Slot-based athermal silicon arrayed-waveguide grating (AWG)

Multistage WDM access architecture employing cascaded AWGs

Utilizing T-band (1000 nm to 1260 nm) for optical communications is promising for short reach, and large capacity networks, such as data centers or access networks. It is feasible to use this with low-cost coarse wavelength division multiplexing (WDM). However, a tunable wavelength light source is necessary for such applications. In this paper, we propose a new configuration for an external cavity laser, which uses a silica-based arrayed waveguide grating (AWG) for the wavelength selecting element. The external cavity laser consists of a gain chip with high reflection (HR) and anti-reflection (AR) coated facets, coupling lenses, an AWG with AR/HR coatings, and an output fiber. The AWG has 17 connection ports, which correspond to 17 wavelengths with a channel spacing of 1.67 nm. The width of the connection port waveguides was optimized to achieve high coupling efficiency. The AWG chip size is 15 mm x 30 mm. The active layer in the gain chip has InAs quantum dots. The spontaneous emission 3-dB bandwidth was 48 nm (1108 nm to 1156 nm) when a current of 150 mA was injected into the gain chip. The lasing wavelength of the external cavity laser was successfully tuned from 1129.9 nm to 1154.4 nm by selecting the connection ports of the AWG. The typical threshold current was about 130 mA.

An interoperable access network architecture based on a coarse array waveguide grating (AWG) is described, displaying dynamic wavelength assignment to manage the network load across multiple PONs. The multi-PON architecture utilizes coarse Gaussian channels of an AWG to facilitate scalability and smooth migration path between TDM and WDM PONs. Network simulations of a cross-operational protocol platform confirmed successful routing of individual PON clusters through 7 nm-wide passband windows of the AWG. Furthermore, polarization-dependent wavelength shift and phase errors of the device proved not to impose restrain on the routing performance. Optical transmission tests at 2.5 Gbit/s for distances up to 20 km are demonstrated.

The terpolymer (PFS–GMA–TFEMA) was prepared and coated on silica waveguide for polymeric optical overclad. In our study, athermal characteristics were realised by adjusting the coefficient of negative thermal expansion of the synthesised terpolymer overclad, and the positive thermo‐optic coefficient of the silica thin film. The measured values were −1.11 × 10 –4 /K and 0.79 × 10 –5 /K (dn/dT). The thermal properties according to the temperature change indicated that the wavelength had shifted by about 0.15 nm from 20 to 90°C, with little change over 50°C. When the temperature increased, the wavelength shift of the silica/terpolymer hybrid arrayed waveguide grating was −0.002 nm/°C, compared to the 0.01 nm/°C of silica arrayed waveguide grating. Terpolymer overclad arrayed waveguide grating showed a centre wavelength loss of 5.334 dB, loss uniformity of 0.864 dB, a polarisation dependent loss of 0.162 dB, and a non‐adjacent crosstalk of −31.67 dB.

We present a detailed study of parameter sweeps of silicon photonic arrayed waveguide gratings (AWG), looking into the effects of phase errors in the delay lines, which are induced by fabrication variation. We fabricated AWGs with 8 wavelength channels spaced 200 GHz and 400 GHz apart. We swept the waveguide width of the delay lines, and also performed a sweep where we introduced increments of length to the waveguides to emulate different AWG layouts and look into the effect of the phase errors. With this more detailed study we could quantitatively confirm the results of earlier studies, showing the wider waveguides reduce the effect of phase errors and dramatically improve the performance of the AWGs in terms of insertion loss and crosstalk. We also looked into the effect of rotating the layout of the circuit on the mask, and here we could show that, contrary to results with older technologies, this no longer has an effect on the current generation of devices.

We have developed multichannel wavelength filters consisting of three-dimensional photonic crystals, which have multiple filter regions with different transmission wavelengths according to differences in the in-plane lattice constants of the crystals. In this study, we improved the design of the photonic crystal (PC) filters by making use of the photonic-bandgap edge and fabricated PC filters with a Ta/sub 2/O/sub 5/-SiO/sub 2/ material system. This improvement enabled us to obtain a transmission wavelength shift of +36 nm at 1550 nm, which agrees well with the results of finite-difference time-domain simulations. By connecting the multichannel wavelength filters to a 100-GHz-spaced 40-channel arrayed waveguide grating (AWG), we suppressed the crosstalk in the AWG from -40 dB to less than -60 dB.

Quadratic electro-optic shift of central wavelength in boron-phosphorous-doped folded Arrayed Waveguide Grating (AWG) multiplexer has been demonstrated. A spectral shift of ~1-GHz/KV was obtained with virtually zero power consumption.

Electronic interconnects are reaching their limit in terms of speed, dimensions and permissible power consumption. This has been a major concern in data centers and large scale computing platforms, creating limits to their scalability especially with respect to power consumption. Silicon photonic-electronic integration is viewed as a viable alternative that enables reliability, high efficiency, low cost and small footprint. In particular, silicon with its high refractive index, has enabled the integration a many individual optical elements (ring resonators) in small areas. Though silicon has a high thermo-optic coefficient (1.8×10^-4/°C) compared to silica, small thermal fluctuations can affect the optical performance especially for WDM applications. Therefore, a passive athermal solution for silicon photonic devices is required in order to reduce thermal sensitivity and power consumption. We have achieved this goal by replacing the silica top cladding with negative thermo-optic coefficient (TOC) materials. While polymers and titanium dioxide(titania) have a negative TOC, polymers can’t handle high temperature processing and titania needs very tight thickness control and expensive deposition under vacuum. In this work we propose to use a sol-gel inorganic-organic hybrid material that has the benefits of both worlds. We were able to find optimum curing conditions to athermalize ring resonators by studying various sol-gel curing times and curing temperatures. Our athermal rings operate in a wide temperature range from 5C – 100C with thermal shifts below 1pm/C and low loss. Furthermore, we demonstrate that our athermal approach does not deleteriously effect critical device parameters, such as insertion loss and resonator Q factors.

We have proposed a silica-polymer hybrid variable optical attenuator that we made by creating two trenches along the core of a straight silica planar waveguide and filling the trenches with a polymer. The polymer, which had a superhigh thermo-optic coefficient, was specially designed and developed in this study to lower the power consumption of the device. We achieved a maximum attenuation of -29 dB for the device by changing the polymer's temperature by only 7 degrees C. The device has a very low power consumption at 2-3 mW/channel, making it a good candidate for integration with arrayed waveguide gratings.

We have demonstrated an ultra-compact birefringence-compensated arrayed waveguide grating (AWG) triplexer based on silicon nanowire waveguide. The cross-order design is employed and the device has a small footprint of 0.18×0.12 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The normalized losses for TM polarization for three channels are less than 4 dB with the crosstalk better than 18 dB. The polarization dependent wavelength shift (PDλ) is less than 2.5 nm for three channels operating at the wavelength range of 1490-1550 nm by using angled star couplers in combination with different diffraction orders for the two polarizations.

The realisation of a monolithic athermalised variable-optical-attenuator-integrated multiplexer (VMUX) implemented in silica-on-silicon waveguide technology is reported. The VMUX incorporates an athermal arrayed waveguide grating, providing <0.05 nm of peak transmission wavelength shift over 20–70°C operating ambient independent of attenuator settings.

We report on the successful design and fabrication of a polarization-insensitive arrayed waveguide grating (AWG), using solgel-derived silica glass films formed on fused-silica substrates. By controlling the waveguide width and making the propagation constants of the polarizations equal, we have found it possible to fabricate polarization-insensitive solgel-based AWGs. Polarization-insensitive design improves the cross talk by approximately 10 dB in the dynamic range.

In the aim of describing the thermo-mechanical behaviour of a thin-film filter, simplified models have been studied. An easy way is to determine the evolution of the optical properties of each layer composing the stack, and thus to derive the features change at the component level. Therefore, the knowledge of physical parameters describing each material, such as the coefficient of thermal expansion, the thermo-optic coefficient, the Poisson's ratio and the elasto-optic coefficients, is required. The main challenge is to evaluate these parameters at a single layer level. We propose here a new optical method, based on the analysis of the thermal behaviour of two dedicated Fabry-Perot (FP) structures including a thin disk of the material under study. In parallel, we show through modelling, that we can determine the physical properties of this material with a high accuracy, only by measuring the shift of FP resonance wavelengths. However, we have to take into account the mechanical deformation of the Fabry-Perot structures induced by the thin-film deposition process as well as its evolution with the temperature change (thermal stresses). In this goal, we carried out an accurate study of the thermo-mechanical behaviour of our interferometric structures by using a Finite Element Method.

The burgeoning field of astrophotonics, the interface between astronomy and photonics, is redefining astronomical instrumentation to replace traditional bulk optical systems with integrated optics. This drives the development of a new promising photonics-integrated interferometric imaging technique, called the segmented planar imaging detector for electro-optical reconnaissance (SPIDER). Compared to conventional imaging systems, SPIDER can reduce the size, weight, and power (SWaP) by one to two orders of magnitude for an equivalent imaging resolution in virtue of photonics-integrated technology. However, SPIDER has a dense lens distribution and tens of separated narrow wavebands demultiplexed by array waveguide gratings. In this paper, we developed a new simplified sparse-aperture photonics-integrated interferometer (SPIN) imaging system. The SPIN imaging system was no more a Michelson configuration interferometer as SPIDER and was designed as a Fizeau configuration interferometer imaging system. This transfer of configuration type affords a more concise structure; the SPIN was designed with much less apertures and fewer wavebands than those of SPIDER. Further, the SPIN yields enhanced modulation transfer function and imaging quality with equivalent aperture diameter, compared with SPIDER. The main barrier of this transfer is the elimination of coupling restriction at the tip of a waveguide, namely the apodization effect. This effect, which is caused by the coupling effect between Fourier lens and waveguide, hinders SPIN imaging systems from getting finer resolution. However, a microscope could be used to eliminate this effect. Moreover, a waveguide array is used to receive these finer details and enlarges the field of view in SPIN. The coupling efficiency of the waveguides and crosstalk errors between waveguides of array were analyzed, which are important for proper parameters setting in SPIN imaging system. Based on these analyses, the imaging principle was derived and a hyper-Laplacian-based imaging reconstruction algorithm was developed. A simulation of the SPIN imaging system with seven apertures and one imaging waveband demonstrated the high imaging quality.

We show that stress engineering can be used to adjust the SOI waveguide birefringence to the stringent polarization tolerances expected of commercial devices, using only standard silicon processes. With decreasing device dimensions and high index contrast the waveguide birefringence becomes increasingly sensitive to device geometry. As a result, it is almost impossible to eliminate waveguide birefringence by adjusting waveguide profile alone. This paper presents, for the first time, a systematic study of the stress-induced birefringence of SOI waveguides. Through full-vectorial finite-element simulations, we investigate the variation of stress-induced birefringence with waveguide core and cladding geometries. It is found that the stress-induced birefringence is determined by the waveguide cross-section, the upper cladding layer thickness, and film stress levels. We develop a waveguide model that predicts the total waveguide birefringence and guides the post-fabrication processing steps. An experimental demonstration of a polarization insensitive SOI arrayed waveguide grating (AWG) demultiplexer is presented. The polarization dependent wavelength shifts measured experimentally agree well with the simulations.