Silicon Channel Waveguides Research Articles

Seamless multi-reticle photonics.

While Moore's law predicted shrinking transistors would enable exponential scaling of electronic circuits, the footprint of photonic components is limited by the wavelength of light. Thus, future high-complexity photonic integrated circuits (PICs) such as petabit-per-second transceivers, thousand-channel switches, and photonic quantum computers will require more area than a single reticle provides. In our novel approach, we overlay and widen waveguides in adjacent reticles to stitch a smooth transition between misaligned exposures. In SiN waveguides, we measure ultralow loss of 0.0004 dB per stitch, and produce a stitched delay line 23 m in length. We extend the design to silicon channel waveguides, and predict 50-fold lower loss or 50-fold smaller footprint versus a multimode-waveguide-based method. Our approach enables large-scale PICs to scale seamlessly beyond the single-reticle limit.

Design and analysis of guided modes in photonic waveguides using optical neural network

We present a deep learning approach using an optical neural network to predict the fundamental modal indices neff in a silicon (Si) channel waveguide. We use three inputs, e.g., two geometric and one material properties, and predict the neff for transverse electric and transverse magnetic polarizations. With the least number (i.e., 33 or 43) of exact mode solutions from Maxwell’s equations, we can uncover the solutions which correspond to 103 numerical simulations. Note that this consumes the lowest amount of computational resources. The mean squared errors of the exact and the predicted results are <10−5. Moreover, our parameter ranges are compatible with current photolithography and complementary metal–oxide–semiconductor (CMOS) fabrication technology. We also show the impacts of different transfer functions and neural network layouts on the model’s performance. Our approach presents a unique advantage to uncover the guided modes in any photonic waveguides within the least possible numerical simulations.

Angular momentum of optical modes in a silicon channel waveguide

This work studies the behavior of angular momentum of highly confined optical modes in a channel waveguide, in which the influence of transverse confinement is characterized by the average transverse wavevectors

Analysis of Silicon Channel Waveguide Thermo-Optic Switches by the Image Charge Method

Employing the “image charge” method, we theoretically study the influence of key physical parameters on the thermo-optic characteristics of a channel waveguide silicon-on-insulator (SOI) Mach–Zehnder Switch. The power consumption and spatial temperature profile of such structures are given as explicit functions of various structural, thermal, and optical parameters, offering physical insight not available in finite-element simulations. Agreement with finite-element simulations is demonstrated. The trends of switching power versus various parameters provide quantitative guide for further device optimization. This approach may also be useful for efficient modeling of an integrated optical circuit containing a large number of thermo-optic devices.

Time-asymmetric loop around an exceptional point over the full optical communications band.

Topological operations around exceptional points1-8-time-varying system configurations associated with non-Hermitian singularities-have been proposed as a robust approach to achieving far-reaching open-system dynamics, as demonstrated in highly dissipative microwave transmission3 and cryogenic optomechanical oscillator4 experiments. In stark contrast to conventional systems based on closed-system Hermitian dynamics, environmental interferences at exceptional points are dynamically engaged with their internal coupling properties to create rotational stimuli in fictitious-parameter domains, resulting in chiral systems that exhibit various anomalous physical phenomena9-16. To achieve new wave properties and concomitant device architectures to control them, realizations of such systems in application-abundant technological areas, including communications and signal processing systems, are the next step. However, it is currently unclear whether non-Hermitian interaction schemes can be configured in robust technological platforms for further device engineering. Here we experimentally demonstrate a robust silicon photonic structure with photonic modes that transmit through time-asymmetric loops around an exceptional point in the optical domain. The proposed structure consists of two coupled silicon-channel waveguides and a slab-waveguide leakage-radiation sink that precisely control the required non-Hermitian Hamiltonian experienced by the photonic modes. The fabricated devices generate time-asymmetric light transmission over an extremely broad spectral band covering the entire optical telecommunications window (wavelengths between 1.26 and 1.675 micrometres). Thus, we take a step towards broadband on-chip optical devices based on non-Hermitian topological dynamics by using a semiconductor platform with controllable optoelectronic properties, and towards several potential practical applications, such as on-chip optical isolators and non-reciprocal mode converters. Our results further suggest the technological relevance of non-Hermitian wave dynamics in various other branches of physics, such as acoustics, condensed-matter physics and quantum mechanics.

Integrating cell on chip—Novel waveguide platform employing ultra-long optical paths

Optical waveguides are the most fundamental building blocks of integrated optical circuits. They are extremely well understood, yet there is still room for surprises. Here, we introduce a novel 2D waveguide platform which affords a strong interaction of the evanescent tail of a guided optical wave with an external medium while only employing a very small geometrical footprint. The key feature of the platform is its ability to integrate the ultra-long path lengths by combining low propagation losses in a silicon slab with multiple reflections of the guided wave from photonic crystal (PhC) mirrors. With a reflectivity of 99.1% of our tailored PhC-mirrors, we achieve interaction paths of 25 cm within an area of less than 10 mm2. This corresponds to 0.17 dB/cm effective propagation which is much lower than the state-of-the-art loss of approximately 1 dB/cm of single mode silicon channel waveguides. In contrast to conventional waveguides, our 2D-approach leads to a decay of the guided wave power only inversely proportional to the optical path length. This entirely different characteristic is the major advantage of the 2D integrating cell waveguide platform over the conventional channel waveguide concepts that obey the Beer-Lambert law.

Dielectric probes for submillimeter and terahertz‐wave range instrumentation and characterizations

AbstractIn this letter, a new set of silicon probes, at submillimeter and terahertz frequency range, for I/O connectivity and instrumentation applications are introduced.The designed probes are optimized for testing of planar silicon‐based integrated circuits using newly introduced network analyzers, e.g., a PNA‐X. The probes have been optimized for different frequency windows matched to the standard metallic rectangular waveguides (WR‐2, WR‐4, and WR‐6) corresponding to the frequency band of 110–500 GHz and higher. The probes comprised of highly resistive silicon channel waveguides, which are tapered on both sides laterally and vertically. The side of the probes which is coupled to the WR waveguide is tapered laterally and the other end which is used to couple the signal to or out of the sample under the test is tapered vertically with an angle of 54.6°. The probes are pressed (side‐coupled) on the sample under the test. The probing system consisting of the input and output tapers and a channel silicon waveguide as the sample under the test are designed and simulated using HFSS v.12 for three windows of frequencies including 110–170, 170–260, and 325–500 GHz. The simulation results show that the insertion loss and return loss are lower than 3 dB and higher than 15 dB, respectively; which are much better than the losses of commercially available high frequency probes. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:2095–2098, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27003

Saturation behaviour of colloidal PbSe quantum dot exciton emission coupled into silicon photonic circuits

We report coupling of the excitonic photon emission from photoexcited PbSe colloidal quantum dots (QDs) into an optical circuit that was fabricated in a silicon-on-insulator wafer using a CMOS-compatible process. The coupling between excitons and sub-μm sized silicon channel waveguides was mediated by a photonic crystal microcavity. The intensity of the coupled light saturates rapidly with the optical excitation power. The saturation behaviour was quantitatively studied using an isolated photonic crystal cavity with PbSe QDs site-selectively located at the cavity mode antinode position. Saturation occurs when a few μW of continuous wave HeNe pump power excites the QDs with a Gaussian spot size of 2 μm. By comparing the results with a master equation analysis that rigorously accounts for the complex dielectric environment of the QD excitons, the saturation is attributed to ground state depletion due to a non-radiative exciton decay channel with a trap state lifetime ~ 3 μs.

Low loss optical channel waveguides for the infrared range using niobium based hybrid sol–gel material

In this work, we report the fabrication of single-mode Nb2O5 based hybrid sol–gel channel waveguides. Nb2O5 based hybrid sol–gel material has been deposited by spin-coating on silicon substrate and channel waveguides have been fabricated by a UV direct laser writing process. Optical guided modes have been observed to confirm single-mode conditions and optical propagation loss measurements have been performed using the cut-back technique. Optical propagation losses were measured to be 0.8dB/cm and 2.4dB/cm at 1.31μm and 1.55μm respectively. These experimental results demonstrate low loss optical waveguiding within the infrared range and are very promising in view of material choice for the development of integrated optical devices for telecommunication.

Transparent amorphous silicon channel waveguides and high-Q resonators using a damascene process

We demonstrate a damascene process for fabricating amorphous silicon (a-Si), single-mode optical channel waveguides and high-Q racetrack resonators. This process is compatible with thermal budget limitations for a-Si phase stability. It offers improved optical transmission and facilitates hydrogen encapsulation for process integration of a-Si waveguide cores. At 1,550 nm, the average measured transmission loss coefficient is 2.5+/-0.1 dB/cm for the TE mode, comparable with high-quality single crystalline silicon counterparts. The racetrack resonators have mid-10(4) to 10(5) quality factors (Q) and extinction ratios as high as 25 dB.

Demonstration of a Tunable Microwave-Photonic Notch Filter Using Low-Loss Silicon Ring Resonators

We present a fully tunable multistage narrowband optical pole-zero notch filter that is fabricated in a silicon complementary metal oxide semiconductor (CMOS) foundry. The filter allows for the reconfigurable and independent tuning of the center frequency, null depth, and bandwidth for one or more notches simultaneously. It is constructed using a Mach-Zehnder interferometer (MZI) with cascaded tunable all-pass filter (APF) ring resonators in its arms. Measured filter nulling response exhibits ultranarrow notch 3 dB BW of 0.6350 GHz, and nulling depth of 33 dB. This filter is compact and integrated in an area of 1.75 mm2. Using this device, a novel method to cancel undesired bands of 3 dB bandwidth of < 910 MHz in microwave-photonic systems is demonstrated. The ultranarrow filter response properties have been realized based on our developed low-propagation loss silicon channel waveguide and tunable ring-resonator designs. Experimentally, they yielded a loss of 0.25 dB/cm and 0.18 dB/round trip, respectively.

Heterodyne near-field scanning optical microscopy with spectrally broad sources

We propose to use low-coherence-length cw optical sources with a broad spectrum in heterodyne near-field scanning microscopy in order to imitate optical pulse propagation and to obtain information about spectrally variant properties of nanophotonic components. The dispersion difference in the interferometer arms for a symmetric acousto-optic modulator arrangement is shown to be negligible over appreciable bandwidths. Demonstration of the principle of operation and viability of this approach is provided by measurement of the group refractive index of a silicon channel waveguide.

Transparent amorphous silicon channel waveguides with silicon nitride intercladding layer

We have experimentally demonstrated single mode amorphous silicon channel waveguides with low optical transmission loss of 2.7±0.4 dB/cm for TE mode in the 1550 nm range. This result was achieved by using hydrogen passivation of a-Si dangling bonds and a thin, low loss silicon nitride intercladding layer prepared by plasma enhanced chemical vapor deposition between the waveguide core and the oxide cladding layer. The silicon nitride intercladding layer reduces waveguide sidewall roughness scattering and preserves the hydrogen passivation.

Silicide Schottky-Barrier Phototransistor Integrated in Silicon Channel Waveguide for In-Line Power Monitoring

An in-line power monitor with a thin nickel silicide layer placed on a silicon channel waveguide for optical absorption is proposed. A two-terminal Schottky-barrier collector phototransistor configuration is used to amplify significantly the primary photocurrent, and the Ni silicide thickness is thinned down to ~5 nm using a two-step rapid thermal annealing procedure to reduce the insertion loss. The demonstrated in-line detectors exhibit ~24-mA/W responsivity around 1550 nm with the insertion loss of ~0.8-1.2 dB. The approaches to further increase the responsivity and simultaneously decrease the insertion loss are addressed.

Towards routine near-field optical characterization of silicon-based photonic structures: An optical mode analysis in integrated waveguides by transmission AFM-based SNOM

We report on the characterization of modal propagation in integrated waveguides using a transmission AFM-based scanning near-field optical microscope. This technique probes the field inside an integrated waveguiding structure by measuring the change in transmission due to the local interaction with the AFM tip. In this paper, we clearly show that it is sensitive to the full spectrum of modes, which includes propagating and counterpropagating guided and radiation modes. For a rather simple waveguiding sample (ion exchange monomode straight waveguide), the technique allows for retrieving the effective indexes of the propagating modes. This is achieved by measuring the standing wave pattern due to interference between the propagating and counterpropagating modes and by performing a Fourier analysis. In the case of porous silicon channel waveguide, although very contrasted, the image was found to be too complex to be analyzed. Phase sensitive measurements are in that case needed to discriminate in k space the different modes involved. Potentiality and limitation of the technique are discussed focusing on the modal analysis.

Compact electro-optic modulator on silicon-on-insulator substrates using cavities with ultra-small modal volumes

We experimentally demonstrate a micron-size electro-optic modulator using a high-index-contrast silicon Fabry-Pérot resonator cavity. This compact device consists of a 1-D cavity formed within a single mode silicon channel waveguide and an embedded p-i-n junction on a silicon-oninsulator platform. The entire device is 6.0 microns in length. We demonstrate modulation depths as large as 5.87 dB at speeds of 250 Mbps limited only by fabrication imperfections, with optimized theoretical speeds of several Gbps.

Highly drop-efficient channel-drop optical filters with Si-based photonic crystal slabs

Channel-drop filters (CDFs) with photonic crystal slabs–connected between silicon channel waveguides and fabricated on an SOI wafer–were designed and fabricated and these demonstrated wavelength division demultiplexing. Results simulated with the two-dimensional finite-difference time-domain and plane-wave methods demonstrated that considering the impedance profile, which is directly correlated with the reflective coefficient at the highly reflective interface, is essential in designing a highly drop-efficient CDF structure. The fabricated filters attained a drop efficiency above 95% at around a wavelength of 1.6 μm and a dropping bandwidth of 1.5 nm.