Multilevel Amplitude Modulation Research Articles

Adaptive PAM-4/PAM-8 graphene-based electro-optical modulator integrated into a polymer waveguide platform for data-center communication

This paper presents a new concept of a graphene-based adaptive modulator for multilevel amplitude modulation on polymer technology platform. This component consists of an electro-optical modulator with a distributed five segments capacitive structure, based on two single-layers of graphene (SLG) and a thin layer of silicon nitride (Si3N4) in the form (SLG-Si3N4-SLG), which shows a dynamic configuration of the modulation scheme, PAM-4/PAM-8, by the applied logic voltage sequence (3Vpp) for an operating wavelength at 1550 nm. Considering an extinction ratio of 5.6 dB for PAM-4, and 6.0 dB for PAM-8, a compact device with 179.6 µm total length, and the maximum simulated cut-off frequency of 48.12 GHz with 122.9 fF of capacitance and total device resistance of 26.9 Ω, were achieved. This cut-off frequency results in a transmission rate of 96.24 Gbps at PAM-4 and 144.4 Gb/s at PAM-8. The simulated insertion loss is 12.0 dB (PAM-4) and 11.5 dB for PAM-8, and the power consumption is 0.54 pJ/bit for PAM-4 and 0.81 pJ/bit for PAM-8. Combining an innovative design with the unique electro-optical characteristics widely demonstrated by the materials used in the construction of the proposed adaptive device, allows it to be seen as a candidate to contribute to the nanotechnology integration and high-performance communication requirements.

Performance of signal detection with trellis code for downlink non-orthogonal multiple access visible light communication

This paper examines the implementation of multi-level amplitude modulation enforced by trellis coding in a downlink non-orthogonal multiple access channel for visible light communication (VLC). The non-orthogonal transmission is applied using superposition coding and successive interference cancellation with the support of a trellis decoder. The VLC is addressed by a channel model according to Lambert. Two levels of maximum likelihood signal detection are observed and compared, each for corresponding 4 and 8 trellis-coded modulation (TCM). The power ratio allotment is examined to investigate the system performance in the bit error rate. The simulation showed that a threshold of power ratio is needed to ensure good performance of signal detection. Further simulation with successive detection had shown effective results for up to three users.

An APD‐Based Evaluation on the Effect of Transient Disturbance over Digital Transmission

In railway electromagnetic environment, transient disturbances usually degenerate the function of railway wireless communication systems, thus may cause severe security issues. To protect communication services, measurement methodology to characterize disturbances keeps evolving. Nowadays, the statistical characteristics of disturbances, such as Amplitude probability distribution (APD), have been proven more efficient to assess the degradation of digital transmission than Quasipeak detection in most Electromagnetic Compatibility standards. To demonstrate the impact of disturbances on error performance more precisely, a more refined method to estimate Bit error probability (BEP) of digital modulation is necessary. The APD value is ideally obtained with the equivalent bandwidth of the radio service under threat, which means specific apparatus of certain radio service is consequently indispensable. This paper proposes a novel method to estimate the maximum BEP of multilevel amplitude modulations based on APD acquired by standard apparatus. The calculated BEP also provides reference for APD emission restriction.

A 9 Gb/s/ch Transceiver With Reference-Less Data-Embedded Pseudo-Differential Clock Signaling for Graphics Memory Interfaces

A 9 Gb/s/ch transceiver with a reference-less data-embedded pseudo-differential clock signaling (RDCS) for graphics memory interfaces is proposed in a 65-nm CMOS technology. In the RDCS transceiver, the output data is embedded into differential clock signal by adopting a multi-level amplitude modulation in the transmitter (TX), and the data is recovered by extracting the data information from clock signal without reference clock in the receiver (RX) side. Because the data is synchronized with the clock at the TX, the received data can be recovered without DLL in the RX side. In addition, the additional pins required in the graphics memory interfaces can be removed by applying the proposed RDCS. The proposed design achieves less than 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-12</sup> bit error rate with 9 Gb/s/ch data rate, and measured jitter in the recovered clock is 1.42 psRMS. In addition, the power efficiencies of the TX and RX are 2.33 and 1.03 pJ/bit, respectively.

Transmission characteristics of vortex beams in a sixfold photonic quasi-crystal fiber

In an optical fiber communication system, vortex beams have aroused great interest in the last several decades. Vortex beams possess many intriguing properties. For example, they have the ability to carry orbital angular momentum (OAM) which is mutually orthogonal. The OAM is a fundamental physical quantity of light which can be used as information carriers for transmission channel of optical fiber. Combined with the existing multiplexing techniques such as wavelength division multiplexing technique, advanced multilevel amplitude modulation formats, etc., the vortex beams provide an alternative to the increase of the transmission capacity and spectral efficiency of the optical fiber transmission system. Recently, long-length transmission of vortex-beam in optical fiber has been realized and there have also occurred some new designs of optical fiber on vortex beams, such as air-core ring shaped fiber, graded index vortex fiber, multi-ring fiber, and supermode fiber. Photonic crystal fiber (PCF) is flexible in design. Therefore, it is easy to regulate the transmission performance of PCF by adjusting the radius and the pitch of the air holes and so on. In this paper, we propose a newly designed sixfold photonic quasi-crystal fiber (SPQCF) to transmit vortex beams stably. Transmission characteristics of this newly designed fiber are simulated and calculated by using COMSOL multiphysics software. When the wavelength of the incident light is 1550 nm, the effective index difference between the vortex modes in a group is more than 10&lt;sup&gt;–4&lt;/sup&gt; which is large enough to preclude the LP modes from being formed, and to transmit 7 vector modes (10 OAM modes). Changing the radius and pitch of the air holes, we can regulate the dispersion characteristic and confinement loss of the SPQCF flexibly. At 1550 nm, the confinement loss of the SPQCF maintains 10&lt;sup&gt;–8&lt;/sup&gt;−10&lt;sup&gt;–7&lt;/sup&gt; which is low enough to confine the vortex beams in the fiber core. When the incident light wavelength of HE&lt;sub&gt;21&lt;/sub&gt; ranges from 1500 nm to 1800 nm (&lt;i&gt;r&lt;/i&gt;&lt;sub&gt;0&lt;/sub&gt; = 1.9 μm), the dispersion coefficient of the SPQCF is between 63.51−65.42 ps·nm&lt;sup&gt;–1&lt;/sup&gt;·km&lt;sup&gt;–1&lt;/sup&gt; which tends to be flat. By changing &lt;i&gt;r&lt;/i&gt;&lt;sub&gt;0&lt;/sub&gt;, the flat trend is adjusted to different wavelength range. This dispersion characteristic possesses great potential for the transmission of optical solitons. The effective mode area (HE&lt;sub&gt;21&lt;/sub&gt;) is about 40 μm&lt;sup&gt;2&lt;/sup&gt; and the nonlinear coefficient (HE&lt;sub&gt;21&lt;/sub&gt;) is maintained on the order of 10&lt;sup&gt;–3&lt;/sup&gt; between 1500−1600 nm. These features suppress the generation of nonlinear effect in the fiber and benefit the transmission of vortex beams. The stable transmission distance is longer than 1 km. In summary, we design a new type of PCF featuring quasi-crystal structure which has a ring shaped fiber core and supports the transmission of vortex beams stably.

Reconfigurable Envelope Generation of Optical Pulse Train Based on Discrete Fourier Transform

We experimentally demonstrate a fiber-based reconfigurable system for programming the envelope of high-speed optical pulse train by using fractional-rate multilevel amplitude modulation. Amplitude-modulated optical pulse trains undergo the discrete Fourier transform (DFT) realized by the temporal Talbot effect in a dispersive fiber. Consequently, rate-multiplied optical pulse trains with programmable envelopes can be achieved. In this letter, we report experimental synthesis of ~80-GHz optical pulse trains with expectant binary patterns, parabolic, square, and triangular envelopes. We also consider practical implementation issues and numerically analyze the influence from the deviation of modulation coefficients and finite extinction ratio of the Mach-Zehnder modulator on the generated pulses.

Linear spectral response of a Fano-resonant graded-stub filter based on pillar-photonic-crystal waveguides.

To achieve high spectral linearity, we developed a Fano-resonant graded-stub filter on the basis of a pillar-photonic-crystal (PhC) waveguide. In a numerical simulation, the availability of a linear region within a peak-to-bottom wavelength span was nearly doubled compared to that of a sinusoidal spectrum, which was experimentally demonstrated with a fabricated silicon-pillar PhC stub filter. The high linearity of this filter is suitable for optical modulators used in multilevel amplitude modulation.

Mitigation of relative intensity noise of quantum dash mode-locked lasers for PAM4 based optical interconnects using encoding techniques.

Quantum dash (Q-Dash) passively mode-locked lasers (PMLLs) exhibit significant low frequency relative intensity noise (RIN), due to the high mode partition noise (MPN), which prevents the implementation of multilevel amplitude modulation formats such as PAM4. The authors demonstrate low frequency RIN mitigation by employing 8B/10B and Manchester encoding with PAM4 modulation format. These encoding techniques reduce the overlap between the modulation spectral content and the low-frequency RIN of the Q-dash devices, at the expense of increased overhead. The RIN of the 33.6 GHz free spectral range Q-dash PMLL was characterized, and the results obtained show very high levels of RIN from DC to 4 GHz, but low levels for higher frequencies. The performance improvement for 28 GBaud 8B/10B and Manchester encoded PAM4 signal has been demonstrated compared to the case when no encoding is used. Finally, the effect of RIN on the system performance was demonstrated by comparing the bit error rate (BER) performance of the PAM4 signaling obtained with an external cavity laser (ECL) to those obtained with Q-dash PMLL.

Design, analysis, and transmission system performance of a 41 GHz silicon photonic modulator.

The design and characterization of a slow-wave series push-pull traveling wave silicon photonic modulator is presented. At 2 V and 4 V reverse bias, the measured -3 dB electro-optic bandwidth of the modulator with an active length of 4 mm are 38 GHz and 41 GHz, respectively. Open eye diagrams are observed up to bitrates of 60 Gbps without any form of signal processing, and up to 70 Gbps with passive signal processing to compensate for the test equipment. With the use of multi-level amplitude modulation formats and digital-signal-processing, the modulator is shown to operate below a hard-decision forward error-correction threshold of 3.8×10-3 at bitrates up to 112 Gbps over 2 km of single mode optical fiber using PAM-4, and over 5 km of optical fiber with PAM-8. Energy consumed solely by the modulator is also estimated for different modulation cases.

Circuit Modeling of Carrier–Photon Dynamics in Composite-Resonator Vertical-Cavity Lasers

We present a circuit model for composite-resonator vertical-cavity lasers (CRVCLs) based on the standard rate equations. This model is compatible with general-purpose circuit analysis program (SPICE), and it can accurately produce the dc and modulation characteristics of the CRVCL, which is verified by comparing the calculated results with the measured experimental data. In addition, using this model we verify that CRVCL has unique abilities to engineer its modulation characteristics by varying cavity asymmetries as well as to produce multilevel amplitude modulation, both of which are consistent with our previous experimental results. We also discuss some advantages and limitations of this model.

Effective homodyne optical phase locking to PSK signal by means of 8b10b line coding

We demonstrate a novel technique that allows effective homodyne optical phase locking to a phase shift keying (PSK) signal with a residual carrier. We exploit 8b10b coding of the signal in order to reduce its low frequency spectral content, suppressing the data-to-phase crosstalk effect. In a transmission experiment on a 10 Gb/s binary PSK signal (8 Gb/s before coding), we achieved transmission over 215 km of dispersion-compensated, installed single-mode fibre, with no penalty compared to back-to-back at a bit error ratio of 10(-3). The proposed solution is applicable to other modulation formats, including multi-level amplitude and/or phase modulation formats.

Multi-Level Amplitude Modulation of a 16.8-GHz Class-E Power Amplifier With Negative Resistance Enhanced Power Gain for 400-Mbps Data Transmission

Multi-level modulation of a 16.8-GHz class-E power amplifier with negative resistance enhanced power gain is demonstrated in a 130-nm CMOS process. The circuit achieves power gain of ~ 30 dB, and power-added efficiency (PAE) of 16% for the highest output power level of 6.8 dBm. The average efficiency for a random data pattern is ~ 8%. The circuit also exhibits 10-dBm saturated output power and ~ 22% maximum PAE. By realigning the highest output power level to the 10-dBm saturated output power, the efficiency can be improved. For a random data pattern, this PA should achieve ~ 2X higher efficiency than Class A PAs. The circuit supports seven amplitude levels for 400 Megabits per second (Mbps) data transmission. The multi-level output signal levels follow a square-root relation. The circuit including an address decoder occupies ~ 1.4 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> .

Analog and Digital Functionalities of Composite-Resonator Vertical-Cavity Lasers

Different modulation approaches for the composite-resonator vertical-cavity laser are described, with an emphasis on direct modulation using either one or both cavities. It is also observed that the unique properties of this device form the basis for analog and digital functionalities. Experimental demonstrations are also shown of multilevel amplitude modulation, preemphasis for direct modulation, microwave signal mixing, and synchronous electrical and optical signaling, none of which can be achieved using a conventional vertical-cavity surface-emitting laser.

Investigation of multilevel amplitude modulation for a dual-wavelength free-space optical communications system using realistic channel estimation and minimum mean-squared-error linear equalization

Fog is a highly dispersive medium at optical wavelengths, and the received pulse waveform may suffer significant distortion. Thus it is desirable to have the impulse response of the propagation channel to recover data transmitted through fog. The fog particle density and the particle size distribution both strongly influence the channel impulse response, yet it is difficult to estimate these parameters. We present a method using a dual-wavelength free-space optical system for estimating the average particle diameter and the particle number density and for approximating the particle distribution function. These parameters serve as inputs to estimate the atmospheric channel impulse response using simulation based on the modified vector radiative transfer theory. The estimated channel response is used to design a minimum mean-square-error equalization filter to improve the bit error rate by correcting distortion in the received signal waveform due to intersymbol interference and additive white Gaussian noise.

Half-Symbol-Rate-Carrier Offset QPSK Transmitter for Bandwidth-Efficient High-Speed Data Communications

This letter proposes a half-symbol-rate-carrier (HSRC) offset quadrature phase shift keying (OQPSK) modulation for high-speed data communications. A prototype transmitter generating the HSRC-OQPSK signal was designed and built. Measurement results confirm the theory that the proposed HSRC-OQPSK modulation improves spectral efficiency by reducing the second lobe of the signal spectrum by 10 dB. Furthermore, HSRC-OQPSK modulation reduces the first null bandwidth by 25% compared to standard non-return-to-zero (NRZ) modulation. Like NRZ, HSRC-OQPSK uses two-level data decision which enables a simpler transceiver architecture than multilevel pulse amplitude modulations (PAMs), such as 4-PAM and duobinary

Modulation principles and code design for multilevel optical data storage

Multilevel optical data storage is an important technology to improve the recording density of optical disc without changing the optical parameters. One approach is multilevel amplitude modulation, which uses the variance of signal amplitude of length-fixed recorded marks to record information. Another one is multilevel runlength-limited (RLL) modulation, which records information in both the signal amplitude and the length of recorded marks, thus can improve the recording density more effectively than the first way. Multilevel RLL coding is a key technology in multilevel RLL modulation optical recording. In this paper, a new 8-ary (1，3) RLL code is designed with state splitting algorithm. The recording density of this code is as high as 3.0 bits/symbol, and the encoder/decoder is simple and easy to implement. The proposed code can be used for future high density multilevel RLL modulation optical disc systems.

40 Gbit∕s, 16-ary (4 bit∕symbol) optical modulation∕demodulation scheme

A practical 16-ary amplitude-phase-shift-keying (16APSK) optical modulation/demodulation scheme (4 bit/symbol) with a combination of multilevel amplitude and phase modulations is proposed, and its feasibility is successfully demonstrated for the first time. The spectral width of return-to-zero 16APSK signal is only 0.27 nm (33.75 GHz) at 20 dB down, even with 40 Gbit/s modulation.

A novel multilevel coherent optical system: 4-quadrature signaling

A novel multilevel coherent optical system is proposed. It is based on the exploitation of the property that the electromagnetic field propagating in a single-mode optical fiber can be represented by a four-dimensional vector whose components are the phase and quadrature terms of the two polarization components of the electrical field. This allows a wider use of the resources of the electromagnetic field for information transmission in order to obtain a spectrally efficient modulation format with a limited end. The net performance gain with respect to multilevel amplitude and phase modulation (N-APK) and N-PSK increases with an increase in the number of levels N. For instance, for N=32 the gain is 1.6 and 7.7 dB with respect to N-APK and N-PSK systems. The effect of laser phase noise on the system performance is evaluated.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Optimization of Trellis Codes with Multilevel Amplitude Modulation with Respect to an Error Probability Criterion

An easily computed upper bound on the error probability of a data communications system with combined trellis coding and multilevel/phase modulation is derived, assuming an additive white Gaussian noise channel and maximum-likelihood decoding. This bound is used to search for codes obtained by set-partitioning that minimize the bound for a fixed number of trellis states. Only amplitude modulated signals typically used in voiceband modem applications are considered. The signal levels that minimize the error probability bound subject to an average power constraint are presented for some specific codes.

Improved Sequential Signaling and Decision Techniques for Nonbinary Block Codes

A situation is postulated whereby the goal is to maximize the average number of bits per second reliably communicated by nonbinary block codes over a channel whose conditions are slowly varying in a largely unpredictable fashion. A feedback channel limited to block retransmission requests is assumed. It is demonstrated that repetition usually is not the best signaling technique for sequential decision making under the postulated situation. Examples of improved sequential signaling techniques are given for multilevel amplitude modulation and multiple phase modulation.