Fiber Optic Devices Pumped with Semiconductor Disk Lasers

The aim of this thesis is to investigate the advantages of pumping fiber optic oscillators utilizing a special type of lasers – semiconductor disk lasers. Relatively novel semiconductor disk laser technology offers low relative intensity noise levels combined with scalable output power, stable operation and nearly diffraction-limited beam quality valuable for an efficient fiber coupling (70- 90%). This pumping technique was applied for optical pumping of fiber lasers. Low-noise fiber Raman amplifier in co-propagation configuration for pump and signal was developed in the 1.3 μm spectral range. A hybrid Raman-bismuth-doped fiber amplifier scheme for an efficient pump light conversion was proposed and demonstrated. Semiconductor disk lasers operating at 1.29 μm and 1.48 μm were used as the pump sources for picosecond Raman fiber lasers at 1.38 and 1.6 μm. The 1.38 μm passively modelocked Raman fiber laser produced 1.97 ps pulses with a ring cavity configuration. The 1.6 μm linear cavity fiber laser with the integrated SESAM produced 2.7 ps output. A picosecond semiconductor disk laser followed by the ytterbium-erbium fiber amplifier offered supercontinuum generation spanning from 1.35 μm to 2 μm with an average power of 3.5 W. By utilizing a 1.15 μm semiconductor disk laser, a pulsed Ho3+-doped fiber lasers for a 2 μm spectral band were demonstrated. 118 nJ pulses at the repetition rate of 170 kHz and central wavelength of 2097 nm were produced by a holmium fiber laser Q-switched by a carbon nanotube saturable absorber. Sub-picosecond holmium-doped fiber laser modelocked with a broadband carbon nanotube saturable absorber and a SESAM were developed. Using the former saturable absorber, ultrashort pulse operation with the duration of ~ 890 fs in the 2030-2100 nm wavelength range was obtained. The results in the presented dissertation demonstrate the potential of the semiconductor disk laser technology for pumping fiber amplifiers and ultrafast lasers

Photonic devices for integrated optical applications

work presented in this thesis encompasses an investigation into the use of ultrafast laser inscription in the fabrication of glass based photonic devices for integrated optical applications. Waveguide fabrication and characterisation experiments were carried out in three categories of glass substrate. Firstly, waveguides were inscribed in an erbium doped glass with the aim of fabricating optical amplifiers and lasers operating in the 1.5 μm spectral region. Low loss waveguides were fabricated in substrates with different dopant concentrations. Fibre to fibre net gain was achieved from one substrate composition, however it was found that ion clustering limited the amount of achievable gain. Laser action was demonstrated by constructing an optical fibre based cavity around the erbium doped waveguide amplifier. Waveguides were also inscribed in bismuth doped glass with the aim of fabricating optical amplifiers and lasers operating in the 1.3 μm spectral region. Low loss waveguides were fabricated, however the initial composition was incapable of providing gain. A proven substrate material was employed, demonstrating ultra-broadband gain spanning more than 250 nm. High losses prevented the achievement of net gain, however the broad potential of the substrate material was highlighted. Finally, waveguides were inscribed in a Chalcogenide glass. Strong refractive index contrasts were observed, with a wide range of waveguiding structures produced. Supercontinuum experiments were carried out in order to confirm the nonlinear behaviour of the waveguides. A spectrally smooth supercontinuum spanning 600 nm was generated, providing a potentially useful source for optical coherence tomography

Wavelength extension in speciality fibres

Since the invention of the laser and its first application, there has been an almost continuous stream of new applications - many of which require specific laser sources. These applications often require a laser source with a specific power, pulse duration, energy and wavelength. In some cases these demands are easily met, whilst in others they have proven rather more difficult to achieve. Traditionally, wavelength versatility has been limited to the regions for which rare earth or gas gain media are available. These lasers themselves can be used to generate other wavelengths through the nonlinear processes of second and third harmonic generation, as well as sum frequency generation. Despite all of this, there still exists a significant section of the visible and infrared spectrum for which no convenient sources exist. This thesis is concerned with the development of sources in these regions along with broadband sources covering significant portions of the spectrum by themselves. These new wavelengths are generated in a variety of speciality fibres using either nonlinear processes or new gain media doped into standard silica fibres. Three types of speciality fibre are used: low concentration bismuth doped fibre which provides gain in the 1.0-1.4 μm region; photonic crystal fibres; and very high (75%) concentration germanium fibres to generate a laser source at 2.1 μm based upon stimulated Raman scattering. Photonic crystal fibres provide high nonlinearities and controllable dispersion which enables the generation of broadband supercontinuum sources based upon the interaction of many nonlinear effects. Each source will be described in depth, with particular attention given to the underlying physics that gives rise to the source. Previous and current limitations will be examined and an outlook of the future development of such sources will be discussed

Modified chalcogenide glasses for optical device applications

This thesis focuses on two different, but complementary, aspects of the modification ofgallium lanthanum sulphide (GLS) glasses. Firstly the addition of transition metal ionsas dopants is examined and their potential for use as active optical materials is explored.It is also argued that the spectroscopic analysis of transition metal ions is a useful toolfor evaluating the local environment of their host. Secondly femtosecond (fs) lasermodification of GLS is investigated as a method for waveguide formation.Vanadium doped GLS displays three absorption bands at 580, 730 and 1155 nmidentified by photoluminescence excitation measurements. Broad photoluminescence,with a full width half maximum of ~500 nm, is observed peaking at 1500 nm whenexciting at 514, 808 and 1064 nm. The fluorescence lifetime and quantum efficiency at300 K were measured to be 33.4 μs and 4% respectively. Analysis of the emissiondecay, at various vanadium concentrations, indicated a preferentially filled, highefficiency, oxide site that gives rise to characteristic long lifetimes and a low efficiencysulphide site that gives rise to characteristic short lifetimes. X-ray photoelectronspectroscopy measurements indicated the presence of vanadium in a broad range ofoxidation states from V+ to V5+. Tanabe-Sugano analysis indicates that the opticallyactive ion is V2+ in octahedral coordination and the crystal field strength (Dq/B) was1.84. Titanium and nickel doped GLS display a single absorption band at 590 and 690nm, and emission lifetimes of 97 and 70 μs respectively. Bismuth doped GLS displaystwo absorption bands at 665 and 850 nm and lifetime components of 7 and 47 μs. Basedon comparisons to other work the optically active ions are proposed to be Ti3+, Ni+ andBi+, all of these displayed emission peaking at ~900 nm.Through optical characterisation of fs laser written waveguides in GLS, a formationmechanism has been proposed. Tunnelling has been identified as the dominantnonlinear absorption mechanism in the formation of the waveguides. Single modeguidance at 633 nm has been demonstrated. The writing parameters for the minimumpropagation loss of 1.47 dB/cm are 0.36 μJ pulse energy and 50 μm/s scanning speed.The observation of spectral broadening in these waveguides indicates that they mayhave applications for nonlinear optical devices. Fs laser written wav

High repetition rate mode-locked erbium-doped fiber lasers with complete electric field control

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2008.Includes bibliographical references (p. 149-159).Recent advances in fully-stabilized mode-locked laser systems are enabling many applications, including optical arbitrary waveform generation (OAWG). In this thesis work, we describe the development of high repetition-rate fiber laser-based systems for the realization of these applications at 1550 nm wavelengths. To realize these systems, frequency comb sources are needed that are compatible with electric field stabilization techniques, are compatible with integrated arrayed waveguide grating and modulator technology, and have high repetition rates to allow full use of current modulator bandwidths. Erbium-doped fiber lasers are one of the leading options to fill this role. To that end, fundamentally mode-locked stretched pulse fiber lasers approaching 250 MHz repetition rate and soliton fiber lasers at over 200 MHz repetition rates are presented, and the limitations of repetition rate scaling in fiber lasers are explored. Using the 200 MHz soliton laser and an external Fabry-Perot cavity, a low-noise, repetition rate multiplied 2 GHz source is demonstrated. Stabilization systems for high repetition rate sources must also be developed. Carrier envelope offset locking experiments using self-referencing techniques at 200 MHz repetition rate are described. Initial demonstrations towards repetition rate locking to a methane-stabilized HeNe single-frequency standard using difference-frequency generation are presented.by Jason William Sickler.Ph.D