RF frequency downconverters are of key importance in communication satellites. Classically, this is implemented using an electronic mixer. In this paper we explore the use of photonic technology to realize the same functionality. The potential advantages of such an approach compared to the classical microwave solutions are that it is lighter weight, has lower power consumption and can be made smaller if photonic technology is used. An additional advantage is the fact that the optical local oscillator (LO) reference can easily be transported over longer distances than the equivalent LO signal in the microwave domain due to the large bandwidth and low loss and dispersion of optical fiber. Another big advantage is that one can envision the use of short pulse trains as the LO – starting off from a sinusoidal RF reference – in order to exploit subsampling. Subsampling avoids the need for high frequency LO references, which is especially valuable if a downconversion over several 10s of GHz is required. In this paper we present the operation principle of such a photonic frequency downconverter and describe the performance of the developed micro-photonic building blocks required for this functionality. These micro-photonic building blocks are implemented on a III-V semiconductor-on-silicon photonic platform. The components include a micro-photonic hybridly modelocked laser, a 30GHz electroabsorption modulator and an intermediate frequency (1.5GHz) photodetector.
In this paper we show that using a DVS-BCB adhesive bonding process compact heterogeneously integrated III-V/silicon single mode lasers can be realized. Two new designs were implemented: in a first design a multimode interferometer coupler (MMI) – ring resonator combination is used to provide a comb-like reflection spectrum, while in a second design a triplet-ring reflector design is used to obtain the same. A broadband silicon Bragg grating reflector is implemented on the other side of the cavity. The III-V optical amplifier is heterogeneously integrated on the 400nm thick silicon waveguide layer, which is compatible with high-performance modulator designs and allows for efficient coupling to a standard 220nm high index contrast silicon waveguide layer. In order to make the optical coupling efficient, both the III-V waveguide and the silicon waveguide are tapered, with a tip width of the III-V waveguide of around 500nm. The III-V thin film optical amplifier is implemented as a 3μm wide mesa etched through to the n-type InP contact layer. In this particular device implementation the amplifier section was 500μm long. mW-level waveguide coupled output power at 20°C and a side mode suppression ratio of more than 40dB is obtained.
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.
In this work we present results from high performance silicon optical modulators produced within the two largest silicon
photonics projects in Europe; UK Silicon Photonics (UKSP) and HELIOS. Two conventional MZI based optical
modulators featuring novel self-aligned fabrication processes are presented. The first is based in 400nm overlayer SOI
and demonstrates 40Gbit/s modulation with the same extinction ratio for both TE and TM polarisations, which relaxes
coupling requirements to the device. The second design is based in 220nm SOI and demonstrates 40Gbits/s modulation
with a 10dB extinction ratio as well modulation at 50Gbit/s for the first time. A ring resonator based optical modulator,
featuring FIB error correction is presented. 40Gbit/s, 32fJ/bit operation is also shown from this device which has a 6um
radius. Further to this slow light enhancement of the modulation effect is demonstrated through the use of both
convention photonic crystal structures and corrugated waveguides. Fabricated conventional photonic crystal modulators
have shown an enhancement factor of 8 over the fast light case. The corrugated waveguide device shows modulation
efficiency down to 0.45V.cm compared to 2.2V.cm in the fast light case. 40Gbit/s modulation is demonstrated with a
3dB modulation depth from this device. Novel photonic crystal based cavity modulators are also demonstrated which
offer the potential for low fibre to fibre loss. In this case preliminary modulation results at 1Gbit/s are demonstrated.
Ge/SiGe Stark effect devices operating at 1300nm are presented. Finally an integrated transmitter featuring a III-V
source and MZI modulator operating at 10Gbit/s is presented.
Hybrid silicon lasers based on bonded III-V layers on silicon are discussed with respect to the challenges and
trade-offs in their design and fabrication. Focus is on specific designs that combine good light confinement in
the gain layer with good spectral control provided by grating structures patterned in silicon.