We present a traveling wave analysis of a general class of semiconductor lasers, which includes multisection DFB/DBR lasers and gain-coupled DFB lasers. The analysis leads to new semianalytic expressions for the small-signal IM and FM modulation responses, the intensity and FM noise spectra, and the linewidth. The expressions are given in terms of solutions to four coupled linear homogeneous differential equations and can easily be evaluated numerically. We also derive a stability parameter /spl sigma/, for which /spl sigma/ >

Traveling wave analysis of semiconductor lasers: modulation responses, mode stability and quantum mechanical treatment of noise spectra

The noise of linear amplifiers is discussed in terms of the fundamental law of quantum mechanics and is analyzed using an electrical circuit model. The operational principles of two types of amplifiers-negative conductance amplifier and nonlinear susceptance amplifier-are studied with a special emphasis on those at optical frequencies. The application of such optical amplifiers to optical telecommunication systems is reviewed.

Noise in amplifiers

After pointing out some questionable assumptions of the standard beating theory, we formulate a new semiclassical wave theory of the noise in optical amplifiers. The theory is simple yet rigorous and uses a few quantum statements in a classical signal framework. The amplifier is modeled as a 2/spl times/2 port device, and the amplified spontaneous emission and associated noise are shown to be just the amplified coherent state (or vacuum state) fluctuation of the field entering the idler input. The new theory can treat other closely related detection schemes as well, correctly supplying both mean signal and noise.

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Noise in an optical amplifier: formulation of a new semiclassical model

A field noise spectral density matrix for the noise from a linear optical device, modeled as an optical multiport, is derived semi-classically. The noise is formulated in the scattering parameters, population inversion factor, and internal efficiency of the device. From this noise expression, a new equation for the amplified spontaneous emission spectral density from an optical amplifier is derived. This equation is more general than those previously published. The derivations are accomplished with the aid of methods from ordinary (classical) electrical network theory and only one quantum mechanical result regarding the noise from a conductance. As a result, the first-mentioned noise expression also includes the so-called vacuum field fluctuations. Further, the current noise spectrum of a square-law detector is derived with classical methods. The optical input to the detector includes the vacuum field fluctuations, which are shown to be the cause of the detector shot noise. Here, a second quantum mechanical result has to be employed, viz., that the vacuum field fluctuations cannot be detected alone. The results in this paper agree with the special cases found in the literature. The noise expressions are well suited for examination of the optical noise performance of arbitrary linear optical networks including, e.g., amplifiers, attenuators, isolators, reflections, filters, and couplers. >

Optical quantum noise treated with classical electrical network theory

Abshact-A field noise spectral density matrix for the noise from a linear optical device, modeled as an optical multiport, is derived semi-classically. The noise is formulated in the scattering parameters, population inversion factor, and internal efficiency of the device. From this noise expression, a new equation for the amplified spontaneous emission spectral density from an optical amplifier is derived. This equation is more general than those previously published. The derivations are accomplished with the aid of methods from ordinary (classical) electrical network theory and only one quantum mechanical result regarding the noise from a conductance. As a result, the first-mentioned noise expression also includes the so-called vacuum field fluctuations. Further, the current noise spectrum of a square-law detector is derived with classical methods. The optical input to the detector includes the vacuum field fluctuations, which are shown to be the cause of the detector shot noise. Here, a second quantum mechanical result has to be employed, viz., that the vacuum field fluctuations cannot be detected alone. The results in this paper agree with the special cases found in the literature. The noise expressions are well suited for examination of the optical noise performance of arbitrary linear optical networks including, e.g., amplifiers, attenuators, isolators, reflections, filters, and couplers.

Quantum Noise Treated with Classical Electrical Network Theory

The amplitude and phase noise spectra of the internal and external fields of a negative resistance oscillator are derived using electrical circuit theory. It is shown that the difference between internal and external fluctuations becomes important in the quantum domain ( h\omega > kT ) where external noise sources are not negligible as they often are in the classical domain ( h\omega ). Using established methods to describe quantum fluctuations in electrical circuits, we obtain results in full agreement with the more exact but less general direct quantum mechanical analysis of a Fabry-Perot laser in Part I.

O. Nilsson

Papers

Internal and external field fluctuations of a laser oscillator: Part II--Electrical circuit theory