We have proposed and demonstrated the optical time-and-polarization interleaving (OTPI) technique, which can effectively extend the transmitter bandwidth for an intensity modulation and direct detection (IM/DD) optical system. The 224-Gbit/s line-rate OTPI-PAM-4 signal is successfully transmitted over a 500-m standard single-mode fiber (SSMF) in the C band, using the transmitter with a bandwidth of 25 GHz and the receiver with a single photodiode. By using a 33%-return-to-zero (RZ) pulse train, a bit-error ratio (BER) below 7% hard-decision forward error correction (HD-FEC) threshold is achieved. BER below 20% soft-decision forward error correction (SD-FEC) threshold is also realized using a carrier suppressed return-to-zero (CSRZ) pulse train. The OTPI technique can also be used for more higher-order pulse amplitude modulation (PAM) formats, making it a promising technique for next-generation high-speed optical interconnects.
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http://dx.doi.org/10.1364/OE.397130 | DOI Listing |
Ultrasonics
December 2024
Universidad Carlos III de Madrid, Avenida de la Universidad, 30, Leganes, Madrid, Spain.
The most common transducers used to generate ultrasound in medical applications are based on short electrical pulses applied to piezoelectric transducers and capacitive micromachined ultrasound transducers. However, piezoelectric transducers have a limited frequency bandwidth, defined by their physical thickness, and capacitive micromachined ultrasound transducers have poor transmission efficiency. The high frequency cutoff limits the spatial resolution of ultrasonic images.
View Article and Find Full Text PDFA novel, to the best of our knowledge, frequency offset estimation (FOE) scheme is proposed and demonstrated for coherent digital subcarrier multiplexing (DSCM) systems, where frequency offset (FO) leads to severe filtering damage of subcarriers due to bandwidth limitations. The scheme exploits the symmetry of the signal spectrum, which naturally arises from the transmitter's frequency response and introduces frequency skewness as a cost function to search for FO. To achieve fast FOE, the false position (FP) method is employed to iteratively compute frequency shifts.
View Article and Find Full Text PDFDirect current biased optical orthogonal frequency division multiplexing (DCO-OFDM) is widely used in blue light-emitting diode (LED)-based underwater optical wireless communication (UOWC), but the limited LED bandwidth leads to nonlinear distortions at higher frequencies. Using experiments, this paper proposes and validates a differential pre-emphasis (DPE) scheme for OFDM signal transmission in underwater channels to mitigate LED modulation bandwidth-induced nonlinearity, therefore improving transmission system performance. It is shown that the optimum DPE value leads to shorter rise time and fall time of the received signal and also avoids over- and under-shoots.
View Article and Find Full Text PDFWe demonstrate externally modulated widely tunable lasers co-integrated with semiconductor optical amplifiers (SOAs) heterogeneously integrated on silicon. The widely tunable laser enables continuous single-mode operation over a tuning range of approximately 40 nm, with a side-mode suppression ratio (SMSR) of at least 50 dB and an average waveguide-coupled optical power of 5 mW. The integrated electro-absorption modulator (EAM) exhibits an extinction ratio (ER) of 16 dB when reversed biased at -2 V.
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