As photonic devices become more complex, the need for efficient nonlinear materials and streamlined fabrication methods has increased. Typically, fabrication of compact, integrated, nonlinear photonic devices involve expensive procedures and environments within a cleanroom. Largely due to the need for phase matching constraints, many of these materials and methods have limited nonlinear efficiency. Recently, low-loss 3D printed waveguides have been demonstrated and hence are an attractive alternative that does not require a cleanroom. In this work, second harmonic generation near telecom wavelengths with a very low-cost 3D printed waveguide and nonlinear ENZ material platform is demonstrated with an efficiency exceeding 1.2%.
KEYWORDS: Tin, Oxides, Indium, Thin films, Signal processing, Phase matching, Nonlinear optics, Sum frequency generation, Second harmonic generation, Prisms
Using a low-power laser, and a thin film of indium tin oxide (ITO) in the Kretschmann configuration, we characterize the efficiency of optical nonlinearities of ITO as an epsilon near zero material across a wide range of wavelengths. Additionally, we explore the relationship between the zero-epsilon wavelength and the efficiency of nonlinear interaction. This was accomplished by testing multiple ITO slides with different zero-epsilon wavelengths and comparing the results.
Numerical simulations have become an essential design tool in the field of photonics, especially for nanophotonics. In particular, 3D finite-difference-time-domain (FDTD) simulations are popular for their powerful design capabilities. Increasingly, researchers are developing or using inverse design tools to improve device footprints and performance. These tools often make use of 3D FDTD simulations and the adjoint optimization method. We implement a commercial inverse design tool with these features for several plasmonic devices that push the boundaries of the tool. We design a logic gate with complex design requirements as well as a y-splitter and waveguide crossing. With minimal code changes, we implement a design that incorporates phase-encoded inputs in a dielectric-loaded surface plasmon polariton waveguide. The complexity of the requirements in conjunction with limitations in the inverse design tool force us to make concessions regarding the density of encoding and to use on–off keying to encode the outputs. We compare the performance of the inverse-designed devices to conventionally designed devices with the same operational behavior. Finally, we discuss the limitations of the inverse design tools for realizing complex device designs and comment on what is possible at present and where improvements can be made.
In modern communications networks, data is transmitted over long distances using optical fibers. At nodes in the network, the data is converted to an electrical signal to be processed, and then converted back into an optical signal to be sent over fiber optics. This process results in higher power consumption and adds to transmission time. However, by processing the data optically, we can begin to alleviate these issues and surpass systems which rely on electronics. One promising approach for this is plasmonic devices. Plasmonic waveguide devices have smaller footprints than silicon photonics for more compact photonic integrated circuits, although they suffer from typically having higher loss than silicon photonic devices. Inverse design software can be used to optimize the plasmonic device topology to maximize the device throughput, mitigating the inherent loss of plasmonics. Additionally, inverse design tools can help us make plasmonic devices with an even smaller footprint and higher efficiency than conventionally designed plasmonic devices. Recently, commercial inverse design tools have become available for popular photonic simulation software suites. Using these commercial inverse design tools with a compatible plasmonic architecture, we create compact, efficient, and manufacturable devices such as XOR gates, grating couplers, y-splitters, and waveguide crossings. We compare the inverse-designed devices to conventional devices to characterize the performance of the commercial inverse design tool.
Vast improvements in communications technology are possible if the conversion of digital information from optical to electric and back can be removed. Plasmonic devices offer one solution due to optical computing’s potential for increased bandwidth, which would enable increased throughput and enhanced security. Plasmonic devices have small footprints and interface with electronics easily, but these potential improvements are offset by the large device footprints of conventional signal regeneration schemes, since surface plasmon polaritons (SPPs) are incredibly lossy. As such, there is a need for novel regeneration schemes. The continuous, uniform, and unambiguous digital information encoding method is phase-shift-keying (PSK), so we chose to focus on developing a regeneration scheme compatible with PSK. Epsilon-near-zero (ENZ) materials have been shown to support SPP modes and have extremely high conversion rates for harmonic generation at their zero-permittivity wavelength, which makes them particularly desirable for developing signal regeneration devices. We have shown second-harmonic generation (SHG) in free space with simulations consisting of ENZ materials. When integrated into plasmonic waveguides, SHG can be used to conduct phase sensitive amplification (PSA), which allows us to combine phase-squeezing and amplification into a single stage instead of relying on conventional gain media for amplification. PSA can be utilized to design a proof-of-concept signal regeneration device with a smaller overall device footprint than previously demonstrated methods. The development of these methods will contribute towards minimizing device footprints of plasmonic components that require signal regeneration, improving their density and performance.
Despite the benefits that optics and photonics have brought to improving communications, there remains a lack of commercialized optical computing devices and systems, which reduces the benefits of using light as an information-carrying medium. We are developing architectures and designs of photonic logic gates for creating larger-scale functional photonic logic circuits. In contrast to other approaches, we are focusing on the development of logic devices which can be cascaded in arbitrary ways to allow for more complex photonic integrated circuit design. Additionally, optical computing often uses on-off keying, which fails to take advantage of denser encoding schemes often used to optically transmit data. We propose that devices that operate on phase-shift keying will not only be more efficient, but easier to cascade. To achieve the goal of cascadable devices operating on phase-shift keying, we have designed a plasmonic waveguide logic device using inverse design tools. These tools have allowed us to create a device with an arbitrary topology that has increased performance and reduced footprint compared to a conventional device with the same operation. In addition, inverse design simplifies the process of designing devices that operate with phase-shift keying, which can become complicated with conventional design methods. In order to implement inverse design tools for plasmonic devices and phase-shift keying, we used fully 3D FDTD simulations. We compare the inverse-designed devices to more conventional devices in order to characterize their performance.
Polarimetric optical fiber-based stress and pressure sensors have proven to be a robust tool for measuring and detecting changes in the Young’s modulus (E) of materials in response to external stimuli, including the real-time monitoring of the structural integrity of bridges and buildings. These sensors typically work by using a pair of polarizers before and after the sensing region of the fiber, and often require precise alignment to achieve high sensitivity. The ability to perform similar measurements in natural and in engineered biomaterials could provide significant insights and enable research advancement and preventative healthcare. However, in order for this approach to be successful, it is necessary to reduce the complexity of the system by removing free-space components and the need for alignment. As the first step in this path, we have developed a new route for performing these measurements. By generalizing and expanding established theoretical analyses for these types of sensors, we have developed a predictive theoretical model. Additionally, by replacing the conventional free space components and polarization filters with a polarimeter, we have constructed a sensor system with higher sensitivity and which is semi-portable. In initial experiments, a series of polydimethylsiloxane (PDMS) samples with several base:curing agent ratios ranging from 5:1 up to 30:1 were prepared to simulate tissues with different stiffnesses. By simultaneously producing stress-strain curves using a load frame and monitoring the polarization change of light traveling through the samples, we verified the accuracy of our theoretical model.
Integrated fluorescent waveguide biosensors have had a substantial impact on the field of biodetection. Many types of
waveguide sensors have been developed, but most of them rely on evanescent field excitation of fluorophores, whose
emission is then detected directly or indirectly. A sensor device which performs detection by measuring the fluorescent
light that back-couples into the device was recently demonstrated. The work for this device did not compare the
efficiency of their detection method with traditional detection methods, nor did they develop a rigorous theoretical model
for understanding the efficiency of the device. Using finite difference time domain simulations and complementary
experiments, we develop and verify a model which can predict the performance of the sensor in air and aqueous
environments. Additionally, we perform spatiotemporal fluorescence measurements using the waveguide device which
allow us to sample the magnitude of the fluorescence along the device at every point in space and time that we recorded.
While many new label-free optical sensing techniques are focusing on increasing the sensitivity or decreasing the limit
of detection, the balance between sensitivity, specificity and collection efficiency are critical, particularly for detection in
complex media. For example, although high Q optical resonant cavities are inherently sensitive, the collection efficiency
of these devices is quite poor, particularly when compared to sensors with larger active sensing areas. By optimizing all
three parameters, even further advancements in sensing technologies are possible.
Recently, a novel integrated optical waveguide 50/50 splitter was developed. It is fabricated using standard lithographic
methods, a pair of etching steps and a laser reflow step. However, unlike other integrated waveguide splitters, the
waveguide is elevated off of the silicon substrate, improving its interaction with biomolecules in solution and in a flow
field. Additionally, because it is fabricated from silica, it has very low optical loss, resulting in a high signal-to-noise
ratio, making it ideal for biosensing.
By functionalizing the device using an epoxy-silane method using small samples and confining the protein solutions to
the device, we enable highly efficient detection of CREB with only 1 μL of solution. Therefore, the waveguide coupler
sensor is representative of the next generation of ultra-sensitive optical biosensors, and, when combined with
microfluidic capabilities, it will be an ideal candidate for a more fully-realized lab-on-a-chip device.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.