Grating couplers with an integrated power splitter for high-intensity optical power distribution

In this letter, we present a fiber grating coupler with an integrated 16-way power splitter. The incoming light from the fiber is split immediately over 16 channels, and therefore, the total optical power is never confined in a single waveguide. This is of particular interest for silicon photonics platforms, because, here, high optical intensities can cause significant non-linear losses. The device has a total coupling efficiency that is similar to standard focusing grating couplers. Furthermore, a channel non-uniformity below 1.1 dB has been obtained. By studying the alignment sensitivity, we found that for high splitting uniformity, a careful positioning of the fiber is necessary. We also experimentally demonstrate that this device is indeed capable of handling high optical powers without introducing additional non-linear losses

Optimized silicon AWG with flattened spectral response using an MMI aperture

We demonstrate compact 12-channel 400 GHz arrayed waveguide grating wavelength demultiplexers (AWG) in silicon with a flattened spectral response. Insertion loss, crosstalk and non-uniformity are -3.29 dB, 17.0 dB and 1.55 dB, respectively. The flattened spectral response is obtained by using an optimized mode shaper consisting of a multi-mode interference coupler as the input aperture of the AWG. The ratio of the 1 dB bandwidth to the 10 dB bandwidth is improved by 50%, from 0.33 to 0.49 compared to a conventional AWG. The device size is only 560x350 mu m(2)

Compact silicon nitride arrayed waveguide gratings for very near-infrared wavelengths

In this letter, we report a novel high-index-contrast silicon nitride arrayed waveguide grating (AWG) for very near-infrared wavelengths. This device is fabricated through a process compatible with a complementary metal-oxide-semiconductor fabrication line and is therefore suitable for mass fabrication. The large phase errors that usually accompany high-index-platform AWGs are partly mitigated through design and fabrication adaptions, in particular the implementation of a two-level etch scheme. Multiple devices are reported, among which a 0.3-mm(2) device which, after the subtraction of waveguides loss, has a -1.2 dB on-chip insertion loss at the peak of the central channel and 20-dB crosstalk for operation similar to 900 nm with a channel spacing of 2 nm. These AWGs pave the way for numerous large-scale on-chip applications pertaining to spectroscopy and sensing

Multi-parameter extraction from SOI photonic integrated circuits using circuit simulation and evolutionary algorithms

We propose a procedure to extract multiple parameters from the spectral characteristic of a single photonic integrated circuit. We applied the method on high order silicon Mach-Zehnder lattice filters:1 these filters are realized by cascading delay stages and directional couplers of different length. Because of their cascaded nature and steep roll-off properties, these devices can be used to accurately extract properties of the waveguides and the directional couplers. The spectral transmission is measured between the inputs and the outputs. This result is compared to a full CAPHE optical circuit simulation with parametric behavioral models for the waveguide and the directional couplers. An evolutionary fitting algorithm based on the covariance matrix adaptation method is used to match the circuit simulation with the measurement. This black box approach gives us fast and accurate parameter extraction with a reduced number of iteration steps. The quadratic error between measurement and simulation of each iteration is used as feedback for the evolutionary algorithm that adapts the test values for the following step. The objective of our analysis is an accurate, wavelength-dependent model for the waveguide group index and the directional couplers. The proposed method has been used for wafer scale parameter extraction. Our fast method makes it possible to extract the parameters in real time, and correlate the functional parameters of the waveguides with process statistics collected during fabrication. The obtained parameters are in substantial agreement with the results of the simulations used in the design, and can be used to further improve behavioral models that correlate the manufacturing process data with the optical performance

Effect of mask discretization on performance of silicon arrayed waveguide gratings

We studied the impact of the lithography mask discretization on silicon arrayed waveguide grating (AWG) performance. When we decreased the mask grid from 5 to 1 nm, we observed an experimental improvement in crosstalk of 2.7-6 dB and cumulative crosstalk improvement of 1.2-5 dB, depending on the wavelength channel spacing and the number of output channels. We demonstrate the effect for the AWGs with 200-and 400-GHz channel spacing, with 4, 8, and 16 output wavelength channels. With 1-nm mask grid, the average crosstalk is -26 and -23 dB for 400- and 200-GHz devices, respectively. This is the lowest crosstalk for silicon AWGs reported to the best of our knowledge. A simulation study is performed by looking specifically at phase errors due to mask grid snapping (ignoring other phase error sources), which shows an expected improvement in crosstalk of 12 dB

Experimental extraction of effective refractive index and thermo-optic coefficients of silicon-on-insulator waveguides using interferometers

We propose and demonstrate an accurate method of measuring the effective refractive index and thermo-optic coefficient of silicon-on-insulator waveguides in the entire C-band using three Mach-Zehnder interferometers. The method allows for accurate extraction of the wavelength dispersion and takes into account fabrication variability. Wafer scale measurements are performed and the effective refractive index variations are presented for three different waveguide widths: 450, 600, and 800 nm, for the TE polarization. The presented method is generic and can be applied to other waveguide geometries and material systems and for different wavelengths and polarizations