Towards an integrated AlGaAs waveguide platform for phase and polarisation shaping

Abstract

We propose, design and fabricate an on-chip AlGaAs waveguide capable of generating a controlled phase delay of π/2 between the guided transverse electric and magnetic modes. These modes possess significantly strong longitudinal field components as a direct consequence of their strong lateral confinement in the waveguide. We demonstrate that the effect of the device on a linearly polarised input beam is the generation of a field, which is circularly polarised in its transverse components and carries a phase vortex in its longitudinal component. We believe that the discussed integrated platform enables the generation of light beams with tailored phase and polarisation distributions.

Spin Angular Momentum of Guided Light Induced by Transverse Confinement and Intrinsic Helicity

“…Let us now study cylindrical waveguides, which support a wealth of guided modes exhibiting a rich spin phenomenology. Incidentally, although we consider cylindrical waveguides, all general statements can be likely applied to strip waveguides, no doubt an interesting platform in terms of practical applications. ,, The fields of the waveguide can be expressed in cylindrical coordinates [see Figure b] and exhibit transverse spatial dependence given by the appropriate Bessel function that matches the boundary conditions Z m ( k t r ) and by its derivative with respect to the argument Z m ′ ( k t r ) (see details in the Supporting Information), where k z and k t are again the longitudinal and transverse component of the wavevector, respectively, and k = n ω/ c is the modulus of the wavevector. Recall that k t is imaginary outside the waveguide.…”

“…Also, Espinosa-Soria and Martı́nez studied through numerical simulations spin–orbit coupling in Si waveguides, focusing on circularly polarized dipole excitation close to the waveguide surface . Hereof, it is worth mentioning that the following experimental works have exploited spin–orbit interaction also in waveguides. − In particular, Coles et al investigated experimentally for the first time unidirectional spin transfer connected to the internal chirality of waveguides upon placing a quantum-dot emitter inside both a nanobeam waveguide and a photonic-crystal waveguide . In connection with photonic crystal waveguides too, the position-dependent transverse spin has been even more extensively studied through circular polarization excitation, in turn applied for unidirectional excitation of modes. ,, Incidentally, transverse SAM has also been predicted in other nonevanescent, structured wavefields, such as tightly focused light beams in free space. − …”

Tunable Four-Wave Mixing in AlGaAs Waveguides of Three Different Geometries

“…The different aluminum content of each layer provides the refractive index contrast necessary for the light confinement. Alternative AlGaAs technologies have been developed in recent years, such as AlGaAs/Al x O y [25,26], AlGaAs-on-AlO x [27,28], AlGaAsOI (AlGaAson-insulator) [29][30][31][32], AlGaAsOS (AlGaAs-onsapphire) [33], GaAs/AlGaAs [34][35][36][37][38][39][40], suspended GaAs [41] and suspended AlGaAs on GaAs [42] and on silicon substrates [43]. Enhanced secondharmonic generation [25,26] and optical parametric oscillation [28] have been demonstrated in AlGaAson-Al x O y technology.…”

“…These devices are made of GaAs thin films deposited on an AlGaAs layer over a GaAs substrate. The targeted applications of GaAs/AlGaAs waveguide are infrared spectroscopy [36], sensing [20,37,44], quantum photonics [39] and controlled π/2-phase delay between the TE and TM modes that results in the generation of a circularly polarised mode [35]. In the suspended GaAs, AlGaAs-on-GaAs and AlGaAson-silicon technologies, the waveguide is suspended in an air layer, which increases the refractive index contrast.…”

Photonic potential for TM waves

“…Nonetheless, the scalar approximation fails even in the presence of discontinuous interfaces between two different isotropic materials, causing for example form birefringence in step-index waveguides [2]. Currently, there is a continuous effort towards the miniaturization of sub-wavelength optical waveguides [3][4][5][6][7][8][9]. In fact, one of the main aims of nanophotonics is to shrink optical waveguides as much as possible [10].…”