Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

An octave spanning chip-based optical ruler

08.08.2011
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
E-mail: tobias.kippenberg@epfl.ch
http://k-lab.epfl.ch/
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
E-mail: pascal.delhaye@mpq.mpg.de
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
E-mail: olivia.meyer-streng@mpq.mpg.de

Dr. Olivia Meyer-Streng | Max-Planck-Institut
Further information:
http://k-lab.epfl.ch/
http://www.mpq.mpg.de

More articles from Physics and Astronomy:

nachricht Astronomers find unexpected, dust-obscured star formation in distant galaxy
24.03.2017 | University of Massachusetts at Amherst

nachricht Gravitational wave kicks monster black hole out of galactic core
24.03.2017 | NASA/Goddard Space Flight Center

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: Giant Magnetic Fields in the Universe

Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.

The results will be published on March 22 in the journal „Astronomy & Astrophysics“.

Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...

Im Focus: Tracing down linear ubiquitination

Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.

Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...

Im Focus: Perovskite edges can be tuned for optoelectronic performance

Layered 2D material improves efficiency for solar cells and LEDs

In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...

Im Focus: Polymer-coated silicon nanosheets as alternative to graphene: A perfect team for nanoelectronics

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...

Im Focus: Researchers Imitate Molecular Crowding in Cells

Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to simulate these confined natural conditions in artificial vesicles for the first time. As reported in the academic journal Small, the results are offering better insight into the development of nanoreactors and artificial organelles.

Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

International Land Use Symposium ILUS 2017: Call for Abstracts and Registration open

20.03.2017 | Event News

CONNECT 2017: International congress on connective tissue

14.03.2017 | Event News

ICTM Conference: Turbine Construction between Big Data and Additive Manufacturing

07.03.2017 | Event News

 
Latest News

Northern oceans pumped CO2 into the atmosphere

27.03.2017 | Earth Sciences

Fingerprint' technique spots frog populations at risk from pollution

27.03.2017 | Life Sciences

Big data approach to predict protein structure

27.03.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>