An ultra-compact hybrid nanolaser diode created by researchers in France is reportedly the first that can be integrated with silicon photonic waveguides without losing light-emitting efficiency. Working at a wavelength of 1.56 µm — the holy grail of telecommunications — the device could revolutionize intra-chip optical interconnects and optical signal processing.
The optical design
“The design of our nanolasers relies on the exploitation of photonic crystals, the photonic analogue to atomic crystals, to achieve excellent wavelength-sized optical cavities,” explains Fabrice Raineri from the Center for Nanoscience and Nanotechnology (C2N), a CNRS-Université Paris Sud laboratory. The device he is describing consists of 10 µm long, 500 nm wide and 450 nm thick InP-based rib waveguides drilled with a single row of 100-nm radii holes.
“The semiconductor heterostructure embeds an N-I-P heterojunction that contains quantum wells acting as active material,” the researcher adds. “The electrical powering of the laser is rendered possible by this specific optical design, which avoids disastrous optical losses due to the presence of metallic contacts.”
Raineri says silicon-on-insulator (SOI) wire waveguides enable very efficient light tunneling into a silicon optical circuitry. The lasers emit at room temperature at the all-important telecommunications wavelength of 1.56 µm and exhibit wall-plug efficiencies higher than 10%.
First integration with SOI photonic circuits
“This is the first time that such compact III-V semiconductor laser diodes are integrated within silicon-on-insulator photonic circuits,” Raineri confirms. He says their fabrication is based on the adhesive bonding of a III-V semiconductor die on a SOI photonic circuitry, and all the lasers are processed simultaneously using electron-beam lithography, followed by plasma etching and metallic deposition. The processing temperature never goes beyond 400° C, which makes it compatible with CMOS back-end of line processing.
“We propose an original way to achieve the electrical powering of these photonic-crystal-based lasers that is compatible with the industry standards,” the expert emphasizes. “Our hybrid nanolaser diodes exhibit performance truly beyond the state of the art, especially in terms of emitted power and efficiency.”
He further notes that with such small structures, it is indeed “a great challenge” to obtain emitted power beyond a few microwatts and efficiency greater than 1%. Beyond his team’s “proposal of a clever design,” Raineri credits the potentially paradigm-shifting research advance to their optimized processing technologies, which allow material patterning with nanometric precision. “Surface treatments as well as dielectric encapsulation were essential aspects to obtain room-temperature continuous wave emission,” he says.
Big challenge to go so small
“It is a great challenge to build an extremely compact laser diode,” Raineri once more points out. “It is even more complex to reach this objective while getting reasonable output powers and fairly good wall-plug efficiency. This is what we did together, tackling another issue that is the possibility of integrating these sources with silicon photonics and electronics.”
Revolutionizing optical communications and optical signal processing
“These devices have a part to play in the revolution that would be brought about by the convergence of microelectronics and photonics on a chip,” says Raineri. “They could provide the solution to intra-chip optical interconnects, ensuring the electro-optical conversion of data in sub-millimeter long links.”
What is more, the expert says the novel devices could also be of interest for near-term applications such as for board-to-board or rack-to-rack optical links as developed as part of their FP7 European Project PhoxTrot. He can also envision the conception and fabrication of complex optical circuits where thousands of lasers on chip are necessary.
A leap toward integrating microelectronics and photonics on a single chip
“The convergence of microelectronics and photonics on a single chip is one of the great challenges of present research,” Raineri says. Achieving this important feat will require novel types of photonic devices that meet all the performance requirements to enhance microelectronics. “Nanolaser diodes are certainly the most awaited component to provide the electro-optical conversion functionality,” he says. “Our demonstration represents a leap towards this objective as it delivers simultaneously the compactness (with a footprint of about 100 µm²), the power efficiency and the silicon compatibility.”
Enabling new types of applications and more advanced devices
Once more driving home the significance of his team’s groundbreaking achievement, Raineri says with this technology, they now can envision the conception and fabrication of complex optical circuits, where thousands of lasers on chip are necessary while consuming reasonable power. The result could have significant impact on the future of datacom, computercom and sensing.
“The next stage of our research involves the development of a novel class of hybrid InP-on-SOI nano-devices based on this technology, such as amplifiers and modulators,” Raineri says. He and his colleagues also want to “exploit this very versatile optical platform to explore more complex optical phenomena and come up with radically new concepts for achieving even more efficient laser diodes with tailor made characteristics.”
The research is detailed in the article “Hybrid indium phosphide-on-silicon nanolaser diode,” published in Nature Photonics.
Written by Sandra Henderson, Research Editor, Novus Light Technologies Today