| CPC G02B 6/2938 (2013.01) [G02B 6/29361 (2013.01); G02B 6/32 (2013.01); G02B 6/3512 (2013.01); G02B 6/4215 (2013.01)] | 30 Claims |

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1. A wavelength division multiplexer (WDM) comprising:
a first gradient-index (GRIN-1) lens including first and second surfaces on opposite sides or ends of the GRIN-1 lens;
a first plurality or array of common optical fibers, each positioned to input light into the first surface of the GRIN-1 lens and to receive light from the first surface of the GRIN-1 lens;
a second plurality or array of reflected optical fibers, each positioned to input light into the first surface of the GRIN-1 lens and to receive light from the first surface of the GRIN-1 lens;
a WDM filter including first and second surfaces on opposite sides or ends of the WDM filter, the first surface of the WDM filter coupled to the second surface of the GRIN-1 lens;
a second gradient-index (GRIN-2) lens including first and second surfaces on opposite sides or ends of the GRIN-2 lens, wherein the first surface of the GRIN-2 lens and the second surface of the WDM filter are spaced from each other by a gap; and
a third plurality or array of transmit optical fibers, each positioned to input light into the second surface of the GRIN-2 lens and to receive light from the second surface of the GRIN-2 lens, wherein:
light having first and second wavelengths output by each common optical fiber propagates through the GRIN-1 lens to the WDM filter which:
(1) reflects the light of the first wavelength back through the GRIN-1 lens to a unique one of the reflected optical fibers but to no other optical fiber of the array of reflected optical fibers, the array of transmit optical fibers, and the array of common optical fibers; and
(2) passes the light of the second wavelength through the gap and the GRIN-2 lens to a unique one of the transmit optical fibers but to no other optical fiber of the array of transmit optical fibers, the array of reflected optical fibers, and the array of common optical fibers.
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