JP2755999B2 - Optical pulse compression amplification method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to an optical fiber communication system for transmitting a signal by propagating a signal light pulse in an optical fiber, and particularly to a signal generated by the dispersion characteristics of the optical fiber. The present invention relates to an optical pulse compression / amplification method for compensating for a spread of an optical pulse width and a decrease in the intensity of a signal optical pulse caused by the loss characteristics of an optical fiber.

(Prior Art) In an optical fiber communication system, the signal light pulse has a wider pulse width and a lower intensity during propagation through the optical fiber due to the dispersion characteristics and loss characteristics of the optical fiber. For this reason, in the conventional optical fiber communication system,
After converting the signal light pulse propagated through the optical fiber by a predetermined length into an electric signal, the waveform of the electric signal is compressed and amplified to return to the original signal waveform, and this signal is again converted to a signal light pulse. Was sent to the optical fiber.

However, this method has a drawback that an optical / electric or electric / optical conversion circuit is required, and the apparatus for compressing and amplifying the signal light pulse becomes complicated.

Therefore, two methods have been conventionally studied to solve this drawback. One is a method of directly compressing and amplifying a signal light pulse without converting it into an electric signal using an optical circuit such as an optical pulse compressor or an optical amplifier.

Another method is to use an optical fiber amplifier.
In recent years, it has become clear that an optical fiber itself has an optical signal amplification function by adding various elements to an optical fiber core. Such an optical fiber amplifier has a structure that is substantially similar to an optical fiber that propagates a signal, and thus has a feature that both can be connected with low loss.

As an example, FIG. 2 shows a configuration of an optical fiber signal system adopting a method of amplifying a signal light pulse using an optical fiber amplifier configured by adding erbium to an optical fiber core (references: Kimura, Nakazawa). "Oscillation characteristics of optical fiber lasers and their application to optical communications," RSM-87-16, pp.31-37, January 1988, report by the Laser Society of Japan.

In FIG. 2, reference numerals 1a and 1b denote optical fibers for transmitting signal light pulses, 2 denotes an erbium-doped optical fiber formed by adding erbium into an optical fiber core, 3 denotes an optical coupler, and 4 denotes signal light pulse generation. Reference numeral 5 denotes a light source for generating excitation light, and reference numeral 6 denotes an optical fiber wiring cord. The optical coupler 3 is
It is composed of an optical fiber coupler or the like, and one example is shown in FIGS. 3 (a) and (b). 3, one end of an optical fiber 1a is connected to a terminal 3A of the optical coupler 3, one end of an erbium-doped optical fiber 2 is connected to a terminal 3B, and one end of an optical fiber wiring cord 6 is connected to a terminal 3C. You.

In such a configuration, the signal light pulse generating light source 4
The signal light pulse generated at the other end of the optical fiber 1a is incident on the other end of the optical fiber 1a.
The light enters the erbium-doped optical fiber 2 from the terminal 3A via the terminal 3B. On the other hand, the excitation light generated by the excitation light generating light source 5 and incident on the other end of the optical fiber wiring cord 6 propagates through the optical fiber wiring cord 6 and then passes from the terminal 3C to the terminal 3B of the optical coupler 3 via the terminal 3B. The light enters the erbium-doped optical fiber 2.

The signal light pulse incident on the erbium-doped optical fiber 2 through the above-described path is propagated through the optical fiber 1a.
Due to the dispersion characteristics and loss characteristics of the optical fiber 1a, the pulse width is widened and the intensity is reduced. However, the excitation light is amplified by exciting the erbium while propagating through the erbium-doped optical fiber 2, and the intensity is reduced. The intensity at the time of incidence on the fiber 1a is recovered.

The amplification mechanism of the signal light pulse by the excitation light in the erbium-doped optical fiber is described in the above-mentioned literature and the literature “Paul Urquhart“ Review of rare earth doped f.
ibre lasers and amplifiers "IEE Proc.Vol.135, Pt.J, N
o.6, pp.385-407 (1988)].

In the case of an erbium-doped optical fiber, when the wavelength of the pump light is set to 0.514 μm, the signal light pulse in the wavelength band of 1.553 to 1.603 μm is obtained. It can be amplified efficiently (Literature: Kimura, Nakazawa “Lasing characteristics of Er ³⁺
-Doped silica fiber from 1553 up to 1603nm "J.App
l.Phys., Vol. 64, No. 2, pp. 516-518 (1988) and Nakazawa,
Kimura, Suzuki “Efficient Er ³⁺ -doped optical fiber am
plifier pumped by a 1.48μm InGaAsP laser diode "Ap
pl. Phys. Lett., Vol. 54, No. 4, pp. 295-297, (1989)).

Moreover, such an erbium-doped optical fiber can amplify an optical signal in the lowest loss wavelength band (1.5 μm band) currently used in the optical fiber communication system by 20 dB or more, so that it is an extremely effective method for amplifying a communication signal light pulse. It is.

(Problems to be Solved by the Invention) However, the former method requires a small-sized optical circuit having stable characteristics, but is difficult to realize. In addition, when such an optical circuit is used, there is a problem that a connection loss between the optical fiber for transmitting the signal light pulse and the optical circuit increases.

Further, in the latter method, although the signal light pulse can be amplified, the pulse width that has been widened due to the dispersion characteristics of the optical fiber 1a cannot be restored to the original.
Therefore, in this method, in order to recover the width of the signal light pulse, an electric circuit, that is, an optical / electrical, electric / optical conversion circuit has to be used. There was a disadvantage that the size was increased.

The present invention has been made in view of such circumstances,
The purpose is to provide a compact and simple signal repeater that can perform signal compression and waveform amplification of signal light pulses sequentially or simultaneously as they are, without converting the signal light pulses into electrical signals. An object of the present invention is to provide an optical pulse compression amplification method that can be realized.

(Means for Solving the Problems) In order to achieve the above object, in claim (1), a compression optical fiber having a normal dispersion characteristic has a wavelength longer than that of a signal light pulse, and a strength and a group velocity. By compressing the pulse width of the signal light pulse by injecting a large excitation light pulse later than the signal light pulse, and then compressing the signal light pulse, at a different wavelength and intensity from the excitation light pulse, and The signal light pulse is amplified by simultaneously inputting a pumping light pulse having a wavelength and intensity necessary for pumping the rare-earth element-doped optical fiber into the rare-earth-doped optical fiber.

Further, in claim (2), a rare-earth element-doped optical fiber having a normal dispersion characteristic is provided with a longer wavelength than the signal light pulse.
In addition, a pumping light pulse having a large intensity and a group velocity is incident with a delay later than the signal light pulse, and another pumping light pulse having a wavelength and intensity required for pumping the rare earth element-doped optical fiber is simultaneously transmitted with the signal light pulse. By being incident, the compression and amplification of the pulse width of the signal light pulse are performed.

(Operation) According to claim (1), the signal light pulse whose pulse width is widened and the intensity is reduced while propagating through the optical fiber as the transmission path is incident on the compression optical fiber. Then, after that, a pumping excitation pulse having a longer wavelength than the signal light pulse, a higher intensity, and a larger group velocity is incident. This causes a negative chirp (frequency decreases with time) at the falling portion of the signal light pulse due to the nonlinear optical effect caused by the pumping light pulse in the compression optical fiber, and the signal light pulse due to the normal dispersion effect. Since the falling portion advances earlier, the pulse width is compressed.

Next, a signal light pulse having a compressed pulse width and an excitation light pulse having a different wavelength and intensity from the compression excitation light pulse are incident on the rare earth element-doped optical fiber. As a result, erbium is excited by the excitation light pulse in the rare earth element-doped optical fiber, and the signal light pulse is amplified by the excitation amplification effect caused by the erbium.

According to claim (2), the nonlinear optical effect and the pump amplification effect by the pump light pulse are simultaneously exhibited in the rare-earth element-doped optical fiber, and the pulse width of the signal light pulse is compressed and amplified. .

(Embodiment) FIG. 1 is a block diagram showing a first embodiment of an optical fiber communication system employing an optical pulse compression / amplification method according to the present invention. The same components as those in FIG. It is represented by the same reference numeral.

That is, 1a and 1b are optical fibers for a transmission path for transmitting a signal light pulse, 2 is an erbium-doped optical fiber for amplifying a signal light pulse which is formed by adding erbium which is a rare earth element in an optical fiber core, and 3a and 3b. Is an optical coupler, and 3A, 3B and 3C are terminals of the optical couplers 3a and 3b.

Reference numeral 4 denotes a signal light pulse generation light source, for example, a wavelength of 1.535 μm.
It is composed of a laser that emits a light pulse of m and intensity 1 μW.

Reference numeral 5a denotes a pumping light pulse generation light source having a longer wavelength than the signal light pulse, for example, 1.842 μm, and a cross phase modulation (cross phase modulation) in the signal light pulse compression optical fiber 7 described later.
It is composed of a laser that generates an excitation light pulse for compression of sufficient intensity, for example, 10 mW, to exhibit a nonlinear optical effect called a so-called nonlinear optical effect.

5b is a light source for excitation light pulse generation, a wavelength and intensity different from the compression excitation light pulse, for example, a wavelength 1.48μm,
In addition, it is constituted by a laser that excites erbium in the erbium-doped optical fiber 2 and generates an excitation light pulse for amplification of sufficient intensity, for example, 30 mW, to enable amplification of the signal light pulse. 6a and 6b are optical fiber wiring cords.

Reference numeral 7 denotes an optical fiber for compressing a signal light pulse (hereinafter, referred to as an optical fiber for compression), which has a normal dispersion characteristic and an optical coupler 3a.
Optical coupler 3b to the terminal 3B of the erbium-doped optical fiber 2
One end is connected to the terminal 3B of the optical coupler 3a, and the other end is connected to the terminal 3A of the optical coupler 3b.

FIG. 4 is a graph showing the group velocity dispersion characteristics of the optical fiber for compression 7, with the horizontal axis representing wavelength and the vertical axis representing group velocity dispersion. In FIG. 4, λ ₀ is the group velocity dispersion (υ
g / λ) becomes zero, that is, a zero-dispersion wavelength (for example, 1.
9 μm). In addition, λ ₁ indicates the wavelength of the pumping light pulse for compression, λ ₂ indicates the wavelength of the signal light pulse, and λ ₃ indicates the wavelength of the pumping light pulse for amplification. In FIG. 4, the group velocity dispersion is positive (+) at a wavelength shorter than the zero dispersion wavelength λ ₀ ,
At a wavelength longer than the zero dispersion wavelength λ ₀ , the group velocity dispersion is negative (−).
It has become.

As can be seen from FIG. 4, in the region where the group velocity dispersion is positive, light having a lower frequency, that is, light having a longer wavelength, has a higher propagation speed in the optical fiber than light having a higher frequency (hereinafter, this region). Is referred to as a normal dispersion area). On the other hand, in the region where the group velocity dispersion is negative, light having a higher frequency has a higher propagation speed in the optical fiber than light having a lower frequency (this region is called an anomalous dispersion region).

Next, the operation of the above configuration will be described step by step with reference to FIG. 4 and FIGS. 5 to 7.

The signal light pulse of wavelength λ ₂ (= 1.535 μm) incident on the optical fiber 1a from the signal light generating light source 4 is transmitted to the optical fiber 1a.
During propagation through a, the optical pulse width (waveform) expands due to the dispersion characteristics of the optical fiber 1a, and the intensity decreases due to the loss characteristics.
As described above, the signal light pulse whose waveform and intensity are deteriorated is incident on the optical fiber for compression 7 from the terminal 3A to the terminal 3B of the optical coupler 3a.

On the other hand, the wavelength λ
A compression excitation pulse of ₁ (= 1.842 μm) is generated. The excitation light pulse for compression is
6a, the light enters the compression optical fiber 7 via the terminals 3C and 3B of the optical coupler 3a. At this time, the compression pumping light pulse having a longer wavelength than the signal light pulse, a higher intensity, and a larger group velocity is incident on the compression optical fiber 7 later than the signal light pulse for the reason described later. Is done.

When the weak signal light pulse and the high-intensity compression pumping light pulse are incident on the compression optical fiber 7 in this manner, the high-intensity compressional pumping light pulse is converted into a nonlinear phase called cross-phase modulation. The optical phenomenon effect is exhibited.

Here, the frequency chirp (frequency shift of light) given by the compression excitation light pulse to the signal light pulse by the cross-phase modulation will be described in detail.

When the optical pulse has a so-called Gaussian distribution shape, the frequency chirp Δν by cross-phase modulation is given by the following equation (1) (Reference: GPAgrawal, PLBaldeck)
and RRAlfano, “Optical wave breaking and pulse
compression due to cross-phase modulation in optic
al fibers "Optical Letters, Vol. 14, No. 2, pp. 137-139
(1989)).

_{Δν = Δν max {exp [-} (τ + τ d -z / L w) 2] -exp [-
(Τ + τ _d ) ² ]｝ (1) where, τ = (t−z / υ _g1 ) / T ₀ τ _d : a signal light pulse at the time when the compression excitation light pulse is incident on the compression optical fiber 7. , The time difference between the signal and the excitation light pulse for compression, z: the length of the signal light pulse propagating through the optical fiber for compression 7, L _w = υ _g1 υ _g2 T ₀ / | υ _g1 -υ _g2 │, υ _g1 : excitation Group velocity of light pulse, υ _g2 : Group velocity of signal light pulse, T ₀ : Pulse width, Δν _max = γ ₂ P ₁ L _w / (τT ₀ ), P ₁ : Peak velocity of excitation light pulse for compression, γ ₂ = 2πn ₂ / (λ ₂ A _eff ): a parameter representing the efficiency at which the nonlinear effect occurs, n ₂ : the nonlinear refractive index, λ ₂ : the wavelength of the signal light pulse, A _eff : the effective core diameter of the compression optical fiber 7. And are respectively shown.

FIGS. 5 to 7 show how the frequency chirp Δν determined from the above equation (1) changes as the signal light pulse and the compression excitation light pulse propagate through the compression optical fiber 7. Is shown in each figure, "τ _d = 3,
“0, (−) 3” is the time when the compression excitation light pulse passes through each point (z / L _w = 2,4,6) in the compression optical fiber 7. That is, based on the position of the compression excitation light pulse at the time when the compression excitation light pulse passes through each point (z / L _w = 2, 4, 6) in the compression optical fiber 7, the signal at that time is determined. The position of an optical pulse and the state of frequency chirp are shown. In each of the figures, a solid curve indicates the frequency chirp, and a broken curve indicates the position of the signal light pulse.

Specifically, FIG. 5 shows “τ _d = 3”, that is, the chirp when the compression pumping light pulse having a large group velocity is incident on the compression optical fiber 7 before the signal light pulse. 6
The figure shows “τ _d = 0”, that is, the chirp when a compression pumping light pulse having a large group velocity is incident on the compression optical fiber 7 simultaneously with the signal light pulse, and FIG. 7 shows “τ _d = (− )
3], that is, chirp when the compression pumping light pulse having a large group velocity is incident on the compression optical fiber 7 later than the signal light pulse.

More specifically, each (a) in FIG. 5 to FIG.
FIGS. 5 to 7 show frequency chirp at L _w = 2, and FIGS. 5 to 7 show frequency chirp at z / L _w = 4, and FIGS. 5 to 7 each show (c). Is a diagram showing the frequency chirp at z / L _w = 6, (d) and (e) in FIG.
FIG. 3 is a diagram showing frequency chirp at z / L _w = 10,20.

As can be seen from FIG. 5, when the compression pumping light pulse having a large group velocity is incident on the compression optical fiber 7 before the signal light pulse (τ _d = 3), the position of the signal light pulse is Then, the frequency chirp is very small. Therefore, in this case, the shape of the signal light pulse hardly changes.

Also, as can be seen from FIG. 6, when a compression pumping light pulse having a large group velocity is incident on the compression optical fiber 7 simultaneously with the signal light pulse (τ _d = 0), z / L _w > At 6, the signal light pulse always receives a positive frequency chirp.
Similarly, when 0 <z / _Lw <6, the signal light pulse mainly receives a positive frequency chirp. Therefore, when the light propagates through the compression optical fiber 7 having the normal dispersion characteristic, the speed of the peak portion having a high frequency becomes slow, and the speed of the foot portion of the signal light pulse becomes fast, and the pulse spreads.

On the other hand, as can be seen from FIG. 7, when the compression pumping light pulse having a large group velocity is incident on the compression optical fiber 7 later than the signal light pulse (τ _d = (−) 3). In the range 0 <z / _Lw <10, the signal light pulse receives a negative frequency chirp, and when 10 <z / _Lw , the frequency chirp becomes almost zero. In particular, when z / L _w = 4, the frequency chirp is zero near the peak value of the signal light pulse, and the chirp decreases almost linearly at the falling part. Therefore, in the compression optical fiber 7 having the normal dispersion characteristic, the falling portion quickly propagates and catches up with the rising portion, so that the pulse is compressed.

As described above, in the compression optical fiber 7, a frequency chirp (frequency shift of light) is generated due to the cross-phase modulation. In particular, as shown in FIG. 7B, z / L _w = 4. In this case, the frequency of the falling portion of the signal light decreases with time.

However, since the wavelength λ ₂ of the signal light pulse is in the normal dispersion region described above, the group velocity of the propagating signal light pulse is different according to the difference in frequency. Specifically, at the falling portion of the signal light pulse (the rear portion of the light pulse) due to chirp, the frequency becomes lower as time passes. Further, in the normal dispersion region, since the speed becomes high in the low frequency part, the rear part (falling part) of the signal light pulse gradually catches up with the rising part while propagating through the optical fiber for compression 7,
As a result, the width of the signal light pulse is reduced.

The degree of compression of such a signal light pulse depends on the difference between the incident times of the signal light pulse and the compression excitation light pulse, and the maximum pulse width compression efficiency can be obtained by optimally selecting the difference in the incident times. The optimum incident time difference depends on the group velocity dispersion value of the compression optical fiber 7, the fiber core diameter, the wavelength and the intensity of the signal light pulse and the compression excitation light pulse (the above-mentioned documents: GPAgrawal, PLBaldeck and RRA).
lfano, “Optical wave breaking and pulse compressio
n due to cross-phase modulation in optical fibers "
Optical Letters, Vol. 14, No. 2, pp. 137-139 (1989)).

Incidentally, in the case of “τ _d = (−) 3” as shown in FIG. 7, this is equivalent to incidence with a delay of three times the pulse width. That is, when the width of the signal light pulse and the width of the compression excitation light pulse are 1 picosecond, the excitation light pulse is delayed by 3 picoseconds to be incident.

Similarly, in the example of FIG. 7, (τ _d = (−) 3), the wavelength λ ₂ and intensity P _{2 of the} signal light pulse and the wavelength λ ₁ and intensity P _{1 of the} compression pump light pulse are expressed by the following (2) ) Satisfies the relationship shown in the expression (3).

λ ₁ / λ ₂ = 1.2 (2) P ₂ / P ₁ = 10 ^-4 (3) Specifically, the values of the wavelength λ _{2 and the} intensity P ₂ of the signal light pulse are λ ₂ = 1.535 μm, When P ₂ = 1 μW, the values of the wavelength λ _{1 and the} intensity P ₁ of the compression excitation light pulse are λ ₁ = 1.
842 μm, P ₁ = 10 mW.

Similarly, when the values of the wavelength λ _{2 and the} intensity P ₂ of the signal light pulse are λ ₂ = 1.3 μm and P ₂ = 1 μW, the values of the wavelength λ _{1 and the} intensity P ₁ of the compression pumping light pulse are: λ ₁ = 1.56μ
m, P ₁ = 10 mW.

Also, as can be seen from FIG. 7, when z / L _w > 6, the frequency is low at the rising portion of the signal light pulse, and the frequency is high at the peak portion and the falling portion as compared with the rising portion. The pulse spreads. Therefore, “τ _d = (−)
3], the length of the compression optical fiber 7 is z / L _w <6.
It is necessary to

Then, weak signal light pulses compressed by the compression optical fiber 7 via the optical coupler 3b, at the same time erbium doped with amplification pumping light pulse having a wavelength lambda ₃ generated by the excitation light pulse generating light source 5b The light enters the optical fiber 2. Thus, the amplification excitation light pulse excites erbium to induce light, which amplifies the signal light pulse.

The wavelength, intensity, and the like of the amplification pumping light pulse for exciting the erbium-doped optical fiber 2 are, for example, about 1000 ppm in doping concentration, 6 μm in core diameter, 0.85% relative refractive index difference of core, and 1.28 μm in cutoff wavelength. Erbium-doped optical fiber (length 3m), wavelength 1.48μm, intensity
When pumped with 30 mW pump light, the signal light of 1.535 μm wavelength (several μW) is amplified by about 10 dB (Reference: Nakazawa, Kimura, Suzuki “Efficient Er ³⁺ -doped optical fiber amplifier”
pumped by a 1.48μm InGaAsP laserdiode "Appl.Phys.L
ett., Vol. 54, No. 4, pp. 295-297, (1988)).

Thus, the signal light pulse whose pulse width is compressed by the signal light pulse compression optical fiber 7 and amplified by the erbium-doped optical fiber 2 is guided to the optical fiber 1b which is the next transmission path.

As described above, according to the first embodiment, the excitation light pulse is applied to the light pulse whose intensity is reduced while the pulse width is widened while propagating through the optical fiber 1a which is the transmission line, and The signal light pulse can be compressed and amplified as it is by the optical fiber 7 for compressing the signal light pulse and the erbium-doped optical fiber 2 for amplifying the signal light pulse, which are similar in structure to the optical fiber. The device can be made compact and simple without the need for complicated electric circuits.

The length and structure of the signal light pulse compression optical fiber 7 need to be designed to be optimal depending on the width, wavelength, and intensity of the signal light pulse to be compressed. As an example, several centimeters to several hundreds of meters having a zero dispersion wavelength in the 1.56 to 1.6 μm band
Long low-loss dispersion-shifted optical fibers. In this case, as described above, the wavelength λ of the signal light pulse
₂ is 1.3 μm, and the wavelength λ ₁ of the excitation light pulse for compression is 1.56 μm.
A value such as m will be selected.

Further, as described in the literature, the erbium-doped optical fiber 2 has an addition amount of about 1000 ppm and a length of 3.5 ppm.
m, a core system of 6.9 μm, and a relative refractive index difference of 0.85% may be used. It is necessary to optimize these parameters depending on the amplification degree, the signal light pulse wavelength, and the like.

FIG. 8 is a block diagram showing a second embodiment of the optical fiber communication system employing the optical pulse compression amplification method according to the present invention.

The difference between the second embodiment and the first embodiment is that one end is connected to the terminal 3B of the optical coupler 3c between the erbium-doped optical fiber 2 for signal light pulse amplification and the optical fiber 1b for the transmission line. The optical fiber 7a for signal light pulse compression which is connected and the other end is connected to the terminal 3A of the optical coupler 3d is inserted, and the terminal 3A of the optical coupler 3c and one end of the optical fiber 1b are connected to the optical coupler 3d. The terminal 3B is connected to the other end of the erbium-doped optical fiber 2, and an optical fiber wiring cord is connected to the terminal 3C of the optical coupler 3c.
An excitation light pulse generation light source 5c having the same configuration as the excitation light pulse generation light source 5a is arranged via 6c, and the optical coupler 3d
On the side of the terminal 3C, an excitation light pulse generation light source 5d having the same configuration as the excitation light pulse generation light source 5b is arranged via an optical fiber wiring cord 6d, and has a symmetrical configuration around the erbium-doped optical fiber 2. I did it.

According to the second embodiment, in addition to the effects of the first embodiment, compression and amplification of signal pulses not only in one direction but also in both directions can be performed.

In the first and second embodiments, the optical fiber for compressing the signal light pulse and the optical fiber for amplifying the signal light pulse are separately configured. However, the present invention is not limited to this. In a fiber, for example, an erbium-doped optical fiber, by selecting parameters of the optical fiber such as a refractive index distribution so as to have a group velocity dispersion as shown in FIG. Compression and amplification can be realized simultaneously.

FIG. 9 is a block diagram showing a third embodiment of the optical fiber communication system employing the optical pulse compression amplification method according to the present invention using one rare earth element-doped optical fiber having both such compression and amplification functions. .

The difference between the third embodiment and the first embodiment is that, instead of the optical fiber 7 for compressing the signal light pulse and the erbium-doped optical fiber 2 for amplifying the signal light pulse, a rare earth element having normal dispersion characteristics (for example, , Erbium) -doped optical fiber 8 and the terminal 3C of the optical coupler 3a are connected to the optical coupler 3e via the optical fiber wiring cord 6a, and the optical coupler 3e is connected to the optical fiber wiring cords 6e and 6f. The point is that the excitation light pulse generation light source 5a for generating the cross-phase modulation via the interface and the excitation light pulse generation light source 5b for exciting the rare earth element-doped optical fiber are connected.

In such a configuration, the excitation light pulse generating light source 5a for generating the cross-phase modulation has a longer wavelength than the signal light pulse, a higher intensity, and a larger group velocity. From the light source 5b for generating a pumping light pulse for pumping the rare-earth element-doped optical fiber, the wavelength required for pumping the rare-earth element-doped optical fiber 8 having normal dispersion characteristics. Amplifying excitation light pulse having intensity is incident simultaneously with the signal light pulse.

However, in this case, the wavelengths of both pumping light pulses are set separately to suppress the interaction between the pumping light pulse for generating cross-phase modulation and the pumping light pulse for amplification for performing amplification. There is a need to.

As a result, the same effect as described in the first embodiment is produced, and the signal light pulse is compressed and amplified in the rare-earth element-doped optical fiber 8 having normal dispersion characteristics.

As described above, according to the third embodiment, the signal light pulse compression optical fiber 7 and the erbium-doped optical fiber 2 in the first embodiment can be integrated, so that a signal relay device in optical communication can be further provided. Downsizing and simplification can be achieved.

(Effects of the Invention) As described above, according to claim (1), for example, a signal light pulse whose pulse width is widened and its intensity is reduced while propagating through a transmission line, and an optical fiber for signal light pulse propagation. Compression and amplification can be performed with light as it is by an optical fiber having a similar structure. Therefore, light / electricity, electricity /
Since a complicated electric circuit such as an optical conversion circuit is not required, the signal light pulse can be relayed by a small and simple device. Further, through simplification of the signal relay device in the optical communication, economical and high reliability of the optical communication system can be achieved.

According to claim (2), in addition to the effect of claim (1), further downsizing of the signal relay device in optical communication,
There is an advantage that simplification can be achieved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of an optical fiber communication system employing an optical pulse compression / amplification method according to the present invention;
FIG. 2 is a diagram showing a configuration of an optical fiber communication system employing a conventional method, FIG. 3 is a diagram showing a configuration example of an optical coupler, and FIG. FIGS. 5 to 7 are graphs showing characteristics, and FIGS. 5 to 7 are diagrams for explaining chirp according to the present invention. FIG. 5 shows that a pumping light pulse for compression is input to a compression optical fiber prior to a signal light pulse. FIG. 6 is a diagram showing a chirp when the compression pumping light pulse is simultaneously input to the compression optical fiber at the same time as the signal light pulse, and FIG. 7 is a diagram showing a chirp when the compression pumping light pulse is the signal light. FIG. 8 is a diagram showing a chirp in a case where light enters a compression optical fiber with a delay from a pulse, FIG. 8 is a configuration diagram showing a second embodiment of an optical fiber communication system employing an optical pulse compression amplification method according to the present invention, FIG. 9 shows the light pulse pressure according to the present invention. A third embodiment of an optical fiber communication system employing amplification method is a diagram showing a. In the figure, 1a, 1b ... optical fiber for transmission line, 2 ... erbium-doped optical fiber for signal light pulse amplification, 3, 3a, 3b, 3c, 3d,
3e …… Optical coupler, 4 …… Light source for signal light pulse generation, 5,5
a, 5b, 5c, 5d: Light source for generating excitation light pulse, 6, 6a, 6b, 6c, 6
d, 6e, 6f: optical fiber wiring cord, 7: optical fiber for signal light pulse compression, 8: rare earth element-doped optical fiber having normal dispersion characteristics.

Claims (2)

(57) [Claims] 1. A pumping optical pulse having a longer wavelength than a signal light pulse, and having a higher intensity and a higher group velocity, is incident on a compression optical fiber having a normal dispersion characteristic with a delay after the signal light pulse. The pulse width of the optical pulse is compressed, and then the compressed signal light pulse and the pump light having a wavelength and intensity different from those of the pump light pulse and having a wavelength and intensity necessary for exciting the rare earth element-doped optical fiber. An optical pulse compression / amplification method, comprising: amplifying a signal light pulse by simultaneously inputting a pulse to the rare earth element-doped optical fiber. 2. A pumping light pulse having a longer wavelength than a signal light pulse, and having a greater intensity and a higher group velocity, is incident on a rare earth element-doped optical fiber having a normal dispersion characteristic with a delay longer than that of the signal light pulse. Optical pulse compression characterized by compressing and amplifying the pulse width of a signal light pulse by simultaneously inputting another excitation light pulse having the wavelength and intensity required for pumping a rare earth element-doped optical fiber at the same time as the signal light pulse Amplification method.