A connectorized single-mode bidirectional transceiver aimed at the cost-sensitive fiber-in-the-loop (FITL) and optical-interconnect market combines connector and transceiver functions in a single component. Under development by AMP Inc. (Harrisburg, PA) in collaboration with Lasertron (Bedford, MA), Digital Optics Corp. (Charlotte, NC), GTE Laboratories (Waltham, MA), BroadBand Technologies (Raleigh, NC), and the University of Colorado (Boulder, CO), the device eliminates components and field assembly time while offering the advantages of economical optoelectronics fabrication methods.
Conventional telecommunications links consist of a fiber pair, with one fiber dedicated to transmission and one dedicated to reception. On the transmission fiber, electronics associated with a laser source convert a digital signal into a modulated optical signal that is launched into the fiber through a separate connector. On the receiving fiber, another connector carries the incoming signal to a detector and receiver unit, where the optical data are converted to digital format.
To increase bandwidth, the industry is turning to bidirectional links—single fibers that transmit data at one wavelength (1.55 µm) and receive at another (1.3 µm). According to Robert Boudreau, project manager for global optoelectronics technology at AMP Inc., bidirectional links offer an alternative for FITL applications that approaches the cost of copper coaxial cable.
Currently available bidirectional components contain source and detector elements but still require external modulators and separate couplers to launch and extract the optical signal, increasing the number of components, installation complexity, and cost. The bidirectional transceiver, being developed as part of the AMP-led, Defense Advanced Research Projects Agency funded program, will integrate all of these tasks into one component, allowing users to send and receive over a single fiber fitted with a single device at each end.
The modules will include passive-aligned optoelectronics and will be connected to the fiber through conventional ferrule-based methods. Each single-mode unit contains an indium phosphide diode laser, silicon complementary metal oxide semiconductor (CMOS) modulation/demodulation electronics, a PIN photodiode, a built-in subscriber connector (SC), and an integrated beamsplitter, all on a silicon waferboard. The optoelectronics are hermetically sealed for environmental robustness, and the high-power driver electronics and high-sensitivity receiver electronics are isolated in separate shielded sections, minimizing electronic noise (see photo). The entire module, including connector, is 85 × 17 × 10 mm.
To separate the incoming and outgoing signals, the group is testing both micro-optical fiber beamsplitters and holographic micro-optical elements. The current unit incorporates a pin array interconnect, with heat sinking through the bottom plate of the module to the customer board. In compliance with Bellcore requirements for FITL, the unit is designed to operate from -40°C to +85°C.
The host-digital-terminal module (at the central office) offers constant 1.2-Gbit/s transmission at 1.3 µm and a burst-mode, 50-Mbit/s receiver operating at 1.55 µm. The optical network unit module (at the home) at the other end provides 1.2-Gbit/s reception at 1.3 µm and 50-Mbit/s burst mode transmission at 1.55 µm. The upstream link from the home operates at a lower rate because of its reduced video content; time multiplexing prevents interference of signals coming from different homes. The pin-compatible family of silicon CMOS electronic chips designed for the project provides a mix-and-match assortment of data rates and modes for receiving and transmitting, including 622-Mbit/s continuous and 155-Mbit/s continuous or burst.
The group has developed initial models, and according to Boudreau, it should demonstrate a working prototype in the first quarter of 1997, to be tested with the BroadBand Technologies Flex digital system; parts should be available for customer sampling and testing by the third quarter of 1997.