JPH10256633A - Optical fiber amplifier with dispersion compensation function - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a compact low noise optical fiber amplifier with dispersion compensation function, by connecting a rare earth doped optical fiber with which a chirp fiber grating is connected, with the second port of a 3-port type circulator. SOLUTION: A WDM coupler 5, an erbium doped optical fiber 3 and a 1.55 μm band linear chirp fiber grating 8 are connected in series with the second port of a 3-port type circulator 1. Through the WDM coupler 5, the erbium doped optical fiber 3 is excited by a 1.48 μm band semiconductor laser 6. Thereby inputted optical pulses of 1.55 μm band are amplified and subjected to dispersion compensation. By connecting the long wavelength side of the chirp fiber grating 8 with the erbium doped optical fiber 3, the longer wavelength side light is the more rapidly reflected, so that the optical signal which has propagated in a 1.33 μm zero-dispersion fiber is subjected to dispersion compensation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber amplifier having a dispersion compensation function for amplifying an optical signal propagating in an optical fiber.

[0002] In the case of long-distance transmission in optical fiber transmission in which communication is performed using an optical fiber, it is necessary to relay the signal by an amplifier on the way. FIG. 1 shows a configuration example of an optical fiber amplifier. In FIG. 1, the WDM fiber coupler 5, the erbium-doped optical fiber 3, and the signal light reflecting mirror 4 are connected to the second port of the three-port optical circulator 1 from which the incident optical signal 2 enters and the output optical signal 7 exits. W
A 1.48 μm band semiconductor laser 6 is connected to the DM fiber coupler 5. This optical amplifier excites the erbium-doped optical fiber 3 with the excitation light from the semiconductor laser 6 and amplifies the incident optical signal 2.

When performing high-speed long-distance relay transmission, an optical pulse spreads due to chromatic dispersion, so that it is necessary to perform not only optical amplification but also dispersion compensation at a relay point. For example, 1.3μ
m When transmission is performed in the 1.55 μm band using a zero-dispersion fiber (SMF), dispersion compensation is performed using a dispersion compensating fiber or a dispersion compensating planar waveguide, and then the optical power is amplified using an erbium-doped optical fiber amplifier. Send out an optical signal.

However, if a dispersion compensating fiber is used when a 1.3 μm zero dispersion fiber (SMF) is used in the 1.55 μm band, for example, a dispersion compensating fiber having a length of about 10 km is required for a 50 km SMF. However, there is a problem that it is not necessarily compact. In addition, since a dispersion compensating fiber generally has a small core diameter, a nonlinear optical effect such as self-phase modulation easily occurs and a signal is easily deteriorated. On the other hand, although the dispersion-compensating planar waveguide is compact, there is a problem that the insertion loss is large and the signal-to-noise (S / N ratio) is easily deteriorated. Accordingly, it has been desired to realize a compact, low-noise optical fiber amplifier with a dispersion compensation function.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a low-noise and compact optical fiber amplifier with a dispersion compensation function in view of the above-mentioned problems in the prior art.

[0006]

In order to achieve the above object, an optical fiber amplifier with a dispersion compensating function according to the present invention uses a rare earth-doped optical fiber connected to a chirped fiber grating at a second port of a three-port optical circulator. It is configured to connect and excite the rare earth-doped optical fiber with the semiconductor laser for excitation.

In the optical fiber amplifier with dispersion compensation function of the present invention, a grating that reflects a rare-earth-doped optical fiber excitation light may be further connected. In this case, the pumping light for pumping the rare earth-doped optical fiber can be used efficiently.

In another optical fiber amplifier with dispersion compensation function of the present invention, a rare earth-doped optical fiber having a chirped fiber grating formed in a part thereof is connected to a second port of a three-port optical circulator, and a pumping semiconductor laser is provided. To excite the rare-earth-doped optical fiber.

Such an optical fiber amplifier with dispersion compensation function of the present invention further comprises a rare earth-doped optical fiber having a grating for reflecting the excitation light of the rare earth-doped optical fiber formed in a part of the second port of the three-port optical circulator. May be connected. In this case, the pumping light for pumping the rare earth-doped optical fiber can be used efficiently.

A chirped fiber grating is a fiber type grating in which the pitch (period of refractive index change) changes in the length direction of the fiber, and the wavelength of reflected light also changes in the length direction. FIG. 2 illustrates this. In FIG. 2, reference numeral 8 denotes a 1.55 μm band chirped fiber grating, 9 denotes long-wavelength light, and 10 denotes short-wavelength light. As shown in FIG. 2, in the grating 8 in which the pitch changes, when light is made incident from the longer pitch (the longer wavelength reflection side), the longer wavelength light 9 is immediately reflected after being incident on the grating. Since the short-wavelength light 10 is reflected after traveling considerably through the grating, the shorter-wavelength light is eventually reflected later. In addition, when light is incident from the shorter pitch, the opposite characteristic is obtained this time. Therefore, a pulse delay characteristic depending on the wavelength is obtained.

As described above, the chirped fiber grating can serve as a dispersion medium, and the sign of the dispersion changes depending on the incident direction. Therefore, if the dispersion of the grating is set in accordance with the state of chirp of the incoming light pulse, the light pulse can be compressed when reflected.

According to the present invention, such a chirped fiber grating is connected to a rare earth-doped optical fiber,
Further, an optical amplifier is configured by combining with a three-port optical circulator. In the optical fiber amplifier of the present invention, when an optical signal whose pulse width is widened and whose power is attenuated through chromatic dispersion by propagating through the optical fiber is incident on the optical circulator, the optical signal is first sent to the rare earth-doped optical fiber, The level of the optical signal is amplified. After that, the light is reflected by the chirped fiber grating, but if the chirped fiber grating is set to have a dispersion opposite to the dispersion of the optical fiber, the light pulse is compressed and enters the rare-earth-doped optical fiber again. . Then, after the light is amplified again, it passes through the optical circulator again and is emitted. In this way, an optical signal whose power is weakened and has a dispersion spread can be returned to the original state.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the drawings. FIG. 3 is a diagram showing a first embodiment of the optical fiber amplifier of the present invention. 3-port optical circulator 1
1.48μm / 1.55μm WDM coupler 5,
An erbium-doped optical fiber 3 and a 1.55 μm band linear chirped fiber grating 8 are connected in series. WDM
The erbium-doped optical fiber 3 is connected through the coupler 5 to 1.48.
By pumping with the μm band semiconductor laser 6, amplification and dispersion compensation are performed on the incoming 1.55 μm band light pulse.

Here, when the long wavelength side of the chirped fiber grating 8 is connected to the erbium-doped optical fiber 3, the light on the long wavelength side is reflected earlier, so that the optical signal in the 1.55 μm band propagated through the 1.3 μm zero dispersion fiber. Is dispersion compensated. 1.5 μm of 1.3 μm zero dispersion fiber (SMF)
The wavelength dispersion at 17 m (17 ps / nm / km) is D ₀ , and the length is L
Then, the total variance is D ₀ L (1).

[0015] On the other hand, the group velocity v _g in the grating,
Let n be the effective core refractive index of the grating (1.45) and c
Is the speed of light in a vacuum (3.0 × 10 ⁸ m), it is approximated as _vg = c / n (2). Therefore, the amount of dispersion that can be compensated for by the grating in the band Δλ (the difference between the reflection wavelength at the incident end and the reflection wavelength at the deepest point) with the length L _g is expressed by 2nL _g / cΔλ (3). Therefore, if the equations (1) and (3) are assumed to be equal, the relationship of L _g / Δλ = cD ₀ L / 2n (4) is obtained. Therefore the length L of 1.3μm zero dispersion fiber grating when 50km length L _g 100
When it is set to mm, the grating band Δλ needs to be 1.2 nm.

FIG. 4 is a diagram showing a second embodiment of the optical fiber amplifier according to the present invention. In this embodiment, in addition to the configuration of the first embodiment, a reflection grating 11 of 1.48 μm band is further connected in series after the chirped fiber grating 8. According to such a configuration, light in the 1.48 μm band that could not be absorbed by the erbium-doped optical fiber 3 can be returned to the erbium-doped optical fiber 3 again, and high efficiency can be achieved by reusing the pump power. Optical amplification can be performed.

FIG. 5 is a diagram showing a third embodiment of the optical fiber amplifier according to the present invention. In this embodiment, an optical fiber amplifier is configured without using a WDM coupler. That is, as shown in FIG. 5, a 1.48 μm band high power semiconductor laser 6 is arranged in series after the chirped fiber grating 8. Even in this case, the erbium-doped optical fiber 3
Can be excited.

FIG. 6 is a diagram showing a fourth embodiment of the optical fiber amplifier according to the present invention. In this embodiment, a 1.48 μm reflection grating 11 is arranged in series between the second port of the three-port optical circulator 1 and the erbium-doped optical fiber 3. In this way, the pump power can be reused as in the second embodiment.

In the above embodiment, the rare-earth doped optical fiber 3 and the 1.55 μm band linear chirped fiber grating 8 and the 1.48 μm band reflection grating 11 are connected in series to provide the optical fiber amplifier of the present invention. Although the configuration is described, instead of this, a rare earth-doped optical fiber having a chirped fiber grating formed on a part thereof, or a chirped fiber grating and a grating reflecting a rare earth-doped optical fiber excitation light are formed on a part thereof. The rare earth-doped optical fiber
The optical fiber amplifier with the dispersion compensation function of the present invention can also be obtained by connecting to the second port of the port type optical circulator and exciting the rare-earth-doped optical fiber with the semiconductor laser for excitation.

In the above embodiment, an example in which light in the 1.48 μm band is used as the excitation light has been described.
Of course, the present invention can be similarly applied to the m-band light by changing the WDM coupler and the excitation light reflection grating.

[0021]

As described above, according to the present invention,
An optical fiber amplifier having a low noise and a compact dispersion compensation function can be obtained. In addition, since a nonlinear optical effect is unlikely to occur, a better signal waveform can be reproduced than a conventional method using a dispersion compensating fiber.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration example of a conventional optical fiber amplifier.

FIG. 2 is a diagram illustrating the operation principle of a chirped fiber grating.

FIG. 3 is a diagram showing a first embodiment of the optical fiber amplifier of the present invention.

FIG. 4 is a diagram showing a second embodiment of the optical fiber amplifier according to the present invention.

FIG. 5 is a diagram showing a third embodiment of the optical fiber amplifier of the present invention.

FIG. 6 is a diagram showing a fourth embodiment of the optical fiber amplifier according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 3-port optical circulator 2 Incident optical signal 3 Erbium-doped optical fiber 4 Signal light reflecting mirror 5 WDM fiber coupler 6 1.48 μm band semiconductor laser 7 Outgoing optical signal 8 1.55 μm band chirped fiber grating 9 Long wavelength light 10 Short wavelength Light 11 1.48μm reflection grating

Claims (4)

[Claims] A rare earth-doped optical fiber to which a chirped fiber grating is connected is connected to a second port of a three-port optical circulator, and the rare-earth-doped optical fiber is pumped by a pumping semiconductor laser to achieve dispersion compensation and high efficiency. An optical fiber amplifier with a dispersion compensation function, which simultaneously realizes optical amplification. 2. A rare earth-doped optical fiber to which a chirped fiber grating and a rare earth-doped optical fiber-grating reflecting optical fiber are connected is connected to a second port of a three-port optical circulator. An optical fiber amplifier with a dispersion compensation function, which realizes both dispersion compensation and highly efficient optical amplification by exciting. 3. Dispersion compensation by connecting a rare earth-doped optical fiber having a chirped fiber grating formed in a part thereof to a second port of a three-port optical circulator and exciting the rare earth-doped optical fiber with a semiconductor laser for excitation. An optical fiber amplifier with a dispersion compensation function, which simultaneously realizes optical amplification with high efficiency. 4. A rare earth-doped optical fiber in which a chirped fiber grating and a grating for reflecting a rare earth-doped optical fiber pumping light are formed in a part thereof are connected to a second port of a three-port optical circulator, and a rare-earth semiconductor laser is used for excitation. By exciting the doped optical fiber,
An optical fiber amplifier with a dispersion compensation function, which realizes both dispersion compensation and highly efficient optical amplification at the same time.