  The future missions for astrophysical studies in the submillimeter region
will need detectors with very high sensitivity and large field of view.
Bolometer arrays can fulfill these requirements over a very broad band. We
describe a technique that enables bolometer arrays that use quarter wave
cavities to have a high spectral response over most of the submillimeter band.
This technique is based on the addition on the front of the array of an
anti-reflecting dielectric layer. The optimum parameters (layer thickness and
distance to the array) are determined by a 2D analytic code. This general
principle is applied to the case of the Herschel PACS bolometers (optimized for
the 60 - 210 micron band). As an example, we demonstrate experimentally that a
PACS array covered by a 138 micron thick silicon layer can improve the spectral
response by a factor 1.7 in the 450 micron band.
