The significant underrepresentation of Blacks in optics and photonics with respect to authors, invited speakers, conference chairs, reviewers, associate editors and editors in chiefs of Optica’s journals demands special attention. In accordance with the Optica June 2020 Commitment to Change and independent statements from the Optica Leadership and the 2016-2020 Optica Ambassadors, a special feature issue to amplify Black voices in optics and photonics was proposed. While, by no means, is this a solution, it is a step in the direction of inclusivity to elevate the visibility of the researchers (and their work) belonging to our optics community.

Through this special issue we highlight the excellent and exciting research in optics and photonics led by some of the Black researchers in the field. It is our intention that this special feature will bring awareness to the research contributions from this community for both present and future optics researchers from all walks of life. Thus, with this special issue, we take a snapshot of this community with 13 selected papers across 5 Optica Publishing Group journals (Applied Optics, Biomedical Optics Express, Optics Express, Optics Letters, and Optica). A companion piece to this special feature was published in a May 2023 Optics and Photonics News feature Breaking Barriers, Advancing Optics [1].

The topics covered in this special feature represent a diverse range of research areas that include metasurfaces, fiber optic biomedical sensors, photoacoustics, optoelectronics, space-time optics, computational optics, and silicon photonics. To facilitate reading through the special feature, we have binned these topics into three broad categories: bioimaging and biosensing, on-chip photonics and optimization in photonic systems, and entangled photons and applications of structured light. We hope that you get as much enjoyment reading these articles as we have.

Bioimaging and biosensing

Dr. Muyinatu Bell, an associate professor of biomedical engineering, electrical and computer engineering, and computer science at Johns Hopkins University and a recently elected Fellow of Optica, is founder and director of the Photoacoustic and Ultrasonic Systems Engineering (PULSE) Lab. New work from the PULSE lab describes new phantom technology aimed to help validate designs for conformal imaging systems. In their Biomedical Optics Express paper “Flexible array transducer for photoacoustic-guided interventions: phantom and ex vivo demonstrations,” Zhang et al. provide the mathematical basis underlying reconstruction of photoacoustic signals from concave sensor geometries and validate their accuracy in a series of phantoms and liver experiments [2]. The promising results of this work will pave the way for improved application of flexible-array transducers for photoacoustic imaging during surgical guidance.

In new work appearing in Applied Optics, “Microfluidic analysis of 3T3 cellular transport in a photonic crystal fiber,” Dr. J. Fu, under the direction of Dr. Rosalind Wynne at Villanova University, explores the use of microfluidic sensors to provide empirical insight into models of cellular transport in confined structures [3]. The experimental system comprised a photonic crystal fiber connected between two microfluidic systems for delivery and collection of 3T3 cells; spectroscopic analysis at the outlet was combined with direct imaging and transcapillary conductance analysis. The surprising result – that an increase in pressure differential does not promote microfluidic transport - is likely to aid in development of optimal designs for microfluidic devices for biomedical and pharmaceutical applications. Dr. Rosalind Wynne is an associate professor of electrical and computer engineering. She directs the Laboratory for Lightwave Devices specializing in the development of fiber optics sensor design.

At Indiana University, new research led by Dr. Patrice Tankam, assistant professor in the School of Optometry, looks at employing a non-contact, polarization-dependent optical coherence microscope (POCM) to inspect human corneal microstructure in vivo. The work, “Non-invasive in vivo imaging of human corneal microstructures with optical coherence microscopy,” published in Biomedical Optics Express [4], leverages polarization to enhance the features of non-birefringent cellular features in the cornea. The researchers demonstrate the clinical potential of their POCM as it is shown to operate fast enough (i.e., a volume of 500 × 500 × 2048 per second) to mitigate the motion artifacts associated with eye movements. The Tankam lab specializes in developing advanced cellular-level resolution imaging systems, including optical coherence microscopy and integrated optical coherence microscopy and fluorescence microscopy, that can track the dynamics of cellular processes in vivo.

In their Optics Letters paper “DiffuserSpec: spectroscopy with Scotch tape,” Dr. Audrey K. Bowden and her team at Vanderbilt University introduce a new strategy for low-cost spectroscopy that leverages a readily accessible technology – Scotch tape [5]. Using tape as a type of optical diffuser, Malone et al. show that spectral features of narrow and broadband sources can be accurately recovered from pseudorandom speckle patterns, a departure from the traditional system designs that rely on bulky, expensive components like prisms and gratings. In short, the use of computational imaging as applied to spectroscopy can enable simpler, more compact analytical systems for a wide range of biomedical and non-biological applications. Dr. Audrey K. Bowden is an associate professor of biomedical engineering and electrical and computer engineering and a Fellow of Optica. She is also a Dorothy J. Wingfield Phillips Chancellor Faculty Fellow. She founded the Bowden Biomedical Optics Laboratory (BBOL) at Vanderbilt University where she develops light-based diagnostic tools for applications in medicine and biology.

In the work titled “Towards rapid colorimetric detection of extracellular vesicles using optofluidics-enhanced color-changing optical metasurface,” published in Optics Express [6], the Ndukaife group at Vanderbilt University demonstrates that the integration of optofluidics with metasurfaces enables spectrometer-free and label-free colorimetric read-out for extracellular vesicles (EV) concentration. In their work, the silicon metasurface exploits the response of multipolar optical modes to the changes in the refractive index of the surrounding medium in order to induce a vivid color change. The combination of optofluidics and this color metasurface enables the detection of extracellular vesicles at femtomolar concentrations within a 2-minute incubation period. Dr. Justus C. Ndukaife is an assistant professor of electrical and computer engineering and of mechanical engineering, and his lab focuses on development of novel nanobiosensors, thermoplasmonics, and nano-optical tweezers.

On-chip photonics and optimization in photonic systems

The paper titled “Near-unity uniformity and efficiency broadband meta-beam-splitter/combiner”, published in Optics Express pertains to development of metasurfaces for high-power lasers [7]. In the work, the researchers, led by Dr. Abdoulaye Ndao, develop a modified version of particle swarm optimization and numerically demonstrate a broadband, reciprocal metasurface beam combiner/splitter with a uniformity > 97% and diffraction efficiency > 90% in the continuous band from λ=1525 nm to λ=1575 nm. To achieve this, they propose to adapt a modified version of particle swarm optimization (PSO) as a global optimization strategy to compensate for unwanted phase discretization effects, which in turn gives rise to undesired higher diffraction orders. They show that this adaption jointly maximizes both diffraction efficiency and uniformity of diffraction orders, and successfully finds an optimum solution in a large parameter space (729 meta-atoms with rotation angles between 0 and 180 degrees). Their numerical results show a respective 16.5% and 15.5% increase in diffraction efficiency and uniformity of the 2D beam splitter, and a 12.2% increase in the diffraction efficiency of the 2D beam combiner following the optimization stage. Their proposed design significantly extends the current state-of-the-art of metasurfaces design in terms of uniformity, bandwidth, and efficiency, and paves the way for devices requiring high power or near-unit uniformity. Dr. Ndao is a Sloan Fellow and assistant professor of electrical and computer engineering in the Jacobs School of Engineering at UC San Diego. He is the founder of the NDAO Lab: Nano Devices and Applied Optics, which specializes in nanophotonics, integrated optics, nanomaterial/structure design, bio photonics, and prototype development of both passive and active devices.

In the collaborative work titled “Emulating the Deutsch-Josza algorithm with an inverse-designed terahertz gradient-index lens” in Optics Express [8], the research team of Profs. Zizwe A. Chase and Thomas A. Searles at the University of Illinois at Chicago (UIC) report a new design for a quantum algorithm emulator in the THz frequency regime based on a simple platform and optimized by machine learning. The simple design and compact size of their device offer the possibility of strongly relaxing the constraints at high frequencies, which are expected to play a larger role in photonics and quantum technology. Leveraging machine learning, the authors designed an optimized all-dielectric metadevice as a component of a quantum algorithm emulator for simulating the Deutsch-Josza algorithm in the THz region. Their resulting terahertz gradient-index (GRIN) lens showed an enhanced performance as demonstrated by a two-fold increase in the thickness of the GRIN lens. Ziswe A. Chase is a Bridge-to-Faculty Scholar and is now an assistant professor electrical and computer engineering. Together with Thomas A. Searles, an associate professor in the department of electrical and computer engineering at UIC, they lead the DOE-funded ReACT-QISE program at the University of Illinois in Chicago.

In the collaborative study “Multistability, relaxation oscillations and chaos in time-delayed optoelectronic oscillators with direct laser modulation” published in Optics Letters by the labs of Dr. Jimmi Talla Mbé from the University of Dschang in Cameroon and Dr. Yanne K. Chembo from the University of Maryland, the researchers explore the nonlinear dynamics of current-modulated optoelectronic oscillators [9]. They show that the system displays a wide variety of interesting dynamical behaviors such as relaxation oscillations and chaos. These systems have numerous applications, including microwave generation, communication engineering and neuromorphic computing. Current-modulated optoelectronic oscillators are particularly promising for their potential of chip-scale integration. Dr. Jimmi Talla Mbé is an associate professor of physics, and his lab focuses on optoelectronics, nonlinear photonics, and applications, at both the theoretical and experimental levels. Dr. Yanne K. Chembo is a professor of electrical and computer engineering, and his lab investigates photonic systems for applications ranging from aerospace systems to quantum networks.

Dr. Aneek James and co-authors, in their work titled “Scaling comb-driven resonator-based DWDM silicon photonic links to multi-Tb/s in the multi-FSR regime” published in Optica, demonstrate the design of a multi-Tb/s Kerr comb-driven photonic link using the multi-free spectral range (FSR) regime [10]. James et al. are members of the Lightwave Research Laboratory directed by Keren Bergman at Columbia University. They develop nanoscale photonic interconnect devices that seamlessly move data from on-chip networks, across memory and large computing systems in an energy efficient manner. Their work in this paper validates the multi-FSR regime as a key strategy in achieving production-ready multi-Tb/s Kerr comb-driven optical interconnects that can support next-generation data centers and high-performance computing. This high-yield design is supported by comprehensive measurements of 704 micro-resonator devices fabricated on a 300-mm wafer in a commercial foundry, suggesting scalability of their link architecture.

The work by the Kanté group at UC Berkeley titled “Interpretable inverse-designed cavity for on-chip nonlinear photon pair generation,” and published in Optica, introduces an inverse design method with interpretable results to enhance the efficiency of the rate of on-chip photon generation through nonlinear processes by controlling the effective phase-matching conditions [11]. The authors fabricate and characterize a compact, inverse-designed device using a silicon-on-insulator platform that permits spontaneous four-wave mixing to generate photon pairs at a rate of 1.1 MHz with a coincidence to accidental ratio of 162. The design method accounts for fabrication constraints and can be used for scalable quantum light sources in large-scale communication and computing applications. Additionally, the authors adopt a hierarchical inverse design strategy–a two-step approach that proposes an initial physics-based guess, followed by a shape optimization using the adjoint method. This approach minimizes computational cost by avoiding the large number of random guesses for initial conditions. Dr. Boubacar Kanté is the Chenming Hu endowed chaired associate professor of electrical engineering and computer sciences at UC Berkeley, who is well-known for his contributions to laser physics such as the scale-invariant lasers and the topological laser.

Entangled photons and applications of structured light

Eshun et al. are a light and matter interaction group within the physical and life science directorate at Lawrence Livermore National Laboratory. In their work titled “Fluorescence lifetime measurements using photon pair correlations generated via spontaneous parametric down conversion (SPDC)”, published in Optics Express, they discuss the use of correlated photon pairs to measure the fluorescence lifetime of organic compounds such as rhodamine 6 G [12]. It is well-known that fluorescence lifetime measurements are conventionally measured in the time or frequency domain, which requires an ultrafast, ultrashort pulse laser or a form of modulated excitation. Eshun et al. show that these measurements can be achieved with pairs of entangled photons generated through SPDC induced by a continuous wave laser source. They exploit the time correlation between entangled photon pairs (signal and idler) to measure the fluorescent lifetime of the sample. The signal photon excites fluorescence from the sample. This interaction breaks the entanglement between the idler and signal photon but the time correlation is maintained between the idler and the fluorescent signal induced by the signal photon. This delayed time is measured then integrated into a decay curve that describes the fluorescent lifetime of the sample. Dr. Audrey Eshun is a postdoctoral researcher at Lawrence Livermore National Laboratory. She was previously an NSF-funded graduate student in quantum optics at the University of Michigan.

N’Gom et al., in their Optics Express work titled “Generation of multiple obstruction-free channels for free space optical communication,” design and implement a hybrid laser system composed of an ultrafast laser filament embedded in a donut shaped beam carrying telecommunication data [13]. The work addresses the need for efficient free-space communication channel technology through the development of a laser system capable of clearing a path in the atmosphere to transmit optical information unobstructed. To achieve this, the researchers produce a multi-filament system generated by structured light to form a waveguide structure in the air, where an axial increase in refractive index is surrounded by a region of relative drop in refractive index, thus mimicking fiber-like transmission line in free space. Dr. Moussa N’Gom is an assistant professor of physics at Rensselaer Polytechnic Institute. The N’Gom research group exploits the versatility of wavefront shaping tools to address challenges in biomedical imaging, and in nonlinear and quantum optics.

In the Optica article “Interferometric phase stability from Gaussian and space–time light sheets,” Dr. Mbaye Diouf et al. demonstrate that a conventional Michelson interferometer could be made passively phase stable simply by using an optical light sheet [14]. This was demonstrated for both a simple (Gaussian-based) light sheet as well as space-time (ST) light sheets, where the latter has been shown to be propagation invariant and exhibit some resistance to speckle generation. The researchers achieved an 80% higher phase stability using ST light sheets in a Michelson interferometer in comparison to using the standard circularly symmetric Gaussian beam. These results have direct implications for general metrology applications, as Michelson interferometry has been used for various high-precision length measurements and sensing, and would often need to employ active dampening techniques to achieve phase stability. Dr. Mbaye Diouf is a senior research associate in the PROBE Lab, which is directed by Optica Fellow and Thomas J. Watson, Sr. Professor of Science, Kimani Toussaint, Jr. at Brown University.

Finally, we thank the contributing authors for submitting their work to this special feature, as we know many of them could have chosen to publish their articles in journals outside of the Optica family of journals. We also thank the reviewers for providing very thoughtful comments and suggested edits to the original manuscripts. As many of us know, being a peer reviewer for scientific journals is extremely important to moving science forward, but it is also quite time consuming. We also acknowledge the leadership of Optica for recognizing the importance of having this special feature.