LV14107B - Wavelength division multiplexing transmission system with narrow-band filter - Google Patents

Abstract

The invention concerns to field of telecommunications, particularly to optically multiplexed transmission systems. Its aim is to enlarge spectral efficiency of wavelength division in multiplexing transmission systems. This aim is achieved by applying in the optical receiver quasi-rectangular optical filter of 18.75 GHz providing transmission bandwidth at 3 dB level. Thus frequency interval between adjacent channels is reduced and data transmission speed for each channel is kept fixed. Invention scheme is realized with frequency interval not less than 37.5 GHz between adjacent channels by keeping fixed data transmission speed 10 Gbit/s for each channel. In such way spectral efficiency of wavelength division multiplexing system is enlarged.

Description

Description of the Invention

The invention relates to the telecommunications industry, in particular to optically densified transmission systems. Various wavelength division multiplexing communication systems are known, with the capability of transmitting information over a fixed frequency distance between adjacent channels and data rates on a particular channel. Currently, most studies have attempted to increase the overall transmission rate per fiber. Most of these studies are based on novel modulation methods for a specific wavelength. Alternatively, a similar solution is to minimize the frequency spacing between adjacent channels while maintaining a constant data rate per channel [1],

The wavelength division multiplexing communication system [2], which provides a frequency spacing between channels of at least 50 GHz and a data rate in the channel of at least 9 Gbit / s, has been chosen as a prototype of the invention. The standard single mode optical fiber is used as the transmission medium. The main disadvantage of the prototype is the optical filter characteristic, which provides a 50 GHz channel spacing. This characteristic curve needs to be improved in order to realize wavelength division multiplexing communication systems with higher spectral efficiency.

The object of the invention is to increase the spectral efficiency of the wavelength division multiplexing communication system. This is achieved by inserting a tunable quasi-rectangular optical filter with a bandwidth of 18.75 GHz minus 3dB into the optical receiver. This reduces the frequency interval between adjacent channels, leaving the transmission rate constant throughout the channel. The scheme of the invention is illustrated in Figure 1.

Scheme of Invention

The wavelength division communication system has three parts. The first part is an optical transmitter consisting of an electrical signal generator (1, 5), a code recorder (2, 6), a laser source (3, 7) and an external signal modulator (4, 8). The electric signal generator (1,5) generates a pseudorandom 2-by ³¹ -bit sequence with an operating frequency of 100 MHz to 12.5 GHz. The code generator (2, 6) generates a non-zero code. The continuous optical signal is formed by a laser (3, 7) with split feedback. The optical signal external modulator (4, 8) is a Mach-Zehnder modulator based on LiNbOs crystal.

The first and second parts of the wavelength division communication system are connected by a 2: 1 optical connector (9). The second part of the wavelength division communication system consists of an optical transmission medium (11) and an optical amplifier (10). The transmission medium is a standard single mode optical fiber (11) compliant with ITU G.652. The optical fiber has a large effective area of 80 pm ² , a attenuation of 0.2 dB / km, a dispersion of 17 ps / nm / km, a slope of dispersion of 0.07 ps / nm / km and a nonlinear factor of 2.5 · 10 ~ ²⁰ cm / W at 1550 nm. The fiber optic line has a standard gain and dispersion compensation area equal to 40 km for a 10 Gbit / s wavelength division multiplexing communications system. The second and third parts of the wavelength division multiplexing communication system are connected to a 1: 2 optical splitter (12).

The third part of the wavelength division multiplexing communication system is a direct reception receiver consisting of an optical filter (14, 18), a semiconductor photodiode (15, 19) and an electric filter (16, 20). The quasi-rectangular optical filter (14, 18) is approximated to the ideal filter characteristics with a tunable bandwidth of 0.15 nm to 0.7 nm minus 3 dB and a central wavelength range variable from 1450 to 1650 nm with a high accuracy of ± 15 pm . The characteristic curve of the quasi-rectangular optical filter (14, 18) is shown in Figure 2. The optical signal is converted into an electrical signal by a PIN photodiode (15, 19) according to the ITU standard with a sensitivity level of minus 15 dBm. After the photodiode, a Bessel-Thomson Grade 4 electrical signal filter (16, 20) is connected.

In the scheme of the invention, the portion of the transmitted signal quality evaluation consists of an electric high frequency oscilloscope (17, 21) and an optical spectrum analyzer (13) connected respectively to an electric filter (16, 20) and to an optical splitter (12).

Description of the operation of the scheme

Electrical 2 ³¹ -1 pseudo-random bit sequence of the operating frequency 10.0 GHz is supplied from the electric signal generator (1, 5) of the code shaper (2, 6) which forms bezatgriešanās at zero code. This code is fed from the code formers (2, 6) to the electrical high frequency input of the external signal modulator (4, 8) of the optical signal. In order to generate the optical flow in addition to the electrical non-return to zero code, the modulator (4, 8) is provided with a continuous optical signal with preselected parameters from the laser (3, 7) with a distributed feedback. The output of the external modulator produces an optical signal with a data rate of 10.0 Gbit / s encoded with a non-return code of zero. Using a 2: 1 optical combiner (9) combines both optical signals of the wavelength division multiplexing communication system and feeds to an optical amplifier (10).

Each of these optical signals has its own carrier frequency of 193,414 THz (2, = 1550,000 nm) and 193,377 THz (T ₂ = 1550,300 nm) with a frequency range of 37.5 GHz. The optical amplifier compensates for the attenuation caused by the propagation of the optical signal through the optical modulator. After the optical amplifier (10), the optical signal is fed to a standard single-mode optical fiber (11) conforming to ITU G.652.

After transmission over a standard single-mode optical fiber, the previously combined optical signal is divided by a 1: 2 optical splitter (12). Following the optical splitter is an optical filter (14, 18), the first of which filters an optical signal with a carrier frequency of 193,414 THz, and the second an optical signal with a carrier frequency of 193,377 THz, and reduces the noise level. After the optical filter returns to zero, the optical code is fed to the PIN photodiode (15, 19). The PIN photodiode (15, 19) converts the optical signal into an electrical signal, and the electric filter (16, 20) filters out the electrical noise. In the scheme of the invention, the quality of the transmitted signal is evaluated by means of an electric high frequency oscilloscope (17, 21) switched on by an electric filter and an optical spectrum analyzer (13) connected to a 1: 2 optical splitter (12).

Used information sources:

1. US Patent Application Publication 0239694 Al - Data Format For High Bit Frame WDM Transmission, 2006.

2. U.S. Pat. 6496615 B2 - WDM Transmission System, 2002 (prototype).

Claim

Claims (1)

1. A wavelength division multiplexing communication system with a frequency of 50 GHz between adjacent channels and a data rate of 9 Gbit / s on each channel, consisting of an optical transmitter, an optical line, and an optical receiver, different from tuning a quasi-rectangular optical filter into an optical receiver A bandwidth of 18.75 GHz minus 3dB is coupled to an optical splitter for splitting optical signals that provides at least 37.5 GHz bandwidth between adjacent channels, maintaining a constant data rate of 10 Gbit / s per channel, which increases wavelength compression spectral efficiency of the communication system.