On-off Keying Signals Research Articles

A Multi-Mode ULP Receiver Based on an Injection-Locked Oscillator for IoT Applications

This paper presents an ultra-low-power receiver based on the injection-locked oscillator (ILO), which is compatible with multiple modulation schemes such as on-off keying (OOK), binary frequency-shift keying (BFSK), and differential binary phase-shift keying (DBPSK). The receiver has been fabricated in 0.18- $\mu \text{m}$ CMOS technology and operates in the ISM band of 2.4 GHz. A simple envelope detection can be used even for the demodulation of BFSK and DBPSK signals due to the conversion capability of the ILO from the frequency and phase to the amplitude. In the proposed receiver, a $Q$ -enhanced single-ended-to-differential amplifier is employed to provide high-gain amplification as well as narrow band-pass filtering, which improves the sensitivity and selectivity of the receiver. In addition, a gain-control loop is formed in the receiver to maintain constant lock range and hence frequency-to-amplitude conversion ratio for the varying power of the BFSK-modulated receiver input signal. The receiver achieves the sensitivity of −87, −85, and −82 dBm for the OOK, BFSK, and DBPSK signals respectively at the data rate of 50 kb/s and the BER lower than 0.1% while consuming the power of $324~\mu \text{W}$ in total.

Photonic Add-Drop-Gate Node Element Based on EML Technology

We propose a novel approach for reconfigurable photonic nodes in short-reach optical networks, which builds on unified component technology for several key functions. The need for fast transmission, reception, and switching components is addressed through use of a widely adopted technology that is particularly known for its cost efficiency: the externally modulated laser (EML). Through consequent use of EMLs as fast and versatile electro-optic node element in combination with a slower yet reconfigurable cross-connect matrix serving as interconnection between several elements, a node architecture can be synthesized on demand – such as known from field-programmable gate arrays that have revolutionized the field of programmable microelectronics. To prove the proposed multi-functional EML-based approach, we experimentally investigate the capabilities of this photonic transmitter as coherent receiver of dropped signals and as optical gate, being the basic element of fast switches. We first demonstrate the polarization-immune coherent homodyne reception of broadband 10 Gb/s on-off keyed signals without further need for digital signal processing. Transmission is shown at an optical budget of 24 dB and in presence of 12 side-channels. Moreover, the EML is applied as fast 1 × 1 switch by proving that gating at the sub-ns regime can be facilitated at a reception penalty of less than 1 dB.

Generation of high-speed PAM4 signal by overdriving two Mach-Zehnder modulators

We propose the generation of a high-speed four-level pulse amplitude modulated (PAM4) signal by combining two on-off keying (OOK) signals obtained by overdriving two Mach-Zehnder modulators (MZMs). By using this method, we can overcome the limited modulation bandwidth of the MZM and generate the high-speed PAM4 signal (faster than the PAM4 signal generated by modulating an MZM with a four-level electrical signal). For a demonstration, we generate the 95-Gb/s PAM4 signal by combining two OOK signals obtained from the bandwidth-limited MZM having a 3-dB bandwidth of only 10.5 GHz. In comparison, when we generate the PAM4 signal by using the conventional method, it is not possible to increase the bit rate to be faster than 60 Gb/s. We also successfully demonstrate the transmission of the 95-Gb/s PAM4 signal generated by the proposed method over 4 km of the standard single-mode fiber.

Silicon-Organic Hybrid (SOH) Mach-Zehnder Modulators for 100 Gbit/s on-off Keying

Electro-optic modulators for high-speed on-off keying (OOK) are key components of short- and medium-reach interconnects in data-center networks. Small footprint, cost-efficient large-scale production, small drive voltages and ultra-low power consumption are of paramount importance for such devices. Here we demonstrate that the concept of silicon-organic hybrid (SOH) integration perfectly meets these challenges. The approach combines the unique processing advantages of large-scale silicon photonics with unrivalled electro-optic (EO) coefficients obtained by molecular engineering of organic materials. Our proof-of-concept experiments demonstrate generation and transmission of OOK signals at line rates of up to 100 Gbit/s using a 1.1 mm-long SOH Mach-Zehnder modulator (MZM) featuring a π-voltage of only 0.9 V. The experiment represents the first demonstration of 100 Gbit/s OOK on the silicon photonic platform, featuring the lowest drive voltage and energy consumption ever demonstrated for a semiconductor-based device at this data rate. We support our results by a theoretical analysis showing that the nonlinear transfer characteristic of the MZM can help to overcome bandwidth limitations of the modulator and the electric driver circuitry. We expect that high-speed, power-efficient SOH modulators may have transformative impact on short-reach networks, enabling compact transceivers with unprecedented efficiency, thus building the base of future interfaces with Tbit/s data rates.

Integrated Hybrid Wavelength-Tunable III–V/Silicon Transmitter Based on a Ring-Assisted Mach–Zehnder Interferometer Modulator

We demonstrate a wavelength-tunable hybrid III–V/Si transmitter based on a Vernier laser with more than 30 nm tuning range and two microring modulators nested in a Mach–Zehnder interferometer. This transmitter circuit has versatile operating modes. It can be used for on–off keying (OOK) generation based on low drive voltage push–pull ring modulators and for quadrature phase-shift keying (QPSK) generation where binary phase-shift keying signal is generated by each ring. We reported the first hybrid III–V/Si integrated wavelength-tunable transmitter based on high-speed ring modulators (BW ∼23 GHz), which can cover more than 30 nm. OOK signal generation with better signal integrity, lower drive voltage, and lower chirp is demonstrated as well as 80 Gbit/s polarization-division multiplexing QPSK signal transmission over 100 km with the integrated hybrid transmitter and a fully packaged silicon-based coherent receiver.

Comparison of VSB PAM4 and OOK Signal in an EML-Based 80-km Transmission System

A comparison between 51.84-Gb/s vestigial sideband 4-level pulse amplitude modulation (PAM4) and ON–OFF keying (OOK) signals at a transmission distance of 80 km is experimentally demonstrated for the first time. An electro-absorption modulated laser-based intensity-modulation and direct-detection 80-km transmission is achieved using both modulation formats without dispersion compensating fiber. The relative frequency between single sideband filter and signal is adjusted to find an optimized condition for both carrier to signal power ratio and sideband suppression ratio. The experimental results show that with linear equalization and without bandwidth limitation, the OOK signal has a 4-dB better sensitivity compared with PAM4 after 80-km standard single-mode fiber transmission.

Spectral Efficiency and Energy Efficiency of Pulse-Amplitude Modulation Using 1.3 μm Wafer-Fusion VCSELs for Optical Interconnects

We compare the modulation efficiency of on–off keying (OOK) and four-level pulse-amplitude modulation (PAM4) using 1.3 μm wafer-fusion vertical-cavity surface-emitting lasers (VCSELs) for single-channel short-reach optical interconnects. O-band wafer-fusion VCSELs combine high optical gain from InP-based active regions with high-reflectivity, low-absorption, and high-thermal-conductive GaAs-based distributed Bragg reflectors. VCSELs offer a low-cost and low-power-consuming light source for optical interconnects in data centers and fiber-based local-area networks, presenting an attractive alternative to common edge-emitting lasers. Our investigation focuses on the highest error-free bit rates and energy efficiency of OOK and PAM4 signaling. We achieved an error-free bit rate of 38 Gbit/s with PAM4 for devices having a small-signal bandwidth of 9.9 GHz, presenting a spectral efficiency of 3.8 bit/s/Hz. These PAM4 values offer an improved error-free bit rate of 26% and consume 32% less energy-per-bit when co...

Multilevel modulation scheme using the overlapping of two light sources for visible light communication with mobile phone camera.

Visible light communication (VLC) with light emitting diodes (LEDs) is an emerging technology for 5G wireless communications. Recently, using complementary metal-oxide-semiconductor (CMOS) image sensor as VLC receiver is developed owing to its flexibility and low-cost. However, two illumination levels such as on-off keying (OOK) signal are used. To improve the system throughput and reduce complexity of the hardware design, in this paper, we propose and experimentally demonstrate a multilevel modulation scheme for VLC system utilizing the overlapping of two light sources for the first time, and the two light sources are modulated by an OOK and a Manchester signal respectively. At the receiver, a CMOS camera can demodulate the Manchester and the OOK signal simultaneously. Meanwhile, a low-pass filter (LPF) is used to enhance the system performance. The experimental results demonstrate that the proposed multilevel modulation scheme can achieve a net data rate of 4.32 kbit/s.

Transmission of 51.56-Gb/s OOK signal using 1.55-μm directly modulated laser and duobinary electrical equalizer.

We demonstrate the transmission of 51.56-Gb/s on-off keying (OOK) signals generated by using a 1.55-μm directly modulated laser (DML) over 15-km long standard single-mode fiber. In this experiment, a duobinary electrical equalizer based on a finite-impulse-response filter is used at the receiver to increase the dispersion-limited transmission distance. We evaluate the performances of the 51.56-Gb/s OOK signals with respect to the transmission distance by using the frequency response analysis of the proposed system. This result is used to explain why it is effective to utilize the duobinary equalization (instead of binary equalization) for increasing the transmission distance.

Multiwavelength Laser Module Based on Distribute Feedback Laser Diode for Broadcast and Communication Systems

In this paper, we proposed a cost-effective broadcast signal transmission scheme using a distributed feedback laser diode (DFB-LD) for wavelength-division-multiplexing passive optical network (WDM-PON) systems. The DFB-LD is directly modulated with a single-tone radio frequency signal to generate multiple optical carriers. An optical signal-to-noise ratio (OSNR) is enhanced using a delay interferometer as a double-pass interferometer. Orthogonal frequency division multiplexing (OFDM) and on-off keying (OOK) signals are experimentally demonstrated to test the broadcasting scheme. We measured the bit-error-rate (BER) and the power penalty after the broadcasting OFDM and OOK signals are transmitted through a 25-km single-mode fiber. An excellent performance of BER is achieved for both OOK and OFDM signals. The proposed scheme is a practical and cost-effective solution for broadcast signal transmissions in WDM-PON systems.

Novel Visible Light Communication Approach Based on Hybrid OOK and ACO-OFDM

In this letter, we present a novel hybrid intensity modulation and direct detection communication system, which integrates asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) and on-off keying (OOK) modulation schemes. First, the negative ACO-OFDM is proposed based on the conventional ACO-OFDM system to accommodate the on case with direct current in the OOK modulation, while the ACO-OFDM can match the off case in the OOK modulation. Therefore, the novel hybrid system combines the ACO-OFDM and OOK modulation schemes, while the signals can be recovered at the receiver to support the different qualities of service with high spectral efficiency and can be adapted to various receivers with different complexities. Simulation results are reported for the visible light channel and show that both the ACO-OFDM and OOK signals can be well recovered.

25-Gb/s OOK Transmission Using 1.5-<inline-formula> <tex-math notation="LaTeX">$\mu{\rm m}$</tex-math> </inline-formula> 10G-Class VCSEL for Optical Access Network

We explore the possibility of transmitting 25-Gb/s on–off keying (OOK) signals generated by using a 1.5- μ m 10G-class vertical-cavity surface-emitting laser (VCSEL) over standard single-mode fiber (SSMF) for optical access applications. A transistor-outline-can packaged VCSEL having a 3-dB modulation bandwidth of 7 GHz is utilized to transmit the 25-Gb/s signals. We experimentally investigate the transmission performances of OOK signals obtained from two different transmitter schemes: with and without a delay interferometer (DI) at the output of the directly modulated VCSEL. In order to maximize the transmission distance without using bulky and lossy dispersion compensation modules, we optimize the extinction ratio of the signals and apply the electrical equalization at the receiver. Also optimized is the free-spectral range (FSR) of the DI when it is utilized. The experimental results show that we can successfully transmit the 25-Gb/s OOK signals over 33- and 45-km long SSMF with and without the DI, respectively. The use of DI not only alleviates the band limitation of the VCSEL but also significantly improves the receiver sensitivity of the 25-Gb/s OOK signal up to 30 km. Moreover, a larger power budget is achieved for transmission distances shorter than 25 km when a DI having an FSR of 25 GHz is utilized at the output of the VCSEL.

MDM-TDM PON Utilizing Self-Coherent Detection-Based OLT and RSOA-Based ONU for High Power Budget

A cost-effective mode-division-multiplexing and time-division-multiplexing passive optical network (MDM-TDM PON) utilizing a self-coherent detection for upstream signal at optical line terminal (OLT) and a high-gain reflective semiconductor optical amplifier (RSOA) as an optical amplifier for a downstream signal at optical network units (ONUs) to enhance bidirectional power budget is proposed. Meanwhile, to further reduce the cost of ONU, RSOA is also used as upstream on–off keying (OOK) signal modulator by time compression multiplexing. A novel dual-modulus algorithm is proposed for OOK signal detection at the OLT. We experimentally verify the proposed MDM-TDM PON architecture with an upstream 1-Gb/s OOK signal and a downstream 10-Gb/s orthogonal frequency division multiplexing (OFDM) signal. Due to the high gain of RSOA and high receiver sensitivity of self-coherent detection, a 30-dB bidirectional power budget is achieved after 10-km few-mode fiber and a 20-km standard single-mode fiber at the bit error rate (BER) of 10−3. Optimal seed power and signal power that input to the RSOA are investigated in this paper.

Demonstration of Bidirectional PON Based on Mode Division Multiplexing

Recently, mode division multiplexing (MDM) has been introduced into optical transmission systems and networks for capacity enhancement. In this letter, we propose a bidirectional passive optical network (PON) architecture based on MDM. The bidirectional optical distribution network of the MDM-PON consists of few-mode fiber, passive mode multiplexer/demultiplexer, and few-mode circulators, all of which are characterized by low modal-crosstalk. Signals in different modes are able to be transmitted and received independently for both downstream and upstream transmission. We experimentally demonstrate the bidirectional MDM-PON transmission over 10-km two-mode optical fiber. The 10-Gb/s ON–OFF-keying signals can be independently transmitted and directly detected without coherent receiver and multiple-input multiple-output processing. Moreover, nonlinear transmission impairments are experimentally investigated.

Free-Space Optical Communications Using on–off Keying and Source Information Transformation

Free-space optical communication using on–off keying (OOK) and source information transformation is proposed. It is shown that the source information transformation allows the proposed system to detect the OOK signal without requiring the knowledge of instantaneous channel state information and the probability density function (pdf) of the turbulence model. Analytical expressions are derived for the pdf of the detection threshold, and an upper bound is obtained on the average bit error rate (BER). Numerical studies show that the proposed system can achieve comparable performance to the idealized adaptive detection system, with a greatly reduced level of implementation complexity and a signal-to-noise ratio performance loss of only $1.8$ dB at a BER of $1\times 10^{-9}$ for a lognormal turbulence channel with $\sigma =0.25$ .

Graphene FET Gigabit ON–OFF Keying Demodulator at 96 GHz

We demonstrate the demodulation of a multi-Gb/s ON–OFF keying (OOK) signal on a 96 GHz carrier by utilizing a 250-nm graphene field-effect transistor as a zero bias power detector. From the eye diagram, we can conclude that the devices can demodulate the OOK signals up to 4 Gb/s.

Direct-Detection Receiver for Polarization-Division-Multiplexed OOK Signals

We propose a direct-detection receiver capable of detecting polarization-division-multiplexed (PDM) ON-OFF keying (OOK) signals without using a dynamic polarization controller. The proposed receiver, consisted of a polarization-beam splitter, three $1\times 2$ directional couplers, three photodetectors, three analog-to-digital converters, and a digital signal processing unit, can discriminate among the four symbol combinations of the PDM-OOK signal with the help of a short training sequence. For a demonstration, we show that the proposed receiver can detect a 20-Gb/s PDM-OOK signal even when its polarization is scrambled at the speed of 3 Mrad/s.

Transmission Performance of OOK and 4-PAM Signals Using Directly Modulated 1.5-μm VCSEL for Optical Access Network

We evaluate the possibility of realizing optical access networks using 1.5-μm vertical-cavity surface-emitting lasers (VCSELs) in the on-off keying (OOK) and four-level pulse amplitude modulation (4-PAM) formats. In order to maximize the power budget of the networks, we optimize the extinction ratio of the 10.7- and 21.4-Gb/s signals and exploit the electrical equalization at the receiver. The experimental comparison made at 10.7 Gb/s shows that the OOK format vastly outperforms the 4-PAM format in terms of tolerance to chromatic dispersion. For example, we achieve the 80-km transmission of the OOK signal over standard single-mode fiber (SSMF), but the maximum reach is halved when the 4-PAM signal is employed. Nevertheless, the 4-PAM format is still an effective way to double the data rate of the VCSEL links in optical access networks. We successfully transmit the 21.4-Gb/s 4-PAM signal generated by using the 1.5-μm VCSEL over 18-km long SSMF.

Improved symbol rate identification method for on–off keying and advanced modulation format signals based on asynchronous delayed sampling

Symbol rate identification (SRI) based on asynchronous delayed sampling is accurate, cost-effective and robust to impairments. For on–off keying (OOK) signals the symbol rate can be derived from the periodicity of the second-order autocorrelation function (ACF2) of the delay tap samples. But it is found that when applied this method to advanced modulation format signals with auxiliary amplitude modulation (AAM), incorrect results may be produced because AAM has significant impact on ACF2 periodicity, which makes the symbol period harder or even unable to be correctly identified. In this paper it is demonstrated that for these signals the first order autocorrelation function (ACF1) has stronger periodicity and can be used to replace ACF2 to produce more accurate and robust results. Utilizing the characteristics of the ACFs, an improved SRI method is proposed to accommodate both OOK and advanced modulation formant signals in a transparent manner. Furthermore it is proposed that by minimizing the peak to average ratio (PAPR) of the delay tap samples with an additional tunable dispersion compensator (TDC) the limited dispersion tolerance can be expanded to desired values.

Temporal Spectrum Sensing for Optical Wireless Scattering Communications

Due to the unlicensed spectrum nature of the optical wireless communication, for a transceiver pair, the receiver needs to periodically sense the communication media, aiming to better schedule its transmission. Considering that the data symbols or channel parameters are unknown, we adopt a generalized likelihood ratio test (GLRT), which is known to be optimal with unknown parameters based on finite samples. This paper proposes two detection rules on whether there are optical signals falling into the receiver field of view within certain time slot(s), based on the sum number of received photons over all sensing slots, as well as the number of received photons in each slot. The formal one is named the sum-counting test and the latter one is named as the general GLRT. We design the corresponding detection schemes for both on-off keying (OOK) and pulse-position modulation (PPM) signal formats. We also provide asymptotic results on the miss detection probability. Numerical results show that, for OOK signal format, the general GLRT outperforms the sum-counting test at the cost of higher computational complexity, but for PPM signal format both detection schemes perform virtually the same.