JPH08227025A - Device for optical communication - Google Patents

Abstract

PURPOSE: To provide a device for optical communication, such as optical multiplexer/demultiplexer, having excellent environmental resistance and reliability. CONSTITUTION: This device for optical communication is used as the optical multiplexer/demultiplexer which introduces the light signal outputted from the other end side of an optical waveguide array 3 having an input/output port array 4 on one end side to a diffraction grating 1 via a lens 2, has this light diffracted by this grating and inputs the light signal diffracted by the diffraction grating 1 via the lens 2 to the other end side of the optical waveguide array 3. The diffraction grating 1 and the lens 2 are fixed into a airtight sealing package 10 consisting of a low-coefft. of thermal expansion material, such as iron-nickel alloy. Further, the diffraction grating 1, the lens 2 and the optical waveguide array 3 are optically coupled via a glass window 11 mounted at a package 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical communication device, and more particularly to a passive device package such as an optical multiplexer / demultiplexer.

[0002]

2. Description of the Related Art Wavelength multiplex communication for efficiently transmitting optical signals of a plurality of channels has been actively studied for future optical communication systems such as backbone systems. Further, the wavelength division multiplex communication can improve the utilization efficiency of the fiber by multiplexing the optical signals having different wavelengths into one fiber. Therefore, as a transmission method for realizing long-distance and large capacity communication in the future, Practical application is expected.

"Optical multiplexing" in which optical signals from a plurality of light sources having different wavelengths are wavelength-multiplexed and bundled in a 1-port fiber,
An optical multiplexer / demultiplexer that performs “optical demultiplexing” that wavelength-demultiplexes multiple wavelength-multiplexed optical signals into multiple ports corresponding to channels of each wavelength is one of the important key devices in wavelength-multiplexed optical communication systems. is there. In order to put wavelength division multiplexing into practical use, it is essential to realize a highly stable optical multiplexer / demultiplexer.

The optical multiplexer / demultiplexer is required to have steep bandpass filter characteristics in high-density wavelength division multiplexing transmission. As a conventional example of such an optical multiplexer / demultiplexer, Applied Optics Vol. 26,
There is a device as shown in FIG. 7 described in No. 11, pp2188, 1987 (known document 1). In this device, the fiber array 103 is fixed to the fiber array holder 102, the diffraction grating 105 is adhesively fixed to the diffraction grating holder 106, and then the two holders 102 and 106 and the lens 104 are fixed.
Are fixed in the cylindrical housing 100.

However, in this structure, the holder 106 is fixed to the cylindrical housing 100 by screwing or using an adhesive or the like as a fixing member. Therefore, the fiber array 103 and the diffraction grating, which are required to have particularly high optical coupling accuracy. In optical coupling with 105, environment (temperature / humidity)
Due to the change, the screwing deviation and the optical axis deviation resulting from the melting and weathering of the adhesive cause a decrease in the bonding accuracy, and there are problems in terms of environmental resistance and reliability.

In addition to such an optical multiplexer / demultiplexer, in optical communication devices, particularly passive devices, in general, optical axis misalignment due to thermal expansion of components due to environmental changes and component fixing are required. The problem of the age resistance and humidity resistance of the adhesive used for this purpose was extremely serious.

[0007]

As described above, the conventional optical communication device has a problem of long-term stability against thermal expansion of the package and environmental changes of the fixing member and the optical component. In optical communication devices such as optical multiplexers / demultiplexers, there is a problem that the optical axis is slightly deviated due to environmental changes, resulting in a decrease in accuracy, although high optical coupling accuracy is required. An object of the present invention is to solve such problems and provide an optical communication device having excellent environmental resistance and reliability.

[0008]

To solve the above problems, the present invention provides an optical communication device having a diffraction grating as a part of its constituent elements, which is made of a material having a low coefficient of thermal expansion and at least shields the diffraction grating from the outside air. It is characterized in that it is provided with a blocking means and an optical coupling means attached to the blocking means for optically coupling the diffraction grating and an optical system provided outside the blocking means.

Further, according to the present invention, in particular, an optical signal output from the other end side of an optical waveguide array having an input / output port array on one end side is guided to a diffraction grating through a lens and diffracted, and diffracted by the diffraction grating. An optical communication device used as an optical multiplexer / demultiplexer for inputting an optical signal to the other end side of an optical waveguide array through a lens, comprising a blocking means which is made of a material having a low coefficient of thermal expansion and which blocks at least a diffraction grating from the outside air. It is characterized by that.

Further, in the optical communication device used as such an optical multiplexer / demultiplexer, the present invention attaches the lens to the blocking means and the other end side of the optical waveguide array provided outside the blocking means. It is characterized in that it further comprises an optical coupling means for optically coupling.

Here, the blocking means is composed of a hermetically sealed package formed by integrally brazing or welding a plurality of members made of a material having a low coefficient of thermal expansion. Also,
The optical coupling means is constructed, for example, by attaching a glass window to an opening formed in a part of the hermetically sealed package.

The low coefficient of thermal expansion material forming the blocking means is
For example, an alloy of iron and nickel, or an alloy of iron, nickel and cobalt is used. Further, it is desirable that the light-transmitting medium near the grating surface of the diffraction grating is a medium such as air or other gas that has a small change in optical length due to a thermo-optical effect.

As described above, according to the present invention, environmental resistance is ensured by shutting off an optical component such as a diffraction grating formed of a resin and a metal thin film, which has a problem in terms of temperature resistance and humidity resistance, from the outside air. . Moreover, by forming the hermetically sealed package, which is the shutoff means, from a material with a low coefficient of thermal expansion such as an alloy of iron and nickel or an alloy of iron, nickel, and cobalt, optical axis misalignment is less likely to occur and high reliability is obtained. To be

Further, if not only the diffraction grating but also the lens is accommodated in the hermetically sealed package, unlike the case where the lens is provided outside the package, it is not necessary to provide a mechanism for holding the lens outside the package, Optical coupling with the optical waveguide array can also be performed through the glass window provided in the package, which simplifies the structure as a whole, facilitates assembly, and further improves optical coupling accuracy. Be advantageous.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, an optical multiplexer / demultiplexer which is an example of an optical communication device according to the present invention will be described with reference to FIG. The optical multiplexer / demultiplexer shown in FIG. 1 includes a diffraction grating 1 and a lens 2.
Also, it is called a Littrow-type multiplexer / demultiplexer configured by arranging the optical waveguide array 3 microscopically. That is, the optical waveguide array 3 is composed of a large number of planar optical waveguides or optical fibers, and has an input / output port array 4 composed of optical fibers at one end thereof. The optical signal input from the input / output port array 4 to one end of the optical waveguide array 3 passes through the optical waveguide array 3 and passes through the optical waveguide array 3
After being output from the other end side of, the light is guided to the diffraction grating 1 through the lens 2 and is diffracted on the grating surface. The optical signal diffracted by the diffraction grating 1 is input to the other end side of the optical waveguide array 3 via the lens 2, passes through the optical waveguide array 3 and is emitted from one end side of the optical waveguide array 3, and then input / output. It is output from the port array 4.

In such an optical multiplexer / demultiplexer, an optical delay is given in the air. If the diffraction condition of the light in the diffraction grating 1 is expressed using an equation, Λ (sinα + sinβ) = ± mλ / n (1) Here, Λ is the grating spacing of the diffraction grating, α and β are the incident angle and diffraction angle of light, λ is the wavelength of light, m is the order of diffraction, and n is the refractive index of air. When the equation (1) is differentiated with respect to the temperature T, it becomes dΛ / dT · (sinα + sinβ) + Λcosβ · dβ / dT = ± mλ / (− n ² ) · dn / dT (2). The first term on the left side of the equation (2) is the influence of the lattice spacing variation on the temperature variation of the diffraction grating 1, the second term on the left side is the variation of the diffraction angle due to the variation of the lattice spacing and the refractive index variation of air, and the right side is the refractive index of air. The fluctuations are shown respectively. The change in the refractive index of air with respect to temperature is described in JCOwens, Applied Optics Vol.6, No.
According to 1, pp. 51, 1967 (known document 2), -2.7 x 10
It is about ^-7 (1 / ° C), which is a sufficiently small value compared to quartz. As described above, since the influence of the change in the refractive index of air is small, it can be seen that the thermal expansion of the diffraction grating 1 mainly affects the transmission characteristics of the optical multiplexer / demultiplexer.

FIG. 2 shows the relationship between the coefficient of thermal expansion of the substrate material of the diffraction grating 1 and the variation ratio of the central transmission wavelength with the temperature of the optical multiplexer / demultiplexer. The transmission bandwidth of the optical multiplexer / demultiplexer is 0.5
nm, the temperature dependence of transmission characteristics is 0.001 nm
It is desirable that the temperature be suppressed below / ° C. Therefore, the thermal expansion coefficient of the substrate material of the diffraction grating 1 is -3.7 × 1.
Those within the range of 0 ^{−7 to} 9.1 × 10 ⁻⁷ (° C. ⁻¹ ) are desirable. Specifically, by selecting a substrate material with a small coefficient of thermal expansion (5.5 × 10 ^-7 (° C ^-1 )) such as quartz, an optical multiplexer / demultiplexer with high stability against temperature can be constructed. it can.

When fixing the diffraction grating 1,
A fixing method that does not give distortion to the diffraction grating 1 is important, and it is desirable that the thermal expansion coefficient of the fixing member does not differ greatly from that of the substrate of the diffraction grating 1. Further, since the wavelength characteristic changes when the incident angle α to the diffraction grating 1 changes, it is necessary to fix each component by a method in which the incident angle does not change due to changes in the outside temperature.

By improving the temperature characteristics of the diffraction grating 1 and its fixing member in this way, not only the loss value of the optical multiplexer / demultiplexer is stabilized, but also the crosstalk value of the optical signal between adjacent channels is significantly stabilized. Turn into. Therefore, the distance between the optical waveguide arrays 3 can be narrowed to realize higher-density wavelength division multiplexing communication.

On the other hand, the grating surface of the diffraction grating 1 is usually formed by adding a thin film of a metal such as aluminum or gold on a metal master grating, and then pressing it onto a blank material coated with resin.
The one that takes a replica is often used because of its cost advantage. Therefore, in order to stabilize the device for a long period of time, in order to prevent weathering of the resin and oxidation of the metal film on the grating surface, it is necessary to hermetically seal the entire diffraction grating 1 with a package filled with argon gas or nitrogen. desirable.

Generally, in the case of performing wavelength division multiplex communication of high density and high speed optical signals, it is possible to avoid the influence of crosstalk between channels having transmission bandwidths and narrow wavelength intervals commensurate with the transmission rate. A steep bandpass characteristic is essential. Therefore, it is difficult to give a large margin to the transmission spectrum with respect to the shift between the center wavelength of the light source and the center transmission wavelength of the corresponding optical multiplexing / demultiplexing characteristics.
The factor that has the greatest effect on this shift is the temperature characteristic of the transmission wavelength. The central transmission wavelength fluctuation of the optical multiplexing / demultiplexing characteristic with respect to the environmental temperature fluctuation should be suppressed to 1/20 or less of the wavelength channel interval. On the other hand, the effect of thermal expansion of the substrate of the diffraction grating 1 on the multiplexing / demultiplexing characteristic is given by the following equation.

Dλ / dT = λ (α + n ⁻¹ · β) (3) However, when the formula (3) is differentiated by the temperature T, the diffraction angle β is fixed and the transmission center wavelength λ is Calculated as variable. Therefore, the substrate material of the diffraction grating 1 is preferably a low thermal expansion material such as quartz, an iron-nickel alloy, or an alloy containing a small amount of cobalt. In the 1.55 μm band optical multiplexer / demultiplexer using a diffraction grating with quartz as the substrate material, the temperature dependence of the transmission wavelength is about 4.3 × 10 ⁻⁴ (nm / ° C.) from equation (3). Become.

Further, when the light transmitting medium near the grating surface of the diffraction grating 1 as shown in FIG. 1, that is, the medium which gives an optical delay is air, a problem is particularly caused by the density of air due to wind or the like. This is because the wavefront of the light wave propagating in the air is disturbed by the change, and the optical multiplexing / demultiplexing characteristic is greatly fluctuated. Therefore, it is desirable to house the diffraction grating 1 in the hermetically sealed package in order to sufficiently reduce the turbulence of the wavefront due to air.

In consideration of the above points, diffraction is performed by a package made of a material having a low coefficient of thermal expansion, for example, an alloy of iron and nickel or an alloy of iron, nickel and cobalt (hereinafter referred to as iron-nickel alloy, iron-nickel-cobalt alloy). Optically coupling the diffraction grating 1 and an optical system outside the package by using a window member that is an optical coupling means that is hermetically sealed in the grating 1 and is attached to the package to input and output an optical signal. As a result, the intended problem of the present invention can be solved.

Next, the configuration of the optical communication device according to this embodiment will be described with reference to FIG. This optical communication device constitutes the optical multiplexer / demultiplexer shown in FIG. In this embodiment, the diffraction grating 1 and the lens 2 are housed inside a box-shaped hermetically sealed package 10. This hermetically sealed package 10 is made of, for example, iron / nickel alloy or iron /
It is made of a low coefficient of thermal expansion material such as a nickel-cobalt alloy. As an iron-nickel alloy, iron 63.5% and nickel 36.
An alloy of 5% can be used, and as the iron-nickel-cobalt alloy, an alloy in which "Invar" contains several% of cobalt, which is known by the trade name of "Super Invar" can be used.

The hermetically sealed package 10 may be integrally formed as a whole, but in this embodiment, as shown in FIG. 4, the outer frame 20 and the bottom plate 21 made of a material having a low coefficient of thermal expansion are brazed with silver solder or the like. , Or integrated by welding and then the outer frame 2
As shown in FIG. 6, a cover 41 is placed on the side opposite to the bottom plate 21 of No. 0, and is integrated by brazing of silver brazing or the like, or welding.

For example, a round opening is provided at the lower end of the hermetically sealed package 10 in the figure, and a glass window 11 for optical coupling with an external optical system is fitted into this opening.
As the material of the glass window 11, quartz glass or zerodur glass, which has a thermal expansion coefficient close to that of iron / nickel alloy or iron / nickel / cobalt alloy, which is the constituent material of the hermetically sealed package 10, is suitable.

The optical waveguide array 3 is fixed by an array holder 12 with one end facing the surface of the hermetically sealed package 10 on which the glass window 11 is provided. An antireflection film may be added to the glass window 11 in order to prevent reflection of light on the surface of the glass window 11, and the optical waveguide array 3 may be fixed obliquely with respect to the optical axis, if necessary. The array holder 12 is fixed to the hermetically sealed package 10 by laser welding. To perform this laser welding fixation,
A pipe-shaped member 22 having an outer diameter substantially equal to that of the array holder 12 is brazed to the glass window 11 of the hermetically sealed package 10, and the array holder 12 is fixed via the pipe-shaped member 22.

The diffraction grating 1 and the lens 2 are hermetically sealed by the optical component holder (not shown), for example.
Is fixed by laser welding while maintaining a predetermined positional relationship on the inner surface of the. In this case, as the material of the hermetically sealed package 10, an alloy capable of laser welding and joining various components is suitable, but the above-mentioned iron / nickel alloy or iron / nickel / cobalt alloy has a low coefficient of thermal expansion. It is suitable for YAG laser welding because it has a low thermal conductivity and a good YAG laser light absorptivity.

Further, the optical component holder on which the diffraction grating 1 and the lens 2 are mounted may be fixed to the inner surface of the hermetically sealed package 10 by brazing or using an adhesive. When the optical component holder is adhered to the inner surface of the hermetically sealed package 10 by using an adhesive, a shallow groove is formed so as to allow the excess adhesive that comes out after being adhered to the holder adhered surface of the hermetically sealed package 10 to escape. It is desirable to keep it.

As described above, the substrate material of the diffraction grating 1 is
In the case of a low thermal expansion material such as quartz, iron-nickel alloy, or iron-nickel-cobalt alloy, as a matter of course, as an optical component holder for fixing the diffraction grating 1 and further the lens 2 to the inner surface of the hermetically sealed package 10. Is preferably one having a coefficient of thermal expansion substantially equal to that of the substrate material of the diffraction grating 1, that is, an iron-nickel alloy or an iron-nickel-cobalt alloy. When the optical component holder is a metal holder such as iron / nickel alloy or iron / nickel / cobalt alloy, laser welding or brazing is possible.

On the other hand, when the material of the optical component holder is quartz, the method of directly fixing the diffraction grating 1 to the substrate is limited to an adhesive or the like, but since the inside of the package 10 is hermetically sealed, it is easy. To ensure long-term reliability.

Since the optical components such as the lens 2 other than the diffraction grating 1 can be formed of a heat-resistant material that does not use resin or the like, the components other than the diffraction grating 1 can be formed by laser welding or brazing. If it can be fixed on the substrate, only the diffraction grating 1 is hermetically sealed, and the other components can be covered with a simple case to achieve stable temperature characteristics.

Next, a method of fixing the optical waveguide array 3 to the array holder 12 will be described with reference to FIG. The first fixing method is an example in which an array mounting groove 30 is provided in the array holder 12 as shown in FIG. 5A, and the optical waveguide array 3 is fitted into the array mounting groove 30 and fixed by an adhesive. is there. In this case, the excess adhesive is removed from the groove 30 by forming the array mounting groove 30 shallowly. The second fixing method is to metallize the back surface of the optical waveguide array 3,
As shown in FIG. 5B, this is brazed to the groove of the array spacer 31 with low melting point solder or the like, and the array holder 12 is provided with an array spacer fixing groove 32 having substantially the same outer shape (width) as the array spacer 31. In this method, the array spacer 31 is fitted into the array spacer fixing groove 32 and fixed by laser welding. FIG. 5C shows a state after the optical waveguide array 3 is fixed to the array holder 12 by the second method.

On the other hand, in a region where air is present between the hermetically sealed package 10 and the end face of the optical waveguide array 3, airtightness is provided in order to prevent disturbance of the light wavefront due to a change in air density due to wind or convection. It is desirable that the outside air does not hit directly, even if it is not so much. Specifically, as shown in FIG. 6A, the array holder 12 may be covered with a cylindrical cap 42.

Further, when fixing the hermetically sealed package 10 to another mounting substrate or the like, the four corners of the package 10 are prevented as shown in FIG. 6B so that the hermetically sealed package 10 is not distorted by screwing or the like. Mounting member 4 with a sufficiently thin thickness
It is preferable to provide 3. The mounting member 43 may be formed integrally with the hermetically sealed package 10, or may be formed separately from the package 10 and brazed to the package 10.

Next, an example of the assembling order of each component of the optical communication device according to this embodiment will be described. (1) The optical waveguide array 3 is fixed to the array holder 12 as shown in FIG. 5 (a) or FIG. 5 (b) (c).

(2) The diffraction grating 1 and the lens 2 are fixed in the hermetically sealed package 10. (3) After the array holder 12 is aligned with the hermetically sealed package 10, the array holder 12 is joined and fixed via the pipe-shaped member 22.

(4) The array holder 12 is covered with the cap 23. At this time, the cap 23 and the input / output array port 4
A resin is filled between the optical fiber and the root of the optical fiber forming the optical fiber, and the glass window 1 of the optical waveguide array 3 and the hermetically sealed package 10 is filled.
Make sure that the outside air does not enter the space between 1 and 1.

In the above embodiment, an example in which the present invention is applied to an optical multiplexer / demultiplexer has been described. However, the present invention can be applied to other various passive optical devices, and as a result, it is excellent as in the above embodiments. It is possible to obtain high environmental resistance and high reliability.

[0041]

As described in detail above, the optical communication device according to the present invention provides stable characteristics in which the optical axis is unlikely to shift with respect to environmental changes such as ambient temperature fluctuations, and long-term stability, It has excellent reliability, and when applied to an optical multiplexer / demultiplexer, it can greatly contribute to the practical application of wavelength division multiplexing optical communication.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an optical multiplexer / demultiplexer.

FIG. 2 is a diagram showing the relationship between the coefficient of thermal expansion of the substrate material of the diffraction grating and the variation rate of the central transmission wavelength with the temperature of the optical multiplexer / demultiplexer.

FIG. 3 is a sectional view showing a configuration of an optical communication device according to an embodiment of the present invention.

FIG. 4 is a view showing a manufacturing process of part of the optical communication device according to the embodiment.

FIG. 5 is a view showing a configuration of an optical waveguide array connected to the optical communication device according to the same embodiment.

FIG. 6 is a diagram showing another part of the manufacturing process of the optical communication device according to the embodiment.

FIG. 7 is an exploded perspective view showing a configuration of a conventional optical multiplexer / demultiplexer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Diffraction grating 2 ... Lens 3 ... Optical waveguide array 4 ... Input / output port array 5 ... Optical fiber or optical waveguide 10 ... Hermetically sealed package (blocking means) 11 ... Glass window (optical coupling means) 12 ... Array holder 20 ... Outer frame of hermetically sealed package 21 ... Bottom plate of hermetically sealed package 22 ... Pipe-shaped member 30 ... Array mounting groove 31 ... Array spacer 32 ... Array spacer fixing groove 41 ... Airtight sealed package lid 42 ... Cap 43 ... Mounting members

Claims (7)

[Claims] 1. A device for optical communication having a diffraction grating as a part of its constituent elements, which is made of a material having a low coefficient of thermal expansion, and which cuts off at least the diffraction grating from the outside air, and is attached to the cutoff means. An optical communication device comprising: an optical coupling means for optically coupling a diffraction grating and an optical system provided outside the blocking means. 2. An optical signal output from the other end side of an optical waveguide array having an input / output port array on one end side is guided through a lens to a diffraction grating to be diffracted, and the optical signal diffracted by the diffraction grating is said. An optical communication device used as an optical multiplexer / demultiplexer for inputting to the other end side of the optical waveguide array through a lens, comprising a blocking means configured of a material having a low coefficient of thermal expansion and at least blocking the diffraction grating from the outside air. An optical communication device characterized by the above. 3. An optical signal output from the other end side of an optical waveguide array having an input / output port array on one end side is guided through a lens to a diffraction grating to be diffracted, and the optical signal diffracted by the diffraction grating is said. In a device for optical communication used as an optical multiplexer / demultiplexer for inputting to the other end side of the optical waveguide array via a lens, a blocking means configured of a material having a low thermal expansion coefficient, for blocking the diffraction grating and the lens from the outside air, An optical device, which is attached to the blocking means and comprises an optical coupling means for optically coupling the lens and the other end side of the optical waveguide array provided outside the blocking means. Communication device. 4. The hermetically sealed package is a hermetically sealed package formed by integrally brazing or welding a plurality of members made of a low thermal expansion coefficient material. The optical communication device according to item 1. 5. The blocking means is a hermetically sealed package having an opening in a part formed by integrally brazing or welding a plurality of members made of a low thermal expansion coefficient material, and the optical coupling means is The optical communication device according to claim 1 or 3, which is a glass window provided in the opening of the hermetically sealed package. 6. The optical communication device according to claim 1, wherein the low thermal expansion coefficient material is an alloy of iron and nickel or an alloy of iron, nickel and cobalt. . 7. The optical communication according to any one of claims 1 to 3, wherein the light transmitting medium near the grating surface of the diffraction grating is a medium having a small change in optical length due to a thermo-optic effect. Device.