Optical Self-interference Cancellation System Research Articles

Optical Analog Noise Encryption With Adaptive Recovery of Two-Dimensional Keys

An optical analog noise encryption system with adaptive recovery of two-dimensional keys is proposed and demonstrated using regular triangle (RT)adaptive algorithm in an optical self-interference cancellation system at the designated receiver. Analog noise encryption and data modulation are performed in a single dual-drive Mach-Zehnder modulator at the transmitter, while decryption is performed in an electro-absorption modulated laser based adaptive cancellation system at the receiver. The weight and delay of the analog noise form the two-dimensional orthogonal encryption keys. Two sets of fingerprints are securely pre-shared for only once between the transmitter and designated receiver and stored before real transmission to ensure that both sides are legitimate users and facilitate adaptive key recovery when using RT adaptive algorithm at the legitimate receiver for retrieving the orthogonal keys. Without receiving the keys from the transmitter, the legitimate receiver is able to adaptively find the two orthogonal keys even under dynamic key changing scenario. In the experiment, a 3.5 GHz wideband analog noise is used to encrypt a 10 Gbps 16 quadrature amplitude modulation (QAM) orthogonal frequency division multiplexing (OFDM) signal at 1.75 GHz. By recovering the orthogonal keys using RT algorithm and the unique pre-shared fingerprints, the designated receiver has successfully decrypted the encrypted signal by removing the analog noise as wide as 3.5 GHz, 28 dB stronger than the sensitive signal, which is by far the best performance in an optical analog noise encryption system.

Real-time IBFD transmission system based on adaptive optical self-interference cancellation using the hybrid criteria regular triangle algorithm.

In this Letter, we first propose and demonstrate a real-time in-band full duplex (IBFD) transmission system based on adaptive optical self-interference cancellation (OSIC). The field programmable gate array (FPGA) is used for high-speed and real-time orthogonal frequency-division multiplexing (OFDM) transmission. The hybrid criteria regular triangle (RT) algorithm is first proposed to combine signal power and the bit error rate (BER) together as the objective function to realize the adaptive control process. With this algorithm, the real-time adaptive OSIC system is able to converge and fully recover the signal of interest (SOI) within 12 sampling times, which is by far the fastest, to the best of our knowledge, convergence under the real-time transmission scenario. Experiments show that the system can achieve 28 dB cancellation depth across 0-1.45 GHz wideband, and 40 dB cancellation depth at 900 MHz, 2.4 GHz, and 5 GHz, which is the best cancellation performance in current real-time adaptive OSIC schemes and shows the potential of our system in different commercial applications.

A switchable self-interference cancellation system for dual-band IBFD system using a monolithic integrated DML array

A dual-band optical self-interference cancellation (OSIC) system is proposed and experimentally demonstrated for in-band full-duplex (IBFD) system using a monolithic integrated multi-channel directly modulated laser (DML) array, tunable optical delay line (TODL) and optical variation attenuator (OVA), and photodetector. The key component of the OSIC system is the integrated DML array which is measured in terms of the spectral characteristic, P–I curve, and small-signal frequency response. The use of the integrated DML array can greatly save the cost as well as reduce the complexity and power consumption of the system. The proposed system is theoretically and experimentally verified. The theoretical analysis shows that the cancellation depth is associated with the attenuation ratio, the time delay and the microwave frequency of the RF signal. Experimentally, the cancellation depth is more than 43 dB in the frequency of 2.4 GHz and 5 GHz. For a broadband RF signal, cancellation depth of 25 dB is achieved with the bandwidth of ∼260 MHz at a center frequency of 2.4 GHz and 5 GHz. In addition, the switchability between double frequencies of the applied microwave signal makes the OSIC system more flexible and fast without adjusting the TODL and OVA, repeatedly

EML-Based Multi-Path Self-Interference Cancellation With Adaptive Frequency-Domain Pre-Equalization

In this letter, for the first time, we propose to employ the adaptive frequency-domain pre-equalization (FDPE) into an electro-absorption modulator laser (EML)-based optical self-interference cancellation (OSIC) system to suppress the time-varying multipath radio frequency (RF) self-interference (SI) signal, which is implemented for in-band full-duplex (IBFD) communication. Faced with time-varying multipath wireless channel, the OSIC system estimates multipath channel response using a least square estimation algorithm, and adjusts the coefficients of frequency-domain pre-equalizer adaptively to combat time-varying multipath SI. Based on the proposed FDPE-aided OSIC, the IBFD transmission of OFDM RF signals with time-varying multipath channel is demonstrated experimentally, achieving 30-dB OSIC depth over 1.22-GHz broad baseband.

Performance analysis of an optical self-interference cancellation system with a directly modulated laser-based demonstration.

In this paper, two main performance indices of the optical self-interference cancellation (OSIC) system are theoretically analyzed: cancellation bandwidth and depth. Delay deviation is investigated to be the determining factor of cancellation bandwidth, based on which the bandwidth advantage of the OSIC system over electrical schemes is also proven theoretically. Cancellation depth in the narrowband is mostly influenced by attenuation and delay-adjusting deviation, while in the broadband case, the performance is mostly limited by frequency-dependent amplitude and phase mismatch. The cancellation performance analysis is suitable for most linear modulation-demodulation OSIC systems, including the directly modulated laser (DML)-based OSIC system verified experimentally in this paper. The cancellation model is well demonstrated by the agreement between experimental cancellation results and predicted performance. For over-the-air demonstration with the employment of antennas, broadband cancellation within 450MHz bandwidth of 22dB and 25dB is achieved at 900MHz and 2.4GHz, respectively. In addition, orthogonal frequency division multiplexing signals are employed to show in-band full-duplex transmission with good performance by the DML-based OSIC system, with successful suppression of self-interference and recovery of the signal of interest.

Wideband Over-the-Air RF Self-Interference Cancellation by an EML-Based Optical System With Baseband Predistortion

In this paper, we propose and experimentally demonstrate an optical self-interference cancellation (OSIC) system with baseband predistortion for wideband over-the-air in-band full-duplex (IBFD) communication. The key factors of OSIC bandwidth limitation are analyzed, and the solution toward it is proposed for the first time. Experimental results show that, by traditional OSIC under over-the-air condition, only narrow even zero band is with enough cancellation depth to satisfy IBFD. But with our proposed baseband predistortion scheme, deep OSIC depth is achieved over the whole 1 GHz/5 GHz baseband within the total 7–25 GHz available band of horn antennas. The employment of baseband predistortion obviously broadens the cancellation bandwidth of an EML-based OSIC system. The largest OSIC bandwidth for over-the-air IBFD communication is demonstrated so far.

Over-the-air in-band full-duplex system with hybrid RF optical and baseband digital self-interference cancellation

In this paper, we propose a hybrid analog optical self-interference cancellation (OSIC) and baseband digital SIC (DSIC) system for over-the-air in-band full-duplex (IBFD) wireless communication. Analog OSIC system is based on optical delay line, electro-absorption modulation lasers (EMLs) and balanced photodetector (BPD), which has the properties of high adjusting precision and broad processing bandwidth. With the help of baseband DSIC, the cancellation depth limitation of OSIC can be mitigated so as to achieve deeper total SIC depth. Experimental results show about 20-dB depth by OSIC and 10-dB more depth by DSIC over 1GHz broad baseband, so that the signal of interest (SOI) overlapped by wideband self-interference (SI) signal is better recovered compared to the IBFD system with OSIC or DSIC only. The hybrid of OSIC and DSIC takes advantages of the merits of optical devices and digital processors to achieve deep cancellation depth over broad bandwidth.