Laser linewidth characterization via self-homodyne measurement under nearly-coherent conditions.

In this work we propose a novel and efficient characterization scheme for a narrow linewidth laser using a nearly-coherent delayed self-homodyne (NC-DSH) technique. The modulated signal of an analog coherent optics (ACO) transceiver, configured in optical loop-back, and the local oscillator (LO) are mixed after a very short optical path difference (OPD), corresponding to an interferometer operating in its nearly-coherent regime. The phase noise is extracted from a digital signal processing algorithm of carrier phase estimation (CPE), while data is transmitted. The interferometric pattern's E-field power spectral density (PSD) enables the extraction of the OPD and the linewidth of the transceiver's laser source in high accuracy. The proposed technique is demonstrated using a commercial integrated coherent transmitter and receiver optical sub-assembly (IC-TROSA).

Stealth and secured optical coherent transmission using a gain switched frequency comb and multi-homodyne coherent detection.

A novel all-optical stealth and secured transmission is proposed and demonstrated. Spectral replicas of the covert signal are carried by multiple tones of a gain switched optical frequency comb, optically coded with spectral phase mask, and concealed below EDFA's noise. The secured signal's spectrum is spread far beyond the bandwidth of a coherent receiver, thus forcing real time all-optical processing. An unauthorized user, who does not possess knowledge on the phase mask, can only obtain a noisy and distorted signal, that cannot be improved by post-processing. On the other hand, the authorized user decodes the signal using an inverse spectral phase mask and achieves a substantial optical processing gain via multi-homodyne coherent detection. A transmission of 20 Gbps under negative -7.5 dB OSNR is demonstrated here, yielding error-free detection by the eligible user.

Demonstration of coherent stealthy and encrypted transmission for data center interconnection.

We show in an experiment a covert transmission of QPSK and 64-QAM over up to 100km of SSMF, digitally encrypted with spectral phase mask, buried under ASE noise with negative -15 dB/0.1nm OSNR. We record a post-FEC error free BER for a stealthy channel, at 16 Gbps on a single polarization.

Photonic-layer encryption and steganography over IM/DD communication system.

We demonstrate a novel low-cost photonic-layer secured communication system that incorporates intensity modulation direct detection (IM/DD) scheme with a 4-level pulse amplitude modulation (PAM-4). In the proposed system, the signal is buried under an amplifier's spontaneous emission (ASE) noise and coded with a spectral phase mask. As a result, the signal is stealthy and encrypted in both frequency and time domains. We analyze the reception performance of the secured signal under direct detection, and analytically compare its SNR with a conventional PAM-4 system, demonstrating that only an eligible receiver achieves a decryption of the stealthy and encrypted signal. Furthermore, we experimentally validate these findings showing a significant processing gain, which allows an error-free reception, despite a negative optical-SNR.

Novel low resolution ADC-DSP optimization based on non-uniform quantization and MLSE for data centers interconnects.

A new generation of combined ADC-DSP scheme is proposed. It is based on a novel non-uniform quantization method, optimized for MLSE based receivers. This inclusive optimization enables the use of extremely low-resolution analog-to-digital-converters devices, which form a major bottleneck in high speed optical communications receivers' architecture. Through Monte-simulation it is demonstrated that the proposed method leads to a significant SNR gain over conventional designs, and may provide low cost and low power consumption digital implementation solution for datacenter interconnects.