Showing papers on "Laser linewidth published in 1990"
TL;DR: The temperature-dependent linewidths of excitons in semiconductors due to the interaction of the exciton with both LO phonons and with acoustic phonons are studied and it is found that the deformation-potential coupling dominates for all of the materials considered.
Abstract: The temperature-dependent linewidths of excitons in semiconductors due to the interaction of the exciton with both LO phonons and with acoustic phonons are studied with use of a Green's-function approach in which the exciton-phonon interaction is treated perturbatively. The interaction between the excitons and the LO phonons is taken to be of the Fr\"ohlich form, and the contribution to the linewidth is obtained in closed form. In this case it is found that scattering of the exciton to both bound and continuum states is important and that it is important to treat the continuum states fully as Coulomb scattering states. In describing optical-absorption processes, the fact that absorption occurs from polariton states, which are states composed of excitons coupled to light, is taken into account. The linewidths due to the exciton--LO-phonon interaction are evaluated for a series of II-VI and III-V compound semiconductors, and are shown to account for the existing experimental results for temperatures \ensuremath{\gtrsim}80 K. The contributions to the linewidth due to the interaction of excitons with acoustic phonons via both the deformation potential and the piezoelectric couplings are treated, and it is found that the deformation-potential coupling dominates for all of the materials considered. Because of the small velocity of sound, scattering to only intraband intermediate states, i.e., those in which the internal exciton quantum numbers do not change, is found to contribute to the linewidth. In the case of acoustic phonons, it is found to be important to treat optical absorption as originating from polariton states in order to evaluate properly the magnitude of this contribution to the linewidth. The acoustic-phonon contribution to the linewidths is compared with experiment for temperatures \ensuremath{\lesssim}80 K, for which it dominates the temperature dependence.
445 citations
TL;DR: In this article, the authors describe a theoretical model that shows how stimulated Brillouin scattering (SBS) is initiated by thermally excited acoustic waves distributed within a SBS-active medium, which predicts how the SBS reflectivity, Stokes linewidth, and fluctuations in Stokes intensity depend upon the laser intensity and upon the physical properties of the medium.
Abstract: We describe a theoretical model that shows how stimulated Brillouin scattering (SBS) is initiated by thermally excited acoustic waves distributed within a Brillouin-active medium. This model predicts how the SBS reflectivity, Stokes linewidth, and fluctuations in Stokes intensity depend upon the laser intensity and upon the physical properties of the SBS medium. This model also leads to the prediction that the value of the single-pass gain (i.e., G=gIL) at the threshold for SBS is not a universal number, but depends upon the laser frequency and on the properties of the SBS medium. For typical organic liquids at room temperature, G is in the range 20--25.
427 citations
TL;DR: In this paper, an analytical model that takes into account the influence of the laser linewidth on Rayleigh backscattering is given, and the backscattered signal is measured for different laser linwidths, and results are compared with the theory.
Abstract: An analytical model that takes into account the influence of the laser linewidth on Rayleigh backscattering is given. For an unmodulated source the power spectral density is found to be identical to the delayed self-homodyne spectrum of the laser. The backscattered signal was measured for different laser linewidths, and the results are compared with the theory. The effects of Rayleigh backscattering noise on fiber gyroscopes and bidirectional optical systems are discussed. >
167 citations
TL;DR: Spectral gain hole-burning at lambda /sub 0/=1.53 mu m was observed in an erbium-doped fiber amplifier at temperatures between 4.2 and 77 K.
Abstract: Spectral gain hole-burning at lambda /sub 0/=1.53 mu m was observed in an erbium-doped fiber amplifier at temperatures between 4.2 and 77 K. The hole width was found to broaden with temperature for T>or=20 K according to a T/sup 1.73/ law. From the data, the room-temperature homogeneous linewidth associated with the 1.531- mu m transition in the /sup 4/I/sub 13/2/-/sup 4/I/sub 15/2/ laser system was determined to be Delta lambda /sub h/=11.5 nm for aluminosilicate fibers. >
150 citations
TL;DR: In this article, a computer model called CLADISS is presented for the analysis of multisection diode lasers, which includes all of the longitudinal variations by dividing each laser section in many short segments.
Abstract: A computer model called CLADISS is presented for the analysis of multisection diode lasers. The model allows for the analysis of a wide variety of multisection devices with discrete or distributed internal reflections. The simulator can carry out a threshold, DC, AC, and a noise analysis. The threshold analysis determines the threshold of the various longitudinal modes of the laser. The power versus current and the wavelength versus current characteristics are found with the self-consistent DC analysis. CLADISS includes all of the longitudinal variations by dividing each laser section in many short segments. Both the optical field and carrier density are discretized according to this segmentation. To demonstrate the capabilities of CLADISS some nonlinear effects in DFB lasers are treated. Instabilities induced in the side-mode suppression ratio by spatial hole burning are considered. The effects of spatial hole burning and side modes on the FM response on the linewidth are discussed. >
147 citations
TL;DR: In this article, an angularly limiting filter is used to distinguish electrons that have traversed a transparent mask in terms of the degree of scattering between the patterned and unpatterned regions.
Abstract: We present a new approach to projection‐electron lithography which allows sub‐0.1 μm resolution to be achieved with short exposure times and a parallel illumination system. We have printed a grating pattern into PMMA with 0.1 μm linewidths. Our new technique consists of using an angularly limiting filter which differentiates electrons that have traversed a transparent mask in terms of the degree of scattering between the patterned and unpatterned regions.
135 citations
Patent•
02 Mar 1990
TL;DR: In this paper, a method whereby the image produced in a coherence probe microscope is modified by means of a specific additive electronic transformation for the purpose of improving the measurement of selected features is presented.
Abstract: A method whereby the image produced in a coherence probe microscope is modified by means of a certain specific additive electronic transformation for the purpose of improving the measurement of selected features. The technique improves measurement accuracy on optically complex materials, in particular it improves the accuracy of linewidth measurement on semiconductor linewidths.
134 citations
TL;DR: The first demonstration of reflection gratings at around 1500 nm written into germanosilicate fibres using an ultraviolet laser is reported in this paper, where reflection coefficients up to 10% with linewidth around 1nm have been observed.
Abstract: The first demonstration of reflection gratings at around 1500 nm written into germanosilicate fibres using an ultraviolet laser is reported. Grating reflection coefficients up to 10% with linewidths around 1nm have been observed. By using one of these gratings, narrow linewidth operation of a 1500 nm Er3+ doped fibre laser has been achieved.
134 citations
TL;DR: In this paper, the first time room-temperature, continuous-wave operation of individual vertical-cavity laser diodes with submilliampere threshold currents was reported.
Abstract: We report for the first time room‐temperature, continuous‐wave operation of individual vertical‐cavity laser diodes with submilliampere threshold currents. A single quantum well active region emitting at 979 nm surrounded by GaAs/AlAs Bragg reflector mirrors was used. Threshold currents were as low as 0.7 mA. A record low linewidth‐power product of 5 MHz mW and a linewidth as narrow as 85 MHz was measured. High yield and good uniformity were demonstrated.
126 citations
TL;DR: In this article, an Er-doped fiber ring-laser was used to achieve a stable lasing spectrum using a single polarisation fiber-cavity, and an optical bandpass filter was incorporated in the ring-Cavity to make the lasing wavelength tunable.
Abstract: A narrow linewidth of 1.4 kHz with single frequency operation is demonstrated in an Er-doped fibre ring-laser. A stable lasing spectrum can be achieved using a single polarisation fibre-cavity. An optical bandpass filter incorporated in the ring-cavity makes the lasing wavelength tunable, and a 2.8 nm tuning range is demonstrated.
122 citations
TL;DR: In this article, a number of important parameters, such as gain, modulation response and threshold current in modulation-doped multi-quantum-well (MD-MQW) lasers are theoretically investigated.
Abstract: A number of important parameters, such as gain, modulation response and threshold current in modulation-doped multi-quantum-well (MD-MQW) lasers are theoretically investigated. The analytical results indicate that the relaxation oscillation frequency of p-type MD-MQW lasers is enhanced by a factor of 4 compared with DH lasers, and that the linewidth enhancement factor of p-type MD-MQW lasers is reduced to 1/4 that of undoped MQW lasers. The threshold current density of n-type MD-MQW lasers is reduced to 1/2~1/4 that of undoped MQW lasers. The improvements in these properties basically result from the unsatisfied charge neutrality due to the modulation doped effect and from asymmetry in density of states between conduction band and valence bands in III-V materials.
TL;DR: First-order Raman scattering from graphite irradiated by an electron beam has been studied by using the laser microprobe technique and an approximately linear relation is exhibited between the linewidth of the E2G mode and the reciprocal of the crystallite size.
Abstract: First-order Raman scattering from graphite irradiated by an electron beam has been studied by using the laser microprobe technique. An approximately linear relation is exhibited between the linewidth of the ${\mathit{E}}_{2\mathit{g}}$ mode and the reciprocal of the crystallite size. The observed linewidths are larger than those calculated by using the known dispersion curve and the wave-vector uncertainty.
TL;DR: In this paper, a doubly resonant optical parametric oscillator (DRO) with the second harmonic of a narrow-linewidth Nd: YAG laser was presented.
Abstract: We describe a doubly resonant optical parametric oscillator (DRO) pumped with the second harmonic of a narrow-linewidth Nd: YAG laser. The linewidth of the DRO signal was less than 13 kHz, the DRO was shown to generate a phase-locked subharmonic of the pump at degeneracy, and the signal and the idler were shown to be mutually coherent with the pump and to be phase anticorrelated with each other away from degeneracy. The signal–idler heterodyne linewidth was 500 Hz, and pump phase modulation was shown to transfer to the DRO phase at degeneracy.
TL;DR: In this paper, the maximum laser linewidth and loop gain in an optical phase-locked loop (OPLL) are calculated as a function of loop delay and filter bandwidth, using a cycle-slipping criterion.
Abstract: Maximum laser linewidth and loop gain in an optical phase-locked loop (OPLL) are calculated as a function of loop delay and filter bandwidth, using a cycle-slipping criterion. It is shown that a loop delay of less than 2 ns would permit the realisation of OPLLs using the recently reported submegahertz linewidth monolithic tunable semiconductor lasers.
TL;DR: In this article, the second-order nonlinear susceptibility in asymmetric GaAs/AlGaAs quantum wells with a cw or Q-switched tunable CO2 laser as the pumping source was investigated.
Abstract: We report on the observation of resonant intersubband second‐harmonic generation in asymmetric GaAs/AlGaAs quantum wells using a cw or Q‐switched tunable CO2 laser as the pumping source. The dependence of the second‐harmonic intensity with the pump photon wavelength is presented for the first time. A Lorentzian‐like second‐harmonic line shape is found with a maximum at 10.9 μm and a linewidth of 0.4 μm (4.1 meV). These results are in good agreement with theoretical predictions. The expected quadratic dependence of the second‐harmonic conversion efficiency with pump intensity is well verified for intensities up to 150 kW/cm2. The calibrated second‐harmonic power reaches 0.13 μW for a cw pump power of 0.8 W. The value of 7.2×10−7 m/V deduced for the second‐order nonlinear susceptibility is about 1900 times greater than that found in bulk GaAs.
TL;DR: In this article, a tunable erbium-doped fiber laser using a liquid-crystal etalon filter (LCF) as the wavelength-selective element is described.
Abstract: Wavelength-tunable lasers in the near infrared have a wide range of applications for fiber-based lightwave systems. A description is given of a tunable erbium-doped fiber laser using a liquid-crystal etalon filter (LCF) as the wavelength-selective element. The laser is continuously tunable over a range of 45 nm (1523-1568 nm) with a voltage of 2.1-3.3 V applied to the LCF, and operates single-mode with a very narrow linewidth ( >
TL;DR: An index coupled antireflection-coated distributedfeedback (DFB)-laser diode which theoretically exhibits a longitudinally uniform power density is proposed in this paper, which is far more efficient in reducing spatial hole burning than multiphase-shift lasers.
Abstract: An index coupled antireflection-coated distributed-feedback (DFB)-laser diode which theoretically exhibits a longitudinally uniform power density is proposed. The structure contains an amplitude modulated grating and is far more efficient in reducing spatial hole burning than multiphase-shift lasers. The laser can be expected to be single mode up to high power levels. It can be of interest when long lasers with a reduced linewidth and a flat FM response are to be used or as a laser with small modulation distortion in analog communication. >
TL;DR: Experimental evidence that the longitudinal eigenmodes of a laser are not orthogonal may affect the quantum limit to the laser linewidth is presented, using single-mode semiconductor lasers with various coatings.
Abstract: In the presence of output coupling the longitudinal eigenmodes of a laser are not orthogonal. This may affect the quantum limit to the laser linewidth, in particular, if the outcoupling is high. We present experimental evidence of this effect, using single-mode semiconductor lasers with various coatings.
TL;DR: In this article, the authors identified injection-recombination shot noise in the tuning region as a significant linewidth broadening mechanism in wavelength-tunable laser diodes.
Abstract: Injection-recombination shot noise in the tuning region is identified as significant linewidth broadening mechanism in wavelength-tunable laser diodes. Depending on the tuning efficiency this power independent linewidth broadening is typically around 4–20 MHz. Useful formulas for the evaluation of this broadening and design rules for an improvement of the devices are given.
TL;DR: The temperature-dependent linewidth of excitons in semiconductor quantum wells due to the interaction of theexciton with LO phonons is studied with use of perturbation theory for the exciton-phonon interaction and by assuming an infinite-barrier-quantum-well model.
Abstract: The temperature-dependent linewidth of excitons in semiconductor quantum wells due to the interaction of the exciton with LO phonons is studied with use of perturbation theory for the exciton-phonon interaction and by assuming an infinite-barrier-quantum-well model. The interaction is taken to be of the Fr\"ohlich form, and the scattering of the exciton to both bound and scattering states of the interacting electron--heavy-hole system has been taken into account. The dependence of the linewidth on the quantum-well width and on the choice of the heavy-hole mass is discussed, and comparison is made with available experimental data. The effects of the confinement of the optical phonons on the exciton linewidth are also studied and are found not to alter substantively the results for the dependence of the linewidth on the quantum-well width.
TL;DR: In this paper, a narrow bandwidth tunable semiconductor laser system operating near 780 nm is described, where the commercial laser diodes are frequency stabilized by optical feedback from an external, confocal Fabry-Perot resonator.
TL;DR: In this paper, an observation of intermodal forward stimulated Brillouin scattering at 514.5 nm in dual-mode optical fibres is reported, where the FSBS signal is shifted by 16.6 MHz and does not depend significantly on the laser linewidth.
Abstract: Observation of intermodal forward stimulated Brillouin scattering at 514.5 nm in dual-mode optical fibres is reported. The FSBS signal is shifted by 16.6 MHz and, unlike in normal background SBS, does not depend significantly on the laser linewidth. The Brillouin gain in backward and forward directions is compared.
TL;DR: In this paper, the variation of differential gain, refractive index, and linewidth enhancement factor with carrier density in InGaAs•GaAs strained-layer quantum well lasers are presented for the first time.
Abstract: Measurements of the variation of differential gain, refractive index, and linewidth enhancement factor with carrier density in InGaAs‐GaAs strained‐layer quantum well lasers are presented for the first time. These results verify predictions of improvement over unstrained bulk or quantum well lasers, but only at certain carrier densities. Differential gain (dg/dN) is found to vary from 7.0×10−16 to 2.5×10−16 cm2 over the range of carrier densities studied, while the carrier dependence of the real part of the refractive index (dn/dN) ranges from a peak of −2.8×10−20 down to −7.0×10−21 cm3. From these measurements the resulting linewidth enhancement factor (α) is found to vary from 5 to a minimum of 1.7. This information is critical to successfully exploiting the potential advantages of strained‐layer lasers for such devices as high‐frequency or narrow linewidth lasers.
TL;DR: In this paper, an erbium-doped-phospho-alumino-silicate-fibre ring laser was used to achieve a 60 kHz linewidth at a wavelength of 1.555 mu m.
Abstract: Operation of an erbium-doped-phospho-alumino-silicate-fibre ring laser in a unidirectional travelling-wave configuration enables narrow linewidth, single frequency emission to be obtained at a wavelength of 1.555 mu m. A 60 kHz linewidth has been measured. >
TL;DR: In this paper, the authors achieved a spectral linewidth of 170 kHz at a 1.5-mu m wavelength in a 1200- mu m long corrugation-pitchmodulated (CPM) distributed feedback (DFB) laser having multiple quantum wells (MQW).
Abstract: A spectral linewidth of 170 kHz was achieved at a 1.5- mu m wavelength in a 1200- mu m long corrugation-pitch-modulated (CPM) distributed feedback (DFB) laser having multiple quantum wells (MQW). This is the narrowest linewidth ever reported for InGaAsP DFB lasers. The CPM structure is effective in maintaining the single longitudinal mode at a high output power by suppressing the spatial hole burning effect. The linewidth-power product is 400 kHz-mW, and the extrapolated residual spectral linewidth is 150 kHz. >
TL;DR: A new technique is proposed and demonstrated for improving the resolution of the delayed self-heterodyne method for laser spectral linewidth measurement by increasing the delay time between two laser beams by using multipass transmission in an optical fiber ring interferometer containing a frequency shifter.
Abstract: A new technique is proposed and demonstrated for improving the resolution of the delayed self-heterodyne method for laser spectral linewidth measurement The delay time between two laser beams is increased by the use of multipass transmission in an optical fiber ring interferometer containing a frequency shifter This technique does not require a longer fiber or complicated curve fitting of the observed spectra
TL;DR: In this paper, a simple and accurate method to measure the linewidth enhancement factor a in DFB semiconductor lasers is proposed, based on the principle of external optical injection locking, does not require the knowledge of the absolute value of optical injection level.
Abstract: A simple and accurate method to measure the linewidth enhancement factor a in DFB semiconductor lasers is proposed. This method, based on the principle of external optical injection locking, does not require the knowledge of the absolute value of optical injection level.
TL;DR: In this article, a Green's function approach to the analysis of semiconductor lasers is formulated in a form suitable for complex cavity structures, and the spontaneous emission rate and the effective phase-amplitude coupling factor can be accurately evaluated.
Abstract: A Green's function approach to the analysis of semiconductor lasers is formulated in a form suitable for complex cavity structures. Both the spontaneous emission rate and the effective phase-amplitude coupling factor can be accurately evaluated. For distributed-feedback (DFB) lasers, the spontaneous emission rate is strongly dependent on both the facet reflectivities and the grating coupling coefficients. The effective phase-amplitude coupling factor depends on the wavelength detuning from the gain maximum. The calculated linewidth of DFB lasers differs considerably from previous calculated results and gives better agreement with experimental results. For composite-cavity lasers, the frequency dependence of the equivalent reflectivity has a strong impact on the phase-amplitude coupling factor and the spontaneous emission rate. Distributed Bragg reflector (DBR) lasers are investigated as an example of a composite-cavity structure. >
TL;DR: Negative electrical feedback was applied to a CSP-type AlGaAs laser, reducing its FM noise at the Fourier frequency range of f > 0 as mentioned in this paper, where the negative electrical feedback is applied to the CSP type AlgaAs laser.
Abstract: Negative electrical feedback was applied to a CSP-type AlGaAs laser, reducing its FM noise at the Fourier frequency range of f >
TL;DR: A semiconductor laser with a linewidth of 7 Hz locking to a supercavity was achieved by using an optical-electrical double-feedback technique to improve frequency stability and power concentration.
Abstract: A semiconductor laser with a linewidth of 7 Hz locking to a supercavity was achieved by using an optical–electrical double-feedback technique. The emitted power concentration within the stabilized field spectrum was 81%. The minimum value of the square root of the Allan variance for the frequency stability was 2.4 × 10−14 at the integration time of 70 msec.