JPH07221402A - Signal light source module, light receiving module, and optical signal transmission system - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a signal light source module with a power amplifier function that is small in size, high in output and low in distortion characteristics. [Structure] The semiconductor laser 3 includes a signal light 10 in the 1.55 μm band.
1 is output. The signal light 101 is coupled to the active layer 201 of the semiconductor laser 2 which outputs the 0.98 μm band pumping light 102. Further, the signal light passes through the active layer 201 and enters the erbium-doped optical fiber 1 through the coupling optical lens 5. On the other hand, 0.98 μm from the semiconductor laser 2
The band excitation light 102 is condensed by the optical lens 5 and enters the erbium-doped optical fiber 1. This excitation light 102
As a result, the erbium-doped optical fiber 1 is excited and amplifies the 1.55 μm band signal light 101 that is incident at the same time. Four
Is an optical isolator, which is used to prevent oscillation due to the high gain of the erbium-doped optical fiber and to prevent the pumping light from leaking into the signal light transmission line.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal light source module having a power amplifier, a light receiving module having a preamplifier, and an optical transmission system.

[0002]

2. Description of the Related Art An optical communication system comprises a semiconductor laser capable of direct modulation as a light source, an optical fiber as an optical transmission line,
It consists of a light receiver. Since this optical fiber has transmission loss even in the 1.55 μm band, which is the lowest loss wavelength band, an amplifier is required for long-distance transmission. Erbium-doped optical fiber amplifier that can directly amplify 1.55μm band signal light is
Research has been actively conducted since the latter half of the 1980s, and is now at the stage of practical application.

Applications of the optical fiber amplifier can be classified into a power amplifier used immediately after the transmitter, an in-line amplifier inserted in the middle of the transmission line, and a preamplifier placed immediately before the light receiver. For example, IEE Photonics Technology Letters is a report to improve the system characteristics by using an optical fiber amplifier as a preamplifier.
Vol.4, No.3 (1992), pages 272 to 275 (IEEE Photo
nics Technology Letters, vol.4, no.3, pp.272-275,
1992.). That is, a power amplifier, a preamplifier, a signal light source, and a light receiver are known as individual devices.

The basic structure of the fiber amplifier is an erbium-doped optical fiber doped with erbium ions, and a 1.48 μm band or 0.98 μm band semiconductor laser as a pumping light source for pumping the erbium-doped optical fiber,
It is composed of a multiplexer for multiplexing the excitation light source and the signal light source. This structure is described in Japanese Patent Laid-Open No. 2-157829. That is, in the conventional optical fiber amplifier, it is customary to use an optical element such as a filter as the multiplexer.

[0005]

When the optical fiber amplifier, the signal light source, and the light receiver are manufactured as individual devices, it is difficult to downsize the entire device and the number of working steps increases. Further, for the same reason, there is a problem in that a loss occurs in the combining portion of the pumping light and the signal light in the optical amplifier, the combining portion between the signal light source and the power amplifier, and the combining portion between the preamplifier and the light receiver. .

In view of the above situation, an object of the present invention is to reduce the size of the device and reduce the loss of signal light and pumping light, and a signal light source module with a power amplifier function and a light receiving module with a preamplifier function. To provide a module. Furthermore, the use of such a signal light source module and a light receiving module constitutes a compact and low-loss optical transmission system.

[0007]

In order to achieve such an object, a signal light source module of the present invention comprises a first semiconductor laser which outputs a signal light having a first wavelength, and a pump having a second wavelength. A second semiconductor laser that outputs light, and an optical fiber in which at least a part of the core is doped with a rare earth element, the first wavelength is longer than the second wavelength, the active layer of the second semiconductor laser. Is coupled with the first semiconductor laser to guide a signal light having a first wavelength,
The optical fiber is coupled to the active layer of the second semiconductor laser so as to simultaneously guide the signal light having the first wavelength and the pumping light having the second wavelength.

Further, the light receiving module of the present invention includes a light receiving element having sensitivity to light having a first wavelength, a second semiconductor laser for outputting pumping light having a second wavelength, and at least a part of the core. An optical fiber doped with a rare earth element, the first wavelength is longer than the second wavelength, and the pumping light having the second wavelength from the active layer of the second semiconductor laser is guided to the optical fiber. The signal light having the first wavelength from the optical fiber is coupled with the light receiving element after passing through the active layer of the second semiconductor laser.

Further, the light receiving module of the present invention comprises:
Described light receiving module, a branching device for branching a part of the output signal of the light receiving module, a driving device for driving a second semiconductor laser of the light receiving module, and the driving device using a signal from the branching device. Is provided with a control device for controlling.

An optical transmission system according to the present invention is characterized by claim 1.
It is characterized by comprising the signal light source module described above, an optical fiber for transmitting the signal light from the signal light source module, and a light receiver having sensitivity to the signal light from the signal light source module.

Further, the optical transmission system of the present invention has a semiconductor laser as a signal light source, an optical fiber for transmitting the signal light from the semiconductor laser, and a sensitivity to the signal light from the semiconductor laser. It is characterized in that it is provided with the light receiving module of.

The optical transmission system according to the present invention has a sensitivity to the signal light from the semiconductor laser as the signal light source, the optical fiber for transmitting the signal light from the semiconductor laser, and the signal light from the semiconductor laser. It is characterized in that it is provided with the light receiving module of.

The optical transmission system according to the present invention comprises:
The signal light source module described above, an optical fiber for transmitting the signal light from the semiconductor laser, and the light receiving module according to claim 2 having sensitivity to the signal light from the semiconductor laser.

Further, the optical transmission system of the present invention comprises:
The signal light source module described above, an optical fiber for transmitting the signal light from the semiconductor laser, and the light receiving module according to claim 3 having sensitivity to the signal light from the semiconductor laser.

[0015]

According to the configuration of the signal light source module with the power amplifier function of the present invention, since the first wavelength of the signal light output from the signal light source module is longer than the second wavelength, the pump light source It arrives at the rare earth-doped optical fiber without being absorbed in the active layer of the, and at the same time, the pumping light of the second wavelength output from the pumping light source is directly input to the rare earth-doped optical fiber. Since the signal light of the first wavelength is amplified in the optical fiber and the optical element for multiplexing is not required compared with the conventional configuration, the loss of the signal light and the excitation light is reduced, and the device is downsized. There is an effect that can be achieved.

According to the configuration of the light receiving module with the preamplifier function of the present invention, the excitation light of the second wavelength output from the excitation light source is directly input to the optical fiber in which the rare earth element is added to the core. The signal light of the first wavelength amplified by the optical fiber reaches the light receiver without being absorbed in the active layer of the pumping light source because the first wavelength is longer than the second wavelength. As compared with the conventional configuration, the optical element for multiplexing is not required, so that the loss of the signal light and the excitation light is reduced, and the size of the device can be reduced.

Further, in the present invention, since the light receiving element also has a function of monitoring the output light amount from the excitation light source, there is an effect that the device can be downsized.

[0018]

[Embodiment] As a rare earth element, if erbium ion capable of directly amplifying 1.55 μm light in the minimum loss wavelength band of an optical fiber is used, the excitation wavelength band is 1.48 μm band, 0.9
8μm band, 0.82μm band, etc. are possible. In these cases, in the active layer of the pumping semiconductor laser, 1.55 μm
Photon energy of band signal light hν _s (= hc / λ _s )
Is smaller than the band gap energy hν _p (= hc / λ _p ). Therefore, the pumping light is amplified as it propagates, while the signal light is transmitted without gain or loss. Here, h is the Boltzmann constant, c is the speed of light, ν _p is the frequency of the pumping light, λ _p is the wavelength of the pumping light, ν _s is the frequency of the signal light, and λ _s is the signal light wavelength.

(Embodiment 1) FIG. 1 shows a configuration diagram of a signal light source module with a power amplifier function which is a first embodiment of the present invention. The semiconductor laser 3 uses the signal light 10 in the 1.55 μm band.
1 is output. The signal light 101 is coupled to the active layer 201 of the semiconductor laser 2 which outputs the 0.98 μm band pumping light 102. Further, the signal light passes through the active layer 201 for the reason described above, and enters the erbium-doped optical fiber 1 through the coupling optical lens 5.

On the other hand, the 0.98 μm band excitation light 102 from the semiconductor laser 2 is condensed by the optical lens 5 and enters the erbium-doped optical fiber 1. The excitation light 102 excites the erbium-doped optical fiber 1 and amplifies the 1.55 μm band signal light 101 which is incident at the same time. An optical isolator 4 is used to prevent oscillation due to the high gain of the erbium-doped optical fiber and to prevent pumping light from leaking into the signal light transmission line.

Here, the 0.98 μm band was used as the pumping light wavelength, but in this case, it has a feature that the noise figure of the power amplifier section can be made small. As mentioned above, other absorption wavelength bands of erbium ions, such as 1.48 μm band and 0.8
It is also possible to use the 2 μm band, and in these cases, high output and low cost can be achieved. Also,
The pumping semiconductor laser used has a waveguide structure that is commonly used at present, but using a surface emitting laser has the advantage of facilitating optical coupling with an optical fiber. In the case of this surface emitting laser, it is possible to further reduce the loss of the signal light in the semiconductor laser 2 by forming a hole in a part of the active layer for transmitting the signal light. An optical lens was used for coupling the signal light and pumping light to the erbium-doped optical fiber. It may be possible to provide a light collecting function by providing. These optical systems reduce the reflection of the signal light,
The end surface of each optical element may be angled with respect to the optical axis. Erbium was used as the rare earth ion, but it was 1.3
It has the function of amplifying μm band signal light.

As described above, since a multiplexer for pumping light and signal light is not required, the size can be reduced. In addition, by adding a power amplifier function to the semiconductor laser, the power amplifier section can amplify the output even if the output of the semiconductor laser itself is small, so the distortion characteristics due to the output are improved, the yield is improved, and the signal light source is improved. Since the semiconductor laser can be modulated with a smaller amplitude, the modulation circuit can be downsized.

(Embodiment 2) FIG. 2 shows a configuration diagram of a light receiving module with a preamplifier function, which is a second embodiment of the present invention. The 0.98 μm band excitation light 102 from the semiconductor laser 2 is condensed by the optical lens 5 and enters the erbium-doped optical fiber 1. The erbium-doped optical fiber 1 is excited by this excitation light 102 and is incident at the same time with 1.55.
The μm band signal light 101 is amplified. The amplified 1.55 μm band signal light 101 is coupled to the active layer 201 of the semiconductor laser 2 which outputs 0.98 μm band pump light 102. This signal light is transmitted through the active layer 201 for the reason described above, enters the PIN photodiode as the light receiving element 6, and is converted into an electric signal. An optical isolator 4 is used to prevent oscillation due to the high gain of the erbium-doped optical fiber and to prevent pumping light from leaking into the signal light transmission line.

Here, the 0.98 μm band is used as the pumping light wavelength, but in this case, it has a feature that the noise figure of the preamplifier section can be made small. As mentioned above, other absorption wavelength bands of the erbium ion are 1.48 μm band and 0.82
It is also possible to use the μm band, and in these cases, high output and low cost can be achieved. Also,
The pumping semiconductor laser used has a waveguide structure that is commonly used at present, but using a surface emitting laser has the advantage of facilitating optical coupling with an optical fiber. In the case of this surface emitting laser, it is possible to further reduce the loss of the signal light in the semiconductor laser 2 by forming a hole in a part of the active layer for transmitting the signal light. An optical lens was used for coupling the signal light and pumping light to the erbium-doped optical fiber. It may be possible to provide a light collecting function by providing. These optical systems reduce the reflection of the signal light,
The end surface of each optical element may be angled with respect to the optical axis. Erbium was used as the rare earth ion, but it was 1.3
It has the function of amplifying μm band signal light.

As described above, by adding the preamplifier function to the light receiver, the signal can be demodulated even when the amount of signal light incident on the light receiver is very small, and the amplification of the electric signal is not required, so that the distortion characteristic is obtained. Does not deteriorate. In addition, since a multiplexer that multiplexes the pumping light and the signal light is not required when configuring the preamplifier unit, the module can be downsized.

(Embodiment 3) FIG. 3 is a block diagram of a light receiving module showing a third embodiment of the present invention. Semiconductor laser 2
The 0.98 μm band excitation light 102 from is condensed by the optical lens 5 and enters the erbium-doped optical fiber 1. The erbium-doped optical fiber 1 is excited by this pumping light 102, and the 1.55 μm band signal light 101 is being simultaneously incident.
To amplify. The amplified 1.55 μm band signal light 101 is 0.9
It is coupled to the active layer 201 of the semiconductor laser 2 that outputs the 8 μm band excitation light 102. This signal light is transmitted through the active layer 201 for the reason described above, enters the PIN photodiode as the light receiving element 6, and is converted into an electric signal.

The output signal from the light receiving element 6 is branched by the branching device 7 and enters the control device 8. The controller 8 controls the device temperature of the semiconductor laser 2 and the injection current amount by the drive device 9 so that the received signal light amount becomes a desired amount. Further, it is possible to control not only the amount of signal light but also the characteristics of the erbium-doped optical fiber amplifier in advance to control the noise figure and distortion characteristics. Four
Is a polarization-independent optical isolator used to prevent oscillation due to the high gain of the erbium-doped optical fiber and to prevent pumping light from leaking into the signal transmission line.

As described above, in this embodiment, since the light receiving element also serves as the output monitor element of the semiconductor laser 2, the amount of received signal light can be kept stable, and the loss due to the optical element can be reduced to reduce the size of the apparatus. .

(Embodiment 4) FIG. 4 shows a block diagram of an optical transmission system according to a fourth embodiment of the present invention. 12 is the wavelength
In the signal light source module described in the first embodiment that outputs a signal light of 1.55 μm, a high output light of 10 dBm or more is obtained because it has a power amplifier function. The dispersion shifted single mode optical fiber used as the transmission line 10 has a length of 20 km. As the light receiver 13, a Ge-PIN photodiode having sensitivity to 1.55 μm band signal light was used.

As described above, since the device capable of obtaining a high output is used in the signal light source module, it is possible to construct an optical transmission system having a longer transmission line and not requiring an amplifier to be inserted in the middle thereof.

(Fifth Embodiment) FIG. 5 shows a block diagram of an optical transmission system according to a fifth embodiment of the present invention. 11 is the wavelength
With a DFB laser that outputs a signal light of 1.55 μm, an output light amount of about 0 dBm is obtained. The dispersion shifted single mode optical fiber used as the transmission line 10 has a length of 20 km. For light reception, the light receiving module 14 with a preamplifier function of the second embodiment, which is sensitive to 1.55 μm band signal light, was used.
In the preamplifier part of this light receiving element, when a small signal light is input
It is possible to obtain a gain of 30 dB or more.

Since the light receiving element is provided with the function of amplifying the received light signal in this way, it becomes possible to construct an optical transmission system capable of demodulating even when the received light signal is weak.

(Sixth Embodiment) FIG. 6 is a block diagram of an optical transmission system according to a sixth embodiment of the present invention. 11 is the wavelength
With a DFB laser that outputs a signal light of 1.55 μm, an output light amount of about 0 dBm is obtained. The dispersion shifted single mode optical fiber used as the transmission line 10 has a length of 20 km. The light receiving module 15 with a feedback function of the third embodiment, which is sensitive to 1.55 μm band signal light, was used for light reception. In the preamplifier section of this light receiving module, the gain is controlled so that the amount of light input to the light receiving element is always 0 dBm.

Since the light receiving element has the function of keeping the received light signal constant, it is necessary to construct an optical transmission system capable of stable demodulation even when the received light signal amount dynamically changes. Is possible.

(Embodiment 7) FIG. 7 shows a block diagram of an optical transmission system according to a seventh embodiment of the present invention. 12 is the wavelength
The signal light source module according to the first embodiment that outputs a signal light of 1.55 μm has a power amplifier function, and thus has a power of 10 dBm.
The output light amount above is obtained. The dispersion-shifted single-mode optical fiber used as the transmission line 11 has a length of 40 km.
Is. For light reception, the light receiving module 14 with a preamplifier function of the second embodiment, which is sensitive to 1.55 μm band signal light, was used. In the preamplifier section of this light receiving element, a gain of 30 dB or more is obtained when a small signal light is input.

As described above, since the signal light source module uses the element capable of obtaining a high output and the light receiving element is provided with the function of amplifying the received light signal light, the light which can be demodulated even when the received light signal is weak. It becomes possible to construct a transmission system.

(Embodiment 8) FIG. 8 shows a block diagram of an optical transmission system according to an eighth embodiment of the present invention. 12 is the wavelength
The signal light source module according to the first embodiment that outputs a signal light of 1.55 μm has a power amplifier function, and thus has a power of 10 dBm.
The output light amount above is obtained. The dispersion-shifted single-mode optical fiber used as the transmission line 10 has a length of 40 km.
Is. The light receiving module 15 with a feedback function of the third embodiment, which is sensitive to 1.55 μm band signal light, was used for light reception. In the preamplifier section of this light receiving element, a light amount of 0 dBm is obtained in the light receiving element when a small signal light is input.

As described above, since the signal light source module uses the element capable of obtaining a high output and the light receiving element has a function of making the received light signal light have a constant light quantity, even when the received light signal dynamically changes. Therefore, it becomes possible to construct an optical transmission system capable of stable demodulation.

[0039]

As described above, according to the configuration of the present invention, it is possible to provide a signal light source module and a light receiving module in which loss of signal light and pumping light is small, distortion characteristics are improved, and miniaturization is possible. The effect is that it will be possible. Further, there is an effect that it is possible to provide an optical transmission system that can be downsized.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a signal light source module with a power amplifier function according to a first embodiment.

FIG. 2 is a diagram showing a configuration of a light receiving module with a preamplifier function according to a second embodiment.

FIG. 3 is a diagram showing a configuration of a preamplifier and a light receiving module with a feedback function according to a third embodiment.

FIG. 4 is a diagram showing a configuration of an optical transmission system that is a fourth embodiment using the signal light source module with the power amplifier function of the first embodiment.

FIG. 5 is a diagram showing a configuration of an optical transmission system according to a fifth embodiment, which uses the light receiving module with a preamplifier function according to the second embodiment.

FIG. 6 is a diagram showing a configuration of an optical transmission system according to a sixth embodiment using the preamplifier and the light receiving module with the feedback function according to the third embodiment.

FIG. 7 is a diagram showing a configuration of an optical transmission system of a seventh embodiment using the signal light source module with the power amplifier function of the first embodiment and the light receiving module with the preamplifier function of the second embodiment.

FIG. 8 is a diagram showing a configuration of an optical transmission system according to an eighth embodiment, which uses the signal light source module with the power amplifier function of the first embodiment and the preamplifier and the light receiving module with the feedback function of the third embodiment.

[Explanation of symbols]

1 erbium-doped optical fiber 2 semiconductor laser having a second wavelength 3 semiconductor laser having a first wavelength 4 optical isolator 5 optical lens 6 light receiving element 7 brancher 8 controller 9 driver 101 1.55 μm band signal light 102 0.98 μm Band excitation light 201 Active layer of second semiconductor laser 10 Optical fiber 11 Signal light source 12 Signal light source module with power amplifier function 13 Light receiver 14 Light receiving module with preamplifier function 15 Light receiving module with feedback function and preamplifier function

Claims (8)

[Claims] 1. A first semiconductor laser that outputs a signal light having a first wavelength, a second semiconductor laser that outputs a pumping light having a second wavelength, and a rare earth element in at least a part of the core. A first wavelength is longer than a second wavelength, and the active layer of the second semiconductor laser is configured to guide the signal light having the first wavelength. A laser, and the optical fiber is coupled to an active layer of the second semiconductor laser so as to simultaneously guide a signal light having a first wavelength and a pumping light having a second wavelength. Signal light source module. 2. A light-receiving element having sensitivity to light having a first wavelength, a second semiconductor laser which outputs excitation light having a second wavelength, and light in which a rare earth element is added to at least a part of the core. And a first wavelength is longer than a second wavelength, the excitation light having a second wavelength from the active layer of the second semiconductor laser is guided to the optical fiber, The light receiving module, wherein the signal light having the first wavelength of (1) is coupled with the light receiving element after passing through the active layer of the second semiconductor laser. 3. The light receiving module according to claim 2, a branching device for branching a part of the output signal of the light receiving module, a driving device for driving a second semiconductor laser of the light receiving module, and the branching device. A light-receiving module comprising a control device for controlling the drive device using the signal of 1. 4. The signal light source module according to claim 1, an optical fiber for transmitting the signal light from the signal light source module, and a light receiver having sensitivity to the signal light from the signal light source module. Characteristic optical transmission system. 5. A semiconductor laser as a signal light source, an optical fiber for transmitting the signal light from the semiconductor laser, and a sensitivity to the signal light from the semiconductor laser.
An optical transmission system comprising the light receiving module described. 6. A semiconductor laser as a signal light source, an optical fiber for transmitting the signal light from the semiconductor laser, and a sensitivity to the signal light from the semiconductor laser.
An optical transmission system comprising the light receiving module described. 7. A signal light source module according to claim 1, and an optical fiber for transmitting signal light from the semiconductor laser.
An optical transmission system comprising the light receiving module according to claim 2, which is sensitive to signal light from the semiconductor laser. 8. A signal light source module according to claim 1, and an optical fiber for transmitting signal light from the semiconductor laser.
An optical transmission system comprising the light receiving module according to claim 3, which is sensitive to signal light from the semiconductor laser.