JP2001296446A - Optical gain equalizer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical gain equalizer which uses a dielectric multi-layer film filter and is easily assembled and its assembling method. SOLUTION: First and second optical fiber terminals and first and second refractive index distributed rod lenses are prepared, and these are provided with all the same outside diameters. The dielectric multi-layer film filter is formed in one side of surface of the first rod lens. In preferable embodiment, the first optical fiber terminal, the first rod lens, the second rod lens and the second optical film terminal are integrated to form a unit by three precise sleeves into which the outside diameter member is fixedly inserted. The unit is stored in a casing and is fixed by a filler.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to optical wavelength division multiplexing (optical W
The present invention relates to an optical gain equalizer used together with a broadband optical fiber amplifier in a DM) transmission system, and particularly to an optical gain equalizer that performs gain equalization using a dielectric multilayer filter (dielectric multilayer half mirror film).

[0002]

2. Description of the Related Art When an optical wavelength-division multiplexed optical signal is transmitted over a long distance, optical band optical amplifiers corresponding to the wavelength band to be transmitted are arranged at predetermined intervals in order to compensate for loss in an optical fiber. However, an optical amplifier has a slightly different gain for each wavelength (wavelength characteristic of gain), and therefore a level difference occurs between signals having different wavelengths. Since this level difference is accumulated for each optical amplifier, it cannot be ignored when the transmission distance increases. Therefore, a wideband optical equalizer is required to compensate for the wavelength characteristic of the gain of the optical amplifier and to equalize the level between optical signals having different wavelengths. As such a broadband optical equalizer, for example, one using a plurality of etalon filters as shown in FIG. 10 is proposed (NEC Technical Report Vo1.5).
1No. 4, PP49-53, 1998).
FIG. 11 shows required equalization characteristics. In the optical gain equalizer shown in FIG. 10, the characteristic curve shown in FIG. 11 is Fourier-transformed to obtain Fourier spectrum intensities at respective wavelengths from the first to fourth order, and the four synthetic quartz substrates 91 to 91 having a thickness of about 18 μm are obtained.
The equalization characteristic is realized by arranging 94 in the optical path so as to be inclined. On each of the synthetic quartz substrates 91 to 94, a half mirror film (not shown) having an appropriate reflectance is formed on both surfaces in order to give each Fourier spectrum intensity. The optical fiber terminals 11 and 12 are fixed to cases 97 and 98 to which lenses 95 and 96 are fixed by YAG laser beam welding 99, respectively. The cases 97 and 98 are also fixed to a case 90 to which an etalon filter is fixed by YAG laser beam welding 99. Is done.

[0003]

However, this structure requires as many as four synthetic quartz substrates (91 to 94) having a special thickness of 18 .mu.m which are difficult to process, and furthermore, a half mirror having different characteristics on both surfaces thereof. Since a complicated operation of forming a film (not shown) is required, the device becomes extremely expensive. In addition, since a YAG laser beam welding machine is required for assembly, capital investment becomes large. The present invention has been made in view of the problems at the preceding stage, and has an equalization characteristic substantially equal to that of the optical gain equalizer of FIG. 10, but is easy to adjust and assemble. It is an object to provide a gain equalizer.

[0004]

In one aspect, the present invention provides a method for assembling an optical gain equalizer using a dielectric multilayer filter. This assembling method includes the steps of aligning the first and second optical fiber terminals and the first and second gradient index rod lenses all with the same outer diameter, and forming a dielectric multilayer film on one surface of the first rod lens. Forming a filter;
Providing at least two precision sleeves for inserting and fixing the outer diameter member, a first optical fiber terminal and a first optical fiber terminal;
Connecting and fixing the rod lenses with one of the precision sleeves so that their respective end faces are in close contact with each other. The first rod lens and the second rod lens are separated by an appropriate gap, Connecting and fixing the second rod lens and the second optical fiber end with the other precision sleeve of the sleeve so that both sides coincide with each other. In another aspect, the present invention provides an optical gain equalizer that is easy to assemble.
The optical gain equalizer of the present invention has a first (tentatively, incident side) having the same outer diameter and arranged so that end faces face each other.
And a second optical fiber terminal, a first (tentatively an incident side) and a first optical fiber terminal having the same outer diameter as the optical fiber terminal and disposed in close contact with the end surfaces of the first and second optical fiber terminals, respectively. A second refractive index distribution rod lens, an incident side,
That is, a dielectric multilayer film filter formed on one end face of the first rod lens, a first precision sleeve for connecting and fixing the first optical fiber terminal and the first rod lens, and a first precision sleeve and an outer. A second precision sleeve having the same diameter and connecting and fixing the exposed portion of the first rod lens and the second rod lens to form a unit, and a second rod lens and a second optical fiber terminal. And fixing means for fixing the connection so that the output of the second optical fiber terminal is maximized.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to embodiments of the present invention and the accompanying drawings. When the same element is shown in a plurality of drawings, the same reference numeral is given. (Embodiment 1) FIG. 1 is a diagram showing a basic configuration of an optical gain equalizer according to a first embodiment of the present invention. In FIG.
The optical gain equalizer 1 includes optical fibers 11 and 1 forming a transmission path.
2 are terminated, and the optical fiber terminals 21 and 22 are disposed so that the terminal surfaces face each other. The outer diameters of the optical fiber terminals 21 and 22 are equal to each other, and the optical fiber terminals 21 and 22 are disposed in close contact with the optical fiber terminals 21 and 22, respectively. The refractive index distribution self-focusing rod lenses 31 and 32, the dielectric multilayer filter (dielectric multilayer filter) 30 formed on the surface of the free end of the rod lens 31, and the optical fiber terminal 21 and the rod lens 31 are connected and fixed. A ceramic precision sleeve 41, a ceramic precision sleeve 42 for connecting and fixing the rod lenses 31 and 32 to each other with an appropriate gap 39 interposed therebetween, and a unit integrated by the precision sleeves 41 and 42, have one end identical to the emission surface of this unit. Adhesively fixed inside so as to form a surface (a surface passing through the line XX ′ and perpendicular to the paper surface (hereinafter referred to as a surface Pxx ′)) Glass pipe 51, and a UV curable adhesive 61, 62 and 63 used the glass pipe 52 is adhesively fixed flush XX 'and to the optical fiber terminal 22, and the adhesive fixing of the. The facing surface between the optical fiber terminal 11 and the rod lens 31 and the facing surface between the rod lens 32 and the optical fiber terminal 12 (that is, the surface Pxx ') are obliquely processed to about 8 degrees in order to avoid reflected return light. The opposite surfaces of the rod lenses 31 and 32 are also obliquely processed to about 2.5 degrees for the same reason. An antireflection coating is applied to optical surfaces other than the dielectric multilayer filter 30. A ceramic split sleeve can also be used as the ceramic precision sleeve.

FIG. 2 shows the configuration of the dielectric multilayer filter 30 and the state of the boundary. As can be seen from the figure, the dielectric multilayer film filter 30 has a silicon dioxide (SiO ₂ ) layer and a titanium dioxide (TiO ₂ ) layer on the substrate of the film 30 (that is, the exit surface of the rod lens 31). 40 layers alternately formed by assist deposition (IAD) (FIG. 2)
Is formed from bottom to top). The refractive index, extinction coefficient and optical thickness of each layer are as shown in the figure. When a wavelength division multiplexed optical signal is input to the optical gain equalizer 1 having the above configuration, the operation is performed as follows.
Light incident from the optical fiber 11 is incident on the gradient index rod lens 31. In this case, the rod lens 31
Since it acts as a collimating lens, the incident light
The light is converted into parallel light and passes through a dielectric multilayer filter 30 formed on the exit surface of the rod lens 31. At this time, the optical signals of various wavelengths constituting the parallel light are converted according to the gain equalization characteristics shown in FIG.
By transmitting at the transmittance according to each wavelength,
Will be equalized. The equalized parallel light is converged by the rod lens 32 and is coupled to the optical fiber 12. FIG. 3 also shows the characteristics of the equalizer of FIG. 10 using an etalon filter. Comparing with this as a reference, it can be seen that an accuracy within ± 10% in absolute value can be realized by one dielectric multilayer filter 30. FIG. 4 is a flow chart showing the main points of the manufacturing process of the optical gain equalizer 1 of FIG. In FIG. 4, first, optical fiber terminals 21 and 22 having the same outer diameter.
And rod lenses 31 and 32, and a precision sleeve for connecting and fixing them are prepared.
The dielectric multilayer filter 30 is formed at one end (step 100). The optical fiber terminal 21 and the rod lens 31 for collimation are connected and fixed by the ceramic precision sleep 41 (step 101). The exposed portion of the rod lens 31 and the converging rod lens 32 are fixed by the ceramic precision sleeve 42 to form an integrated unit (step 102). In step 102, an appropriate gap is provided between the rod lenses 31 and 32, and the obliquely processed surfaces are arranged so as to be parallel. Adjustment is easy because the gap may be appropriately determined. The integrated unit is bonded and fixed to the glass pipe 51 with an ultraviolet curing adhesive so that the rod lens 32 and the 8 ° processed surface of the glass pipe 51 are on the same plane Pxx ′ (step 10).
3). Finally, the position of the optical fiber terminal 22 and the glass pipe 52 is adjusted on the same plane Pxx 'so that the output of the optical fiber 12 is maximized (that is, the rod lens 3).
2 so that the side of the optical fiber terminal 22 coincides with the side of the optical fiber terminal 22), and is fixed with an ultraviolet curing adhesive (step 10).
4). As described above, since expensive equipment such as a YAG laser beam welding machine is not required for assembly and assembly is easy, a low-cost optical gain equalizer can be realized.

(Embodiment 2) FIG. 5 is a diagram showing a basic configuration of an optical gain equalizer according to a second embodiment of the present invention. The optical gain equalizer 2 shown in FIG. 5 is such that the optical system includes optical fiber terminals 21 and 22, rod lenses 31 and 32, and a dielectric multilayer filter 30 formed on the exit surface of the collimating rod lens 31. Is the same as the equalizer 1 in FIG. Therefore, the operation and the performance for the wavelength division multiplexed optical signal input to the optical gain equalizer 2 are the same as those of the equalizer 1. The difference is that the rod lens 3
2 and the optical fiber terminal 22 are also a ceramic precision sleeve 43
The optical fiber terminals 21 and 2
2. Rod lenses 31 and 32 (lens 31 has dielectric multilayer filter 30), and precision sleeves 41 to 4
3 as a unit (tentatively referred to as an optical system unit). By doing this,
The optical fiber terminal 22 is placed on the same plane P as in the case of the equalizer 1.
xx ′, the position is adjusted so that the output of the optical fiber 12 is maximized (the optical fiber terminal 22
And the side surfaces of the rod lens 32)). Further, in FIG. 5, 53 is a case, 7
Reference numeral 0 denotes a filler that fills the gap between the optical system unit and the case 53. As the shape of the case, in addition to the case on the cylinder, a case having a split structure can be considered. As the filler, a silicone resin or a flexible epoxy resin can be used. Also, as in the equalizer 1, a glass pipe 5
Since neither 1 is used, there is no need to adjust the exit surface of the rod lens 32 and the inclined surface of the glass pipe 51. FIG.
9 is a part of a flowchart showing an example of an assembling procedure of the optical gain equalizer 2; The same parts as those in FIG. 4 are omitted. Step 10
Subsequent to 2, the exposed portion of the rod lens 32 and the optical fiber terminal 22 are fixed with a ceramic precision sleeve 43,
An optical system unit in which all the optical systems are integrated is formed (step 113). This optical system unit is placed in the case 53, and the gap is filled with an appropriate filler 70 (step 11).
4). As described above, the optical gain equalizer 2 according to the second embodiment of the present invention includes two refractive index distribution self-focusing rod lenses having the same outer diameter and two optical fiber terminals and three ceramic precision sleeves. As a result, a low-cost optical gain equalizer with extremely excellent assemblability can be realized.

(Embodiment 3) FIG. 7 is a diagram showing a basic configuration of an optical gain equalizer according to a third embodiment of the present invention. The optical gain equalizer 3 in FIG. 7 is the same as the equalizer 2 in FIG. 5 except for the following two points. That is, in FIG. 7, the refractive index distribution self-focusing rod lenses 31 and 32 are replaced with the front spherical processing refractive index distribution self-focusing rod lenses 33 and 34, and accordingly, the dielectric multilayer film filter 30a is replaced with the front spherical processing rod lens. 33 is a point formed on the surface on the incident side. The rod lenses 33 and 34 process the opposing surfaces into spherical shapes. In the refractive index distribution self-converging lens 33,
When the lens length is exactly 0.25 pitch, the input light from the optical fiber becomes collimated light on the output surface, and when the lens length is 0.5 pitch, the input light from the optical fiber becomes the same state as the input light on the output surface. Become. Therefore, when a lens having an effective lens pitch longer than 0.25 pitch and shorter than 0.5 pitch is used, light is converged on the exit surface. Since the convergent light always enters the exit surface obliquely even in a rod lens which is polished at right angles, reflected return light does not occur. By processing the tip of the rod lens into a spherical surface, the reflection angle is further increased, so that the reflected return light to the incident optical fiber is further reduced. FIG. 8 shows a dielectric multilayer filter 30a.
Shows the configuration and the state of its boundary. As can be seen from the figure, the dielectric multilayer film filter 30a is formed such that the film is formed from the incident surface (the lowermost part in FIG. 8) of the spherical lens rod 33 to the top of the table. Again, silicon dioxide (SiO ₂ )
And 40 layers of titanium dioxide (TiO ₂ ) layers alternately formed by ion-assisted deposition (IAD). The refractive index, extinction coefficient and optical thickness of each layer are as shown in the figure. An operation when light such as a wavelength division multiplexed optical signal enters the optical gain equalizer 3 having the above configuration will be described. The light incident from the optical fiber 11 passes through the dielectric multilayer filter 30 a on the incident surface of the rod lens 33. At this time, according to the gain equalization characteristic shown by the solid curve in FIG. 9, the light is transmitted at a transmittance corresponding to each wavelength, thereby being equalized. The transmitted light is converted into convergent light by the rod lens 33. This converged light is again converged after being incident on the rod lens 34 and coupled to the optical fiber 12.

FIG. 9 shows an example of FIG. 1 using an etalon filter.
A zero equalizer characteristic (marked with x) is also shown. Based on this,
By comparison, it can be seen that the accuracy within ± 10% in absolute value can be realized by one dielectric multilayer filter 30a. The assembly of the optical gain equalizer 3 includes rod lenses 33 and 34.
This is the same as the assembly of the equalizer 2 except that the distance between the rod lenses is appropriately adjusted when fixing with the precision sleeve 42. The above is merely an example of the embodiment for the description of the present invention. Therefore, it is easy for those skilled in the art to make various changes, modifications, or additions to the above-described embodiment in accordance with the technical idea or principle of the present invention. Therefore, the present invention should be determined not only by the above-described embodiments but also by the descriptions in the claims.

[0010]

As described above, according to the first embodiment of the present invention, expensive equipment such as a YAG laser beam welding machine is not required for assembly, and assembly is easy. A gain equalizer can be realized. According to the second embodiment of the present invention, two refractive index distribution self-focusing rod lenses having the same outer diameter and two optical fiber terminals are integrated by three ceramic precision sleeves, and adjustment-free assembly is possible. Therefore, a low-cost optical gain equalizer with extremely excellent assemblability can be realized. According to the third embodiment of the present invention, it is possible to obtain an optical gain equalizer that is not only easy to assemble but also has good characteristics with little return light.

[Brief description of the drawings]

FIG. 1 is a diagram showing a basic configuration of an optical gain equalizer according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a dielectric multilayer filter 30 of the optical gain equalizer 1 of FIG.

FIG. 3 is a diagram showing characteristics of the conventional equalizer of FIG. 10 using the etalon filter and the equalizer of the present invention of FIG. 1;

FIG. 4 is a flowchart showing a main point of a manufacturing process of the optical gain equalizer 1 of FIG.

FIG. 5 is a diagram illustrating a basic configuration of an optical gain equalizer according to a second embodiment of the present invention.

6 is a diagram showing a part of a flowchart showing an example of an assembling procedure of the optical gain equalizer 2 of FIG. 5;

FIG. 7 is a diagram showing a basic configuration of an optical gain equalizer according to a third embodiment of the present invention.

8 is a diagram showing a configuration of a dielectric multilayer filter 30a of the optical gain equalizer 3 of FIG. 7 and a state of a boundary thereof.

9 is a diagram showing characteristics of the prior art equalizer of FIG. 10 using the etalon filter and the equalizer of the present invention of FIG. 7;

FIG. 10 is a diagram showing a basic configuration of a conventional optical gain equalizer.

11 is a diagram illustrating gain equalization characteristics of the optical gain equalizer in FIG.

[Explanation of symbols]

 1-3 Optical gain equalizer of the present invention 11, 12 Optical fiber 21, 22 Optical fiber terminal 30 Dielectric multilayer film filter 31, 32 Rod lens 51, 52 Glass pipe 53 Case 61-63 Ultraviolet curing adhesive 70 Filler 33, 34 Front-end processed rod lens

Claims (11)

[Claims] 1. A first and a second optical fiber terminal having the same outer diameter arranged so that end faces thereof are opposed to each other, the first and the second light having the same outer diameter as the optical fiber terminal. A first and a second gradient index rod lenses disposed in close contact with the end surfaces of the fiber ends, a dielectric multilayer filter formed on one end surface of the first rod lens, the first light; A first precision sleeve for connecting and fixing a fiber end and the first rod lens; an outer diameter equal to that of the first precision sleeve, and an exposed portion of the first rod lens and the second rod lens A second precision sleeve which is connected and fixed to form a unit; and a fixing means for connecting and fixing the second rod lens and the second optical fiber end so that their respective side surfaces coincide with each other. Easy multilayer filter light gain equalizer assembly characterized by. 2. A first glass pipe having an inner diameter into which the first and second precision sleeves can be inserted, and a second glass pipe having an inner diameter into which the second optical fiber end can be inserted. The unit is fixed to the inner wall of the first glass pipe with an adhesive such that the end face of the second rod lens forming one end of the unit and the end face of the first glass pipe form the same plane. The fixing means is made of the second glass pipe and an adhesive for bonding and fixing the second optical fiber terminal, the second glass pipe and the same surface. 2. The optical gain equalizer according to 1. 3. The optical gain equalizer according to claim 1, wherein said fixing means is a third precision sleeve for fixing said first rod lens and said second optical fiber terminal. 4. A method according to claim 1, wherein the opposing sides of the first and second rod lenses are spherically processed, and the dielectric multilayer filter is formed on the other end face of the first rod lens. The optical gain equalizer according to claim 3. 5. The apparatus according to claim 1, further comprising a case accommodating the unit integrated by the first to third precision sleeves, and a filler filling a gap between the unit and the case. The optical gain equalizer according to claim 3. 6. The filter according to claim 1, wherein the dielectric multilayer filter is a first filter.
4. An optical gain equalizer according to claim 2, wherein said rod lens is formed on an end surface of said rod lens on the side of said second rod lens. 7. A boundary surface between the first optical fiber terminal and the first rod lens and a boundary surface between the second rod lens and the second optical fiber terminal are both inclined at a predetermined angle. The optical gain equalizer according to any one of claims 1 to 6, wherein the optical gain equalizer is processed and assembled so that the boundary surfaces are parallel to each other. 8. A step of arranging the first and second optical fiber terminals and the first and second gradient index rod lenses all to have the same outer diameter, and a dielectric multilayer on one surface of the first rod lens. Forming a membrane filter, preparing at least two precision sleeves for inserting and fixing the outer diameter member, and bringing the first optical fiber end and the first rod lens into close contact with each other. Connecting and fixing the first rod lens and the second rod lens with the other precision sleeve of the precision sleeve with an appropriate gap therebetween. And a fixing step of connecting and fixing the second rod lens and the second optical fiber terminal so that both side surfaces coincide with each other. Assembling method of the optical gain equalizer using a dielectric multilayer film filter which. 9. A step of preparing a first glass pipe having an inside diameter into which the first and second precision sleeves can be inserted and a second glass pipe having an inside diameter into which the second optical fiber end can be inserted. The unit is formed by the first unit so that an end surface of the second rod lens and an end surface of the first glass pipe forming one end of a unit integrated by the at least two precision sleeves form the same plane. Fixing with an adhesive to the inner wall of the glass pipe, and fixing the second optical fiber terminal, the second glass pipe, and the same surface with an adhesive. 9. The method for assembling an optical gain equalizer according to claim 8, wherein 10. The optical gain equalizer according to claim 8, wherein the fixing step fixes the first rod lens and the second optical fiber terminal with a third precision sleeve. Assembly method. 11. The method further comprises the steps of: forming a spherical surface on opposing sides of the first and second rod lenses; and forming the dielectric multilayer filter on the other end surface of the first rod lens. 11. The method for assembling an optical gain equalizer according to claim 10, wherein: