Showing papers on "Laser linewidth published in 1998"
Book•
27 Mar 1998
TL;DR: In this paper, the authors present a solid-state laser operation and design parameters, including material requirements for Laser Hosts and Active Ions, and material preparation and optical quality.
Abstract: 1. Introduction.- 1.1 Solid-State Laser Operation and Design Parameters.- 1.2 Material Requirements for Laser Hosts and Active Ions.- 1.3 Material Preparation and Optical Quality.- References.- 2. Electronic Energy Levels.- 2.1 Free-Ion Energy Levels.- 2.2 Elements of Group Theory.- 2.3 Crystal-Field Splitting of Energy Levels.- References.- 3. Radiative Transitions.- 3.1 The Photon Field.- 3.2 Selection Rules.- 3.3 Properties of Spectral Lines.- 3.4 Nonlinear Optical Properties.- References.- 4. Electron-Phonon Interactions.- 4.1 The Phonon Field.- 4.2 Weak Coupling: Radiationless Transitions.- 4.3 Weak Coupling: Vibronic Transitions.- 4.4 Weak Coupling: Spectral Linewidth and Line Position.- 4.5 Example: Spectral Properties of SrTiO3: Cr3+.- 4.6 Strong Coupling.- 4.7 Jahn-Teller Effect.- References.- 5. Ion-Ion Interaction.- 5.1 Exchange-Coupled Ion Pairs.- 5.2 Nonradiative Energy Transfer: Single-Step Process.- 5.3 Phonon-Assisted Energy Transfer.- 5.4 Nonradiative Energy Transfer: Multistep Process.- 5.5 Connection with Experiment: Rate Equation Analysis.- References.- 6. Al2O3: Cr3+ Laser Crystals.- 6.1 Energy Levels of Cr3+.- 6.2 Crystal-Field Splitting.- 6.3 Spin-Orbit Splitting and Selection Rules.- 6.4 Strong-Field Laser Materials.- References.- 7. Transition-Metal-Ion Laser Materials.- 7.1 Broad-Band Cr3+ Laser Materials: Alexandrite.- 7.2 Spectral Properties of Cr3+ in Different Hosts and Their Laser Characteristics.- 7.3 Transition-Metal Ions and Host Crystals.- 7.4 Laser Materials Based on Ti3+ Ions.- 7.5 Laser Materials Based on Ions with 3d2 Configurations.- 7.6 Laser Materials Based on Ions with 3d3 Through 3d8Configurations.- References.- 8. Y3A15012: Nd3+ Laser Crystals.- 8.1 Energy Levels of Nd3+.- 8.2 Crystal-Field Splitting.- 8.3 Radiative Transitions: Judd-Ofelt Theory.- 8.4 Example: Y3A15O12:Nd3+.- References.- 9. Rare-Earth-Ion Laser Materials.- 9.1 Nd3+ Lasers.- 9.2 Other Trivalent Lanthanide Lasers.- References.- 10. Miscellaneous Laser Materials.- 10.1 Other Rare-Earth-Ion Lasers.- 10.2 Nonlinear Optical Lasers.- 10.3 Color-Center Lasers.- 10.4 Other Solid-State Lasers.- References.
463 citations
TL;DR: High-efficiency double-peak resonances occurred at nonnormal incidence, with the spectral locations of the maxima vayring with the incidence angle agreed well with the theoretically calculated reflectance curves.
Abstract: A high-efficiency guided-mode resonance reflection filter is reported. The device consists of a surface-relief photoresist grating and an underlying HfO (2) waveguide layer deposited on a fused-silica substrate. The spectral response measured with a dye-laser beam at normal incidence exhibited a peak reflectance of 98% at a wavelength of 860 nm with sideband reflectance below approximately 5% extending over the wavelength range provided by the dye (800-900 nm). At normal incidence the filter linewidth was 2.2 nm. High-efficiency double-peak resonances occurred at nonnormal incidence, with the spectral locations of the maxima vayring with the incidence angle. The filter response at various angles of incidence agreed well with the theoretically calculated reflectance curves.
322 citations
TL;DR: By measuring the gain and loss in thin-film planar waveguides using a standard technique developed for inorganic laser materials, the authors showed that the narrow-line emission from photopumped waveguide of the conjugated polymer poly[2-butyl-5-${(2}^{\ensuremath{'}}$-ethyl-hexyl)-1,4-phenylenevinylene] results from amplification of spontaneous emission (ASE).
Abstract: By measuring the gain and loss in thin-film planar waveguides using a standard technique developed for inorganic laser materials, we show that the narrow-line emission from photopumped waveguides of the conjugated polymer poly[2-butyl-5-${(2}^{\ensuremath{'}}$-ethyl-hexyl)-1,4-phenylenevinylene] results from amplification of spontaneous emission (ASE). The narrowed linewidth of the ASE spectrum is determined by gain saturation. The ASE emitted from the edge of the waveguide is polarized because the waveguide is birefringent and only allows TE modes to propogate and be amplified. We compare our results and conclusions to other reports that claim that spectral narrowing in conjugated polymers is a result of superfluorescence or excitonic interactions. The techniques presented in the paper offer a simple and useful way for evaluating conjugated polymers as materials for solid state lasers.
306 citations
TL;DR: In this paper, the authors evaluate hydrogen silsesquioxane (HSQ) with a three-dimensional framework from the standpoints of resist patterning and its ability to reduce linewidth fluctuation.
Abstract: Linewidth fluctuation of resist patterns is a serious problem in fabricating nanodevices when lithographic resolution is improved to the nanometer scale. As a resist material for reducing linewidth fluctuations, we evaluate hydrogen silsesquioxane (HSQ) with a three-dimensional framework from the standpoints of resist patterning and its ability to reduce linewidth fluctuation. Infrared analyses indicate that SiH bonds in HSQ are broken by electron-beam irradiation, and consequently, the crosslinking required for negative tone patterning is generated. By applying a TMAH developer suitable for the dissolution of the siloxane bonds in HSQ, we improve contrast and reduce the thickness loss of the lightly exposed resist area. In addition, the HSQ resist has relatively high sensitivity for resist materials without any reactive groups. The etching durability sacrificed for the attainment of high sensitivity is improved by oxygen plasma treatment. No damage, such as pattern-shape deformation after the oxygen plasma treatment, is observed. Linewidth fluctuation due to edge roughness of resist patterns results from aggregates in the resist polymer. Aggregates in HSQ are small owing to its three-dimensional framework. In addition, the excellent development property of HSQ avoids any influence from polymer aggregates on development. Consequently, linewidth fluctuation can be reduced to less than 2 nm. This leads to a decrease in the variation of gate capacitance in single-electron transistors.
299 citations
TL;DR: In this paper, the authors present a study of optically pumped waveguide and microcavity laser based on vacuum-deposited thin films of small molecular weight organic semiconductors.
Abstract: We present a study of optically pumped waveguide and microcavity lasers based on vacuum-deposited thin films of small molecular weight organic semiconductors. Lasing action in waveguide lasers is characterized by high output peak power (50 W), high differential quantum efficiency (70%), low lasing threshold (1 μJ/cm2), and long operational lifetime (>106 laser pulses at 100 times the threshold pump power). Microcavity laser characteristics include 3 W peak output power, 300 μJ/cm2 lasing threshold, and lifetimes of >106 pump laser pulses (operating at 6 times the threshold power). We demonstrate wavelength variability from 460 to 700 nm by changing the composition of the organic films. The confinement of excitations on the dopant molecules leads to quantum dot-like behavior such as high temperature stability of the lasing threshold, output power, and emission wavelength in the temperature range from 0 to 140 °C. The linewidth of laser emission from microcavity structures is found to be 0.2±0.1 A and is tr...
255 citations
TL;DR: In this article, an extremely simple laser of this type, built from inexpensive commercial components with only a few minor modifications, has been continuously locked to a Doppler-free rubidium transition for several days.
Abstract: Operating a laser diode in an extended cavity which provides frequency-selective feedback is a very effective method of reducing the laser’s linewidth and improving its tunability. We have developed an extremely simple laser of this type, built from inexpensive commercial components with only a few minor modifications. A 780 nm laser built to this design has an output power of 80 mW, a linewidth of 350 kHz, and it has been continuously locked to a Doppler-free rubidium transition for several days.
254 citations
TL;DR: In this paper, a photopumped distributed feedback laser was fabricated by spincasting thin films of the semiconducting polymer poly(2-butyl, 5-(2′-ethyl-hexyl)-1,4-phenylenevinylene) over gratings in silicon oxide.
Abstract: We have fabricated photopumped distributed feedback lasers by spin-casting thin films of the semiconducting polymer poly(2-butyl, 5-(2′-ethyl-hexyl)-1,4-phenylenevinylene) over gratings in silicon oxide. The lasers have two modes that each have a linewidth of 0.2 nm. The lasing wavelength was tuned from 540 to 583 nm by adjusting the period of the gratings.
236 citations
TL;DR: Optically pumped OVCSELs with an active layer composed of a thin-film organic semiconductor tris-(8-hydroxyquinoline) aluminum doped with DCM laser dye produced very narrow linewidth that could potentially be narrowed further.
Abstract: Lasing action in organic vertical-cavity surface-emitting laser (OVCSEL) structures is demonstrated. Optically pumped OVCSELs with an active layer composed of a thin-film organic semiconductor tris-(8-hydroxyquinoline) aluminum (Alq3) doped with DCM laser dye produced very narrow linewidth (0.2 ± 0.1 angstrom), high-power (3 watts) emission that could be varied in different devices from orange to red. The efficient energy transfer from Alq3 to DCM results in a threshold input energy of 300 microjoules per square centimeter. An operational lifetime >106 laser pulses was achieved for a device operated well above threshold in atmosphere. The linewidths above threshold are Fourier transform–limited and could potentially be narrowed further.
220 citations
TL;DR: In this paper, the authors compare delayed self-homodyne and self-heterodyne detection in the case of a time delay of the order of the coherence time of the laser.
191 citations
TL;DR: In this article, a new resist system providing small linewidth fluctuation has been developed for nanolithography Hydrogen silsesquioxane (HSQ) resist used here has a small polymer size because of its three-dimensional framework.
163 citations
TL;DR: The measurement uncertainty was found to be due to several noise sources, including the effect of asymmetric intensity of the laser modes within the laser linewidth, fluctuations caused by atmospheric turbulence and laser beam/target movement, and background spectral shifts.
Abstract: A smoothly tunable, narrow-linewidth, cw, 32-mW, 2.066-μm
Ho:YLF laser was constructed and used for the first time in preliminary
spectroscopic measurements of atmospheric CO2 and
H2O. The laser was constructed with a 4.5-mm-long,
TE-cooled, codoped 5% Tm and 0.5% Ho yttrium lithium fluoride crystal
(cut at Brewster’s angle) pumped by an Ar+-pumped
500-mW Ti:sapphire laser operating at 792 nm. Intracavity etalons
were used to reduce the laser linewidth to approximately 0.025
cm-1 (0.75 GHz), and the laser wavelength was
continuously and smoothly tunable over approximately 6
cm-1 (180 GHz). The Ho:YLF laser was used to
perform spectroscopic measurements on molecular CO2 in a
laboratory absorption cell and to measure the concentration of
CO2 and water vapor in the atmosphere with an initial
accuracy of approximately 5–10%. The measurement uncertainty was
found to be due to several noise sources, including the effect of
asymmetric intensity of the laser modes within the laser linewidth,
fluctuations caused by atmospheric turbulence and laser beam/target
movement, and background spectral shifts.
TL;DR: In this article, a 5-cm long 1550-nm distributed feedback fiber laser with 4 mW output power is shown to have excellent specifications in terms of optical linewidth, signal-to-noise ratio (SNR), relative intensity noise, sidemode suppression and polarization purity.
Abstract: The device characteristics of Er/sup 3+/,Yb/sup 3+/ single frequency fiber lasers are reported. A 5-cm long 1550-nm distributed feedback fiber laser with 4 mW output power is shown to have excellent specifications in terms of optical linewidth, signal-to-noise ratio (SNR), relative intensity noise, side-mode suppression and polarization purity. For higher power applications, a 1.5 cm single frequency Er/sup 3+/,Yb/sup 3+/ grating-based fiber laser with 60 mW output power and a net efficiency of 12% is demonstrated.
TL;DR: In this article, the authors used electron beam lithography to make very small (<30 nm linewidth) mechanical structures in single-crystal silicon, which can be driven capacitively by applying a voltage between the suspended portion and the underlying substrate.
Abstract: We have used electron beam lithography to make very small (<30 nm linewidth) mechanical structures in single-crystal silicon. These structures can be driven capacitively by applying a voltage between the suspended portion and the underlying substrate. Optical interference techniques are used to detect and measure the motion of the structures with resonant frequencies above 40 MHz. We employed a design consisting of a square mesh with a 315 nm period, which results in a low mass (∼1×10−13 g) and large relative surface area (10−6 cm2). Also, by making suboptical-wavelength features, the optical properties can be altered, leading to an improved measurement sensitivity. We measured the oscillations at small amplitudes where the detected change in the optical reflection is proportional to the drive amplitude.
TL;DR: In this article, a half symmetric cavity structure was proposed for a tunable filter with a 3 dB linewidth of 0.27 nm, more than 70 nm tuning range under a voltage swing of 14 V and less than 0.9 dB insertion loss.
Abstract: A novel microelectromechanical tunable filter with a half symmetric cavity structure is described. The device exhibits a 3 dB linewidth of 0.27 nm, more than 70 nm tuning range under a voltage swing of 14 V and less than 0.9 dB insertion loss. The parameters of the optical cavity were tailored to efficiently couple 1550 nm light in and out of the devices using a singlemode fibre without any lenses. The structure exhibits a frequency response of 150 kHz at the 3 dB cutoff point.
Book•
[...]
01 Jul 1998
TL;DR: In this paper, the fundamental laser diode characeristics single-mode laser diodes are discussed, and the linewidth broadening of discontinuously tunable laser-diodes related components is discussed.
Abstract: Fundamental laser diode characeristics single-mode laser diodes basic concepts for tunable laser diodes continuously tunable single-mode laser diodes linewidth broadening discontinuously tunable laser diodes related components.
TL;DR: In this paper, a 0.1-nm line width laser with 38dB sidemode suppression was obtained by utilizing a 1.3-/spl mu/m semiconductor optical amplifier in a fiber unidirectional ring that consists of a linear polarizer and polarization controllers.
Abstract: We have demonstrated a novel approach to obtain a 0.1-nm line width laser with 38-dB sidemode suppression by utilizing a 1.3-/spl mu/m semiconductor optical amplifier in a fiber unidirectional ring that consists of a linear polarizer and polarization controllers. The laser has a low-threshold current of 22.5 mA as well as a wide tuning range of 28 nm. The new approach is applicable to the 1.55-/spl mu/m region as well. It is expected that nanosecond wavelength tuning speed is feasible using this approach in conjunction with fast electrooptic polarization controllers, short cavities and low-cavity losses.
TL;DR: In this paper, the linewidth fluctuations observed as line edge roughness are mainly caused by polymer aggregates in the resist materials, which remain stuck on the pattern sidewall, and cause linwidth fluctuations.
Abstract: We report on the linewidth fluctuations in resist patterns and their influence on etched patterns. The linewidth fluctuations observed as line edge roughness are mainly caused by polymer aggregates in the resist materials. Polymer aggregates more than 30 nm in diameter are observed in both the positive and negative resist films. Because the polymer aggregates are not dissolved but extracted during development, they remain stuck on the pattern sidewall and cause linewidth fluctuations. When substrates, such as Si, are etched using resist patterns as a mask, the linewidth fluctuations of the resist patterns are faithfully transferred to the substrate. This means that the linewidth fluctuations in device patterns are originally due to the polymer aggregates in the resist films. The linewidth fluctuation is also found to decrease through substrate etching, depending on resist thickness loss. This possibly results from degradation of the resist patterns in lateral directions through etching. However, it does n...
TL;DR: One can increase the angular tolerance of resonant grating filters without modifying the spectral bandwidth by adding a second grating component parallel to the first one, which permits the use of waveguide-grating filters with standard collimated beams.
Abstract: One can increase the angular tolerance of resonant grating filters without modifying the spectral bandwidth by adding a second grating component parallel to the first one. The angular tolerance and the filter linewidth can be controlled by the designer in an independent way. Numerical results show that this property permits the use of waveguide-grating filters with standard collimated beams.
TL;DR: A single-longitudinal-mode erbium-doped fiber laser with a passive multiple-ring cavity (MRC) is proposed for the first time to the authors' knowledge and can successfully suppress side-mode frequencies of as much as 1 GHz and provide an output power of 23 mW.
Abstract: A single-longitudinal-mode erbium-doped fiber laser with a passive multiple-ring cavity (MRC) is proposed for the first time to the authors' knowledge. The laser is fundamentally structured by insertion of three different short ring cavities, which serve as mode filters, into the main cavity. When it is combined with a mode-restricting intracavity fiber Bragg grating, the MRC resonator ensures single-longitundinal-mode laser oscillation. The laser can successfully suppress side-mode frequencies of as much as 1 GHz and provide an output power of 23 mW with a side-mode suppression ratio of 51 dB at 1533 nm. The short-term linewidth of the laser output measured is ~2 kHz . The ability of this fiber laser to act as an AM transmitter source is also demonstrated.
TL;DR: In this paper, an ab initio calculation of the Raman linewidth of transverse and longitudinal phonon in zinc-blende semiconductors GaAs, AlAs, GaP, and InP is presented.
Abstract: In this work we present an ab initio calculation of the Raman linewidth of transverse and longitudinal phonon in zinc-blende semiconductors GaAs, AlAs, GaP, and InP. We propose a simple approximation that permits us to calculate the longitudinal linewidths with the same computational effort as the transverse ones. The microscopic mechanisms responsible for the decay are analyzed and discussed. The temperature dependence of the linewidths is computed. Our results are in good agreement with available experimental data up to room temperature for both transverse and longitudinal optical modes and give reliable predictions in materials difficult to study experimentally.
TL;DR: In this paper, photopumped polymer microlaser was demonstrated using microrings and microdisks of various diameters D ranging from 5 to 200 μm, which were characterized by Q of order 5000, low threshold excitation energy of order 100 pJ/pulse for pulse duration ranging from 100 ps to sub-μs.
Abstract: Substantially improved, photopumped polymer lasers are demonstrated using microrings and microdisks of various diameters D ranging from 5 to 200 μm. Various cavity-dependent laser modes were observed, which for D<10 μm were dominated by a single longitudinal mode with linewidth of less than 1 A. These microlasers were also characterized by Q of order 5000, low threshold excitation energy of order 100 pJ/pulse for pulse duration ranging from 100 ps to sub-μs, and an abrupt increase in the emission directionality and polarization degree. Light emitting diodes with cylindrical geometry, fully compatible with these microlasers are also demonstrated.
TL;DR: In this article, the temperature dependence of the spectral peak and the linewidth of a variety of model systems in the steady-state situation was determined by a Monte Carlo simulation approach.
Abstract: Optical spectra in quantum wells are in many cases strongly influenced by disorder. In particular, energy relaxation of correlated electron-hole pairs through disorder-induced localized states determines the position and shape of photoluminescence lines. By a Monte Carlo simulation approach the energy relaxation is studied and the temperature dependence of the spectral peak and the linewidth are determined for a variety of model systems in the steady-state situation.
TL;DR: In this paper, the photoluminescence investigation at a low temperature was carried out in In0.13Ga0.87N/GaN single quantum well and multiple quantum wells with 10 (10QW) or 5 periods.
Abstract: The photoluminescence investigation at a low temperature was carried out in In0.13Ga0.87N/GaN single quantum well (SQW) and multiple quantum wells with 10 (10QW) or 5 periods. With decreasing number of wells, the emission peak shows a redshift. In the case of a low excitation power, the emission intensity is enhanced by an increase in the number of wells while it decreases in the case of a high excitation power. With increasing excitation power, the emission peak of the SQW exhibits a blueshift and its linewidth decreases, but the emission peak of the 10QW remains unchanged and its linewidth increases. Based on the theory of the quantum confined Stark effect, the behavior of the SQW and the 10QW can be well explained. This result should be highly emphasized in designing InGaN/GaN based optical devices.
Patent•
30 Jun 1998
TL;DR: In this paper, a system and method for photodynamic therapy using a phased array Raman laser amplifier including a beam generator for generating a fundamental laser beam and a Raman seed frequency laser beam, and a fiber optic laser amplifier array for forming a diffraction limited output laser beam at the Ramanseed frequency by amplifying the fundamental beam to a power level corresponding to the Stimulated Raman Scattering (SRS) threshold to thereby pump the SRS process and provide Raman gain.
Abstract: System and method for photodynamic therapy using a phased array Raman laser amplifier including a beam generator for generating a fundamental laser beam and a Raman seed frequency laser beam, and a fiber optic laser amplifier array for forming a diffraction limited output laser beam at the Raman seed frequency by amplifying the fundamental laser beam to a power level corresponding to the Stimulated Raman Scattering (SRS) threshold to thereby pump the SRS process and provide Raman gain to the Raman seed frequency laser beam.
TL;DR: In this article, the out-of-plane angular dependence of the ferromagnetic resonance linewidth, ΔH, has been measured for thin magnetic films coupled to NiO and for uncoupled control films.
Abstract: The out-of-plane angular dependence of the ferromagnetic resonance linewidth, ΔH, has been measured for thin magnetic films coupled to NiO and for uncoupled control films. In the control films, ΔH is described by nearly angle-independent damping parameters. In the NiO-coupled films, however, the damping was found to depend strongly on magnetization orientation, with linewidth values comparable to the control samples at normal orientation, but several times larger when the magnetization lies in plane. The additional linewidth in the NiO-coupled films follows the angular dependence of the number of nearly degenerate spin wave modes, in agreement with the predictions of a two-magnon scattering model of damping which incorporates a spin wave dispersion relation suitable for ultrathin films.
TL;DR: Preliminary theoretical and experimental results illustrate the possibility of the ellipsometric scatterometry technique providing a metrology tool for characterizing sub-0.1-mum-linewidth.
Abstract: We describe a modification to our existing scatterometry technique for extracting the relative phase and amplitude of the electric field diffracted from a grating. This modification represents a novel combination of aspects of ellipsometry and scatterometry to provide improved sensitivity to small variations in the linewidth of subwavelength gratings compared with conventional scatterometer measurements. We present preliminary theoretical and experimental results that illustrate the possibility of the ellipsometric scatterometry technique providing a metrology tool for characterizing sub-0.1-mum-linewidth.
TL;DR: In this article, a dual tunable wavelength operation of Er,Yb:phosphate glass laser is reported, where the spatial separation of the laser eigenstates and the use of two properly designed intracavity etalons permit one to tune the two wavelengths independently from 1540.5 to 1562.7 nm.
Abstract: Dual tunable wavelength operation of Er,Yb:phosphate glass laser is reported. The spatial separation of the laser eigenstates and the use of two properly designed intracavity etalons permit one to tune the two wavelengths independently from 1540.5 to 1562.7 nm. The generated beat note, monitored using a Michelson interferometer, is experimentally shown to be adjustable from dc to 2.7 THz. The linewidth of this beat note is found to be less than 10 kHz. Several applications are discussed.
TL;DR: In this article, an analytical expression for the low-temperature optical susceptibility of quantum-well semiconductor lasers is presented based on a simple parabolic band model, which can be used to analyze the dynamics of multimode devices or devices with large carrier density variations.
Abstract: An analytical expression for the low-temperature optical susceptibility of quantum-well semiconductor lasers is presented based on a simple parabolic band model. The optical susceptibility obtained keeps the nonlinear dependence on the carrier density, providing both a broad gain spectrum and a dispersion curve, so it can be used to analyze the dynamics of multimode devices or devices with large carrier density variations. The resulting peak gain, differential peak gain, and linewidth enhancement factor are discussed. cw operation of a single-mode laser is studied as a function of the frequency of the cavity resonance. An analytical approximation to the finite-temperature gain spectrum is also presented, although the refractive index spectrum must be determined numerically. @S1050-2947~98!07501-5# PACS number~s!: 42.55.Px, 78.66.2w The analysis of the static and dynamical properties of semiconductor lasers requires a knowledge of the coupling between the active semiconductor material and the optical field within the active region. In a semiclassical approach @1#, which constitutes the foundation for simpler descriptions as the rate equation ~RE! approximation @2#, the optical field is described by means of Maxwell’s equations, and its coupling to the material is described by the electrical susceptibility of the active medium. The imaginary part of the electrical susceptibility describes the energy exchange ~absortion or stimulated emission! between the field and the medium, while its real part describes the dispersive effect ~refractive
TL;DR: In this paper, it was theoretically and experimentally shown that Fresnel end reflection at a waveguide under test can degrade the sensitivity of an optical low-coherence reflectometer (OLCR) with a balanced detection scheme.
Abstract: It is theoretically and experimentally shown that Fresnel end reflection at a waveguide under test can degrade the sensitivity of an optical low-coherence reflectometer (OLCR) with a balanced detection scheme. Optical mixing of the local oscillator (LO) light and the end reflection produces beat noise whose current noise spectral density is represented by 2(1+P/sup 2/) //spl delta//spl nu/, where P and /spl delta//spl nu/ are the degree of polarization and the effective linewidth of the light, respectively, and and are the total mean photocurrents of the LO light and the end reflection at the balanced mixer, respectively. The balanced detection technique suppresses the intensity noise of the light and the beat noise becomes the dominant source of sensitivity degradation. The minimum detectable reflectivity is derived which includes the effect of sensitivity degradation caused by beat noise.
TL;DR: In this paper, the authors proposed and demonstrated a frequency-stabilization scheme that provides linewidth narrowing and at the same time is compatible with high-speed frequency agility using a short-external-cavity diode laser equipped with an intracavity electro-optic crystal.
Abstract: We propose and demonstrate a novel frequency-stabilization scheme that provides linewidth narrowing and at the same time is compatible with high-speed frequency agility. The method relies on sensing and control of a heterodyne beat signal derived from a fiber interferometer and functions in the absence of a fixed reference frequency. Our demonstration utilizes a short-external-cavity diode laser equipped with an intracavity electro-optic crystal for frequency correction. The stabilization method is shown to suppress impressed laser frequency modulation by nearly 2 orders of magnitude. Without further modification of our scheme we also demonstrate laser frequency tuning control.