Design and performance of a multiple element slab waveguide spectrograph for multimode fiber-optic WDM systems

Abstract

A new type of compact ( < 7 cm2) multiple element slab waveguide spectrograph suitable for medium resolution fiber-optic wavelength division multiplexing (WDM) applications in the 700 nm to 900 nm optical band is described. The spectrograph consists of a replicated diffraction grating formed on the convex edge of a multilayer glass-ceramic slab waveguide stack. The grating design, based on an aberration corrected derivative of the classic Rowland spectrometer, was first verified holographically, and then implemented by replication from a ruled master grating. A combination of thick-film solder glass glazing, lamination, optical finishing and grating replication was chosen to produce a multiple element spectrograph that enables accurate spectral referencing, and can be interfaced by a passive optical fiber array and detector array alignment procedures.

Advanced grating-based WDM demultiplexer

“…The bandwidth is much smaller than predicted by (7) and is likely a result of the presence of aberrations that arise as the wavelength departs from the stigmatic wavelength. Changing from TE mode to TM mode shifted the output spectrum by approximately I nm.…”

“…An approximate equation can be obtained by treating the section of the grating near the grating pole as a plane grating which gives . _______ lB sinc A1 (7) This equation must be modified somewhat for concave gratings; however, experiments show that this equation qualitatively describes the wavelength dependence of the grating'4. A more precise determination of the bandwidth could be obtained from numerical modeling of the grating'56.…”

“…After finding the optimum values of lB,min and rc, (7) can be used to find m. If the minimum criteria for r and flB cannot be satisfied, the values of (a1, b1), (a2, b2), and (d1 I du1) may have to be changed. For example, increasing the chip size or decreasing the dispersion will permit lower values for ic and flB•…”

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“…A sampling of papers describing some of the late-1980s to mid-1990s fly-by-light hardware and system developments are described in the list of references. [35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53] For the past decade Air Force Research Lab (AFRL) has continued to advance fly-by-light technology for flight control and vehicle management system applications. 54 AFRL's Advanced Vehicle Management Technology and More Electric Aircraft Photonic Vehicle Management System Technology Validation programs developed system level architectures and prototype hardware.…”

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“…Compared with a freespace spectrometer, it is more compact, flexible and stable [1] [3]. For an etched planar grating, the grating profile and the groove distribution can be freely designed to obtain low aberration.…”