Multimode Interference Coupler Research Articles

Two-channel highly sensitive sensors based on 4 \xd7 4 multimode interference couplers

We propose a new kind of microring resonators (MRR) based on 4 × 4 multimode interference (MMI) couplers for multichannel and highly sensitive chemical and biological sensors. The proposed sensor structure has advantages of compactness and high sensitivity compared with the reported sensing structures. By using the transfer matrix method (TMM) and numerical simulations, the designs of the sensor based on silicon waveguides are optimized and demonstrated in detail. We apply our structure to detect glucose and ethanol concentrations simultaneously. A high sensitivity of 9000 nm/RIU, detection limit of 2 × 10‒4 for glucose sensing and sensitivity of 6000 nm/RIU, detection limit of 1.3 × 10‒5 for ethanol sensing are achieved.

Chip-scale demonstration of hybrid III–V/silicon photonic integration for an FBG interrogator

Silicon photonic integration is a means to produce an integrated on-chip fiber Bragg grating (FBG) interrogator. The possibility of integrating the light source, couplers, grating couplers, de-multiplexers, photodetectors (PDs), and other optical elements of the FBG interrogator into one chip may result in game-changing performance advances, considerable energy savings, and significant cost reductions. To the best of our knowledge, this paper is the first to present a hybrid silicon photonic chip based on III–V/silicon-on-insulator photonic integration for an FBG interrogator. The hybrid silicon photonic chip consists of a multiwavelength vertical-cavity surface-emitting laser array and input grating couplers, a multimode interference coupler, an arrayed waveguide grating, output grating couplers, and a PD array. The chip can serve as an FBG interrogator on a chip and offer unprecedented opportunities. With a footprint of 5 mm×3 mm, the proposed hybrid silicon photonic chip achieves an interrogation wavelength resolution of approximately 1 pm and a wavelength accuracy of about ±10 pm. With the measured 1 pm wavelength resolution, the temperature measurement resolution of the proposed chip is approximately 0.1°C. The proposed hybrid silicon photonic chip possesses advantages in terms of cost, manufacturability, miniaturization, and performance. The chip supports applications that require extreme miniaturization down to the level of smart grains.

Integrated Reconfigurable Unitary Optical Mode Converter Using MMI Couplers

Reconfigurable unitary optical mode converters that can convert multiple orthogonal spatial modes into different orthogonal modes without fundamental optical loss are important for mode-division-multiplexed (MDM) optical communication, imaging, and quantum computation. In this letter, we propose a novel integrated reconfigurable unitary optical mode converter, which consists of cascaded multimode interference couplers and phase shifter arrays. We numerically investigate its ability to realize arbitrary unitary mode conversion and demonstrate its applicability to mode unscrambling as well as mode switching in MDM transmission systems.

Disorder effects in subwavelength grating metamaterial waveguides.

Subwavelength grating (SWG) waveguides are integrated photonic structures with a pitch substantially smaller than wavelength for which they are designed, so that diffraction effects are suppressed. SWG operates as an artificial metamaterial with an equivalent refractive index which depends on the geometry of the structure and the polarization of the propagating wave. SWG waveguides have been advantageously used in silicon photonics, resulting in significant performance improvements for many practical devices, including highly efficient fiber-chip couplers, waveguide crossings, broadband multimode interference (MMI) couplers, evanescent field sensors and polarization beam splitters, to name a few. Here we present a theoretical and experimental study of the influence of disorder effects in SWG waveguides. We demonstrate via electromagnetic simulations and experimental measurements that even a comparatively small jitter (~5 nm) in the position and size of the SWG segments may cause a dramatic reduction in the transmittance for wide (multimode) SWG waveguides, while for narrow (single mode) waveguides this effect is negligible. Our study shows that the impact of the jitter on SWG waveguide performance is directly related to the modal confinement.

Hundred gigahertz spacing Si arrayed‐waveguide grating using rib‐waveguide multimode interference coupler at slab–array interface

Silicon arrayed-waveguide grating using rib-waveguide multimode interference coupler at the array and slab waveguide interface is reported. A 100 GHz channel spacing 8ch device showing 2.8 dB insertion loss is obtained. The insertion loss was improved compared with a device using simple width taper.

Design and development of a new architecture of sliceable bandwidth variable transponder

Abstract In this paper we propose a new sliceable bandwidth variable transponder (SBVT) architecture with the separate analysis on the transmitter and receiver section. In transmission section we propose a distance module (DM) which is a programmable module. It divides a data stream/main stream (which employs a super-channel) into sub-stream and assigned modulation technique to each sub-stream based on their light path distance detailing the concept of sub-channel. In this paper, we have also proposed an algorithm for the distance module. Next we propose a modulation and transmission module (M&TM), where, planar light wave circuit (PLC) is used for enabling three modulation techniques (PM-16QAM, PM-QPSK and PM-BPSK). Finally, we propose the receiving section, which is designed to support three modulation techniques. It consists of two demodulator circuits, one for PM-16QAM/PM-QPSK and the other for PM-BPSK. In this proposed work, we focus on the multi-mode interference (MMI) devices (MMI coupler and MMI splitter) because of their photonic integration technology which is necessary for the implementation of SBVT. Lastly, we propose an elastic optical node architecture which removes the limitations of previously discussed node architecture for long distance communication.

Characteristics of Multi-Mode Interference Couplers by the Method of Lines

Characteristics of Multi-Mode Interference Couplers by the Method of Lines

Silicon-Based Integrated Tunable Fractional Order Photonic Temporal Differentiators

Two integrated fractional-order photonic temporal differentiators based on two Mach–Zehnder interferometer (MZI) structures implemented on a silicon-on-insulator (SOI) platform are designed, fabricated, and experimentally evaluated. The first photonic temporal differentiator employs a multimode interference (MMI) coupler as one of the two 3-dB couplers of the MZI. By changing the polarization state of the input optical signal, the coupling coefficient of the MMI is changed, which leads to the change of the phase shift in the destructive interference wavelength, and a photonic temporal differentiator with a tunable fractional order is implemented. The second photonic temporal differentiator is designed to have two cascaded MZIs, a balanced MZI, and an unbalanced MZI. A phase modulator (PM) is incorporated in one of the two arms of each of the MZIs. The balanced MZI with a PM forms an active tunable coupler, which is used to actively tune the fractional order of the temporal differentiator. The PM in the unbalanced MZI is used to tune the operating wavelength. The two photonic temporal differentiators are designed and fabricated in a CMOS compatible SOI platform, and their performance is evaluated experimentally. The experimental results show that both temporal differentiators can have a tunable fractional order from 0 to 1. In addition, the use of the active temporal differentiator to perform high-speed coding with a data rate of 16 Gb/s is experimentally evaluated.

A multi-core fiber based interferometer for high temperature sensing

In this paper, we have verified and implemented a Mach–Zehnder interferometer based on seven-core fiber for high temperature sensing application. This proposed structure is based on a multi-mode-multi-core-multi-mode fiber structure sandwiched by a single mode fiber. Between the single-mode and multi-core fiber, a 3 mm long multi-mode fiber is formed for lead-in and lead-out light. The basic operation principle of this device is the use of multi-core modes, single-mode and multi-mode interference coupling is also utilized. Experimental results indicate that this interferometer sensor is capable of accurate measurements of temperatures up to 800 °C, and the temperature sensitivity of the proposed sensor is as high as 170.2 pm/°C, which is much higher than the current existing MZI based temperature sensors (109 pm/°C). This type of sensor is promising for practical high temperature applications due to its advantages including high sensitivity, simple fabrication process, low cost and compactness.

Fabrication tolerant chalcogenide mid-infrared multimode interference coupler design with applications for Bracewell nulling interferometry.

Understanding exoplanet formation and finding potentially habitable exoplanets is vital to an enhanced understanding of the universe. The use of nulling interferometry to strongly attenuate the central star's light provides the opportunity to see objects closer to the star than ever before. Given that exoplanets are usually warm, the 4 µm Mid-Infrared region is advantageous for such observations. The key performance parameters for a nulling interferometer are the extinction ratio it can attain and how well that is maintained across the operational bandwidth. Both parameters depend on the design and fabrication accuracy of the subcomponents and their wavelength dependence. Via detailed simulation it is shown in this paper that a planar chalcogenide photonic chip, consisting of three highly fabrication tolerant multimode interference couplers, can exceed an extinction ratio of 60 dB in double nulling operation and up to 40 dB for a single nulling operation across a wavelength window of 3.9 to 4.2 µm. This provides a beam combiner with sufficient performance, in theory, to image exoplanets.

An On-Chip Triplexer Based on Silicon Bragg Grating-Assisted Multimode Interference Couplers

A silicon triplexer based on Bragg grating-assisted multimode interference (MMI) couplers is designed and experimentally demonstrated. Compared with the conventional MMI-based triplexers, the device length is not required to be the common multiple of beat length of different wavelengths. The simulated bandwidth is over 100 nm for 1310-nm band with the 3-D finite-different time-domain method. Experimental results of the fabricated on-chip triplexer show extinction ratios higher than 15 dB and insertion losses around 1 dB in all output ports. The total device size is only $5.4 \times 453\,\,\mu \text{m}^{\mathrm {\mathbf {2}}}$ , which is the smallest size over the experimentally demonstrated triplexers ever reported.

Optical mode switch based on multimode interference couplers

In this paper, we propose an optical mode switch based on two cascaded multimode interference (MMI) couplers. After a fundamental mode divided into two equal-power fundamental modes in the first MMI coupler, the thermo-optic effect is employed to modulate the phase of the two fundamental modes before directed to the next MMI for the purpose of mode switching. By adjusting the electric signals applied to the modulation arms, the proposed device can implement mode switching in three states: (a) one first-order and two fundamental modes simultaneously output, (b) one first-order mode output, and (c) two fundamental modes output. As a result, the simulated excess losses are −0.29 dB, −0.10 dB, and −0.63 dB, respectively.

A Design of a Vertical Multimode Interference Coupler With an Ultra-Wide Bandwidth

An ultra-wideband vertical multimode interference coupler (MMIC) is proposed. The proposed coupler replaces the conventional core of MMICs with a digital core of strongly coupled guiding layers. The thickness of the layers is modulated to fit the spectrum of their guided modes to a linear grid. This linearity suppresses the wavelength dependence of the coupling length, which maximizes the coupler bandwidth. Numerical computations demonstrate the ability to design a digital vertical-MMIC that couples more than 70% of optical power between 470 nm × 220 nm silicon-on-insulator nanowires separated by a vertical height of 3.1 μm over an ultra-wide bandwidth of 805 nm.

High bandwidth all-optical 3×3 switch based on multimode interference structures

A high bandwidth all-optical 3×3 switch based on general interference multimode interference (GI-MMI) structure is proposed in this study. Two 3×3 multimode interference couplers are cascaded to realize an all-optical switch operating at both wavelengths of 1550nm and 1310nm. Two nonlinear directional couplers at two outer-arms of the structure are used as all-optical phase shifters to achieve all switching states and to control the switching states. Analytical expressions for switching operation using the transfer matrix method are presented. The beam propagation method (BPM) is used to design and optimize the whole structure. The optimal design of the all-optical phase shifters and 3×3 MMI couplers are carried out to reduce the switching power and loss.

C-band fundamental/first-order mode converter based on multimode interference coupler on InP substrate**Project supported by the National Basic Research Program of China (No. 2014CB340102) and in part by the National Natural Science Foundation of China (Nos. 61274045, 61335009).

The design, fabrication and characterization of a fundamental/first-order mode converter based on multimode interference coupler on InP substrate were reported. Detailed optimization of the device parameters were investigated using 3D beam propagation method. In the experiments, the fabricated mode converter realized mode conversion from the fundamental mode to the first-order mode in the wavelength range of 1530–1565 nm with excess loss less than 3 dB. Moreover, LP01 and LP11 fiber modes were successfully excited from a few-mode fiber by using the device. This InP-based mode converter can be a possible candidate for integrated transceivers for future mode-division multiplexing system.

Dual-mode waveguide crossing utilizing taper-assisted multimode-interference couplers.

A dual-mode waveguide crossing is proposed and realized for the application of on-chip multimode interconnection. The present structure is realized by two 90° crossed multimode-interference (MMI) couplers. By properly choosing the width and length of the MMI section, the self-images for both the incident TM₀ mode and the TM₁ mode could be at the center of the crossing. The characterization results for the fabricated device show that low insertion loss below ∼1.5 dB and low crosstalk below ∼-18 dB can be achieved over a large bandwidth more than 80nm for both the TM₀ and TM₁ modes.

Ultra‐broadband nanophotonic beamsplitter using an anisotropic sub‐wavelength metamaterial

AbstractNanophotonic beamsplitters are fundamental building blocks in integrated optics, with applications ranging from high speed telecom receivers to biological sensors and quantum splitters. While high‐performance multiport beamsplitters have been demonstrated in several material platforms using multimode interference couplers, their operation bandwidth remains fundamentally limited. Here, we leverage the inherent anisotropy and dispersion of a sub‐wavelength structured photonic metamaterial to demonstrate ultra‐broadband integrated beamsplitting. Our device, which is three times more compact than its conventional counterpart, can achieve high‐performance operation over an unprecedented 500 nm design bandwidth exceeding all optical communication bands combined, and making it one of the most broadband silicon photonics components reported to date. Our demonstration paves the way toward nanophotonic waveguide components with ultra‐broadband operation for next generation integrated photonic systems. image

An MMI-Based Mode (DE)MUX by Varying the Waveguide Thickness of the Phase Shifter

A two-mode (de)multiplexer [(DE)MUX] based on multimode interference couplers on InP substrate is proposed and experimentally demonstrated. A phase shifting section with a variation of the waveguide thickness is introduced to precisely control the phase shift to realize 100% mode conversion efficiency and multiplexing. Performance analysis of the (DE)MUX is carried out numerically, showing excellent properties with insertion loss <;1.2 dB and crosstalk <;-18.4 dB for both the TE 0 and TE 1 mode within the whole C-band. The proposed device is also fabricated and demonstrated on InP substrate.

An 8-Channel Wavelength MMI Demultiplexer in Slot Waveguide Structures.

We propose a novel 8-channel wavelength multimode interference (MMI) demultiplexer in slot waveguide structures that operate at 1530 nm, 1535 nm, 1540 nm, 1545 nm, 1550 nm, 1555 nm, 1560 nm, and 1565 nm. Gallium nitride (GaN) surrounded by silicon (Si) was found to be a suitable material for the slot-waveguide structures. The proposed device was designed by seven 1 × 2 MMI couplers, fourteen S-bands, and one input taper. Numerical investigations were carried out on the geometrical parameters using a full vectorial-beam propagation method (FV-BPM). Simulation results show that the proposed device can transmit 8-channel that works in the whole C-band (1530–1565 nm) with low crosstalk (−19.97–−13.77 dB) and bandwidth (1.8–3.6 nm). Thus, the device can be very useful in optical networking systems that work on dense wavelength division multiplexing (DWDM) technology.

Compact On-Chip Optical Components Based on Multimode Interference Design Using High-Contrast Grating Hollow-Core Waveguides

Low-loss high-contrast grating (HCG) hollow-core waveguide (HCW) is shown to be a promising candidate for building a variety of compact multimode interference (MMI) based optical components. First, we show that HCG-HCWs demonstrate self-imaging property essential for designing MMI components. Furthermore, strong confinement of light in the waveguide core and low-index guiding leads to compact optical components. Simulation results show extremely compact 2 × 2 coupler with a length of 26 μm (16 λ), footprint (length × width) of 85 μm2 (35 λ2) and a 3-dB splitter with a length of 3.6 μm (2.4 λ), and a footprint of 12 μm 2 (5 λ2). Simulation results agree well with the predictions of MMI theory and the design can be easily extended to realize 1 × N splitters and N × N couplers. As a proof of concept, a 1 × 4 splitter with equal power splitting ratio and low insertion loss is designed. In addition, an ultracompact 2 × 2 optical switch based on HCG-HCW is proposed and simulated. The two waveguide channels are isolated by a single layer of HCG. By a small change of the refractive index of this HCG, light can switch between the channels. By proper optimization of HCG parameters, only higher order modes are excited in the MMI region resulting in an ultracompact optical switch with a switching length of 60 μm, ∼25× smaller than conventional 2 × 2 MMI coupler.