KR100250615B1 - Gain flat optical fiber amplifier - Google Patents

Abstract

PURPOSE: An optical fiber amplifier for gain flattering is provided to enable amplifying gains with respect to each signal to be graded without restricting level of signal having high gain by using a filter. CONSTITUTION: A control circuit(8) drives and controls a laser diode(13) for pumping on the basis of power levels detected by the first and the second photo diodes(7,11) and thereby producing pumping light(P) for optical amplification. The pumping light(P) outputted from the laser diode(13) is divided into as a predetermined ratio by a dividing coupler(14). The divided pumping lights are applied to a first wavelength dividing coupler(6) mounted at an input terminal of the first optical amplifying unit(21) and to the second wavelength dividing coupler(16) mounted at an input terminal of the second optical amplifying unit(22). A filter(15) removes gain as to the amplified signal having wavelength of 1530 nm to 1540 nm.

Description

Gain Flattened Fiber Optic Amplifier

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber amplifier for amplifying an optical signal. In particular, an amplification gain for each signal is obtained without limiting the level of a signal having a high gain in amplifying various optical signals having different wavelengths transmitted by the wavelength division multiplexing method. It relates to a gain flattening optical fiber amplifier capable of flattening.

As is well known, optical communication technology is mainly used for information communication between countries through a submarine cable since it is possible to transmit a large amount of information at high speed and there is no signal interference or crosstalk due to electromagnetic induction.

The development of optical communication technology is further accelerated by the development of optical fiber amplifiers that can increase the gain in the form of optical signals in the line without making physical changes such as temporarily converting optical signals to electrical signals for signal amplification. Recently, a Wavelength Division Multiplexing (WDM) technique has been developed to improve the transmission efficiency of signals by simultaneously transmitting optical signals having different wavelengths through one transmission line.

Meanwhile, in order to realize the above-described wavelength division multiplexing (WDM) communication technology, an optical fiber amplifier capable of obtaining an even amplification gain in all wavelength ranges is essential. A diagram showing a functional optical fiber amplifier.

In Fig. 1, the input optical signal S is coupled to the first optical path 1, which is coupled as the input of the first tap coupler 4. In the first tap coupler 4, the power of the optical signal input through the first optical path 1 is divided by a predetermined ratio, for example, a ratio of 99: 1, so that the signal corresponding to 99 is passed through the isolator 5 to the first. The optical signal corresponding to 1 is input to the wavelength division coupler 6 and supplied to the first photodiode 7 for monitoring the power of the input optical signal S.

On the other hand, the first photodiode 7 is a photoelectric conversion of the optical signal divided and input by the first tap coupler 4 is applied to the control circuit 8 as a monitor signal, the control circuit 8 is By controlling the operating current of the pumping laser diode 3 on the basis of the power level of the signal applied from the first photodiode 7, the optical fiber amplifier to be described later will be drive-controlled to an optimal state.

Pumping light (P) output from the pumping laser diode (3) is coupled to the optical signal (S) applied through the isolator (5) and the wavelength division coupler (6) by the optical amplification optical fiber (EDF; Erbium Doped Fiber) It is entered as (2). The pumping light P in the optical amplified optical fiber 2 excites rare-earth ions doped in the optical amplified optical fiber 2 to generate induced photons having a predetermined wavelength. At this time, the induced photons are introduced into the optical signal S so that the corresponding optical signal S is amplified.

In this case, the amplification characteristics for each wavelength to be amplified generally show the highest gain in the 1530 nm band and the second highest gain in the 1550 nm band. Thus, a constant gain is obtained for each signal in the wavelength band. In order to form a gain flatness filter 9 at the output terminal of the optical fiber amplifier 2, the gain is limited based on the minimum gain in the gain characteristics for each wavelength.

The amplified optical signal passing through the gain flattening filter 9 is output through the second tap coupler 10 located at the output end, where the second photodiode 11 is driven by the second tap coupler 10. The divided 1% monitor signal is photoelectrically converted and applied to the control circuit 8 to provide a basis for adjusting the amplification gain.

That is, in the conventional gain flattening optical fiber amplifier having the above-described configuration, a filter having a loss for a signal having a corresponding wavelength is used so as to have a reference wavelength gain value for a wavelength having a higher gain based on a minimum gain. As a result, gain flattening is realized by having a constant gain for the entire wavelength range.

However, the gain flattening amplifier of the above-described method is to reduce the gain of the higher wavelength based on the minimum gain with respect to the gain characteristic of each wavelength, which is a disadvantage that it is difficult to implement a high power optical fiber amplifier that requires a large output. have. In addition, since the gain flattening filter 9 is fixed with respect to one gain characteristic for each wavelength, there is a problem that the gain flattening filter 9 cannot be used when the gain characteristic of the entire optical fiber amplifier changes when the intensity of the pumping laser diode 3 changes. .

Accordingly, the present invention has been made in view of the above circumstances, and the amplification gain for each signal can be obtained without limiting the level of a signal having a high gain in amplifying various optical signals having different wavelengths transmitted by the wavelength division multiplexing method. Its purpose is to provide a gain flattening fiber amplifier that can be flattened.

1 is a block diagram showing a general optical fiber amplifier.

2 is a block diagram showing a gain flattening optical fiber amplifier according to an embodiment of the present invention.

3-5 are gain flattening optical fiber amplifiers showing another embodiment of the present invention.

**** Brief description of the main parts of the drawing ****

1: optical path 2, 21, 22: optically amplified optical fiber (EDF)

3, 13: pumping laser diode 4, 10: tap coupler

5: isolator 6, 16: wavelength division coupler

7, 11: photodiode 8: control circuit

9: gain flatness filter

14: Distribution Coupler 15: Filter

The gain flattening optical fiber amplifier according to the first aspect of the present invention for achieving the above object is a light path for transmitting a plurality of optical signals having different wavelengths by a wavelength division multiplexing method, and a pumping light source for generating and outputting pumping light having a predetermined wavelength. And light splitting means for splitting the pumped light into first and second ratios so as to obtain a maximum amplification gain in the shortest wavelength and the longest wavelength band of the optical transmission signal, and the first ratio split pump output from the light distribution means. First and second optical coupling means for coupling the light and the second ratio split pumping light to the optical path, and the length thereof is set such that a maximum amplification gain is obtained at the shortest wavelength band of the optical transmission signal; First optical amplifying means for amplifying the optical signal based on the pumped light supplied by the means, and a maximum amplification gain may be obtained in the longest wavelength band of the optical transmission signal Split pumping is provided between the second optical amplifying means for amplifying the optical signal based on the pumped light supplied by the second optical coupling means, the first and second optical amplifying means, the length thereof is set It characterized in that it comprises a filter means for blocking the light.

That is, according to the present invention having the above-described configuration, it is possible to flatten the amplification gain for each signal without limiting the level of a signal having a high gain with respect to the optical signal transmitted by the wavelength division multiplexing method.

Hereinafter, an embodiment according to the present invention will be described with reference to the drawings.

Figure 2 is a block diagram showing a gain flattening optical fiber amplifier according to an embodiment of the present invention, the same reference numerals for the components performing the same function as the configuration shown in Figure 1, the detailed description It will be omitted.

In FIG. 2, reference numeral 13 denotes a pumping laser diode that generates and outputs a pumping light P for optical amplification under the control of the control circuit 8, and 14 denotes a pumping light applied from the pumping laser diode 13 (P) is a distribution coupler that divides and outputs a predetermined ratio (N: M) so as to have the best gain in the 1540 nm band and the 1550 nm band, respectively, and the pumping light splitting ratio (N: M) of the distribution coupler 14. Is determined according to the characteristics of the first and second optical amplified fiber (EDF) to be described later, the length and the output power of the pumping laser diode (13).

On the other hand, reference numeral 21 is an optical amplification fiber optimized to have the highest gain in the 1540 nm band, the first optical amplification stage for performing the optical amplification based on the pumped light divided by the distribution coupler 14, 22 is An optical amplification optical fiber optimized to have the highest gain in the 1550 nm band, the second optical amplification stage performing optical amplification based on the pumped light M split by the distribution coupler 14, and reference numeral 15 is a gain characteristic for each wavelength. It is a filter for removing the gain in the 1530 nm range showing the first highest gain among the two amplification stages 21 and 22 having different optical amplification characteristics so as not to be affected by the excitation light of the other side.

The operation of the device having the above configuration will be described below.

The control circuit 8 generates the pumping light P for optical amplification by controlling the driving of the pumping laser diode 13 based on the power level detected by the first and second photodiodes 7, 11. As shown, the pumping light P output from the pumping laser diode 13 is divided by the distribution coupler 14 at a predetermined distribution ratio, and each of the first wavelength division couplers installed at the input terminal of the first optical amplifier stage 21. (6) and the second wavelength division coupler 16 provided at the input end of the second optical amplifier stage 22.

As a result, the optical amplification is performed by the N-segmented pumping light in the first optical amplifier stage 21 so that a signal of 1540 nm band is amplified as the maximum gain, and the M-divided pumping is performed in the second optical amplifier stage 22. The optical amplification is performed by the light so that signals in the 1550 nm band are amplified with the same power as the signals in the 1540 nm band.

At this time, the gain for the signal having a wavelength of 1530 nm band is removed by the filter 15, thereby obtaining even gain characteristics for the 1540-1550 nm signal, which is the wavelength band of the effective signal.

That is, in the above configuration, the conventional optical fiber amplifier having the bidirectional structure increases only the amplification degree of the entire optical fiber amplifier by using two excitation laser diodes at the input and output terminals of one optical amplified fiber to increase the overall output strength. On the contrary, when the length of the optical amplified fiber increases, the wavelength having the highest gain shifts to the long wavelength (1560 nm), and when the length decreases, the maximum gain wavelength shifts to the short wavelength (1540 nm) and the excitation laser diode The characteristics of the optical fiber amplifier where the wavelength with the highest gain is shifted to the short wavelength when the power intensity is increased and the overall amplification gain is increased, and the wavelength with the highest gain is shifted to the long wavelength when the output amplification is decreased and the overall amplification gain is decreased. Optimized to emit excitation light at a constant rate through one excitation semiconductor laser The excitation light of one excitation laser diode is used by using a proportional optical distribution coupler to send a large amount of excitation light to the one requiring high output intensity and a small amount of excitation light to the one requiring low output intensity. It is implemented to use both effectively.

Therefore, by using two amplification stages each consisting of an excitation light and an optimized optical fiber length distributed at a constant ratio, the gain characteristics for each wavelength of the entire optical fiber amplifier can obtain a constant wavelength gain through the compensating power of the gain values for each wavelength of the two stages. Will be implemented.

That is, according to the above embodiment, the amplification gain for each signal can be flattened without limiting the level of a signal having a high gain in amplifying various optical signals having different wavelengths. By using a single laser diode rather than using two or more pumping laser diodes, the high power intensity can be obtained and the manufacturing cost can be significantly reduced.

On the other hand, the present invention is not limited to the above embodiment and can be variously modified within the scope not departing from the technical gist of the present invention, for example, as shown in Figures 3 to 5 input of the pumping light to the optical amplifier stage It can also be configured to adjust the intensity and noise figure characteristics of the output light by adjusting the direction and transforming in the forward and reverse directions.

As described above, according to the present invention, the amplification gain for each signal can be flattened without limiting the level of a signal having a high gain in amplifying several optical signals having different wavelengths transmitted by the wavelength division multiplexing method. By using a single laser diode without using two or more pumping laser diodes, not only high output intensity can be obtained but also a significant reduction in manufacturing cost can be achieved.

Claims (5)

An optical path in which a plurality of optical signals having different wavelengths are transmitted by a wavelength division multiplexing method, A pumping light source for generating and outputting pumping light having a predetermined wavelength, Optical distribution means for dividing the pumping light applied from the pumping light source into first and second ratios so as to obtain a maximum amplification gain in the shortest wavelength and the longest wavelength band of the optical transmission signal; First and second optical coupling means for coupling the first ratio split pumping light and the second ratio split pumping light output from the light distribution means to the optical path; First optical amplifying means for amplifying and outputting an optical signal based on the pumping light supplied by the first optical coupling means, the length of which is set so that the maximum amplification gain is obtained at the shortest wavelength band of the transmission signal applied through the optical path; Second optical amplifying means for amplifying and outputting an optical signal on the basis of the pumped light supplied by the second optical coupling means, the length of which is set so that the maximum amplification gain is obtained at the longest wavelength band of the transmission signal applied through the optical path; , A gain flattening optical fiber amplifier, comprising: filter means arranged between the first and second optical amplification means to block split pumping light introduced into each other; The method of claim 1, At least one of the first and second optical coupling means is configured to couple the pumping light of the predetermined split ratio applied from the optical distribution means in the same direction as the signal transmission direction of the optical path, gain flattening optical fiber amplifier . The method of claim 1, At least one of the first and second optical coupling means is configured to couple the pumping light of the predetermined split ratio applied from the optical distribution means in a reverse direction with respect to the signal transmission direction to the optical path. . The method according to any one of claims 1 to 3, A tap coupler for separating a certain ratio of the monitoring signal from the optical signal transmitted through the optical path, photoelectric conversion means for photoelectric conversion of the monitoring signal separated by the tap coupler, and an electrical signal by the photoelectric conversion means. And a control means for controlling an operating current of the pumped light source on the basis of the level of the converted and output monitoring signal. The method of claim 4, wherein The tab coupler is provided at the front end of the first optical amplification means and the rear end of the second optical amplification means, respectively, and the gain flattening optical fiber amplifier, characterized in that provided with a photoelectric conversion means coupled to each of the front and rear tab couplers. .

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