Waveguide-integrated chip-scale optomechanical magnetometer.

Optomechanical magnetometers enable highly sensitive magnetic field sensing. However, all such magnetometers to date have been optically excited and read-out either via free space or a tapered optical fiber. This limits their scalability and integrability, and ultimately their range of applications. Here, we present an optomechanical magnetometer that is excited and read-out via a suspended optical waveguide fabricated on the same silicon chip as the magnetometer. Moreover, we demonstrate that thermomechanical noise limited sensitivity is possible using portable electronics and laser. The magnetometer employs a silica microdisk resonator selectively sputtered with a magnetostrictive film of galfenol (FeGa) which induces a resonant frequency shift in response to an external magnetic field. Experimental results reveal the retention of high quality-factor optical whispering gallery mode resonances whilst also demonstrating high sensitivity and dynamic range in ambient conditions. The use of off-the-shelf portable electronics without compromising sensor performance demonstrates promise for applications.

Generation of λ/12 nanowires in chalcogenide glasses.

Nanowires have been widely studied and have gained a lot of interest in the past decade. Because of their high refractive index and high nonlinearity, chalcogenide glasses (ChGs) are a good candidate for the fabrication of photonic nanowires as such nanowaveguides provide the maximal confinement of light, enabling large enhancement of nonlinear interactions and group-velocity dispersion engineering. Here we report on the generation of λ/12 (∼68 nm) nanowires based on the theoretical and experimental study of the influence of the laser repetition rate on the direct laser fabrication in ChGs (λ = 800 nm). Through a numerical model of cumulative heating, the optimum conditions for high-resolution fabrication in As(2)S(3) are found. Nanowires with dimensions down to ∼λ/12 are for the first time successfully fabricated in ChGs. We show that the generated nanowires can be stacked to form a three-dimensional woodpile photonic crystal with a pronounced stop gap.

Third-harmonic generation in slow-light chalcogenide glass photonic crystal waveguides.

We demonstrate third-harmonic generation (THG) in a dispersion-engineered slow-light photonic crystal waveguide fabricated in AMTIR-1 chalcogenide glass. Owing to the relatively low loss and low dispersion in the slow-light (c/30) regime, combined with the high nonlinear figure of merit of the material (∼2), we obtain a relatively large conversion efficiency (1.4×10(-8)/W(2)), which is 30× higher than in comparable silicon waveguides, and observe a uniform visible light pattern along the waveguide. These results widen the number of applications underpinned by THG in slow-light platforms, such as the direct observation of the spatial evolution of the propagating mode.

Planar defects in three-dimensional chalcogenide glass photonic crystals.

Here we report on the direct laser writing fabrication of Fabry-Perot-type planar microcavities in a three-dimensional (3D) photonic crystal (PhC) embedded within a high-refractive nonlinear chalcogenide glass (ChG) film. The fabricated planar microcavities in a nonlinear ChG 3D PhC facilitate the observation of resonant modes inside the stop gap. The experimental results show that the length of the planar cavity can be well controlled by the fabrication power and thus be used to tune the defect modes. The tunability of the observed defect modes is confirmed by the theoretical prediction.

Fabrication of low loss dispersion engineered chalcogenide photonic crystals.

We demonstrate low loss photonic crystal waveguides in chalcogenide (Ge(33)As(12)Se(55)) glasses. The measured losses are as low as 21 dB/cm. We experimentally determine the refractive index of the thin film chalcogenide glass to be n = 2.6 and demonstrate that dispersion engineering can be performed up to a group index of ng = 40 in this relatively low refractive index contrast system.

Automatic dispersion compensation for 1.28Tb/s OTDM signal transmission using photonic-chip-based dispersion monitoring.

We present automatic dispersion control of 1.28Tb/s optical time domain multiplexed signals. The dispersion is monitored by measuring the power of the 1.28THz tone of the RF spectrum using a photonic-chip-based radio-frequency spectrum analyzer (PC-RFSA) and the dispersion compensation is realized by means of a spectral pulse shaper, via computer-controlled feedback from the PC-RFSA.

Progress in optical waveguides fabricated from chalcogenide glasses.

We review the fabrication processes and properties of waveguides that have been made from chalcogenide glasses including highly nonlinear waveguides developed for all-optical processing.

Photosensitive and thermal nonlinear effects in chalcogenide photonic crystal cavities.

We investigate the photosensitive and thermo-optic nonlinear properties of chalcogenide glass photonic crystal (PhC) cavities at telecommunications wavelengths. We observe a photosensitive refractive index change in AMTIR-1 (Ge(33)As(12)Se(55)) material in the near-infrared, which is enhanced by light localization in the PhC cavity and manifests in a permanent blue-shift of the nanocavity resonance. Thermo-optic non-linear properties are thoroughly investigated by i) carrying out thermal bistable switching experiments, from which we determined thermal switching times of 63 µs and 93 µs for switch on and switch off respectively and ii) by studying heating of the cavity with a high peak power pulsed laser input, which shows that two-photon absorption is the dominant heating mechanism. Our measurements and analysis highlight the detrimental impact of near-infrared photosensitivity and two-photon absorption on cavity based nonlinear optical switching schemes. We conclude that glass compositions with lower two-photon absorption and more stable properties (reduced photosensitivity) are therefore required for nonlinear applications in chalcogenide photonic crystal cavities.

Dispersion engineered Ge11.5As24Se64.5 nanowires with a nonlinear parameter of 136 W⁻¹m⁻¹ at 1550 nm.

We have fabricated 630 × 500 nm nanowires from Ge(11.5)As(24)Se(64.5) chalcogenide glass by electron beam lithography (EBL) and inductively coupled plasma (ICP) etching. The loss of the nanowire was measured to be 2.6 dB/cm for the fundamental TM mode. The nonlinear coefficient (γ) was determined to be ≈136 ± 7 W(-1)m(-1) at 1550 nm by both CW four-wave-mixing (FWM) and modeling. Supercontinuum (SC) was produced in an 18 mm long nanowire pumped by 1 ps pulses with peak power of 25 W.

Low loss Chalcogenide glass waveguides by thermal nano-imprint lithography.

We report the fabrication of low loss rib waveguides from chalcogenide glass films by thermal nano-imprint using a soft stamp. Waveguides 2-4 µm wide and 1 µm high were fabricated with extremely smooth sidewalls and optical losses limited by Rayleigh scattering to values of 0.26 dB/cm for the TM and 0.27 dB/cm for TE polarizations at 1550 nm.

Photowritten high-Q cavities in two-dimensional chalcogenide glass photonic crystals.

We demonstrate a high-Q(approximately 125,000) photonic crystal (PhC) cavity formed using a postprocessing optical exposure technique where the refractive index of a photosensitive chalcogenide PhC is modified locally. The evolution of the cavity resonances was monitored in situ during writing using a tapered fiber evanescent coupling system, and the Q of 125,000 represents 1 order of magnitude increase over previously reported cavities in two-dimensional chalcogenide glass PhC.

Observation of multiple higher-order stopgaps from three-dimensional chalcogenide glass photonic crystals.

For the first time to our knowledge the observation of near-IR multiple higher-order stopgaps in three-dimensional photonic crystals (PhCs) fabricated using the direct-laser-writing method in thick chalcogenide glass films is reported. The fabrication and etching conditions necessary to realize well-defined structures are presented. The fabricated PhCs exhibit higher-order stopgaps, which are only evident in high-quality structures. The higher-order stopgaps observed permit these high-refractive-index and high-nonlinear PhCs to be used directly as functional photonic devices operating at telecommunication wavelengths without further miniaturizing structural dimensions.

Multiple-cladding fibers with reduced bend loss.

We demonstrate that a highly bend-resistant fiber can be realized. It is shown theoretically that, by introducing both depressed and elevated rings into the cladding, bending loss can be reduced significantly. A fiber based on this design has been fabricated and characterized as a first step toward achieving this goal. The results show that a multiple-cladding fiber is highly bend resistant when compared with the standard telecom single-mode fiber.

Broadband wavelength conversion at 40 Gb/s using long serpentine As(2)S(3) planar waveguides.

We demonstrate broadband wavelength conversion of a 40 Gb/s return-to-zero signal by cross-phase modulation in a newly developed chalcogenide glass waveguide based photonic chip. These new serpentine As(2)S(3) waveguides offer a nonlinear coefficient approximately 1700 W(-1)km(-1) with 5x lower propagation loss over a length of 22.5 cm which ensures the full propagation length contributes towards the nonlinear process. This reduces the peak operating power thereby allowing a x4 increase in the data rate compared with previous results. Spectral measurements show the device operates over a span of 40 nm while system measurements show just over 1 dB of power penalty at a bit-error rate of 10(-9). This is primarily due to the compact planar waveguide design which minimizes the effect of groupvelocity dispersion.

Deposition and characterization of silica-based films by helicon-activated reactive evaporation applied to optical waveguide fabrication.

Planar silicon dioxide optical waveguides were deposited by use of a plasma-activated reactive evaporation system, at a low deposition temperature and with reduced hydrogen contamination, on thermally oxidized silicon wafers. The deposited films show a refractive-index inhomogeneity of less than 0.1%, a thickness nonuniformity of less than 5%, and a material birefringence of approximately 5 x 10(-4). Rib-type channel waveguides were formed on the deposited films by means of hydrofluoric acid etching. The transmission loss of the rib waveguides is determined to be as low as 0.3 dB/cm at a wavelength of 1310 nm for TE polarization, after subtraction of the calculated leakage and scattering losses. Owing to the presence of the OH vibrational overtone band, an additional loss peak of 1 dB/cm is found near the 1385-nm wavelength. The experimental results of transmission loss at wavelengths of 1310 and 1550 nm are compared with analytic expressions for interface scattering and leakage loss.