KR100298484B1 - Gain Fixed Optical Amplifier with Dual Optical Feedback Structure - Google Patents

Abstract

The present invention relates to a gain-fixed optical amplifier having a dual optical feedback structure, the apparatus comprising optical feedback means for returning a partial signal of the output side of the optical amplifier to the input side, the optical feedback means is the feedback signal Is distributed in two, and the phases of the two oscillating optical signals distributed are shifted from each other, thereby reducing the vibration width of the optical signal in which the relaxation vibration is generated and providing it to the input side of the optical amplifier. The distributed one optical signal is delayed by a vibration damper forming a first feedback loop and then combined with the other distributed optical signal passing through the second feedback loop. Therefore, the present invention can quickly attenuate the damping vibration which is the biggest disadvantage of the gain fixed optical amplifier.

Description

Gain-clamped optical amplifier with double optical feedback configuration

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gain locked optical amplifier, and more particularly, to a gain fixed optical amplifier in which a double feedback loop is formed to improve transient response characteristics of the optical amplifier.

The gain-fixing scheme is to maintain the constant gain by monitoring the input and output, respectively, so that the gain for the entire signal and the gain per channel are constant even when the input optical power changes or the number of channels changes.

The gain flatness of a gain-locked optical amplifier depends on the characteristics of the Erbium Doped Fiber (EDF) itself, the length of the EDF used, and the accuracy of the initial gain setting. Therefore, if the intensity of the input signal is changed or the number of channels is changed, if the optical amplifier is within the fixed gain guarantee range, the ratio of the input / output change amount is constant. Therefore, there is a restriction to use the proper pump light intensity to guarantee the fixed gain. Follow.

Conventional gain-fixed optical amplifiers have been described in an article published in Volume 16, No. 4, IEEE [1], April 1988, "Experimental and theoretical analysis of relaxation-oscillations and spectral hole burning effects in all-optical gain-clamped EDFA's for WDM." networks ", and in the August 9, 1997 issue of IEEE 9 [2]," Study on noise characteristic of gain-clamped erbium-doped fiber-ring lasing amplifier ".

A schematic view of the conventional gain-locked optical amplifier 130 presented in the paper [1] shows, as shown in FIG. 1, two EDFs 133 and 139, and a 980 nm pump laser diode for making the EDF as an amplifying medium. And 135, and an optical feedback loop. The optical elements not described here are not an integral part of this amplifier. The unexplained 131, 141 is a wavelength insensitive coupler (WIC) to combine or divide the optical signals. 132, 137 and 140 are isolators that prevent light from being reflected. 134 and 138 are wavelength selective couplers (WSCs), which combine or divide optical signals like WIC, but differ only in wavelength characteristics. 144 is a variable attenuator VA, and 143 is a polarization controller (PC) for adjusting the polarization of light. 142 is a tunable filter (TF) for selectively filtering light wavelengths, 101 is an acoustic optical modulator (AOM) for modulating light, 151 and 152 are variable filters, and 160 is a power meter for measuring light intensity.

Not all of the above mentioned optical elements are required to be a gain fixed optical amplifier. This can be clearly seen when comparing [1] and [2]. However, it is important to note that the gain-locked optical amplifier 130 feeds back part of the output from the amplification medium EDFs 133 and 139. In other words, there is a light feedback loop.

In the apparatus of FIG. 1, when the signal of the laser diode A 100 is modulated by the AOM 101, an experiment is performed on how the optical signal intensity of the laser diode B 110 is changed.

To explain in detail, first, if the measured light intensity from each laser diode A (100), B (110) is A [dBm], B [dBm], the total input to the optical amplifier 130 is If we ignore the losses caused by the various optical elements until they enter the optical amplifier, it will be A + B [dBm]. In this state, the size of the signals of the laser diodes A 100 and B 110 is measured by the measuring device 150 through the variable filters 151 and 152 at the output terminal of the optical amplifier. If the gain of amplifier 130 is G [dB], the magnitudes of the two channels will be A + G [dBm] and B + G [dBm], respectively.

However, in this situation, if the laser diode A (100) signal is removed, the input to the amplifier 130 will be B [dBm], the output of the amplifier should be B + G [dBm]. This is because the optical amplifier 130 is designed as a fixed gain amplifier, that is, an amplifier whose gain does not change.

However, the actual measurement result, as shown in Figure 2, as the laser diode A (100) on / off (ON / OFF), the amplified optical signal of the laser diode B (110) oscillates in the form of attenuation, but the average value Does not change. That is, when the laser diode A 100 is turned on / off, the output of the laser diode B 110 has a transient response characteristic that is an optical output amplified by ΔP 1 or ΔP 2. For reference, as a kind of transient response, a form of vibration that is attenuated as shown in FIG. 2 is referred to as relaxation oscillation.

Conventional gain fixed amplifiers can easily maintain a constant gain in an easy way, but the transient response characteristics that occur when the intensity of the input optical signal entering the amplifier changes are very poor. Therefore, there is a problem that the gain of the amplifier vibrates, that is, the output of the amplifier vibrates, and development of a gain fixed optical amplifier capable of reducing this vibration is required.

Accordingly, the present invention is to solve the problems of the prior art as described above, an object of the present invention is to form a double-loop optical feedback loop using a distribution coupler, coupling coupler, variable filter, vibration damper and variable attenuator. By canceling the vibration of the output of the optical amplifier and input to the optical amplifier, to provide a gain fixed optical amplifier that improves the transient response characteristics of the optical amplifier.

1 is a block diagram for experimenting the gain characteristics of a conventional fixed gain optical amplifier;

2 is a view showing the experimental results of FIG.

3 is a block diagram of a gain fixed optical amplifier having a double optical feedback structure according to the present invention.

<Explanation of symbols for the main parts of the drawings>

300: input optical signals 310,311,312,313; Coupler

320: optical amplifier 330: output optical signal

340: variable filter (TF) 350: vibration damper (TD)

360,361: variable attenuator (VA)

The present invention for achieving the above object comprises an optical feedback means for returning a part of the signal on the output side of the optical amplifier, the optical feedback means for distributing a part of the output of the optical amplifier for outputting 311), a second distribution coupler 312 for distributing the optical signal fed back from the outside at a predetermined ratio, and a wavelength for returning the signal distributed by the first distribution coupler to the second distribution coupler. A variable filter 340 for feedback, a vibration damper (TD) 350 for forming a first feedback loop, a variable attenuator 360 for forming a second feedback loop, and the vibration damper 350; The first coupling coupler 313 for coupling the optical signal output through the variable attenuator 360, and the optical signal output by the second variable attenuator 361 a predetermined amount attenuated by the second variable attenuator 361 And input optical signal The second coupling coupler 310 is characterized in that the configuration.

In addition, the present invention is characterized in that the distributed one has a double optical feedback structure coupled with the other after being delayed through the optical fiber.

Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings.

First, to explain the principle of the present invention, the fixed gain optical amplifier is to operate the amplifier to operate the laser, and the part of the optical amplifier output through the optical feedback loop to operate the optical amplifier with the laser again Feedback to the input of the optical amplifier.

However, since all lasers output the desired light intensity after a gentle oscillation for a predetermined time when turned on for the first time, studies to remove these undesirable oscillation characteristics have long been conducted. One way to do this is to reconsider part of the laser output, which is the case in December 1978, Volume 33, in the Journal of the American Physical Society, "Stabilization of semiconductor laser outputs by a mirror close to a laser facet". It has been proposed.

In the above paper, the output is fed back to the semiconductor laser diode, but in the present invention, the feedback principle is applied to the optical amplifier.

In other words, the principle of the present invention is to use a kind of damper to solve the relaxation vibration characteristics. That is, when mitigating vibration occurs in the optical amplifier, the output of the optical amplifier is divided into two, the phases of the two divided optical signals are manipulated so as to cross each other, and combined with each other and input to the optical amplifier, so that the vibration is quickly reduced.

3 is a block diagram of a gain-fixed optical amplifier of the dual optical feedback structure according to the present invention.

The gain fixed optical amplifier 30 includes a first distribution coupler 311 for distributing and outputting a part of the output of the optical amplifier, and a second distribution coupler 312 for distributing an optical signal fed back from the outside at a predetermined ratio. ), A variable filter 340 for selecting a wavelength to be returned from the signal distributed by the first distribution coupler and returning it to the second distribution coupler, and a vibration damper forming a first feedback loop. TD) 350, a variable attenuator 360 for forming a second feedback loop, and a first coupling coupler 313 for coupling an optical signal output through the vibration damper 350 and the variable attenuator 360. And a second coupling coupler 310 for coupling the input signal with the optical signal attenuated by the second variable attenuator 361 and the output signal through the first coupling coupler 361. This optical feedback structure has a double feedback structure.

Here, the optical amplifier 320 may be any shape as long as it is an arbitrary optical fiber amplifier. The present invention does not limit a particular type of amplifier. In addition, the vibration damper 350 may be implemented as a long optical fiber of an appropriate length, and the length is determined experimentally so that the relaxation vibration width may be reduced (preferably erased). The distribution ratio of each coupler 310,311,312,313 should also be determined experimentally.

Referring to the operation of the apparatus, the output of the optical amplifier 320 is divided by the coupler 311, and the variable filter 340 selects the wavelength to be fed back among the divided signals. The feedback optical signal output from the variable filter 340 is 1: 2 divided by the coupler 312 at a constant ratio, one is delayed through the vibration damper 350 forming the first feedback loop, and the other is A predetermined amount is attenuated via the variable attenuator 360 forming the two feedback loops. The optical signal passing through the first feedback loop and the second feedback loop is combined again by the coupler 313, attenuated by a variable amount in the variable attenuator 361, and then coupled with the original input optical signal through the coupler 310 to the optical amplifier. Input 320. That is, the first feedback loop has a longer transmission path than the second feedback loop so that the two signals overlap each other with a time difference.

If a damping vibration has occurred, the vibrating optical signal is divided into two optical signals by the coupler 312, and one of the optical signals passes through the vibration damper 350, which is a long optical fiber, to the coupler 313. This causes the peaks and valleys of the two oscillating optical signals to overlap each other (preferably completely canceled if the phase difference is 180 °) and sends them to the input of the optical amplifier 320. In this way, the acid appearing in the relaxation vibration of the first feedback loop comes to the position of the bone appearing in the relaxation vibration of the second feedback loop, canceling each other, and the effect of lowering the height of the acid to be generated next is produced. This has the effect of lowering the depth of the next bone so that the damping vibration can be removed quickly.

The present invention can be usefully applied to a Wavelength Division Multiplexing Network (WDM) in which a combination and separation of arbitrary channels occur frequently. In the WDM network, when branching / combining, there may be a change in the intensity of the input optical signal entering the optical amplifier, which is susceptible to mitigating vibration in a gain fixed optical amplifier. However, in the present invention, the proposed fixed gain optical amplifier can significantly reduce the relaxation vibration.

Claims (5)

An optical feedback means for feeding back a partial signal on the output side of the optical amplifier and providing it to the input side; The optical feedback means comprises: a first distribution coupler (311) for distributing and outputting a part of the output of the optical amplifier; A second distribution coupler 312 for distributing the feedback optical signal output from the outside at a predetermined ratio; A variable filter 340 for selecting a wavelength to be returned from the signal distributed by the first distribution coupler and returning it to the second distribution coupler; A vibration damper (TD) 350 that forms a first feedback loop to delay one signal distributed through the second distribution coupler; A variable attenuator (360) forming a second feedback loop to attenuate one signal distributed through the second distribution coupler; A first coupler coupler 313 coupling the optical signal output through the vibration damper 350 and the variable attenuator 360; And Dual optical feedback structure, characterized in that the signal output through the first coupling coupler is composed of a second coupling coupler 310 for coupling the input optical signal and the optical signal attenuated by a predetermined amount in the second variable attenuator (361) Gain fixed optical amplifier having a. 2. The divided optical signal of claim 1, wherein the divided optical signal is delayed by a vibration damper forming a first feedback loop and then combined with the other distributed optical signal passing through a second feedback loop. Gain fixed optical amplifier having a dual optical feedback structure. 3. The fixed gain optical amplification device having a dual optical feedback structure according to claim 2, wherein the vibration damper is an optical fiber. 3. The fixed gain optical amplifier of claim 2, wherein the second feedback loop comprises a variable optical attenuator. A gain fixed optical amplifier having a double optical feedback structure according to claim 1, wherein a variable filter for selecting a wavelength to be fed back is added.