Monthly Archives: June 2018

Frequency scanning optoelectronic oscillator

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Post by Ming Li, commissioned by Heather Partner

The original paper in Nature Communications can be read here.

Radar and microwave communication systems have been invented many decades ago, but are still a growing area of research. For example, it is important for modern communication systems to be able to create microwave signals with fast-varying frequencies, called chirps. Optoelectronic oscillators are one way to produce ultra-low-noise microwave signals, but using them to produce a fast-varying signal with high quality is difficult, because a cavity-like component is used to reduce noise within these oscillators, and when the frequency is changed it takes time for a new low-noise frequency signal to build up in the cavity. In work published last month, we showed it is possible to have many frequencies oscillating in the system at once, so that the frequency can be changed rapidly without waiting for this build-up time. These simultaneous oscillations, all with locked phases, are made possible in a scheme known as Fourier-domain mode locking, which was previously applied to optical signals in lasers, but in this work is applied to microwaves using an optoelectronic oscillator .

An optoelectronic oscillator is like a laser, except that it has an optoelectronic cavity rather than a pure optical cavity. Although frequency-tunable optoelectronic oscillators have been widely studied, it is still a challenge to achieve continuous frequency scanning. Following the demonstration of frequency scanning lasers based on the Fourier domain mode locking technique in recent years, we wondered if it would be appropriate to extend this mode-locking principle to an optoelectronic oscillator.

In order to apply this technique to an optoelectronic oscillator, we needed a filter that could scan the selected frequency very rapidly — faster than what is made possible by most electrical schemes — so we decided to employ a microwave photonics solution that could perform faster tuning than electrical solutions.

One of the research interests of our group is semiconductor lasers. It is known that the lasing frequency of certain kinds of semiconductor lasers can be tuned by changing the driving current in a fast way. Fortunately, the passband of a microwave photonics filter based on phase-modulation to intensity-modulation conversion is related to the lasing frequency of the signal laser. Thus we achieved a fast frequency scanning microwave photonics filter by sweeping the frequency of the signal laser. Continuous frequency scanning microwave waveforms with very large time-bandwidth product are generated based on a Fourier domain mode locked optoelectronic oscillator. We run simulations that show that a Fourier domain mode locked optoelectronic oscillator oscillates in the same way as a conventional single-mode optoelectronic oscillator that uses the same optical and electronic components, except that the energy is shared by the many oscillation modes.

The employment of a Fourier domain mode locking technique in an optoelectronic oscillator provides an effective solution to generate frequency scanning microwave signals with large time-bandwidth product, which can find applications in radar and communication systems.

Ming Li

Reference: Hao T. et al, Breaking the limitation of mode building time in an optoelectronic oscillator. Nat. Commun. 9, 1839 (2018)

Built on instability 

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Post by Daniel Rayneau-Kirkhope and Marcelo Azevedo Dias

Built-in motion

From hierarchical architectures to complex composites, nature’s inventive use of geometry yields remarkable functionality from some rather unremarkable construction materials. This same control of geometry alongside a mastery of mechanics is used to transform elastic ‘failure’ into a crucial ingredient in the inner working of plants and organisms. Nature employs elastic instability so that large-scale motions can be triggered by the smallest and most specific stimuli. The Venus flytrap is perhaps the best-known example of this design philosophy — swelling induces an elastic instability that allows its leaves to snap between two stable configurations [1]. Using this snap-through behaviour, the plant moves quickly to capture its prey, allowing for the slow process of digestion to begin. Bacteria exhibit another beautiful example of this design paradigm, whereby their flagella, which are used to create thrust, buckle into a secondary configuration allowing the bacteria to control direction [2].

It is only recently that designers have started to use loss of structural stability in a similar manner. From merely being a mode of failure, buckling has become an increasingly well-trodden route to introducing novel functionality in the design of man-made structures and materials on many different length scales. This transition in perspective has been encapsulated as a move from ‘buckliphobia’ to ‘buckliphilia’ [3].

A powerful example of this paradigm is the use of buckling to turn simple geometries into mechanical machines: work in Physical Review Letters recently demonstrated that the buckling-unbuckling transitions in a hollow spherical shell can be used to create thrust in spherical swimmers [5]. It is well known that a spherical shell will buckle into a new geometry when the internal and external pressures are sufficiently different; as this deformation is elastic, the structure can return to its initial configuration when the pressure differential is removed. It was found that the asymmetry of geometries in the process of buckling and unbuckling allows for a net thrust to be created by cycling through these geometries while the structure is immersed in liquid. Continue reading →

DIY science: open source and low-cost instruments

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Post by Michael Paolillo.

Without hardware there is no science. Equipment, reagents and consumables are all paramount for the execution of experiments, collection of new data and generation of new knowledge. Coupled with the movement for open science, many groups and initiatives are pushing to make Open Science Hardware the new norm in labs worldwide. We interviewed one of the founders of one such initiative, Prometheus Science, that is working to develop easily accessible and usable open science hardware starting from published academic research.

Can you introduce yourself and tell me what are Prometheus‘ goals as a company?
I am André Maia Chagas and I have been with Prometheus since the first tinkering phases. I work on this project with Dr. Maira Bertolessi. Together, we aim to increase the availability of science and education tools by creating affordable, open-source, scientific-grade equipment. We are heavily involved in the open-source and do-it-yourself movements. We are proud to say that our product, the FlyPi, can now be found across the world in more than 10 countries, such as Chile, Argentina, Nigeria, USA, Sweden, France and Germany.

Picture courtesy of Pierre Padilla

You mentioned the FlyPi, what is that?
The FlyPi is our ‘proof of principle’ product, started as a collaboration with the NGO Trend in Africa. It is an open-source compact modular imaging system built out of 3D-printable parts and off-the-shelf electronic components. It is highly modular, so it can be adapted to unique experimental conditions. We have published work demonstrating that the FlyPi can be used for diagnostics and state-of-the art methods in neuroscience, such as optogenetics, calcium imaging, behavioural tracking and fluorescence imaging. As far as the price goes, even after building all the modules, it is still 10−20 times cheaper than traditional systems.

Tell me more about the open-source movement.
Well, the open-source movement started a while ago, mainly with software. The basic idea is that all plans/blueprints describing a piece of software, a protocol, a recipe or a piece of laboratory equipment are made freely available for people to comment, share, modify, improve and customize. This leads to the creation of communities where everyone can build off each other’s ideas and creations. We have held workshops in various countries in Europe and Africa to teach people how to build and use the FlyPi. We also focus on showing people how to use the available open-source technology out there to build their own scientific equipment. It has been an inspiring experience to see how access to a dynamic and powerful new tool like the FlyPi can transform a community and inspire a group of young scientists. We believe that by empowering people with these scientific tools we can increase access to science education and improve the way research is done. For example, we now have an online forum consisting of people from around the world who are develop tools to improve upon the FlyPi’s design.

Can you tell us about what your plans are now?
Of course. There are a lot of published scientific papers describing new open-source equipment, but  normally the researchers who publish the articles are not interested in bringing the tools to a wider market. This is due mostly to the large time commitment and to the fact that academics’ main concern is to do more research. This is a problem, since many people do not have the necessary skills to build these tools from the original blueprints, or have time to spend doing so. This is what we at Prometheus want to do next. We aim to identify interesting open-source equipment described in the literature and to work with the researchers to find a way to bring their designs to market. Researchers interested in bringing their designs to a wider audience can contact us directly at andre[at]prometheus-science.com.

Where can we learn how to get involved with Prometheus?
You can find us at prometheus-science.com and we welcome conversations with open arms on our forum. Come check us out!

Michael Paolillo is a PhD student in Biochemistry and Neuroscience in Tübingen, Germany and he is passionate about science communication. He also created the website Neuromag.net, a science communications website that accepts interesting articles about science around the world.

Picture courtesy of Aga Pokrywka

Spreading the love of light

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Post by Nina Meinzer and Heather Partner

If you have been following this blog for the last few weeks you will already know that some of us at Nature Research really love the science of everything light and its applications. But we didn’t want to stop at talking about different wavelength ranges on the internet, we also wanted to go out there and talk to people directly; and this being the International Day of Light (IDL), we didn’t limit our outreach events to only one country either.

Enlightening the next generation

In London, we went on a journey to the (for us editors) fairly undiscovered country of schools outreach. Thankfully, we found a great partner in UCL who soon took the lead in organising the lectures and the hands-on science stations.

The three short lectures nicely showcased the interdisciplinarity of the IDL. For the first one Andrea Sella joined us from the chemistry department and, after asking the house lights in the lecture theatre to be turned down completely for a moment, talked about how light is generated by fluorescence. But instead of reaching into the chemicals cabinet, he reached into the kitchen cupboard and demonstrated fluorescence from olive oil, chlorophyll (extracted from greens) and even Marmite. The archaeologists Charlotte Friersen and Anne de Vareilles then recapped a million years of humans controlling light, which until the late 19th century meant light from fire. Finally, we delved underwater with Danbee Kim to learn about the vision and the variable colouring of cuttlefish, who can see polarization and whose skin pattern shows their success in hunting shrimp.

Of course, 240 11- to 13-year-olds won’t sit in lectures for a whole day, and science isn’t that much about listening to other people telling facts anyway. The lectures were therefore embedded in two interactive sessions where the students could get more involved in a range of demonstrations: changing the colour of an LED to one of their choice, learning about spectroscopy and its uses for astronomy, getting their brain imaged while doing some maths, and playing with reflection, diffraction and polarization (among other things). Here, they could also speak to active scientist and — unknown to them — a few of our editors who revisited their own research days by helping out on a station. The students also found out that they could get more involved with science themselves in one of the many citizen science projects at UCL.

The day was an enormous success and both the teachers and students told us that they enjoyed themselves greatly and at the same time learned a lot. For us volunteers, seeing the fascination on their faces when they heard about some of the fun and interesting things scientist can do with light, was the best reward we could have wished for.

Bright lights, bright people

Volkhard Kempter — True Lite Standard II (1998) and Don’t look now! – 50 Hz (2017)

In Berlin, we celebrated the Day of Light with an evening at the Springer Nature building. The main event was a public lecture A Closer Look: Seeing atoms with a Laser by Professor Oliver Benson of the Humboldt University of Berlin. He shared his knowledge about lasers with us by first discussing some of the history of their development and the basic concepts behind coherent light. He went on to explain how we use lasers to see the basic pieces of matter — atoms and molecules — including an acoustic analogue demonstration of how monochromatic waves can be coupled resonantly into an atom. Finally, during the questions, Professor Benson shared his views about which future technologies could become as influential as the laser.

As a pre-programme, 5 PhD students met our challenge for them to describe their PhD projects to the audience in 3 minutes each, which as one organiser pointed out, is equivalent to reducing the novel War and Peace to a few words. From research on magnetic memories, biological imaging and flexible displays to measuring gravity and recycling plastic — all using light as a key ingredient — the students managed to explain the essence of their work in only a few minutes. The most popular pitch, selected by the audience via smartphone voting, was Juggling atoms to measure gravity presented by Bastian Leykauf of the Humboldt University of Berlin. As a thank you, all speakers received the very fitting memoir of Theodore Maiman.

Light is not only a topic of science; it also influences our daily lives and culture. To complement the scientific programme, through the Centre for International Light Art in Unna, Germany we joined forces with an artist, Volkhard Kempter, based in Berlin. His work uses light and darkness, and the question of how one evokes the other, as a central element. He brought two installations to our venue for the event: True Light Standard II, a circle of irregularly flashing fluorescent tubes facing inward to form a flickering, very bright source which attracts attention, but is too bright to look into, and Don’t look now! – 50 Hz, a photomontage of 6 different states that a fluorescent tube goes through while being switched on, that we wouldn’t usually notice in the brief moment it takes for the light to arise. These displays provided an opportunity to contemplate how pervasive artificial light is in our lives, which we hope our guests took home with them after they left.