In recent years there has been a rapidly increasing demand for CO2 sensors for applications in health monitoring, control of air quality and horticulture. Amongst the various approaches reported so far, the AlGaInSb quaternary alloy shows great promise for the development of compact Light Emitting Diodes (LEDs) as it offers bandgap Type-I alignments, which enable the design of effective multi-quantum well (MQW) active regions. In this paper we show a more than fourfold improvement in wall-plug efficiency by optimising both the strain in AlGaInSb MQW active regions and the fabrication process flow of LEDs emitting at 4.26 um.
Silicon-on-Insulator devices are particularly sensitive to fabrication errors. As an example, a deviation in waveguide height or width of as little as 1nm translates directly to a 1nm offset in the transfer function of any interferometric devices (such as a ring resonator) constructed using the said waveguide. Therefore, even as fabrication tolerance continues to improve, post-fabrication treatment is often the only way of ensuring device uniformity for particularly demanding applications. This work proposes a novel approach for post fabrication trimming of SOI devices based on localised laser annealing of HSQ cladding layer. HSQ is a versatile material often used in fabrication of SOI devices as both the mask material for electron-beam lithography resist and as a cladding or planarization layer due to its similarity to conventional silica. However, unlike silica, the refractive index of HSQ can be changed significantly (up to ΔnHSQ = 3.26*10-2) by thermal processing. We utilise this property for trimming by cladding a conventional SOI waveguide optimised for TE propagation (height h=220 nm, width=500nm) with a layer of HSQ and then permanently changing the refractive index of the cladding via laser annealing. This approach allows us to select individual devices and only apply the change where necessary. As a demonstrator, we trim a resonance of a racetrack resonator by 1.3nm. The technique has proven to be robust with no parameter drift observed 7 days after trimming and no thermal cross-talk to neighbouring devices. Furthermore, unlike its predecessors, it is based on a standard fabrication process and does not require expensive specialised equipment.
Advanced technologies to implement on-chip monitoring and feedback control operations are required to make silicon photonics scale to large-scale-of-integration. Transparent detectors and energy saving actuators are key ingredients of this paradigm. On-chip detectors are required to be minimally invasive in order to allow their integration in key spots of the circuit, thus easing control operation through the partitioning of complex architectures in smaller cluster of devices and the realization of local feedback control loops. Non volatile integrated actuators, which are reversible switching devices that can maintain the state without the need of “always on” power dissipation, are also needed to reduce the power consumption required by tuning, reconfiguration and stabilization operations. Addressing these issues, in this contribution we report on the performance of a recently developed transparent detector, named ContacLess Integrated Photonic Probe (CLIPP), that can monitor in line the intensity of the light in silicon waveguides without introducing any photon absorption in excess to the waveguide propagation loss. A systematic characterization of the CLIPP detector is here presented, specifically addressing the dependence of the CLIPP performance on the waveguide geometry and on the polarization and wavelength of the light. Concerning the development of non-volatile integrated actuators, we demonstrate the possibility to manipulate the light transmission in silicon waveguides by electrochemical insertion of mobile ions in a mixed ionic and electronic conductor (MIEC) used as upper cladding of a silicon waveguide. A finely controllable and reversible change of the imaginary part of the refractive index of the MIEC film is exploited to trim the loss of a silicon waveguide and to modify the frequency response of a silicon microring resonator.
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