JPH11119006A - Multilayered light attenuation film and optical transmission module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain multilayered light attenuation films which attenuate light to a prescribed light quantity and have functions to suppress or prevent reflection in combination by laminating specific films. SOLUTION: The multilayered light attenuation films are constituted by laminating a first film contg. Cr, NiCr or Ge and a second film contg. SiO2 or MgF2 . Namely, the first layer (Cr film) 101, the second layer (SiO2 ) 102, a third layer (Cr film) 103 and a fourth layer (SiO2 ) 104 are successively formed on a condenser lens 3. SF8 (refractive index 1.785) is used as the glass material of the condenser lens 3. Since the condenser lens 3 is coated with the light attenuation films, the transmitted light of the condenser lens 3 is attenuated down to the prescribed light quantity by absorption of these films. Since the light attenuation films have the functions to suppress and prevent the reflection in combination, there is substantially no return light to a reflection source of a laser. While substrate heating is preferably executed at the time of film formation in terms of reliability, the execution of the coating at ordinary temp. is possible as well.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light attenuation multilayer film and an optical transmission module which can be used, for example, as an optical multilayer film having functions of attenuating transmitted light and suppressing / preventing reflected light. .

[0002]

2. Description of the Related Art Recently, with the rapid spread of computers, high-speed communication has been strongly demanded.
(Local area communication network using light) is being commercialized. In this system, data is exchanged at high speed by connecting between computers or between a computer and peripheral devices such as a printer and a hard disk by an optical fiber link.

FIG. 10 shows an example of an optical transmission module used for such an optical LAN. Hereinafter, the optical transmission module shown in FIG.

That is, as shown in FIG. 1, a laser diode 1 is directly modulated, and a modulated light is emitted from a light emitting unit (light source) 2. The emitted light is narrowed down by passing through the condenser lens 3 and guided into the optical fiber 8. The condenser lens 3 is fixed to a lens holder 4, and the optical fiber 8 can be detached from the ferrule holder 6 together with the ferrule 7. Further, by using the optical axis adjusting holder 5 and the ferrule holder 6, the optical axis can be adjusted so that light is efficiently guided to the optical fiber 8.

Further, since the outer diameter of the ferrule 7 and the inner diameter of the ferrule holder 6 are machined with high precision,
Even if the optical fiber 8 is repeatedly attached and detached together with the ferrule 7, the positioning can be reliably performed, so that a change in the amount of light introduced into the optical fiber 8 due to attachment and detachment can be suppressed.

If such an optical transmission module is used, G
Since high-speed communication on the order of bit / sec is possible and an optical fiber can be attached and detached, a network with extremely high flexibility can be constructed.

[0007] Directly modulated light emitted from the laser diode is condensed by a lens and guided into an optical fiber. As a result, high-speed communication in Gbit / sec order is possible and an optical fiber is detachable, so that a highly flexible network can be constructed.

[0008]

However, in this optical transmission module, it is necessary to make the intensity of the emitted laser light lower than the original light intensity of the laser. This is because the laser light may be directly emitted to the outside when the optical fiber is attached and detached, and this is to ensure safety for eyes. In particular, the output is restricted due to safety standards in the fiber channel standard.

As a means for attenuating light, there is one method for reducing the light emission intensity of the laser itself. However, if the light emission intensity is not increased to some extent, the high-speed response of the laser deteriorates, and to compensate for this, many measures are required in terms of the circuit, resulting in high cost.

[0010] The best one is the transmission module.
By providing a film for attenuating light between the laser of the laser and the optical fiber, there is a possibility that it can be realized with a relatively small increase in cost.

Conventionally, light attenuating films have been widely used in various optical instruments. Usually, a metal film is used as a film material, and light is attenuated by its absorption. However, it is mainly required that the transmittance and the reflectance be constant with respect to the wavelength. FIG. 11 shows a typical metal film material, nichrome (N
i 80%, Cr 20%) ND filter (Neutra
l Indicates the optical characteristics of the Density Filter. Thus, the transmittance and the reflectance can be made constant in a wide wavelength range. Further, by changing the thickness of the nichrome film, the amount of transmission attenuation can be freely controlled. (Reference: "Optical / Thin Film Technology Manual", Optronics Inc., page 265) However, the main purpose of the conventional light attenuating film is to obtain an arbitrary amount of transmitted light, and it is considered to prevent reflected light. Absent. When such a film is coated in the optical path of the optical transmission module, when laser light is incident substantially perpendicularly to the film surface, the reflected light from the film returns to the laser diode. As a result, the oscillation of the laser becomes unstable and the S / N ratio of the optical signal deteriorates. Also, if the film surface is inclined to prevent the reflected light from returning to the laser diode, it is necessary to provide a certain distance between the laser diode and the film, and as a result, the entire module becomes large. It will be.

Therefore, the conventional optical attenuation film has a problem that the optical transmission module cannot be downsized.

The present invention has been made in consideration of such a conventional problem, and provides a light attenuating multilayer film having a function of suppressing or preventing reflection while attenuating light to a predetermined light amount, and a light using the light attenuating multilayer film. It is intended to provide a transmission module.

[0014]

According to a first aspect of the present invention, there is provided a first film containing Cr, NiCr, or Ge;
It is a light attenuation multilayer film in which a second film containing O ₂ or MgF ₂ is laminated.

According to a second aspect of the present invention, there is provided the first aspect including Ge.
And a dielectric film having a refractive index of 1.3 to 2.3.

According to a third aspect of the present invention, the first film is a film containing Cr or NiCr, and the first and second films are alternately laminated to form a four-layer structure. 3. The light-attenuating multilayer film according to claim 1.

According to a fourth aspect of the present invention, the first film is a film containing Ge, and the first and second films are alternately stacked to form a six-layer structure. Item 2. The light-attenuating multilayer film according to Item 1.

According to a fifth aspect of the present invention, there is provided a light emitting source for emitting laser light, a condenser lens for condensing the emitted laser light, an optical transmission path attaching / detaching portion for attaching / detaching an optical transmission path, An optical transmission module comprising the optical attenuation multilayer film according to any one of claims 1 to 4 provided between a light emitting source and the optical transmission path attaching / detaching portion.

[0019]

Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) Here, a first embodiment according to the present invention will be described with reference to FIGS.

FIG. 1 shows the laser beam of the condenser lens 3 (see FIG. 4).
FIG. 3 is a cross-sectional view of a light-attenuating multilayer film 9 coated on a surface on the side of the diode 1. In addition, regarding FIG.
It will be described later.

That is, the multilayer film of the present embodiment
A first layer (Cr film) 101 and a second layer (SiO 2)
₂ layer) 102, 3rd layer (Cr film) 103, 4th layer (Si
O ₂ film) 104.

As shown in the figure, the multilayer film of the present embodiment has a very simple film configuration and is excellent in productivity.

The glass material of the lens 3 is SF8 (refractive index 1.78).
5) is used, and the multilayer film shown in Table 1 is provided thereon. This film configuration is based on the assumption that laser light having a wavelength of 790 nm is incident from above the plane of the paper.

[0025]

[Table 1]

Next, the method of forming the multilayer film shown in Table 1 will be described.
Description will be given with reference to FIG.

FIG. 2 is a schematic view of a vacuum deposition apparatus used for forming a film.

After the lens 100 has been subjected to ultrasonic cleaning, the lens 100 is set in a vacuum evaporation apparatus (vacuum chamber) 201 and evacuated by a vacuum pump 204. The lens 100 is heated to 300 ° C. by the heater 202 while evacuating.
Heating control. After the degree of vacuum reaches 5 × 10 ⁻⁶ torr, the electron gun 203 is used to deposit Cr, Si
O ₂ was alternately heated and melted to perform vapor deposition. At this time,
The thickness control and the film formation rate control of each layer are performed by a quartz crystal sensor (IC6000, manufactured by INFICON) 205.
The deposition rate of SiO ₂ is 1 angstrom /
sec, 3 angstrom / sec.

FIG. 3 shows the optical characteristics of the light attenuating films of Table 1 thus obtained. FIG. 3A shows the wavelength dependence of the transmittance, and FIG. 3B shows the wavelength dependence of the reflectance. The measurement was performed on a monitor flat glass sample on which a film was formed at the same time as coating on the lens.

As described above, a light attenuating film having a transmittance of 22% and a reflectance of 3% was obtained at the target wavelength of 790 nm.
The transmittance and the reflectance are almost constant with respect to the wavelength of 790 ± 50 nm, which indicates that the wavelength variation of the laser which is usually about ± 15 nm can be sufficiently obtained. Also, the transmittance and the reflectance are almost constant in the range of 0 ± 10 ° or more with respect to the incident angle, and the divergence of laser light,
It can sufficiently cope with a change in the incident angle due to the bending of the lens surface.

When the reproducibility of the optical characteristics was examined by performing such a film formation experiment several times, it was confirmed that the variation of the transmittance between batches and within the batch was suppressed to within 2%. Was.

Further, it was confirmed that neither the appearance nor the optical characteristics of the film changed before and after the heat shock test at 80 ° C. and -20 ° C. and the high temperature and high humidity test at 85 ° C. and 95% RH.

The lens coated with the light attenuating film in this manner was incorporated in the light transmitting module shown in FIG. Hereinafter, an example of an optical transmission module using the optical attenuation film according to the present embodiment will be described with reference to FIG.

The laser diode 1 is directly modulated, and modulated light is emitted from the light emitting section (light source) 2. The emitted light is narrowed down by passing through the condenser lens 3 and guided into the optical fiber 8.

Since the condenser lens 3 is coated with the light attenuating film 9, the absorption by the light attenuation film 9 causes the condenser lens 3 to be absorbed.
Is attenuated to a predetermined light amount. Further, since the light attenuating film 9 also has functions of preventing reflection and suppressing light, there is almost no return light of the laser to the light emitting source 2. Condensing lens 3
Is fixed to the lens holder 4.

The optical fiber 8 can be detached from the ferrule holder 6 together with the ferrule 7. Further, by using the optical axis adjusting holder 5 and the ferrule holder 6, the optical axis can be adjusted so that light is efficiently guided to the optical fiber 8.

Further, since the outer diameter of the ferrule 7 and the inner diameter of the ferrule holder 6 are machined with high precision, the optical fiber 8 can be accurately positioned even when it is repeatedly attached and detached together with the ferrule 7.
Fluctuation of the amount of light introduced into the device can be suppressed.

When an optical signal transmission experiment was performed using the optical transmission module having the above-described configuration, no reduction in the SN ratio was observed, and it was confirmed that good performance was obtained. It was also found that the intensity of the laser light emitted from the transmission module was attenuated to a safe level.

That is, it has been proved that the light attenuating film of the present embodiment is very effective for an optical transmission module.

From the viewpoint of reliability, it is desirable to heat the substrate during film formation as in this embodiment, but it is also possible to perform coating at room temperature. Of course, it can be applied to a lens made of plastic. Further, even if the refractive index of the lens is at least in the range of 1.4 to 1.8, the transmittance and the reflectance hardly change even with the same film configuration.

Although it is desirable to coat the optical attenuating film on the lens as in the present invention in order to reduce the size and cost of the module, it is desirable that the optical attenuation film be provided on the optical path between the laser diode and the optical fiber. If so, it may be coated on a portion other than the lens. For example, as shown in FIG. 4B, a glass plate 10 is provided between the laser light emitting section 2 and the condenser lens 3, and the attenuation film 9 is coated on the laser diode 1 side. You may. In FIG. 4B, the same components as those in FIG. 4A are denoted by the same reference numerals.

The method of forming the film is not limited to vapor deposition, but may be, for example, sputtering.

If necessary, an antireflection film such as a MgF ₂ film may be formed on the surface of the light attenuating film opposite to the coating surface.

Although the light attenuating film having a transmittance of about 20% has been described in the present embodiment, the transmittance can be adjusted by increasing or decreasing the thickness of Cr as a result of a more detailed study. . In the multilayer film composed of four layers shown in Table 1, the first and third layers have the same Cr film thickness of 1 to 8 n.
It has been found that when changed to m, the reflectance can be set to 3% or less and the transmittance can be freely set within a range of 65 to 8%. Further, the thickness of the SiO ₂ layer is not limited as shown in Table 1, and the thickness of the second layer is 67 to 200 n.
m, it was confirmed that when the thickness of the fourth layer was in the range of 80 to 175 nm, both effects of transmission attenuation and antireflection could be achieved. Furthermore, instead of SiO ₂ , Mg
Be used F ₂ was confirmed that good performance can be obtained. (Embodiment 2) A second embodiment of the present invention will be described with reference to the drawings.

FIG. 5 shows the laser beam of the condenser lens 3 (see FIG. 4).
FIG. 3 is a cross-sectional view of a light-attenuating multilayer film 9 coated on a surface on the side of the diode 1.

That is, the multilayer film of the present embodiment is
A first layer (NiCr film) 501 and a second layer (Si
An O ₂ film) 502, a third layer (NiCr film) 503, and a fourth layer (SiO ₂ film) 504 are formed in this order.

As shown in the figure, the multilayer film of the present embodiment has a very simple film configuration and is excellent in productivity.

The lens material is SF8 (refractive index: 1.78).
5), and a multilayer film shown in Table 2 is provided thereon. NiCr has a composition ratio of 80% Ni and 20% Cr. This film configuration is based on the assumption that laser light having a wavelength of 790 nm is incident from above the plane of the paper.

[0049]

[Table 2]

The method of forming the multilayer film shown in Table 2 is almost the same as the method described in the first embodiment, and therefore will not be described.

FIG. 6 shows the optical characteristics of the light attenuating films of Table 2 actually formed. FIG. 6A shows the wavelength dependence of the transmittance, and FIG. 6B shows the wavelength dependence of the reflectance. The measurement was performed on a monitor flat glass sample on which a film was formed at the same time as coating on the lens.

As described above, a light attenuating film having a transmittance of 21% and a reflectivity of 3% was obtained at the target wavelength of 790 nm.
The transmittance and the reflectance are almost constant with respect to the wavelength of 790 ± 50 nm, which is sufficient for the wavelength variation of the laser which is usually about ± 15 nm. Also, the transmittance and the reflectance are almost constant in the range of 0 ± 10 ° or more with respect to the incident angle, and can sufficiently cope with the divergence of the laser light and the change of the incident angle due to the bending of the lens surface. .

When the reproducibility of the optical characteristics was examined by performing such a film formation experiment several times, it was confirmed that the variation of the transmittance between batches and within the batch was suppressed to within 2%. Was.

Further, it was confirmed that the appearance and optical characteristics of the film did not change at all before and after the heat shock test at 80 ° C. and −20 ° C. and the high temperature and high humidity test at 85 ° C. and 95% RH.

When the lens coated with the light attenuating film in this way was incorporated in the optical transmission module shown in FIG. 4A and an optical signal transmission experiment was performed, no reduction in the SN ratio was observed. It was confirmed that good performance was obtained. It was also found that the intensity of the laser light emitted from the transmission module was attenuated to a safe level.

That is, it was proved that the light attenuating film of the present embodiment was very effective for use in an optical transmission module.

From the viewpoint of reliability, it is desirable to heat the substrate at the time of film formation as in the present embodiment, but it is also possible to perform coating at room temperature. Of course, it can be applied to a lens made of plastic. Further, even if the refractive index of the lens is at least in the range of 1.4 to 1.8, the transmittance and the reflectance hardly change even with the same film configuration.

The NiCr composition (80% Ni, C
(r20%), which is widely used as an electric resistance material, is inexpensive and is most desirable. However, if the thickness of each layer is optimized, the required characteristics can be realized at least in the range of the Ni ratio of 0 to 80%.

The NiCr of the present embodiment is also C
As in r, the transmittance can be adjusted by increasing or decreasing the film thickness. The film thickness of the SiO ₂ layer is not limited as shown in Table 2, and the film thickness of the second layer is 67%. ~ 200
nm and the thickness of the fourth layer in the range of 80 to 175 nm, it was confirmed that the effects of the transmission attenuation and the anti-reflection were compatible.
Further, it was confirmed that good performance could be obtained even when MgF ₂ was used instead of SiO ₂ as a film material.

Further, it is desirable to coat the optical attenuating film on the lens as in the present invention in order to reduce the size and cost of the module. However, it is desirable that the optical attenuation film be coated on the optical path between the laser diode and the optical fiber. If so, it may be coated on a portion other than the lens. For example, as shown in FIG. 4 (b), a glass plate may be provided between the laser and the condenser lens, and an attenuation film may be coated on the laser diode side.

The method for forming a film is not limited to vapor deposition, and sputtering may be used, for example.

If necessary, an anti-reflection film such as a MgF ₂ film may be formed on the surface of the light attenuating film opposite to the coating surface.

(Embodiment 3) A third embodiment of the present invention will be described with reference to the drawings.

FIG. 7 is a sectional view of a light-attenuating multilayer film coated on the surface of the condenser lens 3 (see FIG. 4) on the laser diode 1 side.

That is, the multilayer film of the present embodiment is
A first layer (Ge film) 701 and a second layer (SiO 2)
₂ ) 702, 3rd layer (Ge film) 703, 4th layer (Si
O ₂ film) 704, fifth layer (Ge film) 705, sixth layer (S
iO ₂ film) 706.

As shown in the figure, the multilayer film of this embodiment has a very simple film configuration and is excellent in productivity.

The glass material of the lens is BK7 (refractive index 1.51)
And a multilayer film shown in Table 3 is provided thereon. This film configuration is based on the assumption that laser light having a wavelength of 790 nm is incident from above the plane of the paper.

[0068]

[Table 3]

The method of forming the multilayer film shown in Table 3 is almost the same as the method described in the first embodiment, and therefore will not be described.

FIG. 8 shows the optical characteristics of the light attenuating films of Table 3 actually formed. FIG. 8A shows the wavelength dependence of the transmittance, and FIG. 8B shows the wavelength dependence of the reflectance. The measurement was performed on a monitor flat glass sample on which a film was formed at the same time as coating on the lens.

As described above, a light attenuating film having a transmittance of 19% and a reflectance of 3% was obtained at the target wavelength of 790 nm.
It is sufficient for the wavelength variation of the laser which is usually about ± 15 nm. 0 ± 1 for the incident angle
The transmittance and the reflectance are almost constant in the range of 0 ° or more, and can sufficiently cope with the divergence of the laser light and the change of the incident angle due to the bending of the lens surface.

When the reproducibility of the optical characteristics was examined by performing such a film formation experiment several times, it was confirmed that the variation of the transmittance between batches and within the batch was suppressed to within 2%. Was.

Further, it was confirmed that neither the appearance nor the optical characteristics of the film changed before and after the heat shock test at 80 ° C. and -20 ° C. and the high temperature and high humidity test at 85 ° C. and 95% RH.

When the lens coated with the light attenuating film in this manner was incorporated into the optical transmission module shown in FIG. 4A and an optical signal transmission experiment was carried out, no reduction in the SN ratio was observed. It was confirmed that good performance was obtained. It was also found that the intensity of the laser light emitted from the transmission module was attenuated to a safe level.

That is, it has been proved that the light attenuating film of this embodiment is very effective for an optical transmission module.

From the viewpoint of reliability, it is desirable to heat the substrate at the time of film formation as in this embodiment, but it is also possible to perform coating at room temperature. Of course, it can be applied to a lens made of plastic. Further, even if the refractive index of the lens is at least in the range of 1.4 to 1.8, the transmittance and the reflectance hardly change even with the same film configuration.

In this embodiment, Ge and Cr and Ni are also used.
Like Cr, the transmittance can be adjusted by increasing or decreasing the thickness. The thickness of the SiO ₂ layer is not limited as shown in Table 3, and the thickness of the second layer is 160 ~ 2
When the thickness is 00 nm, the thickness of the fourth layer is in the range of 160 to 200 nm, and the thickness of the sixth layer is in the range of 75 to 110 nm, both effects of transmission attenuation and reflection prevention can be achieved.

Further, it is desirable to coat the optical attenuation film on the lens as in the present invention, in order to reduce the size and cost of the module. However, it is desirable that the optical attenuation film be coated on the optical path between the laser diode and the optical fiber. If so, the coating may be applied to a part other than the lens. For example, as shown in FIG. 4B, a glass plate may be provided between the laser and the condenser lens, and an attenuation film may be coated on the laser diode side.

The method for forming the film is not limited to the vapor deposition, but may be, for example, sputtering.

Further, if necessary, an antireflection film such as a MgF2 film may be formed on the surface of the light attenuating film opposite to the coating surface.

As a result of further detailed examination, when Ge is used as the metal film as in the present embodiment, a dielectric film having a refractive index of 1.3 to 2.3 can be obtained by appropriately setting the thickness of each layer. It has been found that optical characteristics of transmission attenuation and antireflection can be realized for the body. As an example, Tables 4 and 5 show the film configurations when Al ₂ O ₃ or TiO ₂ is used as the dielectric.

[0082]

[Table 4]

[0083]

[Table 5]

FIG. 9 shows the optical characteristics of the actually formed light attenuating films of Tables 4 and 5. FIG. 9A shows the wavelength dependence of the transmittance, and FIG. 9B shows the wavelength dependence of the reflectance.

The optical attenuating film having such a film configuration has no problem in terms of optical characteristics and reliability at all, and a good evaluation result was obtained in a transmission experiment in which the film was incorporated into an optical transmission module. Could be demonstrated.

As described above, by incorporating the optical attenuating multilayer film of the present invention, which has both transmission attenuation and anti-reflection, which is not heretofore known, into the optical transmission module, the transmission of the optical signal is not adversely affected at all. Ray released from module
The light intensity can be attenuated to a level safe for the human body. Compared with other means, it can be realized at much lower cost and can be mass-produced, which greatly contributes to cost reduction and downsizing of the optical transmission module.

In the above embodiment, the light attenuating multilayer film of the present invention has a four-layer structure of the first film and the second film, which is desirable in terms of performance. However, the present invention is not limited to this. A three-layer structure or the like may be used. Even in this case, an optical multilayer film having both functions of attenuation of transmitted light and suppression / prevention of reflected light can be formed.

In the above embodiment, the light attenuating multilayer film of the present invention has a six-layer structure and is desirable in terms of performance. However, the present invention is not limited to this. An optical multilayer film having both functions of suppressing and preventing light can be formed.

[0089]

As is apparent from the above description, the present invention has an advantage that it is possible to provide a light attenuating multilayer film which attenuates light to a predetermined light amount and also has a function of suppressing or preventing reflection.

Further, the present invention has an advantage that the size of the optical transmission module can be further reduced.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a light attenuation film for an optical transmission module according to a first embodiment of the present invention.

FIG. 2 is a schematic diagram of a vacuum deposition apparatus used for film formation.

FIGS. 3A and 3B are optical characteristic diagrams of a light attenuation film according to the first embodiment of the present invention.

FIG. 4A is a schematic view of an optical transmission module in which a light-attenuating film is coated on a condenser lens according to a second embodiment of the present invention. FIG. Schematic diagram of optical transmission module coated with film

FIG. 5 is a sectional view of an optical attenuating film for an optical transmission module according to a second embodiment of the present invention.

FIG. 6A is an optical characteristic diagram showing the wavelength dependence of the transmittance of the light attenuating film according to the second embodiment of the present invention. FIG. 6B is the reflectance of the light attenuating film according to the second embodiment. Of optical characteristics showing wavelength dependence of

FIG. 7 is a sectional view of an optical attenuation film for an optical transmission module according to a second embodiment of the present invention.

FIG. 8A is an optical characteristic diagram showing the wavelength dependence of the transmittance of a light attenuating film when SiO ₂ is used as a dielectric in the third embodiment of the present invention. Characteristic diagram showing the wavelength dependence of the reflectance of the light attenuating film when SiO ₂ is used as the dielectric in the form

FIG. 9A is an optical characteristic diagram showing the wavelength dependence of the transmittance of a light attenuating film when Al ₂ O ₃ or TiO ₂ is used as a dielectric according to the third embodiment of the present invention. b): In the third embodiment of the present invention, the dielectric is made of Al.
Optical characteristic diagram showing the wavelength dependence of the reflectance of the light attenuating film when ₂ O ₃ or TiO ₂ is used

FIG. 10 is a schematic diagram of a conventional optical transmission module.

FIG. 11 is a diagram showing the optical characteristics of a conventional typical light attenuation film.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Laser diode 2 Light emitting part 3 Condensing lens 4 Lens holder 5 Optical axis adjustment holder 6 Ferrule holder 7 Ferrule 8 Optical fiber 9 Light attenuation film 10 Glass plate 101 First layer (Cr film) 102 Second layer (SiO ₂ film) ) 103 third layer (Cr film) 104 fourth layer (SiO ₂ film)

Continued on the front page (51) Int.Cl. ⁶ Identification code FI G02B 6/42 H01S 3/18 H01S 3/18 G02B 1/10 A

Claims (7)

[Claims] 1. A light-attenuating multilayer film comprising a first film containing Cr, NiCr or Ge, and a _second film containing SiO ₂ or MgF ₂ laminated. 2. A first film containing Ge and a refractive index of 1.3.
A light attenuation multilayer film characterized by laminating the dielectric film of (1) to (2.3). 3. The method according to claim 1, wherein the first film is a film containing Cr or NiCr, and the first and second films are alternately stacked to form a four-layer structure. Item 1
The light-attenuating multilayer film as described in the above. 4. The film according to claim 1, wherein the first film is a film containing Ge,
The light attenuating multilayer film according to claim 1, wherein the first and second films are alternately stacked to form a six-layer structure. 5. A light emitting source for emitting laser light, a condenser lens for condensing the emitted laser light, an optical transmission path attaching / detaching portion for attaching / detaching an optical transmission path, the light emitting source and the optical transmission path An optical transmission module comprising: the optical attenuating multilayer film according to claim 1 provided between the optical transmission module and a detachable portion. 6. The optical transmission module according to claim 5, wherein said light-attenuating multilayer film is coated on said condenser lens. 7. The optical transmission module according to claim 5, wherein the optical attenuating multilayer film is arranged so that the laser light is incident from an air layer side.