KR100345332B1 - Recycled erbium doped fiber amplifier - Google Patents

Abstract

PURPOSE: A recycled erbium doped fiber amplifier is provided to amplify an amplified light again and enhance an amplification efficiency, or smooth a gain without the degradation of the entire gain. CONSTITUTION: A circulator(11) has 3 input and output ports. A pump laser diode(15) provides a pump light. A WDM(Wavelength Division Multiplexer)(12) combines the optical signal inputted from the circulator(11) with the pump light. An erbium doped fiber(13) amplifies the optical signal inputted through the WDM(12) using an energy of the inputted pump light. The first reflective type FGF(Fiber diffraction Grating Filter)(17a) directly connects to the erbium doped fiber(13) and reflects a pump light which remains after being used in amplification to the erbium doped fiber(13). A reflector directly connects to the first reflective type FGF(17a), and reflects an optical signal with a wavelength band in which a gain is relatively low among the amplified optical signals to the erbium doped fiber(13).

Description

Recyclable Erbium Doped Fiber Amplifier

The present invention relates to a recycled erbium doped fiber amplifier, and more particularly, to a recycled erbium doped fiber amplifier that amplifies the amplified light again to increase amplification efficiency or flatten the gain without lowering the overall gain. will be.

1 is a schematic diagram of a conventional single forward erbium-doped fiber amplifier (single forward EDFA). As shown in this figure, a single forward erbium-doped optical fiber amplifier, which has been mainly used up to now, includes first and second isolators (1, 4, isolators) for preventing backflow of light reflected from optical elements of an input / output terminal. A wavelength division multiplexer (2 WDM) that combines signal and pump light with different wavelengths, an erbium doped fiber (EDF) and excitation energy source It consists of a pump laser diode (5, pump laser diode).

The single forward erbium-doped fiber amplifier in this configuration operates as follows.

First, the optical signal incident through the first isolator 1 and the pump light incident from the pump laser diode 5 are combined with each other in the wavelength division multiplexer 2 to be incident on the erbium-doped optical fiber 3. The optical signal incident on the erbium-doped optical fiber 3 is amplified by the pump light and output through the second isolator 4. As such, a graph of gain and noise figure according to the optical signal wavelength of a single forward erbium-doped fiber amplifier operating in the forward direction is shown in FIG. The characteristic graph of the EDFA shown in this figure is measured in the EDFA fabricated with a length of 24m of the erbium-doped optical fiber 3 having the optical signal amplification function, the amplification gain according to the wavelength band of the incident optical signal is 1528nm ~ 1540nm Has a peak value, a flat value in the 1540 nm to 1557 nm wavelength band, and an attenuation value in the 1557 nm to 1563 nm wavelength band. Therefore, the frequency band that can be amplified by the communication system is only optical signals in the wavelength range of 1540 nm to 1557 nm, and optical signals in the wavelength range of 1528 nm to 1540 nm are difficult to use because of their relatively large amplification gains.

The gain planarized erbium-doped fiber amplifiers proposed to improve this problem are those having the structures as shown in FIGS. 3 and 4.

First, in the gain planarized erbium-doped optical fiber amplifier as shown in FIG. 3, two or more rare earth elements are doped together instead of the erbium-doped optical fiber 3, which is an amplification element in the erbium-doped optical fiber amplifier introduced in FIG. Co-doped erbium-doped optical fiber 3 '(co-doped EDF) is used as an amplification device to planarize the gain.

Further, the gain flattened erbium-doped optical fiber amplifier as shown in FIG. 4 reflects only an optical signal of a specific frequency between the erbium-doped optical fiber 3, which is an amplification element, in the erbium-doped optical fiber amplifier introduced in FIG. In order to avoid gain flattening, an optical fiber diffraction grating filter (3 ", FGF) is inserted.

However, a gain flattened erbium doped fiber amplifier using co-doped erbium doped fiber (3 ') or inserting a fiber grating filter (3 ", FGF) is applied to the wavelength of the incident optical signal. The gain is flattened but has the disadvantage of lowering the overall gain.

In addition, since the three erbium-doped fiber amplifiers described above are forward (FORWARD) structure amplifiers, they are used for amplification in the erbium-doped fiber even when erbium-doped fiber is optimized in consideration of gain and noise figure characteristics. More than 30% of the remaining pump optical power is naturally attenuated, making it inefficient. In addition, due to the use of multiple optical devices, the losses incurred at the connecting points of these devices cannot be ignored, and as the number of optical devices increases, it is difficult to package them when the erbium doped fiber amplifier is miniaturized.

The present invention was devised to improve the above problems, and can efficiently extend the life by using the power of the pump light efficiently, reduce the light loss, facilitate the packaging for miniaturization, and at the same time gain a flattening gain flattening gain recycling The object is to provide an erbium doped fiber amplifier.

In order to achieve the above object, the gain flattened recycling erbium-doped fiber amplifier according to the present invention,

Directional optical signal transmitting means having three input / output ports;

A pump laser diode providing a pump light that is an energy source for amplification;

A wavelength division multiplexer for combining the pump light with the optical signal input from the directional optical signal transmitting means;

An erbium-doped optical fiber for amplifying the optical signal input through the wavelength division multiplexer using the energy of the pump light input together; And

Light reflecting means for reflecting the optical signal in the wavelength band of the relatively low gain of the amplified optical signal and the pump light used for the amplification to the erbium-doped optical fiber;

Characterized in that provided.

In the present invention, the directional optical signal transmitting means has a first port, a second port, and a third port, and the optical signal input to the first port must be output only to a second port, and to the second port. Preferably, the optical signal to be input is output only to the third port, and the optical signal input to the third port is preferably made of a circulator that does not output to any one of the first and second ports.

Preferably, the light reflecting means is formed of a reflector having a relatively high reflectance with respect to an optical signal in a wavelength band in which gain is relatively low in the gain characteristic curve for each wavelength band of the erbium-doped optical fiber.

In addition, in order to achieve the above object, the gain flattened recycling erbium-doped fiber amplifier according to the present invention,

Directional optical signal transmitting means having three input / output ports;

A pump laser diode providing a pump light that is an energy source for amplification;

A first wavelength division multiplexer which combines the optical signal input from the directional optical signal transmitting means and the pump light;

An erbium-doped optical fiber of a predetermined length for amplifying the optical signal input through the first wavelength division multiplexer using the energy of the pump light input together;

A second wavelength division multiplexer for dividing the amplified optical signal and the pump light used in the amplification;

An optical filter directly connected to the second wavelength division multiplexer to pass only an optical signal having a relatively low gain among the amplified optical signals divided by the second wavelength division multiplexer;

First light reflecting means connected directly to the optical filter and reflecting the optical signal filtered by the optical filter to the erbium-doped optical fiber; And

Second light reflecting means connected directly to the second wavelength division multiplexer to reflect the pump light used for the amplification divided in the second wavelength division multiplexer to the erbium-doped optical fiber;

Characterized in that provided.

In the present invention, the directional optical signal transmitting means has a first port, a second port, and a third port, and the optical signal input to the first port must be output only to the second port, and the second port It is preferable that the optical signal to be input to only the third port, and the optical signal input to the third port is made of a circulator not to be output to any one of the first and second ports,

The light reflecting means is preferably formed of a reflector having a relatively high reflectance with respect to the optical signal in the wavelength band where the gain is relatively low in the gain characteristic curve for each wavelength band of the erbium-doped optical fiber.

In addition, a recycling filter using a reflective optical fiber diffraction grating filter according to the present invention in order to achieve the above object,

Directional optical signal transmitting means having three input / output ports;

A pump laser diode providing a pump light that is an energy source for amplification;

A wavelength division multiplexer for combining the pump light with the optical signal input from the directional optical signal transmitting means;

An erbium-doped optical fiber for amplifying the optical signal input through the wavelength division multiplexer using the energy of the pump light input together;

A first reflection type optical fiber diffraction grating filter which is directly connected to the erbium-doped optical fiber and reflects the pump light used for the amplification to the erbium-doped optical fiber; And

Second light reflecting means connected directly to the first reflecting optical fiber diffraction grating filter and reflecting an optical signal having a relatively low gain in the amplified optical signal to the erbium-doped optical fiber;

Characterized in that provided.

In the present invention, the directional optical signal transmitting means has a first port, a second port, and a third port, and the optical signal input to the first port must be output only to the second port, and the second port The optical signal input to is necessarily output to only the third port, and the optical signal input to the third port is preferably made of a circulator that does not output to any of the first and second ports.

In addition, a recycling filter using a reflective optical fiber diffraction grating filter according to the present invention in order to achieve the above object,

Directional optical signal transmitting means having three input / output ports;

A pump laser diode providing a pump light that is an energy source for amplification;

A first wavelength division multiplexer which combines the optical signal input from the directional optical signal transmitting means and the pump light;

An erbium-doped optical fiber for amplifying the optical signal input through the first wavelength division multiplexer using the energy of the pump light input together;

A second wavelength division multiplexer for dividing the amplified optical signal and the pump light used in the amplification;

A first reflection type diffraction grating filter connected directly to the second wavelength division multiplexer and reflecting the pump light used for the amplification divided by the second wavelength division multiplexer to the erbium-doped optical fiber; And

A second reflection diffraction grating filter which is directly connected to the second wavelength division multiplexer and reflects an optical signal having a relatively low gain to the erbium-doped optical fiber among the amplified optical signals divided by the second wavelength division multiplexer; ; To

Characterized in that provided.

In the present invention, the directional optical signal transmission means has a first port, a second port, and a third port, and the optical signal input to the first port must be output only to the second port, the second port The optical signal input to is necessarily output to only the third port, and the optical signal input to the third port is characterized in that it is made of a circulator that does not output to any of the first and second ports.

Hereinafter, a recycling erbium doped fiber amplifier according to the present invention will be described with reference to the accompanying drawings.

5 is a schematic structural diagram of a gain flattened recycling erbium-doped fiber amplifier according to the present invention. As shown in the figure, the gain planarized recycled erbium-doped optical fiber according to the present invention includes a circulator 11 having three input / output ports and a pump laser diode providing a pump light as an energy source for amplification. 15, a pump laser diode, a wavelength division multiplexer (WDM) 12 for coupling signal light and pump light from circulators 11 having different wavelengths, and a wavelength division multiplexer 12 as an excitation medium. Erbium-doped optical fiber among the amplified optical signals incident from the erbium-doped optical fiber 13 and the erbium-doped optical fiber 13 for amplifying the optical signal input through the energy using the pump light input together Erbium-doped remaining pump light used for optical signals and amplification in the wavelength band where gain is relatively low in the gain characteristic curve for each wavelength band in (13) A light reflector 14 reflecting the optical fiber 3 is provided.

Here, the circulator 11 has three ports, and light incident to the first port is output only to the second port, and light incident to the second port is output only to the third port, and the third port. The incident light is an optical device having a characteristic of not being output to any one of the first port and the second port. Therefore, it is used as an input port of the first port optical signal, and the third port is used as an output port. The wavelength division multiplexer 12 combines an optical signal of 1532 nm or 1550 nm with a pump light of 980 nm by multiplexing by wavelength division to enter the erbium-doped optical fiber 13. The erbium-doped optical fiber 13 is an element for amplifying an optical signal, and thus, electrons excited by the pump light cause the laser to spontaneously transition according to the optical signal. The reflector 14 is advantageous for gain planarization having a relatively high reflectance for the optical signal in the wavelength band where the gain is relatively low in the gain characteristic curve for each wavelength band of the erbium-doped optical fiber 13. This amplifies by reflecting only the optical signal of the low-gain frequency band among the optical signals amplified by the erbium-doped optical fiber 13 to the erbium-doped optical fiber 13 to reamplify only the low-gain optical signal and increase its gain. This is because the gain is flattened.

The gain flattened recycling erbium-doped fiber amplifier configured as described above operates as follows.

The input signal light passes from port 1 to port 2 of the circulator 11, and the light passes through the wavelength division multiplexer 12 and is then combined with the pump light to be amplified in the erbium-doped optical fiber 13 excited by the pump light. do. The amplified signal light is reflected by the reflector 14, and similarly, the remaining pump light reflected together with the signal light passes through the excited erbium-doped optical fiber again to amplify the optical signal again. The amplified optical signal is passed through the wavelength division multiplexer 12 and finally outputs from port 2 to port 3 of the circulator 11.

In order for the recycled erbium-doped fiber amplifier to operate in this manner to have gain flattening characteristics, if the forward gain characteristic of the amplifier is as shown in FIG. 2, it is shown in FIG. 6 for each wavelength band to maximize gain flattening. As mentioned, it is preferable to use the reflector 14 which has a relatively high reflectance with respect to the optical signal of the wavelength band of about 1540 nm-1560 nm. In fact, the reflector 14 coated to reflect the signal light and the pumping field has a reflectance of 70% for the wavelength of the pump light, and for the signal light, the reflectance varies with wavelength, as shown in FIG.

By constructing the amplifier equipped with such a reflector 14, the gain in the wavelength range of 1540 nm to 1560 nm can be greatly increased in the gain characteristic as shown in FIG. 2 to obtain a flat gain characteristic as shown in FIG. . On the other hand, when comparing the gains for the signal light of 1532 nm wavelength in FIGS. 2 and 7, only 1 dB is increased. This may be due to the fact that the signal light travels back and forth through the EDF, which in turn increases the length of the EDF, which in turn increases the gain on the longer wavelength side, but the main factor is that the reflectance of the used reflector is high at 87% in the 1550 nm band but 40% in the 1532 nm band. Because as low.

In addition, the insertion loss of the circulator 11 used in the amplifier of FIG. 5 varies slightly from port to port, but has a value between approximately 1.2 dB and 1.7 dB, and isolation is 40 dB or more. Since the insertion loss of port 1 → port 2, port 2 → port 3 is 1.28 dB and 1.73 dB, respectively, the circulator 11 considers the influence of the noise figure on the relatively small loss of port 1 → port 2. Use it for the input stage of the optical signal, and place the high loss port 2 → port 3 at the output stage that does not affect the noise figure. As mentioned above, the circulator 11 has an isolation function on its own, and there is no need to install a separate isolator.

Another embodiment of the gain flattened recycling erbium-doped fiber amplifier described above is shown in FIG. The embodiment shown in this figure further includes a wavelength division multiplexer 12 ', a filter 16 and a reflector, respectively, in the embodiment of FIG. In the structure of FIG. 5, since the ASE generated by the erbium-doped optical fiber 13 is reflected by the reflector 14 and re-entered into the erbium-doped optical fiber 13, the efficiency of the entire optical amplifier is reduced, and the noise figure is reduced. In consideration of increasing shortcomings, this is to prevent reentry of ASE. That is, a wavelength division multiplexer 12 'is provided at the rear end of the erbium-doped optical fiber 13 to separate the signal light once amplified and emitted and the remaining pump light used for amplification, and then the pump light is incident on the second reflector 14b to reflect the light. The signal light is incident on the first reflector 14a through the optical filter 16 to reflect the ASE. Such a structure also takes into consideration that the reflector 14 of the embodiment of FIG. 5 is difficult to manufacture so that the reflection efficiency is high with respect to the wavelength of the pump light and the signal light. In addition, a separate protective device is required to protect the coated surfaces of the reflectors 14a and 14b from the outside.

As described above (as in the embodiments of FIGS. 5 and 8), the gain flattened recycling erbium-doped optical fiber amplifier of the operating structure is not significantly affected by the wavelength of the pump light or the pumping structure. That is, even when the wavelength of the pump light is 980 nm or 1480 nm, the reflector may be formed by doping the erbium-doped optical fiber so as to reflect the pump light of each wavelength or reflect only the pump light by using a reflective optical fiber diffraction grating filter (FGF) suitable for these wavelengths. (It is demonstrated in the Example of FIG. 9 and FIG. 10). It can also be used regardless of the forward pumping structure, the backward pumping structure and the double pumping structure.

As another embodiment of the present invention, FIGS. 9 and 10 show a schematic configuration diagram of a recycled erbium-doped fiber amplifier using the reflective optical fiber diffraction grating filter (FGF).

Here, the embodiment of FIG. 9 is the first and second manufactured to be total reflection in the wavelength range of 980nm and 1550nm, respectively, in order to maximize the recycling of the pump light and the gain of the signal light instead of the reflector 14 in the embodiment of FIG. Optical fiber diffraction grating filters 17a, 17b (FGFs) are provided in series. The order of arrangement of the first and second optical fiber diffraction grating filters 17a and 17b may be changed. Since the FGF for reflecting the pump light and the signal light, respectively, is difficult to fabricate to reflect the light of these two wavelengths together, the first optical fiber diffraction grating filter 17a reflects the reflector 14 with respect to the pump light of the 980 nm wavelength. Much higher, and the second optical fiber diffraction grating filter 17b uses a reflectance higher than that of the reflector 14 for signal light having a wavelength of 1550 nm. In general, the reflective optical fiber diffraction grating filters 17a and 17b have a narrow band width of 2 nm or less, thereby preventing reflection of the ASE generated in the erbium-doped optical fiber 13, so that a separate optical filter needs to be attached. There is no advantage.

In addition, the embodiment of FIG. 10 further includes a wavelength division multiplexer 12 'in the embodiment of FIG. 9, and the first and second reflection optical fiber diffraction grating filters ( There is a feature in that 17a and 17b) are arranged in parallel. In the structure of FIG. 9, in the embodiment of FIG. 9, the signal light of 1550 nm wavelength amplified by the erbium-doped optical fiber 13 and the signal light of 1550 nm wavelength reflected by the second reflection optical fiber diffraction grating filter 17b are 980 nm reflective optical fiber diffraction grating filters. This is to prevent insertion loss that may appear while passing through (17a). That is, after separating the signal light once amplified and emitted from the erbium-doped optical fiber 13 and the pump light used for the amplification, the pump light is incident on the second reflection optical fiber diffraction grating filter 17b to be reflected and the signal light is first Incident upon the reflective optical fiber diffraction grating filter 17a, and by varying the reflection paths of the respective wavelengths, which are generated when the first and second reflective optical fiber diffraction grating filters are connected in series as in the embodiment of FIG. This is to prevent insertion loss (i.e., in the embodiment of FIG. 9, since the 1550 nm reflective FGF 17b is disposed behind the 980 nm reflective FGF 17a, the 1550 nm optical signal passes through the 980 nm reflective FGF 17a). If the arrangement of the two reflective FGFs 17a and 17b is reversed, the loss occurs as the 980nm pump light passes through the 1550nm reflective optical fiber diffraction grating filter 17b. All). In this structure, the reflective optical fiber diffraction grating filters 17a and 17b also have a narrow band width of 2 nm or less, which prevents the reflection of the ASE generated in the erbium-doped optical fiber 13, thereby providing a separate optical filter. There is an advantage that does not need to be attached.

As described above, the recycled erbium-doped optical fiber amplifier according to the present invention includes a circulator, a reflector or an optical fiber diffraction grating filter having a high reflectance with respect to the pump light and the signal light, to recycle the remaining pump power for the first amplification and to perform primary amplification. By reflecting the optical signal back to the reflector and re-amplifying, the amplification efficiency is high and the necessary gain can be obtained even if the output of the pump laser diode is not maximized, which can extend the life of the optical fiber amplifier or reduce the gain without reducing the overall gain. Flattening has the advantage of high utilization for CATV.

1 is a schematic configuration diagram of an example of a conventional erbium-doped fiber amplifier;

2 is a graph of gain and noise figure according to the optical signal wavelength of the erbium-doped fiber amplifier of FIG.

3 is a schematic structural diagram of another example of a conventional erbium-doped fiber amplifier,

4 is a schematic configuration diagram of another example of a conventional erbium-doped fiber amplifier,

5 is a schematic configuration diagram of a gain flattened recycling erbium-doped fiber amplifier according to the present invention;

6 is a graph of reflectance according to the optical signal wavelength of the gain flattened recycling erbium-doped fiber amplifier reflector of FIG.

7 is a graph of gain and noise figure according to the optical signal wavelength of the gain flattened recycle erbium-doped fiber amplifier of FIG.

8 is a schematic structural diagram of another gain flattened recycling erbium-doped fiber amplifier according to the present invention;

9 is a schematic configuration diagram of a recycled erbium-doped fiber amplifier using a reflective diffraction grating filter according to the present invention,

10 is a schematic configuration diagram of a gain flattened recycling erbium-doped fiber amplifier using the reflective rotary grating filter according to the present invention.

* Explanation of symbols for main parts of the drawings

1. First isolator 2. Wavelength division multiplexer

3. Erbium-doped fiber optic 3 '. Co-doped Erbium Doped Fiber

3 ". Optical Fiber Diffraction Grating Filter 4. Second Isolator

5. Pump laser diode

11.Circulator 12,12 '. Wavelength Division Multiplexer

13. Erbium-doped fiber 14, 14a, 14b. reflector

15. Pump laser diode 16. Filter

17a, 17b. First and Second Optical Fiber Diffraction Grating Filters

Claims (6)

Directional optical signal transmitting means having three input / output ports; A pump laser diode providing a pump light that is an energy source for amplification; A wavelength division multiplexer for combining the pump light with the optical signal input from the directional optical signal transmitting means; An erbium-doped optical fiber for amplifying the optical signal input through the wavelength division multiplexer using the energy of the pump light input together; A first reflection type optical fiber diffraction grating filter which is directly connected to the erbium-doped optical fiber and reflects the pump light used for the amplification to the erbium-doped optical fiber; And Second light reflecting means connected directly to the first reflecting optical fiber diffraction grating filter and reflecting an optical signal having a relatively low gain in the amplified optical signal to the erbium-doped optical fiber; Recycled erbium-doped fiber amplifier, characterized in that provided. The method of claim 1, The directional optical signal transmitting means has a first port, a second port, and a third port, and the optical signal input to the first port must be output only to the second port, and the optical signal input to the second port. The recycling erbium-doped fiber amplifier, characterized in that only the third port is output, and the optical signal input to the third port is composed of a circulator not to be output to any one of the first and second ports. The method of claim 1, And the second reflective diffraction grating filter is directly connected to the erbium doped optical fiber, and the first reflective diffraction grating filter is directly connected to the second reflective diffraction grating filter. Directional optical signal transmitting means having three input / output ports; A pump laser diode providing a pump light that is an energy source for amplification; A first wavelength division multiplexer which combines the optical signal input from the directional optical signal transmitting means and the pump light; An erbium-doped optical fiber for amplifying the optical signal input through the first wavelength division multiplexer using the energy of the pump light input together; A second wavelength division multiplexer for dividing the amplified optical signal and the pump light used in the amplification; A first reflection type diffraction grating filter and the second wavelength division multiplexer, which are directly connected to the second wavelength division multiplexer and reflect the pump light used for the amplification divided by the second wavelength division multiplexer to the erbium-doped optical fiber. A second reflection diffraction grating filter which is directly connected to reflect an optical signal having a relatively low gain among the amplified optical signals divided by the second wavelength division multiplexer to the erbium-doped optical fiber; To Recycled erbium-doped fiber amplifier, characterized in that provided. The method of claim 4, wherein The directional optical signal transmitting means has a first port, a second port, and a third port, and the optical signal input to the first port must be output only to the second port, and the optical signal input to the second port. The recycling erbium-doped fiber amplifier, characterized in that only the third port is output, and the optical signal input to the third port is composed of a circulator not to be output to any one of the first and second ports. The method of claim 4, wherein The first reflective diffraction grating filter has a reflectivity of 90% or more for light of 980 nm wavelength, and the second reflective diffraction grating filter has a reflectance of 90% or more for light of 1550 nm wavelength. Fiber optic amplifier.