We present a method for fabricating a self-written waveguide (SWW) between two optical fibers that are single-mode (SM) at 850 nm (780HP/ core diameter: 4.4 mu m). The basic principle consists in exposing an acrylic photopolymer formulation sensitive in the near-infrared range (NIR) to a laser beam transmitted simultaneously from both fibers placed face to face, to build a continuous, flexible and self-aligned optical link. The specificity of the presented process (NIR-SM-SWW) lies in the use of a writing wavelength identical to that intended for single-mode propagation in the fibers. This enables the creation in a single step of a SWW directly adapted to the fundamental mode to be transmitted. A precise pre-positioning stage is used to optimize the process. For best photochemical conditions, a coupling efficiency as high as 82 % (-0.86 dB loss) is demonstrated for a 300 mu m-long link. The effect of fiber-to-fiber axial and lateral distances is also investigated to estimate the propagation loss and misalignment tolerance, respectively. In addition, measurements performed by quantitative phase optical microscopy indicate a homogeneous index profile in the guide. Using these data, optical modeling is performed and compared to experiments, confirming that a high efficiency SM link is actually fabricated, without the need for further fabrication of an external cladding. This method could therefore be easily applied to the SM connection of a SM VCSEL (vertical-cavity surface-emitting laser) to a SM fiber, which is of major interest for the development of compact optical communications and instrumentation systems.

We exploit a near-infrared (NIR) photopolymerization process for the creation of a self-written waveguide (SWW) between two single-mode (SM) fibers at 850 nm (780HP) placed in the V-grooves of a compact glass fiber coupler. The coupler is manufactured by femtosecond laser irradiation and chemical etching (FLICE) and enables the study of coupling efficiency tolerance to lateral offsets between the fibers for an axial distance between 95 and 110 mu m. A maximal coupling efficiency of 80% (0.97 dB loss) is obtained for the minimal lateral offset measured (0.36 +/- 0.14 mu m). Moreover, a 3 dB misalignment tolerance of ca. 3 mu m is measured, which should be compared with the small size of the mode field diameters (5 mu m). In addition, an average coupling efficiency of 77.4% is measured in a second glass coupler with no intentional misalignment, showing that the SWW process can overcome the manufacturing tolerances of the FLICE coupler. These results are comparable to those obtained using a complex and bulky alignment system (i.e., a hexapod) and confirm that compensation mechanisms brought by this simple and parallelizable process can actually be exploited for low-cost fabrication of 850 nm single-mode optical links within a compact module for optical communications or sensing applications.

The development of tunable photonic devices is strategic for miniaturized optical instrumentation and sensing systems. Exploiting the birefringence variation of liquid crystals (LCs) instead of MEMS actuation in such devices could bring better spectral stability and lower power consumption. However, aligning LCs inside a III-V semiconductor device is tricky. We demonstrate that self-assembled gallium arsenide (GaAs) quantum dashes (QDHs) could serve as direct planar aligners for LC nematic molecules. The alignment quality and birefringence variation of a LC-microcell embedding QDHs are shown to be similar to those of a polymer nanograting-based reference, with the added advantage of better electrical performance.

A highly emissive blue organic light emitting diodes (OLED) for use as an algae excitation source in a biosensor was designed and optimized to meet spectral filtering requirements of the system. This source needs to exhibit high emission around 470-480 nm (algae absorption) combined with low emission in the algae fluorescence bandwidth (550-600 nm) in order to avoid any overlapping signal in the biosensor's sensitivity range. To address these issues, a microcavity device (MOLED) was studied and optimized. In order to further decrease the residual parasitic emission in the green spectral range, an additional filter was also integrated in the device. An improvement in peak intensity of 2.7 times the reference value was obtained, as well as a significant reduction of the parasitic emission in the green range. These improvements in peak intensity and spectral filtering should lead to a suitable blue OLED excitation source for compact optical biosensors.

Low-loss coupling of VCSELs (vertical-cavity surface-emitting lasers) to optical fibres is a key issue for increasing their use in optical communications and instrumentation systems. However, tolerances on angular tilts and lateral misalignments are tight, particularly in the case of single mode devices. To address this challenge, a new fabrication method based on near-infrared single-mode self-writing (NIR-SM-SWW) of a polymer waveguide was developed and tested for the coupling of two single mode fibers at 850 nm (Thorlabs 780-HP) with a mode field diameter close to that of 850 nm single mode VCSEL. The specificity of our method is to use a writing wavelength identical to that designed for single mode propagation in the fibers, leading to a single step photopolymerization process that will be directly transferable to 850 nm VCSEL-to-fiber coupling. First results show coupling losses at 850 nm as low as 0.86 dB for a distance between the fibers of 100 mu m.

In this work, we present simultaneous organic light-emitting diode (OLED) stack optimization and optical modelling for a blue microcavity-OLED (MOLED) based on AZO anode to be used as algae excitation light in optical biosensor. Fluorescent materials (MADN and DPAVBi) were chosen as host:guest for the doped emissive layer due their known stability compared to phosphorescent and thermally activated delayed fluorescence (TADF) materials. The MOLED modelling was performed by targeting 470 nm as the maximal excitation wavelength and suppressing the emission in the algae fluorescence bandwidth (600-800 nm) in order to fulfil the sensor requirements. By using a bilayer hole transport layer/electron blocking layer (HTL/EBL) instead of a single HTL, the total thickness was adjusted to meet the resonance wavelength condition without loss of efficiency, while at the same time preserving a maximum electric field intensity in the emissive layer (antinode position). MOLED devices were fabricated by organic semiconductor evaporation on three dielectric distributed Bragg reflectors (DBRs) with 3 different numbers of TiO2/SiO2 (high-index/low-index) pairs and aluminum-doped zinc oxide (AZO) transparent electrode. Devices with 1.5 pairs as DBR showed not only an improved external quantum efficiency (+33%) compared to a standard OLED but also an increase of about 3 times the intensity of the peak at 470 nm combined to a lower emission in the 600-800 nm bandwidth, as aimed. This increase in the peak intensity should lead to a longer device lifetime, as the current density necessary to excite algae at 470 nm is significantly lower owing to the microcavity effect. Copyright (C) 2023 Elsevier Ltd. All rights reserved.

In this work, two-photon polymerization three-dimensional laser writing is used to integrate a microlens on the surface of a single mode polarization-stable vertical-cavity surface-emitting laser (VCSEL) to be used as a current-driven tunable source in a compact optical guided-wave gas sensor. The writing conditions are optimized to enable on-demand room temperature and single-step fabrication at a post-mounting stage. We show that a writing time of 5 min is sufficient to fabricate a microlens that efficiently reduces the VCSEL beam divergence, without significant change on its emitted power or polarization stability. The lens addition reduces the spectral available range at high injection currents. A two-dimensional optical modeling of the gain characteristics is used to explain this effect and a new transverse design is proposed to avoid this issue.

Relying on preliminary experiments, in this work we design a tunable 850 nm laser based on a hybrid combination of a liquid crystal micro-cell with nanoimprinted grating and an electrically-pumped GaAs half-VCSEL. The optical design is challenging due to the inherent tolerances of this hybrid technology, the presence of metals in the cavity and the need for single fundamental extraordinary mode emission over the whole tuning range. To ensure proper operation, we introduce for the first time the new concept of anisotropic transverse confinement design. The overall performance is verified by our multiphysics VCSEL suite. Beyond tuning features, we predict side mode suppression ratio and optical power under all working conditions, comparing the performance of liquid crystals with different clearing temperatures. The results qualifies these lasers as viable tunable sources with interesting performance and complementary features compared to other technologies.

In this work, the thermo-optical properties of a nematic liquid crystal are determined through reflectance measurements performed on a high finesse tunable filter fabricated using a polymer-based microcell technology. The final aim is to insert such material in the optical cavity of a 850 nm tunable VCSEL device, in which local self-heating due to CW pumping must be taken into account. These localized interferometric experiments are performed in the near-infra-red range and at temperatures up to 115 °C. A thermal model is derived from the acquired data. Finally, we demonstrate that the birefringence of QYPDLC-36 liquid crystal remains higher than 0.18 at 60 °C, feature well suited to real device operation.

Miniaturized tunable photonic devices can be of great interest for applications in wavelength division multiplexing systems or metrology applications. For a widespread deployment, such systems have to be compact, dynamically reconfigurable in wavelength, and with a low power consumption. To achieve such devices, many studies have been conducted in the past by using the MEMS technologies. However, MEMS solutions may have some drawbacks related to power consumption, high driving voltage or fragility of the MEMS structure. As an alternative to this MEMS approach, the use of the well-known and mature liquid crystals (LC) material within a monolithic microcavity structure has been proposed. In this work, we report InP based materials combined with LC microcells to achieve photodiodes or Vertical Cavity Surface Emitting Lasers (VCSEL) with tunable wavelength capabilities. In the case of photodetection experiments, a wavelength sweeping from 1480 nm to 1561 nm limited by the tuning range of a tunable laser used as a probe is demonstrated. This spectral window is covered with a LC driving voltage of 7V only, corresponding to an extremely low power consumption of few μW. The average sensitivity over the whole spectral range is 0.4 A/W, slightly lower than 0.6 A/W for similar photodiodes that do not integrate such a LC tunable filter. The quality of the filter integrated onto the surfaces of the photodiodes is constant over the full wavelength tuning range, showing a FWHM of 1.5 nm. For emission experiments, we developed tunable VCSEL integrating the same LC microcell technology than the one used for the photodiode. For this device, laser emission in CW operation has been demonstrated. This tunable VCSEL has been characterized under optical pumping with typical threshold very similar to the one obtained with single frequency device. This is an experimental evidence than optical losses introduced by the LC inserted in the VCSEL cavity are very low. Output power in the mW range is also demonstrated and by increasing the applied voltage up to 20 V, a wavelength tuning higher than 23 nm is achieved. For a better understanding of this behavior, thermo-optical simulations have been conducted. By taking into account the heating properties of the LC and the reduction in its birefringence with temperature, the wavelength shift as function of the voltage is completely reproduced. Recently, by using LC with a better thermal tolerance larger tuning ranges are expected.

We present CW operation of a tunable InP based Vertical Cavity Surface Emitting Laser, integrating a liquid crystal micro-cell. In comparison with previous work, a larger 33 nm tuning and stable operation are obtained, according to major improvements presented in this paper.

Most porous silicon-based interferometric sensors targeting biosensing applications consist of vertical porous silicon layers created into a silicon wafer by electrochemical anodization and operate in a flow-over configuration. In this work, we present an alternative porous silicon interferometer based on porous silicon with horizontally oriented pores. This architecture permits the integration of flow-through porous silicon membranes within planar microfluidics. Fourier-transform infrared spectroscopy was used to obtain interference spectra from fabricated lateral porous silicon membranes and red shifts were observed upon filling microfluidic chips integrating the porous membranes with solvents of higher optical indices. This work proves that lateral porous silicon membranes are typical Fabry-Perot interferometers with a sensitivity of more than 150 nm/RIU and a limit of detection less than 10(-3) RIU, that is comparable to vertical porous silicon layers. Moreover, we have conducted simulation studies showing that the addition of Bragg mirrors on the membranes results in spectra with narrower fringes and lateral porous silicon interferometers with improved performances. After appropriate biofunctionalization of the porous silicon surface, lateral porous silicon membrane interferometers should offer alternative solutions for the development of porous silicon flow-through biosensors monolithically integrated on-chip. (C) 2021 Elsevier B.V. All rights reserved.

An InP-based Vertical-Cavity Surface-Emitting Laser (VCSEL) with a liquid crystal (LC) microcell monolithically integrated on its surface for spectral tuning is investigated. Unlike tunable VCSELs integrating a movable membrane, here the physical length of the cavity remains unchanged and only the voltage applied on the LC ensures a refractive index modification for a particular polarization emitted by the VCSEL. This tunable VCSEL operates in CW at room temperature and exhibits more than 23 nm wavelength tuning around $1.55\mu \text{m}$ at a maximum applied voltage of 20 V. The measured laser threshold around 6.5 mW is still comparable to VCSEL without LC microcell, a clear indication that the optical losses related the LC are very low. On the other hand, for this first optically pumped device, the lasing characteristics suggest that the LC birefringence is lower than expected. To assess this hypothesis, thermo-optical simulations have been conducted.

Near infrared (NIR) activable photopolymers suitable for versatile fabrication of micro-optical elements were developed. The first main objective of this article is to show that these new photopolymers can be used for microfabrication and investigate the parameters governing the microfabrication process. The impact of photonic, physico-chemical, and chemical parameters is discussed. High quality microstructures with a good control over their size and shape are demonstrated. The second main objective is to show practical examples of microlenses and waveguides implemented on single core and multiple core optical fibers, VCSELs, and glass slides are then presented. The NIR photosensitivity of this negative tone photoresists allows using the device source itself as to start the crosslinking process, which constitutes a convenient approach for micro-optics self-positioning on NIR sources and justifies the interest of such NIR photopolymer for the fabrication micro-optical elements and optical interconnects.

AbstractNear infrared (NIR) activable photopolymers suitable for versatile fabrication of micro‐optical elements were developed. The first main objective of this article is to show that these new photopolymers can be used for microfabrication and investigate the parameters governing the microfabrication process. The impact of photonic, physico‐chemical, and chemical parameters is discussed. High quality microstructures with a good control over their size and shape are demonstrated. The second main objective is to show practical examples of microlenses and waveguides implemented on single core and multiple core optical fibers, VCSELs, and glass slides are then presented. The NIR photosensitivity of this negative tone photoresists allows using the device source itself as to start the crosslinking process, which constitutes a convenient approach for micro‐optics self‐positioning on NIR sources and justifies the interest of such NIR photopolymer for the fabrication micro‐optical elements and optical interconnects.

In this work we investigate a tunable 850 nm laser based on a hybrid combination of a liquid crystal micro-cell and a half GaAs VCSEL. The target application is optical coherence tomography. The inherent tolerances of the hybrid technology, the presence of metals in the cavity and the need for a pure extraordinary mode lasing make challenging the optical design of this laser. Hence, VELM, a full 3D and vectorial VCSEL optical solver, is utilized to understand loss mechanisms and provide an optimized design.