## 3 Membrane Photonic Devices on Si Substrate
### InGaAlAs Membrane Laser Array Grown on InP-on-Insulator Substrate
Figure 11a shows the measured eye diagrams at 50 \({}^{\circ}\)C. Three adjacent lasers were simultaneously modulated, and the eye diagram of the middle laser was observed to evaluate the effect of electrical crosstalk. The bias currents were from 8.0 to 8.3 mA, the bias voltages were from 1.51 to 1.62 V, and the applied voltage swings were ~0.50 V\({}_{\text{P-P}}\). We observed clear eye openings for all eight channels at 25.8-Gbit/s direct modulation with dynamic extinction ratios greater than 5.0 dB. Figure 11b shows the measured bit-error-rates (BERs) with 2\({}^{7}-\)1 PRBS and 25.8-Gbit/s NRZ signals for back-to-back (BTB) and after 10-km transmissions at 50 \({}^{\circ}\)C. The bias current and voltage swing were kept constant at 9.5 mA and 0.553 V\({}_{\text{P-P}}\), respectively. To evaluate the power penalty caused by the electrical crosstalk, two adjacent lasers were simultaneously modulated with a voltage swing of zero (discrete-device operation) or 0.553 V\({}_{\text{P-P}}\) (simultaneous operation). We achieved BERs of ~10\({}^{-12}\) after the 10-km transmission with no significant penalty even when the adjacent lasers were simultaneously  
Figure 10: (**a**) Photograph of diced wafer that includes 4 8-channel laser arrays, together with top-view photograph of one 8-channel laser array; (**b**) bias-current dependence of optical output power and bias voltages at 25 \({}^{\circ}\)C; (**c**) lasing spectra with bias current of 4 mA at 25 \({}^{\circ}\)C.  
modulated. Figure 11b also shows the BTB BER results at 25 \({}^{\circ}\)C with a bias current of 9.5 mA and voltage swing of 0.759 V\({}_{\text{P-P}}\). The power penalty due to the temperature increase from 25 to 50 \({}^{\circ}\)C was also negligible. Finally, we evaluated the static characteristics of discrete membrane lasers at high temperature [72]. Figure 12a compares the lasing spectra of two membrane lasers processed at the same time. The lasers have almost the same structure, but only the grating pitch are different to vary the lasing wavelength. The lasing wavelengths were 1303.4 and 1311.2 nm when a bias current was 10 mA, corresponding to wavelength detunings between the PL peak and lasing peak of 32.1 and 39.9 nm, respectively. Figure 12b,c compare the temperature dependence of the output power versus the injection current for these two lasers, measured with a photodetector placed in front of the device facet. The laser that has 39.9-nm-detuning exhibited lasing at up to a stage temperature of 95 \({}^{\circ}\)C, whereas the laser that has 32.1-nm-detuning exhibited lasing at up to 85 \({}^{\circ}\)C. This is attributed to the red shift of the material gain peak wavelength as the temperature increases; therefore, a larger detuning wavelength results in better performance at high temperature. Figure 11: (a) Eye diagrams for directly modulated lasers (DMLs) with 25.8-Gbit/s non-return-to-zero (NRZ) signals at 50 \({}^{\circ}\)C; (b) bit-error-rates (BER) characteristics of back-to-back (BTB) and after 10-km transmissions at 50 \({}^{\circ}\)C.  
Figure 12: (a) Lasing spectra of two membrane lasers with different grating pitches; (b,c) temperature dependence of optical output vs. injection current for 32.1- and 39.9-nm-detuned laser.