LightSmyth Technologies - Crafting Light for Industry and Science


Diffraction Gratings:

Flat Substrate Focusing Gratings

Application examples illustrating use of LightSmyth flat-substrate focusing gratings in external-cavity diode lasers. a, the grating functions as both outcoupler and to provide feedback. b, the grating provides feedback via the diode back facet.

LightSmyth Technologies’ family of flat-substrate focusing gratings are designed for use with external-cavity lasers. The gratings focus optical input signals while simultaneously spectrally dispersing them. The focusing function is incorporated into the gratings via holographic design principles using curved and variably-spaced grating lines. Integrating focus function with spectral dispersion through holography rather than by use of curved substrates or lenses reduces system component count and facilitates miniaturization.

Flat-substrate focusing gratings are also relevant to a broad range of applications in spectroscopy and general photonics. For example, fiber coupled miniature spectrometers may be build with minimum number of components: input fiber, focusing grating and output detector array. Such spectrometer may provide spectral coverage of several hundred nanometers and nm-level resolution on less than 15 x 15 mm footprint. 

LightSmyth flat-substrate focusing gratings are optimized for implementation in external-cavity diode laser (ECDL) systems where they provide frequency-selective feedback and thus laser frequency stabilization and linewidth narrowing. The gratings are designed for ECDLs employing the Littrow configuration and focus the first-order diffracted beam back toward the laser providing tunable locking feedback. Grating focal lengths are short (3.75 mm) in order to facilitate large longitudinal mode spacing and to enable convenient wide-range single-mode tuning.

Grating groove depth and duty cycle are optimized to provide maximal diffraction efficiency. Each grating is a master, free from replication flaws. Grating surfaces are cleanable and abrasion-resistant.

Array of flat-focusing gratings
Schematic of grating lines

For additional technical information click here.

Standard Flat-Substrate Focusing Gratings

The focal length of all gratings is 3.75 mm. All gratings are designed to provide laser feedback via the first diffraction order. The working distance between grating and laser diode front facet is d = 7.5 mm for all gratings. Silicon substrate has a thickness of 0.73mm. Substrate height and width tolerances are ± 0.3 mm. Grating substrate: single crystal silicon. Grating coating: aluminum (other coating types are available at additional charge).

Design Input
Angle1 φ
Approx. Line
Size 1
(w × h)
Part number Price first 99 units3
Unit price 100+ 4
405 nm s 40 ° 3175 6 mm × 3 mm SCG-405S-0603A-Al $ 90.00 ea. $ 75.00 ea.
405 nm p 45 ° 3640 3 mm × 6 mm SCG-405P-0306A-Al $ 90.00 ea. $ 75.00 ea.
635 nm s 40 ° 2028 6 mm × 3 mm SCG-635S-0603A-Al $ 90.00 ea. $ 75.00 ea.
635 nm p 65 ° 2857 3 mm × 6 mm SCG-635P-0306A-Al $ 90.00 ea. $ 75.00 ea.
780 nm p 60 ° 2222 3 mm × 6 mm SCG-780P-0306A-Al $ 90.00 ea. $ 75.00 ea.
1 See Figure 1 for design layout and illustration of parameters.
2 At grating midpoint.
3 For orders with the total product value below $250.00, a handling charge of $75.00 will be added, otherwise the handling fee is $5.00.
4 Example of price calculation for 200 unit order: $90*99 (first 99 units)+ $75*101(100+ units)
Figure 1a. Schematic illustrating grating layout for s-input polarization (parallel to the grating lines). d, working distance, h, grating height, w, grating width.
Figure1b. Schematic illustrating grating layout for p-input polarization (polarization perpendicular to grating lines). d, working distance, h, grating height, w, grating width.

Custom Silicon Focusing Gratings

Our optical engineers will be happy to discuss a custom flat-substrate focusing grating solution for your specific application for a custom design wavelength or a wavelength range.