skip to main content

Title: Ultra-high extinction ratio polarization beam splitter with extreme skin-depth waveguide

In this Letter, we present a high extinction ratio and compact on-chip polarization beam splitter (PBS), based on an extreme skin-depth (eskid) waveguide. Subwavelength-scale gratings form an effectively anisotropic metamaterial cladding and introduce a large birefringence. The anisotropic dielectric perturbation of the metamaterial cladding suppresses the TE polarization extinction via exceptional coupling, while the large birefringence efficiently cross-couples the TM mode, thus reducing the coupling length. We demonstrated the eskid-PBS on a silicon-on-insulator platform and achieved an ultra-high extinction ratio PBS (≈<#comment/>60dBfor TE and≈<#comment/>48dBfor TM) with a compact coupling length (≈<#comment/>14.5µ<#comment/>m). The insertion loss is also negligible (<<#comment/>0.6dB). The bandwidth is><#comment/>80(30) nm for the TE (TM) extinction ratio><#comment/>20dB. Our ultra-high extinction ratio PBS is crucial in implementing efficient polarization diversity circuits, especially where a high degree of polarization distinguishability is necessary, such as photonic quantum information processing.

Authors:
; ; ; ;
Award ID(s):
1930784
Publication Date:
NSF-PAR ID:
10223926
Journal Name:
Optics Letters
Volume:
46
Issue:
9
Page Range or eLocation-ID:
Article No. 2164
ISSN:
0146-9592; OPLEDP
Publisher:
Optical Society of America
Sponsoring Org:
National Science Foundation
More Like this
  1. We present an ultra-broadband silicon photonic polarization beam splitter (PBS) using adiabatically tapered extreme skin-depth (eskid) waveguides. Highly anisotropic metamaterial claddings of the eskid waveguides suppress the crosstalk of transverse-electric (TE) mode, while the large birefringence of the eskid waveguide efficiently cross-couples the transverse-magnetic (TM) mode. Two eskid waveguides are adiabatically tapered to smoothly translate TM mode to the coupled port via mode evolution while keeping the TE mode in the through port. The tapered cross-section of the eskid PBS was designed numerically, achieving a large bandwidth at 1400–1650 nm with extinction ratios><#comment/>20dB. We experimentally demonstrated the tapered-eskid PBS and confirmed its broad bandwidth at 1490–1640 nm, limited by laser bandwidth. With its mode evolution, the tapered-eskid PBS is tolerant to fabrication imperfections and should be crucial for controlling polarizations in photonic circuits.

  2. 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 theLP11group 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 theLP11group. We employ two output OAM modesl=+1andl=−<#comment/>1as resultant linear combinations of degenerateLP11aandLP11bmodes inside theLP11group of a∼<#comment/>0.6-kmGI 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 withinLP11group, which is a subset of the full LP TMmore »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 forl=+1andl=−<#comment/>1modes show, respectively, that (i) intra-modal-group crosstalk is reduced by><#comment/>5.8dBand><#comment/>5.6dBand (ii) near-error-free bit-error-rate performance is achieved with a penalty of∼<#comment/>0.6dBand∼<#comment/>3.8dB, respectively.

    « less
  3. The mid-IR spectroscopic properties ofEr3+doped low-phononCsCdCl3andCsPbCl3crystals grown by the Bridgman technique have been investigated. Using optical excitations at∼<#comment/>800nmand∼<#comment/>660nm, both crystals exhibited IR emissions at∼<#comment/>1.55,∼<#comment/>2.75,∼<#comment/>3.5, and∼<#comment/>4.5µ<#comment/>mat room temperature. The mid-IR emission at 4.5 µm, originating from the4I9/2→<#comment/>4I11/2transition, showed a long emission lifetime of∼<#comment/>11.6msforEr3+dopedCsCdCl3, whereasEr3+dopedCsPbCl3exhibited a shorter lifetime of∼<#comment/>1.8ms. The measured emission lifetimes of the4I9/2state were nearly independent of the temperature, indicating a negligibly small nonradiative decay rate through multiphonon relaxation, as predicted by the energy-gap law for low-maximum-phonon energy hosts. The room temperature stimulatedmore »emission cross sections for the4I9/2→<#comment/>4I11/2transition inEr3+dopedCsCdCl3andCsPbCl3were determined to be∼<#comment/>0.14×<#comment/>10−<#comment/>20cm2and∼<#comment/>0.41×<#comment/>10−<#comment/>20cm2, respectively. The results of Judd–Ofelt analysis are presented and discussed.

    « less
  4. We experimentally demonstrate simultaneous turbulence mitigation and channel demultiplexing in a 200 Gbit/s orbital-angular-momentum (OAM) multiplexed link by adaptive wavefront shaping and diffusing (WSD) the light beams. Different realizations of two emulated turbulence strengths (the Fried parameterr0=0.4,1.0mm) are mitigated. The experimental results show the following. (1) Crosstalk between OAMl=+1andl=−<#comment/>1modes can be reduced by><#comment/>10.0and><#comment/>5.8dB, respectively, under the weaker turbulence (r0=1.0mm); crosstalk is further improved by><#comment/>17.7and><#comment/>19.4dB, respectively, under most realizations in the stronger turbulence (r0=0.4mm). (2) The optical signal-to-noise ratio penalties for the bit error rate performance are measured to be∼<#comment/>0.7and∼<#comment/>1.6dBunder weaker turbulence, while measured to be∼<#comment/>3.2and∼<#comment/>1.8dBunder stronger turbulence for OAMl=+1andl=−<#comment/>1mode, respectively.

  5. We study the relationship between the input phase delays and the output mode orders when using a pixel-array structure fed by multiple single-mode waveguides for tunable orbital-angular-momentum (OAM) beam generation. As an emitter of a free-space OAM beam, the designed structure introduces a transformation function that shapes and coherently combines multiple (e.g., four) equal-amplitude inputs, with thekth input carrying a phase delay of(k−<#comment/>1)Δ<#comment/>φ<#comment/>. The simulation results show that (1) the generated OAM order ℓ is dependent on the relative phase delayΔ<#comment/>φ<#comment/>; (2) the transformation function can be tailored by engineering the structure to support different tunable ranges (e.g., l={−<#comment/>1},{−<#comment/>1,+1},{−<#comment/>1,0,+1}, or{−<#comment/>2,−<#comment/>1,+1,+2}); and (3) multiple independent coaxial OAM beams can be generated by simultaneously feeding the structure with multiple independent beams, such that each beam has its ownΔ<#comment/>φ<#comment/>value for the four inputs. Moreover, there is a trade-off between the tunable range and the mode purity, bandwidth, and crosstalk, such that the increase of the tunable range leads to (a) decreased mode purity (from 91% to 75% formore »display='inline'>l=−<#comment/>1), (b) decreased 3 dB bandwidth of emission efficiency (from 285 nm forl={−<#comment/>1}to 122 nm forl={−<#comment/>2,−<#comment/>1,+1,+2}), and (c) increased crosstalk within the C-band (from−<#comment/>23.7to−<#comment/>13.2dBwhen the tunable range increases from 2 to 4).

    « less