Abstract: A single-frequency fiber-optic ring laser exhibits improved frequency stability, reduced laser intensity noise, broad tunability and narrow linewidth. The fiber-optic ring laser includes a ring-resonator with a length of single-mode optical fiber, a gain medium of rare earth-doped fiber, a broad-band fiber Fabry-Perot filter for wavelength tuning of the laser, a narrow-band fiber Fabry-Perot filter for suppression of longitudinal ring modes and an optical isolator for preventing interetalon interactions between the tandem fiber Fabry-Perot filters. Selective positioning of the tandem fiber Fabry-Perot filters, relative to the ring laser's gain medium and output coupler, results in laser intensity noise reduction to the standard quantum limit.

Abstract: A laser Doppler velocimeter is formed using erbium-doped fiber as the lasing medium. Within the velocimeter, all optical signals, transmitted and received, are handled by optical fibers. A telescope with a single optical fiber input/output interface acts as both the transmission device to focus the radiation at a specified point, and as the receiving system for collecting reflected radiation. The portion of the reflected radiation collected by the receiving system is analyzed to determine the Doppler shift caused by targets at the focal point of the telescope.

Abstract: Amplitude or intensity noise in the output of a laser in detuned operation is reduced by application of a frequency dependent transfer function which exploits amplitude-phase coupled noise described by the linewidth enhancement parameter .alpha. by applying an inverse of a replica of the amplitude noise recovered from the phase noise to the laser output. The noise canceling amplitude is applied to the laser output by a filter whose frequency dependent transfer function is related to the inverse of the amplitude-phase noise transfer function of the laser producing the output. The appropriate transfer function may be selected and/or adjusted in response to the magnitude of the amplitude noise. The intensity noise may be reduced by the factor 1/(1+.alpha..sup.2) which may squeeze the intensity noise below normal quantum limits.

Abstract: A controllable semiconductor laser system including a plurality of semiconductor regions operated at unequal saturation photon densities to permit optical and/or electrical control of lasing in at least one resonant cavity formed therebetween. A pair of such regions may operate as a controllable laser at greater than 100% differential quantum efficiency.

Abstract: An improved cathodoluminescence light collection system for use in electron microscopes provides an optical fiber, the facet or aperture of which is positioned adjacent the sample. The cathodoluminescence light, collected by the optical fiber in this manner, may be used to provide spectrally resolved cathodoluminescence images of the sample as well as local cathodoluminescence spectra of the type available in prior art cathodoluminescence light collection systems, but without incurring the numerous disadvantages of such prior art light collection systems. The present invention is relatively inexpensive, far easier to maintain because it does not require use of a mirror and, it is more compact in size thereby making it compatible with the physical limitations of more electron microscopes.