We demonstrate the co-integration of SiN waveguide-based building block components in an established 200 mm Silicon photonics platform, extending its capabilities to the 1 µm wavelength range, and addressing bioimaging applications based on Optical Coherence Tomography (OCT). Measured coupling and propagation loss, at wafer-scale, are low for edge couplers (< 2 dB), and PECVD SiN waveguides (< 0.4 dB/cm) respectively. SiN waveguide-coupled Ge-on-Si photodetectors with 0.6 A/W responsivity at 1060 nm and dark currents lower than 15 nA at -1 V operating voltage were achieved at wafer-scale, with a smaller footprint compared to standard Si-based photodetectors. This platform has the potential to be used for a variety of applications, such as optical communications, imaging, and sensing. The achieved results at 1060 nm pave the way for the deployment of miniaturized OCT-based devices to enable large scale patient diagnosis.
Silicon photonics is now considered the photonics platform of choice for short-reach data center single mode pluggable transceivers. With the emergence of co-packaged optics concepts, it can also enable high performance computing with power-efficient interconnect, but also Lidar system integration or even optical quantum computing. In this paper we will present an overview of what can be achieved in state-of-the-art silicon photonics platforms and we will discuss some of the emerging technology trends. In particular, we will discuss the integration of LPCVD SiN in an active silicon photonics platform.
Based on a previously devised speckle-based set-up for probing minute wavelength changes for a coherent field [1], [2] we will here present the first experiments where these changes are resolved on a millisecond time scale. The setup is based on probing the lateral shift of a speckle pattern arising from a slanted rough object, the speckle displacement being linearly proportional to the wavenumber change. Thus, by shearing the speckle pattern across a grating-like structure [3],[4] and [5], a frequency proportional to the frequency of the wavelength change can be derived as will the irradiance. Thus, a cordial display of the complex field amplitude may be obtained with a high temporal resolution and a reasonable spectral resolution. The spatial filter is here preliminarily implemented by recording the speckle pattern with a CMOS array with subsequent digital image processing mimicking the use of a spatial filter.
A color mixing light-emitting diode (LED) light engine that can replace 2-kW halogen–Fresnel spotlight with high-luminous flux in excess of 20,000 lm is reported for applications in professional stage and studio lighting. The light engine focuses and mixes the light from 210 LEDs of five different colors through a microlens array (MA) at the gate of Ø50 mm. Hence, it produces homogeneous color-mixed tunable white light from 3000 to 6000 K that can be adjustable from flood to spot position providing 10% translational loss, whereas the corresponding loss from the halogen–Fresnel spotlight is 37%. The design, simulation, and optimization of the light engine is described and compared to the experimental characterization of a prototype. The light engine is optimized through the simulated design of reflector, total internal reflection lens, and MA, as well as the number of LEDs. An optical efficiency of 59% and a luminous efficacy of 33 lm/W are achieved, which is three times higher than the 2-kW halogen–Fresnel spotlight. In addition to having color rendering of color rendering index Ra>85 and television lighting consistency index 12>70, the dimmable and tunable white light can be color controlled during the operational time.
KEYWORDS: Control systems, Light emitting diodes, Deep ultraviolet, Sensors, Calibration, LED lighting, Sensor calibration, Monte Carlo methods, Lamps, Color management
A new color control system is described and implemented for a five-color LED light engine, covering a wide white gamut. The system combines a new way of using pre–calibrated lookup tables and a rule-based optimization of chromaticity distance from the Planckian locus with a calibrated color sensor. The color sensor monitors the chromaticity of the mixed light providing the correction factor for the current driver by using the generated lookup table. The long term stability and accuracy of the system will be experimentally investigated with target tolerance within a circle radius of 0.0013 in the uniform chromaticity diagram (CIE1976).
An analytical expression for the bias effect in digital speckle correlation is derived based on a Gaussian approximation of the spatial pixel size and array extent. The evaluation is carried out having assumed an incident speckle field. The analysis is focused on speckle displacements in the order of one pixel, thus having no speckle decorrelation. Furthermore, sensitivity is a main issue wherefore we need speckles close to the pixel size, which means that speckle averaging becomes important, and that Nyquist’s criteria may not be fulfilled. Based on these observations, a new correlation method is introduced, which alleviates the need to know the expected shape of the crosscovariance between the original and the off-set recorded speckle pattern. This concept calls for correlating the crosscovariance with the auto covariance, which essentially carries information on the expected shape of the crosscovariance.
A spectrometer based on the application of dynamic speckles will be disclosed. The method relies on scattering of primarily coherent radiation from a slanted rough surface. The scattered radiation is collected on a detector array and the speckle displacement is monitored during a change in the incident wavelength. The change of wavelength gives an almost linear phaseshift across the scattering surface resulting in an almost linear shift of the speckle pattern, which is subsequently monitored. It is argued that frequency changes close to 100 MHz can be probed using a common CMOS array. Experiments showing agreement with theoretical predictions will be given. An extension of the method, with which fast wavelength changes in the GHz regime can be probed, will be discussed but not experimentally verified. This method relies on shearing the dynamic speckle pattern across a cylindrical lens array as it’s well-known within spatial filtering velocimetry.
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