JP2003084168A - Lens with multilayer film and optical fiber collimator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lens with a multilayer film and an optical fiber collimator having a high performance, being inexpensive, having a long term stability and a high reliability. SOLUTION: In a lens 1, the one face of the two through which light is made incident and emitted, is flat and the other is a curved face and the lens 1 has a uniform refractive index. In the lens 1, a multilayer film filter 3, through which light having a desired wavelength is passed and unnecessary light is not passed, is formed on a part of or over the whole face of at least one face, and an antireflection layer 2 is formed on the other face, thus a the lens with multilayer film is composed. The lens with multilayer film has the function as a lens in addition to the function as a filter, and a desired property is available while miniaturization and a low cost are achieved by using the lens in an optical fiber collimator of an optical filter module.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lens with a multilayer film and an optical fiber collimator used in an optical module for optical communication in an optical communication system or the like.

[0002]

2. Description of the Related Art Multilayer filters include high-pass filters and low-pass filters that transmit only wavelengths longer or shorter than a specific wavelength, band-pass filters that transmit and block specific wavelengths, and notch-pass filters. , Has a structure that utilizes the interference of light. Specifically, a bandpass filter is a dielectric thin film (H) having a high refractive index, for example, on a substrate such as a glass or plastic material.
Layers) and dielectric thin films (L layers) having a low refractive index are alternately laminated to form a dielectric multilayer film.

WDM (Wavelength Division Multiplex)
ng: wavelength division multiplexing system) In a bandpass filter used in an optical communication system, it is necessary to set the bandwidth of the transmission wavelength to be narrow so as to support higher density wavelength multiplexing. Generally, this bandpass filter is used as a bandpass filter module by placing it between a pair of optical fiber collimators that face each other, but it is necessary to align the optical fiber, lens, and filter parts at predetermined positions. It required a complicated process.

Taking a bandpass filter module as an example,
FIG. 5 shows a configuration example of a conventional optical filter module including a multilayer filter. Ferrules 54A and 54B and optical fibers 56A and 56B, respectively, and a lens 51A,
51B is arranged with its position adjusted so that the outgoing beam has a desired profile (beam diameter and beam waist position) and outgoing direction. This ferrule 54A, 5
Parts in which 4B and lenses 51A and 51B are integrated are referred to as optical fiber collimators 55A and 55B. Further, the multilayer film filter substrate 57 includes optical fiber collimators 55A and 5A.
It is fixed in the metal holder 58 while strictly adjusting the incident angle of the beam emitted from 5B.

At this time, the optical fiber collimator 55A,
The 55B and the multilayer filter substrate 57 require a space for alignment and fixing, which limits the miniaturization of the bandpass filter module. Specifically, the pair of optical fiber collimators cannot be brought close to each other to 10 mm or less, and at this time, the length of the bandpass filter module cannot be 20 mm or less. Moreover, it is necessary to use an expensive and complicated device such as a broadband light source or an optical spectrum analyzer (not shown) for position adjustment such as the alignment.

In the structure of FIG. 5, the optical fiber collimator 5
Multiplexed light emitted from 5A (λ1, ..., λn)
Of the wavelength .lambda.1 is transmitted through the multilayer filter substrate 57 and reaches the opposing optical fiber collimator 55B.

FIG. 6 shows a configuration example of a conventional bandpass filter module having a different structure. The structure of FIG. 6 is
The emitting ferrule 54A has two optical fibers 56A,
It is a two-core optical system having 56C. This means that the light of the transmitted wavelength is emitted to the opposing optical fiber collimator 55B,
The light of the wavelength to be cut off is arranged in parallel in the multilayer filter substrate 5
It is reflected at 7, and is incident on the other optical fiber 56C. 6, the same reference numerals as those in FIG. 5 indicate the same elements.

FIG. 7 shows the detailed structure of the main part of the optical filter module of the two-core optical system shown in FIG. In general, the two-core ferrule 54A has a structure in which the optical fibers 56A and 56C are symmetrically arranged with their centers being 125 μm apart. Then, this optical system is configured as an ideal optical system by disposing the optical fibers 56A and 56C and the multilayer film filter substrate 57 at the focal position (f) of the lens 51, respectively. At this time, the light of the cutoff wavelength can be extracted without separately preparing an optical fiber collimator, and the adjustment can be simplified and downsized.

FIG. 8 shows an example of use of the bandpass filter module shown in FIG. As shown in FIG. 8, by arranging the optical filter modules 59 constituting the bandpass filter module in series, the multiplexed light (λ 1, ..., λ
n) can be distributed to individual wavelengths.

On the other hand, consider a case where a multilayer filter is directly formed on the lens of the conventional example. For example, in a bandpass filter module or the like, since the lens shape is cylindrical, a GRIN (Gradient Index) lens is frequently used because of its ease of use. However, the GRIN lens is a gradient index lens in which the refractive index is gradually lowered from the central axis of the lens toward the periphery, and when a multilayer filter is directly formed on the lens surface, an ideal film structure is formed over the entire surface. Could not be applied.

That is, when a multi-layer film filter having desired characteristics is to be formed, since the lens that is the substrate has an in-plane distribution of the refractive index, a multi-layer film that varies depending on its in-plane position is formed. It is necessary to prepare the structure (material and film thickness), but this is impossible in manufacturing. In addition, even if optimal film formation is performed near the central axis where the beam mainly enters and exits, it is difficult to create a low-loss bandpass filter module because the transmittance decreases in the peripheral portion off the central axis. there were. Therefore, the series arrangement of the bandpass filter modules as shown in FIG. 8 causes a large loss,
It was not applicable to optical communication systems.

Further, the temperature stability of the center wavelength to be transmitted is very important, and the lens as the substrate needs to have a coefficient of thermal expansion larger than that of the film constituent material. On the other hand, if it is too large, there is a problem that the multilayer filter formed on the lens is easily peeled off. The coefficient of thermal expansion of the lens formed as described above must be within a certain limited range. Moreover, the GRIN lens has an in-plane distribution not only in the refractive index but also in this thermal expansion coefficient, and the complicated stress application to the multilayer filter has been a serious problem in temperature stability.

[0013]

As described above, when a multilayer film filter substrate is used in a bandpass filter module or the like, the number of parts increases, the number of man-hours for adjustment increases, the cost increases, and the optical module becomes large. There was a problem.

Further, when the multilayer filter is directly formed on the GRIN lens, it is difficult to obtain desired characteristics because the lens surface which is the substrate has an uneven refractive index distribution. Furthermore, since the lens surface has a non-uniform thermal expansion coefficient, it is not possible to obtain a lens with a multilayer film having good temperature characteristics.

An object of the present invention is to provide a lens with a multilayer film and an optical fiber collimator which are inexpensive, can be miniaturized, can obtain desired characteristics, and are highly reliable.

[0016]

According to the present invention, in a lens with a multilayer film used in an optical module for optical communication, the lens with a multilayer film has a uniform refractive index, and the light from the lens with the multilayer film enters and exits. One of the two surfaces on which is performed is a curved surface and the other surface is a flat surface, and a multilayer film that transmits light of a desired wavelength and does not transmit unnecessary light is provided on part or all of the flat surface. A lens with a multilayer film is provided.

Also provided is a lens with a multilayer film, wherein the lens with a multilayer film is formed of a glass or plastic material.

Further, the present invention is an optical fiber collimator comprising a lens and an optical fiber, wherein the lens with a multilayer film is used as the lens and is used in combination with the optical fiber. I will provide a.

Further, there is provided an optical fiber collimator in which the lens with the multilayer film is arranged on the light emitting side or the light incident side of the optical fiber.

The lens of the present invention may be used as a "single lens" or may form a "lens system" having a desired lens function together with other lenses.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. (First Embodiment) FIG. 1 is a sectional view showing the structure of a lens with a multilayer film according to an embodiment of the present invention.

In the lens with a multilayer film according to the first embodiment, one surface is a flat surface and the other surface is, for example, R (radius) = 1.3 m.
The transparent lens 1 is a curved surface having a curvature of m. This lens 1 is a lens having a uniform refractive index, which is formed of a glass or plastic material. In this lens 1, an antireflection film 2 is formed on one surface having a curvature, and a part or the whole of the other surface which is a flat surface transmits light of a desired wavelength and does not transmit unnecessary light. The feature is that the multilayer filter 3 is formed. In FIG. 1, the chain line represents the optical axis.

FIG. 2 shows the spectral transmittance characteristics of the multilayer filter 3. In this example, a multilayer filter 3 that transmits light centered at a wavelength of 1550 nm and does not transmit other light is directly formed on one surface of the lens 1. In addition, the antireflection film 2 can have a transmittance of 99.5% or more in the entire wavelength range from 1450 nm to 1650 nm.

FIG. 3 shows a structural example of an optical filter module using the lens with a multilayer film shown in FIG. In FIG. 3, the antireflection film 2 and the multi-layer film filter 3 are shown as lenses 1 respectively.
The lens with the multilayer film formed on one surface of the
The optical fiber collimator 5A on the emission side is configured by arranging the surface of the lens 1A having the curvature where the antireflection film 2 is formed on the tip side of the ferrule 4A having one end of the optical fiber 6A built therein. It Further, a lens having an antireflection film 2 formed on both surfaces is used as the lens 1B on the incident side opposed to this, and the surface having the curvature of the lens 1B is arranged at the tip side of the ferrule 4B having one end of the optical fiber 6B built therein. By doing so, the optical fiber collimator 5B on the incident side is configured.

At this time, the ferrules 4A and 4B containing the optical fibers 6A and 6B and the lenses 1A and 1B perform positional adjustment so that the outgoing beam has a desired profile (beam diameter and beam waist position) and outgoing direction. However, at the same time, the angle of incidence on the multilayer film filter 3 formed directly on the lens 1A can be strictly adjusted.
Then, the optical fiber collimators 5A and 5B configured as described above are opposed to each other, and their optical axes are adjusted so that the insertion loss is minimized and fixed in the metal holder 8 to obtain an optical module for optical communication. The optical filter module 9 is constructed.

In this optical filter module 9,
The multiplexed light (λ1, ..., λn) emitted from the optical fiber 6A of the optical fiber collimator 5A is transmitted through the multilayer filter 3 of the lens 1B only at the predetermined wavelength λ1, and the other wavelengths are multilayered. It is reflected by the membrane filter 3 and is not transmitted. The transmitted light of wavelength λ1 reaches the opposing optical fiber collimator 5B and reaches the optical fiber 6
It is incident on B.

The optical filter module having the above structure is shown in FIG.
Spectral transmission characteristics of the optical fiber coupling efficiency of about 0.05
Good loss characteristics were obtained by adding dB. At this time, the distance between the optical fiber collimators 5A and 5B facing each other is 1
A small optical filter module having a length of about 10 mm can be produced by being able to approach each other up to about mm.

In the first embodiment, since the multilayer filter is formed directly on the lens having a uniform refractive index,
It has both a lens function and a filter function, and when the optical filter module is configured, the number of parts can be reduced, and the position adjustment process such as alignment that was conventionally individually adjusted / fixed can be simplified, resulting in high cost for adjustment. Since no special device is required, the cost can be reduced, the manufacturing process can be shortened, and the size can be reduced. In addition, since the lens itself has a uniform refractive index, desired characteristics such as spectral transmittance characteristics due to the multilayer filter can be easily obtained, the transmittance can be improved, and the temperature characteristics can be improved. It is possible to realize a multi-layered lens with a wide operating temperature range. Therefore, it is possible to create an optical module that has high performance and long-term stability and high reliability.

Here, instead of the antireflection film 2, a multilayer film may be provided on the plane of the lens 1B. The surface of the lens with a multilayer film facing the optical fiber is a curved surface, and the curved surface constitutes a spherical lens or an aspherical lens. The curvature of the curved surface of the lens with a multilayer film is preferably such that the wavefront of the light becomes a flat surface in the flat portion after the diffused and emitted light from the optical fiber has passed through the lens with a multilayer film.

Further, in the lens of this embodiment, the surface shape is changed according to the refractive index of the material used in order to achieve the required optical characteristics. In other words, if the surface shape is changed, the material used for the lens is not limited, so that a wide range of materials can be selected and a lens with a multilayer film having stable temperature characteristics can be produced.

FIG. 4 shows an example in which the lens with a multilayer film of this embodiment is applied to an optical fiber collimator of a two-core optical system. The ferrule 4A has two optical fibers 6
A and 6C are built-in, and a multi-layer film in which the anti-reflection film 2 is formed on the curved surface of one side (fiber side) of the lens 1 and the multi-layer film filter 3 is formed on the other plane facing the tip side of the ferrule 4A, respectively. An optical fiber collimator is configured by arranging the lenses.

In this two-core optical system, the optical fiber 6
Of the light emitted from A and incident on the lens 1, a desired wavelength is transmitted through the multilayer filter 3 and emitted, and the other wavelengths are reflected by the multilayer filter 3 and reflected by the other optical fiber 6.
It is incident on C. Even with this configuration, simplification of adjustment and miniaturization can be achieved while maintaining high quality filter characteristics.

Next, a method of forming the multilayer filter according to this embodiment will be described. First, many lenses are aligned and fixed to a jig so that the surface of the lens (without the multilayer filter) to be formed faces the opening, and the lens is installed inside the film forming chamber for vacuum deposition. And it arrange | positions so as to oppose the vapor deposition source in which the vapor deposition material was installed. Then, a vacuum pump (not shown) is evacuated to a required high vacuum state and heated by an electron beam (EB) method or a resistance heating method. By heating and evaporating the thin film material in a high vacuum, the vapor deposition particles are deposited on the surface of the lens to form a thin film.

At this time, ion assist is performed so as to increase the density of the film and prevent the center wavelength of the filter from shifting. By selecting the thin film material, controlling the laminated structure of these films, and controlling the film thickness, a multilayer film filter having desired characteristics can be obtained.

If the multilayer filter is formed in the central portion of the lens (that is, in the vicinity of the portion where the lens surface intersects the optical axis), the optical characteristics can be sufficiently exhibited, and therefore the outer periphery of the lens can be obtained. It is a feature of this method that the characteristics of the optical module are not significantly affected even if the part has a slightly different characteristic from the central part. Depending on the material to be deposited, a vacuum deposition method or a sputtering method may be used.

[0036]

As described above, according to the present invention, it is possible to realize a lens with a multilayer film and an optical fiber collimator which are inexpensive, can be miniaturized, have desired characteristics, and are highly reliable.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a configuration of a lens with a multilayer film according to an embodiment of the present invention.

FIG. 2 is a characteristic diagram showing an example of spectral transmittance characteristics of a multilayer filter.

FIG. 3 is a cross-sectional view showing a configuration example of an optical filter module using a lens with a multilayer film.

FIG. 4 is a sectional view showing a configuration example of an optical filter module of a two-core optical system using a lens with a multilayer film and a two-core ferrule.

FIG. 5 is a cross-sectional view showing a configuration example of a conventional optical filter module using a multilayer film filter substrate.

FIG. 6 is a cross-sectional view showing another configuration example of a conventional optical filter module using a multilayer filter substrate and a two-core ferrule.

FIG. 7 is a configuration explanatory view of the conventional optical filter module of the two-core optical system shown in FIG.

FIG. 8 is a configuration explanatory view showing an example of use of the optical filter module.

[Explanation of symbols]

1, 1A, 1B: Lens 2: Antireflection film 3: Multilayer filter 4A, 4B: Ferrule 5A, 5B: Optical fiber collimator 6A, 6B, 6C: optical fiber 8: Metal holder 9: Optical filter module

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Kenro Miyamura             1-12-1 Yurakucho, Chiyoda-ku, Tokyo Asahi             Glass Co., Ltd. F-term (reference) 2H037 AA01 CA10 CA13 CA18 DA04                       DA05 DA06 DA15 DA31

Claims (4)

[Claims] 1. A multilayer-coated lens used in an optical module for optical communication, wherein the multilayer-coated lens has a uniform refractive index, and one of two surfaces on which light from the multilayer-coated lens enters and exits. The lens with a multilayer film has a curved surface and the other surface is a flat surface, and a multilayer film that transmits light of a desired wavelength and does not transmit unnecessary light is provided on a part or the entire surface of the flat surface. . 2. The lens with a multilayer film according to claim 1, wherein the lens with a multilayer film is made of a glass or plastic material. 3. An optical fiber collimator comprising a lens and an optical fiber, wherein the lens with a multilayer film according to claim 1 is used as the lens, and the lens is used in combination with the optical fiber. Fiber collimator. 4. The optical fiber collimator according to claim 3, wherein the lens with a multilayer film according to claim 1 or 2 is arranged on a light emitting side or a light incident side of the optical fiber.