Integration differentiates devices


Optoelectronic integration

ThreeFives Photonics says that its single-chip DWDM receiver is one more step on its roadmap towards developing a complete monolithically integrated optoelectronic subsystem on a chip.

Monolithically integrated optoelectronic chip developer ThreeFive Photonics, spun off from Delft University in 2001, is sampling its first product. The company claims this is the world's first multi-wavelength receiver on a single chip, based on a "previously unseen level of integration for volume-produced opto components".

Instead of separate, discrete components for the functions of the receiver and optical interconnection, the Argo is fabricated on a single indium phosphide (InP) chip. It integrates an arrayed waveguide grating (AWG) wavelength demultiplexer with one high-speed PIN photodetector and one high-gain trans-impedance amplifier per channel into a single compact multi-wavelength receiver, hermetically sealed in a 14-pin butterfly package.

The first product is the 4-channel 2.5Gbit/s Argo A4D2.5 multiwavelength receiver, which has a channel spacing of 100GHz. Uses include:

  • long-haul and metro DWDM (SONET OC-48, SDH STM-16);
  • DWDM datacoms (Gigabit Ethernet and Fibre Channel);
  • DWDM for regional interconnects digital CATV.

Monolithic integration allows a package of 30x30x7.6mm and an area reduction of about 80% compared to equivalent discrete components or hybrid solutions, but at a similar price. "Argo will be applied mainly in metropolitan networks," says ThreeFives CEO Wouter Deelman. "Optoelectronic integration in InP not only leads to very small systems at lower price levels but also systems that are more robust, require less maintenance and repair, and consume less power. The latter is the most critical factor in some metro areas."

ThreeFives' Erik Pennings adds, "Optoelectronic integration introduces economies of scale to the photonic industry as it does in the silicon industry. In silicon-based semiconductor manufacturing, a product becomes cheaper when you produce a larger volume. But photonic systems manufacturing could not be optimised in quite the same way. We had several material systems rather than one, each lacking the required volume for becoming the standard. Photonic systems consisted of discrete components for different functions, connected through optical fibres."

Benefits of integration
Integrated chips have fewer components, giving easier inventory management, less testing of purchased components, and easier assembly of systems with less complex designs, shortening the system design cycle.

Compared to one DWDM demultiplexer and four separate receivers, integrated chip benefits include: lower costs; reduced labour from fibre handling and splicing; and a reduced inventory and component count.

A four-channel Argo receiver reduces the number of components from five to one and the number of parts from two to one.

The Argo technology platform also allows multiple configurations. ThreeFives says that subsequent versions will include the 16-channel 2.5Gbit/s A16D2.5 and the 4-channel 10Gbit/s A4D10 receiver. Advantages are greater for 16 channels, where the component count is cut from 17 to one. This demonstrates "the scalability of integrated optoelectronics and the increasing advantages for larger-scale integration," says Pennings.

ThreeFives states that Argo is just the first of a range of products based on monolithic optoelectronic integration in InP. Integration of the phased array demultiplexer with other opto components such as switches and amplifiers will lead to multi-wavelength transmitters, optical channel monitors, add/drop multiplexers and cross-connects. The ultimate aim: to integrate a complete telecoms subsystem on a single chip.

  • In March, ThreeFive Photonics relocated to: De Molen 25, 3994 DA, Houten, Netherlands; Tel: +31 (0)30 635 5220;

The photonics industry has entered a new stage of development. The manufacturing processes and design philosophies of the past have turned into bottlenecks. The market demand for better system performance at lower prices has created a climate that is favourable for monolithic integration using indium phosphide technology.

Until the end of 2000, carriers expanded their networks rapidly but were limited by the supply of systems and components. Now carriers have cut their capital spending and re-focused from capacity increase to cost reduction and improvement of financial performance. These demands have changed the supply chain, down to the choice of technology.

As the long-haul market and city-to-city backbones are mostly in place, operators short on capital need to address metro access and services without increasing costs. But for metro applications, close to the subscriber, operators need large numbers of systems with more functionality but lower costs per add/drop point (since small changes in unit price can hugely effect deployment cost) as well as reduced floor-space and power consumption.

These requirements cannot be met by current technologies. Traditional individual packaging of components connected by fibre introduces signal loss and mechanical instability. Also, fibre attachment is still mostly manual, which is costly and difficult to scale up.

To improve on this discrete component approach, hybrid integration was developed, where components of different materials are packaged together without internal fibre connection. This reduces size considerably, but introduces complex packaging which cannot be scaled and lacks flexibility.

The industry needs to overcome these limitations with a technology that allows volume manufacturing of components at low unit prices, similar to CMOS silicon manufacturing of electronic semiconductors. The challenge is to develop the optoelectronic equivalent.

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