Fast Fiber Goes on a Diet

Optical fiber is becoming the planet’s nervous system, but the telecommunication companies weaving this global fiber net have grown nervous about profiting from their efforts. That’s because service revenues have not kept up with the rising costs of meeting the ever-expanding demand for bandwidth, says Jozef Straus, co-chairman and CEO of JDS Uniphase, one of the largest makers of fiber-optic components.

Speaking last week at the annual Conference on Lasers and Electro-Optics in Baltimore, Straus highlighted an upcoming generation of fiber components that will help meet the challenges of delivering more bandwidth, transmitting power further and at lower cost, and increasing the flexibility and reliability of data networks.

Upgrading by Remote Control

Cash-strapped service providers want equipment that can expand their transmission capacity gradually, “so systems don’t have to be forklifted out” after brief service lives, Straus said.

Today’s optical fiber telecommunication systems carry data on multiple wavelengths of light. One key goal is the ability to add wavelengths incrementally to existing fibers as traffic increases. This is not as easy as it sounds because long-distance systems require optical amplifiers about every 100 kilometers, and their performance depends on the number of wavelengths being amplified. Adding channels requires adjustments.

JDS is working on “smart” optical amplifiers with microprocessor controls that would sense the number of wavelengths and automatically adjust the optics as needed. This would allow telecommunications carriers to balance loads across their network dynamically, without having to send technicians to remote sites to change equipment.

Tuning Up

Dynamic network management also would require other new components. Existing commercial fiber systems rely on lasers that can transmit at only a single wavelength. JDS is among many companies developing lasers that can be tuned to many possible wavelengths.

Adapting these tunable lasers for remote control would allow a central network operations center to reconfigure the network remotely, changing wavelengths as needed.

Other optics that can be tuned by wavelength are also in development, including optical filters that can be shifted to select different wavelengths, and remotely adjustable optical switches that can could pick different wavelengths from combined signals as needed.

Straus expects these capabilities to become critical in future networks where single fibers could transmit signals at 100 to 150 wavelengths, requiring active monitoring to assure proper operation and automatic restoration of service in case of failures.

Casting Dispersions

New technology also will be needed to raise the highest data rate per wavelength above the 10 gigabits per second of present commercial systems.

Laboratory experiments have shown the possibility of raising the rate per wavelength to 40 gigabits per second, but that requires careful compensation for an effect called dispersion, which causes light pulses to spread as they travel through a fiber.

Passive dispersion compensation works when each wavelength carries 10 gigabits per second, but moving to 40 gigabits is likely to require active compensation systems that can be adjusted separately for each wavelength.

Revving up Manufacturing

The industry also will have to move to large-volume manufacturing, Straus said. Today, most optics are made in small production runs, with a high proportion of hand labor for delicate tasks such as mounting the tiny laser chips.

Companies offering automated production equipment exhibited prominently at last week’s conference and at the Optical Fiber Communication Conference in March.