Showing papers on "Fiber Bragg grating published in 1987"

Dispersion cancellation using linearly chirped Bragg grating filters in optical waveguides.

Abstract: The use of a linearly chirped Bragg grating filter for dispersion cancellation in an optical-fiber link is discussed. Numerical and theoretical calculations are made, which show that, with the proper taper function, the filter can have a high reflectivity and a quasi-constant nonzero dispersion, proportional to the inverse of the chirp. The filter can compress dispersion-broadened pulses by factors of 2-5 or more, if many filters are cascaded. Its compactness and efficiency would make it suitable for on-line implementation.

Over 720 Ghz (5. 8nm) frequency tuning by a 1.5 μm DBR laser with phase and Bragg wavelength control regions

Abstract: A 15 μm distributed Bragg reflector (DBR) laser with phase and Bragg wavelength control regions was newly developed Over 720 GHz (58 nm) continuous frequency tuning with 2mW light output were achieved for the first time

Optical fibre transmission systems

Abstract: A device for producing an optical delay in an optical signal having variable optical frequency, the optical delay varying with the optical frequency, comprises a chirped Bragg reflector formed in an optical fiber and a directional coupler for separating the reflected signal from the input signal. One application of the device is for chromatic dispersion equalization. Various methods of manufacturing the chirped Bragg reflector are described.

Photorefractivity in GeO2‐doped silica fibers

Abstract: Photorefractivity has been observed in several GeO2‐doped fibers. The effect is manifested by formation of a grating in the fiber core introduced by laser radiation in the green part of the spectrum. The grating is a distributed Bragg reflector which selectively reflects light at the writing wavelength. Reflections of up to 50% in a 15 cm length of fiber have been observed. The grating persists for at least five days after being written.

Hybrid distributed bragg reflector laser

Abstract: A mechanism for achieving single frequency output in a semiconductor laser diode is disclosed. In accordance with the invention, a conventional laser diode having an anti-reflection coating on its output facet is coupled to a single mode fiber output pigtail having an anti-reflection coating on its input facet. The anti-reflection coatings suppress Fabry-Perot type feedback which would normally be effective for a large number of wavelengths. The fiber includes a built-in distributed Bragg reflector grating, which grating is located just beyond the output fiber input facet. The grating supplies feedback that is effective only over a narrow wavelength band approximating the wavelength spacing between the actual longitudinal modes of the structure so that the laser produces only a single frequency output.

Fiber Optic Temperature And Strain Sensors

Abstract: Twin-core, polarimetric and in-fiber Bragg grating temperature and strain sensors for point and distributed measurements are reviewed. New applications to the in-situ monitoring of polymer composites are reported including techniques for measuring stress waves, resolving principal stresses and determining flexural strain variations.

Subpicosecond fiber laser

Abstract: A fiber laser for producing subpicosecond pulses is formed by placing a laser fiber in a resonant cavity, in either a linear or closed loop configuration. The laser fiber is formed of two different types of fibers joined in series, a gain fiber which contains the laser gain medium followed by a pulse shaping fiber which uses the phenomenon of solution pulse shaping to shorten the pulses. An initially formed pulse recirculates many times in the resonator; on each pass the pulse is both amplified and shortened until steady state is reached. The zero dispersion wavelength of the pulse shaping fiber is chosen to be slightly less than the laser wavelength. The fiber is pumped by a continuous source, particularly CW laser diodes. The initial pulse can be formed by a self starting technique produced by selecting the proper length of the laser fiber, or else a mode locker/acousto-optic shutter can be placed in the cavity.

Optical fiber sensor

Abstract: In an optical fiber sensor, the fiber has a sensitive zone which cooperates with a retroreflecting surface through the agency of an optical couplant. The function of the retroreflecting surface is to return into the optical fiber all light losses which escape from the fiber in the sensitive zone.

Tunable single-mode fiber reflective grating filter

Abstract: A single-mode fiber tunable reflective filter is demonstrated by translating a fan-shaped grating structure through the evanescent field of a side-polished fiber. Filter linewidths of about 1 nm were measured over tuning ranges in excess of 65 nm. Reflectivities as high as 88 percent were observed. Using the fiber filter as a feedback element, a multimode semiconductor laser was observed to oscillate in a single mode which could be discretely turned over a wavelength range of 26 nm.

Narrow-linewidth fiber laser operating at 1.55 μm

Abstract: We report the fabrication and operation of an Er3+-doped silica single-mode fiber laser operating at 1.55 µm and using a distributed fiber grating to provide feedback. The output bandwidth was measured as 0.04 nm, significantly narrower than the conventional cavity design. The laser had a threshold of 13 mW and a slope efficiency of 5%.

Line narrowing and spectral hole burning in single-mode Nd(3+)-fiber lasers.

Abstract: Line narrowing in the output spectrum of a Nd-doped silica-fiber laser with spectrally flat reflectors is interpreted to indicate a substantial homogeneous contribution to the 1.09-μm fluorescent linewidth. By using a fiber Bragg reflector, frequency-stable operation with 100-GHz bandwidth is obtained, dominated by power broadening and spectral hole burning.

Low loss Bragg reflectors on SiO 2 -Si 3 N 4 -SiO 2 rib waveguides

Abstract: The added waveguide attenuation loss associated with Bragg reflector formation is measured. The added scattering loss due to the roughness of the Bragg grating is found to be only 0.2 ± 0.1 dB/cm for a Bragg reflector with a 15-A stop band. In addition to this background loss, attenuation resonances on the high energy side of the Bragg resonance are found. These are due to the contradirectional coupling of the fundamental waveguide mode into continuum modes of the Si3N4 core layer and into the modes associated with the thick SiO2 cladding layer. The coupling wavelengths of these resonances are in good agreement with theory.

Fiber Optic Pulsed Laser Delivery For Remote Measurements

Abstract: The results of a research program on the delivery of high-peak-power laser light via fiber optics are presented. We discuss the influence of the host medium and the optical signals on the choice of fiber materials, complemented by a consideration of the measurement environment's effects on the quality of the data. We pay close attention to the choice of input/output beam/fiber coupling optics, nonlinear processes in the core, measurement system noise, and baseline drifts. Useful discussions of pulsed laser damage to optical fibers and data for optimization of a given fiber optic laser beam delivery system are given. As an example, details are given of the optical and instrumentational aspects of a particular fiber optic system developed for remote sensing of pressures and temperatures of UF6 gas in an operating advanced gas centrifuge.

Lens Ended Fiber-Fiber Connections For Power Laser Applications

Abstract: Bulb-ended fiber to flat-ended fiber connections and bulb-ended fiber to bulb-ended fiber connections have been tested with large diameter core optical fibers in different filling conditions and different arrangements.The curves of coupling efficiency versus the longitudinal and transverse misalignments show that these kinds of connection can be useful in medium or high power laser application.

Improved optical fiber temperature sensor

Abstract: A temperature measuring device comprises an optical temperature probe (20) and a control module (21). Thermal emission from a recess (28a) in the tip end portion (23) of an optical fiber (22) is transmitted to the remote end of the fiber for detection by the control module. The recess provides an improved sensor capability with regard to maintaining constant emissivity and rapid response time. The recess is suitable for both single crystal optical fiber, and optical fiber with a core-and-cladding construction.

32 Channel Acousto-Optic Bragg Cell For Optical Computing

Abstract: A 32 channel acousto-optical Bragg cell has been developed and evaluated for optical computing applications. This device was designed based on a computer model and was verified in an optical computing system. The Bragg Cell has 1000 resolvable spots per channel, diffraction efficiency of 40%/watt and -0d13 channel to channel isolation. The design and evaluation of this device allow for the prediction of a higher performance multi channel Bragg cell.

Process for producing a grating on an optical fiber

Abstract: A method for imparting a diffraction grating into the cladding layer and core layer of small diameter optical fibers consisting of (a) etching a section of an optical fiber to reduce the thickness of the cladding layer of the optical fiber, (b) coating the etched portion of the fiber with a photoresist, exposing the photoresist to produce the diffraction grating pattern using on-axis interferometry using a laser source (d) dissolving the non-exposed photoresist and (e) etching the diffraction grating pattern into the cladding layer and/or core of the optical fiber

Optical Fiber Powered Pressure Sensor

Abstract: In the system described a pressure sensor and its'associated electronics are optically powered by a 20 mw laser and a photovoltaic cell via an optical fiber. The sensor is periodically interrogated and sends the measures obtained back to the central unit using an LED and a second fiber. The results obtained as well as the expected evolution will be described.

GaAs/GaAlAs RIB waveguide grating filters for λ = 1.5μm

Abstract: First-order Bragg grating filters have been realised in GaAs/GaAlAs rib waveguides for operation at λ 1.5μm. Singlemode devices with rib widths of 2 to 5 μm and incorporating a 2.5 mm length of 225 nm period grating have been evaluated using a tunable T1:KCl colour-centre laser. Rejection ratios of 95% to 39% and 3dB bandwidths of 3.5 A to 7.9 A have been measured.

Advances In Distributed FODAR (Fiber Optic Detection And Ranging)

Abstract: This paper gives an overview on distributed fiber-optic sensors systems (DFOSS), and describes recent advances in the technology. Distributed fiber-optic sensors can use optical radar techniques to access many sensors located along the fiber. Such sensors can be said to employ Fiber Optic Detection and Ranging (FODAR) techniques, similar to those employed in free-space radio frequency and optical radar systems.

Measurement of effective index and dispersion in an index-guided surface-emitting distributed Bragg reflector laser

Abstract: The far-field pattern of a multimode surface-emitting AlGaAs distributed Bragg reflector laser was spectrally resolved with respect to emission angle. A simple analysis of the angular dependence of the far-field spectrum yields the waveguide effective index and the dispersion of the effective index.

Optical fiber modulator

Abstract: A method of modulating light in a optical fiber is disclosed. Light is launched into a multimode fiber in a restricted group of fiber modes. Disturbances placed in the fiber modulates the light being sent therethrough. The modulated light is received by a detector and may be readily interpreted. This method is especially useful in locations where electronic components may not be used.

Loss-Compensation Of Intensity-Modulating Fiber-Optic Sensors

Abstract: This report describes a new type of intensity-modulating fiber-optic sensor which has high immunity to the effects of variations in the losses of the fiber-link. A variable-splitting-ratio transducer is used to differentially modulate the intensities of the light which it transmits and reflects. Using a four-fiber optical link, light is impinged onto the transducer from either direction, and, in each case, the transmitted and reflected signals are measured. These four signals are then processed to remove the effects of the fiber and connector losses. Loss-compensated sensors of angular position and displacement are described, and their outputs are shown to be highly stable despite considerable variations in the transmissivities of the fiber-link components.

Optical fiber multipoint measuring device with time multiplexing

Abstract: Twenty temperature sensors follow one another along a measurement fiber. Each successively reflects a small fraction of the energy of an interrogation light pulse running along said fiber, with the value of the fraction being indicative of temperature. To do this, each sensor is constitutred by a gap between two successive lengths (F2, F3) of an optical fiber, said gap being filled with a transparent glue (36) whose refractive index varies as a fuction of temperature. The interrogation pulse is returned solely by the optical surface constituted by the end face (38) of the upstream length (F2) of the fiber.

Improved Measurement Techniques of Bridgewire Heating Caused by Induced Electromagnetic Radiation

Abstract: A method is proposed for measuring temperatures at low energy levels o f a bridgewire in an electroexplosive device (EED). This passive method utilizes thermal energy transmitted by an infrared-optical fiber, and the temperatures in question are caused by induced electromagnetic energy that is mainly in the microwatt ranges. Signal processing techniques are used to enhance the estimate of temperature caused by the induced energy. The proposed method also minimizes the effects of both coherent background noise and noise due to temperature variations along the length of the infrared-fiber. encountered with this technique is a slow system response time reported as approximately 70 ms. There is a possibility that thermal characteristics could be altered due to the method of sensing temperature. This system is still under study. This paper proposes a new method of measuring the induced currents in die EED's bridgewire. The method makes use of infrared optical fiber which reduces the uncertainties associated with the use of thermocouples to detect induced electromagnetic energy in the EED. The method reduces coherent noise in sensing bridgewire currents, and it also eliminates any appreciable thermal loading on the bridgewire. The response time of this experimental system is approximately 10 ms, and it can be lowered if required. The outline of the paper is as follows, the overall system is presented and discussed, the design criteria are discussed; and various system parameters are shown.

On/Off Fiber Optic Sensors Network Designed For An Industrial Use

Abstract: As we have already mentionned in the past, OTDR is a very interesting tool to monitor several ON/OFF sensors multiplexed along a single fiber. Indeed, Time Domain Multiplexing allows to easily monitor the time position of optical pulses reflected into a fiber line by optical microswitches or by any optical device whose reflection coefficient depends on a physical parameter (temperature, pressure, and son on). Moreover, such a technique allows to use very well known components such as pulsed laser diodes, couplers, avalanche photodiode and particularly multimode fiber whose commercial availability and reliability are now well established.

Optical fiber raman soliton laser

Abstract: PURPOSE:To obtain high output light soliton in a specific range which is the lowest loss band of silica optical fiber by adequately combining the pumping source and the optical fiber. CONSTITUTION:With combination of an optical fiber 25 where P2O5 is doped to the core and a YAG laser 21, shift of wavelength of Stokes light can be set large. Therefore, the Stokes light of 1.5mum band ca be obtained with the direct pumping source of the YAG laser 21. Accordingly, a pumping source of large output can be used and the soliton output, several times larger than that of the color center laser, can be realized. Moreover, since the erbium laser 21 provides the oscillation wavelength of about 1.54mum and an output almost equal to that of YAG laser. With combination of the erbium laser 21 and GeO2 doped quartz core of pure quartz core fiber, the Stokes light can be obtained in the vicinity of 1.65mum. The silica optical fiber shows sufficiently low loss even in the wavelength of 1.65mum and therefore it can sufficiently be put into the practical use.

A Scanning Laser Microscope For Muscle Fiber Studies

Abstract: A scanning laser microscope (SLM) has been constructed for use in imaging single living skeletal muscle fibers The muscle fiber is kept alive and stimulated in a temperature-controlled chamber through which a nutrient solution flows The fiber is attached at each end to force and displacement transducers which are in turn connected to electromagnetic (voice-coil type) linear motors These motors scan the fiber in one axis (x-axis) and are also used to stretch and shorten the fiber during mechanical experiments Each of the x-axis linear motors is in turn mounted on a micro-stepping motor which provides for rotation (r-axis) and twist of the muscle fiber A laser beam is focused at a location within the fiber by high numerical aperture confocal optics which form one path of a mach-Zehnder interferometer The position of the muscle fiber with respect to the laser beam may be further manipulated by two additional electromagnetic linear motors (y-and z-axis) to permit 3-linear and 1-rotary axis scanning The scanning pattern is controlled by a Micro-VAX-II computer which is also used to sample the output of the photo-detector and the force and displacement transducers A complex 3-D image is acquired and processed (eg SLM optical transfer function identification and deconvolution) on the VAX using NEXUS-plus a language for linear and nonlinear signal and system analysis

Optical fiber for fiber laser

Abstract: PURPOSE:To obtain a laser beam which is not mixed with a pumping light from a waveguide core by forming an optical fiber having two or more cores, and doping at least one of the cores with fluorescent substance. CONSTITUTION:An optical fiber 11 for a fiber laser has two cores 12, 13, one 12 of which is of an active core doped with a fluorescent substance 14, such as Nd, Er, Ho, etc., and the other 13 of which is of a normal core (waveguide). When a pumping light l1 from a light emitting element 15 is input to the core 12, a laser oscillation occurs in the core 13 by waveguide coupling, and a laser light l2 not mixed with the light l1 is output from the half mirror 18 of one end.

Fiber Raman laser pumped by a Nd:YAG laser

Abstract: We have pumped a fiber Raman laser with a cw mode-locked Nd:YAG laser operating at 1319 nm and generated pulses as short as 160 fsec using soliton pulse shaping in the fiber. We have also constructed a completely integrated oscillator loop using a fiber optic coupler and fusion splicing.