JP2002236237A - Optical device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical device in which adjustment of the alignment during assembling is rather easy. SOLUTION: The optical device 10 is equipped with a substrate 11, two optical elements 12 and 13 positioned on the substrate so that the two elements can be optically coupled with each other, and an optical lens assembly 14 disposed on the substrate 11 to optically couple the optical elements with each other. The optical lens assembly 14 is an erect imaging lens system in which the posture of an image A at the object point in the input light is identical to the posture of the image A' formed at the imaging point of the output light side.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical device suitable for use in an optical communication system.

[0002]

2. Description of the Related Art In an optical device used in an optical communication system, an optical element such as a laser diode or a photodetector and an optical element such as an optical fiber coupled to the optical element are connected via an optical lens assembly. Substrates such as silicon have been used for optical coupling to one another.

[0003] IEICE TRANS. ELECTRON., VOL. E80-C, N
O.1 JANUARY Pages 107-111 (1997)
A technique is disclosed in which a laser diode and a single-mode optical fiber receiving light from the laser diode are positioned at a distance from each other on a silicon semiconductor substrate called a silicon platform by using a photolithographic etching technique. I have. According to this conventional technique, both optical elements can be arranged with their optical axes aligned with each other, and an optical lens set can be arranged between the two optical elements so as to match their reference optical axis, which is their optical axis. By accurately arranging the three-dimensional object, the two optical elements can be efficiently and optically satisfactorily optically coupled.

In this type of conventional optical lens assembly, an inverted imaging lens system combining a single or a plurality of optical lenses is used. According to this inverted imaging lens system, for example, when the lens system is arranged so that the light emitting end face of the light emitting element is located at the object point, the light receiving surface of the optical fiber arranged at the imaging point of the lens system An inverted real image is formed. Thereby, as long as the optical axis of the lens system coincides with the reference optical axis of the two optical elements, the two optical elements are optically coupled with the highest coupling efficiency.

[0005]

In the optical lens assembly, when the optical axis of the lens system is shifted in one direction from the reference optical axis of the two optical elements, the object point on the incident light side is shifted. The shift is equal to the shift value φ. However, since the lens system used in the conventional lens assembly is an inverted image forming lens system, the image formed on the object point on the output light side is inverted from the image on the object point.
Therefore, the deviation from the reference optical axis at the image forming point of the lens assembly is twice (2φ) the deviation φ. Therefore, in the optical device using the conventional inverted imaging lens system of the optical lens assembly, the tolerance in positioning the optical lens assembly is relatively small, since high-precision positioning is required, Alignment adjustment during assembly was not easy.

Accordingly, an object of the present invention is to provide an optical device in which alignment adjustment at the time of assembly is easier than before.

[0007]

The present invention adopts the following constitution in order to solve the above points. <Constitution> An optical device according to the present invention comprises a substrate, two optical elements positioned on the substrate so as to be capable of being optically coupled to each other, and an optical device for optically coupling the two optical elements to each other. A lens assembly, wherein the optical lens assembly is an erect imaging lens system.

<Operation> The optical lens assembly of the optical device according to the present invention is an erect imaging lens system. Therefore, the optical axis of the lens system of the lens assembly has a shift of a distance φ in one direction from the reference optical axis of the two optical elements, so that the shift φ on the incident light side of the lens assembly. When this occurs, the image formed on the exit light side of the lens assembly is erect, so that on this exit light side, the deviation with respect to the reference optical axis is two times as in the inverted imaging lens system.
The value does not become twice (2φ), but becomes smaller than twice the value of the deviation between the optical axes.

Therefore, the amount of deviation between the reference optical axis of the two optical elements and the optical axis of the lens system of the lens assembly is greatly increased twice or more on the light exit side of the lens assembly. However, the tolerance in positioning the optical lens assembly is larger than that of the related art.

The optical lens assembly can be obtained by connecting an even number of inverted imaging lens systems, each of which inverts the image of an object point and forms an image, in series with each other. By using a crystal substrate as the substrate and using a photolithographic etching technique, both the optical elements and the lens assembly can be accurately positioned on the substrate. Each of the lens systems can be constituted by lens systems having mutually different optical characteristics.
From the viewpoint of simplification of the configuration and reduction of the manufacturing cost, it is desirable to configure them with a lens system having the same optical characteristics.

The imaging magnification of the optical lens assembly can be set to a value other than 1, but in order to prevent the deviation of the optical axis from expanding and set an allowable error as large as possible, It is desirable that the magnification is 1, that is, the same magnification.

Each of the inverted imaging lens systems of the optical lens assembly includes a diffractive optical element such as a CGH element,
Alternatively, it can be constituted by a refractive lens element.

If necessary, a reflecting means can be inserted in the optical path of the optical lens assembly, thereby making the optical path compact. In each of the inverted imaging lens systems of the optical lens assembly, a real image is handled.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the illustrated embodiments. FIG. 1 is an explanatory diagram showing optical characteristics of an optical lens assembly used for an optical device according to the present invention. Prior to the description along FIG. 1, the optical device according to the present invention will be described below with reference to FIG. 2 showing a specific example 1 of the optical device according to the present invention.

<Example 1> Optical device 10 according to the present invention
Is, for example, a silicon semiconductor crystal substrate as shown in FIG.
1 and two optical elements 12 positioned on the substrate,
13 and an optical lens assembly 14 disposed between the two optical elements.

At the center of the surface 11a of the substrate 11,
A recess having a flat bottom surface 15a;
A recess 15 for accommodating the lens assembly is formed by, for example, an etching process so that the lens assembly 14 is mounted thereon.

The two optical elements 12 and 13 are provided in the recess 1
The optical function surfaces 5 are arranged on the front surface 11a of the substrate 11 so as to face each other with a space between them.

One optical element 12 is, for example, a semiconductor laser serving as a light source, and the other optical element 13 for receiving laser light from a light emitting surface, which is an optical functional surface, is, for example, a single mode optical fiber.

The semiconductor laser 12 is positioned at a predetermined position by a solder pad 16 formed at a predetermined position on the substrate 11 with high precision using, for example, the photolithography etching technique as described in the above-mentioned prior art. ing. Further, the optical fiber 13 has an etching groove 17 formed by using the above-described photolithographic etching technique.
The light receiving end face, which is the optical function surface, is placed inside the semiconductor laser 1.
2 are positioned toward the light emitting surface.

By utilizing the photolithographic etching technique described above, both optical elements 12 and 13 have an effective beam radius at their optical functional surface, for example, of several μm.
Even with a fine optical element such as m, both optical elements can be formed by a passive alignment method using no monitor light without using a so-called active alignment method for positioning the optical elements 12 and 13 using actual monitor light. 12
And 13 can be arranged with high precision so that their optical axes 18 coincide with each other to define the reference optical axis 18. For positioning these optical elements 12 and 13, the above-described active alignment method can be used instead of the passive alignment method.

A lens assembly 14 disposed between the two optical elements 12 and 13 mutually positioned on the substrate 11 so that the optical axes coincide with each other to define a reference optical axis 18.
Are the first to fourth optical lenses 1 in the example shown in FIG.
Three optical substrates 20a, 20b and 20 which incorporate 9a, 19b, 19c and 19d and which are transparent to the light to be handled, such as, for example, quartz, glass plates
c are provided on each other. Each optical substrate 2
As described later, the thickness dimension of 0a to 20c has a thickness dimension corresponding to twice the optical path length of the focal length f of each of the optical lenses 19a to 19d.

The first optical lens 19a is formed on an outer surface which is one surface of the first optical substrate 20a, and the first optical lens 19a is provided between the first optical substrate 20a and the second optical substrate 20b. The second optical lens 19b is formed, and the third optical lens 19c is formed between the second optical substrate 20b and the third optical substrate 20c. Also, the third
The fourth optical lens 19d is formed on the outer surface of the optical substrate 20d.

The second optical lens 19b can be formed on one of the other surface of the first optical substrate 20a and the surface of the second optical substrate 20b which is in contact with the first optical substrate 20a. Further, the third optical lens 19c includes a second optical substrate 20b and a third optical substrate 20 which is in contact with the optical substrate.
c can be formed on any one of the contact surfaces.

Each of the optical lenses 19a to 19d is an image forming lens having a focal point on the incident light side and a focal point on the reflected light side, and is a refraction type optical lens utilizing the refraction phenomenon of light. Can be realized by forming it on a predetermined surface. Also, instead of a refractive optical lens, for example, a CGH element (Computer Gener
(dated Hologram element), a diffractive optical lens utilizing a light diffraction phenomenon can be used.

In handling fine light having a beam spot radius of several μm, each of the optical lenses 19a to 19d is
It is desirable to configure with a GH element. As is well known, a CGH element can form a fine optical lens with high precision by subjecting the optical substrate to an etching process using a photolithographic etching technique. Desired optical characteristics such as a collimating function and an image forming function, which will be described later, can be provided by a combination of the etching masks used for the above.

FIG. 1A shows the optical characteristics of the lens assembly 14 of the first embodiment shown in FIG.
The first to fourth optical lenses 19a to 19b constituting the lens assembly 14 are incorporated in the lens assembly 14 such that the respective optical axes 21 coincide. Therefore,
The optical axis 21 is the optical axis of the lens assembly 14. Also,
In the illustrated example, each of the optical lenses 19a to 19d is an imaging lens having a focal length f equal to each of the incident light side and the output light side. In the example shown in FIG.
The optical path length between 2 and 13 is set to eight times the focal length f.

As described above, each of the optical substrates 20a-20
Since c has a thickness dimension corresponding to an optical path length twice as long as the focal length f, c is between the first optical lens 19a and the second optical lens 19b, and between the second optical lens 19b and the third optical lens 19b. Between the first optical lens 19c and the third optical lens 1
An interval corresponding to an optical path length twice as long as the focal length f is set between 9c and the fourth optical lens 19d.

Therefore, the focus of the semiconductor laser 1 is set such that the focus on the incident light side of the first optical lens 19a becomes the object point.
When located on the second light emitting surface, the laser light emitted from this light emitting surface is converted by the first optical lens 19a into a parallel light beam parallel to the optical axis 21 thereof. The parallel light beam from the first optical lens 19a is
By entering the second optical lens as the incident light 9b, the light is focused on the focal point on the emission light side of the second optical lens 19b, thereby inverting the image A at the object point to the focal point. The inverted real image B is formed. As is apparent from this, the first optical lens 19a and the second optical lens 1
9b constitutes an inverted imaging lens system similar to the conventional one. In the illustrated example, both lenses 19a and 19a
Since the focal position of b is the object point and the imaging point, the imaging magnification of this inverted imaging lens system is 1.

An image obtained by a first inverted imaging lens system including a first optical lens 19a and a second optical lens 19b, that is, an inverted real image is formed by a third optical lens 19a.
c, the second inverted imaging lens system, which is composed of the optical lens 19c and the fourth optical lens 19d and operates as a lens system similar to the first inverted imaging lens system, At the focal position of the optical lens 19d of No. 4, an image is formed as an erect real image A 'obtained by further inverting the inverted real image B.

Therefore, by positioning the light receiving end face, which is the optical function surface of the optical fiber 13, at the image forming point, which is the focal point on the emission light side of the fourth optical lens 19d, the lens assembly 14 forms An erect real image having an image magnification of 1 (that is, 1: 1) can be obtained.
By arranging the optical axis 21 of 4 in accordance with the reference optical axis 18 defined by the two optical elements 12 and 13,
The light from the semiconductor laser 12 can be guided to the optical fiber 13 accurately and with high optical coupling efficiency.

By the way, the height dimension of the image A and the erect image A 'of the lens assembly 14 on the optical axis 21 used in the above description is determined by the reference optical axis 18 by the optical elements 12 and 13, and It means the deviation φ of the lens assembly 14 disposed between the two optical elements from the optical axis 21.

That is, when a shift φ occurs between the reference optical axis 18 and the optical axis 21 of the lens assembly 14,
When a shift φ occurs between the first optical lens 19a on the incident light side and the optical axis 18, the image A is inverted in the single first inverted imaging lens system (19a and 19b). As shown by the inverted real image B, the amount of deviation from the reference optical axis 18 is enlarged to twice (2φ) the reference optical axis 18. However, by the second inverted imaging lens system (19c and 19d) serially coupled to the first inverted imaging lens system, the inverted real image B is further inverted in posture, so that the real image B at the object point Since the erect real image A ′ coincides with the height of the image A, the deviation between the reference optical axis 18 and the optical axis 21 at the light receiving end face of the optical fiber 13 is equal to the deviation amount φ. However, only the amount φ is obtained.

On the other hand, as described above, in the conventional lens assembly comprising a single inverted imaging lens system, two lenses
A double shift will occur. This is because, for example, with respect to the optical axis of the optical elements 12 and 13, when the tolerance of the deviation of the optical axis of the lens assembly parallel to the optical axis is designed to be 10 μm, the single inverted imaging lens system can be used. In the conventional lens assembly described above, when a shift of the optical axis of 5 μm occurs, the shift of the optical axis is 10 μm on the emission light side. Therefore, the shift of the optical axis within 5 μm which is half the allowable error is substantially allowed. It just happens.

On the other hand, according to the lens assembly 14 using the first and second inverted imaging lens systems, when the same tolerance as described above is designed, as described above, Since the imaging magnification of the lens assembly 14 is 1 (that is, the same magnification) and the deviation does not increase, a deviation φ of the optical axis within 10 μm substantially equal to the design permissible error is allowed. It will be.

Therefore, according to the optical device 10 according to the present invention, the substantial tolerance of the deviation of the optical axis of the lens assembly 14 with respect to the reference optical axis by the two optical elements 12 and 13 is enlarged as compared with the related art. Therefore, the alignment adjustment between the optical elements 12 and 13 and the lens assembly 14 becomes easy irrespective of the above-mentioned active alignment method and passive alignment method.

Further, the present invention is particularly effective in providing an inexpensive optical device by adopting a passive alignment method that does not use monitor light, because the permissible error is enlarged as compared with the related art. .

In Example 1, the first inverted imaging lens system (19a and 19b) and the second inverted imaging lens system (19c and 19d) are inverted imaging lens systems having the same optical characteristics. Although the configuration example has been described, each lens system can be configured by an optical lens having a different focal length as long as an imaging magnification of 1 can be obtained, whereby an inverted imaging lens having different optical characteristics can be obtained. The systems can be coupled in series to form a lens assembly similar to that described above.

As long as the imaging magnification does not exceed 2, the imaging magnification of the lens assembly 14 can be set to an arbitrary value of 1 or more. However, in order to obtain a large tolerance, as described above, It is desirable that the imaging magnification of the lens assembly 14 be 1.

EXAMPLE 2 FIG. 3 shows an example in which the first inverted imaging lens system and the second inverted imaging lens system are each constituted by a single imaging lens. Optical device 1 shown in FIG.
10 is the same as that of the first embodiment except for the lens assembly 114, and in FIG. 3, the same components as those of the first embodiment are denoted by the same reference numerals as those of the first embodiment. I have.

In the optical device 110 of the second embodiment, the lens assemblies 114 are formed on both surfaces of a single optical substrate 120, and each has a pair of imaging optics having a focal length f on the incident light side and the outgoing light side. It has lenses 119a and 119b. The two optical lenses 119a and 119b are formed on the optical substrate 120 such that their optical axes 21 are aligned. The thickness dimension of the optical substrate 120 corresponds to an optical path length four times the focal length f of each of the optical lenses 119a and 119b.

In the lens assembly 114, the distance from one optical lens 119a to the light emitting surface of the semiconductor laser 12, that is, the optical path length to the object point is twice the focal length f, and the other optical lens 119b transmits the light from the other optical lens 119b. Fiber 13
Is arranged in the recess 15 so as to be located between the semiconductor laser 12 and the optical fiber 13 such that the distance to the light receiving end face, that is, the optical path length to the image forming point is twice the focal length f.

FIG. 1B shows the optical characteristics of the lens assembly 114 of the embodiment 2 shown in FIG. As described above, the distance to the object point of one of the optical lenses 119a is twice as long as the focal length f.
The distance between a and 119b is four times the focal length f,
Since the distance to the imaging point of the other optical lens 119b is set to twice the focal length f, the semiconductor laser 1
The laser light emitted from the light emitting surface 2 is inverted by the first optical lens 19a at a point separated from the lens by a distance twice the focal length f of the image A at the object point. Form B.

As is apparent from this, the first optical lens 119a alone forms an inverted imaging lens system. The inverted real image B obtained by the first inverted imaging lens system is the same as that of the first optical lens 119a.
Is formed as an erect real image A 'having an imaging magnification of 1 on an image point at a distance of twice the focal length f from the lens, that is, on the light-receiving end face of the optical fiber 13. .

Accordingly, as in the first embodiment, by arranging the optical axis 21 of the lens assembly 114 so as to coincide with the reference optical axis 18 defined by the two optical elements 12 and 13, Can be guided to the optical fiber 13 accurately and with high optical coupling efficiency.

The reference optical axis 18 and the lens assembly 1
Even if the first optical lens 119a on the incident light side has a shift φ with respect to the optical axis 18 as in the first embodiment, the shift φ between the optical axis 21 and the fourth optical axis 21 occurs. The image A on the object point is inverted by the first inverted imaging lens system (119a) (inverted real image B), and the second inverted imaging lens system (1
When the image is inverted again at 19b), the image is formed as an erect image A 'of the same magnification, so that the above-described shift is not enlarged.

Therefore, the alignment of the two optical elements 12 and 13 and the lens assembly 14 can be easily adjusted irrespective of the active alignment method and the passive alignment method. Can be configured with a single lens, so that the configuration can be simplified.

The imaging magnification of the lens assembly 114 can be appropriately changed to be less than 1-2 by changing the object point distance and the image point distance of each of the lenses 119a and 119b. , The bifocal distance f of each lens
Each inverted lens system can be constituted by a lens having different.

<Third Embodiment> As shown in FIG. 4, a reflecting means can be inserted into the optical system of the lens assembly 214 disposed between the optical elements 12 and 13.

In the optical device 210 of the third embodiment shown in FIG. 4, the optical elements 12 and 13
Above, the respective optical axes 18a and 18b are arranged parallel to each other with a distance D and with their respective optical functional surfaces facing the recess 15 of the substrate 11.

The lens assembly 214 disposed on the bottom surface 15a of the recess 15 has an optical substrate 220, and one surface of the optical substrate has a pair of optical lenses 219a and 219a.
9b is formed such that the distance between the lens center points is equal to the distance D from each other. Each of the lenses 219a and 219b has a focal length f on the incident light side and the outgoing light side, as in the specific example 2.

A pair of optical lenses 219a and 219a
19b, the optical axes on the atmosphere side are set so as to be parallel to each other with the distance D from each other, and each optical axis in the optical substrate 220 is
20 are symmetrically bent in directions approaching each other so as to intersect with each other on a reflection surface 223 formed of, for example, a mirror surface formed on the other surface of the surface 20. Due to this bending of the optical axis, light directed from one optical lens 219a to the reflection surface 223 is directed by the reflection surface to the other symmetric optical lens 219b.

As described above, the bent optical lenses 219a and 219b whose optical axes are bent are desirably formed of CGH elements, whereby the optical lenses 219a and 219b having desired optical characteristics can be relatively easily formed. And can be formed with high precision.

The pair of optical lenses 219a and 219b of the lens assembly 214 of the third embodiment has a reflection surface 223 formed in the optical path thereof, and is different from the second embodiment except that the optical axis is bent.
The first optical lens 119 of the lens assembly 114 shown in FIG.
a and the second optical lens 119b.

Accordingly, as shown in FIG. 4, the optical axis of each of the two optical elements 12 and 13 is aligned with the parallel optical axis of each of the pair of optical lenses 219a and 219b. Is arranged on the bottom surface 15 a of the substrate 11, the laser light from the semiconductor laser 12 can be efficiently guided to the light receiving end face of the optical fiber 13.

Further, the inverted real image B similar to that in the embodiment 2 obtained on the reflecting surface 223 by the first inverted imaging lens system comprising one optical lens 219a is converted into the second inverted image formed by the other optical lens 219b. Example 2 on the light receiving end face of the optical fiber 13 by an inverted imaging lens system
Is formed as an erect real image A 'similar to the above. Accordingly, a shift φ is generated between the reference optical axes 18a and 18b and the optical axes parallel to each other of the lens assembly 214, thereby causing the first optical lens 219a on the incident light side.
Thus, even if there is a deviation φ from the optical axis 18a, the image A on the object point becomes the same-size erect image A ′ as in the specific example 2.
Therefore, since the image is formed on the light receiving end face of the optical fiber 13, the above-described shift is not enlarged.

Therefore, according to the optical device 210 of the third embodiment, a compact optical device that can be easily aligned can be realized.

Although the present invention has been described above with reference to a lens assembly composed of two inverted imaging lens systems, the invention is not limited to this, and an even number of inverted lens systems of four or more may be employed. it can. Further, the optical characteristics of the optical lenses constituting each inverted imaging lens system can be changed as appropriate. Also, as described above, the optical characteristics are the same.
Although an example in which two inverted imaging lens systems are combined has been described, the present invention is not limited to this, and a lens assembly can be configured by combining a plurality of inverted imaging lens systems having mutually different optical characteristics.

[0058]

In the optical device according to the present invention, since the optical lens assembly disposed between the two optical elements positioned on the substrate is an erect image forming lens system, the outgoing light side of the lens system is used. Does not become twice the value as in the inverted imaging lens system, and becomes a value smaller than twice the value of the deviation between the optical axes of the two optical elements and the lens assembly. Become. Therefore, the deviation of the optical axis described above is not enlarged to a large double value on the outgoing light side of the lens assembly as in the related art, and the allowable error in the positioning of the optical lens assembly is different from that in the conventional art. It will be larger in comparison.

Therefore, according to the present invention, since the permissible error in the positioning of the optical lens assembly is larger than in the prior art, the alignment accuracy required when positioning the optical lens assembly at a predetermined position is improved. Since the degree is reduced, there is provided an optical device in which alignment adjustment at the time of assembly is easier than before.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing optical characteristics of an erect imaging lens system in an optical lens assembly according to the present invention.

FIG. 2 is a longitudinal sectional view showing a specific example 1 of the optical device according to the present invention.

FIG. 3 is a longitudinal sectional view showing a specific example 2 of the optical device according to the present invention.

FIG. 4 is a longitudinal sectional view showing a specific example 3 of the optical device according to the present invention.

[Explanation of symbols]

 10, 110, 210 Optical device 11 Substrate 12 Semiconductor laser (optical element) 13 Optical fiber (optical element) 14, 114, 214 Lens assembly

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Claims (10)

[Claims] An optical lens assembly includes: a substrate; two optical elements positioned on the substrate so as to be capable of being optically coupled to each other; and an optical lens assembly for optically coupling the two optical elements to each other. An optical device, wherein the optical lens assembly is an erect imaging lens system. 2. The optical device according to claim 1, wherein the optical lens assembly includes an even number of inverted imaging lens systems, each of which inverts an image of an object point to form an image, in series with each other. . 3. The optical device according to claim 1, wherein the substrate is a crystal substrate, and the optical element and the optical lens assembly are positioned on the substrate using a photolithographic etching technique. 4. The optical device according to claim 2, wherein each of the lens systems has optical characteristics equal to each other. 5. An imaging magnification of said optical lens assembly is 1
The optical device according to claim 1, wherein 6. The optical device according to claim 2, wherein each of the inverted imaging lens systems comprises a diffractive optical element. 7. The optical device according to claim 6, wherein the diffractive optical element is a CGH element. 8. The optical device according to claim 2, wherein each of the inverted imaging lens systems comprises a refractive lens element. 9. The optical lens assembly according to claim 1, wherein:
The optical device according to claim 1, further comprising a reflection unit. 10. The optical device according to claim 2, wherein the image formed by each of the inverted image forming lens systems is a real image.