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.

Proof of concept for ultrahigh resolution photonic spectral processor.

We propose a novel photonic spectral processor which overcomes current 0.8GHz spectral resolution limitation. The new spectral processor uses a Fabry Perot interferometer array located before the dispersive element of the system, thus significantly improving the spectral separation resolution, which is now limited by the Fabry Perot interferometers' full width at half maximum rather than the dispersive element's spectral resolution. A proof of concept experiment was performed utilizing two Fabry-Perot interferometers and a diffractive optical grating with a spectral resolution of 6.45GHz, achieving high spectral resolution of 577MHz. Further improvement of the experimental setup can result in resolution of about 50MHz.

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.

Analysis of photonic noise generated due to Kerr nonlinearity in silicon ring resonators.

The Kerr effect in silicon ring resonators (RRs) is widely used for switching and regeneration of optical communications signals. In addition, it has been shown to considerably limit the performance of refractive index sensors based on high quality-factor RRs. While the Kerr effect's impact on output signals of silicon RRs is well known, its influence on the properties of the output noise is yet to be explored. In this work, we analytically and numerically analyze the noise properties of Kerr effect in silicon RRs. We show that the input power, RR's bandwidth, and input optical signal to noise ratio (OSNR) have significant influence on the power and distribution of the output noise. We use the developed noise model to evaluate the RR's noise figure and output noise distribution for optical communications and sensing applications. These noise properties can be used for the design and performance evaluation of optical communications systems and sensors using silicon photonic RRs.

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.

Noninvasive blood potassium measurement using signal-processed, single-lead ecg acquired from a handheld smartphone.

OBJECTIVE: We have previously used a 12-lead, signal-processed ECG to calculate blood potassium levels. We now assess the feasibility of doing so with a smartphone-enabled single lead, to permit remote monitoring. PATIENTS AND METHODS: Twenty-one hemodialysis patients held a smartphone equipped with inexpensive FDA-approved electrodes for three 2min intervals during hemodialysis. Individualized potassium estimation models were generated for each patient. ECG-calculated potassium values were compared to blood potassium results at subsequent visits to evaluate the accuracy of the potassium estimation models. RESULTS: The mean absolute error between the estimated potassium and blood potassium 0.38±0.32 mEq/L (9% of average potassium level) decreasing to 0.6 mEq/L using predictors of poor signal. CONCLUSIONS: A single-lead ECG acquired using electrodes attached to a smartphone device can be processed to calculate the serum potassium with an error of 9% in patients undergoing hemodialysis. SUMMARY: A single-lead ECG acquired using electrodes attached to a smartphone can be processed to calculate the serum potassium in patients undergoing hemodialysis remotely.

Novel Bloodless Potassium Determination Using a Signal-Processed Single-Lead ECG.

BACKGROUND: Hyper- and hypokalemia are clinically silent, common in patients with renal or cardiac disease, and are life threatening. A noninvasive, unobtrusive, blood-free method for tracking potassium would be an important clinical advance. METHODS AND RESULTS: Two groups of hemodialysis patients (development group, n=26; validation group, n=19) underwent high-resolution digital ECG recordings and had 2 to 3 blood tests during dialysis. Using advanced signal processing, we developed a personalized regression model for each patient to noninvasively calculate potassium values during the second and third dialysis sessions using only the processed single-channel ECG. In addition, by analyzing the entire development group's first-visit data, we created a global model for all patients that was validated against subsequent sessions in the development group and in a separate validation group. This global model sought to predict potassium, based on the T wave characteristics, with no blood tests required. For the personalized model, we successfully calculated potassium values with an absolute error of 0.36±0.34 mmol/L (or 10% of the measured blood potassium). For the global model, potassium prediction was also accurate, with an absolute error of 0.44±0.47 mmol/L for the training group (or 11% of the measured blood potassium) and 0.5±0.42 for the validation set (or 12% of the measured blood potassium). CONCLUSIONS: The signal-processed ECG derived from a single lead can be used to calculate potassium values with clinically meaningful resolution using a strategy that requires no blood tests. This enables a cost-effective, noninvasive, unobtrusive strategy for potassium assessment that can be used during remote monitoring.

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.

Single channel 112Gbit/sec PAM4 at 56Gbaud with digital signal processing for data centers applications.

112Gbit/sec DSP-based single channel transmission of PAM4 at 56Gbaud over 15GHz of effective analog bandwidth is experimentally demonstrated. The DSP enables use of mature 25G optoelectronics for 2-10km datacenter intra-connections, and 8Tbit/sec over 80km interconnections between data centers.

Noninvasive potassium determination using a mathematically processed ECG: proof of concept for a novel "blood-less, blood test".

OBJECTIVE: To determine if ECG repolarization measures can be used to detect small changes in serum potassium levels in hemodialysis patients. PATIENTS AND METHODS: Signal-averaged ECGs were obtained from standard ECG leads in 12 patients before, during, and after dialysis. Based on physiological considerations, five repolarization-related ECG measures were chosen and automatically extracted for analysis: the slope of the T wave downstroke (T right slope), the amplitude of the T wave (T amplitude), the center of gravity (COG) of the T wave (T COG), the ratio of the amplitude of the T wave to amplitude of the R wave (T/R amplitude), and the center of gravity of the last 25% of the area under the T wave curve (T4 COG) (Fig. 1). RESULTS: The correlations with potassium were statistically significant for T right slope (P<0.0001), T COG (P=0.007), T amplitude (P=0.0006) and T/R amplitude (P=0.03), but not T4 COG (P=0.13). Potassium changes as small as 0.2mmol/L were detectable. CONCLUSION: Small changes in blood potassium concentrations, within the normal range, resulted in quantifiable changes in the processed, signal-averaged ECG. This indicates that non-invasive, ECG-based potassium measurement is feasible and suggests that continuous or remote monitoring systems could be developed to detect early potassium deviations among high-risk patients, such as those with cardiovascular and renal diseases. The results of this feasibility study will need to be further confirmed in a larger cohort of patients.

Blind channel estimation for MLSE receiver in high speed optical communications: theory and ASIC implementation.

Blind channel estimation is critical for digital signal processing (DSP) compensation of optical fiber communications links. The overall channel consists of deterministic distortions such as chromatic dispersion, as well as random and time varying distortions including polarization mode dispersion and timing jitter. It is critical to obtain robust acquisition and tracking methods for estimating these distortions effects, which, in turn, can be compensated by means of DSP such as Maximum Likelihood Sequence Estimation (MLSE). Here, a novel blind estimation algorithm is developed, accompanied by inclusive mathematical modeling, and followed by extensive set of real time experiments that verify quantitatively its performance and convergence. The developed blind channel estimation is used as the basis of an MLSE receiver. The entire scheme is fully implemented in a 65 nm CMOS Application Specific Integrated Circuit (ASIC). Experimental measurements and results are presented, including Bit Error Rate (BER) measurements, which demonstrate the successful data recovery by the MLSE ASIC under various channel conditions and distances.

Spectral and temporal stealthy fiber-optic communication using sampling and phase encoding.

We propose a method for covert fiber-optic communication in both frequency and time domains. The power spectral density of the pulse sequence bearing the information is spread in the frequency domain below the noise level by means of sampling. In addition, temporal phase encryption prevents the coherent addition of the various pulses in the frequency domain, further reducing the signal power spectral density. Thus, there is no need to transmit the signal within the bandwidth of a public user in order to spectrally conceal the signal. Temporal spreading of the pulse sequence is achieved by spectral phase encoding, resulting in a stealthy temporal and spectral transmission.