L.G. de Peralta

Image Formation in Wide-Field Microscopes Based on Leakage of Surface Plasmon-Coupled Fluorescence

A proof-of-concept imaging technique that combines the advantages of wide-field surface plasmon, leakage radiation, and total internal reflection fluorescence microscopy methods is presented. High-contrast non-scanning images with subwavelength resolution of patterned and homogeneous samples coated with a fluorescent material were demonstrated. We show that the image formed in the back focal plane of the objective lens can be reconstructed from the image of the samples surface using an algorithm similar to that used in computerized tomographic imaging. Our experimental results suggest that there is a 1-D Fourier transform relationship between any line amplitude profile at a given angle passing through the center of the samples surface image and a line amplitude profile passing through the center of the back-focal-plane image at the same angle.

Reflective arrayed waveguide grating multiplexer

A high-performance reflective arrayed waveguide grating multiplexer/demultiplexer designed for compatibility with silicon integrated circuit processing is described. The grating, folded by a flat reflecting surface, can be printed in a single-exposure field of a photolithographic stepper. Advanced plasma assisted deposition is used to prepare waveguides with very low loss and minimum birefringence. Multiplexers with 40 channels separated by 100 GHz show intrinsic insertion losses of -2.4 dB, channel uniformity less than 0.6 dB, and very low polarization dependent wavelength shift of 0.012 nm.

Silicon-dioxide waveguides with low birefringence

We describe the use of highly boron-doped silicon dioxide for the preparation of optical waveguides with very low birefringence. Plasma-enhanced chemical vapor deposition was used to vary the boron content from 5 wt% to 10 wt%, at a constant phosphorus content of 4.8%. A transition from compressive to tensile stress was observed at a boron concentration of 9.1%. Pedestal-type waveguides formed with the high-boron top cladding layer show low loss of 0.02 dB/cm. Arrayed waveguide grating devices with a polarization-dependent wavelength shift of 0.01 nm and excellent stability have been demonstrated.

Single-mode operation from an external cavity controlled vertical-cavity surface-emitting laser

Single-mode operation from an index-guided vertical-cavity surface-emitting laser (VCSEL) has been achieved by using a fiber Bragg grating (FBG) as an external selective wavelength reflector. The spectral characteristics of the external cavity controlled VCSEL under static and dynamic conditions have been studied. The FBG provided stable single mode operation under pseudorandom modulation with a sidemode suppression ratio of /spl sim/30 dB from 500 Mb/s up to 4 Gb/s at room temperature.

Reconfigurable optical filter based on digital mirror arrays

We present a reconfigurable optical filter with multiple passband channels based on the combination of a diffraction grating and an array of digital micromirrors. The filter allows for adjustment of the central frequency of its individual passband channels to match standard wavelength grids with precision better than 0.033 nm. The number of channels, the channel passband width, and the channel peak profile can be dynamically reconfigured by changing the periodic pattern imposed to the digital micromirror array. Experimental results are in excellent agreement with basic design relations describing the spectral characteristics of the filter.

Reconfigurable direct space-to-time pulse-shaper based on arrayed waveguide grating multiplexers and digital micromirrors

We describe a dynamic direct space-to-time pulse shaper based on the combination of a reflective arrayed waveguide grating multiplexer and an array of digital micromirrors used as an external reflector. Spatial modulation was obtained by imposing a reconfigurable periodic structure on the digital micromirror array. The period of this structure and the number of reflecting micromirrors within each period was varied to produce pulse sequences with variable repetition rates within the burst and different pulsewidths. Experimental results are in excellent agreement with simulated temporal output response.

Temperature-insensitive reflective arrayed-waveguide grating multiplexers

We present a new approach to temperature compensation of silica-based arrayed-waveguide grating multiplexers. An external mirror rotating with temperature at a constant rate, in combination with a reflective multiplexer, is used to compensate for the temperature-induced change of the refractive index, and the resulting wavelength shift of individual channels, making the device athermal. A wavelength-temperature slope of less than 3.2/spl times/10/sup -4/nm//spl deg/C was obtained in the temperature range 5/spl deg/C-70/spl deg/C, without noticeable degradation in the device performance.

Optical Reflectivity of Asymmetric Dielectric–Metal–Dielectric Planar Structures

We report simulations and experimental results on the incidence-angle dependence of the optical reflectivity of asymmetric dielectric-metal-dielectric planar structures. Transfer-matrix method and 2-D finite-element analysis revealed the presence of multiple resonances that were attributed to the surface plasmon (SP) polariton mode at the metal-dielectric interfaces and guided-wave polariton modes within the asymmetric dielectric-metal-dielectric waveguide. The number of guided-wave polariton resonances scale with the thickness of the dielectric guiding layer while the SP resonance remained essentially unaltered. These findings were validated through reflectivity measurements on sapphire-metal-polymer structures.

Reconfigurable Add–Drop Optical Filter Based on Arrays of Digital Micromirrors

We demonstrate a universal reconfigurable add-drop optical filter based on arrays of digital micromirrors. Our approach allows for reconfiguration of the device parameters for operation in different sets of channel wavelengths, even or uneven channel-to-channel separation, adjustable channel passband, and dynamic add-drop of optical signals. The proposed device shows insertion loss at the center wavelength in the all-pass configuration of 7.6 dB, extinction ratio of 35 dB, channel isolation better than 24dB, negligible loss ripple, and possibility of reconfiguration time in the order of microseconds. Although designed for demonstration on optical telecommunication frequencies, the high-flexibility features of the proposed add-drop filter allow it to be used for other optical wavelength-based filtering/switching applications.

High-resolution pulse shaper based on arrays of digital micromirrors

We describe an optical Fourier transform pulse shaper based on a combination of a diffraction grating and a reconfigurable array of digital micromirrors. The pulse shaper allows for adjustment of separation between consecutive pulses within a pulse burst and the length of the burst. Pulse separation, burst length, and number of pulses can be dynamically reconfigured by changing the periodic pattern imposed to the array of digital micromirrors. Experimental results on binary intensity modulation are in excellent agreement with basic design relations describing the spectral and temporal characteristics of the pulse shaper.