An apparatus for performing nucleic acid amplification reactions includes a thermally-conductive receptacle holder with front and back surfaces. The front surface includes a row of receptacle wells, and an outer surface of each well has a frustoconical shape, an inner surface of each well receives a receptacle, and each well has a through-hole extending between the inner and outer surfaces thereof. One or more thermal elements in contact with the back surface of the holder alter a temperature(s) of the holder. The apparatus includes multiple optical fibers, and each optical fiber provides optical communication between one of the wells and an excitation signal source and/or an emission signal detector. A first end of each optical fiber is disposed outside, within, or extends through the through-hole of a corresponding well, and a second end of each optical fiber is in optical communication with the excitation signal source and/or the emission signal detector.