Meeting the increasing demand for capacity in wireless networks requires the harnessing of higher regions in the radiofrequency spectrum, reducing cell size, as well as more compact, agile and power-efficient base stations that are capable of smoothly interfacing the radio and fibre segments. Fully functional microwave photonic chips are promising candidates in attempts to meet these goals. In recent years, many integrated microwave photonic chips have been reported in different technologies. To the best of our knowledge, none has monolithically integrated all the main active and passive optoelectronic components. Here, we report the first demonstration of a tunable microwave photonics filter that is monolithically integrated into an indium phosphide chip. The reconfigurable radiofrequency photonic filter includes all the necessary elements (for example, lasers, modulators and photodetectors), and its response can be tuned by means of control electric currents. This is an important step in demonstrating the feasibility of integrated and programmable microwave photonic processors. A tunable photonic microwave filter is monolithically integrated in an InP chip. The filter includes all of the required elements — a laser, a modulator and a photodetector — and its response can be tuned by controlling the electric currents.

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A monolithic integrated photonic microwave filter

A single-section, compact, passive polarization converter has been designed and fabricated on GaAs-AlGaAs. The device uses an optimized waveguide structure with angled-facets to obtain 90/spl deg/-polarization rotation in a single section; this waveguide structure eliminates the need for longitudinal variation and hence avoids any section-to-section coupling losses. A transverse electric (TE) to transverse magnetic (TM) polarization conversion of 96% is achieved for a conversion length of /spl ap/720 /spl mu/m.

Realization of a compact and single-mode optical passive polarization converter

A simple and general set of design rules for slanted-angle polarization-rotating waveguides is presented in this paper. These design rules are employed to construct single-mode SOI polarization rotators that offer significant advantages in conversion efficiency, optical loss, fabrication tolerance, spectral response and spatial dimensions relative to III-V components.

Design rules for slanted-angle polarization rotators

Wavelength dispersion (46) and spatial light modulation (50) are combined having regard for polarization management within a feedback control system for dynamically adjusting spectral power distributions among different wavelength channels (12) Micro-optic, hybrid, and planar implementations are proposed along with coupling schemes to larger fiber optic systems (84) Utility is found throughout multi-channel wavelength division multiplexing (WDM) transmission systems

Dynamically configurable spectral filter

Composite optical waveguide structures or mode transformers and their methods of fabrication and integration are disclosed, wherein the structures or mode transformers are capable of bi-directional light beam transformation between a small mode size waveguide and a large mode size waveguide. One aspect of the present invention is directed to an optical mode transformer comprising a waveguide core having a high refractive index contrast between the waveguide core and the cladding, the optical mode transformer being configured such that the waveguide core has a taper wherein a thickness of the waveguide core tapers down to a critical thickness value, the critical thickness value being defined as a thickness value below which a significant portion of the energy of a light beam penetrates into the cladding layers surrounding the taper structure thereby enlarging the small mode size. This primary tapered core structure may be present in either a vertical or horizontal direction and may be combined with further up taper or down taper structures in the directions transverse to the primary taper direction. Another aspect of the present invention is directed to a non-cylindrical graduated refractive index (GRID) lens structure. The non-cylindrical GRIN structure has a graded refractive index having a maximum value at its core and a minimum value at its outer edges. The grading of the refractive index is provided in a either the vertical or horizontal directions and may have either a fixed refractive index or a graded refractive index in the transverse directions. Yet another aspect of the present invention is directed to composite optical mode transformers that are combinations of the taper waveguide structures and the non-cylindrical graduated refractive index structures. Yet another aspect of the present invention is the further integration of the mode transformers with V-grooves for multiple input/output fibers and alignment platform for multiple input/output photonic chips or devices.

Integrated planar composite coupling structures for bi-directional light beam transformation between a small mode size waveguide and a large mode size waveguide

A novel integrated polarization converter based on ultra short bends is presented, which has a potential for low loss and small device size. A conversion value of 85% was experimentally measured with excess loss of 2.7 dB and overall dimensions of 975/spl times/83 /spl mu/m. Also 45% conversion was measured with extremely low excess loss of 0.4 dB for a device size of 760/spl times/86 /spl mu/m.

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Novel compact polarization converters based on ultra short bends

TE to TM converters with constant 45 degrees operation are a key component in OEICs for coherent optical system applications. A passive TE/TM-mode converter with a laterally tilted rib waveguide fabricated on a stepped substrate is proposed and investigated. The conversion effect has been simulated using scalar and vectorial two-dimensional finite difference methods. The device fabricated on

Passive mode converter with a periodically tilted InP/GaInAsP rib waveguide

An integrated optical circuit comprises a first device and a second device, which devices are connected by a polarization convertor The polarization convertor comprises a curved section of a waveguide, integrated in the optical circuit The curved section may comprise several differently curved subsections The conversion ratio is determined in part by the radius of curvature of the curved subsections as well as by the number of transitions between subsections

Integrated optical circuit comprising a polarization convertor

Beam spread transformers are required for chip-fibre couplings and must be polarisation-independent, show low losses and be economically produced. In a beam spread transformer (1) with an integrated structure having several buffer layers (5) mutually separated by conductive layers (6), an uncladded rib waveguide (7, 8) with a tapering area (9) is arranged on the top buffer layer (5). A section (11) over which the rib (8) extends is located between the interface (2) with the fibre and the tapering area (9). The waveguide layer (7) is completely removed from this section and the exposed buffer layer (5) is reduced to a width w2 which exceeds the width w1 of the continuous rib (8) in a symmetrical manner. The thus obtained additional rib (12) makes it possible for the coupling to be polarisation-independent and to be optimised with the increased heights (d1, d2, d3) thanks to the buffer layers (5).

Carl Michael Weinert

Papers

Novel compact polarization converters based on ultra short bends

Passive mode converter with a periodically tilted InP/GaInAsP rib waveguide

Integrated optical circuit comprising a polarization convertor

Integrated optical beam spread transformer

Cost-216 comparative study of S-bend and directional coupler analysis methods