Er-doped Optical Fiber Amplifiers Research Articles

Measurement of carbon dioxide concentration by fiber-loop ring-down spectroscopy for continuous remote measurement

We report on the continuous remote measurement of CO2 concentration using a fiber-loop ring-down spectroscopy system at a wavelength of 1572.334 nm. In fiber-loop ring-down spectroscopy, the effective propagation distance through the CO2 atmosphere determines the minimum detectable CO2 concentration. The effective propagation distance is determined by the signal-to-noise ratio in the fiber loop, including the gain of an Er-doped optical fiber amplifier (EDFA), and the loss in the single-mode fiber, coupling losses, and losses in optical devices. We examined the influence of noise due to the EDFA in the system. A noise figure for the EDFA was measured, and the maximum effective propagation distance through the CO2 atmosphere was 350 m. Using the obtained EDFA gain and the optical loss in the system, we simulated the ring-down time for a CO2 concentration range of 0 to 0.5%. We set up the fiber-loop ring-down spectroscopy system and measured the ring-down waveforms with a CO2 concentration range of 0 to 0.5%. In this CO2 concentration range, the measurement resolution was 0.05%, showing good agreement with the calculated results.

Effect of Helical Bending on Gain Beyond 1650-nm of an Er-Doped Optical Fiber Amplifier

Effect of Helical Bending on Gain Beyond 1650-nm of an Er-Doped Optical Fiber Amplifier

A Study of Four Wave Mixing Nonlinear Effect on Various Fiber Types in DWDM Optical Systems

Dense Wavelength Division Multiplexing (DWDM) transport systems are highly attractive in today’s telecommunication scenario since they offer large capacity with a small number of channels and also achieve high spectrum efficiency. Fiber nonlinearities can have a serious impact on the performance of these systems. The presence of nonlinearities causes the channel capacity to be a nonmonotonic function of the input signal strength. The information throughput can be increased by using dispersion shifted fiber having minimum loss and zero dispersion at 1.55 µm wavelength and Er-doped optical fiber amplifiers in the fiber links. But low dispersion and high intensity of the signal launched enhance the four wave mixing, a third order non-linear effect. Due to this low dispersion and high intensity of light pulse, frequency mixing is made in an efficient manner and new wavelength are generated. This is called four wave mixing penalty. If one of the generated new wavelength is equal to signal wavelength in the DWDM modulated carrier, the interference or cross-talk is produced and that will reduce the signal to noise ratio at the receiver side. To the best of the author’s knowledge and with reference to the literature we have presented in this paper, how the inter modulation products are generated due to four wave mixing effect and are observed experimentally using single mode fiber also simulation is made with dispersion shifted fiber for two channel and sixteen channel wavelength division multiplexed transmission system. In addition, FWM power (cross-talk) is evaluated and compared for three major types of fibers like single mode fiber, dispersion shifted fiber, non-zero dispersion shifted fiber.

Er3+ doped ultra-transparent oxy-fluoride glass-ceramics for application in the 1.54 μm telecommunication window

A major development in telecommunications is due to the Er-doped optical fiber amplifier (EDFA) utilizing the I13/2 → I15/2 emission transition at about 1.54 μm of Er3+ (see e.g. [1] and references therein). Wavelength division multiplexing (WDM), which is based on EDFA, requires that the Er3+ dopants have a broad and flat spectrum, which results in increased transmission capacity of WDM [1]. Recently it was realized that ultra-transparent oxy-fluoride glass-ceramics (GC) can be manufactured, including in fiber form with 100 dB/ km optical loss, see e.g. [2] and references therein. Thus, in addition to the enhanced up-conversion emission capability of rare-earth doped GC [3], potential applications as fiber lasers and optical amplifiers have emerged. In this paper we report the synthesis of Er3+ doped GC, which are ultra-transparent as evidenced by optical transmission spectroscopy and by observation of ultra-low frequency (4 and 7 cm−1) Raman scattering peaks. The chemical composition of our precursor glass (SiO2)(Al2O3)(CdF2)(PbF2)(ZnF2), when undoped, was close to the one reported in [2]. However, in addition, we used Er3+ as a rare-earth dopant (up to 5 mol% of ErF3) and did not use YF3. GC were obtained by heat-treatment of the precursor glass at 25–70 ◦C above the glass transition temperature, Tg, for 3–5 h resulting in typically about 2–12 nm size β-PbF2 crystals [4] hosting Er3+ dopants. Intensity, width and Stark-splitting of emission (I13/2 → I15/2 transition) and absorption (I15/2 → I13/2 transition) spectra of Er3+-dopants at 1.5 μm changed with the size of nano-crystals. In particular, we could obtain the broadest and flattest emission spectrum of Er3+ for the I13/2 → I15/2 transition to date. We also reached the largest wavelength divergence between the maximum of emission and absorption spectra for I13/2 ↔ I15/2 transitions to date, which is of primary importance for reduction of self-absorption and respective noise in the EDFA. Differential thermal analysis (DTA) of our precursor doped and undoped glasses indicated that the

CNR limitations of Er-doped optical fiber amplifiers in AM-VSB video lightwave trunking systems

The CNR limitations of two different types of 980-nm pumped in-line Er-doped optical fiber amplifiers with the same small-signal noise figure to transport multichannel AM-VSB video signals is studied. Experimental results and frequency-domain simulations suggest that the noise figure of a high-power in-line erbium-doped fiber amplifiers (EDFA) should be 5 dB or less when operating deep in saturation (optical input power +3 dBm). Using two such in-line amplifiers produced an AM CNR greater than 50 dB with negligible CSO and CTB distortion degradation for a lightwave trunking link transporting 71 AM-VSB video channels with a total optical link budget of 39 dB. These results can clarify the EDFA selection criteria for AM video lightwave links.

Band-gap renormalization effects on 980 nm strained-layer InGaAs/AlGaAs quantum-well lasers

We calculate the optical gain and threshold current density of strained-layer InGaAs/AlGaAs quantum-well lasers with the band-gap renormalization effects taken into account. It is found that the band-gap renormalization shifts the lasing wavelength as much as 30 nm which is much larger than the allowed bandwidths, ±6 nm, of 980 nm Er-doped optical fiber amplifiers. We also try to optimize the graded-index separate-confinement-heterostructure optical waveguide layer in order to maximize the optical confinement factor and to reduce its fabrication dependence. The threshold current densities are calculated for the optimized structures for which the gain peak positions are predicted to be within the allowed bandwidths of 980 nm.

0.98- mu m strained quantum well lasers for coupling high optical power into single-mode fiber

An investigation of epitaxial-layer structures has yielded narrow ridge waveguide structure lasers capable of coupling high optical power into single-mode fiber (SMF). An optical power of well over 60 mW in SMF was obtained for a 2- mu m-wide ridge waveguide laser with a guided separate-confinement-heterostructure (SCH) epitaxial structure. Calculated results indicate that the stringent limit imposed on 0.98- mu m wavelength detuning is relaxed for such high optical power coupled into a SMF. The 0.98- mu m strained-quantum-well lasers thus show considerable promise as a practical low-noise pumping source for Er-doped optical-fiber amplifiers. >

A 970 nm strained-layer InGaAs/GaAlAs quantum well laser for pumping an erbium-doped optical fiber amplifier

We report the performance of a 970 nm strained-layer InGaAs/GaAlAs quantum well laser and its application for pumping Er-doped optical fiber amplifiers. The laser was grown by molecular beam epitaxy and has three In0.2Ga0.8As/GaAs quantum wells. For a 5-μm-wide and 400-μm-long ridge-waveguide laser, a cw threshold current of 20 mA and an external quantum efficiency of 0.28 mW/mA per facet were obtained. Maximum output power exceeds 32 mW/facet. With antireflection coating, even higher external quantum efficiency (0.40 mW/mA) was achieved, and more than 20 mW of power was coupled into a single mode fiber. Preliminary experiments of pumping the Er-doped fiber amplifier gave 15 dB of gain at 1.555 μm for a pump power of 14 mW into the Er fiber.