JP4471919B2 - Optical communication system and semiconductor optical amplifier - Google Patents

Description

  The present invention optically amplifies an optical signal transmitted through a transmission fiber laid in a city as a transmission path by a non-feed semiconductor optical amplifier installed away from a linear repeater or a terminal device. The present invention relates to an optical communication system or an optical communication system in which an optical signal is optically amplified by a non-powered semiconductor optical amplifier installed in a home network and an optical integrated circuit using an optical fiber.

  As a first configuration of the prior art, FIG. 19 shows a configuration example of a conventional remote pumping system used in a wavelength division multiplexing optical fiber communication system (see, for example, Non-Patent Document 1 or 2). In this remote excitation system, signal light is transmitted from the transmission circuit 10 in the transmitter 1, and the signal light is transmitted through three transmission fibers (transmission fiber # 1, transmission fiber # 2, transmission fiber # 3). ) Through the receiver circuit 20 in the receiver 2.

  An erbium-doped fiber (EDF) is installed between the transmission fiber # 1 and the transmission fiber # 2, and between the transmission fiber # 2 and the transmission fiber # 3. Let these EDF be EDF-F and EDF-R, respectively.

  In the transmitter 1 and the receiver 2, pumping light sources 12 and 22 for remote pumping are installed, and pumping light and signal light from the pumping light sources 12 and 22 are multiplexed using the multiplexers 11 and 21, respectively. Is done. The transmitter 1, the receiver 2, and the excitation light sources 12 and 22 are connected to a power source and are supplied with power.

  The excitation light sources 12 and 22 connected to the transmitter 1 and the receiver 2 will be referred to as a front-stage excitation light source and a rear-stage excitation light source, respectively. The excitation light from these excitation light sources 12 and 22 will be referred to as forward excitation light and backward excitation light, respectively. The forward pumping light pumps the EDF-F after passing through the transmission fiber # 1, and the backward pumping light pumps the EDF-R after passing through the transmission fiber # 3.

  The wavelength of the signal light is a wavelength in the C band (1.55 μm band), and the wavelength of the pumping light is light in the vicinity of 1.48 μm suitable for pumping an erbium-doped fiber (EDF). The signal light emitted from the transmitter 1 is attenuated by the transmission fiber # 1, then amplified by EDF-F, further attenuated by the transmission fiber # 2, amplified by EDF-R, and passes through the transmission fiber # 3. Later, the receiver 2 is reached. Therefore, the combined distance of the transmission fiber # 1, the transmission fiber # 2, and the transmission fiber # 3 can be transmitted without relaying without supplying power in the middle.

  The advantage of this remote excitation is that the non-relay distance, that is, the relay interval, is greatly extended compared to a relay system that does not use remotely excited EDF. However, a configuration using only one of the front excitation light source and the EDF-F, or the rear excitation light source and the EDF-R may be employed.

  Next, as a second configuration of the prior art, a configuration example of a conventional semiconductor optical amplifier used in an optical fiber communication system is shown in FIG. In this semiconductor optical amplifier, the signal light emitted from the optical fiber F1 on the left side of the drawing is condensed by the lens L1 disposed between the optical fiber F1 and the semiconductor element 30 that is an amplification medium, and is an active layer of the semiconductor element 30. 31 is incident. Further, the signal light propagating through the active layer 31 is condensed on the optical fiber F2 on the signal light emission side by the lens L2 installed between the semiconductor element 30 and the optical fiber F2 on the signal light emission side. The

  The semiconductor element 30 has a clad layer 32 on both sides of the active layer 31, a substrate 33 on both sides of the clad layer 32, and electrodes 34 on both sides of the substrate 33. A power source 35 is connected to the electrode 34, and the semiconductor element 30 is current-driven by the power source 35.

K. Aida et al. , IEEE Proceedings, vol. 137, Pt. J, No4, pp. 225-229, 1990 N. Ohkawa et al. , IEICE Trans. Commun. , Vol. E81-B, pp. 586-596, 1998

  In the remote excitation system which is the first configuration of the prior art shown in FIG. 19, the wavelength range of the signal light is limited to the C band (1530 to 1560 nm) which is the EDF gain band. Therefore, generally, optical amplification of signal light of 1600 nm or 1500 nm, which is a wavelength other than the C band, cannot be performed.

  Further, the remote pumping system of the prior art has a drawback that the required power of the pumping light incident on the remote pumping module is determined by the pumping efficiency of the EDF and is limited to a value of about 10 to 20 mW or more.

  Furthermore, in the remote pumping system of the prior art, when the transmission fiber is a dispersion shifted fiber, the difference (A) between the zero dispersion wavelength and the pumping light wavelength of the transmission fiber is the difference between the L-band signal light wavelength and the zero dispersion wavelength. A value close to the difference (B) is shown, and there is a disadvantage that a transfer of intensity noise from the excitation light to the signal light occurs in the transmission fiber.

  Further, when the transmission fiber is a non-zero dispersion shifted fiber, there is a disadvantage that the pumping light wavelength of the transmission fiber is close to the zero dispersion wavelength and the system performance is deteriorated due to the nonlinear effect of the pumping light in the transmission fiber.

  Furthermore, the semiconductor optical amplifier that is the second configuration of the prior art in FIG. 20 requires power supply and cannot be installed at any position in the optical fiber network. In addition, there is a drawback that electrical wiring for power supply is necessary.

  The present invention has been made under such a background, and the nonlinearity of the excitation light that causes the transfer of intensity noise from the excitation light to the signal light, which limits the gain bandwidth and excitation efficiency of the remote excitation module. Solves the problems of the prior art, such as system performance degradation due to the effect, the need to feed power to the semiconductor optical amplifying unit, cannot be installed at any position in the optical fiber network, and the need for electrical wiring for feeding It is an object of the present invention to provide an optical communication system and a semiconductor optical amplifying unit that can be used.

  The present invention is an optical communication system, and is characterized in that an output means for outputting signal light, an input means for inputting the signal light, and between the input means and the output means. A semiconductor optical amplifier including a semiconductor element inserted between installed transmission fibers and remotely pumped, and at least one of the output means or the input means, an excitation light source for exciting the semiconductor element; There is a multiplexer that combines the excitation light from the excitation light source and the signal light.

  As described above, in the optical communication system of the present invention, by using the semiconductor optical amplifier including the semiconductor element that is remotely pumped, it is possible to perform optical amplification without feeding in the middle of the transmission fiber.

  At this time, by setting the wavelength of the pumping light on the short wavelength side of 80 to 280 nm of the signal light wavelength, it is possible to optically amplify with a required pumping light power smaller than that in the case where it does not.

  In addition, since the semiconductor element has a quantum well structure or a quantum dot structure, excitation efficiency can be improved.

  Further, by providing means for intensity-modulating the signal light so that the signal light output power per channel in the wavelength division multiplexing system from the semiconductor element becomes −10 dBm or less, the nonlinear effect in the semiconductor element can be suppressed. it can.

  Alternatively, by providing means for phase-modulating or frequency-modulating the signal light so that the signal light output power per channel in the wavelength division multiplexing system from the semiconductor element is −5 dBm or less, the nonlinear effect in the semiconductor element can be reduced. Can be suppressed.

  Further, by setting the pumping light wavelength on the short wavelength side of the zero dispersion wavelength of the transmission fiber, it is possible to avoid the transfer of relative intensity noise from the pumping light to the signal light. Or the nonlinear effect of the excitation light in a transmission fiber can be avoided.

  As a specific configuration example of the optical communication system of the present invention, a demultiplexer installed before the semiconductor optical amplifier and demultiplexing the signal light and the pumping light, and a branch connected to the demultiplexer Connected to the first output port of the branching device, and to combine the signal light and the pumping light, and to the second output port of the branching device, A second multiplexer that multiplexes the excitation light, and the pump light emitted from the first multiplexer and the excitation light emitted from the second multiplexer are the semiconductor optical amplification unit It can comprise so that it may inject into.

  According to this, bidirectional pumping of forward pumping and backward pumping can be realized using a single pumping light source, and a higher gain can be obtained compared to unidirectional pumping at the same pumping light power.

  Alternatively, a circulator for inputting the signal light and the pumping light from the first port, a polarization beam splitter connected to the second port of the circulator, and connecting the polarization beam splitter and the semiconductor optical amplification unit A fiber ring, and only one arm of the fiber ring is rotated 90 degrees to be connected to the semiconductor optical amplifier.

  Also by this, it is possible to realize bidirectional pumping of forward pumping and backward pumping using one pumping light source, and it is possible to obtain a higher gain than unidirectional pumping at the same pumping light power.

  The semiconductor element can be realized by having an active layer and a cladding layer. According to this, for example, the semiconductor element and the optical fiber can be connected without a lens. That is, the thickness of the active layer is set to be substantially the same as the thickness of the core of the optical fiber, and the refractive index difference between the core and the cladding of the optical fiber is substantially equal to the refractive index difference between the active layer and the cladding of the semiconductor element. In the same manner, the mode diameter of the signal light propagating in the optical fiber is made substantially the same as the mode diameter of the signal light propagating in the semiconductor element, and the gap between the optical fiber and the semiconductor element is as small as 1 μm, for example. In addition, by reducing the coupling loss between the two, and by coating the end faces of the optical fiber and the semiconductor element without reflection, the optical system using the lens can be omitted, and the optical communication system can be simplified and reduced in price. Can do.

  Further, by making the cladding layer of the semiconductor element a non-doped cladding layer or a semi-insulating cladding layer doped with an impurity containing iron, the insulation of the cladding layer is increased, and the cladding of carriers generated in the active layer is increased. Leakage to the layer can be reduced, and the gain of the semiconductor element can be improved.

  In addition, by configuring the semiconductor optical amplifier to be in close contact with the insulating heat conductor, the heat generated in the semiconductor element can be dissipated through the insulating heat conductor. Since the heat is generated in the process where the excitation light is absorbed in the active layer, it is possible to increase the absorption efficiency of the excitation light into the active layer and improve the gain of the semiconductor element by dissipating the heat. it can.

  Further, N input means may be provided, and a branching means for connecting the semiconductor optical amplifier and the N input means in a one-to-N manner may be provided.

  According to this, output signal light from one semiconductor amplifying unit can be distributed to a plurality of receivers and the like, and the present invention can be applied to 1-to-N communication.

  The present invention can also be understood from the viewpoint of the invention of a semiconductor optical amplifier applied to the optical communication system of the present invention. For example, the semiconductor optical amplifier of the present invention is characterized in that the semiconductor element constituting the semiconductor optical amplifier has a quantum well structure or a quantum dot structure. The semiconductor element has, for example, an active layer and a cladding layer. The cladding layer is, for example, a non-doped cladding layer or a semi-insulating cladding layer doped with an impurity containing iron. In addition, the semiconductor optical amplifier of the present invention can be configured in close contact with an insulating heat conductor.

  According to the present invention, the gain band and pumping efficiency of the remote pumping module are limited, the intensity noise is transferred from pumping light to signal light, and the system performance is degraded due to the nonlinear effect of pumping light. It is possible to solve the problems of the prior art that power supply is necessary, cannot be installed at an arbitrary position in the optical fiber network, and electrical wiring for power supply is necessary.

  Embodiments of the present invention will be described below with reference to the drawings.

(First Example)
An optical communication system according to a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a diagram showing an example in which the optical communication system of the first embodiment is realized by a linear repeater. FIG. 2 is a diagram showing an example in which the optical communication system of the first embodiment is realized by a transmitter and a receiver.

  That is, in the prior art, an EDF is used as a gain medium for remote excitation, but in this embodiment, a semiconductor element is used as a gain medium for remote excitation. In FIG. 1, they are installed in the respective semiconductor optical amplifiers -F and -B for forward pumping and backward pumping.

  The excitation light source wavelength is 1.48 μm in the prior art, but is 1.43 μm in this embodiment. Further, the signal light wavelength is 1.55 μm in the prior art, but is 1.58 μm in the present embodiment. In this embodiment, the transmission fibers # 1, # 2, and # 3 are installed between the upstream linear repeater 4-1 and the downstream linear repeater 4-2.

  Further, as shown in FIG. 2, the linear repeater 4-1 may be the transmitter 1, and the linear repeater 4-2 may be the receiver 2. In the example of FIG. 2, the semiconductor optical amplification unit -B is not installed, and the receiver 2 is not provided with an excitation light source and a multiplexer for backward excitation. This is an example in which the distance between the transmitter 1 and the receiver 2 is relatively short. When the distance between the transmitter 1 and the receiver 2 is relatively long, as in the example of FIG. The semiconductor optical amplification unit-B may be installed, and the receiver 2 may be provided with an excitation light source and a multiplexer for backward excitation.

  As is well known, a semiconductor element for optical amplification can amplify signal light of an arbitrary wavelength by changing its semiconductor composition and composition ratio. Examples of the semiconductor composition include InGaAsP. For example, a 1.50 μm signal light can be amplified with a 1.35 μm excitation light using a semiconductor optical amplifier having a composition ratio different from that in FIG. As described above, this embodiment solves the disadvantage that the gain band is limited, which has been a problem in the prior art.

  In the past, semiconductor devices have been used as current-driven devices and have not been used in remote excitation systems.

  FIG. 3 shows the configuration of the semiconductor optical amplifier in the first embodiment. The semiconductor optical amplifier 50 shown in FIG. 3 does not include the electrode 34, the power source 35, and the like, which are parts necessary for current driving, unlike the semiconductor device 30 of the prior art shown in FIG. Further, the excitation light emitted from the excitation light source 55 is combined with the signal light by the multiplexer 54, propagates along with the signal light through the optical fiber F <b> 1, and then enters the semiconductor optical amplifier 50.

  At this time, the distance between the multiplexer 54 and the semiconductor optical amplifier 50 is typically several meters to several tens km. That is, in the case of the remote excitation system of FIG. 1, the lengths of the transmission fibers # 1, # 2, and # 3 are all tens of kilometers. When the semiconductor optical amplifier 50 is installed in a home network using optical fibers, the optical fiber length is about several meters to several tens of meters. However, there are cases where the optical fiber length is about several millimeters to several tens of centimeters, as in the case where the semiconductor optical amplifier 50 is installed in the optical integrated circuit.

  FIG. 11 shows an example of measurement results of the gain and noise figure characteristics of the semiconductor optical amplifier 50 shown in FIG. At this time, the signal light wavelength is 1550 nm and the excitation light wavelength is 1470 nm. However, the pumping light power is an optical fiber output value, that is, a semiconductor optical amplifier input value. When the pumping light power is 100 mW and 200 mW, the gains are about 2.5 dB and about 5.0 dB, respectively. Further, the noise figure is approximately 9.2 dB, which is almost constant in the region where the pumping light power is 100 mW or more.

  However, the semiconductor element as the semiconductor optical amplification unit 50 used for this measurement is not optimized for the waveguide parameters, and the required pumping light power for obtaining the same gain is compared with the optimized one. The value is several times larger.

  On the other hand, FIG. 12 shows a measurement result example of the pumping light wavelength dependence of the gain of the semiconductor optical amplifier 50 shown in FIG. At this time, the signal light wavelength is 1570 nm, and the excitation light wavelengths are 1430 nm, 1470 nm, and 1490 nm. It was found that the dependence of the gain on the pumping light wavelength is small in the pumping light wavelength range (1430 to 1490 nm).

  FIG. 14 shows a required excitation light power spectrum for obtaining a gain of 10 dB when the waveguide parameter of the semiconductor element as the semiconductor optical amplifier 50 is optimized. At this time, the signal light wavelength is 1580 nm. The required pumping light power at the pumping light wavelength of 1300 to 1500 nm has a small wavelength dependency and is about 20 to 30 mW.

  That is, if the difference between the signal light wavelength and the pumping light wavelength is 80 to 280 nm with respect to 1.5 μm band signal light, there is an advantage that a small required pumping light power can be obtained. However, the difference between the signal light wavelength and the excitation light wavelength is slightly different depending on the composition of the semiconductor optical amplification element.

  FIG. 15 shows the semiconductor element structure dependency of the excitation efficiency characteristics of the semiconductor element in this example. It was found that the excitation efficiency improved in the order of bulk, quantum well, and quantum dot. In the remote pumping system, the lower the required pumping light power, the better the system performance. Therefore, it can be seen that it is particularly preferable to use a semiconductor device having a quantum well and quantum dot structure with high pumping efficiency.

  FIG. 16 shows system performance degradation characteristics due to nonlinear effects in the semiconductor optical amplifier in the optical communication system of the present embodiment. When a wavelength multiplexing system is considered, the nonlinear effect in the semiconductor element is mainly determined by the signal light power per channel of the semiconductor element output. Non-linear effects include four-wave mixing, cross gain modulation, and the like.

  As shown in FIG. 16, the degradation amount (power penalty) of the signal light power giving the reception sensitivity depends on the signal light power per channel, and is a considerably small value when the output signal light power is -10 dBm or less. I found out that

  In the remote pumping system (referred to as A), optical amplification is performed in the middle of a transmission line laid in the city. Therefore, the output of the semiconductor optical amplifier is changed to a system using a linear repeater optical amplifier (referred to as B). In comparison, it can be set significantly lower. For example, the typical value of the output signal light power in the system B is about 0 dBm, but it can be set to -10 dBm or less in the system A. Therefore, the system performance deterioration that is remarkable in the system B can be avoided by the output signal light power setting in the system A.

  The above is a case where the signal light is intensity-modulated, but nonlinear effects in the semiconductor optical amplifier can be suppressed by using phase modulation or frequency modulation of the signal light. At this time, it was found that the power penalty was considerably small when the output signal light power was −5 dBm or less.

  Furthermore, FIG. 17 shows the relationship between the signal light wavelength, the pumping light wavelength, and the zero dispersion wavelength of the transmission fiber in the optical fiber communication system of the present embodiment. However, this is the case where the transmission fiber is a dispersion shifted fiber (DSF). The zero dispersion wavelength is in the vicinity of 1550 nm, and the signal light wavelength is in the 1580 nm band (1570 to 1600 nm). The excitation light wavelength is 1480 nm in the prior art and 1430 nm in this embodiment. However, in the prior art, a remote excitation EDF for L band is used.

  In the prior art, the difference between the signal light wavelength and the zero dispersion wavelength of 10 to 50 nm is close to the difference between the zero dispersion wavelength and the excitation light wavelength of 70 nm, and the relative intensity noise from the excitation light to the signal light is transferred in the transmission fiber. Occurs, causing system performance degradation. On the other hand, in this embodiment, the difference of 10 to 50 nm between the signal light wavelength and the zero dispersion wavelength is sufficiently smaller than the difference of 130 nm between the zero dispersion wavelength and the excitation light wavelength, and the system performance deterioration due to the transfer of the relative intensity noise can be avoided. .

  FIG. 18 shows the relationship between the signal light wavelength, the pumping light wavelength, and the zero dispersion wavelength of the transmission fiber when the transmission fiber is a non-zero dispersion shifted fiber (NZ-DSF). However, this is a case where the transmission fiber is a non-zero dispersion shifted fiber (NZ-DSF). The zero dispersion wavelength is around 1470 nm, and the signal light wavelength is 1550 nm. The excitation light wavelength is 1480 nm in the prior art and 1400 nm in this embodiment.

  That is, in the prior art, the zero dispersion wavelength is in the vicinity of the excitation light wavelength. Therefore, the pumping light causes a nonlinear effect in the transmission fiber and induces a deterioration in the transmission characteristics of the signal light. On the other hand, in the present embodiment, the pumping light wavelength of 1400 nm is sufficiently far from the zero dispersion wavelength of 1470 nm to 70 nm, so that the nonlinear effect of the pumping light and hence the deterioration of the transmission characteristics of the signal light can be avoided.

(Second embodiment)
The optical communication system of the second embodiment will be described with reference to FIG. FIG. 4 is an overall configuration diagram of the optical communication system of the second embodiment. The following points are mainly different from the first embodiment of FIG. That is, in this embodiment, the semiconductor optical amplifier 62 is bidirectionally excited. That is, the following components are added in order to make the excitation light enter from both sides of the semiconductor optical amplifier 62.

  The pump light directed toward the semiconductor optical amplifier 62 is separated from the signal light by the duplexer 60 installed on the upstream side of the signal light, introduced into the branch 64, and branched at a desired branch ratio, for example, 1: 1. The bifurcated excitation light is guided to a multiplexer 61 installed on the upstream side of the signal light of the semiconductor optical amplifier 62 and a multiplexer 63 installed on the downstream side of the signal light, and then to the semiconductor optical amplifier 62. Incident.

  FIG. 13 shows the excitation direction dependence of the semiconductor optical amplifier 62. The case where the pumping light power is 50 mW is the one-way pumping, and the case where the pumping light power is 100 mW is the bi-directional pumping. However, the pumping light power is a total power. The gain in the case of bidirectional pumping is sufficiently larger than the gain in the case of unidirectional pumping and the pumping light power is 100 mW, and it has been found that the gain in the case of bidirectional pumping is higher at the same pumping light power.

  Therefore, this embodiment has an advantage that a higher gain can be obtained at the same pumping light power than the first embodiment.

(Third embodiment)
An optical communication system according to a third embodiment will be described with reference to FIG. FIG. 5 is an overall configuration diagram of the optical communication system of the third embodiment. The following points are mainly different from the first embodiment of FIG. That is, in the present embodiment, the following components are added in order to bi-directionally excite the semiconductor optical amplifying unit 72, that is, to make the excitation light enter from both directions of the semiconductor optical amplifying unit 72.

  The signal light and the pump light directed to the semiconductor optical amplifier 72 are guided from the first port to the second port by the circulator 70 and are incident on the polarization beam splitter 71 connected to the second port. The polarization beam splitter 71 causes the signal light to rotate clockwise or counterclockwise in a fiber ring 73 formed of a polarization maintaining fiber that connects the polarization beam splitter 71 and the semiconductor optical amplifier 72 according to the polarization state. It propagates around and enters the semiconductor optical amplifier 72.

  On the other hand, the excitation light is polarization multiplexed, and its power is divided into two by the polarization beam splitter 71, propagates clockwise or counterclockwise in the fiber ring 73, and enters the semiconductor optical amplifier 72. However, only one arm of the fiber ring 73 is rotated 90 degrees and connected to the semiconductor optical amplifier 72.

  The signal light amplified by the semiconductor light amplifier 72 propagates clockwise or counterclockwise in the fiber ring 73, and then is emitted toward the circulator 70 by the polarization beam splitter 71, and is output from the second port of the circulator 70. The light is guided to the three ports and emitted to the output optical fiber F2.

(Fourth embodiment)
The optical communication system of the fourth embodiment will be described with reference to FIG. FIG. 6 is an overall configuration diagram of the optical communication system according to the fourth embodiment. The following points are mainly different from the first embodiment of FIG. That is, in this embodiment, the semiconductor element 86 and the optical fiber 80 are connected without a lens. That is, the thickness of the active layer 84 is set to be substantially the same as the thickness of the core 81 of the optical fiber 80, and the refractive index difference between the core 81 and the cladding 82 of the optical fiber 80 is set to be the active layer 84 of the semiconductor element 86. The mode diameter of the signal light propagating through the optical fiber 80 is made substantially the same as the mode diameter of the signal light propagating through the semiconductor element 86.

  The gap between the optical fiber 80 and the semiconductor element 86 is, for example, as small as 1 μm to reduce the coupling loss between them. Further, the end faces of the optical fiber 80 and the semiconductor element 86 are coated without reflection.

  According to the present embodiment, there is an advantage that the optical system using the lens used in the first embodiment can be omitted, and the optical communication system can be simplified and reduced in price.

(Fifth embodiment)
A semiconductor element of the fifth embodiment will be described with reference to FIG. FIG. 7 is a block diagram of the semiconductor device of the fifth embodiment. The following points are mainly different from the semiconductor device of the first embodiment shown in FIG. That is, in this embodiment, the insulating heat conductive ring 91 is installed outside the semiconductor element 90, and the heat dissipating metal ring 92 is installed outside the semiconductor element 90. However, the material of the insulating heat conductive ring 91 is, for example, resin.

  According to the present embodiment, the heat generated in the semiconductor element 90 can be dissipated through the leading edge heat conductive ring 91 and the heat radiating metal ring 92. It was found that this heat is generated in the process in which excitation light is absorbed in the active layer. For example, the gain of 5 dB in the first embodiment is improved to 10 dB by this embodiment.

  However, the shape of the insulating heat conductive ring 91 and the metal ring 92 for heat dissipation may be rectangular, and the obtained effects are the same.

(Sixth embodiment)
An optical communication system according to the sixth embodiment will be described with reference to FIG. FIG. 8 is an overall configuration diagram of the optical communication system according to the sixth embodiment. The following points are mainly different from the fourth embodiment of FIG. That is, in this embodiment, the thickness of the active layer 101 is changed in a taper shape toward the boundary between the optical fiber 80 and the semiconductor element 103. As a result, the active layer 101 has a spot size conversion function in which the mode diameter in the active layer near the boundary is substantially equal to the mode diameter in the optical fiber 80. The mode diameter near the center of the semiconductor element 103 is smaller than the mode diameter in the active layer 101 near the boundary.

  According to the present embodiment, the coupling loss between the optical fiber 80 and the semiconductor element 103 and the signal light propagation loss in the semiconductor element 103 can be reduced.

(Seventh embodiment)
The semiconductor device of the seventh embodiment will be described with reference to FIG. FIG. 9 is a block diagram of the semiconductor device of the seventh embodiment. The semiconductor device 86 of the first embodiment shown in FIG. That is, in this embodiment, the composition of the clad layer 110 is non-doped or doped with impurities such as iron. With this composition, the insulation of the clad layer 110 is enhanced, and leakage of carriers generated in the active layer 111 to the clad layer 110 can be reduced. For example, the gain of 5 dB in the first embodiment is improved to 7 dB by this embodiment.

(Eighth Example)
The optical communication system according to the eighth embodiment will be described with reference to FIG. FIG. 10 is an overall configuration diagram of the optical communication system of the eighth embodiment. The following points are mainly different from the first embodiment of FIG. That is, in this embodiment, the optical fiber branch 5 is installed in the subsequent stage of the semiconductor optical amplifier-F, and the signal light is distributed to the plurality of receivers 2. At this time, the gain of the semiconductor optical amplifier -F compensates for the insertion loss of the optical fiber branch 5.

  According to the present invention, it is possible to easily construct a high-performance optical communication system as compared with the prior art without requiring electrical wiring for power supply.

1 is an overall configuration diagram of an optical communication system according to a first embodiment (an embodiment as a linear repeater). FIG. 1 is an overall configuration diagram of an optical communication system according to a first embodiment (embodiment as a transmitter and a receiver). FIG. The figure for demonstrating the structure of the semiconductor optical amplifier in a 1st Example. The whole block diagram of the optical communication system of a 2nd Example. The whole block diagram of the optical communication system of a 3rd Example. The whole block diagram of the optical communication system of a 4th Example. The block diagram of the semiconductor optical amplifier part of 5th Example. The whole block diagram of the optical communication system of a 6th Example. The block diagram of the semiconductor element of 7th Example. The whole block diagram of the optical communication system of an 8th Example. The figure which shows the gain and noise figure characteristic of a semiconductor optical amplifier. The figure which shows the excitation wavelength dependence of a semiconductor optical amplifier gain. The figure which shows the excitation direction dependence of a semiconductor optical amplifier gain. The figure which shows the pumping light wavelength dependence of required pumping light power. The figure which shows an excitation efficiency characteristic. The figure which shows the system degradation characteristic by a nonlinear effect. The figure which shows the relationship between the signal light wavelength in the system using DSF, a pumping light wavelength, and the zero dispersion wavelength of a transmission fiber. The figure which shows the relationship of the signal light wavelength in the system using nonzero DSF, a pumping light wavelength, and the zero dispersion wavelength of a transmission fiber. The figure which shows the 1st structure of a prior art. The figure which shows the 2nd structure of a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Transmitter 2 Receiver 4-1 and 4-2 Linear repeater 5 Optical fiber branch 10 Transmission circuit 11, 21, 41, 43, 54, 61, 63 Multiplexer 12, 22, 42, 44, 55 Excitation light source 13 Signal light source 20 Reception circuit 23 Light receiver 30, 86, 90, 103, 113 Semiconductor element 31, 51, 84, 101, 111 Active layer 32, 52, 83, 100, 110 Clad layer 33, 53, 85, 102, 112 Substrate 34 Electrode 35 Power supply 40, 45 Isolator 60 Demultiplexer 50, 62, 72 Semiconductor optical amplifier 64 Branch 70 Circulator 71 Polarization beam splitter 73 Fiber ring 80 Optical fiber 81 Core 82 Clad 91 Insulating heat conductive ring 92 Metal ring for heat dissipation L1, L2 Lens F1, F2 Optical fiber

Claims (14)

And output means for outputting a signal light, input means for inputting the signal light, is inserted between the installed transmission fiber between the input means and the output means, the Rukoto remotely excited by the excitation light A semiconductor optical amplifier including a semiconductor element for amplifying the signal light ,
At least one of the output means or the input means includes an excitation light source that generates the excitation light, and a multiplexer that combines the excitation light and the signal light from the excitation light source,
An optical communication system, wherein an insulating heat conductive ring is closely attached to the outside of the semiconductor element, and a heat radiating metal ring is closely attached to the outside of the insulating heat conductive ring.   The optical communication system according to claim 1, wherein a wavelength of the pumping light is set to a short wavelength side of 80 to 280 nm of the signal light wavelength.   The optical communication system according to claim 1, wherein the semiconductor element has a quantum well structure or a quantum dot structure.   The optical communication system according to claim 1, further comprising means for intensity-modulating the signal light so that a signal light output power per channel in the wavelength division multiplexing system from the semiconductor element is -10 dBm or less.   2. The optical communication system according to claim 1, further comprising means for phase-modulating or frequency-modulating the signal light so that signal light output power per channel in the wavelength division multiplexing system from the semiconductor element is -5 dBm or less.   The optical communication system according to claim 1, wherein the excitation light wavelength is installed on a short wavelength side of a zero dispersion wavelength of the transmission fiber. Installed in the previous stage of the semiconductor optical amplifier, a demultiplexer for demultiplexing the signal light and the excitation light, a branching unit connected to the demultiplexing unit, and a first output port of the branching unit A first multiplexer that combines the signal light and the excitation light, and a second multiplexer that is connected to the second output port of the branching device and combines the signal light and the excitation light. With
The optical communication system according to claim 1, wherein the excitation light emitted from the first multiplexer and the excitation light emitted from the second multiplexer are incident on the semiconductor optical amplifier. A circulator that inputs the signal light and pump light from the first port, a polarization beam splitter connected to the second port of the circulator, and a fiber ring that connects the polarization beam splitter and the semiconductor optical amplifier And
The optical communication system according to claim 1, wherein only one arm of the fiber ring is rotated by 90 degrees and connected to the semiconductor optical amplifier.   The optical communication system according to claim 1, wherein the semiconductor element has an active layer and a cladding layer.   The optical communication system according to claim 9, wherein the cladding layer is a non-doped cladding layer or a semi-insulating cladding layer doped with an impurity containing iron. N input means are provided,
The optical communication system according to claim 1, further comprising a branching unit that couples the semiconductor optical amplifying unit and the N input units in a one-to-N manner. A semiconductor optical amplifier applied to the optical communication system according to any one of claims 1 to 11,
The semiconductor element constituting the semiconductor optical amplification unit has a quantum well structure or a quantum dot structure, and is amplified remotely by excitation light to amplify the signal light,
An insulating heat conducting ring is installed in close contact with the outside of the semiconductor element, and a heat dissipating metal ring is installed in close contact with the outside of the insulating heat conducting ring. The semiconductor optical amplifier according to claim 12 , wherein the semiconductor element has an active layer and a cladding layer. 14. The semiconductor optical amplifier according to claim 13 , wherein the cladding layer is a non-doped cladding layer or a semi-insulating cladding layer doped with an impurity containing iron.

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