Erbium-implanted high-Q silica toroidal microcavity laser on a silicon chip

Lasing from an erbium-doped high-Q silica toroidal microcavity coupled to a tapered optical fiber is demonstrated and analyzed. Average erbium ion concentrations were in the range 0.009–0.09 at. %, and a threshold power as low as 4.5 µW and an output lasing power as high as 39.4 µW are obtained from toroidal cavities with major diameters in the range 25–80 µm. Controlling lasing wavelength in a discrete way at each whispering-gallery mode was possible by changing the cavity loading, i.e., the distance between the tapered optical fiber and the microcavity. Analytic formulas predicting threshold power and differential slope efficiency are derived and their dependence on cavity loading, erbium ion concentration, and Q factor is analyzed. It is shown that the experimental results are in good agreement with the derived formulas

Demonstration of an erbium doped microdisk laser on a silicon chip

An erbium doped micro-laser is demonstrated utilizing $\mathrm{SiO_{2}}$ microdisk resonators on a silicon chip. Passive microdisk resonators exhibit whispering gallery type (WGM) modes with intrinsic optical quality factors of up to $6\times{10^{7}}$ and were doped with trivalent erbium ions (peak concentration $\mathrm{\sim3.8\times{10^{20}cm^{-3})}}$ using MeV ion implantation. Coupling to the fundamental WGM of the microdisk resonator was achieved by using a tapered optical fiber. Upon pumping of the $^{4}I_{15/2}\longrightarrow$ $^{4}I_{13/2}$ erbium transition at 1450 nm, a gradual transition from spontaneous to stimulated emission was observed in the 1550 nm band. Analysis of the pump-output power relation yielded a pump threshold of 43 $\mathrm{\mu}$W and allowed measuring the spontaneous emission coupling factor: $\beta\approx1\times10^{-3}$

NOVEL COMPACT NARROW-LINEWIDTH MID-INFRARED LASERS FOR SENSING APPLICATIONS

The mid-infrared (2-14 μm) spectral region contains the strong absorption lines of many important molecular species, which make this region crucial for several well-know applications such as spectroscopy, chemical and biochemical sensing, security, and industrial monitoring. To fully exploit this region through absorption spectroscopic techniques, compact and low-cost narrow-linewidth (NLW) mid-infrared (MIR) laser sources are of primary importance. This thesis is focused on three novel compact NLW MIR lasers: demonstration and characterization of a new glass-based spherical microlaser, investigation of the performance of a novel fiber laser, and the design of a monolithic laser on a silicon chip. Starting with fabrication of spherical microcavities based on MIR transparent materials, I showed the feasibility of achieving quality factors of more than 10 million in whispering- gallery mode (WGM) microresonators made of different types of fluoride glasses. Next using Erbium doped ZBLAN glass spherical microresonators, I demonstrated a new ultra- low threshold NLW MIR microlaser. In particular, all aspects of this room temperature continuous-wave (CW) microlaser with a wavelength of 2.71 μm are carefully characterized and studied and the origin of the measured mode structure and polarization is described using a simple analysis. To amplify the output power of this laser, I designed and fabricated a MIR fiber amplifier with a record gain of about 30 dB at 2.71 μm that facilitated the characterization process and boosted the MIR power level to usable level while preserving the laser linewidth. To demonstrate the application of MIR microresonators and microlasers, I studied intracavity absorption spectroscopy based on active and passive high quality WGM MIR microlasers and microresonators. I also estimated the sensitivity and detection limit of gas sensors based on these devices. The outcome of my analysis shows that ppm level sensitivity should be achievable using both active and passive microresonators. Next, I modeled the performance of two newly proposed configurations for NLW MIR generation based on stimulated Raman scattering. First, I studied a new family of Raman fiber lasers that are capable of generating any NLW MIR line in the 2.5-9.5 μm spectral region. I demonstrated the feasibility of this MIR laser family, calculated the threshold conditions, identified the condition for its single-mode operation, and laid the foundation for the first experimental demonstration of such lasers. Finally, I explored the performance of silicon-based on-chip Raman lasers and the parameters that have prevented expanding their wavelength to MIR range. Using the outcomes of this study, I proposed and then analyzed a new architecture for on-chip silicon Raman lasers capable of generating single NLW lines around 3.2 μm with sub-mW threshold pump power

Erbium-doped and Raman microlasers on a silicon chip fabricated by the sol–gel process

We report high-Q sol–gel microresonators on silicon chips, fabricated directly from a sol–gel layer deposited onto a silicon substrate. Quality factors as high as 2.5×10^7 at 1561 nm were obtained in toroidal microcavities formed of silica sol–gel, which allowed Raman lasing at absorbed pump powers below 1 mW. Additionally, Er3+-doped microlasers were fabricated from Er3+-doped sol–gel layers with control of the laser dynamics possible by varying the erbium concentration of the starting sol–gel material. Continuous lasing with a threshold of 660 nW for erbium-doped microlaser was also obtained

Controling the coupling properties of active ultrahigh-Q WGM microcavities from undercoupling to selective amplification

International audienceUltrahigh-quality (Q) factor microresonators have a lot of applications in the photonics domain ranging from low-threshold nonlinear optics to integrated optical sensors. Glass-based whispering gallery mode (WGM) microresonators are easy to produce by melting techniques, however they suffer from surface contamination which limits their long-term quality factor to a few 10^8 . Here we show that an optical gain provided by erbium ions can compensate for residual losses. Moreover it is possible to control the coupling regime of an ultrahigh Q-factor three port microresonator from undercoupling to spectral selective amplification by changing the pumping rate. The optical characterization method is based on frequency-swept cavity-ring-down- pectroscopy. This method allows the transmission and dispersive properties of perfectly transparent microresonators and intrinsic finesses up to 4.0x10^7 to be measured. Finally we characterize a critically coupled fluoride glass WGM microresonator with a diameter of 220 mm and a loaded Q-factor of 5.3x10^9 is demonstrated

Fabrication and Characterization of Microlasers by the Sol-Gel Method

The present study explores the application of new materials systems for low threshold microlasers, and characterization of the microcavities. The sol-gel method is used for gain functionalization of high-Q microcavities. A detailed procedure for preparation of the sol-gel films by the spin-on or dip-coating method is presented. The effect of different process conditions on the properties and microstructure of the thin films is investigated through Fourier Transform Infrared (FTIR) Spectroscopy, Scanning Electron Microscopy (SEM), and etching rate test. Surface gain functionalization of microsphere cavities is fabricated by coating the microsphere with a thin layer of Er³⁺-doped sol-gel films. The optical gain is due to the population inversion of rare earth ions in the sol-gel films. A fiber taper is used to both couple the pump power into and extract the laser power out of the microsphere laser. The laser dynamics change between continuous-wave and pulsating operation by varying the doping concentration and the thickness of the sol-gel films outside the microsphere. Surface functionalization is also achieved on the microtoroid on a single silicon chip, which can be fabricated in parallel using wafer-scale processing and has characteristics that are more easily controlled than microsphere. The microtoroid can be selectively coated only at the periphery by making use of the variation of etching rate (in buffered HF) of sol-gel films with different degrees of densification. The laser performance of the gain functionalized microtoroids is investigated. Highly confined whispering gallery modes make possible single-mode microlasers. This work also shows that the high Q microtoroid laser has a linewidth much lower than 300 kHz. The thesis explores fabrication of high Q microcavities directly from the sol-gel silica films deposited on a single silicon wafer. Quality factor as high as 2.5 x 10⁷ at 1561 nm is obtained in toroidal microcavities formed of silica sol-gel, which allows Raman lasing at absorbed pump power below 1 mW. Additionally, Er³⁺-doped microlasers are fabricated from Er³⁺-doped sol-gel layers with control of the laser dynamics possible by varying the erbium concentration of the starting sol-gel material. Continuous lasing with a record threshold of 660 nW for erbium-doped microlaser on a silicon wafer is also obtained. Analytic formulas are derived to predict the laser performance, such as the laser output power, the threshold power, and the differential quantum efficiency, under different loading condition, i.e. the air gap between the fiber-taper coupler and the cavities. The effect of Er3+ concentration on the minimum threshold is also investigated. In addition, we present a theoretical model in which we include paired ions as the saturable absorber. It shows that self-pulsing operation can be expected with paired-ions-induced quenching in the system. The pulsation frequency increases linearly with the square root of the pumping level, which is consistent with the experimental observation.</p