Michael Pochet

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.

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.

Generation and Modulation of a Millimeter-Wave Subcarrier on an Optical Frequency Generated via Optical Injection

A highly tunable millimeter-wave subcarrier signal is generated by optically injecting a Fabry-Perot semiconductor laser. The optically injected light, which enables microwave subcarrier frequencies well beyond the injected lasers free-running relaxation-oscillation frequency, is then on-off keyed by direct-current (dc) modulation of the injected slave laser. Adjustment of the subcarrier frequency is easily accomplished by changing either the dc bias current and/or junction temperature of the injected slave or the injecting master laser. In this paper, we theoretically and experimentally investigate the purity of the modulated microwave subcarrier. The generated microwave signal was then transmitted over 50 km of single-mode fiber, demonstrating the applicability of a directly modulated slave laser optically injected into the period-one state for radio-over-fiber applications.

Modeling the Dynamic Response of an Optically-Injected Nanostructure Diode Laser

We reformulate a dimensionless approach to evaluate the operational dynamics of an optically injected nanostructure laser as a function of the injection strength and the detuning frequency to account for the large nonlinear gain component associated with nanostructure lasers through the nonlinear carrier relaxation rate and gain compression coefficient. The large nonlinear carrier relaxation rate and gain compression coefficient are shown to impact the level of stability numerically predicted in the optically injected laser at low injected power levels. The numerical model is verified experimentally by optically injecting a quantum-dash Fabry-Perot laser with an operating wavelength of approximately 1550 nm. The quantum-dash lasers large damping rate, gain compression coefficient, and sufficiently small linewidth enhancement factor are observed to inhibit period-doubling and chaotic operation under zero frequency-detuning conditions. The inclusion of the nonlinear carrier relaxation rate in the simulation is shown to greatly enhance the agreement between the numerical predictions and the experimentally observed dynamics.

Modulation Response Of A Long-Cavity, Gain-Levered Quantum-Dot Semiconductor Laser

The gain-lever effect enhances the modulation efficiency of a semiconductor laser when compared to modulating the entire laser. This technique is investigated in a long-cavity multi-section quantum-dot laser where the length of the modulation section is varied to achieve 14:2, 15:1 and 0:16 gain-to-modulation section ratios. In this work, the gain-levered modulation configuration resulted in an increase in modulation efficiency by as much as 16 dB. This investigation also found that the 3-dB modulation bandwidth and modulation efficiency are dependent on the modulation section length of the device, indicating the existence of an optimal gain-to-modulation section ratio. The long cavity length of the multi-section laser yielded a distinctive case where characteristics of both the gain-lever effect and spatial effects are observed in the modulation response. Here, spatial effects within the cavity dominated the small-signal modulation response close to and above the cavitys free-spectral range frequency, whereas the gain-lever effect influenced the modulation response throughout the entirety of the response.

On-off keyed microwave signal optically generated using an optically-injected Fabry-Perot semiconductor laser

Large-signal direct-modulation of a diode laser optically-injected into period-one operation is shown to produce an on-off keyed microwave signal. The signal is highly tunable and transmitted over 50 km, suitable for radio-over-fiber applications.

Gamma-radiation-induced degradation of actively pumped single-mode ytterbium-doped optical fibers

The integration of optical components into the digital processing units of satellite subsystems has the potential to remove interconnect bottlenecks inherent to the volume, mass, complexity, reliability and crosstalk issues of copper-based interconnects. Assuming on-board high-bandwidth communications will utilize passive optical fibers as a communication channel, this work investigates the impact of gamma irradiation from a Co-60 source on both passive optical fibers and ytterbium-doped single-mode fibers operated as amplifiers for a 1060-nm light source. Standard optical patch cables were evaluated along with active Yb-doped double-clad fibers. Varied exposure times and signal transmission wavelengths were used to investigate the degradation of the fibers exposed to total doses above 100 krad (Si). The effect on the amplified signal gain was studied for the Yb-doped fibers. The increased attenuation in the fibers across a broad wavelength range in response to multiple levels of gamma radiation exposure along with the effect that the increased attenuation has on the actively pumped Yb-doped fiber amplifier performance, is discussed.

All-optical logic gates and wavelength conversion via the injection locking of a Fabry-Perot semiconductor laser

This work investigates the implementation of all-optical logic gates based on optical injection locking (OIL). All-optical inverting, NOR, and NAND gates are experimentally demonstrated using two distributed feedback (DFB) lasers, a multi-mode Fabry–Perot laser diode, and an optical band-pass filter. The DFB lasers are externally modulated to represent logic inputs into the cavity of the multi-mode Fabry–Perot slave laser. The input DFB (master) lasers’ wavelengths are aligned with the longitudinal modes of the Fabry–Perot slave laser and their optical power is used to modulate the injection conditions in the Fabry–Perot slave laser. The optical band-pass filter is used to select a Fabry– Perot mode that is either suppressed or transmitted given the logic state of the injecting master laser signals. When the input signal(s) is (are) in the on state, injection locking, and thus the suppression of the non-injected Fabry–Perot modes, is induced, yielding a dynamic system that can be used to implement photonic logic functions. Additionally, all-optical photonic processing is achieved using the cavity-mode shift produced in the injected slave laser under external optical injection. The inverting logic case can also be used as a wavelength converter — a key component in advanced wavelength-division multiplexing networks. As a result of this experimental investigation, a more comprehensive understanding of the locking parameters involved in injecting multiple lasers into a multi-mode cavity and the logic transition time is achieved. The performance of optical logic computations and wavelength conversion has the potential for ultrafast operation, limited primarily by the photon decay rate in the slave laser.

Dynamic thermal analysis of a concentrated photovoltaic system

Concentrated photovoltaic (PV) technology represents a growing market in the field of terrestrial solar energy production. As the demand for renewable energy technologies increases, further importance is placed upon the modeling, design, and simulation of these systems. Given the U.S. Air Force cultural shift towards energy awareness and conservation, several concentrated PV systems have been installed on Air Force installations across the country. However, there has been a dearth of research within the Air Force devoted to understanding these systems in order to possibly improve the existing technologies. This research presents a new model for a simple concentrated PV system. This model accurately determines the steady state operating temperature as a function of the concentration factor for the optical part of the concentrated PV system, in order to calculate the optimum concentration that maximizes power output and efficiency. The dynamic thermal model derived is validated experimentally using a commercial polysilicon solar cell, and is shown to accurately predict the steady state temperature and ideal concentration factor.