China
Africa
Explore chapters and articles related to this topic
Wavelength-Division Multiplexed Systems and Applications
Published in Jerry D. Gibson, The Communications Handbook, 2018
transmission distances become limited by the fiber dispersion and optical spectral characteristics. For example, with a conventional (nondispersion shifted) single-mode fiber that is widely deployed in the field, the dispersion level of ~17 ps/km-nm at 1550 nm limits the transmission distances to a mere 11 km when launching a 10-Gb/s signal with a spectral width of 1.0 nm. However, when the spectral width is reduced to 0.1 nm, the transmission distance is extended to 65 km. Such reduction in the optical spectral width can be attained by replacing direct laser modulation with the use of an external modulator. The chromatic dispersion problem can be also alleviated with the use of dispersion-shifted fiber whose zero-dispersion wavelength is in the 1550-nm range instead of the 1300 nm for conventional fiber. However, when such redeployment of fiber is not an option, as the case may be when upgrading a network using already installed fibers, dispersion management techniques can be used to extend the transmission span. For example, a dispersion compensating device or a length of negative-dispersion fiber can be inserted periodically into the fiber span to correct the signal distortions [Lin et al., 1980; Onaka et al., 1996]. In laboratory experiments, several different dispersion management techniques have been successfully employed to extend the regen-eratorless transmission spans into the thousands of kilometers range.
D
Published in Philip A. Laplante, Comprehensive Dictionary of Electrical Engineering, 2018
dispersion shifted fiber single mode optical fibers with zero dispersion in the 1550 nm telecommunications window. Prior to 1985, single mode optical fibers were designed to have zero dispersion in the 1310 nm telecommunications window. dispersive medium (1) a medium for which the permittivity or the permeability (or both) are frequency dependent. (2) in optics, medium in which the index of refraction varies significantly with frequency. displaced frame difference (DFD) the difference between a given digital image frame and its estimate obtained by using the motion compensation technique. It is useful in image (sequence) data compression and motion estimation. displacement current a field quantity that describes the completion of a circuit when a conducting path is not present. displacement parameter complex parameter representing the displacement of the amplitude and phase centers of a Gaussian beam from the axis of an optical system. display a device that provides a visual nonpermanent display of system input and or output. Common display technology includes CRT (cathode ray tube), LED (light emitting diode), PDP (plasma display panel), EL (electroluminescense) and LCD (liquid crystal display).
Introduction to Design of Optical Transmission Systems
Published in Le Nguyen Binh, Optical Modulation, 2017
The limit for a system with a bit rate of Br and a total dispersion factor DT of the fibre is given by BrL≤14|DT|σλ with σχ is the FWHM of the source spectrum. Thus, for a standard optical fibre operating at 1550 nm, the total dispersion factor is about −15 ps/nm · km and a source FWHM of 1.0 nm the bit-rate distance product is about 166.6 (Gb/s)-Km. That is, if a 10 Gb/s operating bit rate system would be able to transmit signals for 16.6 km. If a dispersion-shifted fiber is used with a typical dispersion factor of about 1–2 ps/(nm · km) then the transmission distance can be increased about 15–7.5 times that of the SSMF or more than 100 km and up to 240 km. When these fibers are employed for extremely long distances, the polarization dispersion becomes significant and the PMD DGD parameters must be taken into account to estimate the total allowable transmission distance, especially for 10 Gb/s operating bit rate.
Experimental investigation of VCSEL-based optical heterodyning with PAM 4 and envelop detection for 5G fronthaul systems
Published in Journal of Modern Optics, 2022
R. S. Karembera, K. Nfanyana, G. M. Isoe, T. B. Gibbon
We performed a radio-over-fiber (RoF) transmission of a photonically generated 10-GHz PAM-4 RF carrier signal using the setup of Figure 4. To act as the baseline for system performance evaluation, we initially performed an 8.5-Gbps on-off keying (OOK) data modulation without optical heterodyning. A Mach–Zehnder modulator (MZM) was used to modulate VCSEL 1 with the 8.5-Gbps data. The 8.5-Gbps binary data was received from the N channel of the PPG when the switch of Figure 4 was at position 1. The modulated single optical signal from VCSEL 1 was transmitted and received after 24-km of non-zero dispersion shifted fiber (NZ-DSF) before detected by a 12.1-GHz photo detector as shown in Figure 4. During the second step to photonically generate a modulated 10-GHz RF carrier signal, the modulated VCSEL 1 was coupled with VCSEL 2 as shown in Figure 4. The photonically generated and modulated RF signal was transmitted over the same 24-km NZ-DSF to the PD. In this second step, after the PD, a low-noise linear electrical amplifier (EA) was used to amplify the received photonically generated and modulated RF carrier signal. An electrical mixer was used to down-convert the 10-GHz RF carrier to an IF of 4 GHz. This was achieved when a signal generator was used to generate a 6-GHz RF local oscillator (LO) signal to the LO port of the mixer. The output of the electrical mixer was then recorded by an oscilloscope for offline signal processing.
All-fiber Mach–Zehnder comb filter based on tapered fibers for wavelength switchable erbium-doped fiber lasers
Published in International Journal of Optomechatronics, 2020
He Wei, Zhu Lianqing, Dong Mingli
In recent years, methods have been reported that can generate stable and switchable lasing. In 2019, Cheng and Lin[7] reported a four-wavelength switchable linear-cavity EDF laser based on a Sagnac loop and a chirped fiber grating. In the same year, Kim et al.[8] reported a wavelength switchable fiber laser which employed a long-period fiber grating (LPFG) as a wavelength tuning unit, and the LPFG was inscribed on a polarization photonic crystal fiber (PCF) by a CO2 laser. In turn, Zhao et al.[9] reported a switchable multiwavelength EDF laser based on fiber Lyot filters with parallel structures. In addition, an L-band tunable, dual-wavelength fiber laser was reported by Ahmad et al. based on SOA,[10] whereby the widest spacing obtained for the designed fiber laser was 18.7 nm. In 2018, Yang et al.[11] reported a five-wavelength switchable EDF laser based on a few-mode tilted fiber Bragg grating (FBG). The FBG was fabricated using a phase-mask technique which was exposed to a 193 nm ultraviolet excimer laser. Bianchetti et al.[12] reported a wavelength switchable fiber laser based on the Mach–Zehnder interferometer (MZI) which was fabricated by a nonzero dispersion-shifted fiber. In this case, tunable dual- and triple-wavelength lasing were realized for the proposed fiber laser. Anum et al.[13] reported a single- and dual-wavelength tunable ring-cavity EDF laser based on the Fabry–Pérot (FP) structure, and was fabricated by single-mode fibers (SMFs) and multimode fibers. Additionally, Yang et al.[14] realized a dual-wavelength switchable fiber laser based on a double-ring cavity, while six different groups of lasing conditions were obtained for the proposed fiber laser. Xu et al.[15] designed and realized a switchable single-mode fiber laser based on a θ shaped microfiber filter. In 2017, a switchable dual-wavelength ring cavity fiber laser was realized by Jin et al. using a few-mode FBG.[16] In 2016, a switchable EDF laser based on a hollow-core FBG and a Sagnac loop was realized by Zhao et al.,[17] and tunable single- and dual-wavelength lasers were implemented. Gutierrez et al.[18] reported a linear cavity fiber laser which incorporated a cascaded bubble FP and PCF-MZ structure, whereby four-wavelength switchable lasers could be realized.