Engineers at the California Institute of Technology (Caltech) have developed a switch, one of the most fundamental components of computing, that uses optical rather than electronic components. This development may help enable ultra-fast all-optical signal processing and computing.
By using optical pulses instead of electrical signals, optical devices have the ability to transmit signals faster than electrical devices. This is why modern devices often use optical technology to send data. For example, fiber optic cables provide much faster network speeds than traditional Ethernet cables. By doing more with more speed and less power, the field of optics has the potential to revolutionize computing.
However, one of the major limitations of today’s optics-based systems is that at some point they still need to have electronics-based transistors to process data efficiently. Now, harnessing the power of optical nonlinearity, a team of engineers 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 enable data processing using photons. The research was published July 28 in the journal Nature Photonics.
Alireza Marandi’s team chose a crystalline material known as lithium niobate, a combination of niobium, lithium and oxygen that does not occur in nature but has proven vital to the field of optics over the past 50 years. This material is inherently nonlinear. Due to the particular way the atoms are arranged in the crystal, it produces an optical signal that is not proportional to the input signal.
While lithium niobate crystals have been used in optics for decades, recent advances in nanofabrication technology have enabled teams to create integrated photonic devices based on lithium niobate that allow light to be confined to a tiny space. The smaller the space, the greater the intensity of the light at the same power. As a result, light pulses carrying information through such an optical system can provide a stronger nonlinear response than would otherwise be possible.
Alireza Marandi’s team also confined the light in time. Essentially, they reduced the duration of the light pulses and used a special design that kept the pulses short as they propagated through the device, which resulted in each pulse having a higher peak power. The combined effect of these two strategies greatly enhances the nonlinear strength of a given pulse’s energy, meaning that the photons now have a stronger effect on each other.
The end result is the creation of a nonlinear separator in which the light pulses are delivered to two different outputs depending on their energy, which allows switching to occur in less than 50 femtoseconds (a femtosecond is a quadrillionth of a second). In contrast, the most advanced electronic switches take tens of picoseconds (a picosecond is one trillionth of a second), a difference of many orders of magnitude.
