We propose tunable grating structures implemented by the change of the effective refractive index based on thermo-optic effect in silicon. For resistive heating, p-i-n or pn junction was formed in the grating region and surrounding region was thermally isolated. Fabricated tunable gratings were characterized by fiber-to-fiber measurement and Fourier-imaging system with a variation of the bias voltage applied to the heater. From a p-i-n type structure showing the best data, we achieved a wide tuning of the central wavelength in a range of 40 nm with an efficiency of 0.41 nm/mW. When this tunable grating structure is applied in the radiator of the optical phased array, the radiation angle was actively manipulated in a range of 2.7 in the longitudinal direction.
We propose and demonstrate a temporally and spatially incoherent spectrum-sliced light source for scintillation mitigation in free-space optical (FSO) communications. For the temporal incoherence, we utilize the spectrum-sliced incoherent light (SSIL) modulated by gain-saturated reflective semiconductor optical amplifiers for data modulation and the suppression of excess intensity noise inherent in a narrowband incoherent light source. We then employ offset launching from a single-mode fiber to a multi-mode fiber to add the spatial incoherence to the SSIL source. The experimental demonstration shows that this temporally and spatially incoherent light is effective in mitigating scintillation. For example, this light source reduces the transmitter power required to achieve a bit-error ratio of 10−3 by ∼6 dB in comparison with the laser source. This is an ∼3 dB larger reduction in the transmitter power than the reduction achieved by a temporally incoherent light source.
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