JP4118636B2 - Optical functional parts - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical functional component in which an optical functional element made of a dielectric multilayer film or the like is disposed between two gradient index lenses.
[0002]
[Prior art]
As a kind of optical functional component having an optical functional element made of a dielectric multilayer film or the like, an optical functional element such as an optical multiplexing / demultiplexing filter or an optical branching filter is inserted between one end faces of two collimating lenses, Some collimating lenses have an input / output port made of an optical fiber on the other end face side.
[0003]
FIG. 4 shows an example of a conventional optical functional component disclosed in US Pat. No. 6,347,170. The optical functional component 1 shown in FIG. 1 is a WDM (wavelength dispersion multiplexing) type optical multiplexer / demultiplexer, and includes an optical multiplexing / demultiplexing filter 3 for WDM as an optical functional element. On both sides of the optical multiplexing / demultiplexing filter 3, first and second gradient index lenses 2, 4 are arranged as collimating lenses. A gradient index lens (also called a GRIN lens) is a lens having a substantially cylindrical shape and a refractive index distribution in the radial direction in which the refractive index decreases from the optical axis of the lens toward the outer periphery. is there.
[0004]
A first port 5 and a second port 6 made of optical fibers are connected to an end face 2a of the first gradient index lens 2 opposite to the optical multiplexing / demultiplexing filter 3 for input / output. ing. Similarly, a third port 7 made of an optical fiber is connected to the end surface of the second gradient index lens 4 opposite to the optical multiplexing / demultiplexing filter 3.
The end surfaces 2a and 4a of the end surfaces of the ports 5, 6, and 7 and the end surfaces 2a and 4a of the gradient index lenses 2 and 4 facing the ports 5, 6, and 7 are mixed with the light reflected by the end surfaces. In order to prevent this, it is polished so as to be inclined at a predetermined angle (generally within a range of 6 to 8 °) with respect to the optical axis, whereby the reflected light is diverged out of the optical axis. It is like that.
[0005]
This optical multiplexer / demultiplexer 1 functions as follows. First, when wavelength-multiplexed signal light enters from the first port 5, the light is converged by the first gradient index lens 2 and enters the optical multiplexing / demultiplexing filter 3. Since the optical multiplexing / demultiplexing filter 3 passes only light of a certain wavelength and reflects light of other wavelengths among the wavelength multiplexed signal light, the light that can pass through the optical multiplexing / demultiplexing filter 3 is: After passing through the optical multiplexing / demultiplexing filter 3, the light is emitted to the third port 7 through the second gradient index lens 4. The light reflected by the optical multiplexing / demultiplexing filter 3 is reflected by the optical multiplexing / demultiplexing filter 3 and then emitted to the second port 6 via the first gradient index lens 2. In this way, the incident light incident from the first port 5 can be demultiplexed into two outputs emitted from the second and third ports 6 and 7.
[0006]
[Problems to be solved by the invention]
However, in the conventional optical functional parts as described above, as the gradient index lenses 2 and 4, lenses having the same length and the same specifications are used in order to reduce the manufacturing cost. In addition, since the end faces 2a and 4a are obliquely polished, the optical path length in the lens from the first port 5 to the optical multiplexing / demultiplexing filter 3 and reaching the second port 6 (AD + DB in FIG. 4). Is not equal to the optical path length in the lens from the first port 5 through the optical multiplexing / demultiplexing filter 3 to the third port 7 (AD + EC optical path length in FIG. 4). In FIG. 4, points A to E indicate positions where each signal light enters or exits on the end surfaces of the gradient index lenses 2 and 4.
[0007]
For this reason, both the outgoing light from the point B to the second port 6 and the outgoing light from the point C to the third port 7 cannot be set to the same focal length. Coupling efficiency is reduced, causing a loss increase. In particular, in recent years, there has been a problem in an optical multiplexer / demultiplexer for a high-density wavelength division multiplexing communication system that has been introduced in response to an increase in communication capacity.
Conventionally, in order to solve this problem, the lengths of the gradient index lenses 2 and 4 are made shorter than the focal length (0.25 pitch) of the lenses and face the end faces of the ports 5, 6 and 7. The end surfaces of the gradient index lenses 2 and 4 are separated from each other, and their positional relationship is aligned (positioned) so that the loss is as low as possible, and then fixed using an adhesive or the like. .
However, since this method requires alignment in the lens optical axis direction, alignment of the ports 5, 6, and 7 is difficult and time-consuming, and each of the ports 5, 6, and 7 and each gradient index lens is used. When the distance between the end faces of 2 and 4 is increased, in the case of a structure in which an adhesive is filled between the end faces, the performance of the optical functional component is easily affected by a change in volume due to the mechanical strength of the adhesive or a temperature change. Thus, there remains a problem that the stability of the optical characteristics is deteriorated.
[0008]
The present invention has been made in view of the above circumstances, and in the case of a structure that facilitates alignment of each port and is filled with an adhesive between the end surfaces, the end surfaces of each port and each gradient index lens It is an object of the present invention to provide an optical functional component in which the interval can be narrowed, the thickness of the adhesive filled between the end faces is reduced, and the stability of performance is improved.
[0009]
[Means for Solving the Problems]
In order to solve the above problems, the present invention provides a first gradient index lens in which one end face is obliquely polished,
First and second ports connected to the oblique polishing end face of the first gradient index lens;
An optical functional element connected to the other end face of the first gradient index lens;
A second refractive index profile disposed so that one end face is obliquely polished and the other end face is opposed to the other end face of the first gradient index lens with the optical functional element interposed therebetween. Mold lens,
A third port connected to the oblique polishing end face of the second gradient index lens;
Refractive said first and second gradient index lens, together are equal to each other physician at the inclination angle of the swash Me polished end face, the more the length the second of the first gradient index lens The length of the refractive index distribution type lens is shortened, and the first refractive index distribution type lens and the second refractive index distribution type lens have the longest side of the first refractive index distribution type lens and the The second gradient index lens is opposed so as to match the position of the shortest side.
The first port is disposed on the longest side of the first gradient index lens, and the second port is disposed on the shortest side of the first gradient index lens;
The optical path length in the lens from the first port reflected by the optical functional element to the second port is in the lens from the first port through the optical functional element to the third port. Provided is an optical functional component characterized by being made equal to an optical path length.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail based on embodiments.
FIG. 1 is a diagram illustrating an optical multiplexer / demultiplexer according to the present embodiment. In this figure, the optical multiplexer / demultiplexer 1 includes a first refractive index distribution type lens 2, an optical multiplexing / demultiplexing filter 3 for WDM as an optical functional element, and a second refractive index distribution type lens 4. They are arranged in this order.
[0012]
A first port 5 and a second port 6 made of an optical fiber are connected to the end surface of the first gradient index lens 2 on the side opposite to the optical multiplexing / demultiplexing filter 3, respectively. A third port 7 made of an optical fiber is connected to the end surface of the second gradient index lens 4 opposite to the optical multiplexing / demultiplexing filter 3.
In the embodiment shown in FIG. 1, these ports 5, 6, and 7 are fixed and supported by glass capillaries (capillaries) 10 and 11. However, the present invention is not limited to this, and a V-groove substrate or the like may be used to support the ports 5, 6, and 7, and the optical fiber and the lenses 2 and 4 are directly fused and connected. It may be.
[0013]
The positional relationship between the first port 5 and the second port 6 is such that light incident from the first port 5 is emitted from the second port 6 when reflected by the optical multiplexing / demultiplexing filter 3. It is determined. Further, the positional relationship between the first port 5 and the third port 7 is such that the light incident from the first port 5 is emitted from the third port 7 when passing through the optical multiplexing / demultiplexing filter 3. To be determined.
[0014]
The first and second gradient index lenses 2 and 4 are cylindrical lenses having a refractive index distribution in the radial direction, and are a kind of lens called a GRIN lens or a rod lens. These gradient index lenses 2 and 4 are made of multi-component glass such as Selfoc (trademark of Nippon Sheet Glass Co., Ltd.), as well as quartz-based glass described in Japanese Patent Application No. 2001-104929. A gradient index lens or the like can be used without particular limitation.
[0015]
As shown in FIG. 2, the first and second gradient index lenses 2 and 4 are obliquely polished so that one end face is inclined at a predetermined angle with respect to the optical axis Z. The other end face is polished perpendicular to the optical axis Z.
In the present invention, the length of the gradient index lens is the ratio of the length L on the optical axis to the pitch length of the lens, and the inclination angle of the obliquely polished end surface of the gradient index lens is the end surface. Is defined as an angle θ between the normal N and the optical axis Z.
In the optical multiplexer / demultiplexer of the present embodiment, the first and second gradient index lenses 2 and 4 have the same length and the inclination angle θ, and the lens length is 0.23 to 0.25 pitch. The inclination angle θ is 6 to 8 °.
[0016]
The optical multiplexing / demultiplexing filter 3 is a filter element made of a dielectric multilayer film and having a property of reflecting light of a predetermined wavelength band and transmitting light of another predetermined wavelength band. In general, from a dielectric such as SiO ₂ , TiO ₂ , ZrO ₂ , Nb ₂ O ₅ , Ta ₂ O ₅ , a high refractive index component and a low refractive index component are appropriately selected and used, and at a predetermined film thickness, Those in which several to several hundred layers are alternately laminated are used.
[0017]
Furthermore, in the optical multiplexer / demultiplexer 1 according to the present embodiment, as shown in FIG. 1, the shortest sides (upper sides in FIG. 1) of the first and second gradient index lenses 2 and 4 and the most The long sides (bottom sides in FIG. 1) are aligned.
Therefore, the optical path length in the lens from the optical multiplexing / demultiplexing filter 3 to the second port 6 (optical path length between DB in FIG. 1) and the optical path length in the lens from the optical multiplexing / demultiplexing filter 3 to the third port 7 are as follows. The optical path length (the optical path length between ECs in FIG. 1) becomes equal. Accordingly, the optical path length in the lens from the first port 5 to the second port 6 after being reflected by the optical multiplexing / demultiplexing filter 3 (the optical path length of AD + DB in FIG. 1) is the optical path from the first port 5. Equal to the optical path length in the lens from the point B through the demultiplexing filter 3 to the third port 7 (in FIG. 4, the optical path length of AD + EC), and the outgoing light from the point B to the second port 6; The focal lengths from both lens end faces of the light emitted from the point C to the third port 7 can be made the same.
[0018]
As a result, the distance between the end surfaces of the ports 5, 6, 7 and the end surfaces 2a, 4a of the gradient index lenses 2, 4 facing each other can be made extremely small. Since alignment in the axial direction can be omitted, positioning can be done in a short time, and in the case of a structure in which an adhesive is filled between the end faces, the adhesive film thickness can be reduced, so the mechanical strength of the adhesive part As the temperature increases, the thermal expansion and shrinkage of the adhesive decreases. For this reason, the performance of the optical multiplexer / demultiplexer 1 is less likely to change with respect to changes in the environmental temperature, and stability is improved.
[0019]
Next, a manufacturing method of the above-described optical multiplexer / demultiplexer 1 will be described. In addition, the procedure shown below is only an example and does not limit the present invention.
First, the first gradient index lens 2, the optical multiplexing / demultiplexing filter 3, and the second gradient index lens 4 are fixed in this order using an adhesive such as epoxy. At this time, while observing the direction of the inclined surfaces of the end surfaces 2a and 4a of the gradient index lens 2 and the second gradient index lens 4 with a CCD camera, the first and second gradient index lenses 2, The direction is adjusted by rotating the lenses 2 and 4 around the optical axis so that the positions of the shortest side edges and the longest side edges of the four are aligned.
[0020]
Next, the first port 5 is bonded and fixed at a predetermined position on the end surface 2 a of the first gradient index lens 2. Further, the position of the second port 6 is determined and bonded. At this time, while the light is incident from the first port 5, the second port 6 is connected to one end surface of the first gradient index lens 2. The second port 6 is bonded to that position by adjusting the position so that the intensity of the light emitted from the second port 6 is maximized.
Similarly, while the light is incident from the first port 5, the third port 7 is connected to one end surface 4 a of the second gradient index lens 4, and the end-to-end distance between the end surface 2 a and the second port 6. Is aligned so that the intensity of light emitted from the third port 7 is maximized, and the third port 7 is bonded to that position.
By using such a procedure, the ports 5, 6, and 7 can be aligned so that the insertion loss is minimized, and the optical multiplexer / demultiplexer 1 having an extremely small insertion loss can be manufactured.
[0021]
Although the present invention has been described based on the preferred embodiment, the present invention is not limited to this embodiment, and various modifications can be made without departing from the gist of the present invention.
For example, instead of the optical multiplexing / demultiplexing filter 3 having wavelength dependent characteristics, an optical branching / coupling filter having no wavelength dependent characteristics can be used as an optical functional element, so that the optical functional element can be applied to an optical branching coupler.
[0022]
As shown in FIG. 3, the longest side of the first gradient index lens 2 and the shortest side of the second gradient index lens 4 are aligned to face each other, and the first refractive index A configuration in which the optical path length of AD + DB and the optical path length of AD + EC are made equal by making the length of the second refractive index distribution lens 4 shorter than the length of the refractive index distribution lens 2 is also possible.
[0023]
【The invention's effect】
As described above, according to the optical functional component of the present invention, the optical path length from one port on the first gradient index lens side to the other port via the optical functional element is the first refractive index. Since it is made equal to the optical path length from one port on the refractive index distribution lens side to the second refractive index distribution lens side port through the optical functional element, alignment in the lens optical axis direction can be omitted, Since the aligning operation can be performed in a short time, the cost can be reduced. In the case of a structure in which the adhesive is filled between the end faces, the distance between the end face of the optical fiber and the end face of the gradient index lens can be reduced, and the thickness of the adhesive can be reduced. The mechanical strength of the bonded part of the functional part is increased and the stability against temperature change is improved.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing an example of an optical functional component of the present invention.
FIG. 2 is a perspective view for explaining the length and tilt angle of a gradient index lens.
FIG. 3 is a schematic configuration diagram showing another example of the optical functional component of the present invention.
FIG. 4 is a schematic configuration diagram showing an example of a conventional optical functional component.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Optical functional component (optical multiplexer / demultiplexer), 2 ... 1st refractive index distribution type lens, 3 ... Optical functional element (optical multiplexing / demultiplexing filter), 4 ... 2nd refractive index distribution type lens, 5 ... 1st 6 ... second port, 7 ... third port.

Claims (1)

A first gradient index lens whose one end face is obliquely polished;
First and second ports connected to the oblique polishing end face of the first gradient index lens;
An optical functional element connected to the other end face of the first gradient index lens;
A second refractive index profile disposed so that one end face is obliquely polished and the other end face is opposed to the other end face of the first gradient index lens with the optical functional element interposed therebetween. Mold lens,
A third port connected to the oblique polishing end face of the second gradient index lens;
Refractive said first and second gradient index lens, together are equal to each other physician at the inclination angle of the swash Me polished end face, the more the length the second of the first gradient index lens The length of the refractive index distribution type lens is shortened, and the first refractive index distribution type lens and the second refractive index distribution type lens have the longest side of the first refractive index distribution type lens and the The second gradient index lens is opposed so as to match the position of the shortest side.
The first port is disposed on the longest side of the first gradient index lens, and the second port is disposed on the shortest side of the first gradient index lens;
The optical path length in the lens from the first port reflected by the optical functional element to the second port is in the lens from the first port through the optical functional element to the third port. An optical functional component characterized by being equal to the optical path length.

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