Experimental Demonstration of an Optimized 16-ary Four-Dimensional Modulation Format Using Optical OFDM

We experimentally demonstrate the best known 16-ary 4-d modulation format at 24.8 Gb/s using coherent optical OFDM, achieving 0.58 dB OSNR gain over PDM-QPSK at a SER of 10−2. With 7% overhead optimal codes, a 0.38 dB gain is theoretically achievable

The analysis of various size, visually selected and density and magnetically separated fractions of Luna 16 and 20 samples

Samples of Luna 16 and 20 have been separated according to size, visual appearance, density, and magnetic susceptibility. Selected aliquots were examined in eight British laboratories. The studies included mineralogy and petrology, selenochronology, magnetic characteristics, Mossbauer spectroscopy, oxygen isotope ratio determinations, cosmic ray track and thermoluminescence investigations, and carbon chemistry measurements. Luna 16 and 20 are typically mare and highland soils, comparing well with their Apollo counterparts, Apollo 11 and 16, respectively. Both soils are very mature (high free iron, carbide, and methane and cosmogenic Ar), while Luna 16, but not Luna 20, is characterized by a high content of glassy materials. An aliquot of anorthosite fragments, handpicked from Luna 20, had a gas retention age of about 4.3 plus or minus 0.1 Gy

Experimental investigation of a 16-dimensional modulation format for long-haul multi-core fiber transmission

We experimentally investigate a 16-dimensional modulation format applicable to multi-core fiber transmission, and demonstrate over 14,000 km transmission for a BER of 1E-3, a 55 % improvement in reach compared to DP-BPSK for the same spectral efficiency

Pilot-Aided Joint-Channel Carrier-Phase Estimation in Space-Division Multiplexed Multicore Fiber Transmission

The performance of pilot-aided joint-channel carrier-phase estimation (CPE) in space-division multiplexed multicore fiber (MCF) transmission with correlated phase noise is studied. To that end, a system model describing uncoded MCF transmission where the phase noise comprises a common laser phase noise, in addition to core- and polarization-specific phase drifts, is introduced. It is then shown that the system model can be regarded as a special case of a multidimensional random-walk phase-noise model. A pilot-aided CPE algorithm developed for this model is used to evaluate two strategies, namely joint-channel and per-channel CPE. To quantify the performance differences between the two strategies, their respective phase-noise tolerances are assessed through Monte Carlo simulations of uncoded transmission for different modulation formats, pilot overheads, laser linewidths, numbers of spatial channels, and degrees of phase-noise correlation across the channels. For 20 GBd transmission with 200 kHz combined laser linewidth and 1% pilot overhead, joint-channel CPE yields up to 3.4 dB improvement in power efficiency or 25.5% increased information rate. Moreover, through MCF transmission experiments, the system model is validated and the strategies are compared in terms of bit-error-rate performance versus transmission distance for uncoded transmission of different modulation formats. Up to 21% increase in transmission reach is observed for 1% pilot overhead through the use of joint-channel CPE

4-PAM for high-speed short-range optical communications

In this work, we compare 4-pulse amplitude modulation and on–off keying modulation formats at high speed for short-range optical communication systems. The transmission system comprised a directly modulated verticalcavity surface-emitting laser operating at a wavelength of 850 nm, an OM3Å multimode fiber link, and a photodetector detecting the intensity at the receiver end. The modulation formats were compared both at the same bit-rate and at the same symbol rate. The maximum bit-rate used was 25 Gbps. Propagation distances up to 600 m were investigated at 12.5 Gbps. All measurements were done in real time and without any equalization

Pb/s, homogeneous, single-mode, multi-core fiber systems

We discuss multi Pb/s transmission using homogeneous, single-mode, multi-core fibers. We outline the key components of a recent high capacity demonstration, the consequences of fiber properties and the potential for enhanced efficiency from spatial-super-channel transmission

30 Gbps 4-PAM transmission over 200m of MMF using an 850 nm VCSEL

We present high speed real time, error free 4-PAMtransmission for short range optical links based on a VCSEL operating at 850 nm, a multimode fibre and a simple intensity detector. Transmission speeds of 25 Gbps and 30 Gbps are demonstrated, and the maximum fibre reaches were 300 m and 200 m, respectively. The 4-PAM is also compared with OOK transmission at 25 Gbps, and we find that at this bit rate 4-PAM increases the error free transmission distance in the multimode fibre by 100 m, compared to OOK

Single parity check-coded 16QAM over spatial superchannels in multicore fiber transmission

We experimentally investigate single-parity check (SPC) coded spatial superchannels based on polarization-multiplexed 16-ary quadrature amplitude modulation (PM-16QAM) for multicore fiber transmission systems, using a 7-core fiber. We investigate SPC over 1, 2, 4, 5 or 7 cores in a back-to-back configuration and compare the sensitivity to uncoded PM-16QAM, showing that at symbol rates of 20 Gbaud and at a bit-error-rate (BER) of 10(-3), the SPC superchannels exhibit sensitivity improvements of 2.7 dB, 2.0 dB, 1.7 dB, 1.3 dB, and 1.1 dB, respectively. We perform both single channel and wavelength division multiplexed (WDM) transmission experiments with 22 GHz channel spacing and 20 Gbaud channel symbol rate for SPC over 1, 3 and 7 cores and compare the results to PM-16QAM with the same spacing and symbol rate. We show that in WDM signals, SPC over hl1 core can achieve more than double the transmission distance compared to PM-16QAM at the cost of 0.91 bit/s/Hz/core in spectral efficiency (SE). When sharing the parity-bit over 7 cores, the loss in SE becomes only 0.13 bit/s/Hz/core while the increase in transmission reach over PM-16QAM is 44 %. (C) 2015 Optical Society of Americ

Cross-sectional survey of users of internet depression communities

Background: Internet-based depression communities provide a forum for individuals to communicate and share information and ideas. There has been little research into the health status and other characteristics of users of these communities. Methods: Online cross-sectional survey of Internet depression communities to identify depressive morbidity among users of Internet depression communities in six European countries; to investigate whether users were in contact with health services and receiving treatment; and to identify user perceived effects of the communities. Results: Major depression was highly prevalent among respondents (varying by country from 40% to 64%). Forty-nine percent of users meeting criteria for major depression were not receiving treatment, and 35% had no consultation with health services in the previous year. Thirty-six percent of repeat community users who had consulted a health professional in the previous year felt that the Internet community had been an important factor in deciding to seek professional help. Conclusions: There are high levels of untreated and undiagnosed depression in users of Internet depression communities. This group represents a target for intervention. Internet communities can provide information and support for stigmatizing conditions that inhibit more traditional modes of information seeking

High capacity transmission with few-mode fibers

We experimentally investigate high-capacity few-mode fiber transmission for short and medium-haul optical links. In separate experiments, we demonstrate C + L band transmission of 283 Tbit/s over a single 30 km span and recirculating loop transmission of 159 Tbit/s over 1045 km graded-index three mode fiber. The first experiment reached a data-rate per fiber mode within 90% of the record data-rates reported in the same transmission bands for single-mode fibers. The second experiment demonstrated the feasibility of reaching high data-rates over long distance few-mode fiber transmission, despite strong impairments due to mode-dependent loss and differential mode delay