JPH09318919A - Optical modulator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lower dependence on polarization by providing an optical modulator with a polarization control means for rotating the plane of polarization of light by a prescribed angle near the one end face of a light intensity modulating means and on the optical axis of the light radiated from the end face of an optical waveguide part. SOLUTION: This optical modulator is constituted by the light intensity modulating means 20 inclusive of a waveguide type optical modulating element 200 by a semiconductor and a polarization control means 11 inclusive of a polarization rotating means 12 and a mirror 14. The plane of polarization rotates 90 deg. when the light emitted from the end face on the right side of the waveguide type optical modulating element 200 moves back and forth in the polarization rotating means 12. The TE polarized light advancing in the optical waveguide type optical modulating element 200 from the left to the right turns to TM polarized light and advances from the right to the left when this polarized light is reflected by passing a polarization control means 11. Conversely, the TM polarized light advancing from the left to the right turns to the TE polarized light and advances from the right to the left when the polarized light is reflected by passing the polarization control means 11. The light advancing back and forth in the optical modulator 10 in such a manner eventually exerts the interaction as the TE polarized light and the interaction as the TM polarized light and, therefore, the dependence on the polarization is eliminated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical modulator used for optical fiber communication or the like, and more particularly, to an incident port again after intensity modulation is applied to the light supplied from the other end of communication via the optical fiber to the incident port. The present invention relates to an optical modulation device that does not require a light emitting device on its own side and that facilitates two-way communication by returning to.

[0002]

2. Description of the Related Art As a conventional optical modulator, for example, 19
Proceedings of IEICE Spring Conference 1992 4-18
1 and 1992 IEICE Spring Conference Lecture Proceedings 4-257 Demand Access Optical CATV
There are two-way optical transmission means used in the system.

Such a demand access type optical CAT
As shown in FIG. 11A, the modulator used in the V system is a branch connected to the optical fiber 6, a branch branched from the common branch, and branches 2a and 2b whose refractive index can be controlled by an electric field. And a electrodes 3a, 3b, 3c for applying an electric field to the branches of the Y Bungame waveguide 2.

Further, 4 is a mirror portion formed by the end face of the waveguide, and 5 is a driving device for applying an electric field corresponding to the modulation signal to the electrodes 3a, 3b, 3c. Next, the operation of the modulator will be described. In this modulator, the light incident on the common branch of the Y-branch via the optical fiber 6 propagates through the two branches, reaches the mirror section 4, is reflected, and is reflected again by 2
Propagate through one branch and return to the common branch. While propagating through these two branches, the refractive index of the branches changes due to the electric field applied to the electrodes 3a and 3b, and the phase of light is also changed by detecting it and the light intensity is modulated at the common branch. To be done.
(Hereinafter, this type of optical modulator is referred to as a "folded Mach-Zehnder optical modulator"). The details will be described below with reference to FIGS. 11B and 11C.

FIG. 11B shows the phase of the wave of incident light or reflected light when no electric field is applied to the branch 2a, and the horizontal axis is time and the vertical axis is amplitude. In the figure, Wa is a wave propagating in the branch 2a, and Wb is a wave propagating in the branch 2b. Similarly, FIG. 11C shows the phase of the wave of the incident light or the reflected light when a predetermined electric field is applied to the branch 2a.

As shown in FIGS. 11B and 11C, the incident light propagating through the Y-branch optical waveguide 2 is branched at the branch point Pl of the Y-branch optical waveguide 2 (arrival time t1).
Further, it propagates through the branch 2a or the branch 2b. The incident light propagating through the branch 2a or the branch 2b is reflected by the mirror portion 4 of the end face P2 to become reflected light (arrival time t2) and returns to the branch point P1 (arrival time t3).

For example, when no electric field is applied to the branch 2a (FIG. 11 (b)), since the branches 2a and 2b have the same length, they are branched at the branch point P1, reflected by the mirror portion 4, and again branched at the branch point Pl. The phases of the two waves Wa and Wb returned to are the same. The waves Wa and Wb returning to the branch point Pl are t3 in FIG.
As shown below, the phases match and strengthen each other. At this time,
Propagation loss of Y branch optical waveguides 2, 2a, 2b and mirror section 4
The light is not attenuated except by the loss when reflected at and the coupling loss when re-entering the waveguide.

When an electric field is applied to the branch 2a to lower the refractive index of the branch 2a (FIG. 11 (c)), the incident light propagating through the Y-branch optical waveguide 2 is branched at the branch point Pl to branch 2a.
Propagate. At this time, the light propagating through the branch 2a has a higher propagation speed than the light propagating through the branch 2b. Therefore Wa
11 propagates through the branch 2a, is reflected by the mirror unit 4, propagates through the branch 2a again, and returns to the branch point P1 again, the branch 2b is folded and propagated as shown after t3 in FIG. 11C. The phase is delayed as compared with Wb. Here, when a predetermined electric field for generating an electro-optical effect is applied to the branches 2a and 2b having a predetermined optical path length, the phase of light propagating in the branch 2a and returning to the branch point Pl propagates in the branch 2b. Then, the phase of the light returning to the branch point P1 is delayed by 180 degrees. Therefore, the wave W that propagated through the branch 2a and returned to the branch point P1
The waves Wb propagating through a and the branch 2b and returning to the branch point Pl cancel each other at the branch point Pl, and the light intensity becomes small.

[0009]

However, since the propagation loss of the optical waveguide forming the conventional optical modulator has polarization dependency, there is a problem that the loss varies depending on the polarization. Further, the change in the refractive index of the branch when an electric field is applied also has polarization dependency. Therefore, when the electric field is applied, the phase dependence of the light passing through the two branches also has polarization dependency, and depending on the polarization, the wave Wa that propagates through the branch 2a and returns to the branch point P1 and the branch Wa. The waves Wb propagating through 2b and returning to the branch point Pl do not cancel each other. As a result, there is a problem that the extinction ratio is reduced due to the polarization state, and the modulation efficiency is reduced.

An object of the present invention is to solve such a conventional problem, and particularly to reduce the polarization dependence of the optical modulator.

[0011]

According to a first aspect of the present invention, there is provided a waveguide type light intensity modulating means (20) having at least two end faces in the vicinity of one end face thereof and the waveguide type light intensity. An optical modulator comprising a polarization control means (11) for rotating a polarization plane of light by a predetermined angle on the optical axis of light emitted from the end face of the optical waveguide section (201) of the modulation means (20) ( 10). The polarization control means (11) provided in the optical modulator (10) includes a mirror (14) whose reflection surface is arranged perpendicular to the optical axis, and an end surface of the mirror (14) and the optical waveguide section (201). And a polarization rotation means (12) for rotating the polarization of light propagating back and forth.

By providing such a polarization control means (11), the polarization dependence can be controlled and the polarization independence can be realized. The invention according to claim 2 is an optical modulator (10) comprising a polarization control means (11) and a Y-branch waveguide section (502). The Y-branch waveguide section (502) provided in the optical modulator (10) is provided as a waveguide of the light intensity modulating means (20), and the two branch waveguides (5) are provided.
02a, 502b) having a Y-branch shape, wherein the propagation constant of light propagating in at least one branch waveguide (502a, 502b) of the two branch waveguides (502a, 502b) is electrically determined. Controllable to. The polarization control means (11) is an optical waveguide of the waveguide type light intensity modulating means (20) in the vicinity of one end surface of the waveguide type light intensity modulating means (20) having at least two end faces. The polarization plane of the light is rotated by a predetermined angle on the optical axis of the light emitted from the end face of the section (201). Further, the polarization control means (11) has a mirror (14) and a polarization rotation means (12). The mirror (14) is arranged such that its reflection surface is perpendicular to the optical axis of each of the optical beams emitted from the end faces of the branch waveguides (502a, 502b). The polarization rotation means (12) is arranged between each mirror (14) and the end face of each branch waveguide (502a, 502b), and rotates the polarization of light propagating back and forth through these. .

By providing such a mirror (14) and the polarization rotation means (12) in the polarization control means (11), the polarization dependence can be controlled and the polarization independence can be realized. it can. The invention described in claim 3 is the optical modulator (10) according to claim 2, wherein the polarization control means (11) is provided.
Is a polarization rotation means (12) and each branch waveguide (502a, 5).
02b) and the end face of each branch waveguide (502a, 50a).
2b) is an optical modulator (10) comprising lens means (15) arranged so as to coincide with the optical axes of the light beams emitted from the end faces thereof.

By providing such a lens means (15) in the polarization control means (11), the light beam emitted from the end face of the end face is efficiently reflected by the mirror (14),
Furthermore, the reflected light beam can be efficiently incident on the end face of the end face again, and as a result, the polarization dependence can be controlled more accurately and the polarization independence can be realized.

The optical modulator (1) of the invention described in claim 4
0) has a flat plate shape and a lens means (15) in the optical modulator (10) according to claim 3, wherein the surface facing the polarization rotation means (12) has at least a flat shape. Polarization rotation means (12) and lens means (1
Polarization rotating means (12) and mirror (1) are provided on the flat surface of (5).
4) and a polarization control means (11) configured by laminating and laminating.

By forming the polarization control means (11) -in this way, it becomes easy to miniaturize the optical modulator (10). It also makes it possible to manufacture a large number of lens means (15) relatively easily and inexpensively.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Various embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an optical modulator 10 according to a first embodiment of the present invention. The optical modulator 10 according to the present embodiment is composed of a light intensity modulator 20 including a waveguide type optical modulator 200 made of semiconductor, and a polarization controller 11 including a polarization rotation unit 12 and a mirror 14.

The waveguide type optical modulation element 200 is a semiconductor waveguide type optical modulation element having an i layer 201 of a double heterodyne pin junction as a core and a p layer 202 and an n layer 203 as cladding layers. When a modulation voltage in the reverse direction is applied by the means 20, an electric field absorption effect is caused, and when a modulation current in the forward direction is caused to flow by the light intensity modulation means 20, optical modulation is performed by the basic absorption and the light amplification effect of the core layer 201.

Mirror 14 constituting polarization control means 11
Is formed by vacuum-depositing a dielectric film on a glass substrate, and is arranged so as to be perpendicular to the optical beam emitted from the end face on the right side of the waveguide type optical modulator 200 in the figure. There is. The polarization rotation means 12 is a quarter-wave plate formed by descending quartz into a thin plate shape. An axis corresponding to the polarization direction of the ordinary or extraordinary light of the wave plate and the waveguide type optical modulator 2
No. 00 pn junction is arranged with an accuracy of 45 degrees. By doing so, when the light emitted from the end face on the right side of the waveguide type optical modulation element 200 reciprocates through the polarization rotation means 12, the polarization plane is rotated by 90 degrees.
The waveguide type optical modulator 200 used in the present embodiment is
Light polarized in the direction perpendicular to the paper surface (hereinafter referred to as "TE polarized light")
The modulation efficiency for light that changes in the direction horizontal to the paper surface (hereinafter referred to as “TM polarization”) is different, and in general, TE polarization has a higher modulation efficiency. On the other hand, the polarization of the light propagating through the optical fiber changes from moment to moment. Therefore, if the polarization control means 11 is not provided, the degree of modulation of the light intensity-modulated by the modulator will change every moment.

However, in the optical modulator 10 of the present embodiment, since the polarization control means 11 is provided, the above conventional problems can be solved. Specifically, the TE-polarized light that has traveled from the waveguide type optical modulator 200 from left to right becomes TM-polarized light when it passes through the polarization control means 11 and is reflected, and travels from right to left. Conversely, Figure 1
The TM-polarized light that has traveled from the waveguide type optical modulation element 200 from left to right becomes TE-polarized light when it passes through the polarization control means 11 and is reflected, and travels from right to left. In this way, the light that travels back and forth in the optical modulator 10 of the present embodiment is T
Since the interaction as the E-polarized light and the interaction as the TM-polarized light are evenly exerted, the polarization dependence is eliminated.

The effect of eliminating the polarization dependence according to the present invention is not limited to the case where the waveguide type optical modulation element 200 is a semiconductor waveguide type optical modulation element. For example, even when the waveguide type optical modulation element 200 is a waveguide having a function other than the optical modulation element, the polarization dependence of the waveguide can be eliminated. Furthermore,
In general, even when the medium corresponding to the waveguide-type optical modulation element 200 is an arbitrary medium having a polarization dependence other than the waveguide, by adopting the configuration shown in FIG. Can be eliminated.

In the present embodiment, the quarter wave plate made of quartz is used as the polarization control means 11, but other polarization control means may be used. For example, if the material is a material having a natural invisibility such as mica, the quarter wave plate can be formed by using another material. In addition, a substance such as YIG that exhibits optical rotatory power (Faraday effect) in a magnetic field and a local field (hereinafter, "a substance that exhibits optical rotatory power (Faraday effect) and a local field) is called a Faraday rotator. ) May be arranged. Further, when a converging means such as a spasm is arranged between the right end surface of the waveguide type optical modulator 200 and the polarization control means 11, the optical coupling efficiency at the time of being reflected by the mirror 14 and being coupled again to the optical waveguide is improved. To do.

Next, a second embodiment of the present invention will be described with reference to the drawings. FIG. 2 shows an optical modulator 10 according to the second embodiment of the present invention. The same parts as those already described in the first embodiment are designated by the same reference numerals, and the duplicated description will be omitted.

The optical modulator 10 of the present embodiment has the optical intensity modulator 20 and the polarization controller 1 which have already been described in the first embodiment.
And 1. Furthermore, the polarization control means 1 of the second embodiment
In addition to the polarization rotating means 12 and the mirror 14 described above, 1 is provided between the polarization rotating means 12 and the respective end surfaces of the light guide layers 212 and 213, and The lens means 15 are arranged so as to coincide with the optical axes of the respective light beams emitted.

The optical modulator 10 of the second embodiment will be described in more detail. The optical modulation device 10 of the present embodiment can use the electro-absorption modulation element 200A as one form of the waveguide type optical modulation element 200. Electro-absorption modulator 20
OA is an indium-gallium-arsenic-phosphorus (InGa) layered on an indium-phosphorus (InP) substrate 211.
AsP) optical guide layers 212 and 213, and InGa
AsP barrier layer and indium-gallium-arsenic (I
nGaAs) multiple quantum well layers 20l formed by stacking quantum well layers, an indium-phosphorus (InP) clad layer 2l4, and an indium-phosphorus (InP) substrate 2
12 and electrodes 215 and 21 6 formed on the surface of the indium-phosphorus (InP) cladding layer 21 4. The core portion of the optical waveguide is the multiple quantum well layer 20.
1 and the light guide layers 212 and 21. As shown in FIG. 2, the multi-quantum well layer 20l has a large thickness in its central portion in order to improve optical coupling efficiency.
In addition, the structure is such that it becomes thinner toward the end. Further, a semiconductor layer (specifically, a silicon nitride film layer) 217 is deposited on the end face of the electro-absorption modulator 200A in order to reduce the reflectance of the end face. A more detailed structure is disclosed in JP-A-7-66502.

A Faraday rotator 30 can be used as the polarization rotating means 12 as one form. The Faraday rotator 30 is an yttrium-iron-garnet (Y
(IG) crystal 31 is sandwiched between two magnets 32 and 33. Instead of the YIG) crystal, a substance having optical activity may be used.

The lens means 15 is a cylindrical lens having a distributed refractive index as shown in FIGS. 9 (c) and 9 (d), and as shown in FIGS. 9 (a) and 9 (b). Specifically, FIG.
It is a lens having a distributed refractive index in which the refractive index in the radial direction (that is, on the X axis and the Y axis) of the cross-sectional view shown in FIG. The lens means 15 is arranged so that the central axis of the light beam emitted from the right side surface of the electro-absorption modulator 200A and the central axis of the cylinder of the lens means 15 coincide with each other.

The mirror 14 is a so-called dielectric mirror formed by depositing a dielectric film on a glass substrate. In the optical modulator 10 of the present embodiment, the polarization of the reciprocating light is rotated by 90 degrees by the polarization controller 11 as in the optical modulator 10 of the first embodiment, so that the polarization dependence is eliminated. To be done.

The electro-absorption modulator 20 of this embodiment is used.
In 0A, when the band-cap energy of the thickest part of the multiple quantum well 201 is made equal to the energy of incident light, the light absorbs light when no current or voltage is applied. Also, assuming that the band-cap energy of the thickest part of the multiple quantum well 201 matches the energy of incident light, and injecting a current in the direction indicated by the arrow in the figure (forward direction of pn junction), an optical amplifier is obtained. Therefore, the electro-absorption modulator 200A becomes an optical amplifier having no polarization dependence when the band-cap energy of the thickest part of the multiple quantum well 201 is made equal to the energy of the incident light and the forward current continues to flow. Further, when a pulsed forward current is caused to flow in correspondence with the modulation signal, an optical amplification / light absorption type optical modulator is obtained.

Next, a third embodiment of the present invention will be described with reference to the drawings. FIG. 3 shows a third embodiment. The same parts as those already described in the first embodiment or the second embodiment are designated by the same reference numerals, and duplicate description will be omitted.

The optical modulator 10 according to this embodiment includes a substrate 50.
Y Bunkame waveguide 502 formed in 1 and polarization control means 11
It is a folded Mach-Zehnder modulator 5 composed of. Y-branch waveguide section 502 provided in the optical modulator 10
Is provided as a waveguide of a folded Mach-Zehnder modulator, as shown in FIG.
A Y-branch-shaped waveguide having a and 502b, which can electrically control the propagation constant of light propagating in at least one of the two branch waveguides 502a and 502b. Is.

The quarter-wave plate 40 provided in the polarization controller 11 includes the mirrors 14 and the branch waveguides 502a, 50.
It is arranged between the end face of 2b and the Faraday rotator 30 described above.
It is rotated by 0 degrees. Further, the polarization control means 11
Has a mirror 14 and a polarization rotation means 12. The mirror 14 is arranged for each optical axis of the light beam emitted from the end faces of the branch waveguides 502a and 502b, with its reflection surface being perpendicular to the optical axis.

Such a mirror 14 and polarization rotation means 12
By providing and in the polarization control means 11, polarization dependence
Can be controlled to realize polarization independence. Further
The light modulator 10 of the third embodiment will be described in detail.
Folded Mach-Zehnder modulator of the third embodiment
3, as shown in FIG.
It comprises 502. The substrate 501 is LiNbO _ThreeBase
The plate and the Y-branch waveguide 502 heat the substrate with Ti (titanium).
The diffused one can be used. 503a, 503b
Has an electro-optic effect on the branch waveguides 502a and 502b, respectively.
It is an electrode for generating, and the driver 20B
It is a drive signal source. In addition, the end surface of the Y-branch waveguide 502
In order to suppress reflection, the end face of the wavelength of the signal light to be modulated
A dielectric film (AR in the figure) with a thickness of 1/4 is applied.
You. LiNbO as the substrate 501_ThreeWhen using a substrate
On its surface is silicon oxide SiO_TwoBuffer layer provided
Can be

The polarization control means 11 comprises a polarization rotation means 12 and a mirror 14. Specifically, the polarization rotation means 12
Is a quarter-wave plate formed by a plate-shaped parallel plate crystal, and the mirror 14 is a dielectric mirror formed by depositing a dielectric film on a transparent glass substrate.

The branched optical waveguides 502a and 502 of FIG.
Considering the light emitted from 2b as TE-polarized light and TM-polarized light, the polarization rotation means 12 advances from left to right to become linearly polarized light with the plane of polarization rotated by 90 degrees, thereby forming the optical waveguide 5.
Re-enters 02a and 502. Also in this embodiment,
Since the plane of polarization is rotated by 90 degrees as the light travels back and forth through the polarization rotating means 12, the polarization dependence can be eliminated as in the first and second embodiments.

In this embodiment, the case where LiNbO _{3 in} which Ti is diffused is used for the Y-branch optical waveguide portion 502 in FIG. 3 is described, but the material that can be used for the Y-branch optical waveguide portion 502 is not limited to this. For example, an optical waveguide using an electro-optic crystal other than LiNbO ₃ as a substrate, a waveguide of an organic material such as polyimide (EO polyimide having an electro-optic effect), glass, quartz, silicon oxide, silicon nitride, etc. A waveguide made of an inorganic material having the thermo-optic effect (TO) may be used. In the case of a waveguide made of an organic material, by using a waveguide having a relatively large electro-optic constant, it becomes possible to create the light intensity modulation means 20 utilizing the electro-optic effect as in the present embodiment. In the case of a waveguide made of an inorganic material, it is possible to form a light intensity modulating means 20 that utilizes a change in the refractive index due to the fine optical effect by forming a heater on the waveguide and passing an electric current through it. become.

Next, a fourth embodiment of the present invention will be described with reference to the drawings. FIG. 4 shows a fourth embodiment of the present invention. In the present embodiment, the polarization rotating means 12 of the third embodiment is replaced with a Faraday rotator 30 having a configuration in which an yttrium-iron-garnet (YIG) crystal 31 is sandwiched by two magnets 32 and 33. However, the other configurations have the same configurations as those of the first to third embodiments, and thus the description of the configurations and effects will be omitted. Since the Y-branch optical waveguide section 502 is the same as that of the third embodiment and the polarization control means 11 is the same as that of the second embodiment, the same operation as that described in the third embodiment and the second embodiment is performed. This eliminates the polarization dependence.

Next, a fifth embodiment of the present invention will be described with reference to the drawings. FIG. 5 shows a fifth embodiment. The same parts as already described in any of the first to fourth embodiments are
The same reference numerals are given and duplicated description is omitted.

The optical modulator 10 according to this embodiment includes a substrate 50.
It is composed of the Y-branch optical waveguide part 502 formed in 1 and the polarization control means 11. The modulation means 20 is the same as the modulation means 20 of the third embodiment, and the polarization control means 11 is the third one.
In the polarization control means 11 of the embodiment of FIG.
Lens 15 provided corresponding to one body 1 for each of 2b
This is the same as the one in which the lens means 5 including a and 15b is added. Further, the same lenses as the lens means 15 of the second embodiment are used for the lenses 15a and 15b.

Each of the lenses 15a and 15b collimates the light beams output from the branch waveguides 502a and 502b of the Y branch waveguide section 502, propagating through the polarization rotation means 12 and reflected by the mirror ( It is a so-called collimation lens). The light reflected by the mirror 14 is reflected by the lenses 15a and 15b.
When the light is re-incident on the branch waveguides 502a and 502b of No. 02, the light is collected, so that the effect of reducing the loss can be obtained.

Next, a sixth embodiment of the present invention will be described with reference to the drawings. FIG. 6 shows a sixth embodiment. The same parts as already described in any of the first to fifth embodiments are
The same reference numerals are given and duplicated description is omitted.

As shown in FIG. 6, the optical modulator 10 of this embodiment is the same as the optical modulator 10 of the fourth embodiment except that the same lens means 15 as that of the fifth embodiment is added. The lens means 15 is composed of lenses 15a and 15b provided in one-to-one correspondence with the branch waveguides 502a and 502b, respectively. As described above, each of the lenses 15a and 15b is composed of a cylindrical lens having a distributed refractive index, and the branch waveguide 502 of the Y branch waveguide portion 502.
The light beams output from a and 502b, propagating through the polarization rotation means 12 and reflected by the mirrors, are made parallel to each other.

The light reflected by the mirror 14 by the lenses 15a and 15b as described above is applied to the Y branch waveguide section 5
When the light is re-incident on the branch waveguides 502a and 502b of No. 02, the light is collected, so that the effect of reducing the loss can be obtained. Next, a seventh embodiment of the present invention will be described with reference to the drawings.

FIG. 7 shows a seventh embodiment.
The same parts as those already described in any of the first to sixth embodiments are designated by the same reference numerals, and a duplicate description will be omitted. The optical modulator 10 according to the present embodiment includes a lens unit 15 having a flat surface at least facing the polarization rotation unit 12, a polarization rotation unit 12 having a flat plate shape, and a lens unit. 15
The polarization control means 11 is formed by laminating the polarization rotation means 12 and the mirror 14 on the flat surface of the above and laminating them together.

Specifically, as shown in FIG. 7, the lens means 15 of the fifth embodiment is replaced with a flat plate lens means 15, and the lens means 15, the polarization rotation means 12 and the mirror 14 are replaced. The optical modulator 10 has the same configuration and effect as the optical modulator 10 of the fifth embodiment except that they are laminated and integrally formed.

In order to realize the polarization control means 11 of such a body formation, each of the lenses 15a and 15b has a structure shown in FIG.
As shown in FIGS. 0 (a) and (b), the lens means 15 is formed into a substantially hemispherical shape from the surface to the inside (that is, the Z-axis direction), and as shown in FIG. The refractive index distribution is high and gradually decreases in the radial direction.
Such a refractive index distribution is formed, for example, by replacing sodium ions of sodium glass with silver ions.

By thus forming the polarization control means 11 in the form of a single body, the optical modulator 10 can be easily downsized.
Further, it becomes possible to manufacture a large number of lens means 15 relatively easily and inexpensively. Further, by laminating the lens means 15 having a relatively large area in the form of a flat plate, the quarter-wave plate 40, and the mirror and dividing the layers, it is possible to relatively easily
There is also an effect that it is possible to manufacture a large number of members.

Next, an eighth embodiment of the present invention will be described with reference to the drawings. FIG. 8 shows an eighth embodiment. The same parts as already described in any of the first to seventh embodiments are
The same reference numerals are given and duplicated description is omitted.

In the present embodiment, the polarization rotating means 12 of the seventh embodiment is replaced with the Faraday rotator 12 which is the polarization rotating means 12 of the fourth embodiment, for example. The polarization dependence can be eliminated by the effect obtained by combining the effects described in the first to seventh embodiments.

The present invention is not limited to the configuration of the light intensity modulating means 20 or the core 201 described above, and may be applied to the light intensity modulating means 20 or the core 201 other than those shown in this embodiment. Can be used.

[0051]

According to the optical modulator of the first aspect,
By providing the polarization control means, the polarization dependence can be controlled and the polarization independence can be realized. According to the optical modulator of the second aspect, by providing the mirror and the polarization rotation means in the polarization control means, the polarization dependence can be controlled and the polarization independence can be realized.

According to the optical modulator of the third aspect, by providing the lens means in the polarization control means, the light beam emitted from the end face of the end face is efficiently reflected by the mirror, and the reflected light is further reflected. The beam can be efficiently incident on the end face of the end face again, and as a result, the polarization dependence can be controlled more accurately and the polarization independence can be realized.

According to the optical modulator of the fourth aspect, by forming the polarization control means as a single body, it is easy to downsize the optical modulator. Further, it becomes possible to manufacture a large number of lens means relatively easily and inexpensively.

[Brief description of drawings]

FIG. 1 shows an optical modulator according to a first embodiment of the present invention.

FIG. 2 shows an optical modulator according to a second embodiment of the present invention.

FIG. 3 is a diagram showing a third embodiment of the present invention in which a quarter-wave plate is used as a polarization rotation means.

FIG. 4 shows a fourth embodiment of the present invention in which a Faraday rotator is used as the polarization rotating means.

FIG. 5 shows a fifth embodiment of the present invention using a cylindrical lens and a quarter-wave plate.

FIG. 6 shows a sixth embodiment of the present invention using a cylindrical lens and a Faraday rotator.

FIG. 7 shows a seventh embodiment of the present invention in which a lens, a quarter-wave plate and a mirror are laminated and integrally formed.

FIG. 8 shows an eighth embodiment of the present invention in which a lens, a Faraday rotator and a mirror are laminated and integrally formed.

9 (a) is a perspective view showing a cylindrical shape of the lens means, and FIG. 9 (b) is a cross-sectional view (X-) perpendicular to the Z-axis.
FIG. 9C is a diagram showing the distributed refractive index in the X-axis direction, and FIG. 9D is a diagram showing the distributed refractive index in the X-axis direction.

10A is a perspective view showing a lens shape of lenses 15a and 15b, and FIG.
It is sectional drawing which shows the substantially hemispherical shape of a, 15b.
(A) is a sectional view showing a refractive index distribution of the lenses 15a, 15b.

FIG. 11 shows a conventional optical modulator.

[Explanation of symbols]

 10 Optical Modulator 11 Polarization Control Means 12 Polarization Rotating Means 14 Mirrors 15 Lens Means 15a, 15b Lens 20 Light Intensity Modulating Means 201 Cores 202, 203 Cladding Layers 40 Quarter Wave Plate 30 Faraday Rotator 502 Y Branch Conductor Waveguide portion 502a, 502b Branch waveguide

Claims (4)

[Claims] 1. Light of light emitted in the vicinity of one end face of a waveguide type light intensity modulating means having at least two end faces and from an end face of an optical waveguide portion of the waveguide type light intensity modulating means. On the axis, polarization control means for rotating the polarization plane of the light by a predetermined angle is provided, and the polarization control means comprises a mirror whose reflection surface is arranged perpendicular to the optical axis, the mirror and the optical waveguide section. And a polarization rotation unit that rotates the polarization of light propagating back and forth through the end face of the optical modulator. 2. Light of light emitted in the vicinity of one end face of a waveguide type light intensity modulating means having at least two end faces and from an end face of an optical waveguide portion of the waveguide type light intensity modulating means. A Y-branch-shaped waveguide having two branch waveguides, which is provided on the axis as a polarization control means for rotating the polarization plane of the light by a predetermined angle and as a waveguide of the light intensity modulation means. A Y-branch waveguide part capable of electrically controlling the propagation constant of light propagating in at least one of the two branch waveguides, and the polarization control means is provided for each of the branch waveguides. For each optical axis of the light beam radiated from each end face of the waveguide, between each mirror and the end facet of each branch waveguide, and each mirror disposed with its reflection surface perpendicular to the optical axis. A polarization rotation hand that rotates the polarization of light that is placed and that travels back and forth through these An optical modulator having a step. 3. The polarization control means according to claim 2, wherein the optical beam emitted from each end face of each branch waveguide is between the polarization rotation means and the end face of each branch waveguide. An optical modulator comprising: a lens means disposed so as to match the optical axis of the optical modulator. 4. A surface of the lens means facing the polarization rotation means has at least a flat shape, the polarization rotation means has a flat shape, and the polarization control means has a shape of the lens means. The optical modulator according to claim 3, wherein the polarization rotation means and the mirror are laminated and bonded to each other on a flat surface.