A coaxial 10-Gb/s 1.3-µm distributed feedback (DFB) laser-diode module with a coupled differential feed has been developed. The differential cascaded feed with the characteristic impedance of 100 Omega;, which consists of a 140-Omega; ground-signal-signal-ground (GSSG) leads, a small-sized 60-Omega; feed-through, and a 140-Omega; wire-bonding pad, provides less sensitivity to the lead length. Integrating with 25-Omega; matching resistances and a 60-Omega; differential microstrip line, whose length corresponds to one eighth of wavelength at 7 GHz, gives wide-band impedance matching between the feed and the laser diode portion with small power loss. Experiment shows good return loss of greater than 9 dB at 10 GHz, and small change of bit error rate (BER) up to the lead length of 4 mm. With a newly developed 250-µm cavity laser chip, we have demonstrated stable eye diagrams with the mask margins of 31 and 29% at case temperature of 0 and 85 °C, respectively.
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