Multi-Mode Interferometry: Application to TiO2–SiO2 Sol-Gel Waveguide-Based Sensing in the Aerospace Domain

The optimization of a 2D optical sensor based on TiO2–SiO2 sol-gel waveguides for damage detection in the aerospace domain was performed in the framework of the ADD-ON European project. The sensor is based on the transportation of visible light along numerous waveguides, and damage is detected and localized through the monitoring of the output light from the waveguide grid. In this work, we have developed an architecture, inspired by a multi-mode interferometer (MMI), allowing us to efficiently multiply the number of waveguides that can be probed by a single optical source. For this, the beam propagation method (BPM) was used to model a rectangular MMI coupler (40 × 5624 µm2) operating in the visible region (600 nm), ensuring the propagation of light into three waveguides. The conceived device was then manufactured by UV photolithography (direct laser writing technique). The simulations and experimental results show that light transport into this architecture allows for the successful simultaneous probing of three waveguides. By complexifying the device structure, successful MMI couplers were easily manufactured, allowing us to probe 9, 15, or 45 TiO2–SiO2 waveguides with a unique light source. Finally, a further investigation regarding 24 consecutive thermal cycles from −40 °C to 60 °C, representative of the temperature changes during aircraft cruising, was performed. This study reveals that TiO2–SiO2 sol-gel waveguides are not mechanically damaged by temperature changes, while the light guidance remains unaffected, confirming that this sensor is very promising for aerospace applications. Since a single source can monitor several guides, the production of more compact, low-cost, and less intrusive sensors can be achieved by fulfilling structural health monitoring requirements.

Optical Power Splitter Based on Single Mode Directional Coupler Waveguide Using SnO2 Nanomaterial

Optical power splitter based on waveguide had been simulated numerically using Finite Difference Beam Propagation Method (FDBPM). Proposed waveguide was designed in the form of simple directional coupler waveguide. The waveguide was contained SnO2 nanomaterial as film or the guide part and the other supporting material as cladding with lower refractive index such as flint glasses. The waveguide used 2 μm of width to establish single-mode waveguide. The structure of waveguide is divided into three parts such as input, coupling and output part. While the waveguide was modified with angle in input and output parts to avoid coupling between waveguides. Furthermore, the proposed waveguide was analysed by varying the angle and coupling length. The analysed result shows that the waveguide has best performance in angle of 0.5 degrees and coupling length of 300 μm when the propagation loss was around 0.53%. Using the parameter, the output distribution percentage of waveguide approached 55%:44.5%. This performance indicated that the proposed waveguide can be used as optical power splitter. The application is very useful for optical telecommunication networking development.

Suitability of BPM Simulation for Silicon Photonics

<p>Validated both numerically and experimentally, Beam Propagation Method (BPM) has been proven to be a very efficient and reasonably accurate simulation approach for certain silicon photonics (SiP) devices. This paper clears up some misunderstanding in SiP community that BPM is not suitable for SiP devices. </p>

Suitability of BPM Simulation for Silicon Photonics

<p>Validated both numerically and experimentally, Beam Propagation Method (BPM) has been proven to be a very efficient and reasonably accurate simulation approach for certain silicon photonics (SiP) devices. This paper clears up some misunderstanding in SiP community that BPM is not suitable for SiP devices. </p>

Ultra-Sensitive Intensity Modulated Strain Sensor by Tapered Thin-Core Fiber Based Modal Interferometer

In this paper, to enhance practicality, a novel tapered thin-core fiber (t-TCF) based modal interferometer is proposed and demonstrated experimentally. The light field distribution of t-TCF structure is investigated by a beam propagation method, and the quantitative relationship is gained between light intensity loss and waist diameter. Under ~30 μm waist diameter, multiple t-TCF based sensor heads are fabricated by arc-discharged splicing and taper techniques, and comprehensive tests are performed with respects to axial strain and temperature. The experimental results show that, with near-zero wavelength shift, obvious intensity strain response is exhibited and negative-proportional to the reduced length of TCF. Thus, the maximum sensitivity reaches 0.119 dB/με when the TCF length is equal to 15 mm, and a sub-micro-strain detection resolution (about 0.084 με) is obtained. Besides, owing to the flat red-shifted temperature response, the calculated cross-sensitivity of our sensor is compressed within 0.32 με/°C, which is promising for high precision strain related engineering applications.

Reconfigurable Quantum Photonic Convolutional Neural Network Layer Utilizing Reconfigurable Photonic Gate and Teleportation Mechanism

This article, proposes a reconfigurable quantum photonic convolutional layer (QPCL) based on the reconfigurable photonic gates. The QPCL is used in the classical photonic CNN, where, an array of reconfigurable photonic gates (RPG) are arranged in a systematic way. The designed reconfigurable photonic gate serves as a unit cell for quantum photonic operations such as beam splitting, rotation, displacement, squeezing, and cubic- phase shifting. The designed RPG provides the features namely broadband operation, low insertion loss and compact layout. The entangled states are created based on the normalized pixel value of the input image. The configuration of reconfigurable photonic gate is accomplished using electro-optic P-i-N carrier injection mechanism. As compared to Mach-Zehnder interferometer (MZI) based realization, the proposed silicon reconfigurable photonic gate provides scalable operation and compact footprint. The reconfigurable photonic gate is modeled using 2D finite element beam propagation method (FEBPM). Finally, a compact numerical model is developed which performs Gaussian based continuous-variable (CV) quantum photonic operations and are verified with Xanadu’s strawberryfields quantum photonic simulator and PennyLane deep learning framework. The optimized accuracy (loss) is obtained with the utilization of QPCL layer and the values are 0.7627 (0.9595), this optimum result is obtained using a single QPCL layer with an epoch number of 30. Finally, a comparative analysis is made between quantum CNN and classical photonic CNN, where the quantum CNN resulted in 6.553% high accuracy and 6.988% low loss compared to the classical photonic CNN.

Design of Silicon TE0/TE1 Mode Router Using Mach-Zehnder and Multimode Interferometers

This paper proposes a new design of two-mode three-port optical mode router for mode division multiplexing systems. The device consists of a Mach-Zehnder interferometer (MZI) and a multimode interferometer (MMI), which utilizes silicon material for photonic integrated circuits (PIC). By setting appropriate values for the two butterfly-shaped phase shifters (PSs) at MZI and MMI, the input mode, either transverse electric (TE) modes TE0 or TE1, can be routed to the desired output among the three output ports. The device is designed and optimized via three-dimensional beam propagation method (3D BPM). The proposed device achieves very low insertion loss and small cross-talk, which are less than 0.4 dB and -24.5 dB, respectively, over the whole C band.

Structural Optimization of an Optical 90 Degree Hybrid Based on a Weakly-guided 4x4 Multimode Interference Coupler Using a Parallelized Real-coded Micro-genetic Algorithm

The optimal design of a 4x4 multimode interference (MMI) coupler as an optical 90° hybrid based on a weakly-guided optical waveguide was considered. Seven geometrical parameters of a 4x4 MMI coupler were optimized by a real-coded micro-genetic algorithm, and parallelized using a message-passing interface. The beam-propagation method was used to evaluate the fitness of the MMI coupler in the optimization process. The optimized 4x4 MMI coupler showed a common-mode rejection ratio greater than 28.9 dBe and a phase error less than 2.52° across a wavelength range of 1520 to 1580 nm, which satisfied typical system requirements. The optimization process was executed on a Beowulf-style cluster comprising five identical PCs, and its parallel efficiency was 0.78.