JP2003139962A - Optical module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small-sized optical module which is easy to assemble with high productivity. SOLUTION: The optical axes of a 1st gradient index rod lens and a 2nd gradient index rod lens are aligned with each other, the optical axes of a 1st optical fiber and a 2nd optical fiber are made parallel to each other, and the distance between the center of a light projection surface of the 1st lens and the center of a light incidence surface of the 2nd lens is <=0.5 mm. Consequently, an optical function element is a thin-layer element formed directly on an end surface of a 1st or 2nd lens.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical module mainly used in the field of optical communication, and more particularly to an optical module including a collimator composed of an optical fiber and a lens.

[0002]

2. Description of the Related Art In the field of optical communication, an optical functional element is inserted in an optical path when it is necessary to exert some action on light propagating through an optical fiber. Since the light emitted from the optical fiber diverges, a collimator that converts the divergent light into parallel light is often required in order to efficiently enter the light into these optical functional elements. Practically, it is advantageous to construct the system etc. by modularizing the collimator and the optical function element and using them as an optical module. As an example, FIG. 5 shows a typical example of a filter module that demultiplexes light of wavelengths multiplexed in wavelength division multiplexing optical communication.

For example, light in which two wavelengths λ1 and λ2 are multiplexed enters the lens 121 from the optical fiber 111. In this example, the lens 121 is a gradient index rod lens, and the refractive index is distributed in the radial direction of the circular cross section perpendicular to the optical axis. This lens can convert the divergent light emitted from the optical fiber into parallel light by appropriately designing the lens length. A demultiplexing filter 150 is arranged as an optical functional element in contact with the end surface of the lens 121 opposite to the light incident surface (the end surface facing the optical fiber 111). This filter 1
Reference numeral 50 reflects light of wavelength λ1 and transmits light of wavelength λ2. The light reflected by the filter 150 is again reflected by the lens 121.
The light is condensed by and is incident on the optical fiber 113.

On the other hand, the light (wavelength λ2) that has passed through the filter 150 is made incident on the lens 122 and is made incident on the optical fiber 112 in a condensed manner. Generally, the lens 121 and the lens 12
2 has the same characteristics. The filter module 200 is configured by integrating this optical system in one housing 170.

The basic optical system of the collimator used in such a module will be described with reference to FIG. As shown in FIG. 6A, consider a case where point light sources 211 and 213 are placed on the focal plane 281 of the convex lens 221 on the optical axis 201 and at positions apart from the optical axis, respectively. From the geometrical optics point of view, the light from the light source on the focal plane is convex lens 22.
It is converted into parallel light by 1. However, if the position of the light source is not on the optical axis, the direction of the parallel light is inclined with respect to the optical axis according to the position Δ of the light source. These collimated rays are transmitted to the second convex lens 222 having the same focal length as the first convex lens 221.
It goes without saying that the images 212 and 214 are formed at positions symmetrical with respect to the light source with respect to both lenses when the light enters.

The above-mentioned state of light rays is the same even when the lens is a gradient index rod lens as shown in FIG. 6 (b). This lens has a cylindrical shape, and the refractive index is distributed in the radial direction from the center of the cross section. This refractive index distribution n
(R) is ideally expressed by the following equation. n (r) = n ₀ (1- (A / 2) r ² ), where r is the distance from the center axis of the lens, n ₀ is the refractive index on the center axis of the lens, and A ^1/2 is It is a refractive index distribution constant. The meandering period (pitch) P of light rays in this lens is
It is represented by P = 2π / A ^1/2 . Here for simplicity,
A gradient index rod lens having a lens length of 0.25P will be exemplified. In the 0.25P lens, the light emitted from the point light source on the end face is emitted as parallel light. Consider a case where point light sources 311 and 313 are placed on one end surface of the first lens 321 on the optical axis 301 and at positions apart from the optical axis, respectively. When the position of the light source is not on the optical axis, the direction of the parallel light is inclined with respect to the optical axis according to the position Δ of the light source, as in the case of the convex lens. When these parallel rays are incident on the second lens 322 having the same pitch as that of the first lens 321, the image 312, at a position symmetrical to the light source with respect to both lenses,
Tie 314.

The same applies to the case of a convex lens, but when a lens having a finite effective diameter is placed on the same optical axis, if the inter-lens distance L becomes large, a part of the light rays will enter the second lens. become unable.

In the case of the filter module of FIG. 5, two optical fibers 111 and 11 are provided on one end surface of the lens 121.
3 are connected. Since each optical fiber has a finite diameter, at least one optical fiber will be placed away from the central axis of the lens. The light entering and exiting the optical fiber placed away from the central axis of the lens has an angle with respect to the central axis at the other end surface of the lens. However, for example, if the optical axis of the optical fiber 111 coincides with the central axis of the lens 121, the light at the other end of the lens can be emitted in parallel to the central axis of the lens 121, that is, in the direction perpendicular to the lens end surface. However, in this case, a part of the light reflected by the end surface of the lens returns to the optical fiber 111,
This is not desirable in optical communication. Even if such a problem of reflected return light is not taken into consideration, it is not always easy to manufacture the optical module in order to adjust the position of the incident light so that the light is emitted perpendicularly from the lens end surface.

In order to prevent the reflected return light, the end surface of the optical fiber and the surface of the lens facing the optical fiber are processed into an oblique surface with respect to the optical axis, as shown in FIG. That is usually done. The light emitted from the lens also tilts with respect to the optical axis even when entering and exiting from the surface tilted with respect to the optical axis.

In order to collect the light having a certain angle with respect to the central axis of the lens 121 as described above on the end face of the optical fiber 112 and make the incident with low loss, the central axis of the lens 122 is set to the optical fiber 111. A means for inclining the lens 121 in accordance with the angle of the light ray from the optical axis can be considered. This is the reason why the central axes of the lenses 121 and 122 are arranged at an angle in the filter module of FIG.

In order to take such a lens arrangement,
The inner diameter of the sleeve 160 must be made sufficiently larger than the lens diameter in order to secure a space so that the angle can be adjusted.

A method of assembling the filter module 200 will be described. First, two optical fibers 111 and 11
The collimator 201 including the lens 3, the lens 121, and the filter 150 is assembled. The tips of the two optical fibers are inserted into, for example, a two-hole capillary 131, fixed with an adhesive, and then the end faces are polished. This capillary 131 with an optical fiber is inserted into a glass holder 140 covered with a cylindrical metal tube and fixed with an adhesive. The filter 150 is bonded to the end surface of the lens 121, and the lens 121 is also inserted into the glass holder 142 and fixed with an adhesive. Optical fiber 11
1, the position of the capillary 131 and the lens 121 is set to x ₁ , so that the amount of light reflected from the filter 150 and incident on the optical fiber 113 becomes maximum.
Aligning in three directions of y ₁ and z ₁ and fixing by adhesion. Where x ₁ ,
The y ₁ axis is perpendicular to the center axis of the lens 121 and is perpendicular to each other.
One direction, the z ₁ axis, is taken in the optical axis direction of the lens 121.

Next, the collimator 202 including the lens 122 and the optical fiber 112 is assembled. Optical fiber 112 similarly fixed to lens 122 and capillary 132
Is inserted into a common metal holder 144, and is aligned and fixed in the z ₂ axis direction. The z ₂ axis is taken in the optical axis direction of the lens 122.

Next, the two sets of collimators 201 and 202 assembled as described above are combined to assemble the filter module 200. As mentioned above, it is necessary to set the z ₁ axis and the z ₂ axis to be tilted. Light of wavelength λ2 is incident from the optical fiber 111, and the four axes of X, Y, θ _X , and θ _Y are adjusted so that the amount of light coupled to the optical fiber 112 is maximized. Here, the X and Y axes are two directions perpendicular to each other and perpendicular to the central axis of the housing 170, and the θ _X and θ _Y axes are rotation angles around the X axis and the Y axis, respectively. Although the centering of the housing 170 in the central axis direction (Z axis) may be performed, it may be omitted because the work becomes complicated.

On the other hand, since such an optical communication module uses a light beam having a small diameter, it is sensitive to a positional deviation and an angular deviation, and if the angular deviation exceeds 0.02 °, the loss becomes large and the module is used. Can not stand. Such mechanical stability must be maintained, for example, in the operating temperature range, -20 to 70 ° C. For this reason, solder is generally used to fill a relatively large space and to reliably fix lenses and optical fibers. Resin is easy to handle, but it is not suitable because it shrinks during curing and has a large coefficient of thermal expansion.

In the filter module 200, the solder 1 is used to fix the slanted sleeve 160 and the glass holders 140, 142, 144 covered with metal tubes.
80 is used. The solder is poured from a solder injection hole 182 provided in the sleeve 160. The housing 170 and the sleeve 160 are fixed by the resin 190, which also serves to protect the optical fiber.

[0017]

If the position of the light source of the collimator is not on the optical axis of the lens as described above, the direction of the emitted parallel light is inclined with respect to the optical axis. The optical axis of the collimator that collects the parallel light and couples it again to the optical fiber must be inclined with respect to the optical axis of the collimator that emits the parallel light. Therefore, assembling a conventional optical module requires a number of aligning steps including angle aligning as described above, and has a problem that it takes a long time. Further, since the two collimators have to be inclined and fixed to each other, there is a problem that the entire size becomes large and a large space is required inside.

An object of the present invention is to solve the above problems and provide an optical module which is easy to assemble, has high productivity, and is small in size.

[0019]

In the optical module of the present invention, the light emitted from the first optical fiber is converted into parallel light by the first gradient index lens, and the parallel light is emitted from the same lens. It has an optical system which is made incident on a thin-layer optical functional element formed directly on the end face, and the light transmitted through this optical functional element is condensed by a second gradient index lens and made incident on a second optical fiber. The optical axes of the first lens and the second lens substantially coincide with each other, and the optical axis of the tip of the first optical fiber facing the first lens and the second light facing the second lens. The feature is that the optical axis of the fiber tip is almost parallel. By providing this feature, the two collimators of this optical module can make the optical axes of the lens and the optical fiber collinear or parallel to each other, and therefore, no angle alignment is required, so that the optical module can be assembled. It is possible to realize a small-sized optical module that is easy and has little loss.

In the above optical module, the light reflected from the thin-layer optical functional element is condensed by the first lens, and the third optical fiber has an optical axis parallel to the first optical fiber and separated by a predetermined distance. May be included. Even if the number of optical fibers is further increased by one, the configuration of the optical module is basically the same, and in this case as well, it is possible to realize an optical module which is easy to assemble and has a small loss.

In these optical modules, it is desirable that the distance between the center of the light exit surface of the first lens and the center of the light entrance surface of the second lens facing the center is 0.5 mm or less. Further, it is more preferable that the exit side end surface of the first lens or the entrance side end surface of the second lens is in contact with the surface of the thin-layer optical functional element that faces it. Under this condition, the configuration of the optical module is facilitated, and an optical module with extremely small loss can be realized.

The coefficient of thermal expansion of the first or second lens having the thin-layer optical functional element directly formed on the end face is 1.0 to 1.
It is preferably in the range of 2 × 10 ^-5 ° C ^-1 . Under these conditions, the weather resistance of the optical module in which the thin-layer optical functional element is directly formed on the lens end surface is improved, and an optical module having long-term reliability can be obtained.

[0023]

FIG. 1 shows a filter module according to a first embodiment of the present invention. Light of wavelengths λ1 and λ2 is emitted from the optical fiber 11, and the gradient index rod lens 2
Incident on 1. The lens length of the gradient index rod lens 21 is designed so that the light incident from the optical fiber is emitted as parallel light from the end face on the opposite side. The parallel light emitted from the lens 21 is incident on the demultiplexing filter 50 directly formed on the lens end surface as a thin-layer optical functional element. This filter 50 reflects light of wavelength λ1 and
Designed to transmit the light of. The light of λ1 reflected by the filter 50 is condensed by the lens 21, and the optical fiber 13
Incident on. On the other hand, the light transmitted through the filter 50 is condensed by the second gradient index rod lens 22 and is incident on the optical fiber 12.

Here, the optical fiber has a cladding diameter of 125 μm.
The ordinary single mode optical fiber of (1) was used, and the lens used had an outer diameter of 1.8 mm and A ^1/2 = 0.323 mm ⁻¹ . The two-core capillary 31 is made of glass and has an optical fiber insertion hole having a rectangular cross section so that two optical fibers can be inserted close to each other. Therefore, the center-to-center distance of the core of the optical fiber is approximately 125 μm. When these two optical fibers are arranged symmetrically with respect to the center of the lens and light is incident on the lens from one of the optical fibers, the light emitted from the lens is inclined by about 1.8 ° from the optical axis.

The filter 50 is formed directly on the lens 21 by SiO 2.
It was formed by alternately depositing 30 layers each of a dielectric multilayer film composed of ₂ and TiO ₂ . The film structure is λ1 = 1480n
It was designed by setting m and λ2 = 1550 nm.

A method of assembling this filter module will be described below. Assembling is performed in the following procedure. 1. The lens 21 is inserted so that the surface of the sleeve 60, which is made of a glass tube having an inner diameter larger than the outer diameter of the lens by about 10 μm, is the inner side, and the lens 22 is inserted from the other end. The distance between the filter surface and the end surface of the lens 22 is adjusted to a predetermined value, and the lenses 21 and 22 and the sleeve 60 are fixed with an adhesive.

2. 2 core glass capillary 3 in advance
The ends of the optical fibers 11 and 13 are inserted into the optical fiber 1, fixed with an adhesive, and the end faces are ground. 3. The light having the wavelength λ1 = 1480 nm is coupled to the optical fiber 11, the position of the capillary 31 is aligned so that the reflected light from the filter 50 is sufficiently coupled to the optical fiber 13, and the end faces of the capillary 31 and the lens 21 are made of an adhesive material. Fix with 92.

4.1 After inserting and fixing the tip of the optical fiber 12 into the capillary 32 made of glass, the end face is polished. 5. Wavelength λ transmitted from the optical fiber 11 through the filter 50
The light of 2 = 1550 nm is made incident, and the position of the capillary 32 is aligned in the x, y, and z directions so that the amount of light coupled to the optical fiber 12 becomes larger than a predetermined value, and fixed to the lens 22 with an adhesive 92. To do.

6. The sleeve 60 is inserted into the cylindrical metal housing 70. 7. Resin 90 is filled in the housing 70 including the bonding portions of the capillaries 31, 32 and the lenses 21, 22 to fix the sleeve 60 and the housing 70.

Here, an adhesive 92 having a refractive index of 1.46 is used, and reflection of light having wavelengths of 1480 nm and 1550 nm is -40 dB on the optical fiber side of the lenses 21 and 22.
The following gradient index coating was performed in advance. Further, in the above-mentioned alignment method, a predetermined value is set and the amount of light to be combined is adjusted so as to be more than that, but it may be adjusted so that the amount of light is maximized.

The characteristics of the filter module assembled as described above are shown below. The distance between the filter surface and the end surface of the lens 22 (hereinafter, referred to as interlens distance) was changed, and the loss of light incident on the optical fiber 12 was measured. The results are shown in Figure 2. From the figure, it can be seen that the loss sharply increases when the inter-lens distance exceeds 1 mm, but when the distance between the lenses is 1 mm or less, the loss is sufficiently small as less than 1 dB.

The above results show that even if the light emitted from the lens 21 is obliquely emitted with respect to the central axis, it is taken in from the end face of the lens 22 which is close to the distance of 1 mm or less,
It is shown that light substantially parallel to the central axis can be extracted from a position near the center of the opposite end surface of the lens 22. From the above results, it is desirable that the distance between the end faces of the lenses 21 and 22 be 1 mm or less. This distance is preferably as short as possible, and more preferably 0.5 mm or less. In the present invention, the dielectric multilayer film is directly deposited on the lens end surface. In this embodiment, the film thickness is about 25 μm, which is generally several tens of μm or less. If the other lens is brought into close contact with the surface of the multilayer film, the distance between the lenses can be regarded as almost 0, and the loss can be made extremely small.

When a dielectric multilayer film is deposited directly on the end surface of the lens, in order to obtain weather resistance, particularly stable characteristics in the long term against ambient temperature changes, the coefficient of thermal expansion and the dielectric It is desirable that the thermal expansion coefficients of the body multilayer film be the same. In the case of the above-mentioned dielectric multilayer film composed of SiO ₂ and TiO ₂ , the thermal expansion coefficient is about 1.1 × 10 ^-5 ° C.
^-1 . Therefore, the coefficient of thermal expansion of the lens is 1.0 to
It is preferably in the range of 1.2 × 10 ^-5 ° C ^-1 . Even if a combination of materials other than the above is used, a lens having a thermal expansion coefficient in this range may be used.

In the first embodiment (FIG. 1), a demultiplexing filter is used as the thin-layer optical functional element, and an optical module utilizing reflected light and transmitted light from this filter is illustrated. However, the present invention is not limited to this configuration and can be applied to an optical module in which various thin-layer optical function elements are inserted between collimators. For example, a certain wavelength or more as in the above embodiment, or a cut filter that transmits only light of the following wavelengths, a bandpass filter that transmits only a wavelength range of a certain range, or a constant transmittance over a wide wavelength range. A neutral density (ND) filter or the like may be used.

As a second embodiment, an optical module utilizing only transmitted light is shown in FIG. In this case, the capillary 33 on the incident side may also be a single core. In this case, the position of the optical fiber 11 for incident light is adjusted so as to be on the central axis of the lens 21, and the positional deviation is within ± 10 μm. The other assembly process is the same as that of the first embodiment. As the thin-layer optical functional element 52 formed directly on the end surface of the lens, various filters and other elements having a function for transmitted light can be used.

The third embodiment shown in FIG. 4 is functionally similar to the first and second embodiments, but it is easier to assemble. In this optical module, the outer diameter of the capillary 34 that supports the optical fiber 11 for incident light is made to match the outer diameter of the lens 21. Although not particularly specified in the above embodiment, when adjusting the positional relationship between the lens and the optical fiber, it is not preferable to stick the outer periphery of the capillary to the outside of the outer periphery of the lens at the time of adhesion, so normally the outer diameter of the capillary is set to It is set smaller than the outer diameter of the lens. However, on the side of the optical fiber 11 for incident light in which positioning is performed only by mechanical adjustment, it is preferable that the lens and the capillary have the same diameter.
Since the positioning can be performed only by inserting and fixing 1 and the capillary 34 into the sleeve 60, the position adjustment in 5 of the assembling steps described in the first embodiment becomes easy. However, it is necessary to set the positional accuracy of the optical fiber insertion hole of the capillary 34 to about ± 10 μm.

A glass tube was used as the sleeve. This is because it is desirable to be able to see through from the outside in order to adjust the distance between the end faces of the lens, and the coefficient of thermal expansion is close to that of the material of the lens. However, when both lenses and the optical functional element are used in contact with each other, they may be opaque and may be a metal or ceramic tube as long as there is no problem of difference in thermal expansion coefficient.

Further, the means for fixing the two lenses by aligning the axes thereof is not limited to the sleeve (cylindrical). Cross section is V
The objective can be achieved by arranging and fixing both lenses in a U-shaped, U-shaped or semicircular groove.

According to the above assembling procedure, when the two lenses are fixed, the optical axis shift between the two lenses due to variations in the outer diameters of the lenses is not particularly corrected, and only the mechanical fixing is performed. . Further, since the number of times of alignment performed by using light is small, there is an effect that the assembly can be completed in a shorter time than the conventional method.

[0040]

In the optical module of the present invention, since the optical functional element is directly formed on the lens surface, the distance between the lenses can be reduced and the loss is small. Also, since there are few alignment points, the assembly time is shortened. Furthermore, since the optical axes of the two lenses can be made to coincide with each other, the size of the optical module can be reduced.

[Brief description of drawings]

FIG. 1 is a sectional view of an optical module according to a first embodiment of the present invention.

FIG. 2 is a diagram showing characteristics of the first embodiment.

FIG. 3 is a cross-sectional view of the optical module according to the first embodiment of the present invention.

FIG. 4 is a cross-sectional view of the optical module according to the first embodiment of the present invention.

FIG. 5 is a cross-sectional view of a conventional filter module.

FIG. 6 is an explanatory diagram of an optical system of a collimator.

[Explanation of symbols]

11, 12, 13, 111, 112, 113 Optical fibers 21, 22, 121, 122 Gradient index type rod lens 31, 32, 33, 34, 131, 132 Capillary 50, 150 Demultiplexing filter 52 Thin layer optical functional element 60, 160 Sleeve 70, 170 Housing 90, 190 Resin 92 Adhesive 140, 142, 144 Holder 180 Solder 211, 213 Light source 212, 214 Image 221, 222 Convex lens

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Minoru Taniyama             4-7 28 Kitahama, Chuo-ku, Osaka City, Osaka Prefecture             Within Nippon Sheet Glass Co., Ltd. (72) Inventor Ikuto Oyama             4-7 28 Kitahama, Chuo-ku, Osaka City, Osaka Prefecture             Within Nippon Sheet Glass Co., Ltd. F-term (reference) 2H037 AA01 BA22 BA23 BA32 CA16                       CA17 CA18 CA35 DA18                 2H038 AA21 AA23 BA23

Claims (6)

[Claims] 1. A first optical fiber, a first gradient index rod lens for taking in light emitted from the optical fiber from an incident end surface, and converting parallel light into an outgoing end surface, and an incident light. And a thin-layer optical functional element that acts on the parallel light, and light that has passed through the thin-layer optical functional element and is incident on the incident-side end surface and condensed on the end surface of the second optical fiber. In the optical module including the second gradient index rod lens emitted from the second optical fiber and the second optical fiber, the thin-layer optical functional element is on the emission side end face of the first lens or the incidence of the second lens. An optical module, which is directly formed on a side end surface. 2. The optical axes of the first lens and the second lens are substantially coincident with each other, and the optical axes of the first optical fiber and the second optical fiber are substantially parallel to each other. The optical module described. 3. The light reflected from the thin film optical functional element is first
Of the gradient index rod lens, which comprises a third optical fiber having an optical axis substantially parallel to the first optical fiber into which the convergent light which is incident from the emission side end face and is emitted from the incidence side end face is coupled to the end face. Claim 1 or 2 characterized by
Optical module described in. 4. The optical module according to claim 1, wherein the distance between the exit side end surface of the first lens and the incident side end surface of the second lens is 0.5 mm or less. 5. An end surface on the exit side of the first lens or a second end surface of the first lens.
5. The optical module according to claim 1, wherein the incident side end surface of the lens is in contact with the surface of the thin-layer optical functional element facing the lens. 6. The thermal expansion coefficient of the first or second lens having the thin film optical functional element directly formed on the end face thereof is 1.0 to 1.2.
The optical module according to claim ¹ , which is in the range of × 10 ^-5 ° C ^-1 .