RU2675400C1 - Method of manufacturing divider in integral optical scheme - Google Patents

Abstract

FIELD: optics.SUBSTANCE: group of inventions relates to integrated optics, and in particular to methods for producing a balanced divider in circuits based on waveguides formed in the volume of a solid-state workpiece by pulsed laser radiation. Method of manufacturing a divider in an integrated optical scheme consists in forming in the dielectric preform a region of interaction between contiguous waveguides. To do this, use a billet of quartz and form a waveguide in its volume with a linear cross-sectional size d=1÷6 microns by focusing pulsed laser radiation with a frequency ƒ=2÷4 MHz and the average power of a single pulse p=50÷500 kW when moving the workpiece relative to the focus of the radiation with a speed of V=0.4÷0.8 mm/sec. At the interaction site, the waveguides are brought closer to the distance of g=1÷2 microns.EFFECT: expansion of the arsenal of technical tools for creating wide-range integrated optical dividers.3 cl, 6 dwg

Description

FIELD OF THE INVENTION

The invention relates to integrated optics, namely, to methods for manufacturing a balanced divider in circuits based on waveguides formed in the volume of a solid-state workpiece by pulsed laser radiation.

State of the art

Dividers optical signals find extensive applications in the schemes that are used in basic and applied science and engineering (T. Li, E. Willner, I. Kaminow, Optical fiber telecommunications VA: Components and subsystems, 5 ^th edition, Academic Press, 2008). The ability to divide light signals propagating through free space in the form of beams from one element of the circuit to another, or in the form of waveguide modes that make up fiber optic circuits or integrated optical chips, is indispensable for receiving, processing and transmitting information.

Integrated optics makes it possible to create optical circuits that are resistant to external influences in a compact volume of an integrated chip with great potential for scaling and therefore integrated optical circuits are becoming increasingly popular (L. Chrostowski, M. Hochberg, Silicon Photonics Design. From Devices to Systems, Cambridge Univ. Press, 2015). The basis of integrated optical circuits are waveguide structures. Through waveguides, optical signals propagate from one functional element to another. In addition, a large set of functional elements that convert optical signals can be obtained using waveguide structures. In such optical elements, a significant proportion are divisors.

The prior art method of manufacturing a divider in an integrated optical circuit, which consists in the formation in the dielectric workpiece of the interaction site of the adjacent waveguides (see patent US 2003002127, CL G02B 6/126, publ. 02.01.2003). The known method relates to the dilution of the polarization components of optical radiation along waveguides formed on the substrate by etching in the epitaxial layer.

The main disadvantages of this solution are the complexity of manufacturing and the limited application of the obtained optical element, in particular, a narrow wavelength range in which the characteristics of its conversion change slightly - the conversion characteristics substantially depend on the wavelengths of the converted signals.

There is also a known method of manufacturing a divider, which consists in creating adjacent sections of waveguides in the volume of a transparent billet using femtosecond laser printing (A.M. Streltsov, N.F. Borrelli, Optics Letters, v. 26, No. 1, pp. 42-43 (2001)). The disadvantage of this solution, as in the first example, is the strong dependence of the characteristics of the divider on the wavelength.

Disclosure of invention

, с допустимой величиной отклонения от указанного значения до 10% в широком диапазоне длин волн от 0,3 мкм до 1,6 мкм.The technical problem is the creation of wide-range integrated optical dividers in circuits based on waveguides formed in the volume of a solid-state workpiece by pulsed laser radiation, providing a constant power division coefficient equal to

, with a permissible deviation from the specified value up to 10% in a wide range of wavelengths from 0.3 μm to 1.6 μm.

The technical result consists in solving this problem with the achievement of the above technical parameters of optical dividers.

с допустимой величиной отклонения от указанного значения до 10%, в диапазоне длин волн от 0,3 мкм до 1,6 мкм, представляющий собой размещенные в объеме кварцевой подложки, по меньшей мере, два волновода с поперечным сечением (d) 1÷6 мкм, расположенные на участке, протяженностью не менее 3 мм на расстоянии друг от друга (g) 1÷2 мкм. В одном из вариантов осуществления оптического делителя волноводы использованы с одинаковыми поперечными сечениями.This problem is solved by the fact that the optical divider obtained using the method of femtosecond laser printing provides a constant power factor equal to

with a permissible deviation from the specified value up to 10%, in the wavelength range from 0.3 μm to 1.6 μm, representing at least two waveguides with a cross section (d) of 1 ÷ 6 μm located in the volume of the quartz substrate located on a site with a length of at least 3 mm at a distance from each other (g) 1 ÷ 2 microns. In one embodiment of the optical divider, waveguides are used with the same cross sections.

This problem is also solved by the fact that according to the method of manufacturing the divider in an integrated optical circuit, an interaction section of adjacent waveguides is formed in the dielectric preform, while a quartz preform is used and waveguides are formed in its volume by a linear cross-sectional size d = 1 ÷ 6 μm by focusing the pulse laser radiation with a frequency f = 2-4 MHz and an average power of a single pulse p = 50 ÷ 500 kW when moving the workpiece relative to the focus of radiation with a speed of V = 0.4 ÷ 0.8 mm / s, and in waveguides bring the interactions closer to a distance g = 1 ÷ 2 μm.

Brief Description of the Drawings

The invention is illustrated by drawings, where in FIG. 1 shows the arrangement of waveguides in an integrated optical divider, a top view; in FIG. 2 is a section A-A 'of FIG. one; in FIG. 3 is a graph of the division coefficient R versus wavelength of a signal λ for a divider manufactured according to a conventional method; in FIG. 4 is a graph of the dependences of the normalized power difference Δ on the interaction length obtained theoretically for a traditional divider (identical waveguides) and for a divider made according to the proposed method (modulated waveguides); in FIG. 5 is a graph of the dependence of the normalized power difference Δ on the interaction length L obtained experimentally for a divider made according to the proposed method (circle) with approximation by a formula describing the dependence in the proposed broadband divider (curve); in FIG. 6 is a graph of the dependence of the division coefficient R on the wavelength of the signal λ for a divider manufactured according to the proposed method, with parameters of the divider corresponding to the case of FIG. 5 for the length of the divider L = 8 mm; the diamonds indicate the values obtained in the experiment, and the curve represents the approximation of the experimental data by the theoretical dependence (1.7) (R = (1 + Δ (z)) / 2).

The implementation of the invention

The inventive optical divider is made by femtosecond laser printing, for example, by analogy with the method described in the materials of the patent US 7568365 B2, using pulsed laser radiation with a pulse repetition rate of f = 2 ÷ 4 MHz and an average power of a single pulse p = 50 ÷ 500 kW In this case, two waveguides with a cross section (d) of 1 ÷ 6 μm are formed by laser radiation by moving the substrate relative to the focus of radiation at a speed of V = 0.4 ÷ 0.8 mm / s with providing a communication region between the waveguides in the section, rotyazhennostyu least 3 mm distance from each other (g) 1 ÷ 2 microns.

In traditional integrated dividers, which are formed by the approximation of waveguides manufactured by various optical lithography methods or by laser modification of the refractive index in a transparent workpiece, the frequency response of the power division coefficient R is bell-shaped, i.e. at a given length, a balanced (with a power distribution of 50/50) divider effectively works only for narrow-band radiation of a certain wavelength (Fig. 3).

It was found experimentally that in the manufacture of converged waveguides 1 and 2, an unexpected effect appears in the quartz billet by focusing pulsed laser radiation: the resulting divider remains balanced for a wide frequency range of the propagating signal from 0.3 μm to 1.6 μm, i.e. on the graph of the dependence of the division coefficient R in power on the wavelength λ of the signal there is an extensive plateau (Fig. 6). An experimental study of the field dynamics between the waveguides in the region of the splitter interaction showed that, apparently, during the printing of the waveguides under the influence of high-power pulsed laser radiation an irregular voltage was generated. This means that at the interaction site, the propagation constants of the formed waveguides are subject to irregular (random) small-scale modulation. Based on this assumption, the ranges of the geometric parameters of the pair of waveguides at which the power is redistributed efficiently were calculated, and the ranges of the operating parameters of the action of laser radiation were experimentally determined for which the described effect of the formation of small-scale modulation is observed. Below are the values obtained:

- linear dimensions of the cross section of the waveguides d = 1 ÷ 6 μm (at smaller and larger values, the losses during the propagation of radiation along the waveguide increase sharply);

- the distance between the waveguides in the interaction region g = 1 ÷ 2 μm (at lower values, the integrity of the intermediate wall is violated and scattering increases sharply, at large values, the waveguides practically do not interact and power transfer does not occur);

- the frequency of pulsed laser radiation ƒ = 2-4 MHz (for smaller values of the walls of the formed waveguides, they are indirect even outside the interaction area, and for large ones due to the general heating of the preform, uncontrolled defects are formed throughout the crystal volume) when the preform is moved relative to the radiation focus from speed V = 0.4 ÷ 0.8 mm / s (at lower values, the time of manufacture of the divider unreasonably increases, and at large values, the heterogeneity of the formed waveguides);

- average power of a single pulse p = 50 ÷ 500 kW (at lower values, the above-described effect of the formation of small-scale modulation of the propagation constant is not observed, and at large values, the formed defects are too large and scattering losses increase sharply).

и

(см. фиг. 2), где введены обозначения -

для вектора в поперечной плоскости, отсчитываемого от центра соответствующего волновода (для

отсчитывается от центра волновода 1 - точки О₁ для

отсчитывается от центра волновода 2 - точки O₂), z для продольной координаты, обозначающей расположение плоскости сечения, в которой рассматриваются профили. Следовательно, варьирование этих параметров на этапе изготовления дает возможность создавать делители с разными параметрами преобразования. После области эффективного взаимодействия волноводы разводят для распределения трансформированных сигналов между другими элементами оптической схемы или для ввода/вывода сигналов.In FIG. 1 schematically depicts a design of a conventional type of waveguide dividers based on cross-coupling between waveguides. This element is composed of a pair of waveguides (1 and 2), which, approaching each other, form a cross-interaction region (3) due to the partial overlap of the eigenmode profiles with the cores of adjacent waveguides (A. Snyder, J. Love, “Theory of optical waveguides” , Radio and Communications, 1987). Outside the region of interaction 3, there is no overlap of the eigenmodes of the waveguides and there is no coupling. Thus, the required characteristics of the divider transformation are determined by the geometry of the interaction region — its length, the distance between the waveguides, and also the refractive index profiles of the waveguide cores

and

(see Fig. 2), where the notation -

for a vector in the transverse plane, measured from the center of the corresponding waveguide (for

counted from the center of the waveguide 1 - point O ₁ for

counted from the center of the waveguide 2 - points O ₂ ), z for the longitudinal coordinate, indicating the location of the section plane in which the profiles are considered. Therefore, the variation of these parameters at the manufacturing stage makes it possible to create dividers with different transformation parameters. After the area of effective interaction, the waveguides are bred to distribute the transformed signals between other elements of the optical circuit or to input / output signals.

и

, с амплитудами на его входе,

и

, и может быть записано в матричной формеThe conversion of an arbitrary divider is described by the ratio between the amplitudes at its output,

and

, with amplitudes at its input,

and

, and can be written in matrix form

и

, а параметр ϕ - разность фаз между амплитудами на выходе. Фазовым параметром ϕ можно управлять независимо от преобразования смешения вне делителя, и он несущественен в настоящем изобретении, поэтому без ограничения общности полагаем ϕ=0.where the parameter θ characterizes the mixing of the powers of the input signals

and

, and the parameter ϕ is the phase difference between the amplitudes at the output. The phase parameter ϕ can be controlled independently of the mixing transformation outside the divider, and it is not essential in the present invention; therefore, without loss of generality, we set ϕ = 0.

. В таком случае, полагая спектр длин волн сигналов узким и сконцентрированным около несущей длины волны

, уравнения для амплитуд поля в волноводах 1 и 2 - а ₁ и а ₂ - принимают вид:In traditional waveguide dividers, the profiles of core refractive indices are the same, i.e. in any section AA 'cutting the interaction region in the z coordinate -

. In this case, assuming that the wavelength spectrum of the signals is narrow and concentrated near the carrier wavelength

, the equations for the field amplitudes in waveguides 1 and 2 - a ₁ and a ₂ - take the form:

, а также является функцией длины волны сигнала

. На фиг. 2 схематически представлено сечение делителя в области взаимодействия с обозначениями геометрических параметров. Если на вход традиционного делителя подаются амплитуды сигналов а ₁₀ и а ₂₀, то решая (1.2), находим распределение амплитуд по области взаимодействия:where C = C (λ) is the cross-coupling coefficient between the waveguides, which depends on the distance g between the waveguides and on the refractive index profiles of the waveguide cores

as well as a function of the wavelength of the signal

. In FIG. Figure 2 schematically shows the cross section of the divider in the interaction area with the notation of geometric parameters. If the amplitudes of the signals a ₁₀ and a ₂₀ are fed to the input of a traditional divider, then solving (1.2), we find the distribution of amplitudes over the interaction region:

Thus, the parameter θ from (1.1): θ = Cz. Then, the values quadratic in the field amplitudes are used - the normalized power difference: Δ (z) = (| a ₁ (z) | ² - | a ₂ (z) | ² ) / (| a ₁ (z) | ² + | a ₂ (z) | ² ) and the normalized power division coefficient R (z) = (1-Δ (z)) / 2. Of interest are only dispersion properties, therefore, it is sufficient to limit the consideration to the case of the signal at only one input ( and ₂₀ = 0). In this case, using (1.3), find Δ (z) = cos (2Cz), R (z) = sin ² (Cz).

In optical schemes, dividers with different values of the power division coefficient R are used; however, balanced dividers with R = 1/2 (Δ = 0) are most often encountered. It is worth noting especially interferometers, consisting of two connected in series balanced dividers, which are used, for example, for measurements. In addition, the ability to vary the phase between the waveguides of the interferometer makes it possible to reconfigure the interferometers in such a way that they can be considered as reconfigurable dividers (D.A. B. Miller, Perfect optics with imperfect components, Optics, v. 2, No. 8, 747 (2015)). For this reason, reconfigurable interferometers are the main functional element of integrated optical chips.

, для которой нужно изготовить элемент с требуемым коэффициентом деления мощности R, подбирают длину взаимодействия таким образом, чтобы

, причем вследствие периодичности решения выбирают наименьшее значение L, отвечающее первому периоду перекачки мощности из одного волновода в другой. Недостатком такого подхода является узкая полоса длин волн, в которой может работать делитель с постоянным коэффициентом деления. Вследствие зависимости коэффициента деления от длины волны R проявляет дисперсию.Note that the coupling coefficient C is the larger, the smaller the distance between the waveguides g (A. Snyder, J. Love, Theory of Optical Waveguides, Radio and Communication, 1987) and it rapidly decreases with increasing g. The present invention contemplates a 3D laser printing technology for waveguides in which waveguides are made by focusing high-power pulsed laser radiation into the bulk of a transparent preform while broadcasting this preform to form a waveguide curve (IV Dyakonov et al. Optics Letters, v. 42, No. 20, p. 4231 (2017)). The distance between the waveguides g is significant in the manufacture of waveguide dividers - it must be small enough to provide a sufficiently large value of the coefficient C or, equivalently, a small length of the interaction region L, so that the divider element or a complex element composed of several dividers fits in the workpiece. However, the minimum distance is limited by the ability to create uniform profiles in the interaction area; with strong convergence, a decrease in the quality of waveguides and an increase in losses in them are observed. For this reason, typical distances between waveguides made by laser three-dimensional printing lie in the range of 8 to 15 μm (GD Marshall et al., Laser written waveguide photonic quantum circuits, Optics Express, v. 17, No. 15, 12546 ( 2009)). After choosing the distance g and setting the wavelength of the signal

, for which you want to make an element with the required power division ratio R, select the interaction length so that

moreover, due to the periodicity of the solution, the smallest value of L corresponding to the first period of pumping power from one waveguide to another is selected. The disadvantage of this approach is the narrow wavelength band in which the divider with a constant division factor can operate. Due to the dependence of the division coefficient on the wavelength, R exhibits dispersion.

Below is a quantitative determination of the variance that a traditional waveguide divider exhibits. For a specific example, in theoretical calculations, waveguides with a stepped round profile of the refractive index were considered. The parameters of the waveguides are as follows: the refractive index of the environment corresponds to the material of fused silica, the difference in the refractive index between the core of the waveguide and the environment is 4⋅10 ^-4 , the diameter of the waveguide core is d = 6 μm, the distance between the centers of the waveguides in the interaction region is g + d = 11 μm. The values considered are typical for structures made by laser printing (GD Marshall et al, Laser written waveguide photonic quantum circuits, Optics Express, v. 17, No. 15, 12546 (2009)). Although the considered wavelength range from 0.2 μm to 1 μm is quite wide, a change in the refractive index of the material makes a negligible contribution to the deviation of the field conversion by the divider — the dispersion of the divider is determined by the structural dependence of the eigenmodes.

(540 нм) он был сбалансированным, т.е.

. Как видно из рисунка, отклонения в длине волны приводят к отклонениям в коэффициенте деления, что ограничивает спектральный диапазон, в котором может функционировать рассмотренный волноводный делитель как сбалансированный.In FIG. 3 is a graph of the power division ratio R, the length of which L is selected so that when the signal wavelength

(540 nm) it was balanced, i.e.

. As can be seen from the figure, deviations in the wavelength lead to deviations in the division coefficient, which limits the spectral range in which the considered waveguide divider can function as balanced.

, и

. Тогда уравнения для связанных амплитуд мод принимает вид:To increase the wavelength band, in which the parameters of the divider transform are negligible, a different configuration of the waveguide divider can be used. As mentioned above, waveguides in the field of interaction are trying to produce in such a way that their profiles are identical to each other and do not change with the longitudinal coordinate. This, in particular, is associated with a restriction on the minimum distance between waveguides - if waveguides are fabricated very close to each other, then the condition for the identity of waveguide profiles is not satisfied due to nonequilibrium processes that occur when a second waveguide is printed close to the first. Below is a description of the option when the transverse dimensions and / or the refractive index of the cores of the waveguides 1 and 2 varies depending on the longitudinal coordinate z. As a result of this modulation, the indices of the refractive index of the core of the modes of waveguides 1 and 2 in the interaction region 3 depend on the z coordinate:

, and

. Then the equations for the coupled mode amplitudes take the form:

. Уравнения (1.4) включают в себя (1.2) как частный случай при δ₁(z)=δ₂(z)=0.where (δ ₁ (z) and δ ₂ (z) are functions that describe the modulation of the propagation constants and which appear as a result of the appearance of additives

. Equations (1.4) include (1.2) as a special case for δ ₁ (z) = δ ₂ (z) = 0.

) в зависимости от z должен быть намного меньше, чем характерная длина L₀, на которой происходит существенная перекачка мощности из волновода в волновод при отсутствии модуляции, т.е.

. Другими словами, это означает, что δ_j(z) являются быстро осциллирующими функциями в сравнении с зависимостью с функцией перекачки мощности между волноводами. Во-вторых, спектр δ_j(z) должен содержать множество пространственных частот, чтобы эффект высокочастотной модуляции можно было рассматривать как воздействие случайных флуктуаций. Данное обстоятельство позволяет свести анализ к рассмотрению усредненных величин:To achieve the broadband operation of a balanced divider, the variable components δ _j (z) must satisfy certain conditions. First, the characteristic scale of the change in δ _j (z) (hereinafter, we denote

) depending on z, it should be much smaller than the characteristic length L ₀ , at which a substantial transfer of power from the waveguide to the waveguide occurs in the absence of modulation, i.e.

. In other words, this means that δ _j (z) are rapidly oscillating functions in comparison with the dependence with the power transfer function between the waveguides. Secondly, the spectrum δ _j (z) must contain many spatial frequencies so that the effect of high-frequency modulation can be considered as the effect of random fluctuations. This circumstance allows us to reduce the analysis to the consideration of averaged values:

, на котором происходит усреднение, должен быть много больше, чем характерный масштаб

изменения δ_j(z), чтобы гарантировать обоснованность усреднения флуктуаций. Названные условия вместе с определенной формой проведения усреднения по флуктуациям (1.4) позволяют использовать язык случайных процессов, в терминах которого сформулированы следующие условия для модуляции постоянных распространения. Согласно следующему - третьему условию, необходимо, чтобы δ₁(z) и δ₂(z) не коррелировали друг с другом, т.е.

. В противном случае идеальной корреляции, когда δ₁(z)=δ₂(z), предыдущее неравенство превращается в равенство, эффект модуляции никак не влияет на динамику поля, т.к. только разность δ₁(z)-δ₂(z) оказывает влияние на динамику поля (см. формулу (1.6) ниже). В добавок к перечисленным условиям для простоты анализа можно рассматривать δ_j(z) удовлетворяющими условию стационарности:

.where is the interval

, on which averaging occurs, should be much larger than the characteristic scale

changes in δ _j (z) to guarantee the validity of averaging fluctuations. The aforementioned conditions together with a certain form of averaging over fluctuations (1.4) make it possible to use the language of random processes, in terms of which the following conditions are formulated for modulation of propagation constants. According to the following, the third condition, it is necessary that δ ₁ (z) and δ ₂ (z) do not correlate with each other, i.e.

. Otherwise, the ideal correlation, when δ ₁ (z) = δ ₂ (z), the previous inequality turns into equality, the modulation effect does not affect the field dynamics, because only the difference δ ₁ (z) -δ ₂ (z) affects the field dynamics (see formula (1.6) below). In addition to the listed conditions, for simplicity of analysis, we can consider δ _j (z) satisfying the stationarity condition:

.

, где D_ij имеет смысл мощности («силы») флуктуаций, а

- длина когерентности. Из условия

следуют уравнения для квадратичных величин:We can consider correlation functions of the form:

, where D _ij has the meaning of power (“force”) of fluctuations, and

- length of coherence. From the condition

follow the equations for quadratic quantities:

, решение которого имеет вид затухающих осцилляций:with boundary conditions: Δ (0) = 1, σ (0) = 1, where η (z) = δ ₂ (z) -δ ₁ (z). Equations (1.6) can be transformed using the relation: η (z) σ (z) = iD⋅σ (z), where D = D ₁₁ + D ₂₂ -2D ₁₂ , which allows us to write the analytical solution for Δ (z) (C .A. Akhmanov, Yu.E. Dyakov, AS Chirkin, "Statistical radiophysics and optics. Random oscillations and waves in linear systems", FIZMATLIT, 2010). From equations (1.6) we arrive at the equation for the normalized power difference:

whose solution has the form of damped oscillations:

, т.е. делитель сбалансированн с высокой степенью точности. Отличительной особенностью такого делителя является его независимость стремления к нулю характеристики Δ(L) от коэффициента деления С - этот коэффициент может изменяться из-за дисперсии, что приводит к ограничениям на длины волн в традиционном делителе (см. фиг. 3). Отметим, что параметр D также может зависеть от длины волны, однако эта зависимость определяется дисперсией материалов, из которых изготовлена заготовка, но и это не мешает экспоненциальному затуханию (1.7).Here, the parameter D sets the decay rate of the oscillations of the power difference. A phase parameter Φ was introduced to describe the current pumping of power between closely spaced bends adjacent to the input and output of the rectilinear interaction region (see Fig. 1); even at z = 0 there is a cross interaction and at the entrance to the region of rectilinear interacting waveguides Δ (0) <1. In FIG. Figure 4 shows the curves of the dependence Δ (z) for the case of the traditional divider and for the divider with irregular modulation, described by the dependence of the power difference (1.7). Obviously, the power difference does not exceed the exp (-Dz / 2) in absolute value, therefore, for a sufficiently large interaction length L:

, i.e. the divider is balanced with a high degree of accuracy. A distinctive feature of such a divider is its independence of the zeroing of the Δ (L) characteristic from the division coefficient C - this coefficient can vary due to dispersion, which leads to restrictions on wavelengths in a traditional divider (see Fig. 3). Note that the parameter D can also depend on the wavelength, however, this dependence is determined by the dispersion of the materials from which the workpiece is made, but this does not interfere with the exponential attenuation (1.7).

см, что было сравнимо с характерной длиной перекачки мощности из одного волновода в другой L₀=π/2С. Авторам неизвестны практические примеры искусственного создания модуляции постоянных распространения δ_j(z), удовлетворяющим необходимым условиям.To implement a broadband divider, you need a way to create irregular modulation δ _j (z) that satisfies the conditions described above. In the technology of creating integrated optical devices by femtosecond laser printing, the modulation of effective refractive indices can be realized by varying the speed of movement of the workpiece relative to the focus area of the laser radiation or by changing the average laser power at a constant speed of movement or simultaneously varying the speed of movement and laser power (DN Biggerstaff et al., Nature Communications, v. 7, 11282 (2016)). Previously, such artificial creation of modulation by varying the speed of movement of the slide was performed to create stepwise modulation, in which δ _j (z) had constant values on segments of a fixed length, and the changes were made in steps. However, the characteristic spatial scale of these changes was quite large and amounted to

cm, which was comparable with the characteristic length of the transfer of power from one waveguide to another L ₀ = π / 2C. The authors are not aware of practical examples of the artificial creation of modulation of the propagation constants δ _j (z) that satisfy the necessary conditions.

и широким пространственным спектром гармоник - необходимые требования для получения нужного функционала широкополосного сбалансированного делителя.The presented invention solves the problem of obtaining modulations δ _j (z) (j = 1,2), which has a small characteristic scale

and a wide spatial spectrum of harmonics - the necessary requirements for obtaining the desired functionality of a broadband balanced divider.

For the fabrication of structures by laser printing, a setup was used, the scheme and description of which are given in (I.V. Dyakonov et al. Applied Physics B 122: 245 (2016)). The main elements of the installation are: 1) a Menlo Systems BlueCut fiber laser, which generates pulse sequences of 400 fs duration at a carrier wavelength of 1030 nm with a repetition rate of up to 1 MHz. The pulse repetition rate and the average laser power can be smoothly changed up to a power of 3 W - this is more than enough to realize the required printing mode; 2) a nonlinear BBO crystal, doubling the radiation frequency before entering the workpiece, i.e. pulses at a wavelength of 515 nm are focused into the workpiece; 3) AerotechFiberGlide 3D precision slide, which allows you to move the workpiece mounted on it with positioning accuracy at the level of several nm - this is more than enough for printing integrated optical dividers. As a workpiece, bars of fused quartz with a size of 10 cm * 5 cm * 5 mm were used; The radiation from the frequency doubler at a wavelength of 515 nm was focused through the face of the workpiece of the largest area so that the focal point was located at a depth of 50 μm from this face.

нм, поляризованный в плоскости делителя, излучение которого подавалась на один из входов каждого делителя серии. На выходе из каждого делителя проводилось измерение с помощью камеры, изображение с которой позволяло рассчитать нормированную разность мощности. Результаты измерений представлены на фиг. 5, где точками обозначены измеренные значения нормированной разности мощности в случае. Кривая является аппроксимацией экспоненциально затухающей зависимости (1.7), в которой параметры С и D подобраны, чтобы максимально соответствовать эксперименту (проведена минимизация разности квадратов отклонений параметризованной кривой и экспериментальных точек): С=4.02 мм^-1, D=2.15 мм^-1, Φ=-1.84.A series of 20 dividers with different lengths of the interaction region was made, and measurements were made for each of them. The following laser radiation parameters were used for printing: repetition rate ƒ = 4 MHz, average laser power W = 0.1 W; moving speed V = 0.6 mm / s. In this mode, waveguides with a width in the plane of the divider d = 5 μm are obtained, and the distance between the waveguides in the interaction region, chosen by the movement of the slide, was g = 2 μm (programming of the shift allows you to choose the distance between the centers of the waveguides O ₁ and O ₂ ). To measure the resulting dividers, a laser diode at a wavelength was used

nm polarized in the plane of the divider, the radiation of which was supplied to one of the inputs of each divider of the series. At the output of each divider, a measurement was performed using a camera, the image of which made it possible to calculate the normalized power difference. The measurement results are presented in FIG. 5, where dots indicate the measured values of the normalized power difference in the case. The curve is an approximation of the exponentially decaying dependence (1.7), in which the parameters C and D are selected to match the experiment as much as possible (the difference between the squared deviations of the parameterized curve and the experimental points was minimized): C = 4.02 mm ^-1 , D = 2.15 mm ^-1 , Φ = -1.84.

With the same recording parameters, another divider was made with the interaction region length L = 8 mm - this divider was made in the same printing cycle as a series of 20 dividers, so all laser printing parameters remained the same - only the length changed which has become significantly larger. For the fabricated divider, measurements were made of the normalized power difference for different wavelengths of the signal. For measurements, several laser sources were used, operating in different wavelength ranges: from a tunable telecommunication laser in the region of λ = 1500 nm to a helium-cadmium laser for λ = 325 nm. In FIG. Figure 6 shows a graph of the dependence of the power division coefficient of a broadband balanced divider on the wavelength of the signal at parameters. The points correspond to experimentally measured values, the curve corresponds to their approximation (1.7) taking into account the dispersion dependence of the coupling coefficient C (λ), where the contrast of the refractive index of the Lie between the core of the waveguide and its environment was used as variable parameters.

The appearance of irregular modulation can be explained by random mechanical stresses that occur when printing a second waveguide near the first. In turn, these stresses lead to irregular modulation of the refractive indices of the waveguide cores (I.V. Dyakonov et al. Optics Letters, v. 42, No. 20, p. 4231 (2017)).

For the above reasons, the implementation of the proposed method allows by a simple technological operation to create a highly efficient balanced wide-range integrated optical divider.

The invention allows to expand the arsenal of technical means for creating wide-range integrated optical dividers.

Claims (3)

1. The optical divider obtained using the method of femtosecond laser printing, providing a constant power factor equal to

with a permissible deviation from the specified value up to 10%, in the wavelength range from 0.3 μm to 1.6 μm, representing at least two waveguides with a cross section (d) 1 ÷ 6 μm located in the volume of the quartz substrate, located on a site with a length of at least 3 mm at a distance from each other (g) 1 ÷ 2 microns. 2. The optical divider according to claim 1, characterized in that the waveguides are used with the same cross sections. 3. A method of manufacturing an optical divider according to claim 1, comprising forming at least two waveguides in a quartz substrate by focusing pulsed laser radiation with a pulse repetition rate of ƒ = 2 ÷ 4 MHz and an average power of a single pulse of p = 50 ÷ 500 kW when moving the substrate relative to the focus of radiation with a speed of V = 0.4 ÷ 0.8 mm / s.

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