KR0183909B1 - Optical fiber amplifier having flat gain quality - Google Patents

Abstract

The present invention relates to an erbium-doped optical fiber amplifier having a flat gain characteristic against a change in the intensity of an incident light signal and a pump power, comprising: a first isolator for blocking the reverse travel of the incident light signal; A filter for reducing the signal attenuation on the short wavelength side and increasing the signal attenuation on the long wavelength side of the wavelength range to obtain a flat gain by inputting the signal of the first isolator; A pump laser diode that applies pumping light having a wavelength different from that of the incident light signal to amplify the incident light signal; A wavelength division multiplexer for wavelength division of the incident light passing through the filter and the wavelength of the pumping light; An erbium-doped optical fiber which amplifies the incident light signal applied from the wavelength division multiplexer into the pumping light of the pump laser diode and has a positive gain slope in the wavelength region to obtain a flat gain characteristic; And a second isolator for blocking the reverse propagation of the signal passing through the erbium-doped optical fiber.

According to the present invention, by having a flattened gain over a wavelength range of 10 nm, the amount of transmission that can be transmitted to the optical path of the optical communication system can be extended.

Description

Erbium-doped Fiber Amplifier with Flat Gain

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to optical amplifiers, and more particularly to an erbium doped fiber amplifier having flat gain characteristics against variations in the intensity and pump power of an incident light signal.

In general, optical communication is the transmission of information using light, which uses optical fiber as a transmission line, pulses the light, installs a repeater in the middle of the transmission line, discriminates the optical pulse, and amplifies by correcting a clean waveform for each repeater. Is possible communication. The development of optical communication is accelerating due to the development of technology that can transmit and distribute a large amount of information at high speed with the development of the information industry. The advantages of optical communication over electric and radio communication are various, such as no interference from electromagnetic waves, but the biggest advantage is that a large amount of information can be transmitted at once and communication loss is very low.

However, 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. As a repeater for compensating for this problem and efficiently performing optical amplification, an optical amplifier for amplifying the optical signal itself is required.

As such optical amplification repeaters, 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.

The general structure of EDFA can be classified by the wavelength and position of a pump laser diode, and there are forward pumping, reverse pumping and bidirectional pumping according to the propagation direction of the pump light. Currently used pump wavelengths are 980nm and 1480nm. In addition, depending on the application, the EDFA may be used for a pre-amplifier, an in-line amplifier, a post-amplifier and a CATV power booster.

In addition, the EDFA has a wide amplification band in the region of 1.5 占 퐉 showing the lowest loss of the optical fiber when erbium (Er3 +), which is a rare earth element, is easily spliced with the communication optical fiber, and has high gain characteristics and low There are advantages such as noise and low polarization dependence.

EDFA is also used in a Wavelength Division Multiplexing (WDM) system that bundles information on different wavelengths of light and communicates on a single line. However, in order for EDFA to be used for wavelength division multiplexing (WDM), the spectral gain of EDFA must be high, and flat gain characteristics are required over a wide wavelength range.

Recently, efforts have been actively made to planarize the gain of the EDFA. In general, there is a method of flattening the gain using an isolator or a filter or an optical fiber grating filter between Erbium Doped Fibers (EDFs). It has not been commercialized yet. Until now, a lot of research has been conducted mainly to improve the gain and noise figure of EDFA, and the gain flattening of EDFA is performed only in a certain wavelength region while keeping input signal power or pump power constant.

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) 120, which is a device, excites erbium on a part of an optical fiber core to excite erbium doped fiber (EDF, 120) and erbium, which are amplification mediums that amplify by inductive radiation principle. It is composed of a pumping laser diode 140, which is an active optical device that provides the required energy.

In the EDFA having such a configuration, the pumping laser diode 140 is connected to the EDF, and the pumping light of the pumping laser diode excites Er3 +, a rare earth element doped in the core of the optical fiber, so that spontaneous emission occurs. do. 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. In addition, the isolators 100 and 130 prevent the amplified spontaneous emission (ASE) of the EDF from being reversed, reflected by other photons, and then incident on the EDF to lower the amplification efficiency of the signal light.

EDFA, which is widely used at present, has a high gain only for a specific wavelength and has a large gain deviation depending on the wavelength. In particular, the gain spectrum greatly depends on the operating gain range of EDFA. FIG. 2 shows that the center wavelength of the pump laser diode is 980 nm, the current of the pump laser diode is 160 mA (the pump power is 67 mW), and the aluminium is made of low aluminum-containing alumino-germanosilcate erbium EDF. Fig. 3 is a diagram showing measurement results of gain and noise figure according to signal input power variation at three input signal wavelengths of 1542.3 nm, 1546.8 nm, and 1552.4 nm for an EDF having a concentration of 260 ppm and a length of 17 m. 2 is a diagram illustrating a measurement result of a gain and a noise figure according to a change in the pump laser diode current under the same conditions as in FIG. 2.

For the three wavelengths used in FIG. 2, that is, 1542.3 nm, 1546.8 nm, and 1552.4 nm, the small signal amplification gain is about 3 dB. When the intensity of the input signal light is changed, the gain difference according to these wavelengths is also large.

Similarly in Fig. 3, when the current of the pump laser diode is 160 mA (67 mW), the gain difference at the three wavelengths is 3 dB, but the gain difference is also changed when the pump light intensity is changed.

Therefore, when the EDFA according to the prior art as shown in Figs. 2 and 3 is used in a real system, it is not possible to simultaneously send signals of multiple wavelengths to a single optical line and the intensity of the pump light decreases after a long time of use. The gain reduction range is changed according to the wavelength, so efficient optical transmission is not possible. That is, in the EDFA according to the related art shown in FIGS. 2 and 3, the wavelength range of the signal light transmittable within a gain change of 0.5 dB is only about 3 nm.

The present invention has been made to solve the problem of the extremely limited wavelength range of the transmittable signal light of the general EDFA described above, and an object thereof is to provide an EDFA having a flat gain over a wavelength range of approximately 10 nm. .

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

2 shows a center wavelength of a pump laser diode of 980 nm and a current of the pump laser diode of 160 mA (67 mW of pump power) using a conventional EDFA, and an alumino-low-machosilicate EDF containing low aluminum having an erbium concentration of 260 ppm and a length. Is a diagram showing the measurement results of the gain and noise figure according to the change of signal input power at three input signal wavelengths of 1542.3 nm, 1546.8 nm, and 1552.4 nm for an EDF of 17 m.

3 is a diagram illustrating a measurement result of a gain and a noise figure according to a change in the pump laser diode current under the same conditions as in FIG. 2.

Figure 4 shows a block diagram of an embodiment of the configuration of the EDFA having a flat gain characteristics against the change in the intensity and the pump power of the incident light signal according to the present invention.

5 shows that the center wavelength of the pump laser diode is 980 nm, the current of the pump laser diode is 160 mA (pump power is 67 mW) using EDFA according to the present invention, and the aluminum content of the alumino-low monosilicate silicate EDF is 260 ppm. And a 17m length EDF plot showing the results of gain and noise figure measurements with varying signal input power at three input signal wavelengths of 1542.3nm, 1546.8nm, and 1552.4nm.

FIG. 6 is a diagram illustrating a measurement result of gain and noise figure according to a change in the pump laser diode current under the same conditions as in FIG. 5.

In order to achieve the above object, the erbium-doped optical fiber amplifier having a flat gain characteristics against the change in the intensity of the incident light signal and the pump power, the first isolator to block the reverse progress of the incident light signal to eliminate the gain reduction phenomenon by the reflected wave; A filter for reducing the signal attenuation on the short wavelength side of the wavelength range and increasing the signal attenuation on the long wavelength side of the wavelength range to obtain a flat gain by inputting the signal of the first isolator; A pump laser diode that applies pumping light having a wavelength different from that of the incident light signal to amplify the incident light signal; A wavelength division multiplexer for wavelength division of the wavelength of the incident light passing through the filter and the pumping light; An erbium-doped optical fiber amplifying the incident light signal applied from the wavelength division multiplexer into the pumping light of the pump laser diode and having a positive gain slope in a wavelength region for obtaining a flat gain characteristic; And a second isolator which blocks the reverse propagation of the signal passing through the erbium-doped optical fiber to eliminate the gain reduction phenomenon caused by the reflected wave.

The filter has a peak attenuation at an input signal wavelength of 1554.5 nm, a free spectral range (FSR) of 32 nm, and is preferably a mark-gender filter for filtering signal light according to the wavelength. The erbium-doped optical fiber has a flat gain characteristic. It is preferable that it is a low aluminum containing alumino-low-silosilicate erbium-doped optical fiber having a positive gain slope in the wavelength range to have.

And an erbium-doped fiber amplifier having a flat gain characteristic against the change in the intensity and the pump power of the incident light signal having another configuration according to the present invention for achieving the above object is a gain by the reflected wave by blocking the reverse progress of the incident light signal A first isolator to eliminate the reduction phenomenon; A filter for increasing the signal attenuation at the short wavelength side of the wavelength range and for reducing the attenuation at the long wavelength side of the wavelength range for obtaining a flat gain by inputting the signal of the first isolator; A pump laser diode that applies pumping light having a wavelength different from that of the incident light signal to amplify the incident light signal; A wavelength division multiplexer for wavelength division of the wavelength of the incident light passing through the filter and the pumping light; An erbium-doped optical fiber which amplifies the incident light signal applied from the wavelength division multiplexer into the pumping light of the pump laser diode and has a negative gain slope in a wavelength region to obtain a flat gain characteristic; And a second isolator which blocks the backward movement of the signal passing through the erbium-doped optical fiber and eliminates the gain reduction caused by the reflected wave.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. In the present invention, a Mach-Zehnder filter having a 32 nm free spectral range (FSR) in order to flatten the gain according to the wavelength of the EDFA in the 10 nm wavelength region from 1542 nm to 1552 nm. Was inserted in front of the EDF. FIG. 4 is a block diagram showing an embodiment of the configuration of an EDFA having a flat gain characteristic against a change in the intensity and the pump power of an incident light signal according to the present invention. The first isolator 400 and the mark-gender filter 410, the pump laser diode 420, the wavelength division multiplexer 430, the erbium-doped optical fiber 440, and the second isolator 450.

The first isolator 400 serves to eliminate the gain reduction phenomenon caused by the reflected wave by blocking unnecessary backward propagation of the incident light signal and isolating around 40dB. The Mark-Zehnder filter 410 is inserted at the front end of the EDF 440 to filter signal light according to the wavelength, and to obtain a flat gain by inputting the signal of the first isolator 400. The short wavelength side of the region reduces the signal attenuation and the long wavelength side increases the signal attenuation. Also, the free spectral range (FSR) is 32nm, the absorption ratio is adjustable up to 35dB, the wavelength tuning range is up to 1.4FSR, and the absorption rate has peak attenuation at 1554.5nm. Was adjusted to 3 dB.

The pump laser diode 420 applies pumping light having a wavelength different from that of the incident light signal to amplify the incident light signal. The pump laser diode 420 has better amplification efficiency and better noise figure characteristics than the pump LD having a wavelength of 1480 nm. It is a pump LD with a pump light wavelength of 980 nm of Seastar (the name of a pump laser diode manufacturer) with a maximum power of 77 mW. The wavelength division multiplexer (WDM) 430 divides and combines the incident light passing through the mark-gender filter 410 with the wavelength of the pumping light to the EDF 440. Insertion loss is around 0.3dB and isolation is above 18dB.

Erbium-doped optical fiber (EDF, 440) is an amplifying medium for amplifying the incident light signal applied from the wavelength division multiplexer (WDM, 430) into the pumping light of the pump laser diode (LD, 420). It is a low aluminum-containing alumino-low-silosilicate erbium-doped optical fiber having a positive gain slope in the wavelength range and having an erbium doping concentration of 260 ppm, and has a length of 17 m. The second isolator 450 serves to eliminate the gain reduction caused by the reflected wave by blocking the reverse direction of the signal passing through the erbium-doped optical fiber 440.

Meanwhile, an operation of an embodiment of the configuration of the EDFA having a flat gain characteristic with respect to the change in the intensity and the pump power of the incident light signal according to the present invention will be described. The mark-gender filter 410 used in the above embodiment can tune the FSR region according to the wavelength up to 1.4 times the FSR, and the absorption rate is adjustable up to 35dB. Accordingly, the intensity of the signal light entering the EDF 440 varies depending on the wavelength by varying the attenuation of the input signal with the same power according to the wavelength. The EDF 440 used in the embodiment of the present invention has a small gain on the short wavelength side and a large gain on the long wavelength side in the gain spectrum of 1542 nm and 1552 nm, so that the signal light entering the EDF 440 is a mark-gender filter 410. The short wavelength side has a small attenuation and the long wavelength side has a large attenuation, resulting in the opposite of the gain spectrum of the EDF 440. The attenuation spectrum of the mark-gender filter 410 and the gain spectrum of the EDF 440 complement each other, thereby flattening the gain of the EDFA.

The optimal length of the EDF 440 used was 17 m, and the absorption rate of the mark-gender filter 410 was adjusted to have a peak attenuation of 3.0 dB at 1554.5 nm at 1542 nm for optimal gain flattening in the wavelength range from 1542 nm to 1552 nm. The gain was flattened within ± 0.5 dB in the 10 nm range up to 1552 nm.

If the length or type of EDF is changed, the absorption rate and tuning range of the mark-gender filter 410 should be adjusted according to the gain spectrum of the given EDF.

In the present invention, the gain difference according to the wavelength when the gain is changed to 20.5 dB while changing the pump power is within ± 0.4 dB as shown in FIG. 6, and the gain difference is shown in FIG. It was within ± 0.4 dB as shown. 5 shows that the center wavelength of the pump laser diode is 980 nm and the current of the pump laser diode is 160 mA (pump power is 67 mW) using the EDFA according to the present invention, and the aluminum content of the alumino-low monosilicate silicate EDF is low. For an EDF of 260ppm and 17m in length, it is a graph showing the measurement results of gain and noise figure according to the change of signal input power at three input signal wavelengths of 1542.3nm, 1546.8nm and 1552.4nm. FIG. 6 is a diagram illustrating a measurement result of gain and noise figure according to a change in the pump laser diode current under the same conditions as in FIG. 5.

Meanwhile, another embodiment of the present invention will be described. Another embodiment of the present invention has the same components except for the difference in characteristics of the mark-gender filter and the EDF when compared with the embodiment. That is, the mark-gender filter 410 inputs the signal of the first isolator 400 to increase the signal attenuation in the short wavelength side and the long wavelength side in the wavelength region to obtain a flat gain as opposed to the above embodiment. Reduce the attenuation In addition, the EDF 440 also has a 'negative gain slope' in the wavelength region to obtain flat gain characteristics as opposed to the above embodiment, and has a low aluminum-containing alumino-lower than 260 ppm of erbium doping concentration. It is a monosilicate erbium doped optical fiber. Even in this configuration, the attenuation spectrum of the mark-gender filter 410 and the gain spectrum of the EDF 440 are complemented with each other, thereby flattening the gain of the EDFA.

According to the present invention, the mark-gender filter 410 is used in front of the EDF 440 to flatten the gain of the EDFA to within ± 0.4 dB in the wavelength range from 1542 nm to 1552 nm. That is, even if the intensity of the input signal changes, the gain difference of EDFA is flattened within ± 0.4dB in a given wavelength range, and even if the pump power varies from 0mW to 67mW, the gain difference of EDFA is flattened within ± 0.4dB according to the wavelength.

This is very effective when using several EDFAs in long distance transmission when applied to actual system. When one of several EDFAs is used, and one of them becomes inoperative, the signal light entering the next EDFA has a small intensity, so that the gain difference according to the wavelength is large in the case of the existing EDFA. If the characteristics are slightly different, communication may not be possible. However, the EDFA according to the present invention can use all the channels used initially because the gain difference according to the wavelength is constant even if the signal light intensity is different.

With good control of EDFA's characteristics and mark-gender filters, EDFA's gain planarization can be made smaller in a given wavelength range, as well as widening the current wavelength range from 10nm to more.

In addition, when the optical communication system is applied, when transmitting signals of multiple channels at 1 nm wavelength interval in one optical fiber, only 2-3 channels can be transmitted using the existing EDFA, but when using the EDFA of the present invention, 10 channels can be simultaneously transmitted. The capacity can be tripled.

Claims (6)

In the erbium-doped optical fiber amplifier having a flat gain characteristic against a change in the intensity of the incident light signal and the pump power, A first isolator which blocks a backward movement of the incident light signal to eliminate a gain reduction phenomenon due to the reflected wave; A filter for reducing the signal attenuation on the short wavelength side of the wavelength range and increasing the signal attenuation on the long wavelength side of the wavelength range to obtain a flat gain by inputting the signal of the first isolator; A pump laser diode that applies pumping light having a wavelength different from that of the incident light signal to amplify the incident light signal; A wavelength division multiplexer for wavelength division of the wavelength of the incident light passing through the filter and the pumping light; An erbium-doped optical fiber amplifying the incident light signal applied from the wavelength division multiplexer into the pumping light of the pump laser diode and having a positive gain slope in a wavelength region for obtaining a flat gain characteristic; And And a second isolator for blocking a reverse propagation of a signal passing through the erbium-doped optical fiber to eliminate a gain reduction phenomenon caused by the reflected wave. The method of claim 1, wherein the filter An erbium-doped fiber amplifier with flat gain characteristics, characterized in that the input signal has a peak attenuation at 1554.5 nm, has a free spectral range (FSR) of 32 nm, and is a mark-gender filter for filtering the signal light according to the wavelength. The method of claim 1, wherein the erbium-doped optical fiber An erbium-doped optical fiber amplifier having a flat gain characteristic, characterized in that it is a low aluminum-containing alumino-low monosilicate erbium-doped optical fiber having a positive gain slope in the wavelength region to have a flat gain characteristic. The method of claim 1, wherein the pump laser diode An erbium-doped optical fiber amplifier having a flat gain characteristic, characterized in that the pump laser diode having a wavelength of 980nm pump light. In the erbium-doped optical fiber amplifier having a flat gain characteristic against a change in the intensity of the incident light signal and the pump power, A first isolator which blocks a backward movement of the incident light signal to eliminate a gain reduction phenomenon due to the reflected wave; A filter for increasing the signal attenuation at the short wavelength side of the wavelength range and for reducing the attenuation at the long wavelength side of the wavelength range for obtaining a flat gain by inputting the signal of the first isolator; A pump laser diode that applies pumping light having a wavelength different from that of the incident light signal to amplify the incident light signal; A wavelength division multiplexer for wavelength division of the wavelength of the incident light passing through the filter and the pumping light; An erbium-doped optical fiber which amplifies the incident light signal applied from the wavelength division multiplexer into the pumping light of the pump laser diode and has a negative gain slope in a wavelength region to obtain a flat gain characteristic; And And a second isolator for blocking the reverse propagation of the signal passing through the erbium-doped optical fiber to eliminate gain reduction caused by the reflected wave. The method of claim 5, wherein the erbium-doped optical fiber An erbium-doped optical fiber amplifier having a flat gain characteristic, characterized in that it is a low aluminum-containing alumino-low monosilicate erbium-doped optical fiber having a negative gain slope in the wavelength range to obtain a flat gain characteristic.