KR20140086222A

KR20140086222A - Apparatus and method for scrambling of optical signal, optical transmitter for the same

Info

Publication number: KR20140086222A
Application number: KR1020120156449A
Authority: KR
Inventors: 배준기; 정규현; 남윤호
Original assignee: 에릭슨 엘지 주식회사
Priority date: 2012-12-28
Filing date: 2012-12-28
Publication date: 2014-07-08

Abstract

The present invention relates to an apparatus and method for scrambling an optical signal, capable of improving the quality of an upstream signal by scrambling a downstream signal transmitted from a central base station. The apparatus for scrambling an optical signal according to the present invention forms the upstream signal by scrambling the downstream signal transmitted from an upstream terminal by resonance and modulation.

Description

Technical Field [0001] The present invention relates to an optical signal flattening apparatus and method, and an optical transmitter for the optical transmitter and the optical transmitter.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to wavelength division multiplexing (WDM), and more particularly, to an optical signal flattening apparatus and method capable of improving uplink signal quality by flattening a downlink optical signal transmitted from a central office.

A wavelength division multiplexing (WDM) -PON (wavelength division multiplexing-passive optical network) is a central office (FTTH) based on wavelength division multiplexing (WDM) ) And a subscriber use a method in which communication is performed using each wavelength set for each subscriber. This WDM-PON can provide independent and large-capacity communication service for each subscriber, and is excellent in security. Also, unlike time division multiplexing (TDM), the modulation and demodulation of a light source is performed only for one subscriber, so that a WDM-PON can use a receiver with a narrow modulation speed and low output light source and bandwidth. However, since a WDM-PON requires a light source having an original wavelength as many as the number of subscribers, the WDM-PON has a financial burden on a service provider, which is difficult to implement in practice. Therefore, it is necessary to develop a low-cost WDM-PON light source. Also, in terms of equipment management, preparing a light source with different wavelengths for each subscriber in preparation for installation and malfunction can put a heavy burden on the operators. Therefore, it is necessary to provide the same kind of light source to all subscribers in a wavelength independent manner for the implementation of WDM-PON. As a light source for WDM-PON recently studied, a broadband light source (BLS) having a wide optical bandwidth such as ASE (amplified spontaneous emission) or LED (light emitting diode) is used as an arrayed waveguide grating There is a spectrum sliced light source in which a light source having a plurality of constant wavelength intervals is formed at one time by spectrum slicing with a wavelength division element. The spectrally divided light source can provide the same light source to a subscriber regardless of wavelength, but has a problem of low output power and low modulation speed. Therefore, in order to solve the disadvantage of this spectrum division light source, the ASE-injected FP-LD (ASE injected) which uses the spectrally divided ASE as a single mode light source by injecting into the FP-LD FP-LD) is used. ASE-injected FP-LDs can provide the same light source to wavelength-independent subscribers, but can provide large output power and high modulation speed, while expensive FP-LDs There is a problem in that a separate temperature control is required.

In order to solve the above problem, a method has been proposed in which a subscriber terminal re-modulates an optical signal transmitted from a central base station to an uplink signal and then transmits the modulated downlink optical signal to the central base station. However, since the modulated downlink optical signal can not be completely flattened, It acts as a noise in the signal. In order to reduce the noise in the upstream signal, research has been conducted to maximize the modulation characteristics of the downstream signal by utilizing the optical saturation characteristic of the optical device. However, the extinction ratio of the downstream optical signal is limited to about 3 dB, Therefore, when the extinction ratio is changed according to the wavelength alignment state of the downstream optical wavelengths and the elements constituting the downstream optical link, the quality of the downstream signal may be drastically degraded.

Korean Patent Publication No. 10-2006-0037573 (published on May 3, 2006)

The present invention provides an optical signal flattening apparatus and method capable of improving upstream signal quality by flattening a downstream optical signal transmitted from a central office.

The optical signal flattening apparatus of the present invention performs a flattening by using resonance and modulation on a downstream signal transmitted from an upstream end to form an upstream signal.

The optical transmitter of the present invention may further comprise: the optical signal flattening device; And a modulator for performing modulation of an upstream signal formed in the optical signal flattening apparatus.

According to another aspect of the present invention, there is provided an optical signal flattening method including: receiving a downlink signal transmitted from an uplink; And forming an upstream signal by performing planarization using the resonance and modulation on the downstream signal.

According to the present invention, the modulated downlink signal can be flattened and the quality of the uplink signal can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an exemplary view showing a configuration of an optical signal flattening apparatus according to an embodiment of the present invention. FIG.
FIG. 2 through FIG. 7 are views illustrating the configuration of an optical transmitter according to an embodiment of the present invention. FIG.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, well-known functions or constructions will not be described in detail if they obscure the subject matter of the present invention.

In this embodiment, as a means for flattening the downstream signal transmitted from the central office, the light is oscillated by using the gain medium 110 having a length equal to or greater than a certain length, thereby canceling the modulation characteristics and flattening the downstream optical signal The quality of the upstream signal can be improved.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a diagram showing an example of a configuration of an optical signal flattening apparatus according to an embodiment of the present invention; FIG.

As shown in FIG. 1, the optical signal flattening apparatus 100 includes a gain medium 110, an optical waveguide 120 having a predetermined length or more, and a reflector 130.

The gain medium 110 may perform amplification of the downstream signal transmitted from the upstream terminal.

The optical waveguide 120 can propagate the downward signal in the axial direction within the gain medium 110. [ In one embodiment, the optical waveguide 120 may be set to have a predetermined length L or more. The length of the optical waveguide 120 may be equal to the modulation period of the downlink signal or longer than the modulation period of the downlink signal.

The reflector 130 may be positioned at both ends of the gain medium 110 and the optical waveguide 120 to generate a down signal. At this time, in the gain medium 110, the received optical signals are modulated while being resonated, and the transmitted downstream signals are accumulated and planarized. In one embodiment, the reflective portion 130 may be formed by the cut surface of the gain medium 110.

On the other hand, the modulator M modulates the upstream signal, which is flattened and amplified by the optical signal flattening apparatus 100, and transmits the upstream signal to the upstream path. The quality of the uplink signal can be improved by flattening the downlink signal modulated through the series of processes.

2 is a diagram illustrating an optical transmitter according to an embodiment of the present invention.

2, the gain medium 220 and the optical waveguide 230 having a predetermined length (L? C / (n 占))) or more are provided between the first reflector 211 and the second reflector 212, And the flattened downstream signal is remodulated by the modulator 240 and transmitted as an upstream signal. In one embodiment, the modulator 240 may include a semiconductor optical amplifier (SOA), a fabry-perot laser diode (FP-LD), or an electro-absorption modulator. However, the configuration of the modulator 240 is not limited to the above embodiment. The second reflector 211 between the gain medium 220 and the modulator 240 may be implemented by fresnel reflection by simply spacing the gap between the modulator 240 and the gain medium 220 . The downstream signal is input to the first reflector 211 by the three-terminal optical circulator 250 and the upstream signal output from the modulator 240 is output to the upstream path by the circulator 250 have. That is, the down signal is input to the first terminal of the three-port optical circulator 250 and the up signal is output, the second terminal of the three-terminal optical circulator 250 is connected to the input terminal of the optical signal flattening device, The output terminal of the optical signal flattening apparatus is connected to the input terminal of the modulator 240 and the output terminal of the modulator 240 can be connected to the third terminal of the three-terminal optical circulator 250.

3 is a diagram illustrating an optical transmitter according to an embodiment of the present invention.

The optical transmitter shown in FIG. 3 does not include a 3-terminal optical circulator, unlike the optical transmitter of FIG. 2, and can transmit an upstream signal and a downstream signal using one optical path. That is, a downstream signal is input to an input terminal of a modulator, an upstream signal is output, and an input terminal of the optical signal flattening apparatus can be connected to an output terminal of the modulator.

4 is a diagram illustrating an optical transmitter according to an embodiment of the present invention.

4, the modulator 410 may be connected to the optical waveguide 420 of the optical signal flattening apparatus using a four-terminal optical coupler 421, unlike the optical transmitter of FIGS.

5 is a diagram illustrating an optical transmitter according to an embodiment of the present invention.

The optical transmitter shown in FIG. 5 may implement the first reflector 510 as a fiber loop mirror.

6 is a diagram illustrating an optical transmitter according to an embodiment of the present invention.

The optical transmitter shown in FIG. 6 can configure the optical signal flattening apparatus 600 using the gain medium 610 and the optical coupler 620. In one embodiment, the gain medium 610 may be implemented with a semiconductor optical amplifier 620. The optical coupler 620 is implemented as a four-terminal optical coupler so that one input terminal and one output terminal are connected to the input and output terminals of the gain medium 610, respectively, and the other input and output terminals of the four- And an input terminal and an output terminal.

FIG. 7 is a diagram illustrating an optical transmitter according to an embodiment of the present invention. Referring to FIG.

The optical transmitter shown in FIG. 7 can constitute an optical signal flattening apparatus using a reflective semiconductor optical amplifier 700. A part of the output of the optical signal flattening apparatus is transmitted as an up signal on the up path, and the remaining part of the output can be set to resonate. In one embodiment, the reflective semiconductor optical amplifier 700 may include an erbium-doped fiber amplifier.

Although the method has been described through particular embodiments, the method may also be implemented as computer readable code on a computer readable recording medium. A computer-readable recording medium includes all kinds of recording apparatuses in which data that can be read by a computer system is stored. Examples of the computer-readable recording medium include a ROM, a RAM, a CD-ROM, a magnetic tape, a floppy disk, an optical data storage device, and the like, and may be implemented in the form of a carrier wave (for example, transmission over the Internet) . In addition, the computer-readable recording medium may be distributed over network-connected computer systems so that computer readable codes can be stored and executed in a distributed manner. In addition, functional programs, codes, and code segments for implementing the above embodiments can be easily deduced by programmers of the present invention.

Although the present invention has been described in connection with some embodiments thereof, it should be understood that various changes and modifications may be made therein without departing from the spirit and scope of the invention as understood by those skilled in the art. something to do. It is also contemplated that such variations and modifications are within the scope of the claims appended hereto.

100: optical signal flattening device 110, 220, 610: gain medium
120, 230, 420: optical waveguides 130, 211, 212:
240, 410, M: modulator 250: circulator
510: Fiber Loop Mirror 620: Optocoupler
700: reflective semiconductor optical amplifier

Claims

An optical signal flattening apparatus comprising:
And forming an upstream signal by performing planarization using resonance and modulation on the downstream signal transmitted from the upstream end.

The method according to claim 1,
A gain medium for performing the resonance and the modulation of the downlink signal;
An optical waveguide for propagating the downlink signal in the axial direction within the gain medium; And
And at least one reflector positioned at both ends of the gain medium and the optical waveguide to perform oscillation of the downlink signal.

3. The method of claim 2,
The optical waveguide includes:
Wherein the length of the optical waveguide is set equal to or longer than the modulation period of the downstream signal.

3. The method of claim 2,
Wherein the gain medium comprises:
A semiconductor optical amplifier comprising an optical signal flattening device.

3. The method of claim 2,
Wherein the at least one reflector comprises:
Wherein the gain medium is formed by a cut surface of the gain medium.

3. The method of claim 2,
Wherein the at least one reflector comprises:
A fiber optic signal flattening device comprising a fiber loop mirror.

3. The method of claim 2,
Wherein the at least one reflector comprises:
And reflects a part of the input signal and transmits another part of the input signal.

3. The method of claim 2,
Further comprising a four-terminal optical coupler,
The four-terminal optical coupler has one input terminal and one output terminal respectively connected to the input and output terminals of the gain medium, and the other input and output terminals of the four-terminal optical coupler are respectively configured as an input terminal and an output terminal of the optical signal flattening device Wherein said optical signal flattening device comprises:

The method according to claim 1,
An erbium-doped fiber amplifier that performs the resonance and the modulation of the downlink signal and propagates the downlink signal; And
And at least one reflector for performing oscillation of the downstream signal.

3. The method of claim 2,
Wherein an input terminal of the downstream signal and an output terminal of the upstream signal are the same.

An optical transmitter comprising:
The optical signal flattening apparatus according to any one of claims 1 to 10, And
And a modulator for performing modulation of an upstream signal formed in the optical signal flattening apparatus.

12. The method of claim 11,
The modulator comprising:
A semiconductor optical amplifier, a fabry-perot laser diode (FP-LD), and an electro-absorption modulator.

12. The method of claim 11,
Further comprising a three-terminal optical circulator,
Wherein the first terminal of the three-terminal optical circulator is a terminal for outputting the upstream signal, the second terminal of the three-terminal optical circulator is connected to the input terminal of the optical signal flattening apparatus, And an output terminal of the modulator is connected to a third terminal of the three-terminal optical circulator.

As an optical signal flattening method,
Receiving a downlink signal transmitted from an uplink; And
And forming an upstream signal by performing planarization using the resonance and modulation on the downstream signal.