Quantum Dot Based Mode Locked Semiconductor Lasers And Applications

In this dissertation, self-assembled InAs/InGaAs quantum dot Fabry-Pérot lasers and mode-locked lasers are investigated. The mode-locked lasers investigated include monolithic and curved two-section devices, and colliding pulse mode-locked diode lasers. Ridge waveguide semiconductor lasers have been designed and fabricated by wet etching processes. Electroluminescence of the quantum dot lasers is studied. Cavity length dependent lasing via ground state and/or excited state transitions is observed from quantum dot lasers and the optical gain from both transitions is measured. Stable optical pulse trains via ground and excited state transitions are generated using a grating coupled external cavity with a curved two-section device. Large differences in the applied reverse bias voltage on the saturable absorber are observed for stable mode-locking from the excited and ground state mode-locking regimes. The optical pulses from quantum dot mode-locked lasers are investigated in terms of chirp sign and linear chirp magnitude. Upchirped pulses with large linear chirp magnitude are observed from both ground and excited states. Externally compressed pulse widths from the ground and excited states are 1.2 ps and 970 fs, respectively. Ground state optical pulses from monolithic mode-locked lasers e.g., two-section devices and colliding pulse mode-locked lasers, are also studied. Transformed limited optical pulses (~4.5 ps) are generated from a colliding pulse mode-locked semiconductor laser. The above threshold linewidth enhancement factor of quantum dot Fabry-Pérot lasers is measured using the continuous wave injection locking method. A strong spectral dependence of the linewidth enhancement factor is observed around the gain peak. The measured linewidth enhancement factor is highest at the gain peak, but becomes lower 10 nm away from the gain peak. The lowest linewidth enhancement factor is observed on the anti-Stokes side. The spectral dependence of the pulse duration from quantum dot based mode-locked lasers is also observed. Shorter pulses and reduced linear chirp are observed on the anti-Stokes side and externally compressed 660 fs pulses are achieved in this spectral regime. A novel clock recovery technique using passively mode-locked quantum dot lasers is investigated. The clock signal (~4 GHz) is recovered by injecting an interband optical pulse train to the saturable absorber section. The excited state clock signal is recovered through the ground state transition and vice-versa. Asymmetry in the locking bandwidth is observed. The measured locking bandwidth is 10 times wider when the excited state clock signal is recovered from the ground state injection, as compared to recovering a ground state clock signal from excited state injection.

In this monograph, the authors address the physics and engineering together with the latest achievements of efficient and compact ultrafast lasers based on novel quantum-dot structures and devices. Their approach encompasses a broad range of laser systems, while taking into consideration not only the physical and experimental aspects but also the much needed modeling tools, thus providing a holistic understanding of this hot topic.

In this thesis, novel multi-section laser diodes based on quantum-dot material are designed and investigated which exhibit a number of advantages such as low threshold current density; temperature-insensitivity and suppress carrier diffusion due to discrete nature of density of state of quantum-dots. The spectral versatility in the range of 1.1 μm - 1.3 μm wavelengths is demonstrated through novel mode-locking regimes such as dual-wavelength mode-locking, wavelength bistability and broad tunability. Moreover, broad pulse repetition rate tuning using an external cavity configuration is presented. A high peak power of 17.7 W was generated from the quantum-dot laser as a result of the tapered geometry of the gain section of the laser has led to successful application of such device for two-photon imaging. Dual-wavelength mode-locking is demonstrated via ground (?=1180 nm) and excited (?=1263 nm) spectral bands with optical pulses from both states simultaneously in the 5-layer quantum-dot two-section diode laser. The widest spectral separation of 83 nm between the modes was achieved in a dual-wavelength mode-locked non-vibronic laser. Power and wavelength bistability are achieved in a mode-locked multi-section laser which active region incorporates non-identical QD layers grown by molecular beam epitaxy. As a result the wavelength can be electronically controlled between 1245 nm and 1290 nm by applying different voltages to the saturable absorber. Mode-locked or continuous-wave regimes are observed for both wavelengths over a 260 mA - 330 mA current ranges with average power up to 28 mW and 31 mW, respectively. In mode-locked regime, a repetition rate of 10 GHz of optical pulses as short as 4 ps is observed. Noticeable hysteresis of average power for different bias conditions is also demonstrated. The wavelength and power bistability in QD lasers are potentially suitable for flip-flop memory application. In addition, a unique mode-locked regime at expense of the reverse bias with 50 nm wavelength tuning range from 1245 nm to 1290 nm is also presented. Broad repetition rate tunability is shown from quantum-dot external cavity mode-locked 1.27 μm laser. The repetition rate from record low of 191 MHz to 1 GHz from fundamental mode-locking was achieved. Harmonic mode-locking allows further to increase tuning up to 6.8 GHz (34th-order harmonic) from 200 MHz fundamental mode-locking. High peak power of 1.5 W can be generated directly from two-section 4 mm long laser with bent waveguide at angle of 7° at 1.14 GHz repetition rate without the use of any pulse compression and optical amplifier. Stable mode-locking with an average power up to 60 mW, corresponding to 25 pJ pulse energy is also obtained at a repetition frequency of 2.4 GHz. The minimum time-bandwidth product of 1.01 is obtained with the pulse duration of 8.4 ps. Novel tapered quantum-dot lasers with a gain-guided geometry operating in a passively mode-locked regime have been investigated, using structures that incorporated either 5 or 10 quantum dot layers. The peak power of 3.6 W is achieved with pulse duration of 3.2 ps. Furthermore, the record peak power of 17.7 W and transform limited pulses of 672 fs were achieved with optimized structure. The generation of picosecond pulses with high average power of up to 209 mW was demonstrated, corresponding to 14.2 pJ pulse energy. The improved optical parameters of the tapered laser enable to achieve nonlinear images of fluorescent beads. Thus it is for the first time that QD based compact monolithic device enables to image biological samples using two-photon microscopy imaging technique.

Written by a team of European experts in the field, this book addresses the physics, the principles, the engineering methods, and the latest developments of efficient and compact ultrafast lasers based on novel quantum-dot structures and devices, as well as their applications in biophotonics. Recommended reading for physicists, engineers, students and lecturers in the fields of photonics, optics, laser physics, optoelectronics, and biophotonics.

The book addresses issues associated with physics and technology of injection lasers based on self-organized quantum dots. Fundamental and technological aspects of quantum dot edge-emitting lasers and VCSELs, their current status and future prospects are summarized and reviewed. Basic principles of QD formation using self-organization phenomena are reviewed. Structural and optical properties of self-organized QDs are considered with a number of examples in different material systems. Recent achievements in controlling the QD properties including the effects of vertical stacking, changing the matrix bandgap and the surface density of QDs are reviewed. The authors focus on the use of self-organized quantum dots in laser structures, fabrication and characterization of edge and surface emitting diode lasers, their properties and optimization with special attention paid to the relationship between structural and electronic properties of QDs and laser characteristics. The threshold and power characteristics of the state-of-the-art QD lasers are demonstrated. Issues related to the long-wavelength (1.3-mm) lasers on a GaAs substrate are also addressed and recent results on InGaAsN-based diode lasers presented for the purpose of comparison.

Quantum dots as nanomaterials have been extensively investigated in the past several decades from growth to characterization to applications. As the basis of future developments in the field, this book collects a series of state-of-the-art chapters on the current status of quantum dot devices and how these devices take advantage of quantum features. Written by 56 leading experts from 14 countries, the chapters cover numerous quantum dot applications, including lasers, LEDs, detectors, amplifiers, switches, transistors, and solar cells. Quantum Dot Devices is appropriate for researchers of all levels of experience with an interest in epitaxial and/or colloidal quantum dots. It provides the beginner with the necessary overview of this exciting field and those more experienced with a comprehensive reference source.

An accessible yet rigorous introduction to nanophotonics, covering basic principles, technology, and applications in lighting, lasers, and photovoltaics. Providing a wealth of information on materials and devices, and over 150 color figures, it is the 'go-to' guide for students in electrical engineering taking courses in nanophotonics.

Semiconductor lasers have important applications in numerous fields, including engineering, biology, chemistry and medicine. They form the backbone of the optical telecommunications infrastructure supporting the internet, and are used in information storage devices, bar-code scanners, laser printers and many other everyday products. Semiconductor lasers: Fundamentals and applications is a comprehensive review of this vital technology. Part one introduces the fundamentals of semiconductor lasers, beginning with key principles before going on to discuss photonic crystal lasers, high power semiconductor lasers and laser beams, and the use of semiconductor lasers in ultrafast pulse generation. Part two then reviews applications of visible and near-infrared emitting lasers. Nonpolar and semipolar GaN-based lasers, advanced self-assembled InAs quantum dot lasers and vertical cavity surface emitting lasers are all considered, in addition to semiconductor disk and hybrid silicon lasers. Finally, applications of mid- and far-infrared emitting lasers are the focus of part three. Topics covered include GaSb-based type I quantum well diode lasers, interband cascade and terahertz quantum cascade lasers, whispering gallery mode lasers and tunable mid-infrared laser absorption spectroscopy. With its distinguished editors and international team of expert contributors, Semiconductor lasers is a valuable guide for all those involved in the design, operation and application of these important lasers, including laser and telecommunications engineers, scientists working in biology and chemistry, medical practitioners, and academics working in this field. Provides a comprehensive review of semiconductor lasers and their applications in engineering, biology, chemistry and medicine Discusses photonic crystal lasers, high power semiconductor lasers and laser beams, and the use of semiconductor lasers in ultrafast pulse generation Reviews applications of visible and near-infrared emitting lasers and mid- and far-infrared emitting lasers