Laser micro- and nano-material processing – Part 1

This special issue of Advanced Optical Technologies (AOT) is dedicated to the field of laser-based micro- and nanostructuring methods.

The Master’s Program in Advanced Optical Technologies (MAOT) was established at the Friedrich-Alexander Universitat Erlangen-Nurnberg in 2007 as part of the Elite Network of Bavaria (ENB), an initiative by the Bavarian State Government comprising about 40 elite Master’s programs and doctoral programs. MAOT can be studied after a Bachelor in physics or an engineering subject. The Master’s program realizes an innovative concept combining three core elements: (1) Interdisciplinarity: The program integrates courses and researchers from five engineering subjects and from physics. The degree of interdisciplinarity goes far beyond traditional programs. (2) Internationality: The program is taught entirely in English and special support is given to international students. (3). Individuality: The course curriculum was adapted at several points based on the experience in the initial years. The same is true for the way in which international students are supported and the type of support they need. The students are given an unusually high degree of freedom to develop an individual curriculum and to pursue research projects. Crucial experience and lessons learned are: (1) Lecturers and researchers have to be coordinated and the perspectives of the different disciplines have to be integrated within one program. Students must be guided in order to deal with the demands and challenges of the different disciplines. (2) International students need support with settling in Germany and with learning and working in a German cultural environment. They need support with administrative issues. Furthermore, they need to analyze and understand cultural differences and how they impact on the cooperation between lecturers and students and on the work in research groups. (3) Students must be helped to develop their own curriculum. They must learn how to combine their first-degree qualification with the specialized qualification which they gain after completing their Master’s program. They need to develop the skills to match their preferences with what is realistic and feasible.

Biomedical optics has emerged as a dynamic field encompassing a range of optical devices and technologies, including light sources, lasers, sensors, optical fibers, and optical processing principles. Its impact on medical engineering and clinical applications has been profound, leading to advancements in laboratory practices, optical fibers, biosensing, imaging, radiation grading, absorption spectroscopy, and polarization sensing. This article examines the historical progression of biomedical optics, highlighting its contributions to medical imaging and diagnosis. It focuses particularly on computed tomography, fluorescence imaging, optical molecular imaging, spectroscopy, near-infrared tomography, and optical coherence techniques. Biomedical optics' development has transformed medical science by enabling non-invasive diagnosis, improving treatment planning, and enabling specific therapy. The positive outcomes of these advancements underscore the significance of biomedical optics in promoting progress in the field of medicine. The paper discusses optical technologies and their clinical implications, including spectroscopy, near-infrared tomography, optical coherence tomography, computed tomography, fluorescence imaging, and molecular imaging.

The advent of optogenetics and genetically encoded photosensors has provided neuroscience researchers with a wealth of new tools and methods for examining and manipulating neuronal function in vivo. There exists now a wide range of experimentally validated protein tools capable of modifying cellular function, including light-gated ion channels, recombinant light-gated G protein-coupled receptors, and even neurotransmitter receptors modified with tethered photo-switchable ligands. A large number of genetically encoded protein sensors have also been developed to optically track cellular activity in real time, including membrane-voltage-sensitive fluorophores and fluorescent calcium and pH indicators. The development of techniques for controlled expression of these proteins has also increased their utility by allowing the study of specific populations of cells. Additionally, recent advances in optics technology have enabled both activation and observation of target proteins with high spatiotemporal fidelity. In combination, these methods have great potential in the study of neural circuits and networks, behavior, animal models of disease, as well as in high-throughput ex vivo studies. This review collects some of these new tools and methods and surveys several current and future applications of the evolving field of optophysiology.

Minimizing optical losses in resonant cavities is crucial for improving photonic device performance. This study focuses on the development of a simulation tool to analyze scattering losses in Fabry–Pérot interferometers (FPIs), offering precise modeling of waveguide dynamics and contributing to accurate loss predictions across various platforms. Optical cavities often suffer from scattering losses due to surface roughness and material defects. Our approach integrates theoretical models and simulations to quantify these losses, utilizing the FPI as a model system. We identified upper and lower reflectivity thresholds, beyond which accurate measurement of losses becomes unreliable. For reflectivity below a certain threshold, measurement errors arise, while excessively high reflectivity can reduce fringe visibility and introduce detector sensitivity issues. Simulations were used to validate the model’s ability to predict reflectivity and attenuation in waveguides with varying loss levels. The software’s flexibility to adjust transmission parameters for different cavity configurations enhances its utility for a broad range of photonic systems. Our study offers a novel methodology for optical loss analysis, with practical applications in optimizing photonic devices. By providing a reliable tool for precise loss measurement, this work supports advancements in optical technologies, enabling the design of more efficient, high-performance devices across various applications.

Many of the all-time greats of optics—Newton, Thomas Young, Brewster, Wheatstone, Helmholtz, Maxwell, Rayleigh—have also made important breakthroughs in our understanding of human vision. Vision has, therefore, been an integral part of the portfolio of the Optical Society of America since its inception. Advances in vision science, particularly the psychophysics of spatial, color, and binocular vision and stereopsis, have regularly been reported at meetings and in the journals of the Society from the beginning. Developments in linear systems theory, now used widely in optics, have spilled over into vision, as has also the use of modem optical techniques involving lasers, coherence, and spatial filtering. In the future, advances in optical technology, such as adaptive optics, now highlighted in the proceedings of the Optical Society of America, will find application in vision research and clinical instrumentation.

Advances in optical technologies have enabled the deployment of wavelength division-multiplexed (WDM) transmission systems capable of providing huge amounts of bandwidth across long distances. In this scenario, dynamic routing for direct provisioning of optical paths at the WDM layer becomes a challenging problem. Any distributed algorithm for routing dynamic traffic demands on optical transport infrastructures should be simple, flexible, efficient and scalable. The contribution of this paper is a novel integrated routing and grooming scheme for setting-up bandwidth guaranteed paths on hybrid wavelength and label switched networks. Our proposal exploits and refines the minimum interference routing idea according to an improved and re-optimized resource and traffic-aware approach, where critical links are detected and weighted according to a low complexity all-pairs minimum cut strategy that substantially reduce the overall number of calculations and hence the computational cost. The valuable results achieved in the comparison against other well-known reference techniques clearly demonstrate that our algorithm is very time-efficient while performing better in terms of blocking probability.

Advances in imaging technology over the last two decades have produced significant innovations in medical imaging. Hyperspectral imaging (HSI) is one of these innovations, enabling powerful new imaging tools for clinical use and greater understanding of tissue optical properties and mechanisms underlying eye disease.Hyperspectral imaging is an important and rapidly growing area in medical imaging, making possible the concurrent collection of spectroscopic and spatial information that is usually obtained from separate optical recordings. In this review, we describe several mainstream techniques used in HSI, along with noteworthy advances in optical technology that enabled modern HSI techniques. Presented also are recent applications of HSI for basic and applied eye research, which include a novel method for assessing dry eye syndrome, clinical slit-lamp examination of corneal injury, measurement of blood oxygen saturation in retinal disease, molecular changes in macular degeneration, and detection of early stages of Alzheimer disease. The review also highlights work resulting from integration of HSI with other imaging tools such as optical coherence tomography and autofluorescence microscopy and discusses the adaptation of HSI for clinical work where eye motion is present. Here, we present the background and main findings from each of these reports along with specific references for additional details.

Tumors significantly impact individuals' physical well-being and quality of life. With the ongoing advancements in optical technology, information technology, robotic technology, etc., laser technology is being increasingly utilized in the field of tumor treatment, and laser ablation (LA) of tumors remains a prominent area of research interest. This paper presents an overview of the recent progress in tumor LA therapy, with a focus on the mechanisms and biological effects of LA, commonly used ablation lasers, image-guided LA, and robotic-assisted LA. Further insights and future prospects are discussed in relation to these aspects, and the paper proposed potential future directions for the development of tumor LA techniques.

History of endoscopic spine surgery: where did it all begin? Development of indications and techniques.

The advent of the endoscope has facilitated otological surgery in recent years. Advances in optical technology have led to the development of high definition visualisation, such as 4K magnification. Narrow band imaging (NBI) has been shown to improve visualisation of tissue based on varying degrees of vascularity. This is a feasibility study, the first of its kind, aiming to investigate the appearances of middle ear anatomy and pathology (tympanic membrane, tympanosclerosis, cholesteatoma, granulation, endolymphatic sac hydrops, otosclerosis) under the NBI filter, using a high definition 4K endoscope. Qualitative analysis of image detail and operating time in minutes were recorded. The study demonstrates that these two technologies can be implemented with ease into practice, and show a clear differentiation between pathology and normal anatomy. NBI and 4K magnification prove to be useful adjuncts to the surgeon during endoscopic ear surgery.

Scaling traditional telecommunication networks so that they are able to cope with the volume of future traffic demands and the stringent European Commission (EC) regulations on emissions would entail unaffordable investments. For this very reason, the design of an innovative ultra-high bandwidth power-efficient network architecture is nowadays a bold topic within the research community. So far, the independent evolution of network layers has resulted in isolated, and hence, far-from-optimal contributions, which have eventually led to the issues today's networks are facing such as inefficient energy strategy, limited network scalability and flexibility, reduced network manageability and increased overall network and customer services costs. Consequently, there is currently large consensus among network operators and the research community that cross-layer interaction and coordination is fundamental for the proper architectural design of next-generation Internet networks. This thesis actively contributes to the this goal by addressing the modeling, optimization and performance analysis of a set of potential technologies to be deployed in future cross-layer network architectures. By applying a transversal design approach (i.e., joint consideration of several network layers), we aim for achieving the maximization of the integration of the different network layers involved in each specific problem. To this end, Part I provides a comprehensive evaluation of optical transport networks (OTNs) based on layer 2 (L2) sub-wavelength switching (SWS) technologies, also taking into consideration the impact of physical layer impairments (PLIs) (L0 phenomena). Indeed, the recent and relevant advances in optical technologies have dramatically increased the impact that PLIs have on the optical signal quality, particularly in the context of SWS networks. Then, in Part II of the thesis, we present a set of case studies where it is shown that the application of operations research (OR) methodologies in the desing/planning stage of future cross-layer Internet network architectures leads to the successful joint optimization of key network performance indicators (KPIs) such as cost (i.e., CAPEX/OPEX), resources usage and energy consumption. OR can definitely play an important role by allowing network designers/architects to obtain good near-optimal solutions to real-sized problems within practical running times.

With the advances in optical technology, the span of a broadband access network using passive optical network (PON) technology can be increased from today's standard of 20 km to 100 km or higher, and thereby serve a lot more users. Such an extended-reach PON is known as SuperPON in the literature, and we call it a long-reach PON (LR-PON). A major challenge in LR-PON is that the propagation delay (for data as well as signals) between the telecom central office (CO) and the end user is increased by a very significant amount. Now, traditional PON algorithms for scheduling the upstream transmission, such as dynamic bandwidth allocation (DBA) algorithms, may not be sufficient; actually, they may lead to degraded performance because of the long delay of the CO-to- Users control loop. This challenge motivates us to propose and study a multi-thread polling algorithm to effectively and fairly distribute the upstream bandwidth dynamically. This algorithm exploits the benefits of having multiple polling processes running simultaneously and enabling users to send bandwidth requests before receiving acknowledgement from the CO. We compare the proposed algorithm with traditional DBA, and show its advantage on average packet delay. We then analyze and optimize key parameters of the algorithm, such as initiating and tuning multiple threads, inter-thread scheduling, and fairness among users. Numerical results demonstrate the algorithm's advantage to decrease the average packet delay and improve network throughput under varying offered loads.

<p>Advances in optical technology have led to the commercialization and widespread use of broadband optical frequency combs for multiplexed measurements of trace-gas species. Increasingly available in the mid-infrared spectral region, these devices can be leveraged to interrogate the molecular fingerprint region where many fundamental rovibrational transitions occur. Here we present a cross-dispersed spectrometer employing a virtually imaged phased array etalon and ruled diffraction grating coupled with a difference frequency generation comb centered near 4.5 µm. The spectrometer achieves sub-GHz spectral resolution with a 30 cm<sup>-1</sup> instantaneous bandwidth. Laboratory results for nitrous oxide isotopic abundance retrieval will be presented. Challenges relating to characterizing the instrument lineshape function, constructing a frequency axis traceable to the comb, and accurate spectral modelling will be addressed and progress towards incorporating a more compact laser frequency comb source into the system will be discussed.</p>

Optical fiber communication is known as the backbone of communication today for voice, video, and data transmission. Recent advancements in optical technologies are leading us to many new forms of generation of orbital angular momentum (OAM) waves and its transmission technologies. Among them are hypergeometric waveform (HG), Bessel’s waveforms, Laguerre Gaussian waveforms, and other forms of OAMs. This mode of communication is by the twisted form of electromagnetic wave which can accommodate a larger number of channels making communication simpler for wired and wireless communication. In this paper, various methods of OAM waveform generation are presented and are compared in details discussing the various needs in communication. OAM multiplexing is done by spatial division multiplexing (SDM) and wavelength division multiplexing (WDM). Methods of OAM communication, generation techniques, power analysis, and bit error analysis prove efficient transmission capability of OAM waves using low power consumption and low bit error rate in optical communication networks. OAM from fiber can be directly communicated to atmosphere which is found very useful for short distance wireless communication. Experimental validation is discussed for HG, Bessel’s waveforms, and LG waveforms. Pure Optical Vertices (OV) are generated by VCSELs (vertical cavity surface emitting lasers) and transmitted by (MMF) multimode fibers. Various atmospheric effects and challenges are also elaborated in this paper. RSoft OptSim software is used for simulation.