We used a strain compensation technique to fabricate highly stacked InAs quantum-dot (QD) structures on InP(311)B substrates. We stacked 60 layers of InAs QDs without degrading the crystal quality and produced a structure with a total QD density of $4.73\times {10}^{12}∕{\mathrm{cm}}^2$ . We then fabricated a broad area laser diode with a 30-layer stack of InAs QDs using conventional photolithography. The laser diode showed ground state lasing at $1.58\mu \mathrm{m}$ with a threshold current of $162\mathrm{mA}$ . The achievement of ground state lasing is due to the increase in QD density, which is a result of using the strain compensation technique.

We present the design of a bias-free uni-travelling-carrier photodiode (UTC-PD) that is operational above 110 GHz, and its application to 100-GBd fixed-fiber communication and 109-GHz carrier-photonic wireless communication for advanced optical networks. The design and analysis for bias-free operation were explained in detail using the carrier concentration in the photo-absorption layer and carrier collector layer. In the experimental results, the developed UTC-PD with back-illuminated structure exhibited a wide 3-dB bandwidth of over 110 GHz at 0 V. For fixed-fiber communications, a high-baud-rate photoreceiver based on the UTC-PD was fabricated. Eye diagrams showed clear openings at up to 107 GBd and high photo-currents of 3-7 mA at 100 GHz signal light were observed at zero-bias. Assuming photonic wireless communication using photonic power supply through optical fiber, the developed UTC-PD contributed to reducing bias feeds to the photoreceiver module. Additionally, low power consumption was achieved when using the newly developed 110 GHz InP-PHEMT amplifier with the UTC-PD.

We have fabricated highly packed and ordered ${\mathrm{In}}_{\mathrm{0.4}}{\mathrm{Ga}}_{\mathrm{0.6}}\mathrm{As}$ quantum dots (QDs) array on GaAs(311)B substrate without coalescence of QDs. Reflection high-energy electron diffraction and Auger spectra suggest the inhomogeneous distribution of In and Ga in QD. In concentration near the surface of QD is larger than that of the inside, and the inhomogeneous distribution of In and Ga in QDs prevents QDs from merging.