Cylindrical package

A cylindrical package comprising:

• a cylindrical housing;
• a pedestal at a bottom of a cylindrical space surrounded by said cylindrical housing;
• a first circuit board in said cylindrical space, wherein said first circuit board has a working surface substantially parallel to a central axis of said cylindrical housing;
• an optical splitter in said cylindrical space, wherein said optical splitter has an incident surface configured to receive a main optical beam coaxial with said central axis and split said main optical beam into a first split optical beam and a second split optical beam;
• a first photodetector in said cylindrical space, wherein said first photodetector is configured to optically couple to said first split optical beam;
• a second photodetector in said cylindrical space, wherein said second photodetector is configured to optically couple to said second split optical beam;
• and
• a thermal-electric cooler in said cylindrical space and on said pedestal, wherein said second photodetector is attached onto said thermal-electric cooler;
• wherein said optical splitter, the first photodetector and the second photodetector are mounted onto said working surface, wherein said first split optical beam and said second split optical beam are substantially parallel to said working surface, wherein said second photodetector comprises a second circuit board with a bottom surface attached onto said thermal-electric cooler and a sidewall attached onto said working surface and a photosensitive chip on a top surface of said second circuit board, wherein said photosensitive chip optically couples to said second split optical beam.