White light generation by mixing red, green, and blue laser diodes (RGB LDs) was demonstrated with Commission International de l'Eclairage coordinates of (0.2928, 0.2981), a correlated color temperature of 8382 K, and a color rendering index of 54.4 to provide a maximal illuminance of 7540 lux. All the white lights generated using RGB LDs were set within the risk group-1 criterion to avoid the blue-light hazard to human eyes. In addition, the RGB-LD mixed white light was diffused using a frosted glass to avoid optical aberration and to improve the performance of the lighting source. In addition, visible light communication (VLC) by using RGB-LD mixed white-light carriers and a point-to-point scheme over 1 m was performed in the directly modulated 16-QAM OFDM data format. In back-to-back transmission, the maximal allowable data rate at 10.8, 10.4, and 8 Gbps was determined for R, G, and B LDs, respectively. Moreover, the RGB-LD mixed white light-based indoor wavelength-division multiplexing (WDM)-VLC system yielded a total allowable transmission data rate of 8.8 Gbps over 0.5 m in free space. Such a high-speed RGB-LD mixed WDM-VLC system without any channel interference can be used to simultaneously provide data transmission and white lighting in an indoor environment.The coverage of indoor lighting and visible light communication (VLC) systems is one of the promising approaches for developing smart homes because it can simultaneously provide compact lighting fidelity and convenient data transmission functionality [1][2][3][4][5][6] . Compared with phosphor-coated blue LEDs, the use of red, green, and blue (RGB) light-emitting diodes (LEDs) to generate a white-light source is an attractive lighting system with a high color rendering index (CRI) [7][8][9] . Such a high-directional white-light source generated using RGB LEDs can be used as desk lamps or daylight lamps.

To enable high-speed underwater wireless optical communication (UWOC) in tap-water and seawater environments over long distances, a 450-nm blue GaN laser diode (LD) directly modulated by pre-leveled 16-quadrature amplitude modulation (QAM) orthogonal frequency division multiplexing (OFDM) data was employed to implement its maximal transmission capacity of up to 10 Gbps. The proposed UWOC in tap water provided a maximal allowable communication bit rate increase from 5.2 to 12.4 Gbps with the corresponding underwater transmission distance significantly reduced from 10.2 to 1.7 m, exhibiting a bit rate/distance decaying slope of −0.847 Gbps/m. When conducting the same type of UWOC in seawater, light scattering induced by impurities attenuated the blue laser power, thereby degrading the transmission with a slightly higher decay ratio of 0.941 Gbps/m. The blue LD based UWOC enables a 16-QAM OFDM bit rate of up to 7.2 Gbps for transmission in seawater more than 6.8 m.

Mechanically triturated n- and p-type Bi2Te3 nanoparticles, the nanoscale topological insulators (TIs), are employed as nonlinear saturable absorbers to passively mode-lock the erbium-doped fiber lasers (EDFLs) for sub-400 fs pulse generations. A novel method is proposed to enable the control on the self-amplitude modulation (SAM) of TI by adjusting its dopant type. The dopant type of TI only shifts the Fermi level without changing its energy bandgap, that the n- and p-type Bi2Te3 nanoparticles have shown the broadband saturable absorption at 800 and 1570 nm. In addition, both the complicated pulse shortening procedure and the competition between hybrid mode-locking mechanisms in the Bi2Te3 nanoparticle mode-locked EDFL system have been elucidated. The p-type Bi2Te3 with its lower effective Fermi level results in more capacity for excited carriers than the n-type Bi2Te3, which shortens the pulse width by enlarging the SAM depth. However, the strong self-phase modulation occurs with reduced linear loss and highly nonsaturated absorption, which dominates the pulse shortening mechanism in the passively mode-locked EDFL to deliver comparable pulse widths of 400 and 385 fs with n- and p-type Bi2Te3 nanoparticles, respectively. The first- and second-order Kelly sidebands under soliton mode-locking regime are also observed at offset frequencies of 1.31 and 1.94 THz, respectively.

Nonstoichiometric SiN x with enhancing optical nonlinearity is enabled to facilitate the waveguide microring resonator for cross-wavelength all-optical data processing applications. The Si/N composition ratio of the nonstoichiometric SiN x can be detuned from stoichiometric to Si-rich by adjusting the SiH 4 /NH 3 fluence ratios. Under pumping with incoming pulsed data, the comb-like transmittance of the nonstoichiometric SiN x microring resonator can spectrally red-shift by 100 pm as its effective refractive index changed by more than 1 order of magnitude due to the enhanced nonlinear Kerr effect. The enlarged refractive index of Δn = 1.6 × 10 −4 with increasing nonlinear refractive index to n 2 = 1.6 × 10 −13 cm 2 /W at 1550 nm is observed at a Si concentration of 66.2% in the Si-rich SiN x film. In application, a cross-wavelength all-optical data conversion/inversion processor based on the nonstoichiometric SiN x microring resonator is presented. The dense nanoscale Si content formed by a higher Si/N composition ratio of the SiN x contributes to an enhanced Kerr effect based optical nonlinear switching, which enables the optimized 12 Gbit/s all-optical conversion of the pulsed return-to-zero on−off-keying (RZ-OOK) data with converted or inverted format. The photon lifetime of ∼19 ps in the Si-rich SiN x microring resonator cavity can support the Si-rich SiN x alloptical Kerr switch with a maximal bandwidth of up to 50 GHz. S ilicon photonics has been considered to realize the optical interconnect circuits for decades, and the pure Si-based waveguide devices have played important roles in acting as different functionalities in this field. With the free-carrierinduced plasma dispersion effect, 1,2 a pure Si-based electrooptical modulator and all-optical modulators were demonstrated. 3−7 The all-optical modulation bandwidth extended from hundreds of MHz to several GHz but was limited by the carrier diffusion dominated lifetime of the bulk Si. 8,9 Recently, the free-carrier absorption (FCA) cross-section in the silicon quantum dots (Si-QDs) has been proved to be 1 order of magnitude larger than that in the bulk Si. 10−12 Even though shrinking the Si-QD size can further shorten the carrier relaxation lifetime due to the quantum confinement effect, 13,14 the effective free-carrier lifetime in Si-QDs is still much longer than that of the bulk Si so as to limit the modulation bandwidth of the Si-QD-based FCA modulator at around 1 MHz. 15−17 To develop an ultrafast all-optical modulator that is fully compatible with Si-based CMOS integrated circuits, the most appropriate solution among versatile approaches is to use the enhanced optical nonlinearity of the Si-QDs. Recently, the optical nonlinearity of the Si-QDs doped in SiO x has been analyzed by using the femtosecond Z-scan method. 18−21 The nonlinear Kerr coefficient of the Si-QDs is experimentally proved to be 2 orders of magnitude higher than that of the bulk Si due to the strong quantum confinement effect. 18−22 The excitons generated in the highly confined Si-QDs...

With increasing interest in visible light communication, the laser diode (LD) provides an attractive alternative, with higher efficiency, shorter linewidth and larger bandwidth for high-speed visible light communication (VLC). Previously, more than 3 Gbps data rate was demonstrated using LED. By using LDs and spectral-efficient orthogonal frequency division multiplexing encoding scheme, significantly higher data rates has been achieved in this work. Using 16-QAM modulation scheme, in conjunction with red, blue and green LDs, data rates of 4.4 Gbps, 4 Gbps and 4 Gbps, with the corresponding BER/SNR/EVM of 3.3 × 10⁻³/15.3/17.9, 1.4 × 10⁻³/16.3/15.4 and 2.8 × 10⁻³/15.5/16.7were obtained over transmission distance of ~20 cm. We also simultaneously demonstrated white light emission using red, blue and green LDs, after passing through a commercially available diffuser element. Our work highlighted that a tradeoff exists in operating the blue LDs at optimum bias condition while maintaining good color temperature. The best results were obtained when encoding red LDs which gave both the strongest received signal amplitude and white light with CCT value of 5835K.