I. W. Smith

Bio: I. W. Smith is an academic researcher. The author has contributed to research in topics: Limit (mathematics) & Quantum limit. The author has an hindex of 4, co-authored 4 publications receiving 222 citations.

Laser gyro at quantum limit

Abstract: We show that a certain fundamental limit applies to the accuracy of all optical rotation sensors which use laser light as a probe. We derive this fundamental rotation-rate uncertainty from the Heisenberg uncertainty relations and Glauber's minimum uncertainty states. The same relationship is obtained from a spontaneous-emission noise formulation. We present experimental data on a (nondithered) four-frequency ring laser gyroscope for which this limit is attained.

Laser gyro at quantum limit

Abstract: We show that a certain fundamental limit applies to the accuracy of all optical rotation sensors which use laser light as a probe. We derive this fundamental rotation-rate uncertainty from the Heisenberg uncertainty relations and Glauber's minimum uncertainty states. The same relationship is obtained from a spontaneous-emission noise formulation. We present experimental data on a (nondithered) four-frequency ring laser gyroscope for which this limit is attained.

Frequency locking of modes in a ring laser

Abstract: The locking of two countertraveling ring laser modes due to light scattering is investigated. It is found that the mutual locking of two free-running oscillating modes is different from locking due to an externally injected signal. The text defines two kinds of mode-to-mode scattering: conservative and nonconservative. The former leads to no locking, to a high degree of approximation. Examples of conservative scatterers are nonabsorbing particles, small compared to a wavelength, and loss-free objects of larger size that represent only a weak perturbation of the dielectric constant in the cavity. The presence of two types of scatterers makes it impossible, in general, to calculate lockbands from measured scattering intensities from optical components such as mirrors. The relationship between the present theory, the conventional Adler theory, and measurable laser component properties such as scattering coefficients is discussed. The findings are of importance for the development of mirrors and optical coating processes in ring lasers.

An optical phased array for lasers

Abstract: High-performance, optical phased arrays for electronic control of laser beams have recently been demonstrated. The optical aperture is lithographically fabricated to form a unity-fill-factor array of liquid-crystal-based optical phase shifters. The liquid-crystal phase shifters can be fabricated smaller than a wavelength of light, with spacings equally small, although this is not required in these devices for small angle steering applications. Computer control of the individual phase shifters establishes a phase profile across the optical aperture that steers or otherwise controls an incident optical beam. Prototypes of such optical phased arrays have been used to demonstrate electronically programmable optical beam steering, lensing, fanout, and conditioning. The devices offer high pointing accuracy and resolution in a small size, owing to the much shorter wavelength of light as compared to microwaves. This inertialess technology makes available to optical systems many of the performance capabilities and the functional versatility long afforded microwave systems by microwave phased array antennas. Operation of such optical phased arrays has been successfully demonstrated from the green (doubled Nd:YAG lasers) to the long-wave infrared (carbon dioxide lasers). The capability represents a major technological advance and is expected to enable numerous new optical systems. This paper focuses on a comparison of the new optical phased array technology with that of conventional microwave phased arrays. Operating principles are briefly reviewed from dual perspectives: namely, those of the microwave and optical regimes. A brief discussion of system applications is included.

Ring-laser tests of fundamental physics and geophysics

Abstract: HeNe ring-laser gyros are standard sensors in inertial guidance; mirror reflectances now reach 99.9999%. Present research instruments have an area of , a passive quality factor of , and a resolution of the frequency difference of counter-rotating optical beams approaching microhertz. In the Sagnac effect, this difference is proportional to the angular velocity. Present resolution is limited by thermal drifts in frequency pulling, itself reflecting mirror backscatter. The capability of ring lasers for measurements of geodesic interest, including seismometry and earth tides, and for detection of other sources of non-reciprocal refractive indices, including axions and CP violation, are discussed. In standard polarization geometries the observable is necessarily time-reversal odd. Scaling rules for dimensions, finesse etc summarizing past progress and suggesting future potential are given.

Preparation, measurement and information capacity of optical quantum states

Abstract: The preparation, or generation of coherent states, squeezed states, and photon number states is discussed. The quantum noise is evaluated for various simultaneous measurements of two quadrature components: heterodyning, the beam splitter followed by two single quadrature measurements, the parametric amplifier, the (degenerate and/or nondegenerate) four-wave mixer, the Brillouin and Raman amplifiers, and the laser amplifier. A quantum nondemolition measurement followed by a measurement of the conjugate variable is also categorized as a simultaneous measurement. It is shown that, for all of these schemes, the minimum uncertainty product of the measured variables is exactly equal to that required for a simultaneous measurement of two noncommuting variables. On the other hand, measurements of a single quadrature component are noise-free. Such measurements are degenerate heterodyning, degenerate parametric amplification, and cavity degenerate four-wave mixing and photon counting by a photomultiplier or avalanche photodiode. The Heisenberg uncertainty principle and the quantum-mechanical channel capacity of Shannon are discussed to address the question "How much information can be transmitted by a single photon?" The quantum-mechanical channel capacity provides an upper bound on the achievable information capacity and is ideally realized by photon number states and photon counting detection. Its value is $\frac{\ensuremath{\hbar}\ensuremath{\omega}}{(\mathrm{ln}2)kT}$ bit per photon. The use of coherent or squeezed states and a simultaneous measurement of two quadrature field components or the measurement of one single quadrature field component does not achieve the ultimate limit.

Sub-Poissonian processes in quantum optics

Abstract: The author reviews methods for generating sub-Poissonian light and related concepts. This light has energy fluctuations reduced below the level which corresponds to a classical Poissonian process (shot-noise level). After an introduction to the concept of nonclassical light, an overview is given of the main methods of quantum-noise reduction. Sub-Poissonian processes are exemplified in different areas of optics, ranging from single-atom resonance fluorescence to nonlinear optics, laser physics, and cavity quantum electrodynamics. Emphasis is placed on the conceptual foundations, and on developments in laser theory that lead to the possibility, already demonstrated experimentally, of linewidth narrowing and sub-Poissonian light generation in lasers and masers. The sources of quantum noise in these devices are analyzed, and four noise-suppression methods are discussed in detail: regularization of the pumping, suppression of spontaneous-emission noise, nonadiabatic evolution of the atomic variables, and twin-beam generation.

Semiconductor lasers with optical injection and feedback

Abstract: In this review we discuss the theoretical framework needed for studying the dynamical behaviour of semiconductor lasers exposed to three kinds of optical modulation. We start by a derivation of the single-mode rate-equations for the slowly varying complex electric field and the inversion, and the necessary extensions for monochromatic optical injection and normal external optical feedback. The basic operating characteristics of the solitary semiconductor laser are analysed, including light-current curves and their dependence on the spontaneous emission level, as well as the optical spectrum. The effect of monochromatic injection is discussed in terms of locking and non-locking dynamics, including a thermodynamic potential for phase jumps. The basic ingredients for studying external optical feedback are given, including a derivation of the thermodynamic potential for phase-diffusion. After an introduction on optical phase conjugation, the field rate-equation for feedback from a phase-conjugate mirror is derived.

Ultrahigh enhancement in absolute and relative rotation sensing using fast and slow light

Abstract: We describe a resonator-based optical gyroscope whose sensitivity for measuring absolute rotation is enhanced via use of the anomalous dispersion characteristic of superluminal light propagation. The enhancement is given by the inverse of the group index, saturating to a bound determined by the group velocity dispersion. We also show how the offsetting effect of the concomitant broadening of the resonator linewidth may be circumvented by using an active cavity. For realistic conditions, the enhancement factor is as high as ${10}^{6}$. We also show how normal dispersion used for slow light can enhance relative rotation sensing in a specially designed Sagnac interferometer, with the enhancement given by the slowing factor.