54 research outputs found
Intersymbol interference penalties for OOK and 4-PAM in short-range optical communications
Intersymbol interference penalties of OOK and 4-PAM were compared in the context of short-range optical links with directly modulated VCSELs. The maximum achieved bit rate with 4-PAM was 38 Gbps and 32 Gbps with OOK
35.2 Gbps 8-PAM transmission over 100 m of MMF using an 850 nm VCSEL
We report experimental demonstration of 8-PAM transmission using an 850 nm VCSEL and 100 m of OM4-type MMF. The 8-level driving signal was generated using a 3-bit DAC, the error rates were measured in real time using a conventional error analyzer. Maximum uncoded bit rate was 37.5 Gbps, which corresponds to 35.2 Gbps with 7% FEC overhead
60 Gbits error-free 4-PAM operation with 850 nm VCSEL
60 Gbits over 2 m, 50 Gbits over 50 m and 40 Gbits was transmitted over 100 m of OM4 multimode fibre using four-level pulse amplitude modulation and a directly modulated 850 nm vertical cavity surface emitting laser (VCSEL)
70 Gbps 4-PAM and 56 Gbps 8-PAM using an 850 nm VCSEL
t We present 56 Gbps unequalized 8-PAM real-time transmission over 50 m of MMF and 70Gbps 4-PAM operation with offline equalization. The experiments were performed with an 850 nm VCSEL with 25 GHz bandwidth and a 22 GHz photoreceiver
Comparison of Intersymbol Interference Power Penalties for OOK and 4-PAM in Short-Range Optical Links
We present results of experimental and theoretical investigations of intersymbol interference in 4-PAM transmission in short-range optical communications links based on the power penalty. A test link comprised of a directly modulated 850 nm VCSEL with up to 200 m of multimode fiber and direct detection was used. The link bandwidth was below 10 GHz and the maximum achieved data rate with 4-PAM was 44 Gbps over 100 m of fiber. In the same case and at similar sensitivity, only 32 Gbps could be achieved with OOK. If typical forward error correction could be applied, the sensitivity of the 4-PAM system was improved by up to 4 dB, reaching -10 dBm at 25 Gbps
Energy Efficiency of VCSELs in the Context of Short-Range Optical Links.
We present results from an investigation of the
energy efficiency of VCSELs under large signal modulation. We show that the most important factor influencing the energy consumption of the VCSELs is the required optical modulation amplitude, which drives other VCSEL design requirements. The required optical modulation amplitude also depends on the optical link design. Through this dependence it is possible to better understand the energy consumption of complete short range optical links
Experimental comparison of modulation formats in IM/DD links
We present an experimental comparison of modulation formats
for optical intensity modulated links with direct detection. Specifically, we
compare OOK, QPSK on an electrical subcarrier and a new modulation
format named OOPSK. The OOPSK modulation format is shown to have
better sensitivity than the other modulation formats, in agreement with
theoretical predictions. The impact of propagation in multimode fiber is
also studied and the results show that all modulation formats have similar
sensitivity penalties, with respect to the fibre length
20 Gbit/s error-free operation of 850 nm oxide-confined VCSELs beyond 1 km of multimode fibre
Error-free transmission over 1.1 km of OM4 multimode fibre is demonstrated at 20 Gbit/s bit rate using a narrow spectral width, high-speed 850 nm vertical-cavity surface-emitting laser
22 Gb/s error-free data transmission beyond 1 km of multi-mode fiber using 850 nm VCSELs
The first error-free data transmission beyond 1 km of multi-mode fiber at bit-rates exceeding 20 Gb/s is demonstrated using a high modulation bandwidth, quasi-single mode (SMSR similar to 20 dB) 850 nm VCSEL. A VCSEL with small similar to 3 mu m aperture shows quasi-single mode operation with a narrow spectral width. The top mirror reflectivity of the VCSEL is optimized for high speed and high output power by shallow etching. A combination of narrow spectral width and high optical power reduces the effects of fiber dispersion and fiber and connector losses and enables such a long transmission distance at high bit-rates
The Herschel Planetary Nebula Survey (HerPlaNS) - a comprehensive dusty photoionization model of NGC6781
We perform a comprehensive analysis of the planetary nebula (PN) NGC6781 to
investigate the physical conditions of each of its ionized, atomic, and
molecular gas and dust components and the object's evolution, based on
panchromatic observational data ranging from UV to radio. Empirical nebular
elemental abundances, compared with theoretical predictions via nucleosynthesis
models of asymptotic giant branch (AGB) stars, indicate that the progenitor is
a solar-metallicity, 2.25-3.0 Msun initial-mass star. We derive the best-fit
distance of 0.46 kpc by fitting the stellar luminosity (as a function of the
distance and effective temperature of the central star) with the adopted
post-AGB evolutionary tracks. Our excitation energy diagram analysis indicate
high excitation temperatures in the photodissociation region (PDR) beyond the
ionized part of the nebula, suggesting extra heating by shock interactions
between the slow AGB wind and the fast PN wind. Through iterative fitting using
the Cloudy code with empirically-derived constraints, we find the best-fit
dusty photoionization model of the object that would inclusively reproduce all
of the adopted panchromatic observational data. The estimated total gas mass
(0.41 Msun) corresponds to the mass ejected during the last AGB thermal pulse
event predicted for a 2.5 Msun initial-mass star. A significant fraction of the
total mass (about 70 percent) is found to exist in the PDR, demonstrating the
critical importance of the PDR in PNe that are generally recognized as the
hallmark of ionized/H+ regions.Comment: 34 pages, 13 Figures and 16 Tables, accepted for publication in the
Astrophysical Journal Supplement Serie
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