Electro-absorption modulator provides 'missing link'

Among many potential applications for the new reflective electro-absorption modulator (R-EAM) are 10 Gbit/s wavelength division multiplexing (WDM) passive optical networks (PONs), and a simple means of linking radio antennas to a high speed optical cable - to extend the coverage of high data rate wireless technologies.

"The demand for higher and higher bandwidths is insatiable," says David Smith, CTO of CIP. "The challenge is to find low-cost architectures and components that can deliver progress cost-effectively. Reflective EAMs are potentially a breakthrough in this search, offering system builders a power efficient and low-cost means of extending ultra high speed optical fibre networks into the consumer domain."

The new InP device, the R-EAM-1550-LS, has been designed to suit high volume production and is available immediately in small volumes for development and trials.

R-EAM-1550-LS operates in the C band (1550 nm), and has a very low optical insertion loss of 3.5 dB typical. It will also operate with low drive voltages, and has low polarization-dependent loss (0.3 dB typical). Numerous design features on the die have been incorporated to optimize manufacturability and yield, and simplify coupling to optical fibre.

This economy is aided by the device's need for only a single optical fibre connection. The device also dissipates very little power and will operate uncooled in some configurations, reducing the total electrical power for many target applications.

One of the largest potential applications for R-EAMs is in fibre-to-the-home/premises (FTTH/FTTP) access network architectures. CIP's R-EAM component provides high-speed transmission capability by reflecting and modulating a 'seed' light that is transmitted throughout the network, and will comfortably operate at data rates up to 10 Gbit/s as will be needed in next-generation optical access networks.

Light from the multi-wavelength seed source can be split into different wavelengths easily for use in different segments of the network by means of an arrayed waveguide grating (AWG) - a readily available component.

Such architecture allows a R-EAM to deliver dedicated multi-gigabit optical data transmission facilities for clients without the expense of a tuneable wavelength source. In addition to minimizing the costs of the bidirectional (BIDI) fibre optic assembly required for client premises, this approach allows one standard BIDI to be manufactured and installed for all users.

CIP is already heavily involved in development work and trials in this general area, because of its novel reflective SOA (semiconductor optical amplifier) - launched in 2005. The new R-EAM-1550-LS expands the exciting architectural possibilities of WDM-PON to users requiring operation at 10Gbit/s.

A second major application for R-EAMs can be found in wireless networks. R-EAMs make it possible to extend the coverage of a wireless access point with a network of remote antennas. A single fibre optic cable could easily support 32 antennas operating on different wavelengths for example, providing a low cost means of extending the coverage of short-range, high datarate wireless technologies around a building or plant.

Because of the passive way in which R-EAMs can operate, the cost of remote nodes in this application could be extremely small, as in their simplest form they can be fabricated with just a R-EAM and a simple antenna and operate without any need for local power. As the R-EAM will also operate as a photodiode, these passive nodes can provide both uplink and downlink capabilities.

CIP manufactures the reflective EAM at its UK facility, and is supplying the new device in a butterfly package, including thermoelectric cooler, for engineering trials and initial applications. Other packages are available to order, to suit a customer's target application, and can be manufactured by CIP or its volume manufacturing partners.