Broadband polarization independent nanophotonic coupler for silicon waveguides with ultra-high efficiency

Abstract

Coupling of light to and from integrated optical circuits has been recognized as a major practical challenge since the early years of photonics. The coupling is particularly difficult for high index contrast waveguides such as silicon-on-insulator, since the cross-sectional area of silicon wire waveguides is more than two orders of magnitude smaller than that of a standard single-mode fiber. Here, we experimentally demonstrate unprecedented control over the light coupling between the optical fiber and silicon chip by constructing the nanophotonic coupler with ultra-high coupling efficiency simultaneously for both transverse electric and transverse magnetic polarizations. We specifically demonstrate a subwavelength refractive index engineered nanostructure to mitigate loss and wavelength resonances by suppressing diffraction effects, enabling a coupling efficiency over 92% (0.32 dB) and polarization independent operation for a broad spectral range exceeding 100 nm.

Disorder effects in subwavelength grating metamaterial waveguides

“…A 3-m-thick SiO 2 upper cladding layer was deposited using plasma-enhanced chemical vapor deposition. Broadband and efficient fiber-chip light coupling was achieved with subwavelength engineered mode transformers [3][4][5]. Since these mode transformers are narrow waveguides with a reduced modal confinement for optimum matching with the fiber mode, they are not substantially affected by jitter, as it will be discussed later in this paper.…”

“…Since the first experimental demonstration of an optical waveguide with a subwavelength periodic core [4], these structures, also called subwavelength gratings (SWGs), have found many applications in integrated optics, for example as highly efficient fiber-chip couplers [3][4][5][6][7][8][9], low-loss waveguide crossings, evanescent field sensors [10,11], broadband directional couplers [12] and multimode interference (MMI) [13] couplers, polarization beam splitters [14][15][16], wavelength division [4] and mode division [17] multiplexers, delay lines [18], Fourier-transform spectrometers [19] and suspended (membrane) waveguides for mid-infrared applications [20]. Exhaustive reviews of SWG fundamentals and applications can be found in [21,22].…”

Subwavelength metamaterial engineering for silicon photonics

“…[8][9][10][11][12] Here we provide a short introduction on the general design of subwavelength waveguide devices (section 2), and then discuss two applications: suspended waveguides for the mid-infrared (section 3), and ultra-broadband couplers (section 4).…”

Ideal, constant-loss nanophotonic mode converter using a Lagrangian approach

“…[3] However, at the junction between the interconnecting waveguide and the chip external coupling interface there is an intrinsic mode mismatch requiring mode conversion. [4][5][6][7][8][9][10][11][12] Tapers are used to gradually convert the mode area and the effective index of the guided mode, typically by varying the waveguide width. In Fig.…”