Quadrature Phase Shift Keying Signals Research Articles

Efficient Direct Detection of Twin Single-Sideband Quadrature-Phase Shift Keying Using a Single Detector with Hierarchical Blind-Phase Search

We propose a novel reception scheme for twin single-sideband (twin-SSB) signals using just a single photodetector (PD), significantly reducing the system complexity and cost. To detect a twin-SSB with power-unbalanced quadrature-phase shift keying (QPSK) sidebands upon detection via a single PD at the receiver side, two QPSKs carried in two sidebands are coherently superposed and detected in a 16-ary quadrature amplitude modulation (16-QAM) format. This technique notably diminishes the linearity and effective number of bits required for the transmitter components in high-speed optical transmission systems. Moreover, a hierarchical blind-phase search (HBPS) algorithm is proposed to compensate for the imperfect phase rotation of QPSK signals during transmission. To demonstrate the effectiveness of our proposed method, we successfully conducted simulations of 112 Gb/s 16-QAM signal transmission over a 10 km standard single-mode fiber (SSMF), achieving bit error ratios (BERs) of 7.84×10−4, well below the 7% hard-decision forward error correction (HD-FEC) threshold of 3.8×10−3. In addition, the synthetic transmission scheme proposed in this paper is compared with the traditional 16-QAM signal transmission scheme, and the results show that the proposed scheme does not introduce a performance cost with the same received optical power (ROP) and transmission distance.

All-optical matching systems based on the squarer for QPSK and 8PSK optical signals

Photonic firewall which can conduct the data identification and intrusion detection directly at the optical layer is a high-speed and low-energy network security equipment. For the photonic firewall, the all-optical matching system is the core part. This paper focuses on designing all-optical matching systems for high-order phase modulated optical signals. Based on the squarer, two all-optical matching systems are designed for Quadrature Phase Shift Keying (QPSK) and 8 Phase Shift Keying (8PSK) optical signals respectively. The systems mainly consist of squarers, multiplexers, AND gates and regenerators. The squarer is implemented based on the four-wave mixing (FWM) effect of highly nonlinear fiber (HNLF). The theoretical analysis and simulation verification are conducted for the proposed system. The performances of feasibility and noise impact are evaluated for the proposed system with the data rate of 100 Gbaud. The results show that the system can correctly identify and localize the target sequence with the length of 4 and 8 symbols in the data sequence with the length of 16 symbols. The impact of noise is evaluated by the extinction ratio (ER) and contrast ratio (CR). The ER of two all-optical matching systems reaches 0 dB when the optical signal-to-noise ratio (OSNR) of input optical signal is about 5.59 dB and 9.24 dB respectively. The CR of two all-optical matching systems reaches 0 dB when the OSNR of input optical signal is about 4 dB and 8.62 dB respectively.

SC and OFDM hybrid coherent optical transmission scheme based on 1-bit bandpass delta-sigma modulation.

High-order quadrature amplitude modulation (QAM) can effectively improve the capacity and spectral efficiency of coherent optical transmission systems. However, as the modulation order increases, the signal becomes less tolerant to noise and nonlinear effects during transmission, and the implementation cost also increases. We propose a single carrier (SC) and orthogonal frequency division multiplexing (OFDM) hybrid coherent optical transmission scheme based on a 1-bit bandpass (BP) delta-sigma modulation (DSM). The driving I-channel and Q-channel signals for the optical in-phase/quadrature (I/Q) modulator carry SC-modulated and OFDM-modulated transmitter data, respectively. Optical quadrature-phase-shift-keying (QPSK) modulation is realized by the 1-bit DSM quantizer and I/Q modulator, which can effectively suppress quantization noise and reduce the complexity of digital signal processing (DSP) and the performance requirements of optoelectronic devices. In addition, the hybrid transmission of SC and OFDM can balance the advantages of both to meet the variable channel conditions and complex application scenarios. High-fidelity transmission of SC 512QAM and OFDM 512QAM hybrid signals, in the form of a 60 Gbaud optical QPSK signal, over 60 km single-mode fiber-28 (SMF-28) is verified by offline experiments, and the bit error rates (BERs) of both SC 512QAM and OFDM 512QAM are below the hard-decision forward-error correction (HD-FEC) threshold of 3.8e-3.

All-Optical format conversion from PAM4 to QPSK based on non-degenerate Phase-Sensitive amplification and pump assisted nonlinear optical loop mirror

An all-optical format conversion (AOFC) scheme from 4-ary pulse amplitude modulation (PAM4) to quadrature phase shift keying (QPSK) based on the non-degenerate phase-sensitive amplification (PSA) and the pump assisted nonlinear optical loop mirror (PA-NOLM) is proposed and numerically simulated for the first time. The input unipolar PAM4 signal with equal amplitude distance (UPAM4-A) is coupled with two input pump lights and injected into the symmetric interferometric fiber optic parameter amplifier (FOPA) to achieve the separation of the UPAM4-A and the new pump light generated at the signal frequency based on the non-degenerate PSA. When the filtered out UPAM4-A is coherent added with the new generated pump, the UPAM4-A signal to the biplolar PAM4 (BPAM4) signal. When the converted BPAM4 is sent into the PA-NOLM after adjusting its power, the BPAM4 signal could be converted into the QPSK signal. The error vector magnitude (EVM) and bit error ratio (BER) performance of the system are measured before and after AOFC with different input and receiver optical signal to noise ratio (OSNR). For the input UPAM4-A signal with an input OSNR of 27 dB, there is about 8.2 dB BER performance improvement in receiver OSNR for the final converted QPSK signal. Additionally, the proposed non-degenerate PSA configuration can be extended to realize the AOFC from one QPSK to two on–off keying (OOK) signals. The scheme can be applied in the optical gateway connecting the long-haul and the short-reach optical networks with suitable modulation formats.

Dual vector millimeter-wave signal generation based on optical carrier suppression modulation and direct detection with one photodetector.

We propose a novel, to the best of our knowledge, scheme for dual vector millimeter-wave (mm-wave) signal generation and transmission, based on optical carrier suppression (OCS) modulation, precoding, and direct detection by a single-ended photodiode (PD). At the transmitter side, two independent vector radio frequency (RF) signals with precoding, generated via digital signal processing (DSP), are used to drive an in-phase/quadrature (I/Q) modulator operating at the optical OCS modulation mode to simultaneously generate two independent frequency-doubling optical vector mm-wave signals, which can reduce the bandwidth requirement of transmitter's components and enhance spectral efficiency. With the aid of the single-ended PD and subsequent DSP at the receiver side, two independent frequency-doubling vector mm-wave signals can be separated and demodulated without data error. Based on our proposed scheme, we experimentally demonstrate the generation, transmission, and detection of 2-Gbaud 30-GHz quadrature-phase-shift-keying (QPSK) and 2-Gbaud 46-GHz QPSK signals over 10-km single-mode fiber-28 (SMF-28) and 1-m wireless transmission. The results indicate that the bit-error ratio (BER) of the dual vector mm-wave signals can each reach the hard-decision forward-error-correction (HD-FEC) threshold of 3.8 × 10-3.

Reconfigurable all-optical pattern-matching system for phase modulation formats based on phase-sensitive amplification in highly nonlinear fiber

All-optical pattern-matching system is to compare the input data with the target sequence to implement the data filtering directly in the optical layer. However, for current all-optical pattern-matching systems, one pattern-matching system can only match one modulation format, which limits its application. In this paper, a reconfigurable all-optical pattern-matching system for phase modulation formats is proposed. Taking advantage of phase-sensitive amplification (PSA) in highly nonlinear fiber (HNLF), the system can match various phase modulation formats through optical switches configured by a controller. We first evaluate the feasibility of the proposed system for binary phase-shift keying (BPSK) and quadrature phase-shift keying (QPSK) modulation formats with the transmission rates of 100 Gbaud and 200 Gbaud. The results show that our proposed system can correctly recognize and locate the position of the target sequence. Next, we analyze the extinction ratio (ER), contrast ratio (CR), Q factor, and bit error rate (BER) by changing the optical signal-to-noise ratio (OSNR) values of BPSK and QPSK signals to evaluate the noise performance. The proposed reconfigurable all-optical pattern-matching system provides an effective method to recognize signals with different phase modulation formats, which is suitable for future dynamically reconfigurable optical networks.

Optical channel aggregation based on modulation format conversion by coherent spectral superposition with electro-optic modulators

Spectrally efficient modulation formats become essential for optical network scaling as the demand for routed data streams exceeds the present wavelength-division multiplexing systems’ throughput. However, achieving high spectral efficiency at high data rates requires complex and bandwidth-intensive electronics. In this study, we propose an all-optical aggregation scheme that combines multiple low spectral efficiency optical wavelength channels from an optical frequency comb based transmitter into fewer channels with higher spectral efficiency. Our method utilizes coherent spectral superposition and optical vector summation, eliminating the need for optical nonlinearities and relying on linear signal processing with an electro-optic modulator. By adjusting the phase of the radio frequency signal driving the modulator, we can easily achieve the required optical phase tuning for vector addition in the I-Q plane. Through experimental demonstrations, we show that the proposed approach enables the generation of 10 GBd PAM-4 and 10 GBd quadrature phase shift keying (QPSK) signals by aggregating two 10 GBd binary phase shift keying signals. Similarly, we aggregate two 10 GBd QPSK signals into one 10 GBd quadrature amplitude modulation-16 (QAM-16) signal. The experiments employ both conventional and sinc-shaped Nyquist signals. Our in-line, all-optical aggregation concept significantly enhances operational capacity while reducing complexity. It offers a promising solution for realizing flexible integrated optical transmitters for advanced modulation format signals using lower-quality electronics. Additionally, it aligns with the requirements of future dynamically reconfigurable optical networks that leverage spectral traffic aggregation. Given its reliance on linear signal processing with an electro-optic modulator, the integration of the method into any integrated photonic platform is straightforward.

Reconfigurable all-optical format conversion for 16QAM/8QAM by employing PSA in HNLF.

Extensive investigations are undertaken on the feasibility of utilizing phase sensitive amplification (PSA) in highly nonlinear fiber (HNLF) to achieve a reconfigurable 16QAM/8QAM all-optical format conversion for optical data center networks. A comprehensive theoretical model is developed and subsequently verified, based on numerical simulations undertaken to explore the effectiveness of the nonlinear effects of phase insensitive amplification, PSA, and self phase modulation for the proposed all-optical format conversion scheme. It is demonstrated that the proposed scheme can achieve a reconfigurable all-optical format conversion from a 16QAM signal to two quadrature phase shift keying (QPSK) signals or from an 8QAM signal to one QPSK signal and one binary phase shift keying signal with data rates of 92Gbps and 69Gbps for 16QAM and 8QAM signals, respectively.

Mode add-drop technology based on few-mode fiber Bragg gratings.

By increasing the number of modes of transmission in optical fiber, the mode-division multiplexing (MDM) technology can effectively improve the transmission capacity. The mode add-drop technology is an important part of the MDM system and a key element for realizing flexible networking. In this paper, a mode add-drop technology based on few-mode fiber Bragg grating (FM-FBG) is reported for the first time. The technology utilizes the reflection characteristics of Bragg grating to realize the add-drop function in the MDM system. The grating is written in parallel according to the optical field distribution characteristics of different modes. By changing the writing grating spacing Δa to match the optical field energy distribution of the few-mode fiber, the few-mode fiber grating with high self-coupling reflectivity for the high-order mode is fabricated, and the performance of the add-drop technology is improved. The mode add-drop technology is verified in a 3 x 3 MDM system, which uses quadrature phase shift keying (QPSK) modulation and coherence detection. The experimental results show that the excellent transmission, add, and drop of 3 x 8 Gbit/s QPSK signals in 8 km few-mode fibers are achieved. The realization of this mode add-drop technology only requires Bragg gratings, few-mode fiber circulators, and optical couplers. It has the advantages of high performance, simple structure, low cost, and easy implementation, and it can be widely used in the MDM system.

All-optical aggregation and de-aggregation between OOK, QPSK and 8QAM signals based on nonlinear effects

An all-optical aggregation and de-aggregation scheme between on–off keying (OOK) signals, quadrature phase shift keying (QPSK) signals and 8-ary quadrature amplitude modulation (8QAM) signals is proposed and numerically simulated based on nonlinear effects in the high nonlinear fiber (HNLF). In the de-aggregation processing, the input 30 Gbit/s 8QAM signal is firstly de-aggregated into one 20 Gbit/s QPSK signal and one 10 Gbit/s binary phase shift keying (BPSK) signal by deploying self-phase modulation (SPM), cross-phase modulation (XPM), four-wave mixing (FWM) and parameter amplification (PA) effects. One continuous optical carrier can be extracted from the converted BPSK signal by designing a feed-forward based modulation stripping configuration. The converted OOK signal can be obtained through vector superposition between the extracted optical carrier and the converted BPSK signal. In the aggregation processing, the converted 20 Gbit/s QPSK signal and the 10 Gbit/s OOK signal are fed to another HNLF and aggregated into one 30 Gbit/s 8QAM signal again by utilizing XPM and PA effects. Moreover, the aggregated 8QAM signal keeps the same wavelength and information integrity as the input 8QAM signal. the Error vector magnitude (EVM) and the bit error ratio (BER) for the 8QAM signal before and after aggregation and de-aggregation are measured to evaluate the scheme performance. The proposed all-optical aggregation and de-aggregation scheme for the advanced and simple modulation formats can be applied at the intermediate network node (INN) to solve the network traffic aggregation and de-aggregation with different modulation formats.

All-Optical Regeneration and Format Conversion for 4APSK Signals Based on Nonlinear Effects in HNLF

An all-optical format conversion and regeneration scheme about 4-ary amplitude and phase shift keying (4APSK) signals is proposed and numerically simulated based on nonlinear effects in the high nonlinear fiber (HNLF). The input 4APSK signal is firstly converted into a regular quadrature phase shift keying (QPSK) signal by the nonlinear Mach-Zehnder interferometer (MZI) based on the self-phase modulation (SPM). Secondly, a degenerate phase-sensitive amplification (PSA) based on the four-wave mixing (FWM) is utilized to convert the regular-QPSK into two binary phase shift keying (BPSK) signals. The nonlinear MZI configuration is also used to compress the amplitude noise of BPSK. Thirdly, one phase shifter and one variable optical attenuator (VOA) are used to adjust the relative phase and power relationships of the two amplitude-regenerated BPSK signals. The regenerated 4APSK and converted QPSK signals can be generated in one 3-dB optical coupler through coherent addition of the two regenerated BPSK signals. The error-vector-magnitude (EVM) and the bit-error-rate (BER) are calculated and compared to evaluate the scheme performance. The proposed scheme can be applied as an optical regenerator or format convertor at the network gateway to increase the transmission distance or connect optical networks with different modulation formats.

All-Optical Format Conversion for Star-8QAM Signals Based on Nonlinear Effects in Elastic Optical Networks

An all-optical format conversion (AOFC) scheme for star-octal quadrature amplitude modulation (star-8QAM) signals is proposed and numerically simulated based on nonlinear effects in the high nonlinear fiber (HNLF). In the first stage AOFC processing, the input 30 Gbit/s star-8QAM signal is firstly de-aggregated into one 20 Gbit/s quadrature phase shift keying (QPSK) signal and one 10 Gbit/s typical on-off keying (OOK) signal by deploying the self-phase modulation (SPM), cross-phase modulation (XPM) and parametric amplification (PA) effects. In the second stage AOFC processing, the 20 Gbit/s QPSK signal and the 10 Gbit/s typical OOK signal are aggregated into one 30 Gbit/s star-8QAM signal again by utilizing the XPM and PA effects. Moreover, the amplitude ratio (AR) between the outer ring and inner rings of the aggregated star-8QAM signal can be adjusted flexibly by changing the QPSK and OOK signals power. Other octal modulation formats can also be generated through changing the QPSK and OOK signals power, including the rectangular 8QAM signals, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\pi$</tex-math></inline-formula> /4-8QAM signals and 8-ary phase shift keying (8PSK) signals. Error vector magnitude (EVM) and bit error ratio (BER) for star-8QAM signals before and after AOFC are measured to analyse the scheme performance. The AOFC scheme provides the flexibility to adopt the appreciate modulation formats at the optical nodes to connect different optical networks.

ОБОБЩЕНИЕ ТЕОРИИ НОВОГО МЕТОДА МОДУЛЯЦИИ И ДЕМОДУЛЯЦИИ СЛУЧАЙНОГО СИГНАЛА

A new method of modulation and demodulation of a quasi-deterministic signal is investigated, which in the future opens up great opportunities for improving the efficiency of digital systems. The method contains new technical solutions for transforming a random signal, including the modulation of the characteristic function and the measurement of estimates of the real and imaginary parts of this function. The purpose of this work is the development of optimal algorithms and generalization of the theory of the new modulation and demodulation method by using new elements (algorithms) when transforming a random signal using the arcsine distribution law. Single-channel and dual-channel modems are considered for operation in a radio channel and in a wired channel respectively. The comparison of characteristics of the modems with optimal and non-optimal modulation algorithms is performed, wherein the characteristics of the first modem turn out to be an order of magnitude better than the second modem. It has been established that the modems have different noise immunity in a channel with «white» noise and in this indicator surpass the known modems by at least ten orders of magnitude. The energy efficiency of the modems is high and exceeds the efficiency of QPSK (Quadrature Phase Shift Keying) signal modems by 10 dB at the error probability level of 1∙10-10.

QPSK to BPSK modulation format conversion byphase-sensitive parametric amplification inmulti-slot waveguides.

The optical modulation conversion of a quadrature phase-shift keying (QPSK) signal to two binary phase-shift keying (BPSK) signals is theoretically realized in a phase-sensitive amplification (PSA) conversion system. We propose a multi-slot silicon-carbon nanotube/polydimethylsiloxane hybrid waveguide to achieve high nonlinearity of 108 W -1 m -1 for improving PSA performance. Constellation diagrams, error vector magnitude, and bit error rate (BER) are used to investigate and measure the performance of the output. The results show that the converted BPSK signal has more than a 10dB higher signal-to-noise ratio than the QPSK signal with a BER threshold of 10-3. Furthermore, the system has great potential for hierarchical modulation of advanced format signals and long-distance transmission.

Broadband dual-channel channelizer based on a microwave photonic power tunable image rejection down-conversion.

Radiofrequency (RF) channelization has potential high frequency and wideband advantages in frequency-domain channel segmentation and down-conversion reception. In this paper, we propose a compact dual-channel channelizer that can process high-frequency wideband signals. It uses double-polarization double-sideband electro-optic modulation and Hartley structure photoelectric conversion to realize down-conversion channelization of the high-frequency wideband signal. The power matching between two polarization signals can be realized by controlling the modulator bias, so the crosstalk between the two output signals can be suppressed. The proposed channelizer has a compact structure since the electro-optic modulation is based on one single laser and one single integrated modulator. No filters are used in the structure, contributing to a very wide RF operation bandwidth and low constraints of laser wavelength. In the experiment, the single frequency signal pairs from 9 GHz to 15 GHz can achieve an inter-channel image rejection ratio of 53 dB. Furthermore, the channelizer slices multi-octave bandwidth quadrature phase shift keying (QPSK) signals up to 16 GHz with the wideband isolation higher than 10 dB and outputs them to two channels in parallel. The error vector magnitudes (EVM) of 9-17 GHz and 18-26 GHz band QPSK signals are guaranteed to be under 23.58% after channelized separation. To the best of our knowledge, the proposed channelizer provides high inter-channel interference suppression at dual-band adjacent signals with 8 GHz bandwidth for the first time. Therefore, the proposed channelizer has great application value for the reception and processing of millimeter signals in the future.

Performance Improvement of the Free-Space Optical Communication Link Using Spatial Diversity Reception-Assisted OFDM Signals

Orthogonal frequency division multiplexing (OFDM) technology is presented for use in free-space optical (FSO) communications accompanied by the spatial diversity reception. Using quadrature phase shift keying (QPSK) modulation formats, the OFDM signals show robustness to support high spectral efficiency and compatibility with the spatial diversity reception to improve receiver sensitivity. Compared with the single-carrier QPSK signal, the OFDM-QPSK signal with 64 sub-carriers can reduce the BER from 2.87 × 10−3 to 2.98 × 10−4 at the SNR of 6 dB. Using a two-aperture spatial diversity reception with OFDM, the BER can be reduced from 2.45 × 10−3 of a single receiver to 6.10 × 10−4 under moderate turbulence conditions. Under strong turbulence, the BER of the single receiver is 2.14 × 10−2. It can be improved to 1.16 × 10−3 by using four-aperture receivers, and even 6.87 × 10−4 by using six-aperture receivers. The optimized aperture number should be selected according to channel conditions.

Experimental demonstration of remotely controlled tunable optical correlators of 10–50 Gbaud QPSK channels using linear and nonlinear components and laser-delivered powers

We experimentally demonstrated two enabling architectures for remotely controlled optical quadrature-phase-shift-keying (QPSK) correlators based on both linear and nonlinear elements. The correlator site was located far from the transmitter site and had no access to the local optical power. In the first demonstration, a remote correlator based on a cascade of Mach–Zehnder interferometers (MZIs) was phase-controlled through optical power sent from the transmitter via an optical fiber link. The issue of power loss because of fiber nonlinearities was further addressed by monitoring and managing the backscattered power. In this manner, the power delivered through the link was boosted by ∼13 dB. Another ∼6 dB gain in the delivered power was obtained by adding a second source of light power. The correlator was shown to be able to identify different target patterns within incoming QPSK signals at different baud rates from 10 to 50 Gbaud. In the second architecture, we experimentally demonstrated a tunable optical correlator for a 10/15-Gbaud QPSK data signal using temperature-controlled nonlinear wave mixing at a remote node. A high-power pump was phase-modulated to overcome the link backscattering effect and was sent along with the signal copies to a remote correlator node through an optical fiber link. The waves generated at the output of the correlator were sent back to the transmitter for the monitoring of the operation. We showed a power boost of more than 3 dB for the correlated signal at a temperature drift of 2 °C. Using remote control and monitoring, improved constellation diagrams with lower error vector magnitudes (EVMs) for a temperature drift range of < 2 °C were obtained.

Optical likelihood calculation for quadrature phase‐shift keying signal based on silicon integrated waveguide

All-optical likelihood calculation has the potential to improve the performance of operating speed and power consumption in future communication systems. The author previously proposed a novel scheme of likelihood calculation, which is capable of applying multi-value modulation. However, these studies have a limitation that requires higher integration into an actual system. In this study, an optical device of likelihood calculation for a 4-bit quadrature phase-shift keying (QPSK) modulated signal (i.e. two sequential QPSK symbols) is demonstrated. The integrated device consists of two delayed interferometers with silicon waveguide. The device is designed according to the types of 4-bit code string as follows (00 00), (00 11), (11 00), and (11 11), and the output light waveform from the device is observed by an oscilloscope for a plurality of 4-bit QPSK signals. The light intensity obtained from the device accurately corresponds to the Hamming distance between the code string and the input signal. The results indicate that the proposed scheme correctly calculates a likelihood for a 4-bit QPSK signal at 10 Gbaud.

Independent dual-single-sideband QPSK signal detection based on a single photodetector.

The two sidebands of the independent dual-single-sideband (dual-SSB) signal can carry different information to achieve higher spectral efficiency. However, the two sidebands of the independent dual-SSB vector signal are received independently. Generally, the receiver divides the signal into two channels. For each channel, we use an optical bandpass filter (OBPF) to select the left sideband (LSB) or right sideband (RSB), respectively. Then a photodetector (PD) is used for photoelectric conversion, followed by subsequent digital signal processing (DSP). To reduce the complexity and cost of the receiver, we propose a new independent dual-SSB vector signal detection scheme based on a single PD combined with conventional DSP. An electric bandpass filter (EBPF) filters out high-frequency components after photoelectric conversion, and then the signal is quadrature demodulated and processed by the DSP algorithm. The LSB and RSB are quadrature phase-shift keying (QPSK) modulated with an initial phase difference of π/4. Simulation results show that the proposed scheme performs better bit error rate (BER). For back-to-back (BTB) transmission, the BER of 2-Gbaud independent dual-SSB vector signal (1-Gbuad RSB and 1-Gbaud LSB) can reach the hard-decision forward error correction (HD-FEC) threshold of 3.8 × 10-3 when the input optical power into PD is -20 dBm. For 1-km and 2-km weak turbulence free-space optical (FSO) channel transmission, the BER of 2-Gbaud independent dual-SSB vector signal can reach the HD-FEC threshold when the input optical power into PD is -18.8 and -17 dBm, respectively. For 1-km weak turbulence FSO channel transmission, the BER of 4-, 8-, and 16-Gbuad independent dual-SSB vector signal can reach the HD-FEC threshold when the input optical power into PD is -17.8, -16, and -15 dBm, respectively.

Chaotic optical communications of 12.5-Gbaud OOK and 10-Gbaud QPSK signals based on mutual injection of semiconductor lasers.

Chaotic optical communications can provide a high level of security in data transmission. High-speed chaotic optical communications have hardly been implemented so far limited by the bandwidth of chaotic signals and the difficulties of wideband chaos synchronization. Here, we experimentally demonstrate all-optical wideband chaos synchronization and communications based on mutual injection of semiconductor lasers. Both 12.5-Gbaud on-off keying (OOK) signals and 10-Gbaud quadrature phase shift keying (QPSK) signals are successfully encrypted and transmitted over a 10-km and 2-km single-mode fiber (SMF), respectively.