Showing papers on "Mode scrambler published in 1990"

Bi-domain two-mode single crystal fiber devices

Abstract: A mode converter comprises an a-axis LiNbO3 optical fiber exhibiting a ferroelectric bi-domain structure. The fiber is subject to an electrical field that induces a +π/2 phase retardation in one domain of the fiber and a -π/2 phase retardation in the other domain. A light signal launched in the fundamental mode of the fiber is converted into a light signal propagating in the second order mode. When the electrical field is selected so that the phase retardations are not multiples of π/2, the mode conversion is partial and the LiNbO3 fiber can operate as an optical switch or as an amplitude modulator. The mode converter can also be operated as a second harmonic generator. The fiber is heated to a phase matching temperature so that a signal launched in the fundamental mode of the fiber and at a frequency ω is converted to the second order mode at a frequency 2ω. The LiNbO3 fiber can also simultaneously operate as an optical switch and as a second harmonic generator. Other non-linear interactions are possible such as sum or difference frequency generation or parametric generation. The various embodiments of the present invention are reciprocal.

The mechanism of mode selection for an external cavity laser

Abstract: The process of mode hopping between external cavity modes of a laser diode with optical feedback is described by analogy with noise driven transitions of a particle between potential valleys. The model explains why the dominant mode is the mode with the lowest linewidth and not the mode with the lowest carrier density. It also gives a simple analytic expression for the rate of mode hopping. The expression is shown to predict the results of computer simulations to a good approximation. >

Polarization scrambler for polarization-sensitive optical devices

Abstract: A polarization scrambler comprising a multi-mode fiber spirally or preferably toroidally wrapped about a cylinder or toroid. The multi-mode fiber receives an optical signal from a long single-mode fiber. The optical output of the scrambler has an equal distribution of the two polarization states. Therefore, it can be passed through a polarization-sensitive filter or other optical device. The invention allows a low-cost receiver in a wavelength-division multiplexing communications system.

Noninvasive switchable acousto-optic taps for optical fiber

Abstract: Two novel tap designs are demonstrated based on phase-matched coupling from the fundamental mode of a fiber to a higher-order core-guided or cladding-guided mode through the acoustooptic effect. The acoustic waves are coupled to the fiber using a Hertzian (deformed surface-to-surface) contact with a grooved transducer substrate. The first tap consists of a two-mode fiber coupler in conjunction with a microbend tap. The coupler converts approximately 5% of the fundamental mode power to the second-order mode. At the microbend tap, the higher-order mode is preferentially radiated from the fiber. The second tap uses a similar mode-coupling mechanism to convert a fraction of the fundamental mode power into a cladding-guided mode in a single-mode fiber. >

Fiber optic mode conditioner

Abstract: A fiber optic mode conditioner for obtaining an equilibrium light distribution in a multimode fiber optic link under test. Light is supplied to the link through a gap between two successive fiber optic segments, followed by a high-curvature region created by wrapping the second fiber optic segment around a mandrel. The gap functions as a mode filter, stripping off all but the lowest modes, while the curved region acts as a mode scrambler redistributing the light energy into the intermediate modes.

Fabrication of optical components utilizing a laser

Abstract: A method for fabricating optical components in the cladding of an optical fiber bus by the utilization of a laser. An excimer laser fabricates either an optical coupler opening or an optical mode scrambler by ablatively removing the cladding from the optical core of an optical fiber bus without damaging the optical core. Either coupler housing or a mode scrambler housing is attached to the optical fiber bus where the coupler or mode scrambler is to be fabricated. The coupler housing is used to position the laser, secure and align a coupler fiber, and provide cavities for junction and cladding repair materials. The mode scrambler housing serves a similar purpose.

Bandwidth Limiters For Single Mode Fiber Communication Systems

Abstract: Various techniques for restricting the bandwidth of a single mode fiber are discussed. The limitations of a fiber optic delay line bandwidth limiter are addressed and several alternatives proposed.

Interferometric Measurements Of Birefringence In Single Mode Fibers And Devices

Abstract: A simple method for interferometric measurements of chromatic and polarization mode dispersion os single mode fibres and devices is presented. Accuracy of the method and resolution limits are discussed.

Waveguide type optical circuit element

Abstract: A waveguide type optical circuit element having a directional coupler for converting light intensity between two waveguides, which is used as a polarity-independent optical switch or a variable optical divider for optical fiber communications and the like. The two waveguides (2), (3) have a coupling section length which is in a TE mode about three times a complete coupling length of the TE mode, and in a TM mode about one time a complete coupling length of the TM mode. Electrodes (4), (5) comprise three-part electrodes of different lengths which act as reverse Δβ electrodes for alternately reversing a direction of an electric field. This construction promotes the light-confinement effect of the waveguides, reduces the drive voltage necessary for carrying out an optical switching operation, and realizes optimal element characteristics in accordance with a ratio of variations in the propagation coefficient in the TE mode and TM mode of the directional coupler manufactured.