  A new dielectric Fabry-Perot cavity was designed for a resonant enhancing
optical absorption by a thin absorber layer embedded into the cavity. In this
cavity, the front mirror is a subwavelength grating with $\sim 100$%
retroreflection. For a HgCdTe absorber in a matching cavity of the new type,
the design is shown to meet the combined challenges of increasing the absorbing
efficiency of the entire device up to $\sim 100$% and reducing its size and
overall complexity, compared to a conventional resonant cavity enhanced HgCdTe
absorber, while maintaining a fairly good tolerance against the grating's
fabrication errors.
