Niclas Carlsson

Fabrication and characterization of different types of two-dimensional AlGaAs photonic crystal slabs

Photonic crystals having two-dimensional periodicity on a length scale of 320–450 nm are fabricated by electron beam lithography in combination with high-aspect-ratio dry etching. To achieve three-dimensional control of the optical properties, three kinds of dielectric waveguide structures based on AlGaAs heterostructures, that is, semiconductor-clad, air-bridge, and oxide-clad structures, are investigated. The ability to guide light through such photonic crystal devices is demonstrated by optical transmission measurements. Clear photonic band gap effects resulting in 30 dB attenuation of the transmitted light can be observed in the stop-band regions. The measured results are in good agreement with theoretical band-structure calculations and with numerically computed transmission spectra obtained by the finite-difference time-domain method.

AlGaAs-based two-dimensional photonic crystal slab with defect waveguides for planar lightwave circuit applications

An AlGaAs-based near-infrared 2-D photonic crystal (PC) with an air-bridge structure featuring defect waveguides has been developed. For the sample without defect waveguides, measurements of the optical transmission characteristics in the wavelength range from 850 nm to 1100 nm showed a deep attenuation due to a bandgap with 30-35 dB attenuation and transmittance of nearly 100% for the guided modes. Optical propagation properties of defect waveguides were obtained by two methods: measurements of transmission spectra and plan-view observations of the optical beam trace along the waveguide with an infrared-vidicon camera. 3-D finite-difference time-domain simulations for the band structure and transmission spectra in the air-bridge slab with and without defect waveguides have revealed the appearance of four defect propagation modes specific to the defect waveguide, between two slab modes for the defect-free photonic crystal slab. These defect modes were experimentally identified in the measured transmission spectra.

Experimental verification of guided modes in 60°-bent defect waveguides in AlGaAs-based air-bridge-type two-dimensional photonic crystal slabs

Sixty-degree-bent defect waveguides (DWGs) in an AlGaAs-based air-bridge-type two-dimensional photonic crystal (2D PC) slab were fabricated, and the resulting optical transmission spectra and the plan-view image of the optical beam propagating along the bent DWG were measured in the wavelength range between 850 and 1100 nm. Using the two output ports of the stripe waveguides, one aligned to and another offset from the output edge of the bent DWG, the guided mode specific to the DWG and the slab mode in the defect-free PC slab were experimentally observed with the same sample. These results were verified using the calculated band structure and transmission spectra.

Two-dimensional AlGaAs photonic crystal air-bridge structure with defect waveguides for miniaturized planar light-wave circuit

An AlGaAs-based two-dimensional (2D) photonic crystal (PC) air-bridge structure with defect waveguides has been fabricated for an application to miniaturized planar lightwave circuits. Measured optical transmission characteristics showed a good agreement with theoretical band structure calculation for the sample without waveguides, while optical beam transmission through the waveguide was observed in the wavelength ranging around 1 /spl mu/m for the sample with waveguides.

Light propagation characteristics of photonic crystal waveguide for miniaturized ultrafast optical-pulse control/delay devices

Photonic crystals (PCs) having two-dimensional (2D) periodicity on a length scale of 320-450 nm were fabricated by electron beam lithography in combination with high- aspect-ratio dry etching. To achieve three-dimensional control of the optical properties, three kinds of dielectric waveguide structures based on AlGaAs heterostructures, that is, semiconductor-clad (SC), air-bridge (AB), and oxide-clad (OC) structures, were investigated. Observation of light propagating through such photonic crystal devices was employed by optical transmission measurements. Clear photonic bandgap effects resulting in 30-dB attentuation of the transmitted light could be observed in the the bandgap regions. The measured results were in good agreement with calculated band-structures and transmission spectra using a Fine-Difference Time-Domain (FDTD) method. Straight, sixty degree-bent and Y-branch defect waveguides (D-WGs) in a 2D- PC slab were fabricated, and the resulting light propagation characteristics were measured by two methods. One was measurement of transmission spectra at wavelengths ranging from 850 to 1100nm. Another was plan-view observation of the optical beam race trace along the waveguide measured with an IR-vidicon camera. Three-dimensional FDTD simulations for the band structure and transmission spectra in the air- bridge slab with and without defect waveguides resulted in the appearance of four defect propagation modes specific to the defect waveguide, between two slab modes for the defect- free PC slab. As an example of the future-promising application of the 2D-PC slab, an ultra-small and ultra-fast optical switching device including quantum dots as large optical non-linearity (%chi3+S) media is proposed. To demonstrate such a device, recent advancement of a nano- probe assisted processing of arrayed quantum dots is discussed. Achievement of this technology will provide us with a possibility of extremely miniaturized all-optical switching devices in the OTDM optical communication network.

AlGaAs-based two-dimensional photonic crystal with defect waveguides for miniaturized ultrafast optical-pulse control/delay devices

An AlGaAs-based near IR 2D photonic crystal with an air- bridge structure featuring defect waveguides has been developed. For the sample without defect waveguides, measurement of the optical transmission characteristics in the wavelength ranging form 850 nm to 1100 nm showed a deep bandgap with 30 dB to 35 dB attenuation and transmittance of nearly 100 percent. Optical propagation properties of defect waveguides were obtained by two methods: measurement of transmission spectra at wavelengths ranging from 850 to 1100 nm, and with plan-view observations of the optical beam trace along the waveguide measured with an IR-vidicon camera. 3D FDTD simulations for the band structure and transmission spectra in the air-bridge slab with and without defect waveguides resulted in the appearance of four defect propagation modes specific to the defect waveguide, between two slab modes for the defect-free photonic crystal slab. These defect modes were experimentally identified in the measured transmission spectra. Low group velocity near the band edge was also confirmed through 200-fs pulsed laser- beam propagation measurement.

Characterization of two-dimensional AlGaAs photonic crystals with waveguides as a test device

Summary form only given. A two-dimensional (2D) photonic crystal is expected as one feasible candidate for future compact devices such as remarkably miniaturized planar photonic-circuits with active and passive components integrated. We report on characterization as a test device, of a 2D semiconductor (AlGaAs) photonic crystal equipped with two waveguides of narrow-width for coupling to input and output signals. We fabricated a series of periodic air-rods structures by perforating holes in an epitaxially-grown Al/sub 0.1/Ga/sub 0.9/As core layer (0.5 /spl mu/m-thick) and a 2.0 /spl mu/m-thick Al/sub 0.35/Ga/sub 0.65/As cladding layer on a GaAs substrate.

Characteristics of two-dimensional AlGaAs photonic crystals in a waveguide configuration for test devices

Recently, two-dimensional (2D) photonic bandgap crystals (PBCs) of III-V compound semiconductors have attracted increasing interest for potential in application, in particular, for developing remarkably-miniaturized planar photonic circuits based on active and passive components such as micro-cavity light emitter, optical switch and straight-bent-coupling waveguide. Up until now, however, very few experimental works have been done. We report microfabrication of 2D photonic-crystal test devices with various air-rod patterns for studying in detail optical propagation characteristics for designing PBC-based planar photonic circuits.