Showing papers on "Laser linewidth published in 1985"
TL;DR: In this paper, a theoretical and experimental investigation of injection locking of semiconductor lasers is presented, taking into account the dependence of refractive index on the carrier density expressed by the linewidth enhancement factor α.
Abstract: We present a theoretical and experimental investigation of injection locking of semiconductor lasers. The theoretical analysis takes into account the dependence of refractive index on the carrier density expressed by the linewidth enhancement factor α. Locking conditions and dynamic stability are analyzed. The nonzero value of α results in an increased locking bandwidth, where only part of the range corresponds to a dynamically stable state. Asymmetric characteristics are obtained for the locked power and phase as a function of frequency detuning between the master and slave laser. Outside the stable range, light injection gives rise to beat phenomena and intensity pulsations. The theoretical results were confirmed by experiments on 830 nm CSP lasers and 1.3 μm BH lasers. The experiments include the first measurements of locking bandwidth characteristics reported for 1.3 μm lasers. Power spectra are recorded under locked and near-locked conditions and compared with theory. The 1.3 μm lasers are found to have a better dynamic stability than 830 nm lasers. Even so, the stability problems may exclude the particular application of injection locking where phase modulation is generated for coherent transmission.
432 citations
TL;DR: In this article, the authors describe a novel optical time domain reflectometer which uses a frequency-modulated singlemode semiconductor laser as the optical source, which offers a potential distance resolution of the order of 1 mm over ranges limited by the source linewidth.
Abstract: This paper describes a novel optical time domain reflectometer which uses a frequency-modulated single-mode semiconductor laser as the optical source. The new system offers a potential distance resolution of the order of 1 mm over ranges limited by the source linewidth. In this paper, a theoretical assessment of the features which determine the available performance of the system is followed by some experimental results which confirm these general trends. Applications of this system include short range fault location in situations where resolution of the order of centimeters is required, and as a novel discrimination technique for optical sensor multiplexing systems.
313 citations
TL;DR: In this article, the authors investigate theoretically a number of important issues related to the performance of AlGaAs quantum well (QW) semiconductor lasers, and reveal the existence of gain saturation with current in structures with a small number of wells, pointing to a possible two-fold increase in modulation bandwidth and a ten-fold decrease in the spectral laser linewidth in a thin QW laser compared to a conventional double heterostructure laser.
Abstract: We investigate theoretically a number of important issues related to the performance of AlGaAs quantum well (QW) semiconductor lasers. These include a basic derivation of the laser gain, the linewidth enhancement factor α, and the differential gain constant in single and multiple QW structures. The results reveal the existence of gain saturation with current in structures with a small number of wells. They also point to a possible two-fold increase in modulation bandwidth and a ten-fold decrease in the spectral laser linewidth in a thin QW laser compared to a conventional double heterostructure laser.
269 citations
TL;DR: In this paper, the authors examined the correlation of the interface roughness with the measured intensity oscillations of reflective high energy electron diffraction (RHEED) during the growth of 10 or more atomic layers and found that the growth interruption of 10−100 seconds prior to the interface formation is effective in achieving an atomically flat interface.
Abstract: Photoluminescence spectra of GaAs-AlAs quantum wells are studied to evaluate the flatness of heterointerfaces prepared by molecular beam epitaxy. We examine the correlation of the interface roughness with the measured intensity oscillations of reflective high energy electron diffraction (RHEED) during the growth. The crystal surface is found to roughen after the growth of 10 or more atomic layers. The growth interruption of 10–100 seconds prior to the interface formation is effective in achieving an atomically flat interface, leading to sharp photoluminescence with the linewidth <30 A at 77 K even when the quantum well width is reduced to 40 A.
170 citations
TL;DR: In this paper, the authors measured the intensity of an injection-locked 1.54 μm InGaAsP laser and found that the change in intensity across the locking range is quite asymmetric, with a shape that agrees well with the theory of Lang.
Abstract: Measurements of the intensity of an injection locked 1.54 μm InGaAsP laser are reported. The change in intensity of the locked laser across the locking range is quite asymmetric, with a shape that agrees well with the theory of Lang. A linewidth parameter of \alpha = 6 \pm 1 was determined from the magnitude of the locking range. The injection locked laser was found to be unstable on the high frequency end of the locking range. The physical origin of this instability is explained in terms of a laser intensity change altering the phase of the laser field relative to that of the injected field.
170 citations
TL;DR: In this paper, the second-order phase-locked loops require at least 0.8 pW of signal power per every kilohertz of laser linewidth (this number refers to the system with the detector responsivity 1 A/W, dumping factor 0.7, and rms phase error 10°).
Abstract: Optical homodyne receivers based on decision-driven phase-locked loops are investigated. The performance of these receivers is affected by two phase noises due to the laser transmitter and laser local oscillator, and by two shot noises due to the two detectors employed in the receiver. The impact of these noises is minimized if the loop bandwidth B is chosen optimally. The value of B opt and the corresponding optimum loop performance are evaluated in this paper. It is shown that second-order phase-locked loops require at least 0.8 pW of signal power per every kilohertz of laser linewidth (this number refers to the system with the detector responsivity 1 A/W, dumping factor 0.7, and rms phase error 10°). This signal power is used for phase locking, and is, therefore, lost from the data receiver. Further, the maximum permissible laser linewidth \Delta
u is evaluated and for second order loops with the dumping factor 0.7 found to be 3.1 \times 10^{-4} \cdot R_{b} , where R b (bit/s) is the system bit rate. For R_{b} = 100 Mbit/s, this leads to \Delta
u = 31 kHz. For comparison, heterodyne receivers with noncoherent postdetection processing only require \Delta
u = 0.72-9 MHz for R_{b} = 100 Mbit/s. Thus, the homodyne systems impose much more stringent requirements on the laser linewidth than the heterodyne systems. However, homodyne systems have several important advantages over heterodyne systems, and the progress of laser technology may make homodyning increasingly attractive. Even today, homodyne reception is feasible with experimental external cavity lasers, which have been demonstrated to have \Delta
u as low as 10 kHz.
139 citations
TL;DR: In this article, the temperature dependence of the Si-H linewidth of an adsorbate-substrate mode was measured for the first time, with the use of an accurate ab initio force field and a stochastic method to include quantum effects.
Abstract: The temperature dependence of the natural linewidth of an adsorbate-substrate mode, Si-H, has been measured for the first time. Molecular-dynamics simulations of the infrared line shapes, with the use of an accurate ab initio force field and a novel stochastic method to include quantum effects, are in good agreement with experiment. Linewidths are shown to be dominated by pure dephasing above 250 K and by inhomogeneities at low temperature. The vibrational lifetime, computed to be \ensuremath{\simeq}${10}^{\mathrm{\ensuremath{-}}8}$ s, contributes negligibly to the linewidth.
122 citations
21 May 1985
TL;DR: In this article, an electrical feedback technique was proposed to stably reduce the linewidth of a semiconductor laser without changing its cavity structure, and the minimum attainable linear width was estimated as being narrower than 1 kHz when the reflectance of the interferometer used was higher than 0.9.
Abstract: An electrical feedback technique was proposed to stably reduce the linewidth of a semiconductor laser without changing its cavity structure. Calculations and experiments were carried out to reduce the linewidth of a 1.5 μm InGaAsP laser (DFB type) according to the following procedure. A compact Fabry-Perot interferometer was used as a freqeuncy discriminator. The minimum attainable linewidth, limited by the detector noise, was estimated as being narrower than 1 kHz when the reflectance of the interferometer used was higher than 0.9. The minimum linewidth obtained in the experiment was 330 kHz, which was 15 times as narrow as in the case of a free-running laser. The improvements of this experimental result can be expected by simultaneously reducing the AM noise of the laser.
116 citations
TL;DR: In this paper, a new technique for sinusoidal intensity modulation of light, based on injection-locking of two longitudinal modes of a single laser to FM sidebands of another laser, is described.
Abstract: A new technique for sinusoidal intensity modulation of light, based on injection-locking of two longitudinal modes of a single laser to FM sidebands of another laser, is described. A 35 GHz microwave signal with a linewidth of less than 10 Hz was generated.
114 citations
TL;DR: In this article, a simple formula of the dynamic spectral width of a directly modulated dynamic-single-mode (DSM) laser and the related maximum transmission bandwidth of a single-mode fiber limited by chromatic dispersion are theoretically given.
Abstract: A simple formula of the dynamic spectral width of a directly modulated dynamic-single-mode (DSM) laser, and the related maximum transmission bandwidth of a single-mode fiber limited by chromatic dispersion are theoretically given. The dynamic spectral width of a DSM laser is determined by the modulated optical shape and the linewidth enhancement factor α. The spectral width caused by the dynamic wavelength shift is shown to be larger by ( 1 + \alpha^{2} )1/2than that caused by the sideband of the signal of the intensity modulation. Furthermore, the maximum transmission bandwidth of a conventional single-mode fiber with a DSM laser is expressed by using the parameter α and the chromatic dispersion of the fiber. The product of the maximum bit rate and the square root of the fiber length at the wavelength of 1.55 μm is estimated to be about 25 Gbit/s . km1/2.
102 citations
TL;DR: In this article, a laser fluorescence spectroscopy has been performed on the two-photon 62S1/2 to 52D3/2 transition in Ba+ using signals from an individual laser-cooled ion in a rf trap with an effective wavelength of 2.07 μm.
Abstract: Laser fluorescence spectroscopy has been performed on the two-photon 62S1/2 to 52D3/2 transition in Ba+. Using signals from an individual laser-cooled ion in a rf trap, a laser limited linewidth of less than 3 MHz has been achieved with an effective wavelength of 2.07 μm. The absence of any sidebands in the spectra spaced at the 5.5-MHz oscillation frequency of the ion in the rf quadrupole trap indicates that the ion vibrational motion must be well into the Lamb–Dicke regime. An upper limit of 165 nm is given to the vibrational amplitude.
TL;DR: In this article, a design of laser was described which produces a modeless output giving a continuous spectral distribution and a continuously variable bandwidth, comparable to convetional laser pumped dye laser.
11 Feb 1985
TL;DR: In this paper, the spectral linewidth of distributed feedback (DFB) laser diodes is theoretically studied, and the effects of phase shift and mirror facets on the spectral characteristics of DFB lasers are also analyzed.
Abstract: The spectral linewidth of distributed feedback (DFB) laser diodes is theoretically studied. Numerical calculation shows that DFB lasers with long cavity lengths and large coupling coefficients have very narrow spectral linewidth less than 1 MHz, The effects of the phase shift and mirror facets on the spectral characteristics of DFB lasers are also analyzed, It is shown that the phase-shifter further narrows the spectral linewidth of DFB lasers. Its numerical result and physical meaning are also shown.
TL;DR: In this article, the spontaneous emission inside an injection-locked semiconductor laser does not alter the lasing field and the linewidth is only governed by the injected-field phase noise and may no longer follow the Schawlow Townes dependence on emitted optical power.
Abstract: We show that the spontaneous emission inside an injection-locked semiconductor laser does not alter the lasing field. For injection at the free-running frequency, the linewidth is only governed by the injected-field phase noise and may no longer follow the Schawlow-Townes dependence on emitted optical power.
TL;DR: In this article, the sensitivity of resonance Raman cross sections to the excited state homogeneous width is exploited to separate the homogeneous and inhomogeneous contributions to the optical absorption linewidth in trans-stilbene.
Abstract: The sensitivity of resonance Raman cross sections to the excited state homogeneous width is exploited to separate the homogeneous and inhomogeneous contributions to the optical absorption linewidth in trans‐stilbene. Absolute Raman cross sections have been measured using excitation at 356, 299, 282, and 266 nm, and calculations have been performed to model the intensities of the eleven strongly Raman‐active modes as well as the absorption spectrum. A simple analysis neglecting explicit temperature effects requires a homogeneous Lorentzian linewidth (Γ) of 310 cm−1 and an inhomogeneous Gaussian distribution of zero–zero energies with a standard deviation (θ) of 500 cm−1. Consideration of thermal excitation in the lowest‐frequency single‐bond torsional mode significantly improves the fit to the experimental absorption by broadening the spectrum asymmetrically to higher energies, while allowing Γ and θ to be reduced to 120 and 450 cm−1, respectively. The spectral broadening generated by thermal excitation of ground‐state torsional modes thus contributes significantly to the homogeneous linewidth in trans‐stilbene. The relatively large effective homogeneous width at room temperature is consistent with the low Raman intensity in the ∼200 cm−1 C=C–φ bend compared with the prominence of this vibration in resolved low‐temperature electronic spectra.
TL;DR: In this paper, the spectral linewidth of 1.5 μm external cavity semiconductor lasers was investigated and it was shown that detuning from exact resonance can reduce the linwidth substantially for strong, frequency selective feedback.
Abstract: The spectral linewidth of 1.5 μm external cavity semiconductor lasers is investigated. For nonzero intermediate facet reflectivity, detuning from exact resonance is found to reduce linewidths substantially for strong, frequency-selective feedback. A 10 cm cavity gives linewidths below 1 kHz, while coherent systems requirements will be met by cavities under 2.5 cm.
TL;DR: In this paper, a backward Brillouin amplifier was used to compress the pulse in a backpropagation scheme using SF 6 gas pumped by 0.9 GHz linewidth KrF laser radiation at pressures of 15.3 and 12.6 atm, respectively.
Abstract: Experimental measurements are presented of pulse compression in a backward Brillouin amplifier using SF 6 gas pumped by 0.9 GHz linewidth KrF laser radiation. Average pulse durations of 390 ps and energy extraction effieiencies of 40 percent from 24 ns pump pulses have been demonstrated at pressures of 15.3 and 12.6 atm, respectively.
TL;DR: In this paper, an expression for the FM noise spectrum of an injection-locked semiconductor laser was derived and the ultimate linewidth reduction was obtained if the locking bandwidth is large enough to accommodate the frequency fluctuations and if the detuning is controlled carefully.
Abstract: An expression is derived for the FM noise spectrum of an injection-locked semiconductor laser. For increasing injection level the FM noise spectrum and the lineshape change gradually from those of the slave laser to those of the master laser. The ultimate linewidth reduction is obtained if the locking bandwidth is large enough to accommodate the frequency fluctuations and if the detuning is controlled carefully.
TL;DR: In this article, the phase and amplitude fluctuations of a single-mode laser were compared with the same total average power of a mode-locked single-modal laser, and it was shown that the linewidth of each of the locked modes is the same as that of the single mode.
Abstract: Comparisons are made of the phase and amplitude fluctuations of a laser when it operates single mode and when it is mode locked with the same total average power. Despite the much lower signal-to- (spontaneous emission) noise ratio of the mode-locked laser, the linewidth of each of the locked modes is the same as that of the single mode. The fluctuation of the total intensity of the mode-locked laser, and the linewidth enhancement factor due to intensity fluctuation as recently analyzed by Henry, are the same in both cases.
TL;DR: In this paper, the authors measured the FM and AM noise spectra of 1.3 μm InGaAsP DFB lasers in the frequency range from dc to 4 GHz and compared the relaxation resonances appearing in these spectra to the semiclassical theory of laser noise.
Abstract: The FM and AM noise spectra of 1.3 μm InGaAsP DFB lasers are measured in the frequency range from dc to 4 GHz. The relaxation resonances appearing in these spectra are compared to the semiclassical theory of laser noise. All the resonance parameters, i.e., the linewidth enhancement factor α, the resonance frequency f R , and the damping constant γ e , are determined from the FM noise spectra by successful curve fitting. The estimated value of α is 2.2. Field spectra for various bias currents are measured by using optical heterodyne detection. Theoretical lineshapes are obtained by using four noise-parameter values which have been determined from the FM noise and the linewidth measurements. The results are in excellent agreement with the measured spectra. This agreement verifies the estimation that \alpha = 2.2.
TL;DR: In this article, various techniques for use in spectral narrowing and tuning of excimer laser oscillators are described, including Littrow grating, grazing-incidence grating and prisms.
Abstract: Various techniques for use in spectral narrowing and tuning of excimer laser oscillators are described. Intracavity dispersive elements include Littrow grating, grazing-incidence grating, prisms, a...
TL;DR: In this article, the optical homogeneous linewidth (Γ hom ) in an organic glass from hole-burning experiments, in particular as regards laser power and detection method, is analyzed.
TL;DR: In this paper, background normalization was used for coherent anti-Stokes Raman spectroscopy (CARS) measurements of CO in extracted flame gases and with equilibrium calculations.
Abstract: An investigation of in situ background normalization for obtaining sensitive and accurate concentration measurements with coherent anti-Stokes Raman spectroscopy (CARS) is reported. Flame species concentrations measured with CARS were in good agreement with IR laser absorption measurements of CO in extracted flame gases and with equilibrium calculations. Time-averaged detectivity for CO at the 1000-ppm level was obtained at 1900 K. Background normalization was also shown to be capable of improving CARS pulse-to-pulse signal reproducibility nearly to the shot-noise limit. We consider factors important for concentration measurements with CARS, including laser-induced Stark effects, accuracy of susceptibility calculations, and effects of different laser linewidth models.
TL;DR: The use of gain switching is reported to obtain 60 mW of single-longitudinal-mode peak output power from a laser-diode-excited monolithic Nd:YAG laser.
Abstract: We report the use of gain switching to obtain 60 mW of single-longitudinal-mode peak output power from a laser-diode-excited monolithic Nd:YAG laser. The device is demonstrated to operate at repetition rates in excess of 1 kHz and exhibits a spectral linewidth of less than 8 MHz. This oscillator provides an ideal source for injection seeding of laboratory Nd:YAG laser systems.
TL;DR: The construction and calibration of a low‐field L‐band EPR imaging spectrometer is described with capillary phantoms containing aqueous nitroxides as paramagnetic imaging agents and spin‐label destruction, particularly by biological reducing agents, was compared.
Abstract: The advantages of electron paramagnetic resonance (EPR) imaging at L-band frequencies are discussed. The construction and calibration of a low-field L-band EPR imaging spectrometer is described with capillary phantoms containing aqueous nitroxides as paramagnetic imaging agents. The peak separation induced by the magnetic field gradient is related to the object separation. The linewidth of each (first-derivative) line is used to calculate the dimensions of each paramagnetic object, which is the sum of an intrinsic and a gradient-induced component. By extrapolating the linewidth back to zero field gradient, one obtains the intrinsic linewidth correction factor in computing image size. The nonuniformity caused by deterioration of biological substructure was examined with plant stems where one capillary vessel had become leaky. Spin-label destruction, particularly by biological reducing agents, was compared for three species of plant stems.
TL;DR: In this paper, a negative frequency feedback control was used to reduce frequency modulation (FM) noise linewidth in semiconductor lasers, which is based on the direct frequency modulation capability of a semiconductor laser and an error signal was extracted through optical heterodyne frequency discrimination detection using a stable master laser.
Abstract: Electrical negative frequency feedback control has been shown to reduce frequency modulation (FM) noise linewidth in semiconductor lasers. The method is based on the direct frequency modulation capability of a semiconductor laser. An error signal is extracted through optical heterodyne frequency discrimination detection using a stable master laser. FM noise is reduced by more than 20 dB and linewidth is reduced by one order of magnitude.
TL;DR: The results of this study confirm that quantitative absorption measurements can be readily obtained by ILS and that the sensitivity of ILS detection derives from the overall stability of the dye laser, but especially that of its optical path length.
Abstract: The time-dependent properties of the wavelength-dispersed spectrum for a quasi-cw dye laser were measured (1) to define the operating criteria required for the quantitative application of intracavity laser spectroscopy (ILS) for absorption and (2) to determine the origin of the sensitivity limitations observed in several studies. Time-resolved and wavelength-dispersed spectra of a broadband dye laser were measured as a function of pumping power and of stability of the optical path length of the resonator cavity. The results of this study confirm that quantitative absorption measurements can be readily obtained by ILS and that the sensitivity of ILS detection derives from the overall stability of the dye laser, but especially that of its optical path length.
TL;DR: In this article, it is shown that inhomogeneities in the linewidth enhancement factor in a semiconductor laser exert great influence on the injection current modulation FM response, and that flat carrier induced FM response with either redshift or blueshift can be obtained in a laser with an inhomogeneous linear enhancement factor without the accompanying spurious intensity modulation.
Abstract: It is shown that inhomogeneities in the linewidth enhancement factor in a semiconductor laser exert great influence on the injection current modulation FM response. Several phenomena, which have not been explained so far, such as redshift frequency chirping, flat carrier induced FM response, and absence of phase reversal at the thermal cut‐off frequency, are explained by the present theoretical model. A flat carrier induced FM response with either redshift or blueshift may be obtained in a semiconductor laser with an inhomogeneous linewidth enhancement factor without the accompanying spurious intensity modulation.
TL;DR: In this paper, it was shown that second-order phase-locked loops require at least 0.8 pW of signal power per every kilohertz of laser linewidth (this number refers to the system with the detector responsivity 1 A/W, dumping factor 0.7, and rms phase error 10°).
Abstract: Optical homodyne receivers based on decision-driven phase-locked loops are investigated. The performance of these receivers is affected by two phase noises due to the laser transmitter and laser local oscillator, and by two shot noises due to the two detectors employed in the receiver. The impact of these noises is minimized if the loop bandwidth B is chosen optimally. The value of B opt and the corresponding optimum loop performance are evaluated in this paper. It is shown that second-order phase-locked loops require at least 0.8 pW of signal power per every kilohertz of laser linewidth (this number refers to the system with the detector responsivity 1 A/W, dumping factor 0.7, and rms phase error 10°). This signal power is used for phase locking, and is, therefore, lost from the data receiver. Further, the maximum permissible laser linewidth \Delta v is evaluated and for second order loops with the dumping factor 0.7 found to be 3.1 × 10-4. R b , where R b (bit/s) is the system bit rate. For R_{b} = 100 Mbit/s, this leads to \Delta v = 31 kHz. For comparison, heterodyne receivers with noncoherent postdetection processing only require \Delta v = 0.72-9 MHz for R_{b} = 100 Mbit/s. Thus, the homodyne systems impose much more stringent requirements on the laser linewidth than the heterodyne systems. However, homodyne systems have several important advantages over heterodyne systems, and the progress of laser technology may make homodyning increasingly attractive. Even today, homodyne reception is feasible with experimental external cavity lasers, which have been demonstrated to have \Delta v as low as 10 kHz.
TL;DR: In this paper, a grating-tuned external cavity InGaAsP/InP laser has been developed for use in coherent transmission systems that operate at a wavelength of 1.5 μm.
Abstract: Packaged grating-tuned external cavity InGaAsP/InP lasers have been developed for use in coherent transmission systems that operate at a wavelength of 1.5 μm. The emission wavelength can be selected within a 60 nm range during manufacture, and can subsequently be tuned over 0.5 nm (63 GHz). The lasers have linewidths better than 20 kHz and show long-term relative frequency stability of better than 150 MHz.