Researchers Produce Long-Wavelength VCSEL using a High Contrast Grating
Instead of a distributed Bragg reflector, a high contrast grating (HCG) is used as a top mirror. The HCG can be modified to create a micro-electro-mechanically tunable VCSEL.
The ever-growing demands for bandwidth in telecommunication networks, mainly caused by the unprecedented growth in data traffic in local and access networks, necessitate the development of a new generation of low-cost and high-speed optical links.
Vertical-cavity surface-emitting lasers (VCSELs) promise an efficient and reliable solution to this growing problem. They offer low power consumption compared to the conventional edge-emitting lasers and can be manufactured in volume at low cost.
VCSELs are already widely used in short range data interconnects. However, long-wavelength VCSELs have inherent difficulties in finding appropriate material combinations for implementing both an active region and a top mirror on the same substrate. It is extremely difficult to produce VCSELs beyond 1.3 um using the Gallium arsenide (GaAs) material platform common for 850-980 nm devices.
Researchers at UC Berkeley created a 1.55 um VCSEL fabricated on novel platform that provides continuous-wave operation at room temperature. Instead of a distributed Bragg reflector, a high contrast grating (HCG) is used as a top mirror. The HCG can be modified to create a micro-electro-mechanically tunable VCSEL. An ion implantation process is used to form the current aperture. The device is easy to fabricate, provides a high degree of polarization differentiation, and can be designed to work at up to 2.3 um.
Suggested uses of the VCSEL are in 1.3 - 2.3 um laser sources for data communications, metropolitan and local area networks (LANs) and passive optical networks (PONs). It could also be used in fiber-to-the-home (FTTH) networks and where low loss tunable laser sources are required (e.g. for spectroscopy, biological sensing). Finally, it could be employed in multi-wavelength laser arrays for wavelength-division multiplexing.
Advantages of the design include low cost fabrication (monolithic growth using wet or dry etching) and intrinsic polarization control. Furthermore, there are no degenerate polarization modes and fast tuning speed is possible due to the small mass of the HCG.
The inventors of the product are Connie J Chang-Hasnain, Christopher Chase and Yi Rao and a patent for the device is currently pending.