The fabrication of high-quality microlenses is possible only when it is assisted by efficient and accurate metrology. For this reason, developing expertise in measurement procedures is crucial for the micro-optics manufacturer. We review and comment on this topic by first discussing what features of microlenses must be characterized and controlled. We then review the existing techniques and instruments that can be employed for this task. Finally, we detail the limitations of these different methods, we compare them, and we propose practical guidelines to setup effective metrology methodology. We believe that this paper can be an introduction to the topic but also serves as a reference document for the more experienced reader.

Demand for high integration of optoelectronic and micro-optical components into micro-electronic systems for communication, computing, medical, and sensing applications is increasing. Advanced hybrid packaging technologies are used to enhance glass-based substrates featuring electrical, thermal, and optical functionalities with laser diodes, modulators, isolators, photonic integrated circuits (PIC), beam-splitting components, and micro-lenses. Such glass-based substrates can be thin glass layers on large panels or more mini-bench-like boards that can be embedded into organic printed circuit boards (PCBs). Optical fiber interconnects, connectors, and electrical–optical integration platforms are used for higher level system integration and need to be miniaturized on module and board level to fulfill decreasing channel pitch requirements. We provide background on and discuss thin glass as a suitable base material for ion exchanged waveguide panels and interposers, precise glass structuring for posts and holders, the related high precision assembly techniques, and advanced fiber interconnects. Some examples of PCB photonic integration, micro-bench optical sub-assemblies, including PIC, and 3D optical resonator packages that combine most of these approaches will be shown.

We report on a co-planar light-actuated digital microfluidics device that features a metal mesh grid integrated on the device surface to allow droplets to be exposed from above. We discuss a theoretical circuit model for our co-planar optoelectrowetting (OEW) design that allows for the optimization of droplet actuation while maintaining reliable droplet movement. Basic droplet manipulations such as merging and parallel actuation of droplets are achieved at speeds of up to 4.5  cm  /  s. The co-planar OEW device design benefits from having an open top design that allows for a wider range of system integration configurations than previous generations of OEW devices. A droplet-on-demand dispensing system from above is integrated with the co-planar OEW device to demonstrate the versatility of this optofluidic platform. The ability to inject, collect, and position individual droplets to form large-scale droplet arrays of up to 20  ×  20 is achieved.

Beyond various application-specific photonic integrated circuits (PICs), a programmable PIC comprising identically designed generic building blocks with multiple active functionalities under different operational conditions is an attractive design option. Here, we propose and demonstrate proof-of-concept experiments of a heterogeneously integrated III–V-on-Si microring resonator (MRR) as such a versatile building block. The MRR can function as an electro-optical channel add-drop switch with signal amplification, a directly modulated injection laser, or a microcavity photodetector under different electrical bias conditions. We discuss the fabrication process for our heterogeneous integration platform based on an atomic layer deposition-assisted molecular bonding technique.

We report an objective-lens-free endomicroscopic catheter for compact Lissajous scanned confocal endomicroscopic system using a scanning lensed-fiber. The fiber scanner comprises a single-mode fiber (SMF) spliced with a coreless silica fiber segment and quadrupole piezoelectric tube. An objective lens was directly formed at the distal end of an SMF using a fusion splicer. The lensed fiber eliminates the need for conventional beam focusing elements such as a gradient index rod lens and precise optical alignment, allowing low cost and facile fabrication of an exceptionally short endomicroscopic catheter. The endomicroscopic scanner was fully packaged within a stainless tube of 2.6 mm in outer diameter and 20 mm in length, which can be easily inserted through the working channel of conventional laparoscope or colonoscope. The microscopic images of a stained kidney section and ear of a mouse were successfully obtained with the Lissajous scanning confocal endomicroscope. The compact Lissajous scanning lensed fiber can provide a new route for diverse in vivo endomicroscopic applications.

A 63-electrode optofluidic refractive wavefront modulator enabling spatial frequency correction up to the seventh radial Zernike order, the highest spatial order ever achieved with a refractive dynamic wavefront modulator, is presented. The modulator is designed so that aberration correction performance is nearly identical in both horizontal and vertical orientations, virtually eliminating the gravity-induced parasitic surface deformations typical for optofluidic devices. With 55 of its electrodes located within the 1-cm clear pupil, the modulator offers the versatility of continuous face-sheet deformable mirrors within a compact, high efficiency, and transmissive device. Using a fluidic interfacing method based on wafer-level 3D micro-structuring of glass, the modulator is only 0.86-mm-thick, facilitating the cascading of multiple modulators within close proximity. We demonstrate a bi-directional stroke of more than 13 λ, and replications of Zernike mode shapes up to the seventh radial order with high fidelity, representing a significant leap in the performance of ultra-miniaturized refractive wavefront modulators.

We present a wavelength tunable vertical-cavity surface-emitting laser (VCSEL) constructed by die-bonding a half-cavity InGaAs laser diode (LD) chip onto a silicon-on-insulator chip with a microelectromechanical system electrostatic diaphragm mirror that functions as a Fabry–Perot interferometer. As a result of the short cavity length, the integrated tunable LD has single-mode lasing characteristics with an extremely large coherence length of 150 m or more. The developed wavelength tunable LD is used to perform swept-source optical coherence tomography with a large scan depth, which is applicable to ophthalmic observation for the diagnosis of pathologic nearsightedness based on the measurement of the axial length of an eye.