Showing papers on "Fiber Bragg grating published in 1978"

Theory of Bragg fiber

Abstract: The possibility of using Bragg reflection in a cylindrical fiber to obtain lossless confined propagation in a core with a lower refractive index than that of the cladding medium is proposed and analyzed.

Narrow-band Bragg reflectors in optical fibers.

Abstract: The formation and characterization of narrow-band-waveguide reflection filters in Ge-doped silica optical fibers is described. The filters can have complex response profiles and are tunable in frequency by mechanical strain.

Fiber-optic acoustic sensor

Abstract: An optical fiber acoustical sensor for detecting sound waves in a fluid mum. An optical fiber coil through which a light beam is transmitted is placed in a fluid medium. A sound wave propagating through the fluid medium and incident on the optical fiber coil changes the index of refraction and the length of the optical fiber at the area of incidence. These changes cause a shift in the transmitted light which is detectable to denote the presence of the sound wave.

Improved coupled mode analysis of corrugated waveguides and lasers

Abstract: Corrugated waveguides and lasers in resonant and non-resonant situations are analyzed by an improved coupled mode theory based on a set of the coupled mode equations for guided modes and radiation continuum. The distributed feedback (DFB) coefficient and the radiation loss coefficient are given in closed forms. The formulation can be applicable to arbitrarily shaped gratings and multilayer waveguide structures. The accuracy of the theory is examined by comparing it with Tamir's exact calculation for a nonresonant situation and also with Streifer's one for a DFB structure. Reasonable accuracy is obtained by the proper choice of the unperturbed waveguide parameter. The dependence of the two coefficients on the grating depth, the grating period, the guide layer thickness, and the refractive index difference between core and cladding layers is obtained for all Bragg orders up to the fourth, and for four typical grating shapes, namely, for rectangular, sinusoidal, symmetric triangular, and sawtooth gratings. Both the threshold gain of DFB lasers utilizing higher order Bragg reflection and the output coupling efficiency of grating beam couplers are also calculated for these parameters. A new multilayer structure for controlling the radiation loss is proposed and analyzed. This structure is suitable for the suppression of the radiation loss in DBR reflectors as well as for the improvement of the output coupling efficiency in grating beam couplers.

Holographic interference lithography for integrated optics

Abstract: In this paper, some of our recent work in the use of holographic interference lithography and various material removal techniques to corrugate thin-film optical waveguides are reviewed. The specific applications of these periodic thin-film devices in the distributed feedback and distributed Bragg reflector semiconductor laser, and as output grating couplers, are described. Recent results in the use and fabrication of chirped and curved-line gratings are also summarized.

Optical fiber acoustical sensors

Abstract: This invention relates to an optical fiber acoustical sensor for sensing acoustic vibrations and in combination with an incoherent or coherent source of light such as a LED or a laser and a photo detector to determine the frequency and amplitude of the sound pressure variations. The invention consists of an element of optical fiber without cladding surrounded by a liquid or plastic potting material permeable to sound pressure and having an index of refraction slightly less than the fiber. The intensity of a light beam transmitted by means of fiber optic waveguides, single or multi-mode, from a source of light through the sensor to a photo detector varies with the variation of sound pressure to which the sensor is subjected. If the sensor is in water, the transmitted light intensity varies with the acoustical pressure in the water because the changes in liquid or plastic index of refraction changes with the sound pressure. Generally the fiber sensor is in an element preferably surrounded by a fluid which has an index of refraction close to but less than that of the fiber, and the coil thickness is small relative to the wavelength of the sound to be detected.

Analysis of two-dimensional waveguides with misaligned or curved gratings

Abstract: Periodic corrugated waveguides with wave confinement in both transverse dimensions are analyzed. The description includes the cases of grating misalignment (tilt) and curvature; for a tilt angle θ, the resonant wavelengths vary as (\cos \theta)^{-1} . Coefficients for intramode coupling (identical contradirectional modes) and hybrid (intermode) coupling are calculated as functions of θ. Numerical results for a GaAlAs waveguide, of the type employed in distributed Bragg reflector (DBR) lasers, are included.

Tuning of the emission frequency of a dye laser with a Bragg mirror in the form of a cholesteric liquid crystal

Abstract: Tuning and narrowing of the emission spectrum of a dye laser were achieved for the first time when a cholesteric liquid crystal was used as a selective Bragg reflector. The average emission frequency of this laser was a function of the spectral position of the Bragg reflection maximum of the oriented liquid crystal layer. The position of the reflection maximum was varied by altering the temperature.

Two-way single fiber optical communication system

Abstract: An injection laser diode is at one end of an optical fiber to direct modulated optical radiation into the fiber. At the other end of the fiber is a detector, such as a semiconductor photodetector, for the modulated radiation. Between the other end of the optical fiber and the detector is a reflecting shutter which is adapted to periodically reflect some of the radiation, at a lower frequency rate, back along the optical fiber to the injection laser. The radiation reflected back into the injection laser causes a variation in the characteristics of the laser so that the laser operates as a detector for the reflected radiation.

Single mode grating coupling between thin-film and fiber optical waveguides

Abstract: Optical directional coupling by means of a periodic perturbation is described between a clad, single mode, cylindrical fiber, and a thin-film planar waveguide. Codirectional coupling was achieved to a clad fiber, with 0.4 percent efficiency; allowing for the geometric mismatch, this is effectively 30 percent coupling. The fiber guided mode is accessed by reducing the fiber diameter by heating and pulling. Mode phase matching is achieved with a periodic grating sputter etched into the film. Unwanted grating induced interactions are minimized by restricting the guide parameters or by modifying the coupling mechanism. A perturbation analysis is used to calculate coupling coefficients and the design procedure for an optimum structure is explained. Measurements on grating couplers are described and the film/fiber codirectional coupling is shown to be effected by the grating.

Light circuit element

Abstract: PURPOSE:To enable light of a number of wavelengths propagating in an optical fiber to be branched by disposing a phase diffraction grating which gives diffraction effect only to the light of a specific wavelength between lenses. CONSTITUTION:Since the phase diffraction grating 11 which has been disposed between square-law refractive index distribution type lenses 8, 10 of a 1/4 period length satisfies Bragg's diffraction conditions with respect to the light of a wavelength lambda1 entering from an optical fiber 1, the light of the wavelength L1 is diffracted at equal incident and exit angles with respect to the central axis 9 of the lenses and then enters the square-law refractive index distribution type lens 10 of a 1/4 period length and therefore it turns out that the light has passed the lens of a 1/2 period length as it passes through the lenses 8 and 10, thus the light containing the wavelengths lambda1, lambda2 being propagated in the optical fiber 1 may be respectively separated and propagated in the optical fibers 2, 3 which are provided on the exit face of the positions symmetrical to the central axis 9 of the lenses.

Measuring method for transmission characteristic of optical fiber

Abstract: PURPOSE:To obtain a transmission characteristic measuring method without short measuring optical filber omission by connecting a measuring optical fiber, which can be replaced with a short-measuring optical fiber, to one terminal of a measured optical fiber by using a connector. CONSTITUTION:Light from light source 1 is inputted to one terminal of measuring optical fiber 4 after being focused by excitation lens 2. Measuring optical fiber 4 transmits this light to its other terminal, which is connected to connector 5. Of measured optical fiber OF of Lkm in length, one terminal is connected to measuring optical fiber 4 via connector 5, and the other is to photoelectric wattmeter 3. Through the above-mentioned optical connections, light from light source 1 is detected by photoelectric wattmeter 3 to measure photo power, light-intensity information. Before or after this measurement, measuring optical fiber 4 is connnected to photoelectric wattmeter 3 to measure photo power, light-intensity information, in the same way as above. Then, transmission characteristics of measured optical fiber OF are found on the basis of measured values of photo power.

Aperiodic structures in optics and integrated optics and the transverse Bragg reflector laser

Abstract: The first part of this work describes the uses of aperiodic structures in optics and integrated optics. In particular, devices are designed, fabricated, tested and analyzed which make use of a chirped grating corrugation on the surface of a dielectric waveguide. These structures can be used as input-output couplers, multiplexers and demultiplexers, and broad band filters. Next, a theoretical analysis is made of the effects of a random statistical variation in the thicknesses of layers in a dielectric mirror on its reflectivity properties. Unlike the intentional aperiodicity introduced in the chirped gratings, the aperiodicity in the Bragg reflector mirrors is unintentional and is present to some extent in all devices made. The analysis involved in studying these problems relies heavily on the coupled mode formalism. The results are compared with computer experiments, as well as tests of actual mirrors. The second part of this work describes a novel method for confining light in the transverse direction in an injection laser. These so-called transverse Bragg reflector lasers confine light normal to the junction plane in the active region, through reflection from an adjacent layered medium. Thus, in principle, it is possible to guide light in a dielectric layer whose index is lower than that of the surrounding material. The design, theory and testing of these diode lasers are discussed.

Mode Conversion in Oblique Bragg Gratings for Integrated Optics

Abstract: High density component integration in guided optics needs reflecting devices. A holographic grating on the guide acting under Bragg conditions deviate the guided light. This reflexinn causes polarization changes so that a T.E. incident wave will give some T.M. reflected wave. Devices of this type have been experimentally studied with special attention to mode conversion efficacity. Theorical study is also reported in a two dimensional calculation. Vectorial normalization conditions in the unperturbed case are derived from Maxwell's equations. Coupled mode treatment of the perturbed propagation is given explaining main experimental results.