JPH03274513A - Optical coupling device - Google Patents

Abstract

PURPOSE:To easily diminish the spreading of input light and to widen the allowance for errors by providing and optical coupling means before or behind a condensing point by a condensing means. CONSTITUTION:The light emitted from a semiconductor laser 1 is made to the convergent light which has a point F as a convergent point by a condenser lens 2. This light is passed through a polarized light converting element 3 and is thereby polarized to the concentrically and circularly polarized light, the electric field vector of which exists in a concentrical circle tangent direction. The polarized light is then made incident on a circular coupler 5 which has a concentrical circular grating formed on a waveguide layer 4 orthogonal with the optical axis. The coupler 5 is provided before or behind the point F. Since the input light is made into the convergent light or divergent light, the optical coupling means can be provided in the position of sufficiently small spreading of the input light. In addition, the standard deviation of the wave front aberration of the input light is compressed by adjusting a laser beam source or the optical coupling means or condensing means along the optical axis of the laser beam by a sliding means. The deterioration in the coupling efficiency is sufficiently suppressed to small level in this way and the allowance to the errors is widened.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a device for coupling light into a waveguide. This is a further development of the optical coupling device using the grating coupling method described in International Application No. 88-01344 or Japanese Patent Application No. 1-246808. To explain, FIG. 7 shows a cross-sectional configuration diagram of an optical coupling device in a prior example.

The light emitted from the semiconductor laser 1 is converted into parallel light by the converging lens 1 and the non-condenser 2, and then becomes concentric circularly polarized light whose electric field vector is in the tangential direction of the concentric circle through the polarization conversion element 3, which is formed on the waveguide layer 4 perpendicular to the optical axis. Incident light 6 enters a circular (radius a) coupler 5 with a concentric grating.
(input light) is input coupled by the coupler 5, and the coupler 5
The guided light 7 propagates from the center ○ to the outer circumference.
Although the waveguide layer 4 is constructed on a transparent substrate 8 having a lower refractive index than this, FIG. 8 is a block diagram of the polarization conversion element 3 shown in Japanese Patent Application No. 1-246808. consists of a liquid crystal polarizing element and a retardation film 14. The liquid crystal polarizing element is formed by filling a nematic liquid crystal 16 between two transparent substrates 15A and 15B whose surfaces have been subjected to rubbing treatment. By the rubbing process (rubbing process in one direction on the 15A side and concentrically on the 15B side), the liquid crystal layer is aligned in one direction on the 15A side and in the concentric tangential direction on the 15B side. In general, when linearly polarized light 6L is incident on a TN structure liquid crystal layer, the plane of polarization of the light is rotated along the twist of the TN structure. Therefore, the linearly polarized light 17A incident from the 15A side The light is rotated by an angle approximately equal to the liquid crystal twist angle at each position of the element, and the concentrically polarized light 17B with a vibration plane approximately equal to the alignment direction of the liquid crystal molecules on the exit side (15B side) (the vibration plane is a concentric circle). tangential polarization state), but the two half-lines 18 extending from the center of the element (
The twist angle of the liquid crystal is reversed at the boundary (coinciding with the unidirectional alignment direction on the side 15A), and the rotation direction of the plane of polarization of the light is also reversed. The phase of the light is delayed by π with respect to the light of the other polarization.

In order to correct this phase delay, a λ/2 retardation film 14 is formed on the output side surface of the transparent substrate 15B. By aligning the boundary line 19 of this retardation film 14 with the line 18, the twist angle can be adjusted. Due to inversion, the phases of the concentric circularly polarized light in the two regions are aligned, resulting in almost perfect (aberration-free) concentric circularly polarized light 17
In addition, the polarization conversion element 3 may be an element that converts linearly polarized light into radiation polarized light (a polarized state in which the vibration plane is in the radial direction) or a quarter-wave plate; in this case, the input light 6
are respectively input and coupled in the state of radiation polarization and circular polarization. Here, as shown in Figure 7, the point ○ is in the same mode as the guided light 7.
Consider a backward guided wave 9 (waveguide light propagating from the outer circumferential side to the center 0) that has the same phase on the circumference centered at . Wavefront aberration ΦR(r) is defined by equation (1) a Φ*(r>= r [β+-(to N+2yrq/A))
/---(1) However, Lr is the wave number (-2π/λ, λ: wavelength) of the polar coordinates on the Kabra surface with point ○ as the origin, A is the grating pitch of the Kabra, and β1 is the input light. The propagation constant r-direction component QN is the equipolarized refraction Jq of the waveguide layer, which is the coupling order (≦-1), and in the case of two-beam coupling, q=-1. ) is the product of the input light amplitude and the emitted light amplitude, and the standard deviation ΦG of the wavefront aberration Φ is calculated using the formula (2
), but Φso=[JoAΦR'rdrdφ/, IJ+Ardr
dφ−(ff, AΦRrdrdφ/ E o Ardr
dφ) pl+'a-1~(2) However, LrJo is within the Kabra region (O≦r≦a, 0≦ψ≦2
In general, the input coupling efficiency η of the input light 6 to the guided light 7 is given by the following equation, and η= η・(1− to 2Φsb') −
--(3) However, η is the input coupling efficiency when Φ5O=O. Therefore, under the phase matching condition (ΦR(r)=0) or convergence, the pitch 8 is the following equation for parallel input light (β1=0). Satisfying the following is a condition for joining.

A=λ/N --
-(4) The amplitude distribution of the input light 6 to the cobra at the Gaussian and its radius r is expressed by the following equation.

A = expf-(r/βa)”)
−−−(5) Let β be the kicking rate of Gaussian radiation (Tru
When the grating has a symmetrical cross-sectional shape, the input coupling efficiency η of the two-beam coupling can be expressed as the following equation: η−=4αI'
(1)/βe --- (6) α is the standardized radiation loss coefficient, and Cabra's radiation loss coefficient α
Using
From FIG. 9, the efficiency η- has a maximum value of 0.417 on the ridge A, and the condition for maximum efficiency is that α and β satisfy the following formula: β=o, sa/α (where L β≦0. 50)
---(8) Problems to be Solved by the Invention The following problems were encountered in the optical coupling device of the prior art.The maximum efficiency condition (8) is based on the radiation loss coefficient α2.
fixed (e.g. a = 10.0(1/m+n))
Then, aβ = 0.086mm, and if β-0.3
Then, a=0.29■, the size of the doubler 5 is small, and the spread of the input light 6 must be made small accordingly. is parallel light, and in order to reduce its spread, a condensing lens 2 with a sufficiently small focal length is required, which is not easy to manufacture (first problem).On the other hand, equipolarized refraction due to wavelength variation is required. Assuming that the rate fluctuation is small, the wavelength error i of dA
When there is a uniform refractive index error of dN and a pitch error of dA, the wavefront aberration ΦR deviates from zero and is expressed by the following equation.

ΦR(r)=rNε−(9)
However, ε=dλ/λ0dN/N-dA/Δ −−〜(
10) Therefore, from equation (2), assuming r/a=t, the standard deviation ΦSD is given by the following equation: Φ5o=aN l t IIs""
---(II) However, Is=H5)/I(1)-I"(3)/I"(1)
--- In (12), ■- indicates the degree to which the coupling efficiency deteriorates due to errors. It is also called the efficiency deterioration coefficient. Figure 10 shows the calculation result of the deterioration coefficient 1. with respect to the coordinates (α, β). It is shown as an isocapsular line.a From Figures 9 and 10, on the ridge line A (αβ = 0.86), Φ
The following relationship approximately holds true between sD and β.

ΦIID=0.327Nlε1/αF (However, β≦0.
50) ---(13) -X From equation (3), the condition for suppressing efficiency deterioration to within 20% is given by the following equation: Φso<λ/14 ---(14
) Therefore, from equations (13) and (14), ε λa r/4.58N ---(1
5) Suppose N=1.7. αr==50゜0(1/nm
), λ=780nm, lεl<5xlO−”
Generally, when a semiconductor laser is used as a light source, there is a wavelength variation of about ±0.5% depending on the laser, and a uniform refractive index of about ±0.5% due to film thickness error and refractive index error of the waveguide layer 4. Errors will occur, so if we consider these random combinations, we can expect a total error of about ±1%, but this is not a situation where the condition ``IE+<5X10-'' is always fully satisfied (such as this). Given the current situation, the problem remains as a practical matter of how to widen the tolerance for errors and increase the coupling efficiency (second problem).

In view of these problems, the present invention aims to provide an optical coupling device that can easily reduce the spread of input light and widen the tolerance for errors. A board that uses the following means to solve the problem: A laser light source, a focusing means that focuses the laser light emitted from the light source onto one point, and a polarization conversion means that converts the polarization state of the laser light. , consists of a waveguide layer configured in a plane perpendicular to the optical axis, and an optical coupling means formed on the waveguide layer and having a concentric periodic structure centered on the optical axis, and the optical coupling means focuses light. If the optical coupling means is located at a distance of 2 from the focal point when there is nothing intervening between the optical coupling means and the optical condensing means, the laser beam The wavelength is λ, the equivalent refractive index of the waveguide layer is N,
The pitch of the periodic structure at radius r from the center of the concentric circle is expressed by the following simultaneous equations, where n is the refractive index and t is the plate thickness of the transparent flat plate interposed between the condensing means and the optical coupling means. )) (where Lq is an integer less than or equal to 11, and the sign 10 and - corresponds to the position of the optical coupling means (respectively, to the back of the light condensing point)). or an optical coupling device having a sliding means for moving the light condensing means along the optical axis; The optical coupling means is provided at a position on the optical axis where the iso-intensity line forms an elongated ellipse parallel to the ellipse at the distal axis and an elongated ellipse orthogonal to the ellipse at the paraxial area. ,
a laser light source, a polarization conversion means for converting the polarization state of the laser beam, a waveguide layer formed in a plane orthogonal to the optical axis, and a concentric ring formed on the waveguide layer and centered on the optical axis. When the optical coupling means is located at a distance of 2 from the light source, the wavelength of the laser light is λ.
, where the equivalent refractive index of the waveguide layer is N, the refractive index of the transparent flat plate interposed between the light source and the optical coupling means is n, and the plate thickness is t, and the pitch A of the periodic structure at radius r from the center of the concentric circle is It is characterized by being given as a solution to the following simultaneous equations (%) () ) (where q is an integer less than or equal to -l). It may be a coupling device.1. % To the light emitted from this line light source, the isointensity lines on the surface of the optical coupling means form an ellipse at the distal axis, and form a long ellipse orthogonal to the ellipse at the paraxial section. It is preferable to provide t~ Also, the wavelength of the laser light source is larger (or smaller) than the reference value λ by dA, and the equipolarized refractive index of the waveguide layer is the reference value N.
is larger (or smaller) than the reference value A by dN, and when the pitch of the periodic structure is larger (or smaller) than the reference value A by dA, the value of 1dλ/λ+dN/N-dA/AI is equal to zero. The above-mentioned configuration allows the input Since the light becomes convergent light or diverging light, the light coupling means can be provided at a position where the spread of the input light is sufficiently small, and the laser light source, the light coupling means, or the light condensing means can be placed on the optical axis of the laser light by the sliding means. The standard deviation of the wavefront aberration of the input light can be compressed and the tolerance for errors can be increased by adjusting the input light along the optical axis.Also, the light distribution on the optical coupling means forms a nearly circular line of equal intensity, or the input light is It is possible to guide the wave with an almost isodirectional intensity distribution, and also to improve the coupling efficiency and yield of the input light by bearing between the laser light source and the waveguide layer. The first embodiment of the present invention will be explained based on FIGS. 1 to 5. The first embodiment of the present invention will be explained below based on FIGS. 1 to 5. FIG. 1 shows the optical coupling in the first embodiment. The cross-sectional configuration of the device is shown. Although the same configuration as the previous example is given the same number and the explanation thereof is omitted, the light emitted from the semiconductor laser 1 is focused by the condensing lens 2 to the point F, and the polarization conversion element 3 is As a result, the electric field vector becomes concentrically polarized light in the tangential direction of the concentric circle, and the waveguide layer 4 is perpendicular to the optical axis.
A circular shape with concentric gratings formed on top (
In this example, the incident light enters the turntable 5 with radius a).
is the force fork in front of the point F. It can be in the back. The incident light 6 (input light) is coupled into the coupler 5 and becomes the guided light 7 that propagates from the center O of the coupler 5 to the outer circumference. The waveguide layer 4 is formed on a transparent substrate 8 having a refractive index lower than this, and even though the transparent substrate 8 is fixed coaxially to the hollow part of a cylindrical tube-shaped holder 9, the holder 9 has a cylindrical shape. The hollow part of the guide 10 with a hole in it can be slid along its central axis, and the stopper 11 can be used to fix it.
Even though the center axis of the hollow part of the guide 10 coincides with the optical axis of the focused light, the polarization conversion element 3 has the same configuration as the previous example shown in FIG. 8, so a detailed explanation thereof will be omitted. The conversion element 3 may be an element that converts linearly polarized light into radiation polarized light (a state of polarization in which the plane of vibration is in the radial direction) or a quarter-wave plate, and in this case, the input light 6 is in the state of radiation polarization and circular polarization, respectively. (The same applies to the following embodiments of the invention.) In this embodiment, as shown in FIG.
is placed on the image plane two distances in front of the focal point F (if the cover 5 is placed on the image plane two distances back from the focal point F, the principle is the same as the second embodiment described later). Therefore, we omit the explanation here.) The grating pitch A of the converter 5 is set to satisfy the following formula.

A=λ/(N+r/(r'+z2)"') ---
(16) The propagation constant in the r direction on the image plane is r/
(r'+zl becomes I/2) From equation (1), the wavefront aberration ΦR can be expressed as the following equation: ΦR(r)-r'/(r2+z2)"" -rN +
rλ/A − (17) The pitch A of this example is (16)
Therefore, in this embodiment, the phase matching condition (Φ term (r) = 0) is satisfied, and the input light 6 is efficiently coupled. By moving the fogger 5 toward the light source along the optical axis, tolerance to errors in wavelength and the like can be improved, and this will be explained below.

First, when the coupler 5 is moved by δ along the optical axis toward the light source, the propagation constant of the input light on the coupler 5 in the r direction changes by 1, so the wavefront aberration ΦR deviates from zero and is a value expressed by the following equation. 4 Φ1I(r)−−r”/(rlI+(z+δ)Il)
)I zm +rl /(ra+zl)l '1l--
-(18) In reality, is it okay to set δ<z, r<z? The above equation can be approximated by the following equation, but ΦR<r)=δr Il/z 1l---(19) Therefore, the wavelength error of dλ There is a pitch error of the equipolarized refractive index error base dA of dN, and when the fogger 5 is moved δ along the optical axis toward the light source in order to correct this, Equations (9) and (1
9), the wavefront aberration ΦR can be expressed as the following formula: ΦR(r)
= δr 2/z 9+ r N s ---(2
0) Therefore, the standard deviation ΦSt) of the wavefront aberration ΦR as r/a-t is given by the following formula: Φ5o-((a/z)'I+(δ+lez″Nt/a
)"Il5(aNε2su; long chi) where h = I(9)/I(1)-I"(5)/I"(1)
---(23)b= (I(7)/I(1
)-1(5)I(3)/l2(1))/II-(
24) Is = II-II 122---(25)■
8 indicates the degree of susceptibility to deterioration of the coupling efficiency optimized by position adjustment. Since engineering3〉0, Φs11 is δ=
-l2ZllN ε/a(7) Minimum value a N
This minimum value is (Is/Is)"" times larger than the value when δ-〇. Figure 2 shows the calculation result of the efficiency deterioration coefficient ratio I3/II at the coordinate (α , β).

In Figure 2, at the position corresponding to ridgeline A, Is/b=
0.10 to 0.11, and by adjusting the movement of the coupler 5, the deterioration of the coupling efficiency can be suppressed to about Il10, and I
Considering s/I = 0.10, the margin for error may be 10'72 times wider. Therefore, from equation (14), the condition for suppressing efficiency deterioration to within 20% is given by the following equation: Isl<0,69λcx r/N ---
(26) Suppose N = 1.7. a r = 50.
0(1/nm) and λ=780nm, 1εl<
16XIO-3, and can tolerate an error of about ±1% caused by variations in the wavelength of the light source, errors in the equipolarized refractive index of the waveguide layer, etc. In other words, in this embodiment, the transparent substrate 8 (i.e., the coupler 5) is placed on the optical axis. In this embodiment, the sliding means of the holder 9, guide 10, etc. are connected to the transparent substrate 8 (i.e., the cover 5). However, the same effect can be obtained even if the same means is provided in the semiconductor laser 1 or the condenser 1 and the non-condenser 2 is slid. Since the iso-intensity lines of the emitted light on the image plane perpendicular to the optical axis are ellipsoids, in order to guide the input light 6 with an isotropic intensity distribution to the center O, as shown in Fig. 3. Collimating lens 1 is placed between light source 1 and condensing lens 2.
2 and triangular prism 13 to shape the elliptical beam 2OA into a circular beam 20B.In contrast, the optical coupling device of this embodiment does not require such a complicated configuration. In this embodiment, the light emitted from the semiconductor laser 1 is focused by the condenser lens 2 without beam shaping. , as shown in Figure 4, the light 6A forms an elliptical iso-intensity line on the aperture surface of the condenser lens (at the position of the condensing point, the light 6B forms an elliptical iso-intensity line when the long sleeve is rotated 90 degrees, and the aperture surface There is always light 6C with an almost circular (in the i-density, an ellipse similar to that on the aperture surface at the distal axis and an ellipse similar to the surface on the aperture surface in the paraxial area) isointensity line between the and the focal point. Therefore, by setting the coupler 5 in a region with a circular iso-intensity distribution like the light 6C, the input light 6 can be guided with an almost isotropic intensity distribution without beam shaping. be.

(Second Embodiment) FIG. 5 shows a cross-sectional configuration diagram of an optical coupling device in a second embodiment of the present invention. Components that are the same as those in the first embodiment are given the same numbers and their explanations will be omitted.

The light emitted from the semiconductor laser l passes through the polarization conversion element 3 and becomes concentrically polarized light whose electric field vector is tangential to the concentric circle. ) The incident light 6 (input light) is coupled into the coupler 5 and becomes the guided light 7 which propagates from the center O of the coupler 5 to the outer periphery.The waveguide layer 4 starts from this. A transparent substrate 8 with a low refractive index
Although the transparent substrate 8 is coaxially fixed to the hollow part of the cylindrical tube-shaped holder 9, the holder 9 is fixed along the central axis of the hollow part of the cylindrical-shaped guide 10 with a hole. It can be slid and fixed with stopper 11.
Even if the central axis of the hollow part of the guide 10 coincides with the optical axis, and even if the coupler 5 is placed on the image plane that is 2 points away from the light emitting point of the light source, the grating pitch A of the coupler 5 in this embodiment is as follows. Even if the formula is satisfied, A=λ/(N −r/(r”+z″)””] −−
−(27) The propagation constant in the r direction on the coupler 5 is r
/(r"+zit)j/11 From equation (1), the wavefront aberration Φ can be expressed as the following equation: Φ*(r)-r'/(r'+z")""-rN +rλ
/A---(28) In this example, pitch A is (27)
Since it is given by the formula, the phase matching condition (ΦR(r) = O)
In this embodiment, the input light 6 can be input and coupled efficiently.In this embodiment, the tolerance for errors can be expanded as follows.In this embodiment, the fogger 5 connects the light source along the optical axis. δ in the direction
When the input light r-direction propagation constant on the coupler 5 changes when the coupler moves by z−δ)2))
l/l! , I! /(r2+zJlz2---(2
9) In reality, is it okay to set δ(2, r<z? Technically, the above formula is (1
9) Therefore, the wavelength error i of dλ, the equipolarized refractive index error base dA of dH
There is a pitch error of
As in the first embodiment, the deterioration of the coupling efficiency can be suppressed to about 1710 by adjusting the movement of the cover 5, and considering Is/I = 0.10, the margin for error is IQl 711 times widerA This embodiment does not require the condenser lens 2 compared to the first embodiment, and has a simpler and more compact structure. In other words, to explain using FIG. 4, in this embodiment, the emitted light from the semiconductor laser 1 is the light 6B6t of the elliptical isointensity line immediately after the emission from the light source. At a far-field position that is far enough away, the light 6A becomes an elliptical iso-intensity line with its long axis rotated by 90 degrees, and the distance between the light emitting point and the far-field position is almost circular (strictly speaking, the far-axis part is the same as the far-field position). At the paraxial part of the similar ellipse R, there is always light 6C of isointensity line (of the emitting point and the similar ellipse).Therefore, coupler 5 can be replaced by light 6
By setting the area in a region with a circular iso-intensity line distribution like C, it is possible to guide the human-powered light 6 with an almost iso-directional intensity distribution without beam shaping. This can be said not only for the second embodiment and the previous examples, but even if there are wavelength errors, equal polarized refractive index errors, and pitch errors, the relationship between them holds true, and the overall equation given by equation (10) is It is possible to reduce the error ε, for example, by combining a light source whose wavelength is dλ larger than the reference value λ with a waveguide layer whose equipolarized refractive index is smaller than the reference value N by Ndλ/λ, or by setting the grating pitch to the reference value. By combining with a cobra larger than the value A by Adλ/λ, the error ε can be made zero.

In other words, by measuring the wavelength of the semiconductor laser and the equipolarized refractive index of the waveguide layer in advance, and performing bearings that reduce the overall error ε, it is possible to obtain combinations with even higher coupling efficiency with a higher yield. Is it possible? , the grating pitch is adjusted based on the wavelength and equipolarized refractive index data of the combined semiconductor laser and waveguide layer, and the overall error ε
In both of the first and second embodiments, the focused light passes through parallel flat plates (transparent substrates 15A, 15B, etc.), so the actual grating pitches are (16), (27) ) It is necessary to add a correction term to the equation as appropriate to correct the spherical aberration caused by the above transmission.

FIG. 6 is an explanatory diagram showing the amount of correction for spherical aberration,
Fig. 6(a) shows the case where the coupler shown in the first embodiment is located in front of the condensing point, and Fig. 6(b) shows the case where the coupler shown in the second embodiment is located behind the condensing point. In Fig. 6(a), which corresponds to the case where diverging light from a light source is input and coupled, the convergent light passing through a position with a radius r from the center on the coupler 5 is a parallel plate with a refractive index n and a plate thickness t. By transmitting the light through the parallel plate 20, the image is formed a distance δ from the focal point F when the parallel plate 20 is not present. Given by the following formula, tanθ=r/(z+
δ) ---(30) Also, according to Snell's law, δ is given by the following formula: δ=t (1-(1-si
n2θ)"l'/(n"-sin"θ)"")---
(31) The r-direction propagation constant on the coupler is β! If pitch A satisfies the following formula, the phase matching condition is satisfied, but A=-qλ/(N+sinθ) ---(3
2) (Lq is an integer less than or equal to 1) -X! In Figure 6(b), the radius r from the center on the coupler 5
By passing through the parallel flat plate 20 with refractive index n and plate thickness t, the light converging point (or light emitting point) seen from the coupler 5 side becomes the actual light focusing point (or light emitting point). ) The angle of incidence θ on the parallel plate 20 is given by the following equation, assuming that the distance between the point F and the coupler 5 is 2.

tanθ=r/(z−δ) ---(3
3) Also, according to Snell's law, δ is given by equation (31), but the r-direction propagation constant on the coupler becomes β1=Sinθ, or convergence From equation (1), if pitch A subtracts the following equation, phase matching is achieved. Although the condition is satisfied, A=-qλ/(N-sinθ) ---(34
) (where Lq is an integer less than or equal to 1) Therefore, the actual grating pitch can be given by equation (32) or (34). In addition, it is possible to widen the margin for error, and to obtain an optical coupling device with high coupling efficiency at a high yield.

Also, far field position and focal point (or light emitting point)
Since the coupler is set to form a substantially circular iso-intensity distribution between

[Brief explanation of drawings]

FIG. 1 is a sectional view of a main part of an optical coupling device according to a first embodiment of the present invention. FIG. 2 is a coordinate (α) of the efficiency deterioration coefficient ratio 13/I.
, β). Figure 3 is an explanation of the beam shaping method. Figure 4 is an explanation of changes in the input light equal intensity edge distribution in the first or second embodiment of the present invention @ Figure 5. is a sectional view of a main part of an optical coupling device according to a second embodiment of the present invention.
FIG. 6 is an explanatory diagram showing the amount of correction of spherical aberration in the first or second embodiment of the present invention. FIG. 7 is a sectional view of a main part of the optical coupling device of the prior example. FIG. 8 is a polarization conversion element. The structure of Figure 9 is the isocapsular statement for the input coupling efficiency η coordinates (α, β). Figure 10 is the coordinates of the deterioration coefficient Is (α1β
), 1...semiconductor laser, 2...condensing lens χ3.
...Polarization conversion element, 4... Waveguide 5... Grating coupler, 6... Input light 7... Waveguide light 8
...Transparent substrate 9...Holder, Traver 10...Guide, 11...Name of Su1 Patent attorney Kazutaka Awano and two others ゛, / Pi1--no! 2 Figure A Figure #II Stops and Faint Light Returns 1' Ift Exchange 1 Conjunction 5 II 4 Rishi - Tinku Kabura λ 711 Party Guide Destruction Study aB IE Den Hol 9 - ! Figure 5 - / Figure b = itvw (b comparison σ

Claims (9)

[Claims] (1) A laser light source, a condensing means for condensing the laser light emitted from the light source, a polarization conversion means for converting the polarization state of the laser light, and a waveguide layer configured in a plane orthogonal to the optical axis. and an optical coupling means formed on the waveguide layer and having a concentric periodic structure centered on the optical axis, and the optical coupling means is provided in front of or behind a light converging point by the light condensing means. An optical coupling device characterized in that: (2) If there is nothing intervening between the optical coupling means and the light condensing means, and the optical coupling means is at a distance z from the focal point, the wavelength of the laser beam is λ, and the waveguide is The pitch of the periodic structure at a radius r from the center of the concentric circle, where the equivalent refractive index of the layer is N, the refractive index of the transparent flat plate interposed between the light condensing means and the light coupling means is n, and the plate thickness is t. Λ is the following simultaneous equation Λ=-qλ/(N±sinθ) tanθ=r/(2±δ) δ=t{1-(1-sin^2θ)^1^/^2/(n
^2-sin^2θ)^1^/^2) (However, q is -
2. The optical coupling device according to claim 1, wherein the integers less than or equal to 1 and the sign + and - are given as a solution to the position of the optical coupling means (corresponding to the front and rear of the light condensing point, respectively). (3) The light emitted from the light source forms an elliptical iso-intensity line on the aperture surface of the condensing means, and the iso-intensity line on the surface of the light coupling means forms an elongated ellipse parallel to the ellipse at the far axis. 2. The optical coupling device according to claim 1, wherein the optical coupling means is provided at a position on an optical axis that forms a long ellipse perpendicular to the ellipse at a paraxial portion. (4) a laser light source, a polarization conversion means for converting the polarization state of the laser beam, a waveguide layer configured in a plane orthogonal to the optical axis, and a waveguide layer formed on the waveguide layer and centered about the optical axis. and an optical coupling means having a concentric periodic structure,
When the optical coupling means is located at a distance z from the light source, the wavelength of the laser beam is λ, the equivalent refractive index of the waveguide layer is N, and the refractive index of the transparent flat plate interposed between the light source and the optical coupling means is The pitch Λ of the periodic structure at the radius r from the center of the concentric circle is expressed by the following simultaneous equation Λ=-qλ/
(N-sinθ) tanθ=r/(z-δ) δ=t{1-(1-sin^2θ)^1^/^2/(n
＾2−sin＾2θ)＾1＾／＾2＝(However, q is −
2. The optical coupling device according to claim 1, wherein the optical coupling device is given as a solution of (an integer less than or equal to 1). (5) At a position on the optical axis where the isointensity lines of the light emitted from the light source on the surface of the optical coupling means form an ellipse at the distal axis and an elongated ellipse orthogonal to the ellipse at the paraxial area. 5. The optical coupling device according to claim 4, further comprising the optical coupling means. (6) The optical coupling device according to claim 1 or 4, further comprising a sliding means for moving the laser light source, the optical coupling means, or the condensing means along the optical axis of the laser beam. (7) The wavelength of the laser light source is larger (or smaller) than the reference value λ by dλ, the equivalent refractive index of the waveguide layer is larger (or smaller) than the reference value N by dN, and the pitch of the periodic structure is the reference value. 5. The optical coupling device according to claim 1, wherein the value of |dλ/λ+dN/N−dΛ/Λ| is equal to zero when it is larger (or smaller) than the value Λ by dΛ. (8) The optical coupling device according to claim 1 or 4, wherein a quarter wavelength plate is used as the polarization conversion means. (9) The optical coupling device according to claim 1 or 4, wherein the polarization conversion means converts the polarization plane of the laser beam into a polarization state in a concentric tangential direction or a radial direction.