Showing papers on "Equilibrium mode distribution published in 1988"

Apparatus using two-mode optical waveguide with non-circular core

Abstract: An apparatus utilizes a two-mode optical waveguide with a non-circular core to provide stable spatial intensity patterns in both propagation modes for light propagating therein. The light has a wavelength, and the non-circular core has cross-sectional dimensions selected such that (1) the waveguide propagates light at that wavelength in a fundamental mode and a higher order mode, and (2) substantially all of the light in the higher order mode propagates in only a single, stable intensity pattern. Embodiments of the invention include, for example, modal couplers, frequency shifters, mode selectors and interferometers. One of the interferometer embodiments may be used as a strain gauge.

Local normal mode analysis of guided mode interactions with waveguide gratings

Abstract: The reflection of a guided mode obliquely incident to a periodic, shallow, surface corrugation, waveguide grating is analyzed using the local normal mode expansion of coupled-mode theory. The coupling coefficients which give the strength of the TE-TE, TE-TM, TM-TE, and TM-TM mode interactions are evaluated as a function of incidence angle. The results are compared to the coupling coefficients obtained using a number of other analytical techniques. >

Fiber optic inter-mode coupling single-sideband frequency shifter

Abstract: A birefringent single-mode optical fiber (200) which propagates light into orthogonal polarization modes is subjected to a series of second order traveling flexural waves for propagation within the fiber (200). An acoustic wave generator (202) applies a periodic lateral squeezing force to the fiber (200), thus causing a second order flexural wave to propagate within the fiber (200). The wavelength of the second order flexural wave is selected to cause light propagating in one polarization mode to be coupled to the orthogonal polarization mode. The optical signal in the second orthogonal propagation mode has a frequency which is equal to either the sum of or the difference between the frequency of the optical signal in the first propagation mode and the frequency of the traveling flexural wave. The frequency of the optical signal in the second orthogonal propagation mode is shifted upward of or downward from the frequency of the optical signal in the first propagation mode as determined by the direction of propagation of the first optical signal with respect to the direction of propagation of the traveling flexural wave, and as also determined by whether the phase propagation velocity of the optical signal in the first propagation mode is greater or less than the propagation velocity of the optical signal in the second propagation mode. The centripetal couple of squeezing forces is preferably oriented at an angle of substantially 45° with respect to the axes of birefringence of the fiber (200).

Dynamic coupler using two-mode optical waveguides

Abstract: An optical mode coupling apparatus includes an optical waveguide in which an optical signal at a signal wavelength propagates in a first spatial propagation mode and a second spatial propagation mode of the waveguide. The optical signal propagating in the waveguide has a beat length. The coupling apparatus includes a source of perturbational light signal at a perturbational wavelength that propagates in the waveguide in the first spatial propagation mode. The perturbational signal has a sufficient intensity distribution in the waveguide that it causes a perturbation of the effective refractive index of the first spatial propagation mode of the waveguide in accordance with the optical Kerr effect. The perturbation of the effective refractive index of the first spatial propagation mode of the optical waveguide causes a change in the differential phase delay in the optical signal propagating in the first and second spatial propagation modes. The change in the differential phase delay is detected as a change in the intensity distribution between two lobes of the optical intensity distribution pattern of an output signal. The perturbational light signal can be selectively enabled and disabled to selectively change the intensity distribution in the two lobes of the optical intensity distribution pattern.

Method of measuring polarization and birefringence in single-mode optical fibers

Abstract: A constant force perpendicular to the fiber axis is applied to the fiber so as to cause a power coupling from the fundamental mode, which is guided, to a secondary mode which is irradiated, and the intensity of the scattered radiation associated with that secondary mode is measured. Such intensity depends on the local state of polarization. By dispacing the force application point step by step along the fiber axis and by measuring for each point the intensity of the scattered radiation, beat length is obtained as the distance between two consecutive points where the scattered radiation has the same intensity.

Calculation And Measurement Of Mode Transition Matrices For Differential Mode Attenuation And Differential Mode Delay Characterization Of Optical Fibers

Abstract: A method is described to characterize multimode fiber-optic devices in terms of differential mode attenuation (DMA), differential mode delay (DMD), and mode coupling. It is important to describe these complex properties with only a few data. This is accomplished by the mode transition matrix method, in which each fiber optic component is characterized by one or more 3X3 matrices. Certain trade-offs between simplicity and precision are unavoidable, but it has already been demonstrated that the matrix method yields results that are precise enough to calculate system responses properly. Here, mode or pulse transition matrices are defined for the DMD characterization of fibers. Measurements have been carried out.

Mode Partition Noise In Nearly Single Mode Lasers With Multiple Side Modes

Abstract: The power penalty estimation for fiber optic communication due to mode partition noise in nearly single mode lasers is discussed. Nearly single mode lasers are modeled here as those with a single dominant mode and n side modes with significant strength. The dropout rate of each side mode obeys exponential distribution. The combined distribution of the dropout rate for n side modes is derived here. This distribution is combined with the statistically independent Gaussian receiver noise in estimating error probability and hence the power penalty. Calculations show that to ensure a 10 -12 error rate, the ratio of the main mode to the side modes must be greater than 57:1 for one side mode and greater than 67:1 for two side modes.