December 17, 2004, Santa Clara, CA--RIO (Redfern Integrated Optics) has demonstrated a new type of directly modulated laser, based on planar external-cavity (PLANEX) laser technology. According to the company, the laser offers a new, low-cost choice for small-form-factor 10 Gbps optical interfaces that achieve 80-km transmission distances over standard single-mode fiber without the need for dispersion compensation.
RIO's proprietary design approach uses a planar lightwave circuit (PLC) with an integrated Bragg grating and a high-performance low-cost gain chip (or SOA semiconductor optical amplifier) to form the laser cavity. The gain chip functions as an optical amplifier and the Bragg grating acts as both a partially reflecting mirror and a wavelength locker. According to the company, this design enables the laser to output a controlled-chirp waveform at a very well defined and stable wavelength. The direct modulation approach also reduces complexity and cost while providing output power as well as power dissipation advantages over externally modulated lasers.
According to Radu Barsan, President and CEO of RIO, "Currently the high cost and/or limited performance of lasers used in 10 Gbps pluggable transceivers and transponders is inhibiting the growth of extended reach and DWDM 10 Gbps deployments. By taking advantage of well-developed fabrication processes of optical components on silicon wafers to produce the PLC component of the ECL, RIO is able to improve transmission performance while simultaneously driving down component costs."
Until now, externally modulated lasers have been the only viable solution for transmission in the 1550nm band for implementing extended reach and DWDM optical networks at 10 Gbps. Externally modulated lasers using a DFB laser with a lithium niobate modulator are large, expensive and require a high power driver. Monolithic or hybrid integrated electroabsorption modulated lasers (EMLs) are expensive, especially for distances up to 80 km, and prohibitively expensive for narrow-grid DWDM. EMLs have limited output power, which can increase the need for additional erbium-doped fiber amplifiers (EDFAs). External modulation also dissipates more power than direct modulation, because the laser is turned on to full power at all times and the external modulator consumes additional power to operate. The production yield difficulties associated with the monolithic combination of laser and modulator on the same chip means that EMLs will be only marginally capable of meeting volume and cost requirements for SONET and DWDM performance.