One of the most distinctive features of photonic crystals (PhCs) is their unique wavelength dispersion allowing novel device concepts for enhancement of photonic functionality and performance. Here, we present examples of our design and demonstrations utilizing dispersion properties of 1D and 2D photonic crystals. This includes the demonstration of negative refraction in 2D PhC at optical wavelengths, filters based on 1D and 2D PhC waveguides, and the design of a widely tunable filter involving 1D PhC.
On the foundation of joint experience acquired by several research centres there was defined the roadmap to the desired single technological platform for fabrication of a specific class of photonic integrated circuits, which are controlled by mechanical means. In the paper the challenges of fabrication of such photonic circuits are discussed. The main arguments in favour of the Silicon-on-Insulator materials system as the basis for the platform are presented. Options for the mechanics-to-optics arrangement, materials and processes are described and illustrated with the current achievements from the authors' labs. In the roadmap the preference is given to the vertical arrangement in which, the mechanical part is stacked above the waveguiding layer. A flexible trimming routine is designed to complement the process flow if the technologies developed cannot provide the required reproducibility.
Optical add/drop filters using two-dimensional photonic crystals (PC’s) are presented for different designs. In-plane channel add/drop filter composed of two waveguides and an optical resonator system is very compact, but sensitive to the losses. While add/drop filter based on a contra-directional PC waveguide coupler is much more robust to the losses, and reasonable compactness is possible with careful designs. The possibility to utilize the PC dispersion properties to design optical filters is also discussed briefly.
We report on the fabrication and characterization of 2D photonic crystals (PhCs) in InP/InGaAsP/InP heterostructures. It is demonstrated that Ar/Cl2 based chemically assisted ion beam etching (CAIBE) is a very promising method to obtain high aspect ratio etching of PhCs in the InP-based materials. With this process, it is possible to obtain PC-holes as deep as 3 microns even for feature (PhC-hole) sizes as small as 200-250 nm. The optical characteristic of the fabricated PhC-based elements/devices such as line-defect waveguides, in-plane resonant cavities and drop-filter based on contra-directional coupling will be reported. The devices were measured using end-fire coupling and the obtained results were simulated using the 2D finite difference time domain (FDTD) method including an effective loss-approximation. The etched PhC-waveguides show low transmission losses, less than 1 dB/100 μm. A quality factor of 400 for a 6 micron long cavity with 6-hole mirrors is obtained. Finally, drop-functionality in a PhC-based filter using contra-directional coupling is demonstrated.
Photonic crystal waveguides in InP-based heterostructures are studied experimentally and theoretically. The waveguides are fabricated in an InP/GaInAsP/InP low index contrast heterostructure using Ar/Cl2 Chemical Assisted Ion Beam Etching, and characterized using the end-fire method. The obtained experimental near-infrared transmission spectra are further analyzed by comparing with theoretical results calculated by the finite-difference time-domain method. A loss of 1 dB/100 μm in the photonic crystal waveguides is demonstrated. The mini-stop bands, positioned in agreement with our theory, are observed. In-plane cavities with photonic crystal boundaries inside the waveguide are also realized. A quality factor of 400 for a 6 mm long cavity is obtained.
We model upconversion and migration in an ensemble of inhomogeneously distributed erbium ions. Treating Er- clusters as fractal objects we find the dependence of the upconversion rate on the population inversion for different fractal dimensions.
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