Optical phased arrays are versatile components enabling rapid and precise beam steering. An integrated approach is followed in which a 1D optical phased array is fabricated on silicon-on-insulator. The optical phased array consists of 16 parallel grating couplers spaced 2 m apart. Steering in one direction is done thermo-optically by means of a titanium electrode on top of the structure using the phased array principle, while steering in the other direction is accomplished by wavelength tuning. In this Letter, an integrated approach on siliconon-insulator (SOI) is taken where the phase differences are introduced on a photonic integrated circuit and the light is subsequently coupled off chip. Phase control is done here using the thermo-optic effect in silicon. Silicon has a relatively large thermo-optic coefficient being ‫ץ‬n / ‫ץ‬T = 1.86ϫ 10 −4 K −1 at a wavelength of 1550 nm resulting in an easy, low-cost, and stable way of achieving phase modulation [4].In [5] a similar approach is used with an AlGaAs integrated waveguide array. A continuous deflection over an angle of 0 . 41°at a wavelength of 900 nm with a FWHM divergence of 0 . 09°is reported. The phase modulation was done electro-optically with indium tin oxide/AlGaAs Schottky junctions. The array spacing is much larger than the spacing achievable with the present fabrication technologies on SOI, making the latter attractive for beam steering.A schematic of the component can be found in Fig. 1. The component was fabricated on SOI with an oxide thickness of 2 m and a silicon thickness of 220 nm using standard complementary metal-oxide semiconductor (CMOS) processes in the Interuniversity MicroElectronics Center (IMEC) [6]. Two etching steps are used: one of 220 nm for etching the waveguides and the multimode interference (MMI) splitters and the second of 70 nm to etch the grating couplers. The structure is excited with transverseelectric (TE) polarized light through a lensed fiber via the facet of a 3-m-wide integrated access waveguide. This waveguide is tapered to a width of 500 nm and then split with a MMI-splitter tree into sixteen 800 nm wide parallel waveguides, spaced 2 m apart. On top of each waveguide a second-order diffraction grating intended for light outcoupling is shallow etched, characterized by a period of 630 nm and a duty cycle of 0.5 for efficient outcoupling of the TE polarized light. The grating coupler consists of 50 periods. After approximately 35 periods the measured outcoupled light has decayed by a factor of 1/e 2 . Since transverse-magnetic (TM) polarized light will not be coupled out efficiently by the grating couplers owing to the difference in effective index, the component is highly polarization dependent. Afterward a benzocyclobutene (BCB) layer of approximately 1 m is spun on top and a titanium electrode is sputtered with a thickness of approximately 100 nm. While the BCB does not allow for a very efficient heat transfer to the optical waveguide, this technique requires a minimum of processing to demonstrate the beam steeri...

We investigate an air-slot photonic crystal cavity for high-precision refractive index sensing. The high quality factor ∼2:6 × 10 4 of the cavity, along with a strong overlap between the resonant mode and the hollow core region, allows us to achieve an experimental sensitivity of 510 nm per refractive index unit (RUI) and a detection limit below 1 × 10 −5 RUI. The device has a remarkably low sensing volume of 40 aliters, holding less than 1 × 10 6 molecules.

The dispersive properties of waves are strongly affected by inevitable residual disorder in man-made propagating media, in particular in the slow wave regime. By a direct measurement of the dispersion curve in k space, we show that the nature of the guided modes in real photonic crystal waveguides undergoes an abrupt transition in the vicinity of a band edge. Such a transition that is not highlighted by standard optical transmission measurement, defines the limit where k can be considered as a good quantum number. In the framework of a mean-field theory we propose a qualitative description of this effect and attribute it to the transition from the "dispersive" regime to the diffusive regime. In particular we prove that a scaling law exists between the strength of the disorder and the group velocity. As a result, for group velocities v g smaller than c / 25 the diffusive contribution to the light transport is predominant. In this regime the group velocity v g loses its relevance and the energy transport velocity v E is the proper light speed to consider.

Nanophotonic waveguides are at the core of a great variety of optical sensors. These structures confine light along defined paths on photonic chips and provide light–matter interaction via an evanescent field. However, waveguides still lag behind free-space optics for sensitivity-critical applications such as trace gas detection. Short optical pathlengths, low interaction strengths, and spurious etalon fringes in spectral transmission are among the main reasons why on-chip gas sensing is still in its infancy. In this work, we report on a mid-infrared integrated waveguide sensor that successfully addresses these drawbacks. This sensor operates with a 107% evanescent field confinement factor in air, which not only matches but also outperforms free-space beams in terms of the per-length optical interaction. Furthermore, negligible facet reflections result in a flat spectral background and record-low absorbance noise that can finally compete with free-space spectroscopy. The sensor performance was validated at 2.566 μm, which showed a 7 ppm detection limit for acetylene with only a 2 cm long waveguide.

Abstract:We report a methane sensor based on an integrated MachZehnder interferometer, which is cladded by a styrene-acrylonitrile film incorporating cryptophane-A. Cryptophane-A is a supramolecular compound able to selectively trap methane, and its presence in the cladding leads to a 17-fold sensitivity enhancement. Our approach, based on 3 cmlong low-loss Si 3 N 4 rib waveguides, results in a detection limit as low as 17 ppm. This is 1-2 orders of magnitude lower than typically achieved with chip-scale low-cost sensors.