JP2004093990A - Optical multiplexer / demultiplexer - Google Patents

Abstract

A loss of an optical multiplexer / demultiplexer due to wavelength dispersion of a collimator lens is reduced.
The first and second collimating lenses (2, 4), an optical multiplexing / demultiplexing element (3) inserted between one end surfaces (2b, 4b) of the collimating lenses (2, 4), and a first collimating lens (2) are provided. A first port provided with first and second ports disposed on the other end surface of the second collimating lens and a third port disposed on the other end surface of the second collimating lens; 5 from the first port 5 to the second port 6 after being reflected by the optical multiplexing / demultiplexing element 3 and from the first port 5 to the third port 7 through the optical multiplexing / demultiplexing element 3 In the optical multiplexer / demultiplexer 1 for multiplexing / demultiplexing lights having different wavelengths by using these two optical paths and the optical multiplexing / demultiplexing element 3, the first and second collimating lenses According to the magnitude of chromatic dispersion of 2, 4, the first and second Changing the optical path length difference of the road.
[Selection diagram] Fig. 1

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical multiplexing / demultiplexing component used in the field of optical communication and optical measurement, and in particular, to an optical multiplexing / demultiplexing device in which an optical multiplexing / demultiplexing element made of a dielectric multilayer film or the like is arranged between two refractive index distribution type lenses. Related to demultiplexing parts.
[0002]
[Prior art]
Conventionally, as one type of optical multiplexing / demultiplexing component having an optical multiplexing / demultiplexing element composed of a dielectric multilayer film, an optical multiplexing / demultiplexing element such as an optical multiplexing / demultiplexing element or an optical branching filter is disposed between one end surfaces of two collimating lenses. And an input / output port made of an optical fiber is arranged on the other end face side of each collimating lens.
[0003]
FIG. 8 shows an example of a schematic configuration of an optical multiplexer / demultiplexer (for example, see US Pat. No. 6,347,170).
The optical multiplexer / demultiplexer 1 shown in FIG. 1 includes an optical multiplexer / demultiplexer 3 made of a dielectric multilayer film or the like, and first and second collimating lenses 2 and 4 arranged on both sides of the optical multiplexer / demultiplexer 3. Have. A first port 5 and a second port 6 made of an optical fiber are connected to an end surface 2a of the first collimating lens 2 opposite to the optical multiplexing / demultiplexing element 3. A third port 7 made of an optical fiber is connected to an end face of the second collimating lens 4 opposite to the optical multiplexing / demultiplexing element 3.
Accordingly, when wavelength-multiplexed light is incident on the first port 5, the light is applied to the optical multiplexing / demultiplexing element 3 via the first collimating lens 2 and is multiplexed by the optical multiplexing / demultiplexing element 3. The light is split and output to one of the second and third ports 6 and 7 according to the wavelength.
[0004]
In the optical multiplexer / demultiplexer 1, as the first and second collimating lenses 2, 4, a refractive index distribution type lens having a pitch of about 0.25 is used. However, the length of one pitch in the gradient index lens is a meandering period of a light beam traveling in the gradient index lens.
As a result, the optical path length in the lens from the first port to the optical multiplexer / demultiplexer 3 after being reflected by the optical multiplexer / demultiplexer 3 and the third path passing through the optical multiplexer / demultiplexer 3 from the first port to the third port. The optical path length in the lens up to the port (excluding the space and the optical path length propagating in the optical multiplexing / demultiplexing element 3) is 0.5 pitch in each case. Therefore, the light diverging from the first port and entering is converged on the lens end face. Therefore, if the positions of the ports 5 to 7 are appropriately selected, the collimating lenses 2 and 4 and the ports 5 to 7 Can be combined with high efficiency.
[0005]
[Problems to be solved by the invention]
In recent years, there has been a strong demand for expanding the communication capacity, and therefore, the wavelength range used for communication has been expanding. The difference in the focal length between the wavelengths cannot be ignored between the signal lights having a large wavelength difference due to the wavelength dispersion of the collimating lenses 2 and 4. For this reason, the light emitted from the collimating lenses 2 and 4 is focused on a position shifted from the end faces of the ports 5 to 7, and there is a problem that the loss is increased.
[0006]
The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide an optical multiplexer / demultiplexer that can reduce a loss due to wavelength dispersion of a collimator lens.
[0007]
[Means for Solving the Problems]
In order to solve the above problems, the present invention provides a first and a second collimating lens,
An optical multiplexing / demultiplexing element inserted between one end faces of these collimating lenses,
First and second ports arranged on the other end face side of the first collimating lens;
A third port disposed on the other end face side of the second collimating lens,
A first optical path that is reflected from the first port to the optical multiplexer / demultiplexer and reaches the second port, and a first optical path that is transmitted from the first port through the optical multiplexer / demultiplexer and reaches the third port. An optical multiplexer / demultiplexer that has two optical paths of two optical paths and multiplexes / demultiplexes light having different wavelengths using the two optical paths and the optical multiplexer / demultiplexer,
A light path length difference between the first and second light paths provided in accordance with a difference in focal length of the light beams having different wavelengths due to wavelength dispersion of the first and second collimating lenses. Provide a corrugator.
[0008]
In such an optical multiplexer / demultiplexer, the first and second collimating lenses are gradient index lenses,
These collimating lenses have their end faces facing the ports obliquely polished, and are arranged so that these obliquely polished end faces are parallel to each other, and the optical path length of the first and second optical paths is reduced. It is different,
It is preferable that, of the lights having different wavelengths, light having a longer focal length in the refractive index distribution type lens passes through the longer one of the two optical paths. Can be used. In this case, the lengths of the first and second gradient index lenses are set to 0.23 to 0.25 times the pitch length for the wavelength of the longer refractive index in the gradient index lens. Is preferred.
[0009]
BEST MODE FOR CARRYING OUT 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 optical multiplexer / demultiplexer 1, a gradient index lens is used as the collimating lenses 2 and 4. The first gradient index lens 2, the optical multiplexer / demultiplexer 3, and the second refractive index The distributed lenses 4 are arranged in this order.
[0010]
A first port 5 and a second port 6 made of an optical fiber are connected to an end face 2a of the first gradient index lens 2 opposite to the optical multiplexing / demultiplexing element 3, respectively. A third port 7 made of an optical fiber is connected to an end face 4 a of the second gradient index lens 4 opposite to the optical multiplexing / demultiplexing element 3.
In the embodiment shown in FIG. 1, these ports 5 to 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 as a means for supporting each of the ports 5 to 7, or an optical fiber is directly fusion-spliced to the lenses 2 and 4. May be.
[0011]
The positional relationship between the first port 5 and the second port 6 is such that when the light incident from the first port 5 is reflected by the optical multiplexing / demultiplexing element 3, the light is emitted from the second port 6. Has been determined. Further, the positional relationship between the first port 5 and the third port 7 is such that when light incident from the first port 5 passes through the optical multiplexing / demultiplexing element 3, the light is emitted from the third port 7. Has been determined.
[0012]
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 also called a GRIN lens or a rod lens. These refractive index distribution type lenses 2 and 4 are made of a multi-component glass such as Selfoc (trademark of Nippon Sheet Glass Co., Ltd.), and a quartz glass described in Japanese Patent Application No. 2001-104929. The refractive index distribution type lens can be used without any particular limitation.
In general, in the gradient index lens, when the length is 0.25 pitch, parallel light is focused on one point, and conversely, light incident from one point is emitted as parallel light. In the present embodiment, a length corresponding to 0.25 pitch is referred to as a focal length of the gradient index lens.
[0013]
As shown in FIGS. 1 and 2, the first and second gradient index lenses 2 and 4 have end faces 2a and 4a facing the ports 5 to 7 at a predetermined angle with respect to the optical axis Z. Obliquely polished so as to be inclined.
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 angle of inclination of the obliquely polished end face of the gradient index lens is Is defined as the angle θ between the normal line N and the optical axis Z.
In the optical multiplexer / demultiplexer 1 of the present embodiment, the first and second gradient index lenses 2 and 4 have the same length and the same inclination angle θ, and the lens length is 0.23 to 0.25 pitch. And the inclination angle θ is 6 to 8 °.
[0014]
The optical multiplexing / demultiplexing element 3 is a filter element made of a dielectric multilayer film and reflecting light of a predetermined wavelength band and transmitting light of another predetermined wavelength band. Generally, a dielectric material such as SiO ₂ , TiO ₂ , ZrO ₂ , Ta ₂ O ₅ , and Nb ₂ O ₅ is used by appropriately selecting a high-refractive-index component and a low-refractive-index component. What alternately laminated several to several hundred layers is used.
[0015]
Further, in the optical multiplexer / demultiplexer 1 according to the present embodiment, as shown in FIG. 1, the first and second gradient index lenses 2 and 4 have their obliquely polished end faces 2a and 4a parallel to each other. Are located in Further, as the optical demultiplexing device 3, transmitted through the predetermined long wavelength components lambda _1, and which reflects a predetermined short wavelength components lambda ₂ is used. The first and third ports 5 and 7 are respectively disposed on the long sides of the gradient index lenses 2 and 4, and the second port 6 is disposed on the short side of the first gradient index lens 2. It is arranged on the side.
[0016]
Thereby, the optical path length of the first optical path (the optical path length of AD + DB in FIG. 1) in the lens from the first port 5 to the optical multiplexing / demultiplexing element 3 and reaching the second port 6 is equal to the It is shorter than the optical path length of the second optical path in the lens (the optical path length of AD + EC in FIG. 1) from the first port 5 to the third port 7 through the optical multiplexing / demultiplexing element 3. Assuming that the distance between the cores of the optical fibers forming the first and second ports 5 and 6 is d, and the inclination angle of the obliquely polished end faces of the first and second gradient index lenses 2 and 4 is θ, the first ΔL (equal to the difference between DB and EC) between the optical path length of the second optical path and the optical path length of the second optical path is represented by the following equation (1).
[0017]
ΔL = dtan θ (1)
[0018]
In the optical multiplexer / demultiplexer according to the present embodiment, the deviation of the focal length of the gradient index lenses 2 and 4 is compensated by the optical path length difference ΔL.
[0019]
FIG. 3 shows an example of the wavelength dependence of the on-axis refractive index of a gradient index lens made of glass containing quartz as a main component. FIG. 4 shows an optimum optical path length (0 .5 pitch, ie twice the focal length).
When lambda ₁ is 1550 nm, lambda ₂ is assumed to be 1480 nm, the length of 0.5 pitch, about 3.29mm relative to lambda _1, because relative lambda ₂ is approximately 3.27Mm, the optical path due to wavelength dispersion The length difference is about 0.02 mm.
Therefore, in order to compensate for the deviation of the focal length due to chromatic dispersion, ΔL is set to about 20 μm. For example, if d = 125 μm and θ = 8 °, ΔL is approximately 17.5 μm according to equation (1).
[0020]
Thus, the optical path length of the first optical path (AD + DB) is approximately 0.5 pitch to the wavelength lambda _2, component of the wavelength lambda ₂ incident from the first port 5, the optical multiplexing and demultiplexing device 3 The light is reflected and converges on the end face 2a of the first gradient index lens 2. Moreover, since the optical path length of the second optical path (AD + EC) is substantially 0.5 pitch to the wavelength lambda _1, wavelength component lambda ₁ incident from the first port 5 transmits light demultiplexing element 3 Then, the light is focused on the end surface 4a of the second gradient index lens 4.
[0021]
Accordingly, the coupling efficiency between the second port 6 and the first gradient index lens 2 and between the third port 7 and the second gradient index lens 4 is improved, and the end face of each collimating lens and the port is improved. Since the distance between them can be made extremely small, a decrease in loss can be suppressed, and in a structure in which the space between the end faces is filled with an adhesive, the amount of the adhesive used is reduced, and the thickness of the adhesive is reduced. It can be made thinner. Therefore, the mechanical strength of the bonded portion is increased, and the stability to a temperature change is improved.
[0022]
Next, a method of manufacturing the optical multiplexer / demultiplexer 1 will be described. Note that the procedure described below is merely an example, and does not limit the present invention in any way.
First, the gradient index lenses 2, 4 having predetermined dimensions and characteristics and the optical multiplexing / demultiplexing element 3 are prepared, and the first gradient index lens 2, the optical multiplexing / demultiplexing element 3, and the second refractive index are provided. The distributed lens 4 is fixed in this order using an adhesive such as an epoxy-based adhesive. At this time, while observing the directions 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 end surfaces 2a and 4a are parallel to each other. The orientation is adjusted by rotating the refractive index distribution type lenses 2 and 4 about the optical axis.
[0023]
Next, the first port 5 is bonded and fixed to a predetermined position on the end surface 2a of the first gradient index lens 2. Further, the position of the second port 6 is determined and bonded. At this time, the second port 6 is connected to one end face of the first gradient index lens 2 while light is incident from the first port 5. 2a, the center is adjusted so that the intensity of the light emitted from the second port 6 is maximized, and the second port 6 is bonded to that position. Similarly, the third port 7 is brought closer to one end face 4a of the second gradient index lens 4 while the light is incident from the first port 5, and the intensity of the light emitted from the third port 7 is increased. And the third port 7 is bonded at that position. By using such a procedure, each of the ports 5, 6, and 7 can be aligned so as to minimize the insertion loss, and the optical multiplexer / demultiplexer 1 having an extremely small insertion loss can be manufactured.
[0024]
FIG. 5 is a diagram illustrating an optical multiplexer / demultiplexer according to the second embodiment. The optical multiplexer / demultiplexer 1 according to the first embodiment is different from the optical multiplexer / demultiplexer 1 in that an optical multiplexer / demultiplexer 3 that reflects a long wavelength component λ ₁ and transmits a short wavelength component λ ₂ is used as the optical multiplexer / demultiplexer 3. And different. Further, the third port 7 on the transmission side is arranged on the short side of the second gradient index lens 4.
Thereby, the long wavelength component λ ₁ passes through the first optical path (the optical path length of AD + DB in FIG. 5) from the first port 5 to be reflected by the optical multiplexing / demultiplexing element 3 and reaching the second port 6. The short wavelength component λ ₂ passes through the second optical path (the optical path length of AD + EC in FIG. 5) from the first port 5 through the optical multiplexing / demultiplexing element 3 to reach the third port 7. At the same time, the optical path length of AD + DB can be made longer than the optical path length of AD + EC.
As shown in FIG. 4, since the long wavelength component λ ₁ has a longer focal length than the short wavelength component λ ₂ , each gradient index lens 2 is formed by the same method as that of the optical multiplexer / demultiplexer 1 of the first embodiment. , 4 and each of the ports 5 to 7 can be improved in efficiency and loss can be reduced.
[0025]
Further, as described in the first embodiment, the distance d between the cores of the first and second ports 5 and 6 and the inclination angle of the obliquely polished end face 2 a of the first gradient index lens 2. By appropriately designing θ, the optical path lengths (AD + DB, AD + EC) of the first and second optical paths are set to approximately 0.5 pitch for each of the wavelengths λ ₁ and λ _{2 of the} light passing through the respective optical paths. It can be made to be.
Thereby, the distance between the end faces between the refractive index distribution type lenses 2 and 4 and the ports 5 to 7 can be reduced, the amount of the adhesive used can be reduced, and the film thickness of the adhesive can be reduced. Become. Therefore, the mechanical strength of the bonded portion is increased, and the stability to a temperature change is improved.
[0026]
FIG. 6 is a diagram illustrating a main part of an optical multiplexer / demultiplexer according to a third embodiment of the present invention. In the optical multiplexer / demultiplexer 1 shown in FIG. 1, a two-core fiber pigtail 12 is used as the first and second ports 5 and 6. The end face of the _two- core fiber pigtail 12 is polished obliquely with an inclination angle θ2 with respect to the optical axis. The angle of inclination theta _2, the inclination angle theta ₁ of the oblique polished end face of the first GRIN lens 2 are labeled with a predetermined difference.
Although not shown in FIG. 6, a third port is arranged on the second refractive index distribution type lens 4 on the side opposite to the optical multiplexing / demultiplexing element 3.
[0027]
In this case, the first port 5 is the inter-end-surface distance between the first gradient index lens 2 is L _1, and the second port 6 is the inter-end-surface distance between the first gradient index lens 2 it is L _2. Since θ ₁ ≠ θ ₂ , L ₁ ≠ L ₂ . Thus, the difference between the _{L 1} and _{L 2} is a optical path length difference [Delta] L.
[0028]
According to the present embodiment, even if lenses having the same length are used as the first and second gradient index lenses 2 and 4, the first port is formed due to the difference between the inclination angles θ ₁ and θ _2. 5 from the first port 5 to the second port 6 after being reflected by the optical multiplexing / demultiplexing element 3 and to the third port (not shown) passing through the optical multiplexing / demultiplexing element 3 from the first port 5 An optical path length difference ΔL can be provided between the first optical path and the second optical path.
Accordingly, by appropriately adjusting θ ₁ and θ ₂ and providing a necessary optical path length difference ΔL, it is possible to compensate for a shift in the focal length due to the wavelength dispersion of the gradient index lens. Therefore, the coupling efficiency between the lens and the port can be improved, and the loss of the optical multiplexer / demultiplexer 1 can be reduced.
[0029]
FIG. 7 is a schematic configuration diagram illustrating an optical multiplexer / demultiplexer according to a fourth embodiment of the present invention. In the optical multiplexer / demultiplexer 1, aspherical lenses are used as the collimating lenses 2 and 4. An optical multiplexing / demultiplexing element 3 is arranged between one end surfaces of the collimating lenses 2 and 4. On the other end face side of the first collimating lens 2, a two-core fiber pigtail 12 having first and second ports 5, 6 is arranged. A single fiber pigtail 13 having a third port 7 is arranged on the other end surface side of the second collimating lens 4.
Although FIG. 7 shows a configuration using an aspheric lens as the first and second collimating lenses 2, a sphere (ball) lens, a spherical lens, or the like can be used instead. .
[0030]
In such an optical demultiplexer 1, from the first port 5 with respect to the different light lambda ₁ and the lambda ₂ wavelength is incident, lambda from the second port 6 demultiplexed ₁ Only emitted. The wavelength dispersion of the collimating lens 2, in the wavelength lambda ₁ light, the wavelength lambda ₂ of the light, the focal length of the collimating lens 2 are different. If this difference in focal length is not compensated for, the loss of reflected light will increase.
[0031]
Therefore, in the present embodiment, it is assumed that the end face 12a of the two-core fiber pigtail 12 facing the first collimating lens 2 is polished obliquely. At this time, the distance .DELTA.L in the optical axis direction between the tip of the first port 5 and the tip of the second port 6 is determined by setting the inclination angle of the end face 12a of the two-core fiber pigtail 12 to .theta. When the distance between the second port 6 and the core of the second port 6 is d, it is expressed by the following equation (2).
[0032]
ΔL = dtan θ (2)
[0033]
Therefore, by setting the inclination angle θ and the interval d between the cores to appropriate values so that ΔL becomes equal to the difference between the focal lengths, the centering of the first and second ports 5 and 6 becomes easy, Loss can be reduced.
The alignment of the first and second ports 5 and 6 can be performed, for example, by the following procedure. First, a light source is connected to the first port 5 and an output monitor is connected to the second port 6. The first port 5 is brought closer to the first collimating lens 2 while the input light from the light source is emitted from the first port 5. At this time, when the two-core fiber pigtail 12 is moved to find a position where the reflected light from the optical multiplexing / demultiplexing element 3 is emitted to the second port 6 with the highest intensity, the position is adjusted to that position. By performing such alignment, it is possible to easily manufacture the optical multiplexer / demultiplexer 1 in which the loss of reflected light is extremely low.
[0034]
As described above, the present invention has been described based on the preferred embodiments. However, the present invention is not limited to only the embodiments, and various modifications can be made without departing from the gist of the present invention.
For example, in the above embodiment, an optical multiplexer / demultiplexer using an optical multiplexer / demultiplexer having reversibility has been described, but an element having no reversibility and having only one of the functions of multiplexing and demultiplexing is used. Thus, a configuration of an optical multiplexer or an optical demultiplexer is also possible.
Further, instead of using the two-core fiber pigtail 12 as the first and second ports 5 and 6, two single-core fiber pigtails can be used. Thus, the positions of the end faces of the single fiber pigtails can be individually aligned.
[0035]
【Example】
In the optical multiplexer / demultiplexer 1 shown in FIG. 1, the transmission wavelength λ ₁ of the optical multiplexer / demultiplexer 3 was 1550 nm, and the reflection wavelength λ ₂ was 1480 nm. The lengths of the gradient index lenses 2 and 4 were set to 0.25 pitch, and the inclination angle θ of the oblique end face was set to 8 °. The core interval d between the first and second ports 5 and 6 was 125 μm.
From the equation (1), the optical path length difference ΔL between the first and second optical paths is 17.5 μm. The difference in focal length between λ ₁ and λ _{2 of} the gradient index lenses 2 and 4 used here was about 20 μm.
[0036]
The loss of the reflected light was 0.09 dB when determined from the ratio of the intensity at a wavelength of 1480 nm propagating through the first port 5 to the intensity at a wavelength of 1480 nm emitted to the third port 7.
The loss of the transmitted light was 0.15 dB as determined from the ratio of the intensity at a wavelength of 1550 nm propagating through the first port 5 to the intensity at a wavelength of 1550 nm emitted to the third port 7.
Thus, the loss of both reflected light and transmitted light could be extremely reduced.
[0037]
【The invention's effect】
As described above, according to the optical multiplexer / demultiplexer of the present invention, the optical path length of the first optical path from the first port to the optical multiplexer / demultiplexer to reach the second port, Using the difference between the optical path length of the second optical path from the port to the third port through the optical multiplexing / demultiplexing element, the difference in the focal length of light passing through each optical path and having different wavelengths is compensated. As a result, the coupling efficiency between the port and the collimating lens can be improved, and a decrease in the loss of the optical multiplexer / demultiplexer can be suppressed.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing a first embodiment of an optical multiplexer / demultiplexer according to the present invention.
FIG. 2 is a perspective view illustrating a length and an inclination angle of a gradient index lens.
FIG. 3 is a graph showing an example of the wavelength dependence of the on-axis refractive index of the gradient index lens.
FIG. 4 is a graph showing an example of the wavelength dependence of a 0.5 pitch length of a gradient index lens.
FIG. 5 is a schematic configuration diagram showing a second embodiment of the optical multiplexer / demultiplexer of the present invention.
FIG. 6 is a schematic configuration diagram showing a third embodiment of the optical multiplexer / demultiplexer of the present invention.
FIG. 7 is a schematic configuration diagram showing a fourth embodiment of the optical multiplexer / demultiplexer of the present invention.
FIG. 8 is a schematic configuration diagram illustrating an example of a conventional optical multiplexer / demultiplexer.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Optical multiplexer / demultiplexer, 2 ... 1st refractive index distribution type lens (collimating lens), 2a ... Oblique grinding | polishing end surface of 1st refractive index distribution type lens, 3 ... Optical multiplexer / demultiplexer, 4 ... 2nd refraction Graded index lens (collimated lens), 4a: Obliquely polished end face of second graded index lens, 5: first port, 6: second port, 7: third port, 12: two-core fiber Pigtail.

Claims (4)

First and second collimating lenses;
An optical multiplexing / demultiplexing element inserted between one end faces of these collimating lenses,
First and second ports arranged on the other end face side of the first collimating lens;
A third port disposed on the other end face side of the second collimating lens,
A first optical path that is reflected from the first port to the optical multiplexer / demultiplexer and reaches the second port, and a first optical path that is transmitted from the first port through the optical multiplexer / demultiplexer and reaches the third port. An optical multiplexer / demultiplexer that has two optical paths of two optical paths and multiplexes / demultiplexes light having different wavelengths using the two optical paths and the optical multiplexer / demultiplexer,
A light path length difference between the first and second light paths provided in accordance with a difference in focal length of the light beams having different wavelengths due to wavelength dispersion of the first and second collimating lenses. Corrugator. The first and second collimating lenses are gradient index lenses,
These collimating lenses have their end faces facing the ports obliquely polished, and are arranged so that these obliquely polished end faces are parallel to each other, and the optical path length of the first and second optical paths is reduced. It is different,
The light having a longer focal length in the gradient index lens among the lights having different wavelengths passes through a longer one of the two optical paths. The optical multiplexer / demultiplexer according to claim 1, wherein The length of the first and second gradient index lenses is 0.23 to 0.25 times the pitch length of the longer wavelength of the focal length lens in the gradient index lens. The optical multiplexer / demultiplexer according to claim 2, wherein The first and second ports are optical fibers of a two-core fiber pigtail, and end faces of the two-core fiber pigtail facing the first collimating lens are polished obliquely at a predetermined angle. The optical multiplexer / demultiplexer according to any one of claims 1 to 3, wherein:

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