ES2297981B2 - OPTICAL DEMULTIPLEXER. - Google Patents

Abstract

The optical demultiplexer. The demultiplexer is an ultra-compact device that spatially separates an incident beam (4) into at least two beams (5, 6) with two wavelengths (u1, u2), forming a predetermined angle (u). The device, represented by two bar gratings (2) (1), consists of a plurality of bar layers (1), made of dielectric material. Having a plane (3), which determines the region where such wavelengths (u1, u2) are collected for analysis, located at a distance (xf) from the device, the scattered beams (5, 6) have a certain width (u) and are separated from the axis of the incident beam (4) with a separation distance (d). Both the thickness of the device, the section of the bars, and the material of its manufacture are determined by the angle (u) of separation required, optimizing them to minimize cross-talk between optical channels at said wavelengths (u1, u2).

Description

Optical demultiplexer

Object of the invention

The present invention applies to the field of telecommunications, particularly in communication networks optics, extending its application to the industrial sectors that they use them for high-speed data transmission, such as in mobile telephony, telemedicine, communications in space systems, etc.

The object of the invention is to provide a ultra-compact device, whose structure is based on multiple layers that form a network composed of bars of material dielectric suitable and conveniently configured to separate, with a predetermined angle, a beam of light incident on several of the wavelengths that constitute it, allowing a dispersion of the beams corresponding to said lengths of wave or demultiplexing of optical channels, with a minimum interference between channels, or what is the same, an attenuation Maximum distortion for all channels.

Background of the invention

At present, employment is growing which is made of optical systems to transmit large quantities of information, representing voice, video and / or data, at a very high speed. The demand for bandwidth for communications optical is growing, as they are used to support a high load of channels; for example, on high television definition, in UMTS third generation telephone services, etc.

Within communication technologies optical, it is known that more than one wavelength can be used to transmit the information through different channels. In particular, each wavelength can be a carrier for signals corresponding to analog or digital systems.

One of the widely used techniques for multiplex a number of different signals in a system of Optical transmission is Multiplexing by Length Division of Wave (WDM), whereby the information, transported with digital signaling, is transmitted by modulating each group of digital signals with a different wavelength, traveling all wavelengths simultaneously by the fiber optics.

With WDM multiplexing, bandwidth is increased thanks to the number of independent channels by the diversity of wavelengths used within the same path optical transmission, such as a fiber or a guide waves.

In obvious consequence, when a number of wavelengths is multiplexed and transmitted through a single guide or fiber optic, it is subsequently necessary that multiple channels are demultiplexed at wavelengths separated. Obviously, it is desirable that this process of demultiplexing is carried out at low cost and with a loss minimum signal Losses that may exist due to interference between the different wavelengths should be similar in magnitude for all channels that are demultiplexed.

A problem associated with division by wavelength is that if the physical dispersion between each length wave that crosses the optical fiber is too narrow, it they can join several wavelengths in the same channel, instead single carrier, which would cause noise and distortion over the information contained in that channel. Therefore, it requires a demultiplexer capable of performing a physical separation of the wavelengths in a wide enough area, so that the multiple information channels are divided with the smallest possible interference

A solution to this problem is the diffractive optical elements, described by the authors JL Horner and PD Gianino in Applied Optics , volume 23, of the year 1984, which can model the beam from an optical source, such as a laser, according to virtually any pattern, by controlling the phases of the different dispersed waves. This property is basically achieved by mounting in a layer small optical elements that each manipulate a part of the incident beam. The implementation of these elements is carried out by varying their refractive index and thickness dimensions, parameters that are generated by computer, looking for the optimum with which a beam is obtained by propagating through the layer of such elements in the pattern
wanted.

However, diffractive optical elements they do not allow to control the reflection of a ray of light from the total opacity until complete transparency.

Other devices that come to solve the Channel separation by wavelengths are those collected, citing some examples, in documents EP 0938205 and US 2004/0051868.

The optical demultiplexer described in EP 0938205 is a plurality of interconnected dichroic filters sequentially and optically coupled to each other, which separate each one of the channels in the sequence order of their respective central wavelengths, starting with the smallest channel wavelength until you reach the one with the largest central wavelength eliminating every time a channel of the remaining ones, finally obtaining at the exit of said filters all channels separately.

In US 2004/0051868, a demultiplexer is described holographic that uses the spectroscopy technique to reflect the different wavelengths that make up a light signal, according to different spatial positions on a device detection of one or more of the reflected wavelengths. This device comprises the detector, a dispersion element of the light, such as a prism or diffraction grating, plus several holograms, each hologram constituting an element of dispersion that redirects a specific range of lengths of wave or a specific wavelength, of those contained in the light ray.

Description of the invention

The invention described herein consists of a photonic device that performs the spatial separation between the minus a couple of wavelengths, acting as an element optical scattering of light in multiple beams that correspond at the different central wavelengths, which are divided with a given width for each beam and forming an angle specific to each other.

More specifically, the present invention is conceived for its integration to flat or fiber waveguides optics in order to demultiplex the traveling signal by said waveguide or fiber.

The proposed demultiplexer is composed by a grid or grid of dielectric bars, arranged in less a pair of photonic plates, implemented in two dimensions by a processing procedure on a single integrated circuit and followed by a micromanipulation for its assembly, according to a reverse design technique, which solve Maxwell's equations for a system of two dimensions using the Multiple Dispersion Theory (MST).

This optical demultiplexer provides Substantial characteristics of novelty and notable advantages in as for its dimensions, since in its implementation it get an ultra-compact device, about 2 \ mum thick, while representing a significant improvement in how to separate the beams in space, since it achieves greater efficiency with respect to known light dispersers, assuming an efficiency measured in terms of crosstalk with a value less than -25 dB for each optical channel.

Each of the sheets or layers of bars dielectric, manufactured with a semiconductor such as arsenide Gallium (AsGa) can preferably be grown by techniques usual lithographs.

The method of manufacturing the structure of the photonic device in three dimensions consists essentially in dividing the structure prepared by a semiconductor nanofabrication technique into several, at least two, sheets in two dimensions. Next, these photonic sheets are mounted in a three-dimensional structure by means of micromanipulation, preferably applying the procedures defined in the document "Three-dimensional photonic crystals for optical wavelengths assembled by micromanipulation" of Volume 81 of Applied Physics Leiters , year 2002, as well as in the article "Micro assembly of semiconductor three-dimensional photonic crystals" of volume 2 of the publication Nature Materials of 2003, both by the authors K. Aoki, HT Miyazaki, H. Hirayama, K. Inoshita, T. Baba, N. Shinya and Y. Aoyagi.

Depending on the spatial separation that wants to get from the optical channels, that is, depending on the wavelengths that you want to disperse and the desired angle of separation between beams, in the physical realization of the device photonic certain design parameters are selected, which they are the thickness of the laminar structure, the section of the bars dielectrics and their construction material, chosen after applying in a computer an optimization process, for example, the Algorithm Genetic (GA), which assumes that all dispersion elements they have a fixed position, in combination with the MST Theory. In In general, the optimization method could be combined with others alternative calculation algorithms that define a procedure able to simulate light scattering through center networks dispersers

If you want to go into more detail about the combined implementation technique MST-GA for photonic devices, you can refer to the article written by A. H \ k {a} kansson, J. Sánchez-Dehesa and L. Sanchis, in the publication of the 2005 in the IEEE Journal on selected areas in communications , or, signed by the same authors together with D. López-Zanón and J. Bravo-Abad, in Applied Physics Letters , volume 84, year 2004.

With respect to the background, the proposed optical demultiplexer shapes the flow of light, allowing a control of the parameters that determine the form of dispersion of the beams with a greater degree of freedom, according to the arrangement of the dielectric bars that make up the structure of the device and that differs from the implementations of the existing demultiplexers in the state of the art.

The photonic dispersion device subject to The invention is based on a plurality of layers formed by a network of individual optical dispersers, instead of a single layer of components that control the phase of the scattered beams as is the case with the diffractive optical elements that are known and mentioned above. In addition, the grid structure or Porous of the device of the invention makes it possible to control the reflection of light from absolute opacity, similar to as it happens in a Bragg reflector, until almost transparency total. However, this possibility of controlling the light field in that wide way it cannot be implemented using the conventional diffractive optical elements.

This photonic dispersion device as well described thus constitutes an applicable ultracompact demultiplexer in WDM systems, where the bandwidth of the optical communications in local area networks (LAN), operating in collaboration with the optical multiplexers that route simultaneously different channels of information through a fiber optic network The effect of crossing lines through the expected coupling between fiber optic cabling signals is You can reduce below -25 dB on each channel, thanks to the incorporation of the optical demultiplexer in the communication network with WDM multiplexing.

In short, the main advantage of The demultiplexer described is that, in addition to being a device Passive optical, has a smaller size, characteristic that makes it a practical solution for various applications of optical communications, where other devices, active or liabilities, would not take place or would imply greater dimensions of the system to which they will be integrated.

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Description of the drawings

To complement the description that is being performing and in order to help a better understanding of the characteristics of the invention, according to a preferred example of practical realization of it, is accompanied as part member of this description, a set of figures where with illustrative and non-limiting nature, what has been represented next:

Figure 1.- Shows a representation schematic of the structure of the device object of the invention and its functionality, indicating the parameters involved in the Reverse design process for implementation: x_ {f} defines the distance between the light scattering device and the plane where divided beams are collected, with wavelengths \ lambda_ {1} and \ lambda_ {2} respectively, adopting some default values over a beam width δ and an angle ? between beams.

Figure 2.- Shows a cut in the plane orthogonal to the axes of the dielectric bars that make up the device, according to a preferred embodiment of the invention, representing the disposition in the two coordinate axes spatial and the dimensions of the bars in \ mum.

Figure 3.- Shows a graphic representation of the operation of the disperser / demultiplexer device optical, in the form of a two-dimensional map generated by the simulation of the reverse design algorithm that implements the device and gives the value of the 20 log function (| E (x, y) \ lambda_ {1} | / | E (x, y) \ lambda_ {2} |) in the spatial area of device and its surroundings, according to a possible embodiment of the invention, which predicts crosstalk between channels or wavelengths \ lambda_ {1} and \ lambda_ {2}.

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Preferred Embodiment of the Invention

It can be described as one of the possible embodiments of the invention, an optical device composed of a plurality of layers, in the preferred example are five layers, of dielectric bars (1) constructed with the semiconductor AsGa. Preferably, only five layers of bars are used dielectric (1) to ensure its perfect alignment through the micromanipulation technique.

In view of Figure 1, the function of device as a light scatter or channel demultiplexer It can be described as follows: The beam of light (4) is the beam of photons containing a certain frequency range and impact perpendicularly on the surface of the device, represented by two gratings (2) of bars (1). The device disperser / demultiplexer divides the incident beam (4) into two beams (5, 6) with two wavelengths (\ lambda_ {1}, λ2), centered at 1.50 µm and 1.55 µm respectively, following different paths so that they form an angle (?) that is approximately 28º. Having a plane (3), which determines the region where such wavelengths (\ lambda, \ lambda_ {2}) are collected for its analysis, located at a distance (x_ {f}) of about 20 µm, scattered photon beams (5, 6) have a width (δ) of about 1 µm in said plane (3).

In a practical example, the light beam (4) can be generated by a polarized laser so that its field electric oscillates in a direction parallel to the transverse axis of the bars (1), represented as ordinate axis (and) in the Figure 2.

A cut in the plane is shown in Figure 2 perpendicular to the axes of the dielectric bars that make up the device, representing its layout in two dimensions space. The manufacturing material of the bars (1), their number, section measurements and spatial arrangement in layers can vary, according to the lithographic technique used in the device implementation, while depending on the parameters of distance (x_ {f}), width (δ) and angle (α), relative to the dispersion of the beams (5, 6), as set as optimal operating values of the demultiplexer. Such bars (1), in this embodiment using as material dielectric AsGa, have a dielectric constant equal to 11.36 approximately, for wavelengths (\ lambda_ {1}, \ lambda_ {2}) of interest, that is, in this case, of the order of 1.50 µm.

As seen in the example in Figure 2, each of the dielectric bars (1) has a section square with dimensions of 0.4 µm x 0.4 µm. Market Stall that five layers are arranged, represented on the abscissa axis of Figure 2, the total thickness of the device is 2 µm, so which makes it an ultra-compact demultiplexer.

To avoid crosstalk between the two channels optics consisting of the pair of wavelengths (λ 1, λ 2), the separation (d) between the axis of incidence of the light beam (4) and each of the beams (5, 6) in which is divided by the demultiplexer, as represented in the Figure 1 is set to 5 µm, said defined being separation (d) from the axis of the incident beam (4), transverse to the device, with respect to the position where said beams (5, 6) they are captured within the plane (3). Therefore, the separation  space (2d) between the two beams (5, 6) is worth 10 µm, in the plane (3) located at a distance (x_ {f}) of 20 µm.

In addition, by capturing the beams (5, 6) on said flat (3) a minimum area or width (δ) of 1 µm is provided, As said before. All these parameters (δ, d, x_ {f}) introduced in the reverse design procedure give place to a separation between beams (5, 6) with an angle equal to 28º and a crosstalk on both channels reduced to less than -25 dB, such as It can be seen in Figure 3.

Figure 3 illustrates the two-dimensional mapping of the 20 log function (| E (x, y) \ lambda_ {1} | / | E (x, y) \ lambda_ {2} |), expressing on the axis of abscissa (X) the distance between the first layer of the device and the plane (3) to the distance (x_ {f}) of up to approximately 20 µm, while that the ordinate axis (Y) takes values of the cross section of the beams (5, 6) in said plane (3); that is, between the interval (d + \ delta / 2, d- \ delta / 2) for the beam (5) measured in positive ordinate (Y) values and interval (-d + δ / 2, -d- δ / 2) for the beam (6) considered in the quadrant of the negative (Y) ordinate space.

It's about maximizing the attenuation of the sum of crosstalk in the two established optical channels, that is, guarantee a minimum crosstalk between the two wavelengths (\ lambda_ {1}, \ lambda_ {2}) for the coordinates (x_ {f}, d)  y (x_ {f}, -d), with a resolution equal to the width (δ) of the respective beams (5, 6). In Figure 3, it is indicated with a pair of rectangles (7) the attenuation of about 25 dB achieved in the desired coordinates, 20 \ mum away (x_ {f}) at analysis plane (3) and at a separation (d) of 5 \ mum ± 1 \ mum, which is the value of the width (δ) of the beams (5, 6). The dielectric bars (1) of the device are drawn, in the cited Figure 3, square comma of 0.4 µm x 0.4 µm, according to a possible spatial arrangement in five layers, between 0 µm and 2 µm total thickness of the demultiplexer. The beam of light (1) It is supposed to affect the first layer of the device, in X = 0, according to the direction of abscissa (X) positive.

The terms with which this text has been written memory should always be taken broadly and not limitative.

The invention has been described according to this text and set of figures for some preferred embodiments thereof, but the subject matter expert will understand that multiple variations may be introduced in said embodiments and combine in various ways giving rise to more variants possible, without leaving the scope defined by the claims which are included below.

Claims (6)

1. Optical demultiplexer, capable of being integrated into a flat waveguide or an optical fiber, which spatially separates the wavelengths (λ 1, λ 2) contained in an incident beam of light (4) on the demultiplexer, to give out a plurality of beams (5, 6) corresponding to the different wavelengths (λ 1, λ 2) separated by an angle (α), characterized in that it consists of a plurality of layers of bars (1), made of a dielectric material, configured with an optimum section to obtain a certain angle (?) of separation between the output beams (5, 6), which disperse the beam of light (4) at its multiple wavelengths (λ 1, λ 2). 2. Optical demultiplexer according to claim 1, characterized in that the dielectric material with which the bars (1) are manufactured is AsGa. 3. Optical demultiplexer according to claim 1, characterized in that the section of the bars (1) is square and with a side equal to 0.4 µm. 4. Optical demultiplexer according to claim 1, characterized in that the number of layers of dielectric bars (1) that make up the demultiplexer is five. 5. Optical demultiplexer according to claim 1, characterized in that the angle (?) Of separation between the beams (5, 6) is 28 °. 6. Optical demultiplexer according to claim 1, characterized in that the output beams (5, 6) correspond to the wavelengths (λ 1, λ 2) of 1.50 µm and 1.55 µm respectively.