We review recent theoretical and experimental work on InP membrane microdisk lasers heterogeneously integrated on SOI and coupled to a Si bus waveguide. After a general introduction on the fabrication and the operation principles, we will describe various improvements in the fabrication technology. This includes improvements in the yield of the bonding of the InP die on the SOI die and in the controllability of the bonding layer thickness, as well as an optimization of the alignment of the microdisk with respect to the silicon waveguide and some proposals for better heat sinking and loss reduction. Improvement in the alignment and the bonding has led to interesting results on the uniformity in device characteristics. In a second part, unidirectional behaviour and reflection sensitivity will be briefly discussed. Theoretical, numerical and experimental results will be shown about the unidirectional behavior and it will be explained how unidirectional microdisk lasers can be a lot less sensitive to external reflections than other lasers. We will also show how such lasers can be used as optical signal regenerators that can work with low optical input powers and that have small power consumption. We will end with a description of demonstrations of optical interconnects based on heterogeneously integrated microdisk lasers and heterogeneously integrated photodetectors. Optical interconnects on chip have been demonstrated at 10 Gb/s. An epitaxial layer stack that contains both the laser and the detector structure has been used for this purpose.
In this paper we review our work in the field of heterogeneous integration of III-V semiconductors and non-reciprocal optical materials on a silicon waveguide circuit. We elaborate on the heterogeneous integration technology based on adhesive DVS-BCB die-to-wafer bonding and discuss several device demonstrations. The presented devices are envisioned to be used in photonic integrated circuits for communication applications (telecommunications and optical interconnects) as well as in spectroscopic sensing systems operating in the short-wave infrared wavelength range.
Optical interconnect and optical packet switching systems could take advantage of small footprint, low power lasers and
optical logic elements. Microdisk lasers, with a diameter below 10μm and fabricated in InP membranes with a high
index contrast, offer this possibility at the telecom wavelengths. The lasers are fabricated using heterogeneous
integration of InP membranes on silicon-on-insulator (SOI) passive waveguide circuits, which allows to combine the
active elements with compact, high-index contrast passive elements. The lasing mode in such microdisk lasers is a
whispering gallery mode, which can be either in the clockwise (CW) or counter clockwise direction (CCW) or in both.
The coupling to the SOI wire waveguides is through evanescent coupling. Predefined, unidirectional operation can be
achieved by terminating the SOI wires at one end with Bragg gratings. For all-optical flip-flops, the laser operation must
be switchable between CW and CCW, using short optical pulses. Unidirectional operation in either direction is only
possible if the coupling between CW and CCW direction is very small, requiring small sidewall surface roughness, and if
the gain suppression is sufficiently large, requiring large internal power levels. All-optical flip-flops based on microdisk
lasers with diameter of 7.5μm have been demonstrated. They operate with a CW power consumption of a few mW and
switch in 60ps with switching energies as low as 1.8fJ. Operation as all-optical gate has also been demonstrated. The
surface roughness is limited through optimized etching of the disks and the large internal power is obtained through good
heat sink.
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