CN112099145A - Optical fiber filter - Google Patents

Abstract

The invention discovers defects in the existing optical fiber filter through research, and therefore provides an optical fiber filter based on a diaphragm, which can comprise a lens group, a filtering unit and a light blocking fixing structure. The lens group is used for realizing optical transmission of optical signals between the optical fibers and the filtering unit, the filtering unit is used for filtering the optical signals, and the light blocking fixing structure is used for fixing the lens group and the filtering unit and does not allow the optical signals which are not filtered by the filtering unit to be output outwards. Thereby reducing or eliminating noise caused by stray light in conventional filters.

Description

a fiber filter

technical field

The invention relates to the field of quantum communication, in particular to an optical fiber filter, which is especially suitable for an up-conversion single-photon detector.

Background technique

Applications such as quantum communication, quantum computing, and quantum measurement depend to a large extent on the development level of key technologies and key devices. Therefore, research on key technologies and key devices has always been the focus of all countries. There are three types of single-photon detectors in the international communication band: superconducting single-photon detectors, indium-gallium-arsenide avalanche diode single-photon detectors and up-conversion single-photon detectors. However, commercial superconducting single-photon detectors require a continuous refrigeration device to maintain effective operation, and the equipment is bulky and expensive, setting up obstacles for the practical application of quantum communication. Commercial indium gallium arsenide avalanche diode single-photon detectors work in Geiger mode, which has the advantages of no refrigerant and can be integrated; however, its low count rate, dark count of about 1000Hz and post-pulse of about 2% are also limited. Its application in long-distance quantum communication. Compared with superconducting single-photon detectors, up-conversion single-photon detectors are small in size, do not require external cooling, can be integrated and miniaturized, and are more suitable for commercial applications of quantum communication and quantum measurement. In addition, their performance indicators are much better than indium gallium. Arsenic avalanche diode single-photon detector, so it can be applied in long-distance quantum communication systems.

The noise source of the up-conversion single-photon detector consists of two parts, one part is the noise generated by other nonlinear effects caused by the pump light in the nonlinear sum-frequency process, such as: double frequency and triple frequency of the pump light, pump The spontaneous parametric down-conversion of light, the Raman effect of pump light, etc.; the other part is the background dark count of the silicon detector. The noise generated by the nonlinear effect is the main noise source of the up-conversion single-photon detector, and the fiber filter is the core device for the up-conversion single-photon detector to filter out noise. important device.

Therefore, how to improve the efficiency of fiber filters is also an important research topic in this field.

SUMMARY OF THE INVENTION

FIG. 1 presents a schematic structural diagram of a fiber filter used in an up-conversion single-photon detector in the prior art. As shown in the figure, in this fiber filter structure, the entrance fiber is coupled with the G lens, the incident light beam enters the G lens through the entrance fiber, becomes parallel light and enters the C lens or the G lens, and then converges to the filter 1. The light beam enters the filter 2 through the filter 1, and then becomes parallel light through the C lens or the G lens and enters the final G lens, and finally converges into the fiber for output as the outgoing light. In this fiber filter structure, the G lens, C lens, and filter at the incident end and the outgoing end are respectively filled and fixed with glass sleeves with glue, and the outside of the glass sleeve is encapsulated with a metal sleeve to protect the glass sleeve and the internal Optical lenses. Among them, the G lens is a self-focusing lens, and the C lens is a spherical lens.

In order to further improve the performance of the optical fiber filter, the inventors have conducted in-depth research on the existing optical fiber filter structure, in order to discover the factors affecting the efficiency of the optical fiber filter that have not been realized in the art.

After research, the inventor creatively found that the existing fiber filter has the following defects that adversely affect the efficiency of the fiber filter:

There will be reflection of the incident light at the butt joints of the A and G lenses and the C lens. Since the transmission path of the reflected light is random and the glass sleeve can transmit the light, the reflected light can be emitted from the back end fiber without passing through the filter 1. Since there is no filter filter, many noise photons are directly coupled into the back-end receiving system, and the poor filtering effect leads to high system noise of the up-conversion single-photon detector.

B. After the incident light passes through the filter 1, because there is a gap in the glue fixing of the filter 2 and the glass sleeve can transmit the light, some scattered light will not pass through the filter 2, and will directly enter the lens and exit from the rear fiber, which will also cause filtering. The effect is poor, which in turn leads to high system noise of the up-conversion single-photon detector.

In view of the above-mentioned defects found in the research, the present invention also proposes a novel optical fiber filter structure based on a diaphragm, in which the influence caused by the above-mentioned defects is eliminated by introducing a diaphragm structure.

Specifically, the present invention relates to an optical fiber filter, which may include a lens group, a filter unit and a light blocking fixing structure. Wherein, the lens group is configured for optical transmission of optical signals between the optical fiber and the filter unit; the filter unit is configured to filter the optical signal; the light blocking fixing structure is configured for The lens group and the filter unit are fixed therein, and the optical signal not filtered by the filter unit is not allowed to be outputted to the outside.

The optical fiber filter of the present invention may further include an encapsulation structure configured to encapsulate the lens group, the filter unit and the light blocking fixing structure. Preferably, the packaging structure includes an outer sealing metal tube, and the inner surface of the outer sealing metal tube is oxidized and blackened.

Further, the light blocking fixing structure includes a diaphragm, which is arranged for the filtering unit and extends to cover the filtering unit and the lens group in the longitudinal direction. Alternatively, the light-blocking fixing structure includes an opaque sleeve and a diaphragm; the opaque sleeve is configured to fix the lens group and the filter unit therein; the diaphragm is configured to The filtering unit is connected with the opaque sleeve.

Furthermore, the optical fiber filter of the present invention may further include a light-absorbing filling material, and the light-absorbing filling material is used for filling in the light-blocking fixing structure to fix the lens group and the filter unit. Preferably, the light-absorbing filling material is black silica gel.

Preferably, the diaphragm is made of metal material, and has been oxidized and blackened; and/or the opaque sleeve is made of metal, and has been oxidized and blackened.

Further, the number of the lens group, the filter unit and the light blocking fixing structure is two, and the first one of the two light blocking fixing structures is set to The first one of the two filter units and the first one of the two filter units are fixed therein, and the second one of the two light blocking fixing structures is arranged for connecting the second one of the two lens groups to the the second of the two filtering units is fixed therein;

The first lens group is configured to transmit the optical signal to the first filtering unit, and the optical signal filtered by the first filtering unit is output through the first light blocking fixing structure;

The optical signal output by the first light blocking fixing structure is transmitted to the second filtering unit through the second light blocking fixing structure, and the optical signal filtered by the second filtering unit enters the second filtering unit. lens group.

Further, the first lens group includes a first lens and a second lens, and the second lens group includes a third lens and a fourth lens. Wherein, the first lens is a G lens, the second lens is a G lens or a C lens; and/or the third lens is a G lens or a C lens, and the fourth lens is a G lens.

Description of drawings

The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

In order to explain the embodiments of the present invention or the technical solutions in the prior art more clearly, the following briefly introduces the accompanying drawings used in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only For some embodiments of the present invention, for those of ordinary skill in the art, other drawings can also be obtained according to these drawings without any creative effort.

Fig. 1 schematically shows a structure diagram of an optical fiber filter in the prior art;

FIG. 2 schematically shows an exemplary embodiment of a diaphragm-based fiber filter according to the present invention;

FIG. 3 schematically shows another exemplary embodiment of a diaphragm-based fiber filter according to the present invention.

Detailed ways

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following embodiments are provided by way of example in order to fully convey the spirit of the invention to those skilled in the art to which the invention pertains. Accordingly, the present invention is not limited to the embodiments disclosed herein.

According to the present invention, the optical fiber filter may include a lens group, a filter unit, a light blocking fixing structure and a packaging structure.

In the present invention, the lens group is used to realize the optical transmission of the optical signal between the optical fiber and the filtering unit.

The filtering unit is used for filtering the optical signal.

The light blocking fixing structure is used to fix the lens group and the filtering unit, and it is not allowed to output the light signal that is not filtered by the filtering unit.

The encapsulation structure is used to encapsulate the lens group, the filter unit and the light blocking fixing structure to provide protection.

FIG. 2 shows an exemplary embodiment of the fiber filter of the present invention.

As shown in FIG. 2 , the light blocking fixing structure may include a diaphragm, which is provided for the filter unit and extends to cover the filter unit and the lens group in the length direction, so as to fix the lens group and the filter unit therein.

FIG. 3 shows another exemplary embodiment of the fiber filter of the present invention.

As shown in FIG. 3 , the light-blocking fixing structure may include an opaque sleeve and a diaphragm, the opaque sleeve is used to fix the lens group and the filter unit therein, and the diaphragm is provided for the filter unit and is connected with the opaque sleeve. Tubes are connected.

In the present invention, the material used for filling and fixing the lens group and the filter unit in the light-blocking fixing structure may have light absorption, for example, black silica gel may be used to realize the filling and fixing of the lens group and the filter unit in the light-blocking fixing structure , to facilitate the absorption of reflected and scattered light such as those produced by the lens group.

In a preferred example, the diaphragm may be made of metal. Also, the diaphragm can be oxidized and blackened to facilitate absorption of reflected and scattered light.

In a preferred example, the opaque sleeve may be made of metal, and the metal sleeve may be oxidized and blackened to facilitate absorption of reflected light and scattered light.

With the light-blocking fixing structure proposed by the present invention, for the lens group and the filter unit fixed by the same light-blocking fixing structure, the optical signal input through the lens group can only pass through the filter unit and then travel outward from the light-blocking fixing structure. output; or, only the light signal after being acted by the filtering unit can be output from the light blocking fixing structure through the lens group.

In the present invention, the encapsulation structure can be designed to have a light-tight inner surface. As an example, the packaging structure may include an outer sealing metal tube, the inner surface of which is oxidized and blackened.

The working principle of the optical fiber filter of the present invention will be further illustrated below with reference to FIGS. 2-3.

As shown in FIG. 2 or 3, in some exemplary embodiments, the fiber filter may include first and second lens groups, first and second filter units, and first and second light blocking fixing structures.

The first light blocking fixing structure is used for fixing the first lens group and the first filter unit therein.

The first lens group includes a first lens and a second lens, wherein the first lens is used for converting the optical signal input via the optical fiber into parallel light, and the second lens is used for converging the optical signal to be parallel light to the first filtering unit . As an example, the first lens may be a G lens and the second lens may be a C lens; alternatively, both the first and second lenses may be G lenses.

The second light blocking fixing structure is used for fixing the second lens group and the second filter unit therein.

The second lens group includes a third lens and a fourth lens, wherein the third lens is used for converting the optical signal input via the second filtering unit into parallel light, and the fourth lens is used for converging the optical signal to be parallel light into the optical fiber Inside. As an example, the third lens may be a C lens and the fourth lens may be a G lens; alternatively, both the third and fourth lenses may be G lenses.

The first and second filtering units may comprise filters.

As shown in FIG. 2 or 3, at the input end of the fiber filter, the fiber is coupled to the first lens. The optical signal input through the optical fiber becomes parallel light through the first lens, and the optical signal which is parallel light enters the second lens and is collected on the filter 1 of the first filtering unit. The optical signal is filtered and processed by the filter 1 and output through the aperture of the diaphragm 1 in the first light blocking fixed structure (which is located at the output end of the filter 1 of the first filtering unit in the optical signal propagation direction).

By means of the diaphragm 1 (or the combination of the diaphragm 1 and the opaque sleeve) in the first light-blocking fixing structure, part of the reflected light at the butt joint of the first lens and the second lens in the first lens group can be absorbed or blocked, and The diaphragm 1 arranged at the rear end of the filter plate 1 of the first filter unit can completely block or absorb the remaining part of the reflected light, and at the same time, the inner surface of the encapsulated metal tube (which is used as an encapsulation structure) that has been oxidized and blackened can also further absorb undesired light. Stray light is completely filtered out.

In the exemplary embodiment shown in FIG. 2 or 3 , the optical signal output through the first light blocking fixing structure will enter the filter 2 of the second filtering unit after being acted by the second light blocking fixing structure. The optical signal output by the filter 2 of the second filtering unit enters the third lens and becomes parallel light, and the optical signal which is parallel light enters the fourth lens and is concentrated into the optical fiber for output.

Similarly, by means of the diaphragm 2 (or the combination of the diaphragm 2 and the opaque sleeve) in the second light-blocking fixing structure, the stray light output from the first light-blocking fixing structure can be reflected or absorbed to prevent it from passing through The filter 2 in the second filtering unit enters the back-end fiber output.

It can be seen that the optical fiber filter of the present invention can solve the problem that the noise caused by the reflected light at the joint of the G lens and the C lens enters the receiving end of the system without a filter or only through a filter, and improves the filtering effect of the fiber filter. System noise of upconverting single photon detectors is reduced.

With the help of the optical fiber filter structure of the present invention, the filtering efficiency can be further improved, so as to obtain a filtering effect better than that of the multi-stage optical fiber filter. Effectively reduce system cost and avoid system insertion loss caused by multi-stage series connection.

Those skilled in the art can easily understand that the up-conversion single-photon detector including the fiber filter of the present invention can also correspondingly obtain improved detection efficiency.

Although the present invention has been described above through specific embodiments in conjunction with the accompanying drawings, those skilled in the art will readily recognize that the above-mentioned embodiments are merely exemplary, used to illustrate the principles of the present invention, and do not limit the scope of the present invention. As a limitation, those skilled in the art can make various combinations, modifications and equivalent substitutions to the above embodiments without departing from the spirit and scope of the present invention.

Claims (11)

1. An optical fiber filter comprising a lens group, a filter unit and a light blocking fixing structure, wherein: The lens group is configured for optical transmission of optical signals between the optical fiber and the filter unit; the filtering unit is configured to filter the optical signal; The light-blocking fixing structure is configured to fix the lens group and the filtering unit therein, and does not allow the light signal not filtered by the filtering unit to be outputted to the outside. 2. The optical fiber filter of claim 1, further comprising an encapsulation structure configured to encapsulate the lens group, the filter unit and the light blocking fixing structure. 3 . The optical fiber filter of claim 2 , wherein the encapsulation structure comprises an outer sealing metal tube, and the inner surface of the outer sealing metal tube is oxidized and blackened. 4 . 4 . The optical fiber filter according to claim 1 , wherein the light blocking fixing structure comprises a diaphragm, which is provided for the filtering unit and extends to cover the filtering unit and the filtering unit in a length direction. 5 . lens group. 5. The optical fiber filter of claim 1, wherein the light-blocking fixing structure comprises an opaque sleeve and a diaphragm; the opaque sleeve is configured to connect the lens group and the filter The unit is fixed therein; the diaphragm is provided for the filter unit and is connected to the light-tight sleeve. 6. The optical fiber filter according to claim 4 or 5, further comprising a light-absorbing filling material for filling in the light-blocking fixing structure to fix the lens group and the filter unit. 7. The optical fiber filter of claim 6, wherein the light-absorbing filling material is black silica gel. 8. The optical fiber filter according to claim 4 or 5, wherein the diaphragm is made of a metal material and is oxidized and blackened; and/or the opaque sleeve is made of a metal material and is oxidized Blackened. 9. The optical fiber filter according to any one of claims 1-8, wherein the number of the lens group, the filtering unit and the light blocking fixing structure is two, and the two light blocking fixing structures The first of the structures is configured to fix the first of the two lens groups and the first of the two filter units therein, and the second of the two light-blocking fixing structures a second one of the two lens groups and a second one of the two filter units are fixed therein; The first lens group is configured to transmit the optical signal to the first filtering unit, and the optical signal filtered by the first filtering unit is output through the first light blocking fixing structure; The optical signal output by the first light blocking fixing structure is transmitted to the second filtering unit through the second light blocking fixing structure, and the optical signal filtered by the second filtering unit enters the second filtering unit. lens group. 10. The fiber filter of claim 9, wherein the first lens group includes a first lens and a second lens, and the second lens group includes a third lens and a fourth lens. 11. The optical fiber filter of claim 10, wherein the first lens is a G lens, the second lens is a G lens or a C lens; and/or the third lens is a G lens or a C lens lens, the fourth lens is a G lens.

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