Abstract
We design and fabricate wide wavelength range directly modulated lasers (DMLs) on the same
InP wafer to realize a large-capacity monolithically integrated light source array up to 1 Tb/s.
We demonstrate a 25.8-Gb/s push–pull operation over a 30-nm wavelength range, which is
conventionally about 14 nm for 100 GbE applications. To extend the operating wavelength range, we
design the wavelength dependence of the differential gain
$(\partial {\rm G}/\partial {\rm n})$
for an InGaAlAs multiple quantum well structure, and realize high frequency
relaxation oscillation resulting from the high differential gain over a wide range. Next, we also
design the wavelength detuning (Δλ) under an operating injection current condition by taking
account of the thermal effect of the chip, because Δλ determines
$\partial {\rm G}/\partial {\rm n}$
, and the threshold current of the laser diode (LD). In addition, to achieve a
25.8-Gb/s push–pull operation, we fabricate a ridge waveguide structure buried in benzocyclobutene
(BCB) with a low parasitic capacitance, and electrically isolate the DML from the neighboring chip
by etching off n-InP. By using this design and structure, we achieve a 3-dB-down frequency
bandwidth of over 20 GHz from 1290 to 1320 nm. We also achieve a mean output power of 8.0 dBm, and
a dynamic extinction ratio of 5 dB. We measure the 25.8-Gb/s transmission characteristics, and
obtain clear eye openings for a back-to-back configuration. We also measure the bit-error-rate
performance, and obtain error-free operation for a 30-nm operating wavelength range.
© 2013 IEEE
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