A novel Fourier spectrometer based on a partly transparent thin-film detector in combination with a tunable silicon micromachined mirror was developed. The operation principle based on the detection of an intensity profile of a standing-wave by introducing a partly transparent detector in the standing-wave. Varying the position of the mirror results in a phase shift of the standing-wave and thus in a change of the optical intensity profile within the detector. The photoelectric active region of the sensor is thinner than the wavelength of the incoming light, so that the modulation of the intensity leads to the modulation of the photocurrent. The spectral information of the incoming light can be determined by the Fourier transform of the sensor signal. Based on the linear arrangement of the sensor and the mirror, the spectrometer facilitates the realization of one- and two-dimensional arrays of spectrometers combining spectral and spatial resolution. The operation principle of the spectrometer will be described and the influence of the detector design on the spectrometer performance will be discussed. A spectral resolution of down to 6 nm was achieved under real-time imaging conditions.

A natural scene contains not merely“colors”but spectral emissions that are not fully detectable by conventional imaging systems, such as a digital camera. The usual means to extract spectral information is with a hyperspectral imager, which filters light at different wavelengths and records their intensities. The interferometric imaging spectrometer (IIS) is an experimental device that extracts spectral information a different way, by generating and capturing light interference patterns. The IIS embeds an interferometer within a conventional imaging system. Therefore, a key feature of the IIS is that it detects spectral information at all locations of a 2D scene in parallel. Coupled with perpixel processing implementable using simple analog circuits, the IIS is capable of directly extracting from a scene specific spectral properties of interest – for example, the widths of spectral peaks. Detecting the width of spectral peaks has been the focal point of efforts with the IIS. We examine the processing steps necessary for that purpose and show experimental results and derived applications.

An interferometric sensor based on a partly transparent amorphous silicon n–i–p diode was realized. The combination of the sensor with a tunable micromirror facilitates the realization of a novel microspectrometer. The working principle of the sensor based on the sampling of a standing wave created in front of the tunable mirror. To sample a standing wave the active region of the sensor has to be thinner than the wavelength of the incoming light. Varying the position of the mirror results in a shift of the phase of the standing wave, in a variation of the generation profile within the diode and, thus, in a modulation of the photocurrent. The spectral information of the incoming light can be determined by the Fourier transform of the sensor signal. The spectral resolution of the integrated spectrometer scales reciprocally with the displacement of the mirror. A spectrometer resolution down to 6nm was achieved.

A new coherence-sensing imaging system is designed and built for the visible range and a new invisible tag application that provides a unique method of marking or identifying objects by spectral bandwidth is also demonstrated.

We present an integrated microsensor for time-domain analysis of spectral coherence, with a tunable coherence detection range. The 0.2 cm/sup 3/ device includes a partially transmitting GaAs/AlGaAs photodiode and a large-displacement scanning Si MEMS mirror.

A continuous resolution tuning from 72 nm to 6 nm is demonstrated with an all-silicon standing-wave microspectrometer. In the standing-wave spectrometer, incident light reflects off a micromirror, creating an optical standing wave that is continuously sampled by a partially-transmitting photodetector. The 13 /spl times/ 13 mm Si device consists of a 2 /spl times/ 2 mm reflective mirror pillar connected to four rectangular flexures. High-amplitude continuous harmonic motion is accomplished by driving with a DC-offset sinusoidal voltage at the mechanical resonance frequency. The detector is a Si p-i-n photodiode with transparent ZnO contacts. This microspectrometer offers real-time optimization of device sensitivity and system operating requirements.

The recent research is focused on developing new spectral information processing techniques for adaptive, real-time analysis in the optoelectronic domain. We implement a Fourier transform spectrometer (FTS) that generates a time-varying interferogram signal containing all spectral information in a pixel. The correlation with a set of known spectra is performed in the time-domain by measuring interferograms with a photodetector, multiplying them by electrical reference interferograms that represent the known spectra, and integrating. This architecture eliminates unnecessary data in the optoelectronic front end, enabling extremely simple spectra-selective detection arrays.

Collecting a spectrum for each pixel in an image can give much useful information about a scene, such as chemical content, but generates a vast amount of data. Optical filters can select specific spectral features in advance, but are difficult to adapt in real time to different desired spectra. We have constructed an imaging spectrometer using a time-domain filtering architecture, capable of real-time spectral feature extraction and adaptation to different desired spectra. We demonstrate in real-time the abilities both to (i) recognize multiple specific colors in an image, and (ii) recognize individual colors while suppressing combinations of the same colors, an example of a sophisticated signal processing function that can be performed in this architecture

A novel Fourier spectrometer using thin film technology was developed. The spectrometer based on a semi transparent thin film detector in combination with a tunable micro machined mirror. The semi transparent detector is introduced into a standing wave created in front of the mirror to sample the profile of the standing wave. Varying the position of the mirror results in a shift of the phase of the standing waves and thus in a change of the optical generation profile within the semi transparent detector. The active region of the sensor (thickness-absorption) is thinner than the wavelength of the incoming light, so that the modulation of the intensity results in a modulation of the overall photocurrent. The spectral information of the incoming light can be determined by the Fourier transformation of the sensor signal. Based on the linear arrangement of the sensor and the mirror, the spectrometer facilitates the realization of 1D and 2D arrays of spectrometers combining medium range spectral resolution with medium range spatial resolution. The novel device is filling the gap between solid-state camera technology with only three-color channels (red, green and blue) but high spatial resolution on one hand and precision spectrometers with high spectral resolution but no spatial resolution on the other hand. An analytical optical model of the spectrometer was applied to evaluate different detector concepts. The model was used to study the performance of different device designs regarding the spectral resolution of the spectrometer, the spectral range and the linearity of the response. The calculations will be compared with experimental results of semi transparent amorphous silicon detectors.

The ideal portable microfluidic chip-based fluorescence detection system would include an integrated optical microsensor capable of detecting and flexibly discriminating among a wide range of simultaneous fluorescence emission signals. We present a compact optical microspectrometer based on a standing-wave architecture (1), and we will discuss results of spectral discrimination of optical test sources in the visible (488 nm - 665 nm) and near infrared (633 nm - 866 nm). Spectral resolution of 4 nm (λ = 633 nm) was recently achieved with an integrated near infrared prototype (Figs. 1a-1b). With a surface-normal , linear optical design, the 17 × 13 × 1 mm device is well-suited to integration with a microfluidic chip. Whereas most microspectrometers (commonly grating-based devices with a detector array) have poor spectral multiplexing characteristics, our standing-wave microspectrometer has the multiplexing advantage and simple single detector readout of a Fourier transform (FT) spectrometer. Microspectrometers also usually have fixed spectral resolution, however our device can be easily configured for a particular sensing task by tuning its spectral resolution, allowing real-time optimization of sensitivity. With a visible device, continuous resolution tuning from 72 nm to 6 nm (λ = 633 nm) was demonstrated (Fig. 2). This device is based on the standing-wave transform spectrometer architecture with a moving mirror and a partially transmitting photodetector. Incident light reflecting off the mirror creates an optical standing wave. While the mirror scans along the optical beam axis, the detector samples the moving standing wave; the FT of the resulting time-varying photocurrent yields the optical spectrum. This architecture offers the same advantages as other FT spectrometers, but in an optically 1-D system; this eliminates the need for a beamsplitter and reference mirror. Hybrid integration allows implementation of any photodetector material, and thus detection in any wavelength range. Our near infrared device contains a GaAs/AlGaAs photodiode (2), and our visible device contains an a- SiC:H/a-Si:H photodiode (3). In both cases the mirror component is a parallel-plate electrostatically driven Si MEMS actuator. High-amplitude harmonic oscillation, up to 52 μm at 800 Hz, enables fast, continuous spectral analysis. With an actuator capacitance of only 4.2 pF, it should draw < 0.1% of the power drawn by a typical piezoelectric transducer. We will introduce two unique physical properties of this device that can be used to suppress scattered pump light in fluorescence experiments. The minimum mirror-detector distance can be set by adjusting the actuator drive amplitude; this reduces the sensitivity to sources with low spectral coherence, which allows for preferential suppression of any broadband light source such as a broadband lamp pump. Also, the photodetector thickness can be designed so that there is a minimum of generated AC current for one wavelength, and a relatively strong AC signal for nearby wavelengths; this enables suppression of laser pump light with preferential detection of fluorescence emission. In conclusion, we have investigated and will discuss a number of intriguing capabilities of the standing- wave microspectrometer, with particular attention to those that could make this device useful in microsystems dependent on analysis of fluorescence emission.

Summary form only given. For some sensing applications, even the seemingly fundamental process of breaking a spectrum into frequency components may not be the best way to look for features in the spectrum. We have demonstrated a coherent imaging architecture, with inherent decomposition of the image into coherent and incoherent components. The decomposition at a very early stage of the physical measurement process means that 1) minimal data analysis is needed, and 2) the system never needs to have the resolution that would conventionally be required to resolve the spectral features of interest. These advantages translate into relaxed requirements on the hardware design and faster data collection, and will aid the design and expand the applications of inexpensive, mobile hyperspectral and multispectral imaging systems.

In this paper, we report a novel, miniature Fourier transform spectrometer with a linear architecture that works by sampling a standing wave. The spectrometer consists of an electrostatically actuated microelectromechanical mirror with on-resonance displacement of up to 65 m, a thin-film photodetector, and an electrical back plane for actuating the mirror. The integrated device offers mirror stability and fixed relative alignment of the three components. The spectrometer has better than 32-nm resolution at 633 nm.

We present a method of spectral discrimination that employs time-domain processing instead of the typical frequency-domain analysis and implement the method in a Michelson interferometer with a nonlinear mirror scan. The technique yields one analog output value per scan instead of a complete interferogram by directly filtering a measured scan with a reference function in the time domain. Such a procedure drastically reduces data-processing requirements downstream. Additionally, using prerecorded interferograms as references eliminates the need to compensate for scan nonlinearities, which broadens the field of usable components for implementation in miniaturized sensing systems. With our efficient use of known spectral signatures, we demonstrate real-time discrimination of 633- and 663-nm laser sources with a mirror scan length of 1 microm , compared with the Rayleigh criterion of 7 microm.

We have presented an integrated standing-wave spectrometer operating in the near a mirror flexure uniformity allows for increased mirror scan length without tip-tilt problems, which improves spectral resolution. The GaAs detector provides excellent near IR responsivity. The integrated design allows the mirror to move within a few gm of the detector. The simple operation of this compact device, with a low power continuous-scan mirror, permanent alignment, and only three contacts, should enable implementation in a wide variety of miniaturized sensing systems.

We present a programmable spectral discrimination system with minimal data extraction and processing, insensitive to scan nonlinearities. We demonstrate real-time discrimination of monochromatic sources 30 nm apart, employing a spectrometer with a nominal resolution of 200 nm. ©2001 Optical Society of America OCIS codes: (300.6300) Spectroscopy, Fourier transforms; (120.6200) Spectrometers and spectroscopic instrumentation

We demonstrate a Fourier-transform spectrometer based on a large-displacement MEMS mirror and sampling an optical standing wave with a thin photoconductor. The 1D design should permit integration of many spectrometers into an imaging array

We present an electrostatically actuated MEMS mirror with 65 mum of displacement. This design provides a 2 mm square reflective surface and allows for easy fabrication, making it suitable for a wide range of applications.