JP2004104386A - Optical signal processing apparatus, optical receiver, and method for apparatus and receiving - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical signal processing apparatus which effectively suppresses interference between channels without making polarized waves orthogonal to each other between adjacent channels, and also to provide an optical receiver and a method for the processing and the receiving. <P>SOLUTION: An optical WDM demultiplexer 20 of a reception terminal station 14 demultiplexes a signal light with each wavelength. An optical TDM demultiplexer 22 demultiplexes a signal light with 40Gb/s into four signal lights with 10G/s, and applies them to interference suppression apparatuses 24a to 24d. The signal light from the optical TDM demultiplexer 22 is given to a wavelength dispersion medium 30 of the interference suppression apparatus 24a. A coherent component due to a crosstalk from an adjacent wavelength is shifted to a front edge and a tail edge of an optical pulse by a group delay of the wavelength dispersion medium 30 depending on the wavelength. A branching device 32 divides an output light from the wavelength dispersion medium 30 into two, applies the one to a clock extract device 34 and applies the other to an optical gate device 36. The device 34 extracts a clock from the optical pulse signal from the branching device 32 and controls the optical gate device 36 by using the extracted clock. The optical gate device 36 transits a middle part of the optical pulse signal from the branching device 32 in response to the clock from the device 34. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical signal processing device, an optical receiving device, and a method thereof, and more specifically, to an optical signal processing device, an optical receiving device, and an optical signal processing device capable of suppressing interference between channels in wavelength division multiplexing (WDM) transmission. About the method.
[0002]
[Prior art]
In a wavelength division multiplexing optical transmission system, it is necessary to multiplex wavelengths at a high density in order to effectively utilize a band. However, as the frequency spacing between channels is reduced, interference between channels increases, deteriorating signal quality.
[0003]
As means for avoiding such interference, a configuration in which a polarization multiplexing system for orthogonalizing the polarizations of adjacent channels is used together (for example, T. Ito et al., “6.4 Tb / s (160 × 40 Gb / s) WDM) transmission experiment with 0.8 bit / s / Hz spectrum efficiency ", 26th European Conference on Optical Communication (ECOC 2000), postcard liner with 1.1 channel, and postdeadline liner with postcard liner. For example, see S. Bigo et al., “5.12 Tbit / s (128 × 40 Gbit / s WDM) training over 3 × 100 km of Teralig HT fiber ", 26th European Conference Optical Communication (ECOC 2000), postdeadline paper 1.2) is known. In the latter paper, it is described that wavelength allocation is made unequal in order to suppress interference between adjacent channels.
[0004]
The method of narrowing the band of the optical transmission signal is also known as single sideband (SSB) transmission or vestigial sideband (VSB) transmission, as disclosed in US Pat. No. 6,088,147, US Pat. 213830), U.S. Pat. No. 6,262,834, and JP-A-2001-264710 (or U.S. Publication No. 200207546).
[0005]
[Problems to be solved by the invention]
In the polarization multiplexing method, a circuit for tracking the polarization on the receiving side is required, and the configuration of the receiving apparatus is complicated. Further, when the transmission distance becomes longer, the orthogonal polarization state between adjacent channels cannot be maintained. That is, it is difficult to apply the polarization multiplexing method to long-distance transmission.
[0006]
In the method of limiting the band of the optical transmission signal, if the band is limited too much, the signal quality deteriorates, and eventually the transmission characteristics deteriorate. That is, there is a limit in increasing the density due to band limitation.
[0007]
An object of the present invention is to provide an optical signal processing device, an optical receiving device, and a method thereof that can effectively suppress interference between channels without making the polarization between adjacent channels orthogonal.
[0008]
[Means for Solving the Problems]
An optical signal processing device according to the present invention includes: a separating device that separates an optical signal having a predetermined wavelength from an input optical signal; a wavelength dispersion medium to which the optical signal having the predetermined wavelength separated by the separating device is input; An optical gate device for extracting a predetermined time slot portion from an optical signal output from the medium.
[0009]
In such a configuration, the wavelength dispersion medium moves light components of other wavelengths mixed into the optical signal of the predetermined wavelength separated by the separation device, forward and backward on the time axis. An optical gate device extracts a predetermined time slot portion, typically a central portion, from the optical signal output from the wavelength dispersion medium. As a result, coherent components due to crosstalk from other wavelengths can be suppressed, and the reception characteristics of a signal carried by an optical signal of a predetermined wavelength can be improved and stabilized. Even if the wavelength interval is narrowed so that the spectrum overlaps between the wavelengths in WDM transmission, each signal can be satisfactorily received. That is, the wavelength interval can be narrowed.
[0010]
Preferably, the separation device includes a wavelength separation filter that extracts the optical signal having the predetermined wavelength from the input optical signal. Alternatively, the separation device includes a wavelength separation filter that extracts the predetermined wavelength from the input optical signal, and a down converter that reduces an output optical signal of the wavelength separation filter to a low rate.
[0011]
Preferably, the optical gate device includes a clock extracting device that extracts a clock from the output light of the chromatic dispersion medium, and the predetermined time slot portion of the output light of the chromatic dispersion medium according to the clock extracted by the clock extracting device. And an optical gate element that gates the light. Alternatively, the optical gate device extracts a clock from the input light of the chromatic dispersion medium, and the predetermined time slot portion of the output light of the chromatic dispersion medium according to the clock extracted by the clock extraction device. And an optical gate element to be gated.
[0012]
An optical receiver according to the present invention includes a wavelength separation device that separates signal light of each wavelength from a WDM optical signal composed of signal light of a plurality of wavelengths, and a time separation for the signal light of each wavelength separated by the wavelength separation device. A time axis separating device for separating into a plurality of signal lights on an axis, an interference suppressing device for suppressing interference components of other wavelengths from each output light of the time axis separating device, and a carrier conveyed by the output light of each interference suppressing device. And an optical receiver for receiving a signal.
[0013]
With such a configuration, the signal light of each wavelength transmitted by WDM can be received while suppressing interference due to crosstalk between wavelengths. As a result, even if the wavelength interval is narrowed so that the spectrum overlaps between the wavelengths, each signal can be satisfactorily received. That is, the wavelength interval can be narrowed.
[0014]
Preferably, the interference suppression device includes a chromatic dispersion medium and an optical gate device that extracts a predetermined time slot from an optical signal output from the chromatic dispersion medium.
[0015]
The wavelength dispersion medium moves light components of other wavelengths mixed into the input optical signal forward and backward on the time axis. An optical gate device extracts a predetermined time slot portion, typically a central portion, from the optical signal output from the wavelength dispersion medium. This makes it possible to suppress coherent components due to crosstalk from other wavelengths.
[0016]
Preferably, the optical gate device includes a clock extracting device that extracts a clock from the output light of the chromatic dispersion medium, and the predetermined time slot portion of the output light of the chromatic dispersion medium according to the clock extracted by the clock extracting device. And an optical gate element that gates the light. Alternatively, the optical gate device extracts a clock from the input light of the chromatic dispersion medium, and the predetermined time slot portion of the output light of the chromatic dispersion medium according to the clock extracted by the clock extraction device. And an optical gate element to be gated.
[0017]
The optical signal processing method according to the present invention, a separation step of separating an optical signal of a predetermined wavelength from an input optical signal, and a step of inputting the optical signal of the predetermined wavelength separated in the separation step to a wavelength dispersion medium,
An optical gating step of gating a predetermined time slot portion from an optical signal output from the wavelength dispersion medium by an optical gating device.
[0018]
An optical receiving method according to the present invention includes a wavelength separation step of separating a signal light of each wavelength from a WDM optical signal composed of signal lights of a plurality of wavelengths, and a time separation for the signal light of each wavelength separated in the wavelength separation step. A time axis separation step of separating into a plurality of signal lights on the axis, an interference suppression step of suppressing interference components of other wavelengths from each signal light separated in the time axis separation step, and another wavelength by the respective interference suppression steps. Receiving the signal carried by the signal light in which the interference component is suppressed.
[0019]
【Example】
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0020]
FIG. 1 is a schematic block diagram of an embodiment of the present invention applied to a 40 Gb / s, n-wavelength WDM transmission system.
[0021]
The transmitting terminal station 10 outputs to the optical fiber transmission line 12 a wavelength division multiplexed signal light (WDM signal light) composed of signal light of n wavelengths (λ1 to λn) of 40 Gb / s. FIG. 2 shows an example of an optical spectrum of the WDM signal light. The horizontal axis indicates wavelength, and the vertical axis indicates light intensity. The WDM signal light propagates through the optical fiber transmission line 12 and enters the receiving terminal 14.
[0022]
In the receiving terminal station 14, the WDM signal light is processed as follows. That is, the optical WDM separation device 20 including a wavelength separation element such as an arrayed waveguide grating (AWG) separates the signal light of each wavelength λ1 to λn. FIG. 3 shows the relationship between the filter characteristics of the wavelength λ2 in the optical WDM separation device 20 and the optical spectrum of the transmission signals of the wavelengths λ1, λ2, and λ3. In FIG. 3, the characteristics of the optical filter for separating the wavelength λ2 are indicated by broken lines. Usually, the optical filter characteristics are set so as to extract the optical spectrum component of the target signal light. In the illustrated example, since both sidebands are transmitted, the optical filter characteristics are set to extract a range including the optical carrier frequency, the upper sideband, and the lower sideband. The filter characteristics of other wavelengths are the same as the characteristics shown in FIG. 3 except for the difference in the center wavelength.
[0023]
In FIG. 3, a shaded portion, specifically, an optical spectrum portion of an optical signal of wavelengths λ1 and λ3, which has entered an optical filter characteristic for extracting the wavelength λ2, is a crosstalk with respect to the wavelength λ2, that is, an optical spectrum. It becomes a coherent portion, and becomes noise light for the signal light of wavelength λ2. Since it is coherent, the level of the noise light greatly varies depending on the transmission state. This makes it difficult to receive the signal light having the wavelength λ2. Conventionally, as shown in FIGS. 2 and 3, wavelength intervals are set so that optical spectra do not overlap between adjacent wavelengths. In this embodiment, as described later, this overlapping portion can be effectively suppressed, so that there is no problem even if there is an overlap between adjacent wavelengths as shown in FIGS.
[0024]
The signal light of wavelength λ1 separated by the optical WDM splitter 20 is input to the optical TDM splitter 22. The optical TDM splitter 22 splits the 40 Gb / s signal light of wavelength λ1 from the optical WDM splitter 20 into four signal lights of 10 G / s, and applies them to the interference suppressors 24a, 24b, 24c, and 24d. I do. Since the interference suppression devices 24a, 24b, 24c, 24d have the same configuration, only the internal configuration of the interference suppression device 24a is shown.
[0025]
In the interference suppression device 24 a, 10 Gb / s signal light from the optical TDM separation device 22 is input to the chromatic dispersion medium 30. The wavelength dispersion medium 30 acts to extend the pulse waveform of the incident light on the time axis according to the wavelength. The dispersion amount of the wavelength dispersion medium 30 may be large enough not to overlap with the light pulse of the adjacent time slot. When 40 G / s is reduced to 10 Gb / s as in the present embodiment, the dispersion amount of the wavelength dispersion medium 30 may be about 100 ps / nm. As long as the clock extraction by the clock extraction device 34 described later does not hinder the dispersion, the dispersion amount of the wavelength dispersion medium 30 may be large enough to overlap the optical pulse of the adjacent time slot.
[0026]
FIG. 4 shows an example of chromatic dispersion characteristics of the chromatic dispersion medium 30. The chromatic dispersion medium 30 is made of, for example, an optical fiber, and the chromatic dispersion characteristic of the optical fiber generally changes in a parabolic manner with respect to the wavelength (frequency). The horizontal axis indicates frequency, and the vertical axis indicates group delay. The larger the group delay, the longer the light is delayed, and the smaller the group delay, the faster the light propagates. In this embodiment, a portion where the change in dispersion with respect to the wavelength (frequency) is large is used. For example, as shown in FIG. 5, f0 is the optical carrier frequency of the wavelength λ1, and f2 <f0 <f1, and as shown in FIG. 4, the wavelength at which the group delay increases in the order of f2, f0, f1 It is assumed that a dispersion medium is used as the wavelength dispersion medium 30.
[0027]
FIG. 6 is a schematic waveform diagram of the input light pulse and the output light pulse of the wavelength dispersion medium 30 under the conditions shown in FIG. Since the accumulated chromatic dispersion of the optical fiber transmission line 12 is adjusted to zero or almost zero, the components of the frequencies f0, f1, and f2 in the input pulse of the chromatic dispersion medium 30 are uniformly distributed in the optical pulse. When this optical pulse is input to the wavelength dispersion medium 30, the component of the frequency f2 propagates first with respect to the component of the frequency f0, and the component of the frequency f1 is delayed. Therefore, as shown in FIG. 6 as the output pulse, the waveform on the time axis of the optical pulse is flattened as a whole, but the center of the optical pulse on the time axis has a component of the frequency f0, The component of the frequency f2 gathers in the following, and the component of the frequency f1 gathers in the following part. This means that portions that may interfere with crosstalk from adjacent wavelengths are collected before and after the light pulse. In other words, the optical power of the leading part and the trailing part of the output pulse shown in FIG. 6 tends to fluctuate due to the occurrence of interference, but the optical power of the central part is stabilized in a state according to the signal value to be carried.
[0028]
The demultiplexer 32 divides the output light of the wavelength dispersion medium 30 into two, and applies one to the clock extraction device 34 and the other to the optical gate device 36. The clock extracting device 34 extracts a clock from the optical pulse signal from the duplexer 32, and controls the gate operation of the optical gate device 36 with the extracted clock. The optical gate device 36 transmits about 20 ps of the central portion of the optical pulse signal from the duplexer 32, that is, the portion of the frequency f0 of the pulse waveform illustrated as the output pulse in FIG. 6, according to the clock from the clock extracting device 34. I do. Thereby, a portion having a high SNR (signal-to-noise ratio) that stably carries a signal can be extracted. The output light of the optical gate device 36 is applied to the optical receiver 38a as the output light of the interference suppressor 24a.
[0029]
The optical receiver 38a reproduces a signal from the output light of the interference suppressor 24a by a known method. Since the unstable portion due to interference with other wavelengths is suppressed by the interference suppression device 24a, signal discrimination processing is facilitated.
[0030]
The interference suppression devices 24b to 24d operate similarly to the interference suppression device 24a. The operations of the optical receiving devices 38b to 38d are the same as the operations of the optical resin device 38a.
[0031]
In this manner, in this embodiment, even if the optical spectra overlap between adjacent wavelengths and there is a possibility of partial interference, the filter characteristics of wavelength separation and the optical spectrum components of the adjacent wavelengths are further extracted. Even if it is as wide as possible, the coherent portion can be suppressed by the interference suppression devices 24a to 24d, so that the reception performance of the transmission signal can be improved. In other words, it is possible to narrow the wavelength interval.
[0032]
Although not shown in FIG. 1, the other wavelengths λ2 to λn are processed by the same processing system as the processing system of the wavelength λ1.
[0033]
For example, a signal light obtained by limiting a carrier-suppressed RZ signal (CS-RZ signal) of 42.7 Gb / s to a bandwidth of 35 GHz is multiplexed at 40 GHz intervals and is incident on the optical fiber transmission line 12. In this case, good reception performance is achieved by setting the half-width of the separation optical filter in the optical WDM separation device 20 to 45 GHz, the chromatic dispersion of the chromatic dispersion medium 30 to 100 ps / nm, and the gate width of the optical gate device 36 to 20 ps. did it.
[0034]
In the embodiment shown in FIG. 1, the clock extracting device 34 extracts the clock from the output light pulse of the wavelength dispersion medium 30. However, the clock extracting device 34 extracts the clock from the output light of the optical TDM separating device 22, and controls the optical gate device. You may do so. In this case, the clock extraction device must supply the clock to the optical gate device 36 with a delay by a time considering the time delay in the wavelength dispersion medium 30. Clock extraction is easy, but it is necessary to adjust the delay time in the clock extraction device for each wavelength.
[0035]
Usually, an optical fiber is used as the wavelength dispersion medium 30. In this case, the amount of chromatic dispersion and the average delay time tend to fluctuate depending on the ambient temperature, optical fiber length, and the like. In general, the amount of chromatic dispersion of the chromatic dispersion medium is not so large as to overlap adjacent time slots. In such a situation, the configuration in which the clock is extracted from the output light of the chromatic dispersion medium 30 as in the clock extraction device 34 of the illustrated embodiment is more than the configuration in which the clock is extracted from the input light of the chromatic dispersion medium 30. And adjustment becomes easy.
[0036]
As the chromatic dispersion medium, there is a material having a small expansion and contraction such as a chirped fiber grating, and when this is used as the chromatic dispersion medium 30, even if a clock is extracted from the input light of the chromatic dispersion medium 30, there is little problem. .
[0037]
When handling an optical pulse signal having a small duty ratio, the TDM separation device 22 may be omitted in some cases.
[0038]
Although the embodiment of the RZ transmission has been described, the TDM separation device 22 essentially has a function of converting an NRZ signal into an RZ signal. Therefore, the present invention is also applicable to the case of NRZ transmission.
[0039]
【The invention's effect】
As can be easily understood from the above description, according to the present invention, coherent crosstalk from adjacent channels can be effectively removed, so that the wavelength interval of WDM transmission can be shortened and / or the transmission distance can be reduced. Can be longer.
[Brief description of the drawings]
FIG. 1 is a schematic block diagram of an embodiment of the present invention.
FIG. 2 is an example of an optical spectrum of a WDM signal.
FIG. 3 is a schematic diagram of an optical filter characteristic for separating a signal light having a wavelength λ2.
FIG. 4 is a diagram showing a group delay characteristic of the wavelength dispersion medium 30.
FIG. 5 is a schematic diagram of an optical spectrum of a signal light having a wavelength λ1.
FIG. 6 is a schematic diagram of an input pulse waveform and an output pulse waveform of the wavelength dispersion medium 30.
[Explanation of symbols]
10: transmitting terminal station 12: optical fiber transmission line 14: receiving terminal station 20: optical WDM demultiplexer 22: optical TDM demultiplexers 24a, 24b, 24c, 24d: interference suppressor 30: wavelength dispersive medium 32: demultiplexer 34 : Clock extracting device 36: Optical gate device 38 a, 38 b, 38 c, 38 d: Optical receiving device

Claims (22)

A separation device (20, 22) for separating an optical signal of a predetermined wavelength from an input optical signal;
A wavelength dispersion medium (30) into which the optical signal of the predetermined wavelength separated by the separation device (20, 22) is input;
Optical gate device (34, 36) for extracting a predetermined time slot portion from an optical signal output from the wavelength dispersion medium (30)
An optical signal processing device comprising: The optical signal processing device according to claim 1, wherein the separating device comprises a wavelength separating filter (20) for extracting the optical signal having the predetermined wavelength from the input optical signal. The separation device includes a wavelength separation filter (20) for extracting the predetermined wavelength from the input optical signal, and a down converter (22) for reducing an output optical signal of the wavelength separation filter (20) to a low rate. The optical signal processing device according to claim 1. The optical gate device extracts a clock from the output light of the chromatic dispersion medium (30). The clock extraction device (34), and the chromatic dispersion medium (30) according to the clock extracted by the clock extraction device (34). The optical signal processing device according to claim 1, further comprising: an optical gate element (36) that gates the predetermined time slot portion of the output light of (1). The optical gate device is configured to extract a clock from the input light of the chromatic dispersion medium (30), and a clock extraction device that extracts the clock from the input light of the chromatic dispersion medium (30). The optical signal processing device according to claim 1, further comprising an optical gate element (36) that gates a time slot portion. The optical signal processing device according to claim 1, wherein the predetermined time lot portion is a pulse central portion of an optical signal output from the wavelength dispersion medium. A wavelength separation device (20) for separating signal light of each wavelength from a WDM optical signal composed of signal light of a plurality of wavelengths;
A time axis separation device (22) for separating the signal light of each wavelength separated by the wavelength separation device (20) into a plurality of signal lights on a time axis;
Interference suppression devices (24a to 24d) for suppressing interference components of other wavelengths from each output light of the time axis separation device (22);
Optical receivers (38a to 38d) for receiving signals carried by output lights of the respective interference suppressors (24a to 24d).
An optical receiving device comprising: The interference suppression device (24a to 24d) includes a chromatic dispersion medium (30) and an optical gate device (34, 36) for extracting a predetermined time slot portion from an optical signal output from the chromatic dispersion medium (30). The optical receiving device according to claim 7, comprising: The optical gate device extracts a clock from the output light of the chromatic dispersion medium (30). The clock extraction device (34), and the chromatic dispersion medium (30) according to the clock extracted by the clock extraction device (34). 9. The optical receiving device according to claim 8, further comprising: an optical gating element (36) for gating the predetermined time slot portion of the output light from the optical gate. The optical gate device is configured to extract a clock from the input light of the chromatic dispersion medium (30), and a clock extractor that extracts the clock from the input light of the chromatic dispersion medium (30). 9. The optical receiving device according to claim 8, comprising an optical gate element (36) for gating a time slot portion. The optical receiving device according to claim 8, wherein the predetermined time lot portion is a central portion of a pulse of an optical signal output from the wavelength dispersion medium (30). A separation step (20, 22) for separating an optical signal of a predetermined wavelength from an input optical signal;
Inputting the optical signal of the predetermined wavelength separated in the separation step (20, 22) to the wavelength dispersion medium (30);
An optical gating step of gating a predetermined time slot portion from an optical signal output from the wavelength dispersion medium (30) by an optical gating device (34, 36). The optical signal processing method according to claim 12, wherein the separating step extracts the optical signal having the predetermined wavelength from the input optical signal by using a wavelength separating filter (20). The separation step includes a step of extracting the predetermined wavelength from the input optical signal by the wavelength separation filter (20), and a step (22) of reducing the output optical signal of the wavelength separation filter (20) to a low rate. The optical signal processing method according to claim 12, wherein The optical gate step extracts a clock from the output light of the chromatic dispersion medium (30) (34), and the predetermined time slot portion of the output light of the chromatic dispersion medium (30) is extracted according to the extracted clock. The optical signal processing method according to claim 12, comprising the step of gating (36). The optical gating step extracting a clock from the input light of the chromatic dispersion medium (30); and gating the predetermined time slot portion of the output light of the chromatic dispersion medium (30) according to the extracted clock. The optical signal processing method according to claim 12, comprising (36). 13. The optical signal processing method according to claim 12, wherein the predetermined time lot portion is a pulse central portion of an optical signal output from the wavelength dispersion medium. A wavelength separation step (20) for separating signal light of each wavelength from a WDM optical signal composed of signal light of a plurality of wavelengths;
A time axis separation step (22) of separating the signal light of each wavelength separated in the wavelength separation step (20) into a plurality of signal lights on a time axis;
Interference suppression steps (24a to 24d) for suppressing interference components of other wavelengths from each signal light separated in the time axis separation step (22);
A light receiving step (38a to 38d) for receiving a signal carried by a signal light in which interference components of other wavelengths have been suppressed by the respective interference suppressing steps (24a to 24d). . The interference suppressing step (24a to 24d) is a step of inputting each signal light separated in the time axis separating step (22) to the chromatic dispersion medium (30), and is output from the chromatic dispersion medium (30). 19. The optical receiving method according to claim 18, comprising an optical gating step (34, 36) for extracting a predetermined time slot portion from the optical signal. The optical gate step extracts a clock from the output light of the chromatic dispersion medium (30) (34), and the predetermined time slot portion of the output light of the chromatic dispersion medium (30) is extracted according to the extracted clock. 20. The method of claim 19, comprising the step of gating. The optical gating step extracting a clock from the input light of the chromatic dispersion medium (30); and gating the predetermined time slot portion of the output light of the chromatic dispersion medium (30) according to the extracted clock. The optical receiving method according to claim 19, comprising: (36). 20. The optical receiving method according to claim 19, wherein the predetermined time lot portion is a pulse central portion of an optical signal output from the chromatic dispersion medium.

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