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We investigate the use of low-threshold 980-nm vertical-cavity surface-emitting lasers for free-space optical interconnects. The vertical-cavity surface-emitting lasers and backilluminated detectors are monolithically integrated with microlenses on the back sides of the growth substrates to eliminate the necessity of external optics. With a channel pitch of 250 mum, an interconnect length between boards of the order of 5 to 10 mm with a ?50-mum lateral alignment tolerance can be achieved without external relay optics. The complete link is modeled to predict the system's efficiency and maximum bit rate. Data transmission at 500 Mbits/s per channel is demonstrated. The data rate was limited by parasitics, not the inherent bandwidth of the laser diodes.

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In the infrared region of the spectrum thermoelectric detectors such as the thermopile are extensively used. These detectors rely on the well-known Seebeck effect, in which there is a direct conversion of thermoelectric differentials into electrical voltage. The temperature difference over thermocouple junctions is in general, created by forming a thin membrane connected to the silicon bulk. In many existing thermopiles, materials such as Si and Si 3 N 4 have been used as membrane. These materials suffer from relatively high thermal conductivity, which lowers the membrane temperature and reduces the sensitivity of the detector. A material such as SU-8 2002 has a much lower thermal conductivity and is applied using standard photolithographic processing steps. This work presents thermal simulations regarding the use of SU-8 2002 as a thermal insulating membrane as compared to Si and Si 3 N 4 . The simulation results presented show that the temperature increase in a 5 m SiO 2 SU 8 membrane is about 9% higher than in a 1 m Si 3 N 4 membrane, despite the membrane thickness being increased by a factor of 5. A thermopile consisting of 196 serially interconnected Ti/Ni thermocouples positioned on a 5 m SiO 2 SU 8 2002 membrane has been fabricated. The sensitivity of the fabricated device has been evaluated in the infrared region, using a 1.56 m IR laser and a xenon arc lamp together with a monochromator. The measurement results show a sensitivity of approximately 5 V/W over the wavelength range between 900-2200 nm. Measurements performed in a vacuum chamber show that the sensitivity of the detector could be increased by more than a factor of 3 by mounting the detector in a vacuum sealed capsule.

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Summary In this paper, a basic unit for the nine‐level converter is firstly presented. Then, a new developed basic unit topology for the multilevel converter is proposed. This topology comprises several bidirectional and unidirectional switches along with dc voltage sources. In order to increase the number of generated levels, a cascade topology based on the series connection of developed basic units is studied. Due to the extensive nature of the presented cascade multilevel converter, the optimization analysis is presented for generating the maximum number of levels with minimum numbers of IGBTs, drivers, dc voltage sources, and voltage on switches. All required mathematical analysis consisting of switching losses, conduction losses, and voltage on switches is illustrated. In order to indicate the merits of the proposed multilevel converter, comparison results are provided. It is shown that the presented topology uses the least numbers of power electronic components. Also, the voltage on the switches in the presented cascade topology is low. For controlling the switches, a modified triangular carrier signal for dual pulse generation is proposed. The performance of the proposed multilevel converter is proven with experimental results of a typical 25‐level converter.

At present, optical fiber microducts are joined together by mechanical type joints. Mechanical joints are bulky, require more space in multiple duct installations, and have poor water sealing capability. Optical fiber microducts are made of high-density polyethylene which is considered best for welding by remelting. Mechanical joints can be replaced with welded joints if the outer surface layer of the optical fiber microduct is remelted within one second and without thermal damage to the inner surface of the optical fiber duct. To fulfill these requirements, an electro-thermal model of Joule heat generation using a copper coil and heat propagation inside different layers of optical fiber microducts was developed and validated. The electro-thermal model is based on electro-thermal analogy that uses the electrical equivalent to thermal parameters. Depending upon the geometric shape and material properties of the high-density polyethylene, low-density polyethylene, and copper coil, the thermal resistance and thermal capacitance values were calculated and connected to the Cauer RC-ladder configuration. The power input to Joule heating coil and thermal convection resistance to surrounding air were also calculated and modelled. The calculated thermal model was then simulated in LTspice, and real measurements with 50 µm K-type thermocouples were conducted to check the validity of the model. Due to the non-linear transient thermal behavior of polyethylene and variations in the convection resistance values, the calculated thermal model was then optimized for best curve fitting. Optimizations were conducted for convection resistance and the power input model only. The calculated thermal parameters of the polyethylene layers were kept intact to preserve the thermal model to physical structure relationship. Simulation of the optimized electro-thermal model and actual measurements showed to be in good agreement. Author Contributions: Conceptualization, K.B., S.A., and J.S.; methodology, S.A. and K.B.; software, S.A. and K.B.; validation, S.A. and K.B.; formal analysis, S.A. and K.B.; investigation, S.A. and K.B.; resources, K.B. and J.S.; data curation, K.B., S.A. and J.S.; writing-original draft preparation, S.A.; writing-review and editing, J.S.; visualization, S.A.; supervision, K.B. and J.S.; project administration, J.S.; funding acquisition, K.B. and J.S.Funding: This research work is part of the project FIBER, funded through the European Regional Development Fund. Conflicts of Interest:The authors declare no conflict of interest.