Scanning electron microscope image of the silicon-based micro-loop mirror. Light entering the waveguide from the left is guided around the loop and redirected back into the laser structure. The inset shows the laser spot photographed with an infrared camera. |
Active
optical fibers with silicon photonic chips can carry a lot more
information for data interconnect than copper cables. Silicon photonics
can also be the material of choice for wiring ‘lab-on-a-chip’
devices—however, the construction of such devices is not without its
challenges. One of the greatest difficulties is the implementation of
lasers because silicon is a poor light emitter, but is commonly required
for a photonic system on chip.
Doris
Keh-Ting Ng at the A*STAR Data Storage Institute and co-workers have
now successfully fabricated a laser on top of a silicon chip1. The III-V
semiconductor materials are bonded to silicon to provide optical gain
and the laser has a unique mirror design that promises enhanced device
operation compared to the conventional feedback mirrors based on device
facets.
“Integrated
Si/III-V lasers can take advantage of low-loss silicon waveguides,
while addressing the problem of low light emission efficiency that
silicon devices typically have,” says Ng.
Attaching
a Si/III-V laser on top of silicon requires challenging fabrication
techniques, and device performances can suffer as a result. Furthermore,
any laser requires mirrors to maintain lasing action. Typically, such
designs rely on the interface between air and the semiconductor, that
is, the facets of the chip. These mirrors are not perfect and further
reduce operation efficiency.
To
improve on the latter aspect, the researchers have now come up with a
unique mirror design, known as a micro-loop mirror (MLM). Light emitted
from one end of the laser is guided along the waveguide, around a narrow
bend and is then directed back into the device (see image). The mirror
at the other end of the device is still formed by the interface with
air, so that laser radiation can exit the device. The MLM achieves a
remarkable 98% reflection efficiency of light. Such low losses mean that
the MLM laser is comparatively efficient.
The
successful demonstration of this technique is remarkable, considering
that more than 30 fabrication steps are needed to fabricate the device,
and in view of the fact that the MLM requires delicate and
high-precision fabrication. The researchers aim to further enhance the
laser, for example, by miniaturizing the device.
“Further
improvements, for example, at the interface between the mirror and the
lasing structure itself could lead to even better performance,” says Ng.
“Laser with lower threshold and higher output power can possibly be
achieved, leading to a potential solution to develop high-speed and
low-cost optical communications and interconnects on electronics chips.”
The A*STAR-affiliated researchers contributing to this research are from the Data Storage Institute.
Source: A*STAR
