Showing papers on "Single-mode optical fiber published in 1973"
TL;DR: In this paper, the authors investigated the origins of mode confinement in double-heterostructure GaAs injection lasers and established a distinction between two types of lasing mode guidance: (i) well-behaved, where a single mode substantially filled the entire active region, and (ii) filamentary, where the mode size is much smaller than the width of the active region and its location is random.
Abstract: We investigate the origins of mode confinement, parallel to the junction plane, of stripe‐geometry double‐heterostructure GaAs injection lasers. Based upon the kind of control of the mode extent by the stripe width, we establish a distinction between two types of lasing mode guidance; (i) well‐behaved, where a single mode substantially fills the entire active region, and (ii) filamentary, where the mode size is much smaller than the width of the active region and its location is random. For low‐order well‐behaved modes, it is shown, at least in principle, that gain alone (no refractive index effects are required) can explain not only the confinement but also the approximate waveguide dimensions for which leakage losses, connected with the penetration of the mode into the regions outside the active guide, become important. When only this postulated gain‐guiding prevails in the case of higher‐order modes, we find that their spatial character is markedly different from the Hermite‐Gaussian distributions which have been seen for GaAs lasers. The introduction of a positive incremental index, which may reasonably be associated with the gain and/or with a thermal mechanism, restores agreement with observation. If any incremental index within the active region is negative, then although there is a defocusing effect, confinement may still be maintained by the gain. In the case of filamentary lasing we analyze four focusing mechanisms; two are connected with local built‐in gain (loss) and refractive index variations, while two are current dependent and are related to the saturation of gain‐associated refractive index and the free carrier effect. While all four processes appear to be reasonable candidates for providing the necessary confinement in filamentary lasing, the latter two simultaneously violate a condition necessary for stability of a filament. We conclude that imperfections in lasers are likely to be related to filamentary lasing and that such behavior may not be intrinsic to such devices.
169 citations
TL;DR: In this paper, the authors presented a comprehensive theory of mode coupling in optical fibers with imperfections, and derived a general coupled wave theory based on the modes of the ideal fiber.
Abstract: This paper presents a comprehensive theory of mode coupling in optical fibers with imperfections. The paper begins with the derivation of a general coupled wave theory based on the modes of the ideal fiber. The general theory is applied to a simplified description of guided and radiation modes of the fiber that is valid for small core-cladding index differences. The simplified theory results in expressions for the coupling coefficients that are nearly as simple as those of the slab waveguide. As an example, the theory is applied to the calculation of radiation losses caused by pure core diameter changes and by elliptical deformations of the fiber core.
149 citations
TL;DR: In this paper, a new method of obtaining high power single frequency output is described, where pulses are built up from the single mode radiation in the cavity of a hybrid laser having both low pressure continuous and high pressure continuous, high pressure pulsed gain sections.
106 citations
01 Oct 1973
TL;DR: In this paper, the authors measured the refractive index profile and impulse response of three low-loss multimode optical fibers, each 1 km long, and found that pulse dispersion of about 1.5 ns or less was observed in two of the fibers.
Abstract: The refractive-index profile and impulse response of three low-loss multimode optical fibers have been measured. Pulse dispersion of about 1.5 ns or less was observed in two of the fibers, each 1 km long.
79 citations
TL;DR: Low-loss joints between singlemode optical fibers have been made without microscopic alignment, without fusing the tips, and without monitoring the transmitted power while the joints are assembled as discussed by the authors.
Abstract: Low-loss joints between single-mode optical fibers have been made without microscopic alignment, without fusing the tips, and without monitoring the transmitted power while the joints are assembled. The fibers are tightly held in an embossed groove; an index-matching liquid is added. Average power coupling efficiencies close to 90 percent in the red and to 85 percent in the infrared have been obtained. Mediocre end faces are acceptable. Realistic discrepancies between the fiber cladding diameters (slightly in excess of twice the core diameter) do not deteriorate the results.
50 citations
Patent•
15 Nov 1973TL;DR: In this article, a hemispherical lens is formed to focus and direct the wave into the fiber, which is then used to intercept the wave in the film and prevent it from propagating out of the film.
Abstract: There is disclosed an arrangement for coupling guided optical waves from thin-film waveguides to fiber waveguides, and vice versa. The thin film in the former type of guide is provided with an end region which is gradually tapered in thickness along the path of the wave to be guided therein to a cut-off value for the wave. This tapered region of the film causes the wave to propagate out of the film into the lower refractive index substrate of the guide along a small angle with respect to the film-substrate interface. Situated in the substrate slightly below the film-substrate interface is a cavity having a crosssectional shape and cross-sectional dimensions adapted for receiving an end of the fiber waveguide. By properly selecting the orientation and position of the cavity in the substrate, and of the fiber in the cavity, the fiber can be made to intercept the wave coupled out of the film. To insure efficient coupling of the wave into the fiber, the cavity is provided with a hemispherical end shape and is filled with a transparent material having a refractive index exceeding that of the substrate. A hemispherical lens is thereby formed which focuses and directs the wave into the fiber. Efficient coupling of the guided wave from the thin film to the fiber, or from the fiber to the thin film, is thus possible.
48 citations
TL;DR: In this article, the power of the trapped modes on a semi-infinite optical fiber illuminated by an incoherent source is determined, where all possible modes are excited, each with approximately the same power when V → ∞, V = 2πρ{n12−n22}1/2/λ, where ρ is the fiber radius, λ the wavelength of light in vacuum, and n1, n2 are the refractive indices of the fiber and its surround, respectively.
Abstract: The power of the trapped modes on a semi-infinite optical fiber illuminated by an incoherent source is determined. All possible modes are excited, each with approximately the same power when V → ∞, V=2πρ{n12−n22}1/2/λ, where ρ is the fiber radius, λ the wavelength of light in vacuum, and n1, n2 are the refractive indices of the fiber and its surround, respectively. A ray-optical interpretation is given for the summed power of the modes. For V = ∞, the power corresponds to that found from classical geometric optics, treating all rays as if they are meridional. This result is independent of the degree of coherence of the source. The per cent error of meridional ray optics is 100/V when V is large. The total power within the fiber is the combined power of the trapped modes and the radiation field. In the limit V = ∞, the total power within the fiber at any position z along its axis is that given by classical geometric optics, i.e., that found by tracing all rays, skew and meridional. At the point z = ∞ for arbitrary V, the total power is that due to the trapped modes only.
47 citations
TL;DR: The acceptance property of an optical fiber illuminated by coherent light is very simply found from meridional ray tracing, if the dimensionless quantity 2πρ{n12−n22}1/2/λ is much greater than unity.
Abstract: The amount of light power that is transmitted within a semi-infinite circular optical fiber when it is illuminated obliquely by a coherent beam of light is determined from an electromagnetic-theory analysis. The limit λ→0 is not classical geometric optics, i.e., not that found by tracing all rays along the fiber. Instead, the limit λ→0 corresponds to that of treating all rays as if they were meridional, i.e., as if they cross the fiber axis, ignoring rays skew to the axis. Thus, ray tracing is incorrect for fibers illuminated by coherent light. However, the acceptance property of an optical fiber illuminated by coherent light is very simply found from meridional ray tracing, if the dimensionless quantity 2πρ{n12−n22}1/2/λ is much greater than unity, where ρ is the fiber radius, λ the wavelength of light in vacuum, and n1, n2 the refractive indices of the fiber and its surround, respectively.
47 citations
TL;DR: In this paper, the effects of axial displacement and angular misalignment on the power coupled between single-mode optical fibers were investigated and the absolute accuracy with which fibers must be joined on-centers is reduced for fibers with relatively smaller core; the angular accuracy is increased.
Abstract: Analysis and computations made here, corroborated by experiment, determine the effects of axial displacement and angular misalignment on the power coupled between butt-joined, single-mode optical fibers. The absolute accuracy with which fibers must be joined on-centers is reduced for fibers with relatively smaller core; the angular accuracy is increased.
42 citations
TL;DR: In this article, surface corrugations with a period of 0.115 µm were ion-milled on GaAs dielectric waveguides and laser action was observed under optical pumping.
39 citations
TL;DR: In this article, the first spectroscopic application of the technique of detection of optical resonance using atomic beam deflection by light, is described, and a test has been performed on the hyperfine structure of the sodium resonance lines, and shows that the method allows a very high resolution.
TL;DR: In this paper, a flashlamp-pumped dye laser capable of single transverse and longitudinal mode operation is described, with a maximum untuned power output of 2 MW cm -2, TEM 00 mode.
Patent•
05 Apr 1973TL;DR: In this paper, a multimode optical wave transmission line comprising a plurality of single mode fibers is described, where the propagation constants of adjacent pairs of fibers are made to be different to minimize the delay dispersion.
Abstract: This application describes a multimode optical wave transmission line comprising a plurality of single mode fibers. To minimize the delay dispersion, the propagation constants of adjacent pairs of fibers are made to be different.
TL;DR: In this paper, a Michelson-type mode selector was used for single-mode operation of a flashlamp pumped dye laser with an output power of 1 kW with a linewidth of 0.05 pm.
Abstract: After efficient spectral narrowing with an interference filter and two succesive Fabry‐Perot etalons single‐mode operation of a flashlamp pumped dye laser has been achieved using a Michelson‐type mode selector as proposed by Fox and Smith. Typical output powers of 1 kW with a linewidth of 0.05 pm have been obtained.
Patent•
01 Jun 1973TL;DR: In this article, the material or wavelength dispersion limit on bandwidth in an optical communications system, perhaps utilizing a glass transmission line, is minimized by pulse sharpening, which is accomplished by first spreading the wavelength components within the pulse, for example, by use of a grating, by delaying long wavelength components relative to short wavelength components, and finally, by reconstituting a pulse from the now reordered wavelength components.
Abstract: The material or wavelength dispersion limit on bandwidth in an optical communications system, perhaps utilizing a glass transmission line, is minimized by pulse sharpening. Sharpening is accomplished by first spreading the wavelength components within the pulse, for example, by use of a grating; by delaying long wavelength components relative to short wavelength components, for example, by use of an echelon; and finally, by reconstituting a pulse from the now reordered wavelength components. Wavelength dispersion limits are most significant at this time where mode dispersion is minimized or eliminated by virtue of graded index lines or by use of single mode lines.
Patent•
14 Nov 1973TL;DR: In this paper, the presence or absence of a domain at a given point on the magnetic film is optically determined by a cylindrical magnetic domain apparatus in which one end of a single mode optical waveguide is disposed adjacent to magnetic film at the given point.
Abstract: A cylindrical magnetic domain apparatus in which the presence or absence of a domain at a given point on the magnetic film is optically determined. One end of a single mode optical waveguide is disposed adjacent to the magnetic film at the given point. A plane polarized light beam is radiated into the other end of the waveguide, and the HE11 mode, which is caused to propagate in the waveguide, preserves the linear polarization of the input light beam. Output means employing the Faraday effect is disposed adjacent to that side of the magnetic film opposite that at which the optical waveguide terminates. The output means receives light which radiates from the waveguide and passes through the magnetic film, and it provides an output signal that is indicative of the presence or absence of domains at the given point on the magnetic film.
01 Dec 1973
TL;DR: In this paper, a stripe geometry laser with a very small lateral current spreading and a transverse single-mode oscillation was proposed, with a near-field pattern as narrow as 3 µm.
Abstract: A new type of stripe-geometry laser is proposed. A very small lateral current spreading and a transverse single-mode oscillation are realized in this structure with a near-field pattern as narrow as 3 µm.
Patent•
19 Oct 1973
TL;DR: In this article, a p-n junction photodiode made of a graded bandgap semiconductor material is disclosed as a delay equalizing detector, where the gradient of the bandgap is made in such a manner that the different time delays of drifting charge carriers, generated by the absorption of different wavelengths at different depths in the graded band gap semiconductor, can be made to compensate for the time delays suffered by the optical energy at different wavelengths while propagating through the fiber.
Abstract: In optical fiber transmission, one of the causes of signal distortion (pulse broadening) stems from the fact that energy at different optical wavelengths travels at different velocities in the fiber material (material dispersion), and hence these wavelength components undergo different time delays while propagating through the fiber. In order to reduce this optical distortion, a p-n junction photodiode made of a graded bandgap semiconductor material is disclosed as a delay equalizing detector. The gradient of the bandgap is made in such a manner that the different time delays of drifting charge carriers, generated by the absorption of different wavelengths at different depths in the graded bandgap semiconductor, can be made to compensate for the time delays suffered by the optical energy at different wavelengths while propagating through the fiber.
TL;DR: In this paper, a high-resolution cw dye laser spectrometer is described, which incorporates pressure tuned intra-cavity etalons enabling the single mode output laser frequency to be tuned more than one nm in a continuous scan.
Patent•
11 May 1973
TL;DR: In this article, a plurality of hollow tubes of single-material optical fibers are closely packed together within an optical absorbing housing, and the single material neighborhood regions of tangency of mutually contacting pairs of tubes thereby form optical waveguides which support single mode optical transmission.
Abstract: A plurality of hollow tubes of single-material optical fibers are closely packed together within an optical absorbing housing. The single-material neighborhood regions of tangency of mutually contacting pairs of tubes thereby form optical waveguides which support single mode optical transmission.
TL;DR: In this paper, a hollow-cathode transverse discharge He-Cd ion laser showed single mode operation without using any selection, and a single mode investigation was performed on the same model.
Patent•
18 Sep 1973TL;DR: In this paper, a semiconductor charge carrier drift delay line is located in the path of the optical radiation emanating from the fiber, which is terminated by a charge carrier detector having an inherent gain.
Abstract: The propagation in an optical fiber of an incoherent optical signal pulse containing a moderate spread of optical wavelength carrier components, such as supplied to the optical fiber by a light emitting diode (LED) source, results in a broadening (distortion) of the optical output signal emerging from the fiber. This distortion is caused by the fact that different optical wavelengths propagate at different velocities through the fiber material, that is, by the dependence of refractive index upon wavelength (material dispersion); and also by the fact that different optical modes propagate at different velocities (mode dispersion). In order to compensate for such distortions, a semiconductor charge carrier drift delay line is located in the path of the optical radiation emanating from the fiber. Advantageously, this semiconductor delay line is depleted of bulk majority charge carriers by means of a reverse voltage bias and is terminated by a charge carrier detector having an inherent gain (such as an avalanche diode or a transistor). The delay line is arranged such that the time delays of different wavelengths or modes in the fiber are compensated by the different drift time delays of the charge carriers generated by the different wavelengths or modes absorbed at different locations in the semiconductor delay line. In the case of mode dispersion compensation, the s
TL;DR: In this article, the effect of carrier spectral width on the bandwidth of optical fiber transmission lines was analyzed and a simple generalized expression was deduced relating carrier bandspread and maximum permissible pulse rate.