Source Linewidth Research Articles

光源线宽对相干激光测风雷达探测性能的影响分析

光源线宽对相干激光测风雷达探测性能的影响分析

All-Fiber Passive Alignment-Free Depolarizers Capable of Depolarizing Narrow Linewidth Signals

We report on two fully-fiberized, input polarization independent depolarizer configurations that do not need any alignment once fabricated. This makes them suitable for real-world applications. The first configuration uses polarization-maintaining (PM) fibers and relatively few components. The second configuration uses standard (non-PM) single mode fibers to introduce the large time delays needed to enable narrow-linewidth signal depolarization, albeit at the cost of a slightly increased component count and insertion loss. We theoretically analyze the depolarization performance of the proposed configurations as a function of various depolarizer parameters. Subsequently, we design the depolarizers considering the imperfections of standard commercially available components. Finally, we fabricate prototypes of both configurations, characterize their depolarization performance using sources of variable linewidth, and compare the experimental results with theoretical analysis. The fabricated depolarizers are shown to be capable of the depolarization of 20 MHz and 1 MHz linewidth signals with residual degree of polarization below 4%.

Synthesis of a 30-Hz Linewidth Wave Tunable Over 500 GHz

We report on a compact source of 30-Hz linewidth, low-phase noise electrical waves with 500-GHz tunability. These waves are generated by photomixing two distributed feedback laser diodes at 1550 nm, which are frequency stabilized on a fibered cavity. We demonstrate a phase noise suppression down to −90 dBc/Hz at 100-kHz carrier offset frequency of the beat note at 2-, 10-, 18-, 40-, and 92-GHz frequencies. The setup also displays a ~170-kHz frequency drift of the beat note at 10 GHz in the long term over a continuous 7.5-h locking period.

Spatial mapping of correlation profile in Brillouin optical correlation domain analysis

We report an approach to spatially map the correlation profile along the sensing fiber in Brillouin optical correlation domain analysis by pulsing the pump radiation. Simulations are carried out to demonstrate the influence of frequency modulation parameters of a narrow linewidth source on the width of the correlation profile and its peak position. The simulation results are validated through controlled experiments. The correlation profile is mapped over 1 km long fiber with spatial resolution of 1 m, limited only by the finite lifetime of acoustic phonons in the silica fiber.

Second-order coherence properties of metallic nanolasers

Due to the high spontaneous emission coupled into the resonance mode in metallic nanolasers, there has been a debate concerning the coherence properties of this family of light sources. The second-order coherence function can unambiguously determine the nature of a given radiation. In this paper, an approach to measure the second-order coherence function for broad linewidth sources in the near-infrared telecommunication band is established based on a modified Hanbury Brown and Twiss configuration. Using this set-up, it is shown that metallic coaxial and disk-shaped nanolasers with InGaAsP multiple quantum well gain systems are indeed capable of generating coherent radiation.

Atmospheric propagation and combining of high power lasers: comment.

Nelson etal. [Appl. Opt.55, 1757 (2016)APOPAI0003-693510.1364/AO.55.001757] recently concluded that coherent beam combining and remote phase locking of high-power lasers are fundamentally limited by the laser source linewidth. These conclusions are incorrect and not relevant to practical high-power coherently combined laser architectures.

High power compatible internally sensed optical phased array.

The technical embodiment of the Huygens-Fresnel principle, an optical phased array (OPA) is an arrangement of optical emitters with relative phases controlled to create a desired beam profile after propagation. One important application of an OPA is coherent beam combining (CBC), which can be used to create beams of higher power than is possible with a single laser source, especially for narrow linewidth sources. Here we present an all-fiber architecture that stabilizes the relative output phase by inferring the relative path length differences between lasers using the small fraction of light that is back-reflected into the fiber at the OPA's glass-air interface, without the need for any external sampling optics. This architecture is compatible with high power continuous wave laser sources (e.g., fiber amplifiers) up to 100 W per channel. The high-power compatible internally sensed OPA was implemented experimentally using commercial 15 W fiber amplifiers, demonstrating an output RMS phase stability of λ/194, and the ability to steer the beam at up to 10 kHz.

Millimeter and submillimeter wave spectra of13C methylamine

Context. Methylamine (CH3 NH2 ) is a light molecule of astrophysical interest, which has an intensive rotational spectrum that extends in the submillimeter wave range and far beyond, even at temperatures characteristic for the interstellar medium. It is likely for 13 C isotopologue of methylamine to be identified in astronomical surveys, but there is no information available for the 13 CH3 NH2 millimeter and submillimeter wave spectra.Aims. In this context, to provide reliable predictions of 13 CH3 NH2 spectrum in millimeter and submillimeter wave ranges, we have studied rotational spectra of the 13 C methylamine isotopologue in the frequency range from 48 to 945 GHz.Methods. The spectrum of 13 C methylamine was recorded using conventional absorption spectrometers. The analysis of the rotational spectrum of 13 C methylamine in the ground vibrational state was performed on the basis of the group-theoretical high-barrier tunneling Hamiltonian that was developed for methylamine. The available multiple observations of the parent methylamine species toward Sgr B2(N) at 1, 2, and 3 mm using the Submillimeter Telescope and the 12 m antenna of the Arizona Radio Observatory were used to make a search for interstellar 13 CH3 NH2 .Results. In the recorded spectra, we have assigned 2721 rotational transitions that belong to the ground vibrational state of the 13 CH3 NH2 . These measurements were fitted to the Hamiltonian model that uses 75 parameters to achieve an overall weighted rms deviation of 0.73. On the basis of these spectroscopic results, predictions of transition frequencies in the frequency range up to 950 GHz with J ≤ 50 and K a ≤ 20 are presented. The search for interstellar 13 C methylamine in available observational data was not successful and therefore only an upper limit of 6.5 × 1014 cm-2 can be derived for the column density of 13 CH3 NH2 toward Sgr B2(N), assuming the same source size, temperature, linewidth, and systemic velocity as for parent methylamine isotopic species.

Photonic Integrated Circuits for Radio-Frequency Signal Generation

This paper reviews the current state of the art of photonic-enabled generation of radio-frequency signals with frequencies within the millimeter wave range (30 to 300 GHz) and above using photonic-integrated circuits (RF-PICs). One of the most important applications to date is the generation of carrier wave frequencies for ultrabroadband wireless communications systems, with data rates up to 100 Gb/s. Among the different photonic signal generation techniques that are available, we focus on the approaches for which photonic integrated solutions have been explored. Optical heterodyning is first presented, based on achieving the integration of a dual wavelength sources. The second approach is through onchip integrated mode locked lasers, with excellent performance in terms of frequency stable, low phase-noise narrow linewidth sources. We review the different laser structures that have been reported, to support the advantages of the new structures that we propose.

Spectral Shape Impact of Nonlinear Compensator Signal in LTE RoF System

In this letter, a large scale investigation is carried out, utilizing several spectral shapes as the source for direct modulation based frequency dithering (DMFD). DMFD mitigates the nonlinear effect of long term evolution (LTE) radio-over-fiber (RoF) systems. The dithering signal shapes are; sine, square, saw, sinc and Gaussian with different spectral width characteristics. We show that by varying the dithering signal with increasing spectral width, no additional distortion is introduced in the linear and optimum optical launch power regions, which are dominated by the frequency chirp and chromatic dispersion (CD). Additionally, it is revealed herein that introducing dithering signals with varying spectral widths does not change the nonlinear compensator characteristic towards suppression of nonlinearity. The reason for this is that as long as the optical source linewidth is larger than stimulated Brillouin scattering (SBS) linewidth, the proposed method completely suppresses SBS. Finally, the degree of freedom for the dithering signal is infinite, with an optical power budget improvement of up to 8 dB at an optical launch power of 10 dBm, which can in turn be used towards connecting multiple relay nodes (RNs).

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

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.

Comb-Based 16-QAM Transmitter Spanning the C and L Bands

A multiwavelength source for optical transmitters delivers narrow-linewidth carrriers with 100-GHz spacing spanning the C and L bands. The phase-locked carriers are derived from a single, 3-kHz linewidth source, and a multistage parametric mixer. Bit-error rate measurements for a 20-GBd 16-QAM transmitter based on this source are reported.

Endoscopic filtered Rayleigh scattering for the analysis of ducted gas flows

Laser-induced Rayleigh scattering makes use of the fact that elastically scattered laser light from atoms or molecules hold information on pressure, temperature and velocity inside the observed region of interest. Being several orders of magnitude weaker than other elastic light scattering effects such as Mie scattering from larger particles or laser flare from surfaces, the accuracy of Rayleigh scattering measurements strongly depends on the attenuation of these unwanted but omnipresent noise effects. The image-based technique of filtered Rayleigh scattering makes use of the absorption bands of atomic or molecular gases to remove strong elastic scattering effects from the measured signal. The concept is extended by frequency tuning a narrow line-width continuous wave laser light source along the absorption filter’s transmission profile. In acquiring images at several known frequencies, this results in spectra for each camera pixel from which time-averaged temperature, pressure and velocity fields can be deduced simultaneously. In order to qualify the frequency scanning filtered Rayleigh scattering technique for applications with strongly limited accessibility, it is applied to characterize the flow inside a bell-mouthed circular duct. The image data are acquired endoscopically via a fiberscope that is placed downstream from the measurement plane.

Spin correlations and Dzyaloshinskii-Moriya interaction in Cs2CuCl4

We report on electron spin resonance (ESR) studies of the spin relaxation in Cs${}_{2}$CuCl${}_{4}$. The main source of the ESR linewidth at temperatures $T\ensuremath{\le}150$ K is attributed to the uniform Dzyaloshinskii-Moriya interaction. The vector components of the Dzyaloshinskii-Moriya interaction are determined from the angular dependence of the ESR spectra using a high-temperature approximation. Both the angular and temperature dependencies of the ESR linewidth have been analyzed using a self-consistent quantum-mechanical approach. In addition, analytical expressions based on a quasiclassical picture for spin fluctuations are derived, which show good agreement with the quantum-approach for temperatures $T\ensuremath{\ge}2J/{k}_{\mathrm{B}}\ensuremath{\approx}15$ K. A small modulation of the ESR linewidth observed in the $ac$ plane is attributed to the anisotropic Zeeman interaction, which reflects the two magnetically nonequivalent Cu positions.

Static and dynamic magnetic properties of bcc Fe49Co49V2 thin films on Si(1 0 0) substrates

Thin films of Fe49Co49V2 have been grown on Si(1 0 0) substrates by dc magnetron sputtering varying the substrate temperature in the range from room temperature (RT) to 600 °C. The static magnetic properties of the films were studied using a superconducting quantum interference device and magneto-optic Kerr effect magnetometry, while x-ray diffraction and reflectivity measurements have been used for the evaluation of the structural properties and thickness of the prepared samples. The easy axis coercivity decreases from 60 Oe for the sample grown at RT to 15 Oe for the one grown at 400 °C. We also studied the dynamic magnetic properties of the samples by using the high-frequency vector network analyser ferromagnetic resonance (FMR) technique. Results from FMR measurements show that the extrinsic linewidth decreases with increasing growth temperature up to 450 °C and then increases with further increase of growth temperature. The source of the extrinsic linewidth is two-magnon scattering by small, weak inhomogeneities. The intrinsic Gilbert damping (α) follows a similar trend to the extrinsic linewidth, with the lowest damping constant α ≈ 0.005 found at a growth temperature of 450 °C.

Electrical Modeling of Semiconductor Laser Diode for Heterodyne RoF System Simulation

The increasing use of optoelectronic devices in high data rate communication systems drives the need of precise electrical circuit modeling that allows the study of important parameters on link performances such as nonlinearity and noise level. In 60-GHz band radio over fiber system, the millimeter-wave signal generation offers simple configuration for the base station. Various techniques have been proposed such as optical heterodyning where the frequency difference between two optical carriers mixed in a photodetector generates the desired electrical carrier. Phase noise and linewidth of the optical sources determine the purity of the generated signal. In this paper, the optical phase noise is integrated into an electrical equivalent model of the laser diode to simulate radio over fiber systems in an electrical simulator. The laser output is represented here in the optical field with both intensity and phase noises. The influence of optoelectronic devices on the modulated analog or complex digital signals can be also analyzed. Two uncorrelated laser diodes are used to generate a millimeter-wave signal. Physical parameters of these lasers are determined from static response and relative intensity noise measurements. Phase noise contribution of individual lasers to the millimeter-wave signal is performed and compared with theoretical expectations.

Modeling Coherent Backscattering Errors in Fiber Optic Gyroscopes for Sources of Arbitrary Line Width

We present a new model of the noise and drift induced by coherent backscattering in a fiber optic gyroscope (FOG) interrogated with a light source of arbitrary temporal coherence. This study is critical to understand whether a FOG driven with a laser instead of a broadband source can attain high sensitivity and stability, which would have the overwhelming benefit of improving the FOG scale factor stability by at least ten-fold and would enable the use of FOGs for inertial navigation of aircrafts. Analytical and numerical solutions bring to light two significant new predictions. First, coherent-backscattering noise can be made negligibly small by utilizing a laser with a very narrow linewidth (less than ~ 20 kHz), although in this regime the drift is high. Second, by using a laser with a broad linewidth (greater than ~ 10 MHz), both the noise and the drift are low enough for aircraft inertial navigation. The dependencies of the noise and drift on fiber loss, loop coupling coefficient, and backscattering coefficient are also presented to define the optimum mode of operation of this new class of FOGs.

Narrow Linewidth Surface-Etched DBR Lasers: Fundamental Design Aspects and Applications

Surface-etched distributed Bragg reflector (SE-DBR) semiconductor lasers show potential for use in a variety of communications and spectroscopy applications requiring compact, single-mode, narrow linewidth, and tunable laser sources. This approach eliminates contamination issues associated with forming gratings by regrowth in Al-containing structures by using a single growth step and etching the grating after the entire epitaxy is grown. This paper reviews progress in the development of SE-DBR lasers using InGaAs-GaAs-AlGaAs and GaAs-AlGaAs separate confinement heterostructure. Fabrication techniques, design optimization studies, and device performance characteristics are overviewed. Applications of SE-DBRs toward multiwavelength arrays, THz generation via optical heterodyning, and alkali spectroscopy are discussed.

CONFRONTING COLD DARK MATTER PREDICTIONS WITH OBSERVED GALAXY ROTATIONS

The rich statistics of galaxy rotations as captured by the velocity function (VF) provides invaluable constraints on galactic baryon physics and the nature of dark matter (DM). However, the comparison of observed galaxy rotations against cosmological models is prone to subtle caveats that can easily lead to misinterpretations. Our analysis reveals full statistical consistency between ~5000 galaxy rotations, observed in line-of-sight projection, and predictions based on the standard cosmological model (LCDM) at the mass-resolution of the Millennium simulation (HI line-based circular velocities above ~50 km/s). Explicitly, the HI linewidths in the HI Parkes All Sky Survey (HIPASS) are found consistent with those in S3-SAX, a post-processed semi-analytic model for the Millennium simulation. Previously found anomalies in the VF can be plausibly attributed to (1) the mass-limit of the Millennium simulation, (2) confused sources in HIPASS, (3) inaccurate inclination measurements for optically faint sources, and (4) the non-detectability of gas-poor early-type galaxies. These issues can be bypassed by comparing observations and models using linewidth source counts rather than VFs. We investigate if and how well such source counts can constrain the temperature of DM.

Temperature impairment characterization in radio-over-multimode fiber systems

Arbitrary operating conditions, such as the temperature dependence in the fiber link impose a challenge for the extension of radio-over-multimode fiber techniques. Temperature impairment characterization is analyzed over the broadband transmission bands that can be present in the frequency response of multimode fiber (MMF) supporting multiple-GHz carriers delivering schemes. Experimental results show that these transmission bands are dramatically influenced by the hysteresis of heating and cooling temperature cycles, respectively. The influence of the MMF graded index exponent tolerance on frequency response at higher bands is also analyzed. And this variation can be directly attributed to environmental temperature changes that could affect the MMF link. Additionally, selective mode-launching schemes combined with the use of narrow line-width optical sources are experimentally demonstrated to enable broadband transmission, not only at short but also at middle-reach distances over MMFs.