Elsevier

Optics Communications

Volume 502, 1 January 2022, 127407
Optics Communications

Polarization-insensitive reverse-ridge AlGaAs waveguide for the mid-infrared supercontinuum generation

https://doi.org/10.1016/j.optcom.2021.127407Get rights and content

Highlights

  • A polarization-insensitive reverse-ridge AlGaAs waveguide has been designed.

  • The dispersion coefficient curves coincide well for the quasi-TE and quasi-TM modes.

  • The effect of different pump conditions on supercontinuum generation is studied.

  • The two generated supercontinua for the quasi-TE and quasi-TM modes overlap well.

Abstract

In this paper, a polarization-insensitive reverse-ridge AlGaAs waveguide is designed for the supercontinuum generation. In the considered wavelength range from 3.4 to 8 μm, the dispersion profiles, nonlinear coefficients, and effective mode field areas for the quasi-TE and quasi-TM modes coincide well. The simulation results show that when pump pulse with wavelength of 4.2 μm, peak power of 4.8 kW, and width of 90 fs is launched into the anomalous dispersion region of the quasi-TE and quasi-TM modes of the 3.4-mm-long waveguide, the two generated SCs overlap well. For the quasi-TE and quasi-TM modes, the SCs generated extend from 2.17 to 8.53 μm and 2.23 to 8.61 μm, respectively, spanning more than 1.95 octaves. The proposed reverse-ridge AlGaAs waveguide structure is expected to provide a possible solution for alleviating the undesired polarization effect related to the nonlinear dynamics.

Introduction

Mid-infrared supercontinuum (SC) generation is of great interest for its applications in spectroscopy [1], [2], [3], [4], [5], optical coherence tomography [6], [7], [8], biomedical imaging [9], ladar [10], [11], gas sensing [12], [13], [14], etc. As well known, the interaction of dispersive and nonlinear effects, which includes self-phase modulation (SPM), cross-phase modulation (XPM), four-wave mixing (FWM), stimulated Raman scattering (SRS), soliton fission (SF), contributes to the SC generation [15], [16], [17], [18].

In recent years, lots of investigations on the mid-infrared SC generations in optical waveguides have been reported. Yuan et al. numerically generated the coherent and multi-octaves SC spanning from 1.96 to 12 μm in a suspended Ge-membrane ridge waveguide [19]. Saini et al. investigated the mid-infrared SC generation in the rib As2Se3 waveguides with different core shapes [20]. Sinobad et al. demonstrated the SC generation in the wavelength range from 2.8 to 5.7 μm in the SiGe waveguide with an all-normal dispersion profile [21]. Lu et al. reported the SC generation at the ultraviolet to mid-infrared spectral region in the single-crystalline AlN waveguide [22]. Saini et al. generated the near-infrared to mid-infrared SC in a tellurium-oxide coated silicon-nitride waveguide through pumping in the normal dispersion region [23]. Karim et al. utilized a suspended core channel As2Se3 waveguide for the SC generation covering from 1.5 to 15 μm [24].

AlGaAs is the alloy of AlAs and GaAs. The refractive index of AlGaAs can be easily adjusted by changing the alloy composition [25]. Therefore, the refractive index difference between the waveguide core and substrate and the dispersion characteristic can be flexibly changed. In addition, its large transparency window (more than 15 μm [26], more than twice that of Si) and strong Kerr nonlinear index (on the order of 10−17 m2/W [27], an order of magnitude larger than that of Si [28]) make it suitable for the mid-infrared SC generation. Mei designed the AlGaAs strip waveguides to generate the broadband SC, spanning from 2 to 15.9 μm [29]. Chiles et al. utilized a suspended AlGaAs waveguide to generate the second-harmonic and broadband SC covering from 2.3 to 6.5 μm when pump wavelength was located at 3060 nm [30]. Kuyken et al. experimentally demonstrated an octave-spanning SC generation in the wavelength range from 1055 to 2155 nm in an AlGaAs waveguide [27]. With picojoule-level pulse energy, May et al. experimentally obtained a SC covering 544 nm at the level of −25 dB in AlGaAs-on-insulator waveguides [31].

In recent years, there are some investigations on the polarization insensitivity of the waveguide-based modulator and grating. Tabti et al. demonstrated a polarization-insensitive sampled Bragg grating by exploiting the birefringence compensation in Si3N4 waveguide [32], where the transmission spectra for both the quasi-transverse electric (TE) and quasi-transverse magnetic (TM) modes overlapped over a spectral range of 40 nm. Chen et al. proposed a polarization-insensitive graphene modulator, which was polarization-independent for the TE and TM modes [33]. Zhou et al. reported a polarization-insensitive graphene-based optical modulator integrated in a chalcogenide glass waveguide [34], where the absorption coefficient variation was almost identical in the wavelength range of 2–2.4 μm for the TE and TM modes. However, there is still no report on the polarization-insensitive waveguide for the SC generation. For the SC generation, the nonlinear process is always very sensitive to the polarization state of the pump light because the dispersion and nonlinear characteristics of the quasi-TE and quasi-TM modes of the waveguides are different. Thus, the polarization state of the pump light needs to be controlled by employing the polarization controller [35], [36], [37], [38]. At this time, the complexity of the experimental system is increased, and the undesired polarization effect has an adverse influence on the energy conversion caused by the nonlinear effects. At present, the polarization-dependent problem of the pump light could be effectively solved by reasonably designing the waveguide structure.

In this paper, a polarization-insensitive reverse-ridge AlGaAs waveguide is proposed to generate the mid-infrared SCs. In the design, the influences of the geometrical parameters of the waveguide on the dispersion characteristic are analyzed to optimize the waveguide structure. In addition, the impacts of the pump pulse parameters and waveguide length on the SC generations are also investigated. With the designed 3.4-mm-long waveguide, for the quasi-TE and quasi-TM modes, highly coherent and octave-spanning mid-infrared SCs are generated, spanning from 2.17 to 8.53 μm and 2.23 to 8.61 μm, respectively, when pump pulse with wavelength of 4.2 μm, peak power of 4.8 kW, and width of 90 fs is used.

Section snippets

Theoretical model

The process of the SC generation in the optical waveguides can be described by the modified generalized nonlinear Schrödinger equation (GNLSE) as following [15] Az+α2Am0im+1βmωm!mAtm=iγω0+iγ1ω0t×Az,t0+Rt|Az,tt|2dt, where A(z, t) stands for the slowly varying envelope of the electric field, and the mth order dispersion coefficient calculated from the Taylor expansion of the propagation constant is represented by βm (ω). The last term on the right side of Eq. (1) is the

Waveguide design and characteristics

Fig. 1(a) shows the three-dimensional structure of the designed reverse-ridge AlGaAs waveguide. The Al0.18Ga0.82As layer, where the ratio of AlAs and GaAs is 0.18 to 0.82, is embedded in the Al0.8Ga0.2As substrate, which enhances the mode field confinement. The width of the Al0.18Ga0.82As ridge core is W. The depth of the part embedded in the substrate is Hd, and the protruding part is represented by Hu. Fig. 1(b) shows the mode field distributions of the quasi-TE and quasi-TM modes calculated

Simulation results and discussion

The SC generation in the proposed reverse-ridge AlGaAs waveguide will be numerically investigated by solving Eq. (1) with the Runge–Kutta method. While pumping in the normal dispersion region of the waveguide, the generated SC usually has good coherence with a relatively narrow spectral range. In contrast, while pumping in the anomalous dispersion region, the SC can be easily extended to a considerable range. Furthermore, the coherence of the SC can be improved by appropriately selecting the

Conclusion

In summary, we design a polarization-insensitive reverse-ridge AlGaAs waveguide for the SC generations based on the quasi-TE and quasi-TM modes. The dispersion difference between the quasi-TE and quasi-TM modes could be reduced through exactly adjusting the geometrical parameters of the waveguide. Furthermore, by optimizing the pump pulse parameters, the generated SCs for the quasi-TE and quasi-TM modes can overlap almost completely. When the pump pulse with wavelength of 4.2 μm, peak power of

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

This work was supported by the National Natural Science Foundation of China (61875238).

References (44)

  • LongshoreR. et al.

    Selection of detector peak wavelength for optimum infrared system performance

    Infrared Phys.

    (1976)
  • WerleP. et al.

    Near-and mid-infrared laseroptical sensors for gas analysis

    Opt. Laser. Eng.

    (2002)
  • LuF. et al.

    Tip-enhanced infrared nanospectroscopy via molecular expansion force detection

    Nat. Photonics

    (2014)
  • AmiotC. et al.

    Cavity enhanced absorption spectroscopy in the mid-infrared using a supercontinuum source

    Appl. Phys. Lett.

    (2017)
  • NaderN. et al.

    Versatile silicon-waveguide supercontinuum for coherent mid-infrared spectroscopy

    Apl. Photonics

    (2018)
  • KilgusJ. et al.

    Mid-infrared standoff spectroscopy using a supercontinuum laser with compact Fabry–Pérot filter spectrometers

    Appl. Spectrosc.

    (2018)
  • MikkonenT. et al.

    Broadband cantilever-enhanced photoacoustic spectroscopy in the mid-IR using a supercontinuum

    Opt. Lett.

    (2018)
  • MarksD.L. et al.

    Study of an ultrahigh-numerical-aperture fiber continuum generation source for optical coherence tomography

    Opt. Lett.

    (2002)
  • ZorinI. et al.

    Dual-band infrared optical coherence tomography using a single supercontinuum source

    Opt. Express

    (2020)
  • IsraelsenN.M. et al.

    Real-time high-resolution mid-infrared optical coherence tomography

    Light-Sci. Appl.

    (2019)
  • GuoB.J. et al.

    Laser-based mid-infrared reflectance imaging of biological tissues

    Opt. Express

    (2004)
  • KimJ.H. et al.

    Middle-IR supercontinuum generations and applications

  • Q. Pan, K.E. Jahromi, M.A. Abbas, A. Khodabakhsh, S.M. Cristescu, F.J.M. Harren, Towards Broadband Multi-species Trace...
  • JahromiK.E. et al.

    Mid-infrared supercontinuum-based upconversion detection for trace gas sensing

    Opt. Express

    (2019)
  • AgrawalG.P.

    Nonlinear Fiber Optics

    (2013)
  • DudleyJ.M. et al.

    Supercontinuum generation in photonic crystal fiber

    Rev. Modern Phys.

    (2006)
  • HusakouA.V. et al.

    Supercontinuum generation of higher-order solitons by fission in photonic crystal fibers

    Phys. Rev. Lett.

    (2001)
  • LiZ.L. et al.

    Multi-octave mid-infrared supercontinuum and frequency comb generation in a suspended As2Se3 ridge waveguide

    Appl. Opt.

    (2019)
  • YuanJ.H. et al.

    Mid-infrared octave-spanning supercontinuum and frequency comb generation in a suspended germanium-membrane ridge waveguide

    J. Lightwave Technol.

    (2017)
  • SainiT.S. et al.

    Design and analysis of dispersion engineered rib waveguides for on-chip mid-infrared supercontinuum

    J. Lightwave Technol.

    (2018)
  • SinobadM. et al.

    Mid-infrared supercontinuum generation in silicon-germanium all-normal dispersion waveguides

    Opt. Lett.

    (2020)
  • LuJ.J. et al.

    Ultraviolet to mid-infrared supercontinuum generation in single-crystalline aluminum nitride waveguides

    Opt. Lett.

    (2020)
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