Hello everyone!
I will share with you the light source of WDM. I holp you like it.
The function of light sources is to generate laser or fluorescent light, and light sources are important devices to constitute the optical fiber communication system. The semiconductor laser LD (Laser Diode) and semiconductor LED (Light Emitting Diode) used as light sources for optical fiber communication are both semiconductor devices. Their common features are small in dimension, light in weight, and low in power consumption.
The major difference between LD and LED is that LD generates laser and LED generates fluorescent light. So, LED has a wider spectrum bandwidth with low modulation efficiency and low coupling efficiency with optical fiber; but its output characteristics curve is of better linearity, and it has a long service life and low cost, thus it is suitable for short-distance and small-capacity communication systems. And LD is typically applicable to long-distance and large-capacity communication systems and is widely used in high-speed PDH and SDH equipment.
The light sources used in high-speed optical fiber communication systems are classified into two categories: MLM lasers and SLM lasers. The major difference between the two types of semiconductor lasers in terms of their performance lies in their emitting spectrum. The emitting spectrum bandwidth of MLM laser is comparatively wider and of the nm order, and multiple harmonic peaks can be observed. The emitting spectrum bandwidth of SLM laser is of 0.1 nm order, and only a single harmonic peak can be observed. The monochromatism of SLM laser is better than that of MLM laser.
The operating wavelengths of DWDM systems are relatively dense. Generally, the wavelength spacing is from several nanometers to sub-nanometers. Hence, the laser diode is required to operate at a standard wavelength and possess good stability. On the other hand, the non-electrical regeneration relay distance of DWDM systems is increased from 50~60km transmitted by a single SDH system to 500~600km. The light sources of the DWDM system are required to use lasers more advanced in technology and more excellent in performance in order to elongate the dispersion limited distance of the transmission system and to overcome the nonlinear effects of the fiber {such as stimulated Brillouin scattering (SBS), stimulated Raman scattering (SRS), self-phase modulation (SPM), cross-phase modulation (XPM), modulation instability and four-wavelength mixing (FWM)}.
To sum up, the light source of the DWDM system has two outstanding features:
1) Larger dispersion tolerance value;
2) Standard and stable wavelength.
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