More Like this

1. Utilizing adaptive optics to mitigate intra-modal-group power coupling of graded-index few-mode fiber in a 200-Gbit/s mode-division-multiplexed link

   https://doi.org/10.1364/OL.394307  

   Zhang, Runzhou ; Song, Hao ; Song, Haoqian ; Zhao, Zhe ; Milione, Giovanni ; Pang, Kai ; Du, Jing ; Li, Long ; Zou, Kaiheng ; Zhou, Huibin ; et al ( June 2020 , Optics Letters)

   We experimentally demonstrate the utilization of adaptive optics (AO) to mitigate intra-group power coupling among linearly polarized (LP) modes in a graded-index few-mode fiber (GI FMF). Generally, in this fiber, the coupling between degenerate modes inside a modal group tends to be stronger than between modes belonging to different groups. In our approach, the coupling inside the${\mathrm{L}\mathrm{P}}_{11}$group can be represented by a combination of orbital-angular-momentum (OAM) modes, such that reducing power coupling in OAM set tends to indicate the capability to reduce the coupling inside the${\mathrm{L}\mathrm{P}}_{11}$group. We employ two output OAM modes$l=+1$and$l=-<\#comment/>1$as resultant linear combinations of degenerate${\mathrm{L}\mathrm{P}}_{11\mathrm{a}}$and${\mathrm{L}\mathrm{P}}_{11\mathrm{b}}$modes inside the${\mathrm{L}\mathrm{P}}_{11}$group of a$\sim <\#comment/>0.6\text{-}\mathrm{k}\mathrm{m}$GI FMF. The power coupling is mitigated by shaping the amplitude and phase of the distorted OAM modes. Each OAM mode carries an independent 20-, 40-, or 100-Gbit/s quadrature-phase-shift-keying data stream. We measure the transmission matrix (TM) in the OAM basis within${\mathrm{L}\mathrm{P}}_{11}$group, which is a subset of the full LP TM of the FMF-based system. An inverse TM is subsequently implemented before the receiver by a spatial light modulator to mitigate the intra-modal-group power coupling. With AO mitigation, the experimental results for$l=+1$and$l=-<\#comment/>1$modes show, respectively, that (i) intra-modal-group crosstalk is reduced by$><\#comment/>5.8\mathrm{d}\mathrm{B}$and$><\#comment/>5.6\mathrm{d}\mathrm{B}$and (ii) near-error-free bit-error-rate performance is achieved with a penalty of$\sim <\#comment/>0.6\mathrm{d}\mathrm{B}$and$\sim <\#comment/>3.8\mathrm{d}\mathrm{B}$, respectively.

    

   more » « less
2. Mode-selective few-mode Brillouin fiber lasers based on intramodal and intermodal SBS

   https://doi.org/10.1364/OL.385444  

   Wang, Ning ; Alvarado-Zacarias, J. C. ; Habib, Md Selim ; Wen, He ; Antonio-Lopez, J. E. ; Sillard, Pierre ; Amezcua-Correa, A. ; Schülzgen, Axel ; Amezcua-Correa, R. ; Li, Guifang ( April 2020 , Optics Letters)

   Mode-selective fiber lasers have advantages in a number of applications. Here we propose and experimentally demonstrate a transverse mode-selective few-mode Brillouin fiber laser using the mode-selective photonic lantern. We generated the lowest three orders of linearly polarized (LP) modes based on both intramodal and intermodal stimulated Brillouin scattering (SBS). Their slope efficiencies, optical spectra, mode profiles, and linewidths were measured.

    

   more » « less
3. Scalable non-mode selective Hermite–Gaussian mode multiplexer based on multi-plane light conversion

   https://doi.org/10.1364/PRJ.411529  

   Wen, He ; Zhang, Yuanhang ; Sampson, Rachel ; Fontaine, Nicolas K. ; Wang, Ning ; Fan, Shengli ; Li, Guifang ( January 2021 , Photonics Research)

   Non-mode-selective (NMS) multiplexers (muxes) are highly desirable for coherent power combining to produce a high-power beam with a shaped profile (wavefront synthesis) from discrete, phase-locked emitters. We propose a design for a multi-plane light conversion (MPLC)-based NMS mux, which requires only a few phase masks for coherently combining hundreds of discrete input beams into an output beam consisting of hundreds of Hermite–Gaussian (HG) modes. The combination of HG modes as a base can further construct a beam with arbitrary wavefront. The low number of phase masks is attributed to the identical zero-crossing structure of the Hadamard-coded input arrays and of the output HG modes, enabling the practicality of such devices. An NMS mux supporting 256 HG modes is designed using only seven phase masks, and achieves an insertion loss of$-1.6\mathrm{dB}$, mode-dependent loss of 4.7 dB, and average total mode crosstalk of$-4.4\mathrm{dB}$. Additionally, this design, featuring equal power for all input beams, enables phase-only control in coherent power combining, resulting in significant simplifications and fast convergence compared with phase-and-amplitude control.

    

   more » « less
4. Effect of imperfect homodyne visibility on multi-spatial-mode two-mode squeezing measurements

   https://doi.org/10.1364/OE.379033  

   Gupta, Prasoon ; Speirs, Rory W. ; Jones, Kevin M. ; Lett, Paul D. ( January 2020 , Optics Express)

   We study the effect of homodyne detector visibility on the measurement of quadrature squeezing for a spatially multi-mode source of two-mode squeezed light. Sources like optical parametric oscillators (OPO) typically produce squeezing in a single spatial mode because the nonlinear medium is within a mode-selective optical cavity. For such a source, imperfect interference visibility in the homodyne detector couples in additional vacuum noise, which can be accounted for by introducing an equivalent loss term. In a free-space multi-spatial-mode system imperfect homodyne detector visibility can couple in uncorrelated squeezed modes, and hence can cause faster degradation of the measured squeezing. We show experimentally the dependence of the measured squeezing level on the visibility of homodyne detectors used to probe two-mode squeezed states produced by a free space four-wave mixing process in⁸⁵Rb vapor, and also demonstrate that a simple theoretical model agrees closely with the experimental data.

    

   more » « less
5. Extended focal depth Fourier domain optical coherence microscopy with a Bessel-beam – LP 02 mode – from a higher order mode fiber

   https://doi.org/10.1364/BOE.442081  

   Sen, Dipankar ; Classen, Anton ; Fernández, Alma ; Grüner-Nielsen, Lars ; Gibbs, Holly C. ; Esmaeili, Shahriar ; Hemmer, Philip ; Baltuska, Andrius ; Sokolov, Alexei V. ; Leitgeb, Rainer A. ; et al ( November 2021 , Biomedical Optics Express)

   We present a robust fiber-based setup for Bessel-like beam extended depth-of-focus Fourier-domain optical coherence microscopy, where the Bessel-like beam is generated in a higher order mode fiber module. In this module a stable guided LP₀₂core mode is selectively excited by a long period grating written in the higher order mode fiber. Imaging performance of this system in terms of lateral resolution and depth of focus was analyzed using samples of suspended microbeads and compared to the case where illumination is provided by the fundamental LP₀₁mode of a single mode fiber. Illumination with the LP₀₂mode allowed for a lateral resolution down to 2.5 µm as compared to 4.5 µm achieved with the LP₀₁mode of the single mode fiber. A three-fold enhancement of the depth of focus compared to a Gaussian beam with equally tight focus is achieved with the LP₀₂mode. Analysis of the theoretical lateral point spread functions for the case of LP₀₁and LP₀₂illumination agrees well with the experimental data. As the design space of waveguides and long-period gratings allows for further optimization of the beam parameters of the generated Bessel-like beams in an all-fiber module, this approach offers a robust and yet flexible alternative to free-space optics approaches or the use of conical fiber tips.

    

   more » « less