Advances in local area optical data communication systems

This paper reviews optical fibre technology for local area optical communications systems. Technologies used in local systems include single and multimode fibre, single and multimode lasers, optical modulators, photodetectors, wavelength division multiplexing, multilevel modulation formats, electronic packet switching, electronic equalization and error correction. These methods have enabled the local area optical link data rate to increase from 0.1 Gb s^-1 in 1990 to nearly a Tb s^-1 in 2019. The challenges to increasing link data rates further, while reducing the transmitted power per bit, at reduced cost are discussed. Potential technical solutions and newly proposed methods which might address these challenges are highlighted.

Electrical and Optical Interconnection-Technology based on Ormocer - Inorganic-Organic Hybrid Materials

Photopatternable hybrid inorganic-organic polymers with negative resist behaviour have been developed and tested for evaluation in optical and electrical interconnection technology. They are composed of inorganic oxidic structures cross-linked or substituted by organic groups. The synthesis starts from organosilane precursors reacted by sol-gel-processing in combination with organic crosslinking of polymerisable organic functions. As a result of these functionalities the properties of the ORMOCER®s are adjusted to the particular applications. Systematic variation of composition combined with adaptation to micro system technology allows great flexibility in processing. The main features of these materials are:

• Combined use as dielectric and passivation layers in electrical systems and devices as well as core and cladding for optical applications enables e/o applications with high integration levels.

• Postbaking at moderate temperatures (120 - 170 °C) enables processing on low-cost substrates such as FR-4 (a glass-fibre reinforced epoxy-polymer).

• Easily adaptable to thin film technology: spin-on with planarisation > 90 %, via diameters down to 20 μm and high aspect ratio for optical waveguides have been achieved.

Synthesis, modification of the resins towards technological needs, their thin film technology and the resulting demonstrators will be discussed.

512-channel vertical-cavity surface-emitting laser based free-space optical link

A vertical-cavity surface-emitting laser based bidirectional free-space optical interconnect has been implemented to interconnect two printed circuit boards. A total of 512 clustered channels with a density of 2844 channels/cm2 are transmitted over a distance of 83 mm. The optical interconnect is a combination of refractive microlenses and diffractive minilens relays.

Parallel free-space optical interconnect based on arrays of vertical-cavity lasers and detectors with monolithic microlenses

We investigate the use of low-threshold 980-nm vertical-cavity surface-emitting lasers for free-space optical interconnects. The vertical-cavity surface-emitting lasers and backilluminated detectors are monolithically integrated with microlenses on the back sides of the growth substrates to eliminate the necessity of external optics. With a channel pitch of 250 mum, an interconnect length between boards of the order of 5 to 10 mm with a ?50-mum lateral alignment tolerance can be achieved without external relay optics. The complete link is modeled to predict the system's efficiency and maximum bit rate. Data transmission at 500 Mbits/s per channel is demonstrated. The data rate was limited by parasitics, not the inherent bandwidth of the laser diodes.

Terabit optical local area networks for multiprocessing systems

The design of a scalable optical local area network formultiprocessing systems is described. Each workstation has aparallel-fiber-ribbon optical link to a centralized complementarymetal-oxide silicon (CMOS) switch core, implemented on a singlecompact printed circuit board (PCB). When the Motorola Optobusfiber technology is used, each workstation has a data bandwidth of 6.4Gbits/s to the core. A centralized switch core interconnecting 32workstations supports a 204-Gbit/s aggregate data bandwidth. Theswitch core is based on a conventional broadcast-and-selectarchitecture, implemented with parallel CMOS integrated circuits(IC's). The switch core scales well; by incorporation of theCMOS optoelectronic IC's with optical input-output, the electricalcore can be reduced to a single-chip optoelectronic IC with terabitcapacities. A prototype of an optoelectronic switch core has been fabricated and is described. The appeal of the architectureincludes its reliance on commercially available parallel-fibertechnology, its reliance on the well-developed markets of local areanetworks and networks of workstations, and its smooth scalability from the electrical to optical domains as technology matures.