Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


An octave spanning chip-based optical ruler

Scientists at MPQ develop octave-spanning frequency comb with a microresonator

More than a decade ago, the frequency comb technique was developed at the Max Planck In-stitute of Quantum Optics by Professor Theodor W. Hänsch. The new tool has stimulated fun-damental research as well as laser development and its applications because it gave rise to a major increase in the accuracy of measuring optical frequencies.

Octave spanning frequency comb generation in a microresonator. Panel (a) shows the ex-periment with a glass nano-fiber and a silicon chip with optical resonators. A scanning electron mi-croscope picture of a resonator is shown in panel (b). Panel (c) shows the optical spectrum of the frequency comb generated in such a microresonator seeded by a single frequency laser.

Already a couple of years ago, a team of scientists around Dr. Tobias Kippenberg, formerly Leader of the Max Planck Research Group “Laboratory of Photonics and Quantum Measurements” at MPQ, who has since then become Associate Professor at the Ecole Polytechnique Fédérale de Lausanne (EPFL), succeeded for the first time in generating optical frequency combs using chip-based quartz glass toroids with diameters on the micrometer scale.

Now the scientists made a big step further: their new microresonators produce light over a range of more than an octave and are at the same time precisely tunable (PRL 107, 063901, 1 August 2011). This achievement brings a variety of applications into reach, such as optical telecommunications or the precise calibration of spectrographs in astrophysics.

A frequency comb is a light source containing – similar to a rainbow – a large spectrum of colours. However, the frequencies are not continuously distributed. Instead, up to a million spectral lines are spaced in exactly the same distance. The superposition of this “comb” with another laser beam results in a pattern from which the unknown laser frequency can be determined with very high accuracy. The frequency comb developed by Prof. Hänsch is based on a mode-locking process in short-pulse lasers. This set-up consists of many optical components, even though it is made today relatively compact and commercially available. Indeed, Menlo System a spin-off company established by MPQ which is meanwhile marketing the frequency comb technology worldwide.

A couple of years ago, the group “Laboratory of Photonics and Quantum Measurements”, which was associated with the Laser Spectroscopy Division of Professor Hänsch, has succeeded in generating a frequency comb by means of a tiny microstructure, a toroidal glass resonator with a diameter of less than 100 micrometres. This was done in cooperation with Dr. Ronald Holzwarth from Menlo Sys-tems Ltd. and promises to radically reduce the size of frequency comb generators.

Using a “nanowire” made of glass the scientists couple light from a diode laser into this monolithic structure, where it is stored for a rather long time. This leads to extremely high light intensities inside the resonator, i.e. photon densities, which again produce nonlinear effects such as ‘four-wave mixing’ induced by the Kerr effect: two light quanta of equal energy are converted to two photons of which one light quantum has a higher energy, the other a lower energy than the original ones. The newly produced light fields can in turn interact with the original light fields, thereby producing new frequencies. From this cascade emerges a broad, discrete spectrum of frequencies. By optimizing the geometry of the toroid microresonator, Dr. Pascal Del’Haye (MPQ) and Tobias Herr (EPFL), doc-toral students at the referred experiment, have managed to compensate the effects of dispersion, such that the photon round-trip time inside the resonator remains the same for all light frequencies. Now the microresonators produce light over the range of more than an octave, from von 900 bis 2170 nm (near IR), for the first time. (As on the keyboard of a piano, the range of an octave corresponds to a doubling of the frequency.)

By raising the intensity of the light coupled into the resonator the frequencies of the comb can be shifted simultaneously. The higher intensities increase the temperature of the glass structure by up to 800 degree Celsius whereby the resonator is expanding and changing its index of refraction. Both effects lead to a shift of the comb lines towards lower frequencies, i.e. longer wavelengths. The broad range of frequencies as well as the tunability is an important pre-condition for self-referencing, where the lower range of the spectrum is doubled and compared to the upper part. Self-referencing is an important precondition for the use of frequency combs in metrology.

Also optical telecommunications will profit from the new tool. Whereas in the conventional fre-quency comb the lines are extremely close and of very low intensity, the spectral lines of the mono-lithic frequency comb have a separation of about 850 gigahertz and powers of the order of one milliwatt. This spacing and power level corresponds to the typical requirements for the “carriers” of the data channels in fibre-based optical communications. Tunability and broad range make the device also suitable for very precise calibration of spectrographs for astrophysics. Due to the large variety of possible applications many groups worldwide show interest in using the resonators for the miniaturi-zation of photonic devices. A number of other geometries and materials are investigated, e.g. pol-ished crystals, highly reflective fiber cavities and silicon structures based on computer-chip technol-ogy. [Olivia Meyer-Streng]

Prof. Tobias J. Kippenberg (PhD)
Ecole Polytechnique Fédérale de Lausanne (EPFL)
(Swiss Federal Institute of Technology Lausanne)
Associate Professor
Phone: + 41 21 69 34428 (CH) / +41795350016
Dr. Pascal Del‘Haye
Max-Planck-Institut für Quantenoptik
Hans-Kopfermann-Straße 1
85748 Garching
Phone: +49(0)89 / 32 905 286
Fax: +49(0)89 / 32 905 200
Max-Planck-Institut für Quantenoptik
Dr. Olivia Meyer-Streng
Press and Public Relations
Phone: +49(0)89 / 32 905 213
Fax: +49(0)89 / 32 905 200

Dr. Olivia Meyer-Streng | Max-Planck-Institut
Further information:

More articles from Physics and Astronomy:

nachricht New material for splitting water
19.06.2018 | American Institute of Physics

nachricht Carbon nanotube optics provide optical-based quantum cryptography and quantum computing
19.06.2018 | DOE/Los Alamos National Laboratory

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Overdosing on Calcium

Nano crystals impact stem cell fate during bone formation

Scientists from the University of Freiburg and the University of Basel identified a master regulator for bone regeneration. Prasad Shastri, Professor of...

Im Focus: AchemAsia 2019 will take place in Shanghai

Moving into its fourth decade, AchemAsia is setting out for new horizons: The International Expo and Innovation Forum for Sustainable Chemical Production will take place from 21-23 May 2019 in Shanghai, China. With an updated event profile, the eleventh edition focusses on topics that are especially relevant for the Chinese process industry, putting a strong emphasis on sustainability and innovation.

Founded in 1989 as a spin-off of ACHEMA to cater to the needs of China’s then developing industry, AchemAsia has since grown into a platform where the latest...

Im Focus: First real-time test of Li-Fi utilization for the industrial Internet of Things

The BMBF-funded OWICELLS project was successfully completed with a final presentation at the BMW plant in Munich. The presentation demonstrated a Li-Fi communication with a mobile robot, while the robot carried out usual production processes (welding, moving and testing parts) in a 5x5m² production cell. The robust, optical wireless transmission is based on spatial diversity; in other words, data is sent and received simultaneously by several LEDs and several photodiodes. The system can transmit data at more than 100 Mbit/s and five milliseconds latency.

Modern production technologies in the automobile industry must become more flexible in order to fulfil individual customer requirements.

Im Focus: Sharp images with flexible fibers

An international team of scientists has discovered a new way to transfer image information through multimodal fibers with almost no distortion - even if the fiber is bent. The results of the study, to which scientist from the Leibniz-Institute of Photonic Technology Jena (Leibniz IPHT) contributed, were published on 6thJune in the highly-cited journal Physical Review Letters.

Endoscopes allow doctors to see into a patient’s body like through a keyhole. Typically, the images are transmitted via a bundle of several hundreds of optical...

Im Focus: Photoexcited graphene puzzle solved

A boost for graphene-based light detectors

Light detection and control lies at the heart of many modern device applications, such as smartphone cameras. Using graphene as a light-sensitive material for...

All Focus news of the innovation-report >>>



Industry & Economy
Event News

Munich conference on asteroid detection, tracking and defense

13.06.2018 | Event News

2nd International Baltic Earth Conference in Denmark: “The Baltic Sea region in Transition”

08.06.2018 | Event News

ISEKI_Food 2018: Conference with Holistic View of Food Production

05.06.2018 | Event News

Latest News

Carbon nanotube optics provide optical-based quantum cryptography and quantum computing

19.06.2018 | Physics and Astronomy

How to track and trace a protein: Nanosensors monitor intracellular deliveries

19.06.2018 | Life Sciences

New material for splitting water

19.06.2018 | Physics and Astronomy

Science & Research
Overview of more VideoLinks >>>