Liquid crystal lens, microlens, microlens array, optical transmission module member, and optical transmission module

Abstract

The present invention addresses the problem of providing: a liquid crystal lens that enables miniaturization of an optical transmission module; and a microlens, microlens array, optical transmission module member, and optical transmission module in which this liquid crystal lens is used. This problem is solved by a liquid crystal lens according to the present invention having a liquid crystal alignment pattern in which the orientation of the optical axis derived from a liquid crystal compound changes while continuously rotating along at least one direction in a plane, the liquid crystal alignment pattern being formed to have concentrically circular shapes that face from the inner side to the outer side in one direction, and the minimum distance from the center of the concentric circles to the edge of the liquid crystal lens being 300 μm or less.

Description

Liquid crystal lens, micro lens, micro lens array, member for optical transmission module, and optical transmission module

[0001] The present invention relates to a liquid crystal lens used in an optical transceiver for optical communication and the like, and a micro lens, a micro lens array, a member for an optical transmission module, and an optical transmission module using this liquid crystal lens.

[0002] In optical communication, for example, an optical transceiver mounted on a data server and used for transmitting and receiving information by optical communication is used.

[0003] Generally, an optical transceiver has a transmission unit (TOSA (Transmitter Optical Sub-Assembly)) for transmitting information of a data server to an externally connected device by optical communication, and a reception unit (ROSA (Receiver Optical Sub-Assembly)) for receiving information from the externally connected device by optical communication.

[0004] As an example, in the transmission unit, an optical signal emitted from a light source such as a semiconductor laser is made into parallel light (collimated light) by a lens, and then enters an optical fiber connected for external connection through an optical isolator. In the reception unit, as shown in Patent Document 1 as an example, after parallelizing (collimating) an optical signal emitted from an optical fiber connected for external connection, after performing processes such as wavelength division, it is condensed by a lens as necessary, measured by a photodiode, and the optical signal is converted into an electrical signal.

[0005] In recent years, in optical communication, it has been required to send larger-capacity data at high speed. Therefore, further miniaturization and high integration of the transmission unit and the reception unit, that is, the optical transceiver, are desired.

[0006] Japanese Patent Application Laid-Open No. 2019-191260

[0007] One example of a method for miniaturizing and highly integrating optical transceivers is the miniaturization of lenses. In optical transceivers, as shown in Patent Document 1, silicon lenses (Si lenses) are used as lenses. However, silicon lenses are difficult to miniaturize, and it is difficult to manufacture small lenses with a diameter of 450 μm or less.

[0008] The object of the present invention is to solve the problems of the prior art and to provide a liquid crystal lens that enables miniaturization of optical transmission modules, such as the transmitting section of an optical transceiver used in optical communication, as well as a microlens, a microlens array, an optical transmission module component, and an optical transmission module using this liquid crystal lens.

[0009] To solve this problem, the present invention has the following configuration: [1] A liquid crystal lens containing a liquid crystal compound, used as a microlens for an optical transmission module, wherein the liquid crystal lens has a liquid crystal alignment pattern in which the orientation of the optical axis derived from the liquid crystal compound changes while continuously rotating along at least one direction in the plane, and the liquid crystal alignment pattern has one direction in the form of concentric circles moving from the inside to the outside, and the minimum distance from the center of the concentric circles to the edge of the liquid crystal lens is 300 μm or less. [2] The liquid crystal lens according to [1], wherein the minimum distance from the center of the concentric circles to the edge of the liquid crystal lens is 50 to 200 μm. [3] A microlens having the liquid crystal lens according to [1] or [2] and a λ / 4 plate disposed on one surface side of the liquid crystal lens. [4] A microlens having the liquid crystal lens according to [1] or [2], a first λ / 4 plate disposed on one surface side of the liquid crystal lens and a second λ / 4 plate disposed on the other surface side of the liquid crystal lens. [5] The microlens according to [3] or [4], further having a glass substrate with a thickness of 0.3 mm or less. [6] A microlens according to any one of [3] to [5], further having an anti-reflective coating on its outermost surface. [7] A microlens array having a plurality of liquid crystal lenses according to [1] or [2], or microlenses according to any one of [3] to [6]. [8] An optical transmission module component having a liquid crystal lens according to [1] or [2], or a microlens according to any one of [3] to [6], or a microlens array according to [7], and an optical isolator. [9] An optical transmission module having a liquid crystal lens according to [1] or [2], or a microlens according to any one of [3] to [6], or a microlens array according to [7], or an optical transmission module component according to [8].

[0010] According to the present invention, a liquid crystal lens that enables miniaturization of an optical transmission module, as well as a small microlens using the liquid crystal lens, a microlens array, a component for an optical transmission module, and an optical transmission module are provided.

[0011] This is a conceptual diagram showing an example of a microlens of the present invention. This is a conceptual plan view showing an example of a liquid crystal lens of the present invention. This is a conceptual cross-sectional view showing an example of a liquid crystal lens of the present invention. This is a conceptual diagram for explaining the configuration of the liquid crystal lens of the present invention. This is a conceptual diagram for explaining the operation of the liquid crystal lens of the present invention. This is a conceptual diagram for explaining the operation of the liquid crystal lens of the present invention. This is a conceptual plan view showing another example diagram showing an example of an exposure apparatus for an alignment film. This is a conceptual diagram showing an example of a component for an optical transmission module of the present invention. This is a conceptual diagram showing another example of a component for an optical transmission module of the present invention. This is a conceptual diagram showing an example of an optical transmission module of the present invention.

[0012] The liquid crystal lens, microlens, microlens array, optical transmission module component, and optical transmission module of the present invention will be described in detail below based on preferred embodiments shown in the accompanying drawings. The following descriptions of constituent elements may be based on representative embodiments of the present invention, but the present invention is not limited to such embodiments. Furthermore, the following figures are conceptual diagrams for explaining the present invention, and the shape, size, thickness, and positional relationships of each component do not necessarily correspond to actual objects. In this specification, numerical ranges expressed using "~" mean a range that includes the numbers written before and after "~" as the lower and upper limits.

[0013] Figure 1 conceptually shows an example of the microlens of the present invention. The microlens 10 shown in Figure 1 has, from left to right in the figure, an anti-reflective coating 12, a first λ / 4 plate 14 (first λ / 4 plate 14), an alignment coating 16, a liquid crystal lens 18, an adhesive layer 20, a second λ / 4 plate 24 (second λ / 4 plate 24), an adhesive layer 26, and a glass substrate 28. In this invention, the designations "first" and "second" in the λ / 4 plate are merely for convenience to distinguish between the two λ / 4 plates and have no technical significance. Therefore, in this invention, the first λ / 4 plate 14 may be located on the glass substrate 28 side and the second λ / 4 plate 24 may be located on the anti-reflective coating 12 side.

[0014] The microlens of the present invention uses the liquid crystal lens of the present invention. Therefore, in the microlens 10, the liquid crystal lens 18 is the liquid crystal lens of the present invention. The liquid crystal lens 18 of the present invention contains a liquid crystal compound and has a liquid crystal orientation pattern in which the orientation of the optical axis derived from the liquid crystal compound changes while continuously rotating along at least one direction in the plane, and this liquid crystal orientation pattern has concentric circles from the inside to the outside in one direction in which the orientation of the optical axis derived from the liquid crystal compound changes while continuously rotating. In other words, the liquid crystal lens 18 of the present invention has a liquid crystal orientation pattern in a concentric (radial) manner in which the orientation of the optical axis derived from the liquid crystal compound changes while continuously rotating along at least one direction in the plane.

[0015] Figures 2 and 3 conceptually show an example of a liquid crystal lens 18. Figure 2 is a plan view of the liquid crystal lens 18, and Figure 3 is a cross-sectional view in the thickness direction. As shown in Figures 1 to 3, in the microlens 10, the liquid crystal lens 18 and the alignment film 16 are laminated together. However, the microlens of the present invention is not limited to a configuration having an alignment film 16. For example, the microlens of the present invention may be configured in which the liquid crystal lens 18 (liquid crystal layer) is formed on the alignment film of a laminate having a support and an alignment film, the liquid crystal lens 18 is peeled off from the alignment film and bonded to the second λ / 4 plate 24 by an adhesive layer 20, or bonded to the first λ / 4 plate 14 by an adhesive layer. Furthermore, the microlens of the present invention may have a support between the alignment film 16 and the first λ / 4 plate 14, which was used when the liquid crystal lens 18 was formed.

[0016] The liquid crystal lens 18 shown in Figures 2 and 3 is a liquid crystal layer (optically anisotropic layer) formed on an alignment film 16 using a composition containing a liquid crystal compound 38, in which the liquid crystal compound 38 is oriented and fixed in the liquid crystal alignment pattern described below. As described above, the liquid crystal lens 18 has a liquid crystal alignment pattern in which the direction of the optical axis originating from the liquid crystal compound 38 changes while continuously rotating in one direction, in a concentric circular pattern from the inside outward. In Figures 2 and 3, a rod-shaped liquid crystal compound is exemplified as the liquid crystal compound 38, so the direction of the optical axis coincides with the longitudinal direction of the liquid crystal compound 38.

[0017] More specifically, in the liquid crystal lens 18, the orientation of the optical axis of the liquid crystal compound 38 changes while continuously rotating along multiple directions pointing outward from the center of the liquid crystal lens 18 (the center of the concentric circles), i.e., the optical axis, for example, the direction indicated by arrow A1, arrow A2, arrow A3, arrow A4, etc. Therefore, in the liquid crystal lens 18, the direction of rotation of the optical axis of the liquid crystal compound 38 is the same in all directions (one direction). In the illustrated example, the direction of rotation of the optical axis of the liquid crystal compound 38 is counterclockwise in all directions indicated by arrow A1, arrow A2, arrow A3, and arrow A4. That is, if arrows A1 and A4 are considered as a single straight line, the direction of rotation of the optical axis of the liquid crystal compound 38 reverses at the center of the liquid crystal lens 18, i.e., the center of the concentric circles, along this straight line. As an example, let's assume that the straight line formed by arrows A1 and A4 points to the right in the diagram (in the direction of arrow A1). In this case, the optical axis of the liquid crystal compound 38 initially rotates clockwise from the outside of the liquid crystal lens 18 toward the center, the direction of rotation reverses at the center of the liquid crystal lens 18, and thereafter rotates counterclockwise from the center of the liquid crystal lens 18 toward the outside. The center of the liquid crystal lens 18 is the optical axis of the liquid crystal lens.

[0018] As is well known, a liquid crystal layer (optical anisotropic layer) having a liquid crystal orientation pattern in which the orientation of the optical axis derived from the liquid crystal compound 38 changes while continuously rotating in one direction acts as a transmissive liquid crystal diffraction element that diffracts the incident circularly polarized light in one direction and in the opposite direction of the rotation of the optical axis, depending on the direction of rotation of the optical axis and the direction of rotation of the incident circularly polarized light.

[0019] Specifically, in a liquid crystal lens 18 having a liquid crystal alignment pattern in which the orientation of the optical axis of the liquid crystal compound 38 changes while continuously rotating in one direction, the diffraction direction (refraction direction) of the transmitted light depends on the rotation direction of the optical axis of the liquid crystal compound 38. That is, in this liquid crystal alignment pattern, if the rotation direction of the optical axis of the liquid crystal compound 38, which is moving in one direction, is reversed, the diffraction direction of the transmitted light will be in the opposite direction to the direction in which the optical axis rotates. Furthermore, in a liquid crystal lens 18 having a liquid crystal alignment pattern in which the orientation of the optical axis of the liquid crystal compound 38 changes while continuously rotating in one direction, the diffraction direction of the transmitted light differs depending on the rotation direction of the incident circularly polarized light. That is, in this liquid crystal alignment pattern, the diffraction direction of the transmitted light is reversed depending on whether the incident light is right-circularly polarized or left-circularly polarized.

[0020] Furthermore, when the in-plane retardation (retarder in the plane direction) value of the liquid crystal lens 18 is set to λ / 2, it functions as a general λ / 2 plate, that is, it has the function of giving a half-wavelength, or 180°, phase difference to the polarization component incident on the liquid crystal layer. Therefore, the circularly polarized light incident on this liquid crystal lens 18 and diffracted has its rotation direction reversed. That is, right-circularly polarized light incident on the liquid crystal lens 18 and diffracted is emitted as left-circularly polarized light, and left-circularly polarized light is emitted as right-circularly polarized light.

[0021] In the liquid crystal lens 18, the liquid crystal alignment pattern is such that, when the direction of the optical axis of the liquid crystal compound 38 changes while continuously rotating in one direction, one period is defined as the length of a 180° rotation of the optical axis originating from the liquid crystal compound, the length of one period gradually decreases from the inside to the outside. Here, in a liquid crystal layer having a liquid crystal alignment pattern in which the direction of the optical axis of the liquid crystal compound 38 changes while continuously rotating in one direction, the shorter the length of this one period, the larger the diffraction angle of light. Therefore, in the liquid crystal lens 18 having a concentric liquid crystal alignment pattern, the diffraction angle gradually increases from the center of the concentric circles outward.

[0022] Therefore, a liquid crystal lens 18 having a concentric liquid crystal orientation pattern in which the optical axis derived from the liquid crystal compound rotates and changes continuously can focus or diverge and transmit incident light (light beam) depending on the rotation direction of the optical axis of the liquid crystal compound 38 and the rotation direction of the incident circularly polarized light. In other words, such a liquid crystal lens 18 acts as a convex lens when right-circularly polarized light is incident, and as a concave lens when left-circularly polarized light is incident, depending on the rotation direction of the incident circularly polarized light. Alternatively, the liquid crystal lens 18 acts as a concave lens when right-circularly polarized light is incident and as a convex lens when left-circularly polarized light is incident.

[0023] In Figure 2, in order to simplify the drawing and clearly show the structure of the liquid crystal lens 18, only the liquid crystal compound 38 (liquid crystal compound molecules) on the surface of the alignment film 16 is shown. However, as conceptually shown in Figure 3, the liquid crystal lens 18 has a structure in which aligned liquid crystal compounds 38 are stacked, similar to a liquid crystal layer formed using a composition containing a normal liquid crystal compound.

[0024] Hereinafter, the liquid crystal lens 18 will be described in detail with reference to the liquid crystal lens 18 having a liquid crystal alignment pattern in which the optical axis 38A derived from the liquid crystal compound 38 changes while continuously rotating in one direction indicated by arrow A, as conceptually shown in Figure 4. In the concentric liquid crystal alignment pattern shown in Figure 2, in which the optical axis changes while continuously rotating in one direction radially from the inside to the outside, the same optical effects as those of the liquid crystal alignment pattern shown in Figure 4 are exhibited with respect to the optical axis that changes while continuously rotating in one direction. In the following description, the optical axis 38A derived from the liquid crystal compound 38 will also be referred to as "the optical axis 38A of the liquid crystal compound 38" or "the optical axis 38A".

[0025] In the liquid crystal lens 18, the liquid crystal compound 38 is oriented two-dimensionally in a plane parallel to one direction indicated by arrow A and the Y direction which is perpendicular to the direction of arrow A. In Figures 2 and 3, which will be described later, the Y direction is the direction perpendicular to the plane of the paper. In the following explanation, "one direction indicated by arrow A" will also be simply referred to as "the direction of arrow A". In the liquid crystal lens 18 shown in Figure 2, the circumferential direction of the concentric circles in the concentric liquid crystal orientation pattern corresponds to the Y direction in Figure 4. Also, in the concentric liquid crystal orientation pattern, the direction from the center of the concentric circles outward in the radial direction corresponds to the direction of arrow A in Figure 4.

[0026] The liquid crystal lens 18 has a liquid crystal orientation pattern in which the orientation of the optical axis 38A originating from the liquid crystal compound 38 changes while continuously rotating along the direction of arrow A within the plane of the liquid crystal lens 18. Specifically, the statement that the orientation of the optical axis 38A of the liquid crystal compound 38 changes while continuously rotating in the direction of arrow A (a predetermined one direction) means that the angle between the optical axis 38A of the liquid crystal compound 38 arranged along the direction of arrow A and the direction of arrow A differs depending on the position in the direction of arrow A, and that the angle between the optical axis 38A and the direction of arrow A changes sequentially from θ to θ+180° or θ-180° along the direction of arrow A.

[0027] On the other hand, in the liquid crystal compound 38 forming the liquid crystal lens 18, in the Y direction perpendicular to the direction of arrow A, that is, in the Y direction perpendicular to the direction in which the optical axis 38A rotates continuously, liquid crystal compounds 38 with the same orientation of the optical axis 38A are arranged at equal intervals. In other words, in the liquid crystal compound 38 forming the liquid crystal lens 18, the angle between the orientation of the optical axis 38A and the direction of arrow A is equal for liquid crystal compounds 38 arranged in the Y direction. In the liquid crystal lens 18 shown in Figure 2, regions with the same orientation of the optical axis 38A are formed in a ring shape with a coincident center, forming a concentric liquid crystal alignment pattern.

[0028] As described above, in a liquid crystal alignment pattern in which the optical axis 38A rotates continuously in one direction, the length (distance) over which the optical axis 38A of the liquid crystal compound 38 rotates by 180° is the length Λ of one period in the liquid crystal alignment pattern. That is, in the case of the liquid crystal lens 18 shown in Figure 4, the length (distance) over which the optical axis 38A of the liquid crystal compound 38 rotates by 180° in the direction of arrow A, in which the orientation of the optical axis 38A changes as it rotates continuously within the plane, is defined as one period Λ in the liquid crystal alignment pattern. In other words, one period Λ in the liquid crystal alignment pattern is defined by the distance from θ to θ+180° in the angle between the optical axis 38A of the liquid crystal compound 38 and the direction of arrow A. As described above, one period Λ is the distance between the centers in the direction of arrow A of two liquid crystal compounds 38 whose angles with respect to the direction of arrow A are equal. Specifically, as shown in Figure 4, one period Λ is the distance between the centers in the direction of arrow A of two liquid crystal compounds 38 whose directions of arrow A and the direction of the optical axis 38A coincide. In the liquid crystal lens 18 (liquid crystal layer (optical anisotropy layer)), the liquid crystal alignment pattern repeats this one period Λ in one direction, i.e., the direction of the optical axis 38A, which rotates continuously. As described above, the liquid crystal lens 18 having such a liquid crystal alignment pattern is also a transmissive liquid crystal diffraction element, and this one period Λ becomes the period (one period) of the diffraction structure.

[0029] In the liquid crystal lens 18, the liquid crystal compounds arranged in the Y direction have an equal angle between the optical axis 38A and the direction of arrow A. The region in which these liquid crystal compounds 38, which have an equal angle between the optical axis 38A and the direction of arrow A, are arranged in the Y direction is defined as region R. In this case, it is preferable that the in-plane retardation (Re) value in each region R is half a wavelength, i.e., λ / 2. This in-plane retardation is calculated by the product of the refractive index difference Δn due to the refractive index anisotropy of region R and the thickness of the liquid crystal layer. Here, the refractive index difference due to the refractive index anisotropy of region R in the liquid crystal layer is defined as the refractive index difference between the refractive index in the direction of the slow axis within the plane of region R and the refractive index in the direction perpendicular to the direction of the slow axis. That is, the refractive index difference Δn due to the refractive index anisotropy of region R is equal to the difference between the refractive index of the liquid crystal compound 38 in the direction of the optical axis 38A and the refractive index of the liquid crystal compound 38 in the direction perpendicular to the optical axis 38A within the plane of region R. In other words, the refractive index difference Δn is equal to the refractive index difference of the liquid crystal compound. In a liquid crystal lens 18 having a concentric liquid crystal alignment pattern with a radial liquid crystal alignment pattern in which the optical axis 38A rotates continuously in one direction, the region where the optical axis 38A is oriented in the same direction and is formed in an annular shape with the center coinciding corresponds to region R in Figure 4.

[0030] When circularly polarized light is incident on such a liquid crystal lens 18, the light is diffracted and the direction of the circular polarization is changed. This effect is conceptually illustrated in Figures 5 and 6. The liquid crystal lens 18 is assumed to have a product of the refractive index difference of the liquid crystal compound and the thickness of the liquid crystal layer of λ / 2. As mentioned above, this effect is exactly the same even in a liquid crystal lens 18 having a concentric liquid crystal alignment pattern, where the optical axis 38A has a radial liquid crystal alignment pattern that rotates continuously in one direction.

[0031] As shown in Figure 5, when the product of the refractive index difference of the liquid crystal compound in the liquid crystal lens 18 and the thickness of the liquid crystal layer is λ / 2, and incident light L1, which is left-circularly polarized, is incident on the liquid crystal lens 18, the incident light L1 is given a phase difference of 180° as it passes through the liquid crystal lens 18, and the transmitted light L2 is converted to right-circularly polarized light. Furthermore, since the liquid crystal alignment pattern formed on the liquid crystal lens 18 is a periodic pattern in the direction of arrow A, the transmitted light L2 travels in a direction different from the direction of propagation of the incident light L1. In this way, the left-circularly polarized incident light L1 is converted to right-circularly polarized transmitted light L2, which is tilted by a certain angle in the direction of arrow A with respect to the direction of incidence.

[0032] As shown in Figure 6, when the product of the refractive index difference of the liquid crystal compound in the liquid crystal lens 18 and the thickness of the liquid crystal layer is λ / 2, and right-circularly polarized incident light L4 is incident on the liquid crystal lens 18, the incident light L4 is given a phase difference of 180° upon passing through the liquid crystal lens 18, and the transmitted light L5 is converted to left-circularly polarized light. Furthermore, since the liquid crystal alignment pattern formed on the liquid crystal lens 18 is a periodic pattern in the direction of arrow A, the transmitted light L5 travels in a direction different from the direction of propagation of the incident light L4. Here, since the incident light L4 is right-circularly polarized, the transmitted light L5 travels in a different direction from the transmitted light L2, that is, in the opposite direction to the direction of arrow A relative to the direction of incidence. In this way, the incident light L4 is converted to transmitted light L5, which is left-circularly polarized light tilted by a certain angle in the opposite direction to the direction of arrow A relative to the direction of incidence.

[0033] The liquid crystal lens 18 can adjust the diffraction angles of transmitted light L2 and L5 by changing the period Λ of the formed liquid crystal alignment pattern. Specifically, the shorter the period Λ of the liquid crystal alignment pattern, the stronger the interference between light passing through adjacent liquid crystal compounds 38, thus allowing for greater diffraction of transmitted light L2 and L5. Furthermore, the liquid crystal lens 18 can reverse the direction of diffraction of transmitted light by reversing the rotation direction of the optical axis 38A of the liquid crystal compound 38, which rotates along the direction of arrow A. Moreover, the liquid crystal lens 18 reverses the direction of diffraction of transmitted light depending on the rotation direction of the incident circularly polarized light. That is, the liquid crystal lens 18 reverses the direction of diffraction of transmitted light for right-circularly polarized and left-circularly polarized light. As mentioned above, the same applies to the liquid crystal lens 18 having a concentric liquid crystal alignment pattern.

[0034] The liquid crystal lens 18 is formed using a liquid crystal composition containing a rod-shaped liquid crystal compound or a disc-shaped liquid crystal compound, and the optical axis of the rod-shaped liquid crystal compound or the optical axis of the disc-shaped liquid crystal compound has a liquid crystal alignment pattern oriented as described above. For example, an alignment film 16 having an alignment pattern corresponding to the above-described liquid crystal alignment pattern can be formed on a support, and a liquid crystal composition can be applied to the alignment film 16 and cured to form a liquid crystal lens 18 consisting of a cured layer of the liquid crystal composition. The liquid crystal composition for forming the liquid crystal lens 18 contains a rod-shaped liquid crystal compound or a disc-shaped liquid crystal compound, and may also contain other components such as a leveling agent, an alignment control agent, a polymerization initiator, and an alignment aid.

[0035] Furthermore, it is desirable that the liquid crystal lens 18 has a broad bandwidth with respect to the wavelength of the incident light, and is preferably constructed using a liquid crystal material with inverse dispersion birefringence.

[0036] ―Rod-shaped liquid crystal compounds― Preferably used rod-shaped liquid crystal compounds include azomethines, azoxys, cyanobiphenyls, cyanophenyl esters, benzoic acid esters, cyclohexanecarboxylic acid phenyl esters, cyanophenylcyclohexanes, cyanosubstituted phenylpyrimidines, alkoxysubstituted phenylpyrimidines, phenyldioxanes, trans, and alkenylcyclohexylbenzonitriles. In addition to the low molecular weight liquid crystal molecules mentioned above, high molecular weight liquid crystal molecules can also be used.

[0037] In the liquid crystal lens 18, it is more preferable to fix the orientation of the rod-shaped liquid crystal compound by polymerization, and as the polymerizable rod-shaped liquid crystal compound, Makromol. Chem. Compounds described in Volume 190, page 2255 (1989), Advanced Materials Volume 5, page 107 (1993), U.S. Patent No. 4683327, No. 5622648, No. 5770107, International Publication Nos. 95 / 22586, 95 / 24455, 97 / 00600, 98 / 23580, 98 / 52905, Japanese Patent Publication No. 1-272551, 6-16616, 7-110469, 11-80081, and Japanese Patent Application No. 2001-64627 can be used. Furthermore, as rod-shaped liquid crystal compounds, those described in Japanese Patent Publication No. 11-513019 and Japanese Patent Application Publication No. 2007-279688 can also be preferably used.

[0038] —Disk-shaped liquid crystal compound—As the disc-shaped liquid crystal compound, for example, those described in Japanese Patent Publication No. 2007-108732 and Japanese Patent Publication No. 2010-244038 can be preferably used. When a disc-shaped liquid crystal compound is used in the liquid crystal layer, the liquid crystal compound 38 rises in the thickness direction in the liquid crystal layer, and the optical axis 38A derived from the liquid crystal compound is defined as an axis perpendicular to the disc surface, a so-called phase-advancing axis.

[0039] As described above, the liquid crystal lens of the present invention has a concentric liquid crystal orientation pattern in which the optical axis derived from the liquid crystal compound rotates and changes continuously. In this invention, the minimum distance (shortest distance) from the center of the concentric circle in the liquid crystal orientation pattern to the edge of the liquid crystal lens 18 is 300 μm or less.

[0040] For example, the circular liquid crystal lens 18 shown in Figure 2 is a circle in which the center of the concentric circles coincides with the center of the circle, so the radius of the liquid crystal lens 18 is 300 μm or less. Here, considering the ease and accuracy of alignment when incorporating the liquid crystal lens into various optical elements (optical devices) such as microlenses, microlens arrays, optical transmission module components, and optical transmission modules as shown in Figure 1, it is preferable that the liquid crystal lens of the present invention is a rectangle including a square. In this case, if the liquid crystal lens is a square as conceptually shown in Figure 7, the minimum distance L from the center of the concentric circles to one side of the square liquid crystal lens is 300 μm or less. Alternatively, if the liquid crystal lens is a rectangle as conceptually shown in Figure 8, the minimum distance L from the center of the concentric circles to the short side of the rectangular liquid crystal lens is 300 μm or less.

[0041] In a liquid crystal lens (liquid crystal diffraction lens) having the liquid crystal alignment pattern described above, the region that includes the entire circumference of the rings constituting the concentric circles is the region that functions properly as a lens. That is, the region from the center of the concentric circles in the liquid crystal alignment pattern to the ring corresponding to the minimum distance from the edge of the liquid crystal lens 18 functions as a lens. In other words, the liquid crystal lens of the present invention, in which the minimum distance from the center of the concentric circles in the liquid crystal alignment pattern to the edge of the liquid crystal lens 18 is 300 μm or less, is an extremely small lens. It is extremely difficult to manufacture a lens of this size using silicon lenses, which are used in optical transmission modules such as TOSA.

[0042] In addition, since the liquid crystal lens is basically a coating layer formed by a coating method, it is usually a very thin flat plate with a thickness of 10 μm or less. Therefore, for example, even when the liquid crystal lens is attached to a glass substrate for support, the thickness of the microlens (lens unit) of the present invention can be made very thin. In addition, as described above, the liquid crystal lens can increase the diffraction angle by shortening one cycle. Therefore, in various optical elements incorporating the liquid crystal lens, the optical distance can be easily shortened.

[0043] That is, according to the liquid crystal lens of the present invention, miniaturization of the optical transmission module can be achieved.

[0044] The liquid crystal lens of the present invention has the above-described liquid crystal alignment pattern, and the minimum distance from the center of the concentric circles in the liquid crystal alignment pattern to the end of the liquid crystal lens 18 may be 300 μm or less. In the liquid crystal lens of the present invention, this minimum distance is preferably 50 to 200 μm, and more preferably 100 to 150 μm. By setting this minimum distance within the above range, miniaturization of the optical transmission module can be more suitably achieved.

[0045] There is no limitation on the NA (numerical aperture) of the liquid crystal lens 18 of the present invention, and it may be appropriately set according to the depth of focus of the liquid crystal lens 18 and the divergence angle of the emitted light from the light source in the optical transmission module. Here, the NA of the liquid crystal lens 18 of the present invention is preferably 0.2 to 0.8, and more preferably 0.3 to 0.5.

[0046] Such a liquid crystal lens 18 of the present invention is formed so as to be laminated on the alignment film 16. The liquid crystal alignment pattern in the liquid crystal lens 18 follows the alignment pattern formed on the alignment film 16. Therefore, the same alignment pattern as the liquid crystal alignment pattern of the liquid crystal lens 18 is formed on the alignment film 16 for forming a liquid crystal layer having such a liquid crystal alignment pattern. As an example, the alignment film 16 having such an alignment pattern can be formed by forming a coating film containing a compound having a photo-aligning group, drying this coating film, and then exposing it with an exposure apparatus 80 described later.

[0047] Examples of compounds having photo-aligning groups, i.e., photo-aligning materials used in photo-aligning films, include those described in Japanese Patent Publication No. 2006-285197, 2007-076839, 2007-138138, 2007-094071, 2007-121721, 2007-140465, and 2007-156439. Azo compounds described in Japanese Patent Publication No. 2007-133184, Japanese Patent Publication No. 2009-109831, Japanese Patent Publication No. 3883848 and Japanese Patent Publication No. 4151746, aromatic ester compounds described in Japanese Patent Publication No. 2002-229039, and maco compounds having photo-orienting units described in Japanese Patent Publication No. 2002-265541 and Japanese Patent Publication No. 2002-317013 Examples of preferred examples include reimide and / or alkenyl-substituted nadiimide compounds, photocrosslinkable silane derivatives described in Japanese Patent No. 4205195 and Japanese Patent No. 4205198, photocrosslinkable polyimides, photocrosslinkable polyamides and photocrosslinkable esters described in Japanese Patent Publication No. 2003-520878, Japanese Patent Publication No. 2004-529220 and Japanese Patent No. 4162850, and photodimerizable compounds described in Japanese Patent Publication No. 9-118717, Japanese Patent Publication No. 10-506420, Japanese Patent Publication No. 2003-505561, International Publication No. 2010 / 150748, Japanese Patent Publication No. 2013-177561 and Japanese Patent Publication No. 2014-012823, particularly cinnamate compounds, chalcone compounds and coumarin compounds. Among these, azo compounds, photocrosslinkable polyimides, photocrosslinkable polyamides, photocrosslinkable esters, cinnamate compounds, and chalcone compounds are particularly suitable for use.

[0048] Figure 9 conceptually shows an example of an exposure apparatus that exposes a coating film which will become an alignment film 16 (photo-alignment film) for forming a liquid crystal lens 18, to form an alignment pattern corresponding to a concentric liquid crystal alignment pattern that changes as the optical axis rotates radially. The exposure apparatus 80 shown in Figure 9 includes a light source 84 equipped with a laser 82, a polarizing beam splitter 86 that splits the laser light M from the laser 82 into S-polarized MS and P-polarized MP, a mirror 90A arranged in the optical path of the P-polarized MP and a mirror 90B arranged in the optical path of the S-polarized MS, a lens 92 arranged in the optical path of the S-polarized MS, a polarizing beam splitter 94, and a λ / 4 plate 96.

[0049] The P-polarized MP, split by the polarizing beam splitter 86, is reflected by the mirror 90A and incident on the polarizing beam splitter 94. On the other hand, the S-polarized MS, split by the polarizing beam splitter 86, is reflected by the mirror 90B, focused by the lens 92, and incident on the polarizing beam splitter 94. The P-polarized MP and S-polarized MS are combined in the polarizing beam splitter 94 and, by the λ / 4 plate 96, become right-circularly polarized and left-circularly polarized light according to their polarization directions, and are incident on the alignment film 16. Here, due to the interference of the right-circularly polarized and left-circularly polarized light, the polarization state of the light irradiated onto the alignment film 16 changes periodically in an interference fringe pattern. As you move from the inside to the outside of the concentric circles, the intersection angle of the left-circularly polarized and right-circularly polarized light changes, resulting in an exposure pattern in which the pitch changes from the inside to the outside. As a result, a concentric (radial) orientation pattern in which the orientation state changes periodically is obtained in the alignment film 16.

[0050] In this exposure apparatus 80, the period Λ of the liquid crystal alignment pattern, in which the optical axis of the liquid crystal compound 30 rotates continuously by 180° along one direction, can be controlled by changing the focal length of the lens 92 and the distance between the lens 92 and the alignment film 16. Furthermore, by adjusting the refractive power of the lens 92 (the F-number of the lens 92), the length of one period of the liquid crystal alignment pattern in the direction in which the optical axis rotates continuously can be changed. Specifically, the length of one period of the liquid crystal alignment pattern in the direction in which the optical axis rotates continuously can be changed by the angle of light divergence caused by interference with parallel light and the light divergence angle of the lens 92. More specifically, if the refractive power of the lens 92 is weakened, it approaches parallel light, so the length of one period Λ of the liquid crystal alignment pattern gradually shortens from the inside to the outside. Conversely, if the refractive power of the lens 92 is strengthened, the length of one period Λ of the liquid crystal alignment pattern shortens abruptly from the inside to the outside. In other words, by adjusting the refractive index of lens 92, the refractive index of the liquid crystal lens 18, which acts as a convex lens (concave lens) according to the rotation direction of the incident circularly polarized light as shown in Figure 1, can be adjusted.

[0051] The microlens 10 shown in Figure 1 has a first λ / 4 plate 14 on one surface side of the liquid crystal lens 18, and a second λ / 4 plate 24 on the other surface side of the liquid crystal lens 18.

[0052] The liquid crystal lens 18 of the present invention, that is, the microlens 10 of the present invention having the liquid crystal lens 18 of the present invention, is used as a microlens in optical transmission modules such as TOSA (Transmitter Optical Sub-Assembly) of optical transceivers. In optical communication, semiconductor lasers are often used as the light source for signal light, so the signal light is often linearly polarized. On the other hand, as described above, the liquid crystal lens 18 refracts circularly polarized light in a predetermined direction.

[0053] Therefore, as shown in the illustrated example of the microlens 10, by providing a first λ / 4 plate 14 on one surface side of the liquid crystal lens 18 and a second λ / 4 plate 24 on the other surface side of the liquid crystal lens 18, it becomes possible to emit more accurate signal light. Specifically, first, the first λ / 4 plate 14 converts the incident linearly polarized light (signal light) into circularly polarized light in the direction of rotation that the liquid crystal lens 18 focuses. This allows the liquid crystal lens 18 to properly focus the incident light into, for example, parallel light (collimated light). Subsequently, downstream of the liquid crystal lens 18, the focused circularly polarized light can be converted into, for example, linearly polarized light in the same direction as the incident light by the second λ / 4 plate 24. As a result, by providing λ / 4 plates on both sides of the liquid crystal lens, it becomes possible to perform more accurate optical communication.

[0054] The microlens of the present invention is not limited to having λ / 4 plates on both surfaces of the liquid crystal lens 18, and may have λ / 4 plates on one surface of the liquid crystal lens 18. In this case, it is preferable to provide the λ / 4 plate on the light incident side of the microlens. In the microlens 10 shown in Figure 1, the anti-reflective film 12 side is the light incident side, so it is preferable to have only the first λ / 4 plate 14. However, in order to properly focus the incident light with the liquid crystal lens 18 and to make the emitted light linearly polarized as desired, it is preferable in the microlens of the present invention to have λ / 4 plates on both surfaces of the liquid crystal lens 18, as shown in Figure 1.

[0055] In the microlenses of the present invention, there are no limitations on the λ / 4 plate (λ / 4 wave plate, quarter wave plate, λ / 4 phase difference plate), and any known λ / 4 plate (phase difference plate) can be used as long as it can impart a λ / 4 phase difference to the incident light of the target wavelength. Examples include stretched polycarbonate film, stretched norbornene-based polymer film, transparent film containing and oriented inorganic particles having birefringence such as strontium carbonate, thin film in which an inorganic dielectric is obliquely deposited on a support, film in which a polymerizable liquid crystal compound is uniaxially oriented and orientation fixed, and film in which a liquid crystal compound is uniaxially oriented and orientation fixed.

[0056] In the microlens 10 shown in Figure 1, a glass substrate 28 is provided on the side of the second λ / 4 plate 24 opposite to the liquid crystal lens 18, in a preferred embodiment. The glass substrate 28 supports the liquid crystal lens 18 and the λ / 4 plate in the microlens 10. There are no restrictions on the glass used for the glass substrate; any known glass such as borosilicate glass, quartz glass, and high refractive index glass containing titanium oxide and / or zirconium oxide can be used, as long as it has sufficient transparency for light in the wavelength range targeted by the microlens 10.

[0057] There are no restrictions on the thickness of the glass substrate 28, but it is preferably 0.3 mm or less, more preferably 0.26 mm or less, and even more preferably 0.22 mm or less. There are also no restrictions on the lower limit of the thickness of the glass substrate 28, and the thickness that can support the liquid crystal lens 18 etc. in the microlens 10 can be appropriately set according to the forming material etc., but considering reliable support of the liquid crystal lens 18 etc., it is preferably 0.1 mm or more.

[0058] In the microlens 10 shown in Figure 1, the liquid crystal lens 18 and the second λ / 4 plate 24 are bonded together by an adhesive layer 20, and the second λ / 4 plate 24 and the glass substrate 28 are bonded together by an adhesive layer 26.

[0059] In the microlens 10 of the present invention, there are no restrictions on the adhesive layer. Any adhesive layer made of various known adhesives can be used, as long as it has sufficient transparency to light in the wavelength range targeted by the microlens 10, can adhere the liquid crystal lens 18 (liquid crystal layer) to the member to be attached to the liquid crystal lens 18, and has the necessary heat resistance. Examples of adhesives include UV adhesives (ultraviolet-curing adhesives) and OCA (Optical Clear Adhesive). The thickness of the adhesive layer can be appropriately set to a thickness that provides sufficient adhesive strength depending on the type of adhesive, but a thinner layer is preferable.

[0060] In the microlens 10 shown in Figure 1, an anti-reflective coating 12 is provided on the side of the first λ / 4 plate 14 opposite to the liquid crystal lens 18 (alignment film 16), in a preferred embodiment. That is, in a preferred embodiment, the microlens of the present invention has an anti-reflective coating on its outermost surface. The anti-reflective coating 12 is intended to reduce signal light loss, i.e., optical loss, caused by the reflection of a portion of the signal light emitted from a light source when it enters the microlens 10, for example, when the microlens 10 of the present invention is mounted on an optical transmission module.

[0061] There are no restrictions on the anti-reflective coating 12. Any known anti-reflective coating can be used, as long as it can prevent the reflection of light in the wavelength range targeted by the microlens 10. These include inorganic films such as titanium, titanium dioxide, titanium nitride, chromium oxide, silicon oxide, carbon, and amorphous silicon, laminated films made by stacking two or more of these inorganic films, and organic films made of light absorbers and polymer materials. Since the microlens (liquid crystal lens) of the present invention is used in an optical transmission module, the target light is the O-band (Original-band 1260-1360 nm), C-band (Conventional-band 1530-1565 nm), L-band (Long wavelength-band 1565-1625 nm), and near-infrared light such as the 850 nm wavelength band. There are also no restrictions on the thickness of the anti-reflective coating 12. A thickness that can sufficiently prevent the reflection of the target light should be set as appropriate.

[0062] In the microlens 10 of the present invention, both the glass substrate 28 and the anti-reflective coating 12 are provided in preferred configurations. Therefore, in the microlens of the present invention, either the glass substrate 28 or the anti-reflective coating 12 may be omitted, or both may be omitted. However, considering the strength of the microlens, it is preferable to have the glass substrate 28. Furthermore, considering the reduction of optical loss caused by the microlens, it is preferable to have the anti-reflective coating 12. Therefore, in the microlens of the present invention, it is preferable to have at least the glass substrate 28 or the anti-reflective coating 12, and it is more preferable to have both.

[0063] The microlens array of the present invention comprises a plurality of the liquid crystal lenses of the present invention described above. Therefore, the microlens array of the present invention may also comprise a plurality of microlenses having the liquid crystal lenses of the present invention.

[0064] As described above, the liquid crystal lens of the present invention can be significantly miniaturized compared to silicon lenses and the like that are commonly used in optical transmission modules such as TOSA in optical transceivers. For example, as mentioned above, it is difficult to manufacture lenses with a diameter of 450 μm or less using silicon lenses. In contrast, with the liquid crystal lens of the present invention, for example, a circular liquid crystal lens with a diameter of 240 μm, that is, a minimum distance of 120 μm from the center to the edge of the concentric circles mentioned above, can be manufactured. When this liquid crystal lens is used, a microlens array with eight liquid crystal lenses can be realized with the same size as a microlens array with four silicon lenses with a diameter of 480 μm. Moreover, the liquid crystal lens is a thin, flat plate. In other words, by using this liquid crystal lens, an optical transmission module capable of emitting eight signal light channels with eight liquid crystal lenses can be realized with the same size as an optical transmission module capable of emitting four signal light channels with four silicon lenses with a diameter of 480 μm. In other words, according to the present invention, high integration of optical transmission modules such as TOSA can be achieved.

[0065] The lens array of the present invention may consist of individually independent liquid crystal lenses arranged together, or it may consist of multiple liquid crystal lenses arranged on a single support. That is, the microlens array of the present invention, which consists of the microlenses of the present invention, may consist of multiple liquid crystal lenses, i.e., multiple microlenses of the present invention, arranged on a single glass substrate. In this case, the λ / 4 plate and / or anti-reflective coating may be provided corresponding to each liquid crystal lens, or there may be only one.

[0066] The optical transmission module component of the present invention comprises the liquid crystal lens of the present invention and an optical isolator. Therefore, the optical transmission module component of the present invention may comprise a microlens having the liquid crystal lens of the present invention and an optical isolator, or it may comprise a microlens array having the liquid crystal lens (microlens) of the present invention and an optical isolator.

[0067] Figure 10 conceptually shows an example of a component for an optical transmission module according to the present invention. The optical transmission module component 50 shown in Figure 10 has a liquid crystal lens 18 and an optical isolator 52 according to the present invention. Furthermore, as shown in the optical transmission module component 50 of Figure 10, the optical transmission module component of the present invention may also have a light source 54 in addition to the liquid crystal lens 18 and the optical isolator 52.

[0068] The optical transmission module component 50 shown in Figure 10 focuses (collimates) the signal light, which is diffused light emitted from the light source 54, using the liquid crystal lens 18 to convert it into parallel light (collimated light), which is then incident on and passed through the optical isolator 52. In other words, in this example, the liquid crystal lens 18 acts as a collimating lens.

[0069] The optical isolator 52 is a known optical isolator that transmits only forward light and blocks reverse light. In the optical transmission module component 50 of the present invention, various known optical isolators used in optical transmission modules such as TOSA for optical transceivers can be used as the optical isolator 52. Therefore, the optical transmission module component 50 may be polarization-dependent or polarization-independent.

[0070] Furthermore, various known light sources 54 used in optical transmission modules, such as semiconductor lasers (LD (Laser Diode)), Fabry-Perot lasers (FP (Fabry-Perot) Laser), distributed feedback lasers (DFB (Distributed Feedback) Laser), distributed reflection lasers (DBR (Distributed Bragg Reflector) Laser), electro-absorption modulated lasers (EML (Electro-absorption Modulated Laser)), and vertical cavity surface-emitting lasers (VCSEL (Vertical Cavity Surface Emitting Laser)), can be used as the light source 54. Since the optical transmission module component 50 of the present invention is used for optical communication, the light source 54 emits near-infrared light such as the O-band, C-band, L-band, and 850 nm wavelength band, as described above. Vertical cavity surface-emitting lasers are mainly used in the 850 nm wavelength band.

[0071] The optical transmission module component 50 of the present invention shown in Figure 10 has a liquid crystal lens 18 only on the upstream side (incident side) of the optical isolator 52, but the optical transmission module component of the present invention is not limited to this. That is, the optical transmission module component of the present invention may have liquid crystal lenses 18 on both the upstream and downstream sides (output side) of the optical isolator 52, as conceptually shown in Figure 11 (optical transmission module component 56), to concentrate the emitted signal light. With such a configuration, it becomes possible to appropriately incident the signal light according to the light incident surface of a light receiving component arranged downstream, for example, the light incident surface of an optical fiber.

[0072] In the optical transmission module component of the present invention, when lenses are provided on both the upstream and downstream sides of the optical isolator 52, there is no limitation that both must be liquid crystal lenses of the present invention; one may be a liquid crystal lens of the present invention, and the other may be another known lens. However, in terms of miniaturization and thinning of the optical transmission module, it is preferable that both lenses provided on the upstream and downstream sides of the optical isolator 52 are liquid crystal lenses of the present invention. Furthermore, the optical transmission module component of the present invention may have a liquid crystal lens only on the downstream side of the optical isolator 52.

[0073] Furthermore, the method for making the signal light emitted from the optical transmission module member of the present invention into focused light is not limited to the method of arranging a focusing liquid crystal lens (lens) downstream of the optical isolator 52. For example, the diffraction (refraction) of light by the liquid crystal lens 18 may be used to focus the incident light at a predetermined position, rather than collimating it, thereby making the signal light emitted from the optical transmission module member of the present invention into focused light. Alternatively, the position of the liquid crystal lens 18 acting as a collimating lens may be adjusted to make the signal light emitted from the optical transmission module member of the present invention into focused light.

[0074] The optical transmission module of the present invention uses the liquid crystal lens of the present invention. Therefore, the optical transmission module of the present invention may use a microlens having the liquid crystal lens of the present invention, or a microlens array having the liquid crystal lens of the present invention, or an optical transmission module component having the liquid crystal lens of the present invention. Such an optical transmission module of the present invention can be used in various known optical transmission modules (optical transmission unit, optical transmitter) used in optical communication.

[0075] Figure 12 conceptually shows an example of using the optical transmission module of the present invention in the TOSA (transmitting unit) of an optical transceiver. In Figure 12, the top is a plan view and the bottom is a side view. The TOSA 60 shown in Figure 12 has a drive control unit 62, a light source 54, a liquid crystal lens 18, an optical isolator 52, and a signal optical processing unit 64. The light source 54 and the liquid crystal lens 18 are fixed and supported on a support base 68. In other words, the TOSA 60 shown in Figure 12 uses the optical transmission module components of the present invention.

[0076] Similar to the optical transmission module component 50 described above, the light source 54 can be any type of light source usable in optical transmission modules for optical communication, such as a semiconductor laser. In the TOSA 60 shown in Figure 12, there are four light sources 54, and accordingly, there are also four liquid crystal lenses 18 and four optical isolators 52 (optical transmission module components). In other words, the TOSA 60 in the illustrated example is capable of emitting four sets of optical signals.

[0077] The drive control unit 62 drives each light source 54 in accordance with the optical signal emitted by the TOSA 60, and is a known drive control unit for a known light source 54 having an IC substrate, etc., used in known optical transmission modules such as TOSA. In other words, in TOSA 60, the drive control unit 62 and the light source 54 form a signal light emission section. In the optical transmission module of the present invention, the signal light emission section is not limited to the configuration shown in Figure 12, and various known configurations used in optical transmission modules such as TOSA can be used. Examples include an emission section combining a light source and a silicon photonic chip (SiPh) having a MOD (Modulator), and an emission section combining a plurality of light sources with different wavelengths and a silicon photonic chip having a MUX (Multiplexer) and a MOD.

[0078] In the TOSA 60, the signal light emitted from the light source 54 is, as described above, converted into parallel light by the liquid crystal lens 18, passes through the optical isolator 52, and enters the signal light processing unit 64. The signal light processing unit 64 is the part that emits the signal light from the TOSA 60, and optical fibers for external connection, i.e., connection to external devices, are connected to it.

[0079] The signal light processing unit 64 is a known unit in the TOSA 60 that performs propagation and processing of signal light in order to input optical signals to optical fibers connected for external connection. In other words, the signal light processing unit 64 is a known signal light emission processing unit configured by appropriately combining known elements (devices) used for signal light emission in the TOSA 60, such as MUX, FA (Fiber array), PLC (Planar lightwave circuit), WA (Waveguide array), AWG (Arrayed Waveguide Grating), and TFF (Thin film filter).

[0080] Although the liquid crystal lens, microlens, microlens array, optical transmission module component, and optical transmission module of the present invention have been described in detail above, the present invention is not limited to the examples described above, and various improvements and modifications may be made without departing from the spirit of the present invention.

[0081] The features of the present invention will be further described in detail below with reference to examples. The materials, reagents, amounts used, amounts of substance, ratios, processing content, and processing procedures shown in the following examples can be modified as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be interpreted as being limited by the specific examples shown below.

[0082] [Example] <Fabrication of liquid crystal lens> (Support) A glass plate was prepared as the support.

[0083] (Formation of alignment film) The following alignment film forming coating solution was applied to the support by spin coating. The support coated with this alignment film forming coating solution was dried on a 60°C hot plate for 60 seconds to form an unexposed alignment film.

[0084] Coating solution for forming alignment film ---------------------------------------------------------------- Photo-alignment material A 1.00 parts by mass Water 16.00 parts by mass Butoxyethanol 42.00 parts by mass Propylene glycol monomethyl ether 42.00 parts by mass ----------------------------------------------------------------

[0085] -Photo alignment material A-

[0086] (Exposure of the alignment film) An unexposed alignment film was exposed using the exposure apparatus shown in Figure 9 to form an alignment film P-1 having a concentric alignment pattern. The exposure apparatus used a laser light source with a wavelength of 355 nm. The exposure dose due to interference was 1000 mJ / cm². 2 The alignment film was exposed by adjusting the lens of the exposure apparatus so that one period at a position 200 μm from the center of the concentric circles was 5 μm.

[0087] (Formation of liquid crystal lenses) Composition A-1 was prepared as a liquid crystal composition for forming liquid crystal lenses. Composition A-1 -------------------------------------------------- Liquid crystal compound L-1 10.00 parts by mass Liquid crystal compound L-2 90.00 parts by mass Polymerization initiator (BASF, Irgacure OXE01) 1.00 parts by mass Surfactant F1 0.30 parts by mass Methyl ethyl ketone 550.00 parts by mass Cyclopentanone 550.00 parts by mass --------------------------------------------------

[0088] Liquid crystal compound L-1

[0089] Liquid crystal compound L-2

[0090] Surfactant F1

[0091] The liquid crystal lens was formed by multilayer coating of composition A-1 on an alignment film P-1. Multilayer coating refers to the process of first coating the first layer of composition A-1 onto the alignment film, heating and then UV curing to create a liquid crystal immobilization layer, and then applying subsequent layers on top of this liquid crystal immobilization layer, repeating the process of heating and UV curing. By forming the liquid crystal lens by multilayer coating, the orientation direction of the alignment film is reflected from the bottom surface to the top surface of the liquid crystal lens, even when the total thickness of the liquid crystal lens is increased.

[0092] First, for the first layer, composition A-1 is applied to the alignment film P-1, the coating is heated to 80°C on a hot plate, and then, under a nitrogen atmosphere, ultraviolet light with a wavelength of 365 nm is applied at a rate of 300 mJ / cm using a high-pressure mercury lamp. 2 The orientation of the liquid crystal compound was fixed by irradiating the coating film with a certain irradiation dose. For the second and subsequent layers, the liquid crystal fixed layer was fabricated by applying multiple layers on top of this liquid crystal fixed layer, heating under the same conditions as above, and then curing with ultraviolet light. In this way, a liquid crystal lens was fabricated by repeating the application of multiple layers until the desired film thickness was achieved.

[0093] The birefringence Δn of the cured layer of liquid crystal composition A-1 was determined by applying liquid crystal composition A-1 to a support with an alignment film prepared separately for retardation measurement, aligning the liquid crystal compound director to be horizontal to the substrate, and then fixing it by ultraviolet irradiation. The retardation value and film thickness of the resulting liquid crystal immobilized layer (cured layer) were then measured. Δn can be calculated by dividing the retardation value by the film thickness. The retardation value was measured at the desired wavelength using an AxoScan from Axometrix, and the film thickness was measured using a SEM.

[0094] The liquid crystal lens ultimately produces a Δn of liquid crystal. 1310The thickness (Re(1310)) was confirmed to be 655 nm, and the surface was found to have a periodic orientation, as confirmed by polarizing microscope. In the liquid crystal alignment pattern of this liquid crystal lens, one period, corresponding to a 180° rotation of the optical axis of the liquid crystal compound, was 5 μm at a position 200 μm from the center of the concentric circles. Furthermore, the concentric liquid crystal alignment pattern was such that the period shortened as one period increased outward from the center of the concentric circles.

[0095] <Fabrication of λ / 4 plate> A polyethylene terephthalate film (PET film) with a thickness of 100 μm was prepared. One side of this PET film was subjected to rubbing treatment (rayon cloth, pressure: 0.1 kgf (0.98 N), rotation speed: 1000 rpm (revolutions per minute), transport speed: 10 m / min, number of times: 1 round trip).

[0096] The following coating solution for forming a phase difference layer was prepared. Coating solution for forming a phase difference layer -------------------------------------------------- Mixture 1 100 parts by mass Fluorine-based horizontal orientation agent 1 (orientation control agent 1) 0.05 parts by mass Fluorine-based horizontal orientation agent 2 (orientation control agent 2) 0.01 parts by mass Polymerization initiator IRGACURE OXE01 (manufactured by BASF) 1.0 part by mass Solvent (methyl ethyl ketone) Amount such that the solute concentration is 20% by mass --------------------------------------------------

[0097]

[0098]

[0099] A phase difference layer forming solution was applied to the rubbed surface of a PET film using a wire bar, and then dried. Next, it was placed on a hot plate at 50°C and exposed to an oxygen concentration of 1000 ppm or less under the influence of a Fusion UV Systems electrodeless lamp "D-bulb" (60 mW / cm²). 2A λ / 4 plate was fabricated by irradiating it with ultraviolet light for 6 seconds using a device to fix the coating (liquid crystal layer). The λ / 4 plate (liquid crystal layer) was made 3 μm thick so that the phase difference at a wavelength of 1310 nm was λ / 4.

[0100] <Fabrication of Microlenses> A Schott D263 glass substrate (40 mm x 40 mm, 0.21 mm thick) was prepared. A λ / 4 plate (liquid crystal layer) was transferred and attached to one surface of this glass substrate using UV adhesive to create a second λ / 4 plate. Next, a liquid crystal lens was transferred and attached to the surface of the second λ / 4 plate using UV adhesive. The transfer of the liquid crystal lens was performed so that the center of the concentric circles of the liquid crystal alignment pattern coincided with the center of the glass substrate. Only the liquid crystal lens was transferred, and the alignment film was peeled off from the liquid crystal lens. Furthermore, a λ / 4 plate (liquid crystal layer) was transferred and attached to the surface of the liquid crystal lens using UV adhesive to create a first λ / 4 plate. Finally, a laminated film of TiO2 and SiO2 was formed on the surface of the first λ / 4 plate by deposition using electron beam heating to create an anti-reflective film. The anti-reflective film was formed appropriately so that the reflectance at λ = 1310 nm was 1% or less. As a result, a microlens with a layer structure similar to the microlens 10 shown in Figure 1 was fabricated, except that it does not have an alignment layer.

[0101] The fabricated microlens was cut into a 400 x 400 μm square by dicing. The cutting was performed so that the center of the concentric circles of the liquid crystal lens coincided with the center of the square. This resulted in a microlens having a square liquid crystal lens (see Figure 7) with a minimum distance of 200 μm from the center of the concentric circles. As mentioned above, the period of the liquid crystal alignment pattern at a position 200 μm from the center of the concentric circles in this liquid crystal lens is 5 μm.

[0102] <Mounting to the Optical Transceiver> An optical transceiver manufactured by FS Corporation (400G QSFP-DD, output wavelength 1310 nm, maximum transmission distance 2 km) was disassembled, and the silicon lens immediately after the laser light source on the TOSA side was removed. Next, the fabricated microlens was mounted immediately after the laser light source, with the anti-reflective coating side facing the light source. The position was adjusted so that the focal point of the liquid crystal lens was correct, and it was fixed with adhesive to create an optical transceiver with a TOSA using a liquid crystal lens.

[0103] <Evaluation> When optical communication was performed using the fabricated optical transceiver, it was confirmed that it operated normally without any communication errors.

[0104] [Comparative Example] An attempt was made to fabricate a silicon lens with a radius of 200 μm and a thickness of 0.3 mm using a conventional method employing photolithography and etching. However, cracks formed in the lens during dicing, making it impossible to produce a proper silicon lens. From these results, the effectiveness of the present invention is clear.

[0105] It can be suitably used for optical transmission, such as TOSA in optical transceivers.

[0106] 10 Microlens 12 Anti-reflective coating 14 First λ / 4 plate 16 Alignment film 18 Liquid crystal lens 20, 26 Adhesion layer 24 Second λ / 4 plate 28 Glass substrate 32 Substrate 34 Alignment film 38 Liquid crystal compound 38A Optical axis 50, 56 Components for optical transmission module 52 Optical isolator 54 Light source 60 Optical transmission module 62 Drive control unit 64 Signal light processing unit 80 Exposure apparatus 82 Laser 84 Light source 86, 94 Polarizing beam splitter 90A, 90B Mirror 92 Lens 96 λ / 4 plate

Claims

1. A liquid crystal lens containing a liquid crystal compound, used as a microlens for an optical transmission module, wherein the liquid crystal lens has a liquid crystal orientation pattern in which the orientation of the optical axis derived from the liquid crystal compound changes while continuously rotating along at least one direction in the plane, and the liquid crystal orientation pattern has concentric circles in the one direction moving from the inside to the outside, and the minimum distance from the center of the concentric circles to the edge of the liquid crystal lens is 300 μm or less.

2. The liquid crystal lens according to claim 1, wherein the minimum distance from the center of the concentric circles to the edge of the liquid crystal lens is 50 to 200 μm.

3. A microlens comprising a liquid crystal lens as described in claim 1 and a λ / 4 plate disposed on one surface side of the liquid crystal lens.

4. A microlens comprising a liquid crystal lens as described in claim 1, a first λ / 4 plate disposed on one surface side of the liquid crystal lens, and a second λ / 4 plate disposed on the other surface side of the liquid crystal lens.

5. The microlens according to claim 3 or 4, further comprising a glass substrate with a thickness of 0.3 mm or less.

6. The microlens according to claim 3 or 4, further comprising an anti-reflective coating on its outermost surface.

7. A microlens array having a plurality of liquid crystal lenses as described in claim 1.

8. A component for an optical transmission module, comprising the liquid crystal lens described in claim 1 and an optical isolator.

9. An optical transmission module having the liquid crystal lens described in claim 1 or 2.

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