Propagation and optical interaction of guided acoustic waves in two-mode optical fibers

Engan, Helge E.; Kim, B.Y.; Blake, J.; Shaw, H. J.

doi:10.1109/50.4020

Cited by 165 publications

(90 citation statements)

References 11 publications

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“…Figure 3 shows the acoustic wavelength versus the acoustic frequency for a cylindrical silica-glass rod. 5 The acoustic wavelength has been normalized by the fiber radius (R), and the frequency has been normalized by the factor ct/R, ct being the shear-wave velocity in the bulk material. (ct = 3.76 km/sec for fused silica.)…”

mentioning

confidence: 99%

Analysis of intermodal coupling in a two-mode fiber with periodic microbends

et al. 1987

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Simple expressions for the coupling between the LP 0 1 and LP 11 modes of a two-mode optical fiber with a periodic microbending structure are developed. Implementation of the microbend structure using a flexural acoustic wave is described. The dependences of the acoustic frequency and power requirements on the pertinent fiber parameters are presented.Work has been done recently on periodic coupling between the LP 01 and LP11 modes in an optical fiber. A theory for computing the coupling between various modes of a multimode fiber at a bending point has been developed' and shows that the LP'i and LP 1 1 modes are strongly coupled at a bend. A static device that couples energy between the modes using periodic microbends, spaced by a beat length between the modes, has been demonstrated. Also, an all-fiber single-sideband frequently shifter that couples energy between the modes by a traveling flexural acoustic wave has been demonstrated. 3 To optimize the performance of these and other potential two-mode fiber devices, it is desirable to develop simple expressions for the coupling between the LP 01 and LP 11 modes at a microbend and to relate them to the pertinent fiber parameters. In this Letter the coupling coefficient is calculated, and the result is compared with experimental results. Implementation of a periodic coupler using a flexural acoustic wave that travels down the fiber is then discussed. Attention is given here to the acoustic frequency and power requirements as functions of the pertinent fiber parameters. Figure 1 shows the geometry of an optical fiber with periodic microbends. 0 (assumed small) is the bend angle of a single microbend, a is the total deflection of the fiber, and LB is the beat length between the LP 01 and the LP 11 modes. For the analysis, the fiber is taken to be step index with core and cladding refractive indices nc and ncl, respectively, and nc1 -nc = n, so that the modes can be assumed to be weakly guided.The LP modes in a straight fiber can be accurately used as approximations to the true mutually orthogonal eigenmodes. A microbend in the fiber will perturb the modes, causing energy to be transferred between them efficiently. Optical energy traveling on the inside of the bend experiences less phase delay than the light traveling on the outside of the bend. Therefore the spatial phase profile of the light is changed as it rounds the bend. If a pure LP 01 mode is incident upon the bend from the left, light will emerge from the right of the bend with the same field intensity versus radius but with a distorted phase front. This distorted LP 01 mode can be decomposed into a true LP 01 mode along with higher-order guided modes and radiation modes.In the case of a two-mode fiber, light will couple to one spatial orientation of the LP 11 mode and to unwanted radiation modes.The amplitude coupling coefficient (K) between the LPo 1 and the LP 1 , modes can be calculated by computing the overlap integral (loveriap) of the LP 01 mode with its phase distortion and the LP 11 mode:where EO(r) i...

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confidence: 99%

Analysis of intermodal coupling in a two-mode fiber with periodic microbends

et al. 1987

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“…They were chosen because of their uniform diameter. Figure 1 shows the calculated velocity dispersion relation for the lowest order flexural mode, FlI of the thin gold wire; the lower solid and dotted lines for FlI mode are calculated phase velocities based on exact [11] and approximated (Equation 6) dispersion formulae respectively. The upper solid line represents the exact group velocity.…”

Section: Velocity Dispersion Measurementsmentioning

confidence: 99%

Thin rod flexural acoustic wave devices: a sensor candidate

Jen¹,

Yu²,

Wang³

et al. 1991

NDT & E International

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“…The duration of the pulse was t a = 2.7 μs, corresponding to a frequency spectrum of width Δ f ≈ 1/t a = 0.37 MHz. Using a laser probing technique [3], an acoustic group velocity of v g = 3516 m/s was measured at 7.4 MHz. This gives a pulse length l p = v g t a = 9.5 mm.…”

Section: Acoustic Birefringencementioning

confidence: 99%

“…These devices rely on coupling between two optical modes, induced by a traveling acoustic wave acting as a long period grating [2,3]. By tailoring fiber parameters, it is possible to make broadband and narrow-band filters [4][5][6][7][8][9][10].…”

Section: Introductionmentioning

confidence: 99%

Acoustooptic characterization of a birefringent two-mode photonic crystal fiber

Haakestad¹,

Engan²

2006

Opt. Express

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Abstract:The effect of axial variations in acoustooptic phase-mismatch coefficient of a two-mode birefringent photonic crystal fiber (PCF) is studied experimentally using two different methods. The first method is to determine axial non-uniformities directly from the transmission spectrum, while the second method is to use acoustic pulses. Both methods are seen to be in good agreement. It is found that axial non-uniformities increase the coupling bandwidth significantly as compared to an axially uniform fiber. The effect of acoustic birefringence is also considered.

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Propagation and optical interaction of guided acoustic waves in two-mode optical fibers

Cited by 165 publications

References 11 publications

Analysis of intermodal coupling in a two-mode fiber with periodic microbends

Analysis of intermodal coupling in a two-mode fiber with periodic microbends

Thin rod flexural acoustic wave devices: a sensor candidate

Acoustooptic characterization of a birefringent two-mode photonic crystal fiber

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