JPH09258047A - Optical waveguide device - Google Patents

Abstract

(57) Abstract: A waveguide element having a function of selecting light such as polarized light or wavelength, which does not require precise microfabrication and has a short element length. SOLUTION: Incident light is branched into two directions, and each is bent and propagates in a waveguide. The lengths L _TE and L _TM of the straight waveguide of each curved waveguide are determined so as to satisfy the equation (9). [Equation 9]

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide device used for optical fiber communication, optical measurement, etc., and particularly to a mode splitter for separating TE mode light and TM mode light by using an optical waveguide. Regarding

[0002]

2. Description of the Related Art Integrating optical elements is a system miniaturization,
From various points such as optical reliability, low power consumption, low price, etc., it greatly contributes to opticalization of optical fiber communication networks and optical measurement systems. Among them, the TE / TM mode splitter is used as a very important component of mode separation such as polarization diversity type heterodyne receiver in optical fiber communication and polarization separation in an interferometer in the field of optical measurement.

As a structure of the TE / TM mode splitter element, a directional coupler structure or a double mode waveguide type structure utilizing mode interference has been reported. Techniques reported for putting these into practical use include a waveguide type optical integrated device using a silica glass or a lithium niobate (LiNbO ₃ ) substrate,
There is a compound semiconductor optical integrated device in which a semiconductor laser and an optical waveguide are integrated.

[0004]

However, in the conventional mode splitter, since it is necessary to manufacture the waveguide length and the waveguide interval with high precision, fine processing is required. Further, in order to perform good mode separation, it is necessary to lengthen the element length.

An object of the present invention is to provide a waveguide element having a function of selecting light such as polarized light and wavelength, which does not require precise microfabrication and has a short element length. .

[0006]

In order to achieve the above object, according to the present invention, first and second linear waveguide portions for sequentially propagating incident light and a light propagating direction are predetermined. A curved waveguide including a connecting portion that connects the first linear waveguide portion and the second linear waveguide portion so as to be displaced by an angle is provided, and the first linear waveguide and the second linear waveguide are provided. The polarization selectivity is characterized in that the first linear waveguide section is connected to the waveguide at a predetermined angle, and the length of the first linear waveguide section is a length L satisfying the equation 1 for the polarized light to be propagated. An optical waveguide device having the same is provided.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

First, the optical waveguide device according to the first embodiment of the present invention will be described with reference to FIG. The waveguide element of FIG.
It is a polarization selection element for extracting only TE mode light from the incident light.

The optical waveguide device shown in FIG. 2 has a linear waveguide 12,
The bent waveguide has a structure in which 13, 14, and 15 are sequentially connected by bent portions 16, 17, and 18 so that the light propagation direction is deviated by an angle θ _B. That is, in the bent portion 16, the linear waveguide 12 and the linear waveguide 13 are connected at an angle so that the light propagation direction is deviated by an angle θ _B. Similarly, in the bent portion 17, the linear waveguide 13 and the linear waveguide 14 are connected at an angle such that the light propagation directions are deviated by an angle θ _B , and in the bent portion 18, the linear waveguide 14 and the linear waveguide 14 are connected. And 15 are connected at an angle such that the light propagation direction is deviated by an angle θ _B.
In this embodiment, the angle θ _B is a constant angle of about 1 °.

The linear waveguides 12, 13, 14, 15
The length is set to a constant length L _{TE in} the present embodiment.
L _TE is a length determined so that Expression 6 is satisfied for TE mode light.

[0011]

(Equation 6)

In the present embodiment, the value of Δn _{TE in} the equation 6 is Δn _TM (Δn _TM = Neff _TM -Neff ' _TM , where Ne
ff _TM : _{TM in the} straight waveguides 12, 13, 14, and 15
The effective refractive index of the guided mode of the mode, Neff ' _TM : the average value of the effective refractive index of the non-guided mode of the TM mode in the bent portions 16, 17 and 18) Configured.

Neff _TE is a value obtained by calculation from the structure of the linear waveguide 12 and the like, and Neff _TE 'is a value obtained by experiment.

In the optical waveguide element of FIG. 1 having such a structure, the light incident from the incident end 11 of the linear waveguide 12 is
Each of the TE mode and the TM mode propagates through the linear waveguide 12 and reaches the bending portion 16. In the bent portion 16, since the linear waveguide 13 is connected to the linear waveguide 12 at an angle, a non-guided mode (radiation mode) is excited for each of TE mode and TM mode, and TE mode light and TM mode light are excited. A part is radiated from the straight waveguide 12. At this time, the emitted mode lights are recombined with the linear waveguide 13 and propagate through the linear waveguide 13. The efficiency of recombination of the non-guided mode light into the linear waveguide 13 has a periodicity depending on the length L _TE of the linear waveguide 12, as shown in FIG.

In the present embodiment, the length of the straight waveguide 12 is set to the length L _TE for the TE mode light to satisfy the equation 6, so that the TE mode light and the TE mode light in the bending portion 16 are not guided. The phase difference Φ with the wave mode light is π
Will be an odd multiple of. As a result, the efficiency of recombination of the TE mode non-guided mode light into the linear waveguide 13 is maximized, and the TE mode light is completely coupled into the linear waveguide 13. Therefore, the TE mode light is coupled to the straight waveguide 13 with a loss of almost 0 when the propagation loss of the waveguide is neglected, and propagates this.

[0016]

(Equation 7)

On the other hand, the phase difference Φ between the guided mode light of the TM mode and the non-guided mode light in the bent portion 16 set to L _TE does not satisfy the expression (7). Therefore, TM
The efficiency of recombination of the non-guided mode light of the mode to the linear waveguide 13 becomes low, and the TM mode light is lost at the bending portion 16.

Therefore, in the bent portion 16, most of the TM mode light is lost, whereas the TE mode light is coupled to the straight waveguide 13 without being lost.

The light propagating through the linear waveguide 13 has a curved portion 17, a linear optical waveguide 14, a curved portion 18, and a linear waveguide 1.
It is emitted from the emission end 19 via At this time, in the bent portions 17 and 18, as in the bent portion 16, the TM mode light is largely lost and the TE mode light is recombined without loss. Therefore, the light incident from the incident end 11 passes through the bent portions 16, 17, and 18 in order, whereby most of the TM mode light is repeatedly lost and most of the TM mode light is removed. Therefore, the light emitted from the emission end 12 contains almost no TM mode light, and
Only E mode light can be extracted.

As the linear waveguides 12, 13, 14, 15 for constructing the waveguide element of FIG. 2, any structure may be used as long as the value of Δn _TE of the equation 6 is different from the value of Δn _TM. It may be a structure. For example, it can be achieved by forming the waveguide with a material having optical anisotropy in the TE mode direction and the TM mode direction as the material forming the waveguide. Further, for example, as shown in FIG. 4, the effective refractive index of TM mode light and the effective refractive index of TE mode light can be set to different values depending on the structure of the waveguide. Further, an anisotropic material and a waveguide structure in which anisotropy occurs can be used in combination.

Specifically, a waveguide formed by diffusing Ti into a LiNbO ₃ single crystal substrate, or a waveguide shown in FIG.
Of the structure of GaAs substrate 51, Al _x Ga _1-x As clad layer 52, GaAs waveguide layer 53, and Al _y Ga _1-y.
A waveguide realized by the As (y ≠ x) cladding layer 54 can be used.

Further, the above-described waveguide device of FIG. 2 has a configuration including only three bent portions 16, 17, and 18, but the larger the number of bent portions, the more the TM mode light can be lost. Therefore, the number of bends required for the waveguide element can be determined from the recombination efficiency of the TM mode light and the allowable amount of the TM mode light included in the emitted light.

Next, a waveguide device according to a second embodiment of the present invention will be described with reference to FIG.

In the waveguide device of FIG. 1, TE mode light and TM mode light are extracted from the light incident from the incident end 21 and TE mode light is emitted from the emission end 29, and TM
It is a TE / TM mode splitter that emits mode light from the emission end 34.

As shown in FIG. 1, this waveguide element has a straight waveguide 22 having an incident end 21, and a branching portion 35 for splitting the light propagating through the straight waveguide 22 into two. The linear waveguide 23 and the linear waveguide 30 are connected to the branching portion 35, and the two branched lights propagate respectively.

The linear waveguide 23 has, in order, the linear waveguide 2
4, 25, 26, 27, 28 are bent portions 36, 37,
Angled connections by 38, 39, 40. The angle between the linear waveguides 23, 24, 25, 26, 27 and 28 is the same as the angle θ in the first embodiment.
_B. In addition, the linear waveguides 23, 24, 25, 26,
The length of 27 is the length L _TE that satisfies the equation 6, as described in the first embodiment.

On the other hand, to the linear waveguide 30, linear waveguides 31, 32 and 33 are connected in order by curved portions 41, 42 and 43. Straight waveguides 30, 31, 32, 3
The angle between 3 is θ _A. In addition, the straight waveguides 30, 3
The lengths of 1 and 32 are the length L _TM that satisfies the expression 8.

[0028]

(Equation 8)

Further, in all the linear waveguides 22 and the like constituting the waveguide device of FIG. 1, the value of Δn _{TE in} the equation 6 is Δ in the equation 8.
The structure is such that the value is different from the value of n _TM . Specifically, as described in the first embodiment, the effective refractive index is T
Different waveguide structures are used for the E mode and the TM mode.

In the waveguide element having the structure shown in FIG. 1, the light incident from the incident end 21 propagates through the linear waveguide 22, and is branched into a linear waveguide 23 and a linear waveguide 30 at the branching portion 35. . The light branched into the straight waveguide 23 propagates through the straight waveguide 23 and reaches the bending portion 36. In the bend 36,
Since the length L _TE of the linear waveguide 23 is set to a length that satisfies the formula 6, as described in the first embodiment,
TE mode light is completely recombined into the straight waveguide 24, but TM mode light can be recombined only with low efficiency.
Mode light is largely lost. The TE mode light and the TM mode light recombined in the linear waveguide 24 propagate in the linear waveguides 24, 25, 26, 27, 28 in order. At this time,
In the bent portions 37, 38, 39, 40, TE
Since the mode light is completely recombined, the TM mode light is largely lost, so that the light reaching the emission end 29 has T
Almost all M-mode light is not contained and TE
The mode light is emitted.

On the other hand, since the length L _TM of the linear waveguide 30 is set to satisfy the equation (8), the light branched to the linear waveguide 30 is bent at the bent portion 41.
While the TM mode light is completely recombined into the linear waveguide 31, the TE mode light can be recombined only with low efficiency.
Mode light is greatly lost. The TM mode light and the TE mode light recombined in the linear waveguide 31 propagate in the linear waveguides 32 and 33 in order. At this time, the bent portions 42 and 43
In each case, the TM mode light is completely recombined, but the TE mode light is lost. Therefore, the light reaching the emission end 34 contains almost no TE mode light, and almost all the TM mode light is TM mode light. Light is emitted.

As described above, by using the waveguide element of FIG. 1, a TE / TM mode splitter can be realized in which the TE mode light is emitted from the emission end 29 and the TM mode light is emitted from the emission end 34.

As the linear waveguides 22, 23, 30 and the like for constructing the waveguide device of FIG. 1, the value of Δn _TE of equation 6 is equal to the value of Δn of equation 8 as described in the first embodiment. Any structure may be used as long as it has a structure different from the value of _TM .
Further, as shown in FIG. 4, when a waveguide structure in which the waveguide layer 53 is formed on the GaAs substrate 51 is used, an optical integrated circuit in which semiconductor elements, light receiving elements, etc. are integrated on the same substrate 51 is formed. be able to.

Further, the mode split efficiency can be further improved by increasing the number of the bent portions 36, 41, etc. included in the waveguide element of FIG.
Further, in the first and second embodiments, the angle of the bent portion and the length of the linear waveguide are set to a predetermined constant angle and length, but the angle is changed for each bent portion, and the straight line is changed according to this angle. It is also possible to adopt a configuration in which the length of the waveguide is changed.

The lengths L _TE and L _TM of the straight waveguides which are the segments of the waveguide elements shown in FIGS. 1 and 2 are usually 50 μm.
Since it can be set to the order of 200 μm, the element length can be significantly reduced as compared with the conventional one. In addition, it is possible to easily form a good mode splitter without performing precision microfabrication as in the past.

Further, since the waveguide element of the present invention is composed of a curved waveguide in which the waveguide is refracted for each predesigned length L, the waveguide element of the present invention is positioned at the target position of light. It can also be used as a waveguide for guiding to. In this case, it is not necessary to prepare a space for arranging the mode splitter as in the conventional case,
The element length can be significantly reduced.

Further, by disposing a metal-loaded TE mode polarizer in any of the linear waveguides 23 to 28 for outputting the TE mode, it is possible to further improve the mode split ratio.

Further, the branch portion 35 is made of a material having an electro-optical effect, and an electrode or the like for applying an electric field or injecting a current is arranged in the branch portion 35 to apply an electric field or inject a current. Thus, it is possible to adopt a configuration in which a change in the refractive index is caused. In this case, it is possible to set the ratio of the light branched by the branching portion 35 to the linear waveguide 23 and the linear waveguide 30 to an arbitrary ratio, whereby the emission end 29,
The ratio of the TE mode light and the TM mode light emitted from 34 can be set to an arbitrary ratio.

In the waveguide element of FIG. 1, the fact that Δn has wavelength dependence is used to replace the lengths L _TE and L _TM of the linear waveguides with Lλ ₁ and Lλ ₂ of the equation 5, The waveguide element of FIG. 1 can act as a wavelength demultiplexer. As a result, two wavelengths with different wavelengths (λ1,
Incident light including λ2) can be incident from the incident end 21, light of the wavelength λ1 can be emitted from the emission end 29, and light of the wavelength λ2 can be emitted from the emission end 34.

[0040]

As described above, according to the present invention, a waveguide element having a function of selecting light such as polarized light or wavelength, which does not require precise microfabrication and has a short element length. An element can be provided.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a configuration of a TE / TM mode splitter according to a second embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a configuration of a polarizing element according to the first embodiment of the present invention.

FIG. 3 is a graph showing the relationship between the length L of the straight waveguide and the recombination axis in the first embodiment.

FIG. 4 is a cross-sectional view showing a structure of a waveguide that can be used in the waveguide device of the first and second embodiments.

[Explanation of symbols]

11 ... Incident end, 12, 13, 14, 15 ... Straight waveguide,
16, 17, 18 ... Bent portion, 19 ... Emitting end, 21 ... Incident end, 22, 23, 24, 25, 26, 27, 28, 3
0, 31, 32, 33 ... Linear waveguide, 29, 34 ... Emitting end, 35 ... Branch portion, 36, 37, 38, 39, 40, 4
1, 42, 43 ... Bent part.

Claims (7)

[Claims] 1. A first and a second straight waveguide portion for propagating incident light in sequence, and the first straight waveguide portion and the second straight waveguide portion so that the propagation directions of the light are deviated by a predetermined angle. A first waveguide and a second waveguide, wherein the first straight waveguide and the second straight waveguide are connected at a predetermined angle. The optical waveguide element having polarization selectivity, wherein the length of the waveguide portion is a length L that satisfies Expression 1 for the polarized light to be propagated. [Equation 1] 2. The optical waveguide having polarization selectivity according to claim 1, wherein a plurality of curved waveguides are provided, and the plurality of curved waveguides are arranged so as to sequentially propagate the incident light. element. 3. A straight waveguide portion having a plurality of straight waveguide portions and a bend portion which sequentially connects the plurality of straight waveguide portions so that the propagation direction is displaced by a predetermined angle. The optical waveguide element having polarization selectivity is characterized in that the length L satisfies the expression 2 for the polarized light to be propagated. [Equation 2] 4. A branching part for branching incident light into two directions, a first waveguide and a second waveguide for respectively propagating the light branched at the branching part, The first waveguide has a first curved waveguide, the second waveguide has a second curved waveguide, and the first curved waveguide has the branched light. A third and a fourth linear waveguide portion that propagate in sequence, and a third linear waveguide portion that connects the third linear waveguide portion and the fourth linear waveguide portion such that the propagation direction of light is deviated by a predetermined angle. The second bent waveguide is configured so that the propagation direction of the light is deviated by a predetermined angle from the fifth and sixth straight waveguide parts that sequentially propagate the branched light. And a second connecting portion that connects the fifth linear waveguide portion and the sixth linear waveguide portion to each other. Length of the waveguide portion satisfies L _TE the following equation 3, the length of the straight waveguide portion of the fifth optical waveguide device having polarization selectivity and satisfies the L _TM the following equation 3 . (Equation 3) 5. The fourth waveguide section according to claim 4, wherein the first waveguide section has a plurality of sets of the first bent waveguides, and the plurality of sets of the first bent waveguides sequentially output the branched light. The second waveguide section is arranged so as to propagate, and the second waveguide section has a plurality of sets of the second curved waveguides, and the plurality of sets of the second curved waveguides propagate the branched light in order. An optical waveguide element having polarization selectivity, which is characterized in that 6. A branch portion for splitting incident light into two directions, a first curved waveguide and a second curved waveguide for propagating the light split by the branched portion, respectively. And a plurality of linear waveguide portions are provided in the first curved waveguide,
A plurality of curved portions that sequentially connect the plurality of linear waveguide portions are provided so that the propagation direction of light is deviated by a predetermined angle, and a plurality of linear waveguide portions are provided in the second curved waveguide. ,
A bent portion that sequentially connects the plurality of linear waveguide portions is provided so that the propagation direction of light is deviated by a predetermined angle, and the length of the plurality of linear waveguide portions of the first bent waveguide is provided. _Satisfies L _TE of the following equation 4, and the length of the plurality of straight waveguide portions of the second curved waveguide is L _{TM of the following equation} 4.
An optical waveguide device having a polarization splitting property, which satisfies: (Equation 4) 7. A branch portion for splitting incident light into two directions, a first curved waveguide and a second curved waveguide for propagating the light branched by the branch portion, respectively. However, the first curved waveguide includes a plurality of linear waveguide portions and a plurality of connecting portions that sequentially connect the plurality of linear waveguide portions so that the light propagation direction is deviated by a predetermined angle. The second curved waveguide has a plurality of linear waveguide portions, and a plurality of connecting portions that sequentially connect the plurality of linear waveguide portions so that the light propagation direction is displaced by a predetermined angle. The length of the plurality of linear waveguide portions of the first curved waveguide satisfies Lλ ₁ of the following expression 5, and the length of the plurality of linear waveguide portions of the second curved waveguide is Sa is L of following 5
An optical waveguide device having wavelength selectivity characterized by satisfying λ ₂ . (Equation 5)