Compact Waveguide Devices Research Articles

Femtosecond Laser Micromachining of Cladding Waveguides in KTiOAsO4 Crystal for Second‐Harmonic Generation

Second‐harmonic generation (SHG) of green lasers generated in KTiOAsO4 (KTA) cladding waveguides fabricated by femtosecond laser direct writing (FsLDW) is reported. The minimum propagation loss of the fabricated waveguides is determined to be 2.39 ± 0.24 dB cm−1 at 1064 nm. The SHG performance is characterized by utilizing a 1064 nm pulsed laser. The maximum SHG conversion efficiency reaches 13.67%. This work suggests potential applications of KTA crystals and FsLDW technology in definition of compact waveguide devices for integrated nonlinear optics.

Silicon nitride waveguide devices based on gradient-index lenses implemented by subwavelength silicon grating metamaterials.

The rapid development of photonic integrated circuits demands the design of efficient and compact waveguide devices such as waveguide tapers and crossings. Some components in the silicon nitride (SiN) waveguide platform are superior to their counterparts in the silicon waveguide platform. Designing a compact SiN waveguide taper and crossing is crucial to reduce the size of SiN photonic components. In this paper, we utilize the focusing property of the Luneburg lens to design an SiN taper connecting a 10-µm-wide waveguide to a 1-µm-wide waveguide. Three-dimensional full-wave simulations indicate that the designed 13-µm-long taper has an average transmission efficiency of 92% in the wavelength range of 1500-1600 nm. We also present an in-plane SiN waveguide crossing based on the imaging property of the square Maxwell's fisheye lens designed with quasi-conformal transformation optics. The designed waveguide crossing occupies a compact footprint of 5.65µm×5.65µm, while its average insertion loss is 0.46 dB in the bandwidth of 1500-1600 nm. To the best our knowledge, the designed SiN waveguide taper and crossing have the smallest footprints to date.

Large area three-dimensional photonic crystals with embedded waveguides

Three-dimensional photonic crystals are attractive for very compact waveguide devices. A novel interferometric lithography technique for fabricating three-dimensional photonic crystals is presented, which allows for independent dimensional control of each axis of the crystal. Previous interferometric approaches using 3, 4, 5, or more beams have inherent constraints between the lattice constants and the exposure wavelength. With this new technique, it is possible to control each individual crystal lattice constant largely independent of the exposure wavelength, vastly increasing the available parameter space. Both mathematical models and experimentally realized three-dimensional photonic crystals, over 2 cm2 in size and up to 12 μm, are presented. Photonic crystals with integrated waveguides are of particular significance. A new approach to fabricating waveguides embedded in a three-dimensional photonic crystal is also presented. This approach uses multiple-exposure wavelengths, with one longer wavelength propagating throughout the photoresist for the photonic crystal fabrication and another shorter highly absorptive wavelength for the waveguide fabrication. This new approach to waveguide fabrication leads itself to scalable manufacturing using standard semiconductor lithography equipment.

TO COMPACT WAVEGUIDE DEVICES BY DIELECTRIC AND FERRITE LAYERS

In this paper, a method is proposed to compact waveguide devices at a desired frequency. In this method, a previously designed hollow waveguide is fllled with several dielectric and ferrite layers alternately so that the characteristic impedance of the waveguide is not changed. First, the permittivity and permeability of a flctitiously mixed material is obtained. Then, the required permittivity and permeability of dielectric and ferrite layers are obtained at desired frequency. The usefulness of the proposed method is verifled using some theoretical and simulation examples.