Aiming to advance photonic integration, scientists in Japan have developed a nanowire photonic-crystal hybrid laser that promises to be compatible with silicon integration technology.
“In our method, we have to place sub-wavelength nanowire within a slot in a photonic crystal,” explains Masaya Notomi, PhD, in the Nanophotonics Center at NTT Basic Research Laboratories. He further elaborates that to achieve this, his team employed an atomic force microscope (AFM), which is equipped with a nanoprobe that can scan the surface of a material with nanometer precision. “Usually an AFM is used for obtaining a geometric image of a surface, but we used it for a different purpose,” he says. “We manipulate a nanowire using the nanoprobe of the AFM and place it at the desired position.”
Photonic integration: Overcoming development barriers
Still in its infancy, photonic integration is facing many obstacles. By combining a sub-wavelength nanowire with a photonic crystal platform, Notomi and his colleagues may have solved an important problem. As he points out, CMOS circuits can implement various functionalities by a small set of materials, such as silicon, metal and insulators. Photonic circuits, on the other hand, require a wide variety of materials because each functionality calls for a different material or a different composition. “In other words, lasers, photodetectors, electro-optic modulators or optical switches and memories all require different materials, which makes photonic integration significantly more difficult,” Notomi says. “Our scheme shows that it may be possible to solve this problem.” What is more, he says conventional photonic devices are too large, which hinders large-scale integration. “Our nanowire-based devices can solve this issue as well.”
Photonic crystal nanowire combination on a silicon platform—a game-changer
The scientists in Japan have indeed achieved this photonic crystal nanowire combination on a silicon platform. Could this be a game-changer in integrated photonics? “By our method, we achieved nanolasers within a silicon photonic crystal,” Notomi replies. “If we change the nanowire, we may be able to realize photonic devices other than lasers.” It is well known, he points out, that a silicon photonic crystal can serve as a platform for dense waveguide circuits. “Hence, our demonstration indicates that nanophotonic devices with various functionalities can potentially be integrated within a silicon photonic integrated circuits, which has a significant meaning for photonic integration.”
The team not only demonstrated continuous-wave lasing oscillation by a sub-wavelength nanowire but also high-speed signal modulation by a nanowire laser. “Our latest result clearly shows that nanowire lasers can be employed for high-speed optical signal processing,” Notomi says. “As far as we know, previous nanowire laser works did not show that they can generate high-speed signals.” Additionally, he notes that the operation wavelength is quite important because previous nanowire lasers did not operate at telecom wavelength: “Telecom-band operation is important not only due to the compatibility with optical fiber communication but also due to the fact that the emitted light is transparent in silicon. This latter fact means that our nanowire lasers can work in silicon-photonic-integrated circuits.”
Notomi and his team regard optical communication inside a processor chip as key application for their pioneering technology. However, they think intra-chip optical interconnect and photonic network on-chip applications will be even more significant. “It is predicted that electric communication will consume too much energy in future processor chips, and we should look for a solution in optical communication within chips,” says the expert. “We believe that our result paves the way to this target, though our work is still at a preliminary stage.”
“Obviously, we should improve the laser performance,” Notomi says, noting that room-temperature laser operation with current injection will be an essential step. “Besides that, we think it is important to realize other types of photonic devices, such as switches, by using the same method to demonstrate the potential of our scheme.”
The research is detailed in the article "Continuous-wave operation and 10-Gb/s direct modulation on InAsP/InP sub-wavelength nanowire laser on silicone photonic crystal,” published in APL Photonics.
Written by Sandra Henderson, Research Editor, Novus Light Technologies Today