Ukrit Mankong

Millimeter wave fixed wireless systems in future backhaul and access network applications can be affected by weather conditions. The losses caused by rain attenuation and antenna misalignment due to wind-induced vibrations have greater impacts on the link budget reduction at E-band frequencies and higher. The current International Telecommunications Union Radiocommunication Sector (ITU-R) recommendation has been widely used to estimate rain attenuation, and the recent Asia Pacific Telecommunity (APT) report provides the model to estimate the wind-induced attenuation. This article provides the first experimental study of the combined rain and wind effects in a tropical location using both models at a frequency in the E band (74.625 GHz) and a short distance of 150 m. In addition to using wind speeds for attenuation estimation, the setup also provides direct antenna inclination angle measurements using the accelerometer data. This solves the limitation of relying on the wind speed since the wind-induced loss is dependent on the inclination direction. The results show that the current ITU-R model can be used to estimate the attenuation of a short fixed wireless link under heavy rain, and the addition of wind attenuation via the APT model can estimate the worst-case link budget during high wind speeds.

Silicon photonic devices with either silicon or silicon nitride waveguides have increasingly been used in many applications besides communications, especially as sensors in label-free biosensing, where guided light signals are affected by biorecognition molecules immobilized on the surface. The coating of protein (i.e., bioreceptors) by biochemical process on the waveguide surface is a crucial step in creating a functionalized device that can be used for biosensing. As a conventional method that uses 3-aminopropryltriethoxysilane (APTES) and glutaraldehyde (GA), the APTES-GA method has the limitation of using a GA crosslink, of which the two functional groups can bind to nonspecific proteins, causing irregular binding. In this study, we proposed a new coating technique to avoid such problem by applying APTES silanization with 1-ethyl-3-(3-dimethyl aminopropyl)-carbodiimide (EDC)-N-hydroxysuccinimide (NHS) protein crosslink, denoted by the APTES-(EDC/NHS) method. The EDC/NHS reaction was shown to be able to immobilize protein in ordered orientation due to consistent arrangement between a carboxylic group of protein molecules and an amine group of covalent-linked APTES on surface. By applying APTES silanization, we circumvented the use of hazardous cleaning agent in the conventional EDC/NHS technique. Several surface characterization techniques were carried out to assess and compare the two biocoating techniques, including scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), spectroscopic ellipsometry (SE), and atomic force microscopy (AFM). On silicon, the results of antihuman TNF-alpha antibody coating showed that the proposed APTES-(EDC/NHS) technique has better repeatability in terms of less roughness of the coated protein at 1.5 nm compared with 6.3 nm, due to the ordered arrangement of coated antibody molecules. On a silicon nitride waveguide device, the proposed APTES-(EDC/NHS) technique exhibits dense antibody immobilization on a waveguide in SEM images due to stable amide bond formation via EDC/NHS crosslink mechanism. The specificity of the immobilized antibodies was confirmed by enzyme-linked immunosorbent assays (ELISA), with an average optical density at 450 nm of 0.175 ± 0.01 compared with 0.064 ± 0.009 of negative control. The proposed technique also reduced the overall process time since proteins are crosslinked to the silanized waveguide surface in a single step.

In this paper, we propose a three-dimensional VLC indoor positioning system using smart device camera receiver whereby the rolling shutter effect of CMOS camera sensor to detect the encoded identification data and necessary information regarding transmitter positions from the individual LEDs. No prior assumptions have been made regarding each LED transmit power, this allows for non-identical LEDs and their power deterioration over time. Images of 4 LEDs are required to estimate the receiver position. In the image capturing process, it is necessary to adjust the exposure setting. The captured images are processed by converting them to black and white where the black and white stripes may be decoded. Then by applying a different threshold, we propose a method to use the white pixel area (counted in number of pixels), corresponding to each LED image, to estimate the distance between each LED and the receiver. These estimations are used in trilateration algorithm to determine the receiver position. Through proper calibration, the position error is within 10 cm.

We developed an economical assembly for a silicon photonics resonator device including a device mount and lensed fiber holders for input and output fibers. The parts are fabricated by 3D printing technology using resin with digital light processing (DLP) technique and cured with UV light (405nm). The lensed fibers are aligned to the device waveguides using 6-axis aligner platform and their holders are affixed to the device mount by UV glue. Our in-house assembly module is able to firmly affix the fiber holders to the device mount and align the input and output lens fibers to the device spot size converter (SSC) of dimension 3.4 × 3.5 μm². After alignment completion, the assembly can be detached from the aligner stage to be used in un-stabilized benchtop measurement system. The benchtop measurement system for the silicon photonic sensor device consists of a tunable laser, a polarizer, an optical power meter, and a container housing the device assembly, peristalsis pump and control circuits that was developed inhouse for microfluidics control having flow rate in the level of nanoliter/minute. In addition, a software has been developed for the measurement of the device resonant wavelength and wavelength shift due to sensor activity. We have demonstrated that the silicon photonics resonator that has been mounted on our assembly in the above measurement system showed acceptable performance by comparing the results with those obtained by mounting the device on stabilized fiber alignment platform. Thus, the 3D printed assembly may be used for silicon photonics device mount in early portable sensor prototype development.

We present a method to achieve vector modulation of lightwave using an electroabsorption modulator intregrated laser. The laser section is used for direct phase modulation followed by amplitude modulation of the electroabsorption modulator section in a cascade manner, which is an alternative method to conventional IQ modulator. To allow improved phase demodulation, we propose a digital pre-compensation technique for a transmitter in optical coherent system for the first time, which includes phase-balanced differential phase shift keying encoding and digital domain pre-equalization filtering. The phase-balanced encoding technique applies parallel DC-balance coding with phase-balanced symbol mapping, which results in bounded cumulative phase and constant statistical characteristic of the modulating signal in differential M-ary phase shift keying (M-PSK) and M-ary quadrature amplitude modulation (M-QAM) formats. The digital pre-equalization filter also compensates for the phase response of the laser section. Experimental results show that the pre-digital compensation technique allows the improved complex signal demodulation compared to conventional DQPSK modulation in a back-to-back setup.

In medical diagnostics there is an increasing demand for biosensors that can specifically detect biological analytes in a fluid. Especially label-free sensing, consistings of a transducer with biorecognition molecules immobilized on its surface without relying on fluorescent dye. In this paper we study the design and fabrication of a silicon nanowire photonic ring resonator and its feasibility as a biosensor. We have simulated and fabricated racetrack ring resonators which have a few tenths of micrometer gap, up to 0.5 μm between the input / output waveguides and the resonators. It is found that the devices can be designed with large Q factors. Sensitivity to biomaterial detection has been simulated for antibody (goat anti-mouse IgG) - antigen (mouse IgG) using 3-dimensional Finite Difference Time Domain technique. The simulated results show that the ring resonator has a response 15 nm resonance shift per refractive index unit. Antibody coating method is also discussed in this paper which can be applied to other antibody-antigen types.

Directly modulated laser can be used as phase modulator due to chirp effect. However, accompanying amplitude modulation also results. By using EA Modulator in combination, light amplitude may be compensated enabling both amplitude and phase modulation of lightwave, which is an alternative method to conventional IQ modulator. Since light phase is proportional to intensity, we propose cumulative phasebalance coding to solve the limitation in the laser operating range for differential M-PSK and M-QAM modulation. The technique applies parallel DC-balance coding with phase-balance symbol mapping. The cumulative phase in high-order differential modulation is always bounded, it is for the first time, to our knowledge

We present a method to achieve vector modulation in an electroabsorption modulator with help of a directly modulated laser. We discuss the challenges involved and demonstrate the combined phase and amplitude modulation theoretically and experimentally using a commercial electroabsorption modulator integrated laser.