JP2005227360A - Optical coupler - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stabilize optical coupling efficiency to a micro optical element by facilitating control of incident/outgoing angle of a signal light to the micro optical element. <P>SOLUTION: The optical coupler is constituted of a core 10 for propagating a signal light, an optical waveguide element 11 composed of a clad covering the core 10, and an optical element 12 for circulating the signal light. In a part of the optical waveguide element 11, there is formed a groove 13 at an angle totally reflecting the signal light at the tip end 10a of the core 10, the micro optical element 12 is installed in the groove 13. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical coupler for inputting / outputting light to / from a micro optical element, and more particularly to an optical coupler using an optical waveguide element.

  Industrial use of optical phenomena caused by the total internal reflection of light on the inner surface of micro optical elements, such as optical resonance of circular optical resonators and optical plasmon resonance of metal thin films, along with recent advances in microfabrication technology Is being considered. In a micro-optical element based on the principle of total internal reflection, the light extraction efficiency from the inside of the micro-optical element to the outside of the micro-optical element is remarkably low, and the light from the outside of the micro-optical element to the inside of the micro-optical element is reduced. The disadvantage is that the injection efficiency is also significantly lower.

  As a method for overcoming this drawback, for example, the tip of the optical fiber is cut obliquely, and light is input to the micro-optical element through the optical fiber whose cut surface is polished, whereby the optical coupling efficiency (extraction efficiency) is obtained. (Non-Patent Document 1) describes a technique for significantly increasing the injection efficiency. In this method, light can be propagated while confined in the glass from the light source to the vicinity of the micro optical element by the waveguide function of the optical fiber. Has the advantage of high. Furthermore, it can be said that the feature that the size of the coupling portion of the optical fiber with the micro optical element is about the same as that of the micro optical element to be coupled is indispensable for reducing the device size.

“Pigtailing the high-Q microsphere cavity: a simple fibercoupler for optical whispering-gallery modes”, Opt. Lett., 1999, p.723 -725

  However, in the above method, the tip of the optical fiber needs to be processed at a predetermined angle with respect to the optical axis of the optical fiber and the surface of the cut surface is sufficiently smooth. With the current standard processing technique, There is a problem that it is difficult to control the angle of the tip of the optical fiber. In addition, it is difficult to stably hold the tip of the optical fiber in the micro optical element, that is, it is difficult to control the incident / exit angle of the signal light to the micro optical element, and the optical coupling efficiency to the micro optical element is not stable. was there.

  Accordingly, an object of the present invention is to provide an optical coupler capable of stabilizing the optical coupling efficiency to the micro optical element by facilitating the control of the incident / exit angle of the signal light to the micro optical element.

  To achieve the above object, the invention of claim 1 comprises a core for propagating signal light, an optical waveguide element comprising a clad covering the core, and a micro optical element for circulating the signal light. An optical coupler, wherein a groove is formed in a part of the optical waveguide element at an angle at which the signal light is totally reflected at the tip of the core, and the micro optical element is installed in the groove. It is a coupler.

  In the invention of claim 2, the distance between the micro optical element and the tip of the core is from 0 times the wavelength of the signal light to 1 / (2π (max (n1, n2) ^ 2-n0 ^ 2) ^ ( The optical coupler according to claim 1, which is in the range of -0.5)) times.

  Here, n0 is the refractive index in the groove, n1 is the refractive index of the core, and n2 is the refractive index of the micro optical element.

  The invention according to claim 3 is the optical coupler according to claim 1 or 2, wherein the crossing angle θ between the core and the groove is in the range of 0 ° <θ ≦ (90 ° −θc).

  Here, θc is the total reflection complement angle of the core.

  An invention according to claim 4 is an optical coupler comprising a core for propagating signal light, an optical waveguide element comprising a clad covering the core, and a micro optical element for circulating or reciprocating the signal light. A cut surface is formed in the optical waveguide element so as to traverse the core at an angle at which the signal light is totally reflected at the tip of the core, and the micro optical element is brought into close contact with the tip of the core of the cut surface It is an optical coupler characterized by installing.

  The invention according to claim 5 is the optical coupler according to claim 4, wherein the crossing angle θ between the core and the cut surface is in the range of 0 ° <θ ≦ (90 ° −θc).

  Here, θc is the total reflection complement angle of the core.

  According to the present invention, it is possible to stabilize the optical coupling efficiency to the micro optical element by facilitating the control of the incident / exit angle of the signal light to the micro optical element.

  A preferred embodiment of the present invention will be described below in detail with reference to the accompanying drawings.

  FIG. 1 is a top view of an optical coupler according to an embodiment of the present invention. FIG. 2 is a side sectional view of the optical coupler according to the embodiment of FIG. FIG. 3 is a perspective view of the optical waveguide device according to the embodiment of FIG.

  As shown in FIGS. 1 and 2, the optical coupler is configured to circulate or reciprocate signal light with a core (optical waveguide) 10 for propagating signal light, and an optical waveguide element 11 made of a clad covering the core 10. The micro optical element 12 is provided. The optical waveguide element 11 protects the core 10 and confines signal light in the core 10.

  In the optical coupler of the present embodiment, the optical waveguide element 11 is used as means for optical coupling with the micro optical element 12. As shown in FIG. 3, a core 10 is formed inside the optical waveguide element 11. A groove 13 is formed in a part of the optical waveguide element 11, and the tip 10a of the core 10 faces the side wall 13a. The groove 13 is formed at an angle θ with respect to the optical axis A of the core 10 so that the signal light is totally reflected at the boundary surface between the core 10 and the groove 13. The inside of the groove 13 is filled with a transparent medium (not shown) such as air or resin.

  Here, the crossing angle θ between the core 10 and the groove 13 of the optical waveguide element 11 is determined in the range of 0 ° <θ ≦ (90 ° −θc) based on the optical characteristics of the micro optical element 12 to be coupled. Is done. θc (= Arcsin (n0 / n1)) is the complementary angle (critical angle) of the core 10, n0 is the refractive index of the medium filled in the groove 13, and n1 is the refractive index (equivalent refraction) of the core 10. (Not rate).

  The optical waveguide element (cladding) 11 and the core 10 are formed by any of the methods 1) to 5) shown below.

  1) A clad and a core are formed by introducing a dopant such as Ti, Ge, P, B, Er, and Al for controlling the refractive index into quartz glass.

  2) A clad and a core are formed by irradiating quartz glass with laser light.

  3) In a polymer such as polyimide, polyethylene, polystyrene, polyvinyl alcohol, silicone, or an optical resin, the clad and the core are formed by changing the composition.

4) A clad and a core are formed by introducing protons into an electro-optic crystal such as LiNiO ₃ or LiTaO ₃ .

  5) In a mixed crystal of compound semiconductors such as GaAlAsInP and GaAlN, the refractive index is controlled by changing the composition, and the clad and the core are formed.

  In the present embodiment, a core 10 made of quartz glass made of quartz glass as a substrate and made of Ti-doped quartz glass is formed by using a photolithography technique and a dry etching technique, and then the core 10 is made of pure quartz glass. The upper cladding layer 11a (see FIG. 2) was formed by depositing. The refractive index n1 and the cross-sectional shape of the core 10 are arbitrary. In this embodiment, in order to reduce the connection loss with the optical fiber 14 described later, the relative refractive index difference between the core 10 and the clad (optical waveguide element) 11 is 0.3%, and the cross-sectional shape of the core 10 is vertical and horizontal. The square shape was about 10 μm. The core 10 may have a tapered shape in which the diameter of the groove 13 side of the core 10 is increased (see FIG. 4).

  The groove 13 of the optical waveguide element 11 was formed using a photolithography technique and a dry etching technique. The depth D of the groove 13 (see FIG. 2) is equal to or greater than “(thickness of the upper cladding layer 11a) + (thickness of the core 10) / 2 + (spot size of the core 10 (spot size of signal light))”. Set to value. Here, the minimum diameter of the micro optical element 12 is twice the spot size. The widths W1 and W2 (see FIG. 1) of the groove 13 are arbitrary. In the present embodiment, the width W1 is 100 μm and the width W2 is 1 mm.

  As shown in FIG. 2, the micro optical element 12 is disposed in the groove 13 of the optical waveguide element 11. The micro optical element 12 is made of the same material as that of the optical waveguide element (cladding) 11 and the core 10 described above. Alternatively, the micro optical element 12 may be a thin film made of Au, Ag, or the like formed to have a thickness such that surface plasmons on the metal surface can be observed. The micro optical element 12 of the present embodiment is a glass sphere made of quartz glass.

  Here, as a method for fixing the micro optical element 12 to the groove 13 of the optical waveguide element 11, Au is vapor-deposited on a part of the micro optical element 12, and the metal film and solder provided on the bottom surface of the groove 13 are used. It may be fixed or may be fixed by filling the resin from the bottom surface of the groove 13 to less than the height of the core 10.

  The micro optical element 12 is held by the bottom surface of the groove 13 of the optical waveguide element 11, and the depth from the optical axis A of the core 10 to the bottom surface of the groove 13 is from the bottom of the micro optical element 12 to the optical coupling portion 12a. It is set to match the height up to. That is, the height of the optical axis A of the core 10 and the height of the optical coupling part 12a of the micro optical element 12 are set to coincide with each other.

  The distance between the micro optical element 12 and the tip 10a of the core 10 is that the attenuation length of the evanescent wave from the core 10 toward the micro optical element 12 is L1, and the attenuation length of the evanescent wave from the micro optical element 12 toward the core 10 is L2. In this case, the larger one of the attenuation lengths L1 and L2 is set to L0, and is set to be smaller than three times the attenuation length L0. This is because in order to input / output signal light to / from the micro optical element 12, the signal light needs to reach from one of the core 10 or the micro optical element 12 to the other.

  Here, the attenuation lengths L1 and L2 of the evanescent wave are “L1 = λ / (2π · √ ((n1 · cos θ) ^ 2−n0 ^ 2))”, “L2 = λ / (2π · √ ((n2 Cos θ2) ^ 2-n0 ^ 2)) ”. λ is the wavelength of the signal light, n0 is the refractive index of the medium filled in the groove 13 of the optical waveguide element 11, n1 is the refractive index of the core 10, and n2 is the optical coupling portion 12a of the micro optical element 12. The refractive index at the surface, θ is the crossing angle between the core 10 and the groove 13, and θ 2 is the incident angle of the signal light inside the optical coupling portion 12 a of the micro optical element 12. That is, the distance between the micro optical element 12 and the tip 10a of the core 10 is from 0 times the wavelength λ of the signal light to 1 / (2π (max (n1, n2) ^ 2-n0 ^ 2) ^ (− 0.5 )) Just be in the double range.

  As shown in FIGS. 1 and 2, an optical fiber 14 for entering and exiting signal light is bonded to the end portion of the optical waveguide element 11 using a resin so as to face the core 10. When signal light is incident on the core 10 by the optical fiber 14, the signal light (incident light) is totally reflected at the tip 10 a of the core 10 (boundary surface with the groove 13 of the optical waveguide element 11), and the signal is transmitted to the optical fiber 14. Light (emitted light) is emitted. When the signal light (incident light) is totally reflected, an evanescent wave is generated at the tip 10 a of the core 10, and this evanescent wave is input into the micro optical element 12. As a result, optical resonance occurs inside the micro optical element 12 when the resonance wavelength of the micro optical element 12 matches the wavelength of the evanescent wave.

  According to the present embodiment, the incident / exit angle control of the signal light with respect to the micro optical element 12 is controlled by the intersection angle between the groove 13 of the optical waveguide element 11 and the core 10. The groove 13 of the optical waveguide element 11 can be formed with high accuracy by using a photolithography technique and a dry etching technique. These photolithography techniques and dry etching techniques are standard manufacturing techniques used for manufacturing semiconductors and the like. Further, according to the present embodiment, the micro optical element 12 is installed in the groove 13 of the optical waveguide element 11. Thereby, the micro optical element 12 can be held on the bottom surface of the groove 13 and the optical coupling portion 12a of the micro optical element 12 can be stably held at a predetermined height. By doing so, the optical coupler of the present embodiment can stabilize the optical coupling efficiency to the micro optical element 12 by facilitating the control of the incident / exit angle of the signal light to the micro optical element 12. it can.

  In addition, the optical coupler according to the present embodiment can be easily connected to the optical fiber 14 by a normal method, and the size of the coupling portion between the core 10 and the micro optical element 12 is determined when the core 10 is cut obliquely. The cross-sectional area is approximately the same (same as the micro optical element 12), and the device size is small.

  As shown in FIGS. 5 and 6, the shape of the groove 13 of the optical waveguide element 11 may be a groove having a V-shaped cross section. In this case, the groove surface 13 b of the groove 13 is formed with an inclination angle θ inclined with respect to the core 10. The inclination angle θ is determined based on the optical characteristics of the micro optical element 12 in the range of 0 ° <θ ≦ (90 ° −θc). The length W3 of the groove 13 is not particularly limited, and may be formed over the entire width of the optical waveguide element 11, and may be shorter than the groove width W4 as shown in FIGS. good. When the groove 13 is V-shaped, the groove surface 13a of the groove 13 is in contact with the micro optical element 12, so that the stability when the micro optical element 12 is installed is improved.

  Further, as shown in FIGS. 9 to 11, the optical waveguide element 11 may be cut so as to cross the core 10 to form the surface 11b. In this case, the surface 11b is flattened by optical polishing, and the tip 10a of the core 10 is exposed on the surface 11b. Also in this embodiment, the crossing angle θ between the core 10 and the surface 11b of the optical waveguide element 11 is determined based on the optical characteristics of the micro optical element 12 in the range of 0 ° <θ ≦ (90 ° −θc). Is done. As the micro optical element 12, an element in which Au or the like is deposited at least on the tip 10a of the core 10 is used. That is, the micro optical element 12 is disposed in close contact with the tip 10a of the core. In this embodiment, when signal light (incident light) is incident from the optical fiber 14, the signal light (incident light) is totally reflected on the surface of the micro optical element 12 and is reflected on the surface of the micro optical element (metal film) 12. An evanescent wave is generated. The surface plasmon is resonantly excited when the resonance wavelength of the surface plasmon coincides with the wavelength of the evanescent wave. In the case where the optical waveguide element 11 is made of a crystal, the surface 11b may be formed by cleaving along the cleavage plane so as to cross the core 10 without being cut.

  Further, as shown in FIG. 12, the shape of the micro optical element 12 may be a glass disk (cylindrical body). The refractive index distribution inside the micro optical element 12 may change in a concentric manner and a case where it is uniform in the radial direction.

  Further, the optical coupler of this embodiment can be used as an optical coupling / branching circuit having a wavelength filter function. For example, as shown in FIG. 13, an input core 22 and an output core 23 are formed inside the optical waveguide element 21. In this embodiment, two input cores 22 and two output cores 23 are formed. An optical fiber 24 serving as an input port and an optical fiber 25 serving as an insertion port are connected to each input core 22. Each output core 23 is connected to an optical fiber 26 serving as a branch port and an optical fiber 27 serving as a passage port. In such an optical coupler, only the signal light having a wavelength equal to the resonance wavelength of the micro optical element 29 installed in the groove 28 out of the signal light incident from the input port (optical fiber) 24 is branched (optical fiber). The signal light having a wavelength different from the resonance wavelength of the micro optical element 29 is output to the passage port (optical fiber) 27. The insertion port (optical fiber) 25 outputs (adds) signal light having a wavelength equal to the resonance wavelength of the micro optical element 29 to the passage port (optical fiber) 27 and has a wavelength different from the resonance wavelength of the micro optical element 29. It is used for outputting (adding) signal light to a branch port (optical fiber) 26.

It is a top view of the optical coupler which concerns on one embodiment of this invention. It is side surface sectional drawing of the optical coupler which concerns on embodiment of FIG. FIG. 2 is a perspective view of the optical waveguide device according to the embodiment of FIG. 1. It is a top view of the optical coupler which shows the modification of a core. It is a top view of the optical coupler which shows the modification of the groove | channel of an optical waveguide element. It is side surface sectional drawing of the optical coupler which concerns on embodiment of FIG. It is a top view of the optical coupler which shows the modification of the groove | channel of an optical waveguide element. It is side surface sectional drawing of the optical coupler which concerns on embodiment of FIG. It is a top view of the optical coupler which concerns on other embodiment. It is side surface sectional drawing of the optical coupler which concerns on embodiment of FIG. FIG. 10 is a perspective view of the optical waveguide device according to the embodiment of FIG. 9. It is side surface sectional drawing of the optical coupler which shows the modification of a micro optical element. It is a top view of the optical coupler which concerns on other embodiment.

Explanation of symbols

10 core (optical waveguide)
10a tip 11 optical waveguide element (cladding)
12 Micro-optical element 13 Groove 14 Optical fiber

Claims (5)

  An optical coupler comprising a core for propagating signal light, an optical waveguide element made of a clad covering the core, and a micro optical element for circulating the signal light, wherein the optical coupler is formed in a part of the optical waveguide element. An optical coupler, wherein a groove is formed at an angle at which the signal light is totally reflected at the tip of the core, and the micro optical element is installed in the groove. The distance between the micro optical element and the tip of the core is 0 to 1 / (2π (max (n1, n2) ^ 2-n0 ^ 2) ^ (− 0.5)) times the wavelength of the signal light. The optical coupler according to claim 1, which is in the range of
Here, n0 is the refractive index in the groove, n1 is the refractive index of the core, and n2 is the refractive index of the micro optical element. 3. The optical coupler according to claim 1, wherein an intersection angle θ between the core and the groove is in a range of 0 ° <θ ≦ (90 ° −θc).
Here, θc is the total reflection complement angle of the core.   An optical coupler comprising a core for propagating signal light, an optical waveguide element made of a clad covering the core, and a micro optical element for circulating or reciprocating the signal light, and crossing the core A cut surface is formed on the optical waveguide element at an angle at which the signal light is totally reflected at the tip of the core, and the micro optical element is installed in close contact with the tip of the core of the cut surface. An optical coupler. The optical coupler according to claim 4, wherein an intersection angle θ between the core and the cut surface is in a range of 0 ° <θ ≦ (90 ° −θc).
Here, θc is the total reflection complement angle of the core.

Images