CN106842764B - Method for determining filtering spectrum type of passive temperature compensation gain flattening filter - Google Patents
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Abstract
The invention relates to a method for determining a target filter spectrum type of a passive temperature compensation gain flattening filter. And determining a compensation spectrum type which can be actually achieved by the temperature compensator and a filter spectrum type of the passive temperature compensation gain flattening filter under each temperature condition by combining a formula according to the self property of the temperature compensator. And superposing the reference temperature gain flattening filter spectrum type on the extra compensation spectrum of the temperature compensator according to the actual adjustment to obtain the target filter spectrum type of the passive temperature compensation gain flattening filter. The invention provides theoretical and data basis for the application of the passive temperature compensation gain flattening filter in practice.
Description
Technical Field
The invention belongs to an optical fiber communication system, and particularly relates to a method for determining a filter spectrum shape of a passive temperature compensation gain flattening filter used by an optical fiber amplifier in an erbium-doped optical fiber amplifier.
Background
In optical fiber communication systems, optical fiber amplifiers, especially erbium-doped fiber amplifiers (EDFAs), have become one of the core devices of the systems. The production and practicality of EDFAs has greatly advanced the maturity and development of Wavelength Division Multiplexing (WDM) systems. After an erbium-doped fiber amplifier (EDFA) amplifies a signal, a gain difference, i.e., gain flatness, exists between different wavelengths, which may cause signal errors. As WDM system capacity and speed increase, the impact of EDFA gain flatness on system performance becomes more and more significant.
There are two main types of methods for achieving EDFA gain flattening: one is to add a Gain Flattening Filter (GFF) to the EDFA, and the other is to change the matrix material of the erbium doped fiber or to dope the erbium doped fiber with other substances to change the gain spectrum. However, the matrix material of erbium-doped fibers is typically formed prior to GFF device design, and therefore, gain flattening is usually achieved by incorporating a Gain Flattening Filter (GFF) during device design. The gain flattening filter mainly comprises a dielectric thin film filter, a fiber grating filter, a Mach-Zehnder (M-Z) filter, a photonic crystal fiber grating filter and a filter based on a high-birefringence fiber circulator. The gain flattening filter set forth below of the present invention refers to a Gain Flattening Filter (GFF) based on a dielectric thin film type, as a specific statement is not made.
In an EDFA, changes in ambient temperature cause changes in the stimulated absorption cross-section and stimulated emission cross-section of the gain medium Erbium Doped Fiber (EDF), thereby altering the gain spectrum of the EDFA. This may cause deterioration of the EDFA gain flatness upon temperature change, affecting the communication system performance. In order to improve the negative effect of this degradation of flatness, two aspects can be addressed: firstly, the temperature characteristic of an EDF region is improved, so that the erbium fiber keeps relatively stable temperature; secondly, according to the intrinsic temperature characteristic of the EDF, measures are taken to compensate the gain spectrum change caused by the temperature. For example, US6535329 proposes an arrangement using cassette technology to achieve relatively stable temperatures in the EDF region. The device has simple design and good temperature characteristic, and can keep the stable temperature of the EDF within a wider temperature range. The defects are that a larger space needs to be reserved for placing the heat preservation box in the EDFA mechanical design, a drive control circuit, temperature feedback and the like are needed in the circuit design and the software design, and the power consumption is larger during low-temperature work. A gain compensation device based on the Mach-Zehnder (M-Z) interference principle and temperature sensitive materials is proposed in US 9184554. The device utilizes a temperature sensitive optical coupler to divide collimated light into two beams of light, introduces optical path difference between the two beams of light, and then combines the beams of light for collimation (as shown in figure 2). According to the Mach-Zehnder interference principle, the optical power after wave combination is the cosine function of the wavelength and the extra attenuation, and if the two beams have proper optical path difference, the wavelength-dependent extra loss and the temperature-gain variation trend of the optical amplifier can be basically consistent (as shown in FIGS. 3a-3 b). Thus, the device can realize the temperature self-adaptive compensation of the gain variation of the optical amplifier, and the device is often combined with a thin film type gain flattening filter isolator core piece and a collimator to form a passive temperature compensation gain flattening filter (PTC GFF). The device is small in size and does not generate extra power consumption. Since the operating gains of the EDFAs are different, the lengths of the EDFs in the internal optical paths are very different, and the different lengths of the EDFs will cause the degree of the gain affected by the temperature to be different. In order to obtain a good gain compensation effect, the compensation spectrum type of the temperature-sensitive gain compensator needs to be matched with the gain difference value of the optical amplifier based on the reference temperature gain spectrum type in practical application as much as possible, so that higher requirements are provided for the design, debugging and installation of the compensator in different application occasions.
Disclosure of Invention
In order to solve the above technical problem, the present invention provides a method for determining a target spectral pattern of a passive temperature compensation gain flattening filter, comprising the following steps:
step 1, determining a plurality of characteristic working temperature points of the passive temperature compensation gain flattening filter;
step 2, testing the gain spectral line of the optical amplifier formed by the passive temperature compensation gain flattening filter at each characteristic working temperature point;
step 3, processing the gain spectral line to obtain an expected filter spectral line under a characteristic working temperature point and a corresponding expected compensation attenuation function delta ILGFF(T,λ)Expectation ofWherein T represents temperature and λ represents wavelength;
step 4, compensating attenuation function DeltaIL according to the expectationGFF(T,λ)Expectation ofThe material parameters and/or the structural parameters of the passive temperature compensation gain flattening filter;
and 5, determining a target spectrum type of the passive temperature compensation gain flattening filter according to the material parameters and/or the structure parameters.
In the above technical solution, the structural parameters of the passive temperature compensation gain flattening filter include an optical path difference OPD and a splitting ratio r of the passive temperature compensation gain flattening filter.
In the above technical solution, the structural parameters of the passive temperature compensation gain flattening filter include a shape, a thickness, and a length of a base of the passive temperature compensation gain flattening filter.
In the above technical solution, the material parameter of the passive temperature compensation gain flattening filter includes a thermal expansion coefficient of a base of the passive temperature compensation gain flattening filter.
In the above technical solution, the characteristic operating temperature points at least include two end points and a temperature point near a middle point on an operating temperature range of the passive temperature compensation gain flattening filter.
The invention also provides a method for determining the target spectrum type of the passive temperature compensation gain flattening filter, which comprises the following steps:
step 101, determining the working temperature range T of the passive temperature compensation gain flattening filterrange；
102, according to the working temperature range TrangeSelecting a reference temperature T of the passive temperature compensated gain flattening filterBaseAnd a limit temperature TLimitAnd the reference temperature TBaseAnd a limit temperature TLimitAt least one intermediate temperature T in betweenMid；
Step 103, estimating the average loss IL of the passive temperature compensation gain flattening filter in the working bandwidthPreset value of GFF；
Step 104, leveling the spectrum input into the passive temperature compensation gain flattening filter to ensure that the power difference of each wavelength is less than 1 dB;
step 105: the erbium fiber of the optical amplifier in the optical path to be detected is placed in a device capable of accurately controlling the temperature, and the passive temperature compensation gain flattening filter forms a part of the optical amplifier;
step 106: adjusting the temperature of the precisely controllable temperature device to the reference temperature TBaseSelecting the appropriate input power P of the optical amplifierInMaximum Gain, the output light of the optical amplifier is connected to a spectrum analyzer for spectrum analysis to obtain the Gain spectrum G of the optical amplifierEDF(TBase,λ)；
Step 107, determining the average loss IL estimated in step 103Preset value of GFFIf it is correct, the reference temperature T is obtained by repeating steps 103-106BaseTemporal filtered spectral pattern ILGFF(TBase,λ)；
Step 108, adjusting the temperature of the temperature-accurately controllable device to circulate the operating temperature range Trange；
Step 109, obtaining expected filtering spectral lines IL at different temperatures by processingGFF(TMid,λ)Expectation ofAnd ILGFF(TLimit,λ)Expectation of；
Step 110, determining the temperature TMidAnd TLimitDesired compensation decay function Δ IL in caseGFF(T,λ)Expectation of；
Step 111, determining an optical path difference OPD of the first optical path and the second optical path;
step 112, according to the intermediate temperature TMidAnd a limit temperature TLimitR (T, lambda) at temperature to obtain R (T) with proper spectral ratioLimit) And r (T)Mid)；
Step 113, obtaining r (T) according to step 112Limit) And r (T)Mid) And the material of the temperature-sensitive base is selected by combining the structural characteristics of the temperature-sensitive change base (301) so as to determine the temperature-sensitive material.
Step 114, obtaining a full temperature range T on the basis of step 113rangeR (T) in (A);
and 115, obtaining a target spectrum type of the passive temperature compensation gain flattening filter at any temperature in the full temperature range.
In the above technical solution, the average loss IL estimated in step 103 is determined in step 107Preset value of GFFThe method for judging whether the correctness is achieved specifically comprises the following steps:
computing ILGFF(TBase,λ)＝GEDF(TBase,λ)-MinGEDF(TBaseλ); with ILMean value ofIs ILGFF(TBaseλ) average loss over the entire band if ILPreset value of GFF-ILMean value ofIf | ≧ 0.5dB, the IL in the optical path is modified accordinglyPreset value of GFFUntil this condition is met.
In the above technical solution, the step 109 specifically includes:
calculate G (T)Mid,λ)-G(TBaseλ), the minimum of:
min(G(TMid,λ)-G(TBase,λ))，
calculate G (T)Limit,λ)-G(TBaseλ), the minimum of:
min(G(TLimit,λ)-G(TBase,λ))
the temperature is TMidThe desired gain-flattened filtered spectrum is then:
ILGFF(TMid,λ)expectation of＝G(TMid,λ)-min(G(TMid,λ))+|min(G(TMid,λ)-G(TBase,λ))|
Temperature TLimitThe desired gain-flattened filtered spectrum is then:
ILGFF(TLimit,λ)expectation of＝G(TLimit,λ)-min(G(TLimit,λ))+|min(G(TLimit,λ)-G(TBase,λ))|。
In the above technical solution, r (T) of the spectral ratio determined in the step 112 isLimit) And r (T)Mid) The following relationship is satisfied:
wherein, Δ ILGFF(TMid,λ)Expectation of＝ILGFF(TMid,λ)Expectation of-ILGFF(TBase,λ)
ΔILGFF(TLimit,λ)Expectation of＝ILGFF(TLimit,λ)Expectation of-ILGFF(TBase,λ)。
The invention also provides a passive temperature compensator applied to the optical fiber amplifier, which comprises an incident optical fiber, a temperature sensitive light splitting device, an optical path with a first optical path, an optical path with a second optical path, a wave combining device and an emergent optical fiber; the light beam entering the temperature sensitive light splitting device through the incident optical fiber is split into a first light beam and a second light beam according to a splitting ratio, the first light beam and the second light beam respectively enter the wave combining device after passing through a light path with a first optical path and a light path with a second optical path, and the combined light beam is output through the emergent optical fiber; the temperature sensitive light splitting device comprises a temperature sensitive change base; the temperature-sensitive change base comprises bimetallic strips with different thermal expansion coefficient combinations; the light splitting proportion of the temperature sensitive light splitting device changes under the pushing of the bimetallic strip along with the temperature deformation.
The invention achieves the following technical effects:
compared with the prior art, the invention provides a scheme of adopting bimetallic strips with different thermal expansion coefficients as a temperature sensitive change base, and further provides an experiment and data processing scheme for determining thermal expansion coefficient factors of the temperature sensitive change base by testing EDFA gain spectral lines with different temperatures to obtain a target gain flat filter spectral line. The obtained passive temperature compensation gain flat filter spectrum type at each temperature is highly matched with the practical application environment.
Drawings
FIG. 1 is an example of a prior art intrinsic gain 25dB optical amplifier temperature versus gain variation spectrum;
FIG. 2 is a schematic diagram of a prior art passive temperature gain compensator;
FIG. 3a is a right side view of a schematic diagram of a passive temperature gain compensator of the prior art, showing the splitting of a light beam at a reference temperature;
FIG. 3b is a right side view of a schematic diagram of a passive temperature gain compensator in the prior art, showing beam splitting after temperature changes relative to a reference temperature;
FIG. 3c is a schematic illustration of the bimetallic strip of the present invention at a base temperature;
FIG. 3d is a schematic illustration of the bimetallic strip of the present invention undergoing a change in temperature;
FIG. 4 is an enlarged view of a portion of FIG. 3 b;
FIG. 5 illustrates an example of an OPD of 45um with a temperature compensation device using a specific temperature sensitive material base to compensate for an extra attenuation curve of an intrinsic gain 25dB optical amplifier at different temperatures;
fig. 6 illustrates the gain residual after the temperature compensation device of the present invention is used inside the optical amplifier.
The labels in the figure are:
201-fiber 202-incident light beam
203-temperature sensitive beam splitting device 204-beam 1
205-light beam 2206-optical path L1
207-optical path L2208-optical path 2
209-optical path 1210-wave combining device
211-fiber 212-outgoing beam
301-temperature sensitive change base 302-medium 1
303-Medium 2
Detailed Description
The invention is described in further detail below with reference to the accompanying drawings and detailed description, in order to facilitate the understanding and implementation of the invention by those skilled in the art.
Fig. 1 is an example of the variation of the gain with different temperatures in the case of a built-in GFF setting the intrinsic gain of an optical amplifier to 25dB without temperature compensation measures, wherein the gain variation trend of the optical amplifier is illustrated by the variation of the gain with a typical 25 (celsius), 55 (celsius), and 70 (celsius) degrees relative to a limit operating temperature of-5 (celsius). Temperature-the amount of gain variation is related to the intrinsic gain of the optical amplifier, the greater the intrinsic gain, the greater the amount of gain variation due to temperature variation. If the base temperature is set to TBaseExample T of FIG. 1BaseThe gain changes represented by the curves "25 c-5 c" and "75 c-5 c" in the figure are the gain difference Δ G of the gain spectrum with respect to the base temperature under the condition of temperature change, which is-5 c (c is centigrade, the same applies hereinafter)EDF(T, λ), the amount of gain that the temperature gain compensator is expected to compensate for at different temperatures. The gain of the optical amplifier and the spectrum type of the built-in GFF filter have the following formula:
GEDF(T,λ)＝ΔGEDF(T,λ)+GEDF(Tbase,λ) (1)
ILGFF(T,λ)＝ΔILGFF(T,λ)+ILGFF(Tbase,λ) (2)
ΔILGFF(T,λ)＝ΔGEDF(T,λ)≥0 (3)
g in formula (1)EDF(Tbaseλ) is the gain spectrum at the reference temperature of the optical amplifier, GEDF(T, λ) is the gain spectrum type of the target temperature of the optical amplifier, Δ GEDF(T, λ) is the difference in gain for the base and target temperature cases. IL in formula (2)GFF(Tbaseλ) is the filter spectrum at base temperature, i.e. the filter spectrum of the gain flattening filter, ILGFF(T, λ) is the ideal filter spectrum pattern for the target temperature, Δ ILGFF(T, λ) is the difference between the base temperature filter spectrum pattern and the target temperature filter spectrum pattern, and Δ IL can be consideredGFF(T, λ) is the gain that needs to be compensated for at the ideal case target temperature. Equation (3) illustrates the ideal case of temperature of the gain compensator-the amount of extra attenuation and the intrinsic gain difference at different temperatures of the optical amplifier are consistent. For convenience of calculation, Δ G was determined experimentallyEDF(T, λ) to equivalently obtain Δ ILGFF(T, λ) to obtain desired gain-flattened filtered spectra for different temperatures.
Like the conventional GFF, the PTC GFF also uses attenuation to achieve gain equalization. The temperature compensator is based on the Mach-Zehnder interference principle, utilizes a temperature-sensitive light splitting device to divide collimated light into two parts, introduces an optical path difference into the two beams of light, enables the light power of different wavelengths to be changed after the light is combined, and records the wavelength-the variation of the light power as the temperature-an extra attenuation value.
The working principle of the passive temperature compensator is shown in fig. 2. In practical situations, the optical fiber collimator is arranged in front of the temperature compensator, and the isolator core piece and the GFF filter collimator are arranged behind the temperature compensator to form the PTC GFF, which is not described in detail herein. The collimated incident beam 202 enters the temperature-sensitive light splitting device 203 through the optical fiber 201, is split into a beam 1204 and a beam 2205 according to a certain (tunable) proportion, the beam 1204 and the beam 2205 enter the wave combining device 210 after passing through a light path 1209 and a light path 2208 respectively, and an emergent beam 212 after wave combining is output through the optical fiber 211. The relationship between the optical path L1206 of the optical path 1209 and the optical path L2207 of the optical path 2208 and the light splitting ratio of the temperature sensitive light splitting device 203 satisfy the following requirements.
The transfer function of the output beam 212 after the beam 202 has been compensated by the apparatus of FIG. 2 is expressed as R (T, λ)
Where r is r (T), which is the splitting ratio of the temperature sensitive splitting device 203, OPD is the optical path difference between the light beam 205 and the light beam 204, T is the ambient temperature, and λ is the light beam wavelength. Without considering the intrinsic insertion loss of the compensation device, let the optical power of beam 202 be Pin, the optical power of beam 204 after passing through the temperature sensitive beam splitter 203 be rPin, and the optical power of beam 205 be (1-r) Pin. From equation (4), it can be seen that R (T, λ) is a wavelength dependent cosine function, and the selection of the OPD value affects the period of the function. Schematic diagrams of the change of r with temperature are shown in fig. 3a and 3 b. At the reference temperature (fig. 3a), the temperature compensator does not effectively affect the beam 202, when r is 0; when the temperature changes (fig. 3b), the temperature compensator divides the light beam into 204 and 205 after the temperature changes; it can be seen that the difference in refractive index between the OPD and media 302 and 303 is related to the media thickness. In practice the OPD is chosen in relation to the choice of the operating bandwidth of the optical amplifier and the reference temperature. In order to match the gain variation of each temperature of the optical amplifier relative to the reference temperature as much as possible, the OPD corresponding to the C-BAND optical amplifier with the working bandwidth of 1528nm to 1565nm is usually 38-45 um when the reference temperature is selected to be low temperature, and the OPD is about 55um when the reference temperature is selected to be high temperature; an L-BAND optical amplifier with an operating bandwidth of 1570nm to 1608nm tends to select the lowest temperature in the temperature range as the reference temperature due to its special performance, where the OPD is around 48 um. In the temperature-sensitive change base 301 shown in fig. 3a and 3b, the splitting ratio r changes according to a certain temperature law, and the r can be expected to follow the temperature law by the design of the temperature-sensitive change base 301.
For this reason, a bimetal may be selected as the temperature-sensitive change base. The deformation of bimetallic strip is based on the thermal expansion coefficient difference of metal, and when the temperature changes, the deformation of initiative layer is greater than the deformation of passive layer to the whole of bimetallic strip will be to passive layer one side bending, produce deformation. The bimetallic strip has the characteristic of simple processing, and the temperature-sensitive change base processed by the bimetallic strip has good repeatability and consistency of temperature-deformation under the conditions that the shape of the bimetallic strip is determined and the materials of the active layer and the passive layer are determined. The general passive layer can be made of nickel-iron alloy with nickel content of 34-50%, the active layer is mainly made of manganese-nickel-copper alloy, nickel-chromium-iron alloy, nickel-manganese-iron alloy, nickel and the like, the thermal expansion coefficient of the alloy material can be known by inquiring the linear expansion coefficient of the first coil of material in mechanical design manual, and the temperature-deformation quantity of the bimetallic strip under the condition of different material combinations can be obtained by combining the determined shape parameters of the bimetallic strip through calculation. The deformation quantity of the bimetallic strip temperature-sensitive base expected under different temperatures can be obtained through the formulas (1) to (4), and the bimetallic strip temperature-sensitive base with determined materials can be obtained. Therefore, the bimetallic strip is selected as the temperature-sensitive change base, so that the design option work can be simplified, the production and manufacturing cost is reduced, and the design, the debugging and the installation of the compensator are very facilitated.
For example, fig. 3c shows the bimetal shape at the reference temperature, fig. 3d shows the bimetal shape after the temperature change, and the bimetal shape is not limited to a rectangular shape and may be other shapes.
Fig. 4 is a partially enlarged schematic diagram of fig. 3b, and the temperature-sensitive change base 301 changes the relative position of the interface between the medium 1302 and the medium 2303 and the incident light beam 202 with the temperature change, so that the proportion of the incident light beam 202 entering the medium 1302 and the medium 2303 is related to the height change h of the temperature-sensitive change base 301. If the variation of r with temperature caused by the amount of temperature deformation of the selected bi-metallic material is expected, the wavelength-extra attenuation variation caused by the variation of r and the gain variation trend after the temperature variation of the optical amplifier are very similar according to equation (4). Taking the reference temperature selection of-5 degrees as an example, the gain curve of the C-BAND optical amplifier is compensated, and the appropriate medium 1, medium 2 and appropriate medium thickness can be selected so that the OPD is 45 um.
Fig. 5 shows a graph of the additional attenuation of an optical amplifier with an added temperature compensator based on a reference temperature, for which the example is directed to the same optical amplifier as given in the example of fig. 1. Due to the characteristics of the temperature compensator, the variation of the gain of the light beam passing through the temperature compensator is a cosine curve, and the function of freely designing any gain spectrum type is not provided. The gain flatness of the optical amplifier after the introduction of the temperature gain compensation device still has a residual temperature dependence of about 0.2dB, as shown in fig. 6. This typically does not introduce additional gain flatness degradation unless the residual correlation coincides with the GFF maximum error. The minimum insertion loss of the PTC GFF is equal to the insertion loss of the GFF filter at the reference temperature.
Based on the temperature gain compensation device, the invention provides a method for determining a target spectrum type of a passive temperature compensation gain flattening filter, which comprises the following steps:
step 1: determining PTC GFF operating temperature range Trange。
The determination of the filter spectrum pattern of a conventional optical amplifier is generally performed at a specific temperature without considering the gain spectrum pattern variations of other temperatures. The PTC GFF target spectrum type is determined according to the gain spectrum line of the optical amplifier at different temperatures. The internal temperature of the optical amplifier cannot be simply understood as being equal to the ambient temperature, and the internal temperature gradient is often related to the ambient temperature, the mechanical structure, the position of a heat source (i.e., a pump used in the optical amplifier), and the like, and in some cases, the difference between the ambient temperature and the temperature of the passive device stacking region may reach more than 10 ℃. Since the core of the passive temperature compensator is that the wavelength-dependent loss of the temperature compensator changes with the temperature change, determining the operating temperature range of the PTC GFF requires comprehensive consideration in combination with the operating temperature range of the optical amplifier (i.e., the ambient temperature range), the heat dissipation analysis of the optical amplifier, and the like. This is not discussed in detail since it is not the focus of the present invention. The position temperature of the PTC GFF can be amplified along with the ambient temperature and lightThe mechanical structure of the device is different in design and cannot be simply equal to the ambient temperature. It is therefore necessary first to correctly evaluate the operating temperature range T of PTCGFFrange。
Step 2: the reference temperature of the PTC GFF is selected. In general, in the case of a base temperature determination, the parasitic losses of a passive temperature compensator increase with a single directional change in temperature. For simplicity, an extreme temperature within the operating range, i.e., the maximum temperature Max (T) should be selectedrange) Or minimum temperature Min (T)range) As a reference temperature TBaseAt a reference temperature TBaseTaking the other extreme temperature as the limit temperature T under the selected conditionLimit。
And step 3: the average loss of the GFF over the operating bandwidth is estimated. Since GFF losses at different wavelengths are different, for experimental simplicity, a suitable loss IL can be estimated in advancePreset value of GFFPlaced in the EDFA circuit at a position that replaces the GFF as an average attenuation of the GFF.
And 4, step 4: the input spectrum is leveled such that the test light source flatness is <1 dB.
And 5: the erbium fiber EDF of the optical path to be tested is placed in a device capable of accurately controlling the temperature, such as a temperature circulating box, and in order to simplify the experiment, other optical devices except the EDF can be placed outside the temperature box, so that the influence of temperature-dependent loss (namely TDL) of other optical devices on the experiment result is reduced.
Step 6: at a reference temperature TBaseNext, an appropriate input point, a maximum gain point, is selected, and the optical power is measured using a standard optical power meter. The input light is adjusted to reach the optical power, and the pumping current of the optical amplifier is changed to make the output power equal. The output light is connected to a spectrum analyzer for gain spectrum test of EDFA to obtain GEDF(TBase,λ)
And 7: and evaluating whether the average loss estimated in the step 3 is correct or not. For the spectrum G obtained in step 6EDF(TBaseLambda) is processed within a certain bandwidth,
ILGFF(TBase,λ)＝GEDF(TBase,λ)-MinGEDF(TBase,λ) (5)
with ILMean value ofIs ILGFF(Tbaseλ), if ILPreset value of GFF-ILMean value ofIf | ≧ 0.5dB, IL in the optical path needs to be modified accordinglyGFFRepeating steps 6 and 7 until the correct IL is obtained, according to the preset valueGFF(TBase,λ)。ILGFF(TBaseAnd λ) is a filter spectrum at the base temperature, that is, a filter spectrum of the gain flattening filter.
And 8: changing the temperature of the temperature circulation box according to the temperature range evaluated in the step 1, circulating the whole working temperature range Trange. The whole temperature range T can be adjustedrangeIs divided into three parts TBase，TMidAnd TLimit. Wherein T isMid＝(TBase+TLimit) 2, i.e. TrangeThe median value of (d); t isLimitIs equal to TBaseRelative Max (T)range) Or Min (T)range) I.e. temperature range TrangeMaximum or minimum value of. Repeating step 6 after the temperature is stabilized for 30 minutes to obtain G (T, lambda) at different temperatures, such as the limiting temperature TLimitAnd a reference temperature TBaseG (T) ofLimitλ) and G (T)Baseλ). The current settings of the pumps should be changed accordingly during temperature changes so that the gain of the EDFA remains unchanged.
This step may also subdivide the temperature range according to specific needs. In principle there should be at least 3 temperature test points and the distribution of the temperature test points should cover the entire operating temperature range as uniformly as possible.
And step 9: data processing-G (T, λ) is processed to obtain desired filtering lines IL at different temperaturesGFF(TMid,λ)Expectation ofAnd ILGFF(TLimit,λ)Expectation of. From the above formula (4), it can be known that the temperature compensator can only increase the extra attenuation when the temperature changes from the reference temperature, so that the following formula (6) must be satisfied when data processing is performed in combination with the actual situation
G(T,λ)-G(TBase,λ)≥0
Min{G(T,λ)-G(TBase,λ)}≈0 (6)
And G (T)Limit,λ)>＝G(TMid,λ)>＝G(TBase,λ)
The specific data processing process is as follows:
taking min (G (T)Mid,λ)-G(TBase,λ))，min(G(TLimit,λ)-G(TBase,λ))
The temperature is TMidThe desired gain-flattened filtered spectrum is then:
ILGFF(TMid,λ)expectation of＝G(TMid,λ)-min(G(TMid,λ))+|min(G(TMid,λ)-G(TBase,λ))|
Temperature of TLimitThe desired gain-flattened filtered spectrum is then:
ILGFF(TLimit,λ)expectation of＝G(TLimit,λ)-min(G(TLimit,λ))+|min(G(TLimit,λ)-G(TBase,λ))|
Step 10: temperature compensator at temperature T according to previous step 9MidAnd TLimitDesired compensation decay function Δ IL in caseGFF(T,λ)Expectation of. The following were used:
ΔILGFF(TMid,λ)expectation of＝ILGFF(TMid,λ)Expectation of-ILGFF(TBase,λ)
ΔILGFF(TLimit,λ)Expectation of＝ILGFF(TLimit,λ)Expectation of-ILGFF(TBase,λ)
Step 11: determining an optical path difference OPD
Let λInitiation ofThe starting wavelength being the operating wavelength of the optical amplifier, typically short wavelength, e.g. 1528.6nm；λCut-offCut-off wavelength for the operating wavelength of the optical amplifier, typically long wavelength, e.g. 1566.9nm
From the result obtained in step 10, λ is counted ═ λ0When is, Δ ILGFF(TMid,λ0)Expectation of＝ΔILGFF(TLimit,λ0)Expectation ofE.g. by calculating λ0＝1553.2nm。
Comparison of lambda0-λInitiation ofAnd λCut-off-λ0The larger value between the two is an integer, in the above example λ0-λInitiation of＝24.6nm，λCut-off-λ0＝13.7nm
OPD＝n·λ0Where n is a positive integer greater than the comparison value, and n is 25 in the above example, OPD 25 × 1553.2nm 38830nm
Step 12: determining r (T) in equation (4)Limit) And r (T)Mid) I.e. temperature range TrangeInner highest or lowest limit temperature TLimitAnd intermediate temperature TMidThe light splitting proportion can increase the test points of r (t) according to the requirement so as to obtain more accurate results.
Obtaining T according to the formula (4)MidAnd TLimitR (T) at temperatureMidλ) and R (T)Limitλ), so that the following relationship is satisfied:
selecting proper light splitting ratio r (T)Limit) And r (T)Mid) So that the above two equations hold.
Step 13: the spectral ratio r (T) obtained in step 12Limit) And r (T)Mid) H (T) can be obtained by simple area ratio calculationLimit) And h (T)Mid) And h (t) is the longitudinal displacement of the temperature sensitive base at different temperatures. In the case where the temperature sensitive base 301 is structurally determined, a desired coefficient of thermal expansion dependent factor of the temperature sensitive material can be obtained. Taking the bimetallic strip temperature-sensitive base shown in fig. 3c and 3d as an example, two kinds of temperature-sensitive bases can be obtained by the above stepsThe thermal expansion coefficient difference of the metal materials is used as the basis to compare the thermal expansion coefficient table of the metal, and the required material combination can be obtained.
Step 14: on the basis that the temperature-sensitive material is determined, the light splitting ratio r (t) in the whole temperature range can be obtained through calculation by considering factors such as the thermal expansion coefficient of the material, the structure of the temperature-sensitive change base and the like; taking the bimetal temperature-sensitive base of fig. 3c and 3d as an example, the required r (t) of the full temperature range can be obtained according to the factors such as the difference of the thermal expansion coefficients of the bimetal, the thickness of the bimetal, the length of the bimetal, and the variation of the temperature relative to the reference temperature.
Step 15: the optical path difference OPD and the splitting ratio r (T) are determined according to the steps, and the temperature range T can be obtainedrangeTarget spectral pattern of the passive temperature compensation gain flattening filter at any internal temperature:
it should be emphasized that, in general, in order to obtain the target spectrum pattern of the passive temperature compensation gain flattening filter, at least 3 temperature test points are selected, and the thermal expansion coefficient of the temperature-sensitive change base material can be determined by data processing and calculation under the premise of determining the structure of the temperature-sensitive change base 301. Therefore, the proper selection of more temperature test points can have beneficial effect on determining the thermal expansion coefficient of the temperature-sensitive material.
While the invention has been particularly shown and described with reference to a particular embodiment thereof, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention. Such modifications are intended to fall within the scope of the invention as claimed.
Claims (10)
1. A method for determining a target spectral pattern of a passive temperature compensated gain flattening filter, comprising the steps of:
step 1, determining a plurality of characteristic working temperature points of the passive temperature compensation gain flattening filter;
step 2, testing the gain spectral line of the optical amplifier formed by the passive temperature compensation gain flattening filter at each characteristic working temperature point;
step 3, processing the gain spectral line to obtain an expected filter spectral line under a characteristic working temperature point and a corresponding expected compensation attenuation function delta ILGFF(T,λ)Expectation ofWherein T represents temperature and λ represents wavelength;
step 4, compensating attenuation function DeltaIL according to the expectationGFF(T,λ)Expectation ofDetermining temperature-sensitive base material parameters and/or structural parameters of the passive temperature compensation gain flattening filter;
and 5, obtaining the actual spectrum type of the passive temperature compensation gain flattening filter according to the material parameters and/or the structure parameters of the temperature-sensitive base in the step 4.
2. A method of determining a target spectral pattern for a passive temperature compensated gain flattening filter as defined in claim 1, wherein: the structural parameters of the passive temperature compensation gain flattening filter comprise an optical path difference OPD and a splitting ratio r of the passive temperature compensation gain flattening filter.
3. A method of determining a target spectral pattern for a passive temperature compensated gain flattening filter according to claim 1 or 2, characterized by: the structural parameters of the passive temperature compensation gain flattening filter comprise the shape, the thickness and the length of a base of the passive temperature compensation gain flattening filter.
4. A method of determining a target spectral pattern for a passive temperature compensated gain flattening filter according to claim 1 or 2, characterized by: the material parameters of the passive temperature compensation gain flattening filter include a coefficient of thermal expansion of a base of the passive temperature compensation gain flattening filter.
5. A method of determining a target spectral pattern for a passive temperature compensated gain flattening filter according to claim 1 or 2, characterized by: the characteristic operating temperature points include at least temperature points near two endpoints and a midpoint on an operating temperature range of the passive temperature compensated gain flattening filter.
6. A method for determining a target spectral pattern of a passive temperature compensated gain flattening filter, comprising the steps of:
step 101, determining the working temperature range T of the passive temperature compensation gain flattening filterrange；
102, according to the working temperature range TrangeSelecting a reference temperature T of the passive temperature compensated gain flattening filterBaseAnd a limit temperature TLimitAnd the reference temperature TBaseAnd a limit temperature TLimitAt least one intermediate temperature T in betweenMid；
Step 103, estimating the average loss IL of the passive temperature compensation gain flattening filter in the working bandwidthPreset value of GFF；
Step 104, leveling the spectrum input into the passive temperature compensation gain flattening filter to ensure that the power difference of each wavelength is less than 1 dB;
step 105: the erbium fiber of the optical amplifier in the optical path to be detected is placed in a device capable of accurately controlling the temperature, and the passive temperature compensation gain flattening filter forms a part of the optical amplifier;
step 106: adjusting the temperature of the precisely controllable temperature device to the reference temperature TBaseSelecting the appropriate input power P of the optical amplifierInMaximum Gain, the output light of the optical amplifier is connected to a spectrum analyzer for spectrum analysis to obtain the Gain spectrum G of the optical amplifierEDF(TBase,λ)；
Step 107, determining the average loss IL estimated in step 103Preset value of GFFIf it is correct, the reference temperature T is obtained by repeating steps 103-106BaseTemporal filtered spectral pattern ILGFF(TBase,λ)；
Step 108, adjusting the temperature of the temperature-accurately controllable device to circulate the operating temperature range Trange；
Step 109, obtaining expected filtering spectral lines IL at different temperatures by processingGFF(TMid,λ)Expectation ofAnd ILGFF(TLimit,λ)Expectation of；
Step 110, determining the temperature TMidAnd TLimitDesired compensation decay function Δ IL in caseGFF(T,λ)Expectation of；
Step 111, determining an optical path difference OPD of the first optical path and the second optical path;
step 112, according to the intermediate temperature TMidAnd a limit temperature TLimitR (T, lambda) at temperature to obtain R (T) with proper spectral ratioLimit) And r (T)Mid)；
Step 113, obtaining r (T) according to step 112Limit) And r (T)Mid) The material of the temperature-sensitive base is selected by combining the structural characteristics of the temperature-sensitive change base (301) so as to determine the temperature-sensitive material;
step 114, obtaining a full temperature range T on the basis of step 113rangeR (T) in (A);
and 115, obtaining a target spectrum type of the passive temperature compensation gain flattening filter at any temperature in the full temperature range.
7. A method of determining a target spectral pattern for a passive temperature compensated gain flattening filter according to claim 6, characterized by: in the step 107, the average loss IL estimated in the step 103 is determinedPreset value of GFFThe method for judging whether the correctness is achieved specifically comprises the following steps:
computing ILGFF(TBase,λ)＝GEDF(TBase,λ)-MinGEDF(TBaseλ); with ILMean value ofIs ILGFF(TBaseλ) average loss over the entire band if ILPreset value of GFF-ILMean value ofIf | ≧ 0.5dB, the IL in the optical path is modified accordinglyPreset value of GFFUp to | ILPreset value of GFF-ILMean value of| ≧ 0.5dB is false.
8. A method of determining a target spectral pattern for a passive temperature compensated gain flattening filter as defined in claim 7, wherein: the step 109 specifically includes:
calculate G (T)Mid,λ)-G(TBaseλ), the minimum of:
min(G(TMid,λ)-G(TBase,λ))，
calculate G (T)Limit,λ)-G(TBaseλ), the minimum of:
min(G(TLimit,λ)-G(TBase,λ))
the temperature is TMidThe desired gain-flattened filtered spectrum is then:
ILGFF(TMid,λ)expectation of＝G(TMid,λ)-min(G(TMid,λ))+|min(G(TMid,λ)-G(TBase,λ))|
Temperature TLimitThe desired gain-flattened filtered spectrum is then:
ILGFF(TLimit,λ)expectation of＝G(TLimit,λ)-min(G(TLimit,λ))+|min(G(TLimit,λ)-G(TBase,λ))|
Wherein G (T)Baseλ) is a reference temperatureBaseGain spectrum type of lower, G (T)Midλ) is the gain spectrum pattern of the target temperature of the optical amplifier at intermediate temperature, G (T)LimitAnd lambda) is the gain spectrum type of the target temperature of the optical amplifier at the limit temperature.
9. A method of determining a target spectral pattern for a passive temperature compensated gain flattening filter as defined in claim 8, wherein: r (T) of the spectral ratio determined in said step 112Limit) And r (T)Mid) The following relationship is satisfied:
wherein, Δ ILGFF(TMid,λ)Expectation of＝ILGFF(TMid,λ)Expectation of-ILGFF(TBase,λ)
ΔILGFF(TLimit,λ)Expectation of＝ILGFF(TLimit,λ)Expectation of-ILGFF(TBase,λ)。
10. A passive temperature compensator applied to a fiber amplifier, the passive temperature compensator applied to a method for determining a target spectrum type of the passive temperature compensation gain flattening filter of any one of claims 1-9, comprising an incident fiber (201), a temperature sensitive light splitting device (203), a light path (209) with a first optical path, a light path (208) with a second optical path, a wave combining device (210) and an exit fiber (211); the light beam (202) entering the temperature-sensitive light splitting device (203) through the incident optical fiber (201) is split into a first light beam (204) and a second light beam (205) according to a splitting ratio, the first light beam (204) and the second light beam (205) respectively enter the wave combining device (210) after passing through a light path (209) with a first optical path and a light path (208) with a second optical path, and the combined light beam (212) is output through the emergent optical fiber (211); the method is characterized in that: the temperature-sensitive light splitting device (203) comprises a temperature-sensitive change base (301); the temperature-sensitive change base (301) comprises bimetallic strips with different thermal expansion coefficient combinations; the light splitting proportion of the temperature sensitive light splitting device (203) changes under the pushing of the bimetallic strip along with the temperature deformation.
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