CN2552259Y - Etching diffraction grating wave dividing multiplex device using two-point focusing to realize pass-band evenness - Google Patents
Etching diffraction grating wave dividing multiplex device using two-point focusing to realize pass-band evenness Download PDFInfo
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Abstract
The utility model discloses an etching diffracting grating wave division multiplexing device which uses the two-point focusing to realize the smoothness of the passband. The utility model includes an input wave guide, a free spreading area, a concave diffracting grating, and an output wave guide. The structure of the concave diffracting grating is of a concave diffracting grating system composed of two sub-gratings or more than two sub-gratings. The converging point of the sub-grating A1-An is O1, and the converging point of the sub-grating B1-Bn is O2. When the distance between the O1 and the O2 is adjusted to a proper value, the superposition of the two fields can cause that the whole field distribution on the image surface becomes the bimodal type from the traditional Gaussian type, and the shape of the frequency spectrum response of the device becomes flat-topped. No additional technical procedure is introduced in the utility model, the size of the device is not increased, and the device has the advantages of broad passband and large 1dB bandwidth with less power cost.
Description
Technical Field
The utility model belongs to the optical communication wavelength division multiplexing field, in particular to Etching Diffraction Grating (EDG) type wavelength division multiplexing device with wide band-pass, big 1dB bandwidth.
Background
Wavelength division multiplexing/demultiplexing is a key technology of modern optical fiber communication technology. Wavelength division multiplexing/demultiplexing refers to the synthesis of composite light from light of different wavelengths and the separation of light of different wavelengths from the composite light by a special technique. A wavelength division multiplexing (demultiplexing) device is a device that implements a wavelength division multiplexing/demultiplexing technique. The diffraction etching grating (EDG) type wavelength division multiplexer/demultiplexer is one of the planar waveguide dense wavelength division multiplexing devices with great development potential, and compared with other types of wavelength division demultiplexers (such as array waveguide grating type demultiplexers), the EDG type wavelength division multiplexer/demultiplexer has the advantages of high integration level, compact structure, high wavelength resolution and the like, and is suitable for multi-channel wavelength separation.
Fig. 1 is a schematic structural view of a conventional EDG type multiplexing/demultiplexing device. The traditional EDG type multiplexing/demultiplexing device consists of an input waveguide 1, a free propagation region 2, a concave diffraction grating 3 and an output waveguide 4. The composite light is incident from the input waveguide 1, enters the free transmission area 2 for free dispersion and transmission, and reaches the concave diffraction grating 3, because the concave grating has the functions of convergence and dispersion at the same time, the incident light with different wavelengths is converged at different positions on the imaging curved surface after being reflected, and is output by the output waveguide, namely, the light with different wavelengths is separated, thereby realizing the function of demultiplexing. Generally, the same EDG device can be used as both multiplexer and demultiplexer, the only difference being that the direction of light passing through the device is reversed, and for convenience only the demultiplexer will be described below, and the invention is also applicable to multiplexers.
In a conventional design method, the spectral response shape of a wavelength division multiplexing/demultiplexing device is gaussian, and when the actual wavelength deviates from a design value, the received energy is greatly reduced, so that the wavelength division multiplexing/demultiplexing device has strict requirements on the wavelength deviation of a light source in a system, and thus, the laser and the wavelength division multiplexing/demultiplexing device need to be accurately controlled by temperature. In practical situations, a large number of external factors may cause the operating wavelength to drift (including drift of the light source itself, temperature drift, refractive index change, etc.), especially in WDM ring and bus type networks, the signal needs to pass through a plurality of filters, so that the total bandwidth is narrower, which greatly limits the application of the WDM/demux device in WDM systems. The flat frequency spectrum response can effectively eliminate the influence of the factors on the device performance, greatly improve the stability of the system and reduce the use cost.
There are several methods for flattening the spectrum of a wavelength division multiplexing/demultiplexing device, such as: m.r. amersfoort et al published a paper entitled "phase-aligned waveguide length multiplexed with a flattened waveguide response", electron.length, 1994, 30(4), pp.300-302, which proposes the use of multimode waveguide outputs to achieve planarization, but this approach is only applicable where the wavelength division multiplexer/demultiplexer is directly connected to the detector.
Chiba et al in OECC (2000), 13B2-2 mention the use of interleaver to achieve signal complex conjugation for planarization, but this approach makes the device size too large for integration and also relatively expensive.
Rigney et al published an article, "Double-phased array for a flattened spectral response", Proc.23rd ECOC, Edinburgh, UK, pp.79-82, Sept.1997, which mentions the use of bi-phase arrays to achieve planarization, which is similar to the previous method, with relatively limited planarization effect and increased complexity.
Okamoto et al published a paper entitled "elevation-Channel flat panel multiplexer with asymmetric Mach-Aehnder filters", IEEEP lot, Tech.Lett., vol.8, No.3, march 1996, pp.373-374. the paper relates to a method of using an M-Z interferometer to achieve planarization, but this method results in large device sizes, large insertion loss, and also may cause spot distortion.
Disclosure of Invention
The utility model aims at providing a two point focusing realizes etching diffraction grating wavelength division multiplexing device of passband flattening is with a plurality of sub-gratings that the focus point is different with single concave surface diffraction grating replacement, converges incident light in near two points of output waveguide to realize the passband flattening of device.
The technical scheme of the utility model is that: the waveguide grating comprises an input waveguide, a free propagation area, a concave diffraction grating and an output waveguide. The structure of the concave diffraction grating is a concave diffraction grating system consisting of two sub-gratings or more than two sub-gratings, wherein the sub-grating A1～AnHas a convergence point of O1Sub-grating B1～BnHas a convergence point of O2。。
The utility model has the advantages that: the method does not introduce additional process steps, does not increase the size of the device, and enables the device to have the characteristics of wide passband and large 1dB bandwidth at the lower power cost.
Drawings
Fig. 1 is a schematic structural view of a conventional EDG type multiplexing/demultiplexing device;
fig. 2 is a schematic structural view of an EDG type multiplexing/demultiplexing device of the present invention;
FIG. 3 is a schematic diagram of a concave diffraction grating system consisting of two sub-gratings;
FIG. 4 is a schematic diagram of a concave diffraction grating system composed of N sub-gratings with different convergence points alternately distributed;
FIG. 5 is a comparison of field distribution over an image plane for a conventional etched diffraction grating and that achieved by the present invention;
fig. 6 is a comparison of the gaussian shaped spectral response of a conventional etched diffraction grating and the flat-topped spectral response achieved by the present invention.
Detailed Description
As shown in fig. 2, the present invention includes an input waveguide 1, a free propagation region 2, a concave diffraction grating, and an output waveguide 4. The structure of the concave diffraction grating 5 is a concave diffraction grating system consisting of a plurality of sub-gratings with different convergence points.
For incident light of a certain wavelength impinging on the grating, the sub-grating A1～AnA point O for converging the energy irradiated thereon on the image plane2Irradiated to the sub-grating B1～BnThe upper energy is converged to a point O on the image plane2Converge on O1And O2Both of these fields have a gaussian shape, as shown in fig. 5, however, O is added1And O2The distance between the two fields is adjusted to a proper value, and the superposition of the two fields enables the total field distribution on the image surface to be changed from the traditional Gaussian type to the bimodal type, so that the shape of the spectral response of the device is changed into a flat-top shape.
1. Determination of sub-grating structure
Firstly, the number of sub-gratings constituting the concave grating system is determined, and the imaging point of a part of sub-gratings is O1The imaging point of the rest part is O2. The structure of each sub-grating is then determined separately.
As shown in FIG. 3, which is a schematic diagram of the first embodiment of the present invention, the concave diffraction grating 5 is a concave diffraction grating system structure formed by two sub-gratings, and the grating system is composed of a sub-grating A1And sub-grating B1Two parts, sub-grating A1Is an imaging point of1Sub-grating B1Is an imaging point of2Sub-grating A1Each groove face center PiIt should satisfy: <math> <mrow> <mover> <msub> <mi>IP</mi> <mi>i</mi> </msub> <mo>‾</mo> </mover> <mo>+</mo> <mover> <mrow> <msub> <mi>P</mi> <mi>i</mi> </msub> <msub> <mi>O</mi> <mn>1</mn> </msub> </mrow> <mo>‾</mo> </mover> <mo>-</mo> <mrow> <mo>(</mo> <mover> <mi>IO</mi> <mo>‾</mo> </mover> <mo>+</mo> <mover> <msub> <mi>OO</mi> <mn>1</mn> </msub> <mo>‾</mo> </mover> <mo>)</mo> </mrow> <mo>=</mo> <msub> <mi>imλ</mi> <mn>0</mn> </msub> <mo>/</mo> <msub> <mi>n</mi> <mi>eff</mi> </msub> <mo>.</mo> <mo>.</mo> <mo>.</mo> <mo>.</mo> <mo>.</mo> <mo>.</mo> <mrow> <mo>(</mo> <mn>1</mn> <mo>)</mo> </mrow> </mrow> </math> wherein I is an incident point, O is a grating midpoint, and neffIs the effective refractive index of the free diffraction zone, λ0M is the diffraction order of the grating, i is the number of groove faces from the center point O of the grating, under conditions such that the aberration at the center wavelength is 0, and likewise, the sub-grating B1Of each groove face midpoint P'jIt should satisfy: <math> <mrow> <mover> <msub> <msup> <mi>IP</mi> <mo>′</mo> </msup> <mi>j</mi> </msub> <mo>‾</mo> </mover> <mo>+</mo> <mover> <mrow> <msub> <msup> <mi>P</mi> <mo>′</mo> </msup> <mi>j</mi> </msub> <msub> <mi>O</mi> <mn>2</mn> </msub> </mrow> <mo>‾</mo> </mover> <mo>-</mo> <mrow> <mo>(</mo> <mover> <mi>IO</mi> <mo>‾</mo> </mover> <mo>+</mo> <mover> <msub> <mi>OO</mi> <mn>2</mn> </msub> <mo>‾</mo> </mover> <mo>)</mo> </mrow> <mo>=</mo> <msub> <mi>jmλ</mi> <mn>0</mn> </msub> <mo>/</mo> <msub> <mi>n</mi> <mi>eff</mi> </msub> <mo>.</mo> <mo>.</mo> <mo>.</mo> <mo>.</mo> <mo>.</mo> <mo>.</mo> <mrow> <mo>(</mo> <mn>2</mn> <mo>)</mo> </mrow> </mrow> </math>
meanwhile, the middle point of each groove surface is positioned on a grating circle with the radius of R. The position of the middle point of each groove surface in the two sub-gratings can be obtained according to the conditions, after the middle point of each groove surface is determined, the vertical line passing through the middle point and serving as the incident ray is used as the blazed surface of the grating, and therefore the structure of the whole grating is determined.
Fig. 4 is a schematic diagram of another embodiment of the present invention. The concave diffraction grating 5 is determined by the structure of a concave diffraction grating system formed by N sub-gratings which are alternately distributed, if the total groove surface number of the grating is also N, the whole concave diffraction grating system is formed by N sub-gratings, and each sub-grating is arranged on the surface of the whole concave diffraction grating systemThe sub-grating has only one grating groove surface corresponding to different imaging points O1And O2The sub-gratings are alternately distributed, namely, the center P of each groove surface on one sub-grating in two adjacent sub-gratingsiSatisfies the following conditions: <math> <mrow> <mover> <msub> <mi>IP</mi> <mi>i</mi> </msub> <mo>‾</mo> </mover> <mo>+</mo> <mover> <mrow> <msub> <mi>P</mi> <mi>i</mi> </msub> <msub> <mi>O</mi> <mn>1</mn> </msub> </mrow> <mo>‾</mo> </mover> <mo>-</mo> <mrow> <mo>(</mo> <mover> <mi>IO</mi> <mo>‾</mo> </mover> <mo>+</mo> <mover> <msub> <mi>OO</mi> <mn>1</mn> </msub> <mo>‾</mo> </mover> <mo>)</mo> </mrow> <mo>=</mo> <msub> <mi>imλ</mi> <mn>0</mn> </msub> <mo>/</mo> <msub> <mi>n</mi> <mi>eff</mi> </msub> <mo>.</mo> <mo>.</mo> <mo>.</mo> <mo>.</mo> <mo>.</mo> <mo>.</mo> <mrow> <mo>(</mo> <mn>3</mn> <mo>)</mo> </mrow> </mrow> </math> center P 'of each groove face on the other sub-grating'jSatisfies the following conditions: <math> <mrow> <mover> <msub> <msup> <mi>IP</mi> <mo>′</mo> </msup> <mi>j</mi> </msub> <mo>‾</mo> </mover> <mo>+</mo> <mover> <mrow> <msub> <msup> <mi>P</mi> <mo>′</mo> </msup> <mi>j</mi> </msub> <msub> <mi>O</mi> <mn>2</mn> </msub> </mrow> <mo>‾</mo> </mover> <mo>-</mo> <mrow> <mo>(</mo> <mover> <mi>IO</mi> <mo>‾</mo> </mover> <mo>+</mo> <mover> <msub> <mi>OO</mi> <mn>2</mn> </msub> <mo>‾</mo> </mover> <mo>)</mo> </mrow> <mo>=</mo> <msub> <mi>jmλ</mi> <mn>0</mn> </msub> <mo>/</mo> <msub> <mi>n</mi> <mi>eff</mi> </msub> <mo>.</mo> <mo>.</mo> <mo>.</mo> <mo>.</mo> <mo>.</mo> <mo>.</mo> <mrow> <mo>(</mo> <mn>4</mn> <mo>)</mo> </mrow> </mrow> </math>
meanwhile, the middle point of each groove surface is positioned on a grating circle with the radius of R. The position of the middle point of each groove surface in each sub-grating can be obtained according to the conditions, after the middle point of each groove surface is determined, the vertical line passing through the middle point and serving as the incident ray is used as the blazed surface of the grating, and thus the structure of the whole grating is determined.
2. Spectral response
The spectral response function of a diffraction etched grating to a position output waveguide can be expressed as: <math> <mrow> <mi>I</mi> <mo>=</mo> <mfrac> <msup> <mrow> <mo>|</mo> <msub> <mrow> <mo>∫</mo> <mover> <mi>F</mi> <mo>^</mo> </mover> </mrow> <mi>wg</mi> </msub> <msub> <mi>E</mi> <mi>out</mi> </msub> <mrow> <mo>(</mo> <mi>x</mi> <mo>,</mo> <msub> <mi>z</mi> <mi>c</mi> </msub> <mo>)</mo> </mrow> <mi>dx</mi> <mo>|</mo> </mrow> <mn>2</mn> </msup> <mrow> <msub> <mrow> <mo>∫</mo> <mi>E</mi> </mrow> <mi>in</mi> </msub> <mrow> <mo>(</mo> <msup> <mi>x</mi> <mo>′</mo> </msup> <mo>)</mo> </mrow> <mo>·</mo> <msubsup> <mi>E</mi> <mi>in</mi> <mo>*</mo> </msubsup> <mrow> <mo>(</mo> <msup> <mi>x</mi> <mo>′</mo> </msup> <mo>)</mo> </mrow> <msup> <mi>dx</mi> <mo>′</mo> </msup> </mrow> </mfrac> </mrow> </math>
wherein the operatorRepresenting the coupling characteristics of the output waveguide to the grating image.
Since the spectral characteristics of the diffraction-etched grating determine the local wavelength range, the output position and wavelength are linearly varied. It is also assumed that the single-mode transverse field distribution is the same for wavelengths within a channel spacing range. For a conventional design where the output waveguide is also a single mode waveguide, the spectral response of the diffraction etched grating can be found by the overlap integral equation: <math> <mrow> <mi>I</mi> <mrow> <mo>(</mo> <mi>λ</mi> <mo>)</mo> </mrow> <mo>=</mo> <mfrac> <msup> <mrow> <mo>|</mo> <msub> <mrow> <mo>∫</mo> <mi>E</mi> </mrow> <mi>out</mi> </msub> <mrow> <mo>(</mo> <mi>λ</mi> <mo>,</mo> <mi>x</mi> <mo>)</mo> </mrow> <mo>·</mo> <msubsup> <mi>E</mi> <mi>wg</mi> <mo>*</mo> </msubsup> <mrow> <mo>(</mo> <mi>λ</mi> <mo>,</mo> <mi>x</mi> <mo>)</mo> </mrow> <mi>dx</mi> <mo>|</mo> </mrow> <mn>2</mn> </msup> <mrow> <mo>∫</mo> <msub> <mi>E</mi> <mi>in</mi> </msub> <mrow> <mo>(</mo> <mi>λ</mi> <mo>,</mo> <msup> <mi>x</mi> <mo>′</mo> </msup> <mo>)</mo> </mrow> <mo>·</mo> <msubsup> <mi>E</mi> <mi>in</mi> <mo>*</mo> </msubsup> <mrow> <mo>(</mo> <mi>λ</mi> <mo>,</mo> <msup> <mi>x</mi> <mo>′</mo> </msup> <mo>)</mo> </mrow> <msup> <mi>dx</mi> <mo>′</mo> </msup> <mo>·</mo> <msub> <mrow> <mo>∫</mo> <mi>E</mi> </mrow> <mi>wg</mi> </msub> <mrow> <mo>(</mo> <mi>λ</mi> <mo>,</mo> <mi>x</mi> <mo>)</mo> </mrow> <mo>·</mo> <msubsup> <mi>E</mi> <mi>wg</mi> <mo>*</mo> </msubsup> <mrow> <mo>(</mo> <mi>λ</mi> <mo>,</mo> <mi>x</mi> <mo>)</mo> </mrow> <mi>dx</mi> </mrow> </mfrac> </mrow> </math>
wherein EoutIs the field distribution of the grating on the output face, EinAnd EwgAre the mode field distribution functions of the input and output waveguides, respectively. When the two are equal, a self convolution function can be further obtained.
The distribution of the output mode field can be calculated by scalar fluctuation theory. The optical field distribution at the input waveguide (z ═ 0) is divided into a mode field radius of omega0The fresnel diffraction of the gaussian spot in the slab waveguide is described by a gaussian beam, which yields the field distribution over the grating groove plane: <math> <mrow> <mi>E</mi> <mrow> <mo>(</mo> <mi>x</mi> <mo>,</mo> <mi>z</mi> <mo>)</mo> </mrow> <mo>=</mo> <msup> <mrow> <mo>(</mo> <mfrac> <mn>2</mn> <msup> <mi>πw</mi> <mn>2</mn> </msup> </mfrac> <mo>)</mo> </mrow> <mfrac> <mn>1</mn> <mn>4</mn> </mfrac> </msup> <msup> <mi>e</mi> <mrow> <mo>-</mo> <mfrac> <msup> <mi>x</mi> <mn>2</mn> </msup> <msup> <mi>w</mi> <mn>2</mn> </msup> </mfrac> </mrow> </msup> <msup> <mi>e</mi> <mrow> <mo>-</mo> <mi>ik</mi> <mrow> <mo>(</mo> <mi>z</mi> <mo>+</mo> <mfrac> <msup> <mi>x</mi> <mn>2</mn> </msup> <mrow> <mn>2</mn> <mi>R</mi> </mrow> </mfrac> <mo>)</mo> </mrow> <mo>+</mo> <mi>iη</mi> </mrow> </msup> <mo>.</mo> <mo>.</mo> <mo>.</mo> <mo>.</mo> <mo>.</mo> <mo>.</mo> <mrow> <mo>(</mo> <mn>5</mn> <mo>)</mo> </mrow> </mrow> </math> wherein, <math> <mrow> <msup> <mi>ω</mi> <mn>2</mn> </msup> <mo>=</mo> <msup> <msub> <mi>ω</mi> <mn>0</mn> </msub> <mn>2</mn> </msup> <mo>[</mo> <mn>1</mn> <mo>+</mo> <msup> <mrow> <mo>(</mo> <mfrac> <mi>z</mi> <msub> <mi>z</mi> <mn>0</mn> </msub> </mfrac> <mo>)</mo> </mrow> <mn>2</mn> </msup> <mo>]</mo> <mo>,</mo> <mi>R</mi> <mo>=</mo> <mi>z</mi> <mo>[</mo> <mn>1</mn> <mo>+</mo> <msup> <mrow> <mo>(</mo> <mfrac> <msub> <mi>z</mi> <mn>0</mn> </msub> <mi>z</mi> </mfrac> <mo>)</mo> </mrow> <mn>2</mn> </msup> <mo>]</mo> <mo>,</mo> <mi>η</mi> <mo>=</mo> <msup> <mi>tan</mi> <mrow> <mo>-</mo> <mn>1</mn> </mrow> </msup> <mrow> <mo>(</mo> <mi>z</mi> <mo>/</mo> <msub> <mi>z</mi> <mn>0</mn> </msub> <mo>)</mo> </mrow> <mo>,</mo> <msub> <mi>z</mi> <mn>0</mn> </msub> <mo>=</mo> <msub> <mi>πn</mi> <mi>eff</mi> </msub> <msup> <msub> <mi>ω</mi> <mn>0</mn> </msub> <mn>2</mn> </msup> <mo>/</mo> <mi>λ</mi> <mo>.</mo> </mrow> </math> then, the field of each point on the image surface can be obtained through a two-dimensional Kirchoff-Huygens diffraction formula: <math> <mrow> <msup> <mi>E</mi> <mo>′</mo> </msup> <mrow> <mo>(</mo> <msup> <mi>x</mi> <mo>′</mo> </msup> <mo>,</mo> <msup> <mi>z</mi> <mo>′</mo> </msup> <mo>)</mo> </mrow> <mo>=</mo> <mfrac> <mn>1</mn> <mn>2</mn> </mfrac> <msup> <mrow> <mo>(</mo> <mfrac> <msub> <mi>n</mi> <mi>eff</mi> </msub> <mi>λ</mi> </mfrac> <mo>)</mo> </mrow> <mrow> <mn>1</mn> <mo>/</mo> <mn>2</mn> </mrow> </msup> <mo>∫</mo> <mfrac> <mrow> <mi>E</mi> <mrow> <mo>(</mo> <mi>x</mi> <mo>,</mo> <mi>z</mi> <mo>)</mo> </mrow> </mrow> <msqrt> <msub> <mi>r</mi> <mn>0</mn> </msub> </msqrt> </mfrac> <mrow> <mo>(</mo> <mi>cos</mi> <mrow> <mo>(</mo> <msub> <mi>θ</mi> <mi>i</mi> </msub> <mo>+</mo> <msub> <mi>θ</mi> <mi>d</mi> </msub> <mo>)</mo> </mrow> <mi>exp</mi> <mo>(</mo> <mo>-</mo> <msub> <mi>ikr</mi> <mn>0</mn> </msub> <mo>)</mo> </mrow> <mi>ds</mi> <mo>.</mo> <mo>.</mo> <mo>.</mo> <mo>.</mo> <mo>.</mo> <mo>.</mo> <mrow> <mo>(</mo> <mn>6</mn> <mo>)</mo> </mrow> </mrow> </math>
wherein r is0Is the distance from one point (x, z) on the grating to one point (x ', z') on the image plane, E (x, z) is the electric field on the groove plane of the grating, thetaiAnd thetadThe included angles between the incident light and the scattered light and the normal of the grating groove surface are respectively. The output mode field distribution is obtained, and then the coupling efficiency can be calculated by using the overlapping integration, so that the frequency spectrum response is obtained.
Fig. 6 is a comparison of the flat-topped spectral response of the present invention and the gaussian spectral response of the conventional structure, using the parameters:
| radius of the Rowland circle (mum) | 15000 | Grating order m | 16 |
| Inter-imaging dot spacing (μm) | 10.0 | Center wavelength λ0(nm) | 1550.0 |
| Refractive index n of core layercore | 1.4674 | Refractive index n of claddingclad | 1.46 |
| Total number of teeth of grating | 701 | Wave guide width (mum) | 6 |
Compared with the ordinary Gaussian-shaped spectral response, in the structure of the embodiment 1, the 1dB bandwidth of the device is increased by 283.4%, the 3dB bandwidth is increased by 200.5%, the effective bandwidth ratio is 0.455, and the loss is increased by 4.7 dB; in example 2, the 1dB bandwidth of the device increased 132.0%, the 3dB bandwidth increased 112.2%, the quality factor increased from 0.1513 to 0.3291, and the loss increased by 4.5 dB.
Claims (3)
1. The etching diffraction grating wavelength division multiplexing device for realizing passband flattening by two-point focusing comprises an input waveguide (1), a free propagation region (2), a concave diffraction grating and an output waveguide (4), and is characterized in that: the structure of the concave diffraction grating (5) is a concave diffraction grating system consisting of two sub-gratings or more than two sub-gratings, and the sub-grating A1～AnHas a convergence point of O1Sub-grating B1～BnHas a convergence point of O2。
2. According to the claimsThe etching diffraction grating wavelength division multiplexing device for realizing the passband flattening by the two-point focusing of 1 is characterized in that: the concave diffraction grating (5) is determined by the structure of a concave diffraction grating system consisting of two sub-gratings, and the grating system consists of a sub-grating A1And sub-grating B1Two parts, sub-grating A1Is an imaging point of1Sub-grating B1Is an imaging point of2Sub-grating A1Each groove face center PiIt should satisfy: <math> <mrow> <mover> <mrow> <mi>I</mi> <msub> <mi>P</mi> <mi>i</mi> </msub> </mrow> <mo>‾</mo> </mover> <mo>+</mo> <mover> <mrow> <msub> <mi>P</mi> <mi>i</mi> </msub> <msub> <mi>O</mi> <mn>1</mn> </msub> </mrow> <mo>‾</mo> </mover> <mo>-</mo> <mrow> <mo>(</mo> <mover> <mi>IO</mi> <mo>‾</mo> </mover> <mo>+</mo> <mover> <mrow> <mi>O</mi> <msub> <mi>O</mi> <mn>1</mn> </msub> </mrow> <mo>‾</mo> </mover> <mo>)</mo> </mrow> <mo>=</mo> <msub> <mi>imλ</mi> <mn>0</mn> </msub> <mo>/</mo> <msub> <mi>n</mi> <mi>eff</mi> </msub> <mo>.</mo> <mo>.</mo> <mo>.</mo> <mo>.</mo> <mo>.</mo> <mo>.</mo> <mrow> <mo>(</mo> <mn>1</mn> <mo>)</mo> </mrow> </mrow> </math>
wherein I is an incident point, O is a grating midpoint, and neffIs the effective refractive index of the free diffraction zone, λ0M is the diffraction order of the grating, i is the number of groove faces from the center point O of the grating, under conditions such that the aberration at the center wavelength is 0, and likewise, the sub-grating B1Of each groove face midpoint P'jIt should satisfy: <math> <mrow> <mover> <msub> <msup> <mi>IP</mi> <mo>′</mo> </msup> <mi>j</mi> </msub> <mo>‾</mo> </mover> <mo>+</mo> <mover> <mrow> <msub> <msup> <mi>P</mi> <mo>′</mo> </msup> <mi>j</mi> </msub> <msub> <mi>O</mi> <mn>2</mn> </msub> </mrow> <mo>‾</mo> </mover> <mo>-</mo> <mrow> <mo>(</mo> <mover> <mi>IO</mi> <mo>‾</mo> </mover> <mo>+</mo> <mover> <mrow> <mi>O</mi> <msub> <mi>O</mi> <mn>2</mn> </msub> </mrow> <mo>‾</mo> </mover> <mo>)</mo> </mrow> <mo>=</mo> <msub> <mi>jmλ</mi> <mn>0</mn> </msub> <mo>/</mo> <msub> <mi>n</mi> <mi>eff</mi> </msub> <mo>.</mo> <mo>.</mo> <mo>.</mo> <mo>.</mo> <mo>.</mo> <mo>.</mo> <mrow> <mo>(</mo> <mn>2</mn> <mo>)</mo> </mrow> </mrow> </math>
meanwhile, the middle point of each groove surface is positioned on a grating circle with the radius of R, the position of the middle point of each groove surface in the two sub-gratings can be obtained according to the conditions, after the middle point of each groove surface is determined, the vertical line passing through the middle point as the incident light is used as the blazed surface of the grating, and therefore the structure of the whole grating is determined.
3. The etched diffraction grating wavelength division multiplexing device for passband flattening with two point focusing according to claim 1, wherein: the concave diffraction grating (5) is determined by the structure of a concave diffraction grating system formed by N sub-gratings in an alternate distribution mode, if the total groove surface number of the grating is also N, the whole concave diffraction grating system is formed by N sub-gratings, each sub-grating is only provided with one grating groove surface corresponding to different imaging points O1And O2The sub-gratings are alternately distributed, namely, the center P of each groove surface on one sub-grating in two adjacent sub-gratingsiSatisfies the following conditions: <math> <mrow> <mover> <msub> <mi>IP</mi> <mi>i</mi> </msub> <mo>‾</mo> </mover> <mo>+</mo> <mover> <mrow> <msub> <mi>P</mi> <mi>i</mi> </msub> <msub> <mi>O</mi> <mn>1</mn> </msub> </mrow> <mo>‾</mo> </mover> <mo>-</mo> <mrow> <mo>(</mo> <mover> <mi>IO</mi> <mo>‾</mo> </mover> <mo>+</mo> <mover> <mrow> <mi>O</mi> <msub> <mi>O</mi> <mn>1</mn> </msub> </mrow> <mo>‾</mo> </mover> <mo>)</mo> </mrow> <mo>=</mo> <msub> <mi>imλ</mi> <mn>0</mn> </msub> <mo>/</mo> <msub> <mi>n</mi> <mi>eff</mi> </msub> <mo>.</mo> <mo>.</mo> <mo>.</mo> <mo>.</mo> <mo>.</mo> <mo>.</mo> <mrow> <mo>(</mo> <mn>3</mn> <mo>)</mo> </mrow> </mrow> </math> center P 'of each groove face on the other sub-grating'jSatisfies the following conditions: <math> <mrow> <mover> <msub> <msup> <mi>IP</mi> <mo>′</mo> </msup> <mi>j</mi> </msub> <mo>‾</mo> </mover> <mo>+</mo> <mover> <mrow> <msub> <msup> <mi>P</mi> <mo>′</mo> </msup> <mi>j</mi> </msub> <msub> <mi>O</mi> <mn>2</mn> </msub> </mrow> <mo>‾</mo> </mover> <mo>-</mo> <mrow> <mo>(</mo> <mover> <mi>IO</mi> <mo>‾</mo> </mover> <mo>+</mo> <mover> <mrow> <mi>O</mi> <msub> <mi>O</mi> <mn>2</mn> </msub> </mrow> <mo>‾</mo> </mover> <mo>)</mo> </mrow> <mo>=</mo> <msub> <mi>jmλ</mi> <mn>0</mn> </msub> <mo>/</mo> <msub> <mi>n</mi> <mi>eff</mi> </msub> <mo>.</mo> <mo>.</mo> <mo>.</mo> <mo>.</mo> <mo>.</mo> <mo>.</mo> <mrow> <mo>(</mo> <mn>4</mn> <mo>)</mo> </mrow> </mrow> </math>
meanwhile, the middle point of each groove surface is positioned on a grating circle with the radius of R. The position of the middle point of each groove surface in each sub-grating can be obtained according to the conditions, after the middle point of each groove surface is determined, the vertical line passing through the middle point and serving as the incident ray is used as the blazed surface of the grating, and thus the structure of the whole grating is determined.
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN02265078U CN2552259Y (en) | 2002-06-25 | 2002-06-25 | Etching diffraction grating wave dividing multiplex device using two-point focusing to realize pass-band evenness |
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| Application Number | Priority Date | Filing Date | Title |
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| CN02265078U CN2552259Y (en) | 2002-06-25 | 2002-06-25 | Etching diffraction grating wave dividing multiplex device using two-point focusing to realize pass-band evenness |
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