A synchronization scheme for extraction of low-jitter rf signals from optical pulse trains, which is robust against photodetector nonlinearities, is described. The scheme is based on a transfer of timing information into an intensity imbalance of the two output beams from a Sagnac loop. Sub-100-fs timing jitter between the extracted 2-GHz rf signal and the 100-MHz optical pulse train from a mode-locked Ti:sapphire laser is demonstrated.
Progress in developing high speedAnalog-to-Digital Converters (ADCs) occurs rather slowly due to the inherent jitter in electronic sampling and the difficulty in integrating low noise microwave sources. Currently, this electronic jitter is on the order of 100 femtoseconds in the most advanced CMOS circuitry. Advances in femtosecond lasers and laser stabilization have led to the development of sources of ultrafast optical pulse trains that show timing jitter on the level of a few femtoseconds over the time spans of typical sampling windows and can be made even smaller in the future. This paper reviews the progress made towards low noise femtosecond lasers, its jitter characterization, and its application in high-speed, high-resolution analog-to-digital conversion. Index Terms – Ultrafast optics, timing jitter in mode-locked lasers, photonic analog-to-digital conversion, femtosecond lasers
The ability to generate lower-noise microwaves has greatly advanced high-speed, high-precision scientific and engineering fields. Microcombs have high potential for generating such low-noise microwaves from chip-scale devices. To realize an ultralow-noise performance over a wider Fourier frequency range and longer time scale, which is required for many high-precision applications, free-running microcombs must be locked to more stable reference sources. However, ultrastable reference sources, particularly optical cavity-based methods, are generally bulky, alignment-sensitive and expensive, and therefore forfeit the benefits of using chip-scale microcombs. Here, we realize compact and low-phase-noise microwave and soliton pulse generation by combining a silica-microcomb (with few-mm diameter) with a fibre-photonic-based timing reference (with few-cm diameter). An ultrastable 22-GHz microwave is generated with -110 dBc/Hz (-88 dBc/Hz) phase noise at 1-kHz (100-Hz) Fourier frequency and 10-13-level frequency instability within 1-s. This work shows the potential of fully packaged, palm-sized or smaller systems for generating both ultrastable soliton pulse trains and microwaves, thereby facilitating a wide range of field applications involving ultrahigh-stability microcombs.
This article presents a 7-bit stochastic time-to-digital converter (STDC) with dual time offset arbiters that enables linearity calibration. The dual time offset arbiter with 1-bit mode selection effectively doubles time offsets available for time-to-digital conversion with minimal increase in hardware complexity. A genetic algorithm (GA)-based linearity calibration efficiently searches a huge search space to find the optimal time offset mode selection setting and a set of arbiters that lead to minimal integrated nonlinearity (INL). The combination of dual time offset arbiters and GA-based linearity calibration enables the proposed STDC to achieve ultrafine time resolution and a good linearity simultaneously. The proposed STDC also guarantees robust performance against on-die variation and gains good scalability with process technology as the linearity calibration is performed purely in the digital domain. A test chip prototype fabricated in a 65-nm CMOS technology demonstrates 360-fs time resolution with 0.75-LSB INL at 100 MS/s. The prototype achieves the effective time resolution of 630 fs, which is 1.5 times improvement compared with the prior arts.
I introduce recent progress in ultra-low-noise and robust femtosecond mode-locked fiber lasers and their emerging applications in low-noise optical and microwave signal synthesis, timing and synchronization, stable RF phase transfer, and TOF-based sensing and imaging.
SMPS losses consist of switching loss, conduction loss, and core loss. In case of light load the switching loss takes the most things in SMPS. Conventional burst mode operation meets the requirement of low power consumption. But, it is not sufficient for low frequency switching at no-load condition to provide the source of IC's bias. High frequency switching increases switching loss of SMPS. Moreover recently lower stand-by power, the input power of about 0.09 mW at the no-load condition, is required. This paper presents that during the burst mode decreasing IC's consumption power at the internal block makes system high efficient and prevents malfunction at the minimum load.
During liver transplantation, the thermodilution cardiac output (CO) technique cannot respond to sudden hemodynamic changes associated with postreperfusion syndrome. Photoplethysmography (PPG) can reflect changes in intravascular volume and thus can be used to assess vasomotor tone and arterial stiffness on the pressure-volume relation. We investigated whether a beat-to-beat analysis of the arterial pressure-PPG relationship can estimate dynamic changes in vascular characteristics immediately after liver graft reperfusion.In 10 recipients, arterial blood pressure and PPG waveforms recorded simultaneously were analyzed from the beginning of fall to nadir in systolic blood pressure immediately after reperfusion. On a beat-to-beat basis, we compared the ratio of the amplitude of PPG to arterial pulse pressure (PPGamp/PP, as relative vascular compliance) to total peripheral resistance (TPR) and Windkessel compliance (Cwk) obtained from the Modelflow CO algorithm.Following graft reperfusion, PPGamp/PP and Cwk increased (median 41.5%; P = .005 and 42.0%; P < .001, respectively), whereas TPR decreased (median -46.4%; P < .001). Beat-to-beat PPGamp/PP was negatively correlated with TPR (median r = -0.80 [95% CI -0.85 to -0.76] on linear regression and r = 0.84 [95% CI 0.73-0.92] on curvilinear regression), and was positively correlated with Cwk (median r = 0.86 [95% CI 0.81-0.91] on linear regression and r = 0.88 [95% CI 0.75-0.96] on curvilinear regression).Our results suggest that relative compliance, obtained from beat-to-beat analysis of PPG and arterial pressure waveforms, can track abrupt changes in vascular characteristics associated with postreperfusion syndrome. This simple index would contribute to differential diagnoses of sudden hypotension.
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