JP2014146004A - Optical waveguide having wavelength plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To directly form a wavelength plate, azimuth rotator, and filter in a groove disposed so as to cross a core of an optical waveguide.SOLUTION: The optical waveguide having a wavelength plate includes: one or more grooves 5-2 disposed so as to cut a core 5-1 of the optical waveguide; oriented films 5-3 for liquid crystal having undergone orientation processing in the one or more grooves; and a polymeric liquid crystal 5-5 sandwiched between the oriented films for liquid crystal. The oriented films 5-3 for liquid crystal are oriented films oriented by linear polarization of ultraviolet rays. By adjusting the direction of the linear polarization of radiated ultraviolet rays, the orientation direction of the filled polymeric liquid crystal 5-5 is controlled, and ultraviolet curing is performed.

Description

  TECHNICAL FIELD The present invention relates to an optical waveguide in the field of optical communication, and in particular, a wave plate loaded with a polarization control function for imparting functionality such as polarization control, phase control, and polarization separation function of a quartz optical waveguide and a polymer optical waveguide. It relates to a shaped optical waveguide.

  In the optical communication field, quartz glass-based optical waveguides and polymer-based optical waveguides are widely used because they have functions such as optical multiplexing / demultiplexing, switching, and branching. In particular, silica glass optical waveguides have high reliability. However, by itself, only the light is guided and the active function is limited. For this reason, functionality is often obtained by filling a resin that is compatible with glass.

  An example in which the functionality is given by filling a resin into the following optical waveguide will be described, and the disadvantages will be described.

(1) A polyimide wave plate is inserted for polarization control.
A film having optical anisotropy is used in an optical waveguide as a wave plate as described below.
<1> Since the optical waveguide has polarization dependence, in order to eliminate this, as shown in FIG. 1, a groove 1-2 is formed in the central portion of the waveguide 1-1, and a polyimide stretched film is used. A certain half-wave plate 1-3 is inserted to make the polarization independent (see Patent Document 1). The polyimide wavelength plate has a refractive index difference Δn of about 0.05, and in the case of 1.5 μm light, which is a communication wavelength band, has a thickness of about 15 μm, thereby serving as a half-wave plate. Usually, the groove width is about 20 μm, which is 5 μm wider than the above-mentioned wave plate, and needs to be fixed with an adhesive in the meantime. This adhesive is required to fix the waveguide and the wave plate with high reliability and to reduce the loss. The problem is that the insertion loss is as large as about 0.5 dB. Furthermore, in the optical waveguide of high Δ (Δ represents “difference”), since the core diameter is small, the insertion loss of the wave plate is large, and in the quartz waveguide of Δ = 2.5%, the insertion loss is Increased to 2 dB.
<2> As shown in FIG. 3, polarized wave beams with a wide wavelength band, independent of temperature, by inserting quarter-wave plates in the 0 ° and 90 ° directions into the waveguide-type Y-branch coupler and multimode coupler. A splitter is formed (see Non-Patent Document 1).

  In FIG. 3, 3-1 is an input optical waveguide, 3-2 is a branch coupler, 3-3 is a groove dug by dicing, and 3-4 is a quarter wavelength plate (90 degrees). 3-5 is a quarter wave plate (0 degree), and 3-6 is a 2 × 2 multimode coupler. The 3-4 quarter wave plate (90 degrees) advances the TM wave by 90 degrees, and the 3-5 quarter wave plate (0 degrees) advances the TE wave by 90 degrees. By shifting the phase of the two lights separated by the Y branch 90 ° to + and − and entering 2 × 2 MMI, only the TE polarized wave is output on one side and only the TM polarized wave is output on the other side. In this configuration, temperature dependency and wavelength dependency are small. However, since the grooves are formed by dicing, there is a disadvantage that the width is at least 20 μm and the loss is as large as 0.5 dB. Furthermore, since the core diameter is small in the high Δ optical waveguide, the insertion loss of the wave plate is large, and in the quartz waveguide of Δ = 2.5%, the insertion loss is as large as 2 dB.

(2) Filling the groove dug so as to cross the waveguide for temperature independence In the Athermal AWG, a plurality of thin grooves are provided so as to cross the waveguide of the AWG, and silicone is contained therein. By making the resin filled, temperature independence is achieved. It is known that by making a plurality of thin grooves, the loss can be greatly reduced even if the total groove width is the same.

  Although it is desired to insert the wave plate into a plurality of grooves, at present, a method of inserting a thin wave plate film into one groove and fixing it with an adhesive is used.

  On the other hand, in the field of displays, in recent years, an alignable curable resin called a polymerizable liquid crystal has been developed and used as a retardation film that compensates for visual dependency and color compensation of a liquid crystal display. In addition, since a retardation film patterned with a polymerizable liquid crystal can be realized, a 3D television that does not require liquid crystal glasses is also realized.

  Polymeric liquid crystal does not change its orientation direction even when a voltage is applied like normal liquid crystal, but it is oriented according to the orientation direction when it is applied on the orientation film, and maintains its orientation when mainly irradiated with ultraviolet rays. It has the characteristic of polymerizing to polymerize. Therefore, the polymerizable liquid crystal cured after orientation has a large refractive index anisotropy.

  Conventional retardation films were stretched to have anisotropy and were attached to a liquid crystal display. However, when this polymerizable liquid crystal is used, a retardation film can be realized by coating directly on the substrate. There is an advantage that the sex goes up very much.

The polymerizable liquid crystal is described below. Photopolymerizable liquid crystal can be easily aligned by applying it on the normal liquid crystal alignment means (rubbed alignment film or UV-irradiated photoalignment film) in the monomer state, and the molecular arrangement of the liquid crystal skeleton in the aligned state. Can be fixed to a film by UV irradiation or the like. The polymerizable liquid crystal is called “UV curable liquid crystal”, “photopolymerizable liquid crystal”, “Reactive Mesogens”, trade name Kirakol PLC (Adeka), and trade name Liclive (Merck). (See Patent Document 2, Patent Document 3, and Patent Document 4)
The “polymerizable liquid crystal” has various structures, and the “polymerizable liquid crystal” in the present invention is a polymerizable liquid crystal as defined in the above “polymerizable liquid crystal”.

  Unlike ordinary side-chain polymer liquid crystals, polymerized polymer does not show a liquid crystal phase and becomes a thermally stable cured product. Using these photopolymerizable liquid crystals, a phase difference film having a liquid crystal skeleton forming a homogeneous orientation, a super twist nematic (STN) orientation, or a pattern orientation, or a retardation film having a different retardation depending on the place is put into practical use. ing. In particular, a stretched film has been conventionally used as a retardation compensation film for liquid crystal displays. However, a thinner, more easily polymerizable polymerizable liquid crystal retardation film has been put to practical use and patterned for 3D television. A retardation film has also been put into practical use.

Japanese Patent No. 3501235 Japanese Patent No. 3632220 Japanese Patent No. 3767632 Japanese Patent No. 3842102

Yusuke Nasu, Takayuki Mizuno, Ryoichi Kasahara, Takashi Saida, “Temperature Insensitive and Ultra Wideband Silica-based Dual Polarization Optical Hybrid for Coherent Receiver with Highly Symmetrical Interferometer Design,” Tu.3.LeSaleve.4, 37th European Conference and Exhibition on Optical communication 2011 (September 18-22, 2011, Geneva, Switzerland).

(1) Conventionally, a wave plate of inorganic crystal or a stretched polyimide wave plate has been used as the wave plate. These wave plates have a thickness of about 15 μm, but a groove to be inserted needs about 20 μm, and the loss is as large as about 0.5 dB. Further, in order to reduce the size of the optical waveguide, if Δ of the waveguide glass is increased, the core diameter is decreased, and the groove loss is increased to several dB. (2) Moreover, in order to insert a polyimide wave plate, it was necessary to form a groove by dicing, insert it therein, and fix it with a transparent adhesive. (3) It has been desired that by dividing into a plurality of thin grooves such as the grooves of the athermal AWG, loss in the grooves can be reduced and filled so that it can be used as a wave plate, a phase difference plate, and a polarizer. (4) In order to form a groove by dicing and load a film, a different wave plate is inserted for each waveguide in a plurality of waveguides because the dicing groove is several mm due to the restriction of the diameter of the dicing blade. Since the above length is necessary and the waveguide interval is narrow, it is very difficult. (5) In the conventional half-wavelength version, a groove with a length of about 5 mm is dug in a place where the circuit of the PLC is symmetrical, and a polyimide wavelength plate of several mm square is inserted. In a PLC equipped with a complicated integrated circuit, there is no single point of symmetry, so if a dimming groove with a length of 5 mm is dug in each place, other waveguides will also be cut, limiting the circuit configuration. It was. Grooves may be dug by RIE (Reactive Ion Etching) for wave plate insertion, but for insertion, it is necessary to dug several hundred μm, which requires time and labor. For example, in the circuit as shown in FIG. 2, wave plates are inserted in three places, but there are adjacent waveguides, and a groove must be dug so as not to cut this waveguide by dicing. The dicing blade has a circular shape of 5 cmφ, and it is difficult to dig a groove so as not to cut the adjacent waveguide.

  In the present invention, instead of forming a polymerizable liquid crystal into a film and forming a wave plate, a liquid crystal alignment film is applied to one or a plurality of grooves provided so as to cross the core of the optical waveguide, and linearly polarized ultraviolet rays are applied. Applying alignment treatment by irradiation, filling or applying ultraviolet curable liquid crystal in the groove, curing by irradiating with ultraviolet light, and directly forming the wave plate, optical rotator and filter in the groove Features.

Usually, in order to perform the alignment treatment, it is necessary to perform rubbing, but there is no method for uniformly rubbing a narrow groove wall surface. Therefore, we have found that the groove wall surface can be oriented by applying a photo-alignment film and irradiating linearly polarized light. (Photo of Example 1, FIG. 4)
Also, a trench is dug at an arbitrary position by RIE (reactive ion etching), and if necessary, a horizontal alignment film and a vertical alignment film are formed in a pattern by lift-off. Using the liquid to be absorbed, a desired orientation direction could be realized at a desired location. Since the cured polymerizable liquid crystal has a refractive index anisotropy like a film, it has the same effect as a wave plate and a crystal plate, and functions such as polarization control of various optical waveguides, filters, and polarizers. be able to. The width of the groove may be several μm to several tens of μm, the depth of the groove may be about 30 μm to 100 μm below the core, and the length may be 100 μm to several hundred μm.

  In addition, since there is a small step between the cured polymerizable liquid crystal and the top surface of the waveguide, a heater electrode can be formed thereon, and the refractive index anisotropy Δn of the polymerizable liquid crystal can be easily controlled by temperature, thereby controlling polarization. can do.

  The polymerizable liquid crystal can be used as a 90 ° optical rotator when twisted nematic alignment is achieved by making the alignment directions of the alignment films on the opposing wall surfaces orthogonal.

  Furthermore, the liquid crystal to be filled may be a chiral nematic (cholesteric) liquid crystal to which a chiral agent is added, and a filter that reflects only a specific wavelength by controlling the chiral pitch by adjusting the addition amount of the chiral agent. In addition, a wavelength selective filter with little loss can be manufactured in the waveguide.

The present invention has a structure in which one or more fine grooves provided so as to cut the core of the optical waveguide are filled with a liquid crystal polymerized by orientation treatment, thereby (1) narrowing the groove width or dividing it. Therefore, it is possible to form a filled wave plate with a small loss. (2) Since it can be formed at an arbitrary position by etching technology such as RIE in addition to dicing, the degree of freedom in designing the optical waveguide is increased.
(3) A wave plate with a small loss can be formed even with an optical waveguide having a large Δn.
(4) By making the alignment of the liquid crystal a twist nematic other than the parallel alignment, an optical rotator can be realized,
(5) By adding a chiral agent, a wavelength filter can be realized,
(6) Furthermore, there is an advantage that an optical waveguide type polarization control device can be realized by forming a fine heater electrode thereon.

It is a figure which shows having made the polarization independent by inserting the wavelength plate into the conventional silica-type optical waveguide. This is an example in which three wave plates are inserted into a conventional integrated waveguide circuit. It is a schematic diagram which shows the structure of a waveguide type polarization beam splitter. It is a polarization micrograph of the photopolymerized in-groove polymerizable liquid crystal. It is a schematic diagram which shows the preparation process of 1/2 wavelength using the polymeric liquid crystal based on this invention. It is a schematic diagram which shows the manufacturing process of the quarter wavelength plate using the polymeric liquid crystal based on this invention, and a waveguide type | mold polarization beam splitter. It is a schematic diagram which shows the optical waveguide filled with the twist nematic liquid crystal based on this invention. It is a schematic diagram which shows the chiral nematic liquid crystal filling optical waveguide based on this invention. FIG. 9 is a graph showing the wavelength dependence of reflection of the amount of polymerizable liquid crystal added with a chiral agent in the optical waveguide of FIG. 8. It is a graph which shows the temperature dependence of (DELTA) n of a polymeric liquid crystal. It is a schematic diagram which shows the preparation process and structure of a waveguide type polarization | polarized-light controller using polymeric liquid crystal.

[Example 1: Filling with fine half-wave plate, polarization independent of optical waveguide]
A quartz optical waveguide has a polarization dependency because a phase difference occurs between TE and TM polarization. In order to solve this problem, a groove of about 20 μm is dug in the center of symmetry of the optical waveguide, and a 15 μm-thick polyimide film having an optical anisotropy of Δn of about 0.05 is inserted to make polarization independent. I am trying. The total loss is as large as 0.5 dB. Furthermore, a high Δ (for example, Δ = 2.5%) quartz-based waveguide with a large refractive index difference has a core size of only about 3 μm, and the radiation angle of the light radiated into the groove increases. The loss at the time of insertion becomes very large as about 2 dB.

  The polymerizable liquid crystal can be directly filled into the groove and cured by ultraviolet rays or heat, Δn is as large as 0.15 to 0.25, the groove width can be reduced to several μm, and the loss can be greatly reduced. . Further, the loss can be further reduced by narrowing the width of one groove by dividing the groove into a plurality of grooves instead of one. The grooves can be formed narrowly by RIE, and a plurality of grooves can be formed at arbitrary positions.

  First, a preliminary experiment was performed to confirm that the polymerizable liquid crystal filled in the groove was aligned. A groove having a width of 20 μm is formed by dicing so as to cross the quartz waveguide on the quartz glass or the Si substrate, the photo-alignment film is applied to the groove wall surface by a spinner, and deep UV is irradiated to form the photo-alignment film in the groove. The orientation was 0 ° and 20 °. A substrate in which the photo-alignment film is aligned at 0 degrees with respect to the groove is referred to as a substrate 1, and a substrate in which the optical alignment film is aligned at 20 degrees is referred to as a substrate 5. This groove was filled with a polymerizable liquid crystal and irradiated with ultraviolet rays to fix the alignment of the polymerizable liquid crystal. UV light with fixed orientation of the photo-alignment film and polymerizable liquid crystal was irradiated to the whole without being squeezed by the lens. A polarizing microscope photograph is shown in FIG. At this time, on the optical path of the substrate filled with polymerizable liquid crystal, two polarizers are arranged so as to sandwich the substrate, the two polarizers are orthogonally crossed by 90 degrees to form crossed Nicols, and the groove is the light traveling direction of the waveguide Seen from. When crossed Nicol is used, only when the polarization state is changed by the substrate sandwiched between two polarizers, the light passes and the field of view becomes brighter. The polarization direction of the polarizer in front of the substrate with respect to the light traveling direction of the two polarizers was parallel to the y-axis, and the polarization direction of the polarizer behind it was parallel to the x-axis. 4A shows a case where the substrate 1 is tilted with respect to the crossed Nicols axis, FIG. 4B shows a case where the substrate 1 is made coincident with the crossed Nicols axis, and FIG. When tilted to a greater degree, (d) shows the case where the substrate 5 is tilted by 20 degrees with respect to the crossed Nicol axis and the crossed Nicol axis and the alignment direction of the polymerizable liquid crystal are matched. When the orientation direction of the polymerizable liquid crystal coincides with the crossed Nicol axis, it becomes dark and when it reaches 45 °, it becomes brighter. Therefore, the polymerizable liquid crystal coincides with the crossed Nicol axis depending on the brightness of the light passing through the substrate. It can be seen whether or not it is oriented in the direction. FIG. 4 shows that the polymerizable liquid crystal is well aligned by the photo-alignment film.

  FIG. 5 shows a manufacturing process of a half-wave plate filled with polymerizable liquid crystal. 5A is a diagram showing that a 5.4 μm groove has been formed by RIE, FIG. 5C is a diagram showing that a photo-alignment film has been applied, and FIG. 5E is a diagram showing a 45 ° direction linear deviation on the photo-alignment film. FIG. 5 (b) is a diagram showing that the UV light is irradiated and then cured, and (g) is a diagram showing that the polymerizable liquid crystal is filled, dried, irradiated with UV light, and then cured. (D) (f) (h) is the schematic diagram which expanded the cross section of each groove part of Fig.5 (a) (c) (e) (g). FIG. 5 (i) shows an example in which the groove width is narrowed to reduce the loss. A groove 5-2 having a width of 5.4 μm is formed so as to cut the core 5-1 of the waveguide by reactive ion etching (RIE) (FIGS. 5A and 5B). The groove wall surface etched by RIE is flatter than the wall surface formed by dicing, and the alignment treatment is very easy. 5.4 μm × Δn = 0.74 μm (Δn = 0.137), which is almost ½ wavelength, and operates as a ½ wavelength plate. However, by increasing the annealing temperature and UV curing, Δn tends to decrease, and it is necessary to optimize the conditions for ½ wavelength.

  The polymerizable liquid crystal is a homogeneous liquid crystal aligned in parallel with the wall surface. The refractive index anisotropy of the polymerizable liquid crystal is Δn, the groove width is L, the wavelength of light passing through the waveguide is λ, and the ultraviolet irradiation energy is Since Δn decreases with E (denoted as Δn (E)), it is necessary to optimize the ultraviolet energy E so that Δn (E) × L = λ / 2 or λ / 4. is there.

The method for forming the groove is not limited to RIE, and a dicing saw may be used. Next, the liquid crystal photo-alignment film 5-3 is applied (FIGS. 5C and 5D). Nissan chemical photo-alignment film RN-2413 (0421) is applied with a spinner under the condition of 3000 rpm × 20 sec. The alignment film is thinly formed on the waveguide surface and the groove wall surface. Thereafter, annealing is performed at 230 ° C. for 30 minutes. The thickness of the alignment film formed on the wall surface was several tens of nm. Thereafter, light 5-4 having a wavelength of 250 to 300 nm from the ultrahigh pressure mercury lamp is irradiated as linearly polarized light by the Grande Taylor prism (FIGS. 5E and 5F). The orientation direction is perpendicular to the direction of linear polarization. Here, in order to form the half-wave plate in a 45 ° direction, ultraviolet rays were irradiated so that the linearly polarized wave was inclined at 45 ° with respect to the substrate. The irradiation energy is 1.0 to 1.8 J / cm ² . Thereafter, pure water ultrasonic cleaning was performed for 1 minute, and post-baking was performed in order to fix the alignment at 250 ° C. for 30 minutes. In this case, the UV light may be irradiated to the whole or locally using a bundle fiber of about 1 mmφ.

Merck's photopolymerizable liquid crystal Liclivee RMS03-013C (Δn = 0.137) 5-5 is filled into the groove (FIGS. 5G and 5H). The liquid crystal enters the groove by capillary action when attached to the groove end face. Since this liquid crystal contains a solvent, the liquid crystal is filled so as to rise above the groove so that the liquid crystal remains in the groove even if the solvent evaporates. Dry at 55 ± 5 ° C. for 1 minute to drive off the solvent. The remaining liquid crystal is aligned by the photo-alignment film. The light of wavelength 365nm is irradiated with UV irradiation 5-6 at 20 ± 5 nW / cm ² for 60 seconds. At this time, it is desirable to attach an IR filter so that the polymerizable liquid crystal is not heated. By this irradiation, the liquid crystal is polymerized into a polymer.

  A bundle fiber guide is effective for irradiating a minute portion with linearly polarized UV light. A bundle fiber capable of guiding ultraviolet rays with a diameter of 1 mmφ to 10 mmφ is commercially available. In order to apply to a waveguide, a thing of about 1 mmφ may be used. Light from an ultraviolet lamp is converted into a linearly polarized light through a polarizer, collected by a lens, introduced from the end face of a bundle fiber, and directly irradiated to the waveguide groove from the exit end. . At this time, it is also effective to attach a condensing lens at the end of the bundle fiber and further irradiate the UV light. Even with a normal bundle fiber, if the distance is as short as about 1 m, the polarization is preserved. If polarized light is incident from the input end without twisting the bundle fiber, the output is emitted while maintaining the polarized light. If it is desired to maintain the polarization completely, it is desirable to use a polarization maintaining fiber that is a bundle fiber.

  The liquid crystal becomes (1) easier to align as the groove width becomes narrower, and (2) about 20 μm of the end face of the groove becomes a boundary region, and the alignment is disturbed. Therefore, if the groove width L is 20 μm or less, the grooves are uniformly oriented, the groove length is (core width + 2 × 20 μm), and the depth is 20 μm or more from the lower surface of the core. The orientation becomes uniform. For example, when the core is a waveguide having a 10 μm square and a cladding thickness of 20 μm, the groove width may be 20 μm or less, the groove length is 50 μm, and the depth is 50 μm or more.

  When TE polarized light was incident on this waveguide using Panda fiber, the emission was TM polarized. The loss at the groove was 0.1 dB.

  Usually, when inserted into a 15 μm-thick polyimide wave plate and a 20 μm groove, the insertion loss is about 0.5 dB in a waveguide of Δ = 0.7%. However, due to the miniaturization of the waveguide, Δ tends to increase, and when Δ = 2.5%, the insertion loss is 2 to 3 dB. In order to reduce the insertion loss, the core width is widened or conversely narrowed to reduce the loss to about 1.5 dB. FIG. 5 (i) shows an example in which the groove width is narrowed to reduce the loss so that a plurality of grooves are formed.

  The conventional waveguide-type polarizing beam splitter shown in FIG. 3 can be similarly manufactured. The manufacturing process is shown in FIG. FIG. 6A is FIG. 3, FIG. 6B shows that a groove having a width of 2.7 μm is formed by RIE, FIG. 6D shows that a photo-alignment film is applied, and FIG. 6F shows photo-alignment. It shows that the film was cured by irradiating only 90% polarized UV light using a mask and (h) was cured by irradiating the remaining one side of the photo-alignment film with 0 degree polarized UV light using a mask. (J) indicates that the polymerizable liquid crystal is filled, dried, UV-irradiated, and cured, and (l) indicates that the optical alignment film is irradiated with 90-degree polarized UV light using an optical fiber. (M) indicates that the photo-alignment film was irradiated with 0-degree polarized UV light using an optical fiber, and (n) indicates that the polymerizable liquid crystal was filled, dried, and UV-irradiated and cured. (P) shows that UV linearly polarized light was irradiated locally with a bundle fiber. 6 (c) (e) (g) (i) (k) (o) is an enlarged view of the cross section of each groove portion in FIGS. 6 (b) (d) (f) (h) (j) (n). FIG. As shown in FIG. 6, the groove width is set to 2.7 μm, and the polarization of the UV light applied to the optical alignment films of the two waveguides is set to 0 ° and 90 °. Here, 6-1 is an extracted waveguide portion of the polarizing beam splitter of FIG. 3, 6-2 is a groove formed by RIE, and 6-3 and 6-4 are couplers forming the polarizing beam splitter. 6-5 is a photo-alignment film for liquid crystal, 6-6 is 250-300 nm linearly polarized deep UV light, and 6-7 does not apply light to one of the waveguides. 6-8 is a polymerizable liquid crystal, 6-9 is a UV light centering on 360 nm for curing the polymerizable liquid crystal, and 6-10 is a linearly polarized UV light. A fiber for inputting light into a waveguide. Since the groove width is as narrow as 2.7 μm, there is an advantage that loss is reduced. Furthermore, the groove can be divided to reduce the loss. It can be formed as thin as an athermal groove by RIE instead of dicing.

  Here, in order to change the orientation direction of the two grooves, the UV light is cut using a mask. However, differently polarized UV light may be incident on the two waveguides. When a 6-10 optical fiber is bad-joined to a waveguide and irradiated with UV light of linear polarization, the alignment film on the wall surface of the groove is oriented in this direction. In this case, only the portion through which the waveguide light passes is oriented, but the function as a wave plate can be sufficiently achieved.

  Alternatively, a bundle fiber guide is effective for irradiating a linear portion with UV linearly polarized light (FIG. 6 (p)). A bundle fiber capable of guiding ultraviolet rays with a diameter of 1 mmφ to 10 mmφ is commercially available. For application to a waveguide, an object having a diameter of about 1 mmφ may be used. The light from the ultraviolet lamp is converted into a linearly polarized light through a polarizer, collected by a lens, and introduced from the end face of the bundle fiber 6-11, and directly from the exit end to the waveguide groove. Irradiate. At this time, it is also effective to attach a condensing lens at the end of the bundle fiber and further irradiate the UV light.

  Even with a normal bundle fiber, if the distance is as short as about 1 m, the polarization is preserved. If polarized light is incident from the input end without twisting the bundle fiber, the output is emitted while maintaining the polarized light. If it is desired to maintain the polarization completely, it is desirable to use a polarization maintaining fiber that is a bundle fiber.

[Example 2: twisted nematic liquid crystal, super twisted nematic liquid crystal]
FIG. 7 shows an example in which an optical rotator (an element that rotates 90 ° polarization) is inserted instead of a wave plate. FIG. 7 (a) is a diagram showing that a UV-absorbing liquid is filled in the groove, and the photo-alignment film is cured after being irradiated with linearly polarized UV light in the 90-degree direction. Only one of the wall surfaces is photo-aligned. (C) is a diagram showing that the photo-alignment film is cured after being irradiated with linearly polarized UV light in the 0 degree direction. Like FIG. 7 (a), only one of the wall surfaces is photo-aligned. (E) is a diagram showing that the polymerizable liquid crystal is filled, dried, cured after UV irradiation, and a state of alignment of liquid crystal molecules. 7B, 7D, and 7F are schematic views in which the cross sections of the respective groove portions in FIGS. 7A, 7C, and 7E are enlarged. The steps from forming the groove 7-1 to applying the photo-alignment film 7-2 are the same as in FIG. 5, but the alignment directions of the opposing surfaces of the groove are orthogonal. For this reason, when irradiating the ultraviolet ray 7-3, the groove is filled with a liquid 7-4 that absorbs the ultraviolet ray. This may be water-soluble ink mixed with black pigment, oil-based ink, paint, etc., as long as it can cut ultraviolet rays even if it is thin. Alternatively, a white solution (for example, a correction solution) that completely scatters light may be used. 7-3 is 90 degree direction linearly polarized UV light, and 7-5 is 0 degree direction linearly polarized UV light. After UV irradiation, the liquid is washed away by immersing it in a solution. Thereafter, the polymerizable liquid crystal 7-6 for parallel alignment is filled. For this, Merck's photopolymerizable liquid crystal Licrive RMS03-013C (Δn = 0.137) is preferable. When UV curing is performed, the liquid crystal molecules 7-7 are twisted nematically aligned and can be converted from TE to TM polarization and from TM to TE polarization, as shown in FIG. Since a groove having a width of several μm, a depth of several 10 μm, and a transverse length of several hundred μm can be formed by RIE at an arbitrary position on the waveguide, there is an advantage that an optical rotator can be installed at an arbitrary position.

  This embodiment can be applied to any of twisted nematic liquid crystal and super twisted nematic liquid crystal.

[Example 3: Chiral nematic liquid crystal filter]
FIG. 8 shows an example in which a chiral nematic filter is inserted instead of a wave plate. FIG. 8A shows that the photo-alignment film 9-2 is applied after the groove 9-1 is formed, and FIG. 8C shows that the photo-alignment film is irradiated with 90-degree linearly polarized UV light 9-3. FIG. 8E is a diagram showing curing, FIG. 8B is a diagram showing that the polymerizable liquid crystal 9-4 to which a chiral agent is added is emphasized, dried, UV-irradiated 9-5, and cured. FIG. (D) (f) is the schematic diagram which expanded the cross section of each groove part of Fig.8 (a) (c) (e). FIG. 8G shows the incident spectrum, FIG. 8H shows the pitch P of the chiral nematic liquid crystal, and FIG. 8I shows the output spectrum. In the chiral nematic liquid crystal, by adding a chiral agent to the nematic liquid crystal, the liquid crystal is aligned in a spiral shape with a period to form a grating. The pitch P has a relationship between the concentration D of the chiral agent and PＤ1 / D, and the pitch becomes shorter as the chiral agent is added. The peak wavelength λ of the transmission spectrum as a filter has a relationship of P = m × λ (m is an integer). Therefore, P was adjusted so that the transmission wavelength was 1.55 μm. About 1 to 5 wt% of Merck's chiral agent was added to Merck's Liquive RMS03-013C (Δn = 0.137), and the pitch P was measured. The reflection spectrum was measured by varying the amount of chiral agent added. The amount of chiral agent added and the reflection-wavelength dependence are shown in FIG. When about 3 wt% of a chiral agent is added, the central wavelength of reflection becomes 1.55 μm.

  As shown in FIG. 8, a wavelength selective filter can be realized on the waveguide by groove formation → alignment film formation → chiral additive-containing polymerizable liquid crystal filling → UV curing in the same process as the wave plate formation.

  Since a groove of several μm in width × several 10 μm in depth × 100 μm in length in the lateral direction can be formed by RIE at an arbitrary location on the waveguide, there is an advantage that a filter can be installed at an arbitrary location.

[Example 4: Waveguide type polarization controller]
It is possible to make a polarization controller by changing the Δn of the polymerizable liquid crystal part by locally filling the groove with a polymerizable liquid crystal, aligning and polymerizing it, and attaching a local heater on it. Is possible. Similarly, a waveguide type polarization controller can be realized with a polyimide wavelength plate, but the polyimide film itself is large and cannot be heated locally. By filling the grooves and forming local electrodes thereon, local heating can be performed, and a polarization controller with low power consumption can be realized.

Birefringence of conventional polymerizable liquid crystal _{n e, n o (n e} : extraordinary ( extraordinary light), n _o: ordinary (ordinary)) decreases with temperature, also the temperature further Δn = n _e -n _o Decrease. FIG. 10 shows the temperature dependence of Δn of the polymerizable liquid crystal of DIC. When the temperature is raised from room temperature to 80 ° C. to 100 ° C., Δn decreases by about 10%. If the total groove width L is increased so that the amount of Δn × L can be varied by λ / 2 or more, three variable retardation plates oriented in the directions of 0 °, 45 °, and 0 ° can be produced. , Complete polarization control becomes possible. That is, if the groove width L is 7.5 μm, Δn × L changes by 0.75 μm, and the π phase changes at a wavelength of 1.5 μm.

  Since the groove is formed by RIE, it is easy to form a width 7.5 μm × depth 50 μm × lateral direction length several 100 μm square. Only a very small electric power is required to raise the temperature from room temperature to 100 ° C., and the response speed is as fast as several ms.

FIG. 11 shows a manufacturing process and a completed structure of the waveguide polarization controller. First, (a) grooves 11-2 having a width of 7.5 μm, a depth of 50 μm, and a lateral direction length of several hundreds of μm are dug in three locations so as to cut the waveguide 11-1. (b) A photo-alignment film (not shown) is applied and irradiated with linearly polarized ultraviolet rays so as to be oriented in the directions of 0 °, 45 ° and 0 °. (c) The polymerizable liquid crystal 11-3 is filled and UV cured. (d) The heater electrode 11-4 is formed.
(D) is the final structure of the waveguide polarization controller. By adjusting the current flowing through the heater electrode and controlling from room temperature to 100 ° C, the temperature of the polymerizable liquid crystal aligned at 0 °, 45 °, and 0 ° can be adjusted, and each Δn can be adjusted arbitrarily. Complete polarization control can be performed to convert the polarized wave into an arbitrary polarized wave. The response speed is about 1 ms because of the polarization control element based on the thermo-optic effect.

1-1 Waveguide 1-2 Groove 1-3 Half-wave plate 3-1 Input optical waveguide 3-2 Y-branch coupler 3-3 Groove 3-4 1/4 wavelength plate (90 degrees)
3-5 1/4 wavelength plate (0 degree)
3-6 2 × 2 MMI
5-1 Core 5-2 Groove 5-3 Optical Alignment Film for Liquid Crystal 5-4 UV Light 5-5 Photopolymerizable Liquid Crystal 5-6 UV Irradiation 6-1 Waveguide Portion of Polarized Beam Splitter 6-2 Groove 6-3 6-6 Waveguide 6-5 Photo-alignment film for liquid crystal 6-6 Linearly polarized deep UV light 6-7 Light blocking mask 6-8 Polymerizable liquid crystal 6-9 UV light 6-10 Fiber 6-11 Bundle fiber 7 -1 Groove 7-2 Photo-alignment film 7-3 90 degree direction linearly polarized UV light 7-4 Liquid 7-5 absorbing ultraviolet rays 0 degree direction linearly polarized UV light 7-6 Polymerizable liquid crystal 7-7 Liquid crystal molecule 9-1 Groove 9-2 Photo-alignment film 9-3 90-degree linearly polarized UV light 9-4 Polymerizable liquid crystal 9-5 with added chiral agent UV irradiation 11-1 Waveguide 11-2 Groove 11 -3 Polymerizable liquid crystal 11-4 Heater electrode

Claims (8)

One or more grooves provided to cut the core of the optical waveguide;
An alignment film for liquid crystal that has been subjected to an alignment treatment inside the one or more grooves,
A wave-plate-loaded optical waveguide comprising: a polymerizable liquid crystal sandwiched between the liquid crystal alignment films.   2. The optical waveguide according to claim 1, wherein the alignment film for liquid crystal is an alignment film that is aligned by the linear polarization of ultraviolet light, and the polymerizable property that is filled is adjusted by adjusting a direction of the linear polarization of the ultraviolet light to be irradiated. 1. A wave plate-loaded optical waveguide characterized by being UV-cured by controlling the alignment direction of liquid crystal.   3. The optical waveguide according to claim 1, wherein the groove is formed by reactive ion etching, and the groove has a width of 20 [mu] m or less.   3. The optical waveguide according to claim 1, wherein the polymerizable liquid crystal is a homogeneous liquid crystal aligned in parallel with a wall surface, the refractive index anisotropy of the polymerizable liquid crystal is Δn, the groove width is L, and the number of grooves is. Wave plate loading, wherein the groove width L is determined so that Δn × L × n = λ / 2 or λ / 4, where n is the wavelength of light passing through the optical waveguide, and λ. Optical waveguide.   5. The optical waveguide according to claim 1, wherein when aligning the alignment film for liquid crystal by irradiating with ultraviolet light, the groove is filled with an ultraviolet absorber or a shielding agent, and the wall facing the groove is used. A wavelength plate-loaded optical waveguide, wherein the alignment of the polymerizable liquid crystal becomes a twisted nematic alignment or a super twisted nematic alignment (for an optical rotator) by irradiating ultraviolet linearly polarized waves at different angles.   6. An optical waveguide according to claim 1, wherein a Δn of the aligned polymerizable liquid crystal is controlled by temperature by providing a heater electrode on the polymerizable liquid crystal. Waveguide.   2. The wave plate-loaded optical waveguide according to claim 1, wherein the liquid crystal to be filled is a chiral nematic (cholesteric) liquid crystal (for a filter) obtained by adding a chiral agent to a nematic liquid crystal. First, second, and third grooves provided continuously to cut the core of the optical waveguide;
In the first and third grooves, an alignment film for liquid crystal aligned in the direction of 0 degrees;
In the second groove, the alignment film for liquid crystal aligned in a 45 degree direction,
A polarization controller comprising: a liquid crystal alignment film aligned in the 0 degree direction; and a polymerizable liquid crystal sandwiched between the liquid crystal alignment films aligned in the 45 degree direction.