RU180123U1 - DEMULTIPLEXOR WITH SPECTRAL DIVISION OF CHANNELS - Google Patents

Abstract

The utility model relates to optics, namely, demultiplexers that separate the input signal by wavelengths and can be used primarily as an optical element in telecommunication systems for spectral separation of channels. The main technical result of the utility model is to increase the level of signal transmission due to the exclusion of the focusing lens and the implementation of the dispersing element in the form of a focusing-dispersing element. Also, the technical result is the correction of astigmatism for the selected central wavelength with increased signal input efficiency. The main technical result is achieved by the fact that in a demultiplexer with spectral separation of channels, containing sequentially located optical fiber for transmitting an incoming undivided signal, a collimating lens, a dispersing element made of two truncated cylinders, interconnected by coaxial end surfaces, while on one of the connected end truncated cylinder surfaces, a transmissive volume-phase hologram holographic diffraction grating, and a group of optical fibers for According to the present utility model, the front end surface of the first truncated cylinder and the rear end surface of the second truncated cylinder located on the side of the corresponding secant planes, as well as the joined end surface of one of the truncated cylinders, are convex, and the connected end surface of the other cylinder is made concave. The technical result is also achieved by the fact that the transmissive volume-phase hologram diffraction grating has strokes that are made curved and unequally spaced from each other. The angle between the secant plane and the side surface of the first truncated cylinder receiving the input signal lies in the range of 80 ° -86 °, and the angle between the secant plane and the side surface of the second truncated cylinder that focuses the output signal lies in the range of 78 ° -83 °. 2 s.p. f-ly, 5 ill.

Description

The utility model relates to optics, namely to demultiplexers that separate the input signal by wavelengths, and can be used mainly as an optical element in telecommunication systems for spectral separation of channels.

Known demultiplexer with spectral separation of channels, containing a dispersing element in the form of a prism (journal article Optical Engineering 44 (2), 025006 (February 2005), p. 1-8; "Design and fabrication of a dense wavelength division demultiplexer with grism structure) ); Jyh-Rou Sze, Mao-Hong Lu).

The main disadvantage of the analogue is the low image quality, due to the fact that a prism is used as a dispersing element, on one side of which a lattice is deposited by diamond turning, which causes the so-called “Lyman spirits” and “Rowland spirits” reducing image quality.

Another disadvantage of the known demultiplexer is the increased level of scattered light due to the diffraction grating made by diamond turning, which leads to a decrease in the signal transmission efficiency.

The prototype is a demultiplexer with spectral separation of channels, containing sequentially located optical fiber for transmitting an incoming undivided signal, a collimating lens, a dispersing element made of two truncated cylinders, interconnected coaxially by the end surfaces, while a transmissive volumetric cylinder is made on the end face of the second truncated cylinder phase hologram diffraction grating, focusing lens and image plane, which takes outgoing split signal (“Features of the development of dispersive optical elements (grism) for telecommunications systems”, Belokopytov AA, Korennoy KS, Shigapova NM Conference proceedings “Optical technologies in telecommunications”, 2014, UDC 681.7- 1 / -9, p. 146, fig. 2).

In the prototype, through the use of a transmissive volume-phase hologram diffraction grating, there are no so-called “Lyman spirits” and “Rowland spirits”, and the level of scattered light is minimal.

The main disadvantage of the prototype is a significant reduction in signal transmission due to the presence of flat end surfaces in the truncated cylinders of the dispersing element, which ultimately leads to the need for a focusing lens.

The disadvantages of the prototype are the high value of astigmatism for the selected central wavelength due to the strokes of the diffraction grating made straight and equally spaced from each other, which leads to an increase in the scattering spot, as well as low signal input efficiency due to non-optimized angle parameters between the cutting plane and the lateral surface of the first truncated cylinder receiving the incoming signal and the angle between the secant plane and the lateral surface of the second truncated focusing cylinder yhodnoy signal.

The objective of the utility model is to develop a demultiplexer design with spectral separation of channels, in which the disadvantages of the analogue and prototype are eliminated.

The main technical result of the utility model is to increase the level of signal transmission due to the exclusion of the focusing lens and the implementation of the dispersing element in the form of a focusing-dispersing element.

Also, the technical result is the correction of astigmatism for the selected central wavelength with increased signal input efficiency.

The main technical result is achieved by the fact that in a demultiplexer with spectral separation of channels, containing sequentially located optical fiber for transmitting an incoming undivided signal, a collimating lens, a dispersing element made of two truncated cylinders connected to each other by coaxial end surfaces, while on one of the end faces connected truncated cylinder surfaces, a transmissive volume-phase hologram holographic diffraction grating, and a group of optical fibers for According to the present utility model, the front end surface of the first truncated cylinder and the rear end surface of the second truncated cylinder located on the side of the corresponding secant planes, as well as the joined end surface of one of the truncated cylinders, are convex, and the connected end surface of the other cylinder is made concave.

The technical result is also achieved by the fact that the transmissive volume-phase hologram diffraction grating has strokes that are made curved and unequally spaced from each other.

The angle between the secant plane and the side surface of the first truncated cylinder receiving the input signal lies in the range of 80 ° -86 °, and the angle between the secant plane and the side surface of the second truncated cylinder that focuses the output signal lies in the range of 78 ° -83 °.

The essence of the utility model is illustrated by drawings, where in FIG. 1 shows the proposed demultiplexer with spectral separation of channels, FIG. 2 - components of the dispersing element, in FIG. 3 shows the strokes of a transmissive volume-phase hologram diffraction grating; FIG. 4 is a scatter plot diagram for a central wavelength of a spectral-division multiplexed demultiplexer obtained in the ZEMAX program; FIG. 5 is a geometric image analysis characterizing the efficiency of inputting a signal into a group of optical fibers transmitting a divided signal obtained in the ZEMAX program.

In FIG. 1, 2, 3 elements and nodes of the demultiplexer with spectral separation of channels are indicated by the following positions:

1 - Optical fiber transmitting the incoming undivided signal,

2 - collimating lens,

3 - Dispersing element,

4 - Group of optical fibers transmitting a split signal,

5 - The first truncated cylinder,

6 - Transmitting volume-phase hologram diffraction grating,

7 - The second truncated cylinder,

8 - Frame,

9 - The front end surface of the first truncated cylinder (receiving the incoming signal),

10 - Connectable end surface of the first truncated cylinder (second),

11 - The lateral surface of the first truncated cylinder,

12 - Connectable end surface of the second truncated cylinder (on which a transmissive space-phase hologram diffraction grating is made),

13 - The rear end surface of the second truncated cylinder (focusing the output signal),

14 - The lateral surface of the second truncated cylinder,

15 - Strokes of a transmissive space-phase hologram diffraction grating.

The demultiplexer with spectral separation of channels contains sequentially located optical fiber 1 for transmitting an incoming undivided signal, a collimating lens 2, a dispersing element 3, made of two truncated cylinders 5 and 7, interconnected coaxially by the end surfaces 10 and 12, while on one of the connected end surfaces of truncated cylinders, for example, on the connected end surface 12 of the second truncated cylinder 7, a transmissive volume-phase hologram diffraction sieve is made and 6 and group 4 of optical fibers for transmitting exiting divided signal.

The difference of the proposed demultiplexer with spectral separation of channels is that the front surface 9 of the first truncated cylinder 5 and the rear surface 13 of the second truncated cylinder 7 located on the side of the corresponding secant planes, as well as the connected end surface of one of the truncated cylinders are convex, and the connected end surface another cylinder is made concave.

The transmitting volume-phase hologram diffraction grating 6 has strokes 15, which are made curved and unequally spaced from each other.

The angle α between the secant plane and the lateral surface 11 of the first truncated cylinder receiving the input signal lies in the range 80 ° -86 °, and the angle β between the secant plane and the lateral surface 14 of the second truncated cylinder focusing the output signal lies in the range 78 ° - 83 °.

The above optimal ranges of angles α and β are determined by computer simulation.

An example of a specific implementation.

A demultiplexer with spectral division of channels contains optical fiber 1 for transmitting an incoming undivided signal, a collimating lens 2, a dispersing element 3 and a group of optical fibers 4 for transmitting an output split signal (Fig. 1).

Fiber optic 1 (for example, MM (105/125) 0.15 fiber, Special Systems. Photonics LLC) is connected via a SMA connector to a collimating lens 2 to create collimated radiation.

Fiber optic 1 has the following characteristics:

1) Operating spectral range: 800-1750 nm;

2) Numerical aperture: 0.13-0.17;

3) Core diameter: 105 microns;

4) Attenuation: ≤20 dB / km.

The collimating lens 2 has the following characteristics:

1) Operating spectral range: 1050-1620 nm;

2) Focal length 75 mm;

3) Numerical aperture: 0.16.

The operating spectral range of the dispersing element 3 is from 1471 nm to 1611 nm. The dispersing element 3 is made in the form of gluing two elements: the first truncated cylinder 5, the secant plane of which with respect to the side surface 11 of the cylinder is located at an angle a, selected in the range 80 ° -86 °, and the second truncated cylinder 7, the secant plane of which is relative to to the side surface 14 of the cylinder is located at an angle β, selectable in the range of 78 ° -83 °, while a transmissive volume-phase hologram diffraction grating 6 is made on the connected end surface 12 of the second truncated cylinder 7. Each The first of the truncated cylinders 5 and 7 of the dispersing element 3 is made of TF-7 glass from the LZOS company. The front end surface 9 of the first truncated cylinder 5 receiving the input signal and the rear end surface 13 of the second truncated cylinder 7 focusing the output signal have an antireflection coating for the selected wavelength range, which reduces the reflection coefficient of the end surfaces 9 and 13.

The end surfaces 9, 10, 13 are convex, and the connected end surface 12 of the second truncated cylinder 7, on which a transmissive space-phase hologram diffraction grating 6 is made, is concave.

The front end surface 9 of the first truncated cylinder 5 (receiving the input signal) and the rear end surface 13 of the second truncated cylinder 7 (focusing the output signal) are aspherical. A layer of bichromated gelatin of a transmissive volume-phase hologram diffraction grating 6 is applied to the joined end surface 12 of the second truncated cylinder 7. The first truncated cylinder 5 is connected to the second truncated cylinder 7, on the connecting end surface 12 of which a transmissive volume-phase hologram diffraction grating 6 is made, at using special optical glue OK-50. The glued end surfaces 10 and 12 have a spherical shape, while the glued surface 10 of the first truncated cylinder has a convex shape, and the glued surface 12 of the second truncated cylinder is concave. The radius of curvature of the glued end surfaces 10 and 12 of the truncated cylinders is 500 mm.

Both truncated cylinders 5 and 7 have a thickness "d" of 15 mm, a height of "h" of 30 mm, and the angle α is 84 ° and the angle β is 80 °.

A photosensitive layer of bichromated gelatin was deposited onto the glued end surface 12 of the second truncated cylinder 7, onto which, using a laser, an interference pattern was recorded. The transmitting volume-phase hologram diffraction grating 6 was recorded using two coherent sources, the rays of which have a spherical wavefront, one of them being located at the center of curvature of the grating surface, and the second at an arbitrary place of recording the interference pattern from two coherent sources with a spherical wave front (a more detailed technology for recording diffraction gratings is described in the book: Lebedeva VV Technique of optical spectroscopy. - M.: Publishing House of Moscow University. 1977. - 384 p.).

The transmissive volume-phase hologram diffraction grating 6 is three-dimensional and not embossed, since the embossed grating cannot be glued.

The resulting transmissive space-phase hologram diffraction grating 6 has strokes 15, which are curved and unequally spaced from each other, and the step of the strokes and the radius of curvature of the grating strokes are determined by the following formulas:

e = e ₀ × (m × y + n × y ² + k × y ³ ) and r = r ₀ + p × y,

where e is the step of strokes, microns;

e ₀ is the stroke pitch in the center of the lattice, microns;

m, n, k are the coefficients of the unevenness of the stroke pitch;

y is the lattice coordinate;

r is the radius of curvature of the strokes of the lattice, mm;

r ₀ is the radius of curvature of the strokes at the top of the lattice, mm;

p is a coefficient characterizing changes in the radius of curvature of the strokes of the lattice.

In the example of a specific implementation:

1) e ₀ = 0.028645 μm

2) m = 0.436776

n = 0.186545

k = 0,080256

3) r ₀ = 2.228 mm

4) p = 0.9667

A demultiplexer with spectral separation of channels can significantly increase the level of signal transmission due to the fact that the dispersing element 3 is a focusing-dispersing element. The dispersing element 3 is aligned and secured using a plastic frame 8, while, compared with the prototype, due to the exclusion of the focusing lens and the connection of the optical fiber 1 with the collimating lens 2, simplification of alignment is achieved. A spectral-division multiplexed demultiplexer has the characteristics shown in FIG. 4, 5.

In FIG. 4 is a scatter plot diagram for a central wavelength of 1.551 μm. As a result of the analysis of the scatter spot diagram, we can conclude that the proposed demultiplexer with spectral separation of channels has corrected astigmatism for the central wavelength in comparison with the prototype.

In FIG. 5 shows a geometric image analysis characterizing the efficiency of signal input to a group of optical fibers 4 transmitting a divided signal. A demultiplexer with spectral division of channels with the parameters indicated above has a signal input efficiency of 88%.

Demultiplexer with spectral separation of channels works as follows.

The signal from the optical fiber 1, which is collimated by a collimating lens 2, is incident on the frontal end surface 9, which receives an incoming signal containing several wavelengths, and the collimated signal, falling on the frontal end surface 9, which receives the incoming signal, is the first truncated cylinder 5, refracted depending on the wavelength due to the dispersion of the optical material.

The optical path of the signal passing through the first truncated cylinder 5 depends on the type of optical material of the truncated demultiplexer cylinder 5, the radius of curvature of the front end surface 9 receiving the incoming signal, etc.

After the signal passes through the first truncated cylinder 5 of the demultiplexer, it falls on the interface of the "first truncated cylinder 5 - transmitting volume-phase hologram diffraction grating 6". The signal is refracted and, falling on a transmitting volume-phase hologram diffraction grating 6, decomposes into several signals at wavelengths. After these signals pass through a transmissive space-phase hologram diffraction grating 6, they arrive at the second truncated cylinder 7 of the dispersing element 3 and are refracted again. Further, the signals passing through the second truncated cylinder 7 of the demultiplexer are focused on a group of optical fibers 4 transmitting a divided signal, and the positions of the foci, aberration characteristics, and the sizes of scattering spots depend on the parameters of the truncated cylinders 5 and 7 of the dispersing element 3 and the transmitting volume-phase hologram diffraction grating 6, such as the radii of curvature and the shape of the end surfaces 9, 10, 12 and 13 of the truncated cylinders 5 and 7, the materials of the truncated cylinders 5, 7 and the transmission of the volume-phase hologram diffraction of the lattice 6, the curvilinearity parameter and the stroke pitch coefficient 15 of the transmitting volume-phase hologram diffraction grating 6, the angles α and β of the truncated cylinders, 5 and 7, respectively.

Using the proposed demultiplexer with spectral separation of channels will significantly increase the level of signal transmission, as well as correct astigmatism for the selected central wavelength, increase the efficiency of signal input, and also simplify the adjustment of the entire system due to the proposed combination of distinguishing features of the utility model.

Claims (3)

           1. A demultiplexer with spectral separation of channels, comprising a sequentially located collimating lens, the front surface of which receives an input signal from an optical fiber, a dispersing element made of two truncated cylinders interconnected coaxially by the end surfaces, and the end surface of the second truncated cylinder is configured to focus the output signal on a group of optical fibers, while on one of the connected end surfaces of the truncated cylinders and a transmissive space-phase hologram diffraction grating, characterized in that the frontal end surface of the first truncated cylinder and the rear end surface of the second truncated cylinder located on the side of the corresponding secant planes, as well as the connected end surface of one of the truncated cylinders are convex, and the connected end surface another cylinder is made concave. 2. The demultiplexer according to claim 1, characterized in that the transmissive volume-phase hologram diffraction grating has strokes that are made curved and unequally spaced from each other. 3. The demultiplexer according to claim 1, characterized in that the angle between the secant plane and the side surface of the first truncated cylinder receiving the incoming signal lies in the range 80 ° -86 °, and the angle between the secant plane and the side surface of the second truncated cylinder focusing the output signal lies in the range of 78 ° -83 °.

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