ANALYSIS AND COMPARISON OF THE NEW TO-CAN HEADER AND CONVENTIONAL TO-56 HEADER

The electrical characteristics of the new TO-Can header and a convention TO-56 header with the electrical field diagrams and S-parameters by using HFSS is simulated and analyzed. The simulated configurations and the electrical field diagrams of the new TO-Can header and the TO-56 header are shown in Fig. 6(a) and (b), respectively. A lumped port is inserted at the center of the header to represent the load. The lumped port directly links to the stem of the electrical ground. We can simulate the situations of different load by varying the impedance of lumped port. A perfect conductor plane is placed between the inside feed-lead and the lumped port to conduct the electrical signal. In a real case, bonding wires are used to connect the inside feed-lead and the load.

Bonding wires induce parasitic inductance and degrade the electrical characteristics. However, the appearance of bonding wires will blur the inherent performance of the header. So the bonding wires are replaced by a perfect conductor. The operating frequency and the load are set at 15-GHz and 50-Ωin the simulation of Fig. 6. The discretized vectors of the electrical field distribution are both TEM mode in the coaxial feed-lead. The intensity of electrical field of the TO-56 header is apparently small and weak than the new TO-Can header. Because the TO-56 header has a bigger drop of impedance between the coaxial feed-lead and the inside feed-lead, the power of microwave propagation is sharply reduced. However, the impedance discontinuity of the new TO-Can header has minimized between the coaxial feed-lead and the inside feed-lead. The microwave power can be propagated completely in the two-section coaxial feed-lead. Therefore, the intensity of electrical field of the new TO-Can header is apparently stronger than the TO-56 header in the coaxial feed-lead. The impedance matching of coaxial feed-lead of the new TO-Can header has a significant improvement for electrical field propagation.

Inside feed-lead Perfect conductor plane Lumped port

(a)

Inside feed-lead Perfect conductor plane Lumped port

(b)

Fig. 5. Electrical field diagrams of (a) the proposed new TO-Can header and (b) the conventional TO-56 header

By referring the intrinsic electrical equivalent circuit, the rise and fall of imaginary impedance of a laser diode in high frequency is negligible compared with the real impedance [7, 8, 18]. Therefore, the impedance of laser diode is only considering real part in this study. Usually, the load impedance inside a coaxial TOSA has different values. When there is no external matching resistor, the load is the impedance of the laser diode only and can be presented by a few Ohms [7, 8]. To have a better impedance matching result, researchers will insert external matching resistors and the load impedance is increased from a few Ohms to 25-Ω or50-Ω [6-8].

Therefore, we set both 5-Ω and 50-Ω astheload impedancein thesimulation ofS-parameters. The simulated reflection loss, insertion loss, and the phase curves of S21 of the new TO-Can header and conventional TO-56 header are shown in Fig. 7 (a), (b), and (c), respectively. The simulated reflection loss of new TO-Can header can be controlled beneath –10 dB with a load of 50-Ω before 15-GHz. The 3-dB transmission bandwidth of the new TO-Can header achieves over than 23-GHz and 37-GHz with a load of 5-Ωand 50-Ω, respectively, while the 3-dB transmission bandwidth of the TO-56 header is only 15-GHz. The linear region of the phase curves of the new TO-Can header is better evidently compared with the conventional TO-56 header. It’salmostadouble increment of a conventional TO-56 header.

0 5 10 15 20 25 30 35 40

Fig. 7. The simulation results of S-parameters for the new TO-Can and the conventional TO-56 header with loads of 5-Ω and 50-Ω.(a) The S11 curves, (b) the S21 curves, and (c) the phase curves of the S21

6. CONCLUSION

In summary, a new TO-Can header for the low-cost coaxial laser package has been proposed and demonstrated by a 3D full-wave electromagnetic simulation. The applicability of the simulation tool has been verified with an experimental result. The reflection loss, insertion loss, and phase of this TO-Can header show significant improvements by comparing with the conventional TO-56 header. The simulated reflection loss is beneath –10-dB under 15-GHz at a 50-load impedance, the 3-dB modulated bandwidth achieves 23-GHz and 37-GHz for a 5- and 50- load impedance, respectively, and the phase was linear in the interesting operation range. This superior TO-Can header provides a low-cost solution for coaxial laser package and can be applied in the emerging 100-Gigabits Ethernet (100GbE) network and the next generation Fiber Channel (20GFC) of storage area network.

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