Nathan B. Terry

Modeling the Injection-Locked Behavior of a Quantum Dash Semiconductor Laser

Using the conventional rate equations describing an injection-locked system, a novel modulation response function is derived, which implicitly incorporates nonlinear gain through the free-running relaxation oscillation frequency and damping rate of the slave laser. In this paper, it is shown that the model presented can be used to extract the characteristic parameters of the coupled system from experimental data. The number of fitting parameters in the model is reduced by determining the fundamental slave parameters through the conventional free-running response function; these parameters are considered to be constant during the curve-fitting of the injection-locked system. Furthermore, in order to reduce the number of possible solutions generated during the least-squares-fitting process, the remaining fitting parameters are tightly constrained based on the physical limits of the coupled system. By reducing the number of unknown fitting parameters and constraining the remaining terms, a stronger confidence in the extracted parameters is achieved. Using a series of response curves measured from an injection-locked quantum dash laser, characteristic parameters of the system are extracted and validity of the model is examined. The verified model is used to analyze the impact of the linewidth enhancement factor on the characteristics of the response function in the microwave domain.

Dynamic behavior of an injection-locked quantum-dash Fabry-Perot laser at zero-detuning.

This work investigates the behavior of a zero-detuned optically-injected quantum-dash Fabry-Perot laser as the injected field ratio is increased from near-zero to levels resulting in stable locking. Using a normalized model describing optically-injected semiconductor lasers, variations in the slave lasers free-running characteristics are shown to have a strong impact on the coupled systems behavior. The theoretical model is verified experimentally using a high resolution spectrometer. It is found that the quantum-dash laser has the technological advantage of a low linewidth enhancement factor at low bias currents that suppresses undesirable Period-2 and chaotic behavior. Such observations suggest that optically-injected quantum-dash lasers can be used as an enabling component for tunable photonic oscillators.

Giant nonlinear gain coefficient of an InAs/AlGaInAs quantum dot laser

The linewidth enhancement factor (LEF) and nonlinear gain coefficient of an InAs/AlGaInAs quantum dot (QD) laser are measured using an injection locking technique. The nonlinear gain coefficient was found by curve-fitting the measured LEF as a linear function of the output power. The LEF of the InAs/AlGaInAs quantum dot laser was measured to be 1.2 to 8.6 at output powers from 2 to 10.2 mW, leading to a corresponding nonlinear gain coefficient of 1.4 x 10-14 cm3. This value for the nonlinear gain coefficient is three orders of magnitude higher than the typical quantum well nonlinear gain coefficient of 10-17 cm3. Consequently we expect that the dynamics under optical injection and external feedback of this type of quantum dot laser will be dramatically different than in quantum well lasers, suggesting that a careful re-examination of the dynamics of this type of laser is needed.

Linewidth enhancement factor and dynamical response of an injection-locked quantum-dot Fabry-Perot laser at 1310nm

This work investigates the linewidth enhancement factor (alpha-factor) and stability of an optically-injected InAs/InGaAs quantum-dot Fabry-Perot laser. Using the injection-locking technique, the above threshold alpha-factor is measured to be as low as 0.6 at 1.3X the threshold current. The below threshold alpha-factor is also measured using the Hakki-Paoli technique. The measured alpha-factor values are used to simulate the dynamic response (stable locking, period-one, period-doubling, or chaos) in the context of single-mode rate equations under zero-detuning injection conditions for external injected power ratios ranging from -11dB to +15dB and slave current bias levels of 1.3X, 2X, and 2.6X threshold. Legacy literature has shown that optically-injected diode lasers typically follow the period-doubling route into a chaotic region as the injection level is increased. Simulations show that at 2X the threshold current, a small region of period-one operation will be observed followed by stable-locking as the injection ratio is increased. This predominantly stable behavior is driven largely by the low alpha-factor. Experimental results support this prediction, where under zero-detuning conditions, only unlocked and stable-locking operation is observed. Experimentally, periodone operation was not observed at a slave laser bias current of 2X threshold, as it was predicted to occur below an external power ratio of -20 dB, a level which was not attainable in this work. Such findings suggest that a quantum-dot device can be employed in an optically-injected configuration for photonic tunable-clock applications.

Modulation Response of an Injection Locked Quantum-Dash Fabry Perot Laser at 1550nm

The microwave domain modulation response of an injection-locked laser system is analyzed in the context of a Quantum Dash Fabry-Perot laser. This work demonstrates the applicability of a newly-derived modulation response function by using it to least-squares fit data collected on an injection-locked system with a Quantum-Dash Fabry-Perot semiconductor slave laser. The maximum injection strength, linewidth enhancement factor, coupled phase between the master and slave, and field enhancement factor characterizing the deviation of the locked slave laser from its freerunning value are extracted by least-squares fitting the collected data with the function. The extracted values are then compared with theoretically expected values under the given detuning conditions. The correlation between the frequency of the resonance peak of the modulation response at the positive frequency detuning edge and a pole in the modulation response function under this detuning condition is illustrated. The calculation of the injection strength based on the experimental operating conditions is verified by applying the modulation response function to the experimental data. With the modulation response function, injection-locked behaviors can be accurately simulated in the microwave domain and used to predict operating conditions ideal for high-performance RF links.

Extraction of operating parameters from an injection-locked quantum-dash fabry-perot laser at 1.55μm

Using a series of modulation response curves for an injection-locked quantum dash laser, characteristic parameters of the system were extracted by means of a theoretical model that incorporates nonlinear gain.

3-dB bandwidth enhancement via strong optical injection-locking of a quantum dot DFB @ 1310 nm

Optical injection-locking in quantum dot distributed-feedback lasers is investigated as a function of injection strength and detuning. The stability boundaries of the laser are also examined.