JP4113162B2 - Optical waveguide and method for manufacturing the same - Google Patents

Description

  The present invention relates to an optical waveguide and a method for manufacturing the same, and more particularly to an optical waveguide using a holographic wave transmission medium that transmits waves holographically by a two-dimensional refractive index distribution and a method for manufacturing the same.

  In the optical communication field, integrated optical components using an optical waveguide structure have been developed as an optical circuit that can easily realize branching and interference of light. Integrated optical components that utilize the properties of light waves make it easy to manufacture optical interferometers by adjusting the optical waveguide length, and to easily integrate optical components by applying circuit processing technology in the semiconductor field. Become.

Such an optical waveguide structure is an “optical confinement structure” that realizes spatial light confinement of light propagating through the optical waveguide by utilizing a spatial distribution of refractive index. As shown in FIG. 1, a typical optical waveguide has a two-stage refractive index distribution comprising a refractive index N ₀ cladding layer 103 and a core portion 102 having a refractive index N ₁ on a substrate 101. In addition, an optical waveguide having a three-stage refractive index distribution including a lower cladding layer having a refractive index N ₀ , a core portion having a refractive index N ₁ , and an upper cladding layer having a refractive index N ₂ is widely used. The advantage of the conventional optical waveguide is that the optical waveguide can be manufactured from two to three kinds of materials, and the manufacturing process is simple.

  In order to manufacture the integrated optical component, not only the optical waveguide connecting each optical component on the substrate but also various types of optical waveguides such as a crossed waveguide, a tapered waveguide, and a Y-branch waveguide are used. Further, by changing the refractive index distribution of a part of the optical waveguide, it is possible to configure an optical waveguide circuit such as a filter circuit that transmits only a specific wavelength. For example, a method of creating a Bragg grating by irradiating an optical waveguide made of a photosensitive optical medium such as an optical fiber with ultraviolet rays having an interference pattern and periodically and continuously modulating the refractive index over a certain length. It is known (see, for example, Patent Document 1). Similarly, a long-period grating of about 50 to 1500 μm is produced by irradiating ultraviolet rays (see, for example, Patent Document 2).

Japanese Patent Laid-Open No. 7-140497 Japanese Patent Laid-Open No. 10-123346

  FIG. 2 shows an example of a crossed waveguide in a conventional optical waveguide. FIG. 2A shows the refractive index distribution and FIG. 2B shows the optical electric field distribution. If the optical waveguides are crossed at such a small angle, the optical signal input from the input port shown in the figure will leak not only to the desired output port but also to the other output port. End up. Therefore, in the conventional optical waveguide, in order to prevent such crosstalk, the crossing angle has to be set to about 30 degrees, and there is a problem that there is a great restriction on the layout design of the optical circuit.

  Further, the conventional optical waveguide has a problem that the performance of the optical waveguide is limited by the processing shape of the core portion. FIG. 3 shows an example of a conventional Y-branch waveguide. The Y branch waveguide is a single element mode and has an acute angle portion 104 having a small branch angle. Further, it is necessary to provide the tapered portion 105 in order to prevent the occurrence of the second transverse mode. It is difficult to faithfully manufacture such a fine structure, and there is a problem that branching characteristics are deteriorated due to manufacturing errors.

  The present invention has been made in view of such problems. The object of the present invention is to apply a holographic wave transmission medium, obtain desired transmission characteristics, and reduce the size of an optical circuit. An object of the present invention is to provide an optical waveguide and a manufacturing method thereof.

In order to achieve the above object, the present invention provides a light source comprising a cladding layer and a core portion having a refractive index higher than that of the cladding layer embedded in the cladding layer. In an optical waveguide provided with a waveguide region, in a cross section perpendicular to the light propagation direction, a place on the circuit where a cross section of the light field is to be provided is a port, and input light incident from the input port is A wave transmission medium in which a spatial refractive index distribution is formed in at least a part of the core portion so as to be emitted as output light from the output port, and the spatial refractive index distribution is the input light but when propagating along the propagation direction of the light, the input field of the input light is converted into an output field of the output light, one or more input fields that are output from the output port Set For each of the coordinate z in the propagation direction of the light, the location of the cross-section X when the coordinate x of the perpendicular direction in the waveguide region of the light propagation direction of the light (z, x), the input and fields field order propagation phase, as the phase difference between the previous SL field obtained by back propagation to the phase conjugate of the output field phase is equal to or less than a predetermined error, each of said locations (z, x) is determined by performing repeatedly the core refractive index as a variable calculated, this calculation is based on the (q-1) -th refractive index distribution obtained by the calculation {n _q-1}, the input-output For the j-th input field ψ ^j (x) and output field φ ^j (x) of the field set, the forward propagation field ψ ^j (z, x, {n _q-1 }) and the back propagation field φ ^j _{(z, x, {n q} -1}) when the refractive index at each location (z, x) _q the (z, x),
n _q (z, x) = n _q-1 (z, x) −αΣ _j Im [φ ^j (z, x, {n _q-1 }) ^* · ψ ^j (z, x, {n _q-1 })]
Where the symbol “*” is a complex conjugate, the symbol “•” is an inner product operation, Im [] is the imaginary component of the field inner product operation result in [], and α is the convergence of the calculation Σ _j represents the sum of j, and the field of the input light is subjected to a change in phase in multiple stages by the refractive index distribution of the cross section X along the propagation direction of the light. Thus, the propagation is performed while changing the shape of the light field due to the interference phenomenon caused by the multiple scattering of the propagation waves generated in the wave transmission medium.

The invention described in claim 2 is characterized in that the core portion described in claim 1 is quartz glass to which GeO ₂ is added.

The invention according to claim 3 is a method for manufacturing an optical waveguide, comprising: a first step of forming a lower cladding layer on a substrate; and a core layer having a higher refractive index than the cladding layer on the lower cladding layer. A second step of forming, a third step of forming a patterned core portion from the core layer, a fourth step of forming an upper clad layer on the lower clad layer and the core portion, and the core portion And a fifth step of forming a wave transmission medium having a spatial refractive index distribution in at least a part of the wave transmission medium, wherein the wave transmission medium has a light field cross section in a cross section perpendicular to the light propagation direction. The spatial refractive index distribution is formed so that input light incident from the input port is emitted as output light from the output port, and the spatial refractive index is formed so that a place on the circuit to be given is a port. distribution The input light and propagates along the propagation direction of the light, the input field of the input light is converted into an output field of the output light, one or more input fields that are output from the output port For each of the groups, the coordinate z in the light propagation direction and the coordinate x in the direction perpendicular to the light propagation direction in the light waveguide region, at the location (z, x) of the cross section X, and the forward propagation of the field in the input field phase, so that the phase difference between the previous SL phase field obtained by back propagation to the phase conjugate of the output field is equal to or less than a predetermined error, each of said locations (z, x ) is determined by performing the repeated calculations of the refractive index of the core as a variable, the calculation is based on the (q-1) -th refractive index distribution obtained by the calculation {n _q-1}, the entering Output field pair j th input field [psi ^j (x) and the output field phi ^j for (x), the forward propagating field ^{ψ j (z, x, {} n q-1}) and the field phi ^j of the back propagation (z, x , {n _q-1 }), the refractive index n _q (z, x) at each location (z, x) is
n _q (z, x) = n _q-1 (z, x) −αΣ _j Im [φ ^j (z, x, {n _q-1 }) ^* · ψ ^j (z, x, {n _q-1 })]
Where the symbol “*” is a complex conjugate, the symbol “•” is an inner product operation, Im [] is the imaginary component of the field inner product operation result in [], and α is the convergence of the calculation Σ _j represents the sum of j, and the field of the input light is subjected to a change in phase in multiple stages by the refractive index distribution of the cross section X along the propagation direction of the light. Thus, the propagation is performed while changing the shape of the light field due to the interference phenomenon caused by the multiple scattering of the propagation waves generated in the wave transmission medium.

According to a fourth aspect of the present invention, in the fifth step according to the third aspect, the core layer is irradiated with a laser beam having a peak power intensity at a condensing point of 10 ⁵ W / cm ² or more, and the laser beam The refractive index at each location (z, x) is given by adjusting the irradiation time.

According to a fifth aspect of the present invention, in the fifth step according to the third aspect, the core layer is irradiated with a laser beam having a peak power intensity at a condensing point of 10 ⁵ W / cm ² or more, and the laser beam Is adjusted to give a refractive index at each of the locations (z, x).

According to a sixth aspect of the present invention, in the fifth step according to the third aspect, the core layer is uniformly irradiated with ultraviolet light through a gray scale mask, and each of the gray scale masks changes the density. It is characterized by giving a refractive index at a location (z, x).

The invention according to claim 7, the said core layer according to claim 4 or 5, GeO2 a silica-based glass is added, the fifth step, irradiating a laser beam from the ultraviolet ray laser It is made by this.

As described above, according to the present invention, at least a portion of the core portion, by forming the wave propagation medium having a spatial refractive index distribution, a desired transmission characteristic is obtained, compact optical circuit Can be achieved.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The optical waveguide of this embodiment is a waveguide circuit that forms a wave transmission medium having a spatial refractive index distribution in at least a part of a core portion and controls the optical path of guided light. The waveguide circuit is manufactured by applying a design method for a holographic wave transmission medium.

  First, the basic concept of the wave transmission medium used in the present invention will be described. Here, since it is applied to an optical circuit, the “wave” propagating in the wave transmission medium is “light”. The theory relating to the wave transmission medium specifies the characteristics of the medium based on a general wave equation, and can also hold in principle in general waves. In order to input a coherent light pattern and output a desired light pattern, the wave transmission medium has a phase difference between forward propagation light and back propagation light propagating in the wave transmission medium. The refractive index distribution is determined so as to be small even at the location. A desired light pattern is output by repeatedly repeating holographic control at a local level according to the refractive index distribution.

The basic structure of the wave transmission medium according to the present embodiment will be described with reference to FIG. As shown in FIG. 4A, an optical circuit design area 1-1 configured by a wave transmission medium exists in the optical circuit board 1. One end surface of the optical circuit is an incident surface 2-1 on which the input light 3-1 is incident. The input light 3-1 propagates through an optical circuit having a spatial refractive index distribution formed of a wave transmission medium, and is output as output light 3-2 from the exit surface 2-2 which is the other end face. Coordinate z in FIG. 4 (a) in the coordinates (z = 0 is the incident surface, z = z _e is output surface) of the propagation direction of the light is, the coordinate x is at a transverse coordinates for the light propagation direction is there. In this embodiment, it is assumed that the wave transmission medium is made of a dielectric, and the spatial refractive index distribution is based on the theory described below for the local refractive index of the dielectric constituting the wave transmission medium. This is realized by setting based on this.

  The “field” (input field) formed by the input light 3-1 is modulated according to the spatial distribution of the refractive index of the wave transmission medium constituting the optical circuit, and the “field” formed by the output light 3-2 "(Output field). In other words, the wave transmission medium of the present invention is (electromagnetic) field conversion means for correlating the input field and the output field according to the spatial refractive index distribution. For these input field and output field, the light field in the cross section (cross section along the x axis in the figure) perpendicular to the propagation direction (z axis direction in the figure) in the optical circuit is represented by its location (x, This is referred to as a (forward) propagation image (propagation field or propagation light) in z) (see FIG. 4B).

  Here, “field” generally means an electromagnetic field (electromagnetic field) or a vector potential field of an electromagnetic field. The control of the electromagnetic field in this embodiment corresponds to changing the spatial refractive index distribution provided in the optical circuit, that is, the dielectric constant distribution. Although the dielectric constant is given as a tensor, since the transition between the polarization states is usually not so large, it is an approximation that may be a scalar wave approximation for only one component of the electromagnetic field. Therefore, in this specification, the electromagnetic field is treated as a complex scalar wave. Since the “state” of light includes an energy state (wavelength) and a polarization state, when the “field” is used to express the state of light, the light wavelength and polarization state are also included. Will get.

  In general, in an optical circuit that does not cause amplification or attenuation of propagating light, when the spatial distribution of the refractive index is determined, an image (input field) of the input light 3-1 other than the focal point is an image of the output light 3-2. (Output field) is determined uniquely. Such a field of light traveling from the exit surface 2-2 side to the entrance surface 2-1 side is referred to as a back propagation image (a back propagation field or a back propagation light) (see FIG. 4C). Such a back propagation image can be defined for each place in the optical circuit. That is, when a light field at an arbitrary place in the optical circuit is considered, if the place is considered as an emission point of a virtual “input light”, the image of the output light 3-2 can be obtained in the same manner as described above. The back-propagation image at that location can be considered. In this way, a back propagation image can be defined for each location in the optical circuit.

  In particular, in a single optical circuit, when the outgoing field is a propagation field of the incident field, the propagation field and the reverse propagation field coincide with each other at any point of the optical circuit. The field is generally a function over the entire target space, but the term “incident field” or “exit field” means a cross section of the field on the entrance surface or exit surface. In addition, even in the case of “field distribution”, when a discussion is made regarding a specific cross section, it means a cross section of the field with respect to that cross section.

  In order to explain the method of determining the refractive index distribution, it is better to use symbols, so the following symbols are used to represent each quantity. Note that the target light (field) is not limited to light in a single state. Therefore, an index j is assigned to light in each state so that light in which a plurality of states are superimposed can be targeted. In general.

Ψ ^j (x): j-th incident field (complex vector value function, defined by intensity distribution and phase distribution set on the incident surface, and wavelength and polarization)
Φ ^j (x): j-th outgoing field (complex vector value function, defined by intensity distribution and phase distribution, wavelength and polarization set on the outgoing face)
Note that ψ ^j (x) and φ ^j (x) have the same total light intensity (or a negligible loss) unless intensity amplification, wavelength conversion, and polarization conversion are performed in the circuit. Their wavelength and polarization are the same.
{Ψ ^j (x), φ ^j (x)}: Input / output pair (a set of input / output fields)
{Ψ ^j (x), φ ^j (x)} is defined by the intensity distribution and the phase distribution, the wavelength and the polarization at the entrance surface and the exit surface.
{N _q }: Refractive index distribution (a set of values for the entire optical circuit design area)
Since one field of light is determined when one refractive index distribution is given to a given incident field and outgoing field, it is necessary to consider a field for the entire refractive index distribution given by the qth iterative operation. Therefore, the entire refractive index distribution may be expressed as n _q (x, z) with (x, z) as an indefinite variable, but the refractive index value n _q (x, z) at the location (x, z) For distinction, {n _q } is used for the entire refractive index distribution.
N _core : A symbol indicating a high refractive index value with respect to the surrounding refractive index, such as a core portion in an optical waveguide.
N _clad : a symbol indicating a low refractive index value with respect to n _core , such as a clad portion in an optical waveguide.
Ψ ^j (z, x, {n _q }): field at location (x, z) when the ^jth incident field ψ ^j (x) is propagated through the refractive index profile {n _q } to z The value of the.
Φ ^j (z, x, {n _q }): at the location (x, z) when the j-th outgoing field φ ^j (x) is propagated back to z in the refractive index profile {n _q } The field value.

In the present embodiment, the refractive index distribution, all j for _{^{ψ j (z e, x,}} {n q}) is given = φ ^j (x), or the so close state {n _q}.

  “Input port” and “output port” are “areas” where the fields at the entrance end face and the exit end face are concentrated. For example, by connecting an optical fiber to the part, the optical intensity can be propagated to the fiber. It is an area. Here, since the field intensity distribution and phase distribution can be designed to be different for the j-th and k-th ones, a plurality of ports can be provided on the entrance end face and the exit end face. Furthermore, when considering a pair of an incident field and an outgoing field, the phase generated by the propagation between them differs depending on the frequency of light. Therefore, for light having different frequencies (that is, light having different wavelengths), the field shape including the phase Regardless of whether they are the same or orthogonal, they can be configured as different ports.

Here, the electromagnetic field is a field of a real vector value, and has a wavelength and a polarization state as parameters, but the value of the component is displayed as a complex number that can be easily handled in a general mathematical manner, and represents the solution of the electromagnetic wave. In the following calculation, it is assumed that the strength of the entire field is normalized to 1. As shown in FIG. 4B and FIG. 4C, the propagation field and the back propagation field are respectively set to the j-th incident field ψ ^j (x) and the output field φ ^j (x). As complex vector value functions, they are expressed as ψ ^j (z, x, {n}) and φ ^j (z, x, {n}). Since the values of these functions vary depending on the refractive index distribution {n}, the refractive index distribution {n} is a parameter. According to the definition of the symbols, ψ ^j (x) = ψ ^j (0, x, {n}) and φ ^j (x) = φ ^j (z _e , x, {n}). The values of these functions can be easily calculated by a known method such as a beam propagation method, given an incident field ψ ^j (x), an outgoing field φ ^j (x), and a refractive index distribution {n}. it can.

In the following, a general algorithm for determining the spatial refractive index distribution will be described. FIG. 5 shows a calculation procedure for determining the spatial refractive index distribution of the wave transmission medium. Since this calculation is repeatedly executed, the number of repetitions is represented by q, and the state of the qth calculation when the calculation is executed up to the (q−1) th is shown. Based on the refractive index distribution {n _q-1 } obtained by the (q-1) th calculation, the propagation field and the ^jth incident field ψ ^j (x) and the outgoing field φ ^j (x) The back propagation field is obtained by numerical calculation, and the results are expressed as ψ ^j (z, x, {n _q-1 }) and φ ^j (z, x, {n _q-1 }), respectively (step S220). ).

Based on these results, the refractive index n _q (z, x) at each location (z, x) is obtained by the following equation (step S240).
n _q (z, x) = n _q-1 (z, x) −αΣ _j Im [φ ^j (z, x, {n _q-1 }) ^* · ψ ^j (z, x, {n _q-1 })] (1)
Here, the symbol “·” in the second term on the right side means an inner product operation, and Im [] means an imaginary number component of the field inner product operation result in []. The symbol “*” is a complex conjugate. The coefficient α is a value obtained by dividing a value equal to or less than a fraction of n _q (z, x) by the number of field pairs, and is a small positive value. Σ _j means that the sum is taken for the index j.

Step S220 and S240 and repeats the value in the exit plane of the propagation field _{^{ψ j (z e, x,}} {n}) the absolute value of the difference between the exit field φ ^j (x) is than desired error d _j When it becomes smaller (step S230: YES), the calculation ends.

In the above calculation, the initial value {n ₀ } of the refractive index distribution may be set appropriately. However, if this initial value {n ₀ } is close to the expected refractive index distribution, the calculation converges faster accordingly ( Step S200). When calculating φ ^j (z, x, {n _q-1 }) and ψ ^j (z, x, {n _q-1 }) for each j, , J (that is, φ ^j (z, x, {n _q-1 }) and ψ ^j (z, x, {n _q-1 })). Thus, calculation efficiency can be improved (step S220). If the computer is configured with a relatively small memory, an appropriate j is selected for each q in the sum of the index j in equation (1), and φ ^j (z, x, { It is also possible to calculate only n _q-1 }) and ψ ^j (z, x, {n _q-1 }) and repeat the subsequent calculations (step S220).

In the above ^{operation, φ j (z, x,} {n q-1}) in the case of values and ^{ψ j (z, x, {} n q-1}) and the value of the near, the formula (1) Im [φ ^j (z, x, {n _q-1 }) ^* · ψ ^j (z, x, {n _q-1 })] is a value corresponding to the phase difference, and by reducing this value, It is possible to obtain a desired output.

  The calculation contents for determining the refractive index distribution described above are summarized as follows. An input port and an output port are provided in a medium capable of transmitting a wave in a holographic manner (dielectric in the case of light). Field distribution 1 (forward propagation light) of propagating light incident from the input port and from the input port A field distribution 2 (reverse propagation light) of phase conjugate light in which an output field expected when an incident optical signal is output from the output port is propagated backward from the output port side is obtained by numerical calculation. In the field distribution 1 and the field distribution 2, a spatial refractive index distribution in the medium is obtained so as to eliminate the phase difference at each point (x, z) of the propagating light and the counter propagating light. If the steepest descent method is adopted as a method for obtaining such a refractive index distribution, the refractive index is calculated by changing the refractive index in the direction obtained by the steepest descent method using the refractive index of each point as a variable. By changing as in (1), the difference between the two fields can be reduced. If such a wave transmission medium is applied to an optical component that emits light incident from an input port to a desired output port, an effective optical path length is reduced due to interference phenomenon caused by multiple scattering of propagation waves generated in the medium. An optical circuit having a sufficiently high optical signal controllability can be configured even with a long and gentle refractive index change (distribution).

The refractive index distribution is calculated by applying the above-described algorithm to a waveguide having the same structure as the crossed waveguide shown in FIG. By repeating about 200 times, a continuous- tone local refractive index modulation section is obtained. This refractive index modulation unit has a refractive index modulation amount composed of a plurality of non-periodic peaks, and when applied to a crossing waveguide, the refractive index distribution shown in FIG. 6 is obtained. The refractive index of the clad assumes the refractive index of quartz glass, and the refractive index of the core has a value that is higher by 0.75% than the relative refractive index of quartz glass. The size of the optical circuit constituting the crossing waveguide having a crossing angle of 1.6 degrees is 6.0 μm in length and 7.0 μm in width.

FIG. 7 is a diagram showing an optical electric field distribution of a crossing waveguide according to an embodiment of the present invention. Even if the optical waveguides are crossed at such a small angle, the optical signal input from the input port shown in the figure is output to the desired output port. According to this configuration, a cross waveguide that conventionally requires a crossing angle of about 30 degrees can be realized even with a small crossing angle of 1.6 degrees, and the degree of freedom in designing the layout of the optical circuit is increased. The refractive index distribution shown in FIG. 6 is a continuous gradation local refractive index modulation unit, but may be, for example, 16 pseudo continuous gradations .

Next, a manufacturing method will be described. FIG. 8 shows a method of creating a crossed waveguide having a continuous tone refractive index distribution. A lower clad glass soot 302 mainly composed of SiO ₂ is deposited on the silicon substrate 301 by a flame deposition method (FIG. 8A). Next, a core glass soot 303 in which GeO ₂ is added to SiO ₂ is deposited (FIG. 8B). Then, glass transparency is performed at a high temperature of 1000 ° C. or higher. At this time, the glass is deposited so that the lower clad glass layer 302 is 30 microns thick and the core glass 303 is 7 microns thick.

Subsequently, an etching mask 304 is formed on the core glass soot 303 using a photolithography technique (FIG. 8C), and the core glass soot 303 is patterned by reactive ion etching to form a core portion 305 ( FIG. 8D). After removing the etching mask 304 (FIG. 8E), the upper cladding glass 306 is formed again by the flame deposition method (FIG. 8F). The upper cladding glass 306 is SiO _{2 to} which a dopant such as B ₂ O ₃ or P ₂ O ₅ is added. As a result, the glass transition temperature is lowered so that the upper clad glass 306 also enters the narrow gap between the core portions 305.

FIG. 9 shows a first example of a method for producing a continuous tone refractive index distribution. The continuous- tone refractive index distribution shown in FIG. 6 is created in the crossed waveguide manufactured by the method shown in FIG. In the first example, the light from the ultraviolet laser is condensed by the lens 311 and irradiated to the core unit 305, and distribution is given according to the peak of the refractive index modulation. Light having a peak power intensity at the condensing point of 10 ⁵ W / cm ² or more is irradiated onto the optical waveguide, and the irradiation time is adjusted according to the amount of change in the refractive index at a predetermined position of the intersecting waveguide.

Alternatively, the refractive index may be changed by irradiating with a laser beam having an ultraviolet irradiation amount of 1440 J / cm ² , 20 Hz, 100 mJ / cm ² / pulse for 2 hours. Here, not the laser beam irradiation time but the light intensity is adjusted.

FIG. 10 shows a second example of a method for producing a continuous tone refractive index profile. In the second example, a femtosecond laser is used instead of the ultraviolet laser. The light from the femtosecond laser is condensed by the lens 311 and irradiated to the core unit 305, and distribution is given according to the peak of the refractive index modulation.

  FIG. 11 shows a refractive index distribution of a tapered waveguide according to an embodiment of the present invention. By applying the above-described algorithm, the refractive index distribution of the holographic wave transmission medium is calculated, and this is a tapered waveguide in which a Y-branch waveguide is formed. FIG. 12 shows an optical electric field distribution of the tapered waveguide according to one embodiment of the present invention. Optical signals input from the input ports shown in the figure are output to two desired output ports. In this way, a Y-branch waveguide can be realized using a tapered waveguide that does not require a fine processing technique. Further, a smaller Y branch circuit can be realized as compared with the conventional Y branch waveguide shown in FIG.

FIG. 13 shows a method for producing a tapered waveguide having a continuous- tone refractive index distribution. The continuous- tone refractive index distribution shown in FIG. 11 is formed in the tapered waveguide manufactured by the method shown in FIG. The core 305 is irradiated with light from an ultraviolet laser through the gray mask 312 to give a refractive index distribution. At this time, a gray mask 312 having a transmittance corresponding to the amount of change in refractive index to be given is used.

  In this way, a refractive index modulation section having a desired refractive index distribution can be easily built into a waveguide by applying a design method for a holographic wave transmission medium. The manufactured optical waveguide can obtain a desired transmission characteristic, and can realize downsizing of the optical circuit.

It is sectional drawing which shows an example of the conventional optical waveguide structure. It is a figure which shows an example of the conventional crossing waveguide. It is a figure which shows an example of the conventional Y branch waveguide. It is a figure for demonstrating the basic structure of a wave transmission medium. It is a flowchart which shows the calculation procedure for determining the spatial refractive index distribution of a wave transmission medium. It is a figure which shows the refractive index distribution of the crossing waveguide concerning one Embodiment of this invention. It is a figure which shows the optical electric field distribution of the crossing waveguide concerning one Embodiment of this invention. It is a figure which shows the production method of the crossing waveguide which has a refractive index profile of a continuous tone . It is a figure which shows the 1st example of the method of producing the refractive index distribution of a continuous tone . It is a figure which shows the 2nd example of the method of producing refractive index distribution of a continuous tone . It is a figure which shows the refractive index distribution of the taper-type waveguide concerning one Embodiment of this invention. It is a figure which shows the optical electric field distribution of the taper-type waveguide concerning one Embodiment of this invention. It is a figure which shows the production method of the taper-type waveguide which has a refractive index distribution of a continuous tone .

Explanation of symbols

1-1 Optical Circuit Design Area 1-2 Substrate 1-11 High Refractive Index Section 1-12 Low Refractive Index Section 2-1 Entrance Surface 2-2, 2-3 Exit Surface

Claims (7)

In an optical waveguide provided with a light guiding region composed of a cladding layer and a core portion having a higher refractive index than the cladding layer embedded in the cladding layer,
In the cross section perpendicular to the light propagation direction, a place on the circuit where the cross section of the light field is to be given is a port, and input light incident from the input port is emitted as output light from the output port. A wave transmission medium in which a spatial refractive index distribution is formed on at least a part of the core part,
The spatial refractive index distribution indicates that when the input light propagates along the propagation direction of the light, the input field of the input light is converted into an output field of the output light and output from the output port. For each of the one or more input / output field pairs, the location of the cross section X when the coordinate z of the light propagation direction and the coordinate x of the light guide region perpendicular to the light propagation direction are set. In (z, x), the phase difference between the phase of the forward propagation field of the input field and the phase of the field back-propagated to the phase conjugate of the output field is less than a predetermined error, respectively. The refractive index distribution {n _q−1 } obtained by the (q−1) -th calculation is determined by repeatedly calculating the refractive index of the core at the location (z, x) of Based on For the set of the j-th input field of the input and output field [psi ^j (x) and the output field φ ^j (x), the forward propagating field ^{ψ j (z, x, {} n q-1}) field between the counter-propagating When φ ^j (z, x, {n _q-1 }), the refractive index n _q (z, x) at each location (z, x) is
n _q (z, x) = n _q-1 (z, x) −αΣ _j Im [φ ^j (z, x, {n _q-1 }) ^* · ψ ^j (z, x, {n _q-1 })]
Where the symbol “*” is a complex conjugate, the symbol “•” is an inner product operation, Im [] is the imaginary component of the field inner product operation result in [], and α is the convergence of the calculation Where Σ _j is the sum for j, and
Interference phenomenon due to multiple scattering of propagating waves generated in the wave transmission medium when the input light field is subjected to phase changes in multiple stages by the refractive index distribution of the cross section X along the propagation direction of the light. An optical waveguide characterized by propagating while changing the shape of the field of light. The optical waveguide according to claim 1, wherein the core portion is made of quartz glass to which GeO ₂ is added. A first step of forming a lower cladding layer on the substrate;
A second step of forming a core layer having a higher refractive index than the cladding layer on the lower cladding layer;
A third step of forming a patterned core portion from the core layer;
A fourth step of forming an upper cladding layer on the lower cladding layer and the core portion;
And a fifth step of forming a wave transmission medium having a spatial refractive index distribution on at least a part of the core part,
In the wave transmission medium, in the cross section perpendicular to the light propagation direction, a place on the circuit where a cross section of the light field is to be given is used as a port, and input light incident from the input port is used as output light from the output port. The spatial refractive index distribution is formed so as to be emitted,
The spatial refractive index distribution indicates that when the input light propagates along the propagation direction of the light, the input field of the input light is converted into an output field of the output light and output from the output port. For each of the one or more input / output field pairs, the location of the cross section X when the coordinate z of the light propagation direction and the coordinate x of the light guide region perpendicular to the light propagation direction are set. In (z, x), the phase difference between the phase of the forward propagation field of the input field and the phase of the field back-propagated to the phase conjugate of the output field is less than a predetermined error, respectively. The refractive index distribution {n _q−1 } obtained by the (q−1) -th calculation is determined by repeatedly calculating the refractive index of the core at the location (z, x) of Based on For the set of the j-th input field of the input and output field [psi ^j (x) and the output field φ ^j (x), the forward propagating field ^{ψ j (z, x, {} n q-1}) field between the counter-propagating When φ ^j (z, x, {n _q-1 }), the refractive index n _q (z, x) at each location (z, x) is
n _q (z, x) = n _q-1 (z, x) −αΣ _j Im [φ ^j (z, x, {n _q-1 }) ^* · ψ ^j (z, x, {n _q-1 })]
Where the symbol “*” is a complex conjugate, the symbol “•” is an inner product operation, Im [] is the imaginary component of the field inner product operation result in [], and α is the convergence of the calculation Where Σ _j is the sum for j, and
Interference phenomenon due to multiple scattering of propagating waves generated in the wave transmission medium by the phase of the input light being subjected to phase changes in multiple stages by the refractive index distribution of the cross section X along the propagation direction of the light. A method of manufacturing an optical waveguide, characterized by propagating while changing the shape of the field of light. In the fifth step, the core layer is irradiated with a laser beam having a peak power intensity of 10 ⁵ W / cm ² or more at the condensing point, and the irradiation time of the laser beam is adjusted, so that each location (z, x The method of manufacturing an optical waveguide according to claim 3, wherein a refractive index is given. The fifth step irradiates the core layer with a laser beam having a peak power intensity of 10 ⁵ W / cm ² or more at a condensing point, adjusts the intensity of the laser beam, and adjusts each location (z, x) The method of manufacturing an optical waveguide according to claim 3, wherein the refractive index is given. In the fifth step, the core layer is uniformly irradiated with ultraviolet light through a gray scale mask, and the refractive index at each location (z, x) is given by the shade of the gray scale mask. The method for manufacturing an optical waveguide according to claim 3. The core layer, GeO2 a silica-based glass is added, the fifth step, the optical of claim 4 or 5, characterized in that is made by irradiating a laser beam from the ultraviolet ray laser A method for manufacturing a waveguide.

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