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.
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.
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.
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.
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
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.
To realize the superiority of data transmission with reduced modal dispersion in OM4- and OM5-mulitmode fiber (MMF), a single transverse mode (SM) vertical cavity surface emitting laser (VCSEL), ...directly encoded with large-capacity data formats for transmissions in OM5-MMF and OM4-MMF, are compared. The SM-VCSEL contains a 12-μm mesa formed by double-oxidized AlGaAs layers, which confines a current-flow area within an aperture of 3 μm. The SM-VCSEL is lasing with a carrier-to-noise ratio of 34.4 dB and a linewidth of 0.05 nm. The SM-VCSEL is biased at 10Ith to provide a modulation bandwidth of 21.4 GHz and a relative intensity noise of -138 dBc/Hz. By encoding the SM-VCSEL with four-level pulse amplitude modulation (PAM-4) at 64 Gbit/s, the bit error ratio (BER) of 32-GBaud PAM-4 data is improved from 7.9 × 10 -5 to 4.9 × 10 -5 under a KP4-FEC criterion by replacing OM4-MMF with OM5-MMF. After OM5-MMF transmission, a bathtub BER plot shows bottom-eye, middle-eye, and top-eye jitter tolerances of 9.3, 10.6, and 7.1 ps, which are much wider than 6.9, 10.1, and 6.5 ps for OM4-MMF, respectively. When encoding the 16-QAM OFDM at 100 Gbit/s, OM5-MMF allows data transmission at 96-Gbit/s with a corresponding error vector magnitude, signal-to-noise ratio, and BER of 16.7%, 15.4 dB, and 3.6 × 10 -3 under preleveling at a slope of 0.3 dB/GHz. Because of the high effective modal bandwidth and low modal dispersion of the OM5-MMF, a relatively low receiving power penalty of 0.1 dB between 100-m and back-to-back (BtB) transmissions is obtained with either the pre-emphasized PAM-4 or the preleveled QAM-OFDM data format. By contrast, the receiving power penalty is 1.04 dB between 100 m and BtB cases during OM4-MMF transmission.
By using a nully biased MZM to modulate an incoming single-mode light into a double sideband (CCA-DSB or CCS-DSB) master with preserved or suppressed central carrier, the directly OFDM encoded ...dual-mode colorless laser diode is performed for a successful fusion between wired and wireless links to establish a 5G-based MMWoF system. The dual-mode L-band optical carrier successfully delivers a 36-Gb/s OFDM data with a BER of 3.2 × 10 -3 , while the stabilized 39-GHz mm-wave carrier can provide wireless 4-Gb/s 16-QAM OFDM data with 16.6-dB SNR. The in-situ 39-GHz mm-wave carrier can be synthesized by optically heterodyne mixing the dual-mode carrier at remote node. When injection-locking with the CCS-DSB master, the dual-mode slave colorless laser diode improves its central carrier suppression ratio and RIN to 38 dB and -104 dBc/Hz, respectively. In comparison, the dual-DFBLD master injection-locking mixed mm-wave carrier is relatively unstable due to the individual DFBLDs at free-running condition. With the CCS-DSB master, the mm-wave carrier self-beat from the dual-mode optical carrier exhibits a narrow linewidth of <;3 kHz with high purity and stability. Such a dual-mode colorless laser diode-based MMWoF link is capable of fusing the fiber wired and the 5G wireless links demanded in the near future.
With the use of central carrier suppressed master which contains a double sideband carrier, a directly encoded dual-color laser diode with low coherence based millimeter-wave (MMW) carrier generation ...for hybrid wired and wireless MMW over fiber (MMWoF) system is demonstrated. The maximal transmission capacities for optical wired band at 36 Gb/s and for MMW wireless band at 12 Gb/s are achieved in the proposed MMWoF link. Three MMW carrier frequencies of 28, 39, and 47 GHz are synthesized for implementing the fifth generation (5G) mobile network and satellite communication. The dual-color injection-locking effectively suppresses the central carrier power to -37 dBm, which provides the dual-color optical carrier with a central carrier suppression ratio of 38 dB. The 47-GHz double sideband carrier injection has shown its capability to carry 64-QAM OFDM data at 36 Gb/s with the lowest bit-error-rate (BER) of 2.1 × 10 -3 over 25-km single-mode fiber, as its weakest four-wave-mixing modes greatly suppress the fiber chromatic dispersion. After optical baseband transmission, the photonic mixed 28-, 39-, and 47-GHz MMW carriers are heterodyne beat from the dual-color carrier to show similar spectral linewidth of <;1.2 Hz and carrier-to-noise ratio of >41 dB. The 28-GHz MMW carrier can wireless transmit 12-Gb/s 16-QAM OFDM data over 1.6-m free-space to show an average signal-to-noise ratio of 15.3 dB, an error vector magnitude of 17.1%, and a receiving BER of 3.3 × 10 -3 .
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
, 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
, respectively, after 25-km SMF and 1.6-m free-space transmission.
An optical heterodyned 28-GHz carrier generation is demonstrated for synthesizer-free fifth-generation (5G) millimeter wave over fiber (MMWoF) link by using orthogonally polarized dual-mode ...vertical-cavity surface-emitting laser (VCSEL) as the frontend transmitter, and the power envelope detection is employed for self-heterodyne down-conversion of the generalized frequency division multiplexing (GFDM) data stream. The demonstrated MMWoF link exhibits superior immunity to the residual frequency and phase noises as well as the inter-carrier interference induced by the free-running dual-mode carrier. For back-to-back optical downstream wireline transmission, the receiving GFDM data optimizes its bit error rate (BER) to 2.2×10 −4 by adjusting the bias current of the dual-mode VCSEL to 8 mA (3 I th ), and by grouping the GFDM data matrix with total symbols of N = K×M with K = 2 subcarriers and M = 24 timeslots. After a long-reach delivering the optical data stream over 50-km dispersion-managed single-mode fiber (DM-SMF), the qualified receiving power sensitivity is −12 dBm, whereas the decoding GFDM data reveals improved receiving sensitivity with an extremely low power penalty of only 0.3 dB. For the wireless transmission after optical downstream receiving at the remote node, the self-heterodyned MMW carrier exhibits peak power of −62.3 dBm and carrier-to-noise (CNR) of 26.8 dB over long-reach 50-km DM-SMF downstream optical link. In comparison with the mutual heterodyned from two incoherent optical carriers, the self-heterodyned frequency fluctuation can be suppressed from >500 to <330 MHz with significantly suppressed phase noise. After wireless delivering over 2 m in free space, the self-heterodyne down-conversion by power envelope detection guarantees the down-converted quadrature amplitude modulation GFDM (QAM-GFDM) data stream with an average power of -48.4 dBm after optimizing the impedance matching by selecting the appropriate frequency response of the power envelope detector. As a result, the wireless MMW transmission of 8-Gbit/s 4-QAM GFDM data stream is qualified with error vector magnitude (EVM) of 16.9%, signal-to-noise ratio (SNR) of 8.5 dB, and BER of 3.8×10 −3 . By combining the free-running dual-mode source with two advanced techniques including mode-power equalization and self-heterodyned power envelope detection, the proposed synthesizer-free MMWoF network has demonstrated excellent immunity to the phase/frequency noise, inter-carrier interference which is particularly suitable for building up the compact and simplified optical transmitter and microwave receiver modules with cost-effective MMW self-heterodyne scheme.
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