A glass optical filter is described that optically connects two optical fibers and may filter a single or group of channels from a WDM signal that is being communicated between the optical fibers. The glass optical filter may be comprised of two pigtail tubes having smaller interior diameters than a center piece tube that couples the two pigtail tubes together. In one embodiment of the invention, D-lenses are positioned within the glass optical filter and function as focusing lenses. The characteristics of the glass housing and D-lens provide a preferred environment for aligning optical fiber pigtails to the focusing lenses.