WO2020098093A1 - 一种双mzi多电平pam信号全光整形器及其设计方法 - Google Patents
一种双mzi多电平pam信号全光整形器及其设计方法 Download PDFInfo
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- WO2020098093A1 WO2020098093A1 PCT/CN2018/123697 CN2018123697W WO2020098093A1 WO 2020098093 A1 WO2020098093 A1 WO 2020098093A1 CN 2018123697 W CN2018123697 W CN 2018123697W WO 2020098093 A1 WO2020098093 A1 WO 2020098093A1
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/29—Repeaters
- H04B10/291—Repeaters in which processing or amplification is carried out without conversion of the main signal from optical form
- H04B10/293—Signal power control
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/25—Arrangements specific to fibre transmission
- H04B10/2589—Bidirectional transmission
- H04B10/25891—Transmission components
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/50—Transmitters
- H04B10/516—Details of coding or modulation
- H04B10/54—Intensity modulation
- H04B10/541—Digital intensity or amplitude modulation
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- the invention relates to the technical field of optical fiber communication, in particular to a dual MZI multilevel PAM signal all-optical shaper and a design method thereof.
- Wavelength division multiplexing technology has long been used in the industry on a large scale. At present, it has achieved 50G channel spacing and 96 channel wavelength division multiplexing technology. Its subsequent improvement is subject to optimization of processing technology, and progress is relatively slow.
- On-Off Keying On-Off Keying
- OOK On-Off Keying
- the increase in the bit rate is limited by the electronic rate bottleneck.
- the multi-level pulse amplitude modulation (PAM) signal has a higher bit rate; at the same time, on the client side, the PAM modulated signal is better than coherent modulation More cost advantage. Therefore, in the 100G and 400G solutions on the client side, PAM signals have been widely concerned and applied in the industry.
- Multi-level PAM optical signals are prone to signal degradation during transmission, and the degraded signals need to be regenerated. Although all-optical shapers for multi-level PAM signals have appeared, the shaping performance still needs to be further optimized.
- the present invention provides a dual MZI multilevel PAM signal all-optical shaper, which includes a matched dimmable amplifier and a dual MZI shaping unit connected in front and behind.
- the lower arm is provided with optical fibers
- the upper and lower arms of the embedded MZI module are respectively provided with optical fibers of the same length
- the dual MZI shaping unit further includes an input coupler C1 and an output coupler C3, and the embedded MZI module also Including input coupler C4 and output coupler C2;
- the multi-level PAM signal After being amplified by the matched dimmable amplifier, the multi-level PAM signal is divided into two channels by the input coupler C1 to enter the dual MZI shaping unit, one channel through the upper arm embedded MZI module to produce a nonlinear effect, and the other channel through A nonlinear effect occurs on the lower arm fiber, and the two signals are coupled and output by the output coupler C3 to obtain a shaped multi-level PAM signal;
- the multi-level PAM signal is divided into two channels by the input coupler C4 to enter the embedded MZI module, and then a nonlinear effect occurs in the optical fibers of the same length on both arms , Two signals are coupled out by the output coupler C2.
- the present invention also provides a design method of a dual MZI multilevel PAM signal all-optical shaper, which is used to design the all-optical shaper described in the first aspect, the design method includes:
- the transmission coefficient ratio formula of the two arms of the dual MZI shaping unit and the value of the reference power point determine the fiber length difference of the two arms of the dual MZI shaping unit and the value of k in the transmission coefficient ratio formula
- the through efficiency of the input coupler C4 is a predetermined fixed value, and the k value is related to the through efficiency of the input coupler C1, the output coupler C2, and the output coupler C3.
- the value of the reference power point satisfies the following condition: p ref ⁇ n + 0.5; where p ref is the reference power point, and n is the number of levels of the multi-level PAM signal.
- the transmission coefficient ratio of both arms of the dual MZI shaping unit is a fixed value, and the transmission coefficient ratio formula is specifically:
- the transmission coefficients of the two arm fibers in the MZI module embedded in the upper arm are equal, denoted as R 1
- the transmission coefficient of the lower arm fiber is denoted as R 2
- p ref is the reference power point
- ⁇ 1 , ⁇ 2 and ⁇ 3 are the direct efficiency of input coupler C1, output coupler C2 and output coupler C3, respectively.
- L 1 is the length of the two-arm optical fiber embedded in the MZI module in the upper arm of the dual MZI shaping unit
- L 2 is the length of the lower-arm optical fiber in the dual MZI shaping unit
- ⁇ is the attenuation coefficient of the optical fiber
- the non-linear shaping unit MZI arms double phase shift difference between the normalized input power p in a linear relationship
- the nonlinear phase shift difference formula is specifically:
- the nonlinear phase shift generated by the two-arm fiber in the MZI module embedded in the upper arm is equal, which is recorded as
- the nonlinear phase shift produced by the lower arm fiber is written as
- the method further includes:
- the all-optical shaper provided by the invention forms a double MZI structure by embedded mode, and the shaping performance is further optimized.
- the parameters of the double MZI shaping unit determine the working range of the double MZI shaping unit, and then adjust the optical amplifier
- the gain makes the multilevel PAM signal match the working range of the dual MZI shaping unit, effectively solves the problem of signal degradation of the multilevel PAM signal in the optical fiber communication system, and enriches the realization of the multilevel PAM signal in the field of all-optical shaping Way, and ensure the long-distance effective transmission of multi-level PAM optical signals in the optical fiber communication system.
- the value of the reference power point can also be increased to further improve the shaping performance.
- FIG. 1 is a schematic structural diagram of a dual MZI multilevel PAM signal all-optical shaper provided by an embodiment of the present invention
- FIG. 2 is a design flow chart of a dual MZI shaping unit provided by an embodiment of the present invention
- FIG. 3 is a graph showing the relationship between double MZI shaping units L 1 -L 2 and k provided by an embodiment of the present invention
- FIG. 5 is a waveform diagram of a degraded 4PAM signal of an input all-optical shaper provided by an embodiment of the present invention
- FIG. 6 is a waveform diagram of the shaping effect when the reference power point is 4.5 provided by an embodiment of the present invention.
- FIG. 8 is a schematic structural diagram of an existing single MZI multilevel PAM signal all-optical shaper.
- the terms “inner”, “outer”, “longitudinal”, “lateral”, “upper”, “lower”, “top”, “bottom”, etc. indicate the orientation or positional relationship based on the drawings
- the orientation or positional relationship shown is only for the convenience of describing the present invention and does not require that the present invention must be constructed and operated in a specific orientation, so it should not be construed as limiting the present invention.
- An embodiment of the present invention provides a dual MZI multilevel PAM signal all-optical shaper. As shown in FIG. 1, it includes a matched dimmable amplifier and a dual MZI shaping unit connected in front and behind; wherein, the dual MZI shaping The unit is of MZI structure, and the upper MZI shaping unit is provided with an embedded MZI module and the lower arm is provided with an optical fiber; the embedded MZI module is also an MZI structure, and the upper and lower arms of the embedded MZI module are respectively Equipped with optical fibers of the same length; the dual MZI shaping unit further includes an input coupler C1 and an output coupler C3, and the embedded MZI module further includes an input coupler C4 and an output coupler C2; wherein, the optical signal shaping process details as follows:
- the degraded multi-level PAM signal in the optical communication transmission link is input from port A. After being amplified by the matched tunable optical amplifier, it is divided into two channels by the input coupler C1 and enters the dual MZI shaping unit.
- the MZI module is embedded in the upper arm, and the multi-level PAM optical signal has a nonlinear effect in the two-arm optical fiber of the embedded MZI module, and the other way passes through the lower arm fiber.
- the multi-level PAM optical signal has a nonlinear effect in the lower arm optical fiber;
- the channel signal is coupled and output by the output coupler C3, and the shaped multi-level PAM signal is obtained at port B; the finally shaped signal continues to be transmitted in the optical communication transmission link, or is connected to the receiver.
- the multi-level PAM signal when the multi-level PAM signal is divided into two channels by the input coupler C1, in the embedded MZI module, the multi-level PAM signal is divided into two channels by the input coupler C4 to enter the Built-in MZI module, and then the non-linear effect occurs in the two arms of the same length of fiber, the two signals are coupled out by the output coupler C2, and finally output to the output coupler C3, and the lower arm fiber Signal coupling, as shown in Figure 1.
- the MZI shaping unit is a double MZI structure, and the multi-level PAM optical signal has a nonlinear effect in the optical fiber to complete the shaping of the multi-level PAM signal, and Compared with single MZI, the structure is further optimized, which effectively solves the problem of signal degradation of multi-level PAM signals in optical fiber communication systems, enriches the implementation of multi-level PAM signals in the field of all-optical shaping, and ensures multi-level PAM Optical signals are effectively transmitted over long distances in optical fiber communication systems.
- the shaping performance can be further improved.
- the embodiments of the present invention provide a design method of a dual MZI multilevel PAM signal all-optical shaper, and optimize the design based on the all-optical shaper described in Embodiment 1.
- the direct efficiency ⁇ 4 of the input coupler C4 is predetermined Fixed value, that is, the value of ⁇ 4 is selected in the range of (0, 1) before design.
- the through-efficiency of C4 is designed and optimized.
- the transmission coefficients of the two arm fibers in the MZI module embedded in the upper arm are equal, denoted as R 1
- the transmission coefficient of the lower arm fiber is denoted as R 2
- the transmission coefficients of the two arms of the dual MZI shaping unit The ratio is fixed and meets the following relationship:
- formula (1) is the transmission coefficient ratio formula
- ⁇ 1 , ⁇ 2 and ⁇ 3 are the direct efficiency of input coupler C1, output coupler C2 and output coupler C3 respectively
- p ref is the reference power point
- the reference power point p ref is defined as the reference power P ref and multi
- the ratio of the level PAM signal step size P 0 : p ref P ref / P 0 ; where the expressions of the transmission coefficient R 1 of the two-arm fiber and the transmission coefficient R 2 of the lower-arm fiber in the embedded MZI module are:
- L 1 is the length of the two-arm fiber in the MZI module embedded in the upper arm of the dual MZI shaping unit
- L 2 is the length of the lower-arm fiber in the dual MZI shaping unit
- the nonlinear phase shifts generated by the two arms of the MZI module embedded in the upper arm are equal, which is recorded as The nonlinear phase shift produced by the lower arm fiber is written as
- the nonlinear shaping unit MZI arms double phase shift difference between the normalized input power p in linear relationship:
- the expressions are:
- ⁇ is the nonlinear coefficient of the optical fiber.
- ⁇ 12W -1 / km is taken as an example.
- the design of the dual MZI shaping unit in Embodiment 1 can be completed.
- the design method includes steps S11-S16, where S11-S15 are In the process of parameter design and working range determination of the dual MZI shaping unit, S16 is the design adjustment of the matched dimmable amplifier. details as follows:
- the shaping performance of the dual MZI shaping unit is positively related to the selection of the reference power point: n ⁇ p ref -0.5; then when the level number n of the multi-level PAM signal is determined, the reference power The value of the point satisfies the following condition: p ref ⁇ n + 0.5.
- the value of k needs to be selected according to equation (1) and the reference power point p ref value, so that the absolute value of L 1 -L 2 is as small as possible. This is because in actual design, the closer the length of the two-arm optical fiber of the dual MZI shaping unit is, the better.
- ⁇ 2 and ⁇ 3 can have many other values, and only a set of examples are given here, which is not intended to limit the present invention.
- the working range of the dual MZI shaping unit can be determined to be 0.75W, 1.25W, 1.75W, 2.25W.
- parameter optimization is a compromise and iterative process. If the parameters do not meet the actual physical requirements, return to repeat S11-S15 for repeated optimization until the parameters that meet the actual physical requirements are obtained.
- the value of the reference power point may be further increased, and the all-optical shaper may be performed according to the new reference power point.
- the provided all-optical shaper includes a linear matching optical amplifier and an MZI shaping module, as shown in FIG. 8, the MZI shaping module includes an input, an output coupler, an optical nonlinear unit and an optical shift
- the phase device adopts a single MZI structure as a whole. With this single MZI structure, under the same normalized amplitude jitter, the waveform of the corresponding shaped signal only reaches Figure 6.
- the dual MZI structure provided by the embodiment of the present invention not only achieves FIG.
- the dual MZI shaping unit is designed according to the number of regeneration levels, the working range of the dual MZI shaping unit is determined, and then passed Adjust the gain of the optical amplifier so that the multi-level PAM signal matches the working range of the dual MZI shaping unit, thus effectively solving the problem of signal degradation of the multi-level PAM signal in the optical fiber communication system, and enriching the multi-level PAM signal in all
- the realization method in the field of optical shaping and ensures the long-distance effective transmission of multi-level PAM optical signals in the optical fiber communication system.
- the dual MZI shaping unit is the core of the all-optical shaper. In the case of a multi-level PAM signal, the value of the reference power point can be increased to further improve its shaping performance and effectively suppress the noise at each level. .
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Abstract
一种双MZI多电平PAM信号全光整形器及其设计方法,其中,全光整形器包括前后连接的匹配可调光放大器和双MZI整形单元,双MZI整形单元的上臂为内嵌MZI模块,下臂设有光纤,内嵌MZI模块的上下两臂分别设有同长度的光纤;双MZI整形单元还包括输入耦合器C1和输出耦合器C3,内嵌MZI模块还包括输入耦合器C4和输出耦合器C2。提供了一种双MZI结构的全光整形器,通过进行参数设计,有效解决了多电平PAM信号的劣化问题,丰富了多电平PAM信号在全光整形领域的实现方式,并确保了多电平PAM光信号在光纤通信系统中的长距离有效传输,而且通过增加参考功率点的值,可进一步提升整形性能。
Description
本发明涉及光纤通信技术领域,具体涉及一种双MZI多电平PAM信号全光整形器及其设计方法。
在光纤通信系统中,随着全球通信业务的快速增长,人们对传输容量的要求越来越高,而且近年来,随着大数据、物联网以及5G相关技术的发展,尤其是近几年数据中心的发展,人们对传输容量需求的增速也越来越快。通常,增加通信容量一般有两种方式:提升比特速率和增加波分复用的通道数。波分复用技术早已在业界获得大规模的应用,目前已做到50G通道间隔、96通道的波分复用技术,其后续的提升有待于加工工艺的优化,目前进展较为缓慢。在提升比特速率中,对于通断键控(On-Off Keying,简写为OOK)调制信号,其比特速率的提升受限于电子速率瓶颈。相比于OOK调制信号,在相同的波特速率下,多电平的脉幅调制(pulse amplitude modulation,简写为PAM)信号的比特率更高;同时在客户侧领域,PAM调制信号比相干调制更具成本优势。因此,目前在客户侧100G、400G方案中,PAM信号已经受到业界的广泛关注与应用。
在光通信系统中,由于光放大器自发辐射噪声积累以及光纤损耗等因素的影响,致使信号在传输过程中劣化,造成信息的丢失,为此需要对劣化的信号整形再生。相比于OOK信号,PAM信号的整形技术更难,虽然目前在电域有比较成熟的方案,但是在光域整形要困难的多,这需要一种多电平PAM信号的全光整形器加以指导。目前已有多电平PAM信号的全光整形器用于对劣化的信号整形再生,比如在专利文件CN201610163853.6 中,提供了一种马赫曾德尔干涉(Mach-Zehnder Interferometer,简写为MZI)结构的多电平PAM信号全光整形器,包括线性匹配光放大器和MZI整形模块,但是整形性能仍需进一步优化,还急需一种更优性能的多电平PAM信号全光整形器加以指导。
鉴于此,克服上述现有技术所存在的缺陷是本技术领域亟待解决的问题。
【发明内容】
本发明需要解决的技术问题是:
多电平PAM光信号在传输过程中容易发生信号劣化,需要对劣化的信号整形再生,虽然目前已出现多电平PAM信号的全光整形器,但整形性能仍需进一步优化。
本发明通过如下技术方案达到上述目的:
第一方面,本发明提供了一种双MZI多电平PAM信号全光整形器,包括前后连接的匹配可调光放大器和双MZI整形单元,所述双MZI整形单元的上臂为内嵌MZI模块,下臂设有光纤,所述内嵌MZI模块的上下两臂分别设有同长度的光纤;所述双MZI整形单元还包括输入耦合器C1和输出耦合器C3,所述内嵌MZI模块还包括输入耦合器C4和输出耦合器C2;
多电平PAM信号经过所述匹配可调光放大器放大后,被所述输入耦合器C1分为两路进入所述双MZI整形单元,一路通过上臂内嵌MZI模块发生非线性效应,另一路通过下臂光纤发生非线性效应,两路信号由所述输出耦合器C3耦合输出,得到整形后的多电平PAM信号;
其中,在所述内嵌MZI模块中,多电平PAM信号又被所述输入耦合器C4分为两路进入所述内嵌MZI模块,进而分别在两臂同长度的光纤中发生非线性效应,两路信号由所述输出耦合器C2耦合输出。
优选的,所述双MZI整形单元的整形性能与参考功率点的选取正相关, 具体满足以下关系式:n≤p
ref-0.5;其中,n为所述双MZI整形单元可整形的电平数,p
ref为参考功率点,且所述参考功率点p
ref定义为参考功率P
ref与多电平PAM信号步长P
0的比值:p
ref=P
ref/P
0。
第二方面,本发明还提供了一种双MZI多电平PAM信号全光整形器的设计方法,用于设计上述第一方面所述的全光整形器,所述设计方法包括:
根据多电平PAM信号的电平数以及整形性能的设计要求,选取参考功率点的值;
根据双MZI整形单元两臂的透射系数比公式以及参考功率点的取值,确定双MZI整形单元两臂的光纤长度差以及透射系数比公式中的k值;
根据双MZI整形单元两臂的非线性相移差公式以及所述光纤长度差,确定输入耦合器C1的直通效率、双MZI整形单元两臂的光纤长度以及多电平PAM信号步长;
根据所述透射系数比公式中的k值以及输入耦合器C1的直通效率的取值,确定输出耦合器C2与输出耦合器C3的直通效率;
根据以上参数,确定所述双MZI整形单元的工作范围;
调节匹配可调光放大器的增益,使多电平PAM信号与双MZI整形单元的工作范围相匹配;
其中,所述输入耦合器C4的直通效率为预先确定的固定值,所述k值与输入耦合器C1、输出耦合器C2、输出耦合器C3的直通效率有关。
优选的,所述参考功率点的取值满足以下条件:p
ref≥n+0.5;其中,p
ref为参考功率点,n为多电平PAM信号的电平数。
优选的,所述双MZI整形单元两臂的透射系数比为定值,所述透射系数比公式具体为:
在所述双MZI整形单元中,上臂内嵌MZI模块中两臂光纤的透射系数相等,记为R
1,下臂光纤的透射系数记为R
2;p
ref为参考功率点,ρ
1、ρ
2、ρ
3分别为输入耦合器C1、输出耦合器C2以及输出耦合器C3的直通效率。
优选的,所述参考功率点p
ref定义为参考功率P
ref与多电平PAM信号步长P
0的比值:p
ref=P
ref/P
0。
优选的,所述双MZI整形单元两臂的非线性相移的差值与归一化输入功率p
in呈线性关系,所述非线性相移差公式具体为:
其中,γ为光纤的非线性系数,归一化输入功率p
in定义为输入功率P
in与多电平PAM信号步长P
0之间的比值:p
in=P
in/P
0。
优选的,在所述调节匹配可调光放大器的增益之后,所述方法还包括:
对完成设计后的所述全光整形器的整形效果进行验证,当整形效果不满足使用要求时,增加所述参考功率点的取值,根据新的参考功率点对所述全光整形器进行重新设计,直至整形效果满足使用要求。
本发明的有益效果是:
本发明提供的全光整形器通过内嵌的方式形成双MZI结构,整形性能进一步优化,使用时先设计双MZI整形单元的各参数,确定双MZI整形单元的工作范围,再通过调节光放大器的增益,使得多电平PAM信号与双MZI整形单元的工作范围相匹配,有效解决了多电平PAM信号在光纤通信系统中信号劣化问题,丰富了多电平PAM信号在全光整形领域的实现方式,并确保了多电平PAM光信号在光纤通信系统中的长距离有效传输。而且,在多电平数PAM信号给定的情形下,还可通过增加参考功率点的值,进一步提升整形性能。
为了更清楚地说明本发明实施例的技术方案,下面将对本发明实施例中所需要使用的附图作简单地介绍。显而易见地,下面所描述的附图仅仅是本发明的一些实施例,对于本领域普通技术人员来讲,在不付出创造性劳动的前提下,还可以根据这些附图获得其他的附图。
图1为本发明实施例提供的一种双MZI多电平PAM信号全光整形器的结构示意图;
图2为本发明实施例提供的一种双MZI整形单元的设计流程图;
图3为本发明实施例提供的双MZI整形单元L
1-L
2与k的关系曲线图;
图4为本发明实施例提供的双MZI整形单元中P
0与L
1的关系曲线图;
图5为本发明实施例提供的输入全光整形器的劣化4PAM信号波形图;
图6为本发明实施例提供的参考功率点为4.5时的整形效果波形图;
图7为本发明实施例提供的参考功率点为5.5时的整形效果波形图;
图8为现有的一种单MZI多电平PAM信号全光整形器的结构示意图。
为了使本发明的目的、技术方案及优点更加清楚明白,以下结合附图 及实施例,对本发明进行进一步详细说明。应当理解,此处所描述的具体实施例仅仅用以解释本发明,并不用于限定本发明。
在本发明的描述中,术语“内”、“外”、“纵向”、“横向”、“上”、“下”、“顶”、“底”等指示的方位或位置关系为基于附图所示的方位或位置关系,仅是为了便于描述本发明而不是要求本发明必须以特定的方位构造和操作,因此不应当理解为对本发明的限制。
此外,下面所描述的本发明各个实施方式中所涉及到的技术特征只要彼此之间未构成冲突就可以相互组合。下面就参考附图和实施例结合来详细说明本发明。
实施例1:
本发明实施例提供了一种双MZI多电平PAM信号全光整形器,如图1所示,包括前后连接的匹配可调光放大器和双MZI整形单元两部分;其中,所述双MZI整形单元为MZI结构,且所述双MZI整形单元的上臂设有内嵌MZI模块,下臂设有光纤;所述内嵌MZI模块也为MZI结构,且所述内嵌MZI模块的上下两臂分别设有同长度的光纤;所述双MZI整形单元还包括输入耦合器C1和输出耦合器C3,所述内嵌MZI模块还包括输入耦合器C4和输出耦合器C2;其中,光信号的整形过程具体如下:
光通信传输链路中劣化的多电平PAM信号由端口A输入,经过所述匹配可调光放大器放大后,被所述输入耦合器C1分为两路进入所述双MZI整形单元,一路通过上臂内嵌MZI模块,多电平PAM光信号在内嵌MZI模块的两臂光纤中发生非线性效应,另一路通过下臂光纤,多电平PAM光信号在下臂光纤中发生非线性效应;两路信号由所述输出耦合器C3耦合输出,在端口B得到整形后的多电平PAM信号;最后整形后的信号继续在光通信传输链路中继续传输,或者接入接收机。
其中,当多电平PAM信号被所述输入耦合器C1分为两路时,在所述内嵌MZI模块中,多电平PAM信号又被所述输入耦合器C4分为两路进入 所述内嵌MZI模块,进而分别在两臂同长度的光纤中发生非线性效应,两路信号由所述输出耦合器C2耦合输出,并最终输出至所述输出耦合器C3,与下臂光纤中的信号耦合,如图1所示。
本发明实施例提供的多电平PAM信号全光整形器中,MZI整形单元为双MZI的结构,多电平PAM光信号在光纤中发生非线性效应,完成多电平PAM信号的整形,与单MZI相比在结构上进一步优化,有效解决了多电平PAM信号在光纤通信系统中信号劣化问题,丰富了多电平PAM信号在全光整形领域的实现方式,并确保了多电平PAM光信号在光纤通信系统中的长距离有效传输。
在本发明实施例提供的全光整形器中,所述双MZI整形单元为全光整形器的核心,而所述双MZI整形单元的整形性能又与参考功率点的选取正相关,具体满足以下关系式:n≤p
ref-0.5;其中,n为所述双MZI整形单元可整形的电平数,p
ref为参考功率点,且所述参考功率点p
ref定义为参考功率P
ref与多电平PAM信号步长P
0的比值:p
ref=P
ref/P
0。其中,在多电平数PAM信号给定的情形下,通过增加参考功率点p
ref的值,可进一步提升整形性能。
在利用上述全光整形器对劣化的多电平PAM信号进行整形前,需要先根据整形性能要求对所述双MZI整形单元进行参数设计,进而确定双MZI整形单元的工作范围,再通过调节光放大器的增益,使得多电平PAM信号与双MZI整形单元的工作范围相匹配,从而实现多电平PAM信号在光纤通信系统中的整形。具体设计流程将在实施例2中展开介绍,此处不再赘述。
实施例2:
在上述实施例1的基础上,本发明实施例提供了一种双MZI多电平 PAM信号全光整形器的设计方法,以实施例1所述的全光整形器为基础进行优化设计。在介绍具体设计方法之前,首先结合实施例1,对所述双MZI整形单元中各参数间的关系进行说明;其中,为便于计算,所述输入耦合器C4的直通效率ρ
4为预先确定的固定值,即在设计前先在(0,1)范围内对进行ρ
4取值,本实施例中以选取ρ
4=0.5为例进行设计,从而便于其他三个耦合器根据所述输入耦合器C4的直通效率进行设计与优化。本发明实施例中使用的各公式也是在ρ
4=0.5的基础上得到,具体如下:
在所述双MZI整形单元中,上臂内嵌MZI模块中两臂光纤的透射系数相等,记为R
1,下臂光纤的透射系数记为R
2,所述双MZI整形单元两臂的透射系数比为定值,并满足以下关系:
其中,式(1)即为透射系数比公式,
ρ
1、ρ
2、ρ
3分别为输入耦合器C1、输出耦合器C2以及输出耦合器C3的直通效率,p
ref为参考功率点,所述参考功率点p
ref定义为参考功率P
ref与多电平PAM信号步长P
0的比值:p
ref=P
ref/P
0;其中,内嵌MZI模块中两臂光纤的透射系数R
1与下臂光纤的透射系数R
2的表达式分别为:
L
1为所述双MZI整形单元上臂内嵌MZI模块中的两臂光纤的长度,L
2为所述双MZI整形单元下臂光纤的长度,α为光纤的衰减系数,本实施例中以α=0.21km
-1为例。
其中,式(4)即为非线性相移差公式,归一化输入功率p
in定义为输入功率P
in与多电平PAM信号步长P
0之间的比值:p
in=P
in/P
0;内嵌MZI模块两臂光纤产生的非线性相移
与下臂光纤产生的非线性相移
的表达式分别为:
γ为光纤的非线性系数,本实施例中以γ=12W
-1/km为例。
根据以上所述的参数间的公式关系,可完成对实施例1中所述双MZI整形单元的设计,参考图2,所述设计方法包括步骤S11-S16,其中,S11-S15是对所述双MZI整形单元的参数设计及工作范围确定的过程,S16是对所述匹配可调光放大器的设计调整。具体如下:
S11.根据多电平PAM信号的电平数n以及整形性能的设计要求,选取参考功率点p
ref的值。
由实施例1可知,所述双MZI整形单元的整形性能与参考功率点的选取正相关:n≤p
ref-0.5;则当多电平PAM信号的电平数n确定时,所述参考功率点的取值满足以下条件:p
ref≥n+0.5。假设多电平PAM信号为4PAM信号,即n=4,对应的电平分别为0.375W、0.625W、0.875W、1.125W,则p
ref≥4.5,可选取参考功率点p
ref=4.5。
S12.根据双MZI整形单元两臂的透射系数比公式以及参考功率点p
ref 的取值,确定双MZI整形单元两臂的光纤长度差以及透射系数比公式中的k值。
在该步骤中,需根据式(1)和参考功率点p
ref值,选取k的值,使得L
1-L
2的绝对值尽可能的小。这是因为在实际设计中,所述双MZI整形单元两臂光纤的长度越接近越好,比如此处可直接选取L
1=L
2,则根据式(2)、(3)可知此时
将
与p
ref=4.5代入式(1)中,得到k=28.24,此时L
1=L
2。
具体取值时,可先将式(2)和式(3)带入式(1)中,得到:
继续将α=0.21km
-1,p
ref=4.5带入式(7)中,得到:
当式(8)中分别取“+”号和“-”号时,可得到两条不同的L
1-L
2与k的关系曲线图,如图3所示:当取“+”号时,对应曲线a,随k值减小,L
1-L
2由负变为正,两臂光纤长度先逐渐接近,后逐渐远离,即k值越小,两臂光纤长度越接近,当k值减小到一定值后,两臂光纤长度开始远离;当取“-”号时,对应曲线b,随k值增大,L
1-L
2由正变为负,两臂光纤长度先逐渐接近,后逐渐远离,即k值越大,两臂光纤长度越接近,当k值增大到一定值后,两臂光纤长度开始远离,可根据规律在对应的曲线上进行k和L
1-L
2的取值。假设式(8)中取“-”号优化,参考曲线b,为满足L
1-L
2的绝对值尽可能的小,可选择曲线b上的点N(28.24,-2.639e-5),此时k=28.24,L
1=L
2。
S13.根据双MZI整形单元两臂的非线性相移差公式以及所述光纤长度差,确定输入耦合器C1的直通效率ρ
1、双MZI整形单元两臂的光纤长度L
1、L
2以及多电平PAM信号步长P
0。
在该步骤中,需根据式(4)-(6),先在(0,1)范围内选取ρ
1的值,再确定L
1、L
2和P
0的值,并考虑L
1及L
2尽量小的情形下,使得步长P
0尽可能小。具体为,先将式(5)和式(6)带入式(4)中,得到:
继续将α=0.21km
-1,γ=12W
-1/km带入式(9)中,得到:
根据式(10)可知,ρ
1越小,P
0越小,而在实际使用中直通效率常用的最小取值为0.01,故此处可选取ρ
1=0.01,但并不用以限制本发明。然后将ρ
1=0.01与l
1=L
2代入式(10),可得到如图4所示的P
0与L
1的关系曲线图,进而可在曲线上进行L
1、L
2和P
0的取值。假设选取曲线中的点M(1.197,0.4999),则可确定L
1=1.197km,L
2=1.197km,并优化出P
0=0.5W。
S14.根据所述透射系数比公式中的k值以及输入耦合器C1的直通效率ρ
1的取值,确定输出耦合器C2与输出耦合器C3的直通效率ρ
2、ρ
3。
在该步骤中,根据
以及ρ
1=0.01,可通过代入计算得到ρ
2和ρ
3的关系式,进而可在(0,1)的取值范围内进行ρ
2和ρ
3的取值,比如ρ
3=0.8896、ρ
2=0.5。当然,ρ
2、ρ
3还可有许多其他的取值情况,此处只给出一组举例,并不用以限制本发明。
S15.根据以上参数,确定所述双MZI整形单元的工作范围。
假设在该4PAM信号,归一化输入幅度P
in/P
0电平为1.5、2.5、3.5和4.5,根据P
0=0.5W,则可确定所述双MZI整形单元的工作范围为0.75W、 1.25W、1.75W、2.25W。其中,参数优化是一个折中反复的过程,如参数不符合实际物理要求,应返回重复S11-S15进行反复优化,直至得到符合实际物理要求的参数。
S16.调节匹配可调光放大器的增益,使多电平PAM信号与双MZI整形单元的工作范围相匹配。
根据前述步骤分析可知,所述双MZI整形单元的工作范围为0.75W、1.25W、1.75W、2.25W,而输入的4PAM信号对应的电平分别为0.375W、0.625W、0.875W、1.125W,进而调节所述可调放大器的增益G=2,使得多电平PAM信号与双MZI整形单元的工作范围相匹配。
在通过所述S11-S16设计完成全光整形器的设计后,即可利用设计完成之后的全光整形器对多电平PAM信号进行整形,假设该4PAM信号,在归一化输入幅度
电平
上,都存在归一化幅度抖动σ
in=0.02的高斯噪声,对应的波形图如图5所示,该劣化的4PAM信号经过上述设计的双MZI结构的全光整形器后,p
ref=4.5对应的整形信号波形图如图6所示,显然各电平上的噪声都得到了抑制。
结合本发明实施例,还存在一种优选的实现方案,当整形效果不满足使用要求时,可进一步增加所述参考功率点的取值,根据新的参考功率点对所述全光整形器进行重新设计,即重新执行所述S11-S16,直至整形效果满足使用要求。比如,在给定4PAM信号的情形下,假设p
ref=4.5时对应的图6未达到使用要求,则继续增加P
ref,当选取p
ref=5.5时,在归一化幅度抖动相同的情形下,对应整形信号的波形如图7所示,显然各电平上的噪声都得到了抑制,而且整形性能优于p
ref=4.5情形。由此可知,在多电平数PAM信号给定的情形下,通过增加参考功率点的值可进一步提升整形性能。
其中,在专利文件CN201610163853.6中,提供的全光整形器包括线性匹配光放大器和MZI整形模块,如图8所示,所述MZI整形模块包括输入、 输出耦合器、光学非线性单元和光移相器,整体采用的是单MZI结构。通过该单MZI结构,在归一化幅度抖动相同的情形下,对应整形信号的波形图只达到了图6。而通过本发明实施例提供的双MZI结构,不仅可达到图6,当继续增加参考功率点p
ref的值时,还能进一步提升整形性能,使各电平上的噪声进一步得到抑制,从而达到图7的整形效果,而且继续增大参考功率点的值,其整形性能可进一步优化。
综上所述,本发明提供的双MZI结构的多电平PAM信号全光整形器的设计方法中,先根据再生电平数设计双MZI整形单元,确定双MZI整形单元的工作范围,再通过调节光放大器的增益,使得多电平PAM信号与双MZI整形单元的工作范围相匹配,从而有效解决了多电平PAM信号在光纤通信系统中信号劣化问题,丰富了多电平PAM信号在全光整形领域的实现方式,并确保了多电平PAM光信号在光纤通信系统中的长距离有效传输。其中,双MZI整形单元是全光整形器的核心,在多电平数PAM信号给定的情形下,还可通过增加参考功率点的值进一步提升其整形性能,有效抑制各电平上的噪声。
以上所述仅为本发明的较佳实施例而已,并不用以限制本发明,凡在本发明的精神和原则之内所作的任何修改、等同替换和改进等,均应包含在本发明的保护范围之内。
Claims (10)
- 一种双MZI多电平PAM信号全光整形器,其特征在于,包括前后连接的匹配可调光放大器和双MZI整形单元,所述双MZI整形单元的上臂设有内嵌MZI模块,下臂设有光纤,所述内嵌MZI模块的上下两臂分别设有同长度的光纤;所述双MZI整形单元还包括输入耦合器C1和输出耦合器C3,所述内嵌MZI模块还包括输入耦合器C4和输出耦合器C2;多电平PAM信号经过所述匹配可调光放大器放大后,被所述输入耦合器C1分为两路进入所述双MZI整形单元,一路通过上臂内嵌MZI模块发生非线性效应,另一路通过下臂光纤发生非线性效应,两路信号由所述输出耦合器C3耦合输出,得到整形后的多电平PAM信号;其中,在所述内嵌MZI模块中,多电平PAM信号又被所述输入耦合器C4分为两路进入所述内嵌MZI模块,进而分别在两臂同长度的光纤中发生非线性效应,两路信号由所述输出耦合器C2耦合输出。
- 根据权利要求1所述的双MZI多电平PAM信号全光整形器,其特征在于,所述双MZI整形单元的整形性能与参考功率点的选取正相关,具体满足以下关系式:n≤p ref-0.5;其中,n为所述双MZI整形单元可整形的电平数,p ref为参考功率点,且所述参考功率点p ref定义为参考功率P ref与多电平PAM信号步长P 0的比值:p ref=P ref/P 0。
- 一种双MZI多电平PAM信号全光整形器的设计方法,其特征在于,全光整形器包括前后连接的匹配可调光放大器和双MZI整形单元,所述双MZI整形单元的上臂设有内嵌MZI模块,下臂设有光纤,所述内嵌MZI模块的上下两臂分别设有同长度的光纤;所述双MZI整形单元还包括输入耦合器C1和输出耦合器C3,所述内嵌MZI模块还包括输入耦合器C4和输出耦合器C2,则所述设计方法包括:根据多电平PAM信号的电平数以及整形性能的设计要求,选取参考功率点 的值;根据双MZI整形单元两臂的透射系数比公式以及参考功率点的取值,确定双MZI整形单元两臂的光纤长度差以及透射系数比公式中的k值;根据双MZI整形单元两臂的非线性相移差公式以及所述光纤长度差,确定输入耦合器C1的直通效率、双MZI整形单元两臂的光纤长度以及多电平PAM信号步长;根据所述透射系数比公式中的k值以及输入耦合器C1的直通效率的取值,确定输出耦合器C2与输出耦合器C3的直通效率;根据以上参数,确定所述双MZI整形单元的工作范围;调节匹配可调光放大器的增益,使多电平PAM信号与双MZI整形单元的工作范围相匹配;其中,所述输入耦合器C4的直通效率为预先确定的固定值,所述k值与输入耦合器C1、输出耦合器C2、输出耦合器C3的直通效率有关。
- 根据权利要求3所述的双MZI多电平PAM信号全光整形器的设计方法,其特征在于,所述参考功率点的取值满足以下条件:p ref≥n+0.5;其中,p ref为参考功率点,n为多电平PAM信号的电平数。
- 根据权利要求4-6任一所述的双MZI多电平PAM信号全光整形器的设计方法,其特征在于,所述参考功率点p ref定义为参考功率P ref与多电平PAM信号步长P 0的比值:p ref=P ref/P 0。
- 根据权利要求3所述的双MZI多电平PAM信号全光整形器的设计方法,其特征在于,在所述调节匹配可调光放大器的增益之后,所述方法还包括:对完成设计之后的所述全光整形器的整形效果进行验证,当整形效果不满足使用要求时,增加所述参考功率点的取值,根据新的参考功率点对所述全光整形器进行重新设计,直至整形效果满足使用要求。
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