JPH0389644A - Transmission method for wavelength multiplex optical signal - Google Patents

Abstract

PURPOSE:To equalize the allowable transmission line loss assigned to each optical signal and to transmit the optical signal by setting the signal band of each optical signal in proportion to the gain of each wavelength band based on the gain band characteristic of an optical amplifier to transmit the optical signal. CONSTITUTION:Outputs from the first and second light sources 1 and 2 are synthesized by an optical synthesizer 5 and are amplified by a first long-sized optical fiber amplifier 7. This Er (erbium) dope fiber amplifier 7 is excited by a third light source 8 having 1.49mum wavelength, and 30dB gain is obtained for 1.536mum wavelength, and 20dB gain is obtained for 1.552mum wavelength. The loss margin from the output of the Er dope fiber amplifier 7 to first and second optical receivers 11 and 12 is 43dB in the case of 1.536mum wavelength as well as 1.552mum wavelength, and the signal is received with 5dB margin in the case of both wavelengths even when 37dB loss of a second optical fiber 9 and 1dB loss of a wavelength demultiplexing filter 10 are taken into consideration.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a wavelength multiplexed signal transmission method, and more particularly to a wavelength multiplexed signal transmission method using an optical amplifier.

(Prior Art) Wavelength multiplexing signal transmission is considered to be one of the effective means for expanding transmission capacity. In this wavelength multiplexed signal transmission, since light is multiplexed and demultiplexed in the transmitting and receiving section, multiplexing and demultiplexing loss occurs there. The use of an optical amplifier is effective as a means to compensate for this multiplexing/demultiplexing loss and transmission line loss.

Examples of optical amplifiers here include semiconductor optical amplifiers, fiber rammer amplifiers, and rare earth-doped fiber amplifiers, but erbium (Er)-doped fiber amplifiers in particular are capable of low-loss coupling with optical fibers, are non-polarized light dependent, and can be pumped by semiconductor lasers. (For example, a paper (c-622) rl presented at the 1989 Spring National Conference of the Institute of Electronics, Information and Communication Engineers by Noyama 3, Optical amplification characteristics of a 49 μm semiconductor laser-pumped erbium-doped fiber. ”
).

(Problems to be Solved by the Invention) When using an Er-doped fiber amplifier, the wavelength dependence of its gain becomes a problem. FIG. 2 is a diagram showing typical gain characteristics of an Er-doped fiber amplifier.

As is clear from FIG. 2, the Er-doped fiber amplifier can obtain a gain of 20 dB or more over a wide wavelength band of 1.53 μm to 1.56 μm, but the gain has a large wavelength dependence. Therefore, when attempting to perform wavelength multiplexed signal transmission in the above-mentioned wavelength band, there is a drawback that the gain obtained differs depending on the wavelength, and the allowable transmission line loss obtained differs depending on the wavelength.

Therefore, an object of the present invention is to provide a wavelength multiplexing optical signal amplification transmission method that can effectively utilize the amplification band of the optical amplifier by equalizing the allowable transmission line loss at each wavelength even when performing wavelength division multiplexing transmission using optical amplifiers with different gains depending on the wavelength. Our goal is to provide the following.

(Means for Solving the Problems) In a first aspect of the wavelength-multiplexed optical signal amplification and transmission method according to the present invention, a wavelength-multiplexed signal is transmitted after booster amplifying or repeating amplification of a plurality of wavelength-multiplexed signal lights using an optical amplifier. In the transmission method, the allowable transmission line loss assigned to each signal light is equalized by setting the signal band of each signal light in proportion to the gain of each wavelength band based on the gain band characteristics of the optical amplifier. is being transmitted.

In addition, in the second R, in a wavelength multiplexed signal transmission method in which multiple wavelength-multiplexed signal lights are booster-amplified or relay-amplified and transmitted using an optical amplifier, the gain of each wavelength band is determined based on the gain band characteristics of the optical amplifier. By allocating the loss for wavelength multiplexing and demultiplexing in proportion to , the allowable transmission line loss allocated to each signal light is made equal and transmitted.

Furthermore, in a third aspect, in a wavelength multiplexed signal transmission method in which a plurality of wavelength-multiplexed signal lights are booster-amplified or relay-amplified and transmitted using an optical amplifier, a signal in a wavelength band with a large gain is determined based on the gain band characteristics of the optical amplifier. Light is transmitted using a direct detection system, and signal light in a wavelength band with small gain is transmitted using a coherent communication system, thereby making the allowable transmission path loss assigned to each wavelength-multiplexed signal equal to each other.

<Function> When the signal speed increases by 10 times, the reception sensitivity realized in a normal optical communication system deteriorates by about 10 to 12 times.

Therefore, for example, if the gain of the optical amplifier differs by 10 dB between two wavelengths in a wavelength division multiplexing optical signal transmission system using an optical amplifier, the signal speed of the wavelength with lower gain should be set to about 1710 of that of the wavelength with higher gain. In this system, the allowable transmission path losses achieved at both wavelengths can be made approximately equal.

In addition, even when transmitting signals with the same transmission speed between both wavelengths, if the multiplexing and demultiplexing loss when performing multiplexing and demultiplexing of signal light is made different between both wavelengths, the allowable transmission path loss for both wavelengths can be made equal. Is possible. For example, if an optical fiber coupler with a branching ratio of 10:l is used as a multiplexer on the transmitting side, even if the optical amplifier gains differ by 10 dB between the two wavelengths, approximately the same allowable transmission line loss can be achieved for both wavelengths.

Furthermore, consider the use of coherent optical communication. It is known that coherent optical communication improves optical reception sensitivity by more than 10 dB compared to a normal direct detection system. Therefore, for example, if the gains of optical amplifiers differ by 10 dB, by using the wavelength band with large gain in the direct detection system and the wavelength band with small gain in the coherent system, the allowable transmission line loss will be equal in CX in both wavelength bands. becomes possible.

(Embodiment) FIG. 1 is a block diagram for explaining a first embodiment of the present invention.

In this embodiment, wavelength multiplex transmission is performed using a first light source 1 with a wavelength of 1.536 μm and a second light source 2 with a wavelength of 1.552 μm.

Distributed feedback semiconductor lasers are used for the first and second light sources 1.2, and the first light source 1 is
G b /s, and the second light sources 2 are each modulated by the second signal sources 4 at 100 M b /s.

The outputs from the first and second light sources 1.2 are combined by an optical multiplexer 5 and then amplified by a long first optical fiber amplifier 7. This Er-doped fiber amplifier 7 has a wavelength of 1.4
It is excited by a third light source 8 with a wavelength of 9 μm and a wavelength of 1.
30dB at 536μm, 20dB at 1.552μm
gains have been obtained.

After the signal light amplified by the E'r-doped fiber amplifier 7 propagates through the long second optical fiber 9, it is separated by the wavelength separation filter 10 into a wavelength of 1.536 μm and a wavelength of 1.552 μm.
After being separated, the first and second optical receivers 11.
It is received at 12. Each received signal is demodulated by first and second demodulation circuits 13 and 14, and the signal is reproduced.

Here, the optical reception sensitivity for a signal light of IGb/s with a wavelength of 1.536 μm is -38 dBm and a wavelength of 1.552 μm.
, the optical reception sensitivity of 100 Mb/s signal light is -48 dBM.
Met.

In this embodiment, the wavelength after being combined by the optical multiplexer 5 is 1.53.
The intensities of the 6 μm and 1.552 μm signal lights are both OdBm, and after propagating through the 1100k first optical fiber 6, the input level of the Er-doped fiber amplifier 7 is -25 dBm. Here, the two signal lights each receive a gain (30 dB, 20 dB) according to their wavelength, and then propagate again through the 150 km second optical fiber 9 and are received by the first and second optical receivers 11 and 12, respectively. be done.

The loss margin from the output of the Er-doped fiber amplifier 7 to the first and second optical receivers 11.12 is 1.536 wavelength.
μm and 1.552 μm were both 43 dB, and even considering the loss of 37 dB of the second optical fiber 9 and the loss of 1 dB of the wavelength separation filter 10, it was possible to receive the signal with a margin of 5 dB for both wavelengths.

In this embodiment, the case where two wavelengths are transmitted in the same direction has been described, but the same thing can be applied to bidirectional transmission. In bidirectional transmission, a large capacity is required for the downlink, while a relatively low capacity is often sufficient for the uplink. Therefore, the wavelength of 1.536 μm is used for the downlink, and the wavelength of 1.552 μm is used for the uplink.
By applying , it becomes possible to effectively utilize the amplification band of the Er-doped fiber amplifier 7.

In addition, by introducing a coherent optical communication system in the 1.552 μm band in this embodiment, both wavelengths can be used as IGb/S.
It is also possible to transmit the following signals. For example, an IGb/s CPFSK optical heterogain detection system can achieve an optical receiving sensitivity of -46 dBm.

If this system is introduced in the 1.552 μm wavelength band, it will be possible to transmit IG b/s over the same distance as in the 1.536 μm band in this wavelength band.

FIG. 3 is a block diagram for explaining a second embodiment of the present invention.

In this embodiment as well, the Er-doped fiber amplifier 7 is used as the optical amplifier. In this embodiment, the wavelength is 1.536.
400 Mb/s first signal light group 20 in μm band
The first optical multiplexing element 22 multiplexes the 16 waves of
The eight waves of the second signal light group 21 of Mb/s are multiplexed at 10 GHz intervals by the second optical multiplexing element 23, and these are further multiplexed by the optical multiplexer 5.

Here, the input level of the Er-doped fiber amplifier 7 is -15 dB at 1.536 μm due to the difference in loss during optical multiplexing.
m, it was -11 dBm at 1552 μm. In the Er-doped fiber amplifier 7, the average within the band is 30 dB in the wavelength band of 1.536 μm, and the average within the band is 22 dB in the wavelength band of 1.552 μm.
A gain of dB was obtained. - After the amplified signal light group propagates through the optical fiber 9, it passes through the wavelength separation filter 10 at wavelength 1.
It is separated into a 536 μm band and a 1.552 μm band. Signal light groups in each wavelength band are transmitted through first and second optical frequency separation elements 24 each formed by a Matsuhatsu Ender interferometer.
．． 25, the signal is separated into signals of each wavelength. It is received by the second optical receiver group 26 and 27.

In this example, the wavelength 1°536 μm band is 1.552 μm.
Compared to the m band, an 8 dB larger gain is obtained in the Er-doped fiber amplifier 7, but due to the large number of wavelengths multiplexed, the optical multiplexing element 22 and the optical frequency separation element 24 suffer an 8 dB larger loss compared to the 1.552 μm band. . Therefore, the overall margin of the system is equal in both wavelength bands. Therefore, this embodiment enables wavelength division multiplexing transmission by effectively utilizing the band of the Br-doped fiber amplifier 7.

In addition to the above-described embodiments, various modifications of the present invention can be considered. For example, in the embodiment, the Er-doped fiber amplifier 7
Although the case where the optical amplifier is used has been described, the optical amplifier can also be used in other optical amplifiers whose gain is wavelength dependent, such as a Raman amplifier.

Further, even in the case of a semiconductor amplifier, when wavelength multiplexing is performed using a gain peak wavelength and a wavelength that is significantly different from that wavelength, a gain difference occurs between the two wavelengths, so the present invention can be applied.

Further, the three methods of the present invention may be combined, that is, the signal speed between each channel and the multiplexing/demultiplexing loss reception method may be combined to equalize the allowable transmission line loss for each wavelength multiplexed signal in the system.

(Effects of the Invention) As described in detail above, by using the present invention, even when using an optical amplifier whose gain is wavelength dependent, it is possible to configure a wavelength division multiplexing transmission system by effectively using the entire gain band. can.

[Brief explanation of drawings]

Fig. 1 is a block diagram for explaining the first embodiment of the present invention. Fig. 2 is a diagram showing the gain characteristics of an Er-doped fiber amplifier. Fig. 3 is a block diagram for explaining the second embodiment of the present invention. FIG. 1.2... Light source, 5... Optical multiplexer, 6, 9... Optical fiber, 7... Er-doped fiber amplifier, 1o.
... Wavelength separation filter, 11.12 ... Optical receiver, 2
0°21... Signal light group, 22.23... Optical multiplexing element, 24°25... Optical frequency separation element, 26.27...
・Optical receiver group.

Claims (3)

[Claims] (1) In a wavelength multiplexed signal transmission method in which a plurality of wavelength-multiplexed signal lights are booster-amplified or relay-amplified and transmitted using an optical amplifier, the gain of each wavelength band is approximately proportional to the gain based on the gain band characteristics of the optical amplifier. A wavelength multiplexing optical signal transmission method, characterized in that by setting and transmitting a signal band of each of the signal lights, transmission is performed with equal allowable transmission line loss assigned to each of the signal lights. (2) In a wavelength multiplexed signal transmission method in which a plurality of wavelength-multiplexed signal lights are booster-amplified or relay-amplified and transmitted using an optical amplifier, the gain of each wavelength band is approximately proportional to the gain based on the gain band characteristics of the optical amplifier. 1. A wavelength multiplexing optical signal transmission method, characterized in that by allocating losses for wavelength multiplexing and demultiplexing to each signal light, transmission is performed with equal allowable transmission line losses assigned to each of the signal lights. (3) In a wavelength multiplexed signal transmission method in which a plurality of wavelength-multiplexed signal lights are booster-amplified or relay-amplified and transmitted using an optical amplifier, the signal light in a wavelength band with a large gain is determined based on the gain band characteristics of the optical amplifier. A wavelength characterized in that by transmitting signal light in a direct detection system and transmitting signal light in a wavelength band with small gain through a coherent communication system, transmission with equal allowable transmission path loss assigned to each wavelength-multiplexed signal light is performed. Multiplex optical signal transmission method.