily.

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Optical frequency combs emit a continuous train of very brief, closely spaced pulses of light containing a million different colors, spanning from the invisible infrared through the visible and into the ultraviolet spectrum.

Thanks to a technique called “mode locking,” all of the frequencies in each pulse start in phase, in sync with each other.

The result resembles the teeth of a comb, separating each frequency into a distinct spike — hence the name of the device. The spacing of those teeth is very fine and exactly even, and they act like ticks on a ruler to measure light emitted by stars, atoms, other lasers, etc. with extreme precision and accuracy.

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How were optical frequency combs created?

While they may sound simple, optical frequency combs are the result of decades of research and innovation, including significant contributions from NIST.

Physicists had been toying with the idea of this specialized laser since the 1970s, when Theodor Hänsch of the Max Planck Institute for Quantum Optics in Germany proposed a model for the first optical frequency comb while he was at Stanford University. Scientists knew that continuous lasers could only produce one color of light, but pulsed lasers could generate multiple colors. The shorter the pulse, the more frequencies the laser could produce.

Scientists needed to know the spacing between the “teeth” — the individual frequencies of light — of the comb. This required mode locking lasers. Mode locking forces all the colors in each pulse to start out in phase with each other.

(Video) Fundamentals of frequency combs: What they are and how they work

In the mid-1990s, lasers made with titanium-doped sapphire crystals could produce these synchronized frequencies in femtoseconds — millionth of a billionth of a second pulses.

Optical Frequency Combs (7)

Scientists also needed to calibrate the comb, to adjust it to a known frequency. Calibrating the comb would determine the offset frequency, or where the “ticks” on the comb start in an absolute sense. Hänsch realized that the best way to do that was to get the comb to produce an octave of frequencies, where the highest frequency was at least double the lowest frequency. Interfering a frequency with its double — called “self-referencing” — let scientists determine each frequency exactly.

That wasn’t possible until a team of scientists at Bell Laboratories created a hair-thin optical fiber that could deliver more than an octave range of frequencies. This was a crucial development for optical frequency combs, and the final piece of the puzzle. With this optical fiber, Jan Hall and his colleagues at JILA could develop the self-referencing technique they needed in 1999. They were the first to compare the operation of multiple femtosecond frequency combs, thereby demonstrating reproducibility.

Hall and his team of physicists at JILA, including Steven Cundiff, Scott Diddams, David Jones and Jun Ye, developed several other techniques that pushed the optical frequency comb closer to reality. In the late 1990s, the team developed a calibration system for the femtosecond laser, creating controllable, well-defined pulses containing thousands of colors. They had also improved stabilization for the laser, making it steady. In 2005, Hall and Hänsch shared part of the Nobel Prize in Physics for their contributions to the optical frequency comb.

What’s next for optical frequency combs?

Since 1999, NIST and JILA scientists have rapidly advanced the comb, and are still at the forefront of optical frequency comb advancement and innovation. Today’s optical frequency combs span a greater range of electromagnetic frequencies than their earlier counterparts, from the deep infrared into the extreme ultraviolet. The ultraviolet comb can one day be used to drive transitions in the nucleus of atoms, which would unlock new possibilities for clocks and spectroscopy to study the nano world.

Optical Frequency Combs (8)

Fiber laser frequency combs were the next significant advance in optical frequency combs. NIST and JILA scientists contributed significantly to creating and refining these combs. Using common fiber components from telecommunications, these combs can operate continuously and are more compact than the original optical frequency comb. This makes them “workhorses” for metrology. They are currently used for numerous experiments (including clocks) in NIST and other laboratories, and in field applications like lidar and the aerospace industry. Fiber laser frequency combs are also being considered and tested to go into space. NIST scientists and engineers are continually improving fiber laser combs’ performance, power and durability to use in new applications and environments.

While many frequency combs currently are about the size of a shoebox and are widely available for use in and outside of laboratories, scientists have been working diligently to shrink them. Scientists have been working to produce optical frequency combs so small they can fit on a microchip.

Many scientists hope that if frequency combs can fit on a microchip, they can have even greater commercial applications. Microcombs have the potential to improve communications systems, particularly within data centers and other high performance computing systems. The spectroscopy power of optical frequency comb could be incorporated into smartphones and wearable technology to monitor health.

Those applications are far in the future, however. Currently microcombs require tools outside of the chip to operate, such as power supplies, amplifiers and pump lasers. Many of these parts have been miniaturized, but integrating them all onto a single chip is very challenging. But perhaps the greatest hurdle to overcome is making these microcombs self-referencing, which is necessary to make the combs accurate.

Research is making progress to overcome those hurdles. Even if a complete comb-on-a-chip is never realized, microcombs are already finding uses in research. With miniature dual frequency combs, NIST has already developed a chip-scale atomic clock. Scientists at NIST and their collaborators will continue to explore the vast potential for microcombs, fiber laser frequency combs and optical frequency combs.

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FAQs

How does an optical frequency comb work? ›

How do optical frequency combs work? Frequency combs measure an unknown optical frequency by measuring the repetition rate of a continuous train of light pulses — which lies in the larger, easy-to-measure radio frequency range. Light encompasses a broad spectrum of colors, which travel in waves.

What is frequency comb spectroscopy? ›

A laser frequency comb is a broad spectrum composed of equidistant narrow lines. Initially invented for frequency metrology, such combs enable new approaches to spectroscopy over broad spectral bandwidths, of particular relevance to molecules.

How do I make a frequency comb? ›

Frequency combs can be generated by a number of mechanisms, including periodic modulation (in amplitude and/or phase) of a continuous-wave laser, four-wave mixing in nonlinear media, or stabilization of the pulse train generated by a mode-locked laser.

What is optical frequency? ›

The optical frequency ν expresses the number of wave cycles per unit time. Also commonly used in quantum mechanics is the circular frequency ω = 2πν (radians per unit time), in terms of which the photon energy is E = ℏω where ℏ = h/2π.

What is a high frequency comb? ›

The high-frequency hair treatment machine is a transparent rod-like tool with two different removable knobs or combs that generate electrical stimulation at a frequency of 250,000 Hz when it touches the scalp. A glass bulb is fixed to the high-frequency rod during treatment to expose the scalp to high-frequency rays.

What is a Kerr soliton? ›

Main. A dissipative Kerr soliton is a self-organized optical wave defined by its ability to propagate through a dispersive, nonlinear and lossy medium while preserving its shape and amplitude1,2. The spreading of the wave packet due to dispersion is balanced by self-phase modulation induced by the Kerr effect.

What is a comb laser? ›

The comb-laser is a light source with a spectrum consisting of equidistant lines, each corresponding to one longitudinal cavity mode. The emitted spectrum also shares one singular frequency.

What is a femtosecond comb? ›

The resulting spectrum consists of a comb of sharp spectral lines with well-defined frequencies. These new techniques and capabilities are generally known as "femtosecond comb technology." They have had dramatic impact on the diverse fields of precision measurement and extreme nonlinear optical physics.

What is Microcomb? ›

A microcomb is a photonic device capable of generating a myriad of optical frequencies on a tiny cavity known as microresonator. The frequencies are uniformly distributed, and the device can be used to measure or generate frequencies with extreme precision.

How do you measure optical frequency? ›

The optical frequency can be calculated as the vacuum velocity of light divided by the vacuum wavelength: ν = c / λ.

What frequency is a laser? ›

The laser current and the LO tuning voltage are modulated at a low frequency (500 Hz–30 kHz), and the photodetector voltage is demodulated at this frequency.

What is the range of optical spectrum? ›

The optical spectrum is generally defined to encompass electromagnetic radiation with wavelengths in the range from 10 nm to 103 μm, or frequencies in the range from 300 GHz to 3000 THz (Fig. 1).

Can I use high-frequency everyday? ›

A high-frequency machine can be used daily as it is a very safe and non-invasive procedure with no side effects if responsible precautions are being exercised. It is a beneficial treatment that caters to all skin types and addresses multiple skin concerns ranging from acne to wrinkles and even hair loss.

What does high-frequency comb do for hair? ›

The tingling and the vibration from high frequency improves the blood circulation in the scalp and helps revitalizing the dormant hair follicles. This leads to better hair growth, controls hair loss, helps with dandruff issues as well.

How often can you use high-frequency on your face? ›

For the best result, a series of high-frequency services — 3 to 6 is recommended. These initial treatments can be spaced one week apart, treatments can continue on a monthly basis for the best maintenance.

Do laser combs work? ›

You may have heard that laser combs, brushes, hoods, and caps can help halt hair loss. The theory is that when hair follicles absorb laser light at a certain level, it stimulates hair to grow. But there's not enough evidence that any of these devices restore hair or prevent balding.

How do you use a laser comb for hair growth? ›

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How fast is a femtosecond? ›

(A femtosecond is equal to one quadrillionth of a second.)

HOW DOES A femtosecond laser work? ›

Each pulse of the laser generates free electrons and ionized molecules leading to formation of microscopic gas bubbles dissipating into surrounding tissue. Multiple pulses are applied next to each other to create a cleavage plane and ultimately the LASIK flap. Suction is then released.

What is a soliton Microcomb? ›

Abstract. Soliton microcombs—phase-locked microcavity frequency combs—have become the foundation of several classical technologies in integrated photonics, including spectroscopy, LiDAR and optical computing.

What is Gillette Microcomb? ›

Gillette's most advanced blade cartridges, Fusion5 ProGlide and Fusion5 ProShield, feature a Microcomb, a line of ports that help feed the hairs through, and present them in an upright fashion, ready for the blades to do their job.

What frequency is the speed of light? ›

Frequency, Wavelength, and the Speed of Light - YouTube

How do you find energy from frequency? ›

How to Convert Energy to Frequency - YouTube

How do you go from wavelength to frequency? ›

How to Convert Wavelength to Frequency - YouTube

What is a Class 4 laser? ›

Class 4 is the highest class in terms of laser hazards. If you're within the hazard zone, you're exposed to severe eye and skin injuries. In addition, combustible materials shouldn't be in the laser's surroundings to avoid fire hazards. Diffuse reflections of class 4 lasers are also hazardous.

How far can laser beam travel? ›

Factors like cloud coverage, fog, and if you're at a high point of elevation should be considered, but as a basic rule, you can expect over 10 miles of visible distance on green 200mW+ lasers and 1,000mW+ blue lasers.

What color has the highest frequency? ›

What colour has the highest frequency?
  • Violet colour light has the highest frequency.
  • The frequency of violet colour light is. 5 × 10 14 Hz .

What frequency is UV light? ›

The UV region covers the wavelength range 100-400 nm and is divided into three bands: UVA (315-400 nm) UVB (280-315 nm) UVC (100-280 nm).

How many frequencies are there? ›

Today, civilian radio signals populate the radio spectrum in eight frequency bands, ranging from very low frequency (VLF), starting at 3 kilohertz, and extending to extremely high frequency (EHF),…

What is an optical signal? ›

Optical signal is an electromagnetic signal. It has electric and magnetic fields that are orthogonal to each other. Typically, the frequency of this EM wave is extremely high (in the order of THz). Therefore, it is more convenient to. measure it in terms of wavelength.

What is bandwidth in optical fiber? ›

Bandwidth refers to the amount of data you can transfer in a unit of time, as well as the range of frequencies used to transmit the data. Fiber-optic bandwidth is high both because of the speed with which data can be transmitted and the range of frequencies over which data can travel without attenuation.

What is the microwave frequency range? ›

Microwave frequencies range between 109 Hz (1 GHz) to 1000 GHz with respective wavelengths of 30 to 0.03 cm. Within this spectral domain are a number of communication systems applications that are important in both the military and civilian sectors.

Which optical Fibre is used for long distance communication? ›

Single Mode fibers are used for high speed data transmission over long distances. They are less susceptible to attenuation than multimode fibers.

How do you make an optical signal? ›

Two techniques, know as (a) direct modulation and (b) external modulation, can be used to generate the corresponding optical bit stream.

How do optical signals work? ›

Fiber-optic cables transmit data via fast-traveling pulses of light. Another layer of glass, called “cladding,” is wrapped around the central fiber and causes light to repeatedly bounce off the walls of the cable rather than leak out at the edges, enabling the single to go farther without attenuation.

How does optical communication work? ›

An optical communication system uses a transmitter, which encodes a message into an optical signal, a channel, which carries the signal to its destination, and a receiver, which reproduces the message from the received optical signal.

How many MHz is fiber optic cable? ›

Increased bandwidth: The high signal bandwidth of optical fiber provides a significantly greater information-carrying capacity. Typical bandwidths for multimode fibers are between 200 and 600 MHz.km, and > 10 GHz.km for singlemode fibers. Typical values for electrical conductors are 10 to 25 MHz.km.

What limits the optical frequencies used in fiber? ›

Bandwidth Limitations

The mechanism that limits a fiber's bandwidth is known as dispersion. Dispersion is the spreading of the optical pulses as they travel down the fiber. The result is that pulses then begin to spread into one another and the symbols become indistinguishable.

Which cable has highest bandwidth? ›

Since Fiber Optic Cable has the highest bandwidth. Support Teachoo in making more (and better content) - Monthly, 6 monthly, yearly packs available!

What frequency is xray? ›

X-ray, electromagnetic radiation of extremely short wavelength and high frequency, with wavelengths ranging from about 108 to 1012 metre and corresponding frequencies from about 1016 to 1020 hertz (Hz).

Is 5G a microwave? ›

Technically speaking, 5G radiation is the same as microwave radiation. Microwaves have a frequency between 3GHz to 30GHz; the same range of frequencies used by 5G technology.

Can microwaves go through walls? ›

The microwave signals bounce off objects and return real-time images to a screen and can even penetrate concrete walls, though with limited ability.

How far can a fiber optic signal travel? ›

Modern fiber optic cables can carry a signal quite a distance -- perhaps 60 miles (100 km).

What are the 2 types of fiber optic cable? ›

There are two types of fibre optic cables – multimode and single-mode. Multimode optical fibre or OFC is capable of carrying multiple light rays (modes) at the same time as it has varying optical properties at the core. Single-mode fibre has a much smaller core size (9 microns).

What are the 3 basic components of an optic fiber system? ›

The three basic elements of a fiber optic cable are the core, the cladding and the coating. Core: This is the light transmission area of the fiber, either glass or plastic. The larger the core, the more light that will be transmitted into the fiber.

Videos

1. What a Comb Can Do
(National Institute of Standards and Technology)
2. Menlo Systems' FC1500-ULN Optical Frequency Comb
(Menlo Systems)
3. Frequency combs... The lab of Prof. Tobias Kippenberg
(EPFL School of Engineering)
4. Making a Mini Laser Frequency Comb in Minutes
(National Institute of Standards and Technology)
5. Why would I need an optical frequency comb? - Menlo Systems webinar in Chinese language
(Menlo Systems)
6. DLS: Nathalie Picqué - Frequency Comb Interferometry and Spectroscopy
(MPI for the Science of Light)
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