JP2000332684A - Light receiver and light repeater and light transmitting system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light receiver, a light repeater and a light transmitting system for reducing costs by reducing the required quantity of light amplifiers and dispersion compensation fibers occupying a large part in terms of costs. SOLUTION: An optical signal inputted through an optical circulator 201 is amplified by a direct light preamplifier 202, and then dispersion at a transmission path is compensated by a dispersion compensation fiber 208. The output light signal of the dispersion compensation fiber 208 is reflected on a fiber Bragg grating 209, and inputted to the dispersion compensation fiber 208 and the direct light preamplifier 202 again. The dispersion quantity of the dispersion compensation fiber 208 is set as the half of required dispersion quantity. The optical signal returned and transmitted through the direct light preamplifier 202 is inputted through the optical circulator 201 to an optic/electric conversion circuit 213.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical receiver for receiving an optical signal, an optical repeater for amplifying and outputting the optical signal, and an optical transmission system for transmitting the optical signal. The present invention relates to an optical receiver, an optical repeater, and an optical transmission system capable of removing signal noise and compensating for dispersion of a transmission path.

[0002]

2. Description of the Related Art FIG. 13 shows an example of a conventional configuration of an optical receiver including a dispersion compensation circuit. The received optical signal is input to the pre-optical direct amplifier 1001. Pre-optical direct amplifier 10
The optical signal input to 01 is input to the EDF 1003 after passing through the optical coupler 1002. In the EDF 1003, induced amplification is performed by the excitation light supplied from the excitation LD 1004. As a result, the level of the optical signal whose signal level has dropped after passing through the transmission path is recovered. The optical signal output from the pre-optical direct amplifier 1001 continues to be D
The signal is input to a CF (dispersion compensation fiber) 1005. DC
In F1005, dispersion generated in the transmission path is compensated. DC
While passing through F1005, the dispersion is compensated for, while the power of the optical signal is reduced due to transmission loss.

In order to compensate for this power drop, amplification is performed again by the optical direct amplifier 1006. The noise component of the amplified optical signal is cut by the BPF 1013.
The subsequent optical direct amplifier 1006 includes the optical / electrical conversion circuit 10
An ALC circuit 1012 is provided so that the optical power level becomes optimum for the 13 input units. The optical coupler 1010 branches the signal into a main signal and a monitor signal.
The light is received at 1. The bias current of the pumping LD 1008 is controlled by the ALC circuit 1012 in accordance with the level of the monitor signal, and the constant optical power level is controlled by the pre-optical direct amplifier 100.
2 to be output. The optical signal whose level is controlled to be constant is input to the optical / electrical conversion circuit 1013. light/
The electric conversion circuit 1013 outputs a data signal and a clock signal.

[0004]

In the conventional optical receiver described above, in order to prevent the minimum light receiving sensitivity characteristic from deteriorating, D
A total of two optical direct amplifiers are required before and after the CF. Since the optical direct amplifier is expensive, an increase in the cost of the optical receiver is inevitable.

Further, when the above-mentioned conventional optical receiver is used in a wavelength division multiplexing optical transmission system, a bandpass filter provided in an output section of a direct optical direct amplifier usually transmits the entire wavelength band covering all wavelength division multiplexed light. An optical filter is used. However, with such an optical filter alone, a noise component (ASE) between the channels constituting the wavelength-division multiplexed light.
Noise).

The present invention solves the above-mentioned problems of the prior art, and provides an optical receiver and an optical repeater capable of reducing the cost of the optical receiver by reducing the number of necessary optical direct amplifiers. The purpose is to: Another object of the present invention is to provide an optical receiver and an optical repeater capable of improving light receiving sensitivity characteristics by removing even a noise component between channels in a wavelength division multiplexing optical transmission system.

[0007]

In order to achieve the above object, an optical receiver according to the present invention is an optical receiver for receiving an input optical signal input through an input terminal, wherein the optical receiver receives the input optical signal. And an optical amplifier that outputs an amplified optical signal, the amplified optical signal is input, a dispersion compensator having a predetermined dispersion value, and an output light of the dispersion compensator is input, and a wavelength of the input optical signal is input. An optical filter having a wavelength transmission characteristic having a transmission peak at the optical filter, and light reflecting means for reflecting the output light of the optical filter and re-entering the output end of the optical filter.

Here, the optical receiver is further inserted between the input terminal and the optical amplifier, a first input / output terminal is connected to the input terminal, and a second input / output terminal is connected to the optical amplifier. The optical circulator may further include an optical circulator to which the terminal is connected, and an opto-electrical converter connected to the third input / output terminal of the optical circulator to convert the input light into an electric signal.

Further, the dispersion compensating means may include a dispersion compensating optical fiber.

An optical receiver having a second configuration according to the present invention is an optical receiver for receiving an input optical signal input through an input terminal, wherein the optical receiver amplifies the input optical signal, and amplifies the amplified optical signal. An optical amplifier that outputs a signal, the amplified optical signal is input, a dispersion compensating unit having a predetermined dispersion value is input, and the output light of the dispersion compensating unit is input, and a wavelength having a reflection peak at a wavelength of the input optical signal. An optical filter having reflection characteristics.

Here, the optical filter may include a fiber Bragg grating.

The optical receiver is further inserted between the input terminal and the optical amplifier, a first input / output terminal is connected to the input terminal, and a second input / output terminal is connected to the optical amplifier. And a photoelectric converter connected to the third input / output terminal of the optical circulator for converting input light into an electric signal.

[0013] The optical receiver may further include an optical terminator for terminating light transmitted through the optical filter.

An optical receiver having a third configuration according to the present invention is an optical receiver for receiving a wavelength-division multiplexed optical signal that is input via an input terminal and includes a plurality of optical signals having different wavelengths. An optical receiver that amplifies the wavelength-multiplexed optical signal and outputs an amplified optical signal; a dispersion compensating unit to which the amplified optical signal is input and having a predetermined dispersion value; and an output light of the dispersion compensating unit. And an optical filter having a wavelength reflection characteristic having a reflection peak at each of the different wavelengths.

Here, the optical filter may include a plurality of cascaded fiber Bragg gratings each having a reflection peak at one of the different wavelengths.

Further, the optical filter may include a dispersion compensating fiber grating.

[0017] The optical receiver may further include an optical terminator for terminating light transmitted through the optical filter.

The optical receiver is further inserted between the input terminal and the optical amplifier, a first input / output terminal is connected to the input terminal, and a second input / output terminal is connected to the optical amplifier. Optical circulator, an optical splitter for separating light output from a third input / output terminal of the optical circulator into the plurality of optical signals, and a plurality of optical demultiplexers for converting each of the plurality of optical signals into an electric signal. May be provided.

An optical repeater of a first configuration according to the present invention is an optical repeater that amplifies an input optical signal input through an input terminal and outputs the amplified optical signal. An optical amplifier for outputting a signal; a dispersion compensating unit having a predetermined dispersion value to which the amplified optical signal is inputted; and a wavelength having a transmission peak at a wavelength of the input optical signal to which the output light of the dispersion compensating unit is inputted. An optical filter having transmission characteristics, and light reflecting means for reflecting the output light of the optical filter and re-entering the output end of the optical filter.

Here, the optical repeater is further inserted between the input terminal and the optical amplifier, a first input / output terminal is connected to the input terminal, and a second input / output terminal is connected to the optical amplifier. An optical circulator to which a terminal is connected may be provided.

The dispersion compensating means may include a dispersion compensating optical fiber.

An optical repeater of a second configuration according to the present invention is an optical repeater that amplifies and outputs an input optical signal input through an input terminal, and amplifies the input optical signal. An optical amplifier for outputting an amplified optical signal, the amplified optical signal being input, dispersion compensation means having a predetermined dispersion value, and the output light of the dispersion compensation means being input, and a reflection peak at a wavelength of the input optical signal. And an optical filter having a wavelength reflection characteristic.

Here, the optical filter may include a fiber Bragg grating.

Further, the optical repeater is further inserted between the input terminal and the optical amplifier, a first input / output terminal is connected to the input terminal, and a second input / output terminal is connected to the optical amplifier. May be provided with an optical circulator connected thereto.

[0025] The optical repeater may further include an optical terminator for terminating light transmitted through the optical filter.

An optical repeater of a third configuration according to the present invention is an optical repeater that amplifies and outputs a wavelength-division multiplexed optical signal that is input via an input terminal and includes a plurality of optical signals having different wavelengths. An optical amplifier that amplifies the wavelength-division multiplexed optical signal and outputs an amplified optical signal, the amplified optical signal is input, dispersion compensation means having a predetermined dispersion value, and output light of the dispersion compensation means are input. And an optical filter having a wavelength reflection characteristic having a reflection peak at each of the different wavelengths.

[0027] The optical filter may comprise a plurality of cascaded fiber Bragg gratings each having a reflection peak at one of the different wavelengths.

[0028] The optical filter may include a dispersion compensating fiber grating.

[0029] The optical repeater may further include an optical terminator for terminating light transmitted through the optical filter.

The optical repeater is further inserted between the input terminal and the optical amplifier, a first input / output terminal is connected to the input terminal, and a second input / output terminal is connected to the optical amplifier. May be provided.

An optical transmission system according to the present invention is an optical transmission system for transmitting an optical signal between an optical transmitter and an optical receiver connected via an optical transmission line, wherein the optical transmission system is inserted into the optical transmission line. At least one optical repeater;
Each of the two optical repeaters includes any one of the optical repeaters described above.

As described above, the optical receiver and the optical repeater of the present invention employ a configuration in which the input optical signal reciprocates through both the optical amplifier and the dispersion compensating means. Therefore, the required number of optical amplifiers can be halved. As for the dispersion compensating means, a dispersion compensating means having a dispersion amount of about half of a required dispersion amount according to an optical transmission line through which an input optical signal propagates may be prepared. Therefore,
The cost reduction can be realized by the combined effect of reducing the required quantity of both. Furthermore, since an input optical signal is passed through an optical filter, noise added from an optical amplifier or the like can be removed, and transmission characteristics can be improved.

[0033]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration and operation of an optical transmission device and an optical transmission system according to the present invention will be described with reference to FIGS.

FIG. 1 shows the configuration of the optical receiver according to the first embodiment of the present invention. The optical receiver shown in FIG. 1 includes an optical circulator 201 whose output terminal changes according to the optical input direction, a direct optical amplifier 202 for amplifying an optical signal passing through the transmission line, and a DCF for compensating for dispersion of the optical signal passing through the transmission line. (Dispersion compensating fiber) 208, a fiber Bragg grating 209 that reflects only the wavelength component of the optical signal, an optical terminator 210 that terminates the optical signal transmitted through the fiber Bragg grating 209, and converts the optical signal into an electric signal, and outputs a data signal. -To-electric conversion circuit 21 for outputting clock signal and clock signal
3 is included.

Next, the operation of the optical receiver according to the first embodiment will be described. FIG. 4 shows an optical signal propagating in the circuit. S which is an optical transmission line constituting an optical transmission system
S passing through MF (single mode fiber)
The TM64 optical signal (wavelength λ [nm]) is first input to the optical circulator 201. Optical circulator 201
The output terminal changes depending on the input terminal to which the optical signal is input. The optical signal input from the “a” part shown in FIG.
Output from the "b" part.

The signal output from the optical circulator 201 is input to the optical direct amplifier 202. In the optical preamplifier 202, the optical signal is converted into a 10: 1 optical coupler 20.
4. The light passes through an optical coupler 205 and is input to an EDF (erbium-doped fiber) 206. Excitation LD20
The pump light supplied from 7 causes induced amplification in the EDF 206, amplifies the input optical signal, and recovers the level reduction due to the transmission path loss.

The optical signal that has passed through the pre-optical direct amplifier 202 has passed through a DCF (Dispersion Compensating Fiber) 208 and has a total dispersion amount of the optical transmission line on which the optical signal has propagated before reaching the optical receiver. Appropriate predetermined dispersion compensation is performed.

After passing through the DCF 208, it is input to the fiber Bragg grating 209. The fiber Bragg grating 209 has a high light reflectance with respect to the wavelength λ [nm] of the optical signal, and is designed to transmit the optical signals of other wavelengths as they are. FIG. 5 schematically shows the transmission characteristics of the fiber Bragg grating 209. The optical signal transmitted through the fiber Bragg grating 209 is terminated by the optical terminator 210. This allows
Noise components other than the optical signal are removed.

The optical signal reflected by the fiber Bragg grating 209 passes through the DCF 208 again. The dispersion amount of the DCF 208 is set to half of the required dispersion amount to be compensated. In this embodiment, the DCF 20
By going back and forth, the vehicle has passed twice in total. For this reason,
Although the amount of dispersion required by the DCF 208 alone is less than the required amount, the required amount of dispersion is ensured by round-trip propagation.

The signal that has passed through the DCF 208 passes through the pre-optical direct amplifier 202 again (the dashed line route in FIG. 1). The optical signal is amplified again by the EDF 206 and the BP
The noise component is removed by F203. Subsequently, the optical signal is split by an optical coupler (branch ratio 10: 1) 204 into a main signal (10 components of the branch ratio 10: 1) and a monitor signal (1 component of the branch ratio 10: 1). . The branched monitor signal is received by the PD 211 and input to the ALC circuit (auto level control circuit) 212.

In the ALC circuit 212, E is calculated from the monitor signal.
The power level of the DF206 output is detected, and this EDF2
The bias current of the excitation LD 207 is controlled so that the level of the 06 output becomes a constant level (the optimum power level for the input section of the optical / electrical conversion circuit 213 described later, which is +2 dBm in this case).

The optical signal controlled to be fixed at a predetermined level is input to the “b” part of the optical circulator 201. The optical signal input to the “b” section is output from the “c” section. The output optical signal is converted to an optical / electrical conversion circuit 213.
Is input to the optical / electrical conversion circuit 213.
A data signal (electricity) and a 9.95328 GHz clock signal (electricity) are output.

Next, a second embodiment of the present invention will be described. FIG. 2 shows the configuration of the optical receiver according to the second embodiment.
In this embodiment, the fiber Bragg grating 109 in the first embodiment is replaced by an optical BPF (bandpass filter) 114, and the optical terminator 110 is changed to an optical total reflector 115. The operation of this embodiment is the same as that of the first embodiment, and the description of the operation is omitted.

In this embodiment, the light BPF passes twice back and forth. For this reason, the same light B
As in the case of passing through two PFs, a larger out-of-band suppression characteristic can be obtained as compared with the case where transmission is performed only once. Therefore,
In the present embodiment shown in FIG. 2, the effect of removing noise can be improved and the receiving sensitivity can be improved as compared with the configuration in which the optical BPF is transmitted only once to achieve noise removal.

Further, the noise level due to the optical amplifier 102 or the like is not so large as to affect the transmission characteristics, and the BPF 1
In addition to the case where it is not necessary to remove the optical filter before inserting another optical filter in addition to the BPF 03, as shown in FIG.
109 may be deleted.

Next, a third embodiment of the present invention will be described. In this embodiment, it is assumed that wavelength multiplexed light is input to the optical receiver. FIG. 6 shows the configuration of the optical receiver according to the third embodiment. The optical receiver shown in FIG. 6 includes an optical circulator 501, a direct optical direct amplifier 502, a DCF (dispersion compensation fiber) 508, fiber Bragg gratings 509, 510, 511, an optical terminator 512, and an optical demultiplexer 5.
14, optical / electrical conversion circuits 515, 516, and 517 are included.

Next, the operation of the third embodiment will be described. SMF which is an optical transmission line constituting a wavelength division multiplexing transmission system
The wavelength multiplexed optical signal that has passed through the (single mode fiber) is first input to the optical circulator 501. The wavelength multiplexed optical signal has a wavelength of λ1 [nm],
.. Are composed of optical signals of wavelength λ2 [nm],..., Wavelength λn [nm], and each optical signal is supposed to conform to STM64.

The optical signal input from the "a" section shown in FIG. 6 is output from the "b" section. Optical circulator 501
Is output to the pre-optical direct amplifier 502. In the pre-optical direct amplifier 502, the optical signal is 10:
1 passes through the optical coupler 504 and the optical coupler 505, and
(Erbium-doped fiber) 506. The excitation light from the excitation LD 507 causes the EDF 506
The optical signal that has been induced and amplified in the circuit recovers the level decrease due to the transmission path loss.

The optical signal that has passed through the optical direct amplifier 502 passes through a DCF (dispersion compensating fiber) 508 and has a predetermined dispersion compensation amount corresponding to the total dispersion amount of the optical transmission line on which the wavelength multiplexed optical signal has propagated. Is applied.

After passing through the DCF 508, it is input to the fiber Bragg grating 509. The fiber Bragg grating 509 is designed to have a high light reflectance with respect to the wavelength λ1 [nm], and to transmit signals of other wavelengths as they are. Therefore, the wavelength λ1 [nm] is obtained by the fiber Bragg grating 509.
Is reflected and the wavelength λ2 [nm] and the wavelength λn [n
m] and other components are transmitted. Subsequently, in the fiber Bragg grating 510, the wavelength λ2 [n
m] with the fiber Bragg grating 510
In, each fiber Bragg grating is designed to reflect a component of wavelength λn [nm].
Thus, the optical main signal of each wavelength is reflected by each of the fiber Bragg gratings 509, 510, and 511, and components other than the main signal are transmitted.

Each fiber Bragg grating 50
FIG. 7 shows an outline of the reflection characteristics of 9, 510 and 511. The transmitted component is terminated by the optical terminator 512. At this time, not only noise components outside the wavelength band in which the wavelength multiplexed optical signal is arranged, but also noise components between the optical signals of wavelengths λ1 to λn are removed (see FIG. 8).

Each fiber Bragg grating 50
The optical signals reflected by 9, 510, 511 are again D
The optical signal passing through the CF 508 is subjected to dispersion compensation. D
The dispersion amount of the CF 508 is set to a half of the dispersion amount required for the transmission path. By going back and forth through the DCF 508, a required amount of dispersion is ensured by passing twice in total.

The signal that has passed through the DCF 508 again passes through the optical preamplifier 502 again (the dashed line route in FIG. 6). The optical signal is re-amplified in the EDF 506,
The noise component is cut by the BPF 503. Subsequently, an optical coupler (branch ratio of 10: 1) 504 causes the main signal (10 components of the branch ratio of 10: 1) and a monitor signal (branch ratio of 1: 1).
(1 component of 0: 1). The branched monitor signal is received by the PD 513 and input to an ALC circuit (auto level control circuit) 514. The ALC circuit 514 detects the power level of the output of the EDF 506 from the monitor signal, and sets the level of the output of the EDF 506 to a constant level (optical / electrical conversion circuits 516, 517, and 5 described later).
The bias current of the excitation LD 507 is controlled so that the power level becomes optimum for the 18 input units.

The wavelength-division multiplexed optical signal controlled to be fixed at a predetermined level is input to the “b” part of the optical circulator 501. The light input to the “b” part is output from the “c” part. The optical signal output from the section “c” is split by the optical splitter 515 for each wavelength component, and is input to the optical / electrical conversion circuits 515, 516, and 517, respectively. Each optical / electrical conversion circuit 515, 516, 51
7 is an STM64 data signal (electric) and 9.9532
An 8 GHz clock signal (electricity) is output.

Here, as the optical demultiplexer 515, an arrayed waveguide diffraction grating (Arrayed Waveguide) is used.
Grating, AWG) or the like can be used.

Next, a fourth embodiment of the present invention will be described. In the present embodiment, as in the third embodiment, it is assumed that wavelength multiplexed light is input to the optical receiver. FIG. 9 shows the configuration of the optical receiver according to the fourth embodiment. The optical receiver according to the present embodiment includes an optical circulator 801 and a pre-optical direct amplifier 8.
02, dispersion compensating fiber grating 808, optical terminator 809, optical demultiplexer 812, optical / electrical conversion circuit 81
3, 814 and 815.

Next, the operation of the fourth embodiment will be described.
STM64 optical signal (wavelength λ1 [nm], wavelength λ2 [nm],... Wavelength λn [n] that has passed through the SMF (single mode fiber) transmission line of the wavelength division multiplexing transmission system
m]) is first input to the optical circulator [801]. The optical signal input from the “a” part shown in FIG.
Output from the "b" part. The signal output from the optical circulator 801 is input to the pre-optical direct amplifier 802. In the pre-optical direct amplifier 802, the optical signal is 10: 1
The light passes through an optical coupler 804 and an optical coupler 805 and is input to an EDF (erbium-doped fiber) 806.
The pump light from the pump LD 807 is induced and amplified in the EDF 806, and the input optical signal recovers from a level drop due to transmission path loss.

The optical signal that has passed through the direct optical direct amplifier 802 is input to the dispersion compensating fiber grating 808. The dispersion-compensating fiber grating 808 has a non-uniform grating interval, and the signal on the long wavelength side is reflected on the side closer to the input side. On the other hand, the signal on the short wavelength side is reflected on the side closer to the output side. That is, a delay occurs for each wavelength, and a pulse spread due to dispersion is compensated.
FIG. 10 shows an example of the operation of the dispersion compensating fiber grating 808 and an example of the relationship between the wavelength and the delay amount. Each wavelength λ of main signal
The components of 1, λ2 and λn are compensated by the dispersion compensating fiber grating 808 and again enter the pre-optical direct amplifier 802 (the dashed line route in FIG. 9).

The component transmitted through the dispersion compensating fiber grating 808 is terminated by an optical terminator 809. The optical signal is amplified again by the EDF 806, and the noise component is cut by the BPF 803. Then, an optical coupler (branch ratio 1
0: 1) 804, the signal is split into a main signal (a component on the 10 side of the 10: 1 split ratio) and a monitor signal (a component on the 1 side of the split ratio 10: 1). The branched monitor signal is PD
The light is received at 810 and input to an ALC circuit (auto level control circuit) 811. ALC circuit 811
Then, the power level of the output of the EDF 806 is detected from the monitor signal, and the level of the output of the EDF 806 is set to a constant level (optimum power level for the input sections of the optical / electrical conversion circuits 813, 814, and 815 described later). LD
807 is controlled.

The optical signal whose level has been controlled to be constant is input to the “b” part of the optical circulator 801. The light input to the “b” part is output from the “c” part. The optical signal output from the “c” section is split by the optical demultiplexer 812 for each wavelength component, and the optical / electrical conversion circuits 813 and 813 respectively.
14, 815. Each of the optical / electrical conversion circuits 813, 814, and 815 outputs an STM64 data signal (electricity) and a 9.95328 GHz clock signal (electricity).

In each of the above embodiments, the optical receiver provided at the receiving end of the optical transmission line has been described.
However, each of the above embodiments can be applied to an optical repeater inserted into an optical transmission line. in this case,
"A" of the optical circulator used in each of the above embodiments
The part may be inserted into the optical transmission line with the input terminal and the “c” part as the output terminal. FIG. 11 shows an example of the configuration of the optical repeater thus configured. In this configuration, a part of the configuration of the optical receiver according to the first embodiment shown in FIG. 1 is applied to the optical repeater, but the optical repeater is similarly configured in the other embodiments described above. It is possible.

FIG. 12 shows the configuration of an optical transmission system in which such optical repeaters are connected in multiple stages. In FIG. 12, optical signals transmitted from an optical transmitter 1204 are sequentially relayed by optical repeaters 1201 to 1203, and
It reaches 05. Each optical repeater has a configuration shown in FIG.
By inserting this optical repeater into the transmission line, it becomes possible to amplify the optical signal without accumulating unnecessary noise components in each optical repeater, so that the optical signal can be relayed and transmitted over a long distance. It is possible to do. As the optical repeater, an optical repeater having a configuration other than that of FIG. 1 may be used.

[0063]

As described above, in the present invention,
The following effects can be expected in the optical receiver and the optical repeater having the dispersion compensator. 1. Since the number of optical amplifiers that occupy a large part of the cost can be reduced as compared with the conventional configuration, the cost can be significantly reduced. DCF is used for dispersion compensation.
In the case of using the DCF, the DCF having a dispersion amount that is half that of the conventional DCF is sufficient, so that the cost can be reduced in this regard. 2. In particular, the second embodiment employs a configuration in which the light passes through the optical filter twice, so that the effect of noise removal is great, and therefore, improvement in the receiving sensitivity can be expected. 3. Particularly, in the third and fourth embodiments, in the wavelength division multiplexing optical transmission system, by connecting a plurality of fiber Bragg gratings, it is possible to remove noise components between optical signals constituting the wavelength division multiplexed light. S / N of signal
The ratio increases, and the receiving sensitivity can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration of an optical receiver according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a configuration of an optical receiver according to a second embodiment of the present invention.

FIG. 3 is a diagram illustrating a configuration of another optical receiver according to a second embodiment of the present invention.

FIG. 4 is a diagram for explaining an operation of the optical receiver according to the first embodiment of the present invention.

FIG. 5 is a diagram illustrating transmission characteristics of a fiber Bragg grating.

FIG. 6 is a diagram illustrating a configuration of an optical receiver according to a third embodiment of the present invention.

FIG. 7 is a diagram illustrating transmission characteristics of cascaded fiber Bragg gratings.

FIG. 8 is a diagram for explaining an effect of noise removal according to a third embodiment of the present invention.

FIG. 9 is a diagram illustrating a configuration of an optical receiver according to a fourth embodiment of the present invention.

FIG. 10 is a diagram for explaining the operation of the dispersion compensating fiber grating.

FIG. 11 is a diagram illustrating a configuration of an optical repeater according to the present invention.

FIG. 12 is a diagram illustrating a configuration of an optical transmission system in which an optical repeater according to the present invention is inserted.

FIG. 13 is a diagram illustrating a configuration of an optical receiver according to a conventional technique.

[Explanation of symbols]

101, 201, 501, 801: Optical circulators 102, 202, 502, 802, 1001, 100
6: Pre-optical direct amplifier 108, 208, 508, 1005: DCF 209, 509, 510, 511: Fiber Bragg grating 115: Total optical reflector 210, 512, 809: Optical terminator 113, 213, 516, 517, 518, 813, 8
14, 815, 1014: optical / electrical conversion circuit 515, 812: optical demultiplexer 808: dispersion compensating fiber grating 1201, 1202, 1203: optical repeater 1204: optical transmitter 1205: optical receiver

Claims (25)

[Claims] 1. An optical receiver for receiving an input optical signal input via an input terminal, wherein the optical receiver amplifies the input optical signal and outputs an amplified optical signal; A dispersion compensating unit that receives the amplified optical signal and has a predetermined dispersion value; and an optical filter that receives the output light of the dispersion compensating unit and has a wavelength transmission characteristic having a transmission peak at a wavelength of the input optical signal; A light reflecting means for reflecting the output light of the optical filter and re-entering the output end of the optical filter. 2. The optical receiver according to claim 1, wherein the optical receiver is further inserted between the input terminal and the optical amplifier, and a first input / output terminal is connected to the input terminal. An optical circulator having a second input / output terminal connected to the optical amplifier; and an opto-electrical converter connected to the third input / output terminal of the optical circulator and converting input light into an electric signal. An optical receiver. 3. The optical receiver according to claim 1, wherein said dispersion compensating means includes a dispersion compensating optical fiber. vessel. 4. An optical receiver for receiving an input optical signal input through an input terminal, wherein the optical receiver amplifies the input optical signal and outputs an amplified optical signal. An amplifier, the amplified optical signal being input, dispersion compensation means having a predetermined dispersion value, and light having wavelength reflection characteristics to which the output light of the dispersion compensation means is input and having a reflection peak at the wavelength of the input optical signal An optical receiver, comprising: a filter. 5. The optical receiver according to claim 4, wherein said optical filter includes a fiber Bragg grating. 6. The optical receiver according to claim 5, wherein the optical receiver is further inserted between the input terminal and the optical amplifier, and a first input / output terminal is connected to the input terminal. An optical circulator having a second input / output terminal connected to the optical amplifier; and an opto-electrical converter connected to the third input / output terminal of the optical circulator and converting input light into an electric signal. An optical receiver. 7. The optical receiver according to claim 4, wherein the optical receiver further terminates light transmitted through the optical filter. An optical receiver comprising: 8. An optical receiver that receives a wavelength-division multiplexed optical signal input through an input terminal and includes a plurality of optical signals having different wavelengths, wherein the optical receiver converts the wavelength-division multiplexed optical signal into An optical amplifier that amplifies and outputs an amplified optical signal; a dispersion-compensation unit that receives the amplified optical signal and has a predetermined dispersion value; and an output light of the dispersion-compensation unit that is input to each of the different wavelengths An optical filter having a wavelength reflection characteristic having a reflection peak. 9. The optical receiver according to claim 8, wherein the optical filter comprises a plurality of cascaded fiber Bragg gratings, each having a reflection peak at one of the different wavelengths. An optical receiver characterized by the above-mentioned. 10. The optical receiver according to claim 8, wherein the optical filter includes a dispersion compensating fiber grating. 11. The optical receiver according to claim 8, wherein the optical receiver further terminates light transmitted through the optical filter. An optical receiver comprising: 12. The optical receiver according to claim 8, wherein the optical receiver is further inserted between the input terminal and the optical amplifier. An optical circulator having a first input / output terminal connected to the input terminal and a second input / output terminal connected to the optical amplifier; and a light output from a third input / output terminal of the optical circulator, An optical receiver comprising: an optical demultiplexer that separates the plurality of optical signals into a plurality of optical signals; and a plurality of photoelectric converters that convert each of the plurality of optical signals into an electric signal. 13. An optical repeater for amplifying and outputting an input optical signal input through an input terminal, wherein the optical repeater amplifies the input optical signal and outputs an amplified optical signal. An amplifier, the amplified optical signal being input, dispersion compensating means having a predetermined dispersion value, and light having a wavelength transmission characteristic having a transmission peak having a transmission peak at a wavelength of the input optical signal, receiving the output light of the dispersion compensating means. An optical repeater comprising: a filter; and a light reflecting unit that reflects output light of the optical filter and reenters the output end of the optical filter. 14. The optical repeater according to claim 13, wherein the optical repeater is further inserted between the input terminal and the optical amplifier, and a first input / output terminal is connected to the input terminal. And an optical circulator having a second input / output terminal connected to the optical amplifier. 15. An optical repeater according to claim 13, wherein said dispersion compensating means comprises a dispersion compensating optical fiber. vessel. 16. An optical repeater for amplifying and outputting an input optical signal input through an input terminal, wherein the optical repeater amplifies the input optical signal and outputs the amplified optical signal. An optical amplifier that outputs the amplified optical signal, a dispersion compensator having a predetermined dispersion value, and a wavelength reflection characteristic that receives an output light of the dispersion compensator and has a reflection peak at a wavelength of the input optical signal. An optical repeater comprising: an optical filter having: 17. The optical repeater according to claim 16, wherein the optical filter includes a fiber Bragg grating. 18. The optical repeater according to claim 17, wherein the optical repeater is further inserted between the input terminal and the optical amplifier, and a first input / output terminal is connected to the input terminal. And an optical circulator having a second input / output terminal connected to the optical amplifier. 19. The optical repeater according to claim 16, wherein the optical repeater further terminates light transmitted through the optical filter. An optical repeater comprising: 20. An optical repeater for amplifying and outputting a wavelength-division multiplexed optical signal including a plurality of optical signals having different wavelengths input through an input terminal, wherein the optical repeater comprises: An optical amplifier that amplifies an optical signal and outputs an amplified optical signal; a dispersion compensating unit to which the amplified optical signal is input, the dispersion compensating unit having a predetermined dispersion value; And an optical filter having a wavelength reflection characteristic having a reflection peak in each of the optical repeaters. 21. The optical repeater of claim 20, wherein the optical filter comprises a plurality of cascaded fiber Bragg gratings, each having a reflection peak at one of the different wavelengths. An optical repeater characterized by the above-mentioned. 22. The optical repeater according to claim 20, wherein the optical filter includes a dispersion compensating fiber grating. 23. The optical repeater according to claim 20, wherein the optical repeater further terminates light transmitted through the optical filter. An optical repeater comprising: 24. The optical repeater according to claim 21, wherein the optical repeater is further inserted between the input terminal and the optical amplifier, An optical repeater, comprising: an optical circulator having a first input / output terminal connected to the input terminal and a second input / output terminal connected to the optical amplifier. 25. An optical transmission system for transmitting an optical signal between an optical transmitter and an optical receiver connected via an optical transmission line, wherein the optical transmission system is inserted into the optical transmission line. An optical device comprising at least one optical repeater, wherein each of the at least one optical repeater comprises the optical repeater according to any one of claims 13 to 24. Transmission system.