Green semiconductor lasers are still undeveloped, so high-power green lasers have heavily relied on nonlinear frequency conversion of near-infrared lasers, precluding compact and low-cost green laser systems. Here, we report the first Watt-level all-fiber CW Pr3 + -doped laser operating directly in the green spectral region, addressing the aforementioned difficulties. The compact all-fiber laser consists of a double-clad Pr3 + -doped fluoride fiber, two homemade fiber dichroic mirrors at visible wavelengths, and a 443-nm fiber-pigtailed pump source. Benefitting from > 10 MW / cm2 high damage intensity of our designed fiber dielectric mirror, the green laser can stably deliver 3.62-W of continuous-wave power at ∼ 521 nm with a slope efficiency of 20.9%. To the best of our knowledge, this is the largest output power directly from green fiber lasers, which is one order higher than previously reported. Moreover, these green all-fiber laser designs are optimized by using experiments and numerical simulations. Numerical results are in excellent agreement with our experimental results and show that the optimal gain fiber length, output mirror reflectivity, and doping level should be considered to obtain higher power and efficiency. This work may pave a path toward compact high-power green all-fiber lasers for applications in biomedicine, laser display, underwater detection, and spectroscopy.
Discrete Multitone Transmission (DMT) transmission over standard multimode fiber (MMF) using high-speed
single (SM) and multimode (MM) Vertical-Cavity Surface-Emitting Lasers (VCSELs) is studied. Transmission speed in
the range of 72Gbps to 82Gbps over 300m -100m distances of OM4 fiber is realized, respectively, at Bit-Error-Ratio
(BER) <5e-3 and the received optical power of only -5dBm. Such BER condition requires only 7% overhead for the
conversion to error-free operation using single Bose-Chaudhuri-Hocquenghem forward error correction (BCH-FEC)
coding and decoding. SM VCSEL is demonstrated to provide a much higher data transmission capacity over MMF. For
100m MMF transmission SM VCSEL allows 82Gbps as compared to MM VCSEL resulting in only 34Gbps at the same
power (-5dBm). Furthermore, MM VCSEL link at 0dBm is still restricted at 100m distance by 63Gbps while SM
VCSEL can exceed 100Gbps at such power levels. We believe that with further improvement in SM VCSELs and fiber
coupling >100Gbps data transmission over >300m MMF distances at the BER levels matching the industry standards
will become possible.
We manufacture and compare parallel optical transceiver and receiver assemblies on test boards for parallel data transmission over multimode fiber using single mode (SM) and multimode (MM) vertical-cavity surface-emitting laser (VCSEL) arrays. VCSELs, GaAs PIN photodetector arrays, commercially-available 12 channel VCSEL driver arrays and 12 channel limiting amplifier arrays were assembled into multi-channel transceiver and receiver assemblies on testboards designed to operate up to 16 channels and coupled to multimode fiber ribbon through industrial connectors. MM VCSEL arrays easily allow 25 Gb/s error-free data transmission over 100m of OM4 fiber with only a minor penalty in the sensitivity (0.5 dB). As opposite increasing the distance to 150-200 m causes a strong increase in the noise level making the error free transmission at 200 m impossible. Using of single mode SM VCSEL arrays allows error-free 25 Gbit/s NRZ PRBS 215-1 transmission over 1 km distances over OM4 fiber and above 600 m over OM3 fiber. In a different set of experiments PAM4 transmission up to 50 Gbit/s using SM VCSEL arrays is studied.
We address demands and challenges for GaAs–based Vertical–Cavity Surface–Emitting Lasers (VCSEL) in data communication. High speed modulation (~50Gb/s) at a high reliability can be realized with a proper VCSEL design providing a high differential gain. In cases where extreme temperatures are required electrooptic modulation in duo– cavity VCSELs can be applied as the modulation speed and the differential gain are decoupled. Single mode operation of VCSELs is necessary to counteract the chromatic dispersion of glass fibers and extend distances to above 1 km while using standard multimode fibers. Oxide layer engineering or using of photonic crystals can be applied. Parallel error–free 25Gb/s transmission over OM3 and OM4 multimode fiber (~0.5 and 1 km, respectively) is realized in large aperture oxide–engineered VCSEL arrays. Passive cavity VCSELs with gain medium placed in the bottom DBR and the upper part made of dielectric materials a complete temperature insensitivity of the emission wavelength can be realized. Engineering of the oxide aperture region enables near field vertical cavity lasers. Such devices can operate in a high– order transverse mode with an effective mode angle beyond the angle of the total internal reflection at the semiconductor–air interface. Near filed coupling to optical fibers and waveguides becomes possible in this case.
We have demonstrated a coherent OTDR based on log-detector. The effect of laser linewidth and electrical filter
bandwidth on coherent OTDR performance is theoretically analyzed and experimentally investigated.
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