This PDF file contains the front matter associated with SPIE Proceedings Volume 12882, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

The field of optical materials has seen significant advancements in recent years due to the demand for improved optical properties. Polymers nanoparticle composites have emerged as promising candidates for optical applications due to their unique characteristics. Polymer-based materials offer advantages such as flexibility, low cost, and ease of processing, while nanoparticles possess unique optical properties. This study explores the integration of neodymium-doped sodium yttrium fluoride nanocrystals (NaYF4) into a commercial photo-polymer for two-photon polymerization (2PP) 3D printing. The resulting compound material. Characterization includes fluorescent lifetime and emission spectrum analysis, along with investigations into visible light scattering due to nanoparticle accumulations. The findings contribute to the understanding of incorporating nanoparticles into 3D printed polymers for optical applications, addressing challenges and advancing the potential for designing resonators with 3D printed gain media.

Degraded visual environments (DVEs) are the result of a high concentration of obscurants in the air, and occur often during rotary wing aircraft landings. When the obscurants are comprised of sand this leads to a condition called “brownout.” Current DVE penetrating technology is severely limited by a weak return signal in severe brownout conditions. One method of overcoming this weak return signal is to use light tuned to the Christiansen wavelength, the wavelength at which the refractive index of the scatterer matches that of the surrounding medium, eliminating the scattering effect associated with the obscurant particles. We have previously shown a novel method for determining the optical constants of particulate samples using spectroscopic ellipsometry and determined that, for several different sand samples, the Christiansen wavelength is approximately 8 microns. We present data from falling sand of several different types using Fourier transform infrared (FTIR) spectroscopy showing a higher transmission percentage at the Christiansen wavelength. We explain features in this data using previous measurements of the optical properties of these sands.

In this work, we have investigated self-injection locking effects on a full spectral system with selective single-channel injection and full-channel injection in a quantum dot mode-locked comb laser through an optical feedback loop. It has been noticed that self-injection locking can not only improve the performance of a single-channel laser system but also has a strong effect on the whole spectral behavior. In the case of single-channel self-injection, we investigated the effects under a locked regime above the injection-locking threshold P_SIL. The locked lines were strongly enhanced with intensities high above the broad spectrum and also intensified even outside of the original spectral bandwidth. The typical feature is a big dip (or hole) appearing on the high-energy side of the lines if it is within the free-running spectral region. We have investigated this asymmetric phenomenon. It is considered that the locked modes are highly intensified at the expense of higher energy carriers excited by currents. The locking process transferred the energy from the lasing mode to the locked mode. For the full channel self-injection, the system was set under a controllable self-injection locking condition. A bandwidth enhancement phenomenon can be observed when injected power reaches the self-injection locking threshold PSIL, and the broadening gets stronger till to the locked regime. Finally, the original spectral bandwidth had been significantly broadened. This bandwidth broadening goes to both sides of the free-running spectrum and the broadening is remarkable.

We report on tailoring capabilities in the 7xx nm wavelength range utilizing GaAsP or InGaAsP quantum wells (QW) embedded in AlGaAs. Laser structures are grown using metal-organic chemical vapor deposition. Wafers and manufactured lasers are thoroughly characterized, and lifetime tests are performed to validate laser reliabilities. Changing QW parameters enables us to tune the wavelength or polarization of the laser emission.

We demonstrated a mid-infrared source architecture based on difference frequency generation of two tunable pulsed fiber laser sources. The mid-infrared source is tunable from 2910 nm to 3520 nm with up to 250 mW average power. The timing between pumps is controlled electronically to achieve modulation rates exceeding 10 kHz with over 35 dB extinction ratio. Spatially, the mid-infrared beam has a M² value of 1.06 and 1.08 (across its principal axes). Spectrally, the linewidth is 0.6 nm, with a wavelength accuracy of ± 0.3 nm.

Phosphate glasses with components of aluminum oxide and/or silica (“multi component” phosphate glasses) have been investigated for some time, as a means of increasing the chemical durability of phosphate glasses. For purposes of UV transmission, such multi-component glasses are typically not optimal, as they usually shift the absorption edge to the red. To compensate for this, fluorine is often added to such multi-component glasses, which complicates the fabrication due to safety requirements. However, BaO-CaO phosphate glasses have stability in the ambient adequate for many purposes. Furthermore, these glasses have the capacity for high doping expected from phosphate glasses, as well as UV transmission to about 295nm. We present here a brief look at the stability and Gd-doping of a BaO-CaO phosphate glass, of composition optimal for UV transmission.

The behavior of erbium doped fiber amplifiers (EDFA) in a master oscillator power amplifier (MOPA) configuration was characterized using a ⁶⁰Co γ-ray source. The results indicate that power degradation and photo-anneal recovery processes simultaneously exist for erbium doped fibers with relatively low concentrations of the co-dopants cerium and germanium added. For fibers with relatively high concentrations of germanium and comparable levels of cerium co-dopants highly effective radiation hard behavior is exhibited. A fiber optimized for efficiency also provides a radiation hard EDFA where after a 100 kRad (1000 Gy) exposure, the degradation in signal gain was only 5 dB at a MOPA pump power of 315 mW.

In this work, we demonstrate the establishment of a self-injection locking threshold in a quantum dot (QD) comb laser with a Fabry-Perot cavity and an external feedback loop. This process involves controlling injection power and polarization to inject a controlled fraction of lasing power back into the QD laser source. The study is focused on the single line self-injection locking effects. The self-injection locking process was characterized by a self-injection locking threshold power (P_SIL) and a locked power (P_locked). The self-injection locking process begins from the threshold power P_SIL and followed by a magnified enhancement till it reaches the locked power (P_locked). Once in the locked region, the enhancement effect starts to stabilize and is only weakly influenced by injection power. The established threshold provides a distinctive condition for the measurements of the modified optical properties of the coupled cavity system. Additionally, the locked single lines tested at different currents indicated a very broad spectral coverage which are much larger than the original bandwidth of free running QD laser.

We have developed a reflective polarization volume grating using liquid crystal applicable to the wavelength band of optical communication. This diffraction element has the features of realizing both high diffraction angle and high diffraction efficiency which could not be achieved with conventional elements. In order to apply these features to the optical communication wavelength bands, we achieved the alignment of liquid crystal with the required film thickness (7 μm), and, we confirmed high diffraction efficiency (95%) with large diffraction angle (1800 lines/mm) at the optical communication wavelength (1550 nm). In addition, we also confirmed that the high efficiency is maintained approximately 100 nm wavelength band width. We believe that this liquid crystal polarization volume grating can contribute to increasing the transmission speed with low error due to mixed wavelengths in the high wavelength resolution transmission.

We propose a novel design and control mechanism to achieve a widely tunable add-drop filtering element based on silicon photonic Grating-Assisted Contra-Directional Couplers. The proposed device has been simulated considering integration on the silicon photonics platform, allowing for wide deployment and cost-effective implementation as an integrated building block for different filtering/switching applications (e.g., multiplexers and demultiplexers). The segmented design and optimization of the coupler have been shown to enable a large drop bandwidth tunability while keeping a constant central wavelength, avoiding channel drifts. This add-drop element can be envisioned for flex-band wavelength-division multiplexing (WDM) applications as a component of wavelength-selective switches (WSS) or other switching devices.

We present a novel planar polymer ridge waveguide evanescent sensor for lab-on-a-chip applications. The integrated sensor is based on post-processing of Bragg gratings for the near-infrared (NIR) wavelength range by applying a femtosecond laser point-by-point (pbp) inscription technique. In general, this pbp inscription method offers a flexible selection of the Bragg grating wavelength from UV to NIR. The optical evanescent field sensor was tested with different substances with different refractive indices, demonstrating an increased sensitivity. Finally, the sensor was coated with palladium nanoparticles. With this functional coating, the polymer Bragg grating sensor is capable of hydrogen detection up to 4% concentration.

A silicon-integrated Schottky metal-insulator-semiconductor plasmonic modulator with remarkable optical loss performance is demonstrated. The proposed device architecture is realized through the heterogeneous integration of amorphous aluminum, silica, and indium tin oxide, forming a metal-insulator-semiconductor plasmonic stack housed on an SOI substrate. The device exhibited extinction ratio and insertion loss levels of 1 dB/μm and 0.128 dB/μm, respectively for a 10 μm-long waveguide. By taking advantage of the absence of diffraction limits in plasmonic structures, strong modal confinement proved possible as evidenced by simulation results, paving the way for improved optical processes and miniaturized photonic circuits.

Optical-profilometric measurements provide fast, meaningful descriptions of structured surfaces, such as power spectral density and surface roughness parameters. Conventionally, profilometric height data is used to calculate the far-field scatter of a randomly-structured surface. Random nanostructures were monolithically etched on fused silica (FS) sample surfaces, to enhance spectral transmission of light beyond the boundary’s Fresnel value, within a ±2.5° projection angle in the axial direction. We fabricated several FS samples with statistically different roughness, but similar optical performance over the VIS to NIR wavelength band and compared their power spectral density and optical scatter performance. Surface height map profiles were measured using UV confocal profilometry, and the data was leveraged to produce conventional (spatial) power spectral densities for each surface. Using surface height and transverse feature size data, scatter was calculated using both Rayleigh-Rice and Harvey-Shack surface scatter models, and then compared to experimental radiometric scatter data. Using experimentally obtained profilometric height data as input, the scatter models were able to accurately predict diffuse scatter from mechanical rough surfaces compared to experimental scatter measurements; however, the models were unable to predict the axial scatter for high-density transmission-enhancing nanostructured surfaces.

Applying the highly versatile and flexible MCVD technology at Leibniz-IPHT two new designs for optical sensing fibers were realized by co-doping of fused silica. For FBG sensing a Ge/B co-doped fiber with a mode field diameter adapted to standard single mode telecom fibers was prepared. The influence of boron on the attenuation at the inscription wavelength 1550 nm is visible. For distributed Brillouin sensing applications a preform with lateral separated germanium and aluminum doped regions and nearly step-index characteristic was fabricated by the MCVD in combination with the solution doping technique. Theoretical analysis of the acoustic properties and Brillouin spectrum have been shown, that this design is a potential candidate for strain and temperature discrimination. Because of the high temperatures during the preparation processes the radial refractive index and dopant concentration profiles of both fiber designs are influenced by diffusion.

Dense wavelength division multiplexing techniques are widely used in terrestrial state-of-the-art telecom applications. The optical link between the terminals requires a data rate in the terabyte range which is typically realized by transmitting multiple wavelengths though one common channel. For satellite communications, completely new requirements and demands arise where the common technologies cannot be used without further ado. In space, it is also completely impractical to set up repeaters at short distances, so the WDM must have a capacity of tens of Watts power capability to cover the very long propagation length. The development and realization of a space-suitable Dense Wavelength Division Multiplexer and Demultiplexer are described. Both units combine (or split, respectively) ten channels into / from one common channel. The design central wavelength is around 1070 nm and the channels are chosen with a separation of 92-GHz corresponding to approximately 0.35 nm. The multiplexer has a target power handling of at least five Watts per channel. The input channels are equipped with PM fibers, whereas the multiplexed output is free space propagating, avoiding nonlinear effects and thermally induced fiber damage. The Demultiplexer is fiber coupled at input and output ports due to the reduced power requirements of sub Milliwatts. In both cases a diffraction grating is used as wavelength selective element. Its nonlinear angular dispersion is compensated with a non-equidistant fiber arrangement. The WDMs are characterized regarding optical parameters. The components are designed for space suitability, using appropriate materials and thermal design.

Calibrating thermal detection systems for target recognition and accuracy can be challenging when live assets are not an option as a target. Infrared scene projection provides a cost effective and realistic alternative to assess missile capability. Infrared scene projection systems allow the generation of a thermally simulated scene for hardware-in-the-loop calibration of missile targeting. Previously, infrared scene projection technology has used resistor arrays, digital micromirror devices and laser diode arrays to name a few. Recent advancements in dynamic metamaterials provide a novel approach for the design of an infrared scene projection system. Reciprocal plasmonic metasurfaces are a metal-insulator-metal configuration of high aspect ratio dielectric pillars with sub-wavelength periodicity contained between a conductive top and bottom layer. Reciprocal plasmonic metasurfaces display an extreme sensitivity to ambient refractive index. This sensitivity in synergy with a conformal coating of a phase change material, such as vanadium dioxide, provide an excellent mechanism to implement a spatial light modulator as the scene generation component of an infrared scene projector. We report on the operating mechanism of the metasurface and characterize its sensitivity to changes in the ambient refractive index by applying a thin, conformal layer of aluminum oxide. We then expand on the experimental results by employing dielectric function data of optically characterized vanadium dioxide to inform calculations for predicting the effects of a thin conformal coating applied on the metasurface. Results indicate that pairing the sensitive metamaterial with the fast switching optical properties of vanadium dioxide provide a novel platform for infrared scene generation.

Electro-optic crystals suffer can suffer from piezo-electric ringing, a phenomenon that can degrade the efficiency of the device. Piezo-electric ringing is a coupling of the elasto-optic and piezo-electric effects and can be detrimental when the modulation frequency excites the acoustic modes of the crystal. This mechanical phenomenon is also highly dependent on the geometry and physical properties of the crystal. The piezo-electric ringing stress waves are complex, but can be modeled using a dynamic Finite Element Analysis (FEA) simulation of the crystal and a simple beam propagation simulation. This model can produce accurate results with proper material and modulation parameters. In this effort, the piezoelectric response of a Deuterated Dihydrogen Potassium Phosphate (DKDP) crystal is analyzed. The simulation results are then compared to experimental results to demonstrate model accuracy. This method can be used on other electro-optic crystals.

We report the first, to our knowledge, linear HCPCF-bundle for USP laser beam-delivery, power-modulation, and spatial-shaping. This bundle comprises four identical inhibited coupling HCPCFs arranged in a linear array with a relative pitch-variation of less than 2% relative variation in array pitch. Each HCPCF is equipped with an acousto-optic modulator (AOM) for independent power modulation. A laser beam, from 1030 nm wavelength, 100μJ energy USP laser, is split into four beams and coupled to each of the HCPCFs in the bundle using a diffractive optic element. The system's insertion loss (from input to output through the AOM) is measured to be over 70%. The bundle system emits an array of four Gaussian beams, each with equal energy and beam size (both having less than 1% variation beam to beam). Each beam's power can be modulated independently. This development marks a significant advancement in harnessing HCPCF technology in applications requiring high-power light with spatial and temporal structuring.

PANDA polarization maintaining (PM) fibers for tight bend applications are presented that can satisfy both optical and mechanical characteristics. Optical optimization of conventional-cladding structures and trench-cladding structures is discussed regarding effective cutoff wavelength under short-length and tight bend conditions. Both trench-cladding PM fiber and conventional PM fiber with 80 μm cladding diameter had similar effective cutoff wavelengths for lengths of 0.5 m. Bending loss at 2 mm radius was less than 0.1 dB/turn at 1550 nm. Additionally, improved mechanical reliability by incorporating a reinforcing outer glass layer is demonstrated on PM fiber for the first time.

Photomechanical actuators are a promising alternative to electrical actuators. Photomechanical actuators can be made of lightweight materials arranged in a simple system with few components, being powered solely by a light source. The result of this would be lighter motorized systems that are less prone to malfunction and damage. Such an actuator was developed in the form of a fiber backfilled with a low melting point wax, eicosane. The operating mechanisms for this fiber are based on bimorph actuator theory and the use of a photoactive additive. By drawing a PMMA fiber with a continuous and uniform cavity throughout the entirety of the length of fiber, and then backfilling it with eicosane, which has disparate mechanical and thermal properties, a bimorph actuator is made. Filled fibers were observed during actuation under an optical microscope with a heated stage and their mechanical response is discussed.

For many applications using Photomultiplier tubes (PMT) that require an efficient measurement of very weak light, it is a continuous challenge to collect as much light as possible. Regarding the improvement of the collection efficiency, there are some possible solutions, e.g., using a detector with a larger effective area or adding a large optical lens. However, there is also a demand to miniaturize detectors in certain application fields such as immunoassay analysis and underwater wireless optical communications. To overcome this challenge, we have developed a novel freeform condenser lens which shows a drastic size reduction and high light collection efficiency simultaneously. The lens has a very high collection efficiency to collect not only collimated light but also diffused light, which is usually difficult to collect for common detectors with a limited entrance aperture and acceptance angle. In this paper, we present the design and characteristics of this lens. We also present exemplary applications of the developed freeform condenser lens in an immunoassay analyzer and in underwater wireless optical communication by combining developed lens with a PMT.

Solid-state imaging devices, commonly found in cameras and scientific instruments, rely on charge-coupled device (CCD) technology. However, CCD photodetector arrays have constrained spectral range (< 1.0 μm) due to absorption characteristics of silicon (Si), and inadequate quantum efficiency (QE) over broad spectral ranges. To overcome these limitations, we propose a novel photodetector structure that enable broad spectral range detection, covering visible to shortwave infrared (VIS-SWIR) wavelength. This breakthrough detector achieves high QE (>90%) over wide spectral ranges and offers high frequency response >10 GHz. To address the challenge of absorption beyond the visible region, we utilize III-V compound semiconductor material as the absorption layer fabricated on matured InP substrates. The objective is to develop a monolithic photodiode and array that covers wavelengths from 400 nm to 1750 nm, with high frequency response (>8 GHz) and high QE. The use of matured substrates and III-V semiconductor materials simplifies manufacturing, improves spectral coverage, and enhances performance significantly compared to existing technologies. The photodiodes can be either top or bottom illuminated and feature a single set of absorption layers designed to achieve desired QE and speed. They can be used as single element or in an array configuration, with a metal line connection scheme enabling rapid and random addressing of individual pixels. Additionally, these uncooled photodiodes offer the advantage of performing reliably under various temperature variations. This detector holds great potential benefits for multispectral imaging, advanced communication systems, and sensing applications. We present characterization results of the fabricated test structures.

The performance of the photodetector is often the primary limiting factor affecting a free space communication or LiDAR system's sensitivity. Avalanche photodiodes (APDs) can be used to improve the signal to noise ratio (SNR) compared to conventional p-i-n photodiodes. Our study focuses on demonstrating an APD operating in the eye-safe short-wave infrared (SWIR) spectrum (>1400 nm) with high multiplication (M>1200) and low excess noise (F<7 at M=200) at room temperature. This device utilizes GaAsSb and Al_0.85Ga_0.15AsSb in a separate absorber, charge, and multiplication (SACM) configuration on an InP substrate. Notably, this device exhibits more than 40 times improvement in maximum achievable multiplication and 6.5 times lower excess noise at M=25 compared to commercially available InGaAs/InP devices.

Tellurite glasses, known for their high viscosity changes on a short temperature range make fiber drawing of tellurite glass-air difficult. This work demonstrates how to synthesize a highly air-filled (33%), with controlled air-hole sizes, tellurite glass-air Transversely Disordered Optical Fiber.

The method of sensitive detection of ultraviolet (UV) radiation using integration of Cesium-Lead-Bromide perovskitebased nanocolloids with silicon avalanche photodiodes (APDs) was investigated. The perovskite nanoparticles (NPs) were synthesized using the sonication method with a conventional ultrasonic cleaning bath. The synthesis resulted in perovskite NPs in the form supercrystals of 200-nm diameter. The NPs being pumped with a 372-nm UV laser produced visible photoluminescence (PL) with a spectral peak at 514 nm. Integration of the perovskite nanocolloid with a silicon APD resulted in the increase of APD’s sensitivity to UV by ~7.6 dB. Degradation of the response of the perovskite-APD system to pulsed UV radiation at high frequencies was thus mainly due to the time delay in the APD (100-kHz cut-off frequency) rather than relaxation of the PL. Composition, crystalline structure, and UV-excited PL of two oxysulfide phosphors doped with Terbium (Y₂O₂S:Tb and Gd₂O₂S:Tb) were investigated with the view of their potential use in combination with silicon APDs for sensitive detection of x-ray radiation. Both phosphors contained oxide impurities Y₂O₃ and Gd₂O₃, respectively, partially reducing their x-ray scintillation capability. The obtained results might be useful for the applications in the field of sensitive detection of short wavelength (UV and x-ray) radiation.

Variable angle spectroscopic ellipsometry was used to determine the optical properties of n- and p-type GaAs over a doping range of 4.6×10¹⁶ to 9.3×10¹⁸ cm^-3 and a spectral range of 190 nm to 30 μm. Increased doping concentration was observed to have several distinct effects on the samples’ optical properties: the band edge broadens and shifts to a higher energy; the E₁ and (E₁ + Δ₁) absorption peaks blur together; the E₂ absorption peak decreases; sub-bandgap, infrared absorption increases. Additionally, the doping effects are generally stronger for n-type than for p-type GaAs. These findings will help inform future design of optoelectronics.

The multimode interference inside a multimode fiber is used to design a tunable filter by utilizing a moving mirror in front of the fiber facet. Theoretical model is used to produce design curves for the center wavelength, filter bandwidth, tuning range, and the scanning range of the mirror. Experimental setups were performed to verify the theoretical results. A trade-off between the mirror scanning range and filter linewidth is found. Overall performance is observed to be better for smaller sections of multimode fibers, despite the difficulties encountered in handling (cleaving and splicing.)

Very Large Telescope Interferometers (VLTI) are based on interferometry to combine the light collected by more than one telescopes (such as ESO’s telescopes combining light collected by four 8.2-metre Telescopes), enabling the observation of new phenomena, opening up new research areas. The light beams are brought together using a complex system of free space components based on pairwise combination utilising the ABCD scheme. Currently bulky free space optics, with complex and very voluminous setups (10 beam input results in 180 outputs), are too sensitive to operate in ambient, while require the path difference must be kept in sub-millimetre scale. Photonic Integrated Circuits (PIC) advantages of miniaturization, stability, and precise active phase control, make them good candidates to develop the beam combining circuits. Key elements towards realization of these circuits are power splitters, low-loss crossings and directional couplers, all operating in a wide range of wavelengths (600 nm – 820 nm). However, the splitting ratio of conventional directional couplers is very sensitive to wavelength, which limits the bandwidth and the transmission performance of the devices. In this paper, we present the design methodology on a low-loss, broadband, and large fabrication tolerance, bend directional coupler realised on Silicon Nitride integration platform. FDE simulation tool was employed for waveguide modes and coupled system supermodes calculation, 2D-FDTD for propagation simulations, while the results were verified via 3D-FDTD simulations. The proposed bend directional coupler enhances conventional couplers performance, achieving splitting ratio of +-10% around target splitting value for the whole 220 nm target wavelength range, for a footprint of 100 μm x 20 μm.