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A new transistor outline-Can (TO-Can) header for a low-cost coaxial laser module for 25-Gbit/s transmission is proposed and demonstrated using a 3-D full-wave electromagnetic simulation. The simulation result is compared with the measured results of a conventional TO-56 header to verify its applicability. A two-section feedthrough hole is employed, and a wire-over-ground feed lead is introduced to overcome the impedance matching problems. The simulation results show that the proposed TO-Can header provides a transmission bandwidth in excess of 40 GHz and reflection loss less than -10 dB below 26 GHz, with an ideal 50-Ω terminal. Taking the bonding wires into account, the transmission bandwidth still reaches 28 GHz. The electrical characteristics of this TO-Can package were extracted and combined with a small-signal equivalent circuit model of a 24.5-GHz laser diode to simulate the electrical characteristics of a full coaxial laser module. The 3-dB bandwidth is 20.5 GHz, which allows the laser module to operate at 25 Gbit/s. This superior TO-Can header provides a low-cost coaxial laser package solution and can be applied in the emerging 21-Gbit/s fiber channel (20 GFC) and 100-gigabit (4 × 25 Gbit/s) Ethernet (100 GbE) networks.