Optical amplifier and optical communication system

Abstract

Provided is an optical amplifier with a small operating current. An optical amplifier (G) has one or more rare-earth element-doped optical fibers (EF) each including one or more cores (Ce); a number of excitation light sources (L) corresponding to the operating current, which respectively emit excitation light for exciting the rare-earth element doped in the rare-earth element-doped optical fiber (EF), the number of excitation light sources (L) being more than one for each core (Ce) of the rare-earth element-doped optical fiber (EF); and a combining section (PB) which combines the excitation light (Lp) respectively emitted by the number of excitation light sources (L) more than one for each core (Ce), the number of cores (Ce) being two or more in total, and which introduces the excitation light (Lp) combined by the number of excitation light sources (L) more than one for each core (Ce) for each core (Ce).

Description

Technical Field

[0001] This invention relates to optical amplifiers and optical communication systems. Background Technology

[0002] Non-Patent Document 1 discloses an optical communication system having a submarine optical cable and an optical amplifier that is powered from a power supply unit installed at a land site via a power supply line.

[0003] Non-patent literature 1: NEC Technical Publication, 2009, Vol. 62, No. 4, pp. 20-23, 32-35, 44-47

[0004] However, the optical amplifier described in Non-Patent Document 1 has a large operating current, and the resistive loss of the optical communication system increases accordingly with the operating current of the optical amplifier. Therefore, there is a need for an optical amplifier with a small operating current. Summary of the Invention

[0005] Therefore, the object of the present invention is to provide an optical amplifier with low operating current.

[0006] The optical amplifier G of the present invention comprises: one or more rare-earth element-doped optical fibers EF, each comprising one or more fiber cores Ce; excitation light emitting in accordance with the operating current to excite the rare-earth elements doped in the rare-earth element-doped optical fibers EF, and more than one number of excitation light sources L for each fiber core Ce of the rare-earth element-doped optical fibers EF; and a combining unit PB, which combines the excitation light Lp emitted by more than one number of excitation light sources L for each fiber core Ce, wherein there are a total of two or more fiber cores Ce, and introduces the combination of the excitation light Lp emitted by more than one number of excitation light sources L for each fiber core Ce.

[0007] The effects of the invention

[0008] According to the present invention, an optical amplifier with low operating current can be provided. Attached Figure Description

[0009] Figure 1 This is an equivalent circuit diagram of the power supply structure of the optical communication system according to the illustrated implementation.

[0010] Figure 2 This is a diagram illustrating the structure of the optical amplifier according to the first embodiment.

[0011] Figure 3 This is a cross-sectional view illustrating the structure of an erbium-doped optical fiber.

[0012] Figure 4 This is an equivalent circuit diagram of the semiconductor laser driving circuit of the optical amplifier according to the first embodiment.

[0013] Figure 5 This is the first example of a graph showing the relationship between the operating current of an optical amplifier, the power consumption of an optical communication system, and the supply voltage.

[0014] Figure 6 This is the second example of a graph showing the relationship between the operating current of an optical amplifier and the power consumption and supply voltage of an optical communication system.

[0015] Figure 7 This is a diagram illustrating the structure of the optical amplifier involved in the modified example.

[0016] Figure 8 This is a diagram illustrating the structure of the optical amplifier according to the second embodiment.

[0017] Figure 9 This is an equivalent circuit diagram of the semiconductor laser driving circuit of the optical amplifier according to the third embodiment.

[0018] Figure 10 This is a diagram illustrating the semiconductor laser of the optical amplifier according to the fourth embodiment.

[0019] Figure 11 This is an equivalent circuit diagram of the semiconductor laser driving circuit of the optical amplifier according to the fifth embodiment.

[0020] Figure 12 This is a diagram illustrating the structure of the optical amplifier according to the sixth embodiment. Detailed Implementation

[0021] [Description of embodiments of the present invention]

[0022] First, embodiments of the present invention will be described. One aspect of the present invention relates to an optical amplifier comprising: one or more rare-earth-doped optical fibers, each comprising one or more fiber cores; excitation light emitted in response to a driving current to excite rare-earth elements doped in the rare-earth-doped optical fibers, wherein there are more than one number of excitation light sources for each fiber core; and a combining unit that combines the excitation light emitted by more than one number of excitation light sources for each fiber core, wherein there are a total of two or more fiber cores, and the excitation light emitted by more than one number of excitation light sources for each fiber core is combined and introduced relative to each fiber core.

[0023] If the number of more than one excitation source per fiber core is set to K, the aforementioned optical amplifier will combine the light emitted by K excitation sources and direct it to one fiber core to excite that fiber core. With this structure, the driving current of the excitation source required to obtain the optical power to excite the fiber core can be set to approximately 1 / K, thus providing an optical amplifier with a small operating current.

[0024] An optical amplifier is an amplifier that amplifies optical signals directly without converting them into electrical signals. Furthermore, one or more rare-earth-doped optical fibers, each containing one or more cores, include the following types of rare-earth-doped optical fibers: a single rare-earth-doped optical fiber containing one core; a single rare-earth-doped optical fiber containing multiple cores; multiple rare-earth-doped optical fibers, each containing one core; and multiple rare-earth-doped optical fibers, each containing multiple cores. Rare-earth-doped optical fibers containing multiple cores include coupled multi-core fibers, multimode fibers, and uncoupled multi-core fibers. In the following descriptions, "multi-core fiber" is defined as at least one of coupled multi-core fibers, multimode fibers, and uncoupled multi-core fibers.

[0025] The number exceeding one per fiber core refers to either an integer or a decimal. For example, in the case of the optical amplifier described above with four excitation sources for every two fiber cores, the number exceeding one per fiber core is 2. In the case of the optical amplifier described above with three excitation sources for every two fiber cores, the number exceeding one per fiber core is 1.5.

[0026] The operating current of an optical amplifier refers to the current used to operate the amplifier in order to achieve the desired amplification. The drive current used to drive the excitation light source is at least a portion of the operating current of the optical amplifier. Because the drive current is smaller, the operating current of the optical amplifier is also smaller.

[0027] In the aforementioned optical amplifier, more than one excitation light source per fiber core can be driven by drive current supplied from multiple drive circuits connected in series. For example, when supplying drive current to K excitation light sources, if K drive circuits are connected in parallel, approximately equal drive current I needs to be supplied to each of the K drive circuits, thus requiring a total drive current of K×I, increasing the operating current of the optical amplifier. With K drive circuits connected in series, all K drive circuits can be driven by the drive current I, allowing the drive current to be set to approximately 1 / K compared to the case of K drive circuits connected in parallel.

[0028] In the aforementioned optical amplifier, the combining unit can combine excitation light emitted from more than one excitation light source for each fiber core using at least one of the following methods: polarization combining, optical injection synchronization, composite resonator, and master oscillator power amplifier (MOPA). The aforementioned optical amplifier, through various methods or combinations thereof, can combine excitation light emitted from more than one excitation light source for each fiber core.

[0029] Polarization combining refers to the method of combining multiple different polarizations using polarizing elements such as a polarizing beam splitter (PBS). Polarization refers to the regularity of the vibration direction of electromagnetic waves such as light or radio waves. Optical injection synchronization refers to the method of combining multiple different beams using the optical injection synchronization phenomenon. The optical injection synchronization phenomenon refers to the phenomenon where light with a wavelength close to the oscillation wavelength is incident on a self-oscillating semiconductor laser from the outside, thereby introducing the oscillation wavelength of the semiconductor laser to the wavelength of the incident light.

[0030] The composite resonator method refers to the method of combining multiple different lights using a composite resonator. A composite resonator is a resonator in which multiple resonators are connected along a specified direction. The master oscillator output amplifier method refers to the method of combining multiple different lights using a master oscillator output amplifier. The master oscillator output amplifier independently controls the first master oscillator (or seed light) and the high-output second oscillator, and extracts the high-output light from the second oscillator side, which is the result of combining the light emitted by the first and second oscillators respectively.

[0031] In the aforementioned optical amplifier, there may be more than one excitation source per fiber core, at least a portion of which comprises a semiconductor laser group. This semiconductor laser group includes multiple semiconductor lasers connected in series, and the multiple semiconductor lasers within the semiconductor laser group are driven by a common driving current. The phrase "at least a portion of which comprises a semiconductor laser group" includes two cases: the case where more than one excitation source per fiber core is composed of multiple such semiconductor laser groups, and the case where a portion of the excitation source comprises such a semiconductor laser group.

[0032] For example, when the drive circuit driving the excitation light source has a current source, and this current source includes a resistor, the more the number of drive circuits increases, the greater the voltage drop becomes, and the greater the operating current of the optical amplifier becomes. In contrast, the optical amplifier described above drives multiple semiconductor lasers within a semiconductor laser array with a common drive current, thereby reducing the number of drive circuits corresponding to the number of semiconductor laser arrays. This suppresses the voltage drop and reduces the operating current of the optical amplifier. Furthermore, by reducing the number of drive circuits, the area required to configure the drive circuits can be reduced.

[0033] In the aforementioned optical amplifier, the rare-earth-doped fiber is preferably a multi-core fiber with multiple cores covered by a single cladding. The multi-core fiber characteristic of the optical amplifier increases the number of cores, which aims to enhance the suppression of the operating current of the optical amplifier for each core.

[0034] When the rare-earth-doped fiber is a coupled multi-core fiber, the power coupling coefficient between adjacent cores is preferably 10[ / m] or higher. In an optical amplifier with practical characteristics, the length of the rare-earth-doped fiber is set to approximately 10[m] or higher. In this case, using a coupled multi-core fiber with a power coupling coefficient of 10[ / m] or higher between adjacent cores effectively suppresses mode-dependent gain (MDG). Due to the redundancy obtained by suppressing MDG, the optical amplifier can reduce the gain difference between modes even when the optical power of the excitation light introduced into each core deviates significantly from the optimal state.

[0035] The power coupling coefficient is the ratio of the power of components coupled to other waveguide modes per unit length in a given waveguide mode transmission, and is defined as a coefficient in the power coupling equation. [m] represents the unit of meter, and [ / m] represents the reciprocal of the meter. Below, the English text marked in brackets [] refers to units.

[0036] Furthermore, the optical communication system of the present invention includes one or more optical fibers for transmitting optical signals and the aforementioned optical amplifier for amplifying the optical signals transmitted by the optical fibers. By including the aforementioned optical amplifier in this optical communication system, the operating current of the optical amplifier can be reduced, thereby reducing the resistive loss of the optical communication system. In addition, suppressing the temperature rise of components such as the excitation light source and power transistors of the optical amplifier can extend the lifespan of each component.

[0037] [Detailed Description of Embodiments of the Invention]

[0038] Hereinafter, specific examples of optical amplifiers according to embodiments of the present invention will be described with reference to the accompanying drawings. Furthermore, the present invention is not limited to these examples, but is shown in the claims and includes all modifications equivalent to and within the scope of the claims. Additionally, in the description, the same reference numerals are used for the same elements or elements having the same function, and repetitive descriptions are appropriately omitted.

[0039] [Implementation Method]

[0040] (Structure of optical communication system 100)

[0041] An optical communication system 100 having the optical amplifier G according to an embodiment of the present invention will be described. The optical communication system 100 is, for example, a submarine optical cable system that uses a submarine optical cable that crosses the Pacific Ocean for long-distance optical communication between Japan and the United States. The optical communication system 100 includes one or more optical fibers for transmitting optical signals and an optical amplifier G for amplifying the optical signals transmitted through the optical fibers.

[0042] One or more optical fibers are installed within a submarine optical cable. In the optical communication system 100, multiple repeaters are configured on the submarine along the transmission path of the optical fiber to compensate for transmission loss of the optical signal transmitted through the optical fiber. Optical amplifiers G are respectively installed in these multiple repeaters.

[0043] Figure 1 This is an equivalent circuit diagram illustrating the structure of a power supply system in an optical communication system 100 that supplies power to multiple repeaters. The optical communication system 100, as a power supply system, includes a first power supply unit 10, a second power supply unit 20, and power supply lines PL1 to PL2. N+1 In addition, N is a natural number, and power supply line PL1 and power supply line PL N+1 The suffixes (subscripts) are used to distinguish the N+1 power supply lines individually. In the following description, unless otherwise specified, the suffixes are sometimes omitted and the lines are collectively referred to as power supply line PL. This also applies to repeaters T, optical amplifiers G, semiconductor lasers L, driver circuits D, and erbium-doped fiber EF, which are marked with suffixes in the following description.

[0044] In optical communication systems, to improve the reliability of the power supply system, power supply devices capable of providing the required power are set up at multiple land stations. A land station refers to a location on land where submarine optical cables laid from the seabed are brought up.

[0045] In the optical communication system 100, a first power supply unit 10 is located at a first land station (e.g., Japan), supplying a constant DC current to the repeaters from a DC current source Ai. A second power supply unit 20 is located at a second land station (e.g., the United States), supplying a constant DC current to the repeaters from a DC current source Ao. Both the first power supply unit 10 and the second power supply unit 20 are grounded in the sea. The optical communication system 100 provides power to both sites, enabling power supply to be shared between the first and second land stations.

[0046] Power supply line PL1 to power supply line PL N+1 It is to transfer the power supplied from the first power supply device 10 and the second power supply device 20 to the series-connected repeaters T1 to T2. N+1 Separate power supply paths.

[0047] Voltage Vs represents the voltage from repeater T1 to repeater T. N+1 The overall supplied voltage. Voltage VL1 to voltage VL N+1 Indicates the connection between repeater T1 and repeater T. N+1 The voltage supplied in pairs. Resistors R1 to R... N+1 Indicates the connection between power supply line PL1 and power supply line PL N+1 Each resistor is in pairs.

[0048] In submarine optical cable systems such as optical communication system 100, through resistor R1 to resistor R N+1 Resistance loss occurs due to the resistance of the repeater. Resistance loss is proportional to the square of the current, so it is preferable to reduce the supplied current. However, in submarine optical cable systems, the voltage-to-current ratio adjustment is limited in order to supply DC power to the repeater, requiring the required current to flow through the power supply line. Therefore, to reduce resistance loss in submarine optical cable systems, the optical amplifiers included in the repeaters must have low operating current.

[0049] [First Implementation]

[0050] (Structure of optical amplifier G)

[0051] Reference Figure 2 and Figure 3 The structure of the optical amplifier G is explained. Figure 2 This is a diagram illustrating the structure of the optical amplifier G included in the repeater T of the optical communication system 100. Figure 3 This is a cross-sectional view illustrating the structure of the erbium-doped fiber EF in the optical amplifier G. Figure 3 The cross-sectional view corresponds to a diagram of the erbium-doped fiber EF viewed from the direction of light transmission when the erbium-doped fiber EF is cut using a plane approximately orthogonal to the direction of light transmission.

[0052] like Figure 2As shown, repeater T includes optical amplifier G1, optical amplifier G2, and optical amplifier G... M Including M optical amplifiers G. Furthermore... Figure 1 The repeaters T1 to T2 shown N+1 All have with Figure 2 The structure shown is the same. M is a natural number representing the number of fiber cores (hereinafter referred to as "signal cores") included in an optical fiber that transmits optical signals in any direction, either uplink from the first land station to the second land station or downlink from the second land station to the first land station. In this embodiment, M is 8. However, it is not limited to this, and the value of M can be appropriately changed.

[0053] Repeater T is connected to an uplink fiber Fu that transmits optical signals from the first land station side to the second land station side, and a downlink fiber Fd that transmits optical signals from the second land station side to the first land station side. The uplink fiber Fu consists of signal cores Cs1, Cs3, and Cs... 2M－1 Eight signal cores Cs, including the odd-numbered signal core Cs, are covered by a single cladding in a multi-core optical fiber. The downlink fiber Fd consists of signal cores Cs2, Cs4, and Cs... 2M The eight signal cores Cs, including the even-numbered signal core Cs, are a multi-core optical fiber covered by a single cladding. The uplink fiber Fu and the downlink fiber Fd transmit, for example, a signal light Ls with a wavelength of approximately 1550 nm as an optical signal. However, the wavelength of the signal light Ls is not limited to approximately 1550 nm and can be appropriately varied.

[0054] Optical amplifier G amplifies the signal light Ls that enters from the first land station side via uplink fiber Fu and is transmitted to repeater T, so that the amplified signal light Ls is transmitted to the second land station side via uplink fiber Fu. Additionally, optical amplifier G amplifies the signal light Ls that enters from the second land station side via downlink fiber Fd and is transmitted to repeater T, so that the amplified signal light Ls is transmitted to the first land station side via downlink fiber Fd.

[0055] exist Figure 2 Optical amplifier G comprises an erbium-doped fiber EF, a semiconductor laser L, and polarization elements PB. More specifically, optical amplifier G1 comprises four semiconductor lasers L (erbium-doped fiber EF1, erbium-doped fiber EF2, and semiconductor lasers L1 to L4) and two polarization elements PB1 to PB2. Optical amplifier G2 comprises four semiconductor lasers L (erbium-doped fiber EF3, erbium-doped fiber EF4, and semiconductor lasers L5 to L8) and two polarization elements PB3 to PB4. Optical amplifier G... M Erbium-doped fiber EF2M－1 Erbium-doped fiber EF 2M Semiconductor laser L 4M－3 To semiconductor laser L 4M These four semiconductor lasers L, and polarization element PB 2M－1 To PB 2M These two polarization elements are PB.

[0056] Erbium-doped fiber (EF) is an example of one or more rare-earth element-doped optical fibers, each comprising one or more cores. Ce, the core (hereinafter referred to as the "excitation core") that amplifies the signal light in the rare-earth element-doped optical fiber, is an example of one or more cores contained in the rare-earth element-doped optical fiber.

[0057] like Figure 3 For example, erbium-doped fiber EF 2M－1 and erbium-doped fiber EF 2M These are multi-core fibers where eight excitation cores (Ce) are covered by a single cladding (CL). Additionally, there are erbium-doped fibers EF1 to erbium-doped fibers EF... 2M All erbium-doped optical fibers (EF) have the same structure.

[0058] In this embodiment, the uplink fiber Fu and the downlink fiber Fd are also multi-core fibers in which eight signal cores Cs are covered by a single cladding CL. In this embodiment, a structure is shown where the number of signal cores Cs and the number of excitation cores Ce are equal, but the two numbers do not necessarily have to be equal.

[0059] Erbium-doped fiber EF 2M－1 With excitation core Ce1 to Ce 2M－1 These 8 excitation fiber cores Ce, respectively passing through the odd-numbered signal fiber core Cs1 to the signal fiber core Cs 2M－1 The transmitted signal light Ls is amplified. Erbium-doped fiber EF 2M With excitation core Ce2 to Ce 2M These 8 excitation fiber cores Ce, respectively passing through the even-numbered signal fiber core Cs2 to the signal fiber core Cs 2M The transmitted signal light Ls is amplified. When using a coupled multi-core fiber as erbium-doped fiber EF, the power coupling coefficient between adjacent excitation cores Ce among the multiple excitation cores Ce is preferably 10[ / m] or higher.

[0060] exist Figure 2A semiconductor laser L is an example of an excitation source that emits excitation light Lp that excites erbium doped in an erbium-doped fiber EF in accordance with the driving current. The semiconductor laser L, for example, emits excitation light Lp with a wavelength of approximately 1480 nm or approximately 980 nm capable of exciting erbium. However, the excitation source is not limited to a semiconductor laser L; any other source can be used as long as it can emit excitation light with a wavelength capable of exciting erbium.

[0061] In this embodiment, the optical amplifier G has two semiconductor lasers L for each excitation core Ce of the erbium-doped fiber EF. Specifically, in order to amplify the signal light Ls transmitted through a total of 16 signal cores Cs contained in the uplink fiber Fu and downlink fiber Fd respectively, the optical amplifier G has 16 excitation cores Ce of the erbium-doped fiber EF. In addition, the optical amplifier G has two semiconductor lasers L for each excitation core Ce of the erbium-doped fiber EF, and a total of 32 semiconductor lasers L.

[0062] Semiconductor lasers L1 and L2 are used for erbium-doped excitation fiber core Ce1. Semiconductor lasers L3 and L4 are used for erbium-doped excitation fiber core Ce2. Semiconductor lasers L5 and L6 are used for erbium-doped excitation fiber core Ce3. Semiconductor lasers L7 and L8 are used for erbium-doped excitation fiber core Ce4. 4M－3 and semiconductor laser L 4M－2 Doping Ce in the excitation core 2M－1 Erbium excitation. Semiconductor laser L 4M－1 and semiconductor laser L 4M Doping Ce in the excitation core 2M Erbium excitation.

[0063] In optical amplifier G1, excitation light Lp emitted by semiconductor lasers L1 and L2 is incident on polarization element PB1. Polarization element PB1 is an example of a combining unit that combines the excitation light Lp emitted by semiconductor lasers L1 and L2 (two for each excitation fiber core Ce). The method of combining the excitation light Lp by polarization element PB1 corresponds to the polarization combining method.

[0064] The polarization element PB1 is a polarization beam splitter containing an optical surface that allows the P-polarized component to pass through and reflects the S-polarized component. For example, the polarization element PB1 combines the P-polarized linearly polarized light (excitation light Lp) emitted from semiconductor laser L1 by allowing it to pass through and reflecting the S-polarized linearly polarized light (excitation light Lp) emitted from semiconductor laser L2. By utilizing polarization, the polarization element PB1 can efficiently combine the excitation lights Lp emitted from semiconductor lasers L1 and L2, respectively. The excitation light Lp emitted from semiconductor laser L is not limited to linearly polarized light; it can also be elliptically polarized light, etc., but linearly polarized light is preferred from the viewpoint of suppressing optical loss.

[0065] Similarly, the excitation light Lp emitted by semiconductor lasers L3 and L4 is injected into polarization element PB2 and synthesized by polarization element PB2.

[0066] The excitation light Lp synthesized by polarization element PB1 and the excitation light Lp synthesized by polarization element PB2 are respectively injected into 3dB coupler B1. 3dB coupler B1 is a passive optical element that, after synthesizing the two incoming lights, branches them into two with a branching ratio of approximately 1:1. One of the excitation lights Lp branched from 3dB coupler B1 is guided towards pump combiner P1 and then injected into pump combiner P1.

[0067] The pump combiner P1 is, for example, a wavelength division multiplexing (WDM) coupler. One of the excitation beams Lp branched from the 3dB coupler B1 is combined with the signal beam Ls transmitted from the signal core Cs1 by the pump combiner P1, and together with the signal beam Ls, is injected into the excitation core Ce1 of the erbium-doped fiber EF1.

[0068] In other words, the excitation light Lp emitted by the two semiconductor lasers L1 and L2 is combined by the polarization element PB1 and then introduced into the excitation fiber core Ce1 via the pump combiner P1.

[0069] Erbium-doped fiber EF1 excites the erbium doped in the excitation core Ce1 with incoming excitation light Lp, thereby forming an inverted distribution. The erbium ions in the inverted distribution state amplify the signal light Ls transmitted through erbium-doped fiber EF1 through stimulated emission. The amplified signal light Ls is then transmitted again towards the second land station side through the signal core Cs1.

[0070] On the other hand, another excitation light Lp from the excitation light Lp branched out by the 3dB coupler B1 is injected into the pump combiner P2, and after merging with the signal light Ls transmitted through the signal fiber core Cs2, it is injected together with the signal light Ls into the excitation fiber core Ce2 of the erbium-doped fiber EF2.

[0071] Erbium-doped fiber EF2 excites the erbium doped in the Ce2 core by an incoming excitation light Lp, thereby creating an inverted distribution. The erbium ions in the inverted distribution state amplify the signal light Ls transmitted through EF2 via stimulated emission. The amplified signal light Ls is then directed towards the first land station and transmitted again through the signal core Cs2.

[0072] Optical amplifier G1 amplifies the signal light Ls transmitted through the signal core Cs1 of the uplink fiber Fu and the signal light Ls transmitted through the signal core Cs2 of the downlink fiber Fd in pairs, thereby redundanting the relay connection through repeater T. That is, even if some of the semiconductor lasers L1 to L4 fail to emit excitation light Lp due to faults, optical amplifier G1 can still disperse their influence, preventing a portion of the optical signal transmitted through the uplink fiber Fu and the downlink fiber Fd from being unamplified.

[0073] Similarly, optical amplifier G2 amplifies the signal light Ls transmitted through signal fiber cores Cs3 and Cs4 by using the excitation light Lp emitted from each of the semiconductor lasers L5 to L8. M By using a semiconductor laser L 4M－3 To semiconductor laser L 4M The excitation light Lp emitted by each semiconductor laser L causes the light passing through the signal fiber core Cs to... 2M－1 and signal fiber core Cs 2M The transmitted signal light Ls is amplified.

[0074] Optical amplifier G2 to optical amplifier G M Except for the signal fiber core Cs, which is the object of optical amplification, the structure and function are the same as those of optical amplifier G1.

[0075] (Example of the structure of the driving circuit D for a semiconductor laser L)

[0076] Figure 4 This is an equivalent circuit diagram illustrating the structure of the drive circuit D that drives the semiconductor laser L contained in the optical amplifier G. The optical amplifier G drives the semiconductor laser L1 to the semiconductor laser L2... 4M (M=8) These 32 semiconductor lasers L are driven by driving circuits D1 to D2. 4MThese are 32 driving circuits D. Driving circuits D1 to D2 are... 4M Series connection. Drive circuit D1 to drive circuit D... 4M Corresponding to at least a portion of the operating current S supplied from the first power supply device 10, namely the drive current I, the semiconductor laser L1 to the semiconductor laser L2 are turned... 4M Each semiconductor laser L is driven to emit light. Voltage VL represents the voltage supplied to the repeater T.

[0077] exist Figure 4 The drive circuit D1 has a constant voltage circuit Cv1 and a constant current circuit Ci1. The constant voltage circuit Cv1 includes a Zener diode Z1, which provides constant voltage control in a manner that keeps the reference voltage Vr across the drive circuit D1 approximately constant.

[0078] The constant current circuit Ci1 includes current sources A11 and A21 to perform constant current control in a manner that keeps the current flowing in the drive circuit D1 approximately constant. Current source A11 is connected in series with the semiconductor laser L1 to supply current in a manner that keeps the drive current I1 flowing in the semiconductor laser L1 approximately constant. Current source A12 is connected in parallel with the semiconductor laser L1 to supply current to the drive circuit D1 other than that flowing through the semiconductor laser L1. s1 The current is supplied in a roughly constant manner. Drive current I1, current I... s1 and the reference current I flowing through the constant voltage circuit Cv1 r After flowing through drive circuit D1, the currents combine and are supplied to drive circuit D2 as the operating current S. Reference current I r Drive current I1 and current I s1 The sum of these is approximately equal to the operating current S.

[0079] Drive circuit D2 to drive circuit D 4M The structure and function of the drive circuit are the same as those of the drive circuit D1, except that the semiconductor laser L, which is the object being driven, is different.

[0080] (The effect of the optical amplifier G)

[0081] As described above, the optical amplifier G according to this embodiment includes: an erbium-doped fiber EF (rare-earth element-doped fiber) comprising eight excitation fiber cores Ce; and two semiconductor lasers L (excitation light sources) that emit excitation light Lp corresponding to the driving current to excite the erbium (rare-earth element) doped in the erbium-doped fiber EF for each excitation fiber core Ce. Furthermore, the optical amplifier G includes a polarization element PB (combining unit) that combines the excitation light Lp emitted by the two semiconductor lasers L for each excitation fiber core Ce. There are a total of eight excitation fiber cores Ce, and the excitation light Lp emitted by the two semiconductor lasers L for each of the eight excitation fiber cores Ce is combined and introduced.

[0082] Optical amplifier G drives two semiconductor lasers L together via a drive current I, and excites a single excitation fiber core Ce by combining the excitation beams Lp emitted by the two semiconductor lasers L. Therefore, compared to the case where a single excitation fiber core is excited by excitation beam from a single semiconductor laser, optical amplifier G can set the drive current I to approximately half. By reducing the drive current I, an optical amplifier with a small operating current can be provided.

[0083] Here, Figure 5 and Figure 6 This figure illustrates the simulation results showing the relationship between the operating current of the optical amplifier, the power consumption of the optical communication system, and the voltage supplied to the optical communication system. Figure 5 This illustrates the case where the excitation core Ce has 4 elements. Figure 6 The case where the excitation core Ce is 8 is shown.

[0084] Figure 5 and Figure 6 The horizontal axis represents the operating current of the optical amplifier [A], and the vertical axis represents the power consumption [kW] and supply voltage [kV]. Additionally, Figure 5 and Figure 6 The dashed curve represents the supplied voltage, and the solid curve represents the consumed electricity.

[0085] exist Figure 5 The power consumption Gp1X shows the power consumption of the optical amplifier GX involved in the comparative example, and the supply voltage Gv1X shows the supply voltage of the optical amplifier GX involved in the comparative example. The comparative example is the result obtained by simulation based on numerical conditions as described in Non-Patent Document 1. The power consumption Gp1 shows the power consumption of the optical amplifier G involved in this embodiment, and the supply voltage Gv1 shows the supply voltage of the optical amplifier G involved in this embodiment.

[0086] Similarly, in Figure 6The power consumption Gp2X shows the power consumption of the optical amplifier GX in the comparative example, and the supply voltage Gv2X shows the supply voltage of the optical amplifier GX in the comparative example. The power consumption Gp2 shows the power consumption of the optical amplifier G in this embodiment, and the supply voltage Gv2 shows the supply voltage of the optical amplifier G in this embodiment.

[0087] The operating current of optical amplifier GX is approximately 1.1 [A], while the operating current of optical amplifier G is approximately half that, around 0.5 [A]. Figure 5 For example, as the operating current decreases, the power consumption Gp1 decreases to about 6 kW relative to the power consumption Gp1X of about 12 kW. Furthermore, the supply voltage Gv1 decreases to about 9 kV relative to the supply voltage Gv1X of about 11 kV.

[0088] exist Figure 6 For example, the power consumption Gp2 decreased to about 9 kW compared to the power consumption Gp2X of about 15 kW. In addition, the supply voltage Gv1 increased by about 1 kV to about 15 kV compared to the supply voltage Gv2X of about 14 kV.

[0089] Based on these results, it can be seen that by incorporating the optical amplifier G according to this embodiment, the resistive loss of the optical communication system is reduced, and the power consumption of the optical communication system can be reduced to about half that of the comparative example. Furthermore, it can be seen that the supply voltage is reduced compared to the comparative example, or if it increases, the increase is only slight.

[0090] (Modified Example)

[0091] The optical amplifier Ga involved in the modified example will be described. Furthermore, elements that are the same as or have the same function as those in the first embodiment will use the same reference numerals, and repeated descriptions will be omitted where appropriate. This also applies to the other embodiments described thereafter.

[0092] In this variant, the optical amplifier Ga has three semiconductor lasers L for every two excitation cores Ce of the erbium-doped fiber EF.

[0093] Figure 7 This is a diagram illustrating the structure of the optical amplifier Ga contained in the repeater Ta. Figure 7Optical amplifier Ga1 comprises three semiconductor lasers (L1, L2, L1 to L3) and three polarization elements (PB1 to PB3). Optical amplifier Ga2 comprises three semiconductor lasers (L4, L4 to L6) and three polarization elements (PB4 to PB6). M Erbium-doped fiber EF 2M－1 Erbium-doped fiber EF 2M Semiconductor laser L 3M－2 To semiconductor laser L 3M These three semiconductor lasers L and polarization element PB 3M－2 To PB 3M These three polarization elements are PB.

[0094] To amplify the signal light Ls transmitted through a total of 16 signal cores Cs contained in the uplink fiber Fu and downlink fiber Fd, the optical amplifier Ga has 16 excitation cores Ce of the erbium-doped fiber EF. Furthermore, the optical amplifier Ga has three semiconductor lasers L for every two excitation cores Cea of ​​the erbium-doped fiber EF.

[0095] In optical amplifier Ga1, excitation light Lp emitted from semiconductor laser L1 enters polarization element PB1. Excitation light Lp emitted from semiconductor laser L2 enters polarization element PB2. Excitation light Lp emitted from semiconductor laser L3 enters polarization element PB3.

[0096] A portion of the excitation light Lp emitted by semiconductor laser L2, polarized by polarization element PB2, and the excitation light Lp emitted by semiconductor laser L1 are combined and injected into 3dB coupler B1. Similarly, a portion of the excitation light Lp emitted by semiconductor laser L2, polarized by polarization element PB2, and the excitation light Lp emitted by semiconductor laser L3 are combined and injected into 3dB coupler B1.

[0097] The excitation light Lp emitted by the semiconductor laser L2 is preferably polarized by the polarization element PB2 with approximately equal optical power, and the difference in optical power between the polarizations is particularly preferably less than 1 [dB].

[0098] After combining the two incoming excitation beams Lp, the 3dB coupler B1 branches them into two beams with a branching ratio of approximately 1:1. One of the excitation beams Lp branched from the 3dB coupler B1 is injected into the pump combiner P1, where it merges with the signal beam Ls transmitted through the signal core Cs1. Together with the signal beam Ls, they are injected into the excitation core Ce1 of the erbium-doped fiber EF1. The erbium in the erbium-doped fiber EF1 is inverted by the excitation beams Lp, thus amplifying the signal beam Ls passing through the erbium-doped fiber EF1.

[0099] On the other hand, another excitation light Lp branched from the 3dB coupler B1 is injected into the pump combiner P2, where it merges with the signal light Ls transmitted through the signal core Cs2. Together with the signal light Ls, they are injected into the excitation core Ce2 of the erbium-doped fiber EF2. The erbium in the erbium-doped fiber EF2 is inverted by the erbium excited by the excitation light Lp, thus amplifying the signal light Ls passing through the erbium-doped fiber EF2.

[0100] Similarly, optical amplifier Ga2 amplifies the signal light Ls transmitted through signal fiber cores Cs3 and Cs4 by using excitation light Lp emitted from semiconductor lasers L4 to L6. M By using a semiconductor laser L 3M－2 To semiconductor laser L 3M The excitation light Lp emitted by each semiconductor laser L causes the light passing through the signal fiber core Cs to... 2M－1 and signal fiber core Cs 2M The transmitted signal light Ls is amplified.

[0101] Optical amplifier Ga2 to optical amplifier Ga M Except for the difference in the signal fiber core Cs of the optical amplifier, its structure and function are the same as those of the optical amplifier Ga1.

[0102] The drive circuit that drives the semiconductor laser L in the optical amplifier Ga, besides matching the number of semiconductor lasers L to 3M, is also... Figure 4 The driving circuit D shown is the same.

[0103] As described above, the optical amplifier Ga drives three semiconductor lasers L together via a drive current I, and excites two excitation fiber cores Ce by combining the excitation light Lp emitted by the three semiconductor lasers L. Therefore, compared to the case where the excitation fiber cores are excited by excitation light from a single semiconductor laser, the optical amplifier Ga can set the drive current I to approximately 2 / 3. Reducing the drive current I provides an optical amplifier with a low operating current.

[0104] In the first embodiment, an example is shown where excitation light Lp emitted by four semiconductor lasers L for every two excitation fiber cores Ce is combined and introduced. In a modified example, an example is shown where excitation light Lp emitted by three semiconductor lasers L for every two excitation fiber cores Ce is combined and introduced, but the embodiment is not limited to this. As long as there are a total of two or more excitation fiber cores, and excitation light is introduced for each excitation fiber core by combining excitation light emitted by more than one semiconductor laser L for each fiber core Ce, the number of excitation fiber cores Ce and the number of semiconductor lasers L are not particularly limited.

[0105] [Second Implementation]

[0106] The optical amplifier Gb according to the second embodiment will be described. In this embodiment, the optical amplifier Gb synthesizes the excitation light Lp emitted by more than one number of semiconductor lasers L for each excitation fiber core Ce by optical injection synchronization.

[0107] Figure 8 This is a diagram illustrating the structure of the optical amplifier Gb included in the repeater Tb. Figure 8 The optical amplifier Gb1 has four semiconductor lasers L1 through L4: erbium-doped fiber EF1, erbium-doped fiber EF2, and semiconductor lasers L1 through L4. Semiconductor lasers L1 and L2 are connected in series, and semiconductor lasers L3 and L4 are connected in series.

[0108] Optical amplifier Gb2 has four semiconductor lasers L: erbium-doped fiber EF3, erbium-doped fiber EF4, and semiconductor lasers L5 to L8. Semiconductor lasers L5 and L6 are connected in series, and semiconductor lasers L7 and L8 are connected in series.

[0109] Optical amplifier Gb M Erbium-doped fiber EF 2M－1 Erbium-doped fiber EF 2M and semiconductor laser L 4M－3 To semiconductor laser L 4M These are four semiconductor lasers L. Semiconductor lasers L 4M－3 To semiconductor laser L 4M Among them, semiconductor laser L 4M－3 and semiconductor laser L 4M－2 Series connection, in addition, semiconductor laser L 4M and semiconductor laser L 4M－1 Series connection.

[0110] To amplify the signal light Ls transmitted through a total of 16 signal cores Cs contained in the uplink fiber Fu and downlink fiber Fd, the optical amplifier Gb has 16 excitation cores Ce of the erbium-doped fiber EF. Additionally, the optical amplifier Gb has two semiconductor lasers L for each excitation core Ce of the erbium-doped fiber EF.

[0111] In the optical amplifier Ga1, if excitation light Lp emitted by semiconductor laser L1 is incident on the self-oscillating semiconductor laser L2, a light injection synchronization phenomenon occurs where the oscillation wavelength of semiconductor laser L2 is introduced to the wavelength of the incident excitation light Lp, and the excitation light Lp emitted by semiconductor laser L1 and semiconductor laser L2 are combined. The combined excitation light Lp is then incident on the 3dB coupler B1.

[0112] Similarly, if an excitation light Lp emitted by a semiconductor laser L4 is incident on a self-oscillating semiconductor laser L3, a light injection synchronization phenomenon occurs where the oscillation wavelength of the semiconductor laser L3 is introduced into the wavelength of the incident excitation light Lp, and the excitation light Lp emitted by the semiconductor laser L4 and the excitation light Lp emitted by the semiconductor laser L3 are combined. The combined excitation light Lp is then incident on a 3dB coupler B1.

[0113] After combining the two incoming excitation beams Lp, the 3dB coupler B1 branches them into two beams with a branching ratio of approximately 1:1. One of the branched excitation beams Lp is pumped to the excitation core Ce1 of the erbium-doped fiber EF1 via the pump combiner P1 to excite it with erbium, thereby amplifying the signal beam Ls transmitted through the signal core Cs1. The other branched excitation beam Lp is pumped to the excitation core Ce2 of the erbium-doped fiber EF2 via the pump combiner P2 to excite it with erbium, thereby amplifying the signal beam Ls transmitted through the signal core Cs2.

[0114] Similarly, optical amplifier Gb2 amplifies the signal light Ls transmitted through signal fiber cores Cs3 and Cs4 by using the excitation light Lp emitted from each of the semiconductor lasers L5 to L8. M By using a semiconductor laser L 4M－3 To semiconductor laser L 4M The excitation light Lp emitted by each semiconductor laser L causes the light passing through the signal fiber core Cs to... 2M－1 and signal fiber core Cs 2M The transmitted signal light Ls is amplified.

[0115] Optical amplifier Gb2 to optical amplifier Gb MExcept for the difference in the signal fiber core Cs of the optical amplifier, its structure and function are the same as those of the optical amplifier Gb1.

[0116] The driving circuit that drives the semiconductor laser L in the optical amplifier Gb is connected to Figure 4 The driving circuit D shown is the same.

[0117] As described above, the optical amplifier Gb is synthesized by optical injection synchronization using excitation light Lp emitted from more than one semiconductor laser L for each excitation fiber core Ce. This reduces the drive current I, enabling the optical amplifier to operate with low current.

[0118] [Third Implementation]

[0119] The optical amplifier Gc according to the third embodiment will be described. In this embodiment, the number of semiconductor lasers Lc, which exceeds one for each excitation fiber core Ce, is composed of multiple semiconductor laser groups LG, each semiconductor laser group LG containing multiple semiconductor lasers Lc connected in series. The multiple semiconductor lasers Lc contained in the semiconductor laser group LG are driven by a common driving current. Furthermore, the semiconductor laser group LG is a collective designation for multiple semiconductor laser groups.

[0120] Figure 9 This is an equivalent circuit diagram illustrating the structure of the drive circuit Dc that drives the semiconductor laser Lc included in the optical amplifier Gc. Semiconductor lasers Lc1 to Lc2 are shown. 4M (M=8) These 32 semiconductor lasers Lc are from semiconductor laser group LG1 to semiconductor laser group LG 2M These 16 semiconductor lasers are composed of LG.

[0121] Optical amplifier Gc enables semiconductor laser group LG1 to semiconductor laser group LG 2M These 16 semiconductor laser groups are driven by LG and have drive circuits Dc1 to Dc. 2M These are 16 driving circuits Dc. Driving circuit Dc1 to driving circuit Dc 2M Series connection. From drive circuit Dc1 to drive circuit Dc 2M Corresponding to at least a portion of the operating current S supplied from the first power supply device 10, namely the drive current I, the semiconductor laser Lc1 to the semiconductor laser Lc 4M Each semiconductor laser Lc emission driver.

[0122] Each of the 16 semiconductor laser groups LG comprises two semiconductor lasers Lc connected in series. Specifically, semiconductor laser group LG1 comprises semiconductor lasers Lc1 and Lc2 connected in series. Semiconductor lasers Lc1 and Lc2 are driven by a common drive current I1. Semiconductor laser group LG2 comprises semiconductor lasers Lc3 and Lc4 connected in series. Semiconductor lasers Lc3 and Lc4 are driven by a common drive current I2. 2M Includes a series-connected semiconductor laser Lc 4M－1 and semiconductor laser Lc 4M Semiconductor laser Lc 4M－1 and semiconductor laser Lc 4M Driven by a common driving current I 2M drive.

[0123] Except for the structure of the semiconductor laser Lc, the structure and function of the driving circuit Dc are the same as those of the driving circuit D described in the first embodiment.

[0124] The optical amplifier Gc drives two semiconductor lasers Lc through a common drive current I. Therefore, compared to the optical amplifier G according to the first embodiment, it reduces the number of drive circuits Dc required to drive two semiconductor lasers Lc for each excitation fiber core Ce, and also reduces the number of current sources A1. This suppresses voltage drop in the optical amplifier Gc, reducing its operating current. Furthermore, the reduced number of drive circuits Dc in the optical amplifier Gc allows for a smaller arrangement area of ​​the drive circuits Dc. Other than these, the effects are the same as in the first embodiment.

[0125] The number of semiconductor lasers Lc constituting the semiconductor laser array LG is not limited to two; it can also be three or more. Furthermore, the driving circuit Dc can be applied to both the optical amplifier Ga and the optical amplifier Gb. For example, when the driving circuit Dc is applied to the optical amplifier Ga, three semiconductor lasers Lc can be configured in one driving circuit Dc.

[0126] [Fourth Implementation]

[0127] The optical amplifier Gd according to the fourth embodiment will be described. In this embodiment, the optical amplifier Gd synthesizes the excitation light Lp emitted by more than one semiconductor laser Ld for each excitation fiber core Ce through a composite resonator.

[0128] Figure 10 This is a diagram illustrating semiconductor lasers Ld1 and Ld2, which are among the multiple semiconductor lasers Ld included in the optical amplifier Gd.

[0129] like Figure 10 As shown, semiconductor lasers Ld1 and Ld2 are cascaded along the resonant direction 50 to form a composite resonator. Semiconductor lasers Ld1 and Ld2 have an upper surface electrode 51, a lower surface electrode 52, and a current blocking layer 53 on the upper surface electrode 51 side. Furthermore, each of semiconductor lasers Ld1 and Ld2 has an anti-reflective film 54 on its facing end faces. Reflective surfaces are provided on the opposite end faces of both semiconductor lasers Ld1 and Ld2. The upper surface electrode 51 is connected to a current source A11 via a wiring 55.

[0130] The driving current I1 is supplied from the current source A11 through wiring 55 and the upper surface electrode 51 to the semiconductor laser Ld1. After flowing through the semiconductor laser Ld1, the driving current I1 is supplied to the semiconductor laser Ld2 through wiring 56. That is, a common driving current I1 is supplied to both semiconductor lasers Ld1 and Ld2.

[0131] Semiconductor lasers Ld1 and Ld2 cause the light emitted by the driving current I1 flowing through each active layer 57 to reciprocate along the resonant direction 50 within the active layer 57, oscillating to produce laser light through stimulated emission. The combined laser light emitted by semiconductor lasers Ld1 and Ld2 is then output as excitation light Lp towards the output direction 58.

[0132] The current blocking layer 53 is provided, for example, to seal light within the active layer 57. The anti-reflection film 54 is provided, for example, to prevent reflection at the boundary between semiconductor lasers Ld1 and Ld2 when light oscillates back and forth within the active layer 57 along the resonant direction 50, thereby improving the oscillation efficiency of the laser.

[0133] The driving circuit of the optical amplifier Gd can be applied Figure 9 The driving circuit Dc. In this case, Figure 10 semiconductor laser Ld1 and Figure 9 Corresponding to the semiconductor laser Lc1, Figure 10 semiconductor laser Ld2 and Figure 9 The semiconductor laser Lc2 corresponds to this.

[0134] Among the multiple semiconductor lasers Ld contained in the optical amplifier Gd, the semiconductor lasers Ld other than semiconductor lasers Ld1 and Ld2 have the same structure and function as semiconductor lasers Ld1 and Ld2.

[0135] As described above, the optical amplifier Gd is synthesized by combining the excitation light Lp emitted by more than one semiconductor laser Ld for each excitation fiber core Ce through a composite resonator. This reduces the drive current I, enabling the optical amplifier to operate with low current.

[0136] Furthermore, the optical amplifier Gd drives the two semiconductor lasers Ld through a common drive current I. Therefore, compared to the optical amplifier G according to the first embodiment, it reduces the number of drive circuits Dc supplying drive current to the two semiconductor lasers Ld for each excitation fiber core Ce, and reduces the number of current sources A1. As a result, the optical amplifier Gd suppresses voltage drop and reduces its operating current. Additionally, the optical amplifier Gd reduces the number of drive circuits, thereby reducing the area of ​​the drive circuitry. Other than these, the effects are the same as in the first embodiment.

[0137] In this embodiment, the synthesis of the excitation light Lp is illustrated using a composite resonator method, but a master oscillator output amplifier method can also be applied. In the case of the master oscillator output amplifier method, in Figure 10 Semiconductor laser Ld1 corresponds to the first oscillator, and semiconductor laser Ld2 corresponds to the second oscillator. The first oscillator is, for example, a highly stable oscillator for generating high-quality beams. The second oscillator is, for example, a high-output oscillator. The high-output excitation light Lp, resulting from the combination of the excitation light Lp emitted by semiconductor laser Ld1 and the excitation light Lp emitted by semiconductor laser Ld2, is extracted from the semiconductor laser Ld2 side along the output direction 58.

[0138] [Fifth Implementation]

[0139] The optical amplifier Ge according to the fifth embodiment will be described. In this embodiment, the number of semiconductor lasers Le, which is more than one for each excitation fiber core Ce, is configured in a portion comprising a semiconductor laser group LG, which includes a plurality of semiconductor lasers Le connected in series. The plurality of semiconductor lasers Le included in the semiconductor laser group LG are driven by a common driving current.

[0140] The structure of the optical amplifier Ge can be applied to... Figure 7 The repeater Ta shown has the same structure as the optical amplifier Ga.

[0141] Figure 11 This is an equivalent circuit diagram illustrating the structure of the drive circuit De that drives the semiconductor laser Le contained in the optical amplifier Ge. Drive circuit De1 to drive circuit De2 2M Series connection. Drive circuit De1 to drive circuit De 2MCorresponding to at least a portion of the operating current S supplied from the first power supply device 10, namely the drive current I, the semiconductor laser Le1 to the semiconductor laser Le 4M Each semiconductor laser Lc emission driver.

[0142] In the driving circuit De1 to the driving circuit De 2M The odd-numbered driving circuit De is equipped with a semiconductor laser Le. The even-numbered driving circuit De is equipped with a semiconductor laser group LG comprising two semiconductor lasers Le connected in series.

[0143] Specifically, a semiconductor laser Le1 is provided in the driving circuit De1. A semiconductor laser group LG2, comprising semiconductor lasers Le2 and Le3 connected in series, is provided in the driving circuit De2. Semiconductor lasers Le2 and Le3 are driven by a common driving current I2. In the driving circuit De... 2M The device includes a semiconductor laser Le connected in series. 3M－1 and semiconductor laser Le 3M LG's semiconductor laser array 2M Semiconductor laser Le 3M－1 and semiconductor laser Le 3M Driven by a common drive current I2.

[0144] Except for the structure of the semiconductor laser Le, the structure and function of the driving circuit De are the same as those of the driving circuit D described in the first embodiment.

[0145] As described above, the optical amplifier Ge drives three semiconductor lasers Le together with a drive current I, and excites two excitation fiber cores Ce by combining the excitation light Lp emitted by the three semiconductor lasers Le respectively into an excitation light Lp. Therefore, compared to the case where the excitation fiber cores are excited by excitation light from a single semiconductor laser, the optical amplifier Ge can set the drive current I to approximately 2 / 3. By reducing the drive current I, an optical amplifier with a small operating current can be provided.

[0146] Furthermore, the optical amplifier Ge drives two of the three semiconductor lasers Le using a common drive current I. Therefore, compared to the optical amplifier G of the first embodiment, it reduces the number of drive circuits De supplying drive current to the three semiconductor lasers Le for each pair of excitation fiber cores Ce, and reduces the number of current sources A1. This allows the optical amplifier Ge to suppress voltage drop and reduce its operating current. Additionally, the optical amplifier Ge reduces the number of drive circuits De, thereby reducing the area of ​​the drive circuits De. All other effects are the same as in the first embodiment.

[0147] [Sixth Implementation]

[0148] The optical amplifier Gf according to the sixth embodiment will be described. In this embodiment, the number of semiconductor lasers Lf, which is more than one for each excitation fiber core Ce, is configured as a semiconductor laser group LG, which includes multiple semiconductor lasers Lf connected in series. The multiple semiconductor lasers Lf included in the semiconductor laser group LG are driven by a common driving current. In addition, there are three semiconductor lasers Lf for every two excitation fiber cores Ce of the erbium-doped fiber EF, and the excitation light Lp emitted by the three semiconductor lasers Lf are synthesized by optical injection synchronization.

[0149] Figure 12 This is a diagram illustrating the structure of the optical amplifier Gf contained in the repeater Tf.

[0150] exist Figure 12 The optical amplifier Gf1 consists of erbium-doped fiber EF1, erbium-doped fiber EF2, and three semiconductor lasers Lf1 to Lf3. The semiconductor lasers Lf1 to Lf3 are connected in series.

[0151] Optical amplifier Gf2 consists of erbium-doped fiber EF3, erbium-doped fiber EF4, and three semiconductor lasers Lf4 to Lf6. Semiconductor lasers Lf4 to Lf6 are connected in series.

[0152] Optical amplifier Gf M Erbium-doped fiber EF 2M－1 Erbium-doped fiber EF 2M and semiconductor laser Lf 3M－2 To semiconductor laser Lf 3M These are three semiconductor lasers (Lf). Semiconductor laser (Lf) 3M－2 To semiconductor laser Lf 3M Series connection.

[0153] The optical amplifier Gf has 16 excitation cores Ce for the erbium-doped fiber EF. In addition, the optical amplifier Gf has three semiconductor lasers Lf for every two excitation cores Ce of the erbium-doped fiber EF.

[0154] In optical amplifier Gf1, if excitation light Lp emitted by semiconductor laser Lf2 is incident relative to the self-oscillating semiconductor laser Lf1, an optical injection synchronization phenomenon occurs where the oscillation wavelength of semiconductor laser Lf1 is introduced to the wavelength of the incident excitation light Lp, and the excitation light Lp emitted by semiconductor laser Lf2 and semiconductor laser Lf1 are combined. The combined excitation light Lp is then incident on 3dB coupler B1.

[0155] Similarly, if excitation light Lp emitted by semiconductor laser Lf2 is incident relative to the self-oscillating semiconductor laser Lf3, a light injection synchronization phenomenon occurs where the oscillation wavelength of semiconductor laser Lf3 is introduced to the wavelength of the incident excitation light Lp, and the excitation light Lp emitted by semiconductor laser Lf2 and semiconductor laser Lf3 are combined. The combined excitation light Lp is then incident on the 3dB coupler B1.

[0156] The light power incident from semiconductor laser Lf2 onto semiconductor lasers Lf1 and Lf3 is preferably approximately equal, and the difference in light power between the two is particularly preferably less than 1 dB.

[0157] After combining the two incoming excitation beams Lp, the 3dB coupler B1 branches them into two beams with a branching ratio of approximately 1:1. One of the branched excitation beams Lp is injected into the excitation core Ce1 of the erbium-doped fiber EF1 via the pump combiner P1. The other branched excitation beam Lp is injected into the excitation core Ce2 of the erbium-doped fiber EF2 via the pump combiner P2. The optical amplifier Gf1 excites the erbium beams using the excitation beams Lp, thereby amplifying the signal beams Ls transmitted through the signal cores Cs1 and Cs2 respectively.

[0158] Similarly, optical amplifier Gf2 amplifies the signal light Ls transmitted through signal fiber cores Cs3 and Cs4 by using the excitation light Lp emitted from each of the semiconductor lasers Lf4 to Lf6. M By using a semiconductor laser Lf 3M－3 To semiconductor laser Lf 3M The excitation light Lp emitted by each semiconductor laser Lf causes the light passing through the signal fiber core Cs to... 2M－1 and signal fiber core Cs 2M The transmitted signal light Ls is amplified.

[0159] Optical amplifier Gf2 to optical amplifier Gf M Except for the difference in the signal fiber core Cs of the optical amplifier, its structure and function are the same as those of the optical amplifier Gf1.

[0160] The drive circuit that enables the semiconductor laser Lf driven by the optical amplifier Gf to be applied Figure 11 The driving circuit De is shown.

[0161] As described above, the optical amplifier Gf is synthesized by optical injection synchronization using excitation light Lp emitted from three semiconductor lasers Lf for every two excitation fiber cores Ce. This reduces the drive current I, resulting in an optical amplifier with low operating current. Furthermore, the optical amplifier Gf can suppress voltage drop, reduce the operating current of the optical amplifier Ge, and decrease the configuration area of ​​the drive circuit De.

[0162] This embodiment illustrates an optical injection synchronization method, but a composite resonator method or a master oscillator output amplifier method can also be used. Furthermore, the optical amplifier Gf can combine polarization combining, optical injection synchronization, composite resonator, or master oscillator output amplifier methods to combine the excitation light Lp.

[0163] The above descriptions of various embodiments and modifications are provided, but the embodiments disclosed herein are illustrative in all respects and should not be considered limiting. The scope of the present invention is not limited to the above descriptions, but is shown in the claims, including all modifications equivalent to the claims and within their scope.

[0164] In the above-described embodiments, a submarine optical cable system is illustrated as an optical communication system, but the implementation is not limited to this. The embodiments can also be applied to optical communication systems other than submarine optical cable systems.

[0165] The ordinal numbers, quantities, and other figures used in the description of the embodiments are all illustrative for the purpose of specifically illustrating the technology of the present invention, and the present invention is not limited to the illustrative figures.

[0166] Explanation of the label

[0167] 100… Optical communication system,

[0168] 10…First power supply unit,

[0169] 20…Second power supply unit,

[0170] 50…resonance direction,

[0171] 51… Upper surface electrode,

[0172] 52…lower surface electrode,

[0173] 53…current blocking layer,

[0174] 54…Anti-reflective film,

[0175] 55, 56… wiring,

[0176] 57…Active Layer,

[0177] 58… Output direction,

[0178] M…number of signal fiber cores,

[0179] Ai, Ao… DC current sources

[0180] T, Ta, Tb, Tf… repeaters

[0181] PL... power supply line,

[0182] R…resistance,

[0183] V, Vs, VL… voltage,

[0184] G, Ga, Gb, Gc, Gd, Ge, Gf… optical amplifiers

[0185] L, Lc, Ld, Le, Lf… semiconductor lasers (excitation light sources),

[0186] PB…polarization element (combination section),

[0187] B…3dB coupler,

[0188] P…pump combiner,

[0189] EF…Erbium-doped fiber (rare earth element-doped fiber),

[0190] Fu…uplink fiber optic cable,

[0191] Fd…downlink fiber,

[0192] Lp…excitation light,

[0193] Ls…signal light,

[0194] Cs…signal fiber core,

[0195] Ce…excites the fiber core (fiber core),

[0196] CL…cladding,

[0197] Cv…constant voltage circuit,

[0198] Ci…constant current circuit,

[0199] I…drive current,

[0200] Is…current,

[0201] Vr…reference voltage,

[0202] Ir…reference current,

[0203] Current sources A1, A2…

[0204] Gv1, Gv1X, Gv2, Gv2X… supply voltage,

[0205] Gp1, Gp1X, Gp2, Gp2X... consume electricity.

Claims

1. An optical amplifier, comprising: One or more rare earth element-doped optical fibers, each containing one or more fiber cores; The excitation light emitted in accordance with the driving current excites the rare-earth elements doped in the rare-earth element-doped optical fiber, and there are more than one excitation light sources for each core of the rare-earth element-doped optical fiber; and The synthesis unit combines the excitation light emitted from more than one of the excitation light sources for each of the fiber cores. The fiber core consists of two or more fibers. The excitation light emitted by more than one of the excitation light sources for each fiber core is introduced relative to the fiber core. More than one of the excitation light sources for each of the fiber cores are driven by drive current supplied from a plurality of drive circuits connected in series.

2. The optical amplifier according to claim 1, wherein, The synthesis unit synthesizes the excitation light emitted from more than one excitation light source for each fiber core using at least one of the following methods: polarization synthesis, optical injection synchronization, composite resonator, and master oscillator output amplifier. The polarization combining method is a method of combining multiple different polarizations using polarization elements. The optical injection synchronization method involves externally injecting light with a wavelength close to the oscillation wavelength into a self-oscillating semiconductor laser. This optical injection synchronization phenomenon, where the oscillation wavelength of the semiconductor laser is introduced to match the wavelength of the injected light, allows for the synthesis of multiple different beams. The composite resonator method is a way to combine multiple different lights using a composite resonator connected to multiple resonators. The aforementioned master oscillator output amplifier method involves using a master oscillator output amplifier to combine multiple different beams of light. The main oscillator output amplifier takes out the combined light emitted by the first and second oscillators from the second oscillator side.

3. An optical amplifier, comprising: One or more rare earth element-doped optical fibers, each containing one or more fiber cores; The excitation light emitted in accordance with the driving current excites the rare-earth elements doped in the rare-earth element-doped optical fiber, and there are more than one excitation light sources for each core of the rare-earth element-doped optical fiber; and The synthesis unit combines the excitation light emitted from more than one of the excitation light sources for each of the fiber cores. The fiber core consists of two or more fibers. The excitation light emitted by more than one of the excitation light sources for each fiber core is introduced relative to the fiber core. The synthesis unit synthesizes the excitation light emitted from more than one excitation light source for each fiber core using at least one of the following methods: polarization synthesis, optical injection synchronization, composite resonator, and master oscillator output amplifier. The polarization combining method is a method of combining multiple different polarizations using polarization elements. The optical injection synchronization method involves externally injecting light with a wavelength close to the oscillation wavelength into a self-oscillating semiconductor laser. This optical injection synchronization phenomenon, where the oscillation wavelength of the semiconductor laser is introduced to match the wavelength of the injected light, allows for the synthesis of multiple different beams. The composite resonator method is a way to combine multiple different lights using a composite resonator connected to multiple resonators. The aforementioned master oscillator output amplifier method involves using a master oscillator output amplifier to combine multiple different beams of light. The main oscillator output amplifier takes out the combined light emitted by the first and second oscillators from the second oscillator side.

4. The optical amplifier according to any one of claims 1 to 3, wherein, For each of the aforementioned fiber cores, more than one of the excitation light sources comprises at least a portion of a semiconductor laser array, which includes multiple semiconductor lasers connected in series. The plurality of semiconductor lasers included in the semiconductor laser group are driven by a common driving current.

5. The optical amplifier according to any one of claims 1 to 3, wherein, The rare earth element-doped optical fiber is a multi-core optical fiber in which multiple cores are covered by a single cladding.

6. The optical amplifier according to claim 5, wherein, The power coupling coefficient between adjacent fiber cores among the plurality of fiber cores is 10 [ / m] or higher.

7. An optical communication system, comprising: One or more optical fibers for transmitting optical signals; and An optical amplifier according to any one of claims 1 to 6, which amplifies the optical signal transmitted by the optical fiber.

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