Multimode Interference Power Splitter Research Articles

Design of a 1 × 3 Power Splitter Based on Multimode Interference in a Parabolic-Type Slot-Waveguide Structure

Multimode interference (MMI) couplers based on silicon slot-waveguide structures have received widespread attention in recent years. The key issues that need to be addressed are the size and loss of such devices. This study introduces a 1 × 3 silicon-based slot-waveguide multimode interference power splitter. The device uses a gallium-nitride slot-waveguide structure to reduce the length of the coupling region and decrease additional losses. To reduce the width of the coupling region, the multimode interference coupling area is designed with a parabolic-shaped structure. The introduction of a tapered structure between the input/output waveguides and the coupling region improves additional losses and non-uniformity. Furthermore, we conducted an analysis of the fabrication tolerances of the coupling region. In this paper, we use mode solution to simulate the design of the device in the 1550 nm optical wavelength range. The eigenmode expansion method is used to simulate and optimize the parameters of the device. The device is simulated using the eigenmode expansion solver. The simulation results show that the total length of the coupling region for the device is only 4 μm. The normalized transmission of the device is 0.992, and its excess loss and imbalance are 0.036 dB and 0.003 dB, respectively. The proposed power splitter can be applied to integrated optical circuit design, optical sensing, and optical power measurement.

Ultra-broadband MMI power splitter from 1.26 to 1.67 μm with photonic bound states in the continuum

Photonic bound states in the continuum (BIC) have excellent effects in localizing light fields. Low propagation loss of TM mode has been achieved in different orders of BICs on an etchless lithium niobate (LiNbO3) platform. Herein, we simulatively demonstrate a 1 × 2 MMI (Multimode interference) power splitter based on waveguides constructed by low-refractive-index structure (ZEP-520A) on a high-refractive-index thin membrane (LiNbO3), which can optimize the bandwidth, insertion loss and other performance indicators of optical devices. Simulation results show that the working wavelength cover the entire communication band ranging from 1260 nm to 1675 nm, and the transmission efficiency is more than 48.7%, while the insertion loss is less than 0.01 dB covering a 415 nm bandwidth. The field distribution results verify that the designed MMI demonstrated high mode purity at the output, and the mode field is well localized in the LiNbO3 film, leading to a reduce of the dependence of the transmission efficiency originated from the quality of the sidewall of the device, and the device can evenly distribute the TM0 mode of the ultra-broadband incident light to the two output ports. Furthermore, the fabrication process of the MMI device can be immensely simplified by a one-step exposure method, which reduces the scattering loss and asymmetry caused by the fabrication.

Fabrication of Polymer Optical Waveguides by Digital Ultraviolet Lithography

We present the design, fabrication and characterization of polymer optical waveguides using a digital ultraviolet (UV) lithography. Grayscale optical exposure with a nonlinear compensation in quadratic form is applied to minimize the stitching loss of the transition zone between two adjacent subpatterns. Proximity effects in lithography process are compensated based on an exposure dose-map that is calculated under the approximation of scattered light pixel with a Gaussian distribution. The bending loss and propagation loss of the fabricated polymer waveguides are experimentally characterized to be around 0.1 dB/90°-bend and 0.238 dB/mm, respectively. Moreover, 1 × 2 multimode-interference power splitter, 1 × 2 Y-branch power splitter and microring resonator are demonstrated to show the feasibility of the lithography technology on rapid fabrication of waveguides. Such a UV lithography technology flexibly manipulates huge-number light pixels for all-digital grayscale and dynamic optical exposure and thus can enable the fabrication of novel optical waveguide-based devices and sensors, such as 2.5D waveguides for multimode crossing and polymer waveguide devices for biosensing.

Inverse design of the MMI power splitter by asynchronous double deep Q-learning.

The asynchronous double deep Q-learning (A-DDQN) method is proposed to design the multi-mode interference (MMI) power splitters for low insertion loss and wide bandwidth from 1200 to 1650 nm wavelength range. By using A-DDQN to guide hole etchings in the interference region of MMI, the target splitting ratio (SR) can be obtained with much less CPU time (about 10 hours for one design) and more effective utilization of the computational resources in asynchronous/parallel manner. Also, this method can simplify the design by using relatively few holes to obtain the same SR with small return loss.

Compact and Low-Insertion-Loss 1×N Power Splitter in Silicon Photonics

In this paper, a novel design of a 1×N multimode-interference power splitter is proposed and investigated. By using the finite difference time domain method and particle swarm optimization algorithm, our proposed 1×N optical power splitter can be optimized to realize compact size, good uniformity, low insertion loss, and broad bandwidth. To verify the effectiveness of this design, the designed 1×4 and 1×8 multimode-interference power splitters are experimentally demonstrated on an silicon-on-insulator platform. The lengths of the designed 1×4 and 1×8 power splitters are 36 μm and 47.8 μm, respectively. Experimental results show that, for the fabricated 1×4 power splitter, the uniformity ranges from 0.07 to 0.89 dB and the corresponding maximum insertion loss is 0.62 dB within a bandwidth from 1520 to 1624 nm. For the fabricated 1×8 power splitter, within a bandwidth from 1519 to 1623 nm, the uniformity varies from 0.19 to 0.83 dB and a maximum insertion loss of 0.64 dB are obtained.

Goos–Hänchen effect in a metal‐coated sidewall hybrid plasmonic multimode interference power splitter

A novel InP-based metal-coated sidewall, hybrid plasmonic multimode interference (MCS-HP-MMI) power splitter has been proposed. Based on two methods of multimode interference self-imaging and finite difference time domain simulations, a 1 × 2 MCS-HP-MMI power splitter was numerically analysed and compared with an HP-MMI power splitter with the same specifications showing 70% reduction in length due to the negative Goos–Hanchen shift in the metal-coated sidewalls of the MCS-HP-MMI power splitter. The width and layer stack specifications of the device were optimised using response surface methodology to minimise the multimode interference length and maximise the optical power transmission. The total optical power transmission of 98% was achieved for an MCS-HP-MMI width and length of 662 and 190 nm, respectively, with a wavelength of 1550 nm.

Visible-light silicon nitride waveguide devices and implantable neurophotonic probes on thinned 200 mm silicon wafers.

We present passive, visible light silicon nitride waveguides fabricated on ≈ 100 µm thick 200 mm silicon wafers using deep ultraviolet lithography. The best-case propagation losses of single-mode waveguides were ≤ 2.8 dB/cm and ≤ 1.9 dB/cm over continuous wavelength ranges of 466-550 nm and 552-648 nm, respectively. In-plane waveguide crossings and multimode interference power splitters are also demonstrated. Using this platform, we realize a proof-of-concept implantable neurophotonic probe for optogenetic stimulation of rodent brains. The probe has grating coupler emitters defined on a 4 mm long, 92 µm thick shank and operates over a wide wavelength range of 430-645 nm covering the excitation spectra of multiple opsins and fluorophores used for brain stimulation and imaging.

Lithographic Mask Defects Analysis on an MMI 3 dB Splitter

In this paper, we present a simulation study that intends to characterize the influence of defects introduced by manufacturing processes on the geometry of a semiconductor structure suitable to be used as a multimode interference (MMI) 3 dB power splitter. Consequently, these defects will represent refractive index fluctuations which, on their turn, will drastically affect the propagation conditions within the structure. Our simulations were conducted on a software platform that implements the Beam Propagation numerical method. This work supports the development of a biomedical plasmonic sensor, which is based on the coupling between propagating modes in a dielectric waveguide and the surface plasmon mode that is generated on an overlaid metallic thin film, and where the output readout is achieved through an a-Si:H photodiode. By using a multimode interference 1 × 2 power splitter, this sensor device can utilize the non-sensing arm as a reference one, greatly facilitating its calibration and enhancing its performance. As the spectral sensitivity of amorphous silicon is restricted to the visible range, this sensing device should be operating on a wavelength not higher than 700 nm; thus, a-SiNx has been the material hereby proposed for both waveguides and MMI power splitter.

Decoding of Multilevel Stokes-Vector Modulated Signal by Polarization-Analyzing Circuit on InP

Of-late research on Stokes vector receivers for the short-reach optical communications has gained significant attention due to its capability to decode information in multidimension using cost-effective direct-detection technique. Here, we consider the use of InP for potentially low-cost direct-detection-based Stokes vector (SV) receiver. It consists of a 1 × 4 multimode interference power splitter with different combination of polarization converters on output arms, so that input SV is projected onto distinct vectors on the Stokes space. By using the fabricated device, we experimentally demonstrate decoding of two-level and four-level SV-modulated signals at 3 Gbaud. With the potential of monolithically integrating high-speed InP photodetector array on the same chip, it paves the way to realize compact and low-cost SV receivers for multilevel SV modulation formats in future short-reach optical communication links.

Grating Coupler Design for Reduced Back-Reflections

A grating coupler having asymmetric grating trenches for low back reflections is experimentally demonstrated. Conventional and asymmetric-trench grating couplers have been fabricated on a silicon nitride waveguide platform. Both grating couplers have fully etched trenches, which normally result in higher back reflections than shallow-etched trenches. For evaluating the back reflection characteristics, test structures based on a 3-dB multimode interference power splitter have been measured and the backreflection has been extracted from each grating coupler using an equivalent optical circuit. The designed grating coupler has no critical penalty (<0.2 dB) in coupling efficiency and ~5 dB lower back reflections than a conventional grating coupler design. Using ray transfer matrix modeling, further improvements to the back reflection characteristics of the asymmetric grating coupler are expected.

A novel reconfigurable radio-over-fiber system based on flexible optical devices

In this paper, a reconfigurable Radio over Fiber system based on optical switches, optical multimode interference power splitter and tunable optical filters is designed, which can achieve quadrature phase shift keying wireless modulation in optical domain and switch carrier frequency between 30 and 60 GHz. The scheme can make good use of bandwidth resource and realize signal transmission in fiber within 10 km.

Multimode Interference Power-Splitter Using InP-Based Deeply Etched Hybrid Plasmonic Waveguide

The present study proposes a novel nanoscale multimode interference (MMI) power splitter utilizing an InP-based hybrid plasmonic waveguide at an optical communication wavelength. The layer stack has the potential to realize monolithic integrated hybrid plasmonic passive and active components. The 1 × 2, 1 × 3, and 2 × 2 MMI power splitters were simulated and optimized using a three-dimensional finite difference time domain method. The effect of MMI length, width, and wavelength on optical power transmission was investigated. Transmission was higher than 90% at 1.55 μm wavelengths. This study also presents an ultracompact shallow to deep transition between shallow-etched conventional waveguide and a hybrid plasmonic waveguide on an InP-substrate. It was shown that shallow to deep transition with a length of 2 μm has a coupling efficiency of 87.5%.

Ultra-compact tunable graphene-based plasmonic multimode interference power splitter in mid infrared frequencies

In this paper, we propose graphene-based plasmonic multimode interference power splitters with ultra-compact size working in mid infrared range. Further, the arbitrary-ratio 1$\times$2 power splitter with a size of 140 nm$\times$232 nm, where the splitting ratio can be tuned continuously from 1:1 to 100:0, is numerically demonstrated. Meanwhile, the graphene-based arbitrary-ratio 1$\times$2 power splitters with different frequencies and chemical potentials are also investigated. The proposed multimode interference structure with a deep nanoscale footprint might be a fundamental component of the future high density integrated plasmonic circuit or on-chip plasmonic interconnect techniques.

All-optical spatial light modulator for reconfigurable silicon photonic circuits

Reconfigurable photonic devices capable of routing the flow of light enable flexible integrated-optic circuits that are not hard-wired but can be externally controlled. Analogous to free-space spatial light modulators, we demonstrate all-optical wavefront shaping in integrated silicon-on-insulator photonic devices by modifying the spatial refractive index profile of the device employing ultraviolet pulsed laser excitation. Applying appropriate excitation patterns grants us full control over the optical transfer function of telecommunication-wavelength light travelling through the device, thus allowing us to redefine its functionalities. As a proof-of-concept, we experimentally demonstrate routing of light between the ports of a multimode interference power splitter with more than 97% total efficiency and negligible losses. Wavefront shaping in integrated photonic circuits provides a conceptually new approach toward achieving highly adaptable and field-programmable photonic circuits with applications in optical testing and data communication.

Vertically Stacked Multilayer Photonics on Bulk Silicon Toward Three-Dimensional Integration

Vertically stacked hydrogenated amorphous silicon (a-Si:H) and aluminum nitride (AlN) photonic circuits are fabricated on bulk silicon using complementary metal-oxide semiconductor back-end-of-line-compatible technology. The 0.5 μm × 0.22 μm a-Si:H and 1 μm × 0.4 μm AlN channel waveguides exhibit relatively low propagation losses of ∼3.8 and ∼1.4 dB/cm at 1550-nm telecom wavelengths, respectively, thus enabling the realization of various high-performance photonic devices on these two layers, such as multimode interference power splitters, waveguide ring resonators, arrayed-waveguide gratings, etc. In particular, the a-Si:H layer is suitable for ultra-compact thermo-optic (TO) devices because of its large refractive index of ∼3.5 and large TO coefficient (TOC) of ∼2.60 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−4</sup> K <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1 </sup> , whereas the AlN layer is suitable for large-size temperature-insensitive devices because of its relatively small refractive index of ∼2.0 and small TOC of ∼3.56 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−5</sup> K <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1 </sup> . A cascade directional coupler structure is proposed for connection between these two layers, which provides coupling efficiency of ∼ –1.0 dB, as estimated from numerical simulations. The feasibility of stacking different photonic layers on bulk Si paves the way to realize complex 3-D photonic circuits on chip which are not possible in the conventional single-layer configuration.

Arbitrary-ratio 1 × 2 power splitter based on asymmetric multimode interference.

Free choice of splitting ratio is one of the main properties of a power splitter required in integrated photonics, but conventional multimode interference (MMI) power splitters can only obtain a few discrete ratios. This Letter presents both numerical and experimental results of an arbitrary-ratio 1×2 MMI power splitter, which is constructed by simply breaking the symmetry of the multimode region. In the new device, the power splitting ratio can be adjusted continuously from 100:0 to 50:50, while the dimension of the multimode section stays in the range of 1.5×(1.8-2.8) μm. The experimental data also indicate that the proposed arbitrary-ratio splitter keeps the original advantages of MMI devices, such as low excess loss, weak wavelength dependence, and large fabrication tolerance.

The role of group index engineering in series-connected photonic crystal microcavities for high density sensor microarrays.

We experimentally demonstrate an efficient and robust method for series connection of photonic crystal microcavities that are coupled to photonic crystal waveguides in the slow light transmission regime. We demonstrate that group index taper engineering provides excellent optical impedance matching between the input and output strip waveguides and the photonic crystal waveguide, a nearly flat transmission over the entire guided mode spectrum and clear multi-resonance peaks corresponding to individual microcavities that are connected in series. Series connected photonic crystal microcavities are further multiplexed in parallel using cascaded multimode interference power splitters to generate a high density silicon nanophotonic microarray comprising 64 photonic crystal microcavity sensors, all of which are interrogated simultaneously at the same instant of time.

Simulation of an Ultra-Compact Multimode Interference Power Splitter Based on Kerr Nonlinear Effect

We propose an ultra-compact multimode interference (MMI) power splitter based on the Kerr nonlinear effect from simulations using modal propagation analysis. Crystalline polydiacetylene is used as the core layer to allow for the creation of a power splitter with a high number of outputs with the shortest possible multimode waveguide length operating in the nonlinear regime. The 11 high-contrast, high-resolution images at the end of the multimode waveguide in the simulated power splitter have a high power balance, whereas access to a high number of self-images is not possible under the linear regime in the proposed length range. The compact dimensions and ideal performance of the device are established according to optimized parameters. The proposed regime can be extended to the design of M × N power splitters. The results of this study indicate that nonlinear modal propagation analysis solves the miniaturization problem for all-optical devices based on MMI couplers to achieve multiple functions in a compact planar integrated circuit and also overcomes the limitations of previously proposed methods for nonlinear MMI. The results are verified using a numerical method.

Multiplexed detection of xylene and trichloroethylene in water by photonic crystal absorption spectroscopy

We experimentally demonstrate simultaneous selective detection of xylene and trichloroethylene (TCE) using multiplexed photonic crystal waveguides (PCWs) by near-infrared optical absorption spectroscopy on a chip. Based on the slow light effect of photonic crystal structure, the sensitivity of our device is enhanced to 1ppb (v/v) for xylene and 10ppb (v/v) for TCE in water. Multiplexing is enabled by multimode interference power splitters and Y-combiners that integrate multiple PCWs on a silicon chip in a silicon-on-insulator platform.

A Library of Ultra-Compact Multimode Interference Optical Couplers on SOI

A library of compact multimode interference (MMI) couplers with MMI region widths ranging from 1.1 μm to 3.2 μm is presented for 220-nm silicon-on-insulator-based photonic circuits. By optimizing the MMI geometrical parameters and considering the Goos-Häanchen shift, insertion losses of lower than 0.1 dB with moderate experimental errors are achieved for 3-dB MMI power splitters at <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</i> band, with the power imbalance around 0.2 dB.