DE202006007966U1 - Optical multi-format transmission system for optical transmission channel, has optical IQ-homodyne receiver in reception circuit - Google Patents

Abstract

An optical multi-format transmission system has on the optical side (OS) an optical IQ-modulator (IQM) independent of the modulation format in the transmission circuit (SK), and an optical IQ-homodyne receiver (IQE) in the reception circuit (EK) for converting M-value PSK- and M-value QAM-modulation formats, and on the electrical side in the transmission circuit (SK) for driving the optical IQ- modulator (IQM) and in the reception circuit (EK) for signal processing the received data for an actual sampled M-value PSK- and M-value QAM modulation format.

Description

The Innovation relates to a multi-format optical transmission system for one optical transmission channel with a transmission circuit with a light source and an optical modulator to modulate the data to be sent in different, depending from the characteristics of the transmission channel selectable Modulation formats and a receiving circuit with a demodulator for Demodulation of the received in different modulation formats Dates.

In the modern optical transmission technology are used for the efficient use of the optical bandwidth and the Improvement of transmission characteristics complex, higher quality (M = order) modulation method applied. Here, symbols encode a certain number of bits (for example 2 or 4) and have the optical carrier a certain amplitude (length the vector to the constellation point) and phase (angle of the vector) to. In the case of M-valued PSK (phase shift keying) all constellation points on one and the same circle (an amplitude state, M phase states). By contrast, in M-valued QAM (Quadrature Amplitude Modulation) the optical carrier assigned to several amplitude and phase states. For example, names the quadrature PSK (QPSK) 4 constellation points, the square 16 QAM however, already 16 constellation points. Such M-valued PSK and M-valued QAM signals are used, for example, in optical access, Metro and wide area networks transmitted.

State of technology

A well-known from modulation theory, for electrical and wireless transmission usual and also for the optical transmission technology Applicable transmitter variant for generating M-valued PSK and M-valued QAM signals is the IQ transmitter. This allows the direct conversion of complex data symbols to an optical one Carrier frequency. The principle of the IQ transmitter is based on the optical carrier the complex modulation information (amplitude and phase) over the Use of a two-arm structure with one arm (the quadrature arm) the adjacent carrier relative to 90 ° to the other arm (the in-phase arm) is phase-shifted by a to apply simple amplitude modulation in the inphase and quadrature arm. This leads in particular for square QAM modulation formats to simpler electrical drive signals and also to a specific Course of the temporal signal at the symbol transitions. In principle this is However, this method is applicable to all M-PSK and M-QAM formats.

Of the optical IQ transmitter whose optical part (IQ modulator), for example from the publication I by Keang-Po Ho et al .: "Generation of Arbitrary Quadrature Signals Using One Dual-Drive Modulator "(Journal of Lightwave Technology, Vol. 23, No.2, Feb. 2005, pp 764-770) or the publication II by M. Seimetz: "Multiformat Transmitters for Coherent Optical M-PSK and M-QAM Transmission "(in Proc. ICTON 2005, Barcelona, 2005), may be described as follows shortly become: the original one Data information will be first demultiplexed to the symbol rate. The parallel information goes then to a differential pre- or encoder (which takes place here Coding is for the receiver side Compensation of the phase noise laser light source necessary) and then on an electrical level generator, which accordingly the currently applied bit sequence and the currently selected modulation format multi-level control signals for generates the in-phase branch and quadrature branch of the IQ transmitter. The Drive signals are amplified by a modulator driver and then into the two high-frequency inputs of the optical IQ modulator fed. In the optical IQ modulator, the light of a light source, for example, a CW laser (continuous wave, continuous wave) on split two arms (for example, by a 3-dB coupler) and in one arm to create the quadrature carrier phase-shifted by 90 °. After the amplitude modulation by a respective Mach-Zehnder modulator (MZM) in both arms, the light is brought together again (for example again through a 3 dB coupler) and so the optical modulation signal for the transmission educated.

At the receiving end, the information modulated on the carrier can be detected by an IQ homodyne receiver. This is described (also with digital phase estimation), for example in the publication III of K. Kikushi: "Coherent Detection of Phase-Shift Keying Signals using Digital Carrier-Phase Estimation" (in Proc. OFC 2006, paper OTul4) and the publication IV of M. Seimetz: "Performance of Coherent Optical Square-16-QAM Systems Based on IQ Transmitters and Homodyne Receivers with Digital Phase Estimation" (in Proc. NFOEC 2006, paper NWA4). The operation of the IQ homodyne receiver is based on the principle of heterodyne reception. Therefore, first the signal light and the light of a local laser (LO, local oscillator) are superimposed on each other. This can be done, for example, in a 2 × 4 90 ° hybrid, which then provides four optical signals at the outputs, two of which are detected by a differential receiver. A differential receiver consists of two photodiodes whose output currents are subtracted. The output currents of the differential receivers then describe the inphase and quadra tur signals, which are still disturbed by the phase noise of the laser light sources. To eliminate this phase noise, a special module for digital phase estimation can be used after analog-to-digital conversion by the most recently available high-speed digital signal processing. The phase noise-removed in-phase and quadrature signals downstream of the phase estimation module are then fed to an electrical decision module, a differential decoder and a demultiplexer to reconstruct the original data information.

The state of the art from which the present innovation originates is disclosed in the Japanese Abstract JP 05284111 A disclosed. Described here is an optical multi-format transmission system for a free-jet optical transmission channel, in which the modulator in the transmitting circuit modulates the transmission data alternatively with a 4 PPM or a 2 PPM modulation format. The switching between the two modulation formats is performed by a switch acted upon by a frequency divider. However, the switching is not the adaptation of the respective modulation format to the current channel state or varying transmission conditions, but the safe transmission of a tracking signal with sufficient receiver sensitivity and moderate interaction with the data signal. A flexibility in the choice of the modulation format to adapt the transmission to the current channel properties is thus not given. In the receiving circuit, the received signal is reconverted by an electrical demodulator according to the selected modulation format. However, the known transmission system is limited to the use of only two different, power-efficient modulation formats and their exclusively electrical conversion. This corresponds to an optical subcarrier modulation system. Modular extensions to other modulation formats or a conversion to purely optical modulation are not possible.

task

The Task for The present innovation is therefore to be seen as an optical one Multi-format communications system to create, which is flexible, time-independent and without much effort the Realization of all possible Modulation formats, in particular also special higher value ones Modulation formats for specific optical transmission conditions allows.

The renewal solution for this Task is basically first characterized in that both in the transmitting and in the receiving circuit the optical components and the electrical components consistently are separated from each other. Furthermore, the optical components so selected on both sides, that they are independent of the chosen Modulation format for the implementation of all possible modulation formats and thus also the higher quality M-valued PSK and M-valued QAM modulation formats can. For this purpose, an optical IQ transmitter and in the receiving circuit is in the transmission circuit an optical IQ homodyne receiver stationary used. Both optical components are at the innovation summarized in a common system and are structured that their function for all possible Modulation formats runs the same way. Both optical components are thus when generating and receiving all possible Modulation formats generally and permanently involved.

The entire adaptation of the optical transmission system after the innovation to the different modulation formats takes place on the electrical side by exchanging or controlling special electronic modules. This makes a quick, flexible and easy adjustment possible. In the implementation on the electrical side to modulation modulation dependent in the transmitting circuit for driving the optical IQ modulator and in the receiving circuit for signal processing of the received data each for a currently selected M-valued PSK and M-valued QAM modulation format several components present and in one combined common electronic module. The various electronic modules for all M-valued PSK and M-valued QAM modulation formats are either alternatively mobile and are manually interchangeable with each other or they are all parallel stationary in an array and are selected individually depending on the modulation format. As a result of these measures, the transmission system according to the invention can be used flexibly for different network segments. In this case, a temporally constant, individual adaptation of the selected modulation format can take place. However, it is also possible to achieve temporally varying adaptation to dynamically changing properties of the optical transmission channel, as is the case for example with the digital subscriber line (DSL) technique for electrical transmission. In an embodiment of the transmission system according to the invention, it may be provided that the individual electrical control of individual electronic modules takes place adaptively as a function of the modulation formats currently selected in each case according to the dynamic properties of the transmission channel. In the technical realization of a control loop and a return channel from the receiving to the transmitting circuit, the transmission system according to the invention can, in particular, automatically adjust itself to dynamic channel changes, and this can be done automatically adjust the current modulation format to the current channel conditions.

in the Transmitting circuit of the transmission system according to the innovation can be the entire optical part of the optical IQ transmitter for all M-valued PSK and M-valued QAM modulation formats used equally only part of the electronics is on both sides modulation specific interpreted (required for the IQ modulator electrical Modulator driver is also universally applicable). The modulation format dependent part of the Electronics can be combined in one electronic module. This can be advantageously provided according to a further embodiment be that the electronics module in the transmitting circuit a demultiplexer for parallelizing the data to be sent to the symbol rate, a differential precoder for the reception-side compensation of the phase noise the light sources and an electric level generator for generating multistage drive signals comprises. The transmission-side adaptation to a special modulation format is therefore only in one modulation-specific design of the demultiplexer with 1: N, where N represents the number of bits per symbol of the differential Precoders through the implementation of the appropriate logic circuit and the respective generation of the for a respective modulation format necessary in-phase and quadrature drive signals by means of a modulation-specific Level generator. For the Square-M-QAM modulation format is for all M-ary orders also the differential Precoder universally usable. With the said electrical components is an optical IQ modulator, such as he from the publication II is known, in an optimal manner electrically controllable and flexible for all potential Modulation formats can be used.

in the recipients of the multi-format transmission system After the innovation, the optical and electrical components also separated. The one required behind the IQ homodyne receiver electrical analog-to-digital converter As the only electrical component, it is again universal for all possible modulation formats applicable. All other electrical components work according to modulation format and can be summarized in a common electronic module. Therefore it is advantageous if the electronic module in the receiver circuit a digital phase estimation and decision module to compensate for phase noise and recovery the data to be sent and a multiplexer for de-parallelization the recovered data. To eliminate the phase noise can after the analog-to-digital conversion by a recent to disposal high-speed digital signal processing (cf. publication IV) a special module with a modulation-specific algorithm to the digital phase estimation be used, its exact realization - in contrast to the optical Part of the receiver - from the used Modulation format depends. The phase noise-free inphase and quadrature signals behind the phase estimation module then become an electrical decision module, a differential Decoder and a multiplexer with N: 1, where N is the number of bits represents per symbol, fed, which modulationsspecific are to be interpreted and the original Data information realized by appropriate decisions in a corresponding decision logic and decoder logic as well by reconstructing the parallel bits by multiplexing. The Differences in the necessary modulation-specific interpretation of the decision-making module are only in the necessary Number as well as the levels of the thresholds of the decision makers as well as the appropriate ones Decider logic for the reconstruction of the data information from the phase-canceled inphase and quadrature signals.

in the Regard to a possible general application for different M-valued PSK and M-ary QAM modulation formats in the transmission system After the innovation can thus be determined that in the receiving circle the entire optical part, the analog-to-digital converter and an optional Module for electrical compensation of interference effects (see above) for all modulation formats can be used. Only the phase estimation module, the electrical decision module, the differential decoder as well the multiplexer must modulation-specific designed. further explanation to the mentioned electrical components are the specific description part refer to.

Should with the transmission system after the innovation to double the spectral efficiency of the transmission additionally Polarization multiplex executed be so doubled the transmission circuit in its optical components become. Continue to have additional optical components for splitting the two orthogonal polarization planes be provided. On the electrical side in the receiving circuit must additionally a digital polarization estimation module be provided. Furthermore, to master general polarization problems in heterodyne reception for commercial Applications the front part of the receiver (consisting of the 2 × 4 90 ° hybrid and the difference receivers, s.u.) can be duplicated and interpreted with polarization diversity. For laboratory experiments however, a simple polarization control is sufficient.

In addition, the optical homodyne receiver has compared to a direct optical receiver the advantage that occurring dispersion can be electrically compensated very effectively. Therefore, it is advantageous in the transmission system after the novelty, if in the receiver circuit on the electrical side, a digital suppression module for the compensation of electrical interference, usable equally for all possible M-valued PSK and M-valued QAM modulation formats, stationary and permanent is controlled.

For commercial For applications, an integrated optoelectronic construction technique is recommended. It is therefore advantageous if all optical and electrical Components are executed in an integrated construction technique. So it is possible to send side Electronics and optics, each integrated, in a housing for disposal deliver or even monolithically integrate both together. Receptionist provides for the integration of the optical IQ homodyne receiver the Using a multimode interference (MMI) coupler as a 2 × 4 90 ° hybrid one promising variant, because this component with adequate design inherent a stable 90 ° phase relationship for one good IQ balance provides and advantageous with the two differential receivers (Balanced Detectors) can be integrated on a chip. The remaining part Recipient also has potential for an integrated commercial design.

Mentioned the subject of innovation already in the publication V "Coherent Systems using Multi-Level Modulation Formats and Electronic Distortion Equalization "(WOTE 2005, paper B1, Shanghai, November 11, 2005) by M. Seimetz et al. and the publication VI "Performance of Coherent Optical Square-16-QAM Systems based on IQ transmitters and Homodyne Receivers with Digital Phase Estimation "(in Proc. NFOEC 05.03.2006, paper NWA4,) by M. Seimetz, in which further details, such as a special algorithm for the phase estimation module in square 16 QAM modulation. The publications mentioned of the inventor were within the applicable for a utility model Novelty grace period published. Their quote is intended to fully endorse the publications mentioned above The disclosure content of the present utility model application belong.

embodiment

The optical multiformat transmission system after the innovation with a modulation-specific adaptable transmission and receiving circle will be used for further understanding of the innovation on the basis of the following Figures explained. It shows the

1 the transmitting circuit and

2 the receiving circuit of the optical multi-format transmission system after the innovation.

In the 1 is in the right part of the image an optical side OS and in the left part of the image an electrical side ES of a transmitting circuit SK of the optical multi-format transmission system MFÜ after the innovation shown. On the optical side OS there are only optical components. In the embodiment, a light source LQ, in the 1 a CW laser, and an optical IQ transmitter IQS permanently arranged and operating. The continuous-wave light of the light source LQ is transmitted through an optical coupler OK1 in the 1 a 3dB coupler, equally divided between an inphase branch IZ and a quadrature branch QZ. In quadrature branch QZ, it is phase-shifted by 90 ° via a phase shifter PS. In two Mach Zehnder modulators MZM1, MZM2 then the two light signals are amplitude modulated, the electrical drive signals AS I (t) and Q (t) in the electrical side ES in depending on the selected M-PSK and M-QAM modulation format Form be generated. After the amplitude modulation, the two resulting optical signals E _I (t) and E _Q (t) in another optical coupler OK2, in the 1 also a 3dB coupler, merged again. At the output of the transmitting circuit SK is now the multi-format modulation signal MFMS ready for transmission in the optical transmission channel OÜK ready. In this case, the optical transmission channel OÜK is formed, for example, by an optical glass fiber.

The electrical drive signals AS for the IQ modulator IQM be generated on the electrical side ES of the transmission circuit SK. Here are exclusively electrical components ELK. Those which are modulation specific are to be interpreted are summarized in an electronic module EM. The to be transferred Data bits DB are first in a demultiplexing DM parallelized according to the chosen symbol rate and subsequently encoded in a differential precoder DPC. This preprocessing is required in the receiving circuit EK, the phase noise in the received Compensate signal. The preprocessed signal is then applied to an electrical level generator LG directed, according to the applied bit sequence and the chosen one high-order Modulation format according to multi-stage electrical control signals AS generated. The electrical drive signals AS are still through a modulator driver MT that can be used universally for all modulation formats is strengthened and then into the two high-frequency inputs of the IQ modulator IQM on the optical side OS fed.

The described electrical components ELK within the electronic module EM are for a special modulation format preset. In this case, the universally applicable modulator driver MT can be included in the electronic module EM (and thus made available separately for each modulation format) or be provided outside the electronic module EM once on the electrical side ES of the transmission circuit SK. Depending on the selected modulation format, the electronic module EM can be easily replaced manually. This is a static adaptation to the optical transmission channel OÜK. However, it is also possible to provide a plurality of electronic modules EM for different modulation formats in a common array. Depending on the currently selected modulation format, the corresponding electronic module is always activated. The presetting of the electronic modules EM allows adaptation of the modulation format in real time. This is then a dynamic adaptation to the optical transmission channel OÜK. In both cases, the optical multi-format transmission system MFÜ thus achieves maximum flexibility with optimum static or dynamic adaptation of the selected modulation format to the respective transmission conditions or the current channel state after the innovation.

2 shows the receiving circuit EK of the multi-format transmission system MFÜ after the innovation. This too is consistently divided into an optical side OS and an electrical side ES. The optical side OS forms an IQ homodyne receiver IQE, which operates on the principle of heterodyne reception. Therefore, the received multi-format modulation signal MFMS is superimposed with the light of a frequency-adjustable local laser LO (local oscillator). This is done in the illustrated IQ homodyne receiver IQE in a 2 × 4 90 ° hybrid HB, designed for example as a multimode interference coupler MMI, which then delivers four optical signals at its outputs, of which two each from a differential receiver DE1, DE2 (Balanced Detector), which includes two photodiodes whose output currents are subtracted to be detected. The output currents of the two differential receivers DE1, DE1 then describe the received in-phase signal I * (t) and the received quadrature signal Q * (t), which, however, are still disturbed by the phase noise of the lasers (LQ, LO). The two differential receivers DE1, DE2 are still located on the optical side OS of the receiving circuit EK and form the interface to the electrical side ES of the receiving circuit EK.

to Elimination of the phase noise of the received in-phase signal I * (t) and the received quadrature signal Q * (t) become these the electrical side ES first digitized in an analog-to-digital converter ADW and then a Phase estimation module PSM supplied. Here is a modulation-specific algorithm (see publication IV) using high-speed digital signal processing carried out. The inphase and quadrature signals thus freed from phase noise then become one electrical decision module EDM, a differential decoder DDK and a multiplexer MU supplied, which depends on selected Modulation format the original Data bits DB through appropriate decisions and appropriate Decision and decoder logic as well as by multiplexing the parallel reconstruct present bits into serial data streams.

In addition to Phase estimation module PSM (parallel or integrated) can still a digital suppression module ETM for the compensation of electrical disturbances (Electronic Distortion Equalization) may be provided. However, this works independently of modulation format for all possible ones M-valued PSK and M-valued QAM modulation formats and becomes so stationary and constantly operated operated. The described modulation format dependent electrical Components ELK of the receiving circuit EK are again in electronic modules EM summarized, which - like in the electronic modules EM of the transmission circuit SK - depending on of the chosen current modulation format either alternatively in the receive circuit EK are present or all arranged together in an array and individually controlled. Here, the universally applicable Analog-to-digital converter ADW added to the electronic module EM (and thus for each modulation format can be provided separately) or but outside of the electronic module EM once on the electrical side ES of the receiving circuit EK be provided.

ADW

Analog to digital converter

AS

control signal

CW

Continuous wave laser

DDK

differential decoder

DB

to be transferred Data bits

DE

Differential receiver

DM

demultiplexer

DPC

differential precoder

E _I (t)

modulated In-phase signal

E _Q (t)

modulated Quadrature signal

ELK

electrical component

EM

electronic module

EDM

decision module

EK

receiving circuit

IT

electrical page

ETM

interference suppression module

HB

2 × 4 90 ° hybrid

I * (t)

received electrical in-phase signal

I (t)

electrical In-phase signal

IQE

IQ homodyne

IQM

IQ modulator

IQS

IQ transmitter

IZ

In-phase branch

LG

Level generator

LO

local laser

LQ

light source

MFMS

Multi-format modulation signal

MFÜ

optical Multi-format transmission system

MMI

Multimode interference coupler

MT

modulator driver

MU

multiplexer

MZM

Mach-Zehnder modulator

OK

optical coupler

OS

optical page

OÜK

optical transmission channel (Glass fiber)

PS

phase shifter

PSM

Phase estimation module

Q * (t)

received electric quadrature signal

Q (t)

electrical Quadrature signal

QZ

Quadrature branch

SK

transmission circuit

Claims (10)

Optical multi-format transmission system for an optical transmission channel comprising a transmitting circuit with a light source and a modulator for modulating the data to be transmitted in different modulation formats that can be selected depending on the properties of the transmission channel and a receiving circuit with a demodulator for demodulating the data received in different modulation formats, characterized in that • an optical IQ modulator (IQM) on the optical side (OS) independent of modulation format in the transmission circuit (SK) and an optical IQ homodyne receiver (IQE) in the reception circuit (EK) for the respective conversion of all possible M-valued PSK signals and M-valued QAM modulation formats is stationary and permanently driven and that • on the electrical side (ES) modulation format dependent in the transmitting circuit (SK) for driving the optical IQ modulator (IQM) and in the receiving circuit (EK) for signal processing of the received Data jewe For a currently selected M-ary PSK and M-ary QAM modulation format, a plurality of electrical components (ELK) are present and combined in a common electronic module (EM), wherein the various electronic modules (EM) are used for all M-valued PSK and M-valued QAM modulation formats either alternatively mobile present and against each other manually replaceable or parallel stationary in an array available and are electrically controlled individually. Optical multi-format transmission system according to claim 1, characterized in that the individual use of individual Electronic modules (EM) adaptive depending on the after dynamic Properties of the transmission channel (OÜK) respectively currently selected Modulation formats takes place. Optical multi-format transmission system according to claim 1 or 2, characterized in that the electronic module (EM) in the transmitting circuit (SK) a demultiplexer (DM) for parallelizing the data to be sent to the symbol rate, a differential Precoder (DPC) for the reception-side compensation of the phase noise the light sources (LQ, LO) and an electrical level generator (LG) for generating multi-stage control signals (AS). Optical multi-format transmission system according to claim 3, characterized in that for the square M-QAM modulation format for all M-valued Orders a common differential precoder (DPC) outside the electronic modules (EM) is provided. Optical multi-format transmission system after a the claims 1 to 4, characterized in that the electronic module (EM) in recipients (EK) a digital phase estimation and decision module (PSM, EDM) and a differential decoder (DDK) to compensate for phase noise and recovery of the data to be transmitted (DB) and a multiplexer (MU) for de-parallelization the recovered data. Optical multi-format transmission system after a the claims 1 to 5, characterized in that in the receiver circuit (EK) on the electrical Page (ES) a digital suppression module (ETM) for the compensation of electrical disturbances for all possible M-valued PSK and M-valued QAM modulation formats is stationary and permanent is controlled. Optical multi-format transmission system after a the claims 1 to 6, characterized in that in the transmitting circuit (SK) on the electrical side (ES) is a modulation format independent modulator driver (MT) and in the receiving circuit (EK) on the electrical side (ES) modulation format independent Analog to digital converter (ADW) inside or outside of the respective electronic module (EM) is arranged. Multiformat optical transmission system according to one of Claims 1 to 7, characterized in that, for polarization multiplexing, the transmitting circuit (SK) is designed to be doubled on the optical side (OS) and additional optical components for splitting into the two orthogonal polaris are provided and on the electrical side (ES) in the receiving circuit (EK) additionally provided a digital polarization estimation module. Optical multi-format transmission system after a the claims 1 to 8, characterized in that in the IQ homodyne receiver (IQE) the 2 × 4 90 ° hybrid (HB) as a multi-mode interference coupler (MMI) and together with two differential receivers (DE) integrated on a common chip. Optical multi-format transmission system after a the claims 1 to 9, characterized in that all optical and electrical Components are executed in an integrated construction technique.