We report on a monolithic dual-mode semiconductor laser operating in the 1550-nm range as a compact optical beat source for tunable continuous-wave (CW) terahertz (THz) generation. It consists of two distributed feedback (DFB) laser sections and one phase section between them. Each wavelength of the two modes can be independently tuned by adjusting currents in micro-heaters which are fabricated on the top of the each DFB section. The continuous tuning of the CW THz emission from Fe(+)-implanted InGaAs photomixers is successfully demonstrated using our dual-mode laser as the excitation source. The CW THz frequency is continuously tuned from 0.17 to 0.49 THz.
The formation characteristics on the vertical stacks of shape-engineered InAs∕InAlGaAs quantum dots (QDs), which were formed by the alternate growth method (AGQDs), were studied in terms of the modulation in strain field and phase separation. The threshold current of the broad-area laser diodes (LDs) with five stacks of the AGQDs (AGQD-LDs) was 4.5 times smaller than that of the LDs with seven stacks of the conventionally grown QDs (CQD-LDs). The slope efficiency for the AGQD-LDs was 0.16W∕A, which was higher than that of the CQD-LDs of 0.9W∕A. These results can be attributed to better confinement of the electron wave function in QDs.
Asymmetric multiple-quantum-well laser diodes with wide and flat gain spectra were designed, fabricated, and analyzed. The active layer was composed of three 10-nm, one 8-nm, and two 6-nm 0.5% compressive strained wells and four 10-nm and one 5-nm 0.4% tensile strained barrier layer. Measured spectra of antireflection-coated ridge waveguide laser diodes with such quantum-well structures have shown that -1-dB spectral gain bandwidth can be as large as 90 nm.
We demonstrated monolithic integration of a continuous wave probe source consisting of a loss-coupled distributed feedback laser diode (DFB LD) and a Mach-Zehnder interferometric wavelength converter. The integrated device was fabricated using a modified buried ridge stripe (BRS) structure with an undoped InP clad layer on the top of a passive waveguide to reduce high propagation loss. A propagation loss in the passive waveguide as low as 5.29 ± 0.92 dB cm −1 was achieved. For the first time, wavelength conversion at 10 Gb s −1 was achieved with an extinction ratio of 7 dB and a power penalty of 2.8 dB at a 10 −9 bit error rate. The proposed BRS structure is very useful for fabrication of photonic integrated circuits consisting of monolithic integration of active and passive waveguides.
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