Optofluidics is a rising technology that combines microfluidics and optics. Its goal is to manipulate light and flowing liquids on the micro/nanoscale and exploiting their interaction in optofluidic chips. The fluid flow in the on-chip devices is reconfigurable, non-uniform and usually transports substances being analyzed, offering a new idea in the accurate manipulation of lights and biochemical samples. In this paper, we summarized the light modulation in heterogeneous media by unique fluid dynamic properties such as molecular diffusion, heat conduction, centrifugation effect, light-matter interaction and others. By understanding the novel phenomena due to the interaction of light and flowing liquids, quantities of tunable and reconfigurable optofluidic devices such as waveguides, lenses, and lasers are introduced. Those novel applications bring us firm conviction that optofluidics would provide better solutions to high-efficient and high-quality lab-on-chip systems in terms of biochemical analysis and environment monitoring.

Optofluidics: the interaction between light and flowing liquids in integrated devices

Enhancement of silicon-wafer solar cell efficiency with low-cost wrinkle antireflection coating of polydimethylsiloxane

A new ultrafast all-optical solid-state framing camera (UASFC) capable of single-shot ultrafast imaging is proposed and experimentally demonstrated. It is composed of an ultrafast semiconductor chip (USC), an optical time-series system (TSS), and a spatial mapping device (SMD) with an USC to transform signal beam information to the probe beam, a TSS to convert the time axis to wavelength-polarization, and a SMD to map wavelength-polarization image to different spatial positions. In our recent proof-of-principle experiment, better performance than ever of this technique is confirmed by giving six frames with ~3 ps temporal resolution and ~30 lp/mm spatial resolution.

Ultrafast all-optical solid-state framing camera with picosecond temporal resolution.

A rapid method is developed for fabricating low-cost and high-numerical-aperture photosensitive-gel microlens arrays (MLAs) with well-controlled curvatures. An UV-curable photosensitive-gel film beneath the microholes of a silicon mold can be flexibly deformed by thermally manipulating the surface tension of the photosensitive gel and the pressure difference across the air–photosensitive-gel interface. The concave interface is then solidified through UV curing, forming a MLA with a concave curvature. MLAs with a focal length ranging from 51.4 to 71.9 μm and a numerical aperture (NA) of 0.49 were fabricated. The photocured MLA has high mechanical and thermal strength and is suitable as a master mold for the further production of convex MLAs. The fabricated microlenses have uniform shapes and smooth surfaces. In a demonstration of imaging and focusing performance, clear and uniform images and focused light spots were observed using concave and convex MLAs.

Fabrication of a Microlens Array with Controlled Curvature by Thermally Curving Photosensitive Gel Film beneath Microholes

Optofluidics incorporates optics and microfluidics together to construct novel devices for microsystems, providing flexible reconfigurability and high compatibility. Among many novel devices, a prominent one is the in-plane optofluidic lens. It manipulates the light in the plane of the substrate, upon which the liquid sample is held. Benefiting from the compatibility, the in-plane optofluidic lenses can be incorporated into a single chip without complicated manual alignment and promises high integration density. In term of the tunability, the in-plane liquid lenses can be either tuned by adjusting the fluidic interface using numerous microfluidic techniques, or by modulating the refractive index of the liquid using temperature, electric field and concentration. In this paper, the in-plane liquid lenses will be reviewed in the aspects of operation mechanisms and recent development. In addition, their applications in lab-on-a-chip systems are also discussed.

Optofluidic Tunable Lenses for In-Plane Light Manipulation.

Serial time-encoded amplified microscopy (STEAM) is a novel ultrafast imaging technique that is based on space-to-time-to-wavelength mapping. Nevertheless, the technique requires a high-cost electronic digitizer of several tens of gigahertz sampling rate to read out sufficient image information. To acquire a large amount of image information by using a relatively low-sampling-rate electronic digitizer, an anti-aliasing technique based on optical time-division multiplexing is proposed. A 38.88 MHz line-scan imaging system is demonstrated experimentally. By using the proposed anti-aliasing technique, a 20 GS/s sampling rate is achieved by employing a 10 GS/s electronic digitizer. Defects and scratches on the target that were not identifiable originally can be clearly distinguished after using the proposed technique. Numerical analysis shows that the image quality can be improved by 4.16 dB, compared to that not using the anti-aliasing technique and at least 2.3 dB comparing to those obtained by bilinear, bicubic, and nearest-neighbor interpolation and Lanczos resampling techniques.

Ultrafast imaging with anti-aliasing based on optical time-division multiplexing

This paper presents an in-plane hydrodynamically reconfigurable optofluidic microlens, which is formed by the laminar flow of two streams of a low-refractive-index fluid and two streams of a high-refractive-index fluid in the two microchannels connecting to an expansion chamber where the microlens finally forms. In the expansion chamber, the stream of high-refractive-index fluid, acting as core, is sandwiched by the two streams of low-refractive-index fluid, acting as cladding. The interfaces between the streams can be flexibly manipulated by controlling the flow rate ratio between the two fluids in real time. Thus, the biconvex and biconcave microlens with different curvatures can be formed. By adjusting the microlens, the light beam can be continuously manipulated from focusing to collimation and then to divergence. In the experiment, a wide focus tuning range from 2.75 (focusing) to -1.21 mm (diverging) via collimation is achieved.

Hydrodynamically reconfigurable optofluidic microlens with continuous shape tuning from biconvex to biconcave.

A liquid plano-convex lens with focal length tuning is proposed, which is formed by sinking an oil droplet onto the bottom of an elastomer. A simple and low-cost fabrication method is presented. The lens aperture and initial focal length can be controlled during the fabrication. Furthermore, focal length tuning is demonstrated. The lens made of a 40 mg oil droplet can achieve the tuning range from 12 to 17 mm. The effective aperture of the lens is about 2.8 mm. In the demonstration of an imaging system, the lens assists in focusing and a clear image can be observed.

Focal-length-tunable elastomer-based liquid-filled plano-convex mini lens.

The invention relates to an optical Hilbert transform and differential operation system. An optical signal is inputted from a first port of an optical fiber circulator and shoots out from a second port to enter a collimator, after the light beam is adjusted by virtue of a combined beam expander, the light beam enters a glittering grating, the light beam in different wavelengths is dispersed to expand by virtue of the glittering grating, then the light beam is focused by virtue of a double convex lens and focused onto a reflection mirror with a step structure, a lower step of the reflection mirror is a focal point surface of the double convex lens, the phase difference is generated by virtue of an upper step and the lower step of the reflection mirror, the light reflected by the reflection mirror is returned to the second port of the optical fiber circulator along the original path, and then the light is outputted from a third port of the optical fiber circulator. The size of a light beam spot focused on the reflection mirror with the step structure is changed, and the optical differential operation function and an optical Hilbert transform function can be respectively realized; the position of the reflection mirror is adjusted, so that the center wavelength responded by the system can be tuned; the optical Hilbert transform and differential operation system is simple in structure, convenient to control, low in production cost and stable in performance.

Optical Hilbert transform and differential operation system

The invention provides an ultrafast imaging apparatus and method based on optical time division multiplexing. The apparatus is characterized by comprising a light beam emission unit; a light beam acquisition unit in optical path connection with the light beam emission unit; a light beam processing unit in optical path connection with an information acquisition unit for processing pulse light beams comprising image information of detected objects; and a light beam receiving unit in optical path connection with the light beam processing unit for receiving pulse light beams after processed by the light beam processing unit and restoring images of the detected objects, wherein the light beam processing unit comprises a first coupler, an adjustable light delay line, an attenuator and a second coupler. The ultrafast imaging apparatus based on the optical time division multiplexing solves the problem of the image aliasing, can improve the pixel point quantity of the images and realizes high-fidelity imaging. The ultrafast imaging method based on the optical time division multiplexing is simple to operate and easy to realize.

Ran Zhuo

Papers

Ultrafast imaging with anti-aliasing based on optical time-division multiplexing

Hydrodynamically reconfigurable optofluidic microlens with continuous shape tuning from biconvex to biconcave.

Focal-length-tunable elastomer-based liquid-filled plano-convex mini lens.

Optical Hilbert transform and differential operation system

Ultrafast imaging apparatus and method based on optical time division multiplexing