{'fraction_non_alphanumeric': 0.02756244616709733, 'fraction_numerical': 0.034453057708871665, 'mean_word_length': 4.481132075471698, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
8x622Mb/s HD-WDM optical fiber transmission over 420 km

The high density wavelength division multiplexing (HD-WDM) system presented here has 8 channels in 1.55 micrometers optical band with wavelength spacing of 100 GHz. Each channel operates at 622 Mb/s by using directly modulated DFB-LD. Accurate temperature control and current control methods have been taken to ensure the wavelength stability of 200 MHz in standard deviation. Three high-quality EDFA's are used in the 420 km optical fiber transmission to compensate the loss of fiber, star couplers and F-P optical filter. An F-P filter with 0.3 nm bandwidth and 1.2 dB insertion loss is used as a demultiplexer in front of the receiver to select every channel and reduce amplified spontaneous emission noise. An optical receiver with PIN-FET front-end has been used, which has sensitivity of -31 dBm BER equals 10-10. Good SNR characteristic is obtained for all channels after the transmission. In this paper we describe an 8 X 622 Mb/s HD-WDM experiment system and its 420 km optical fiber transmission. Some critical problems in long distance HD-WDM transmission also have been studied in this paper.