KR102211485B1 - Receiver and method for coherent optical communication - Google Patents

Abstract

The present invention provides a coherent receiving apparatus and a method thereof. The apparatus comprises: an optical filter unit which filters a received optical signal transmitted through an optical fiber in different frequency bands to obtain a baseband optical signal and a stimulated Brillouin scattering (SBS) tone generated by SBS; and a coherent receiving unit which obtains a beating optical signal by beating the baseband optical signal and the SBS tone, and obtains a received signal by detecting the detected beating optical signal. Therefore, the present invention enables self-coherent reception by beating the SBS tone generated by SBS with the received optical signal, thereby reducing manufacturing costs, solving a phase noise problem, and achieving stable operation.

Description

A receiving apparatus and method for coherent optical communication TECHNICAL FIELD [RECEIVER AND METHOD FOR COHERENT OPTICAL COMMUNICATION}

The present invention relates to a receiving apparatus and method for coherent optical communication, and to a self-coherent receiving apparatus and method using induced Brillouin scattering.

In coherent optical communication, the receiving device determines the received signal by beating the received optical signal and the local oscillating optical signal generated by a local oscillator light source, and converting the beating optical signal into an electrical signal. do.

In coherent optical communication, not only the intensity of a light source, but also field components such as phase and polarization can be received, so that bandwidth can be used efficiently. In addition, as the received optical signal acquires an optical gain through optical beating with a local oscillation light source having a relatively stronger intensity than the received optical signal, reception sensitivity may be improved. Accordingly, coherent optical communication can solve the problem of reception sensitivity of a conventional direct detection reception technique.

However, for coherent optical communication, as described above, the receiving device must have a separate local oscillation light source. Also, it is vulnerable to phase noise by beating the received optical signal and the local oscillation optical signal. Since the phase noise is caused by unstable temperature or current control of a light source such as a laser provided in a transmitter and a receiver, current and temperature must be precisely controlled in order to stably operate the local oscillation light source. Therefore, there is a problem that the manufacturing cost is high and operation is not easy.

Korean Patent Registration No. 10-182345 (registered on January 24, 2018)

An object of the present invention is to provide a coherent receiving apparatus and method that can be implemented at low cost without having a separate local oscillation light source and capable of stable operation.

Another object of the present invention is to provide a coherent receiving apparatus and method capable of self-coherent reception by beating a tone generated by induced Brillouin scattering with a received optical signal.

In order to achieve the above object, a coherent receiving apparatus according to an embodiment of the present invention filters a received optical signal transmitted through an optical fiber in different frequency bands to obtain a baseband optical signal and stimulated Brillouin scattering. : An optical filter unit for obtaining an SBS tone generated by SBS); And a coherent receiver configured to obtain a beating optical signal by beating the baseband optical signal and the SBS tone, and detecting the detected beating optical signal to obtain a received signal.

The optical filter unit includes a low-pass filter for obtaining the baseband optical signal by low-pass filtering the received optical signal according to a predetermined frequency band; And a band pass filter for obtaining the SBS tone by band pass filtering the received optical signal according to a predetermined frequency band.

In the band pass filter, a filtering frequency band may be varied according to a property of a material constituting the optical fiber.

The coherent receiving apparatus may further include an optical splitter that separates the received optical signal transmitted through the optical fiber and transmits the separated received optical signal to the low pass filter and the band pass filter.

The coherent receiver comprises: an optical synthesizing unit for obtaining the beating optical signal by synthesizing the SBS tone with the baseband optical signal using the local oscillation light source; And an optical detector configured to detect the beating optical signal and convert it into an electrical signal to obtain the received signal.

The coherent receiver may further include a down converter for lowering the frequency band of the beating optical signal and transmitting it to the optical detector.

The coherent reception method according to another embodiment of the present invention to achieve the above object is to filter the received optical signal transmitted through the optical fiber in different frequency bands, the baseband optical signal and stimulated Brillouin scattering (Stimulated Brillouin Scattering). : Acquiring an SBS tone generated by SBS); And obtaining a beating optical signal by beating the baseband optical signal and the SBS tone, and obtaining a received signal by detecting the detected beating optical signal.

Therefore, the coherent receiving apparatus and method according to the embodiment of the present invention can be self-coherent reception by beating the tone generated by the induced Brillouin scattering with the received optical signal, so that a separate local oscillation light source is not provided. So that the manufacturing cost can be reduced. In addition, since it is a self-heterodyne reception method, the phase noise problem can be solved, stable operation is possible, and high reception sensitivity can be provided.

1 shows a schematic structure of a coherent receiving apparatus according to an embodiment of the present invention.
FIG. 2 is a diagram illustrating an operation of acquiring a received signal by the coherent receiving apparatus of FIG. 1 in a self-coherent method.
3 shows a spectrum of a received optical signal and a tone generated by induced Brillouin scattering.
4 shows a coherent reception method according to an embodiment of the present invention.

In order to fully understand the present invention, the operational advantages of the present invention, and the objects achieved by the implementation of the present invention, reference should be made to the accompanying drawings illustrating preferred embodiments of the present invention and the contents described in the accompanying drawings.

Hereinafter, the present invention will be described in detail by describing a preferred embodiment of the present invention with reference to the accompanying drawings. However, the present invention may be implemented in various different forms, and is not limited to the described embodiments. In addition, in order to clearly describe the present invention, parts irrelevant to the description are omitted, and the same reference numerals in the drawings indicate the same members.

Throughout the specification, when a part "includes" a certain component, it means that other components may be further included, rather than excluding other components unless specifically stated to the contrary. In addition, terms such as "... unit", "... group", "module", and "block" described in the specification mean units that process at least one function or operation, which is hardware, software, or hardware. And software.

1 shows a schematic structure of a coherent receiving apparatus according to an embodiment of the present invention, and FIG. 2 is for explaining an operation in which the coherent receiving apparatus of FIG. 1 acquires a received signal through a self-coherent method. 3 shows a spectrum of a received optical signal and a tone generated by induced Brillouin scattering.

Referring to FIG. 1, a coherent receiving apparatus according to the present embodiment includes an optical splitter 100, an optical filter unit 200, and a coherent receiving unit 300.

The optical splitter 100 separates the received optical signal ROS transmitted to the coherent receiving device through an optical fiber into two optical signals and transmits it to the optical filter unit 200. That is, when the received optical signal ROS is transmitted as shown in (a) of FIG. 2, the optical splitter 100 separates into two optical signals as shown in (b) and (c) and transmits it to the optical filter unit 200. .

The optical splitter 100 may separate the received optical signal (ROS) by an intensity of a predetermined ratio, and as an example, the two optical signals may be separated into light having the same intensity, but separated to have different intensity. You may. And the intensity ratio of the separated light is adjustable.

The optical filter unit 200 obtains a baseband optical signal (BOS) and an SBS tone (SBST) signal by performing low-pass filtering and band-pass filtering of the light divided into two by the optical splitter 100 in a predetermined frequency range, respectively. do.

The optical filter unit 200 may include a low pass filter (LPF) 210 and a band pass filter (BPF) 220. The low-pass filter 210 receives one of the light split into two by the optical splitter 100 and performs low-pass filtering in a predetermined frequency range, as shown in FIG. 2(d), and the baseband optical signal BOS ). On the other hand, the band pass filter 220 receives the rest of the light divided into two by the optical splitter 100 and performs band pass filtering in a predetermined frequency range, as shown in (e) of FIG. 2, SBS tone (SBST). ).

When an optical signal is transmitted through an optical fiber in an optical communication network, non-linear reflection occurs in which a wavelength is shifted within the optical fiber. When the optical signal is transmitted, energy is absorbed within the optical fiber to generate an acoustic wave that creates a Fiber Bragg grating. At this time, energy is absorbed as much as the fiber Bragg grating frequency and is in the opposite direction to the light traveling direction. Reflection occurs.

This is mainly caused by the non-uniform molecular structure of the optical fiber, and it is because the lattice vibration of molecules in the optical fiber medium vibrates loosely in some areas, but vibrates very strongly in some areas. When light of a strong intensity travels in a certain direction in the optical fiber according to such irregularity of vibration, scattering occurs due to irregular grating vibrations, and such scattering causes reflection in a direction opposite to the direction of light travel.

This is referred to as stimulated Brillouin Scattering (SBS). SBS has a unique frequency depending on the material properties of the optical fiber.

In general, most commercially available single mode fibers have an SBS natural frequency in the vicinity of 10 GHz. In contrast, the bandwidth of most optical modulators is generally within 10 GHz.

3 shows the spectrum of the actually measured received optical signal and SBS tone (SBST) (Tone).

As shown in FIG. 3, it can be seen that the received optical signal ROS is transmitted at a frequency within approximately 2 GHz, while the SBS tone SBST is generated at 14 GHz. As described above, the frequency at which the SBS tone (SBST) is generated may vary depending on the material properties of the optical fiber used as a medium, but is generally generated within a frequency range of 10 to 15 GHz. In the case of using the C-band optical fiber of the 1550 nm band, which is the most commonly used, it is known that the SBS tone (SBST) is generated at a frequency of 10.8 GHz.

In addition, the generated SBS tone SBST is generated as a signal having a very strong intensity compared to the received optical signal ROS, as shown in FIG. 3.

That is, when an optical signal is transmitted through an optical fiber, a very strong SBS tone (SBST) is unintentionally generated in a high frequency band. This unintentionally generated high-frequency SBS tone (SBST) is a noise component that is not used in an optical communication system, and conventional reception devices extract only the baseband optical signal (BOS) by low-pass filtering the transmitted optical signal. The SBS tone (SBST) was removed. In particular, SBS tone (SBST) is a signal that must be filtered because it has a strong signal strength.

However, in this embodiment, as shown in FIG. 1, the optical filter unit 200 includes not only the low pass filter 210 but also the band pass filter 220, and the low pass filter 210 is a baseband The optical signal (BOS) is acquired, while the band pass filter 220 acquires the SBS tone (SBST). Here, the baseband optical signal (BOS) may be viewed as a signal including a signal light source and a transmission signal to be transmitted by the transmission device.

In addition, the optical filter unit 200 transmits the acquired baseband optical signal BOS and SBS tone SBST to the coherent receiving unit 300.

The coherent receiving unit 300 obtains a received signal by beating the baseband optical signal (BOS) and the SBS tone (SBST) transmitted from the optical filter unit 200, detecting the beating optical signal, and converting the signal into a signal. .

The coherent reception unit 300 may include a light synthesis unit 310 and a light detection unit 320. The optical synthesis unit 310 synthesizes the baseband optical signal (BOS) and SBS tone (SBST) transmitted from the optical filter unit 200. That is, the optical synthesis unit 310 outputs a beating optical signal as shown in (f) of FIG. 2 by beating with a baseband optical signal (BOS) using the SBS tone (SBST) as a local oscillation light source. do.

Here, the beating optical signal may be obtained as a signal including a transmission signal based on a frequency corresponding to a frequency difference between a signal light source included in the baseband optical signal BOS and the SBS tone SBST. As described above, since the SBS tone (SBST) is generally mainly generated in the 10.8 GHz frequency band, the beating optical signal can be obtained as an optical signal centered on approximately 10 GHz.

In addition, the light detector 320 may detect the beating light signal obtained by the light synthesis unit 310 and convert it into an electrical signal, thereby obtaining a received signal corresponding to the transmission signal. The photo detector 230 may include, for example, a photo detector, and may further include a D/A converter that converts the detected analog electrical signal into a digital signal.

However, it is not easy to detect a beating optical signal in a high frequency band with approximately 10 GHz as the center frequency as it is. Accordingly, the light detection unit 320 may further include a down converter for lowering the frequency band of the high-frequency beating optical signal.

The reception device according to the present embodiment operates as a coherent reception device that performs coherent reception because the SBS tone (SBST) and the baseband optical signal (BOS) are beating, and the baseband optical signal (BOS) and the SBS Since the frequency bands of the tone SBST are different from each other, it can be regarded as a heterodyne receiver. In particular, in the receiving apparatus according to the present embodiment, since the baseband optical signal (BOS) is beating using the SBS tone (SBST) extracted from the received optical signal (ROS) without having a separate local oscillation light source, self-coherent ( self-Coherent) (or self-heterodyne).

Here, the received optical signal (ROS) is an optical signal generated by a light source (not shown) of an optical line terminal (OLT) through an optical fiber.Reflective optical network unit (R-ONU) It may be a signal that is transmitted by the R-ONU and retransmitted by modulating an optical signal in the R-ONU.

As described above, since the receiving device according to the present embodiment enables self-coherent reception by beating the tone generated by the induced Brillouin scattering with the received optical signal, it is not necessary to have a separate local oscillation light source, thereby reducing manufacturing cost. It can be reduced, and since it is a self-heterodyne reception method, the phase noise problem can be solved and stable operation is possible. In addition, since the SBS tone (SBST) having a very strong intensity is beaten with the baseband optical signal (BOS), a large optical beating gain can be obtained. Therefore, high reception sensitivity can be ensured.

4 shows a coherent reception method according to an embodiment of the present invention.

Referring to FIGS. 1 to 3, when the coherent reception method of FIG. 4 is described, first, when the received optical signal ROS is applied through an optical fiber, the received optical signal ROS is separated into two optical signals. (S10). Then, one of the separated two received optical signals ROS is low-pass filtered in a predetermined frequency range to obtain a baseband optical signal BOS (S20). The rest of the two separate received optical signals ROS are band-pass filtered in a predetermined frequency range to obtain an SBS tone (SBST) generated by the induced Brillouin scattering (S30).

When the baseband optical signal (BOS) and the SBS tone (SBST) are obtained, the baseband optical signal (BOS) is beaten by using the obtained SBS tone (SBST) to obtain a beating optical signal (S40). Then, the beating optical signal is detected and converted into an electrical signal to obtain a received signal (S50). Although not shown, the step of lowering the frequency band of the high-frequency beating optical signal may be further included before the step of obtaining the received signal. In addition, when the received signal is detected as an analog signal in the step of acquiring the received signal, the step of converting the received signal into a digital signal may be further included.

The method according to the present invention can be implemented as a computer program stored in a medium for execution on a computer. Here, the computer-readable medium may be any available medium that can be accessed by a computer, and may also include all computer storage media. Computer storage media includes both volatile and nonvolatile, removable and non-removable media implemented in any method or technology for storage of information such as computer readable instructions, data structures, program modules or other data, and ROM (Read Dedicated memory), RAM (random access memory), CD (compact disk)-ROM, DVD (digital video disk)-ROM, magnetic tape, floppy disk, optical data storage device, and the like.

The present invention has been described with reference to the embodiments shown in the drawings, but these are merely exemplary, and those of ordinary skill in the art will appreciate that various modifications and other equivalent embodiments are possible therefrom.

Therefore, the true technical protection scope of the present invention should be determined by the technical spirit of the appended claims.

100: optical splitter 200: optical filter unit
210: low pass filter 220: band pass filter
300: coherent receiving unit 310: optical synthesis unit
320: light detection unit

Claims (12)

An optical filter unit for filtering the received optical signal transmitted through the optical fiber in different frequency bands to obtain a baseband optical signal and an SBS tone generated by stimulated Brillouin Scattering (SBS); And
A coherent receiver configured to obtain a beating optical signal by beating the baseband optical signal and the SBS tone and detecting the detected beating optical signal to obtain a received signal,
The optical filter unit
A low pass filter for obtaining the baseband optical signal by low-pass filtering the received optical signal according to a predetermined frequency band; And
And a band pass filter for obtaining the SBS tone by band pass filtering the received optical signal according to a predetermined frequency band.

delete The method of claim 1, wherein the band pass filter is
A coherent receiving device in which a filtering frequency band is varied according to a characteristic of a material constituting the optical fiber. The method of claim 1, wherein the coherent receiving device
A coherent reception apparatus further comprising an optical splitter for separating the received optical signal transmitted through the optical fiber and transmitting the separated optical signal to the low pass filter and the band pass filter. The method of claim 1, wherein the coherent receiver
An optical synthesizing unit for obtaining the beating optical signal by synthesizing the SBS tone with the baseband optical signal using the local oscillation light source; And
A coherent receiving apparatus comprising a light detector configured to detect the beating optical signal and convert it into an electrical signal to obtain the received signal. The method of claim 5, wherein the coherent receiver
The coherent receiving apparatus further comprises a down converter for lowering the frequency band of the beating optical signal and transmitting the beating optical signal to the optical detection unit. Filtering the received optical signal transmitted through the optical fiber in different frequency bands to obtain a baseband optical signal and an SBS tone generated by Stimulated Brillouin Scattering (SBS); And
Beating the baseband optical signal and the SBS tone to obtain a beating optical signal, and detecting the detected beating optical signal to obtain a received signal,
The step of obtaining the SBS tone
Low-pass filtering the received optical signal according to a predetermined frequency band to obtain the baseband optical signal; And
And band pass filtering the received optical signal according to a predetermined frequency band to obtain the SBS tone.
delete The method of claim 7, wherein the band pass filtering step
A coherent receiving method in which a filtering frequency band is varied according to a characteristic of a material constituting the optical fiber. The method of claim 7, wherein the coherent receiving method
Separating the received optical signal transmitted through the optical fiber, and transmitting the signal to the low pass filter and the band pass filter, respectively. The method of claim 7, wherein obtaining the received signal comprises:
Synthesizing the baseband optical signal with the baseband optical signal using the SBS tone as a local oscillation light source to obtain the beating optical signal; And
And converting the beating optical signal into an electrical signal to obtain the received signal. The method of claim 11, wherein obtaining the received signal comprises:
Before the step of converting to an electrical signal, the coherent reception method further comprising the step of lowering the frequency band of the beating optical signal.

Images