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7. Focusing Gratings聚焦光栅LightSmyth’s 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’s 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.
7.1 Standard Flat-Substrate Focusing Gratings标准平板基板聚焦光栅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).
Part Number | Design Wavelength (nm) | Design Input Polarization1 | Incidence Angle1 φ | Approx. Line Density2 (l/mm) | Size 1 (w × h) |
SCG-405S-0603A-Al | 405 | s | 40 ° | 3175 | 6 mm × 3 mm |
SCG-405P-0306A-Al | 405 | p | 45 ° | 3640 | 3 mm × 6 mm |
SCG-635S-0603A-Al | 635 | s | 40 ° | 2028 | 6 mm × 3 mm |
SCG-635P-0306A-Al | 635 | p | 65 ° | 2857 | 3 mm × 6 mm |
SCG-780P-0306A-Al | 780 | p | 60 ° | 2222 | 3 mm × 6 mm |