KR20010029213A - Gain clamped fiber amplifier - Google Patents

Abstract

PURPOSE: An optical fiber optical amplifier is provided to improve noise peculiarity by solving problems that a wave length oscillated by a laser is out of optical signal wave length band amplified or maintains a wave length interval to some degree from optical signals, and by solving problem that the wave length oscillated by a laser is mixed with the optical signal amplified. CONSTITUTION: An optical fiber optical amplifier for fixing gain comprises the first Mach-Zehnder interferometer filter(MZIF1), the second Mach-Zehnder interferometer filter(MZIF2), a pump part, an erbium-doped fiber(EDF), an isolator(ISO), a band pass filter(BPF) and an attenuator(ATT). The first Mach-Zehnder interferometer filter(MZIF1) is connected between an input terminal(IN) and one end of the pump part. The second Mach-Zehnder interferometer filter is connected between one end of the EDF and an output terminal. The attenuator is connected to one end of the second Mach-Zehnder interferometer filter(MZIF2) and controls a magnitude of an optical loss of a resonator in response to an output signal of the MZIF2. The band pass filter(BPF) is connected to an output terminal of the attenuator and determines an ingredient of a wave length of oscillation in response to an output signal of the attenuator(ATT). The isolator(ISO) is connected between an output terminal of the BPF and an input terminal of the MZIF1 and determines a progressive direction of a wave length of oscillation in response to an output signal of the BPF.

Description

Gain clamped fiber amplifier

The present invention relates to a gain fixed type optical fiber amplifier for wavelength division multiple optical signal amplification. In detail, when the laser resonator is configured in the gain-fixed optical amplifier, the Mach-Zehnder interferometer optical filter having periodic and symmetrical transmission characteristics is used to separate the laser oscillated wavelength and the amplified signal wavelength for gain fixing, and then at the amplifier output stage. The present invention relates to a fixed gain optical fiber amplifier with good noise characteristics without being mixed with each other.

To cope with the rapidly increasing demand for communication, wavelength division multiplexing optical communication technology has been steadily developed. One of its key technologies is the optical amplifier. The optical amplifier for wavelength division multiple signal varies its amplification characteristics according to the number of input signal channels. That is, if the optical pumping is constant, the gain decreases as the number of input channels increases. On the contrary, the gain increases when the number of channels decreases.

As such, there is an electronic method of controlling the output of the pump light and an optical method using laser oscillation as a method of maintaining a constant gain of the amplifier that varies with the number of input channels.

Literatures dealing with electronic methods include U.S. Patent No. 5923462 registered by Johannes Christiaan van der Plaats of Lucent Technologies Inc. under the title Dynamic gain control system for optical amplifier and method approx. and output power control in a gain-flattened erbium-doped fiber amplifier, IEEE Photonics Technology Letters, vol 10, no 6, pp. 787-789 (1998).

On the other hand, the literature dealing with the optical method includes Gain-clamped fiber amplifer with a loop mirror configuration published by KC Bryon of Northern Telecom Limited, Canada, under the title Gain clamped amplifier, and K. Inoue of NTT, Japan. , IEEE Photonics Technology Letters, vol 11, no 5, pp. 533-535 (1999).

In particular, the constant gain in an optical method is called a gain fixed fiber optic optical amplifier. The amplifier forms a resonator containing a gain medium to oscillate the laser at a specific wavelength, thereby fixing the gain regardless of the number of signal channels entering the amplifier. In this case, the oscillated wavelength should have a certain distance from the amplified signal wavelengths. This is because, if the oscillation wavelength is similar to the signal wavelength to be amplified, the amplified signal is passed out to the laser resonator, and thus the amplification is difficult. It is also better to separate the amplified signal from the amplified wave since the wavelength generated by the laser can be mixed with the amplified signal and affect the performance of the system.

To this end, K. Inoue uses a fiber optic nonlinear mirror, and K. C. Bryon et al. Separated the amplified and laser oscillation signals from each other using a Bragg grating pair and a Mach-Zehnder interferometer.

However, since the composition of K. Inoue must be configured using a polarization maintaining optical fiber, it is difficult to configure and there is a problem that the laser oscillation wavelength component may be mixed to the output end when the optical fiber nonlinear mirror is affected by external conditions such as rotation.

The composition of KC Bryon is a composition that separates the oscillation wavelength component by installing a Mach-Zehnder interferometer having the same wavelength Bragg grating with the center wavelength in the two optical paths behind the output stage mixed with the amplified signal light. Since interference is used, there is an unstable problem under external influence.

SUMMARY OF THE INVENTION An object of the present invention is a problem that a laser oscillation wavelength and a problem of having a wavelength gap outside of an optical signal wavelength band to be amplified by a laser or having a certain wavelength spacing with optical signals in a gain fixed optical fiber optical amplifier that fixes gain by an optical method It is to provide a gain fixed optical fiber optical amplifier that can improve the noise characteristics by simultaneously solving the problems mixed in the amplified optical signal.

1 is a block diagram of an optical fiber Mach-Zehnder interferometer optical filter which is a core optical component of the present invention

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

Explanation of symbols on the main parts of the drawings

Δl: length difference between two optical paths of the interferometer

3 dB DC: 50% fiber optic coupler

IN: Amplifier Input Terminal

OUT: Amplifier Output Terminal

EDF: Erbium-doped fiber

Pump: Light pump light source

WDM: Wavelength Multiplexing Coupler

ISO: isolator

BPF: band pass filter

MZIF: Mach-Zehnder interferometer filter

ATT: optical attenuator

In order to achieve the above object, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

1 is a block diagram of an optical fiber Mach-Zehnder interferometer optical filter for explaining the periodic transmission characteristics of the Mach-Zehnder optical filter used in an embodiment of the present invention described below.

Λ ₁ , λ ₂ , λ ₃ , λ ₄ , λ ₅ , λ ₆ , ... with a wavelength interval of Δλ / 2 at the input terminal 1 of the Mach-Zehnder interferometer optical filter with a transmission wavelength interval of Δλ. When a wavelength channel signal is incident, it is separated into odd and even channels through two output terminals. When λ ₁ , λ ₃ , λ ₅ , ...... comes out of one output stage (3), λ ₂ , λ ₄ , λ _{6 ......} emerges from the other output stage 4 and are separated from each other. .

Depending on the wavelength component, the straight light paths, i.e., (1) ↔ (3) and (2) ↔ (4), or the cross light paths, i.e., (1) ↔ (4) and (2) ↔ (3) do. Therefore, the periodic and symmetrical output characteristics of the output of the Mach-Zehnder interferometer optical filter make it possible to construct a gain-fixed optical fiber amplifier with a laser oscillation wavelength independent of the signal wavelength band but not mixed with signals amplified through the amplifier output stage. .

For the transmission characteristics of the Mach-Zehnder interferometer optical filter, see J. T. Ahn et al. A stabilised fiber-optic Mach-Zehnder interferometer filter, Optics Communications, Vol. 157, pp. 62-66 (1998) or Continuously tunable multi-wavelength transmission filter, Optics Communications, Vol. 165, pp. 33-37 (1999).

FIG. 2 is a block diagram of a gain fixed optical fiber optical amplifier according to an embodiment of the present invention implemented using the Mach-Zehnder optical filter of FIG. 1.

As shown, the fixed gain optical fiber optical amplifier of the present embodiment has a wavelength multiplexing coupler (WDM) between the input terminal (IN) and the output terminal (OUT), an optical fiber (EDF) added with erbium as a gain medium, and an optical pumping means ( A gain fixed type optical fiber amplifier having a pump),

A first multi-channel wavelength division multiplexer is provided between the input terminal IN and the optical pumping means, and a second multi-channel wavelength division multiplexer is provided between the erbium-doped optical fiber EDF and the output terminal OUT. And an advertiser (ISO), a bandpass optical filter (BPF), and an optical attenuator (ATT) between the other input terminal of the first multichannel wavelength division multiplexer and the other output terminal of the second multichannel wavelength division multiplexer. It is characterized in that to configure the annular resonator by connecting through.

Here, the Mach-Zehnder interferometer optical filters MZIF1 and 2 are used as the first and second multi-channel wavelength division multiplexers.

In addition, the adsorber (ISO) is for determining the propagation direction of the oscillating wavelength component, the bandpass optical filter (BPF) is for determining the oscillating wavelength component, and the optical attenuator (ATT) is used to determine the amount of optical loss of the resonator. To adjust.

The two Mach-Zehnder interferometer optical filters MZIF1 and 2 are configured to exactly match the phase difference in accordance with the period of the signal wavelengths so as to transmit the signals to be amplified (λ _S1 , λ _S2 , λ _S3 , ......) well. Should be.

The characteristics of the fixed gain optical amplifier of the present embodiment will be described.

The annular resonator laser oscillates as the output of the pump light source increases in the light pumping means. In this case, the wavelength λ _lasing oscillated in the resonator is determined by a band pass optical filter (BPF), and has a value between signal wavelengths according to the symmetrical transmission characteristic of the Mach-Zehnder interferometer optical filter of FIG. 1.

Therefore, when the oscillation wavelength component is minimized by adjusting the band pass optical filter (BPF), the oscillation wavelength component continuously proceeds in the resonator and only the amplified signals are output to the output stage.

As described above, since the oscillation wavelength component is separated from the amplified signals, the stability of the system can be improved.

The oscillation condition of the laser is the moment when the gain obtained by the optical pumping is equal to the optical loss of the resonator, so that the larger the loss of the resonator, the smaller the gain. Therefore, the gain of the fixed gain optical fiber amplifier can be controlled by adjusting the loss value of the resonator with the optical attenuator ATT.

See also K. Inoue's paper on gain clamped fiber amplifiers with a loop mirror configuration ", IEEE Photonics Technology Letters, vol 11, no 5, 1999. It is closely related to the noise characteristic of, that is, the noise characteristic is good when traveling in the same direction as the signal wavelengths, while the noise characteristic is worse when the direction is opposite.

In the present embodiment, since the advancing direction of the oscillation wavelength can be adjusted by adjusting the direction of the adsorber ISO, the noise characteristic can be improved.

In another embodiment of the present invention, an optical fiber coupler may be used to configure a gain-fixed optical fiber optical amplifier in place of any of the first and second multi-channel wavelength division multiplexers described above.

In this case, a slight optical loss due to the optical fiber coupler and the noise characteristic of the amplifier is slightly worsened, but it is sufficient to achieve the object of the present invention.

In another embodiment of the present invention, instead of any one of the first and second multi-channel wavelength division multiplexers described above, an optical circulator may be used, and a gain fixed optical fiber amplifier may be configured by removing an adsorber (ISO).

In this case, since the oscillation wavelength propagates the optical fiber (gain medium) in the opposite direction to the signal light, the noise characteristic of the amplifier is slightly lowered, but it is sufficient to achieve the object of the present invention.

As described above, the gain-fixed optical fiber optical amplifier proposed by the present invention uses the periodic and symmetric filtration characteristics of the Mach-Zehnder optical filter to separate the oscillation wavelength component from the amplified signal wavelength components more efficiently than the conventional composition, This has the effect of improving the noise characteristics of the amplifier.

Claims (6)

A fiber amplifier comprising a wavelength multiplexing combiner (WDM), an optical pumping means, and an optical fiber (EDF) added with erbium as a gain medium between an input terminal (IN) and an output terminal (OUT), A first multi-channel wavelength division multiplexer is provided between the input terminal IN and the optical pumping means, and a second multi-channel wavelength division is performed between the erbium-doped optical fiber (EDF) gain medium and the output terminal (OUT). An oscillator (ISO) for oscillating wavelength between the other input terminal of the first multichannel wavelength division multiplexer and the other output terminal of the second multichannel wavelength division multiplexer A gain-fixing optical fiber optical amplifier, characterized in that it is connected through a band-pass optical filter (BPF) for determining the component, and an optical attenuator (ATT) for adjusting the amount of optical loss of the resonator. A fiber amplifier comprising a wavelength multiplexing combiner (WDM), an optical pumping means, and an optical fiber (EDF) added with erbium as a gain medium between an input terminal (IN) and an output terminal (OUT), An optical fiber coupler is provided between the input terminal IN and the optical pumping means, and a multi-channel wavelength division multiplexer is provided between the erbium-doped optical fiber (EDF) gain medium and the output terminal (OUT). Between the other input terminal of the coupler and the other output terminal of the multi-channel wavelength division multiplexer, an adsorber (ISO) for determining the propagation direction of the wavelength component, a bandpass optical filter (BPF) for determining the oscillating wavelength component, and a resonator A gain fixed optical fiber optical amplifier, characterized in that to form an annular resonator by connecting through an optical attenuator (ATT) for adjusting the amount of light loss. A fiber amplifier comprising a wavelength multiplexing combiner (WDM), an optical pumping means, and an optical fiber (EDF) added with erbium as a gain medium between an input terminal (IN) and an output terminal (OUT), A multi-channel wavelength division multiplexer is provided between the input terminal (IN) and the optical pumping means (Pump), and an optical fiber coupler is provided between the erbium-doped optical fiber (EDF) gain medium and the output terminal (OUT). Between the other input terminal of the channel wavelength division multiplexer and the other output terminal of the optical fiber coupler, an adsorber (ISO) for determining the propagation direction of the wavelength component, a bandpass optical filter (BPF) for determining the oscillating wavelength component, and a resonator A gain fixed optical fiber optical amplifier, characterized in that to form an annular resonator by connecting through an optical attenuator (ATT) for adjusting the amount of light loss. A fiber amplifier comprising a wavelength multiplexing combiner (WDM), an optical pumping means, and an optical fiber (EDF) added with erbium as a gain medium between an input terminal (IN) and an output terminal (OUT), An optical cycler is provided between the input terminal IN and the optical pumping means, and a multi-channel wavelength division multiplexer is provided between the erbium-doped optical fiber (EDF) gain medium and the output terminal (OUT), and the optical Connection is made through a bandpass optical filter (BPF) for determining the wavelength component oscillating between the other input of the circulator and the other output of the multi-channel wavelength division multiplexer, and an optical attenuator (ATT) for adjusting the optical loss magnitude of the resonator. Gain fixed optical fiber optical amplifier, characterized in that to constitute an annular resonator. An optical fiber amplifier comprising a wavelength division split coupler (WDM), an optical pumping means, and an optical fiber (EDF) added with erbium as a gain medium between an input terminal (IN) and an output terminal (OUT), wherein the input terminal (IN) And a multi-channel wavelength division multiplexer between the optical pump and the optical pumping means, an optical cycler between the erbium-doped optical fiber (EDF) gain medium and the output terminal (OUT), and different input terminals of the optical cycler. A cyclic resonator is constructed by connecting through a bandpass optical filter (BPF) for determining the wavelength component oscillating between different output stages of the channel wavelength division multiplexer, and an optical attenuator (ATT) for adjusting the optical loss magnitude of the resonator. Gain fixed optical fiber optical amplifier, characterized in that. The method according to any one of claims 1 to 5, And the multichannel wavelength division multiplexer is a multichannel Mach-Zehnder interferometer optical filter.