Barrie Keyworth

ROADM subsystems and technologies

ROADM (reconfigurable optical add/drop multiplexers) subsystems can be implemented using a variety of architectures and technologies, each with their own trade-offs in performance and functionality. This paper describes the available technology options, and corresponding subsystem features, while highlighting the key advantages and implementation challenges associated with each.

Addressing Manufacturability and Reliability of MEMS-based WSS

Initial design-in of WSS-based modules posed many uncertainties due to several technology firsts. We discuss key challenges and steps taken to successfully complete qualification and validation and will demonstrate the level of stability achieved.

Optoelectronic switching: technology and architecture

In optical networks using wavelength routing the ability to assign wavelength channels independently on each link is very useful but to maintain optical transparency then becomes very difficult. In fact optical transparency is not a specific requirement of networks that transmit signals independent of their format. Transponders can provide wavelength conversion if adequate performance can be achieved in the electronic routing of signals independent of format. We demonstrate experimentally a 10 multiplied by 10 matrix switch that is bit-rate, format, and modulation transparent for analogue signals and data at various rates up to 2.5 Gbps. The switch architecture is suitable for use in a wavelength converting transponder node. Prospects for staging these devices at OC-48 and OC-192 rates are discussed.

Wideband four-channel optical transmitter package using vertical cavity surface emitting laser arrays

We report on the fabrication of a prototype multichannel optical transmitter based on vertical-cavity surface- emitting lasers (VCSELs). The package consists of an array of four VCSELs, mounted directly on a RF circuit board, and UV-curable polymer microlenses and waveguides which couple the laser output to a multimode fiber ribbon. Light from the lasers is captured by refractive polymer microlenses positioned on a glass substrate above the VCSEL array. The lenses focuses the light signals onto angled reflective end facets in the polymer waveguides. These waveguides are situated on a separate glass substrate which is bonded to the lens substrate. The light is then coupled form the waveguides to a multimode fiber ribbon; the average measured coupling efficiency was 47.5 percent +/- 3 percent. Experimental measurements reveal an analog bandwidth of 2.65 GHz per channel with better than 30 dB isolation between adjacent channels for frequencies up to 2 GHz without active heatsinking. In addition, it has been experimentally verified that this isolation is limited by the parasitics inherent in the VCSEL array rather than the parasitics of the device driver circuitry.

Beam extractor card for free-space optical backplanes

The fabrication of an interface card to extract free-space beams from an optical backplane and deliver them to either photodetectors on a printed circuit board or to fiber, is described. Experimental results are presented for polymer waveguides with 45 degree end reflectors and refractive polymer microlens arrays used in the fabrication of the card. Results for 1 by 4 and 4 by 4 prototypes which intercept 4 and 16 free-space beams, respectively, are also discussed. The 1 by 4 prototype extractor card coupled 4 free-space beams on 500 micrometer centers to direct-dispensed polymer waveguides with 45 degree end reflectors and finally to 100 micrometer core multimode fibers. Total throughput losses (free-space to fiber) for each of the four channels were 2.1, 2.4, 2.5, and 2.8 dB. In order to implement a fully connected 4 by 4 extractor card, laser-written waveguides were developed which have smaller cross-sections thereby allowing more channels and standard 62.5 micrometer core fiber to be used. The second prototype card intercepts 16 free-space beams in a 4 by 4 array (500 micrometer centers) and couples them into two sets of eight laser-written waveguides (50 by 50 micrometer cross-sections), which in turn are coupled to two multimode fiber ribbon cables with 62.5 micron cores on 250 micrometer centers. Total insertion losses from free-space to fiber ribbon are typically 4 - 5 dB. The refractive microlens arrays, which are used to focus the light onto the waveguide end-reflectors, are fabricated using an extremely simple direct- dispense technique which achieves excellent quality and uniformity. Experimental results are reported.