Showing papers on "Laser linewidth published in 1988"

Laser Diode Modulation and Noise

Abstract: 1 Introduction.- 2 Basic Laser Characteristics.- 2.1 Double heterostructure characteristics.- 2.2 Direct and indirect semiconductors.- 2.2.1 Energy- and momentum conservation.- 2.2.2 Semiconductor materials for direct and indirect semiconductors.- 2.3 Emission and absorption.- 2.3.1 Density of photon oscillation states.- 2.3.2 Principal mechanisms of radiative transitions.- 2.3.3 Carrier lifetime and lifetime of spontaneous emission.- 2.3.4 Gain and stimulated emission.- 2.4 Lasing characteristics of Fabry-Perot-type lasers.- 2.4.1 Lasing conditions.- 2.4.2 Dynamic characteristics of laser operation.- 2.4.3 Light current characteristics, threshold current and quantum efficiency.- 2.4.4 Basic laser structures.- 2.4.5 Modifications for the spontaneous emission term.- 2.5 Dynamic single-mode laser structures.- 2.5.1 DFB laser characteristics.- References.- 3 Longitudinal Mode Spectrum of Lasing Emission.- 3.1 Multimode rate equations.- 3.2 Spectral envelope for Fabry-1 Introduction.- 2 Basic Laser Characteristics.- 2.1 Double heterostructure characteristics.- 2.2 Direct and indirect semiconductors.- 2.2.1 Energy- and momentum conservation.- 2.2.2 Semiconductor materials for direct and indirect semiconductors.- 2.3 Emission and absorption.- 2.3.1 Density of photon oscillation states.- 2.3.2 Principal mechanisms of radiative transitions.- 2.3.3 Carrier lifetime and lifetime of spontaneous emission.- 2.3.4 Gain and stimulated emission.- 2.4 Lasing characteristics of Fabry-Perot-type lasers.- 2.4.1 Lasing conditions.- 2.4.2 Dynamic characteristics of laser operation.- 2.4.3 Light current characteristics, threshold current and quantum efficiency.- 2.4.4 Basic laser structures.- 2.4.5 Modifications for the spontaneous emission term.- 2.5 Dynamic single-mode laser structures.- 2.5.1 DFB laser characteristics.- References.- 3 Longitudinal Mode Spectrum of Lasing Emission.- 3.1 Multimode rate equations.- 3.2 Spectral envelope for Fabry-Perot-type lasers (linear gain).- 3.3 Influence of nonlinear gain on the spectral characteristics.- 3.3.1 Symmetric nonlinear gain.- 3.3.2 Asymmetric nonlinear gain.- 3.3.3 Nonlinear gain, conclusions.- References.- 4 Intensity-Modulation Characteristics of Laser Diodes.- 4.1 Modulation characteristics by studying single-mode rate equations.- 4.1.1 Turn-on delay.- 4.1.2 Rate equations, small signal analysis.- 4.1.3 Relaxation oscillation damping.- 4.1.4 Upper limits for the modulation bandwidth of laser diodes.- 4.2 Influence of lateral carrier diffusion on relaxation oscillation damping.- 4.3 Modulation bandwidth limits due to parasitic elements.- 4.4 Examples for high speed modulation of laser diodes.- 4.5 Modulation and longitudinal mode spectrum.- 4.5.1 Transient spectra of laser diodes.- 4.5.2 Lasing spectra under high speed modulation.- 4.5.3 Dynamic single-mode condition.- 4.6 Modulation with binary signals.- 4.7 Harmonic and intermodulation distortions (without fibre interaction).- 4.7.1 Harmonic and intermodulation distortions for low modulation frequencies.- 4.7.2 Harmonic and intermodulation distortions for high modulation frequencies.- References.- 5 Frequency-Modulation Characteristics of Laser Diodes.- 5.1 Relation between intensity-modulation and frequency modulation.- 5.2 Current/frequency-modulation characteristics.- 5.3 Chirp effects in directly modulated laser diodes.- 5.3.1 Spectral line broadening due to laser chirping.- 5.3.2 Chirp-reduction by proper pulse shaping.- 5.3.3 Time-bandwidth product of chirped pulses.- 5.3.4 Transmission of chirped pulses over single-mode fibres.- 5.4 Possibilities of modifying the chirp parameter ?.- 5.4.1 Dispersion of the chirp parameter ?.- 5.4.2 Chirp of laser diodes, coupled to optical cavities.- References.- 6 Instabilities and Bistability in Laser Diodes.- 6.1 Repetitive self-pulsations due to lateral instabilities.- 6.2 Instability and bistability in laser diodes with segmented contacts.- References.- 7 Noise Characteristics of Solitary Laser Diodes.- 7.1 Relative intensity noise (RIN).- 7.1.1 Basic properties of noise signals.- 7.1.2 Definition and measurement of RIN.- 7.1.3 Requirement of RIN for intensity modulated systems.- 7.2 Introduction of the spontaneous emission noise.- 7.3 Intensity noise of laser diodes.- 7.3.1 Intensity noise of laser diodes by studying single-mode rate equations.- 7.3.2 Mode partition noise.- 7.3.3 Mode partition noise analysis for nearly single-mode lasers.- 7.3.4 Mode-hopping noise.- 7.3.5 1/f-intensity noise.- 7.4 Statistics of intensity noise.- 7.4.1 Statistics of amplified spontaneous emission.- 7.4.2 Probability density distribution for the total laser light output.- 7.4.3 Statistics of mode partition noise.- 7.4.4 Turn-on jitter in laser diodes.- 7.5 Mode partition noise for the transmission of pulse-code modulated (PCM)-signals.- 7.5.1 Multimode lasers.- 7.5.2 The mode partition coefficient k.- 7.5.3 Nearly single-mode lasers.- 7.6 Phase and frequency noise.- 7.6.1 Phase and frequency noise characterization in general.- 7.6.2 Spectral line shape for white frequency noise.- 7.6.3 Spectral line shape for 1/f-frequency noise.- 7.6.4 Frequency noise and spectral linewidth for single-mode laser diodes.- 7.6.5 Power-independent contribution to the linewidth of laser diodes.- 7.6.6 Correlation between FM-noise and AM-noise.- References.- 8 Noise in Interferometers Including Modal Noise and Distortions.- 8.1 Noise in interferometers.- 8.1.1 Complex degree of coherence.- 8.1.2 Interferometric noise analysis for single-mode lasers.- 8.1.3 Interferometric set-ups for measuring the linewidth and the degree of coherence.- 8.1.4 Interferometric noise analysis for multimode lasers.- 8.2 Modal noise.- 8.2.1 Modal noise for monochromatic light sources.- 8.2.2 Modal noise for single-mode lasers with finite spectral linewidth.- 8.2.3 Modal noise for multimode laser diodes.- 8.2.4 Modal distortions.- 8.3 Modal noise and distortions in single-mode fibres.- References.- 9 Semiconductor Lasers with Optical Feedback.- 9.1 Amplitude and phase conditions for laser diodes with external cavities.- 9.1.1 Short external reflectors for longitudinal mode stabilization.- 9.1.2 Emission frequency shifts due to optical feedback.- 9.1.3 Single external cavity mode condition.- 9.1.4 Spectral linewidth for laser diodes with external optical feedback.- 9.2 Dynamics of laser diodes with external reflections.- 9.2.1 Derivation of the time-dependent electric field.- 9.2.2 Modulation characteristics of external-cavity lasers.- 9.3 Laser diodes with distant reflections.- 9.3.1 Classification of feedback regimes.- 9.3.2 Phase and frequency noise of laser diodes with distant reflectors.- 9.3.3 Intensity noise in laser diodes with distant reflectors.- 9.3.4 Coherence collapse.- 9.3.5 Tolerable feedback levels.- References.- 10 Laser Diodes with Negative Electronic Feedback.- 10.1 Modulation characteristics of laser diodes with negative electronic feedback.- 10.2 Linewidth narrowing and phase noise reduction with negative electronic feedback.- References.- 11 Circuitry for Driving the Laser Diode.- 11.1 Schemes for stabilizing the bias current.- 11.2 Laser drivers with optoelectronic integration.- References.

Observation of atoms laser cooled below the Doppler limit

Abstract: The generally accepted theory of laser cooling of free atoms predicts that the lowest achievable temperature is given by kaT = hγ/2, where kB is Boltzmann's constant arid γ is the natural linewidth of the transition for laser cooling. This "Doppler cooling limit" results from the minimization of the detuning-dependent temperature at low laser power1:

Guided-wave optoelectronics

Abstract: 1. Introduction..- 1.1 Overview.- 1.2 Organization of the Book.- References.- 2. Theory of Optical Waveguides. (With 32 Figures).- 2.1 Ray Optics of the Slab Waveguide.- 2.1.1 Refraction and Reflection.- 2.1.2 Guided Modes.- 2.1.3 The Goos-Hanchen Shift.- 2.1.4 Effective Guide Thickness.- 2.2 Fundamentals of the Electromagnetic Theory of Dielectric Waveguides.- 2.2.1 Maxwell's Equations.- 2.2.2 Modes of the Waveguide.- 2.2.3 The Wave Equations for Planar Guides.- 2.2.4 Mode Properties Following from Symmetry.- 2.2.5 Orthogonality of the Modes.- 2.2.6 Mode Expansion and Normalization.- 2.2.7 The Variation Theorem for Dielectric Waveguides.- 2.2.8 Power Flow and Stored Energy in a Dielectric Waveguide.- 2.2.9 Variational Properties of the Propagation Constant.- 2.3 Modes of the Planar Slab Guide.- 2.3.1 TE Modes.- 2.3.2 TM Modes.- 2.3.3 Multilayer Slab Guides.- 2.4 Planar Guides with Graded-Index Profiles.- 2.4.1 The Parabolic Profile (Harmonic Oscillator).- 2.4.2 The "1/cosh2" Profile.- 2.4.3 The Exponential Profile.- 2.4.4 Index Profiles with Strong Asymmetry.- 2.4.5 The WKB Method.- 2.5 Channel Waveguides.- 2.5.1 Channel Guide Geometries.- 2.5.2 The Vector Wave Equation.- 2.5.3 Numerical Analysis.- 2.5.4 Separation of Variables.- 2.5.5 The Method of Field Shadows.- 2.5.6 The Vector Perturbation Theorem.- 2.5.7 The Effective-Index Method.- 2.6 Coupled-Mode Formalism and Periodic Waveguides.- 2.6.1 Excitation of Waveguide Modes.- 2.6.2 Waveguide Deformations.- 2.6.3 Coupled-Wave Solutions.- 2.6.4 Periodic Waveguides.- 2.6.5 TE-to-TM Mode Conversion.- References.- 3. Waveguide Transitions and Junctions (With 43 Figures).- 3.1 Waveguide Modes and Coupled-Mode Theory.- 3.1.1 Normal Modes of Coupled Waveguides.- 3.1.2 Coupled-Mode Theory Representation.- 3.2 Fast and Slow Transitions.- 3.2.1 Local Normal Modes.- 3.2.2 Adiabatic Transition.- 3.2.3 Abrupt Transition.- 3.2.4 Tapered Velocity Coupler.- 3.2.5 3 dB Coupler.- 3.2.6 Directional Coupler.- 3.3 Mode Coupling Between Local Normal Modes.- 3.3.1 Coupled-Amplitude Equations.- 3.3.2 Differential Form of Coupled-Amplitude Equations.- 3.3.3 Coupled-Mode Theory Representation of Cij.- 3.4 Two-Arm Branches.- 3.4.1 Step Approximation for a Waveguide Branch.- 3.4.2 Analytic Solution for Shaped Branches.- 3.4.3 Experimental Results.- 3.4.4 Superposition of Solutions.- 3.5 Waveguide Horns.- 3.5.1 Mode-Conversion Coefficient Cij for Channel Waveguides.- 3.5.2 Approximation for ??ij.- 3.5.3 Approximation for Cij.- 3.5.4 Parabolic Solution.- 3.6 Branches with Three Arms.- 3.6.1 Normal Modes of Three Coupled Waveguides.- 3.6.2 3 X 2 Waveguide Coupler.- 3.7 Conclusion.- References.- 4. Titanium-Diffused Lithium Niobate Waveguide Devices (With 39 Figures).- 4.1 Waveguide Fabrication.- 4.1.1 Titanium Diffused Waveguides.- 4.1.2 Proton Exchange LiNbO3 Waveguides.- 4.1.3 Post-Waveguide Processing.- 4.2 Basic Device Considerations.- 4.2.1 Electro-Optic Effect.- 4.2.2 Phase Modulator.- 4.2.3 Insertion Loss.- 4.2.4 Voltage/Loss Tradeoffs: Waveguide Tailoring.- 4.3 Switch/Modulator.- 4.3.1 Directional Coupler.- 4.3.2 Balanced-Bridge Interferometer.- 4.3.3 Intersecting-Waveguide Switch.- 4.4 On/Off Modulators.- 4.4.1 Y-Branch Interferometer.- 4.4.2 Voltage and Bandwidth Consideration for Switch/ Modulators.- 4.5 Polarization Devices.- 4.5.1 TE - TM Conversion.- 4.5.2 Polarization Controller.- 4.5.3 Polarization-Selective Devices.- 4.6 Wavelength Filters.- 4.6.1 Interferometric Filters.- 4.6.2 Coupled-Mode Filters.- 4.7 Polarization-Insensitive Devices.- 4.8 Some Ti:LiNbO3 Integrated-Optic Circuits.- 4.8.1 Coherent Lightwave Receiver.- 4.8.2 Optical Switch Arrays.- 4.9 Applications.- 4.9.1 External Modulators.- 4.9.2 High-Speed Analog to Digital Conversion.- 4.9.3 Fiber Gyroscope Chip.- References.- 5. Mode-Controlled Semiconductor Lasers (With 55 Figures).- 5.1 Organization of the Chapter.- 5.1.1 Notation.- 5.2 Laser Basics.- 5.2.1 Epitaxial Materials and Heterostructure.- 5.2.2 Waveguide Propagation, Amplification and Oscillation.- 5.2.3 Laser Gain.- 5.2.4 Spontaneous Emission.- 5.2.5 Photon Rate Equation.- 5.2.6 Spectral Hole Burning.- 5.2.7 Carrier Injection in a Heterojunction.- 5.2.8 Modal Rate Equations.- 5.2.9 Longitudinal Variation of Photon Density.- 5.2.10 Steady-State Solution of Rate Equations.- 5.2.11 Measurement of Modal Reflectivity and Laser Gain.- 5.3 Structures for Transverse-Mode Control.- 5.3.1 Stripe Geometry Laser, Blocking Layer.- 5.3.2 Buried Heterostructure Lasers.- 5.3.3 Ridge Waveguide Lasers.- 5.4 Longitudinal Mode Control.- 5.4.1 Three- and Four-Mirror Resonators.- 5.4.2 Distributed Bragg Gratings.- 5.4.3 Semiconductor DFB Lasers.- 5.4.4 DBR and Phase-Slip DFB Lasers.- 5.5 Linewidth.- 5.5.1 Linewidth of Fabry-Perot Laser.- 5.5.2 Linewidth Reduction Using Extended Cavities.- 5.6 High-Speed Modulation.- 5.6.1 Modulation Response.- 5.6.2 Origin of Chip Parasitics.- 5.6.3 Evaluation of Parasitics.- 5.6.4 Dependence of Parasitics on Device Structure.- 5.6.5 The Intrinsic Laser - Small-Signal Intensity Modulation Response.- 5.6.6 High-Frequency Limitations.- 5.6.7 Design Considerations for Wideband Lasers.- 5.6.8 Large-Signal Modulation - PCM.- 5.6.9 Large-Signal Modulation - Gain Switching.- 5.6.10 Active Mode-Locking.- 5.7 Luminescent Diodes and Laser Amplifiers.- 5.7.1 Edge-Emitting and Superluminescent Diodes.- 5.7.2 Linear Amplification and Amplified Spontaneous Emission in TWAs and ELEDs.- 5.7.3 Fabry-Perot Amplifiers and ELEDs.- 5.7.4 Amplifier Gain Compression.- 5.7.5 Receiver Noise.- 5.8 Tunable and FM Lasers.- 5.8.1 Tunable DBR.- 5.8.2 Tunable DFB.- Appendix 5A: Glossary of Symbols.- References.- 6. Semiconductor Integrated Optic Devices (With 66 Figures).- 6.1 Semiconductor Waveguide Theory.- 6.1.1 Methods of Index Change in Semiconductors.- 6.1.2 Slab Waveguides.- 6.1.3 Channel Waveguides.- 6.1.4 Coupling Effects.- 6.1.5 Optical Loss.- 6.1.6 Curvature Loss.- 6.2 Material Technology.- 6.2.1 Liquid Phase Epitaxy (LPE).- 6.2.2 Vapor Phase Epitaxy (VPE).- 6.2.3 Metal Organic Chemical Vapor Deposition (MOCVD).- 6.2.4 Molecular Beam Epitaxy (MBE).- 6.2.5 Summary.- 6.3 Passive Waveguide Devices - Fabrication and Characterization.- 6.3.1 Channel Waveguides.- 6.3.2 Couplers.- 6.3.3 Bends and Branches.- 6.3.4 Grating Filter.- 6.4 Electro-Optic Guided-Wave Modulators - Theory.- 6.4.1 Electro-Optic Effect in III-V Semiconductors.- 6.4.2 Modulator Design.- 6.4.3 Modulation Frequency Analysis.- 6.4.4 Traveling-Wave Phase Modulators.- 6.4.5 TE-TM Coupling Analysis.- 6.4.6 Infrared Waveguide Modulators - Wavelength Scaling.- 6.4.7 Electro-Absorption Modulation.- 6.4.8 Carrier-Injection Modulator.- 6.4.9 Nonlinear Waveguide Modulator.- 6.5 Electro-Optic Guided-Wave Modulator Characteristics.- 6.5.1 Phase Modulators.- 6.5.2 Directional-Coupler Switches.- 6.5.3 Interferometric Modulators.- 6.5.4 Integrated Waveguides/Optoelectronics/Electronics.- 6.5.5 Electro-Absorption Modulators.- 6.5.6 Multiple-Quant urn-Well Modulators.- 6.5.7 Nonlinear Waveguide Modulators.- 6.6 Optoelectronic Integrated Circuits (OEIC).- 6.7 Concluding Remarks.- References.- 7. Recent Advances (With 1 Figure).- 7.1 Introduction.- 7.2 Theory of Optical Waveguides.- 7.3 Waveguide Transitions and Junctions.- 7.4 Titanium-Diffused Lithium Niobate Waveguide Devices.- 7.5 Mode-Controlled Semiconductor Lasers.- 7.6 Semiconductor Integrated Optic Devices.- References.

Numerical analysis of the feedback regimes for a single-mode semiconductor laser with external feedback

Abstract: The effect of external feedback on a single-mode semiconductor laser is estimated by a numerical solution of the nonlinear rate equations. The analysis yields an excellent description of published experimental results. It is found that the lasing mode with the minimum linewidth is most stable rather than the mode with minimum threshold gain. The transition to the coherence-collapse regime is of particular interest. It usually occurs for feedback fractions approximately=10/sup -4/, but it can be shifted to considerably larger feedback levels either by increasing the emitted optical power or the laser length or by decreasing the linewidth enhancement factor alpha . >

Laser stabilization at the millihertz level

Abstract: The main task of this paper is to identify a number of physical problems that must be successfully addressed to achieve stabilized laser linewidths well below 1 Hz. After presentation of the basic stability characteristics of available laser sources, it is shown that if any of these lasers were optimally locked to a high-finesse Fabry-Perot cavity it would be theoretically possible to obtain a laser linewidth in the millihertz domain. Problems of optical feedback, modulation waveform errors, mechanical support and isolation of the reference cavity, thermal stabilization of the environment, etc. are considered, and interim solutions are discussed. Experimentally, locking accuracy to successive cavity orders of less than 0.00002 linewidths (+ or - 1.5 Hz) was achieved; mirror birefringence pulled the lock point approximately 10-fold more. Relative phase coherence between two independent lasers locked onto adjacent cavity orders was preserved for 8 sec, corresponding to a linewidth of each optical source of about 50 mHz.

Stability of phase locking in coupled semiconductor laser arrays

Abstract: It is shown that amplitude phase coupling (as described by the linewidth enhancement factor α) leads to unstable phase locking in semiconductor laser arrays with evanescent coupling.

Single frequency and tunable laser diodes

Abstract: The state-of-the-art technologies for single-frequency and frequency-tunable laser diodes are reviewed. Spectral linewidth characteristics for distributed-feedback laser diodes are discussed, based on experimentally observed discrepancies from the theory and improvements obtained with quantum-well active regions. Frequency-tunable mechanisms are reviewed mainly for monolithic tunable laser diodes with distributed-Bragg-reflector (DBR) or distributed-feedback configurations. >

Visible BaB2O4 optical parametric oscillator pumped at 355 nm by a single‐axial‐mode pulsed source

Abstract: A visible BaB2O4 optical parametric oscillator (OPO) pumped by a single-axial-mode 355-nm source has been demonstrated. An average output power of 140 mW with a signal wave conversion efficiency of 13 percent and an idler conversion efficiency of 11 percent for a total conversion efficiency of 24 percent has been achieved. The oscillator has continuously tuned from 412 nm to 2.55 microns limited by the infrared transmission range of the crystal. Through injection seeding, single-axial-mode OPO operation with a corresponding OPO linewidth of less than 3 GHz was obtained.

Longitudinal Mode Competition and Asymmetric Gain Saturation in Semiconductor Injection Lasers. II. Theory

Abstract: Gain saturation in semiconductor lasers is analyzed using a density matrix formalism. A refined treatment of the density matrix formalism reveals that nonlinear gain has a component which is asymmetric with respect to the lasing frequency. The asymmetric component originates from refractive-index modulation due to a carrier-density pulsation induced by the optical-intensity beat. Based on the analysis, mode competition behavior is numerically examined using appropriate values of the linewidth enhancement factor and the intraband relaxation time. It is shown that the output power decreases at mode jumping from a shorter to a longer wavelength mode while it increases at mode jumping toward shorter wavelengths. The results agree with the features of the mode competition behavior observed in transverse-mode-controlled AlGaAs lasers.

A theoretical model of multielectrode DBR lasers

Abstract: A theoretical model for two- and three-section tunable distributed Bragg reflector (DBR) lasers is presented The static tuning properties are studied in terms of threshold current, linewidth, oscillation frequency, and output power Regions of continuous tuning for three-section DBR lasers are presented Different routes for continuous tuning, when the injection currents to the passive sections are varied, are discussed and the limitations on the continuous tuning range are clarified By proper control of these currents, a tuning range of approximately 400 GHz is predicted at 155 mu m wavelength, which is in good agreement with the experimental results published thus far >

Modulation performance of a semiconductor laser coupled to an external high-Q resonator

Abstract: The dynamic response of a semiconductor laser coupled to an external resonator is studied using the single-mode rate equations modified to account for the dispersive feedback. Both the frequency and the damping rate of relaxation oscillations are affected by the feedback. The frequency chirp that invariably accompanies amplitude modulation is significantly reduced. The feedback also reduces the phase noise and the linewidth. To investigate the usefulness of external-resonator lasers in high-speed optical communication systems, the rate equation have been solved numerically to obtain the emitted chirped pulse; the pulse is propagated through the fiber, detected, and filtered at the receiver. The simulated-eye diagrams show that such lasers can be operated at high bit rates with negligible dispersion penalty owing to their reduced frequency chip. >

Miniature packaged external-cavity semiconductor laser with 50 GHz continuous electrical tuning range

Abstract: Miniature, packaged, grating-external-cavity lasers have been developed for use in PSK. and DPSK coherent transmission systems at 1.5μm. The outside dimensions of the package are 30 × 30 × 50 mm and the optical cavity length is nominally 30 mm, resulting in a spectral linewidth < 100 kHz. The lasing wavelength is mechanically adjustable over the range 1510–1560 nm and electrically tunable over a range of 0.8 nm. With appropriate control of the grating piezos, a continuous (hop-free) tuning range of 50 GHz (0.4 nm) can be obtained.

Modulatable narrow‐linewidth semiconductor lasers

Abstract: We find that using the technique of optical feedback locking, to narrow semiconductor linewidths, does not sacrifice the ability to modulate the laser’s frequency via the injection current. The frequency of a laser is stabilized to a separate Fabry–Perot reference cavity using resonant optical feedback and can be modulated efficiently at frequencies related by rational fractions to the free‐spectral range of the reference cavity. This system can provide an array of narrow‐linewidth, frequency‐stable laser lines and shows promise for applications in frequency‐division‐multiplexed coherent communications, as well as laser frequency control and precision measurement systems.

Single-longitudinal-mode operation of an Nd3+-doped fibre laser

Abstract: We report the first operation of an Nd3+-doped monomode fibre laser oscillating in a single longitudinal mode. The laser incorporated an integral fibre grating used as a narrowband reflector. The lasing linewidth was measured as 1.3MHz FWHM at a wavelength of 1082nm.

Method and apparatus for stabilizing the frequency of a laser beam

Abstract: For stabilizing the frequency of a narrow-band Excimer laser beam the interference rings of a Fabry-Perot interferometer 16 are projected onto a solid-state image sensor 18 and by means of the solid-state image sensor an electrical signal is generated which is dependent on the frequency of the laser beam. The electrical signal is compared with a stored reference signal to derive an adjusting signal 32 for an optical reflection grating 38 with which the frequency of the laser beam 12 is regulated to a desired value. The absolute value of the frequency of the laser beam 12 is determined by means of the optogalvanic effect.

Electrical and optical interactions between integrated InGaAsP/InP DFB lasers and electroabsorption modulators

Abstract: Electrical and optical interactions occurring in InGaAsP/InP integrated light sources composed of DFB lasers and electroabsorption modulators have been studied. Static measurements indicated that an isolation resistance between the laser and the modulator should be as large as 100 k Omega or more in order to reduce a lasing wavelength shift associated with biasing the modulator. The useful guided light out of the modulator was about 1-2 percent of the laser output. At high frequency modulation, asymmetric sidebands were observed in dynamic spectra measured at the modulator facet, which were caused by additional modulation of the laser part. Such additional modulation was relatively large at the relaxation oscillation frequency of the laser, but it was reduced by connecting an RF bypass condenser in parallel to the laser diode and by depositing an antireflection coating at the modulator facet. After eliminating the additional modulation, an integrated device showed a high frequency response of 5.7-GHz 3-dB bandwidth and a small linewidth enhancement factor of alpha =0.8. >

The semiconductor laser linewidth due to the presence of side modes

Abstract: The laser linewidth is evaluated by solving the rate equations for a nearly single-mode laser with two modes. The resulting linewidth contribution due to the presence of side modes is introduced by the nonlinear gain in the laser diode. For weak side modes, the linewidth contribution is proportional to the third power of the side mode intensity. A linewidth contribution of about 20 MHz for a side-mode power of 100 mu W has been found experimentally for a 1.3- mu m buried-heterostructure laser. >

Extremely sharp erbium‐related intra‐4f‐shell photoluminescence of erbium‐doped GaAs grown by metalorganic chemical vapor deposition

Abstract: A drastic change is observed in the 1.5 μm Er‐related photoluminescence spectra for GaAs:Er grown by metalorganic chemical vapor deposition, when the growth temperature and arsine partial pressure are reduced. An optically efficient Er‐emitting center which shows a photoluminescence spectrum with narrow linewidth (less than 0.03 nm at 2 K) and high peak intensity is preferentially photoexcited in the crystal grown at 550 °C with a V/III ratio of 3. The linewidth of the luminescence is comparable to rare‐earth‐related luminescence of rare‐earth‐doped insulators such as YAG:Nd.

Systems driven by colored squeezed noise: The atomic absorption spectrum.

Abstract: We derive stochastic density-matrix equations for an atom strongly driven by finite-bandwidth squeezed light The quantum properties of the light are accounted for by a doubling of dimensions of the stochastic process for c-number electric field amplitudes Saturation properties and the weak-field absorption spectrum of a two-level atom embedded in finite-bandwidth squeezed light and driven by a coherent field are calculated We discuss the effect of finite bandwidth of the squeezed light in obtaining subnatural linewidth in the atomic absorption spectra, based on nonperturbative solutions of the stochastic optical Bloch equations

Effect of injection-current fluctuations on the spectral linewidth of semiconductor lasers.

Abstract: The effect of current fluctuations on the linewidth of semiconductor lasers is analyzed using the single-mode rate equations. Since the time scale of such fluctuations can generally be longer than the intrinsic time scale of relaxation oscillations, current fluctuations are modeled using a non-Markovian random force in the rate equation governing the carrier dynamics. In the absence of nonlinear-gain effects, the contribution of current fluctuations to the linewidth is negligible at all power levels. However, when the gain saturation resulting from spectral hole burning is included, current fluctuations are found to give rise to a power-independent contribution to the linewidth. At low operating powers, this contribution is small compared with the spontaneous-emission contribution. For InGaAsP lasers, the power-independent contribution is estimated to be \ensuremath{\sim}1 MHz/\ensuremath{\mu}A and can significantly affect the intrinsic linewidth at high power levels (g10 mW). Furthermore, the line shape is not strictly Lorentzian and tends towards Gaussian with increasing power. We have discussed the dependence of the line shape and linewidth on various device parameters.

Theory for optical heterodyne narrow-deviation FSK receivers with delay demodulation

Abstract: A theoretical model is presented that includes the effects of laser phase noise, receiver noise, imperfect modulation, IF bandwidth, and postdetection filtering. Detailed numerical results for 140-Mb/s and 400-Mb/s systems are presented, showing excellent agreement with independent published experimental results and strongly supporting the theoretical analysis. It is found that an IF linewidth of less than 0.25% of bit rate is required to avoid degrading the receiver sensitivity by more than 1 dB in a system with a strong local oscillator and modulation index of 0.7. A larger modulation index allows a larger linewidth to be accommodated. If the demodulation is not optimal, a narrower linewidth is necessary. >

Dependence of spectral linewidth on cavity length and coupling coefficient in DFB laser

Abstract: The dependence of the spectral linewidth of DFB lasers on cavity length and coupling coefficient has been investigated. It was shown experimentally that the long cavity was very effective at reducing the spectral linewidth of DFB lasers, whereas a large coupling coefficient was ineffective. With a corrugation depth of 15 nm and a cavity length of 1200 mu m, a narrow linewidth of 1.7 MHz was obtained at 11 mW.< >

Pulsed tunable solid state laser

Abstract: A tunable solid state laser oscillator with very narrow spectral line width for pulsed output comprises a solid state laser medium that generates a laser beam along a resonant path, a beam expander, such as a prism beam expander or cylindrical optic, and a grating mounted with an adjustable angle of incidence with respect to the laser beam. By adjusting the angle of incidence of the beam on the grating, the laser output wavelength is tuned. Further, the reflectivity of the grating provides very narrow spectral line width for oscillation in the laser over the entire tuning range.

GaInP/AlInP Quantum Well Structures and Double Heterostructure Lasers Grown by Molecular Beam Epitaxy on (100) GaAs

Abstract: GaInP/AlInP single quantum well structures and double heterostructure lasers have been grown by molecular beam epitaxy at 510°C with the dimetric phosphorus beam. The peak energy and linewidth of the photoluminescence spectrum at 10 K from quantum wells as a function of well width have been studied. A 10- µm wide stripe-geometry GaInP/AlInP laser diode has shown a room temperature CW operation with a threshold current of 93 mA and an emission wavelength of 671 nm.

The relationship between accelerating voltage and electron detection modes to linewidth measurement in an SEM

Abstract: The basic premise underlying the use of the scanning electron microscope (SEM) for linewidth metrology in semiconductor research and production applications is that the video image acquired, displayed, analyzed, and ultimately measured accurately reflects the structure of interest. However, it has been clearly demonstrated that image distortions can be caused by the detected secondary electrons not originating at the point of impact of the primary electron beam and by the type and location of the secondary electron detector. These effects and their contributions to the actual image or linewidth measurement have not been fully evaluated. Effects due to uncertainties in the actual location of electron origination do not affect pitch (line center-to-center or similar-edge-location-to-similar-edge-location spacing) measurements as long as the lines have the same edge geometries and similar profiles of their images in the SEM. However, in linewidth measurement applications, the effects of edge location uncertainty are additive and thus give twice the edge detection error to the measured width. The basic intent of this work is to demonstrate the magnitude of the errors introduced by beam/specimen interactions and the mode of signal detection at a variety of beam acceleration voltages and to discuss their relationship to precise and accurate metrology.

Quantum fluctuations in the stimulated-Raman-scattering linewidth.

Abstract: Measurements of the single-shot power spectrum of stimulated Raman scattering from an ${\mathrm{H}}_{2}$ Raman generator at 10 and 32 atm using a Fabry-Perot interferometer are presented. The results show that the single-shot linewidth can be much narrower than the ensemble average predicted by quantum mechanics. However, when the spectra of numerous shots are averaged together the resulting linewidth is in close agreement with the predicted result. In addition, the power spectrum exhibits large shot-to-shot fluctuations within the gain-narrowed profile which may be related to observed soliton decay in stimulated Raman scattering.

Narrow-linewidth resonant optical device, transmitter, system, and method

Abstract: Highly frequency-selective reflectivity is realized in an optical device including a waveguide and an evanescent-field coupled grating resonator cavity. The device may include a light source and serve as a low-chirp, narrow-linewidth communications laser for use, e.g., for transmission over a fiber having non-negligible dispersion and also in wavelength-multiplexed coherent systems.

Linewidth reduction and optical frequency stabilization of a distributed feedback laser by incoherent optical negative feedback

Abstract: A new, incoherent, optical negative feedback method is proposed and demonstrated for spectral linewidth reduction and optical frequency stabilization of distributed feedback lasers. The spectral linewidth and the optical frequency drift are simultaneously reduced to about 50 kHz and less than 10 MHz, respectively.

Wide-linewidth phase diversity homodyne receivers

Abstract: The use of phase diversity homodyne receivers, which have excellent performance even when the laser linewidth is of the same order of magnitude as the bit rate, to construct coherent systems with semiconductor lasers and moderate bandwidth receivers is considered. Theoretical, experimental, and computer simulation results of a study of a linewidth homodyne phase-diversity receiver is presented. A 150-Mb/s system with an IF linewidth of more than 50% of the bit rate is investigated in depth and is experimentally shown to operate within 1.8 dB from its theoretical limit. >

State of polarisation and phase noise independent coherent optical transmission system based on Stokes parameter detection

Abstract: A novel detection scheme for polarisation modulation is proposed. It is independent of the polarisation fluctuations of the received signal and is greatly insensitive to phase noise, allowing the use of powerful lasers whose linewidth is not compatible with traditional system requirements.