KR100359724B1 - method for demultiplexing using a photorefractive multi-hologram and system for performing the same - Google Patents

Abstract

A demultiplexing method using optical refraction multiple holograms suitable for wavelength division multiplexing (WDM) optical communication systems using optical refraction crystals and multiple recording techniques, and a system for performing the same are disclosed. The present invention comprises the steps of: fixing the incidence angles of two recording beams by the Bragg condition and then recording N different diffraction gratings at one position in the optical refraction crystal while rotating the optical refraction crystal; A beam having a wavelength of λ1-λN is incident on an optical refraction crystal in which a plurality of diffraction gratings are multiplexed at an angle, and reflected by different diffraction gratings, thereby spatially separating beams having a wavelength of λ1-λN. It comprises the step of. The demultiplexing method according to the present invention is simple to manufacture, easy to implement a device, easy channel spacing and channel expansion, and can minimize losses.

Description

Method for demultiplexing using a photorefractive multi-hologram and system for performing the same

The present invention relates to a demultiplexing method using optical refraction multiple holograms and a system for performing the same. In particular, the present invention relates to an optical refraction multiple hologram suitable for a wavelength division multiplexing (WDM) optical communication system using optical refraction crystals and multiple recording techniques. Demultiplexing method and system for performing the same.

In general, a wavelength division multiplexing (WDM) method is a signal transmission technique using an optical fiber. Recently, high-capacity optical transmission technology using high-density wavelength division multiplexing (WDM) has been actively researched to meet exponentially increasing communication demands. Compared to a conventional optical signal transmission using a single optical fiber within a single optical fiber, the wavelength division multiplex (WDM) method uses a single optical fiber 20 as shown in FIG. ) Multiplexes and transmits optical signals of different wavelengths through the multiplexer 15, and the receiving terminal 30 can increase the transmission capacity of the optical fiber by separating the optical signals through the demultiplexer 35 according to the wavelength. .

Therefore, wavelength division multiplexing (WDM) can increase network capacity without the need for additional fiber optics and high-speed transmission equipment, resulting in increased Internet use, broadband networking, and the emergence of new high-bandwidth applications. It is attracting attention as a technology capable of accommodating a large amount of information.

In order to commercialize the optical communication technology using the WDM, optical components such as an optical wavelength filter, a multi-channel wavelength multiplexer (MUX) and a demultiplexer (DMUX), an optical amplifier, and an optical wavelength conversion element are used. Need development In particular, the multi-channel multiplexer (MUX) and the de-multiplexer (DMUX) for combining signals from light sources having different wavelengths and transmitting them through a single optical fiber and separating the signals according to wavelengths at the receiving end are high density multi-channel wavelengths. It is an essential device for realizing optical communication system using division multiplexing (WDM).

In general, DMUX devices used in WDM optical transmission systems employ an array waveguide (AWG), an optical fiber coupler and a Fabry-Perot filter (FPF). Combined filter, multiple fiber grating filters and optical circulators in series

The way to do it is used.

The optical demultiplexing device using the arrayed waveguide has a configuration as shown in FIG. The demultiplexing device using the arrayed waveguide 40 is useful when the channel (Ch1-ChN) spacing is constant, and when the number of channels is large, the loss is less than that of other methods, and the channel spacing can be adjusted during manufacturing. It has a stable advantage against temperature changes. However, when the channel spacing is not constant, there is a problem in that the implementation of the device is difficult due to manufacturing difficulties.

In the optical demultiplexing device combining the optical fiber coupler and the Fabry-Perot filter (FPF), as shown in FIG. 3, the optical fiber coupler 50 outputs a signal having a plurality of wavelengths (λ 1 -λ N) to the output terminal. It serves to separate into N optical fibers (Ch1-ChN) connected, the Fabry-Perot filter 52, each coupled to the optical fiber to separate only the desired wavelength. That is, the Fabry-Perot filter 52 coupled to the optical fiber of Ch1 separates the wavelength of λ1, and the Fabry-Perot filter 52 coupled to the optical fiber of ChN separates the wavelength of λN and is coupled to each channel. The filter separates the different wavelengths to perform the function of the demultiplexer.

The optical demultiplexing device combining the optical fiber coupler and the Fabry-Perot filter (FPF) is easy to separate the channels, but the optical signal is divided into N channels by using the optical fiber coupler. There is a problem.

As shown in FIG. 4, the optical demultiplexing element in which a plurality of fiber grating filters and an optical circulator are coupled in series, the fiber grating filter 62 selects any one of a plurality of wavelengths. The optical circulator 60 serves to spatially separate the selected wavelengths reflected by the fiber grating filter 62.

Although the optical demultiplexing device of this type has a low loss, it is advantageous when the number of channels is small because a circulator and a fiber grating filter equal to the number of channels are required, but the loss and noise component increase proportionally as the number of channels increases. There is a problem that the efficiency is uneven, and it is also difficult to accurately control the center wavelength of the fiber grating filter.

The present invention was invented to solve all the problems of the conventional optical demultiplexing device as described above, and the first object of the present invention is simple fabrication and easy device implementation using photorefractive crystal and multiple recording techniques. It is to provide a demultiplex method using optical refraction multiple hologram that can easily adjust the channel spacing, channel expansion and minimize the loss.

Another object of the present invention is to provide a system for carrying out the first object described above.

1 is a block diagram showing an optical transmission system employing a wavelength division multiplexing scheme.

2 is a block diagram showing an optical demultiplexing device using an arrayed waveguide.

3 is a block diagram showing an optical demultiplexer combining an optical coupler and a Fabry-Perot filter.

4 is a block diagram illustrating an optical demultiplexer in which a plurality of fiber grating filters and an optical circulator are coupled in series.

5 is a block diagram illustrating a method of selecting a wavelength using the optical refraction multiple hologram according to the present invention.

6 is a block diagram illustrating a multiple recording method using a rotation multiplexing technique used in a demultiplexing apparatus using an optical refractive multiple hologram according to the present invention.

7 is a block diagram illustrating a demultiplexing apparatus using the optical refraction multiple hologram according to the present invention.

8 is a graph showing test results of the demultiplexing apparatus using the optical refraction multiple hologram according to the present invention.

<Explanation of symbols for the main parts of the drawings>

110: optical refraction crystal 112: diffraction grating

120: beam splitter 130: lens

140: optical fiber 130: vertical rotating roller

λw: recording beam

The present invention for performing the first object described above,

Fixing the incidence angles of the two recording beams by the Bragg condition and then recording N different diffraction gratings at one position in the optical refraction crystal while rotating the optical refraction crystal;

A beam having a plurality of wavelengths (λ1-λN) is incident on an optical refraction crystal in which a plurality of diffraction gratings are multiplexed at an angle, thereby reflecting different wavelengths by each diffraction grating, and thus a plurality of wavelengths (λ1-λN) Spatially separating the beams.

In addition, the present invention for performing the above second object,

An optical refraction crystal in which N different diffraction gratings are multi-recorded at one position by being exposed to two recording beams while being placed and rotated on an upper portion of a rotating plate rotated by a motor;

A beam splitter formed at a position at which light reflected by the light refraction crystal can be input, and configured to divide light reflected by the light refraction crystal;

A lens formed at an output side of the beam splitter and configured to correct a path of a beam output from the beam splitter;

A plurality of lenses are formed on the output side of the lens and include an optical fiber for entering the divided beam.

The demultiplexing method according to the present invention is simple to manufacture, easy to implement a device, easy channel spacing and channel expansion, and can minimize losses.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

5 is a block diagram illustrating a method of selecting a wavelength using the optical refraction multiple hologram according to the present invention, Figure 6 is used in a demultiplex apparatus using the optical refraction multiple hologram according to the present invention A configuration diagram for explaining a multiple recording method using a rotation multiplexing technique.

And, Figure 7 is a block diagram showing a demultiplexing apparatus using a light refractive multiple hologram according to the present invention, Figure 8 is a graph for showing the test results of the demultiplexing apparatus using a light refractive multiple hologram according to the present invention to be.

First, referring to FIG. 5, a basic principle of selecting one wavelength among a plurality of wavelengths by using a photorefractive crystal will be described. When two recording beams λw are incident on the photorefractive crystal 110, the optical refraction crystal 110 A diffraction grating 112 is formed in the dot. When a beam having a wavelength of λ 1 -λ N is incident on the diffraction grating 112, only a wavelength λ 1 that satisfies the Bragg condition of <Equation 1> is reflected and detected by the diffraction grating 112, and the wavelength of λ 2 -λ N is transmitted as it is. .

Therefore, it is possible to apply to an inverse multiple device that separates multiple wavelengths by using the wavelength selection principle of the diffraction grating 112 of the photorefractive crystal 110. To this end, a process of recording a plurality of diffraction gratings 112 in the photorefractive crystal 110 and a process of detecting a plurality of diffraction gratings 112 recorded in the photorefractive crystal 110 are required.

The process of recording the plurality of diffraction gratings 112 in the optical refraction crystal 110 is shown in FIG. 6, in the state where the optical refraction crystal 110 is placed on the rotating plate 114 rotated by the motor M. The first diffraction grating is recorded after fixing the incident angle of the recording beam [lambda] w to the angle calculated by the Bragg condition of <Equation 1>.

Thereafter, the motor M is operated to rotate the optical refraction crystal 110 placed on the top of the rotating plate 114, and then record the second diffraction grating. If this process is repeated N times, N different diffraction gratings 112 are formed at one position in one optical refraction crystal 110.

As described above, there are a method of changing the angle of the recording beam λw and a method of rotating the light refraction crystal 110 in order to record the plurality of diffraction gratings 112 in the light refraction crystal 110. The method of changing the angle is to record the plurality of diffraction gratings 112 in the optical refraction crystal 110 by changing the incident angle of one of the two recording beams λw with the optical refraction crystal 110 fixed. In this method, the optical refraction crystal 110 is rotated and the crystal is rotated and recorded while the incident angles of the two recording beams λw are fixed.

The multiplexing technique of varying the angles makes it difficult to record multiple diffraction gratings 112 at one position in the optical refraction crystal 110, and the wavelength selection characteristics of each diffraction grating 112 are changed to be applied as demultiplexing elements. Inappropriate for On the contrary, the multiplexing technique of rotating the optical refraction crystal 110 can obtain the same multiple recording characteristics, it is easy to record multiple diffraction gratings 112 at the same position in the optical refraction crystal 110, and each diffraction grating Since the wavelength selection characteristic of 112 remains the same, it is most suitable for application as a demultiplexing element.

Therefore, in the present invention, after placing the optical refraction crystal 110 on the top of the rotating plate 114 that is rotated by the motor (M), N different diffraction gratings 112 at one position within the optical refraction crystal 110 ) Forms. The time at which the optical refraction crystal 110 is exposed to the two recording beams λw is varied to form N different diffraction gratings 112 at one location within the optical refraction crystal 110.

That is, when the first diffraction grating 112 is recorded on the optical refraction crystal 110 and the second diffraction grating 112 is recorded, a part of the first diffraction grating 112 already recorded is erased. Therefore, when several diffraction gratings are recorded for the same time, the first diffraction grating has the lowest diffraction efficiency and the later recorded grating has the highest diffraction efficiency. If multiple gratings having non-uniform diffraction efficiencies are applied to the demultiplexer, it is difficult to detect the original signal.

In order to solve such a problem, the longest recording time is allocated to the first diffraction grating 112, that is, the time exposed to the two recording beams λw, and the longest recording time is recorded. By shortening the exposure time, the exposure time is changed so that the diffraction efficiency of all the diffraction gratings 112 recorded in the optical refraction crystal 110 is constant.

The optical refraction crystal 110 in which the plurality of diffraction gratings 112 is recorded can detect N wavelength signals using the N diffraction gratings 112 recorded in the optical refraction crystal 110 as shown in FIG. 7. have. N diffraction gratings 112 are already recorded in the optical refraction crystal 110, and when the beam having a plurality of wavelengths (λ 1 -λ N) is incident into the diffraction grating 112, the first recorded diffraction gratings If the wavelength satisfying the Bragg condition of (112) is λ 1, the first diffraction grating 112 reflects λ 1, and the second recorded diffraction grating 112 reflects the other wavelength λ 2.

That is, assuming that N and diffraction gratings 112 are recorded in the optical refraction crystal 110, each diffraction grating 112 reflects different wavelengths and spatially separates a plurality of incident wavelengths λ 1 -λ N. Done. Therefore, referring to FIG. 7, the optical refraction crystal 110 and the beam splitter 120 in which the multiple diffraction gratings 112 are multiplexed are installed at positions for dividing the light reflected from the optical refraction crystal 110, The lens 130 for correcting the path of the beam output from the beam splitter 120 is installed at the output side of the beam splitter 120, and the optical fiber 140 is installed at the output side of the lens 130 to allow the split beam to be incident. ) Installs a demultiplexer that separates the incident N wavelengths by channel.

In the demultiplexing system using the optical refraction multi-hologram according to the present invention, since a beam having a plurality of wavelengths (λ1-λN) is incident at a fixed angle after multiple recording of the diffraction grating, the device is easy to manufacture and easy to implement. Instead, the loss is minimized, and the distance between the channels is determined by the angle of rotating the optical refraction crystal 110, so that the channel interval can be set freely by adjusting the rotation angle. That is, since the number of channels is the same as that of the diffraction grating 112 to be recorded in the optical refraction crystal 110, when the angle of rotating the optical refraction crystal 110 is large, the distance between the channels becomes large and the optical refraction crystal 110 is rotated. If the angle is small, the number of channels is small and the channel is very easy to expand.

In addition, since the multiplexing technique is used to record a plurality of diffraction gratings 112 in the optical refraction crystal 110, the passbands of each channel are the same, and it is easy to record a plurality of gratings in one position. It is easy to manufacture and there is no increase and accumulation of loss and noise even if the number of channels increases.

In general, the thickness of the optical refraction crystal is about 1 cm, which is very thick compared to a general medium capable of recording a diffraction grating. The thickness of the medium has a dominant influence on the bandwidth of each channel. The thicker the thickness, the narrower the passband characteristics. In the present invention, since the 1cm thick photorefractive crystal 110 is used, narrow band characteristics can be obtained.

As a result of testing the demultiplexing apparatus using the optical refraction multi-hologram according to the present invention, the 3db passband of each channel showed a very narrow band characteristic of 0.16nm ± 0.005nm, by fully utilizing the thickness of the photorefractive crystal 110 Since it is applied as a wavelength selection device, a narrow passband can be obtained compared to the channel bandwidth of the conventional demultiplexing device. The interval between the 16 channels is 0.5 nm to adjust the angle of rotating the optical refraction crystal 110, it is possible to freely adjust the channel interval. The diffraction efficiency of each channel is 8.3% ± 0.62%, which shows almost the same efficiency characteristics, and can be obtained by changing the exposure time of multiple diffraction gratings 112.

The loss due to Fresnel reflection and absorption in the demultiplexer according to the present invention is on the order of 2.22 dB / cm. The loss due to double absorption is not a big problem because it is negligibly small in the optical communication wavelength region of 1560 nm. The loss due to Fresnel reflections on the crystal surface may currently have a reflectance of less than 0.2% when anti-reflection coding is performed on the crystal surface.

As described above, the demultiplexing system using the optical refraction multi-hologram according to the present invention is not only easy to manufacture, but also easy to implement a device, minimizes loss, freely sets the channel spacing, and very easy to expand the channel.

In addition, the passbands of each channel are all the same, and it is easy to manufacture a plurality of grids in one location, so it is easy to manufacture, and there is no increase and accumulation of loss and noise even if the number of channels increases.

Although the preferred embodiments of the present invention have been described in detail with reference to the accompanying drawings, the present invention is not limited thereto and may be improved or modified by those skilled in the art within the scope of the technical idea of the present invention.

Claims (7)

Iv) fix the incidence angles of the two recording beams λw by the Bragg condition, and then rotate the optical refraction crystal 110 to place N different diffraction gratings 112 at one position within the optical refraction crystal 110. Multi-recording to expand the channel; Ii) a beam having a plurality of wavelengths (λ 1 -λ N) is fixed at an angle to the optical refraction crystal 110 in which the multiple diffraction gratings 112 are multi-recorded in the above step and incident to the respective diffraction gratings 112 And reflecting different wavelengths to spatially separate beams having the plurality of wavelengths (λ 1 -λ N). 2. The method of claim 1, wherein the step V changes the exposure time to the two recording beams? W according to the order of the diffraction gratings 112 recorded in the optical refraction crystal 110. Demultiplexing method using optical refraction multiple hologram with diffraction efficiency. The optical diffraction grating 112 according to claim 1 or 2, wherein the diffraction grating 112 with a high order of writing in the optical refraction crystal 110 allocates a long time to be exposed to the two recording beams? The diffraction grating (112) having a late order of recording in the crystal (110) shortly allocates the time exposed to the two recording beams ([lambda] w). The demultiplexing using optical refraction multiple hologram according to claim 1, wherein the step (b) adjusts a channel interval at which the diffraction grating 112 is recorded by changing an angle at which the optical refraction crystal 110 rotates. Way. The optical refraction crystal 110 in which N different diffraction gratings 112 are multi-recorded at one position by being exposed to two recording beams λw while being placed and rotated on an upper portion of the rotating plate 114 rotated by the motor M. ); A beam splitter (120) formed at a position where light reflected by the light refraction crystal (110) can be input, and for splitting the light reflected by the light refraction crystal (110); A lens (130) formed at an output side of the beam splitter (120) for correcting a path of a beam output from the beam splitter (120); A plurality of systems formed on the output side of the lens 130, the demultiplexing system using an optical refraction multiple hologram comprising an optical fiber (140) for entering the divided beam. 6. The demultiplexing system using optical refraction multi-hologram according to claim 5, characterized in that the antireflection coating is performed on the surface of the optical refraction crystal (110) to minimize the loss. 7. The demultiplexing system according to claim 5 or 6, wherein the optical refraction crystal (110) has a thickness of at least 1 cm or more.