Parameter matching method for grating with dispersion linear output

Abstract

The application provides a grating pair parameter matching method for dispersion linear output, which comprises the following steps: determining a target time delay value D corresponding to a center wavelength of an optical signal λ , a first grating equation when two gratings in the grating pair are parallel, and a first delay group equation related to the target time delay value D λ ; determining a vertical interval h of the grating pair and an incident angle i of the optical signal on a first grating in the grating pair according to the first delay group equation; calculating group time delays of two spectral components in the optical signal according to a second delay group equation when the two gratings in the grating pair are not parallel, the determined vertical interval h and the incident angle i; determining a group time delay-wavelength slope of the two spectral components according to the group time delays and wavelengths of the two spectral components; making the determined group time delay-wavelength slope equal to a target slope k of the group time delay-wavelength; and calculating an offset angle ε of a second grating in the grating pair. The application can make the optical signal output by the grating pair meet the set time delay-wavelength linear requirement.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of optical dispersion regulation, and particularly relates to a grating pair parameter matching method for linear dispersion output. BACKGROUND

[0002] With the development of science and technology, distance measurement is very important in the fields of aerospace, shipbuilding industry, etc. Traditional distance measuring tools such as tape measure have small measurement range, inaccurate scale and human eye recognition error, and cannot be applied to large-scale distance measurement. With the development of technology, there are more accurate and larger range distance measuring tools, such as infrared distance measurement, laser distance measurement and ultrasonic distance measurement. With the emergence of optical frequency comb, femtosecond optical frequency comb is used as an absolute distance measurement light source, which improves the measurement range, measurement accuracy and measurement speed. Chirped interferometric distance measurement uses the difference frequency signal formed by the reference signal and the measurement signal to obtain distance information, which has excellent metrological characteristics. In order to improve the accuracy and resolution of the distance measurement system, linear chirp signal is necessary. Usually, linear chirp pulse can be obtained by using dispersion compensation devices such as chirped fiber grating, dispersion fiber and grating pair.

[0003] The grating pair has simple structure, flexible adjustment, easy control of parameter change and strong dispersion capacity, and has good effect on generating linear chirp signal. However, in practice, the dispersion of the spectral components of the optical signal after passing through the grating pair with fixed structure may not present a linear change relationship with the wavelength, and the parameters of the grating pair such as grating vertical spacing h, grating offset angle ε and incident angle i of the optical signal on the grating pair will affect the linear relationship between time delay and wavelength.

[0004] Therefore, it is urgent to find a method for matching and regulating the parameters of the grating pair according to the wavelength range of the input optical signal, so that the time delay of each spectral component of the optical signal after passing through the grating pair has a linear relationship with the wavelength. SUMMARY

[0005] The application provides a grating pair parameter matching method for linear dispersion output, to solve the problem that there is no method for matching and regulating the parameters of the grating pair at present, and the output group delay-wavelength does not meet the linear requirement.

[0006] According to a first aspect of an embodiment of the application, a grating pair parameter matching method for linear dispersion output is provided, comprising:

[0007] In step S110, a target delay value D corresponding to the center wavelength of the optical signal incident to the grating pair is obtained. λ , a first grating equation when the two gratings in the grating pair are parallel, and the target delay value D λa first delay group equation related to the first grating pair, the vertical distance h and the incident angle i of all spectral components in the optical signal on the first grating in the grating pair are determined;

[0008] In step S120, according to the second delay group equation related to the two gratings in the grating pair not being parallel, the vertical distance h and the incident angle i, the group delay of the corresponding two spectral components in the optical signal is calculated, only the offset angle ε is unknown in the delay group, according to the group delay and the wavelength of the two spectral components, the group delay-wavelength slope of the two spectral components is determined, the determined group delay-wavelength slope is equal to the target slope k of the group delay-wavelength, and the offset angle ε of the second grating in the grating pair is calculated.

[0009] In an optional implementation, the step S110 specifically includes:

[0010] In step S111, for the central wavelength spectral component in the optical signal, the influence of the offset of the grating pair on the optical path of the spectral component is ignored, the two gratings in the grating pair are regarded as parallel, the first optical path equation of the spectral component in the grating pair is established, the first optical path equation is related to the vertical distance h and the incident angle i and the diffraction angle θ of the spectral component on the first grating;

[0011] In step S112, according to the first optical path equation and the speed of light, the first delay group equation of the spectral component is established, the first delay group equation is related to the target delay value D λ , the vertical distance h, the incident angle i and the diffraction angle θ of the spectral component on the first grating;

[0012] In step S113, according to the first delay group equation and the first grating equation, the combination of the vertical distance h and the incident angle i is obtained.

[0013] In another optional implementation, in step S111, the first optical path equation of the spectral component in the grating pair is established according to the following formula:

[0014]

[0015] Wherein, P represents the optical path of the spectral component in the grating pair, AB represents the distance between the incident points A and B of the spectral component on the two gratings in the grating pair, BC represents the distance from the incident point B to the exit receiving point C of the spectral component on the second grating in the grating pair, θ2 represents the diffraction angle of the spectral component on the second grating, i2 represents the incident angle of the spectral component on the second grating, and when the influence of the offset of the grating pair on the optical path of the spectral component is ignored, θ2 = i, i2 = θ, i represents the incident angle of the spectral component on the first grating, and θ represents the diffraction angle of the spectral component on the first grating.

[0016] In another optional implementation, the step S112 comprises establishing the first delay group equation of the spectral component according to the following formula:

[0017]

[0018] Wherein, P represents the optical path of the spectral component in the grating pair, and c represents the speed of light.

[0019] In the step S113, the first grating equation when the two gratings in the grating pair are parallel is:

[0020] (sin i + sin θ) = Gmλ

[0021] Wherein, G is the ruling density of the grating, m is the diffraction order, m = 1, and λ is the wavelength of the spectral component.

[0022] In another optional implementation, the step S120 specifically comprises:

[0023] In the step S121, the two gratings in the grating pair are considered to be non-parallel by taking into account the influence of the offset of the grating pair on the optical path of the optical signal, and the second optical path equation of each spectral component in the optical signal in the grating pair is established, which is related to the incident angle i and the diffraction angle θ of the corresponding spectral component on the first grating, the offset angle ε of the grating pair, the diffraction angle increment δ of the spectral component on the second grating when the offset angle of the grating pair is ε, and the vertical distance h.

[0024] In the step S122, the second delay group equation of each spectral component in the optical signal is established according to the second optical path equation, the relationship between the speed of light and the wavelength, and the second grating equation when the two gratings in the grating pair are non-parallel, which is related to the incident angle i and the diffraction angle θ of the corresponding spectral component on the first grating, the offset angle ε of the grating pair, the diffraction angle increment δ of the spectral component on the second grating when the offset angle of the grating pair is ε, the vertical distance h, and the frequency f of the spectral component.

[0025] Step S123, for each determined vertical interval h and incidence angle i, two spectral components are selected from the light signal, for each selected spectral component, the vertical interval h, the incidence angle i, the diffraction angle θ on the first grating corresponding to the wavelength of the spectral component, the diffraction angle increment δ on the second grating, and the frequency f of the spectral component are substituted into the second delay group equation respectively, the group delay of the spectral component is calculated, only the offset angle ε in the delay group is unknown, according to the group delay and wavelength of the two spectral components, the group delay-wavelength slope of the two spectral components is determined, the determined group delay-wavelength slope is equal to the target slope k, and the offset angle ε of the second grating in the grating pair is calculated.

[0026] In another optional implementation, in the step S121, the second optical path equation of each spectral component in the light signal in the grating pair is established according to the following steps:

[0027] P = AB + BC (1)

[0028] Wherein, P represents the optical path of the spectral component in the grating pair, AB represents the distance between the incident points A and B of the spectral component on the two gratings in the grating pair, and BC represents the distance from the incident point B to the exit receiving point C of the spectral component on the second grating;

[0029]

[0030] Wherein, AD represents the distance from the incident point A of the spectral component on the first grating to the second grating, i2 represents the incidence angle of the spectral component on the second grating, when considering the influence of the offset of the grating pair on the optical path of the spectral component, i2 = θ + ε, and θ2 = i + δ;

[0031] BC = BM - CM (3)

[0032] Wherein, M is the vertical intersection of the straight line passing through the incident point A and the straight line on which BC is located, BM represents the distance between the incident point B of the spectral component on the second grating and the vertical intersection M, and CM represents the distance between the exit receiving point C and the vertical intersection M;

[0033] BM = AB cos (θ2 - i2) = AB cos (i + δ - θ - ε) (4)

[0034] CM = AM tan (ε - δ) = AB sin (i + δ - θ - ε) tan (ε - δ) (5)

[0035] Wherein, AM represents the distance from the incident point A to the straight line on which BC is located;

[0036] Combining the above equations (1) to (5), the second optical path equation is obtained:

[0037]

[0038] In another optional implementation, in the step S122, the second grating equation when the two gratings in the grating pair are not parallel is: (sin(θ+ε)+sin(i+δ))=Gmλ

[0039] wherein G is the ruling density of the grating, m is the diffraction order, m=1, and λ is the wavelength of the spectral component;

[0040] In the step S122, according to the second optical path equation, the relationship between the speed of light and the wavelength c=λ*f, and the second grating equation, the second delay group equation of each spectral component in the optical signal is established according to the following equation:

[0041] D f represents the delay group.

[0042] In another optional implementation, the step S123 specifically includes:

[0043] For each group of vertical spacing h and incident angle i determined, two spectral components are selected from the optical signal, for each selected spectral component, the vertical spacing h, the incident angle i, the diffraction angle θ on the first grating corresponding to the wavelength of the spectral component, the diffraction angle increment δ on the second grating, and the frequency f of the spectral component are respectively substituted into the second delay group equation, and the group delay of the spectral component is calculated;

[0044] After the group delays D f1 and D f2 of the two spectral components are calculated, the group delay-wavelength slope of the two spectral components is determined according to the following equation, and the determined group delay-wavelength slope is equal to the target slope k:

[0045]

[0046] wherein, represents the group delay-wavelength slope of the two spectral components.

[0047] In another optional implementation, after the step S120, the method further includes:

[0048] In the step S130, for each group of grating pair parameters: vertical spacing h, incident angle i, and offset angle ε, if the offset angle ε in the group of grating pair parameters is zero, i.e., the two gratings in the grating pair are parallel, it is determined whether the first relationship is established, the first relationship is xgrating , the diffraction angle of the maximum wavelength spectral component in the light signal on the first grating max , the diffraction angle of the minimum wavelength spectral component on the first grating min and the vertical distance h of the two gratings in the grating pair, if yes, it indicates whether each spectral component in the light signal can be incident on the second grating, and the set of grating pair parameters is taken as the grating pair parameter to be output, if no, the set of grating pair parameters is deleted;

[0049] If the offset angle ε in the set of grating pair parameters is not zero, i.e. the two gratings in the grating pair are not parallel, then for each spectral component in the light signal, it is judged whether a second relationship is established, the second relationship is related to the grating pair size x grating , the diffraction angle of the maximum wavelength spectral component in the light signal on the first grating max , the diffraction angle of the central wavelength spectral component on the first grating mid , the diffraction angle of the minimum wavelength spectral component on the first grating min , the diffraction angle of the spectral component on the first grating, if the second relationship is established for each spectral component in the light signal, it indicates whether each spectral component in the light signal can be incident on the second grating, and the set of grating pair parameters is taken as the grating pair parameter to be output, otherwise, the set of grating pair parameters is deleted;

[0050] Step S140, calculating the linearity L of the group delay-wavelength curve corresponding to each set of grating pair parameters to be output n , selecting the set of grating pair parameters to be output with the smallest linearity L n as the final output grating pair parameter.

[0051] In another optional implementation, in the step S130, the first relationship is:

[0052] h[tan(θ max )-tan(θ min )]<x grating

[0053] The second relationship is:

[0054] l1+l2<x grting

[0055]

[0056] Wherein, A=90-ε+θ, C=90-θ.

[0057] The beneficial effects of the present application are:

[0058] 1、The present application calculates the vertical interval h of the grating pair, the offset angle ε of the second grating in the grating pair and the incident angle i of the optical signal on the first grating in the grating pair according to the wavelength range of the input optical signal and the required time delay-wavelength linear relationship, and sets the position of the grating pair and the incident angle of the optical signal by using the calculated parameters, so that the output optical signal can meet the set time delay-wavelength linear requirement, thus the linear chirp signal can be quickly obtained, which is of great significance in chirp interferometric ranging.

[0059] 2、The present application considers the size of the grating pair after obtaining a plurality of grating pair parameters, and selects the grating pair parameters as the output grating pair parameters only when all spectral components in the optical signal can be incident on the second grating, and then selects a group with the smallest linearity and the smallest linear error as the final output grating pair parameters from all the output grating pair parameters, so that the group delay-wavelength linear relationship of the chirp pulse obtained after the optical signal passes through the grating pair is better after setting the position of the grating pair and the incident angle of the optical signal based on the final output grating pair parameters. BRIEF DESCRIPTION OF DRAWINGS

[0060] Figure 1 is an embodiment flow chart of the grating pair parameter matching method for dispersion linear output of the present application;

[0061] Figure 2 is a schematic diagram of the grating pair structure and the optical path of a plurality of spectral components in the optical signal in the grating pair when the two gratings in the grating pair are parallel;

[0062] Figure 3 is a schematic diagram of the grating pair structure, the optical path of a single spectral component in the optical signal in the grating pair and its auxiliary line when the two gratings in the grating pair are not parallel;

[0063] Figure 4 (a) and (b) are schematic diagrams of the size limit of the grating pair when the two gratings in the grating pair are parallel and when the two gratings in the grating pair are not parallel, respectively;

[0064] Figure 5 is an embodiment schematic diagram of the dispersion output result of the grating pair of the present application. DETAILED DESCRIPTION

[0065] In order to enable the personnel in the technical field to better understand the technical solutions in the embodiments of the present application, and to make the above-mentioned purposes, features and advantages of the embodiments of the present application more apparent and easy to understand, the technical solutions in the embodiments of the present application will be further described in detail below with reference to the drawings.

[0066] In the description of the present application, unless otherwise specified and limited, it is necessary to explain that the term "connection" should be understood broadly, for example, it can be mechanical connection or electrical connection, it can be the internal communication of two elements, it can be direct connection or indirect connection through intermediate medium, and the specific meaning of the above-mentioned term can be understood according to the specific circumstances by those skilled in the art.

[0067] Referring to Figure 1 , an embodiment flow chart of the parameter matching method of the dispersion linear output grating pair of the present application. The parameter matching method of the dispersion linear output grating pair can include the following steps:

[0068] Step S110, according to the target time delay value D corresponding to the center wavelength of the optical signal incident to the grating pair λ , the first grating equation when the two gratings in the grating pair are parallel and the first delay group equation related to the target time delay value D λ , determine the vertical interval h of the grating pair and the incident angle i of all spectral components in the optical signal on the first grating in the grating pair, execute step S120. Wherein the incident angle i of all spectral components in the optical signal on the first grating is the same, after the optical signal is incident to the grating pair, the first grating in the grating pair will separate each spectral component in the optical signal by wavelength in space, as shown in Figure 2 .

[0069] The step S110 can specifically include:

[0070] Step S111, for the center wavelength spectral component in the optical signal, ignoring the influence of the offset of the grating pair on the optical path of the spectral component, considering the two gratings in the grating pair as parallel, establishing the first optical path equation of the spectral component in the grating pair, the first optical path equation is related to the vertical interval h and the incident angle i of the spectral component on the first grating and the diffraction angle θ.

[0071] In this step, for the center wavelength spectral component in the optical signal, the influence of the offset of the grating pair on the optical path of the spectral component can be ignored during the transmission of the spectral component in the grating pair, and the point B where the spectral component is incident to the second grating is regarded as the rotation center point of the second grating. Combined with Figure 3 , in the step S111, the first optical path equation of the spectral component in the grating pair can be established according to the following formula:

[0072] Wherein, P represents the optical path of the spectral component in the grating pair, AB represents the distance between the incident points A and B of the spectral component on the two gratings in the grating pair, BC represents the distance from the incident point B to the exit receiving point C of the spectral component on the second grating in the grating pair, θ2 represents the diffraction angle of the spectral component on the second grating, i2 represents the incident angle of the spectral component on the second grating in the grating pair, θ2 = i when the influence of the offset of the grating pair on the optical path of the spectral component is ignored, i2 = θ, i represents the incident angle of the spectral component on the first grating, and θ represents the diffraction angle of the spectral component on the first grating. It should be noted that the above first grating and second grating refer to the gratings through which the optical signal passes in turn in the grating pair.

[0073] In step S112, a first delay group equation of the spectral component is established according to the first optical path equation and the speed of light, and the first delay group equation is related to the target time delay value D λ , the vertical spacing h, the incident angle i and the diffraction angle θ of the spectral component on the first grating.

[0074] In step S112, the first delay group equation of the spectral component can be established according to the following formula:

[0075]

[0076] Wherein, D λ represents the target time delay value of the central wavelength spectral component in the optical signal, P represents the optical path of the spectral component in the grating pair, and c represents the speed of light.

[0077] In step S113, the vertical spacing h and the incident angle i are obtained by simultaneously solving the first delay group equation and the first grating equation.

[0078] Since the influence of the offset of the grating pair on the optical path of the central wavelength spectral component in the optical signal can be ignored, the two gratings in the grating pair are regarded as parallel, and at this time all the spectral components in the optical signal incident to the grating pair satisfy the first grating equation. In step S113, the first grating equation when the two gratings in the grating pair are parallel is:

[0079] (sin i + sin θ) = Gmλ

[0080] Wherein, G is the ruling density of the grating, m is the diffraction order, m = 1, and λ is the wavelength of the spectral component.

[0081] Since the first grating equation expresses the relationship between the incident angle i and the diffraction angle θ, the first grating equation is substituted into the first delay group equation to eliminate the diffraction angle θ, and a relationship expression for only expressing the vertical interval h and the incident angle i is obtained, so the combination of the vertical interval h and the incident angle i can be obtained according to the first delay group equation and the first grating equation.

[0082] In step S120, the group delay of the two spectral components in the optical signal is calculated according to the second delay group equation of the two gratings in the grating pair when the two gratings are not parallel, the determined vertical interval h and the incident angle i, the group delay of the two spectral components and the wavelength, the determined group delay-wavelength slope is equal to the target slope k of the group delay-wavelength, and the offset angle ε of the second grating in the grating pair is calculated.

[0083] In combination Figure 3 As shown in the figure, L1 and L2 respectively represent the normal lines of the first grating and the second grating, and the step S120 can specifically include:

[0084] In step S121, the influence of the offset of the grating pair on the optical path of the optical signal is considered, the two gratings in the grating pair are regarded as not parallel, the second optical path equation of each spectral component in the grating pair in the optical signal is established, and the second optical path equation is related to the incident angle i and the diffraction angle θ of the corresponding spectral component on the first grating, the offset angle ε of the grating pair, the diffraction angle increment δ of the spectral component on the second grating when the offset angle of the grating pair is ε, and the vertical interval h.

[0085] In the step S121, the second optical path equation of each spectral component in the grating pair in the optical signal can be established according to the following steps:

[0086] P = AB + BC (1)

[0087] Wherein, P represents the optical path of the spectral component in the grating pair, AB represents the distance between the incident points A and B of the spectral component on the two gratings in the grating pair, and BC represents the distance from the incident point B to the exit receiving point C of the spectral component on the second grating.

[0088]

[0089] Wherein, AD represents the distance from the incident point A of the spectral component on the first grating to the second grating, i2 represents the incident angle of the spectral component on the second grating (the normal line L2 of the second grating is parallel to the straight line AD), i2 = θ + ε when the influence of the offset of the grating pair on the optical path of the spectral component is considered, and θ2 = i + δ.

[0090] BC = BM - CM (3)

[0091] where M is the vertical intersection point of the straight line through the incident point A and the straight line where BC is located, BM represents the distance between the incident point B on the second grating and the vertical intersection point M of the spectral component, and CM represents the distance between the exit receiving point C and the vertical intersection point M;

[0092] BM = AB cos (θ2-i2) = AB cos (i+δ-θ-ε) (4)

[0093] CM = AM tan (ε-δ) = AB sin (i+δ-θ-ε) tan (ε-δ) (5)

[0094] where AM represents the distance from the incident point A to the straight line where BC is located;

[0095] In combination with the above formulas (1)-(5), the second optical path equation is obtained:

[0096]

[0097] In step S122, a second delay group equation of each spectral component in the optical signal is established according to the second optical path equation, the relationship between the speed of light and the wavelength, and the second grating equation when the two gratings in the grating pair are not parallel, the second delay group equation being related to the incident angle i and the diffraction angle θ of the corresponding spectral component on the first grating, the offset angle ε of the grating pair, the diffraction angle increment δ of the spectral component on the second grating when the offset angle of the grating pair is ε, the vertical distance h, and the frequency f of the spectral component.

[0098] In the step S122, the second grating equation when the two gratings in the grating pair are not parallel is:

[0099] (sin (θ+ε) + sin (i+δ)) = Gmλ

[0100] where G is the ruling density of the grating, m is the diffraction order, m = 1, and λ is the wavelength of the spectral component;

[0101] In the step S122, the second delay group equation of each spectral component in the optical signal is established according to the second optical path equation, the relationship between the speed of light and the wavelength c = λ*f, and the second grating equation, according to the following formula:

[0102] D f represents the delay group.

[0103] Step S123, for each determined set of vertical interval h and incident angle i, two spectral components are selected from the optical signal, for each selected spectral component, the vertical interval h, the incident angle i, the diffraction angle θ on the first grating corresponding to the wavelength of the spectral component, the diffraction angle increment δ on the second grating, and the frequency f of the spectral component are respectively substituted into the second delay group equation, the group delay of the spectral component is calculated, only the offset angle ε in the delay group is unknown, according to the group delay and the wavelength of the two spectral components, the group delay-wavelength slope of the two spectral components is determined, the determined group delay-wavelength slope is equal to the target slope k, and the offset angle ε of the second grating in the grating pair is calculated.

[0104] The step S123 can specifically include:

[0105] For each determined set of vertical interval h and incident angle i, two spectral components are selected from the optical signal, for each selected spectral component, the vertical interval h, the incident angle i, the diffraction angle θ on the first grating corresponding to the wavelength of the spectral component, the diffraction angle increment δ on the second grating, and the frequency f of the spectral component are respectively substituted into the second delay group equation, the group delay of the spectral component is calculated;

[0106] After the group delays D f1 and D f2 of the two spectral components are calculated, the group delay-wavelength slope of the two spectral components can be determined according to the following formula, and the determined group delay-wavelength slope is equal to the target slope k:

[0107]

[0108] Wherein, represents the group delay-wavelength slope of the two spectral components.

[0109] As can be seen from the above embodiment, according to the wavelength range of the input optical signal and the delay-wavelength linearity required for output, the vertical interval h of the grating pair, the offset angle ε of the second grating in the grating pair, and the incident angle i of the optical signal on the first grating in the grating pair are calculated, and the calculated parameters are used to set the position of the grating pair and the incident angle of the optical signal, so that the output optical signal can meet the set delay-wavelength linearity requirement, and thus the linear chirp signal can be quickly obtained, which is of great significance in chirp interferometric ranging.

[0110] In order to match the grating pair parameters as soon as possible according to the input optical signal wavelength range, so as to meet the user's required time delay-wavelength linearity requirement, a matching model of the grating pair parameters can be established. When establishing the model, the following steps can be included: model preparation: first understand the structure of the grating pair and its dispersion effect on the incident light, determine the requirements of the output results and the functions to be achieved. Model construction: according to the structure of the grating pair, the corresponding mathematical model is established, and the input, output and invariant parameters are determined. Model solution: there are many constraint relationships in the structure of the grating pair, according to the design purpose, the best value of the to-be-determined parameters is selected by focusing on analysis.

[0111] The model preparation includes: the model is the input of the desired group delay and the slope of the group delay-wavelength curve, the corresponding grating pair parameters are obtained, and the linearity optimal condition is met. Then the design purpose of the method is: according to the target group delay and the slope, the corresponding grating pair parameters are calculated; the output result meets the linearity optimal; the model is equivalent to the model of the single-mode fiber.

[0112] The grating pair structure and its optical path diagram are shown in Figure 2 The optical signal containing multiple wavelength spectral components is incident on the first grating at point A to diffract, the incident angle is i, the diffraction angles θ of different wavelength spectral components are different, and different wavelength spectral components are separated in space and incident on different points of the second grating, and it is assumed that the spectral components diffract at point B of the second grating and are finally received at point C. Then the output group delay D λ , the slope k of the group delay-wavelength and the linearity L n of the grating pair are related to the wavelength λ of the incident light, the incident angle i, the vertical spacing h of the grating pair, and the offset angle ε of the grating pair. The matching model can be defined as:

[0113] (D f , k, L n ) = f(λ, i, h, ε)

[0114] As can be seen from the above, the establishment of the matching model also takes into account the size problem and the linearity problem of the grating pair. Therefore, the present application can further include the following steps after the step S120:

[0115] Step S130, for each set of grating pair parameters: vertical spacing h, incident angle i and offset angle ε, if the offset angle ε in the set of grating pair parameters is zero, i.e. the two gratings in the grating pair are parallel, then it is judged whether the first relationship is established or not, the first relationship is related to the size x grating of the grating pair, the diffraction angle θ max of the maximum wavelength spectral component in the optical signal on the first grating, and the diffraction angle θ minand the vertical distance h between the two gratings in the grating pair, if yes, it indicates whether each spectral component in the light signal can be incident on the second grating, and if no, the grating pair parameters are deleted;

[0116] If the offset angle ε in the grating pair parameters is not zero, i.e., the two gratings in the grating pair are not parallel, then for each spectral component in the light signal, it is determined whether a second relationship is established, the second relationship being related to the grating pair size x grating , the diffraction angle θ max of the spectral component with the maximum wavelength on the first grating mid , the diffraction angle θ min of the spectral component with the minimum wavelength on the first grating max , the diffraction angle θ min of the spectral component on the first grating, if the second relationship is established for each spectral component in the light signal, it indicates whether each spectral component in the light signal can be incident on the second grating, and if not, the grating pair parameters are deleted.

[0117] In combination with Figure 4 (a) and (b), the first relationship in the step S130 can be:

[0118] h[tan(θ max )-tan(θ min )]<x grating

[0119] The size x grating of the grating pair can be the length of the grating in the grating pair in a first direction, the first direction being the direction in which the first grating in the grating pair separates each spectral component in the light signal in space according to wavelength after the light signal is incident on the grating pair, or the side length when the gratings in the grating pair are square.

[0120] The second relationship can be:

[0121] l1+l2<x grating

[0122]

[0123] Wherein, A = 90-ε+θ, C = 90-θ.

[0124] In the step S140, the linearity L n of the group delay-wavelength curve corresponding to each set of grating pair parameters to be output is calculated, and the linearity L nThe minimum set of grating pair parameters to be output is taken as the final output grating pair parameters.

[0125] The present application considers the size of the grating pair after obtaining multiple sets of grating pair parameters, and takes the set of grating pair parameters as the grating pair parameters to be output only when all spectral components in the optical signal can be incident on the second grating, and then selects the set with the minimum linearity and the minimum corresponding linearity error from all the grating pair parameters to be output as the final output grating pair parameters. Thus, based on the final output grating pair parameters, the position of the grating pair and the incident angle of the optical signal are set, and the group delay-wavelength linearity of the chirped pulse obtained after the optical signal passes through the grating pair is better.

[0126] Taking the wavelength range of the incident optical signal as 1530-1570nm, with the center wavelength being 1550nm, the dispersion coefficient D of the commonly used single-mode fiber at 1550nm is 17ps / (nm*km), which refers to the time delay difference of two wavelengths with a 1nm interval passing through a unit length of fiber. The slope kps / nm of the group delay-wavelength required by the present application refers to the time delay difference kps of two wavelengths with a 1nm interval passing through the dispersion system, which is equivalent to the dispersion of k / Dkm of single-mode fiber.

[0127] If the grating ruling density G used is 600 / mm, the grating size is 25mm*25mm*6mm (the side length*side length*vertical spacing of the square grating), and the group delay of about 4ns and the slope of 1.2ps / nm are desired. The grating pair structure parameters obtained by using the method of the present application are: h=630mm, i=45°, and ε=1°. The corresponding linearity error of the dispersion is 4.343*10 -5 , and the output result is shown in Figure 5 . The equivalent length of the single-mode fiber is about 0.0706km.

[0128] Those skilled in the art will readily understand that the application is amenable to other embodiments upon reading the foregoing description and practicing the application disclosed herein. The application is intended to cover any variations, uses or adaptations of the application including departures from the present disclosure that are within its general purview and come within the purview of the claims. The foregoing description and examples have been set forth merely to illustrate the application and are not intended to be limiting. The true scope and spirit of the application is indicated by the appended claims.

[0129] It should be understood that the application is not limited to the precise construction and method described above and illustrated in the drawings, and that various modifications and changes can be made without departing from the scope thereof. The scope of the application is indicated by the appended claims rather than by the description and figures.

Claims

1. A method for matching parameters of a grating pair with linear dispersive output, characterized in that, include: Step S110: Based on the target time delay value D corresponding to the center wavelength of the optical signal incident on the grating pair. λ The first grating equation when the two gratings are parallel during grating alignment, and the time delay value D of the target. λ The relevant first delay group equation determines the vertical spacing h of the grating pair and the incident angle i of all spectral components in the optical signal on the first grating of the grating pair; Step S120: Based on the second delay group equation when the two gratings in the grating pair are not parallel, the determined vertical spacing h and incident angle i, calculate the group delay of the corresponding two spectral components in the optical signal. Only the offset angle ε is unknown in this delay group. Based on the group delay and wavelength of the two spectral components, determine the group delay-wavelength slope of the two spectral components, making the determined group delay-wavelength slope equal to the target slope k of the group delay-wavelength, and calculate the offset angle ε of the second grating in the grating pair.

2. The grating pair parameter matching method for dispersive linear output according to claim 1, characterized in that, Step S110 specifically includes: Step S111: For the center wavelength spectral component in the optical signal, ignore the influence of the offset of the grating pair on the optical path of the spectral component, regard the two gratings in the grating pair as parallel, and establish the first optical path equation of the spectral component in the grating pair. The first optical path equation is related to the vertical spacing h and the incident angle i and diffraction angle θ of the spectral component on the first grating. Step S112: Based on the first optical path equation and the speed of light, establish the first delay group equation for the spectral component. The first delay group equation and the target time delay value D λ The vertical spacing h and the spectral component are related to the incident angle i and diffraction angle θ of the first grating; Step S113: Solve the equations of the first delay group and the first grating simultaneously to obtain the combination of the vertical spacing h and the incident angle i.

3. The grating pair parameter matching method for dispersive linear output according to claim 2, characterized in that, In step S111, the first optical path equation for the spectral component within the grating pair is established according to the following formula: Where P represents the optical path length of the spectral component within the grating pair, AB represents the distance between the incident points A and B of the spectral component on the two gratings in the grating pair, BC represents the distance from the incident point B of the spectral component on the second grating in the grating pair to the exit receiving point C, θ2 represents the diffraction angle of the spectral component on the second grating, and i2 represents the incident angle of the spectral component on the second grating. When the effect of the offset of the grating pair on the optical path length of the spectral component is ignored, θ2 = i, i2 = θ, where i represents the incident angle of the spectral component on the first grating, and θ represents the diffraction angle of the spectral component on the first grating.

4. The grating pair parameter matching method for dispersive linear output according to claim 2 or 3, characterized in that, In step S112, the first delay group equation for the spectral component is established according to the following formula: Where P represents the optical path length of the spectral component within the grating pair, and c represents the speed of light; In step S113, the first grating equation when the two gratings are parallel in the grating alignment is: (sini+sinθ)=Gmλ Where G is the grating line density, m is the diffraction order (m = 1), and λ is the wavelength of the spectral component.

5. The grating pair parameter matching method for dispersive linear output according to claim 1, characterized in that, Step S120 specifically includes: Step S121: Considering the effect of the offset of the grating pair on the optical path of the optical signal, the two gratings in the grating pair are regarded as non-parallel. The second optical path equation of each spectral component in the optical signal is established in the grating pair. The second optical path equation is related to the incident angle i and diffraction angle θ of the corresponding spectral component on the first grating, the offset angle ε of the grating pair, the diffraction angle increment δ of the spectral component on the second grating when the offset angle of the grating pair is ε, and the vertical spacing h. Step S122: Based on the second optical path equation, the relationship between light speed and wavelength, and the second grating equation when the two gratings in the grating pair are not parallel, establish the second delay group equation for each spectral component in the optical signal. The second delay group equation is related to the incident angle i and diffraction angle θ of the corresponding spectral component on the first grating, the offset angle ε of the grating pair, the diffraction angle increment δ of the spectral component on the second grating when the offset angle of the grating pair is ε, the vertical spacing h, and the frequency f of the spectral component. Step S123: For each determined vertical spacing h and incident angle i, select two spectral components from the optical signal. For each selected spectral component, substitute the vertical spacing h, incident angle i, diffraction angle θ on the first grating corresponding to the wavelength of the spectral component, diffraction angle increment δ on the second grating, and frequency f of the spectral component into the second delay group equation to calculate the group delay of the spectral component. Only the offset angle ε is unknown in this delay group. Based on the group delay and wavelength of the two spectral components, determine the group delay-wavelength slope of the two spectral components, making the determined group delay-wavelength slope equal to the target slope k. Calculate the offset angle ε of the second grating in the grating pair.

6. The grating pair parameter matching method for dispersive linear output according to claim 5, characterized in that, In step S121, the second optical path equation for each spectral component of the optical signal within the grating pair is established according to the following steps: P = AB + BC (1) Where P represents the optical path length of the spectral component within the grating pair, AB represents the distance between the incident points A and B of the spectral component on the two gratings in the grating pair, and BC represents the distance from the incident point B of the spectral component on the second grating to the exit receiving point C. Where AD represents the distance from the incident point A of the spectral component on the first grating to the second grating, and i2 represents the incident angle of the spectral component on the second grating. When considering the effect of the offset of the grating pair on the optical path of the spectral component, i2 = θ + ε, θ2 = i + δ. BC = BM - CM(3) Wherein, the perpendicular intersection of the straight line passing through the incident point A and the straight line containing BC is M, BM represents the distance between the incident point B and the perpendicular intersection point M on the second grating, and CM represents the distance between the outgoing receiving point C and the perpendicular intersection point M. BM=AB cos(θ2-i2)=AB cos(i+δ-θ-ε) (4) CM=AM tan(ε-δ)=AB sin(i+δ-θ-ε)tan(ε-δ) (5) Where AM represents the distance from the incident point A to the line containing BC; Combining the above formulas (1) to (5), we obtain the second optical path equation:

7. The grating pair parameter matching method for dispersive linear output according to claim 5 or 6, characterized in that, In step S122, the second grating equation when the two gratings in the grating pair are not parallel is: (sin(θ+ε)+sin(i+δ))=Gmλ Where G is the grating line density, m is the diffraction order, m=1, and λ is the wavelength of the spectral component; In step S122, based on the second optical path equation, the relationship between light speed and wavelength c = λ * f, and the second grating equation, the second delay group equation for each spectral component in the optical signal is established according to the following formula: D f This indicates a time delay group.

8. The grating pair parameter matching method for dispersive linear output according to claim 7, characterized in that, Step S123 specifically includes: For each set of vertical spacing h and incident angle i, two spectral components are selected from the optical signal. For each selected spectral component, the vertical spacing h, incident angle i, diffraction angle θ on the first grating corresponding to the wavelength of the spectral component, diffraction angle increment δ on the second grating, and frequency f of the spectral component are substituted into the second delay group equation to calculate the group delay of the spectral component. After calculating the group delay D of the two spectral components f1 and D f2 Then, the group delay-wavelength slope of the two spectral components is determined according to the following formula, and the determined group delay-wavelength slope is made equal to the target slope k: in, This represents the group delay-wavelength slope of the two spectral components.

9. The grating pair parameter matching method for dispersive linear output according to claim 1, characterized in that, Following step S120, the method further includes: Step S130: For each grating pair parameter: vertical spacing h, incident angle i, and offset angle ε, if the offset angle ε in the grating pair parameter is zero, that is, the two gratings in the grating pair are parallel, then determine whether the first relationship holds. The first relationship is related to the grating pair size x. grating The diffraction angle θ of the maximum wavelength spectral component in the optical signal on the first grating. max The diffraction angle θ of the minimum wavelength spectral component on the first grating min The parameters are related to the vertical spacing h between the two gratings in the grating pair. If the condition is met, it means that each spectral component in the optical signal can be incident on the second grating. The parameters of this grating pair are then used as the parameters of the grating pair to be output. If the condition is not met, the parameters of this grating pair are deleted. If the offset angle ε in the parameters of the grating pair is non-zero, that is, the two gratings in the grating pair are not parallel, then for each spectral component in the optical signal, it is determined whether the second relation holds. The second relation is related to the grating pair size x. grating The diffraction angle θ of the maximum wavelength spectral component in the optical signal on the first grating. max The diffraction angle θ of the center wavelength spectral component on the first grating mid The diffraction angle θ of the minimum wavelength spectral component on the first grating min The diffraction angle θ of the spectral component on the first grating. If the second relationship holds for each spectral component in the optical signal, it means that each spectral component in the optical signal can be incident on the second grating. The set of grating pair parameters is then used as the output grating pair parameters. Otherwise, the set of grating pair parameters is deleted. Step S140: Calculate the linearity L of the group delay-wavelength curve corresponding to the parameters of each set of output gratings. n Select the linearity L n The smallest set of parameters to be output gratings is used as the final output grating pair parameters.

10. The grating pair parameter matching method for dispersive linear output according to claim 9, characterized in that, In step S130, the first relation is: h[tan(θ max )-tan(θ min )]<x grating The second relation is: l1+l2＜x grating Among them, A=90-ε+θ, C=90-θ.

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