The dual interface module is used to connect optical heads ( Keysight 8162x ) to the mainframes 8163A/B, 8164A/B or 8166A/B Following optical heads are used with these interfaces: 81620B Si, +10dBm to -90dBm 81623B Ge, +10dBm to -80dBm 81624B 5mm InGaAs, +10dBm to -90dBm 81626B InGaAs, +27 dBm to - 70 dBm 81628B InGaAs, +40 dBm to - 60 dBm Features fully compatible with all 8162x Optical Heads fits in all 8163/8164/8166-series 2-channel option