LV14546B - Communication system based on spectra effective wavelength division multiplexing - Google Patents

Abstract

The invention relates to the telecommunications industry, particularly to the optical transmission systems. The aim of invention is to increase the spectral efficiency of wavelength division multiplexing system. This aim is completed by employment of different modulation formats for each wavelength division multiplexing system channel, as well as by use of new type of polarization modulation format for system's middle channel. This solution enables to arrange the channels of wavelength division multiplexing system closer to each other, thereby achieving higher spectral efficiency.

Description

The present invention relates to the telecommunications industry, in particular to optically densified communication systems.

The transmission speed in wavelength division multiplexing communication systems is gradually increased depending on the amount of information demand. This can be done step by step by incorporating a channel with the same data rate and modulation format into the wavelength division multiplexing communication system, or a channel with a higher data rate and a new, more compact power spectral density modulation format that allows for spectrally efficient wavelength division multiplexing systems. The latter solution allows to reduce the number of channels needed to transmit the same amount of information [1, 2],

A wavelength division multiplexing communication system having a frequency spacing of at least 100 GHz and a data rate in a channel of at least 10 Gbit / s has been chosen as a prototype of the invention [1]. The main disadvantage of the prototype is the use of one type of modulation format across all channels in the wavelength division compression communication system. To create wavelength division multiplexing communication systems with higher spectral efficiency, it is necessary to use higher data rates and new modulation formats in communication system channels.

The object of the invention is to increase the spectral efficiency of the wavelength division multiplexing communication system. This objective is achieved by modulating each channel of the wavelength division multiplexing communication system with a different modulation format, as well as by applying a new kind of polarization modulation format to the center channel of the system. Such a solution, as defined in the claim, makes it possible to position the channels of the wavelength division multiplexing communication system much closer to each other, thereby achieving higher spectral efficiency.

Scheme of Invention

A schematic diagram of a spectrally efficient wavelength division multiplexing communication system according to the invention is shown in Figure 1. The communication system has three parts and three channels. The first part is a generator consisting of an electrical signal generator (1, 2, 3), a code generator (4, 5, 6), a laser source (7, 8, 9) and an external signal modulator (10, 11, 12). The electrical signal generator (1, 2, 3) generates a ³¹ -bit sequence of pseudorandom type 2. The code generator (4, 5, 6) generates a non-zero code. The continuous optical signal is formed by a laser (7, 8, 9) with split feedback. The external modulator of the optical signal is different for each channel: the first channel modulator (10) is a LiNbO3 crystal based modulator, the second channel modulator (11) is an AlGaAs polarization modulator, and the third channel modulator is a LiNbO3 crystal modulator. The first and second parts of the wavelength division communication system are connected by a 3: 1 optical connector (13). The second part of the wavelength division multiplexing communication system consists of 10 km of dispersion compensation fiber (14), optical amplifier (15) and 50 km of standard single mode optical fiber (16). The second and third parts of the wavelength division multiplexing communication system are connected to a 1: 4 optical splitter (17). The third part of the wavelength division communication system is a receiver consisting of a Gaussian optical band filter (19, 20, 21), a detector (22, 23, 24) and an electric filter (25, 26, 27). The optical signal detector is different in each channel: the first channel detector is a quadrature detector consisting of one semiconductor photodiode (22), the second channel detector is a polarization detector consisting of a polarization state divider and two semiconductor photodiodes, and the third channel detector is a phase detector consisting of a Mach-Zender interferometer and two semiconductor photodiodes. A low-frequency electric filter (25, 26, 27) is connected to the detector. In the scheme of the invention, the evaluation part of the transmitted signal quality consists of an eye chart analyzer (28, 29, 30) and an optical spectrum analyzer (18) connected respectively to an electric filter (25, 26, 27) and an optical splitter (17).

Working principle of the measurement scheme

The electrical signal generator (1, 2, 3) provides an electric pseudorandom type 2 ³¹ 1 bit sequence with an operating frequency of 10.0 GHz and 40.0 GHz, which is fed to a code generator (4, 5, 6) which produces a non-return to zero code. This code is fed from the code formers (4, 5, 6) to the electrical high frequency input of the modulator (10, 11, 12). In order to generate an optical flow for additional electrical non-return to zero code, the modulator (10, 11, 12) supplies a continuous optical signal with preselected parameters from a laser source (7, 8, 9). The output of the external modulator produces an optical signal with a data rate of 10.0 Gbit / s or 40.0 Gbit / s, which is encoded with a non-return code of zero. Using a 3: 1 optical combiner (13), the wavelength division communication system channels are combined and fed successively to 10 km of dispersion compensation fiber (14), optical amplifier (15), and 50 km of standard single mode optical fiber (16). After transmission over a standard single-mode optical fiber, the previously combined wavelength division multiplexing communication channels are split with a 1: 4 optical splitter (17). Following the optical splitter is a Gaussian optical bandpass filter (19, 20, 21) which filters the relevant channel spectrum and reduces noise. After the optical filter returns to zero, the code is fed to a detector (22, 23, 24), which converts the optical signal into an electrical signal and filters the electrical noise through the electric filter (25, 26, 27). In the scheme of the invention, signal quality estimation is performed with an eye chart analyzer (28, 29, 30) connected to an electric filter (25, 26, 27) and an optical spectrum analyzer (18) connected to a 1: 4 optical splitter (11). .

Used information sources:

1. United States Patent Application - Spectrally Efficient Parallel Optical WDM Channels for Long-Haul MAN and WAn Optical Networks; publication 0021166 Al, 2010 (prototype)

2. Latvian patent LV14262 - Combined wavelength division multiplexing communication system, 2011.

Claims (1)

1. A spectrally efficient wavelength division multiplexing communication system comprising an optical transmitter, an optical line, and an optical receiver, characterized in that a second channel of the wavelength division multiplexing communication system employs a polarization modulator to provide a more compact power spectral density modulation format that provides data. increasing the transmission rate of the second and third channels to 40 Gbit / s with a frequency spacing between adjacent channels of at least 0.6 nm or 75 GHz and increasing the spectral efficiency of the wavelength division multiplexing system to 0.40 bit / s / Hz.