1. What are the two commonly used single longitudinal mode semiconductor lasers?

Answer: DFB lasers and DBR lasers are both distributed feedback lasers, and their optical feedback is provided by distributed feedback Bragg gratings in the optical cavity.

2. What are the two main types of light-receiving devices?

Answer: There are mainly photodiodes (PIN tubes) and avalanche photodiodes (APDs).

3. What are the factors that cause the noise of the optical fiber communication system?

Answer: There are noises caused by unqualified extinction ratio, noise caused by random variation of light intensity, noise caused by time jitter, point noise and thermal noise of receiver, mode noise of optical fiber, noise caused by pulse broadening caused by chromatic dispersion, and noise caused by LD. Mode partition noise, noise due to frequency chirp of the LD, and noise due to reflections.

4. What are the main optical fibers currently used for transmission network construction? What are its main features?

Answer: There are three main types, namely G.652 conventional single-mode fiber, G.653 dispersion-shifted single-mode fiber and G.655 non-zero dispersion-shifted fiber.

The dispersion of G.652 single-mode fiber in the C-band 1530~1565nm and L-band 1565~1625nm is relatively large, generally 17~22psnm·km. When the system rate reaches 2.5Gbit/s or more, dispersion compensation is required. At 10Gbit/s When the system dispersion compensation cost is relatively large, it is the most common type of optical fiber laid in the transmission network at present.

The dispersion of G.653 dispersion-shifted fiber in the C-band and L-band is generally -1~3.5psnm·km, and it is zero dispersion at 1550nm. The system rate can reach 20Gbit/s and 40Gbit/s, which is a single-wavelength ultra-long distance transmission. Best fiber. However, due to its zero dispersion characteristics, when using DWDM for capacity expansion, nonlinear effects will occur, resulting in signal crosstalk, resulting in four-wave mixing FWM, so DWDM is not suitable.

G.655 non-zero dispersion-shifted fiber: The dispersion of G.655 non-zero dispersion-shifted fiber in the C-band is 1~6psnm·km, and the dispersion in the L-band is generally 6~10psnm·km. The dispersion is small and avoids zero dispersion. The dispersion region not only suppresses the four-wave mixing FWM, it can be used for DWDM capacity expansion, and it can also enable high-speed systems. The new G.655 fiber can expand the effective area to 1.5~2 times that of the general fiber, and the large effective area can reduce the power density and reduce the nonlinear effect of the fiber.

Fiber hope fiber optic cable and patch cord manufacturers can provide high-quality fiber optic cables,

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