Tailoring Quantum Dot Saturable Absorber Mirrors for Ultra-Short Pulse Generation
- PDF / 1,738,803 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 13 Downloads / 170 Views
1076-K09-04
Tailoring Quantum Dot Saturable Absorber Mirrors for Ultra-Short Pulse Generation Matthew Lumb1, Edmund Clarke1, Dominic Farrell2, Michael Damzen2, and Ray Murray1 1 EXSS Physics, Imperial College London, The Blackett Laboratory, Imperial College, Prince Consort Road, London, SW7 2BZ, United Kingdom 2 Photonics, Imperial College London, The Blackett Laboratory, Imperial College, Prince Consort Road, London, SW7 2BZ, United Kingdom ABSTRACT We have designed and grown a series of quantum dot semiconductor saturable absorber mirrors (QD-SESAMs) for a range of operating wavelengths, incorporating innovative design and processing features to optimise the device performance. Using a range of reflectivity studies, ellipsometric measurements and both time-integrated and time-resolved spectroscopic studies, we have conducted detailed investigations of device performance. Extensive modelling work of dielectric multilayers has been undertaken which supports our experimental findings and allows us to understand and design novel structures in order to improve and tailor device characteristics, including dielectric capping and non-normal incidence. We demonstrate samples designed for operation with the higher excited-states of the QDs which produced a self-starting train of modelocked pulses with a temporal duration of 200 ps at a repetition rate of 78 MHz in a Nd:YVO4 solid-state laser. We also present SESAMs incorporating electronically coupled QD bilayers, allowing long wavelength operation. INTRODUCTION Semiconductor saturable-absorber mirrors (SESAMs) are well suited as passive modelocking elements in lasers due to their ultrafast carrier dynamics, high spectral tunability and low toxicity compared with dye-based absorbers. A SESAM consists of a multilayer mirror with an absorbing layer in the cavity region between the distributed Bragg reflector (DBR) and the surface. The entire structure can be monolithically grown by molecular beam epitaxy (MBE) and the absorber regions are usually positioned at the anti-nodes of the field distribution at the design wavelength of the sample for maximum effectiveness. The absorber is usually a quantum well (QW) whose absorption band edge can be tuned to the design wavelength of the SESAM. Recently, quantum dots (QDs) have been used as the absorber region in SESAM structures at a range of wavelengths[1,2,3,4]. QDs have numerous advantages over QWs for use in SESAMs operating in the near-IR. They have ultra-fast absorption recovery times[5] and large inhomogeneous line-widths relative to QWs. This makes them ideal candidates for laser systems where large absorption bandwidths are required. The emission wavelength of the ground-state (GS) quantum dot transition using single QD layers capped with GaAs ranges from 1500nm using QD bilayers[6]. Therefore QD-SESAMs have the potential to operate with a very wide range of gainmedia out to the telecommunications wavelengths. There are several key parameters which govern a SESAM’s performance and which must be suited to a particular laser
Data Loading...
