Showing papers on "Fiber laser published in 1985"

Neodymium-doped silica single-mode fibre lasers

Abstract: We report the first CW operation of a neodymium-doped silica single-mode fibre laser pumped by a GaAIAs laser diode. A laser threshold of less than 1 mW has been obtained.

Theoretical analysis of optical fiber laser amplifiers and oscillators

Abstract: Using the formalism of mode overlap, a theoretical analysis of optically pumped fiber laser amplifiers and oscillators is developed. The concept of normalized overlap coefficients is introduced to account for the effects of the transverse structure of the interacting signal and pump modes on the device characteristics. Simple and accurate closed-form expressions are derived for the gain of fiber amplifiers and the threshold and energy conversion efficiency of fiber laser oscillators in terms of the fiber and laser material parameters and the pump and signal modes. When applied to step-index Nd:YAG fiber lasers, this study predicts optimum fundamental mode oscillation in fibers with a V number of 5-25 with submilliwatt thresholds and nearly quantum-limited conversion efficiencies.

Pulsed laser damage to optical fibers.

Abstract: This paper describes some observations of pulsed laser damage to optical fibers with emphasis on a damage mode characterized as a linear fracture along the outer core of a fiber. Damage threshold data are presented which illustrate the effects of the focusing lens, end-surface preparation, and type of fiber. An explanation based on fiber-beam misalignment is given and is illustrated by a simple experiment and ray trace.

Apparatus and method for performing laser material processing through a fiber optic

Abstract: Pulse laser energy in the near infrared and visible spectrum is passed through a single fiber optic at power levels required for material and metal processing. A neodymium-YAG laser used in pulsed mode is coupled to the end of a quartz fiber optic which transmits peak powers in the kilowatt range. In order to transmit higher amounts of average power, a prepared fiber end allows beam coupling through core-air and core-cladding zones. The beam at the output of the fiber optic is focused to achieve power densities capable of cutting, drilling, and welding of metals etc. The main advantage is greater flexibility of laser beam manipulation.

Analysis of the spectral linewidth of distributed feedback laser diodes

Abstract: The spectral linewidth of distributed feedback (DFB) laser diodes is theoretically studied. Numerical calculation shows that DFB lasers with long cavity lengths and large coupling coefficients have very narrow spectral linewidth less than 1 MHz, The effects of the phase shift and mirror facets on the spectral characteristics of DFB lasers are also analyzed, It is shown that the phase-shifter further narrows the spectral linewidth of DFB lasers. Its numerical result and physical meaning are also shown.

A Double Wavelength Laser Doppler System to Investigate Skin Microcirculation

Abstract: A new experimental laser Doppler setup has been designed to discriminate between total and superficial skin blood flow. This selectivity is based on the use of two wavelengths with different penetration depths into the skin. An argon ion and helium-neon laser are mounted on the same optical bench and are stabilized by an optical feedback loop. A single optical fiber directs the beams to the skin and collects the reflected light back to a photodetector, the signal of which is sampled and Fourier transformed to give a frequency power spectrum. Several models of light scattering by the skin are examined, and a single Lorentzian function is found to be the best fit for our experimental power spectra. Flow parameters have been thus measured for several in vitro and in vivo situations. In vitro calibration indicates that there is a constant ratio between the frequency responses at both wavelengths used. The decrease of this ratio encountered in in vivo measurements is attributed to different depths of investigated skin microcirculation according to the incoming wavelengths.

Low-loss dispersion-shifted single-mode fiber manufactured by the OVD process

Abstract: The development of a low-loss dispersion-shifted single-mode fiber with a segmented-core profile is reported. The combination of low dispersion in the 1550-nm window, 0.21-dB/km median attenuation at 1550 nm, excellent bend resistance ( \lambda_{c} = 1200 nm), and good splicing behavior make this fiber an economically viable alternative for long-haul high-data-rate operation utilizing multilongitudinal mode lasers. System experiments have demonstrated bit rates as high as 1.3 Gbit/s over 107 km and repeaterless spans of up to 233 km.

Single Crystal Fibers By The Laser-Heated Pedestal Growth Method

Abstract: The versatility of the laser-heated pedestal growth method for producing a wide range of compounds in single-crystal fiber form is discussed, along with some potential applications. Some preliminary results on the growth of single-domain LiNbO3 crystals, and crystals of BaF2 and CaF2, sapphire, and several laser materials are discussed.

Low-loss laser-to-fiber coupling with negligible optical feedback

Abstract: A novel lens design for the coupling of single-frequency lasers to monomode fibers achieves both high coupling efficiency (> 40 percent, best value 70 percent) and extremely low optical power feedback ( \sim 10^{-7} of the emitted power). The lens is formed out of a ∼ 1 mm length of a silica thread fused to the monomode fiber, with the open end of the silica thread modeled as an aspherical lens.

Laser nibbling of optical waveguides

Abstract: A fused silica glass optical fiber 10 is machined by a pulsed infrared laser beam 20 from a carbon dioxide laser 22 focussed by a germanium lens 24. The beam has a power density of about 70,000 watts per square centimeter at the focussed machining region b and is pulsed at about one pulse per second with a one-half second pulse duration. The fiber workpiece edge is gradually brought into the beam from the side to result in progressive flash evaporation.

Grating-fiber coupler as a high-resolution spectrometer.

Abstract: An in-line, single-mode fiber-optic spectrometer is described and analyzed. Its key element is a photoresist grating placed in the evanescent field near the core on a side-polished fiber. Fabrication and nearly diffraction-limited performance (resolution Deltalambda asymptotically equal to 1 nm) are reported, and means are proposed to increase the resolution by several orders of magnitude.

Fiber laser sensor

Abstract: A fiber laser sensor is comprised of two fiber lasers which are each optically coupled to a third fiber so that energy is exchanged between each of the laser fibers and the third fiber. The coupling is accomplished by arranging the laser fibers parallel to and on either side of a third fiber and properly spacing the three fibers to produce optical coupling along the length of the fibers. The central fiber ends are non-reflective so that light generated by one of the lasers and coupled to the central fiber is lost except for a small fraction of the energy transferred to the other laser. Accordingly, the structure operates with the least loss when the two lasers oscillate at a common frequency but 180° out-of-phase. The resonant cavities of the two fiber lasers are made non-identical by making the path length one cavity slightly longer than the other to produce Vernier tuning of the laser resonant frequency orders relative to each other with only one common resonant frequency. The device can be used as a sensor because the common laser output frequency is sensitive to changes in the optical path length of either or both of the laser cavities.

High-power 1.3-µm InGaAsP P-substrate buried crescent lasers

Abstract: High performance of newly developed InGaAsP P-substrate buried crescent (PBC) laser diodes is described. It is shown that the PBC laser has superior characteristics to the conventional buried crescent (BC) laser with n-InP substrate. The maximum output power of 140 mW under a CW condition is realized at room temperature. CW light output power of 10 mW up to 110°C is achieved. A maximum CW temperature of 135°C is obtained. Stable CW operations have been confirmed in 70°C 5-mW and 70°C 20-mW aging tests. The reason for the high performance is discussed in relation to the leakage current which flows through the current blocking layers.

A new confocal combination lens method for a laser-diode module using a single-mode fiber

Abstract: A new confocal combination lens method is proposed, which can overcome severe misalignment tolerances for an InGaAsP laser diode to single-mode fiber coupling. Lens 2 in the confocal two-lens method is divided into two lenses, that is, lenses 21 and 22. The optimal distance between lenses 1 and 21 is found to be shorter than that for a confocal condition. Lens 22 is attached to the input endface of the single-mode fiber, thus forming a virtual fiber. Using 0.06- and 0.18-pitch GRIN rod lenses as lenses 21 and 22, the lateral and axial misalignment tolerances for the virtual fiber are improved by three and nine times, respectively, in comparison with those for the single-mode fiber. High-coupling efficiency of -3.0 dB of the laser diode to the single-mode fiber can be easily obtained including Fresnel reflections.

Single-mode-fiber ring dye laser

Abstract: Pulsed dye-laser operation in a single-mode fiber is demonstrated by incorporating an evanescent field amplifier into an all-fiber ring resonator. Laser threshold is obtained with 60 mW of pump power. Characteristics of the evanescent fiber amplifier are investigated as functions of pump power and dye solution index.

4 Gb/s Transmission over 103 km of Optical Fiber Using a Novel Electronic Multiplexer/Demultiplexer

Abstract: We have conducted an experiment which demonstrates 4 Gb/s operation over 103 km of single-mode optical fiber. Previous transmission experiments have been limited to about 2 Gb/s [1,2,3], in part because this is the highest bit rate for which commercial error-rate measuring equipment is available. We have used a multiplexer and demultiplexer built with discrete GaAs FETs to generate a 4 Gb/s NRZ tat pattern from a 2 Gb/s pseudorandom sequence, and to recover 2 Gb/s for error-rate measurements from the 4 Gb/s receiver output. The 4 Gb/s pattern was used to directly modulate a 154 μm vapor phase transported buried heterostructure (VPTBH) distributed feedback laser [4].

Synchronously pumped fiber Raman gyroscope.

Abstract: A new optical gyroscope has been proposed that uses stimulated Raman scattering in a single-mode fiber. It is theoretically shown that highly sensitive detection of inertial rotation can be attained by using a synchronously pumped fiber Raman laser operating in the zero-chromatic-dispersion region of the fiber.

Simultaneous Wavelength Comparison of Lodine-Stabilized Lasers at 515 nm, 633 nm, and 640 nm

Abstract: The wavelengths of an Ar+ laser at 515 nm and of He-Ne lasers at 633 and 640 nm, all stabilized by saturated absorption in iodine-127, have been compared simultaneously by means of a servo-controlled Michelson interferometer. A new technique has been developed using a single polarization fiber for coupling the light to the interferometer and for examining the adjustment condition. This technique facilitates a comparatively simple and almost perfect optical adjustment. Relative uncertainties of less than 4 X 10-11 have been obtained for the comparison measurements.

Apparatus for measuring transmission characteristics of an optical fiber

Abstract: An apparatus for measuring transmission characteristics of a short optical fiber comprises a streak tube having a photoelectron-emitting surface for receiving through a connector light pulses transmitted simultaneously through a reference optical fiber and an optical fiber under test. The light pulses are generated by a laser and cause the streak tube to generate an optical output signal indicating time-wise changes in the luminance of the pulses transmitted through each of the optical fibers such that differences in light transmission characteristics between the reference optical fiber and the optical fiber under test may be determined.

Hot-wire height gauge using a laser and photodiodes

Abstract: A simple method for measuring the height of a hot-wire anemometer from the wall surface is described. The system consists of a laser and photodiodes joined by optical glass fibres. The position of the wire is indicated when it interrupts the laser beam, which is emitted through the fibre along the wall surface and is observed by the photodiode. The measurement accuracy depends upon the glass fibre and is within 0.01 mm in the present system.

Method of optical pumping of erbium-doped laser material and apparatus therefor

Abstract: A method of optical pumping of an erbium laser and an apparatus therefor with an erbium laser medium, a light source for side-pumping the erbium laser medium, a neodymium laser medium for emitting a laser beam upon optical pumping by the light source, and an optical system for directing the laser beam from the neodymium laser medium to the erbium laser medium for side-pumping the erbium laser medium Thus the erbium laser medium is side-pumped by the light source and also end-pumped by the laser beam emitted from the neodymium laser medium side-pumped at the same time by the light source in the same lamp house Therefore the erbium laser can be optically pumped with high efficiency and offer a low threshold value

Alteration Of The Transmission Characteristics Of Fused Silica Optical Fibers By Pulsed Ultraviolet Radiation

Abstract: Several all-silica fibers advertises as transmitting ultraviolet radiation were tested with a rare-gas-fluoride excimer laser Test wavelengths were 193nm (ArF*), 248nm (KrF*), and 351nm (XeF*) Pulse duration was 15ns, repetition rates were from 1 to 25 Hz, and in-put fluences ranged from a few millijoules per square centimeter up to the surface damage threshold Under some conditions the fiber changed its transmission as it was irradiated The effects of wavelength, fluence and previous history of the fiber have been characterized Macroscopic inhomogeneities, such as inclusions in the fiber, contribute to the transient effects along with molecular processes in the drawn fused silica

Propagation of chirped semiconductor laser pulses in monomode fibers.

Abstract: A basic result for the dynamic behavior of semiconductor lasers is combined with the propagation properties of optical fibers. The frequency chirp observed when a semiconductor laser is modulated gives an enhanced time–bandwidth product. Pulse compression due to fiber dispersion is shown to be directly related to the laser properties.

Alignment-tolerant optical-fiber tips for laser transmitters

Abstract: A procedure is given for designing the tip of a single-mode fiber so that the coupling efficiency with a single-mode semiconductor laser is as large as possible under the constraint that the tolerance for offset misalignment has any prescribed value.

Pulsed Fiber Holography: A New Technique For Hologram Interferometry

Abstract: The advantage of the rapid development of fiber optics for communication purposes is that now holographic investigations can be made much more flexible if fibers are used. The use of optical fibers in connection with cw lasers has already found interferometric applications within metrology. The possibility of using a pulsed laser with fibers will open important new applications for hologram interferometry within science, industry, and medicine. A fiber coupling technique for pulsed lasers is described, as well as suitable equipment for pulsed or cw laser holographic investigations. Possible applications also are discussed.

Stimulated Brillouin scattering mirror in the form of a multimode optical fiber in a four-pass neodymium phosphate glass laser amplifier

Abstract: A multimode optical fiber was used as a wavefront-reversing mirror in a four-pass laser amplifier utilizing neodymium phosphate glass.

Multi-mode, optical fiber laser coupler

Abstract: An apparatus for efficiently coupling laser light to multi-mode fiber uses a solid state laser focussed by a spherical microlens onto a partially reflecting mirror. The mirror is formed by polishing the ends of two fibers at 45 degrees and assembling them such that the ends abut and are substantially parallel. High efficiency is obtained by using the spherical lens to direct most of the laser light into the acceptance cone of the fiber and by orienting the laser such that the electric vector of the light is perpendicular to the fiber axis.

Single-pass mode-locked or Q-switched pump operation of D2 gas-in-glass fiber Raman lasers operating at 1.56-microm wavelength.

Abstract: Single-pass operation of a D2 gas-in-glass fiber Raman laser operating at 1.56-μm wavelength, pumped by a Nd:YAG laser operating either Q-switched or mode-locked has been demonstrated. The group velocities in the single-mode host fiber at the pump wavelength (1.06 μm) and the Raman-shifted wavelength (1.56 μm) were matched, thereby providing long interaction lengths and concomitant efficient conversion of pump light to 1.56-μm radiation.