Gerd Leuchs - Academia.edu (original) (raw)

Papers by Gerd Leuchs

Optics Express, May 10, 2010

Coherent beam combining refers to the process of generating a bright output beam by merging indep... more Coherent beam combining refers to the process of generating a bright output beam by merging independent input beams with locked relative phases. We report the first quantum mechanical noise limit calculations for coherent beam combining and compare our results to quantum-limited amplification. We highlight a favourable noise scaling for both pure and noisy input states.

Higher order modes LP0,m in specially designed fibers have recently shown to offer robust light p... more Higher order modes LP0,m in specially designed fibers have recently shown to offer robust light propagation in record-large effective areas (Aeff) with negligible mode-coupling or bend distortions. Such beams can be generated with greater than 99% coupling-efficiencies using in-fiber gratings. However, this conversion technique may not be suitable at the output of a high-power fiber-laser or amplifier comprising a higher order mode fiber because converting back to the (small-Aeff) fundamental mode of a fiber would lead to high intensities at the fiber output which could destroy the fiber. In this paper, a combination of a phase plate and an optical filtering system was used to convert the output of a HOM fiber into a nearly fundamental Gaussian beam. Simulations show that by only loosing 22%-25% of the light power due to the filtering, i.e. a loss between 0.97 dB and 1.25 dB, the output will be nearly Gaussian.

ABSTRACT In this paper, an asymmetric nonlinear optical loop mirrors (NOLM) was used to analyse o... more ABSTRACT In this paper, an asymmetric nonlinear optical loop mirrors (NOLM) was used to analyse optimum splitting ratio for erbium doped optical fibre amplifier (EDFA) noise reduction. To measure the noise reduction of the NOLM, we compare the noise power at the NOLM output with the noise power at the EDFA output, acting as a reference level. This 12 dB of noise reduction is the best result experimentally achieved with an asymmetric NOLM. It is concluded that the setup shown becomes attractive for commercial optical telecommunication systems with pulse durations longer than 1.3 ps.

Ytterbium-doped fiber laser amplifiers are known for their high single-pass gain and average powe... more Ytterbium-doped fiber laser amplifiers are known for their high single-pass gain and average powers up to the kilowatt range, while maintaining single-mode output. An upper limitation for the achievable output power is given by transverse mode instabilities (TMI). Due to the interference with higher order modes that create a thermally induced long period grating, chaotic power transfer happens above a certain threshold, which degrades the beam quality. It has been shown that this effect can be influenced by manipulating the grating strength itself. It has also been shown that a certain phase relation of the grating to the guided modes is necessary to efficiently transfer power or hinder the effect by phase disturbance [1]. A natural phase disturbance is given by noise, which is introduced by the pump or seed source in a fiber amplifer. In this contribution, we experimentally investigate the amount of intensity noise in a fiber-pre-amplifer, which is typically used in kW experiments and relate it to the fundamental shot noise limit (SNL). In the experiments, we used a single-frequency external cavity diode laser as a low noise source and amplify it by 30 dB from 10 mW to an output power of 10 W. This is a typical pre-amplifier configuration, before such sources can be amplified to the kW level. The fiber amplifier is a double-clad fiber with a 10/125 μm geometry, pumped by a wavelength stabilized pump diode at 976 nm via a monolithic pump coupler. In order to prevent stimulated Brillouin scattering, the seed laser is phase modulated by a combination of a sinusoid and white noise and thus broadened to 50 GHz linewidth. The noise measurements are done by balanced self-homodyne detection including optimized photodiode readout circuits spanning different frequency ranges. The recorded spectra are given in Fig. 1. The SNL was verified through an attenuation measurement for the subtracted detector signals. Finally, the measured excess noise values are fitted by their corresponding second-order polynomial power dependency and extrapolated to the full power of the amplifier. The seed source, phase modulator and fiber amplifier have been characterized in this setup separately to investigate their contributions. For the fiber amplifier, both co- and counter-pumping configuration, are analysed. Due to detector limitations, all given spectra are measured at an optical power in the mW regime corresponding to approx. 30 dB of attenuation in the amplifiers.

Kluwer Academic Publishers eBooks, Mar 11, 2006

ABSTRACT We demonstrate the geometric spin Hall effect of light by focusing a specially polarizat... more ABSTRACT We demonstrate the geometric spin Hall effect of light by focusing a specially polarization tailored beam of light, resulting in the generation of purely transverse angular momentum in the focal plane.

Proceedings of SPIE, Jan 23, 2010

ABSTRACT A nonlinear optical loop mirror with a bidirectional attenuator has been used for regene... more ABSTRACT A nonlinear optical loop mirror with a bidirectional attenuator has been used for regeneration of return-to-zero differential phase-shift-keyed (RZ-DPSK) signals. A 2.5 ps, 10 Gb/s signal with amplitude fluctuations of 28 % was regenerated with a negative power penalty of 2 dB practically back to the quality of the undistorted reference signal. Parameters limiting system performance and optimization possibilities will be discussed.

Optics Express, Mar 31, 2011

Applied optics, Jul 9, 2007

Optics Express, May 10, 2010

Optics Letters, Jan 12, 2022

Proceedings of the National Academy of Sciences of the United States of America, Aug 11, 2014

Advances in Optics and Photonics, Mar 1, 2021

Advanced quantum technologies, Jan 26, 2023

Scientific Reports, Jan 29, 2016

The duality principle, a cornerstone of quantum mechanics, limits the coexistence of wave and par... more The duality principle, a cornerstone of quantum mechanics, limits the coexistence of wave and particle behaviours of quantum systems. This limitation takes a quantitative form when applied to the visibility V of interference fringes and predictability P of paths within a two-alternative system, which are bound by the inequality . However, if such a system is coupled to its environment, it becomes possible to obtain conditional measures of visibility and predictability, i.e. measures that are conditioned on the state of the environment. We show that in this case, the predictability and visibility values can lead to an apparent violation of the duality principle. We experimentally realize this apparent violation in a controlled manner by enforcing a fair-sampling-like loophole via postselection. This work highlights some of the subtleties that one can encounter while interpreting familiar quantities such as which-alternative information and visibility. While we concentrated on an extreme example, it is of utmost importance to realise that such subtleties might also be present in cases where the results are not obviously violating an algebraic bound, making them harder (but not any less crucial) to detect.