Showing papers on "Fiber laser published in 1981"
TL;DR: In this paper, the feasibility of coherent optical fiber transmission systems was studied from the view point of device and system consideration and expected performance, in which laser coherence is utilized to carry information.
Abstract: The feasibility of coherent optical fiber transmission systems, in which laser coherence is utilized to carry information, are studied from the view point of device and system consideration and expected performance. Modulation scheme comparison among optical ASK, FSK, and PSK, transmitter and receiver configurations, single-polarization transmission through fibers, problems in providing stable local oscillator waves, and wide-band photodetectors are discussed together with alternative technologies to realize high performance systems. A study on digital system impairments caused by FM quantum noise of laser oscillators, interferometric FM-AM conversion noise, IF frequency fluctuation, and optical fiber transmission turbulence show the feasibility of the systems. Repeater spacing is estimated by considering the transmitting and receiving signal levels, optical fiber loss, and fiber transmission capacity. Repeater spacing of 240 km is feasible by 400 Mbit/s PSK homodyne-detection system and 220 km by 400 Mbit/s FSK heterodyne-discrimination detection system. The regenerative repeater spacing can be expanded further by employing intermediate repeaters with direct optical signal amplification. Based on the performance of semiconductor laser amplifiers, such as traveling wave type, Fabry-Perot cavity type, and injection locked devices, it is estimated that regenerative repeater spacing of more than 104km is feasible with 50 km intermediate repeater spacing. These systems will find application in transoceanic optical fiber cable transmission as well as terrestrial long distance transmission systems.
384 citations
TL;DR: In this article, a new coupling method of a laser diode to a single-mode fiber is described, which consists of a spherical ruby lens and a graded index (GRIN) rod lens positioned under a confocal condition.
Abstract: A new coupling method of a laser diode to a single-mode fiber is described. It consists of a spherical ruby lens and a graded index (GRIN) rod lens positioned under a confocal condition. A high coupling efficiency of more than 40 percent has been easily obtained for InGaAsP laser diodes. Alignment sensitivities of the proposed coupling circuit have been studied both experimentally and theoretically. The dependence of the coupling efficiency on misalignments has been found to be in agreement with the theoretical consideration, and it has been apparent that the stringent alignment tolerances required for conventional coupling methods have been overcome. A laser diode module using the proposed circuit was also fabricated with high coupling efficiency into the single-mode fiber, and good reproducibility and performance have been obtained.
117 citations
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TL;DR: In this article, the cancellation of the Doppler shift in standing-wave two-photon absorption has been used for high-resolution spectroscopy of laser light by atoms and molecules.
Abstract: During the past decade, electronic two-photon transitions [1] have been observed and largely utilized in two-photon absorption of laser light by atoms and molecules. In particular, cancellation of the Doppler shift in standing-wave two-photon absorption has turned into a powerful tool for high-resolution spectroscopy [2].
75 citations
TL;DR: By stabilizing the fiber cavity, this work achieved stable single-frequency Brillouin-laser output with a linewidth determined primarily by the 100-kHz modulation used in the feedback system.
Abstract: The detailed behavior of the cw stimulated Brillouin fiber laser has been studied by using a narrow-linewidth cw pump argon laser at 5145 A and an 83-m fiber ring cavity. By stabilizing the fiber cavity, we achieved stable single-frequency Brillouin-laser output with a linewidth determined primarily by the 100-kHz modulation used in the feedback system. Lasing threshold for the 4.5-μm-core fiber used was observed at a pump power of 77 mW, and the maximum Brillouin output was 13 mW for a pump of 320 mW. The Brillouin gain medium was shown to exhibit homogeneouslike behavior.
55 citations
TL;DR: A practical laser Doppler velocimeter with optical fibers in the whole system was developed; vibration amplitude down to 1.0 microm p-p can be measured at a frequency of 120 Hz with high accuracy.
Abstract: A practical laser Doppler velocimeter with optical fibers in the whole system was developed. The novel optical probe designed for this LDV is constructed of a graded-index rod lens attached to the end of an optical fiber. Since the laser beam from the probe is well collimated, the velocity accuracy and sensitivity are significantly improved. Mechanical vibration measurements were also carried out with this LDV; vibration amplitude down to 1.0 μm p-p can be measured at a frequency of 120 Hz with high accuracy.
50 citations
TL;DR: In this article, the authors found that the intensity noise due to reflected waves from the singlemode fibers was about 10 dB larger than those of the multimode fibers due to the large coupling coefficient to a specific mode between the laser and the coupled optical fibers.
Abstract: The intensity noises due to reflected waves from the single-mode fibers were found to be about 10 dB larger than those of the multimode fibers due to the large coupling coefficient to a specific mode between the laser and the coupled optical fibers. The noise enhancement of about 20 dB was observed in the both types of fibers when the direct modulation was applied for the laser diode with reflected waves, and the lower cutoff modulation frequency related to noise enhancement was found to be about 10 kHz. It was found that the noise of the narrow stripe laser is about 10 dB smaller than that of the wide stripe laser, and it was estimated that the optical isolator with a reverse isolation loss of 30 dB provides noise reduction of 40 dB.
33 citations
TL;DR: In this article, the present status of mode-stabilized semiconductor injection lasers emitting in the 0.8-0.9 and 1.1-1.6 \mu m wavelength regions are described.
Abstract: The present status of mode-stabilized semiconductor injection lasers emitting in the 0.8-0.9 and 1.1-1.6 \mu m wavelength regions are described. The double-heterostructure GaAlAs/GaAs and InGaAsP/ InP crystals have been developed. Transverse-mode stabilization by means of gain guiding or index guiding is a key issue to realized high linearity, low noise operation. The mode-stabilized laser structures as well as the corresponding lasing characteristics are shown in detail. Longitudinal mode control is possible by grating feedback, but the fabrication technology is still immature. Reliability of the mode-stabilized lasers is also mentioned.
27 citations
TL;DR: In this paper, a laser light injection technique was studied to realize a semiconductor laser transmitter oscillating in a 1.55 μm single-longitudinal mode, and no dispersion degradation was observed in the error rate characteristics after transmitting through 44.3 km single-mode fibers at 100 Mbits/s.
Abstract: A laser light injection technique was studied to realize a semiconductor laser transmitter oscillating in a 1.55 μm single-longitudinal mode. When -15 dBm optical power was injected into the directly modulated laser, no dispersion degradation was observed in the error rate characteristics after transmitting through 44.3 km single-mode fibers at 100 Mbits/s. Effective gain coefficient g-\alpha , measured by the light injection method, was 45 cm-1near threshold. As this gain was sufficiently saturated at the -15 dBm injection power, undesired longitudinal modes in the modulated laser were suppressed.
26 citations
TL;DR: In this article, the authors describe the experimental investigation of stimulated Raman scattering obtained from a multimode fiber and obtain 10 orders of stimulated Stokes scattering of wavelengths in the 546-702 nm region.
Abstract: This paper describes the experimental investigation of stimulated Raman scattering obtained from a multimode fiber. 10 orders of stimulated Stokes scattering of wavelengths in the 546–702 nm region were obtained from a 480m multimode, low-loss, graded-index quartz fiber pumped by a 532 nm frequency-doubled YAG-Nd laser beam with a pulse duration of 7 ns, output power of 0.7 MW and repetition rates of 5 and 10 pps.
26 citations
TL;DR: This device has demonstrated a marked reduction in blood loss during surgery of organs where bleeding is normally a major problem, such as the debridement of third-degree burns.
Abstract: This paper presents the physical theory and engineering development of a new hemostatic scalpel, the photocoagulating dielectric waveguide scalpel. (laser blade). This device has demonstrated a marked reduction in blood loss during surgery of organs where bleeding is normally a major problem, such as the debridement of third-degree burns. The scalpel utilizes an argon laser for optical power (25 W) and a fiber-optic waveguide to flexibly transport the laser radiation to a fused silica scalpel blade. The blade is a dielectric waveguide which carries the laser radiation to a tapered cutting edge which is used for the mechanical incision of tissue and provides the means by which the laser radiation couples (tapered waveguide coupling) into the surrounding tissue for photocoagulation. The optical characteristics of the blade are analyzed and experimentally verified.
25 citations
TL;DR: In this paper, a small signal gain of 430 at 600 nm has been measured in a long fiber with a 2 cm long fiber optic amplifier, where the evanescent field interacted with the excited Rhodamine 6 G solution surrounding the fiber.
Abstract: A laser signal propagating in an optical fiber is amplified by the evanescent field interacting with the excited Rhodamine 6 G solution surrounding the fiber. A small signal gain of 430 at 600 nm has been measured in a long fiber with a 2 cm long fiber optic amplifier.
Patent•
17 Aug 1981TL;DR: In this article, a laser diode is coupled to a transmission fiber via a coupling path, where the coupling path includes a monomode fiber or the series arrangement of a monomerode fiber and a pluraity of multimode fiber lengths, the crosssection of which increases in size.
Abstract: Optical transmission system comprising a laser diode which is coupled to a transmission fiber via a coupling path. The coupling path includes a monomode fiber or the series arrangement of a monomode fiber and a pluraity of multimode fiber lengths, the cross-section of which, see from the laser, increase in size. As a result thereof the modal noise and the reflection noise in the optical system in drastically reduced.
TL;DR: Polycrystalline KRS-5 optical fibers were experimentally demonstrated to have high-power transmission capabilities for a cw CO(2) laser beam and to remain free from damage at an incoming laser intensity up to 30 kW/cm(2).
Abstract: Polycrystalline KRS-5 optical fibers were experimentally demonstrated to have high-power transmission capabilities for a cw CO2 laser beam. A typical sample of fibers provided by extrusion, 1 mm in diameter and 0.87 m in length, carried a laser power of 68 W to its output end and was found to remain free from damage at an incoming laser intensity up to 30 kW/cm2.
TL;DR: In this article, the Raman spectra of hollow quartz fibers were compared quantitatively to conventional Raman spectrum using identical laser, spectrometer, detector, and scan speed, and they found the fiber signal to be enhanced by a factor of 250/m of fiber in good agreement with calculations based on geometrical optics.
Abstract: Raman spectra of samples contained in hollow quartz fibers are compared quantitatively to conventional Raman spectra using identical laser, spectrometer, detector, and scan speed. We find the fiber signal to be enhanced by a factor of 250/m of fiber, in good agreement with calculations based on geometrical optics. A fiber spectrum of 2 mol% trans-stilbene in benzene is good enough to allow essentially perfect solvent subtraction.
TL;DR: In this paper, double heterostructures of AlGaAasb quaternary alloys on (100)-GaSb substrates were grown by LPE technique and were studied as laser devices.
Abstract: Double heterostructures of AlGaAasb quaternary alloys on (100)-GaSb substrates were grown by LPE technique and were studied as laser devices. The active layer thickness was in the range 0.3-1.5 μm. Threshold current density for 300 K was as low as 15-2.5 kA/cm
2
in the wavelength range of 1.7-1.8 μm. Shorter wavelength lasers showed a higher threshold. At 77 K CW lasing was observed in the wavelength range up to 1.41 μm. Optical confinement calculations in DH lasers have been supported by observations of the angular distribution of the laser emission, depending on the cladding layer composition and the active layer composition and thickness. The vertical beam spreading angle passed the maximum of 50° at a thickness of the active layer of about 0.8 μm. Temperature dependence of the threshold current has been measured between 100 and 300 K and the exponent temperature constant T
0
was found to be close to 60-80 K in typical diodes. "Kinky" behavior of the light output power versus current was observed in the stripe-geometry lasers, as well as in the broad-area lasers.
TL;DR: Experimental results of nonlinear optical image processing by a saturable Fabry-Perot filter are described and the spatial resolution is found to be more than 10 lines/mm over a 30-mm-diameter aperture.
Abstract: Experimental results of nonlinear optical image processing by a saturable Fabry–Perot filter are described. Fulgide, a photochromic compound, in toluene is used as a saturable absorber for the green light of an Ar-ion laser. Image thresholding using a steep increase of transmission with a critical power density of 700 mW/cm2 is demonstrated. The spatial resolution is found to be more than 10 lines/mm over a 30-mm-diameter aperture.
TL;DR: Bit-error-rate measurement values of <10(-9) prove the feasibility of optical fiber transmission at 5 Gbit/sec.
Abstract: A Gbit/sec optical fiber communication experiment was performed. The maximum speed was 3 Gbit/sec with a BH laser and 5 Gbits/sec with a TJS laser. A 500-m single-mode fiber was used, and the power was coupled by mounting the laser butt-end to the fiber, giving a minimum loss of 10 dB. The receiver employed a Si-avalanche photodiode with an impulse-response width of 210 psec (FWHM) and a 10-Gbit/sec and gate built from GaAs MESFETs. Bit-error-rate measurement values of <10−9 prove the feasibility of optical fiber transmission at 5 Gbit/sec.
TL;DR: An optical system for easy introduction of phase-difference bias to optimize the sensitivity of the fiber-optic laser gyro is proposed and the rotation detection experiment has been performed.
Abstract: An optical system for easy introduction of phase-difference bias to optimize the sensitivity of the fiber-optic laser gyro is proposed. The theory of using a laser diode has been considered, and the rotation detection experiment has been performed. The experimental setup consists of a 300-m long single-mode optical fiber, individual optical components, and a laser diode stabilized by a thermal controller and an optical isolator. Short-time resolution of the rotation rate better than 0.87 mrad/sec has been achieved with good linearity.
TL;DR: In this article, the power-delivery characteristics of GdF3-BaF2-ZrF4-AlF3 glass fibers were investigated using an HF laser emitting at 2.6-3.0 µm wavelengths.
Abstract: The 2.7 µm-band power-delivery characteristics of GdF3-BaF2-ZrF4-AlF3 glass fibers were investigated using an HF laser emitting at 2.6–3.0 µm wavelengths. Typical delivered power, without fiber damage, exceeded 0.6 W for a 300 µm core diameter and 4 meter long fiber, corresponding to a transmission efficiency of about 30%. The power-transmission capability in the 2.7 µm band makes the fluoride glass fiber very attractive as a flexible waveguide for laser printers and other applications.
TL;DR: The Pharos II laser system has recently been upgraded for ablative acceleration studies at the Naval Research Laboratory (NRL) as discussed by the authors, and the design was optimized to produce uniform illumination of millimeter-size targets at intensities between 1013 and 1014W/cm2 in a multinanosecond pulse.
Abstract: The Pharos II laser system has recently been upgraded for ablative acceleration studies at the Naval Research Laboratory (NRL). The design was optimized to produce uniform illumination of millimeter-size targets at intensities between 1013and 1014W/cm2in a multinanosecond pulse. Key elements of the design were the use of high-gain phosphate laser glass in disk amplifiers, and optimal relaying and beam shaping in the neat field. These design elements are discussed, as well as the overall performance of the completed system.
TL;DR: A fiber Raman laser generating a subnanosecond pulse in the extremely broad spectral region between 0.6 and 1.8 microm has been developed using an ultra-low-loss single-mode fiber as the generating medium, pumped by a high-power mode-locked and Q-switched Nd:YAG laser at lambda = 1.06 microm.
Abstract: A fiber Raman laser generating a subnanosecond pulse in the extremely broad spectral region between 0.6 and 1.8 μm has been developed using an ultra-low-loss single-mode fiber as the generating medium, pumped by a high-power mode-locked and Q-switched Nd:YAG laser at λ = 1.06 μm. The fiber length dependence of the Raman emission is investigated by varying the generating fiber length from several meters to ∼1 km. As a result, pulses with 3-dB widths <0.4 nsec are obtained in the 1.0–1.7-μm spectral region by using an ∼200-m long generating fiber with a pump peak power of 0.4 kW. Timing jitter occurring in the displayed pulse train on an oscilloscope is reduced to ±0.02 nsec with the newly constructed delay system.
TL;DR: A variation of the time delay multiplexing technique where more than one time delay tap is assigned to a single sensor device to enable one to transmit a digital representation of the measured parameter is reported.
Abstract: A technique for passive multiplexing has been previously described that functions in the manner of an optical radar system. By injecting a short duration light pulse into a bus fiber and spacing sensor taps at discrete locations along the bus, a pulse reflected from each sensor location can be made to produce a sequence of time resolved pulses at the receiver end of the fiber. Simple time division demultiplexing techniques then suffice to separate the time delayed pulses returned from each sensor. By periodically injecting light pulses into the fiber, selecting the pulse train returned from a given sensor, and filtering the resultant signal to remove the pulse repetition frequency, parameters such as pressure, temperature, and displacement may be monitored by a sensor designed to modulate the intensity of the incident light in accordance with ambient conditions. Prior work addresses primarily the construction and multiplexing of analog sensors, specifically for optical hydrophones, for which case small changes in the intensity of the returned signal are to be detected. Here we report a variation of the time delay multiplexing technique where more than one time delay tap is assigned to a single sensor device to enable one to transmit a digital representation of the measured parameter. A digital signal is of great interest both because of the ease of handling digital data and because a digital system generally requires a far smaller SNR. The net result is that a practical digital time delay multiplexed system can be constructed and operated with very high multiplexing ratios. Conversely, the relaxation in optical power requirements for a digital system implies that a smaller number of sensors may be multiplexed using only reliable low power LEDs in place of lasers. Figure 1 shows one example of a digital fiber-optic angle position sensor as part of a system that uses time delay multiplexing. Light pulses are injected into a main fiber bus by an LED or pulsed laser source. A directional tap is placed at a preselected point along the bus fiber to extract a small portion of the optical pulse, and the light from the tap is sent to a star coupler to create a number of equal intensity components. Each component is transmitted via a fiber coil of
01 Jan 1981
TL;DR: In this paper, fiber optic laser anemometer systems capable of measurements in two-phase bubbly flows have been developed These instruments m have great potential for use in the many twophase flow research areas associated with nuclear reactors and other power generating systems Multimode graded-index optical fibers were used to transmit both the illuminating light from the laser to the point of measurement, and the scattered light to the photodetector.
Abstract: Fiber optic laser anemometer systems capable of measurements in two-phase bubbly flows have been developed These instruments m have great potential for use in the many two-phase flow research areas associated with nuclear reactors and other power generating systems Multimode graded-index optical fibers were used to transmit both the illuminating light from the laser to the point of measurement,and the scattered light to the photodetector The use of such optical fibers allowed miniaturization of the anemometer and remote measurements from the laser and photodetector The two optical geometries developed in this work were the prism-fiber optic Doppler anemometer and the Dot-fiber optic Doppler anemometer Single phase axial velocity and turbulence intensity distributions measured with these anemometers showed Q good agreement with emperical power law profiles, the classical data of Laufer and data taken with a conventional LDA in the same flow The anemometers were also used to make axial velocity and turbulence intensity measurements in two-phase flows of varying quality The results indicate that when the anemometers are used in conjunction with the described data acquisition techniques, measurements of the individual phases in two-phase air
TL;DR: In this paper, a direct method of observing the wavelength versus time of modulated single-mode GaAlAs lasers is described using a grating spectrometer and an avalanche photodiode and achieves resolutions of 0.01 A and 1 ns.
Abstract: A direct method of observing the wavelength versus time of modulated single-mode GaAlAs lasers is described. The method uses a grating spectrometer and an avalanche photodiode and achieves resolutions of 0.01 A and 1 ns. Although the laser consists of a multi-layer heterostructure, a simple cylindrical thermal model is in good agreement with the experimental results.
01 Jan 1981
TL;DR: In this article, high-speed data transmission at average power levels exceeding 20 mW (50% duty cycle) of coupled light in graded index fiber was demonstrated for AM systems.
Abstract: Experimental results on digital and analog modulation experiments with high power CDH-LOC laser diodes are reported. High-speed data transmission at average power levels exceeding 20 mW (50% duty cycle) of coupled light in graded index fiber was achieved. Enhanced signal-to-noise ratio (approaching 30 dB) for AM systems is demonstrated.
TL;DR: In this article, the amplitude and frequency of the signal fluctuation at the output end of a multimode fiber have been investigated and a method to suppress the amplitude fluctuation has been proposed for transmission characteristics measurement on long fibers.
Abstract: Theoretical investigation has been made on fluctuation in detected signal at the end of a multimode fiber. It has been predicted that the fluctuation is caused by oscillation frequency fluctuation of a laser diode in association with interference, taking place at the detector surface, among nonorthogonal axial Components of field vectors for different modes. The prediction has been confirmed using a two-mode fiber and multimode graded-index fibers, by measuring amplitude and frequency of the signal fluctuation at the output end of the fiber. A method to suppress the amplitude fluctuation has been proposed for transmission characteristics measurement on long fibers.
TL;DR: In this article, a high-power CW TE CO 2 laser using graphite anode structure and a novel Mo wire cathode was described, and a uniform discharge for laser excitation was obtained.
Abstract: A high-power CW TE CO 2 laser using a new graphite anode structure and a novel Mo wire cathode is described. A uniform discharge for laser excitation is obtained. The device produces a CW output of 6 kW.
TL;DR: In this article, the authors reported the operation of optically pumped 12-μm laser in NH 3 using peak pumping powers as low as 2 W. These low pumping powers represent a 1-2 order-of-magnitude improvement over previously published threshold values.
Abstract: We report the operation of optically pumped 12 μm lasers in NH 3 using peak pumping powers as low as 2 W. These low pumping powers represent a 1-2 order-of-magnitude improvement over previously published threshold values. Measurements of the lasing offset frequency clearly demonstrate that a two-photon Raman process is responsible for optical gain at 12 μm. In light of our results, we discuss the feasibility of an optically pumped CW 12 μm laser.