KR19980067576A - Fiber Optic Amplifier Using Fiber Optic Reflector - Google Patents

Abstract

The present invention relates to an optical fiber amplifier using an optical fiber reflector, comprising: a pump light source for applying pumping light to amplify incident signal light; A WDM coupler which combines the incident signal light and the pump light of the pump light source and transmits the light to one optical fiber; An optical fiber amplifying medium for amplifying the incident light signal output from the WDM coupler by the pumping light of the pump light source and conversely amplifying the reflected signal light; Optical fiber that reflects the signal light amplified through the optical fiber amplification medium with different reflectance according to the wavelength of the signal light, outputs the reflected signal light to the optical fiber amplification medium, and pumps the remaining pump light of the pump light source and reflects the remaining pump light back into the optical fiber amplification medium. reflector; And a circulator that transmits the incident signal light to the WDM coupler, and outputs the amplified signal light that is reflected by the optical fiber reflector and re-entered into the optical fiber amplification medium and then amplified signal light received through the WDM coupler.

According to the present invention, it is possible to flatten the gain of the EDFA by using a reflector coated with a different reflectance according to the wavelength, thereby to flatten the small signal gain over a wider wavelength range, and by removing the isolator used in the input / output stage in the conventional structure. The structure of the EDFA is simplified, and the length of the EDF required to obtain the same gain characteristics can be reduced by half.

Description

Fiber Optic Amplifier Using Fiber Optic Reflector

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber amplifier, and more particularly, to an optical fiber amplifier having an optical fiber reflector having a different reflectance according to a wavelength.

In general, in the repeater for long-distance optical communication, the conventional optical communication relay method is a method of converting the weakened optical signal into an electrical signal to amplify and then converting it into an optical signal to communicate. In such a relay method, there are many problems such as excessively enlarged and increased noise of the relay amplifier system. An optical amplifier that amplifies the optical signal itself is required as a repeater to compensate for this problem and to efficiently perform the optical amplification.

As such optical amplifiers, Erbium Doped Fiber Amplifiers (hereinafter referred to as EDFAs) are receiving a lot of attention as next-generation optical communication optical repeaters. The EDFA is used to amplify the optical signal periodically to prevent attenuation of the optical signal due to the long distance transmission when a large amount of data is transmitted over a long fiber.

If the EDFA is classified according to the use, it can be divided into a pre-amplifier, an in-line amplifier, a post-amplifier, and a CATV power booster. In addition, the EDFA is 1.51 showing the lowest loss of the optical fiber when the rare earth element erbium (Er3 +) is added In addition to a wide amplification band in the m region, it is easy to splic with communication optical fibers, and has high gain characteristics, low noise, and low polarization dependence.

EDFA is used in a Wavelength Division Multiplexing (WDM) system in which information carried on different wavelengths of light is bundled and communicated on a single line. However, in order for EDFA to be used for wavelength division multiplexing (WDM), the gain of EDFA must be high, and a flat gain characteristic is required over a wide wavelength range.

FIG. 1 is a block diagram illustrating a general EDFA configuration, and includes two optical isolators 100 and 130 for preventing reverse flow of signals to prevent oscillation of light waves other than signals, and passive light for combining pump light and signal light into a single optical fiber. A wavelength division multiplexer (WDM) coupler (120), an erbium doped fiber (EDF, 120), which is an amplifying medium that amplifies the inductive radiation principle by doping erbium on a part of the optical fiber core; It is composed of a pumping laser diode 140, which is an active optical element that provides the energy required to excite the erbium ions in the ground state in the EDF. In the EDFA having such a configuration, a pumping laser diode 140 is connected to the EDF, and the pumping light of the pumping laser diode excites Er3 ⁺ , which is a rare earth element doped in the core of the optical fiber, to produce a stimulated emission. Get up. The center wavelength of the pumping laser diode 5 is 980 nm, and the pumping light output is incident on the erbium-doped optical fiber 120 through the wavelength division multiplexer 110 together with the weak optical signal through the isolator 100 on the input side. . The wavelength division multiplexer 110 combines an optical signal having a wavelength of 1530 nm to 1560 nm and a pumping light having a wavelength of 980 nm to enter the EDF 120. In the EDF 120, optical signals having a wavelength of 1530 nm to 1560 nm are amplified by pumping light having a wavelength of 980 nm. The isolators 100 and 130 prevent distortion of the input signal due to reflected light reflected by other photons and light traveling in the reverse direction among the output light by the ASE (amplified spontaneous emission) of the EDF.

However, the EDFA has a high gain only for a specific wavelength and has a large gain deviation depending on the wavelength. In particular, there is a problem that the gain spectrum greatly depends on the operating gain range of the EDFA. Thus, when the EDFA is mounted on a real system, it is not only possible to send signals of multiple wavelengths to a single optical line at the same time, but also to reduce the efficiency of optical transmission because the gain decreases depending on the wavelength when the intensity of the pump light decreases after a long time of use. . That is, the wavelength range of the signal light transmittable within the gain change of 0.5 dB is only about 3 nm.

In addition, optical communication aims to transmit a large amount of information quickly and accurately, and at the same time, many new concepts such as time division, code division, and wavelength division are emerging to send more information. In recent years, the optical transmission has been focused on a wavelength division transmission method, and research on this has been actively conducted. This requires a fiber amplifier with a constant gain regardless of wavelength. Since the EDFA has different amplification gains depending on the wavelength, even when the transmitter transmits the signal intensity having the same intensity regardless of the wavelength, the intensity of the signal received at the receiver varies depending on the wavelength. You cannot receive all of the original signals beyond. This phenomenon causes more serious use of more fiber amplifiers, and ultimately the fiber amplifiers cannot be used for communication except for signals of a certain wavelength.

The present invention has been made to solve the above-mentioned problems, and improves the small signal gain in the long wavelength band (1550 nm to 1560 nm), which was not possible in the conventional optical fiber amplifier, and increases the wider wavelength band (about 1530 nm to 1560 nm or more). In order to reduce the gain difference of the optical fiber amplifier and to flatten the gain, an object of the present invention is to provide an optical fiber amplifier having a flat gain using an optical fiber reflector coated with a reflectance differently depending on the wavelength.

Figure 1 shows a block diagram of the configuration of a typical EDFA.

2 is a block diagram showing the configuration of the optical fiber amplifier according to the present invention.

Figure 3 shows the reflectance characteristics of the optical fiber reflector according to the signal light wavelength of the optical fiber reflector used in the optical fiber amplifier according to the present invention.

Figure 4 shows the gain characteristics according to the wavelength of the EDFA and normal EDFA using the optical fiber reflector according to the present invention.

5 shows gain characteristics according to the intensity of signal light for two wavelengths, REDFA and Normal EDFA.

FIG. 6 shows the reflectance of an optical fiber reflector to have a flat gain characteristic in a wider wavelength band.

FIG. 7 is a block diagram illustrating a configuration of an optical fiber amplifier in which a second pump LD is added between the EDF and the optical fiber reflector of FIG. 2.

Explanation of symbols for the main parts of the drawings

200: circulator, 210: WDM coupler,

220: pump LD, 230: EDF,

240: optical fiber reflector

According to the present invention for achieving the above object, the optical fiber amplifier using an optical fiber reflector whose reflectance is different depending on the wavelength of the pump light source for applying the pumping light to amplify the incident signal light; A WDM coupler which combines the incident signal light and the pump light of the pump light source and transmits the light to one optical fiber; An optical fiber amplifying medium for amplifying the incident light signal output from the WDM coupler by pumping light of the pump light source, and amplifying the reflected signal light; Reflects the signal light amplified by the optical fiber amplification medium with different reflectances according to the wavelength of the signal light, outputs the reflected signal light to the optical fiber amplification medium, reflects the pumped pump light of the pump light source, and reflects the remaining pump light to the optical fiber amplification medium. An optical fiber reflector to be incident; And a circulator for transmitting an incident signal light to the WDM coupler and outputting the reflected and re-amplified signal light received through the WDM coupler.

Another optical fiber amplifier according to the present invention for achieving the above object, the first pump light source for applying the pumping light to amplify the incident signal light; A WDM coupler which combines the incident signal light and the pump light of the pump light source and transmits the light to one optical fiber; A second pump light source for applying pumping light to amplify the reflected signal light; An optical fiber amplifying medium for amplifying the incident light signal output from the WDM coupler by the pumping light of the first pump light source, and amplifying the reflected signal light by the pumping light of the second pump light source; An optical fiber reflector reflecting the signal light amplified by the optical fiber amplification medium with different reflectances according to the wavelength of the signal light; A second WDM coupler that receives the signal light amplified by the optical fiber amplification medium and outputs the signal light as it is, and combines the reflected signal light and the pump light of the second pump light source; And a circulator for transmitting an incident signal light to the first WDM coupler and outputting the reflected and re-amplified signal light received through the first WDM coupler.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. FIG. 2 is a block diagram showing the configuration of an optical fiber amplifier according to the present invention, and is used to excite Erbium ions in an EDF (Erbium Doped Fiber) 230, which is an optical fiber amplification medium, and a ground state in the EDF 230. A light source includes a pump laser diode (LD) 220, a wavelength division multiplexer (WDM) coupler 210, a circulator 200, and an optical fiber reflector 240.

The pump LD 220 is a pump light source for applying pumping light to amplify the incident signal light. In addition, in order to compare the results of the present invention with a normal single forward EDFA, the pump LD 220 has a wavelength of 980 nm and forward pumping in the same direction as the signal light. Fixed with.

The WDM coupler 210 combines the incident signal light and the pump light of the pump LD 220 and transmits the light to the EDF 230, and has a fuse type.

The EDF 230 is an optical fiber amplifying medium for amplifying the incident light signal output from the WDM coupler 210 by the pumping light of the pump LD 220 and amplifying the reflected signal light. In addition, the EDF 230 is a high aluminum doped (High Al-doped) EDF, Erbium (Erbium) concentration of 165ppm used 24m.

The optical fiber reflector 240 is a core device of the present invention, and reflects the signal light amplified through the optical fiber amplification medium EDF 230 at different reflectances according to the wavelength of the signal light, and is reflected from the optical fiber reflector 240. The reflected signal light is output to the EDF 230, and the remaining pump light of the pump LD 220 is reflected to be reincident to the EDF 230. The optical fiber reflector 240 is coated on the EDF 230 according to the wavelength of the reflectance is different, its characteristics are as shown in Figure 3. In addition, the optical fiber reflector 240 was coated to totally reflect the pump wavelength of 980 nm in order to efficiently use the intensity of the pump light remaining after pumping the EDF 230.

The circulator 200 causes the incident signal light to enter the EDF 230 through the WDM coupler 210, and the final output light of the reflected signal light reflected from the optical fiber reflector 240, that is, the WDM coupler 210. It outputs the amplified signal light of the EDF 230 received through the, has a three-port structure. Port 1 → port 2 of the circulator 200 passes the input signal light and port 2 → port 3 passes the output signal light. The insertion loss of the input / output port is 1.2 dB and 1.73 dB, respectively. Isolation of port 2 → port 1 and port 3 → port 2 is more than 60dB and includes the function of the isolator used in the input / output stage in the existing structure, so there is no need to use a separate isolator.

On the other hand, the operation of the present invention based on the configuration of the present invention as described above are as follows. The present invention is based on the measured results to planarize the gain of the optical fiber amplifier within a certain range in a wide wavelength range from 1530nm to 1560nm using optical reflectors with different reflectances according to the wavelength, reflecting the optical reflector according to the wavelength more precisely This different coating is intended to reduce the gain difference in the wider wavelength range.

The incident signal light enters the EDF 230 after passing from port 1 to port 2 of the circulator 200, and is amplified firstly, and the amplified signal light is reflected from the optical fiber reflector 240 and passes again through the EDF 230. After the amplification, the final output is performed from port 2 to port 3 of the circulator 200. In general, at an optimized length, the EDF 230 has a large gain for wavelengths of 1530 nm and a small gain of 1550 nm. Therefore, the output of the signal light amplified first is 1530nm larger than 1550nm. However, since the optical reflector 240 used has a low reflectance at 1530 nm and a high reflectance at 1550 nm, the intensity of the signal light reflected by the reflector 240 is 1530 nm smaller than 1550 nm, and the signal light is returned to the EDF 230 again. When incident and amplified, it is possible to reduce the gain difference depending on the wavelength.

Figure 4 shows the gain characteristics according to the wavelength of the EDFA and the normal EDFA using the optical fiber reflector according to the present invention, the intensity of the input signal light is -35dBm and the intensity of the pump light used is fixed to 65mW. In FIG. 4, Gr represents the gain of Reflected EDFA, and Gn represents the gain of normal EDFA. In order to compare the measured data with the normal EDFA (Single forward EDFA), optical devices such as WDM used the same product, and the same length was used for the same EDF. The wavelength of input signal light was measured about 1528 nm, 1533 nm, 1540 nm, 1546 nm, 1551 nm, 1557 nm, and 1563 nm. In Fig. 4, data denoted by ■ is a gain characteristic of Normal EDFA, and data denoted by ◆ is a gain characteristic of REDFA using the optical fiber reflector according to the present invention. Comparing these two data between wavelength 1528nm and 1557nm, the optical fiber amplifier using the prior art has a gain of about 5 ~ 7dB lower in the 1550nm wavelength band and a small signal gain difference of more than 11dB in the 30nm wavelength range from 1528nm to 1557nm compared to the 1530nm wavelength band. very big. To compensate for this drawback, the optical reflector coated with low reflectance in the 1530 nm wavelength band and high reflectance in the 1550 nm wavelength band is used to increase the gain in the 1550 nm wavelength band while maintaining the gain in the 1530 nm wavelength band. The difference could be reduced. In this way, the small signal gain within the 30nm wavelength region can be flattened within +/- 3dB. This result shows that the gain difference is reduced by half in the same wavelength region while the gain is higher than that of the conventional EDFA.

FIG. 5 shows gain characteristics according to the intensity of signal light for two wavelengths of REDFA and Normal EDFA. Using the optical fiber reflector of the present invention, the same gain characteristics can be obtained, and the length of the EDF can be reduced by half. 5 is a result of measuring the gain characteristics of the EDFA at 5 dBm intervals from -40 dBm to -20 dBm while maintaining the intensity of the pump light at signal wavelengths of 1532 nm and 1551 nm. The EDF used here is the same kind, 24m in normal EDFA and 12m in REDFA using fiber reflector. Especially in small signal (-40dBm ~ -30dBm), it can be seen that the gain of these two structures shows almost the same characteristic. And Gr 1532nm shows the gain of REDFA at 1532nm, Gr 1551nm shows the gain of REDFA at 1551nm. Gn 1532 nm represents the gain of normal EDFA at 1532 nm, and Gn 1551 nm represents the gain of normal EDFA at 1551 nm.

On the other hand, in the above embodiment, a small signal gain average of 34 dB is obtained in the wavelength region of 1528 nm to 1557 nm (30 nm), but the gain difference is relatively large as +/- 3 dB. This is because the reflection characteristics of the optical fiber reflector did not have the desired performance depending on the wavelength. FIG. 6 illustrates reflectance of an optical fiber reflector to have a flat gain characteristic in a wider wavelength band. In order to flatten a small gain difference of the optical fiber amplifier in a wider wavelength band, as shown in FIG. In addition, it is necessary to correct the reflectance according to the wavelength of the optical fiber reflector such as to increase the reflectance of the 1540 nm wavelength. By adjusting the reflectance of the optical fiber reflector according to the wavelength in this way it is possible to flatten the gain difference in a wider wavelength range.

FIG. 7 is a block diagram illustrating a structure of an optical fiber amplifier in which a second pump light source, that is, a second pump LD is added between the EDF 230 and the optical fiber reflector 240 of FIG. 2, to amplify incident signal light. The first pump LD (710) for applying the pumping light for the first, the first WDM coupler (720) for combining the incident signal light and the pump light of the pump light source and transmits to one optical fiber, the pumping light is applied to amplify the reflected signal light The second pump LD 740 and the incident light signal output from the first WDM coupler 720 are amplified by the pumping light of the first pump LD 710, and conversely, the reflected signal light is converted into the second pump LD 740. EDF 730 to amplify by the pumping light of the optical fiber), an optical fiber reflector 760 that outputs the reflected signal light reflected at different reflectances according to the wavelength of the signal light, and receives the signal light amplified by the EDF (730) as it is The reflected signal light and the second firm The second WDM coupler 720 and the incident signal light for coupling the pump light of the LD 740 to the first WDM coupler 720, the amplified signal light of the EDF (730) received through the first WDM coupler 720 It consists of a circulator 700 for outputting.

7 is an operation principle similar to that of FIG. 2, and thus the description of the operation is omitted here. Only the pump light used to amplify the reflected signal light reflected from the optical fiber reflector 760 in the EDF 730 may include a first pump LD ( Not only the reflected pump light of 710 but also the pump light output from the second pump LD 740 differs in its features.

In the present invention, by using the reflector coated with a different reflectance according to the wavelength, the gain of the EDFA can be flattened to flatten the small signal gain over a wider wavelength range. In addition, the structure of the EDFA is simplified by removing the isolator used in the input / output stage in the conventional structure, and has the advantage of reducing the length of the EDF required to obtain the same gain characteristics in half.

The optical fiber reflector is designed to reflect the pump light at the same time as the signal light, so it is more efficient to pump the EDF and to recycle the remaining power. The strength of the pump LD used in the present invention is 65mW, but the low power of the pump LD has been increasing in recent years, the use of such LD will further increase the effect of the present invention.

The optical fiber reflector used in the present invention has the advantage of being able to produce a large amount of reflector at one time because it can coat several optical fibers at the same time once the coating conditions are set. With the present invention, there is a long way to fabricate an optical fiber amplifier that has high gain and can flatten the gain in a wide wavelength band, and many applications are expected in the future.

Claims (4)

A pump light source for applying pumping light to amplify the incident signal light; A WDM coupler which combines the incident signal light and the pump light of the pump light source and transmits the light to one optical fiber; An optical fiber amplifying medium for amplifying the incident light signal output from the WDM coupler by pumping light of the pump light source, and amplifying the reflected signal light; Reflects the signal light amplified by the optical fiber amplification medium with different reflectances according to the wavelength of the signal light, outputs the reflected signal light to the optical fiber amplification medium, reflects the pumped pump light of the pump light source, and reflects the remaining pump light to the optical fiber amplification medium. An optical fiber reflector to be incident; And And a circulator for transmitting the incident signal light to the WDM coupler and outputting the amplified signal light of the optical fiber amplifying medium received through the WDM coupler. The method of claim 1, wherein the pump light source An optical fiber amplifier using an optical fiber reflector characterized in that the pump laser diode. According to claim 1, wherein the optical fiber reflector The optical fiber amplifier using the optical fiber reflector, characterized in that for reflecting the signal light at a predetermined reflectance according to the wavelength of the signal light irrespective of the wavelength of the pump light source. A first pump light source for applying pumping light to amplify the incident signal light; A WDM coupler which combines the incident signal light and the pump light of the pump light source and transmits the light to one optical fiber; A second pump light source for applying pumping light to amplify the reflected signal light; An optical fiber amplifying medium for amplifying the incident light signal output from the WDM coupler by the pumping light of the first pump light source, and amplifying the reflected signal light by the pumping light of the second pump light source; An optical fiber reflector for outputting reflected signal light reflecting the signal light amplified by the optical fiber amplification medium at different reflectances according to the wavelength of the signal light; A second WDM coupler that receives the signal light amplified by the optical fiber amplification medium and outputs the signal light as it is, and combines the reflected signal light and the pump light of the second pump light source; And And a circulator for transmitting the incident signal light to the first WDM coupler and outputting the amplified signal light of the optical fiber amplification medium received through the first WDM coupler.