Rib Waveguide Research Articles

Design and fabrication of GeAsSeS chalcogenide waveguides with thermal annealing* *Project supported by the National Natural Science Foundation of China (Grant Nos. 61904091 and 61775111), Zhejiang Provincial Natural Science Foundation of China (Grant No. LR18E010002), the Natural Science Foundation of Ningbo City, China (Grant No. 2019A610065), the International Cooperation Project of Ningbo City, China (Grant No. 2017D10009), and K. C.

We reported a chalcogenide glass-based rib waveguide fabricated using photolithography and dry etching method. A commercial software (COMSOL Multiphysics) was used to optimize the waveguide structure and the distribution of the fundamental modes in the waveguide based on the complete vector finite component. We further employed thermal annealing to optimize the surface and sidewalls of the rib waveguides. It was found that the optimal annealing temperature for GeAsSeS films is 220 °C, and the roughness of the films could be significantly reduced by annealing. The zero-dispersion wavelength (ZDW) could be shifted to a short wavelength around ∼ 2.1 μm via waveguide structural optimization, which promotes supercontinuum generation with a short wavelength pump laser source. The insertion loss of the waveguides with cross-sectional areas of 4.0 μm × 3.5 μm and 6.0 μm × 3.5 μm was measured using lens fiber and the cut-back method. The propagation loss of the 220 °C annealed waveguides could be as low as 1.9 dB/cm at 1550 nm.

CMOS-Compatible Photonic Phase Shifters With Extremely Low Thermal Crosstalk Performance

We report a thorough analysis of the thermal crosstalk issue for silicon photonic circuits using metal and doped silicon heaters for the two waveguide configurations, rib and strip waveguides. Full-wave thermal and optical simulations are performed and it is observed that integrated doped heaters with strip waveguides have the best thermal crosstalk performance. Also, the effect of metal contacts on the heater power consumption is investigated. Furthermore, to alleviate the phase crosstalk and improve the phase tuning efficiency, a deep trench is implemented to thermally shield an adjacent waveguide. Two well-known photonic components, namely, integrated Mach-Zehnder modulators and PN phase shifters are designed and the thermal crosstalk performance is analyzed rigorously. The proposed photonic phase shifter is outperformed in terms of thermal crosstalk over the existing designs. Such phase shifters are viable for compact silicon photonic circuits operating at a very high temperature.

Rib Waveguide Based Liquid Crystal EO Switch

We report electrically re-configurable liquid crystal core rib waveguide based electro-optic switch. It is proposed to use single side anchored in-plane switching (IPS) configuration for optical switching in view of its low threshold voltage and low switching voltage in comparison to that in a double-side anchored LC waveguide switch. Further, the proposed LC waveguide based switch has better response time than that in a double side anchored configuration at operating voltage close to threshold voltage of a double side anchored. The device has been realized on a BK7 glass substrate using E7 LC. We also show wavelength re-configurability of the switch over a wide wavelength range (1 - 3 μm) by externally applied voltage. Proposed work would be useful for optical signal processing on integrated optic platform.

Generation of 280 THz-spanning near-ultraviolet light in lithium niobate-on-insulator waveguides with sub-100 pJ pulses

Integrated optics has weak ultraviolet and near-ultraviolet (NUV) light conversion due to its strong material dispersion and large propagation losses. To reach this spectral range, we use non-centrosymmetric waveguides that convert near-infrared (NIR) supercontinuum light into broadband NUV light. We measure a 280 THz span that reaches the upper frequency of 851 THz (352 nm) in a 14-mm long rib waveguide of lithium niobate-on-insulator, with an engineered dispersion for supercontinuum generation in the NIR range. The results on broadband NUV signals promote integrated optics for spectroscopy and fluorescence applications such as atomic clocks and chemical sensors.

A compact and low-driving-voltage silicon electro-absorption modulator utilizing a Schottky diode operating up to 13.2 GHz in C-band

This paper demonstrates a 1 Vpp low-driving-voltage silicon electro-absorption modulator (EAM) utilizing a Schottky diode. Optical modulation using a Schottky diode was achieved through the intensity change of the guiding light due to free-carrier absorption in the semiconductor to change its absorption coefficient, not through conventional interference effects. The proposed EAM consists of a lateral metal–semiconductor junction that helps maximize free-carrier injection and extraction through a Schottky contact on rib waveguide. In order to achieve high-speed operation, traveling-wave type electrodes were designed. The fabricated EAM demonstrates a broad operational wavelength range of 50 nm for C-band with a uniform extinction ratio (ER) of 3.9 dB, even for a compact modulation length of 25 μm with a driving voltage of 1 Vpp. Also, the traveling-wave type electrodes enabled the modulator to operate at up to 26 GHz with 13.2 GHz of 3 dB electro-optic bandwidth experimentally.

Design and simulation of strip loaded and rib waveguide with integration of 2D material

Objective- To design Graphene-Silicon based rib waveguide and reduce the losses in the strip in order to meet the requirement for ultra-fast & ultrahigh optical bandwidth communication and computing in integrated optical devices. Method –Propagation losses and effective refractive index are the two key parameters. In order to meet the objective, the effects of Graphene for manufacturing passive devices/components in the field of Integrated Photonic like integrated optical waveguide have been analysed by measuring the changes in propagation losses and effective refractive index of the silicon photonics devices for operating at different wavelengths. Findings- We have presented the design and simulation of SOI (Silicon-on-Insulator) platforms with 2D layer materials (graphene) which has been used along with their mode of propagation, effective refractive index (ne f f ), propagation losses (dB/cm) and varying wavelength range for optimum performance. In addition to this, we have also calculated the boundary limit for both the speed and bandwidth. We also reported the development of Silicon rib waveguide, Graphene-Silicon based rib waveguide and Ge on SOI with graphene later at the top of strip waveguide.Minimum loss of strip waveguide is 2.9 dB/cm which has been obtained for Mid-IR wavelength generally used for high power mid- IR sensing.

Silicon waveguide as virtual photonic bandgap structure array for realizing compact optical filters

ABSTRACT An engineered silicon rib waveguide on Silicon-On-Insulator platform which can act as virtual photonic bandgap structure is proposed. Selective periodic etching of materials from a rib waveguide is done to create a periodic rib-ridge structure. Each of the rib-ridge sections will therefore have different effective refractive indices and will act as virtual multilayered periodic structure or one-dimensional photonic bandgap structure. Their spatial positions and widths can be controlled to realize different type of photonic filters for integrated photonics applications. Realization of narrowband, multi-band and band-pass filter are shown here. These types of waveguide based monomaterial optical filters avoid the challenges generally faced while fabricating multilayer structures of different heterogeneous materials having different refractive indices. Moreover, as the device is waveguide based, its size is very small and will be useful for compact integrated photonics.

A Complete Si Photonics Platform Embedding Ultra-Low Loss Waveguides for O- and C-Band

We report ultra-low propagation losses in silicon sub-micrometric waveguides on a 200 mm CMOS compatible photonics platform. We show median losses in C-band (O-band) as low as 0.1 dB/cm and 0.7 dB/cm (0.14 dB/cm and 1.1 dB/cm) in monomode rib and strip waveguides, respectively, thanks to a H2 smoothing annealing. In addition to the significant loss reduction, we show that the performance characteristic of the main passive and active components of the photonics platform are preserved or even improved by the smoothing process.

Waveguide cavity optomagnonics for microwave-to-optics conversion

Cavity optomagnonics has emerged as a promising platform for studying coherent photon-spin interactions as well as tunable microwave-to-optical conversion. However, current implementation of cavity optomagnonics in ferrimagnetic crystals remains orders of magnitude larger in volume than state-of-the-art cavity optomechanical devices, resulting in very limited magneto-optical interaction strength. Here, we demonstrate a cavity optomagnonic device based on integrated waveguides and its application for microwave-to-optical conversion. By designing a ferrimagnetic rib waveguide to support multiple magnon modes with maximal mode overlap to the optical field, we realize a high magneto-optical cooperativity, which is three orders of magnitude higher compared to previous records of the magneto-optical cooperativity obtained on polished yttrium iron garnet spheres. Furthermore, we achieve tunable conversion of microwave photons at around 8.45 GHz to 1550 nm light with a broad conversion bandwidth as large as 16.1 MHz. The unique features of the system point to novel applications at the crossroad between quantum optics and magnonics.

High Bandwidth Capacitance Efficient Silicon MOS Modulator

This article analysed and optimised horizontal Silicon insulator Silicon capacitor (H-SISCAP) phase shifter structures with insulator thickness tox up to 40 nm. The phase shifter has an effective capacitance ( C eff) around 0.5 fF/μm and a phase change efficiency 1.8 V ·cm, of which the balance between capacitance and phase efficiency is comparable with silicon rib waveguide based depletion type phase shifters. Silicon Mach–Zehnder interferometer (MZI) modulators with 200 μm long H-SISCAP phase shifters optimised for TM polarised light have been fabricated and demonstrated with a 3 dB EO bandwidth above 35 GHz and intrinsic H-SISCAP RC bandwidth around 150 GHz. The modulator displays open eye-diagrams for data rates up to 60 Gbit/s without detection equalization and 72 Gbit/s with 2 taps equalization in NRZ-OOK operation. The demonstrated H-SISCAP phase shifter paves the way to build high bandwidth segmented, travelling wave and compact ring resonators modulators for applications of optical transmitters, microwave generations, and LIDAR applications, etc.

Low-Loss and Small 2 × 4λ Multiplexers Based on 2 × 2 and 2 × 1 Mach–Zehnder Interferometers With On-Chip Polarization Multiplexing for 400GbE

Two silicon, 4λ O-band multiplexers (MUXs) for 400GbE using two Mach-Zehnder interferometers (MZIs) having 90-degree phase shift in their output with the help of on-chip polarization multiplexing are demonstrated. By using 2 × 2 and 2 × 1 MZIs for first 3200-GHz filters, the relative position of their spectra has 90-degree phase difference, leading to significant simplification of the tuning of peak wavelength position of the two filters. The polarization MUX is done by using an on-chip polarization-splitter-rotator (PSR) based on an asymmetric directional coupler (ADC) and a TE1-TM0 mode converter (MC) using tapered rib waveguide, designed for O-band application. Two 4λ MUXs for 1.28 and 1.3 μm bands are designed, aiming to the specified wavelength range in 400GbE. Tolerance analysis shows the proposed MUX is robust to the change of waveguide width occurring in the fabrication process, compared with those of conventional multi-stage 4λ MUXs. The averaged insertion loss of eight wavelength is 1.86 dB for the fabricated device and the demonstration of 8λ (2×4λ) MUX for 400GbE based on Si-waveguide is for the first time.

Heterodyne interferometry applied to the characterization of nonlinear integrated waveguides.

We demonstrate that heterodyne interferometry makes it possible to accurately measure minute nonlinear phase shifts with little constraint on the propagation loss or chromatic dispersion. We apply this technique to characterize the effective nonlinearity of silicon nitride rib waveguides in the normal and anomalous dispersion regimes.

TE/TM-pass polarizers based on lateral leakage in a thin film lithium niobate-silicon nitride hybrid platform.

TE/TM-pass polarizers based on the lithium niobate-silicon nitride hybrid platform are numerically proposed for the first time, to the best of our knowledge. By utilizing the lateral leakage of a shallowly etched rib waveguide, 1-mm-long TE/TM-pass polarizers with high extinction ratios of 28.72/24.03 dB are obtained. Because of the anisotropy of the lithium niobate, the lateral leakage of TE/TM polarization modes can occur along crystallographic z/y directions, respectively. Such TE/TM-pass polarizers can be integrated in the same wafer.

Integration of low loss vertical slot waveguides on SOI photonic platforms for high efficiency carrier accumulation modulators.

Silicon accumulation type modulators offer prospects of high power efficiency, large bandwidth and high voltage phase linearity making them promising candidates for a number of advanced electro-optic applications. A significant challenge in the realisation of such a modulator is the fabrication of the passive waveguide structure which requires a thin dielectric layer to be positioned within the waveguide, i.e. slotted waveguides. Simultaneously, the fabricated slotted waveguide should be integrated with conventional rib waveguides with negligible optical transition losses. Here, successful integration of polysilicon and silicon slot waveguides enabling a low propagation loss 0.4-1.2 dB/mm together with an ultra-small optical mode conversion loss 0.04 dB between rib and slot waveguides is demonstrated. These fabricated slot waveguide with dielectric thermal SiO2 layer thicknesses around 6 nm, 8 nm and 10 nm have been characterized under transmission electron microscopy allowing for strong carrier accumulation effects for MOS-capacitor electro-optic modulators.

Ultra-broadband fabrication-tolerant mode division (de)multiplexer on thin film Lithium niobate

Mode division (de) multiplexers based on asymmetric directional coupler are designed and analysed on the emerging thin film lithium niobate platform in rib, buried and strip waveguide configurations. Rib configuration offers a large bandwidth of ∼215 nm with a crosstalk level lower than −10 dB, and provides a large fabrication tolerance of ±50 nm. Strip configuration exhibits a better crosstalk of −19.7 dB at the design wavelength of 1550 nm, and has a reasonable fabrication tolerance of ±30 nm. Performance of (de) multiplexers on all three waveguide configurations are analysed in terms of modal crosstalk, mode conversion efficiency, bandwidth, along with fabrication tolerance to width and sidewall angle. The influence of electro-optic effect on the coupling length of lithium niobate mode multiplexers is also investigated.

Performance characteristics of phase-change integrated silicon nitride photonic devices in the O and C telecommunications bands

The evaluation and comparison of the optical properties in the O and C bands of silicon nitride rib waveguides with integrated Ge2Sb2Te5 phase-change cells is reported. In straight rib waveguides, a high transmission contrast is observed in both bands when the Ge2Sb2Te5 cell is switched between states, being up to 2.5 dB/μm in the C-band and 6.4 dB/μm in the O-band. In the case of silicon nitride ring resonator waveguides, high quality factor resonances (Q ∼ 105) are found in both bands, leading to the provision of an ON-OFF switch characterized by an extinction ratio of 12 and 18 dB in O and C bands respectively. Finally, with the view to provide a comparison of the wavelength-dependent optical switching of the phase-change cell, a 3-dimensional finite-element method simulation is performed and a comparison of the optical-to-thermal energy conversion in both bands given.

Low-Loss and Broadband Silicon Photonic 3-dB Power Splitter with Enhanced Coupling of Shallow-Etched Rib Waveguides

A silicon photonic 3-dB power splitter is one of the essential components to demonstrate large-scale silicon photonic integrated circuits (PICs), and can be utilized to implement modulators, 1 × 2 switches, and 1 × N power splitters for various PIC applications. In this paper, we reported the design and experimental demonstration of low-loss and broadband silicon photonic 3-dB power splitters. The power splitter was realized by adiabatically tapered rib waveguides with 60-nm shallow etches. The shallow-etched rib waveguides offered strong coupling and relaxed critical dimensions (a taper tip width of 200 nm and gap spacing of 300 nm). The fabricated device exhibited an excess loss as low as 0.06 dB at a 1550-nm wavelength and a broad operating wavelength range from 1470 nm to 1570 nm. The relaxed critical dimensions (≥200 nm) make the power splitter compatible with standard fabrication processes of existing silicon photonics foundries.

Waveguide platform for quantum anticentrifugal force.

This work is a proposition of an experimental platform to observe quantum fictitious anticentrifugal force. We present an analytical and numerical treatment of a rectangular toroidal dielectric waveguide. Solving the Helmholtz equation, we obtain analytical solutions for transverse spatial modes and estimate their number as a function of system characteristics. On top of that, the analysis of the structure is extended onto a real material platform, a thin-film lithium niobate on insulator rib waveguide. The framework presented here can be applied directly to analyze the phenomenon of quantum anticentrifugal force.

Computational design & analysis of GeSe2-As2Se3-PbSe based rib waveguide for mid-infrared supercontinuum generation

We report computational modelling and numerical analysis of rib optical waveguide composed of chalcogenide GeSe2-As2Se3-PbSe and MgF2 glasses for mid infrared supercontinuum generation. Employing finite element method, we analyse the influence of geometrical parameters on waveguide dispersion & nonlinearity and perform dispersion engineering to minimize dispersion effects. Later, we analyse the influence of laser operating conditions on spectral broadening. Our simulations report a waveguide featuring zero dispersion wavelength at 2680 nm and 3310 nm in the mid infrared region, 1.4–7.6 μm spectral broadening when pumped at 3.1 μm wavelength with 85 fs pulses at peak power of 5.2 kW in a 10 mm long waveguide and nonlinearity of 991 W−1 km−1 making it suitable for mid infrared nonlinear applications.

Prospect of CW Raman Laser in Silicon- on- Insulator Nano-Waveguides


 Numerical analysis predicts that continuous-wave (CW) Raman lasing is possible in Silicon-On-insulator (SOI) nano-waveguides, despite of presence of free carrier absorption. The scope of this paper lies on lasers for communication systems around 1550 nm wavelength. Two types of waveguide structures Strip and Rib waveguides have been incorporated. The waveguide structures have designed to be 220 nm in height. Three different widths of (350, 450, 1000) nm were studied. The dependence of lasing of the SOI Raman laser on effective carrier lifetime was discussed, produced by tow photon absorption. At telecommunication wavelength of 1550 nm, Raman lasing threshold was calculated to be 1.7 mW in Rib SOI waveguide with dimensions width (W= 450 nm) and Length (L= 25 mm). The obtained Raman lasing is the lowest reported value at relatively high reflectivities. Raman laser in SOI nano-waveguides presents the important step towards integrated on-chip optoelectronic devices.