A paper recently published in the journal Nature Communications demonstrated an effective method to realize on-chip nanophotonic topological rainbow devices using the concept of synthetic dimensions.
Importance of Synthetic Dimensions for the Construction of Topological Nanophotonics Device
Topological photonics witnessed significant advancements in the last few years. Due to topological protection, photonic devices have become more immune to scattering and robust against disorder. However, realizing topological nanophotonic devices are still considerably difficult owing to the challenges in nano-scale measurement, inherently weak magnetic response for natural materials in the near-infrared and visible range, and complexity in the fabrication process.
Synthetic dimensions can offer an insight into topological photonics beyond the geometric dimensions. Thus, synthetic dimensions can facilitate the fabrication of on-chip all-dielectric topological nanophotonic components, eliminating the limitations of magnetic materials.
Existing Limitations of Multi-frequency Topological Nanophotonic Devices
Multi-wavelength/multi-frequency devices are crucial components in nanophotonic chips used for applications with large information processing capacity. Among these multi-wavelength devices, the topological rainbow, a basic multi-frequency topological photonic device, can slow, separate, and trap topological photonic states of different frequencies into various positions.
However, this type of device has not been thoroughly investigated in studies until now. Additionally, effective methods for the direct measurement of multi-frequency topological photonic devices at the nanoscale are yet to be identified. Thus, these challenges restricted the application and development of the topological rainbow and different topological nanophotonic devices, such as topological temporary storage and topological router.
Schematic diagram of the topological rainbow configuration. a1, a2 denote the lattice vectors. The red and blue regions denote the barrier and dispersing regions, respectively. The displacement vector of ith layer is denoted by ξia2. Na, Nξ, Nb denote the number of layers of regions I, III along a1 direction, and Nu, Nd denote the number of layers of undeformed region and the deformed region in region II. Light is incident from the dielectric waveguide with a width w = 8 μm. b Evolution of Zak phases with parameter ξ. The inset shows the geometric structure for different ξs. c The TE-like bands of triangular hole structure with side length l = 0.75a and thickness h = 220 nm. The geometry of the unit cell is shown in the inset. © Lu, C., Hu, X., Wang, C. et al. (2022)
Novel Way to Fabricate Nanophotonic Topological Rainbow Device Based on Synthetic Dimension
In this study, researchers fabricated an on-chip nanophotonic topological rainbow device based on translational deformation freedom as a synthetic dimension, which represents an approach that is applicable for all wavelength ranges, dimensions, materials, symmetries, and optical lattice types.
In a topological rainbow device, the light can be trapped and slowed by controlling the topological photonic state group velocities. In the study, the topological photonic states were realized by fabricating topological “Chern insulators” without requiring a magnetic field.
Design of the Topological Rainbow
The topological rainbow geometric structure was composed of three regions, including a dispersing region and two barrier regions. The dispersing region distributes and separates different frequencies of the topological photonic states into various positions owing to the non-trivial topology in the synthetic dimension. The barrier regions acted as a bandgap to prevent any leakage of light.
The barrier regions were composed of ordinary photonic crystals (PCs) with a full bandgap, and the lattice vectors were designated as a2 and a1. The dispersing region was fabricated by a graded translationally deformed PC on one side and an undeformed PC on the other side.
The ratio between the lattice vector and the ith layer displacement was defined as the translational parameter. A waveguide acted as the source of the external light signal, and the frequency range was located within the PC bulk bandgap.
The topological rainbow proposed in this study was experimentally verified in the optical frequency range using silicon-based technologies.
Fabrication and Evaluation of Nanophotonic Topological Rainbow Device
The 4.5 micrometers × 22 micrometers PC samples were fabricated on a silicon on insulator (SOI) chip using the focused-ion-beam system. The SOI chip was composed of two micrometers thick silicon dioxide layer and 220 nanometers thick silicon layer. A tunable laser with less than 100 kilohertz of line width and a wavelength between 1520 nanometers and 1630 nanometers was used to illuminate the fabricated samples.
A fiber directional coupler was employed to separate the continuous-wave laser light into a reference arm and signal arm. In the Mach–Zehnder interferometer (MZI) signal arm, a lensed fiber was used to launch the light into the waveguide and collect the modulated reflection light generated by the atomic force microscope (AFM) probe. The quasi-transverse electric (TE) polarization in the guided modes in the waveguide was ensured using the three-paddle polarization controller.
In the MZI reference arm, the light was frequency shifted by 30 kilohertz using an in-line lithium niobate phase modulator equipped with a saw-tooth waveform generator. The all-fiber characteristic of the experiment led to low background noise, convenience, and compactness, which was necessary for near-field imaging of on-chip photonic circuits.
Subsequently, both the reference and the signal arm were combined and sent to an indium gallium arsenide-amplified photodetector. The photocurrent can precisely yield the phase and amplitude of the signal light through a lock-in amplifier at demodulation frequency.
A reflection-based homemade scattering scanning near-field optical microscope (s-SNOM) comprising a fiber-MZI with heterodyne detection and an AFM module was utilized to precisely determine the topological rainbow effect of the fabricated on-chip topological rainbow device.
The s-SNOM system possessed the capability of scanning repeatability, high optical collection efficiency, and sub-structure spatial resolution. A cantilevered AFM probe was used as a near-field probe for near-field microscopy.
The bands of the edge states and the bulk states were calculated using the finite element method, while the topological rainbow intensity distribution was determined by the finite-difference time-domain (FDTD) method.
a The top view of the FDTD model, where coordinate axes are marked and light is incident from the waveguide. b The light intensity distributions (|E|2) of the calculated results for different wavelengths. c The topographic image of the sample. The color denotes the height of the surface of the sample. d The light intensity distributions of experimental results for different wavelengths. The comparison between interface intensity and projected bands for calculated (e) and experimental (f) results. In b, d, the position with maximal intensity is marked by the cyan dashed rhombuses, and the corresponding y coordinates are marked in the left. The wavelength of incident light is marked on the top of each figure. © Lu, C., Hu, X., Wang, C. et al. (2022)
News
Common Medication Could Save Half a Million Lives Each Year – So Why Isn’t It?
A recent study conducted by scientists at the University of Southern California sheds light on the reasons why children are not receiving an affordable and effective diarrhea treatment. Medical professionals in developing nations are [...]
X Marks the Spot: AI’s Treasure Maps Lead to Early Disease Detection
Medical diagnostics expert, doctor’s assistant, and cartographer are all fair titles for an artificial intelligence model developed by researchers at the Beckman Institute for Advanced Science and Technology. Their new model accurately identifies tumors [...]
Scientists Discover Method To Identify Alzheimer’s Disease Before It Progresses to Dementia
Researchers at Aarhus University have discovered a method to identify Alzheimer’s disease before it progresses to dementia, potentially opening up new avenues for treatment. A groundbreaking study could pave the way for early detection [...]
Startling Discovery: COVID-19 Virus Can Stay in the Body More Than a Year After Infection
The COVID-19 virus can persist in the blood and tissue of patients for more than a year after the acute phase of the illness has ended, according to new research from UC San Francisco that offers potential [...]
New bioengineered protein design shows promise in fighting COVID-19
In the wake of the COVID-19 pandemic, scientists have been racing to develop effective treatments and preventatives against the virus. A recent scientific breakthrough has emerged from the work of researchers aiming to combat [...]
Sugar-coated gold nanoparticles can quickly eliminate bacterial infections, no antibiotics required
If left to their own devices, bacteria on our teeth or wounded skin can encase themselves in a slimy scaffolding, turning into what is called biofilm. These bacteria wreak havoc on our tissue and, [...]
Liquid Lightning: Nanotechnology Unlocks New Energy
EPFL researchers have discovered that nanoscale devices harnessing the hydroelectric effect can harvest electricity from the evaporation of fluids with higher ion concentrations than purified water, revealing a vast untapped energy potential. Evaporation is a natural [...]
Unmasking the Illusion: AI-Generated Faces Challenge Perceptions
Research shows survey participants duped by AI-generated images nearly 40 percent of the time. If you recently had trouble figuring out if an image of a person is real or generated through artificial intelligence [...]
New Discovery Reveals How Cells Defend Themselves During Stressful Situations
Stress granules play a crucial role in the stress response, arising from the aggregation of non-translating mRNAs and proteins. Although significant knowledge exists about stress granules, the mechanisms behind their mRNA localization remain partially [...]
Scientists use a new type of nanoparticle that can both deliver vaccines and act as an adjuvant
Many vaccines, including vaccines for hepatitis B and whooping cough, consist of fragments of viral or bacterial proteins. These vaccines often include other molecules called adjuvants, which help to boost the immune system's response [...]
Not Science Fiction: How Optical Neural Networks Are Revolutionizing AI
A novel architecture for optical neural networks utilizes wavefront shaping to precisely manipulate the travel of ultrashort pulses through multimode fibers, enabling nonlinear optical computation. Present-day artificial intelligence systems rely on billions of adjustable [...]
Turning skin cells into limb cells sets the stage for regenerative therapy
In a collaborative study, researchers from Kyushu University and Harvard Medical School have identified proteins that can turn or “reprogram” fibroblasts — the most commonly found cells in skin and connective tissue — into [...]
AI reveals prostate cancer is not just one disease
Artificial Intelligence has helped scientists reveal a new form of aggressive prostate cancer, which could revolutionise how the disease is diagnosed and treated in the future. A Cancer Research UK-funded study, published in Cell Genomics, has revealed [...]
New Study Finds That Persistent COVID-19 Infections Are Surprisingly Common
Recent research conducted by the University of Oxford has found that a high proportion of SARS-CoV-2 infections in the general population lead to persistent infections lasting a month or more. The findings have been published in the journal Nature. [...]
Innovative nanosheet method revolutionizes brain imaging for multi-scale and long-term studies
The human brain has billions of neurons. Working together, they enable higher-order brain functions such as cognition and complex behaviors. To study these higher-order brain functions, it is important to understand how neural activity [...]
Scientists Have Discovered a Potential Universal Antivenom
Scientists at Scripps Research identified antibodies that protect against a host of lethal snake venoms. Scripps Research scientists have developed an antibody that can block the effects of lethal toxins in the venoms of [...]