JP2003258340A - Optical waveguide, optical fiber, and optical amplifier - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a miniature inexpensive optical amplifying medium and optical amplifier having a wide amplifying wavelength band. <P>SOLUTION: In an optical waveguide 1 having a core section, the core section is formed with an organic rare earth complex represented by the following general formula (1), and an optical amplifier 10 is obtained where the optical waveguide 1 is used as an optical amplification medium. Hereby, the miniature inexpensive optical amplifier 10 having a wide amplification wavelength band is obtained. In the general formula (1) M represents a rare earth element selected from a group comprising praseodymium, thulium, erbium, and neodymium. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide and an optical fiber and an optical amplifier using these as an optical amplification medium.

[0002]

2. Description of the Related Art In recent years, research and development of wavelength division multiplexing (WDM) have been actively conducted for the purpose of expanding transmission capacity and improving functions in optical communication systems. This WDM transmission technology
By combining or demultiplexing optical signals of multiple wavelengths, 1
This is a technique for transmitting optical signals of a plurality of wavelengths using the optical fiber of the present invention, whereby the transmission capacity of optical signals can be expanded.

On the other hand, in the optical communication technology, technical development for long-distance transmission has been actively carried out. The long-distance transmission technology is a technology for solving the limitation of the transmission distance caused by the optical loss of the optical fiber transmission line, and the technology that enables the long-distance transmission by the relay amplification by the optical amplifier has been developed. ing. In the WDM transmission system as well as in other transmission systems, it is necessary to perform relay amplification according to the transmission distance in order to deal with optical loss, but especially in the WDM transmission system, optical signals of multiple wavelengths are transmitted. Therefore, an optical amplifier having a wide amplification wavelength band is required.

Further, in recent years, the need for this optical amplifier has been extended to access systems, and there is a growing demand for downsizing and cost reduction. This is due to the rapid introduction of optical fibers into access systems due to the spread of broadband in the Internet.

Under the above circumstances, high performance WD
In order to realize the M system, development of an optical amplifier which has a wide amplification wavelength band and can be downsized and reduced in price is an important and urgent issue.

Conventionally, various methods have been studied for expanding the amplification wavelength width in an optical amplifier (optical fiber amplifier) in which a rare earth element is added to the core of a glass optical fiber.

As one of the methods, there is a method of expanding the amplification wavelength band by changing the kind of the rare earth element contained in the core part. As a result, praseodymium (Pr), 1.55 to 1.61 μ in the 1.3 μm band
Erbium (Er), 1.45 and 1.65 μm for m band
An optical fiber amplifier having a core portion in which a band is doped with thulium (Tm) has been developed. At a practical level, E
In an optical fiber amplifier having an r-doped core portion, an optical fiber amplifier using a 980 nm and 1480 nm band semiconductor laser as a pumping light source was developed, and commercial WD
Introduced into M communication system.

However, in this optical fiber amplifier, when the concentration of the rare earth element added to the core portion is increased, the gain efficiency is reduced due to energy transfer due to the interaction between the rare earth elements and cooperative up-conversion. Therefore, in order to obtain a large gain, the concentration of the rare earth element in the core is 100 to 1000 pp.
Instead of suppressing the length to about m, the length of the optical amplification medium (optical fiber) needs to be lengthened to about several tens to several hundreds of meters to secure a so-called density multiplication product. For this reason, it is difficult to reduce the cost, and it is necessary to wind a long optical amplification medium in a bobbin shape, and there is a big problem in miniaturization.

On the other hand, there is also a method in which the amplification wavelength band is expanded by changing the type and composition of the glass-based material forming the core to expand the photoluminescence width of the added rare earth element. This method is a method that utilizes the fact that the bandwidth of the amplification wavelength band is determined by the bandwidth of photoluminescence, but in the combination of the rare earth element and the glass-based material, a significant subband in the photoluminescence spectrum. As a result of the appearance of the structure, there is a problem that the emission band is narrow and the band width cannot be wide.

In addition to the above-mentioned problems, in a higher performance WDM system, the WD input to the optical amplifier is
It is necessary to solve the problem of crosstalk between the WDM signals due to the control of constant gain against the change in the number of M signals or the signal light amount of each signal wavelength and the spectrum hole burning effect. To solve this problem, a method is considered in which a WDM signal is once demultiplexed by a demultiplexer, each signal light is amplified by an individual optical amplifier, and then recombined.
Since optical amplifiers are required for the number of DM signals, there is an essential problem in terms of cost and device scale when using the conventional optical fiber amplifier.

[0011]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
No. 9 and Japanese Patent Laid-Open No. 7-5505 propose an optical fiber amplifier using a polymer optical fiber as an optical amplification medium, in which an organic dye and an organic rare earth complex are added to the core of the optical fiber. ing. The inventions disclosed in these publications obtain an optical amplifier that is low in cost and downsized by utilizing the excellent processability and handleability of polymer materials and the high fluorescence efficiency of organic dyes. It is an object.

However, the photoluminescence wavelength of the added organic dye and organic rare earth complex is 1 from the visible wavelength band.
It is limited to the μm band, and the polymer material used for the core portion has a large transmission loss in the communication wavelength band of 1.3 μm band or 1.5 μm band. To 1 μm band.

The present invention has been made in view of the above-mentioned problems, and provides an optical waveguide or optical fiber which has a wide amplification wavelength band and is small and inexpensive, and an optical amplifier using these as an optical amplification medium. The purpose is to do.

[0014]

An optical waveguide according to claim 1 for solving the above-mentioned problems is an optical waveguide characterized in that a core portion is composed of an organic rare earth complex represented by the following general formula (1). is there.

[0015]

[Chemical 4]

However, in the general formula (1), M represents a rare earth element selected from the group consisting of praseodymium, thulium, erbium and neodymium.

The quinoline ring, which is the organic ligand of the organic rare earth complex represented by the above general formula (1), does not have a substituent, but even if it has a substituent, similar effects can be obtained. it can. Examples of the substituent include an alkyl group, an aryl group, a hydroxyl group, a carboxyl group, an amino group, and the like, and a plurality of or the same or different substituents may be bonded.

In the optical waveguide according to claim 2 or the optical fiber according to claim 3, the core portion has the above-mentioned general formula (1).
An optical waveguide or an optical fiber having an organic rare earth complex represented by.

In the optical waveguide according to claim 4 or the optical fiber according to claim 5, the core has a resin selected from the group consisting of polyimide, a silicone resin, a UV-curable acrylate and a UV-curable epoxy resin. An optical waveguide or an optical fiber having an organic rare earth complex.

The resin may be any one resin selected from the group consisting of polyimide, silicone resin, UV curable acrylate and UV curable epoxy resin, or a composite resin composed of a plurality of resins selected from the above group. May be

The optical waveguide according to claim 6 or the optical fiber according to claim 7 is an optical waveguide or optical fiber characterized in that the core portion comprises sol-gel glass and the organic rare earth complex.

The optical waveguide or optical fiber according to any one of claims 1 to 7 can be used not only as an ordinary optical waveguide or optical fiber, but also as an optical amplification optical waveguide or optical amplification optical fiber. It can also be used.

The optical amplifier according to the present invention comprises an optical waveguide which is an optical amplification medium, and an input means for inputting pumping light or signal light for exciting the optical waveguide to the optical waveguide. And the optical waveguide is claim 1,
An optical amplifier, which is the optical waveguide according to any one of claims 2, 4, and 6.

An optical amplifier according to a ninth aspect is an optical amplifier including an optical fiber as an optical amplification medium and an input means for inputting pumping light or signal light for exciting the optical fiber to the optical fiber. An optical amplifier is characterized in that the optical fiber is the optical fiber according to any one of claims 3, 5, and 7.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION In order to develop an optical amplification medium having desired characteristics, an organic rare earth complex that plays a central role in the optical amplification action and a host medium (polymer or glass material to which the organic rare earth complex is added) are added. ) It is indispensable to optimize both developments and the combination of both. For example,
Even when an organic rare earth complex having the same rare earth element is used, its photoluminescence wavelength and efficiency largely depend on the type of the organic ligand coordinated with the rare earth element. Even when an organic rare earth complex exhibiting highly efficient photoluminescence in a desired wavelength band is used, a large optical amplification is realized when combined with a host medium having a large optical loss in this wavelength band. It's difficult.

Based on these, we have made earnest studies on the solubility of the organic rare earth complex in the polymer and the photoluminescence wavelength of the organic rare earth complex in the combination of various organic rare earth complexes with the polymer and glass. As a result, in some combinations,
An optical waveguide or optical fiber having desired characteristics and an optical amplifier using these as an optical amplification medium have been developed.

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a configuration diagram of an optical amplifier according to an embodiment of the present invention. As shown in the figure, the optical amplifier 10 is composed of an optical waveguide 1, which is an optical amplification medium, a WDM coupler 2, an isolator 3, a pump light source 4, and a bandpass filter 5, and an input signal light 6 is amplified by the optical waveguide 1. The output signal light 7 is output.

The optical amplifier 10 shown in the figure is an optical waveguide 1
Is a front pumping arrangement type in which the pump light source 4 is installed on the input side of, but is a rear pumping arrangement type in which the pump light source 4 is installed on the output side of the optical waveguide 1, or both the input side and the output side of the optical waveguide 1. A bidirectional excitation arrangement type in which the pump light source 4 is installed may be used.

Next, an example of a method for producing the optical waveguide 1 which is an optical amplification medium will be described, including the steps of synthesizing an organic rare earth complex used for the core portion of the optical waveguide 1, the step of producing a thin film to be the core portion, and the thin film The steps of processing and manufacturing the optical waveguide 1 will be described in order. After description of each step, a performance test of the optical amplifier 10 using the produced optical waveguide 1 as an optical amplification medium will be described. It should be noted that the process for producing the thin film and the subsequent steps will be described by two examples.

[Synthesis of Organic Rare Earth Complex] First, an example of a method for synthesizing an organic rare earth complex used in the core portion of the optical waveguide 1 which is an optical amplification medium will be described below. 6.68 g of 8-hydroxyquinone was dissolved in 80 ml of a mixed solution of methanol / water (80/20% by volume). This is solution A. In addition, erbium chloride hexahydrate (Er (III) Cl ₃ .6H
₂ O) 5.73 g was dissolved in 100 ml of water. This is solution B. Next, solution B was added dropwise to solution A, and orange erbium 8-hydroxyquinolinate (Erbium
(III) 8-hydroxyquinolinate) (hereinafter referred to as “ErQ”) was produced. Water was added to the mixed solution of the solution A and the solution B to make the total volume 300 ml. The ErQ formed by suction filtration was filtered off, then the ErQ was washed with dilute hydrochloric acid and dried in a vacuum. The obtained ErQ is about 0.5.
It was g. The chemical structure of the obtained ErQ is a chemical structure in which M is erbium (Er) in the general formula (1), when described with reference to the general formula (1).

By the same method as this synthetic method,
In the general formula (1), it is possible to obtain an organic rare earth complex having a chemical structure in which M is a rare earth element such as Nd, Pr or Tm. Hereinafter, in the general formula (1), an organic rare earth complex having a chemical structure in which M is Nd is “NdQ” and M is Pr.
Is set to "PrQ", and when M is Tm, it is set to "TmQ".

[Fabrication of Thin Film as Core of Optical Waveguide: Example 1] In Example 1, four kinds of organic rare earth complexes synthesized as described above were used, and a thin film composed of only the organic rare earth complex was used. It was made. An example of a method for producing a thin film is shown below. The organic rare earth complex was put in a crucible made of BN composite and set in a vacuum vapor deposition apparatus. By the resistance heating method, a vapor deposition film of an organic rare earth complex was formed on a glass substrate at a vacuum degree of 5 × 10 ⁻⁶ Torr. The rare earth element concentration in the deposited film corresponds to about 278700 ppm. Four kinds of vapor deposition films were produced by this method.

FIG. 2 is an absorption spectrum of the vapor-deposited film of the organic rare earth complex thus produced, showing the absorption spectrum of the vapor-deposited film of ErQ as an example.

FIG. 3 shows the results of using an argon ion laser.
Organic rare earth obtained by excitation at a wavelength of 457.9 nm
It is the photoluminescence spectrum of the evaporated film of the complex.
As an example, photoluminescence of ErQ vapor deposition film
The spectrum is shown. In Fig. 3, emission of 1.5 μm band
The width of the band (full width at half maximum) was about 80 nm. Conventionally widely
Optical fiber with Er used in silica glass
Width of photoluminescence spectrum in amplifier
(Full width at half maximum) is used in quartz glass to control the refractive index.
Added germanium oxide (GeO₂) And Al oxide
Minium (Al₂O ₃) It changes according to the addition ratio.
As a result, the full width at half maximum is at least 26.5 nm (Al₂O₃
Up to 47 nm (without GeO)₂Change to no addition)
However, the emission band width is larger in this embodiment than these.
You can see that it is expanding.

[Production of Optical Waveguide: Example 1] A ridge type optical waveguide 1 having a length of 1 cm was produced by a reactive ion etching method using the four kinds of vapor deposition films produced as described above.

[Measurement of Amplification Characteristics of Optical Amplifier Using Optical Waveguide According to Example 1 as Optical Amplification Medium] An optical amplifier 10 shown in FIG. 1 was produced using the ridge waveguide according to Example 1 as an optical amplification medium. Table 1 shows the results of measuring the amplification characteristics of the optical amplifier 10. In Table 1, the “organic rare earth complex” column indicates the type of organic rare earth complex that constitutes the core portion of the ridge waveguide. The number in the "amplification degree" column is the amplification degree of the output signal light 7 amplified by the ridge waveguide (optical waveguide 1) with respect to the input signal light 6, and is the wavelength described in the "signal light wavelength" column. The amplification degree (dB) of the signal light when the experiment is performed using the laser light having various wavelengths described in the “Pump light wavelength” column as the pump light source. As the pump light, a plurality of laser lights may be used, and for example, the description in the “Pump light wavelength” column
1.047 (Nd-YLF) + 1.550 (LD) "is 1.047 μm Nd
-It shows that two laser lights of YLF laser light and LD light of 1.550 μm were used as pump lights.

[0037]

[Table 1]

[Fabrication of Thin Film for Core of Optical Waveguide: Example 2] In Example 2, ErQ described above was used, and Er was used.
A thin film made of a polymer containing Q was prepared. An example of a method for producing a thin film is shown below. ErQ was mixed and dissolved with a UV curable acrylate resin oligomer in dichloroethane. The concentration of ErQ at this time is 50,000ppm
Met. This is spin-coated to a thickness of 50 μm.
After being made into a thin film, the film was cured by irradiating it with ultraviolet rays.

[Production of Optical Waveguide: Example 2] Using a cured film of an acrylate resin containing ErQ produced as described above, a previously reported method (for example, J. Lightwave) was used.
Technol., Vol.14, pp.1704-1713,1996 or Proc.SPIE,
Vol.3234, pp.161-174, 1997), a ridge type optical waveguide 1 having a length of 1 cm was produced.

[Measurement of Amplification Characteristics of Optical Amplifier Using Optical Waveguide According to Example 2 as Optical Amplification Medium] An optical amplifier 10 shown in FIG. 1 was produced using the ridge waveguide according to Example 2 as an optical amplification medium. As a result of measurement of the amplification characteristic of the optical amplifier 10, 1.
With the signal light of 55 μm, the amplification of 10 dB could be obtained by the pump light of 980 nm.

As described above, by using the organic rare earth complex shown in the embodiment, the core portion containing the organic rare earth complex corresponding to the high rare earth element concentration is provided in the first embodiment and the second embodiment. It could be an optical waveguide. As a result, it is possible to manufacture an optical amplifier having a sufficient optical amplification capability even though the optical waveguide has a length of 1 cm, and it is possible to reduce the size and cost of the optical amplifier. Furthermore, by optimizing the organic rare earth complex and the host medium, it is possible to fully utilize the photoluminescence of the organic rare earth complex having a wide emission band in the communication wavelength band of 1.55 μm, and to improve the amplification wavelength of the optical amplifier. It became possible to expand the belt.

The organic rare earth complex usable in the present invention may be an organic rare earth complex having an 8-hydroxyquinoline derivative having various substituents bonded to the quinoline ring of 8-hydroxyquinoline as an organic ligand. .

The organic rare earth complex in which a specific substituent is bonded to the quinoline ring has an advantage that it has a high affinity for a material forming an optical waveguide such as plastic or glass and can be doped at a high concentration. As such a substituent, for example, an alkyl group, an aryl group, a hydroxyl group, a carboxyl group, an amino group and the like are preferable, but any group that increases the solubility of the organic rare earth complex in a polymer or the like may be used. However, especially UV-curable acrylate or U
When it is added to the V-cured epoxy resin, it is preferable not to contain an amino group in order to avoid an unnecessary chemical reaction between the organic rare earth complex and the polymer when polymerizing by UV irradiation. The organic rare earth complex in which a substituent is bonded to the quinoline ring can be synthesized by the same method as the method for synthesizing the organic rare earth complex exemplified in the above-mentioned Examples.

Examples of the alkyl group include methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group, heptyl group, octyl group, nonyl group,
Examples thereof include a decyl group, an undecyl group and a dodecyl group.
In addition, examples of the aryl group include a phenyl group, a naphthyl group, and an anthryl group.

Further, materials in which ions of the above various organic rare earth complexes are pendant on a polymer may be used for producing an optical amplification medium.

The polymer material has a small loss in the optical communication wavelength band of 1.3 μm or 1.5 μm and has a high concentration of the organic rare earth complex, preferably 1000 pp.
Any material can be used as long as it can be doped at a concentration of m or more. Specific examples include acrylate, epoxy resin, polyimide, and silicone resin. In particular, in order to efficiently add a high-concentration organic rare earth complex, a type in which a monomer or oligomer that is liquid at room temperature is cured by UV irradiation to be polymerized is desirable.

As the host medium to which the organic rare earth complex is added, a glass material can be used in addition to the polymer material. However, it is difficult to add an organic rare earth complex to the existing glass-based optical amplification medium. This is because the current optical fiber amplifiers are mainly made of quartz glass, tellurite glass or fluoride glass, and in the production of these optical amplifiers, in the process of preform production and drawing from preform to fiber, 1000 ° C
This is because the above high temperature conditions are necessary. Therefore, sol-gel glass is desirable as the glass material. Sol-gel glass uses metal alkoxide as a starting material,
Since it is a glass material synthesized by hydrolysis / dehydration condensation reaction and can be synthesized at room temperature, it can be added to glass without decomposing the organic rare earth complex.

In the above embodiment, the optical waveguide having the organic rare earth complex in the core portion is used as the optical amplification medium. However, an optical amplifier is manufactured using the optical fiber having the organic rare earth complex in the core portion as the optical amplification medium. Also, the same effect can be obtained.

[0049]

According to the present invention, in an optical amplifier using an optical waveguide or an optical fiber as an optical amplifying medium, the core portion contains an organic rare earth complex represented by the above general formula (1), whereby a high rare earth element is obtained. Since an organic rare earth complex corresponding to the element concentration can be added and the optical amplification efficiency can be improved, a small-scale and low-cost optical amplifier can be manufactured.

Further, in the 1.55 μm band which is a communication wavelength band, the organic rare earth complex exhibits a photoluminescence spectrum having a wide emission band width, and a resin such as a UV-curable acrylate that does not cause optical loss in this wavelength band is used as a core part. By using this as the host medium, an optical amplifier having a wide amplification wavelength band can be manufactured.

That is, according to the present invention, it is possible to provide a small-sized and inexpensive broadband optical amplification medium and an optical amplifier using the same.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an optical amplifier according to an embodiment of the present invention.

FIG. 2 is an absorption spectrum diagram of a deposited film of ErQ according to Example 1 of the present invention.

FIG. 3 is a photoluminescence spectrum diagram of an ErQ vapor deposition film according to Example 1 of the present invention.

[Explanation of symbols]

1 Optical waveguide 2 WDM coupler 3 Isolator 4 pump light source 5 band pass filter 6 Input signal light 7 Output signal light 10 Optical amplifier

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 2H047 KA04 MA05 NA08 PA02 PA15                       PA24 PA28 QA05 RA08 TA11                       TA41                 2H050 AB18X AC03 AD00                 5F072 AB20 AK06 JJ01 JJ02 PP07                       PP10 RR01 YY17

Claims (9)

[Claims] 1. An optical waveguide having at least a core portion, wherein the core portion is made of an organic rare earth complex represented by the following general formula (1). [Chemical 1] However, in the general formula (1), M represents a rare earth element selected from the group consisting of praseodymium, thulium, erbium and neodymium. 2. An optical waveguide having at least a core portion, wherein the core portion contains an organic rare earth complex represented by the following general formula (1). [Chemical 2] However, in the general formula (1), M represents a rare earth element selected from the group consisting of praseodymium, thulium, erbium and neodymium. 3. An optical fiber having at least a core part, wherein the core part contains an organic rare earth complex represented by the following general formula (1). [Chemical 3] However, in the general formula (1), M represents a rare earth element selected from the group consisting of praseodymium, thulium, erbium and neodymium. 4. The core according to claim 2, wherein the core portion is polyimide, silicone resin, UV-curable acrylate, and U.
An optical waveguide comprising a resin selected from the group consisting of V-curable epoxy resins and the organic rare earth complex. 5. The core according to claim 3, wherein the core portion is polyimide, silicone resin, UV-curable acrylate, and U.
An optical fiber comprising a resin selected from the group consisting of V-curable epoxy resins and the organic rare earth complex. 6. The optical waveguide according to claim 2, wherein the core portion includes sol-gel glass and the organic rare earth complex. 7. The optical fiber according to claim 3, wherein the core portion includes sol-gel glass and the organic rare earth complex. 8. An optical amplifier comprising an optical waveguide which is an optical amplification medium, and an input means for inputting pumping light or signal light for exciting the optical waveguide to the optical waveguide, wherein the optical waveguide. An optical amplifier comprising the optical waveguide according to claim 1, claim 2, claim 4, or claim 6. 9. An optical amplifier comprising: an optical fiber which is an optical amplification medium; and an input means for inputting pumping light or signal light for exciting the optical fiber to the optical fiber.
An optical amplifier, wherein the optical fiber is the optical fiber according to any one of claims 3, 5, and 7.