Showing papers on "Laser linewidth published in 2010"
TL;DR: A simple approach to this relation with an approximate formula for evaluation of the laser linewidth that can be applied to arbitrary noise spectral densities is presented.
Abstract: Frequency fluctuations of lasers cause a broadening of their line shapes. Although the relation between the frequency noise spectrum and the laser line shape has been studied extensively, no simple expression exists to evaluate the laser linewidth for frequency noise spectra that does not follow a power law. We present a simple approach to this relation with an approximate formula for evaluation of the laser linewidth that can be applied to arbitrary noise spectral densities.
520 citations
TL;DR: Numerical simulations revealed that the experimentally observed splitting of the 3s3p⁶4p ¹P line is caused by the coupling between two short-lived highly excited states in the strong laser field.
Abstract: Autoionization of argon atoms was studied experimentally by transient absorption spectroscopy with isolated attosecond pulses. The peak position, intensity, linewidth, and shape of the $3s3{p}^{6}np$ $^{1}P$ Fano resonance series (26.6--29.2 eV) were modified by intense few-cycle near infrared laser pulses, while the delay between the attosecond pulse and the laser pulse was changed by a few femtoseconds. Numerical simulations revealed that the experimentally observed splitting of the $3s3{p}^{6}4p$ $^{1}P$ line is caused by the coupling between two short-lived highly excited states in the strong laser field.
317 citations
TL;DR: In this paper, the authors report sub-nanometer linewidth uniformity in silicon nanophotonics devices fabricated using high-volume CMOS fabrication tools, using wavelength-selective devices such as ring resonators, Mach-Zehnder interferometers, and arrayed waveguide gratings to assess the device nonuniformity within and between chips.
Abstract: We report subnanometer linewidth uniformity in silicon nanophotonics devices fabricated using high-volume CMOS fabrication tools. We use wavelength-selective devices such as ring resonators, Mach-Zehnder interferometers, and arrayed waveguide gratings to assess the device nonuniformity within and between chips. The devices were fabricated using 193 or 248 nm optical lithography and dry etching in silicon-on-insulator wafer technology. Using 193 nm optical lithography, we have achieved a linewidth uniformity of 2 nm (after lithography) and 2.6 nm (after dry etch) over 200 mm wafer. Furthermore, with the developed fabrication process, using wavelength-selective devices, we have demonstrated a linewidth control better than 0.6 nm within chip and better than 2 nm chip-to-chip. The necessity for high-resolution optical lithography is demonstrated by comparing device nonuniformity between the 248 and 193 nm optical lithography processes.
311 citations
TL;DR: In this paper, a quaternary phase-shift-keying (QPSK) partition scheme was proposed for 16-ary quadrature amplitude modulation (16-QAM) coherent optical systems.
Abstract: The laser linewidth tolerance for 16-ary quadrature amplitude modulation (16-QAM) coherent optical systems is investigated using a quaternary phase-shift-keying (QPSK) partition scheme. The different stages needed to partition the square-16-QAM into QPSK constellations for carrier phase estimation are discussed. It is shown that at 1 dB above sensitivity at a bit-error rate of 10-3, a combined linewidths symbol duration product of 1 × 10-4 is tolerable. The performance of the algorithm with different bits resolution in the analog-to-digital converter is also presented.
243 citations
TL;DR: A miniature self-injection locked distributed-feedback laser using resonant optical feedback from a high-Q crystalline whispering-gallery-mode resonator that possesses excellent spectral purity and good long-term stability is demonstrated.
Abstract: We demonstrate a miniature self-injection locked distributed-feedback laser using resonant optical feedback from a high-Q crystalline whispering-gallery-mode resonator. The linewidth reduction factor is greater than 10,000, with resultant instantaneous linewidth of less than 200Hz. The minimal value of the Allan deviation for the laser-frequency stability is 3×10−12 at the integration time of 20μs. The laser possesses excellent spectral purity and good long-term stability.
232 citations
TL;DR: It is demonstrated that fiber-based frequency combs with multi-branch configurations can transfer both linewidth and frequency stability to another wavelength at the millihertz level and the frequency noise in the out-of-loop beat originates mainly from phase noise in branched optical fibers.
Abstract: We demonstrate that fiber-based frequency combs with multi-branch configurations can transfer both linewidth and frequency stability to another wavelength at the millihertz level. An intra-cavity electro-optic modulator is employed to obtain a broad servo bandwidth for repetition rate control. We investigate the relative linewidths between two combs using a stable continuous-wave laser as a common reference to stabilize the repetition rate frequencies in both combs. The achieved energy concentration to the carrier of the out-of-loop beat between the two combs was 99% and 30% at a bandwidth of 1 kHz and 7.6 mHz, respectively. The frequency instability of the comb was 3.7×10−16 for a 1 s averaging time, improving to 5-8×10−19 for 10000 s. We show that the frequency noise in the out-of-loop beat originates mainly from phase noise in branched optical fibers.
180 citations
TL;DR: A comprehensive investigation of the frequency-noise spectral density of a free-running midinfrared quantum-cascade laser is presented, providing direct evidence of the leveling of this noise down to a white- noise plateau, corresponding to an intrinsic linewidth of a few hundred hertz.
Abstract: A comprehensive investigation of the frequency-noise spectral density of a free-running midinfrared quantum-cascade laser is presented for the first time. It provides direct evidence of the leveling of this noise down to a white-noise plateau, corresponding to an intrinsic linewidth of a few hundred hertz. The experiment is in agreement with the most recent theory on the fundamental mechanism of line broadening in quantum-cascade lasers, which provides a new insight into the Schawlow-Townes formula and predicts a narrowing beyond the limit set by the radiative lifetime of the upper level.
167 citations
TL;DR: This is the highest-power fiber laser that has been coherently locked using any method that allows brightness scaling, and the measured combining efficiency agreed with estimated decoherence effects from fiber nonlinearity, linewidth, and phase-locking accuracy.
Abstract: A three-stage Yb-fiber amplifier emitted 1.43 kW of single-mode power when seeded with a 25 GHz linewidth master oscillator (MO). The amplified output was polarization stabilized and phase locked using active heterodyne phase control. A low-power sample of the output beam was coherently combined to a second fiber amplifier with 90% visibility. The measured combining efficiency agreed with estimated decoherence effects from fiber nonlinearity, linewidth, and phase-locking accuracy. This is the highest-power fiber laser that has been coherently locked using any method that allows brightness scaling.
165 citations
TL;DR: Using a resonant pump laser, this work has demonstrated optical frequency conversion via the dynamically modulated QD, which is the physical mechanism underlying laser sideband cooling a nanomechanical resonator by means of an embedded QD.
Abstract: The dynamic response of InAs/GaAs self-assembled quantum dots (QDs) to strain is studied experimentally by periodically modulating the QDs with a surface acoustic wave and measuring the QD fluorescence with photoluminescence and resonant spectroscopy. When the acoustic frequency is larger than the QD linewidth, we resolve phonon sidebands in the QD fluorescence spectrum. Using a resonant pump laser, we have demonstrated optical frequency conversion via the dynamically modulated QD, which is the physical mechanism underlying laser sideband cooling a nanomechanical resonator by means of an embedded QD.
160 citations
TL;DR: An efficient single frequency fiber laser by using a newly-developed Er(3+)/Yb(3+) co-doped single mode phosphate glass fiber with the net gain coefficient of 5.2 dB/cm and propagation loss coefficient has been demonstrated.
Abstract: An efficient single frequency fiber laser by using a newly-developed Er(3+)/Yb(3+) co-doped single mode phosphate glass fiber with the net gain coefficient of 5.2 dB/cm and propagation loss coefficient of 0.04 dB/cm has been demonstrated. Over 300 mW stable continuous -wave single transverse and longitudinal mode seed lasering at 1.5 microm has been achieved from a 2.0 cm-long active fiber. The measured slope efficiency and the calculated quantum efficiency of laser emission are found to be 30.9% and 0.938 +/- 0.081, respectively. It is found that the linewidth of the fiber laser is less than 2 kHz, and the measured relative intensity noise (RIN) is around -120 dB/Hz in the frequency range of 50 to 500 kHz.
159 citations
TL;DR: A highly efficient OPO with a WGM resonator using natural temperature phase matching, where the individual optical fields have narrow optical linewidth is presented.
Abstract: In whispering gallery mode (WGM) resonator light is guided by continuous total internal reflection along a curved surface. Fabricating such resonators from an optically nonlinear material one takes advantage of their exceptionally high quality factors and small mode volumes to achieve extremely efficient optical frequency conversion. Our analysis of the phase-matching conditions for optical parametric down-conversion (PDC) in a spherical WGM resonator shows their direct relation to the sum rules for photons' angular momenta and predicts a very low parametric oscillation threshold. We realized such an optical parametric oscillator (OPO) based on naturally phase-matched PDC in lithium niobate. We demonstrated a single-mode, strongly nondegenerate OPO with a threshold of 6.7 μW and linewidth under 10 MHz. This work demonstrates the remarkable capabilities of WGM-based OPOs.
TL;DR: A truly random number generator is presented based on measuring the phase noise of a single-mode vertical cavity surface emitting laser and a continuously generated random bit sequence is verified by two additional criteria for its true randomness.
Abstract: We present a simple approach to realize truly random number generator based on measuring the phase noise of a single-mode vertical cavity surface emitting laser The true randomness of the quantum phase noise originates from the spontaneous emission of photons and the random bit generation rate is ultimately limited only by the laser linewidth With the final bit generation rate of 20 Mbit/s, the truly random bit sequence guaranteed by the uncertainty principle of quantum mechanics passes the three standard randomness tests (ENT, Diehard, and NIST Statistical Test Suites) Moreover, a continuously generated random bit sequence, with length up to 14 Gbit, is verified by two additional criteria for its true randomness
HGST1
TL;DR: This sensor's performance relies predominantly on STO properties such as spectral linewidth and frequency dispersion with magnetic field, rather than signal amplitude as in conventional magnetoresistive sensors, and is shown in measured devices to achieve large signal to noise ratios.
Abstract: Magnetic field detection with extremely high spatial resolution is crucial to applications in magnetic storage, biosensing, and magnetic imaging. Here, we present the concept of using a spin torque oscillator (STO) to detect magnetic fields by measuring the frequency of the oscillator. This sensor's performance relies predominantly on STO properties such as spectral linewidth and frequency dispersion with magnetic field, rather than signal amplitude as in conventional magnetoresistive sensors, and is shown in measured devices to achieve large signal to noise ratios. Using macrospin simulations, we describe oscillator designs for maximizing performance, making spin torque oscillators an attractive candidate to replace more commonly used sensors in nanoscale magnetic field sensing and future magnetic recording applications.
TL;DR: In this paper, a self-injection-locked DFB laser using resonant optical feedback from a high-Q crystalline whispering gallery mode resonator has been demonstrated with a linewidth reduction factor greater than 10,000.
Abstract: We demonstrate a miniature self-injection locked DFB laser using resonant optical feedback from a high-Q crystalline whispering gallery mode resonator. The linewidth reduction factor is greater than 10,000, with resultant instantaneous linewidth less than 200 Hz. The minimal value of the Allan deviation for the laser frequency stability is 3x10^(-12) at the integration time of 20 us. The laser possesses excellent spectral purity and good long term stability.
TL;DR: In this article, the continuous wave laser action on GaN-based vertical cavity surface emitting laser at room temperature was demonstrated. But the laser structure consists of a ten-pair Ta2O5/SiO2 distributed Bragg reflector (DBR), a 7λ-thick optical cavity, ten-pairs InGaN/GaN multiquantum wells with an AlGaN electron blocking layer, and a 29-pair AlN/ GaN DBR.
Abstract: We report the demonstration of the continuous wave laser action on GaN-based vertical cavity surface emitting lasers at room temperature. The laser structure consists of a ten-pair Ta2O5/SiO2 distributed Bragg reflector (DBR), a 7λ-thick optical cavity, ten-pairs InGaN/GaN multiquantum wells with an AlGaN electron blocking layer, and a 29-pair AlN/GaN DBR. The laser has a threshold current of about 9.7 mA corresponding to the current density of about 12.4 kA/cm2 and a turn-on voltage about 4.3 V at 300 K. The lasing wavelength was 412 nm with a linewidth of about 0.5 nm. A spontaneous emission coupling efficiency factor of about 5×10−3 and the degree of polarization of about 55% were measured, respectively. The laser beam has a narrow divergence angle of about 8°.
TL;DR: In this article, a pre-activated acoustic field and an optical phase control over the interrogating pulse were used for high spatial and spectral resolution Brillouin sensing with enhanced signal to noise ratio.
Abstract: High spatial ( cm) and spectral ( MHz) resolution Brillouin sensing is realized with enhanced signal to noise ratio using a pre-activated acoustic field and an optical phase control over the interrogating pulse. Pre-activation of the acoustic field preserves the Brillouin natural linewidth and a differential gain technique extends the method to long ranges. Experimentally, fully resolved measurements of the Brillouin frequency shift of a 5 cm spot perturbation at the far end of a 5 km fiber have been performed with a frequency resolution of 3 MHz (2) , using a 500 ps (5 cm) phase shift pulse.
TL;DR: In this article, a 280-nm light-emitting diodes (LEDs) were fabricated by employing high-crystal-quality AlN templates and optimized epitaxial structures.
Abstract: We fabricated high-output-power 280-nm light-emitting diodes (LEDs) by employing high-crystal-quality AlN templates and optimized epitaxial structures. The emission wavelength, output power, forward voltage, spectral linewidth, and external quantum efficiency of the fabricated device measured at 20 mA were 281.0 nm, 2.45 mW, 7.53 V, 10.6 nm, and 2.78%, respectively. In the case of DC operation, the output power increased with time probably resulting from enhanced p-type activation by junction heating. We also fabricated a multi-chip device which consisted of 26 small-chip LEDs. It produced 223 mW at a pulse injection current of 1850 mA.
TL;DR: This work reports the realization and performance of a distributed feedback channel waveguide laser in erbium-doped aluminum oxide on a standard thermally oxidized silicon substrate and the diode-pumped continuous-wave laser, which demonstrated a threshold of 2.2 mW absorbed pump power and a maximum output power of more than 3 mW.
Abstract: We report the realization and performance of a distributed feedback channel waveguide laser in erbium-doped aluminum oxide on a standard thermally oxidized silicon substrate. The diode-pumped continuous-wave laser demonstrated a threshold of 2.2 mW absorbed pump power and a maximum output power of more than 3 mW with a slope efficiency of 41.3% versus absorbed pump power. Single-longitudinal-mode and single-polarization operation was achieved with an emission linewidth of 1.70+-0.58 kHz (corresponding to a Q factor of 1.14 × 10e11), which was centered at a wavelength of 1545.2 nm.
TL;DR: In this paper, the authors present arcsecond-scale Submillimeter Array observations of the CO(3-2) line emission from the disks around the young stars HD 163296 and TW Hya at a spectral resolution of 44 m/s.
Abstract: We present arcsecond-scale Submillimeter Array observations of the CO(3-2) line emission from the disks around the young stars HD 163296 and TW Hya at a spectral resolution of 44 m/s. These observations probe below the ~100 m/s turbulent linewidth inferred from lower-resolution observations, and allow us to place constraints on the turbulent linewidth in the disk atmospheres. We reproduce the observed CO(3-2) emission using two physical models of disk structure: (1) a power-law temperature distribution with a tapered density distribution following a simple functional form for an evolving accretion disk, and (2) the radiative transfer models developed by D'Alessio et al. that can reproduce the dust emission probed by the spectral energy distribution. Both types of models yield a low upper limit on the turbulent linewidth (Doppler b-parameter) in the TW Hya system (<40 m/s), and a tentative (3-sigma) detection of a ~300 m/s turbulent linewidth in the upper layers of the HD 163296 disk. These correspond to roughly <10% and 40% of the sound speed at size scales commensurate with the resolution of the data. The derived linewidths imply a turbulent viscosity coefficient, alpha, of order 0.01 and provide observational support for theoretical predictions of subsonic turbulence in protoplanetary accretion disks.
TL;DR: A compact, lightweight, and efficient fiber laser lidar system has been developed to measure water vapor profiles in the lower atmosphere of Earth or Mars and has made preliminary atmospheric measurements.
Abstract: A compact, lightweight, and efficient fiber laser lidar system has been developed to measure water vapor profiles in the lower atmosphere of Earth or Mars. The line narrowed laser consist of a Tm:germanate fiber pumped by two 792 nm diode arrays. The fiber laser transmits ~0.5 mJ Q- switched pulses at 5 Hz and can be tuned to water vapor lines near 1.94 μm with linewidth of ~20 pm. A lightweight lidar receiver telescope was constructed of carbon epoxy fiber with a 30 cm Fresnel lens and an advanced HgCdTe APD detector. This system has made preliminary atmospheric measurements.
TL;DR: Results indicate that this comb can readily support radial velocity measurements below 1 m/s in the near IR, and potential wavelength biases in spectrograph calibration are estimated.
Abstract: A 12.5 GHz-spaced optical frequency comb locked to a global positioning system disciplined oscillator for near-infrared (IR) spectrograph calibration is presented. The comb is generated via filtering a 250 MHz-spaced comb. Subsequent nonlinear broadening of the 12.5 GHz comb extends the wavelength range to cover 1380–1820 nm, providing complete coverage over the H-band transmission window of earth’s atmosphere. Finite suppression of spurious sidemodes, optical linewidth, and instability of the comb has been examined to estimate potential wavelength biases in spectrograph calibration. Sidemode suppression varies between 20 and 45 dB, and the optical linewidth is ∼350 kHz at 1550 nm. The comb frequency uncertainty is bounded by ±30 kHz (corresponding to a radial velocity of ±5 cm/s), limited by the global positioning system disciplined oscillator reference. These results indicate that this comb can readily support radial velocity measurements below 1 m/s in the near IR.
TL;DR: High power (2.1W) low noise single frequency operation of a tunable compact verical-external-cavity surface-emitting- laser exhibiting a high beam quality and key parameters limiting the laser power and coherence are studied.
Abstract: We demonstrate high power (2.1 W) low noise single frequency operation of a tunable compact verical–external–cavity surface–emitting–laser exhibiting a high beam quality. We took advantage of thermal lens–based stability to develop a short (3 – 10 mm) plano–plano external cavity without any intracavity filter. The semiconductor structure emitting at 1µm is optically pumped by a 8W commercial 808 nm multimode diode laser at large incidence angle. For heat management purpose the GaAs-based VECSEL membrane was bonded on a SiC substrate. We measured a low divergence quasi-circular TEM00 beam (M2 = 1.2) close to diffraction limit, with a linear light polarization (> 30 dB).We simulated the steady state laser beam of this unstable cavity using Fresnel diffraction. The side mode suppression ratio is > 45 dB. The free running laser linewidth is 37 kHz limited by pump induced thermal fluctuations. Thanks to this high-Q external cavity approach, the frequency noise is low and the dynamics is in the relaxation-oscillation-free regime, exhibiting low intensity noise (< 0.1%), with a cutoff frequency ~ 41MHz above which the shot noise level is reached. The key parameters limiting the laser power and coherence are studied. This design/properties can be extended to other wavelengths.
TL;DR: Two different laser configurations for high-power tunable thulium fiber lasers are reported on: one is a single oscillator utilizing a volume Bragg grating for wavelength stabilization; the other is a master oscillator power amplifier system with the oscillator stabilized and made tunable by a diffraction grating.
Abstract: Applications requiring long-range atmospheric propagation are driving the development of high-power thulium fiber lasers. We report on the performance of two different laser configurations for high-power tunable thulium fiber lasers: one is a single oscillator utilizing a volume Bragg grating for wavelength stabilization; the other is a master oscillator power amplifier system with the oscillator stabilized and made tunable by a diffraction grating. Each configuration provides >150W of average power, >50% slope efficiency, narrow output linewidth, and >100nm tunability in the wavelength range around 2μm.
TL;DR: In this article, the authors showed that the information content of human brain NMR spectra appears very similar to that measured in the past decade in rodent brains at the same field strength, in spite of broader linewidth in human brain.
TL;DR: It has been shown that the RF-pilot-based phase noise compensation scheme allows for a considerable increase in tolerable laser linewidth as compared to conventional common-phase error compensation at the cost of an increase in system complexity.
Abstract: In coherent optical long-haul transmission systems, orthogonal frequency-division multiplexing represents a promising modulation format. However, due to long symbol length, laser phase noise can be a major impairment. In this manuscript, the RF-pilot-based phase noise compensation scheme is analyzed and compared to conventional common-phase error compensation. It has been shown that the RF-pilot-based phase noise compensation scheme allows for a considerable increase in tolerable laser linewidth as compared to conventional common-phase error compensation at the cost of an increase in system complexity. For a 112-Gb/s transmission scheme, the tolerable linewidth is increased by a factor of ten as compared to common-phase error compensation.
TL;DR: By mixing two frequencies generated from a single Q-switched Nd:YLF laser in a GaSe crystal, an average terahertz output power reaches 1 μW within a bandwidth of 65 GHz at 1.64 THz.
Abstract: We have demonstrated a compact and portable terahertz (THz) source, based on difference-frequency generation in a GaSe crystal. The two input frequencies, required for achieving frequency mixing, are generated by a single Q-switched Nd:YLF laser incorporating two laser resonators. The average power of the THz output reaches 1μW at 1.64THz (182μm) within a linewidth of 65GHz. Such a THz source can be packaged into a compact and portable system.
TL;DR: In this paper, the dynamics of two coupled vortices driven by spin transfer were investigated and shown to exhibit a linear frequency evolution with a perpendicular field, with coherence conserved even at zero magnetic field.
Abstract: We investigate the dynamics of two coupled vortices driven by spin transfer. We are able to independently control with current and perpendicular field, and to detect, the respective chiralities and polarities of the two vortices. For current densities above $J=5.7*10^7 A/cm^2$, a highly coherent signal (linewidth down to 46 kHz) can be observed, with a strong dependence on the relative polarities of the vortices. It demonstrates the interest of using coupled dynamics in order to increase the coherence of the microwave signal. Emissions exhibit a linear frequency evolution with perpendicular field, with coherence conserved even at zero magnetic field.
TL;DR: This work constructs microcavities comprising ultralow-loss micromirrors fabricated by laser ablation and reflective coatings with quality factors of 3.3×10 and finesses of 1.5×10 so that strong coupling or lasing with a single quantum emitter may be achieved.
Abstract: Ultralow-loss concave micromirrors with radius of curvature below 60μm were fabricated by laser ablation and reflective coatings. A 10-μm-long microcavity with a mode volume of 40μm3 was set up with two such mirrors, and the cavity linewidth was measured both spectrally and temporally. The smallest linewidth obtained was 96MHz, corresponding to a quality factor of 3.3×106 and a finesse in excess of 1.5×105. With these parameters, we estimate that a variety of solid-state quantum emitters coupled to the cavity may enter the strong coupling regime.
TL;DR: In this paper, phase and amplitude noise analysis of spin transfer torque nano-oscillators is performed using a single shot time domain technique, where the phase and nonlinear contributions to the phase noise are separate due to the coupling between phases and amplitude, and the coupling strength as well as amplitude relaxation rate can be directly extracted.
Abstract: The microwave emission linewidth of spin transfer torque nano-oscillators is closely related to their phase and amplitude noise that can be extracted from the magnetoresistive voltage signal V(t) using single shot time domain techniques. Here we report on phase and amplitude noise studies for MgO based magnetic tunnel junction oscillators. The analysis of the power spectral densities allows one to separate the linear and nonlinear contributions to the phase noise, the nonlinear contribution being due to the coupling between phase and amplitude. The coupling strength as well as the amplitude relaxation rate can be directly extracted.
TL;DR: Here, it is demonstrated how the carrier phase can be fixed in a semiconductor laser: a quantum cascade laser (QCL), performed by injection seeding a QCL with coherent terahertz pulses, which forces laser action to start on a fixed phase.
Abstract: The amplification of spontaneous emission is used to initiate laser action. As the phase of spontaneous emission is random, the phase of the coherent laser emission (the carrier phase) will also be random each time laser action begins. This prevents phase-resolved detection of the laser field. Here, we demonstrate how the carrier phase can be fixed in a semiconductor laser: a quantum cascade laser (QCL). This is performed by injection seeding a QCL with coherent terahertz pulses, which forces laser action to start on a fixed phase. This permits the emitted laser field to be synchronously sampled with a femtosecond laser beam, and measured in the time domain. We observe the phase-resolved buildup of the laser field, which can give insights into the laser dynamics. In addition, as the electric field oscillations are directly measured in the time domain, QCLs can now be used as sources for time-domain spectroscopy.