Wavelength-scale stationary-wave integrated Fourier-transform spectrometry

Spectrometry is a general physical-analysis approach for investigating light-matter interactions. However, the complex designs of existing spectrometers render them resistant to simplification and miniaturization, both of which are vital for applications in micro- and nanotechnology and which are now undergoing intensive research. Stationary-wave integrated Fourier-transform spectrometry (SWIFTS)-an approach based on direct intensity detection of a standing wave resulting from either reflection (as in the principle of colour photography by Gabriel Lippmann) or counterpropagative interference phenomenon-is expected to be able to overcome this drawback. Here, we present a SWIFTS-based spectrometer relying on an original optical near-field detection method in which optical nanoprobes are used to sample directly the evanescent standing wave in the waveguide. Combined with integrated optics, we report a way of reducing the volume of the spectrometer to a few hundreds of cubic wavelengths. This is the first attempt, using SWIFTS, to produce a very small integrated one-dimensional spectrometer suitable for applications where microspectrometers are essential

Miniaturization of optical spectrometers

Spectroscopic analysis is one of the most widely used analytical tools across both scientific research and industry. Whilst laboratory bench-top spectrometer systems offer superlative resolution and spectral range, their miniaturization is crucial for applications where portability is paramount, or in-situ measurements must be made. Advancement in this field over the last three decades is now yielding microspectrometers with performance and footprint near those viable for lab-on-a-chip systems, smartphones and other consumer technologies. In this review, we briefly summarize the technologies that have emerged toward achieving these aims - including miniaturized dispersive optics, narrowband filter systems, Fourier transform interferometers and reconstructive microspectrometers - and discuss the challenges associated with improving spectral resolution while device dimensions shrink ever further.EPSRC: EP/L016087/1 National Natural Science Foundation of China (51706141, 51976122

MEMS based heavy metal detector

Water pollution by toxic heavy metals is one of the most serious environmental hazards to humans’ health. As they are emitted into the water resources and adsorbed by soil, plants, fish and animals and eventually accumulate in human bodies causing a variety of serious diseases. Therefore, there is an urgent need to develop a continuous, rapid, automatic, and on-site heavy metals environmental monitoring system for the online detection of heavy metals pollution at various water resources and industrial waste networks. In this thesis the main objective is to develop a microfluidic platform for heavy metal analyte sensing in which a variety of sensing schemes can be applied. The proposed platform contains microfluidic microchannels for the handling and separation of heavy metal analytes to improve the selectivity, integrated with a sensing device for the optical detection and monitoring of various heavy metal analytes and concentrations. In this context, the design and micro-fabrication of polymer based microchannels were conducted as the microfluidic platform on which the integration of the various optical sensing materials can take place. Afterward a novel design of MEMS based Fourier transform spectrometer is proposed, in which a new scheme for input Gaussian beam splitting into symmetrically two semi Gaussian beam is introduced using V shape mirror. The design is fully integrated and can operate in the Infrared and visible region. The analysis shows that, a minimum resolution of 9nm at a wavelength of 1.45μm and a mechanical displacement of 160μm is achievable. Unlike the traditional Michelson interferometer which returns half of the optical power to the source, this design uses the full optical power to get the interference pattern using movable reflecting mirrors thus enhancing the signal to noise ratio, and allowing the use of differential moving scheme for the mirrors which increase the optical path difference by a factor of four. An analytical model that describes the beams propagation and interference is derived using Fourier optics techniques and verified using Finite Difference Time Domain (FDTD) method. Then, a mechanical model that describes the mirror displacement to produce optical pass difference is derived and verified using finite element method (FEM). Finally, the effect of different design parameters on the interference pattern, interferograme and resolution are also shown

Design of infrared microspectrometers based on phase-modulated axilenses

We design and characterize a novel axilens-based diffractive optics platform that flexibly combines efficient point focusing and grating selectivity and is compatible with scalable top-down fabrication based on a 4-level phase mask configuration. This is achieved using phase-modulated compact axilens devices that simultaneously focus incident radiation of selected wavelengths at predefined locations with larger focal depths compared to traditional Fresnel lenses. In addition, the proposed devices are polarization insensitive and maintain a large focusing efficiency over a broad spectral band. Specifically, here we discuss and characterize modulated axilens configurations designed for long-wavelength infrared (LWIR) in the $6~\mu$m--12~$\mu$m wavelength range and in the $4~\mu$m--6~$\mu$m mid-wavelength infrared (MWIR) range. These devices are ideally suited for monolithic integration atop the substrate layers of infrared focal plane arrays (IR-FPAs) and for use as compact microspectrometers. We systematically study their focusing efficiency, spectral response, and cross talk ratio, and we demonstrate linear control of multi-wavelength focusing on a single plane. Our design method leverages Rayleigh-Sommerfeld (RS) diffraction theory and is validated numerically using the Finite Element Method (FEM). Finally, we demonstrate the application of spatially modulated axilenses to the realization of compact, single-lens spectrometer. By optimizing our devices, we achieve a minimum distinguishable wavelength interval of $\Delta\lambda=240nm$ at $\lambda_0=8{\mu}m$ and $\Delta\lambda=165nm$ at $\lambda_0=5{\mu}m$. The proposed devices add fundamental spectroscopic capabilities to compact imaging devices for a number of applications ranging from spectral sorting to LWIR and MWIR phase contrast imaging and detection

Etalon Array Reconstructive Spectrometry.

Compact spectrometers are crucial in areas where size and weight may need to be minimized. These types of spectrometers often contain no moving parts, which makes for an instrument that can be highly durable. With the recent proliferation in low-cost and high-resolution cameras, camera-based spectrometry methods have the potential to make portable spectrometers small, ubiquitous, and cheap. Here, we demonstrate a novel method for compact spectrometry that uses an array of etalons to perform spectral encoding, and uses a reconstruction algorithm to recover the incident spectrum. This spectrometer has the unique capability for both high resolution and a large working bandwidth without sacrificing sensitivity, and we anticipate that its simplicity makes it an excellent candidate whenever a compact, robust, and flexible spectrometry solution is needed

Real-Time High Resolution Integrated Optical Micro-Spectrometer

A real-time integrated planar single-mode waveguide grating micro-spectrometer with high resolution of 0.5 nm in 120 nm wide range of visible spectrum, from 525 nm to 645 nm is demonstrated. A CMOS sensor is used for capturing the output image of micro-spectrometer. A f = 1cm lens is used to focus the diffracted monochromatic light onto the CMOS sensor. An algorithm is developed using simple polynomial equation which uses two known reference wavelengths to convert x-pixel numbers of the CMOS sensor to wavelength spectrum. The output of micro-spectrometer in this design has comparatively less noise than usual spectrometric measurements. This design uses built-in matlab functions such as \u27findpeaks\u27 to find the input laser peaks and the central pixel numbers for that peaks and \u27polyfit\u27 to find the coefficients essential for the calibration of wavelength spectrum