ABSTRACT
Controlled generation and inhibition of externally-triggered picosecond optical pulsating regimes are demonstrated experimentally in a quantum dot mode locked laser (QDMLL) subject to external injection of an amplitude modulated optical signal. This approach also allows full control and repeatability of the time windows of generated picosecond optical pulses; hence permitting to define precisely their temporal duration (from <1 ns spans) and repetition frequency (from sub-Hz to at least hundreds of MHz). The use of a monolithic QDMLL, operating at 1300 nm, provides a system with a very small footprint that is fully compatible with optical telecommunication networks. This offers excellent prospects for use in applications requiring the delivery of ultrashort optical pulses at precise time instants and at tunable rates, such as optical imaging, time-of-flight diagnostics and optical communication systems.
ABSTRACT
We present an experimental investigation on the period-one dynamics of an optically injected InAs/GaAs quantum dot laser as a photonic microwave source. It is shown that the microwave frequency of the quantum dot laser's period-one oscillation is continuously tunable through the adjustment of the frequency detuning. The microwave power is enhanced by increasing the injection strength providing that the operation is away from the Hopf bifurcation, whereas the second-harmonic distortion of the electrical signal is well reduced by increasing the detuning frequency. Both strong optical injection and high detuning frequency are favorable for obtaining a single sideband optical signal. In addition, particular period-one oscillation points of low sensitivity to the frequency detuning are found close to the Hopf bifurcation line.
ABSTRACT
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 laser's differential gain is found.
ABSTRACT
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 cavity's free-spectral range frequency, whereas the gain-lever effect influenced the modulation response throughout the entirety of the response.
ABSTRACT
Tunable microwave signal generation with frequencies ranging from below 1 GHz to values over 40 GHz is demonstrated experimentally with a 1310 nm Quantum Dot (QD) Distributed-Feedback (DFB) laser. Microwave signal generation is achieved using the period 1 dynamics induced in the QD DFB under optical injection. Continuous tuning in the positive detuning frequency range of the quantum dot's unique stability map is demonstrated. The simplicity of the experimental configuration offers promise for novel uses of these nanostructure lasers in Radio-over-Fiber (RoF) applications and future mobile networks.
Subject(s)
Computer Communication Networks/instrumentation , Lasers , Microwaves , Quantum Dots , Equipment Design , Equipment Failure AnalysisABSTRACT
Current pulse measurement methods have proven inadequate to fully understand the characteristics of passively mode-locked quantum-dot diode lasers. These devices are very difficult to characterize because of their low peak powers, high bandwidth, large time-bandwidth product, and large timing jitter. In this paper, we discuss the origin for the inadequacies of current pulse measurement techniques while presenting new ways of examining frequency-resolved optical gating (FROG) data to provide insight into the operation of these devices. Under the assumptions of a partial coherence model for the pulsed laser, it is shown that simultaneous time-frequency characterization is a necessary and sufficient condition for characterization of mode-locking. Full pulse characterization of quantum dot passively mode-locked lasers (QD MLLs) was done using FROG in a collinear configuration using an aperiodically poled lithium niobate waveguide-based FROG pulse measurement system.
Subject(s)
Lasers, Semiconductor , Models, Theoretical , Quantum Dots , Computer Simulation , Computer-Aided Design , Equipment Design , Equipment Failure Analysis , Light , Scattering, RadiationABSTRACT
We demonstrate stable, single-frequency output from single, as-fabricated GaN nanowire lasers operating far above lasing threshold. Each laser is a linear, double-facet GaN nanowire functioning as gain medium and optical resonator, fabricated by a top-down technique that exploits a tunable dry etch plus anisotropic wet etch for precise control of the nanowire dimensions and high material gain. A single-mode linewidth of ~0.12 nm and >18 dB side-mode suppression ratio are measured. Numerical simulations indicate that single-mode lasing arises from strong mode competition and narrow gain bandwidth.
ABSTRACT
The timing jitter performance of a 5 GHz quantum dot passively mode-locked laser is investigated at different harmonics in the RF spectrum. The necessity of measuring the phase noise at relatively large harmonic numbers is motivated experimentally in the context of determining the corner frequency, its correlation to the RF linewidth, and the related white noise plateau level. The single-sideband phase noise with an integrated timing jitter of 211 fs (4-80 MHz) is reported. An all-microwave technique has been used to determine a pulse-to-pulse rms timing jitter of 96 fs/cycle. This low timing jitter value makes the chip-scale quantum dot mode-locked laser an attractive source for low noise applications such as optical clocking and sampling.
ABSTRACT
Passive harmonic mode-locking in a quantum dot laser is realized using the double interval technique, which uses two separate absorbers to stimulate a specific higher-order repetition rate compared to the fundamental. Operating alone these absorbers would otherwise reinforce lower harmonic frequencies, but by operating together they produce the harmonic corresponding to their least common multiple. Mode-locking at a nominal 60 GHz repetition rate, which is the 10(th) harmonic of the fundamental frequency of the device, is achieved unambiguously despite the constraint of a uniformly-segmented, multi-section device layout. The diversity of repetition rates available with this method is also discussed.
ABSTRACT
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.
