Ronan F. O'Dowd

Tunable transform-limited pulse generation using self-injection locking of an FP laser

Wavelength-tunable, near transform-limited pulses have been generated using a Fabry-Perot laser diode coupled to a fiber loop containing a fiber Fabry-Perot resonator (FFPR) and a polarization controller. The ratio of transmitted to reflected light from the loop can be adjusted using the polarization controller. Single-mode operation of the gain-switched laser is achieved by self-injection locking, which is induced by light reflected from the fiber loop. The resulting output pulse has a time-bandwidth product of 0.4 and is tunable over about 15 nm by varying the tuning voltage of the FFPR.<<ETX>>

Frequency plan and wavelength switching limits for widely tunable semiconductor transmitters

As wavelength-division-multiplexing (WDM) channel spacing continues to decrease in size, and with the application of tunable lasers in dense wavelength-division-multiplexing (DWDM) systems, we demonstrate the ability of tunable semiconductor lasers to cope with demanding channel spacing and inevitable low frequency setting error. By finding the stable operating points of a single tunable laser at the desired frequencies, using advanced software a lookup table to drive the laser was generated. Once the drive currents to access 2000 channels with the laser are found, their frequency setting error and side mode suppression ratio (SMSR) were found. These results open up new possibilities for DWDM access networks as well as providing a limit of achievement for channel density in the network. Meanwhile, since the sampled-grating distributed Bragg reflector (SG-DBR) laser is among the most attractive sources for DWDM, it is important to investigate its wavelength switching characteristics. This behavior will affect wavelength routing and the capability limits for channel reallocation in future networks. We present new detailed experimental studies on a high-speed SG-DBR laser by using a Fabry-Perot interferometer technique adapted for the noncontinuous wave case. Measurements of fast intramodal (i.e., cavity mode) and intermodal (i.e., supermode) wavelength switching and insights into the devices dynamic behavior are obtained. Implications are given for transmitter design in dynamic wavelength routing and channel reallocation.

Performance implications of wide-band lasers for FSK modulation labeling scheme

Optical labeling via frequency-shift keying (FSK) modulation capability of a grating-assisted codirectional coupler with sampled grating reflector laser is investigated for the first time. FSK modulation can be best implemented with only the phase section current and optical frequency deviation of 20 GHz is achieved. The measured frequency modulation response indicates the limitation of the maximum modulation rate is sufficient for Internet protocol packet optical labeling.

Influence of mode competition on the fast wavelength switching of an SG-DBR laser

Because the sampled grating distributed Bragg reflector (SG-DBR) laser is among the most attractive sources for wavelength division multiplexing (WDM) systems, it is important and necessary to investigate its wavelength switching characteristics. This behavior will set the capability limits for reallocation in wavelength-routed optical networks. In this paper, that mode competition plays an important role in the wavelength switching dynamics of DBR-type tunable lasers is confirmed experimentally. By using a time-resolved spectrum technique, the loss-dependent mode competition behavior has been directly observed, for the first time, from measurements of wavelength switching on an SG-DBR laser.

On the Role of High-Order Coherent Population Oscillations in Slow and Fast Light Propagation Using Semiconductor Optical Amplifiers

In this paper, we present a numerical investigation of the phase shift experienced by the detected envelope of a sinusoidally modulated optical carrier propagating in a nonlinear semiconductor optical amplifier. The model we employed accounts for high-order coherent population oscillations. As such, it allows for large gain levels and arbitrary modulation indexes of the input field. We highlight the role of the fields that are generated by high-order nonlinearities and compare the results with those of more common small-signal nonlinear models. We find that conventional models suffice only for low powers, small modulation indexes, and moderate amplifier gain levels.

Time-resolved spectral measurements on a multielectrode DFB laser using a Fabry-Perot interferometer

A Fabry-Perot interferometer based time-resolved spectral measurement system capable of transform limited performance is described here. The system results from a model developed for the Fabry-Perot interferometer from which the mirror reflectivity emerges as the critical parameter in determining both the temporal and spectral response. Using this system, the response of a multi-electrode DFB laser under a number of different modulation formats is investigated.<<ETX>>

Thermal transient measurement, modeling, and compensation of a widely tunable laser for an optically switched network

The continuous growth of telecommunications traffic has placed huge demands on the traditional networks. Bottlenecks are particularly evident at the routers, where optical to electrical conversion must take place to read the routing information. Using optical-only routing, the traffic flow would be much faster, and more streamlined. A key component in this optical router is the tunable laser. When the laser is switched at high speeds, red-shifted thermal effects, due to the heating effects of the applied currents, cause a drift in the frequency, in the opposite direction to the blue-shifted carrier effects. The thermal effects have been quantified theoretically and experimentally here. The impact of the thermal effects, both on the frequency switching and on the frequency-shift keying (FSK), has been investigated. Methods of compensating for the thermal effects have been developed and verified by simulation and by experiment.

A transfer matrix-based analysis of multielectrode DFB lasers

A numerical model for characterizing the steady-state operation of multielectrode distributed feedback lasers (DFB) is presented. The model is based upon the transfer matrix method which allows a wide range of structures to be analyzed. Using the model to compare a two-electrode device and a three-electrode device reveals that the latter has superior operating characteristics for tunability or FSK.<<ETX>>

Interpretation of wavelength switching effects of widely tunable lasers

Wavelength switching dynamics of widely tunable transmitters are particularly important in switching systems for wavelength-division-multiplexing applications. By using a time-resolved spectrum technique, the wavelength switching OD behavior of a sampled grating distributed Bragg reflector laser a CD has been successfully characterized. The switching transient and related physical effects have been linked and clarified for the first time.

Tunable and Agile Laser Transmitter Developments for Future DWDM Optical Networks: Towards Managed Wavelength Control and Switching Invited Paper

The International Telecommunications Union (ITU) has defined the laser wavelengths to be used in the frequency plan for dense wavelength division multiplexed (DWDM) optical fiber networks. It is up to the equipment manufacturers to supply suitable transmitters which network planners must use. The options involve a rack or array of many lasers or tunable lasers. We review the latter which are complex, four-section devices and discus their operation. More importantly we consider how recent work has permitted characterization and then control of these so that a single laser can access the full ITU bandwidth. We also consider the new functionality only recently available through fast wavelength switching. This may permit improved management of the fibers full capacity at all times despite peak-to-mean traffic fluctuations per wavelength channel. The possibilities for new functionality mean a closer interaction between device and network designers in future.