Pixel super-resolution using wavelength scanning

Undersampling and pixelation affect a number of imaging systems, limiting the resolution of the acquired images, whichbecomes particularly significant for wide-field microscopy applications. Various super-resolution techniques have been implemented to mitigate this resolution loss by utilizing sub-pixel displacements in the imaging system, achieved, for example, byshifting the illumination source, the sensor array and/or the sample, followed by digital synthesis of a smaller effective pixel bymerging these sub-pixel-shifted low-resolution images. Herein, we introduce a new pixel super-resolution method that is basedon wavelength scanning and demonstrate that as an alternative to physical shifting/displacements, wavelength diversity can beused to boost the resolution of a wide-field imaging system and significantly increase its space-bandwidth product. We confirmedthe effectiveness of this new technique by improving the resolution of lens-free as well as lens-based microscopy systems anddeveloped an iterative algorithm to generate high-resolution reconstructions of a specimen using undersampled diffraction patterns recorded at a few wavelengths covering a narrow spectrum (10–30 nm). When combined with a synthetic-aperture-baseddiffraction imaging technique, this wavelength-scanning super-resolution approach can achieve a half-pitch resolution of250 nm, corresponding to a numerical aperture of ~ 1.0, across a large field of view (420 mm^(2)). We also demonstrated theeffectiveness of this approach by imaging various biological samples, including blood and Papanicolaou smears. Compared withdisplacement-based super-resolution techniques, wavelength scanning brings uniform resolution improvement in all directionsacross a sensor array and requires significantly fewer measurements. This technique would broadly benefit wide-field imagingapplications that demand larger space-bandwidth products.

Fiber Methane Gas Sensor and Its Application in Methane Outburst Prediction in Coal Mine

Fiber optic methane gas detecting system based on distributed feedback （DFB） laser wavelength scanning technique is demonstrated. Wavelength scan of methane absorption peak at 1665.9 nm is realized by saw tooth modulation of current which is injected to DFB laser. A reference methane gas cell is used to find the methane absorption peak around 1666 nm, and normalization is used to reduce the outside affection such as power drift, fiber loss. Concentration is got by arithmetic processing absorption coefficient of the methane gas. In-situ test is carried out in coal mine and long time precision of 0.05% is achieved. Some spot data of coal mine is introduced. By the system, methane outburst can be measured.

Optical Humidity Sensor Based on Air Guided Photonic Crystal Fiber

We proposed a novel relative humidity （RH） sensor based on the air guided photonic crystal fiber （AGPCF） using the direct absorption spectroscopic method in this paper. The wavelength scanning around the water vapor absorption peak around 1368.59nm was realized by injecting the saw-tooth modulated current to a distributed-feedback laser diode. A reference signal was used as a zero absorption baseline and to help reduce the interference from the distributed-feedback laser source and probed region. The humidity level was determined by the normalized voltage difference between the reference signal and sensor signal at the peak of water vapor absorption. We demonstrated that a length of 5-cm AGPCF with a fixed small air gap between the single mode fiber （SMF） and hollow core fiber as an opening achieved a humidity detection resolution of around 0.2%RH over the range 0 to 90%RH which did not require the use of any hygroscopic coating material.