New optical switch could lead to ultrafast all-optical signal processing

Caltech engineers have developed a switch, one of the most fundamental components of computing, using optical components instead of electronic ones. The development could aid efforts to achieve ultrafast all-optical signal processing and computation.

Optical devices have the ability to transmit signals much faster than electric appliances using pulses of light rather than electrical signals. That’s why modern devices often employ optics to send data; For example, consider fiber optic cables that provide much faster Internet speeds than conventional Ethernet cables.

The field of optics has the potential to revolutionize computing by doing more, faster, and with less energy. However, one of the main limitations of optics-based systems today is that, at a certain point, they still need electronics-based transistors to process data efficiently.

Now, using the power of optical nonlinearity (more on that later), a team led by Alireza Marandi, an assistant professor of electrical engineering and applied physics at Caltech, has created an all-optical switch. Such a switch could eventually allow data processing using photons. The research was published in the journal photonics of nature the 28th of July.

Switches are among the simplest components of a computer. A signal enters the switch and, depending on certain conditions, the change allows the signal to advance or stops it. That on/off property is the basis of logic gates and binary computing, and it’s what digital transistors were designed to do. However, until this new work, achieving the same function with light has proven difficult. Unlike electrons in transistors, which can strongly affect each other’s flux and thus cause a “flip,” photons generally don’t easily interact with each other.

Two things made the breakthrough possible: the material the Marandi team used, and the way they used it. First, they chose a crystalline material known as lithium niobate, a combination of niobium, lithium and oxygen that does not exist in nature but which, over the last 50 years, has proven to be essential in the field of optics. The material is inherently non-linear: due to the special way the atoms are arranged in the crystal, the optical signals it produces as output are not proportional to the input signals.

While lithium niobate crystals have been used in optics for decades, more recently, advances in nanofabrication techniques have enabled Marandi and his team to create lithium niobate-based integrated photonic devices that enable confinement of the light in a tiny space. The smaller the space, the greater the intensity of light with the same amount of energy. As a result, the light pulses transporting information through such an optical system could provide a stronger nonlinear response than would otherwise be possible.

Marandi and his colleagues also temporarily confined the light. Essentially, they shortened the duration of the light pulses and used a specific design that would keep the pulses short as they propagated through the device, resulting in each pulse having a higher peak power.

The combined effect of these two tactics, the spatiotemporal confinement of light, is to substantially enhance the strength of nonlinearity for a given legumes energy, which means that the photons now affect each other much more strongly.

The net result is the creation of a nonlinear splitter in which light pulses are routed to two different outputs based on their energies, allowing switching to occur in less than 50 femtoseconds (a femtosecond is one billionth of a second). second). By comparison, state-of-the-art electronic switches take tens of picoseconds (a picosecond is a trillionth of a second), a difference of many orders of magnitude.

The paper is titled “Femtojoule femtosecond all-optical switching in lithium niobate nanophotonics.”