Cost-efficient half-duplex 10 Gbit/s all-optical indoor optical wireless communication enabled by a low-cost Fabry-Perot laser/photodetector.

To develop an indoor optical wireless communication (OWC) system, both the system complexity/cost and data rate need to be taken into consideration. In this Letter, a cost-efficient half-duplex OWC system for photonic home area network applications is proposed and experimentally demonstrated. A low-cost Fabry-Perot laser diode is proposed to be employed as both the downlink receiver (Rx) and uplink transmitter at the user side. Enabled by the Fabry-Perot transceiver, the indoor transmission of 10 Gbit/s four-level pulse-amplitude-modulation signal for both downlinks and uplinks is experimentally achieved over a 1.7 km single-mode fiber and 1.1 m free space. Moreover, the proposed scheme also enables us to operate an orthogonal frequency division multiplexing (OFDM) signal. The bit error rate levels of multi-gigabit OFDM data for both downlinks and uplinks over a 10 h measurements are all under a 7% forward error correction limit of 3.8×10-3, which indicates that the proposed system is robust and, thus, can provide a promising solution for high-speed low-cost home area OWC networks.

Realizing multi-functional all-optical data processing on nanoscale SiC waveguides.

All-optical logics are realized on nanoscale SiC waveguides with add-drop micro-ring functionality, including the TE/TM polarized data decoding, the dual-port Kerr switching and gating beyond 12 Gbit/s. With employing the C-C bond enriched SiC thin film upon thermal oxide, the nonlinear refractive index of up to 2.44 × 10-12 cm2/W enables the asymmetric waveguide with polarization distinguishable transmission, which provides a polarization-selectivity to discreminate the TE/TM polarized data decoding with an nearly 9-dB extinction ratio. The TE/TM polarized decoding performance is comparable with a state-of-the-art fiberized in-line polarizer. The complementary transmission in the bus waveguide port facilitates the dual-port Kerr switching for data format conversion/inversion in both add/drop channels. Owing to the TE/TM polarization discriminated throughput, the asymmetric add-drop waveguide micro-ring also permits all-optical AND logic gating functions, where the ON-state outputs only if the pump bit is set at ON state and the probe bit with matched polarization. These results reveal the multi-functionality of the nanoscale SiC add-drop micro-ring waveguide for future photonic logics on chip.

Ultrahigh-speed violet laser diode based free-space optical communication beyond 25 Gbit/s.

Violet laser diode (VLD) based ultrahigh-speed free-space optical (FSO) system is demonstrated for point-to-point data transmission. By directly encoding the VLD with 64-quadrature amplitude modulation discrete multi-tone (64-QAM DMT) data stream for optical wireless communication through 0.5-10 m in free space, the point-to-point VLD-based FSO link allows delivering the 64-QAM DMT data at an ultrahigh bit rate of up to 26.4 Gbps. After receiving with a high-speed p-i-n photodiode, such a VLD-FSO link can provide clear constellation plot with error vector magnitude (EVM) of 8.57%, signal-to-noise ratio (SNR) of 21.34 dB and bit error ratio (BER) of 3.17 × 10-3 under forward-error-correction criterion. The EVM increases from 8.8% to 9.4% and the SNR decreases from 21.1 to 20.6 dB to slightly degrade the reachable data rate from 25.8 to 24 Gbit/s with transmission distance lengthening from 3 to 10 m.

Blue Laser Diode Based Free-space Optical Data Transmission elevated to 18 Gbps over 16 m.

Up to 18-Gbps direct encoding of blue laser diode (BLD) is demonstrated for free-space data transmission. By reshaping the orthogonal frequency multiplexed (16-QAM OFDM) stream with sidelobe filtering, the raw data rate expedites from 17.2 to 18.4 Gbps. Employing an ultrafast p-i-n photodiode with smaller active area diameter and lower noise equivalent power significantly enlarges the data rate by 1.6 Gbps or upgrades the signal-to-noise ratio (SNR) by 0.2 dB. Replacing the 80-mW BLD with the 120-mW one essentially increases the received SNR by 0.4 dB under enhanced modulation throughput. Reinforcing the beam collimation and collection by increasing the numerical aperture with a plano-convex hyper-hemispherical lens further improves the SNR by 0.6 dB. After optimization, the 16-QAM OFDM data with and without sidelobe filtering are respectively delivered at raw data rates of 16.4 and 18 Gbps with spectral-density usage efficiency as high as 4 bit/s/Hz over 16 m in free space, wherein the BLD carried QAM-OFDM data stream remains its capacity after reformation with sidelobe filtering as the superior inter-carrier-interference immunity reinforces.

Blue Laser Diode Enables Underwater Communication at 12.4 Gbps.

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.

Tricolor R/G/B Laser Diode Based Eye-Safe White Lighting Communication Beyond 8 Gbit/s.

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.

Dual-mode laser diode carrier with orthogonal polarization and single-mode modulation for remote-node heterodyne MMW-RoF.

A remote-node heterodyne millimeter-wave radio-over-fiber (MMW-RoF) link was proposed by a dual-mode optical carrier with orthogonal polarizations and single-wavelength modulation, which effectively suppresses the chromatic dispersion and four-wave mixing. For optical wireline transmission, the bit error rate (BER) of a 25-km single-mode fiber (SMF) transmitted baseband 24-Gbit/s 64-QAM OFDM can be improved to 5.9×10-4 with an error vector magnitude (EVM) of 7.1%. Moreover, the beat 35-GHz MMW carrier with a 32-dB carrier-to-noise ratio was generated for wireless transmission. The BER and EVM of passband 8-Gbit/s 16-QAM OFDM at 35-GHz MMW carrier were 3.4×10-3 and 17.1%, respectively, after 25-km SMF and 1.6-m free-space transmissions.

Remote beating of parallel or orthogonally polarized dual-wavelength optical carriers for 5G millimeter-wave radio-over-fiber link.

A novel millimeter-wave radio over fiber (MMW-RoF) link at carrier frequency of 35-GHz is proposed with the use of remotely beating MMW generation from reference master and injected slave colorless laser diode (LD) carriers at orthogonally polarized dual-wavelength injection-locking. The slave colorless LD supports lasing one of the dual-wavelength master modes with orthogonal polarizations, which facilitates the single-mode direct modulation of the quadrature amplitude modulation (QAM) orthogonal frequency division multiplexing (OFDM) data. Such an injected single-carrier encoding and coupled dual-carrier transmission with orthogonal polarization effectively suppresses the cross-heterodyne mode-beating intensity noise, the nonlinear modulation (NLM) and four-wave mixing (FWM) sidemodes during injection locking and fiber transmission. In 25-km single-mode fiber (SMF) based wireline system, the dual-carrier under single-mode encoding provides baseband 24-Gbit/s 64-QAM OFDM transmission with an error vector magnitude (EVM) of 8.8%, a bit error rate (BER) of 3.7 × 10-3, a power penalty of <1.5 dB. After remotely self-beating for wireless transmission, the beat MMW carrier at 35 GHz can deliver the passband 16-QAM OFDM at 4 Gbit/s to show corresponding EVM and BER of 15.5% and 1.4 × 10-3, respectively, after 25-km SMF and 1.6-m free-space transmission.

4.8 Gbit/s 16-QAM-OFDM transmission based on compact 450-nm laser for underwater wireless optical communication.

We experimentally demonstrate an underwater wireless optical communications (UWOC) employing 450-nm TO-9 packaged and fiber-pigtailed laser diode (LD) directly encoded with an orthogonal frequency division multiplexed quadrature amplitude modulation (QAM-OFDM) data. A record data rate of up to 4.8 Gbit/s over 5.4-m transmission distance is achieved. By encoding the full 1.2-GHz bandwidth of the 450-nm LD with a 16-QAM-OFDM data, an error vector magnitude (EVM) of 16.5%, a signal-to-noise ratio (SNR) of 15.63 dB and a bit error rate (BER) of 2.6 × 10(-3), well pass the forward error correction (FEC) criterion, were obtained.

Going beyond 4 Gbps data rate by employing RGB laser diodes for visible light communication.

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.

Si-rich SiNx based Kerr switch enables optical data conversion up to 12†Gbit/s.

Silicon photonic interconnection on chip is the emerging issue for next-generation integrated circuits. With the Si-rich SiNx micro-ring based optical Kerr switch, we demonstrate for the first time the wavelength and format conversion of optical on-off-keying data with a bit-rate of 12 Gbit/s. The field-resonant nonlinear Kerr effect enhances the transient refractive index change when coupling the optical data-stream into the micro-ring through the bus waveguide. This effectively red-shifts the notched dip wavelength to cause the format preserved or inversed conversion of data carried by the on-resonant or off-resonant probe, respectively. The Si quantum dots doped Si-rich SiNx strengthens its nonlinear Kerr coefficient by two-orders of magnitude higher than that of bulk Si or Si3N4. The wavelength-converted and cross-amplitude-modulated probe data-stream at up to 12-Gbit/s through the Si-rich SiNx micro-ring with penalty of -7 dB on transmission has shown very promising applicability to all-optical communication networks.

4-Gbit/s visible light communication link based on 16-QAM OFDM transmission over remote phosphor-film converted white light by using blue laser diode.

Visible Light Communication (VLC) as a new technology for ultrahigh-speed communication is still limited when using slow modulation light-emitting diode (LED). Alternatively, we present a 4-Gbit/s VLC system using coherent blue-laser diode (LD) via 16-quadrature amplitude modulation orthogonal frequency division multiplexing. By changing the composition and the optical-configuration of a remote phosphor-film the generated white light is tuned from cool day to neutral, and the bit error rate is optimized from 1.9 × 10(-2) to 2.8 × 10(-5) in a blue filter-free link due to enhanced blue light transmission in forward direction. Briefly, blue-LD is an alternative to LED for generating white light and boosting the data rate of VLC.

Optical 16-QAM-52-OFDM transmission at 4 Gbit/s by directly modulating a coherently injection-locked colorless laser diode.

Coherently injection-locked and directly modulated weak-resonant-cavity laser diode (WRC-FPLD) for back-to-back optical 16-quadrature-amplitude-modulation (QAM) and 52-subcarrier orthogonal frequency division multiplexing (OFDM) transmission with maximum bit rate up to 4 Gbit/s at carrier frequency of 2.5 GHz is demonstrated. The WRC-FPLD transmitter source is a specific design with very weak-resonant longitudinal modes to preserve its broadband gain spectral characteristics for serving as a colorless WDM-PON transmitter. Under coherent injection-locking, the relative-intensity noise (RIN) of the injection-locked WRC-FPLD can be suppressed to ?105 dBc/Hz and the error vector magnitude of the received optical OFDM data is greatly reduced with the amplitude error suppressed down 5.5%. Such a coherently injection-locked single-mode WRC-FPLD can perform both the back-to-back and the 25-km-SMF 16-QAM-52-OFDM transmissions with a symbol rate of 20-MSa/s in each OFDM subcarrier. After coherent injection locking, the BER of the back-to-back transmitted 16-QAM-52-OFDM data is reduced to 2.5 × 10(-5) at receiving power of ?10 dBm. After propagating along a 25-km-long SMF, a receiving power sensitivity of ?7.5 dBm is required to obtain a lowest BER of 2.5 × 10(-5), and a power penalty of 2.7 dB is observed when comparing with the back-to-back transmission.