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This paper reports on the progress related to a multichannel photonic alignment concept, which aims to achieve submicrometer alignment of the waveguides of two photonic integrated circuits (PICs). The concept consists of two steps: chip-to-chip positioning and fixing provide a coarse alignment after which waveguide-to-waveguide positioning and fixing result in a fine alignment. For the waveguide-to-waveguide alignment, mechanically flexible waveguides are used. Positioning of the waveguides is performed by integrated MEMS actuators. The flexible waveguides and the actuators are both integrated in one of the PICs. This paper reports on the fabrication and the mechanical characterization of the suspended waveguide structures. The flexible waveguide array is created in a PIC which is based on TriPleX technology, i.e. a silicon nitride (Si 3 N 4 ) core encapsulated in a silicon dioxide (SiO 2 ) cladding. The realized flexible waveguide structures consist of parallel cantilevered waveguide beams and a crossbar that connects the free ends of the waveguide beams. The fabrication of suspended structures consisting of a thick, i.e. 15 µm, TriPleX layer stack is challenged by the compressive mean stress in the SiO 2 . We have developed a fabrication method for the reliable release of flexible TriPleX structures, resulting in a 96% yield of cantilever beams. The realized suspended waveguide arrays have a natural out-of-plane deformation, which is studied using white light interferometry. Suspended waveguide beams reveal a downward slope at the base of the beams close to 0:5_. In addition to this slope, the beams have a concave upward profile. The constant curvature over the length of the waveguide beams is measured to range from 0:2 µm to 0:8 µm. The profiles measured over the length of the crossbars do not seem to follow a circular curvature. The variation in deflection within crossbars is measured to be smaller than 0:2 µm.

We propose a novel way of mechanical perturbation of photonic crystal cavities for on-chip applications. We utilize the equivalence of the 2D photonic crystals with perfect electric conductor (PEC) boundary conditions to the infinite height 3D counterparts for rod type photonic crystals. Designed structures are sandwiched with PEC boundaries above and below and the perturbation of the cavity structures is demonstrated by changing the height of PEC boundary. Once a defect filled with air is introduced, the metallic boundary conditions is disturbed and the effective mode permittivity changes leading to a tuned optical properties of the structures. Devices utilizing this perturbation are designed for telecom wavelengths and PEC boundaries are replaced by gold plates during implementation. For 10 nm gold plate displacement, two different cavity structures showed a 21.5 nm and 26 nm shift in the resonant wavelength. Optical modulation with a 1.3 MHz maximum modulation frequency with a maximum power consumption of 36.81 nW and impact sensing with 20 μs response time (much faster compared to the commercially available ones) are shown to be possible.

We revisit the scaling laws in micro-optical systems to highlight new phenomena arising beyond a conventional optical regime, especially when the size of the system approaches to the operational wavelength. Our goal is to visualize the impact of the scaling effect in the micrometer-sized domain. First, we will show where the conventional optical regime fades away and unexpected responses arise. We will show this by using a ball-lens as an example. Second, we discuss the scaling effect in the Fresnel number of lens systems. Moving toward wavelength-scale microlenses, a specific value of Fresnel numbers leads to a giant focal shift with strong focal power. Our study will give comprehensive insights into the birth of unanticipated phenomena in miniaturized optical systems.

We present an optical spectroscopic technique, making use of both Raman signals and fluorescence spectroscopy, for the identification of five brands of commercially available extra-virgin olive-oil (EVOO). We demonstrate our technique on both a ‘bulk-optics’ free-space system and a compact device. Using the compact device, which is capable of recording both Raman and fluorescence signals, we achieved an average sensitivity and specificity of 98.4% and 99.6% for discrimination, respectively. Our approach demonstrates that both Raman and fluorescence spectroscopy can be used for portable discrimination of EVOOs which obviates the need to use centralised laboratories and opens up the prospect of in-field testing. This technique may enable detection of EVOO that has undergone counterfeiting or adulteration. One of the main challenges facing Raman spectroscopy for use in quality control of EVOOs is that the oxidation of EVOO, which naturally occurs due to aging, causes shifts in Raman spectra with time, which implies regular retraining would be necessary. We present a potential method of analysis to minimize the effect that aging has on discrimination efficiency; we show that by discarding the first principal component, which contains information on the variations due to oxidation, we can improve discrimination efficiency thus improving the robustness of our technique. © (2017) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only. Publisher PDF

We investigate the transition of optical regimes of miniaturized optical systems using two canonical examples, where the refraction of light limits the system performance. A ball-lens and a solid immersion lens (SIL) are considered, whose refractive responses can be intuitively described by ray optics when the system size is relatively large. For miniaturized systems, the optical response differs from that of conventional large systems. Since such new responses occur when the refractive response of light start to disappear, this boundary is called the refraction limit. Our intension is to bring insights into new phenomena beyond such a boundary.. First, the refraction limit of the ball-lens is identified with three different criteria: the focal length, the spot size, and the amount of depolarization. The light confinement effect of nanoscale SILs, which have an intentionally deformed shape, demonstrates the diminishing effect of the refractive response of light. Likewise, beyond the refraction limit of the miniaturized systems, the signature of refractive degradations vanishes, and the shape errors of elements become negligible.

This work reports a simple, miniaturized optical sensing module for liquid refractometry. It is based on a stable Fabry-Perot resonator consisting of two silicon cylindrical mirrors with a cylindrical lens in the core. The lens is formed by a capillary tube through which the analyte to be analyzed passes. This setup enables volume refractometry, where light propagates through the sample realizing high interaction depth. The cylindrical surfaces achieve light confinement, reducing the light escaping loss encountered in classical cavities with straight mirrors; and hence high quality factor (Q) over 1,000 is attained. Exploiting this high Q, we adopt uncommon refraction index (RI) measurement criterion: we operate at a fixed wavelength and detect the power drop caused as a consequence to the spectral shift with RI change. Performing experimental testing using a tunable laser and a power-meter, the normalized spectra for different mixture ratios of acetone and deionized water are obtained. The wavelength corresponding to the maximal power transmission from pure acetone is taken as a reference. A vertical line at this wavelength cuts the successive transmission curves and enables measuring the power drop in the linear region, and from it the refractive index change Delta n above the refractive index of the reference solution can be determined for 0.0023