Nader A. Naderi

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.

Two-color multi-section quantum dot distributed feedback laser

A dual-wavelength emission source is realized by asymmetrically pumping a two-section quantum-dot distributed feedback laser. It is found that under asymmetric bias conditions, the powers between the ground-state and excited-state modes of the two-section device can be equalized, which is mainly attributed to the unique carrier dynamics of the quantum-dot gain medium. As a result, a two-color emission with an 8-THz frequency difference is realized that has potential as a compact THz source. It is also shown that the combination of significant inhomogeneous broadening and excited-state coupled mode operation allows the manipulation of the quantum-dot states through external optical stabilization.

rf linewidth reduction in a quantum dot passively mode-locked laser subject to external optical feedback

The effect of external optical feedback on an InAs/GaAs quantum dot passively mode-locked laser is investigated. The rf linewidth narrows from 8 KHz in the free-running situation to a value as low as 350 Hz under relatively low feedback. The rf linewidth characterization under resonant feedback at a multiple of the laser cavity length validates the prediction of a previous numerical simulation. It is also confirmed that the integrated rms timing jitter varies as the square root of the rf linewidth. The results are promising for the development of compact, monolithic semiconductor mode-locked lasers as low noise optoelectronic oscillators.

Variation of the feedback sensitivity in a 1.55 μm InAs/InP quantum-dash Fabry–Perot semiconductor laser

Dynamic feedback properties of a 1.55 μm InAs/InP quantum dash laser are reported. The ground state linewidth enhancement factor (αH-factor) is found to be enhanced from ∼1 to ∼14 as the bias current is increased beyond the threshold value. As a consequence of the variation in the αH-factor, the feedback sensitivity of the quantum dash semiconductor laser is dramatically affected over the entire range of operational currents. The onset of its critical feedback regime, which is incompatible with data transmission, is shown to exhibit a variation of approximately 20 dB for the quantum dash device.

Tunable Photonic Oscillators Using Optically Injected Quantum-Dash Diode Lasers

An analytical approximation is described and experimentally verified for predicting the resonance frequency of an optically injected quantum-dash Fabry-Pe¿rot laser in the period-one (P1) state. Due to the large spontaneous and nonlinear carrier relaxation rates measured in nanostructure lasers, the P1 resonance frequency is modified appreciably. The function presented accounts for these effects, and it also identifies the role of the linewidth enhancement factor of the optically injected slave laser. The resulting equation is shown to improve the P1 resonance frequency calculation when compared to previous models. Calculating the P1 resonance frequency is critical in using optically injected lasers as a building block for tunable photonic oscillators.

Optical feedback instabilities in a monolithic InAs/GaAs quantum dot passively mode-locked laser

The impact of optical feedback on the direct performance of a monolithic InAs/GaAs quantum dot passively mode-locked laser intended for applications such as multigigahertz interchip/intrachip clock distribution is experimentally investigated. Evaluation of the feedback resistance is an important feature, as the laser is to be monolithically integrated on chip with other devices, in which case optical isolation is difficult. This work shows that a feedback level on the order of −24 dB is detrimental for mode-locking operation, enhancing noise in the rf electrical signal, strongly narrowing the useful mode-locking region as well as causing central frequency shift, and severe instabilities.

Enhancing the 3-dB Bandwidth via the Gain-Lever Effect in Quantum-Dot Lasers

We investigate the small-signal modulation response of two-section, gain-lever, quantum-dot semiconductor lasers. A three-pole modulation function is derived from a 3-D set of rate equations, and a 70% 3-dB bandwidth enhancement is computed and experimentally realized in an undoped quantum-dot gain-lever laser under extreme asymmetric-bias conditions. Finally, it is demonstrated that the 3-dB bandwidth is three times the free-running relaxation oscillation frequency in these types of laser structures, as opposed to 1.55 times in the case of conventional single-section lasers.

Modulation Properties of Self-Injected Quantum-Dot Semiconductor Diode Lasers

This paper investigates the modulation properties of self-injected quantum-dot semiconductor lasers. Using a semianalytical approach, the modulation characteristic of a quantum-dot nanostructure laser operating under the influence of optical feedback is successfully modeled. This novel approach derives a feedback-induced modulation response model based on the incorporation of the specific quantum nanostructure carrier dynamics as well as the effects of nonlinear gain. This study investigates the impacts of the carrier capture and relaxation time as well as other material parameters such as linewidth enhancement factor, differential gain, and gain compression factor for different feedback configurations. It is also shown that, under the short external cavity configuration, the dynamic properties such as the relaxation frequency as well as the lasers bandwidth can be improved through controlled optical feedback. On the other hand, numerical results show that under the long external cavity configuration, any small back-reflection from the lasers facets combined with the large variations of linewidth enhancement factor would significantly alter the lasers modulation response.

A dual-mode quantum dot laser operating in the excited state

A dual-mode laser operating in the excited states (ESs) of a quantum dot is realized by combining asymmetric pumping and external optical feedback stabilization. In generating two single-mode emission peaks, a mode separation ranging from 1.3-THz to 3.6-THz is demonstrated over temperature. This effect is attributed to the unique carrier dynamics of the quantum-dot gain medium via the excited state inhomogeneous linewidth coupled with a proper external control. These results are particularly important towards the development of future THz optoelectronic sources with compact size, low fabrication cost, and high performance.

Strong optical injection and the differential gain in a quantum dash laser

By optically injecting a quantum dash laser and simultaneously producing a significant lowering of the device threshold, a large enhancement in the differential gain is realized. This effect is observed by way of a dramatic reduction in the linewidth enhancement factor and a large increase in the 3-dB modulation bandwidth, especially as the injection wavelength is blue-shifted. Compared to its free-running value, a 50X improvement in the lasers differential gain is found.