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Fabrication variability significantly impacts the performance of photonic integrated circuits (PICs), which makes it crucial to quantify the impact of fabrication variations before the final fabrication. Such analysis enables circuit and system designers to optimize their designs to be more robust and obtain maximum yield when designing for manufacturing. This work presents a simulation methodology, Reduced Spatial Correlation Matrix-based Monte-Carlo (RSCM-MC), to efficiently study the impact of spatially correlated fabrication variations on the performance of PICs. First, a simple and reliable method to extract physical correlation lengths, variability parameters that define the inverse of the spatial frequencies of width and height variations over a wafer, is presented. Then, the process of generating correlated variations for MC simulations using RSCM-MC methodology is presented. The methodology generates correlated variations by first creating a reduced correlation matrix containing spatial correlations between all the circuit components, and then processing it using Cholesky decomposition to obtain correlated variations for all circuit components. These variations are then used to conduct MC simulations. The accuracy and the computation performance of the proposed methodology are compared with other layout-dependent Monte-Carlo simulation methodologies, such as Virtual wafer-based Monte-Carlo (VW-MC). A Mach-Zehnder lattice filter is used to study the accuracy, and a second-order Mach-Zehnder filter and a 16x16 optical switch matrix system are used to compare the computational performance.

Large-scale optical switch networks employ wavelength division multiplexing to expand and facilitate multiple input and outputs. Such networks can be implemented with the Mach-Zehnder interferometer (MZI) as the building block. A fully-loaded MZI switch, meaning one with two optical signals at its two inputs and one that is capable of simultaneously switching those inputs to its two outputs, reduces the number building blocks within the network, and as a result makes them more power and area efficient. However, for practical operation, such MZI switches need to be automatically controlled for overcoming fabrication and thermal variations. We present an interference-based monitoring method that enables automatically switching, tuning, and stabilizing of a fully-loaded 2×2 MZI optical switch and demonstrate a prototype on an SOI platform. Using the proposed device and off-the-shelf electronics, we demonstrate automatic tuning and stabilization of an MZI switch with 12.5 Gb/s and 25 Gb/s data rates and channel spacing as small as 1 nm.

We designed and fabricated a polarization splitter-rotator (PSR) on a silicon-on-insulator (SOI) platform based on an asymmetric directional coupler. The asymmetric directional coupler consists of a regular strip waveguide and a sub-wavelength grating (SWG) waveguide. The SWG waveguide used in the design provides the freedom to engineer the dispersion properties of the supermodes, which allow the design to be fabrication tolerant to the waveguide width variations. A measured peak polarization conversion efficiency of −0.3 dB and crosstalks below −10 dB were achieved. The designed SWG PSR has a compact size of 35 ${\mu} \text{m} \times 5\,{\mu} \text{m}$ .

We experimentally demonstrate compact broadband directional couplers using subwavelength gratings for silicon-on-insulator wafers with silicon layers of 220 nm. The dispersion properties of the optical modes are engineered using subwavelength gratings, which allow broadband operation. Finite-difference time-domain (FDTD)-based band structure calculations, with significantly reduced simulation time, were used to analyze the design, which included both the structure and material dispersions. Compact broadband direction couplers, with device lengths shorter than 14 $\mu\text{m}$, which cover a bandwidth of 100 nm for power splitting ratios of 50/50, 40/60, 30/70, and 20/80, are designed and fabricated for the fundamental transverse electric mode with a central operating wavelength of 1550 nm.

We demonstrate photonic ultra-efficient thermo-optic switches on a 220-nm silicon-on-insulator platform. We used several approaches to increase the tuning efficiency of the switches. We used folded waveguides in a Michelson interferometer configuration to increase the optical interaction length of the light with the heated region, and used a suspended structure to improve thermal isolation. An ultra-low switching power of 50 $\mu \text{W}$ is realized with an extinction ratio of over 26 dB for the transverse electric mode at 1550 nm. The 10%–90% response time of the switch is 1.28 ms, including a 780 $\mu \text{s}$ rise time and a 500 $\mu \text{s}$ fall time. Compared with the best thermo-optic switch in the literature, our device shows approximately an order of magnitude reduction in power consumption.

We experimentally demonstrate apodized focusing subwavelength grating couplers for both the fundamental transverse electric (TE00) mode and the fundamental transverse magnetic (TM00) mode. A measured insertion loss of 3.2 dB with a 1-dB bandwidth of 36 nm has been obtained for the TE00 mode, and a measured insertion loss of 3.3 dB with a 1-dB bandwidth of 37 nm has been obtained for the TM00 mode. Back reflections of -24 dB and -21 dB have been obtained for the TE00 and TM00 modes, respectively.

This work develops an enhanced Monte Carlo (MC) simulation methodology to predict the impacts of layout-dependent correlated manufacturing variations on the performance of photonics integrated circuits (PICs). First, to enable such performance prediction, we demonstrate a simple method with sub-nanometer accuracy to characterize photonics manufacturing variations, where the width and height for a fabricated waveguide can be extracted from the spectral response of a racetrack resonator. By measuring the spectral responses for a large number of identical resonators spread over a wafer, statistical results for the variations of waveguide width and height can be obtained. Second, we develop models for the layout-dependent enhanced MC simulation. Our models use netlist extraction to transfer physical layouts into circuit simulators. Spatially correlated physical variations across the PICs are simulated on a discrete grid and are mapped to each circuit component, so that the performance for each component can be updated according to its obtained variations, and therefore, circuit simulations take the correlated variations between components into account. The simulation flow and theoretical models for our layout-dependent enhanced MC simulation are detailed in this paper. As examples, several ring-resonator filter circuits are studied using the developed enhanced MC simulation, and statistical results from the simulations can predict both common-mode and differential-mode variations of the circuit performance.

We design and demonstrate a compact broadband polarization beam splitter (PBS) using a symmetric directional coupler with sinusoidal bends on a silicon-on-insulator platform. The sinusoidal bends in our PBS suppress the power exchange between two parallel symmetric strip waveguides for the transverse-electric (TE) mode, while allowing for the maximum power transfer to the adjacent waveguide for the transverse-magnetic (TM) mode. Our PBS has a nominal coupler length of 8.55 μm, and it has an average extinction ratio (ER) of 12.0 dB for the TE mode, an average ER of 20.1 dB for the TM mode, an average polarization isolation (PI) of 20.6 dB for the through port, and an average PI of 11.5 dB for the cross port, all over a bandwidth of 100 nm.

We studied both numerically and experimentally electromagnetic behaviors of a bilayered metal helical structure in the microwave-frequency. Two resonances are found in the transmission spectrum of the circularly polarized wave which has the same handedness with the helices. The resonance frequencies are almost independent on the distance between the two layers. In addition, the center frequency of full width at half-maximum (FWHM) in the transmission spectrum is approximately inversely proportional to the distance between the two layers.

We propose a design of a novel optical metamaterial absorber that is broadband and independent to polarization. The absorber consists of opposite-handedness metallic triple-helix array. Simulated by the finite-difference time-domain (FDTD) method, an average absorbance of 89.10% is observed in the region of 0.33-1.22 μm as well as an absorption peak of 97.57% at 0.43 μ m. Compared with many existing planar metamaterial absorbers, this helical metamaterial absorber shows advantages of broadband and polarization independence. In addition, we systematically study the dependence of the absorptive property on its geometric parameters and materials. It is expected that the superior absorptive properties of this helical MM absorber can also be realized in other region of spectrum by appropriately scaling the sub-wavelength structures.

We demonstrate photonic ultra-efficient thermo-optic switches on a 220-nm silicon-on-insulator platform. We used several approaches to increase the tuning efficiency of the switches. We used folded waveguides in a Michelson interferometer configuration to increase the optical interaction length of the light with the heated region, and used a suspended structure to improve thermal isolation. An ultra-low switching power of 50 μW is realized with an extinction ratio of over 26 dB for the transverse electric mode at 1550 nm. The 10%–90% response time of the switch is 1.28 ms, including a 780 μs rise time and a 500 μs fall time. Compared with the best thermo-optic switch in the literature, our device shows approximately an order of magnitude reduction in power consumption.

Polarization beamsplitters (PBSs) and polarization rotators (PRs) are essential components for polarization control in silicon photonic integrated circuits. Here, we review our recent work on both component and circuit designs for polarization control.

We report on a compact, broadband, 2×2 adiabatic 3 dB coupler using sub-wavelength gratings (SWGs) for silicon-on-insulator waveguides. In our device, two SWG waveguides that support two transverse electric modes and have tapered waveguide widths were used to achieve an adiabatic mode evolution of the two-waveguide system for broadband 3 dB power splitting. We present results for a SWG adiabatic 3 dB coupler that has an overall coupler length of 50 μm and achieves broadband power splitting over a 130 nm wavelength range with an imbalance of no greater than ±0.3 dB and with low excess losses of less than 0.5 dB.

We experimentally demonstrate an automated polarization receiver that couples light from any polarization state output from a single-mode fiber into the fundamental quasi-TE mode of a single-mode waveguide in an integrated silicon photonic circuit.

In this letter, we demonstrate the relationship between the incident angles and the polarization states of transmitted beams on the basis of a kind of helical metamaterials. Through finite-difference time-domain simulations, it is found that the polarization states of the transmitted lights can be tuned by changing the incident angles. When the angles vary from 20° to -20°, the axial ratios of the transmitted lights have significant changes from 1:0.93 to 1:0.59. This phenomenon of the tunable polarization can be explained qualitatively through the analysis of the surface current on the helical wires.

In the last few years, much attention has been paid to the researches of metallic helical metamaterials due to their giant circular dichroism for transmitted lights. However, so far as we know, there is little work concerning the study of their reflection properties, which are also significant questions for the helical metamaterials. In this work, we study the reflection properties of the helical metamaterials by using the Finite-Difference Time-Domain (FDTD) method. The circular dichroism and the reflected polarization states of left-handed single-, double-, triple-, and quadruple-helical structures are investigated, respectively. It's found that both the single- and the double-helical structures perform giant circular dichroism, and their reflected polarization states are related to the handedness of helical structure; while triple- and quadruple-helical structures exhibit no circular dichroism at all, and their reflected polarization states are irrelevant to the handedness of helical structure.

In the last few years, there has been growing interest in the research of helical metamaterials due to the advantages of giant circular dichroism, broad operation bands, and compact structures. However, most of the researches were in the cases of single-, circular-helical metamaterials, and normal incidences. In this paper, we reviewed recent simulation works in the helical metamaterials with the finite-difference time-domain (FDTD) method, which mainly included the optical performances of double-, three-, four-helical metamaterials, performances of elliptical-helical metamaterials, and the polarization properties under the condition of oblique incidences. The results demonstrate that the double-helical metamaterials have operation bands more than 50%, which is broader than those of the single-helical structures. But both of them have low signal-to-noise ratios about 10 dB. The three- and four-helical metamaterials have significant improvement in overall performance. For ellipticalhelixes, simulation results suggest that the transmitted light can have elliptical polarization states. On the condition of oblique incidences, the novel property of tunable polarization states occurred in the helical metamaterials, which could have much broader potential applications such as tunable optical polarizers, tunable beam splitters, and tunable optical attenuators.

We analyze and demonstrate a method for increasing the efficiency of thermo-optic phase shifters on a silicon-on-insulator platform. The lack of cross-coupling between dissimilar waveguides allows highly dense waveguide routing under heating elements and a corresponding increase in efficiency. We demonstrate a device with highly dense routing of 9 waveguides under a 10 µm wide heater and achieve a low switching power of 95 µW, extinction ratio greater than 20 dB, and less than 0.1 dB ripple in the through spectrum with a footprint of less than 800 µm × 180 µm. The increase in waveguide density is found not to negatively impact the switch response time.

We experimentally demonstrate sinusoidal anti-coupling silicon-on-insulator strip waveguides, separated by 200 nm, that have a minimum inter-waveguide crosstalk suppression of 26.8 dB within the C-band for the fundamental transverse electric mode.

We demonstrated adiabatic 3-dB couplers on silicon-on-insulator strip waveguides. We obtained average splitting ratios, from 1500 nm to 1600 nm, of 44.5%/55.5% and 50.5%/49.5% for our transverse electric and transverse magnetic couplers, respectively.

We experimentally demonstrate apodized focusing fully etched sub-wavelength grating couplers for the transverse electric (TE) mode. An insertion loss of 4.2 dB, 1-dB bandwidth of 36 nm, and back reflection of −24 dB have been obtained.

We demonstrate a 1 cm long Bragg grating filter, on a compact spiral SOI waveguide, for the fundamental transverse magnetic mode, that has a 0.5 nm bandwidth, 40 dB extinction ratio, and 1 dB/cm loss.

We demonstrate 3-dB broadband directional couplers that use asymmetric-waveguide-based phase compensation. Average coupling ratios of 46.57% and 48.28% were obtained from 1500 nm to 1600 nm for transverse electric and transverse magnetic modes, respectively.

The three-dimensional (3D) and two-dimensional (2D) chiral metamaterials (CMMs) have been proved to exhibit circular dichroism and circular conversion dichroism, respectively. The layer-by-layer chiral metamaterials, as a category of 3D CMMs, are expected to show the same properties as bulk 3D structures (e.g. helices). However, in this paper, we demonstrated that the layer-by-layer CMMs exhibit circular dichroism and circular conversion dichroism simultaneously by using both theoretical and experimental methods. This work showed that asymmetric transmissions of circular polarizations can also be observed in layer-by-layer CMMs. Moreover, we provided some necessary requirements for the existing of asymmetric transmissions in layer-by-layer CMMs.

In this work, a novel optical metamaterial absorber is proposed which has properties of broad band and independent to polarization. The absorber consists of opposite-handedness metallic triple-helix array. Simulated with the finite-difference time-domain (FDTD) method, an average absorbance of 89.10% is observed in the region of 0.33~1.22 μm as well as an absorption peak of 97.57% at 0.43 μm, Compared with many existing planar metamaterial absorbers, this helical metamaterial absorber shows advantages of broad-band and polarization independence.

We design and demonstrate a wideband silicon photonic polarization beamsplitter on a silicon-on-insulator platform. The device consists of two 3 dB broadband couplers cascaded in a point-symmetric network. The transverse electric (TE) and transverse magnetic (TM) modes are coupled to different output ports due to a large difference between their coupling strengths. The device exhibits large isolation at both the two output ports, of more than 20 dB over a large bandwidth of 125 nm, and a small excess loss, of less than 0.5 dB for the entire C-band.

We present a methodology to design broadband grating couplers using one-dimensional subwavelength gratings. Using the presented method, we design subwavelength grating couplers (SWGCs) with 1-dB bandwidths ranging from 50 to 90 nm. Our designed SWGCs have competitive coupling efficiency, as high as -3.8 dB for the fundamental TE mode, and state-of-the-art back reflections, as low as -23 dB.

We demonstrate spiral Bragg grating waveguides (BGWs) on the silicon-on-insulator (SOI) platform for the fundamental transverse magnetic (TM) mode. We also compare TM spiral waveguides to equivalent transverse electric (TE) spiral waveguides and show that the TM spiral waveguides have lower propagation losses. Our spiral waveguides are space-efficient, requiring only areas of 131×131 µm(2) to accommodate 4 mm long BGWs, and, thus, are less susceptible to fabrication non-uniformities. Due to the lengths and reduced susceptibility to fabrication non-uniformities, we were able to obtain narrow bandwidth, large extinction ratio (ER) devices, as narrow as 0.09 nm and as large as 52 dB, respectively. Finally, we demonstrate a 4 mm long TM chirped spiral Bragg grating waveguide with a negative, average, group delay slope of -11 ps/nm.

We design and demonstrate broadband directional couplers that use asymmetric-waveguide based phase control sections, on the silicon-on-insulator platform. Broadband directional couplers with various power splitting ratios, including 10%/90%, 20%/80%, 30%/70%, 40%/60% and 50%/50%, were realized for both transverse electric (TE) and transverse magnetic (TM) modes. Some of the devices exhitbit bandwidths in excess of 100 nm, and all in excess of 75 nm. The footprints of the TE mode couplers are 32 μm ×1.3 μm, or less, and those of the TM mode couplers are 13 μm ×1.3 μm, or less.

We studied numerically the transmission properties of a kind of layer-by-layer nonchiral metamaterial. Simulation results show that under certain off-normal incidence, giant circular polarization conversion occurs for both the right and left circularly polarized waves with a roughly 1 GHz operation band. Meanwhile, the copolarization transmissions are almost suppressed to zero, leading to the high purity circular polarization transformation. This phenomenon of giant circular polarization conversion is assumed to suffer from the strong magnetic response, which is illustrated by the surface current distributions of the structure. Compared with chiral structures, this nonchiral structure is easier to design and fabricate and is expected to be used as a promising circular polarization transformer.

We present two kinds of broadband and polarization-insensitive metamaterial (MM) absorbers operating in about 0.3–2.5 μm, including a racemic type and a reflected type. Through finite-difference time-domain simulation, we find that both designs are broadband in function and insensitive to polarization. In comparison, we find that the reflected type absorber possesses broader bandwidth (0.36–2.5 μm) and exhibits higher average absorbance (88.9%), while the racemic type is superior in its polarization-insensitivity characteristic. Differing from designs of most planar MM absorbers based on perfect impedance matching, our designs are based on the principle of mutual radiation.

We fabricated three-dimensional metallic helix arrays with single-, double-, and triple-helical structures. The transmission performances with the normal incident angle were measured in the microwave frequency of 12-18 GHz. For the single- and double-helical structures, giant circular dichroism with fairly wide bands is observed in the transmission spectra. However, the triple-helical structure does not exhibit circular dichroism. Based on the phenomenon of circular dichroism, the single- and double-helical structures can be used as broadband circular polarizers in the microwave region, but triple-helical ones cannot. The experiments have a good agreement with our simulation results, which were studied by the finite-difference time domain method.

SmTbFeCO amorphous films were r.f.-magnetron sputtered from a mosaic target onto glass substrate. The magnetic and magneto-optical properties of SmTbFeCo thin films deposited at different argon pressure, sputtering power and negative substrate bias voltage were studied. It is shown that the deposition conditions strongly affect the reflectivity R, the coercivity Hc and Kerr rotation angle (theta) k. In order to meet the requirement of magneto-optical recording, it is optimal to choose Ar pressure of 0.47 approximately 0.73 Pa, sputtering power of 300 approximately 350W, and negative substrate bias voltage of -80V approximately -110V.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.