JP2013254975A - Burst mode erbium-doped fiber amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical amplifier for optical packet communication having excellent characteristics, where transient response is suppressed, even if traffic and rare-earth-doped fiber are small.SOLUTION: In an optical amplifier for optical packet communication using a rare-earth-doped fiber, the rare-earth-doped fiber has a diameter of 3.4 μm or more and 10 μm or less in an active region. In the optical amplifier, the non-saturation region is expanded in the amplifier operation, by reducing the numerical aperture so that the integral value of erbium ion and the mode field of light decreases in a duplicate region. The numerical aperture of the rare-earth-doped fiber is 0.2 or less, and the length of the rare-earth-doped fiber is 1-4 m.

Description

  The present invention relates to a burst mode rare earth-doped fiber such as an erbium-doped fiber amplifier and a method for manufacturing the same.

  The principle of optical amplification in practical use is based on stimulated emission (or stimulated scattering, parametric amplification). In either case, gain is obtained by the number of electrons in the upper energy state. A process in which the number of upper electrons is reduced by light amplification and recovered by the supplied energy is given a time constant determined by the basic process of energy supply, material constants, and structural constants. The most common optical amplifier, an erbium-doped fiber amplifier (hereinafter referred to as “EDFA”), has a time constant of several ms, and is therefore suitable for amplification of high-speed signals of the gigabit per second class or higher (time constant). (Semiconductor optical amplifiers with short circuit lengths cause pattern effects, so improvement measures are required for high-speed signals). However, if the modulation signal is not a continuous bit string but a data format with a small granularity such as a burst / packet, even if the time constant of the EDFA is relatively long, transient fluctuations occur in the waveform and envelope ( E. Schulze, M. Malach, F. Raub, “All-Raman amplified links in comparison to EDFA links in case of switched traffic,“ in ECOC 2002, Sy.

  On the other hand, many fluctuation suppression techniques have been reported, which are roughly divided into an optical method using an optical loop circuit or the like and an electrical method using an automatic gain control circuit (AGC) or the like. However, the optical method is not practical due to the complexity of the configuration and the low controllability (CL. Zhao, H. Tam, B. O. Guan, X. Dong, P. K. A. Wai. , X. Dong, “Optical automatic gain control of EDFA using two oscillating lasers in a single feedback loop,” Optics communications 225, 157, 157-1. On the other hand, electrical methods have achieved certain results for networks that switch at a relatively low speed. However, as the granularity of the data format has decreased and communication methods with high circuit utilization efficiency such as optical burst / optical packets have been studied, it has been found that electrical control methods alone are not sufficient.

  According to the research literature, the time constant of the electric circuit for suppressing the gain fluctuation is sub-microsecond (C. Tian a EDFA pumped by 1480- and 980-nm lasers, "IEEE JLT 21 (8), 1728- 1734 (2003), H. Nakaji, Y. Nakai, M. Shigematsu and M. Nishimura, “Super high-fed ri er ed” It cannot respond to the typical length (shortness) of optical packets that accommodate high-speed payloads of the gigabit per second class or higher, and an optical control method has also been proposed. Are, but is incomplete or suppression, etc. or a method is complicated, not put to practical use because of home to various problems.

  Also, an approximate expression of a process in which a burst-like change of an input signal in a WDM environment causes a transient response of an EDFA is given (see Non-Patent Document 1 below). However, as specific countermeasures against such transient response, many methods for adaptively controlling the operating state of the EDFA using various external circuits as described above have been proposed. There is no specific way to suppress the response itself.

  FIG. 1 is a diagram illustrating an example of a change in a packet waveform caused by an EDFA. FIG. 1 shows an example of an optical packet of 9.95328 bits with a 128-bit preamble and a 3814-bit payload and a duration of about 400 ns. As shown in FIG. 1, the waveform of the optical packet is broken due to the gain variation of the EDFA.

  Also, when the traffic is low, the average power is small if the intensity of all pulses remains constant. Therefore, it can be understood that the traffic has decreased. However, the network control side does not always recognize the label of the packet (for example, optical amplification in the transmission path: 1R relay, etc.). At that time, a method generally used is monitoring of the average power. However, simply monitoring the average power cannot determine whether the traffic is low or the pulse intensity is low when a low average power is detected. In conventional optical communication systems, the EDFA controlled by the average power monitor is often operated by APC (constant power control). Although such an EDFA has the same average power as a signal with dense traffic and low pulse intensity, when an optical signal with low traffic is incident, it obtains a very high peak power, resulting in nonlinear phenomena and damage to optical elements. Such problems arise. On the other hand, when the gain of the EDFA is changed, other characteristics (for example, gain flatness) are affected. Furthermore, since it is assumed that the optical packet passes through various paths, the optical loss and the optical gain accumulation experienced for each packet are different, and the pulse intensity is also different.

There are two types of countermeasures for such cases. One countermeasure is to adaptively control the pump light intensity of the EDFA to change the gain. However, since this method uses current control of a relatively large current charge, there are many problems such as a slow response speed and noise figure degradation. As another countermeasure, it is assumed that the EDFA is driven by, for example, ACC (constant current control) and controlled so that the incident average power and the intensity of the optical pulse included therein are kept within a certain range. In this method, the pulsed light intensity is adaptively controlled. Generally, the pulse intensity is attenuated. One specific implementation of this method is to use an optical modulator. Since there are many voltage-driven types of optical modulators, the optical intensity can be controlled at high speed when the optical modulator is used. In such a case, if the incident average power changes greatly (specifically, 10 dB or more), the operating conditions of the EDFA optimized for the incident power and gain in the specifications change with respect to the length and pump light intensity. It becomes. Specifically, WDM gain flatness is lost. If the gain flatness of WDM is lost, not only is there a defect in WDM, but transient gain fluctuations change for each wavelength band. Therefore, a rare earth-doped fiber that can amplify the intensity of each wavelength channel equally, and an optical information communication system using such a rare earth-doped fiber are desired even when the traffic is particularly low.
Sun, Y., Zyskind, J. L., Srivastava, A. K., Zhang, L .: Analytical formal for the 16 p.

  An object of the present invention is to provide a rare earth-doped fiber such as an erbium-doped fiber amplifier with suppressed transient response.

  An object of the present invention is to provide an optical information communication system using a rare earth-doped fiber such as an erbium-doped fiber amplifier with suppressed transient response.

  An object of the present invention is to provide a rare earth-doped fiber that can amplify the intensity of each wavelength channel equally even when there is particularly little traffic, and an optical information communication system using such a rare earth-doped fiber. .

  An object of the present invention is to provide a construction program for an optical information communication system including a rare earth doped fiber such as a rare earth doped fiber such as an erbium doped fiber amplifier with suppressed transient response.

  The present invention is based on the knowledge that an EDFA with a suppressed transient response can be obtained by using a rare earth-doped fiber having an expanded active region, and that such an EDFA can be preferably used for optical information communication. Is based.

  In the present invention, the gain equalization filter is installed in front of the EDFA, so that the optical power at the gain medium edge and the wavelength dependence of gain fluctuation can be reduced, thereby suppressing the transient response. Based on knowledge.

  The present invention is also based on the knowledge that the excessive noise generated in the gain equalization filter can be suppressed by installing a preamplifier. Furthermore, the present invention can reduce the input power dependency of the rare earth-doped fiber by performing overpumping, and can obtain a constant gain. As a result, gain flatness (gain uniformity with respect to wavelength) can be maintained. It is based on the knowledge that.

  The first aspect of the present invention relates to an optical amplifier for optical packet communication using a rare earth doped fiber having an active region diameter of 3.4 μm or more and 10 μm or less. That is, an optical amplifier for optical packet communication has conventionally used a fiber amplifier for optical communication with a small output. This is because the high-power fiber amplifier is expensive, requires a large space, and cannot be handled easily. In addition, high-power fiber amplifiers are considered unsuitable as amplifiers for optical information communication using optical pulses because of large gain fluctuations (changes in gain with time). However, in the present invention, the gain fluctuation can be suppressed by using the fiber amplifier used for such high-power optical communication in the optical packet communication. The diameter of the active region may be 3.5 μm to 10 μm, 4 μm to 6 μm, 4 μm to 5 μm, and so on.

  A preferred embodiment of the first aspect of the present invention is the amplifier as described above, wherein the rare earth-doped fiber is an optical fiber doped with erbium as a rare earth.

  In a preferred embodiment of the first aspect of the present invention, the non-saturation region in the amplifier operation is expanded by reducing the numerical aperture so that the integral value of the overlapping region of the erbium ion and the light mode field is reduced. About things. Specifically, the present invention relates to the amplifier as described above, wherein the erbium-doped fiber has a numerical aperture of 0.2 or less. A preferred numerical aperture is 0.13 or less. For example, the numerical aperture can be controlled by adjusting the concentration of erbium contained in the core and cladding. For example, the optical fiber generally has a high numerical aperture as described in the column of 1.7.2 fiber structure dependency of “Erbium-doped fiber amplifier” written by Shoichi Sudo, page 150-152 of Optonics Corporation. Things were considered highly efficient. It was common knowledge to design an erbium-doped fiber so that the numerical aperture is as high as possible. In the present invention, a fiber having a low numerical aperture is used in order to suppress gain fluctuations. By reducing the numerical aperture, the integrated value of the overlapping region between the erbium ion and the light mode field can be reduced, and the unsaturated region in the amplifier operation can be expanded.

  In a preferred embodiment of the first aspect of the present invention, the erbium-doped fiber has a core and a clad existing around the core, erbium is added as a rare earth to the core, and the core includes the core. The amplifier according to any one of the above, which is an optical fiber to which erbium is added at a concentration lower than the erbium concentration contained in. One embodiment of reducing the numerical aperture is such an optical fiber.

  A preferred embodiment of the first aspect of the present invention relates to an optical packet communication system using the amplifier described above. Since the fiber amplifier as described above is included, a signal including an optical packet such as a header and a payload can be amplified while suppressing gain fluctuation.

  According to a second aspect of the present invention, there is provided a step of inputting an optical packet to the fiber amplifier using a rare earth doped fiber having an active region diameter of 3.4 μm to 10 μm, and an intensity of the optical packet input to the fiber amplifier. And a method of amplifying the intensity of the optical packet signal. As the rare earth-doped fiber used in the optical amplification method according to this aspect, the fiber described above can be used as appropriate. In particular, an erbium-doped fiber having a low numerical aperture can be preferably used.

  A preferred embodiment of the second aspect of the present invention includes a gain equalization filter and a rare earth-doped fiber having an active region diameter of 3.4 μm or more and 10 μm or less on which light transmitted through the gain equalization filter is incident. The present invention relates to an optical amplifying apparatus for optical packet communication.

  A preferred embodiment of the second aspect of the present invention is a preamplifier, a gain equalization filter on which light amplified by the preamplifier is incident, and a diameter of an active region on which light transmitted through the gain equalization filter is incident is 3 The present invention relates to an optical amplifying apparatus for optical packet communication, including a rare earth doped fiber having a size of 4 μm to 10 μm.

  A third aspect of the present invention is a step of adjusting the intensity of each wavelength channel so that the light intensity of the wavelength channel incident on the rare earth doped fiber and transmitted through the rare earth doped fiber is equalized by the gain equalization filter. , And a step of making the optical packet that has undergone the above-described process enter a rare earth-doped fiber.

  According to a fourth aspect of the present invention, the first rare earth doped fiber (31) having an active region diameter of 3.4 μm or more and 10 μm or less and light transmitted through the first rare earth doped fiber (31) are incident. , An intermediate gain equalizing filter (32), and a second rare earth doped fiber (33) having a diameter of an active region of 3.4 μm or more and 10 μm or less to which light transmitted through the intermediate gain equalizing filter (32) enters. The first rare earth doped fiber is shorter in length than the second rare earth doped fiber, and the intermediate gain equalizing filter is provided for each wavelength channel transmitted through the second rare earth doped fiber. This is an optical amplifying device for optical packet communication that adjusts the intensity of each wavelength channel so that the optical intensities are equal. As the rare earth-doped fiber used in the optical amplifying device according to this aspect, the fiber described above can be used as appropriate. In particular, an erbium-doped fiber having a low numerical aperture can be preferably used.

  Thus, by including two adjusted rare earth-doped fibers and a gain equalization filter provided therebetween, gain fluctuation is reduced and flatness is not impaired (for example, the intensity difference of each channel is within 1 dBm). , The allowable width of the input signal is increased, and the noise characteristic is also improved. As a result, the above-described optical amplifying device can give amplification characteristics to input light that are the same as when there is much traffic, even when there is little traffic.

  The two rare earth doped fibers are designed by comprehensively considering the wavelength range of the input signal, the magnitude of the gain, the intensity of the input signal, the intensity of the output signal, and the like. Specifically, when a rare earth-doped fiber having an active region of a certain size is used, its length is adjusted as appropriate. The main role of the first rare earth doped fiber (31) is, for example, light incident on the intermediate gain equalization filter (22) so that excessive noise is not generated due to loss by the intermediate gain equalization filter (22). Is a small gain. On the other hand, the second rare earth-doped fiber has a main role of amplifying an optical signal. For this reason, it is preferable that the gain of the second rare earth-doped fiber is larger than that of the first rare earth-doped fiber. Usually, since these same or similar rare earth-doped fibers are used, the length of the first rare earth-doped fiber is preferably not more than half the length of the second rare-earth doped fiber. .

  As specific lengths of the two rare earth doped fibers, the length of the first rare earth doped fiber is 25 cm or more and 75 cm or less, and the length of the second rare earth doped fiber is 1 m or more and 3 m or less. Those are preferred. In the embodiment, as actually designed and confirmed in function, this range can be suitably used for normal optical packet communication and the like.

  The intermediate gain equalizing filter adjusts the intensity of each wavelength channel so that the light intensity of each wavelength channel transmitted through the second rare earth doped fiber becomes equal. In order for the intermediate gain equalizing filter to function as described above, it is only necessary to have a characteristic that compensates for gain fluctuations caused by two rare earth-doped fibers. As a result, the flatness of the gain of the output optical pulse can be ensured. Controlling the characteristics of the gain equalization filter is a known technique. Therefore, if a gain fluctuation combining the gain characteristics of two rare earth doped fibers is known, a gain equalization filter may be designed and manufactured to compensate for the gain fluctuation.

  As demonstrated by the examples described later, an optical amplifying device for optical packet communication having extremely good characteristics can be provided by using an overpumping light source as a light source of light incident on the first rare earth doped fiber.

  Specific output power of the overpumping light source (34) is 200 mW or more and 1 W or less.

A fifth aspect of the present invention is a method for manufacturing an erbium-doped fiber amplifier, wherein the erbium-doped fiber is designed so that the active region has a diameter of 3.4 μm to 10 μm, and the erbium-doped fiber is opened. numerical aperture becomes 0.2 or less by number and 0.2 or less, gamma and _j, when the coefficient representing the integral value of the overlap region of the mode field of erbium ions and the light at wavelength channel, gamma _j The present invention relates to a method of manufacturing an erbium-doped fiber amplifier including a step of designing so as to be small.

According to a sixth aspect of the present invention, the computer inputs means for inputting the cross-sectional area S of the active region of the rare earth-doped fiber, and reads out the first coefficient, and the cross-sectional area S of the active region and the first coefficient And the means for obtaining the intrinsic saturation output P ^IS (λ _j ) in each wavelength channel, the light intensity P ^OUT (λ _j ) after passing through each wavelength channel, and the read P ^OUT (lambda _j) a value obtained by dividing the previously obtained intrinsic saturation power ^{P iS} (λ _j), calculated for all the wavelength channels, the value of the obtained _{^{P OUT (λ j) / P}} iS (λ j) A means for adding, reading the predetermined number and the second coefficient, and adding the value obtained by adding the values of P ^OUT (λ _j ) / P ^IS (λ _j ) and the predetermined number for all the wavelength channels And The values after, and means for multiplying said second coefficient, by to function, for determining the initial value and the time variation of the gain variation of the rare earth-doped fiber, a program.

  According to a sixth aspect of the present invention, there is provided an optical communication system design program using a computer, wherein at least the computer displays an icon relating to a rare earth-doped fiber on an output device, and the operation of the optical communication system. Means for displaying the icon at a position on the design screen to be obtained, and when the icon is displayed at a position on the design screen, the optical pulse input to the rare earth-doped fiber is multiplied by a prestored amplification factor. The present invention relates to a program that functions as a means for amplifying and outputting the amplitude of an input optical pulse.

In a preferred embodiment of the sixth aspect of the present invention, the program reads the computer with means for inputting the cross-sectional area S of the active region of the rare earth-doped fiber, the first coefficient, and the cross-sectional area S of the active region. And the first coefficient to obtain the intrinsic saturation output P ^IS (λ _j ) in each wavelength channel, and the intensity P ^OUT (λ _j ) of the light after passing through each wavelength channel In addition to reading, a value obtained by dividing the read P ^OUT (λ _j ) by the intrinsic saturation output P ^IS (λ _j ) obtained previously is obtained for all wavelength channels, and the obtained P ^OUT (λ _j ) / P ^IS Means for adding the value of (λ _j ), a value obtained by reading the predetermined number and the second coefficient, and adding the values of P ^OUT (λ _j ) / P ^IS (λ _j ) for all the wavelength channels; Above Optical communication considering the initial value of gain variation and time variation of rare earth doped fiber by adding a constant number and functioning as a means for multiplying the value after addition by the second coefficient. The present invention relates to a program described above for designing a system.

  A preferred embodiment of the sixth aspect of the present invention is a program for designing an optical communication system using a computer, and at least an optical packet in which a computer is combined with a prefilter and a rare earth doped fiber as an output device. Means for displaying an icon relating to an optical communication device for communication; means for displaying the icon at a position on a design screen for requesting an operation of the optical communication system; and when the icon is displayed at a position on the design screen. The present invention relates to a program that functions as means for amplifying and outputting the amplitude of an optical pulse that is input by multiplying an amplification coefficient stored in advance with respect to the optical pulse input to the optical packet communication optical amplifier.

  A preferred embodiment of the sixth aspect of the present invention relates to a computer-readable information recording medium storing any of the programs described above.

  A preferred embodiment of the sixth aspect of the present invention relates to a computer for designing an optical information communication system that includes any of the above-described programs and includes a rare earth-doped fiber.

  According to the present invention, it is possible to provide a rare earth-doped fiber such as an erbium-doped fiber amplifier having a suppressed transient response.

  According to the present invention, an optical information communication system using a rare earth doped fiber such as an erbium doped fiber amplifier with suppressed transient response can be provided.

  According to the present invention, it is possible to provide a rare earth-doped fiber that can amplify the intensity of each wavelength channel equally even when the traffic is particularly low, and an optical information communication system using such a rare earth-doped fiber.

  ADVANTAGE OF THE INVENTION According to this invention, the construction program etc. of an optical information communication system including rare earth addition fibers, such as an erbium addition fiber amplifier which suppressed the transient response, can be provided.

  Hereinafter, the best mode for carrying out the present invention will be described. The first aspect of the present invention relates to an optical amplifier for optical packet communication using a rare earth doped fiber having an active region diameter of 3.4 μm or more and 10 μm or less. That is, an optical amplifier for optical packet communication has conventionally used a fiber amplifier for optical communication with a small output. This is because the high-power fiber amplifier is expensive, requires a large space, and cannot be handled easily. Also, high-power fiber amplifiers were considered unsuitable as optical information communication amplifiers using optical pulses because of large gain fluctuations. However, in the present invention, the gain fluctuation can be suppressed by using the fiber amplifier used for such high-power optical communication in the optical packet communication.

  FIG. 14 is a diagram for explaining a schematic configuration of an optical amplifier for optical packet communication according to the present invention. As shown in FIG. 14, the optical amplifier for optical packet communication includes a rare earth doped fiber (1). The rare earth doped fiber (1) is generally configured to include a core (3) and a clad (4). On the other hand, normally, the entire core (2) is the active region (2), but as shown in FIG. 14, there is a region where the core (3) is the active region (2).

  FIG. 15 is a diagram showing a cross section of a specific rare earth doped fiber. 15A shows an example of a cross section of a single mode fiber, FIG. 15B shows an example in which the active region is concentric with the core, and FIG. 15C shows the active region substantially equal to the core. Examples of things are shown. In many rare earth-doped fibers, the core has almost the same size as the active region as shown in FIG. On the other hand, as shown in FIG. 15B, the core and the active region may not be the same.

  The active region means a certain area in the core of the fiber called a gain area or an active erbium area when the rare earth to be added is erbium. The core is a region having a higher relative refractive index than the surrounding due to wave guiding. Where the pump light intensity is weak, the absorption is greater than the amplification of the signal light. For this reason, the active region is usually arranged so as to overlap with the region where the pump light intensity is high near the center of the core. The active region is a region to which rare earth ions are added, and is uniquely determined at the time of designing the fiber. After the fact, the region can be confirmed by light emission of spontaneous emission by pump light irradiation.

  A preferred embodiment of the first aspect of the present invention is the amplifier as described above, wherein the rare earth is erbium. That is, as the rare earth-doped fiber, an optical fiber doped with erbium as a rare earth can be mentioned, and an erbium-doped fiber amplifier is preferable as demonstrated in Examples.

  A preferred embodiment of the first aspect of the present invention relates to the amplifier as described above, wherein the erbium-doped fiber has a numerical aperture of 0.2 or less. A preferred numerical aperture is 0.13 or less. The numerical aperture can be controlled by adjusting the concentration of erbium contained in the core and cladding. For example, the optical fiber generally has a high numerical aperture as described in the column of 1.7.2 fiber structure dependency of “Erbium-doped fiber amplifier” written by Shoichi Sudo, page 150-152 of Optonics Corporation. Things were considered highly efficient. It was common knowledge to design an erbium-doped fiber so that the numerical aperture is as high as possible. In the present invention, a fiber having a low numerical aperture is used in order to suppress gain fluctuations. By reducing the numerical aperture, the integrated value of the overlapping region between the erbium ion and the light mode field can be reduced, and the unsaturated region in the amplifier operation can be expanded.

  In a preferred embodiment of the first aspect of the present invention, the erbium-doped fiber has a core and a clad existing around the core, erbium is added as a rare earth to the core, and the core includes the core. The amplifier according to any one of the above, which is an optical fiber to which erbium is added at a concentration lower than the erbium concentration contained in. One embodiment of reducing the numerical aperture is such an optical fiber.

  A preferred embodiment of the first aspect of the present invention relates to an optical packet communication system using the amplifier described above. Since the fiber amplifier as described above is included, a signal including an optical packet such as a header and a payload can be amplified while suppressing gain fluctuation. This optical packet communication system can appropriately adopt a known configuration in the optical packet communication system. In general, the fiber amplifier of the present invention may be used as a fiber amplifier in an optical packet communication system. Specifically, the optical packet communication system includes a transmitter and a receiver, a node for connecting them, and an optical fiber for connecting them. And as the communication distance becomes longer, the intensity of the light pulse gradually becomes weaker, so the amplitude is appropriately increased by using a fiber amplifier. As a means for amplifying such amplitude, the fiber amplifier of the present invention may be appropriately installed.

  According to a second aspect of the present invention, there is provided a step of inputting an optical packet to the fiber amplifier using a rare earth doped fiber having an active region diameter of 3.4 μm to 10 μm, and an intensity of the optical packet input to the fiber amplifier. And a method of amplifying the intensity of the optical packet signal. That is, as demonstrated by the examples described later, it is preferable to use the fiber amplifier of the present invention because the optical packet signal can be amplified while suppressing gain fluctuation. As the rare earth-doped fiber used in the optical amplification method according to this aspect, the fiber described above can be used as appropriate. In particular, an erbium-doped fiber having a low numerical aperture can be preferably used.

  A preferred embodiment of the second aspect of the present invention includes a gain equalization filter and a rare earth-doped fiber having an active region diameter of 3.4 μm or more and 10 μm or less on which light transmitted through the gain equalization filter is incident. The present invention relates to an optical amplifying apparatus for optical packet communication. That is, the normal optical packet includes a plurality of optical pulses. The amplification characteristics of the fiber amplifier differ depending on the wavelength of the input light. When the optical packet includes a plurality of optical pulses having different wavelengths, the intensity amplified by the fiber amplifier differs for each wavelength. Therefore, when an optical packet including optical pulses having a plurality of wavelengths is amplified by a fiber amplifier, the amplitude after amplification is not uniform. Therefore, a gain equalization filter is used.

  FIG. 7 is a conceptual diagram showing an increase characteristic of an erbium-doped fiber amplifier. As shown in FIG. 7, the erbium-doped fiber amplifier has the maximum amplification in the vicinity of 1530 nm, and the gain fluctuation in the vicinity thereof is also maximum. On the other hand, the amplitude amplification is not so large in the vicinity of 1580 nm. On the other hand, when an optical signal having a wavelength near 1530 nm is amplified, noise increases. Therefore, in the present invention, it is preferable to use light having a wavelength in the range of 1535 nm to 1570 nm, more preferably light in the range of 1535 nm to 1565 nm as the input signal.

  In a normal optical packet communication system, the amplitude of an optical packet is once amplified by an erbium-doped fiber amplifier. Then, the degree of amplification differs depending on the wavelength of the optical pulse included in the optical packet. Therefore, the gain is equalized by using a gain equalization filter for the optical pulse that has been amplified and whose gain differs for each wavelength. When all the channels included in the optical packet are used, such a leveling method has few problems. However, especially when only a part of the channels is used, a large gain fluctuation occurs as shown in the equation (1) described later. Therefore, in a preferred embodiment of the present invention, the amplitude is amplified by a fiber amplifier after passing through a gain equalizing filter in advance. By doing so, it is possible to suppress the gain fluctuation even when only a part of the channels are used. That is, by using the gain equalization filter, in the present invention, the wavelength band dependence of the transient gain fluctuation can be reduced.

  A preferred embodiment of the second aspect of the present invention is a preamplifier, a gain equalization filter on which light amplified by the preamplifier is incident, and a diameter of an active region on which light transmitted through the gain equalization filter is incident is 3 The present invention relates to an optical amplifying apparatus for optical packet communication, including a rare earth doped fiber having a size of 4 μm to 10 μm. As the preamplifier, a known preamplifier used for optical communication can be appropriately used. By using the preamplifier, in the present invention, it is possible to suppress excess noise generated in the gain equalization filter.

  A third aspect of the present invention is a step of adjusting the intensity of each wavelength channel so that the light intensity of the wavelength channel incident on the rare earth doped fiber and transmitted through the rare earth doped fiber is equalized by the gain equalization filter. , And a step of making the optical packet that has undergone the above-described process enter a rare earth-doped fiber.

  FIG. 8 is a conceptual diagram for explaining an optical packet amplification method according to the third aspect of the present invention. As shown in FIG. 8, an optical packet (11) is transmitted through a transmission line (10) such as an optical fiber. The optical packet includes optical pulses having a plurality of wavelengths. The optical packet (11) including optical pulses having a plurality of wavelengths is input to the gain equalization filter (12). However, normally, the gain equalization filter is such that the gain of each pulse after passing through it is made equal, but the gain equalization filter (12) in this embodiment is rare earth added. The light intensity of the wavelength channels that enter the fiber and pass through the rare earth doped fiber is set to be equal. For this reason, the gain of the optical pulse of each wavelength included in the optical packet (13) that has passed through the gain equalization filter is not uniform. On the other hand, when the optical packet (13) that has passed through the gain equalization filter passes through the fiber amplifier (14), the gain of the optical pulse (15) that has passed through the fiber amplifier is uniform (for example, the deviation of the optical intensity of each channel). , Within 10% above and below the average intensity, preferably within 5% above and below the average intensity, more preferably within 3% above and below the average intensity).

  By using the gain equalization filter as described above, the gain of the optical pulse (15) that has passed through the fiber amplifier becomes uniform when it passes through the fiber amplifier (14). Therefore, the above fiber amplifier can be preferably used for optical packet communication. On the other hand, when the traffic is low, there is a problem that the packet is affected by the gain fluctuation and the inclination of the packet is emphasized. Furthermore, when the traffic is low, the phenomenon that the peak value of the packet becomes abnormally high occurs. Such an abnormally high peak value not only gives further gain fluctuations but also extremely increases the possibility of damaging the optical element. Therefore, this is detected by some means and the incident power to the fiber amplifier is reduced. Need to be restricted. However, as a result, an incident light condition having an extremely low average power occurs. Therefore, a fiber amplifier is desired in which the optical intensity of each channel does not vary even if the traffic volume varies.

  The above problem is solved by an apparatus including two rare earth doped fibers and a gain equalizing filter provided therebetween. FIG. 10 is a block diagram showing a schematic configuration of an optical amplifying apparatus for optical packet communication according to an aspect of the present invention. That is, as shown in FIG. 10, the fourth aspect of the present invention is the first rare earth doped fiber (31) having an active region diameter of 3.4 μm or more and 10 μm or less, and the first rare earth doped fiber. The intermediate gain equalizing filter (32) in which the light transmitted through (31) is incident and the diameter of the active region in which the light transmitted through the intermediate gain equalizing filter (32) is incident are 3.4 μm or more and 10 μm or less. A second rare earth doped fiber (33), wherein the first rare earth doped fiber is shorter in length than the second rare earth doped fiber, and the intermediate gain equalizing filter includes the second rare earth doped fiber (33). The optical amplifying device for optical packet communication adjusts the intensity of each wavelength channel so that the light intensity of each wavelength channel transmitted through the rare earth doped fiber becomes equal.

  Thus, by including two adjusted rare earth doped fibers and a gain equalization filter provided between them, gain fluctuation is reduced and flatness is not impaired (for example, the difference in intensity of each channel is within 1 dBm). ). As a result, the above-described optical amplifying device can give amplification characteristics to input light that are the same as when there is much traffic, even when there is little traffic.

  The two rare earth doped fibers are designed by comprehensively considering the wavelength range of the input signal, the magnitude of the gain, the intensity of the input signal, the intensity of the output signal, and the like. Specifically, when a rare earth-doped fiber having an active region of a certain size is used, its length is adjusted as appropriate. The main role of the first rare-earth doped fiber (31) is, for example, light incident on the intermediate gain equalization filter (32) so that excessive noise is not generated due to loss by the intermediate gain equalization filter (32). Is a small gain. On the other hand, the second rare earth-doped fiber has a main role of amplifying an optical signal. For this reason, it is preferable that the gain of the second rare earth-doped fiber is larger than that of the first rare earth-doped fiber. Usually, since these same or similar rare earth-doped fibers are used, the length of the first rare earth-doped fiber is preferably not more than half the length of the second rare-earth doped fiber. .

  As specific lengths of the two rare earth doped fibers, the length of the first rare earth doped fiber is 25 cm or more and 75 cm or less, and the length of the second rare earth doped fiber is 1 m or more and 3 m or less. Those are preferred. In the embodiment, as actually designed and confirmed in function, this range can be suitably used for normal optical packet communication and the like.

  The intermediate gain equalizing filter adjusts the intensity of each wavelength channel so that the light intensity of each wavelength channel transmitted through the second rare earth doped fiber becomes equal. The intermediate in the intermediate gain equalizing filter means that it is located between the second rare earth doped fibers. Therefore, a known gain equalization filter processed as the intermediate gain equalization filter can be used as appropriate. In order for the intermediate gain equalizing filter to function as described above, it is only necessary to have a characteristic that compensates for gain fluctuations that combine the gain characteristics of the two rare earth doped fibers. Controlling the characteristics of the gain equalization filter is a known technique. Therefore, if a gain fluctuation combining the gain characteristics of two rare earth doped fibers is known, a gain equalization filter may be designed and manufactured to compensate for the gain fluctuation.

  As demonstrated by the examples described later, an optical amplifying apparatus for optical packet communication having extremely good characteristics is provided by using an overpumping light source (34) as a light source of light incident on the first rare earth doped fiber. it can. An over-pumping light source means a light source having an output exceeding an appropriate pump intensity, and is usually a light source having an output far exceeding an assumed pump intensity. More specifically, an overpumping light source is a proper design method such as an ordinary EDFA, which is determined from the active region of EDF, added concentration, length, and various conditions of an assumed incident signal. It is a light source whose output is much higher than the pump light intensity, and most of its optical power means that it does not directly contribute to optical amplification. For overpumping in rare-earth doped fibers such as EDFA, see, for example, M.C. Karasek et al., “Suppression of Dynamic Cross Saturation in Cascades of Overprinted Ebium-Doped Fiber Amplifiers, IEEE Phononic Technology. 10, no. 7, see July, 1998. By using an overpumping light source, in the present invention, the incident power dependency of the amplifier can be reduced, and the gain approaches a constant gain. As a result, the gain flatness of the output pulse can be maintained.

  Specific output power of the overpumping light source is 200 mW or more and 1 W or less. The higher the output power of the overpumping light source, the better. However, since the cost of the apparatus becomes high, 300 mW or more and 600 mW or less are preferable, and those with 550 mW are preferable.

  A pulse signal from the overpumping light source is incident on the first rare earth doped fiber through the coupler. Then, in the first rare earth-doped fiber (31), gain is given to the optical signal so that excessive noise does not occur due to loss due to the intermediate gain equalization filter (32). The intermediate gain equalizing filter (32) adjusts the intensity of each wavelength channel so that the light intensity of each wavelength channel transmitted through the second rare earth doped fiber becomes equal. Specifically, the intermediate gain equalization filter is designed and manufactured to compensate for gain fluctuations that combine the gain characteristics of two rare earth doped fibers, so that these gain characteristics are compensated. The output optical signal is output. The optical signal that has passed through the intermediate gain equalization filter (32) enters the second rare earth doped fiber. The light intensities of the respective wavelength channels transmitted through the second rare earth doped fiber are made approximately equal.

According to a sixth aspect of the present invention, the computer inputs means for inputting the cross-sectional area S of the active region of the rare earth-doped fiber, and reads out the first coefficient, and the cross-sectional area S of the active region and the first coefficient And the means for obtaining the intrinsic saturation output P ^IS (λ _j ) in each wavelength channel, the light intensity P ^OUT (λ _j ) after passing through each wavelength channel, and the read P ^OUT (lambda _j) a value obtained by dividing the previously obtained intrinsic saturation power ^{P iS} (λ _j), calculated for all the wavelength channels, the value of the obtained _{^{P OUT (λ j) / P}} iS (λ j) A means for adding, reading the predetermined number and the second coefficient, and adding the value obtained by adding the values of P ^OUT (λ _j ) / P ^IS (λ _j ) and the predetermined number for all the wavelength channels And The values after, and means for multiplying said second coefficient, by to function, for determining the initial value and the time variation of the gain variation of the rare earth-doped fiber, a program.

  According to a sixth aspect of the present invention, there is provided an optical communication system design program using a computer, wherein at least the computer displays an icon relating to a rare earth-doped fiber on an output device, and the operation of the optical communication system. Means for displaying the icon at a position on the design screen to be obtained, and when the icon is displayed at a position on the design screen, the optical pulse input to the rare earth-doped fiber is multiplied by a prestored amplification factor. The present invention relates to a program that functions as a means for amplifying and outputting the amplitude of an input optical pulse.

  FIG. 9 is a conceptual diagram for explaining a program according to the sixth aspect of the present invention. As shown in FIG. 9, a computer in which this program is installed performs a display as shown in FIG. 9 on an output device such as a monitor. That is, the icon menu (21) displays an icon (22) related to the fiber amplifier, an icon (23) related to the gain equalization filter, and the like. Then, by dragging and dropping those icons onto the design screen (24) as appropriate, devices and the like related to the dragged icons are drawn on the design screen. In this design screen, when an optical pulse is input to the fiber amplifier, the amplification coefficient stored in the storage device is read out, multiplied by the intensity of the input optical pulse, and output. In addition to an icon related to a normal fiber amplifier, a separate icon related to the fiber amplifier in the present invention is a preferable aspect of the present invention.

In a preferred embodiment of the sixth aspect of the present invention, the program reads the computer with means for inputting the cross-sectional area S of the active region of the rare earth-doped fiber, the first coefficient, and the cross-sectional area S of the active region. And the first coefficient to obtain the intrinsic saturation output P ^IS (λ _j ) in each wavelength channel, and the intensity P ^OUT (λ _j ) of the light after passing through each wavelength channel In addition to reading, a value obtained by dividing the read P ^OUT (λ _j ) by the intrinsic saturation output P ^IS (λ _j ) obtained previously is obtained for all wavelength channels, and the obtained P ^OUT (λ _j ) / P ^IS Means for adding the value of (λ _j ), a value obtained by reading the predetermined number and the second coefficient, and adding the values of P ^OUT (λ _j ) / P ^IS (λ _j ) for all the wavelength channels; Above Optical communication considering the initial value of gain variation and time variation of rare earth doped fiber by adding a constant number and functioning as a means for multiplying the value after addition by the second coefficient. The present invention relates to a program described above for designing a system.

  A preferred embodiment of the sixth aspect of the present invention is a program for designing an optical communication system using a computer, and at least an optical packet in which a computer is combined with a prefilter and a rare earth doped fiber as an output device. Means for displaying an icon relating to an optical communication device for communication; means for displaying the icon at a position on a design screen for requesting an operation of the optical communication system; and when the icon is displayed at a position on the design screen. The present invention relates to a program that functions as means for amplifying and outputting the amplitude of an optical pulse that is input by multiplying an amplification coefficient stored in advance with respect to the optical pulse input to the optical packet communication optical amplifier.

  Specifically, for example, as shown in FIG. 9, when the gain equalization filter and the fiber amplifier are arranged in this order, it is preferable to provide output characteristics and gain variation as described in this specification.

  A preferred embodiment of the sixth aspect of the present invention relates to a computer-readable information recording medium storing any of the programs described above.

  A preferred embodiment of the sixth aspect of the present invention relates to a computer for designing an optical information communication system that includes any of the above-described programs and includes a rare earth-doped fiber. The computer of the present invention stores, for example, any of the above programs in the main memory. When there is an input from a pointing device or the like, the CPU reads the program stored in the main memory, receives the command of the read program, reads the information stored in the memory as appropriate, performs a predetermined calculation, Output. In order to realize such an operation, the control unit is connected to the input unit, the output unit, the storage unit, and the calculation unit so as to be able to exchange information via a bus or the like.

  In the present invention, a rare earth-doped fiber such as a known erbium-doped optical fiber having a relatively large active region diameter can be used. In addition to erbium, praseodymium, thulium, or neodymium can be used as the rare earth in the rare earth doped fiber. On the other hand, since a typical example of an optical fiber amplifier is an erbium-doped optical fiber, an erbium-doped optical fiber will be described below as an example. An erbium-doped optical fiber has 10 to 20% by weight of germanium added to the active region, and 500 to 2000 ppm of erbium as an amplification medium as a dopant for increasing the refractive index. Has excellent properties. Further, the amplification wavelength band is 1.55 μm, and it is widely used as an optical amplifier for 1.5 μm band.

  An erbium-doped optical fiber is composed of an active region and a cladding, and the active region is quartz glass containing erbium, aluminum, and germanium.

  The content of germanium is less than 1.5% by weight, preferably 0.5 to 1.0% by weight. Thereby, the gain flatness and energy conversion efficiency of the erbium-doped optical fiber can be improved. When the content of germanium is 1.5% by weight or more, aluminum ions suppress the action of suppressing erbium cluster formation, which is not preferable.

  The content of aluminum is not particularly limited, but is usually less than 4% by weight. By containing aluminum, the wavelength dependency of gain in the 1540 to 1560 nm band can be flattened, and the gain flatness can be improved. In addition, aluminum ions can coordinate to erbium ions and suppress the formation of erbium clusters. As a result, energy exchange between erbium ions can be reduced, and excellent energy conversion efficiency can be realized. The content of erbium in the active region is not particularly limited and can be appropriately determined depending on the intended use.

  Fiber amplifiers such as erbium-doped optical fiber amplifiers are doped with elements such as germanium at a desired concentration by known techniques such as chemical vapor deposition such as MCVD and VAD, and immersion using an aluminum compound solution. It can be manufactured by manufacturing a fiber base material and drawing it by melt drawing.

  The technical scope of the present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention. As described above, the active region may contain other elements as long as it contains erbium, aluminum, and germanium in a desired concentration. In addition, for example, by containing 0.5 to 2.0% by weight of cerium, ytterbium, and lanthanum in the active region, the bond between erbium ions can be further suppressed, and the energy conversion efficiency can be further improved. Therefore, even when erbium is contained at a high concentration, excellent energy conversion efficiency can be realized. In addition, the crystal structure is stabilized and light loss due to structural defects can be reduced.

  When the gain of the EDFA is G (t), the gain fluctuation G ′ (0) of the EDFA is approximately given by the following equation (1) (Sun, Y., Zyskind, J. L., Srivastava, A. K. , Zhang, L .: Analytical formula for the transient response of erbium-doped fiber amplifiers. Applied optics 38, 9 (1999) 1682-1685.

In the above equation (1), G (0) is a gain before transmission, and G (∞) is a gain when a steady state is obtained after transmission. τ ₀ means the intrinsic lifetime of the erbium ion in the excited state. τ ₀ can be obtained by turning on / off the excitation light. Although there are cases where three excitation levels exist, a system of two levels of Er ³⁺ related to emission transition is assumed here. P ^IS (λ _j ) means the intrinsic saturation output in each wavelength channel (λ _j ). hv means the intensity of light. S means the active erbium cross section in EDF. σ _a and σ _e mean the cross sections of absorption and stimulated emission in each wavelength channel, respectively. σ _a and σ _e can be determined by a known spectroscopic analysis such as a lateral fluorescence lifetime measurement method. Γ _j means a coefficient (overlap factor) indicating an integral value of an overlapping region between the erbium ion and the optical mode field in each wavelength channel. In the above formula, the signal light and the pump light are handled in the same way.

G ′ (0) indicates the slope of the initial gain fluctuation. On the other hand, optical fibers having a large active region diameter have been used to obtain high output. That is, since the optical fiber having a large active region diameter is used when P ^OUT is large, normally, if such an optical fiber is used, P ^OUT inevitably increases and gain fluctuation increases. In the present invention, an optical fiber having a large active region diameter, which is usually used for such a high output, has a low output (for example, the output is 1 mW to 1 W, preferably 10 mW to 500 mW, more preferably 50 mW to 400 mW) It is used for the optical pulse of

  As shown in the above equation, G ′ (0) indicates the slope of the initial gain fluctuation and is inversely proportional to S. Therefore, gain variation can be improved by using an EDF having a large active erbium cross section. Further, the erbium-doped fiber amplifier of the present invention can be combined with the electrical control method of the conventional invention to constitute a gain fluctuation suppressing optical amplifier having a wide time response.

As described above, in order to reduce G ′ (0), P ^IS (λ _j ) may be increased. For this purpose, in addition to increasing S, Γ _j may be decreased. The burst mode erbium-doped fiber amplifier may be designed so that the unsaturated region is expanded and the numerical aperture is decreased. In a preferred embodiment of the present invention, the numerical aperture of the erbium-doped fiber is 0.2 or less. It is more preferable if the numerical aperture is 0.13 or less. The numerical aperture can be controlled by adjusting the concentration of erbium contained in the core and cladding. For example, an optical fiber in which erbium is added to the cladding as well as erbium to the cladding may be used. That is, in the present invention, it is preferable to use an optical fiber having a cladding to which erbium is added at a concentration lower than the erbium concentration contained in the core. Alternatively, an optical fiber in which erbium is added only to the cladding without adding a rare earth such as erbium to the core may be used. A fifth aspect of the present invention is a method for manufacturing an erbium-doped fiber amplifier, wherein the numerical aperture of the erbium-doped fiber is 0.2 or less, and Γ _j is defined as an erbium ion and a mode field of light in a wavelength channel. The present invention relates to a manufacturing method of an erbium-doped fiber amplifier including a step of designing so that Γ _j is reduced when the coefficient indicates an integral value of an overlapping region. It can be designed such that Γ _j is reduced by the same method as that for reducing the numerical aperture.

  In the following embodiment, a WDM packet divided into 8 wavelengths by 10G-Ethernet frame input was transferred. FIG. 2 is a conceptual diagram showing a packet format and traffic intensity in the present embodiment. The payload bit rate was OC-192 (9.995328 Gbps), the packet included a 128-bit preframe and a 3814-bit payload, and the packet duration was 400 ns. In this embodiment, two average link utilization rates (LU [%] defined as the sum of packet durations in 1 second) of 33% and 0.4% were used. The numerical aperture was 0.18.

  Expressions (1) and (2) are approximate expressions, unlike the mounting system. Therefore, there are residual continuous light and amplified spontaneous emission (ASE). For example, considering that the ratio of the mark in the packet is 50:50, the total of the light energy forming the bit of the mark “1” when LU = 0.4% is 1/50 of all the light energy. Not too much. The remaining light energy is used for DC components with a space “0” or used for white space between packets. In such situations, the energy used for the effective light pulse is not the main one. On the other hand, according to the above equation, a high-speed switch WDM network is assumed in which the bit stream is continuous, and the pumping energy of EDF is efficiently used by effective optical pulses and clear ASE components. Become. However, in this embodiment, the above formula is followed, and more accurate and quantitative examination is a future problem.

  FIG. 3 is a conceptual diagram showing a state of a packet at each wavelength and timing in the WDM environment. The packet generator simultaneously generates 8-wavelength packets at 100 GHz intervals (pattern 1). Here, an uncorrelated WDM stream was also observed for comparison (pattern 2). Whether to select the pattern 1 or the pattern 2 is determined by the network structure from the viewpoint of the transient response of the EDFA.

  The above equation also means that the light intensity at other wavelengths affects gain fluctuations, which is a serious problem in WDM. In order to investigate the influence of other wavelengths, pattern 3 and pattern 4 were also observed here.

  FIG. 4 is a schematic configuration diagram of an apparatus according to the embodiment. This device assumed a typical optical packet switching (OPS) system using five consecutive EDFAs. This system can also be applied to other optical packet network models with several hops. The average intensity of the light input to the first EDFA takes between −8 to −12 dBm and is increased to +13 dBm depending on the LU value. The light input to the EDFA is attenuated to -3 dBm by a 7.6 nm band pass filter and input to the next EDFA. The gain was set to 16 dB by each EDFA. For simplicity, in the following, only λ4 (1550.12 nm) was observed.

  For reference, a commercially available EDFA (type A) is used with 33% LU and pattern 1, and a commercially available EDFA (type B) is LU with 0.4% and pattern 2 We also observed what was used in. As the EDFA (type C) of the present invention, a pattern 3 having an active region diameter of 4.3 μm was used.

  In conclusion, the one using the EDFA of the present invention (type C) was the most excellent (type A was the most inferior. Type B exhibited performance close to that of type C, but was slightly inferior. When LU was examined, when the LU was 33%, there was no major failure except for the type A. A slight noise was observed with the type A. On the other hand, when the LU was 0.4%, there was a lot of noise. In addition, it was found that the failure was also affected by the number of consecutive EDFAs.

  FIG. 5 is a graph showing a failure caused by gain fluctuation and crosstalk. FIG. 5A shows a pattern 1 of type B, FIG. 5B shows a pattern 2 of type A, and FIG. 5C shows a pattern 3 of type A. 5 (d) shows a pattern 4 of type A.

  As shown in FIG. 5A, the optical packet is subjected to gain fluctuation by five consecutive EDFAs. Such an obstacle is an unavoidable problem at present. Type B tends to have less fluctuation, but accumulation of fluctuation occurs even when all wavelengths have the same timing.

  5 (b) to 5 (d) show bad examples using type A. FIG. In FIG. 5B, the noise due to other wavelengths that are no longer correlated is extremely high. In Fig. 5 (c) and Fig. 5 (d), when other channels are added or lost compared to the observation target, seven channels other than the observation target are clearly observed instead of the observation target. ing. To emphasize the obstacles, the timing of the seven channels was the same. This indicates that an optical packet is damaged when an unoptimized EDFA is used in a WDM environment.

  In all cases in this example, the best results were obtained when using type C having a large erbium active region. FIG. 6 is a graph showing the case corresponding to each case of FIG. 6A shows the pattern 1, FIG. 6B shows the pattern 2, FIG. 6C shows the pattern 3, and FIG. 6D shows the pattern 4. Indicates.

  The result of FIG. 6A was almost the same as that of FIG. 5A, but 30% better. Furthermore, in the case of using Type A, although there are obvious obstacles, FIGS. 6 (b) to 6 (d) show that there are slight obstacles, but a new one derived from crosstalk. There were no major obstacles. This clearly shows that the present invention can improve the effects of gain fluctuations and crosstalk.

Study on characteristics of rare earth doped fiber with expanded active region We investigated the characteristics of rare earth doped fiber with expanded active region. FIG. 11 is a schematic view of an active region expanded rare earth doped fiber manufactured to study the characteristics of the active region expanded rare earth doped fiber. The fiber amplifier used was an erbium-doped fiber amplifier that can be used in burst mode. The active region having a diameter of 7.6 μm and a length of 3 m-4 m was used. The intensity of the input signal was −3 dBm. In order to obtain the characteristics of the manufactured fiber amplifier when the traffic is low, computer simulation was performed. The numerical aperture was 0.13.

  FIG. 12 is a graph replaced with a drawing showing the characteristics of the active region expanded rare earth doped fiber. FIG. 12A shows the signal strength of each channel, and FIG. 12B shows the shape of a rectangular pulse. From FIG. 12A, it can be seen that when there is little traffic, the signal of each channel is affected by gain fluctuation. Also, from FIG. 12B, it can be seen that the shape of the rectangular pulse is partially inclined. Further, it can be seen from FIG. 12 that amplification of small signals tends to have higher gain than amplification in the saturation region.

Study of characteristics of system including overpump light source, two active region expanded rare earth doped fibers, and intermediate gain equalization filter. A system configured as shown in FIG. 10 was constructed, and the overpump light source, two active region expanded rare earth doped The characteristics of the system including fiber and intermediate gain equalization filter were studied. The intensity of the overpump light source was −3 dBm. The two active region expanded rare earth doped fibers were erbium doped fiber amplifiers that could be used in burst mode. The diameter of the active region was 7.6 μm, the length of the first rare earth doped fiber was 50 cm, and the length of the second rare earth doped fiber was 2 m. The intermediate gain equalizing filter was designed and manufactured so as to have a filter characteristic that compensates for gain variations caused by the first and second rare earth doped fibers. Computer simulation was performed to determine the characteristics of the manufactured system when there was little traffic.

  FIG. 13 is a graph instead of a drawing showing the characteristics of a system including an overpump light source, two active region expanded rare earth doped fibers, and an intermediate gain equalization filter. FIG. 13A shows the signal intensity of each channel, and FIG. 13B shows the shape of a rectangular pulse. From FIG. 13A, it can be seen that when the traffic is small, the influence of the gain fluctuation given to the signal of each channel is small. Also, from FIG. 13B, it can be seen that the shape of the rectangular pulse is maintained almost rectangular. In FIG. 12 and FIG. 13, the value of the vertical axis of the spectrum is different. This means that by using an overpump and a gain equalization filter, a static gain can be obtained close to a constant value without depending on the average power of incident light.

Relationship between numerical aperture and overlap factor Next, the relationship between the numerical aperture and the overlap factor in the light wavelength region of 1530 nm to 1580 nm was simulated.
FIG. 16 is a graph replaced with a drawing in which the relationship between the numerical aperture and the overlap factor is obtained. As shown in FIG. 16, in the region of 1530 nm to 1580 nm, it can be seen that the overlap factor can be effectively reduced by setting the numerical aperture to 0.2 or less. In particular, it can be seen that when the numerical aperture is 0.13 or less, the overlap factor can be drastically reduced.

  The erbium-doped fiber amplifier of the present invention can be used in fields such as optical information communication. Further, the erbium-doped fiber amplifier of the present invention can be combined with the electrical control method of the conventional invention to constitute a gain fluctuation suppressing optical amplifier having a wide time response.

FIG. 1 is a diagram illustrating an example of a change in a packet waveform caused by an EDFA. FIG. 2 is a conceptual diagram showing a packet format and traffic intensity in the present embodiment. FIG. 3 is a conceptual diagram showing a state of a packet at each wavelength and timing in the WDM environment. FIG. 4 is a schematic configuration diagram of an apparatus according to the embodiment. FIG. 5 is a graph showing a failure caused by gain fluctuation and crosstalk. FIG. 5A shows a pattern 1 of type B, FIG. 5B shows a pattern 2 of type A, and FIG. 5C shows a pattern 3 of type A. 5 (d) shows a pattern 4 of type A. FIG. 6 is a graph showing the case corresponding to each case of FIG. 6A shows the pattern 1, FIG. 6B shows the pattern 2, FIG. 6C shows the pattern 3, and FIG. 6D shows the pattern 4. Indicates. FIG. 7 is a conceptual diagram showing an increase characteristic of an erbium-doped fiber amplifier. FIG. 8 is a conceptual diagram for explaining an optical packet amplification method according to the third aspect of the present invention. FIG. 9 is a conceptual diagram for explaining a program according to the sixth aspect of the present invention. FIG. 10 is a block diagram showing a schematic configuration of an optical amplifying apparatus for optical packet communication according to an aspect of the present invention. FIG. 11 is a schematic view of an active region expanded rare earth doped fiber manufactured to study the characteristics of the active region expanded rare earth doped fiber. FIG. 12 is a graph replaced with a drawing showing the characteristics of the active region expanded rare earth doped fiber. FIG. 12A shows the signal strength of each channel, and FIG. 12B shows the shape of a rectangular pulse. FIG. 13 is a graph instead of a drawing showing the characteristics of a system including an overpump light source, two active region expanded rare earth doped fibers, and an intermediate gain equalization filter. FIG. 13A shows the signal intensity of each channel, and FIG. 13B shows the shape of a rectangular pulse. FIG. 14 is a diagram for explaining a schematic configuration of an optical amplifier for optical packet communication according to the present invention. FIG. 15 is a diagram showing a cross section of a specific rare earth doped fiber. 15A shows an example of a cross section of a single mode fiber, FIG. 15B shows an example in which the active region is concentric with the core, and FIG. 15C shows the active region substantially equal to the core. Examples of things are shown. FIG. 16 is a graph replaced with a drawing in which the relationship between the numerical aperture and the overlap factor is obtained.

DESCRIPTION OF SYMBOLS 1 Fiber 2 Active region 3 Core 4 Cladding 10 Transmission path, such as optical fiber 11 Optical packet 12 Gain equalization filter 13 Optical packet that has passed through gain equalization filter 14 Fiber amplifier 15 Optical pulse that has passed through fiber amplifier
21 Icon Menu 22 Fiber Amplifier Icon 23 Gain Equalization Filter Icon 24 Design Screen 31 First Rare Earth Doped Fiber 32 Intermediate Gain Equalization Filter 33 Second Rare Earth Doped Fiber 34 Overpumping Light Source

Claims (9)

An optical amplifier for optical packet communication using rare earth doped fibers,
The rare earth-doped fiber has an active region diameter of 3.4 μm to 10 μm,
The optical amplifier expands the non-saturation region in the amplifier operation by reducing the numerical aperture so that the integral value of the overlapping region of the erbium ion and the optical mode field is reduced.
The numerical aperture of the rare earth doped fiber is 0.2 or less,
The length of the rare earth doped fiber is not less than 1 m and not more than 4 m.
Optical amplifier. The rare earth doped fiber is an erbium doped fiber in which erbium is added as a rare earth,
The optical amplifier according to claim 1. Further including a gain equalization filter;
The rare earth-doped fiber is a light incident through the gain equalizing filter,
The gain equalizing filter adjusts the intensity of each wavelength channel so that the light intensity of each wavelength channel transmitted through the rare earth-doped fiber is equal.
The optical amplifier according to claim 1 or 2. Including a preamplifier,
The gain equalizing filter receives light amplified by a preamplifier,
The optical amplifier according to claim 3. The preamplifier is a first rare earth doped fiber;
When the rare earth doped fiber is a second rare earth doped fiber,
The first rare earth doped fiber is shorter in length than the second rare earth doped fiber.
The optical amplifier according to claim 4. The length of the first rare earth doped fiber is not more than half of the length of the second rare earth doped fiber.
The optical amplifier according to claim 5. The length of the first rare earth doped fiber is 25 cm or more and 75 cm or less,
The length of the second rare earth doped fiber is not less than 1 m and not more than 3 m.
The optical amplifier according to claim 6. As a light source of light incident on the first rare earth doped fiber,
Using an overpumping light source,
The optical amplifier according to claim 7. The output power of the overpumping light source is 200 mW or more and 1 W or less,
The optical amplifier according to claim 8.

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