Caltech engineers have developed a switch – one of the most fundamental components of a computer – using optical rather than electronic components. The development could aid efforts to achieve ultrafast all-optical signal processing and computing.

Optical devices have the capacity to transmit signals much faster than electrical devices, using light pulses rather than electrical signals. This is why modern devices often use optics to send data; for example, consider fiber optic cables, which provide much faster Internet speeds than conventional Ethernet cables.

The field of optics has the potential to revolutionize computing by doing more, at higher speeds, and with less energy. However, one of the main limitations of optical-based systems at the moment is that at some point they still need to have electronics-based transistors for efficient data processing.

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

Switches are among the simplest computer components. A signal comes into the switch and depending on certain conditions the switch either allows the signal to move forward or stops it. This on/off property is the basis of logic gates and binary calculations and is what digital transistors are designed for. However, until this new work, achieving the same function with light proved difficult. Unlike electrons in transistors, which can strongly influence each other’s flow and thus cause “switching”, photons usually do not easily interact with each other.

Two things made the breakthrough possible: the material Marandi’s 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 occur in nature, but over the past 50 years has proven essential to the field of optics. The material is inherently non-linear: because of the special way the atoms are arranged in the crystal, the optical signals it produces as outputs are not proportional to the input signals.

While lithium niobate crystals have been used in optics for decades, recent advances in nanofabrication techniques have allowed Marandi and his team to create lithium niobate-based integrated photonic devices that allow light to be confined in a small space. The smaller the space, the greater the light intensity with the same amount of power. As a result, light pulses carrying information through such an optical system could provide a stronger non-linear response than would otherwise be possible.

Marandi and his colleagues also limited the light temporary. Essentially, they shorten the duration of the light pulses and use a specific design that will keep the pulses short as they propagate through the device, resulting in a higher peak power per pulse.

The combined effect of these two tactics – spatio-temporal light confinement—is to significantly increase the strength of the nonlinearity for a given pulse energy, meaning that the photons now interact much more strongly.

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

Original article: A new optical switch could lead to ultrafast all-optical signal processing

Since: California Institute of Technology


An all-optical switch could eventually enable data processing using photons

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