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.
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.
KEYWORDS: Solar cells, Sun, Solar energy, Photovoltaics, Temperature metrology, Thermal modeling, Cooling systems, Semiconductors, Systems modeling, Diodes
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.
In this manuscript, we will theoretically compute and experimentally investigate the dynamics of an optically injected
nanostructure laser as a function of the injection strength and the optical detuning frequency. A model describing the
optically-injected semiconductor laser is derived in dimensionless format that accounts for the large nonlinear gain
component associated with nanostructure semiconductor lasers through the gain coefficient's derivative with respect to
perturbations in the carrier and photon density. The nonlinear gain (carrier) relaxation rate and gain compression
coefficient account for the perturbation in the slave laser's photon density, and are theoretically shown to have a strong
impact on the level of stability exhibited by the optically-injected laser. The theoretical model is experimentally verified
through the optical-injection of a quantum-dash Fabry-Perot laser at an operating wavelength of 1550 nm. The quantum-dash
laser's large damping rate and sufficiently small linewidth enhancement factor are observed to inhibit period-doubling
and chaotic operation under zero frequency-detuning conditions. Additionally, the optically injected quantum-dash
laser is found to exhibit a large period-one operational state as the injection strength and the detuning frequency are
varied, resulting in a highly tunable microwave frequency in the coupled system's equilibrium state. The enhanced and
undamped relaxation oscillations of the period-one state are discussed as a building block for tunable photonic
oscillators in various RF photonics applications. Finally a path towards realizing an optically-injected diode laser with a
THz resonance frequency will be reviewed.
The high-speed modulation characteristics of an injection-locked quantum dot Fabry-Perot (FP) semiconductor laser
operating at 1310-nm under strong injection are investigated experimentally with a focus on the enhancement of the
modulation bandwidth. The coupled system consists of a directly-modulated Quantum Dot (QD) slave injected-locked
by a distributed feedback (DFB) laser as the master. At particular injection strengths and zero detuning cases, a unique
modulation response is observed that differs from the typical modulation response observed in injection-locked systems.
This unique response is characterized by a rapid low-frequency rise along with a slow high-frequency roll-off that
enhances the 3-dB bandwidth of the injection-locked system at the expense of losing modulation efficiency of about 20
dB at frequencies below 1 GHz. Such behavior has been previously observed both experimentally and theoretically in
the high-frequency response characteristic of an injection-locked system using an externally-modulated master; however,
the results shown here differ in that the slave laser is directly-modulated. The benefit of the observed response is that it
takes advantage of the enhancement of the resonance frequency achieved through injection-locking without experiencing
the low frequency dip that significantly limits the useful bandwidth in the conventional injection-locked response. The
second benefit of this unique response is the improvement in the high frequency roll-off that extends the bandwidth.
Finally a 3-dB bandwidth improvement of greater than 8 times compared to the free-running slave laser has been
achieved.
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.
The dramatic variation in the linewidth enhancement factor (αΗ-factor) that has been reported for quantum dot lasers
makes them an interesting subject for optical feedback studies. A low αΗ-factor combined with a high damping factor is
especially interesting because it should increase the tolerance to optical feedback in these devices and may offer
potential advantages for direct modulation. In the particular case of QD lasers, the carrier density is not clearly clamped
at threshold. The lasing wavelength can switch from the ground state (GS) to the excited state (ES) as the current
injection increases meaning that a carrier accumulation occurs in the ES even though lasing in the GS is still occurring.
The filling of the ES inevitably enhances the αΗ-factor of the GS above threshold as experimentally and numerically
shown. Consequently, this strong variation of the GS αΗ-factor in comparison to QW devices, should theoretically
produce a significant variation in the onset of coherence collapse due to feedback. This coherence collapse regime, in
which the laser is subject to instabilities, is incompatible with data transmission because of the induced high bit-error
rate. One method to investigate the tolerance to optical feedback is to compare experiment with the theoretical work
introduced by Petermann. It will be presented that under specific conditions, i.e., in the case of a strong enhancement in
the αΗ-factor, the feedback sensitivity of the laser can vary by as much as 10dB within the same device.
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.
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