Showing papers on "Equilibrium mode distribution published in 1993"

Beam quality factor of the LP01 mode of the step-index fiber

Abstract: The beam quality factor M2Q of the LP01 mode of the step-index fiber is calculated in a closed form. Propagation of the mode through an optical system can thereafter be described using the ABCD ray's matrix.

Nonlinear optical coupler using a doped optical waveguide

Abstract: An optical mode coupling apparatus includes an Erbium-doped 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 pump 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.

Long-range optical modes supported by a strongly absorbing thin organic film

Abstract: We report the observation of the optical excitation of a long-range mode supported by coupling to Frenkel-type excitons in a highly absorbing organic thin film of metal-free phthalocyanine. The long-range mode is examined over a wavelength range from 400 to 740 nm, and the results are compared both with Fresnel’s theory for planar systems and with analytic expressions that describe the mode in the thin-film limit. Numerical analysis shows that this long-range mode, which like the long-range coupled surface mode has a quadratic dependence of wave vector on film thickness, actually evolves from a TM0 bulk polariton mode. We call the mode that we have observed a long-range excitonic guided mode.

Wideband TM01 -to-TE11 circular waveguide mode convertor

Abstract: The mode convertor employs two intermediate modes, a coaxial TEM and a rectangular waveguide TE 10 mode, in the transition between the TM 01 and TE 11 circular waveguide modes. The coaxial line provides isolation while acting as a mode filter between the device input and output ports. The rectangular waveguide provides a wide mode separation ratio between the TE 10 and TM 11 modes. The TE 10 mode then transitions into the TE 11 in the circular output waveguide. The coaxial section keeps the output TE 11 mode from scattering back to the input, and the rectangular section keeps the TM 01 from being excited in the output.

Mode evolution in optical resonators with a radial gain profile.

Abstract: A Fox and Li analysis [Bell Syst. Tech J. 40, 453 (1961); Proc. IEEE 51, 80 (1963); IEEE J. Quantum Electron QE-4, 460 (1968)] for a laser resonator with a radially varying gain yields a picture of the mode evolution dynamics and a steady-state mode distribution which are different from the constant-gain case. When an axially maximal gain is sharply peaked, the mode-settling time is markedly reduced and the final mode distribution is more tightly focused. When the gain distribution is sharply annular, an annular or ``doughnut''-shaped mode develops. In some intermediate cases, which may be relevant to some gas lasers, a stable transverse mode never definitively evolves. Misalignments of the gain with the cavity yield distortions to the mode shape and these are also explored.

Determination of the longitudinal mode spectrum and mode suppression ratio in a quantum-well laser

Abstract: The longitudinal mode spectrum and the mode suppression ratio of a quantum-well laser are derived in terms of the simulated emission lifetime of the photons in a mode. Analytic expressions are obtained from the Fermi level as a function of current and power as the limiting value of Fermi energy is approached. The model predicts the growth in spontaneous emission as the mirror reflectivity is reduced and predicts mode suppression ratios in good agreement with published values. >

Axial strain sensitivity of single-mode optical fibers (exact solution)

Abstract: Axial strain may be determined by monitoring the phase shift of a single mode optical fiber. Whenever an optical fiber is under stress, the optical path length, the index of refraction, and the propagation constants of each fiber mode change. In consequence, the phase term, (beta) (Zeta) , is also modified. In this paper, a relationship for the phase shift, due to axial strain, of the hybrid modes HE1n and EH1n is presented using the exact field solution. This relation is applied to single mode fibers in order to determine phase sensitivity characteristics.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Temperature effects in the modal phase shift of a weakly guiding fiber

Abstract: Temperature may be determined by monitoring the modal phase shift of an optical fiber. We present the results of a numerical model that has been developed to calculate the phase shift of a weakly guiding optical fiber due to thermal strain. Whenever an optical fiber is subjected to temperature changes, the optical path length, the index of refraction and the propagation constants of each fiber mode change. In consequence, the modal phase term, beta(ln)L, of the fields is also modified. A relationship for the modal phase shift is presented. This relation is applied to both single mode and two-mode fibers in order to determine the sensitivity characteristics of fibers that are subjected to temperature changes.

Quantum propagation in single-mode fiber

Abstract: This paper presents a theory for quantum light propagation in a single-mode fiber which includes the effects of the Kerr nonlinearity, group-velocity dispersion, and linear loss. The theory reproduces the results of classical self-phase modulation, quantum four-wave mixing, and classical solution physics, within their respective regions of validity. It demonstrates the crucial role played by the Kerr-effect material time constant, in limiting the quantum phase shifts caused by the broadband zero-point fluctuations that accompany any quantized input field. Operator moment equations - approximated, numerically, via a terminated cumulant expansion - are used to obtain results for homodyne-measurement noise spectra when dispersion is negligible. More complicated forms of these equations can be used to incorporate dispersion into the noise calculations.

TE/TM mode splitter with waveguide photodetectors

Abstract: We propose a novel TE/TM mode splitter for an integrated optical detection device for magneto-optical disk pickup. The new mode splitter is monolithically integrated on a Si substrate with pin-photodiodes. This device is composed of optical waveguides A and B with effective indices of refraction NA and NB, where NA > NB. These two waveguides are connected by a tapered transition region. The light wave guided in waveguide A is incident on the tapered transition region at an angle of incidence greater than the critical angle for the TE0 mode and smaller than the critical angle for the TM0 mode. The TE0 mode is totally reflected and the TM0 mode is totally transmitted at that region so that this device works as a TE/TM mode splitter. We fabricated the mode splitter's tapered transition region using a novel wet etching process, then examined the TE/TM mode splitting operation using a GaAlAs laser diode ((lambda) equals 0.788 micrometers ). When both TE0 and TM0 modes were exited in waveguide A, the extinction ratios of the TE0 and TM0 modes were measured with the integrated photodiodes. The extinction ratios were -25.4 dB for the TE0 mode and -23.3 dB for the TM0 mode. These values are sufficient for practical application. Furthermore, the polarization detection function was experimentally confirmed using a Faraday rotator.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Fiber-optic mode converter with a narrow-band or broadband spectrum.

Abstract: The spectral properties of a LP01 ↔ LP02 mode converter by using a photoinduced fiber grating are investigated. A fiber with given parameters is considered, and the wavelength dependence of power conversion between the two modes is calculated. The results show that the spectrum can be narrowed by selecting the operating wavelength close to the cutoff wavelength of the LP02 mode. The methods for obtaining a mode converter with a broadband spectrum and a mode converter with a spectrum having two peaks are also discussed.

Desired mode excitation by power additive signal injection in a multiple‐device cavity combiner

Abstract: This paper describes the elimination of undesired mode suppression in a multiple-device cylindrical cavity combiner caused by the effect of excitation of the desired power-combining mode due to external signal injection. Mode analysis is carried out to derive the condition of undesired mode suppression and of sustaining the desired mode oscillation and to prove the capability of perfect combining of the output powers of the multiple-device structure and the power of injected signal. Experiments with TM020-mode cavity confirmed the theory.