Matt Pearson

Planar waveguide echelle gratings in silica-on-silicon

Silica planar waveguide echelle grating demultiplexers with 48 channels and 256 channels are described and demonstrated. Polarization effects due to stress birefringence and polarization-dependent grating efficiency have been eliminated using a modified polarization compensator and grating design. The devices have a polarization-dependent wavelength shift of less than 10 pm, and a polarization-dependent loss below 0.2 dB. The 48-channel device has a measured crosstalk of -35 dB, an insertion loss better than 4 dB, and a uniformity of 1 dB across the C-band.

Silicon-on-Insulator-Based Planar Circuit for Passive Optical Network Applications

A novel design of a silicon-on-insulator (SOI) filter for passive optical network applications is described. The SOI filter comprises a monolithically integrated planar reflective grating and a multistage Mach-Zehnder interferometer. The fabricated device showed low insertion losses and high optical isolation. To the best of our knowledge, this letter describes the first demonstration of an SOI circuit comprising monolithically integrated planar reflective grating and cascaded Mach-Zehnder interferometer

Arrayed waveguide grating demultiplexers in silicon-on-insulator

This paper presents theoretical and experimental results detailing the design and performance of arrayed waveguide grating (AWG) demultiplexers fabricated in silicon-on- insulator (SOI). The SOI waveguide is inherently multimode because of the high refractive index difference between Si and SiO2, although appropriate tailoring of the rib width to height ratio can be used to make single mode rib waveguides. This single mode condition cannot be met in the input and output combiner sections, which can therefore support many higher order modes. Modeling results demonstrate that coupling from a single mode ridge waveguide to the fundamental slab mode is typically two orders of magnitude larger than the coupling to higher modes. Hence the effect of multimode combiners on performance should be minimal. We also present calculations of bending losses which indicate that with a Si thickness of 1.5 micrometers , single mode rib waveguides can be made with radii of curvature as low as 200 micrometers . Such waveguides can also be made with zero birefringence. AWG devices were fabricated with 8 channels centered around (lambda) equals 1550 nm, and chip sizes less than 5 X 5 mm. The performance of these devices is compared with our modeling results.

Novel architecture for design of planar lightwave interleavers

This paper reports a novel architecture for the design of dense wavelength-division multiplexing interleavers based on planar echelle gratings. Double astigmatic point design of the echelle grating is discussed. The important and inherent limitation of aberrations associated with the echelle grating has been eliminated by the introduction of aberration free elliptical facets. A mechanism for compensating the variations of the refractive index with wavelength is also described. The theoretical analysis was used to design and manufacture remarkably low footprint 50/100 and 100/200 GHz interleavers in silica-on-silicon with the waveguide refractive index contrast of 0.62%. The comparison between the theoretical and experimental results shows an excellent agreement. The fabricated devices based on the proposed approach showed low nonuniformity in insertion loss, high dynamic range, and precise channel periodicity over the entire C band.

Planar comb filters based on aberration-free elliptical grating facets

A new approach for eliminating aberration effects through introduction of elliptical grating facets in optical comb filters is presented. Simulation results show remarkable improvements of comb filter performance for aberration-free elliptical facets compared to traditional flat facet designs. The proposed theory was validated through design and fabrication of 100-GHz-period planar silica-on-silicon comb filters for use in multiwavelength optical sources. Multimode interference structures were used to achieve both flat-top and Gaussian spectral comb filter responses. All devices showed high extinction ratio, low nonuniformity in insertion loss, and high degree of passband shape control.

The scalable planar waveguide component technology: 40 and 256-channel echele grating demultiplexers

Echelle grating demultiplexers with 40 channels (100 GHz channel spacing) and 256 channels (25 GHz channel spacing) have been fabricated on a silica-on-silicon planar waveguide platform. The optical performance is comparable for both devices, apart from the expected increase in insertion loss for the 256-channel demultiplexer. Adjacent channel crosstalk for both devices is -30 dB or better. The polarization dependent wavelength shift of the output channels is less than 0.01 nm. The echelle grating itself has been designed to reduce intrinsic polarization dependent loss to less than 0.2 dB. The 256-channel demultiplexer including output waveguides occupies a chip approximately 2 × 4 cm in size.

Planar waveguide echelle gratings: an embeddable diffractive element for photonic integrated circuits

We have demonstrated a 40-channel echelle grating demultiplexer with a 100 GHz channel spacing, using silica-on-silicon planar waveguides. We show the output spectrum of several channels, measured using a tunable laser source. The measured cross-talk is better than -35 dB, the insertion loss is approximately 5 dB including fibre-to-waveguide coupling, and the polarization birefringence has been eliminated using a modified compensator design which eliminates losses due to mode mismatch. Planar waveguide EG devices are also easily scalable to higher channel counts and the device described here is currently being adapted to a 256-channel demultiplexer chip.

Cascaded optical microspectrometer based on additive dispersion planar gratings

We demonstrate that planar reflective gratings can be used to design a cascaded microspectrometer that is capable of processing optical signals with different spectroscopic signatures. The filter is based on a double-grating additive dispersion architecture. The first planar grating is used to multiplex single-mode signals from the 1310-nm band into the fiber and weakly demultiplex the band around 1550 nm from the fiber. The second grating doubles the dispersion of the first grating, improves the rejection of stray light, and produces a box-like spectral response around 1550 nm at the output. The device was fabricated using a standard silica-on-silicon process with a refractive index contrast of 0.82% and has a remarkably small footprint of only 0.29 cm/sup 2/. Experimental measurements of the device show Gaussian-shaped spectral response at 1310 nm with a 1-dB bandwidth of 21 nm and box-like transmission at 1550 nm with a bandwidth of 33 nm. The insertion losses for the two channels were measured to be -4.7 and -5.8 dB, respectively. To the best of our knowledge, this is the first demonstration of an integrated planar lightwave circuit that is based on multiple reflective gratings. Applications of the microspectrometer for biophotonics, spectroscopy, and telecommunications are discussed.

Si/Si1−xGex photodetectors using three-dimensional growth modes to enhance photoresponse at λ=1550 nm

This article explores the use of Si1−xGex quantum-well layers with a coherent-wave or island-growth morphology in Si1−xGex based telecommunications photodetectors. The structural properties of such heterostructures have been determined by transmission electron microscopy, atomic force microscopy, x-ray diffraction, and Raman scattering. Photoluminescence and photocurrent spectroscopy measurements establish that strained, dislocation free Si0.5Ge0.5/Si superlattices were produced with band gaps as low as 0.745 eV, corresponding to an absorption edge near λ=1650 nm. These anomalously low band gaps result from a combination of reduced quantum confinement and higher local Ge concentration at the quantum-well thickness maxima. Waveguide photodetectors based on a coherent-wave Si/Si0.50Ge0.50 superlattice have achieved a photoresponse of 0.16 A/W at 1550 nm.

Silicon-on-insulator platform for building fiber-to-the-home transceivers

A silicon-on-insulator platform is proposed for building bi-directional transceivers for fiber-to-the-home applications. The platform includes a monolithically integrated planar reflective grating and a multi-stage interferometer combined with hybridization structures for placement of lasers and photodetectors.