The microlens arrays have been widely used for different optoelectronic applications. The demand for compact optical devices necessitates the deployment of even smaller microlens arrays; however, as the spacing between individual lens reduces and the lens diameter approaches to the length scale of the incident wavelength of light, the diffraction starts playing a critical role and produces a significant impact on the final focusing properties of the optical field. In this paper, we analyze the focusing characteristics of alldielectric ultra-compact metasurface lens arrays for efficient optical device applications, constructed by a kind of broadband planar lenses composed of subwavelength nanoscatterers. By using the 3D finite-difference time-domain (FDTD) method, the focusing and diffraction-based crosstalk effects caused by the changing physical spacing between adjacent metalenses, the diameter of microlenses, the operating wavelength, and the array size are rigorously investigated. Analysis of the achieved results show that a larger spacing, a larger lens size, a shorter wavelength can lead to a weaker focusing crosstalk effect. Moreover, the crosstalk effect does not have a significant dependence on the array overall size. This research study may provide an important technological reference to design an array of all-dielectric planar metasurface lenses with a well-controlled focusing performance and pave the way further toward application of metasurface lens arrays in compact optical sensing, coupling and detecting system designs.

Abstract-In this paper, we propose tunable optical interleaver filters based on the combined Michelson interferometer (MI) and the Gires-Tournois interferometer (GTI) with polarization diversity. The tuning capability is achieved by integrating liquid crystals into the interleaver. In addition to the tunability, it is also shown that the response for this proposed interleaver has a flat-top. Various GTI-MI LC-based interleaver structures are discussed in this paper and their performance, in terms of the flat-top and the pass band ripple, are judged. These structures have the advantages of low operation voltage requirements and design simplicity. A GTI-MI interleaver has been fabricated and tested. The experimental results show that the interleaver has tunable response.

In this paper, a coupled Fabry-Perot cavities filter, using the liquid crystal as the tunable medium, is investigate to achieve tunable flat top filtering performance across the C and L bands. A tandem coupled Fabry-Perot is presented for a tunable passband filter with flat top and minimum ripple in the passband. The overall tuning range of the filter is 172 nm. Several designs are shown with comparable performance to the commercial available 100 GHz fixed single channel filters.

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BACKGROUND: Fetal heart activity adds significant information about the status of the fetus health. Early diagnosis of issues in the heart before delivery allows early intervention and significantly improves the treatment. OBJECTIVE: This paper presents a new adaptive filtering algorithm for fetal electrocardiogram (FECG) extraction from the maternal abdominal signal, known in literature as abdominal electrocardiogram (AECG) signal. Fetal QRS complex waves will be identified and extracted accurately for fetal health care and monitoring purposes. METHODS: We use discrete wavelet transform recursive inverse (DWT-RI) adaptive filtering algorithm for this objective. Thoracic maternal electrocardiogram (MECG) is used as a reference in the proposed algorithm and FECG components are extracted from AECG signal after suppressing the MECG projections. The proposed algorithm is compared to other typical adaptive filtering algorithms, least mean squares (LMS), recursive least squares (RLS), and recursive inverse (RI). RESULTS: Fetal QRS waveforms successful identification and extraction from AECG signal is evaluated objectively and visually and compared to other algorithms. We validated the proposed algorithm using both synthetic data and real clinical data. CONCLUSIONS: The proposed algorithm is capable of extracting fetal QRS waveforms successfully from AECG and outperforms other adaptive filtering algorithms in terms of accuracy and positive predictivity.