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New Method to Develop MOF-Based All-Optical Switch

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May 19 2020

Globally, researchers are facing the task of producing optical switches. Such optical devices will allow data to be transmitted in binary code through light, which, in the days to come, will prove handy for developing extremely fast optical memory cells.

With the help of a femtosecond laser, ITMO University researchers have demonstrated the development of an all-optical switch based on a metal-organic framework (MOF). The MOF can be produced in vitro and is often used in chemistry for absorbing gases. The study has been published in the Angewandte Chemie journal.

Throughout the world, programmers, engineers, and physicists are increasingly discussing the potential of the so-called optical memory elements. Such elements may supersede contemporary devices, where data is processed depending on the motion of electrons.

Computing elements working on photons are anticipated to operate faster, more efficiently, and most significantly, use minimal amounts of energy. However, to reach closer to bringing these daring ideas to life, several engineering and theoretical problems have to be solved. One of the problems is to accomplish low-cost, energy-efficient, and reliable light control.

All of today’s digital electronics are built on so-called triggers. These are devices for switching between two states, 0 and 1. For optical devices which might in the future take the place of our electronic devices, we also need a special switch.

Nikita Kulachenkov, Study Co-Author and Junior Research Associate, ITMO University

One of the alternatives for such a change comes in the form of MOFs. MOFs are a group of functional materials that integrate the properties of organic compounds and crystal lattice substances.

However, when it comes to producing optical computing devices, the most significant aspect is that certain MOFs comprise unique photochromic compounds that can alter their optical properties upon exposure to light. But this process often occurs across a comparatively long duration of time, ranging from several minutes to several days, thus considerably limiting the viable application of these structures as switchers.

Under the guidance of Valentin Milichko, a research team from Russian-French laboratory at ITMO University has decided to adopt a different method. The team employed standard MOFs that lack photochromic compounds and have been used in the chemical sector for a long time.

We decided, why not use a group of MOFs that demonstrate the property of changing their structure under external stimuli such as pressure, temperature or others.

Nikita Kulachenkov, Study Co-Author and Junior Research Associate, ITMO University

Kulachenkov continued, “Among these metal-organic frameworks was HKUST-1. It was very well-researched in the field of gas absorption, but no one could ever have thought that its properties, and consequently its structure, could undergo significant changes when exposed to light.”

Experiments conducted with HKUST-1 MOFs have demonstrated that when these MOFs are exposed to an ultra-short pulse of an infrared laser, they instantly start transmitting less light.

The number of photons passing through the MOF decreased by about a hundred times. The switch-over period amounted to several dozen milliseconds. This is two to three orders better than offered by existing MOF-based organic systems.

Nikita Kulachenkov, Study Co-Author and Junior Research Associate, ITMO University

From the physics perspective, this change has the following justification—the femtosecond effect produced by the infrared laser is sufficient to actually evaporate the water from the MOF. This causes the MOF to become less transparent for the light produced by a laser. However, once the light is turned off, the framework again absorbs the atmospheric water molecules and reverts to its original state.