Non-return-to-zero On-off Keying Research Articles

Effect of Chirped Dispersion and Modal Partition Noise on Multimode VCSEL Encoded With NRZ-OOK and PAM-4 Formats

Chirp-dispersion and data transmission analyses of the multimode vertical-cavity surface-emitting laser (MM-VCSEL) with a 7.5-μm oxide-confined aperture and a root-mean-square spectral linewidth of 1 nm is performed for intra-data-center application. For directly modulating the non-return-to-zero on-off keying (NRZ-OOK) and the 4-level pulse amplitude modulation (PAM-4) data streams, an optimized bias current of 17 mA and a data amplitude of 800 mV are selected to provide the MM-VCSEL with an output optical power of 6.1 mW and a transverse mode number of 17. Such an optimized operation enables the MM-VCSEL with a differential resistance of 45.3 Ω to approach the impedance matching by driving the circuit such that the -3-dB bandwidth can be achieved to 23.8 GHz. The relative intensity noise and mode-partition-noise of the MM-VCSEL are analyzed to perform the optimized NRZ-OOK/PAM4 data encoding. By utilizing the pre-emphasis technique to compensate for the intensity and phase variation, the encoded NRZ-OOK and PAM-4 can be respectively promoted to 61 Gbit/s and 96 Gbit/s in the back-to-back (BtB) case. After passing through the 100-m OM5 multi-mode-fiber (MMF) link to suffer the severe modal dispersion, the data rate would respectively degrade to 45 Gbit/s (or 4.5 Gbit·km/s) and 70 Gbit/s (or 7 Gbit·km/s) for OOK and PAM-4 transmission.

Ultra-wide band (O to L) photonic integrated polymer cross-bar switch matrix.

We present an ultra-wide band photonic integrated 4×4 polymer cross-bar switch matrix based on total internal reflection and the thermo-optic effect. The photonic integrated polymer switch owns low insertion loss, low power consumption, wavelength, and polarization-independent operation for all switching paths. The experimental results show ultra-wide band (O- to L-band) operation with fiber-to-fiber insertion losses ranging from -3.7 to -6.5dB, 0.1 to 0.6 dB polarization-dependent losses, switching the on-off ratio above 36 dB on average, and 25 mW power consumption per path. Error-free operation with a power penalty <0.2dB at 1 E-9 bit error rate (BER) for ultra-wide band non-return-to-zero on-off keying (NRZ-OOK) wavelength-division multiplexing (WDM) switched signals at 10, 25, 40, and 50 Gbit/s, and 510 Gbps dual polarization 64-QAM switched data with a negligible penalty were measured.

Multi-Band Photonic Integrated Wavelength Selective Switch

As fiber-optic systems turn toward multi-band transmission (MBT), exploiting the complete low loss window of optical fibers, novel optical components, able to operate in bands other than the conventional C-band, become necessary. In light of this, we report on a multi-band photonic integrated <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathbf {1\times 2}$</tex-math></inline-formula> wavelength selective switch (WSS) operating in the O, S, C and L-bands. The photonic integrated WSS presented in this work uses a folded arrayed-waveguide grating (AWG) as the filtering element, while the wideband operation of the thermo-optic switches allows the routing of the individual channels from those bands to any of the device output ports. The operation of the WSS is experimentally validated for different bands and modulation formats. Results show error-free operation with limited penalty with intensity-modulation direct-detection (IM/DD) non-return-to-zero on-off keying (NRZ-OOK) up to 35 Gb/s in O, S, C and L-bands and up to 169.83 Gb/s with coherent 64-quadrature amplitude modulation (QAM) data transmission in the S, C and L-bands.

Experimental demonstration of pre-electronic dispersion compensation in IM/DD systems using an iterative algorithm.

To combat chromatic dispersion (CD) in intensity modulation and direct detection (IM/DD) systems, three chirp-free demonstrations are experimentally performed with an iterative pre-electronic dispersion compensation (pre-EDC) algorithm at the transmitter end, for 28 GBaud non-return-to-zero on-off keying (NRZ-OOK), 56 GBaud NRZ-OOK and 28 GBaud four-level pulse-amplitude-modulation (PAM-4) signals, over distances of 100 km, 50 km and 40 km of single mode fiber (SMF), respectively. The iterative pre-EDC algorithm is based on the Gerchberg-Saxton (GS) algorithm, which treats the unconstrained phase at the direct detection receiver as a degree of freedom. At the receiver side, only a linear fractionally-spaced (T/2) post-feed-forward equalizer (post-FFE) is employed to combat the residual inter-symbol interference (ISI). Experimental results show that the aforementioned three demonstrations can approach the forward error correction (FEC) bit error rate (BER) threshold of 3.8 × 10-3 with (15 pre-EDC iterations and 5-tap post-FFE), (30 pre-EDC iterations and 15-tap post-FFE), and (10 pre-EDC iterations and 25-tap post-FFE), respectively. The results indicate the applicability of the pre-EDC algorithm in high-capacity IM/DD systems for transmission distances below 100 km of SMF.

1.3 Gbps OOK modulated phosphorescent white LED using optimized lattice pre-equalization circuit in visible spectrum

A visible light communication (VLC) system that utilizes a single phosphorescent white light emitting diode (LED) under a 3 m line of sight (LOS) indoor free space transmission length has been established in this work. Proposed lattice pre-equalization circuit in it is opted to overwhelm the bandwidth constraint of LED. This VLC system allows non-return to zero on-off keying (NRZ-OOK) data transmission up to 1.3 Gbps with the bit error rate (BER) of 18.241e-009, which is under a pre-forward error correction limit of 3.8*10-03 by employing an optimized pre-equalizer. The concise assess on the characteristic features of an equalizer are also done. In addition, the intention of all the components in this scheme and its results are conferred. This VLC system clearly demonstrates the capability of constant resistance recurrent equalizer structure for this LED device. The upshots show that this scheme has immense prospective for a low cost and better indoor wireless broadband access VLC applications. To date, to the best of the authors’ knowledge, this is an uppermost data rate reached by exploiting an optimized single stage lattice pre-equalization circuit for OOK modulated phosphorescent white LED based VLC system.

Investigating the performance of all-optical AND logic gate based on FWM effect in SOA at low power

Abstract In the present work, the performance of the all-optical AND logic gate using four wave mixing in wide band semiconductor optical amplifier (SOA) has been analyzed for different modulation formats. The two binary inputs of all-optical AND gate are modulated by return to zero and non-return to zero (NRZ) modulation formats. The quality factor (Q-factor) has been examined on the basis of critical parameters of SOA. The obtained results show that the acceptable Q-factor (&gt;6) is possible with the proposed design at input signal power even as low as 50 μW (−13 dBm), when the data is modulated in NRZ on-off keying (OOK) format.

A Heuristic Approach for Optical Transceiver Placement to Optimize SNR and Illuminance Uniformities of an Optical Body Area Network

The bi-directional information transfer in optical body area networks (OBANs) is crucial at all the three tiers of communication, i.e., intra-, inter-, and beyond-BAN communication, which correspond to tier-I, tier-II, and tier-III, respectively. However, the provision of uninterrupted uplink (UL) and downlink (DL) connections at tier II (inter-BAN) are extremely critical, since these links serve as a bridge between tier-I (intra-BAN) and tier-III (beyond-BAN) communication. Any negligence at this level could be life-threatening; therefore, enabling quality-of-service (QoS) remains a fundamental design issue at tier-II. Consequently, to provide QoS, a key parameter is to ensure link reliability and communication quality by maintaining a nearly uniform signal-to-noise ratio () within the coverage area. Several studies have reported the effects of transceiver related parameters on OBAN link performance, nevertheless the implications of changing transmitter locations on the uniformity and communication quality have not been addressed. In this work, we undertake a DL scenario and analyze how the placement of light-emitting diode (LED) lamps can improve the uniformity, regardless of the receiver position. Subsequently, we show that using the principle of reciprocity (POR) and with transmitter-receiver positions switched, the analysis is also applicable to UL, provided that the optical channel remains linear. Moreover, we propose a generalized optimal placement scheme along with a heuristic design formula to achieve uniform and illuminance for DL using a fixed number of transmitters and compare it with an existing technique. The study reveals that the proposed placement technique reduces the fluctuations in by and improves the illuminance uniformity up to as compared to the traditional approach. Finally, we show that, for very low luminous intensity, the values remain sufficient to maintain a minimum bit error rate (BER) of with on-off keying non-return-to-zero (OOK-NRZ) modulation format.

C-Band Silicon Waveguide Modulation With 50-Gbit/s NRZ-OOK Over 10-km SMF and DSF

A low-power-consumption single-arm-driven silicon (Si) Mach-Zehnder modulator (MZM) operated at C-band ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda =1550$ </tex-math></inline-formula> nm) for non-return-to-zero on-off-keying (NRZ-OOK) transmission beyond 50 Gbit/s over 10-km single-mode fiber (SMF) and dispersion-shift fiber (DSF) is demonstrated to guarantee the IEEE 802.3bs standardized 400GBASE-FR8/LR8 operation. The Si MZM exhibits asymmetric waveguide arms and 2-mm-contact-length phase shifter under carrier depletion operation in its p-n junction, which is DC biased as low as 2 V to provide a low <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{V}_{\pi }\text{L}$ </tex-math></inline-formula> product of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.909~\text {V}\cdot \text {cm}$ </tex-math></inline-formula> . For the error-free transmission of the NRZ-OOK data-stream, the single-arm-driven Si MZM supports the highest data rates of 53, 53 and 50 Gbit/s over optical back-to-back, 2-km SMF and 10-km DSF transmissions, respectively. The 50-Gbit/s receiving power penalties are respectively 0.2 and 0.25 dB after 2-km SMF and 10-km DSF propagation.

Ambient LED Light Noise Reduction Using Adaptive Differential Equalization in Li-Fi Wireless Link.

For Li-Fi wireless links based on a white light emitting diode, an adaptive differential equalization (ADE) technique that reduces various noises such as interference noise and shot one generated from ambient light sources is pro-posed. The ADE technique reduces noise by taking advantage of the fact that the derivative between adjacent sampling points of signal with digital waveform is very different from that of noise with the random analog waveform. Furthermore, a weighting function that reflects the Poisson characteristics of shot noise is applied to the ADE technique in order to maximize the reduction efficiency of ambient noise. The signal-to-noise ratio of input non-return-to-zero-on–off keying (NRZ-OOK) signal is improved by 7.5 dB at the first-generation forward error correction (FEC) threshold (the bit error rate (BER) of 8 × 10−5) using the optical wireless experimental link. In addition, it is confirmed that it is possible to maintain the transmission performance corresponding to the BER of 1 × 10−5 by using the proposed ADE technique, even when the intensity of the ambient light source increases by 6 dB.

Full-duplex high-speed indoor optical wireless communication system based on a micro-LED and VCSEL array.

We built a full-duplex high-speed optical wireless communication (OWC) system based on high-bandwidth micro-size devices, for which micro-LED and VCSEL arrays are implemented to establish downlink and uplink, respectively. The high-capacity downlink based on a single-pixel quantum dot (QD) micro-LED can reach a data rate of 2.74 Gbps with adaptive orthogonal frequency division multiplexing (OFDM). VCSEL-based line-of-sight (LOS) and non-line-of-sight (NLOS) uplinks are designed with lens-free receiving functions for a 2.2-m communication distance. Experimental results have been demonstrated and confirmed that both downlink and uplinks are capable of providing sufficient bandwidth for a multi-gigabit OWC. Besides, the lens-free uplink receiver can alleviate requirements for aligning and improve the mobility of the transmitter. The VCSELs implemented for both systems work with low driving currents of 140-mA and 190-mA under consideration of the human eye safety. For non-return-to-zero on-off keying (NRZ-OOK), both uplinks can achieve 2.125 Gbps with bit-error-rate (BER) lower than the forward error correction (FEC) threshold of 3.8×10-3 for Ethernet access.

Optimal Modulation Technique for Underwater Visible Light Communication Using Rolling-Shutter Sensor

The visible light communication (VLC) technique using a rolling-shutter sensor-based commercial camera has an advantage in that the LED and camera mounted on an underwater device ( e.g. , drone, sensor) can be effectively used as a transmitter (Tx) and a receiver (Rx), respectively, under water. On the other hand, a suitable modulation technique has not been well considered to realize a VLC system using a rolling-shutter sensor in an underwater channel that includes high ambient light conditions. In this paper, we design VLC systems using phase-shift keying (PSK), non-return-to-zero on- off keying (NRZ-OOK), and orthogonal frequency division multiplexing (OFDM), and evaluate them through simulations and experiments. The results suggested that the VLC system using PSK or OFDM is more resilient than that using NRZ-OOK in an underwater channel with low-frequency ambient light, and that a VLC system using PSK or NRZ-OOK is more tolerant than that using OFDM in environments with high ambient light, resulting in pixel saturation. In conclusion, the present study has demonstrated that PSK is the most suitable modulation technique for a VLC system using a rolling-shutter sensor in an underwater channel that includes high ambient light conditions.

Experimental Demonstration of Over 14 AL Underwater Wireless Optical Communication

Turbidity of water significantly affect the system performance of underwater wireless optical communication (UWOC). In this letter, we proposed and experimentally demonstrated a loss-tolerant UWOC system using a compact high-power 520-nm laser diode (LD) and a highly sensitive silicon photomultiplier (SiPM). The LD is directly modulated by the on-off keying-non-return-to-zero (OOK-NRZ) data. A precise collimation system is designed in the transmitter so that the maximum beam divergence angle is fixed at 0.75 mrad. The performance of the proposed system is investigated over a 24-m underwater channel with different attenuation lengths (ALs) mimicking the different levels of water turbidity in coastal water. Experimental results show that the data rates of 20 Mbps, 40 Mbps, 80 Mbps and 100 Mbps can be achieved under 14.3 AL, 13.2 AL, 13.2 AL and 12.3 AL with bit error rates (BERs) lower than the forward error correction (FEC) limit.

Experimental demonstration of 62.5 Mbps VLC link for healthcare infrastructures by incorporating limiting amplifier as an amplification scheme

The ongoing pandemic situation of COVID-19 has alarmed global public healthcare and epidemic response mechanisms to a significant extent. In this context, communication services can play an important role in hospitals to drive emergency response mechanisms accurately. Visible light communication (VLC) can become an excellent solution to provide communication services in hospitals as it uses low-cost LEDs to transmit information in the form of light signals which can not interfere with medical equipment and does not impact patient health. However, low bandwidth of LEDs is one of the major challenges, which limits the transmission capacity and distance in VLC system. In this work, we propose a post-amplification scheme based on low-pass filter and limiting amplifier to overcome the inherent bandwidth limitation of commercial LEDs. A 62.5Mbps non-return to zero on-off keying (NRZ-OOK) modulation-based VLC link with error-free transmission can be achieved over a transmission distance of 6 ​m.

Indoor Fine Particulate Matter Monitoring in a Large Area Using Bidirectional Multihop VLC

These particulate matter (PM) causes lethal diseases to humans, and both short term and long term exposure are known to have hazardous effects. PM10 and PM2.5 have diameters less 10 and $2.5~\mu \text{m}$ , respectively, which makes them more dangerous to the human body. Thus, information regarding PM concentrations in indoor environments of dust-sensitive places is essential for proper precaution. In this study, we measured PM values in a large area and transferred this information using visible light communication (VLC) to the monitoring node. VLC is considered as an efficient technique due to its unique advantages and is currently unregulated. We applied bidirectional VLC to transfer information to ensure two-way communication. We also applied a multihop strategy to make the system function as a query answering system at extended distances. At one end, we generated a request to relay the request to the proper node and received the response in the form of PM data. In our experiment, we implemented four nodes and conducted multihop communication utilizing only a VLC link. We achieved a distance of 13.5 m with a zero-error rate between the two nodes using nonreturn to zero on-off keying (NRZ-OOK) modulation. In case of multihop, we achieved a distance greater than 40 m using four nodes to send dust information with a minimal error rate. This can be applied to large indoor areas where radio frequency is restricted.

Optical Power Budget of 25+ Gbps IM/DD PON with Digital Signal Post-Equalization

While infrastructure providers are expanding their portfolio to offer sustainable solutions for beyond 10 Gbps in the access segment of optical networks, we experimentally compare several modulation format alternatives for future passive optical networks (PONs) aiming to deliver 25+ Gbps net-rates. As promising candidates, we consider the intensity modulation direct detection (IM/DD) schemes such as electrical duobinary (EDB) and 4-level and 8-level pulse amplitude modulations (PAM-4/8). They are more spectrally efficient than the conventional non-return-to-zero on-off-keying (NRZ-OOK) used in current 10G PONs. As we move to higher rates, digital equalization enhances the performance by smoothening the systems imperfection. However, the impact that such equalization has on the optical power budget remains unclear. Therefore, in this article, we fairly compare the optical power budget values of a time division multiplexed PON (TDM-PON) exploiting a linear digital signal equalization at the receiver side. We consider the conventional PON configuration (20 km of single-mode fiber (SMF), 1:N optical power splitting) with IM/DD and net-rates above 25 Gbps. Furthermore, we focus on a downstream transmission imposing the bandwidth limitations of 10G components using a digital filter before the detection. The obtained results show that the use of a digital post-equalization with 43 feed-forward (FF) and 21 feedback (FB) taps can significantly improve the signal quality enabling new alternatives and enhancing the optical power budget.

Self-biasing of carrier depletion based silicon microring modulators.

We report on the self-biasing effect of carrier depletion based silicon microring modulators (MRM) by demonstrating that a silicon MRM can generate open eye diagrams for non-return-to-zero (NRZ) on-off keying (OOK) modulation without an external reverse bias supplied to it. Two modulator configurations are investigated namely single-ended drive in a ground-signal-ground and differential drive in a ground-signal-signal-ground pad configurations. The single-ended modulator is designed with an on photonic integrated circuit (PIC) 50 Ω termination. Open eye diagrams are obtained at 25 Gbit/s and 36 Gbit/s NRZ OOK modulations. We carry-out thorough experimental characterization of the self-biasing of single-ended MRM under various operating conditions of input optical power, carrier wavelength, ring quality factor and extinction ratio as well as modulation speeds, driving voltage swing and pattern length. We demonstrate that the self-biasing is robust and works well in almost all tested conditions. The differential drive MRM is designed with a high impedance without an on-PIC 50 Ω termination. Open eye diagrams are obtained at 30 Gbit/s and 60 Gbit/s NRZ OOK modulations for modulating voltage swing of ∼2.5 Vpp. As demonstrated, the self-biasing works well in both single-ended and differential drive configurations as well as for on-PIC 50 Ω terminated and non-terminated MRMs. The electrical passive parts are all co-designed and fabricated on the same silicon chip as the PIC. The reported self-biasing eliminates the need of having bipolar DC biases supplied to the anode and cathode of the differential drive modulator and allows for simpler driver / modulator interfaces without inductive bias tees.

Research of hybrid WDM-PON data transmission system with embedded ASE-powered stealth channels for steganography applications

Abstract The frequency spectrum is becoming busier, thereby it might be appealing for more and more, for instance, eavesdroppers to try to gather some valuable data or identify the transmission frequencies for this specific data. To mitigate the possible risks concerning that, not only data encryption but also hiding of the data channels (creation of stealth channels) is necessary. For the success of stealth signal integration, channel spacing, and power customization is required. During this research, in the simulation environment, we show a successful realization of the 8-channel 10 Gbit/s non-return-to-zero on–off keying (NRZ-OOK) modulated wavelength-division-multiplexed passive optical network (WDM-PON) with the embedded additional amplified spontaneous emission (ASE) powered hidden 7-channel 2.5 Gbit/s NRZ-OOK modulated spectrum-sliced data transmission system. Such as a hybrid optical transmission system can be used to improve the protection of sensitive data. Our results show that the introduction of the stealth data transmission system leads to an estimated power penalty below 0.02 dB at the pre-FEC BER level of 10−3, which may be considered as negligible and shows the viability of this hybrid system. The proposed approach can be applied not only in the WDM-PON architecture but also in other types of fiber optical access or metro-access systems.

180 Gbit/s 4:1 power multiplexer for NRZ‐OOK signals with high output voltage swing in SiGe BiCMOS technology

A 4:1 multiplexer (MUX) circuit in SiGe BiCMOS technology intended to directly drive a plasmonic Mach-Zehnder modulator for transmitter applications is presented. To achieve the highest data rates at a high output voltage swing, a power MUX concept is applied that maps the high-speed performance of the final clock signal onto the output data. In the clock tree a novel wideband 90° clock phase shifter circuit is utilised for timing adjustment and frequency doubling. Electrical measurements of the chip demonstrate open eye diagrams for non-return-to-zero on-off-keying (NRZ-OOK) signals up to 180 Gbit/s, which is record speed for Si-based technologies. A differential output voltage swing of 300 mV pp was measured that corresponds to an output voltage swing of more than 1 V pp without the bandwidth limit of the measurement equipment.

Comparative investigation on 10G-class and 25G-class receivers for O-band DML-based 25/50 Gbps TDM-PON

Abstract Reliable and cost-efficient transceivers are desired for next generation high-speed passive optical network (PON). In this paper, we experimentally demonstrate 25/50 Gbps transmissions based on an O-band directly modulated laser (DML), and the receiver-side solutions are investigated in detail to realize a low-cost high-speed PON system. Specifically, a comprehensive comparison of two commercially available receiver candidates is presented, which are the 10G-class receiver and the 25G-class receiver. Three typical transmission cases for next generation PON systems based on these two receivers are demonstrated, and the system bandwidth limitation induced signal distortions in corresponding cases are compensated by equalization-based digital signal processing (DSP). System performances and the DSP-induced implementation complexity of the two receivers are comprehensively analyzed and compared. Results indicate that, for the 25 Gb/s transmission, the 25G-class receiver without any DSP is more favorable than the 10G-class one with post-equalization, and a power budget of 25.4 dB is achieved without amplification for non-return-to-zero on-off keying (NRZ-OOK) signal. While for the 50 Gb/s case, the two receivers manifest similar performances and DSP-induced hardware complexities, making both feasible solutions for real deployments, and after 20 km fiber transmission, an optimum power budget of 20.3 dB is achieved for the 4-level pulse amplitude modulation (PAM4) system.

Iterative Algorithm for Electronic Dispersion Compensation in IM/DD Systems

A novel iterative algorithm for electronic dispersion compensation (EDC) at the transmitter is described and demonstrated for intensity modulation and direct detection (IM/DD) systems. The proposed algorithm is based on the Gerchberg-Saxton (GS) algorithm, where the link dispersion performs time-to-frequency mapping, while the unconstrained phase at the direct detection receiver acts as a degree of freedom. Simulation results for a transmitter employing a single drive Mach-Zehnder modulator (MZM) operating at 28 Gb/s non-return-to-zero on-off keying (NRZ-OOK), show pre-compensation of upto 100 km of single mode fiber (SMF), with 1 dBQ margin above the forward error correction (FEC) bit error rate (BER) limit of $3.8 \times 10^{-3}$ . It is shown that with five iterations of the proposed EDC algorithm in digital-signal processing (DSP) coupled with an 8-bit 56 GSa/s digital-to-analog converter (DAC), the transmission reach is extended by a factor of 5 in unamplified SMF links. Simulations for a 56 Gb/s four-level pulse-amplitude-modulation (PAM-4) show the compensation of upto 10 km with five iterations of the EDC algorithm at 1 dBQ above the FEC limit.