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Nanopatterned Diffraction Gratings

Monolithic Silicon Grating Arrays for high-resolution and extended range spectra

Figure 1. Photograph of LightSmyth monolithic grating array.

LightSmyth Technologies is proud to introduce monolithic, single-substrate, silicon grating arrays (Figure 1) that uniquely provide continuous high-resolution access to optical bandwidths beyond that achievable with a single grating. No moving parts are required. LightSmyth monolithic grating arrays are consistent with single-shot data acquisition for many broadband applications, e.g. laser-induced breakdown spectroscopy and can help reduce system component numbers dramatically. Each array consists of multiple primary gratings – all formed coherently on a single substrate. The primary gratings have contiguous, slightly overlapping active spectral ranges. Additionally, auxiliary gratings at the top and bottom of the substrate produce optical outputs used for the straightforward calibration of the output field using a single reference wavelength such as a HeNe laser.

Figure 2. Schematic illustrating operation of monolithic LightSmyth grating array in spectrometer setup with 2D detector.

In Figure 2, a grating array is shown in a simple spectrometer arrangement. A two-dimensional detector array is used to record output of the grating array. Figure 3 shows a schematic of the grating array output as seen on the 2D detector array when illuminated by white light and a copropagating HeNe laser. Each near horizontal line comprises output of one of the four primary gratings and corresponds to the spectral range indicated. Also shown as red dots are the calibration reference marks produced by the 6 auxillary gratings when exposed to HeNe light. Details of the device operation and design are described further in an application note.

Figure 3. Schematic of array output signal on detector.

Calibration/Alignment Features

The six small gratings at the top and bottom of the array (see Figure 1) provide markers for calibrating the spectral output as well as assisting in system alignment. The calibration marks, here for HeNe illumination, are shown schematically in Figure 4. The calibration marks provide two principal functions: First, they indicate the beginning and end points of the calibrated portion of the primary grating output. They thus allow the user to calibrate the wavelength as a function of position along each of the primary gratings’ dispersion lines - note that the wavelength range denoted by the calibration spots is independent of the grating input angle, making the LightSmyth grating array extraordinarily versatile with respect to possible device layouts. Second, the auxiliary gratings aid in system alignment. When the detector surface is properly positioned in the focal plane of the post-array focusing mirror, the two pairs of alignment marks are designed to coincide, indicating proper far-field operation. The two center marks enable correct horizontal alignment of array and detector surface.

Figure 4. Schematic illustrating function of calibration/alignment gratings.

Monolithic Silicon Grating Array

*The symbol X at the end of the part number specifies surface type and must be replaced with the appropriate designation (see below).

**Note: The calibration markers listed are produced by a HeNe laser incident on the small calibration gratings. Use of a different calibration light source having a different wavelength will produce markers (see Fig. 4) coinciding with different values of the dispersed spectra of the four primary gratings. Using a common input angle for calibration light and signal, the calibration marks delinate spectral output ranges of the primary gratings that are independent of grating input angle.

The silicon substrates have a thickness of 0.73 mm. Substrate height and width tolerances are ± 0.3 mm. In the part number, X refers to the coating and X=Si, Al, AlM and Au for bare silicon, bare Aluminum, Aluminum + MgF₂, and gold, respectively. Bare Silicon and Al + MgF₂ are standard. Other coatings are available at additional charge.

More technical details of the LightSmyth Monolithic grating array can be found in the following application note.

Pricing Information *

* Academic discounts are available for eligible institutions. To determine eligibility complete our account application procedure.