Showing papers on "Laser linewidth published in 2014"

Fiber lasers and their applications [Invited]

Abstract: Fiber lasers have seen progressive developments in terms of spectral coverage and linewidth, output power, pulse energy, and ultrashort pulse width since the first demonstration of a glass fiber laser in 1964. Their applications have extended into a variety of fields accordingly. In this paper, the milestones of glass fiber laser development are briefly reviewed and recent advances of high-power continuous wave, Q-switched, mode-locked, and single-frequency fiber lasers in the 1, 1.5, 2, and 3 μm regions and their applications in such areas as industry, medicine, research, defense, and security are addressed in detail.

Integrated frequency comb source of heralded single photons

Abstract: We report an integrated photon pair source based on a CMOS-compatible microring resonator that generates multiple, simultaneous, and independent photon pairs at different wavelengths in a frequency comb compatible with fiber communication wavelength division multiplexing channels (200 GHz channel separation) and with a linewidth that is compatible with quantum memories (110 MHz). It operates in a self-locked pump configuration, avoiding the need for active stabilization, making it extremely robust even at very low power levels.

Nanoconstriction-based spin-Hall nano-oscillator

Abstract: We experimentally demonstrate magnetic nano-oscillators driven by pure spin current produced by the spin Hall effect in a bow tie-shaped nanoconstriction. These devices exhibit single-mode auto-oscillation and generate highly-coherent electronic microwave signals with a significant power and the spectral linewidth as low as 6.2 MHz at room temperature. The proposed simple and flexible device geometry is amenable to straightforward implementation of advanced spintronic structures such as chains of mutually coupled spin-Hall nano-oscillators.

Room temperature electrically injected polariton laser.

Abstract: Room temperature electrically pumped inversionless polariton lasing is observed from a bulk GaN-based microcavity diode. The low nonlinear threshold for polariton lasing occurs at 169 A/cm(2) in the light-current characteristics, accompanied by a collapse of the emission linewidth and small blueshift of the emission peak. Measurement of angle-resolved luminescence, polariton condensation and occupation in momentum space, and output spatial coherence and polarization have also been made. A second threshold, due to conventional photon lasing, is observed at an injection of 44 kA/cm(2).

Fitting of calibration-free scanned-wavelength-modulation spectroscopy spectra for determination of gas properties and absorption lineshapes.

Abstract: The development and initial demonstration of a scanned-wavelength, first-harmonic-normalized, wavelength-modulation spectroscopy with nf detection (scanned-WMS-nf/1f) strategy for calibration-free measurements of gas conditions are presented. In this technique, the nominal wavelength of a modulated tunable diode laser (TDL) is scanned over an absorption transition to measure the corresponding scanned-WMS-nf/1f spectrum. Gas conditions are then inferred from least-squares fitting the simulated scanned-WMS-nf/1f spectrum to the measured scanned-WMS-nf/1f spectrum, in a manner that is analogous to widely used scanned-wavelength direct-absorption techniques. This scanned-WMS-nf/1f technique does not require prior knowledge of the transition linewidth for determination of gas properties. Furthermore, this technique can be used with any higher harmonic (i.e., n>1), modulation depth, and optical depth. Selection of the laser modulation index to maximize both signal strength and sensitivity to spectroscopic parameters (i.e., gas conditions), while mitigating distortion, is described. Last, this technique is demonstrated with two-color measurements in a well-characterized supersonic flow within the Stanford Expansion Tube. In this demonstration, two frequency-multiplexed telecommunication-grade TDLs near 1.4 μm were scanned at 12.5 kHz (i.e., measurement repetition rate of 25 kHz) and modulated at 637.5 and 825 kHz to determine the gas temperature, pressure, H2O mole fraction, velocity, and absorption transition lineshape. Measurements are shown to agree within uncertainty (1%–5%) of expected values.

Ferromagnetic resonance of sputtered yttrium iron garnet nanometer films

Abstract: Growth of nm-thick yttrium iron garnet (YIG) films by sputtering and ferromagnetic resonance (FMR) properties in the films were studied. The FMR linewidth of the YIG film decreased as the film thickness was increased from several nanometers to about 100 nm. For films with very smooth surfaces, the linewidth increased linearly with frequency. In contrast, for films with big grains on the surface, the linewidth-frequency response was strongly nonlinear. Films in the 7–26 nm thickness range showed a surface roughness between 0.1 nm and 0.4 nm, a 9.48-GHz FMR linewidth in the 6–10 Oe range, and a damping constant of about 0.001.

Ultra-narrow linewidth, stable and tunable laser source for optical communication systems and spectroscopy

Abstract: A novel ultra-narrow linewidth, stable and tunable single-line laser source is demonstrated and experimentally performed. The single spectral line laser is achieved by selecting and amplifying one spectral comb line of a femtosecond-fiber laser via polarization pulling assisted stimulated Brillouin scattering. Stabilization and tuning is performed by additional modulation. First proof of concept results show possible linewidths below 1 Hz and an SNR of 47 dB with a tunability of more than 100 nm and a relative stability of ±160 mHz over 5 h. Such a laser source gives high potential for many different applications like spectroscopy and optical communications.

CMOS-compatible, multiplexed source of heralded photon pairs: towards integrated quantum combs

Abstract: We report an integrated photon pair source based on a CMOS-compatible microring resonator that generates multiple, simultaneous, and independent photon pairs at different wavelengths in a frequency comb compatible with fiber communication wavelength division multiplexing channels (200 GHz channel separation) and with a linewidth that is compatible with quantum memories (110 MHz). It operates in a self-locked pump configuration, avoiding the need for active stabilization, making it extremely robust even at very low power levels.

High-coherence semiconductor lasers based on integral high-Q resonators in hybrid Si/III-V platforms

Abstract: The semiconductor laser (SCL) is the principal light source powering the worldwide optical fiber network. The ever-increasing demand for data is causing the network to migrate to phase-coherent modulation formats, which place strict requirements on the temporal coherence of the light source that no longer can be met by current SCLs. This failure can be traced directly to the canonical laser design, in which photons are both generated and stored in the same, optically lossy, III-V material. This leads to an excessive and large amount of noisy spontaneous emission commingling with the laser mode, thereby degrading its coherence. High losses also decrease the amount of stored optical energy in the laser cavity, magnifying the effect of each individual spontaneous emission event on the phase of the laser field. Here, we propose a new design paradigm for the SCL. The keys to this paradigm are the deliberate removal of stored optical energy from the lossy III-V material by concentrating it in a passive, low-loss material and the incorporation of a very high-Q resonator as an integral (i.e., not externally coupled) part of the laser cavity. We demonstrate an SCL with a spectral linewidth of 18 kHz in the telecom band around 1.55 μm, achieved using a single-mode silicon resonator with Q of 106.

Pseudo-random binary sequence phase modulation for narrow linewidth, kilowatt, monolithic fiber amplifiers.

Abstract: We report on pseudo random binary sequence (PRBS) phase modulation for narrow-linewidth, kilowatt-class, monolithic (all-fiber) amplifiers. Stimulated Brillouin scattering (SBS) threshold enhancement factors for different patterns of PRBS modulated fiber amplifiers were experimentally analyzed and agreed well with the theoretical predictions. We also examined seeding of the SBS process by phase modulated signals when the effective linewidth is on the same order as the Brillouin shift frequency. Here ~30% variations in SBS power thresholds were observed from small tunings of the modulation frequency. In addition, a 3 GHz PRBS modulated, 1.17 kW fiber amplifier was demonstrated. Near diffraction-limited beam quality was achieved (M2 = 1.2) with an optical pump efficiency of 83%. Overall, the improved SBS suppression and narrow linewidth achieved through PRBS modulation can have a significant impact on the beam combining of kilowatt class fiber lasers.

Generation of 103 fs mode-locked pulses by a gain linewidth-variable Nd,Y:CaF2 disordered crystal.

Abstract: We have demonstrated a diode-pumped passively mode-locked femtosecond Nd,Y:CaF2 disordered crystal laser for the first time to our knowledge. By choosing appropriate Y-doping concentration, a broad fluorescence linewidth of 31 nm has been obtained from the gain linewidth-variable Nd,Y:CaF2 crystal. With the Nd,Y:CaF2 disordered crystal as gain medium, the mode-locked laser generated pulses with pulse duration as short as 103 fs, average output power of 89 mW, and repetition rate of 100 MHz. To our best knowledge, this is the shortest pulse generated from Nd-doped crystal lasers so far. The research results show that the Nd,Y:CaF2 disordered crystal will be a potential alternative as gain medium of repetitive chirped pulse amplification for high-peak-power lasers.

Room temperature continuous wave lasing of electrically injected GaN-based vertical cavity surface emitting lasers

Abstract: Continuous wave (CW) lasing of electrically injected GaN-based vertical cavity surface emitting lasers (VCSELs) was achieved at room temperature. First, a high quality factor (Q) VCSEL-structured device with very narrow linewidth of 0.12 nm, corresponding to a Q-value of 3570 was obtained through two-step substrate transfer technique. However, poor heat dissipation ability prevented the device from lasing. Based on the high-Q resonant cavity design, we further fabricated vertical-structured VCSELs through metal bonding technique on Si substrate. CW lasing from vertical-structured VCSELs was observed with threshold current of density of 1.2 kA/cm2 and lasing linewidth of about 0.20 nm.

Coherence and incoherence in an optical comb.

Abstract: We demonstrate a coexistence of coherent and incoherent modes in the optical comb generated by a passively mode-locked quantum dot laser. This is experimentally achieved by means of optical linewidth, radio frequency spectrum, and optical spectrum measurements and confirmed numerically by a delay-differential equation model showing excellent agreement with the experiment. We interpret the state as a chimera state. © 2014 American Physical Society.

Measurement of the intrinsic damping constant in individual nanodisks of Y3Fe5O12 and Y3Fe5O12|Pt

Abstract: We report on an experimental study on the spin-waves relaxation rate in two series of nanodisks of diameter φ =300, 500 and 700 nm, patterned out of two systems: a 20 nm thick yttrium iron garnet (YIG) film grown by pulsed laser deposition either bare or covered by 13 nm of Pt. Using a magnetic resonance force microscope, we measure precisely the ferromagnetic resonance linewidth of each individual YIG and YIG|Pt nanodisks. We find that the linewidth in the nanostructure is sensibly smaller than the one measured in the extended film. Analysis of the frequency dependence of the spectral linewidth indicates that the improvement is principally due to the suppression of the inhomogeneous part of the broadening due to geometrical confinement, suggesting that only the homogeneous broadening contributes to the linewidth of the nanostructure. For the bare YIG nano-disks, the broadening is associated to a damping constant α = 4 · 10 −4. A 3 fold increase of the linewidth is observed for the series with Pt cap layer, attributed to the spin pumping effect. The measured enhancement allows to extract the spin mixing conductance found to be G ↑↓ = 1.55 · 10 14 Ω −1 m −2 for our YIG(20nm)|Pt interface, thus opening large opportunities for the design of YIG based nanostructures with optimized magnetic losses.

Achieving resonance in the Advanced LIGO gravitational-wave interferometer

Abstract: Interferometric gravitational-wave detectors are complex instruments comprised of a Michelson interferometer enhanced by multiple coupled cavities. Active feedback control is required to operate these instruments and keep the cavities locked on resonance. The optical response is highly nonlinear until a good operating point is reached. The linear operating range is between 0.01% and 1% of a fringe for each degree of freedom. The resonance lock has to be achieved in all five degrees of freedom simultaneously, making the acquisition difficult. Furthermore, the cavity linewidth seen by the laser is only _(~1) Hz, which is four orders of magnitude smaller than the linewidth of the free running laser. The arm length stabilization system is a new technique used for arm cavity locking in Advanced LIGO. Together with a modulation technique utilizing third harmonics to lock the central Michelson interferometer, the Advanced LIGO detector has been successfully locked and brought to an operating point where detecting gravitational-waves becomes feasible.

Measurement of the intrinsic damping constant in individual nanodisks of YIG and YIGjPt

Abstract: We report on an experimental study on the spin-waves relaxation rate in two series of nanodisks of diameter˚=300, 500 and 700 nm, patterned out of two systems: a 20 nm thick yttrium iron garnet (YIG) lm grownby pulsed laser deposition either bare or covered by 13 nm of Pt. Using a magnetic resonance force microscope,we measure precisely the ferromagnetic resonance linewidth of each individual YIG and YIGjPt nanodisks.We nd that the linewidth in the nanostructure is sensibly smaller than the one measured in the extended lm.Analysis of the frequency dependence of the spectral linewidth indicates that the improvement is principallydue to the suppression of the inhomogeneous part of the broadening due to geometrical con nement, suggestingthat only the homogeneous broadening contributes to the linewidth of the nanostructure. For the bare YIGnano-disks, the broadening is associated to a damping constant = 4 10

Application of taguchi method in the optimization of laser micro-engraving of photomasks

Abstract: Photomasks are needed to generate various design patterns in the fabrication of liquid crysral displays (LCDs). This paper discusses the use of the Taguchi method of experimental design in optimising process parameters for micro–engraving of iron oxide coated glass using a Q–switched Nd:YAG laser. The effects of five key process parameters – beam expansion ratio, focal length, average laser power, pulse repetition rate and engraving speed – have been explored. The primary response under study is the engraving linewidth. An L16 orthogonal array was used to accommodate the experiments. The study indicated that a minimum linewidth of 18 pm could be obtained with beam expansion ratio of 5x, focal length of 50 mm, laser average power of 0.4 W, pulse repetition rate of 5 kHz, and engraving speed of 5000 mm/min.

Efficient 1.9 μm emission in H2-filled hollow core fiber by pure stimulated vibrational Raman scattering

Abstract: We report here efficient 1.9 μm emission by pure stimulated vibrational Raman scattering in a hydrogen-filled anti-resonant hollow-core fiber pumped with a 1064 nm microchip laser. A maximum quantum conversion efficiency ~48% was achieved by using a 6.5 m length of fiber filled with 23 bar hydrogen, with a maximum peak output power >2 kW. By properly designing the transmission bands of the fiber, selecting alternative pump sources and active gases, the emission wavelength could be extended into the mid-infrared. This provides a potential route for generating efficient, compact, broadly tunable, high power, and narrow linewidth mid-infrared fiber gas lasers with broad application in defense, environmental, and medical monitoring.

Micro-integrated extended cavity diode lasers for precision potassium spectroscopy in space

Abstract: We present a micro-integrated, extended cavity diode laser module for space-based experiments on potassium Bose-Einstein condensates and atom interferometry. The module emits at the wavelength of the potassium D2-line at 766.7 nm and provides 27.5 GHz of continuous tunability. It features sub-100 kHz short term (100 μs) emission linewidth. To qualify the extended cavity diode laser module for quantum optics experiments in space, vibration tests (8.1 g(RMS) and 21.4 g(RMS)) and mechanical shock tests (1500 g) were carried out. No degradation of the electro-optical performance was observed.

Two-colour spin noise spectroscopy and fluctuation correlations reveal homogeneous linewidths within quantum-dot ensembles

Abstract: 'Spin noise spectroscopy' is an optical technique for probing electron and hole spin dynamics that is based on detecting their intrinsic fluctuations while in thermal equilibrium. Here we show that fluctuation correlations can be further exploited in multi-probe noise studies to reveal information that in general cannot be accessed by conventional linear optical spectroscopy, such as the underlying homogeneous linewidths of individual constituents within inhomogeneously broadened systems. This is demonstrated in singly charged (In,Ga)As quantum-dot ensembles using two weak probe lasers: When the lasers have similar wavelengths, they probe the same quantum dots in the ensemble and show correlated spin fluctuations. In contrast, mutually detuned probe lasers measure different subsets of quantum dots, giving uncorrelated fluctuations. The noise correlation versus laser detuning directly reveals the quantum dot homogeneous linewidth even in the presence of a strong inhomogeneous broadening. Such noise-based correlation techniques are not limited to semiconductor spin systems, but are applicable to any system with measurable intrinsic fluctuations.

Spectroscopy and frequency measurement of the 87Sr clock transition by laser linewidth transfer using an optical frequency comb

Abstract: We performed spectroscopic observations of the 698-nm clock transition in 87Sr confined in an optical lattice using a laser linewidth transfer technique. A narrow-linewidth laser interrogating the clock transition was prepared by transferring the linewidth of a master laser (1064 nm) to that of a slave laser (698 nm) with a high-speed controllable fiber-based frequency comb. The Fourier-limited spectrum was then observed for an 80-ms interrogating pulse. We determined that the absolute frequency of the 5s2 1S0–5s5p 3P0 clock transition in 87Sr is 429 228 004 229 872.0 (1.6) Hz referenced to the SI second.

Ultranarrow Luminescence Linewidth of Silicon Nanocrystals and Influence of Matrix

Abstract: The luminescence linewidth of individual silicon nanocrystals was characterized by single-dot spectroscopy, and an ultranarrow linewidth of ∼200 μeV at 10 K was found. This value is, in fact, limited by system resolution and represents only the upper limit of the homogeneous linewidth. In addition, the effect of the matrix was investigated for nanocrystals coated with organic ligands, embedded in silicon dioxide, as well as for nanocrystals with only a thin passivating layer. It was found that, depending on the matrix, the room-temperature bandwidth may vary by an order of magnitude, where values as small as ∼12 meV (∼5 nm) at 300 K were detected for nanocrystals with a thin passivation. The observed values for silicon nanocrystals are similar and even surpass some of those for direct-band-gap quantum dots. The narrow linewidth at room temperature enables the use of silicon nanocrystals for nontoxic narrow-band labeling of biomolecules and for application as phosphors in white-light-emitting devices.

Mean-field theory of nearly many-body localized metals

Abstract: We develop a mean-field theory of the metallic phase near the many-body localization (MBL) transition, using the observation that a system near the MBL transition should become an increasingly slow heat bath for its constituent parts. As a first step, we consider the properties of a many-body localized system coupled to a generic ergodic bath whose characteristic dynamical timescales are much slower than those of the system. As we discuss, a wide range of experimentally relevant systems fall into this class; we argue that relaxation in these systems is dominated by collective many-particle rearrangements, and compute the associated timescales and spectral broadening. We then use the observation that the self-consistent environment of any region in a nearly localized metal can itself be modeled as a slowly fluctuating bath to outline a self-consistent mean-field description of the nearly localized metal and the localization transition. In the nearly localized regime, the spectra of local operators are highly inhomogeneous and the typical local spectral linewidth is narrow. The local spectral linewidth is proportional to the DC conductivity, which is small in the nearly localized regime. This typical linewidth and the DC conductivity go to zero as the localized phase is approached, with a scaling that we calculate, and which appears to be in good agreement with recent experimental results.

Introduction to Cavity Enhanced Absorption Spectroscopy

Abstract: In this introductory chapter we will begin with an historical outline of the development of cavity enhanced absorption methods, with just enough attention to the applications that either motivated them or became conceivable after their development. Given the number of publications in this domain, we will consider only the first demonstrations, and those works leading to substantial improvement or innovation in the state of the art.

Precision spectroscopy by photon-recoil signal amplification

Abstract: Precision spectroscopy of atomic and molecular ions offers a window to new physics, but is typically limited to species with a cycling transition for laser cooling and detection. Quantum logic spectroscopy has overcome this limitation for species with long-lived excited states. Here we extend quantum logic spectroscopy to fast, dipole-allowed transitions and apply it to perform an absolute frequency measurement. We detect the absorption of photons by the spectroscopically investigated ion through the photon recoil imparted on a co-trapped ion of a different species, on which we can perform efficient quantum logic detection techniques. This amplifies the recoil signal from a few absorbed photons to thousands of fluorescence photons. We resolve the line centre of a dipole-allowed transition in (40)Ca(+) to 1/300 of its observed linewidth, rendering this measurement one of the most accurate of a broad transition. The simplicity and versatility of this approach enables spectroscopy of many previously inaccessible species.

Enhanced Dynamic Performance of Quantum Dot Semiconductor Lasers Operating on the Excited State

Abstract: The modulation dynamics and the linewidth enhancement factor of excited-state (ES) lasing quantum dot (QD) semiconductor lasers are investigated through a set of improved rate equation model, in which the contribution of off-resonant states to the refractive index change is taken into account. The ES laser exhibits a broader modulation response associated with a much lower chirp-to-power ratio in comparison with the ground-state (GS) lasing laser. In addition, it is found that the laser emission in ES reduces the linewidth enhancement factor of QD lasers by about 40% than that in GS. These properties make the ES lasing devices, especially InAs/InP ones emitting at 1.55 μm, more attractive for direct modulation in high-speed optical communication systems.

Inductance of Circuit Structures for MIT LL Superconductor Electronics Fabrication Process with 8 Niobium Layers

Abstract: Inductance of superconducting thin-film inductors and structures with linewidth down to 250 nm has been experimentally evaluated. The inductors include various striplines and microstrips, their 90-degree bends and meanders, interlayer vias, etc., typically used in superconducting digital circuits. The circuits have been fabricated by a fully planarized process with 8 niobium layers, developed at MIT Lincoln Laboratory for very-large-scale superconducting integrated circuits. Excellent run-to-run reproducibility and inductance uniformity of better than 1% across 200-mm wafers have been found. It has been found that the inductance per unit length of stripline and microstrip line inductors continues to grow as the inductor linewidth is reduced deep into the submicron range to the widths comparable to the film thickness and magnetic field penetration depth. It is shown that the linewidth reduction does not lead to widening of the parameter spread due to diminishing sensitivity of the inductance to the linewidth and dielectric thickness. The experimental results were compared with numeric inductance extraction using commercial software and freeware, and a good agreement was found for 3-D inductance extractors. Methods of further miniaturization of circuit inductors for achieving circuit densities > 10^6 Josephson junctions per cm^2 are discussed.

Tunable and switchable dual-wavelength single polarization narrow linewidth SLM erbium-doped fiber laser based on a PM-CMFBG filter

Abstract: A tunable and switchable dual-wavelength single polarization narrow linewidth single-longitudinal-mode (SLM) erbium-doped fiber (EDF) ring laser based on polarization-maintaining chirped moire fiber Bragg grating (PM-CMFBG) filter is proposed and demonstrated. For the first time as we know, the CMFBG inscribed on the PM fiber is applied for the wavelength-tunable and-switchable dual-wavelength laser. The PM-CMFBG filter with ultra-narrow transmission band (0.1 pm) and a uniform polarization-maintaining fiber Bragg grating (PM-FBG) are used to select the laser longitudinal mode. The stable single polarization SLM operation is guaranteed by the PM-CMFBG filter and polarization controller. A tuning range of about 0.25 nm with about 0.075 nm step is achieved by stretching the uniform PM-FBG. Meanwhile, the linewidth of the fiber laser for each wavelength is approximate 6.5 and 7.1 kHz with a 20 dB linewidth, which indicates the laser linewidth is approximate 325 Hz and 355 Hz FWHM.

A single adiabatic microring-based laser in 220 nm silicon-on-insulator.

Abstract: We demonstrate a laser for the silicon photonics platform by hybrid integration with a III/V reflective semiconductor optical amplifier coupled to a 220 nm silicon-on-insulator half-cavity. We utilize a novel ultra-thin silicon edge coupler. A single adiabatic microring based inline reflector is used to select a lasing mode, as compared to the multiple rings and Bragg gratings used in many previous results. Despite the simplified design, the laser was measured to have on-chip 9.8 mW power, less than 220 KHz linewidth, over 45 dB side mode suppression ratio, less than -135 dB/Hz relative intensity noise, and 2.7% wall plug efficiency.