Another approach to shrinking transceiver size

As other companies strive to halve the size of standard optical transceivers, Bookham Technology of Abingdon, Oxfordshire, UK, has come up with a way to integrate a trans-impedance amplifier directly into its transceiver package, which fits on a silicon chip.

Like the companies coming out with small-form-factor transceivers, Bookham Technologies is aware that "real estate" is a concern for customers. "Developing a range of transceiver products that allows them to reduce the size and complexity of the external circuitry needed, and hence cut the physical size of their equipment, is a logical step for us," Jeremy Mills, Bookham`s director of marketing, said in a prepared statement.

Bookham uses "asoc" technology to build standard and custom optical circuits on a silicon chip. Instead of optical fiber, asoc devices use on-chip silicon waveguides to channel light between the optical components on the chip. Each circuit consists of basic optical components such as transmitters, receivers, switches, and routers, which are integrated on the chip.

Bookham`s new transceiver design improves the transmission of the electrical signals produced by the photodiodes in an access network application. With an external transimpedance amplifier, the electrical signal travels from the photodiode onto the external circuitry printed circuit board through a pin on the transceiver package. Bookham officials say the signal can be degraded by electrical interference from other parts of the customer`s external circuitry, and the inductance of electrical connection can limit the quality of the signal.

By moving the transimpedance amplifier into the transceiver package, Bookham says it can reduce those effects and improve the sensitivity of the receiver. That means network designers can either increase the distance between successive transmitters and receivers, or support a larger number of splits from a single headend transmitter. The result is a lower number of components in the network.

The transceivers operate at rates to 155 Mbits/sec and are compatible with Synchronous Optical Network and Synchronous Digital Hierarchy standards. In addition to moving the transimpedance amplifier into the transceiver package, asoc design changes have reduced the size of the optical transceiver. Both the transceiver and trans-impedance amplifier can now fit within a low-profile 14-pin dual-inline package. Reducing the size of the transceiver means more can be built on a wafer.

The transceivers with hybridized trans-impedance amplifiers are available with two output powers--transmitting at 1310 nm and receiving at 1550 nm, or vice versa. Samples of all Bookham transceivers are scheduled for availability in the second quarter of 1998.