Monolithic widely-tunable transmitters are key enablers in reducing the component size, power consumption, and simplifying DWDM network provisioning. We discuss design and performance of monolithic transmitters based on SGDBR laser and electroabsorption or Mach-Zehnder modulators.

Widely-tunable Sampled-Grating Distributed Bragg Reflector (SG-DBR) lasers with integrated Semiconductor Optical Amplifiers (SOAs) simultaneously exhibit high (20 mW CW) fiber-coupled output power, high (>40) side mode suppression ratio, low noise (below -140 dB/Hz RIN), low line-width (<5 MHz), and high reliability, across a 40 nm C-band tuning range.

Tunable semiconductor lasers have been listed in numerous critical technology lists for future optical communication systems. Lasers with full band tuning ranges (C or L) allow reduction of the inventory cost and simplify deployment and operation of existing systems in addition to enabling wavelength agile networking concepts in future systems. Furthermore, monolithic integration of full band tunable lasers with modulators to form complete transmitters offers the most potential for reducing system size, weight, power consumption, and cost. This paper summarizes design, fabrication technology, and performance characteristics of widely tunable CW sources and transmitters based on chip scale integration of a Sampled Grating Distributed Bragg Reflector (SG DBR) laser with a Semiconductor Optical Amplifier (SOA) and Electroabsorption (EA) or Mach Zehnder (MZ) modulator. Widely tunable CW sources based on SG-DBR lasers exhibit high fiber coupled output power (20 mW CW) and side mode suppression ratio (>40 dB), low relative intensity noise (below -140 dB/Hz) and line width (<5 MHz) across a 40 nm C-band tuning range. Characteristics of EA-modulated optical transmitters include fiber-coupled time-averaged powers in excess of 5 dBm, RF extinction ratios > 10 dB, and error-free transmission over 350 km of standard fiber at 2.5 Gb/s across a 40 nm tuning range. Monolithic integration of widely tunable lasers with MZ modulators allow for further extension of bit rate (10 Gb/s and beyond) and transmission distances through precise control of the transient chirp of the transmitter. Systematic investigations of accelerated aging confirm that reliability of these widely-tunable transmitters is sufficient for system deployment.

A novel module/firmware implementation of mode control for widely-tunable sampled-grating distributed Bragg reflector lasers, which uses the local gain voltage control surface to ensure operation at mode center, exhibits excellent stability and robustness across all channels spanning the C band.

We report on a widely tunable transmitter based on a sampled-grating distributed bragg reflector (SG-DBR) laser monolithically integrated with a semiconductor optical amplifier (SOA) and an electroabsorption (EA) modulator. Modulated time-averaged powers in excess of 5 dBm, RF extinction ratios > 10 dB, and error-free transmission at 2.5 Gb/s for 350 km of standard single-mode fiber have been demonstrated across a 40-nm tuning range. In CW mode of operation, the module meets all long-haul system requirements for externally modulated laser sources: stability, power (> 10 mW), RIN (< - 140 dB Hz), and linewidth (< 2 MHz) over 90 50-GHz spaced ITU channels. Implementation of wavelength, power, and mode control in module firmware ensures long-term stability for system deployment. Systematic investigations of accelerated aging performed on laser tuning and gain sections showed excellent wavelength stability and reliability with median times to failure of > 100 yr for output wavelength stability and power across all channels.

Summary form only given. The intensity noise, intermodulation distortion and dynamic range characteristics of sampled-grating DBR lasers are measured across the whole tuning range. The shot noise limited RIN property, which is below - 160 dB/Hz, is reported for a widely tunable laser. The spur-free dynamic range is between 100-112 dB.Hz23/. Both the noise and linearity are uniform over the tuning range of 50 nm, and are relatively insensitive to detuning.

In this letter, we present new experimental results obtained for direct intensity modulation of widely tunable sampled-grating distributed Bragg-reflector (SGDBR) lasers. These results are of significance to SGDBR applications in wavelength-division-multiplexing systems. The devices described operate in the C-band (wavelength range 1525-1565 nm). A 6-GHz small-signal modulation bandwidth and >10-dB signal extinction ratio under large-signal operation were obtained. We have also recorded an undistorted eye pattern for a nonreturn-to-zero random signal 2/sup 31/-1 word length at 2.5-Gb/s bit rate during transmission over 75-km of standard single-mode fiber.

The intensity noise of a sampled-grating distributed Bragg reflector laser with 50-nm tuning range and 45-dB side-mode suppression ratio has been measured. The resonance frequency, damping factor, and modified Schawlow-Townes linewidth are extracted from the noise spectra. At high output power, the relative intensity noise (RIN) of the laser is below the photodiode shot noise limit, which is -160 dB/Hz. The laser has uniform shot noise limited RIN properties along the whole tuning range. The maximum resonance frequency is 5.4 GHz at a bias current of 120 mA and the K factor is 0.58 ns.

The dynamic range of sampled-grating distributed Bragg reflector lasers is investigated. The system noise is limited by the photodiode shot noise, which is below - 160 dBm/Hz at normal bias current. The spur-free dynamic range is between 100 112 dB . Hz(2.3). Both the noise and linearity are uniform over the whole tuning range of 50 nm, and are relatively insensitive to mode detuning.

While tunable lasers have been a focus of research and development efforts for over 10 years, they have only recently gained market acceptance in optical transport and networking. Tunable lasers offer many compelling advantages over fixed wavelength solutions in optical networks in that they reduce inventories, allow dynamic wavelength provisioning, and simplify network control software. More interesting, is that tunable lasers have been featured in optical network development efforts in every segment: access/enterprise, metropolitan, and long haul networks leading to a variety of desired specifications and approaches. In fact, the term 'tunable laser' has come to describe an increasingly broad range of technologies from monolithic semiconductor lasers, to MEMS (Micro-Electro-Mechanical Systems) based lasers and fiber lasers. This presentation will focus on monolithic, widely-tunable lasers which are promising candidates to satisfy the needs of all the market segments mentioned.