We demonstrate the coherent detection of 10 Gb/s return-to-zero (RZ) binary phase-shift keying (BPSK) signal based on a homodyne Costas optical phase-locked loop (OPLL). It demonstrates time misalignment tolerance of +/- 10% of the transmitted RZ-BPSK signal, i.e. -20 to +20 ps between the pulse carver and the phase modulator for 5 Gb/s RZ-BPSK signal, -10 to +10 ps or 10 Gb/s RZ-BPSK signal. Besides, the Costas coherent receiver shows a 2.5 dB sensitivity improvement over conventional 5 Gb/s NRZ-BPSK and a 1.4 dB over 10 Gb/s NRZ-BPSK only at the cost of slightly higher residual phase error. Those merits of sufficient tolerance to misalignment, higher receiver sensitivity, and low residual phase error of RZ-BPSK modulation are beneficial to be applied in free space optical (FSO) communication to achieve higher link budget, longer transmission distance.
We propose a time delay fluctuation measurement method with high precision and wide range. The round-trip time delay fluctuation of a 40 km optical fiber link from the phase of a transmitted 20.02 GHz signal is transferred into the one of an intermediate frequency by using dual heterodyne phase error transfer. It allows a precise measurement of the time delay fluctuation by measuring the phase of the RF signal. Frequency division of the intermediate frequency is applied to realize the wide range of delay fluctuation measurement. The resolution of the measurement can be reached at 27 fs and the range can be 6.25 ns.
We design and experimentally demonstrate a highly efficient coherence transfer based on composite optical phaselocked loop comprising multiple feedback servo loops. The heterodyne offset-locking is achieved by conducting an acousto-optic frequency shifter in combination with the current tuning and the temperature controlling of the semiconductor laser. The adaptation of the composite optical phase-locked loop enables the tight coherence transfer from a frequency comb to a semiconductor laser in a fully dynamic manner.
Phase error compensation is necessity for high resolution optical frequency modulated continuous wave (OFMCW). In the phase error compensation of OFMCW, the precise measurement of laser source phase is the most significant. In this paper, we proposed a phase-smooth unwrapping algorithm to settle the issue of phase leap over 2π, thus could restore precisely the real phase of laser source, then could compensated the phase error in OFMCW. With that method, OFMCW's resolution could be promoted to 0.5 mm at over 200 m.
Optical frequency domain reflectometry is a suitable and promising measurement technique for optical network components characterization; however its performance is severely limited by sweep nonlinearity of the laser chirp. We demonstrate precise linearization of broadband optical frequency chirp using optoelectronic feedback loop. The sweep rate and the laser chirp shape is locked to and determined by the frequency of a reference electronic signal, an agile, high coherence swept-frequency semiconductor laser source with a bandwidth of 66GHz in 100ms is achieved. The laser source is applied to a coherent optical frequency domain reflectometry; a transform-limited spatial resolution of 1.5mm at a distance of 200 meters is demonstrated.
We proposed and experimentally demonstrated a delay-match sampling method to measure and compensate the laser phase error in optical frequency-domain reflectometry system. By using the error signal extracted from a simple auxiliary Mach-Zehnder interferometer with only a 10-ns delay, the laser phase error is effectively compensated. Considerable improvement is achieved in spatial resolution from 200 m to 7 cm at a measurement distance over 10 times the round-trip laser coherence length.
KEYWORDS: Signal generators, Phase modulation, Frequency combs, Extremely high frequency, Radio optics, Microwave radiation, Modulation, Linear filtering, Modulators, Continuous wave operation
We demonstrated a photonic approach to generate a phase-continuous frequency-linear-chirped millimeter-wave (mm-wave) signal with high linearity based on continuous-wave phase modulated optical frequency comb and cascaded interleavers. Through linearly sweeping the frequency of the radio frequency (RF) driving signal, high-order frequency-linear-chirped optical comb lines are generated and then extracted by the cascaded interleavers. By beating the filtered high-order comb lines, center frequency and chirp range multiplied linear-chirp microwave signals are generated. Frequency doubled and quadrupled linear-chirp mm-wave signals of range 48.6 to 52.6 GHz and 97.2 to 105.2 GHz at chirp rates of 133.33 and 266.67 GHz/s are demonstrated with the ±1 st and ±2 nd optical comb lines, respectively, while the RF driving signal is of chirp range 24.3 to 26.3 GHz and chirp time 30 ms.
We propose a novel scheme to realize unicast and multicast in WDM-PON. Unicast data and multicast data are
modulated in Amplitude Shift Keying (ASK) format and Differential Phase Shift Keying (DPSK) format respectively.
Reflective Semiconductor Optical Amplifier (RSOA) is used to selectively erase the DPSK signal by controlling the
optical switch, and multicast is realized.
In this work, we use a low-pass filter in the burst-mode receiver between PIN+TIA and LA to optimize the receive bandwidth, and finally to improve the receiver performance of uncooled Reflective-SOA-based WDM-PON significantly. In addition, an extra power budget is earned for further development.
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