Abstract: In some implementations, a wavelength division multiplexing (WDM) device includes a spacer; a first filter component; and a second filter component. The spacer is configured to propagate a light beam emitted from an input fiber of the WDM device within the spacer to the first filter component. The first filter component is configured to filter the light beam to create and direct a once-filtered light beam to the spacer. The spacer is configured to propagate the once-filtered light beam within the spacer to the second filter component. The second filter component is configured to filter the once-filtered light beam to create and direct a twice-filtered light beam to the spacer. The spacer is configured to propagate the twice-filtered light beam within the spacer to another component of the WDM device, such as another filter component, a mirror component, or an output fiber of the WDM device.