Digital Light Processing Technology Optimizes Spectroscopy Applications

Digital Light Processing Technology Optimizes Spectroscopy Applications

Spectroscopy has proven to be a powerful technique for recognizing and characterizing materials through their absorption and emission of light. Although there are numerous types of spectroscopy solutions, Texas Instruments’ (TI) Digital Light Processing (DLP) technology offers a novel single-element approach compared to conventional large-array architectures. TI recently announced a near-infrared (NIR) micro electromechanical system (MEMS) digital micromirror device (DMD), the DLP4500NIR, as well as the DLP NIRscan evaluation module (EVM).

The DLP4500NIR (pictured left), when paired with a detector, allows engineers to replace expensive linear detector arrays in order to create high-performance spectrometer designs. This is due to an array of approximately 1 million digitally programmable micromirrors at the center of the device, which can be controlled to produce set patterns.  From there, spectral resolution and wavelength ranges can be refined, integration time can be adjusted, and light throughput can be equalized.

It is optimized for use with 700- to 2500-nm light and can be programmed to select and attenuate multiple wavelengths at speeds up to 4 kHz. The technology further enables improved signal-to-noise ratios (SNRs) greater than 30,000:1 over a set period of time, providing more accurate results compared to traditional solutions. The device’s small-form factor offers greater flexibility, compared to expensive array detectors, in the creation of systems.

The DLP NIRscan EVM (pictured right) includes a variety of interfaces to facilitate design versatility. TI’s SitaraTM AM3358 ARM Cortex A8 Processor is the main source of processing power as well as a 24-bit, 30-kSPS delta-sigma analog-to-digital converter. It also features a built-in Ethernet port and two USB ports for both wired and wireless connectivity options. The EVM comes pre-loaded with a Linux operating system and an integrated Web server that is based on the BeagleBone Black architecture. This Web-driven interface simplifies setting up without the need for special downloads.

The system block diagram for the EVM (All images courtesy of TI.)

The DLP technology, in conjunction with broadband detectors across the VIS-NIR ranges, allows for the pre-dispersive selection of multiple wavelengths for high-speed transmission or absorption measurements. This enables the generation of dynamic measurement schemes and algorithms, gained speed and accuracy for critical applications, and the protection of samples from unnecessary exposure.

According to the white paper, “Texas Instruments DLP Technology for Spectroscopy,” by Pascal Nelson, “The unique architecture of the DLP DMD facilitates a spectrometer architecture that uses a larger, single detector to displace an expensive array detector, while still allowing for a robust (no moving parts) optical platform.” Nelson goes on to list other performance benefits including: a larger spatial area that supports a greater detector area and light- capture efficiency, the aforementioned better SNR, and the elimination of scan errors due to pixel defects thanks to the single-element detector approach.

The architecture also enables adaptive scanning techniques that are not possible with array detectors or rotating grating designs. Sample methods include auto SNR adjust/constant SNR scan, auto optical flux control, “on the fly” control of resolution and wavelength ranges, and chemometric methods with multiple patterns. This further helps in the overall design of high performance, robust, flexible, and cost effective spectroscopy solutions.

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