Abstract:Third order grating filters fabricated in small Silicon-on-Insulator rib waveguides are demonstrated. Variations in grating etch depth and duty cycle are considered, and a maximum experimental reflection of 42% is demonstrated for gratings of 1500 µm in length, with a grating period of approximately 689 nm and an etch depth of 200 nm. Agreement with modeling is shown to be good.
“…First reports on Bragg gratings in silicon waveguides were published in early 2000s [19][20][21]. Since then, several papers were published on Bragg gratings based on longitudinally uniform rib or channel SOI waveguides , for applications including spectral filtering [23,25,33,35,46], sensing [24,40] and optical signal processing [37,43]. Design of Bragg grating in SWG waveguides was first reported only recently [47].…”
Properties of reflection and transmission spectral filters based on Bragg gratings in subwavelength grating (SWG) metamaterial waveguides on silicon-on-insulator platform have been analyzed using proprietary 2D and 3D simulation tools based on Fourier modal method and the coupled-mode theory. We also demonstrate that the coupled Bloch mode theory can be advantageously applied to design of Bragg gratings in SWG waveguides. By combining different techniques, including judiciously positioning silicon loading segments within the evanescent field of the SWG waveguide and making use of its dispersion properties, it is possible to attain sub-nanometer spectral bandwidths for both reflection and transmission filters in the wavelength range of 1550 nm while keeping minimum structural features of the filters as large as 100 nm. Numerical simulations have also shown that a few nanometer jitter in the size and position of Si segments is well tolerated in our filter designs.
“…First reports on Bragg gratings in silicon waveguides were published in early 2000s [19][20][21]. Since then, several papers were published on Bragg gratings based on longitudinally uniform rib or channel SOI waveguides , for applications including spectral filtering [23,25,33,35,46], sensing [24,40] and optical signal processing [37,43]. Design of Bragg grating in SWG waveguides was first reported only recently [47].…”
Properties of reflection and transmission spectral filters based on Bragg gratings in subwavelength grating (SWG) metamaterial waveguides on silicon-on-insulator platform have been analyzed using proprietary 2D and 3D simulation tools based on Fourier modal method and the coupled-mode theory. We also demonstrate that the coupled Bloch mode theory can be advantageously applied to design of Bragg gratings in SWG waveguides. By combining different techniques, including judiciously positioning silicon loading segments within the evanescent field of the SWG waveguide and making use of its dispersion properties, it is possible to attain sub-nanometer spectral bandwidths for both reflection and transmission filters in the wavelength range of 1550 nm while keeping minimum structural features of the filters as large as 100 nm. Numerical simulations have also shown that a few nanometer jitter in the size and position of Si segments is well tolerated in our filter designs.
“…Different approaches were presented for the realization of Bragg gratings on waveguides. The modulation of the core refractive index was achieved with ion implantation [1,2] or with a periodic corrugation of the waveguide, either on the waveguide sidewalls [3] or on the top surface [4][5][6][7][8][9]. Both approaches lead to comparable results, even though the latter alternative can be implemented with a less expensive and simpler technology.…”
We present the design, fabrication and characterization of Bragg reflectors on silicon-on-insulator rib waveguides. The fabrication is based on a new double lithographic process, combining electron-beam lithography for the grating and photolithography for the waveguides. This process allows the realization of low loss reflectors, which were fully characterized. The influence of the etching depth and of the waveguide geometry on the reflector performance is considered. We demonstrate a reflectivity larger than 80% over a bandwidth of 0.8 nm with an insertion loss of only 0.5 dB. A thermal tunability of the device is also considered, showing that a shift of the reflected wavelength of 77 pm/K is possible.
“…1c), opening a new route to implement high-performance waveguide Bragg filters. Conventional high-order Bragg filters exhibit narrower notch and substantially longer periods, compared to first-order counterparts, but are hampered by radiation loss in the pass band 24 . On the contrary, the proposed grating allows operating around the third-order Bragg resonance without necessarily meeting the radiation condition, overcoming the off-band loss limitation.…”
Section: Resultsmentioning
confidence: 99%
“…The grating teeth and trench lengths are L Si and L tr , respectively, being the period of the structure Λ = L Si + L tr . A duty cycle of DC = L Si /Λ = 0.3 has been considered to promote the third order Bragg resonance 24 .Figure 2( a ) Schematic view of the proposed diffraction-less Si membrane grating waveguide with long grating period and waveguide width larger than 1 μ m. ( b ) Calculated transmittance for the for the first three modes of the proposed Si membrane waveguide as a function of the period, considering 1-cm-long grating. Diffraction-less light propagation is observed only for the fundamental mode (), within the region predicted by Eq.…”
Sub-wavelength grating (SWG) metamaterials have garnered a great interest for their singular capability to shape the propagation of light. However, practical SWG implementations are limited by fabrication constraints, such as minimum feature size. Here, we present a new nanophotonic waveguide grating concept that exploits phase-matching engineering to suppress diffraction effects for a period three times larger than those with SWG approaches. This long-period grating not only facilitates fabrication, but also enables a new diffraction-less regime with additional degrees of freedom to control light propagation. More specifically, the proposed phase-matching engineering enables selective diffraction suppression, providing new tools to shape propagation in the grating. We harness this flexible diffraction control to yield single-mode propagation in, otherwise, highly multimode waveguides, and to implement Bragg filters that combine highly-diffractive and diffraction-less regions to dramatically increase light rejection. Capitalizing on this new concept, we experimentally demonstrate a Si membrane Bragg filter with record rejection value exceeding 60 dB. These results demonstrate the potential of the proposed long-period grating for the engineering of diffraction in nanophotonic waveguides and pave the way for the development of a new generation of high-performance Si photonics devices.
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