BO-and Monolithic Quantum Dot Semiconductor Optical Amplifier on Silicon

From an Information and Communication Technology (ICT) perspective, the 21st century is characterized by an explosion of requests for communication capabilities, high-performance computing, and cloud storage. Over the last few years, global Internet traffic has been growing exponentially. In this picture, transporting such an amount of data with existing electrical- interconnects and switching technologies will soon reach the "bottleneck" in terms of thermal loading, capacity, latency and power consumption. Optical- interconnects and switch fabrics combined with photonic integrated circuits (PICs) are seen as one of the most promising routes to push such limits. Silicon (Si) photonics is now considered as a reliable photonic integration platform. The beauty of Si Photonics stems from its ability to integrate microelectronics and photonics on a single Si chip utilizing standard CMOS IC technology. An important subset of this area is hetero-integration of III-Vs on Si, where the aim is the make use of III-V materials, with superior optical properties, to provide an efficient optical gain medium to circumvent the fundamental physical limitation of Si, i.e. Si cannot efficiently emit light, yet keeping the capability of light-routing, modulating, detecting and cost advantages of Si.

In a breakthrough development, the investigators' group in UCL have shown that it is possible to grow epitaxially high-performance quantum dot (QD) lasers directly on Si substrates, opening up the possibility to monolithically integrate various types of III-V optoelectronic devices on Si. The pace of research on monolithic III-V/Si integration has then been dramatically accelerated and an increasing number of prestigious research groups including Bowers' group at UCSB and Arakawa's group at Tokyo University, and major Si chip companies, i.e. Intel, are currently devoting considerable programmes in this area. In addition to III-V/Si lasers, monolithic III-V/Si semiconductor optical amplifiers (SOAs) are also attracting significant interest as the key components for next-generation photonic integrated optical- interconnects and switching fabrics, as the application of SOAs is not limited only to compensate for loss and maintain signal levels as the signal propagates throughout a large number of optical components within the PICs, it is also used as a mature gating element for optical switches and has the advantages of ease of control, smaller footprint, low operating voltage, high ON/OFF extinction ratio, and fast transition times of the order of nanoseconds. However, such a III-V/Si SOA has not been developed to date.

Building on the established expertise in monolithic III-V/Si QD lasers at UCL, this project proposal aims to develop the world's first monolithic III-V QD SOA on CMOS-compatible on-axis Si (001) substrates. In contrast to conventional native substrate based SOAs or III-V/Si SOAs using either flip-chip bonding or wafer bonding, the proposed method is fundamentally different, since the III-V SOAs will be integrated on Si by direct epitaxial methods, offering the possibility to achieve high-yield, low-cost and large-scale Si-based PICs, which is expected to be the technology platform to address next-generation optical- interconnect and switching solutions. With further development in Si photonics, i.e., providing the microelectronics world with the ultra-large-scale integration of photonic components, there will be scope to target applications in important areas such as consumer electronics, high-performance computing, medical and sensor solutions, and defence.

This project will benefit from guidance from and joint work with both industrial as well as academic partners and will leverage major UK-based industrial and academic strengths in materials (e.g., CSC, EPSRC NEF) device processing (e.g., EPSRC CSHub, Glasgow) and photonics (e.g., Rockley, Lumentum), who are also well positioned to exploit this research.

This project represents a significant opportunity to deliver impacts in the academic community and create industrial impact with IP and potential products.

Academic and research community:
Monolithic integration of III-Vs on silicon (Si) is a rapidly growing research area due to the potential of combining the advantages of advanced III-V semiconductor materials with the capabilities of well-established Si technologies. Currently, the proposed research is unique to the UK, and so will have an immediate impact on UK research activities. The research outcomes from this project will be made available to research groups across the UK through the EPSRC National Epitaxy Facility and EPSRC Future Compound Semiconductor Manufacturing Hub. The applicant will target high-impact journals (e.g. Nature Photonics, Optica, ACS Photonics) as the applicant did before. This will automatically draw a lot of academic attention. Also, the applicant will present research work at top international conferences (CLEO, ECOC, ISLC).

Creation of new products:
Monolithic III-V/Si O-band quantum dot semiconductor optical amplifiers, the key outcome of this research, will be open to immediate exploitation and thus the applicant will explore potential product development through the collaboration with the industrial partners (Rockley Photonics, CSC), UCL Business will be consulted to identify opportunities for IP protection and commercialization so that silicon photonics manufacturers and data centre operators can make use of the technology.

Educate future engineers, researchers and innovators:
Skills development will be first applied to the involved student and PDRA. The industrial partners will dedicate effort and time to train the student and PDRA involved in this project. The PI is one of the supervisors in the UCL-Cambridge Doctoral Training (CDT) in Connected Electronic and Photonic Systems. Through the CDT and UCL's postgraduate lectures, the PI will educate and train new researchers and innovators with the necessary skills for this research field.