Light blocking fixing structure for optical fiber filter and optical fiber filter

Abstract

Defects existing in an existing optical fiber filter are found through research, the light blocking fixing structure for the optical fiber filter and the optical fiber filter are provided, and the optical fiber filter comprises a lens group, a filtering unit and the light blocking fixing structure. The lens group is used for realizing optical transmission of an optical signal between the optical fiber and the filtering unit, the filtering unit is used for filtering the optical signal, and the light blocking fixing structure is used for fixing the lens group and the filtering unit and does not allow the optical signal which is not filtered by the filtering unit to be output outwards. Therefore, noise caused by stray light in an existing filter is reduced or eliminated.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of quantum communication, in particular to a light blocking fixing structure for a fiber filter and a corresponding fiber filter, which is especially suitable for use in an up-conversion single photon detector. BACKGROUND

[0002] Quantum communication, quantum computing, quantum measurement and other applications are largely dependent on the development level of key technologies and key devices, so the research on key technologies and key devices has always been the focus of attention of various countries. There are three types of commonly used communication band single photon detectors internationally: superconducting single photon detectors, indium gallium arsenide avalanche diode single photon detectors and up-conversion single photon detectors. However, commercial superconducting single photon detectors need a continuous refrigeration device to maintain effective operation, and the equipment is large in size and expensive in cost, which sets up an obstacle for the practicalization of quantum communication. Commercial indium gallium arsenide avalanche diode single photon detectors work in Geiger mode, and have the advantages of not needing refrigerant and being integrable; however, their low count rate, about 1000 Hz of dark count and about 2% of afterpulse also limit their application in long-distance quantum communication. The up-conversion single photon detector is small in size, does not need external refrigeration, can be integrated and miniaturized, is more suitable for commercial application of quantum communication and quantum measurement, and has performance indicators much better than those of the indium gallium arsenide avalanche diode single photon detector, so it can be applied in long-distance quantum communication systems.

[0003] The noise sources of the up-conversion single photon detector include 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: second harmonic generation and third harmonic generation of pump light, spontaneous parametric down-conversion of pump light, 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 filtering noise of the up-conversion single photon detector, so it is important to study the important device of the up-conversion single photon detector with high efficiency and low noise.

[0004] Therefore, how to improve the efficiency of the fiber filter is also an important research topic in the field. SUMMARY

[0005] Figure 1A structural diagram of a prior art fiber filter applied in an upconversion single photon detector is presented. As shown in the diagram, in the fiber filter structure, the entrance fiber is coupled with a G lens, the incident light beam enters the G lens through the entrance fiber, becomes parallel light incident to a C lens or a G lens, and then converges to filter 1. The light beam is incident to filter 2 through filter 1, and then becomes parallel light incident to the last G lens through the C lens or the G lens, and finally converges into the fiber to be output as the outgoing light. In the fiber filter structure, the G lenses, the C lenses and the filters at the incident end and the outgoing end are fixed by filling glue in the glass sleeve, and the glass sleeve and the internal optical lenses are protected by the metal sleeve outside the glass sleeve. The G lens is a self-focusing lens, and the C lens is a spherical lens.

[0006] In order to further improve the performance of the fiber filter, the inventors have conducted in-depth research on the existing fiber filter structure in order to find factors that affect the efficiency of the fiber filter which have not been realized in the field.

[0007] Through research, the inventors have creatively found that the existing fiber filter has the following defects which adversely affect the efficiency of the fiber filter: A. Reflection of incident light at the interface of the G lens and the C lens. Since the transmission path of the reflected light is random and the glass sleeve can transmit light, the reflected light can be emitted from the rear fiber without passing through filter 1. Since the reflected light does not pass through the filter, many noise photons directly couple into the rear receiving system, which results in poor filtering effect and high system noise of the upconversion single photon detector.

[0008] B. After the incident light passes through filter 1, due to the gap at the glue fixing position of filter 2 and the fact that the glass sleeve can transmit light, part of the scattered light does not pass through filter 2, directly enters the lens and is emitted from the rear fiber, which also results in poor filtering effect and high system noise of the upconversion single photon detector.

[0009] In view of the above defects found in the research, the present application also proposes a new type of fiber filter structure based on an aperture, in which the aperture structure is introduced to eliminate the influence caused by the above defects.

[0010] Specifically, the first aspect of the present application relates to a light-blocking fixing structure for a fiber filter, which comprises a light-tight sleeve and an aperture. The light-tight sleeve has a first end and a second end, and is filled with light-absorbing filling material inside to fix the first lens, the second lens and the filter unit therein, wherein the first lens, the second lens and the filter unit are arranged in sequence along the direction from the first end to the second end. The aperture is connected to the second end of the light-tight sleeve. The diaphragm has an opening formed thereon, and is arranged such that the opening has a range in a vertical cross section with respect to a direction from the first end to the second end smaller than a range of the filter unit in the vertical cross section.

[0011] Optionally, the light-proof sleeve and the diaphragm are integrally formed.

[0012] Further, the first lens is arranged to transmit the input light from the optical fiber into parallel light, or to converge the parallel light from the second lens into the optical fiber. The second lens is arranged to converge the parallel light into the filter unit, or to change the input light from the filter unit into parallel light.

[0013] Preferably, the light-absorbing filling material is black silica gel.

[0014] Further, the diaphragm is a metal material subjected to oxidation and blackening treatment, and / or the light-proof sleeve is a metal material subjected to oxidation and blackening treatment.

[0015] Further, the first lens is a G lens, and the second lens is a G lens or a C lens.

[0016] The second aspect of the present application relates to an optical fiber filter, which comprises the above-mentioned light-blocking fixed structure, and the first lens, the second lens and the filter unit fixedly arranged in the light-blocking fixed structure.

[0017] Further, the optical fiber filter of the present application further comprises a packaging structure for packaging the light-blocking fixed structure inside.

[0018] Still further, the packaging structure comprises an outer metal tube with an inner surface subjected to oxidation and blackening treatment.

[0019] Further, the number of the light-blocking fixed structure and the first lens, the second lens and the filter unit inside the light-blocking fixed structure is two. BRIEF DESCRIPTION OF DRAWINGS

[0020] The specific embodiments of the present application will be further described in detail below with reference to the accompanying drawings.

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the accompanying drawings needed to be used in the embodiments or prior art description will be briefly introduced. Obviously, the accompanying drawings in the following description are only some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor based on these drawings.

[0022] Figure 1 A structural diagram of an optical fiber filter in the prior art is schematically shown; Figure 2 An exemplary embodiment of an optical fiber filter based on an optical stop according to the present application is schematically shown; Figure 3 Another exemplary embodiment of an optical fiber filter based on an optical stop according to the present application is schematically shown. DETAILED DESCRIPTION

[0023] The technical solutions in the embodiments of the present application will be apparently and completely described below with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by a person of ordinary skill in the art without any creative work fall within the protection scope of the present application.

[0024] According to the present application, the optical fiber filter can include a lens group, a filter unit, a light-blocking fixing structure and a packaging structure.

[0025] In the present application, the lens group is used to realize optical transmission of optical signals between the optical fiber and the filter unit, and includes a first lens and a second lens.

[0026] The filter unit is used to filter the optical signals.

[0027] The light-blocking fixing structure is used to fix the lens group and the filter unit, and does not allow the optical signals not filtered by the filter unit to be outputted outward.

[0028] The packaging structure is used to package the lens group, the filter unit and the light-blocking fixing structure to provide protection.

[0029] Figure 2 An exemplary embodiment of the optical fiber filter of the present application is shown.

[0030] As shown in Figure 2 The light-blocking fixing structure can include an optical stop, which is arranged for the filter unit and extends in the length direction to cover and surround the filter unit and the lens group, so as to fix the lens group and the filter unit therein.

[0031] Figure 3 Another exemplary embodiment of the optical fiber filter of the present application is shown.

[0032] As shown in Figure 3 The light-blocking fixing structure can include a light-tight sleeve and an optical stop, the light-tight sleeve is used to fix the lens group and the filter unit therein, and the optical stop is arranged for the filter unit and connected with the light-tight sleeve.

[0033] In this invention, the material used to fill and fix the lens group and filter unit within the light-blocking fixing structure can have light-absorbing properties. For example, black silicone can be used to fill and fix the lens group and filter unit within the light-blocking fixing structure to facilitate the absorption of reflected and scattered light generated by the lens group.

[0034] In a preferred example, the aperture may be made of metal. Furthermore, the aperture may be oxidized and blackened to facilitate the absorption of reflected and scattered light.

[0035] In a preferred example, the opaque sleeve can be made of metal, and the metal sleeve can be oxidized and blackened to facilitate the absorption of reflected and scattered light.

[0036] With the light-blocking fixing structure proposed in this invention, for a lens group and a filter unit fixed by the same light-blocking fixing structure, the light signal input through the lens group can only be output outward from the light-blocking fixing structure after being processed by the filter unit; or, only the light signal processed by the filter unit can be output outward from the light-blocking fixing structure through the lens group.

[0037] In this invention, the encapsulation structure can be designed to have an opaque inner surface. As an example, the encapsulation structure may include an outer metal tube whose inner surface is treated with anodizing and blackening.

[0038] The following will continue to combine Figures 2-3 The working principle of the fiber optic filter of the present invention will be further illustrated with examples.

[0039] like Figure 2 As shown in Figure 3, in some exemplary embodiments, the fiber optic filter may include first and second lens groups, first and second filtering units, and first and second light-blocking fixing structures.

[0040] The first light-blocking fixing structure is used to fix the first lens group and the first filter unit therein.

[0041] The first lens group includes a first lens as lens one and a second lens as lens two, wherein the first lens is used to convert the optical signal input via the optical fiber into parallel light, and the second lens is used to converge the parallel light signal to the first filtering unit. As an example, the first lens can be a G lens and the second lens can be a C lens; or, both the first and second lenses can be G lenses.

[0042] The second light-blocking fixing structure is used to fix the second lens group and the second filter unit therein.

[0043] The second lens group comprises a third lens as lens two and a fourth lens as lens one, wherein the third lens is used to change the light signal inputted through the second filter unit into parallel light, and the fourth lens is used to converge the light signal which is parallel light into the optical fiber.

[0044] The first and second filter units can comprise filter plates.

[0045] As shown in Figure 2 At the input end of the optical fiber filter, the optical fiber is coupled with the first lens. The light signal inputted through the optical fiber is changed into parallel light by the first lens, and the light signal which is parallel light enters the second lens and is converged onto the filter plate 1 of the first filter unit. After being filtered by the filter plate 1, the light signal is outputted through the opening of the diaphragm 1 in the first light-blocking fixed structure, which is located at the output end of the filter plate 1 of the first filter unit in the light signal propagation direction.

[0046] By means of the diaphragm 1 (or the combination of the diaphragm 1 and the light-tight sleeve) in the first light-blocking fixed structure, part of the reflected light at the 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. Meanwhile, the inner surface of the outer sealing metal tube (which serves as a packaging structure) which is subjected to blackening treatment by oxidation can further absorb the stray light which is not completely filtered out.

[0047] In the exemplary embodiment shown in Figure 2 In the exemplary embodiment shown in

[0048] Similarly, by means of the diaphragm 2 (or the combination of the diaphragm 2 and the light-tight sleeve) in the second light-blocking fixed structure, the stray light outputted from the first light-blocking fixed structure can be reflected or absorbed, so as to avoid entering the rear-end optical fiber without passing through the filter plate 2 in the second filter unit.

[0049] Therefore, the optical fiber filter of the present application 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 system receiving end without passing through the filter plate or only passing through one filter plate, improve the filtering effect of the optical fiber filter, and reduce the system noise of the up-conversion single-photon detector.

[0050] With the optical fiber filter structure of the present application, the filtering efficiency can be further improved, thereby obtaining a filtering effect superior to that of a multi-stage optical fiber filter, and thus it is not necessary to connect a plurality of optical fiber filters in series to improve the filtering efficiency as in the prior art, and the system cost can be effectively reduced, and the system insertion loss caused by the multi-stage connection can be avoided.

[0051] Those skilled in the art can easily understand that the up-conversion single-photon detector including the optical fiber filter of the present application can also correspondingly improve the detection efficiency.

[0052] Although the present application has been described above with reference to specific embodiments, those skilled in the art will readily appreciate that the above embodiments are only exemplary and are used to explain the principles of the present application, and do not limit the scope of the present application, and those skilled in the art can make various combinations, modifications and equivalent replacements to the above embodiments without departing from the spirit and scope of the present application.

Claims

1. A light-blocking fixture for an optical fiber filter, comprising a light-tight sleeve and a diaphragm. The light-tight sleeve has a first end and a second end and is internally filled with a light-absorbing filler material to secure the lens one, the lens two and the filter unit within it, wherein The lens one, the lens two and the filter unit are arranged in sequence along a direction from the first end to the second end. The diaphragm is connected with the second end of the light-tight sleeve. The diaphragm has an opening formed thereon, and is arranged such that a range of the opening on a vertical cross section with respect to the direction from the first end to the second end is smaller than a range of the filter unit on the vertical cross section.

2. The light blocking fixture of claim 1, wherein, The light-tight sleeve and the diaphragm are integrally formed.

3. The light blocking fixture of claim 1, wherein, The lens one is configured to transmit input light from the optical fiber to the lens two in the form of parallel light, or to converge parallel light from the lens two into the optical fiber. The lens two is configured to converge parallel light into the filter unit, or to change input light from the filter unit into parallel light.

4. The light blocking fixture of claim 1, wherein, The light-absorbing filling material is black silica gel.

5. The light blocking fixture of claim 1, wherein, The diaphragm is a metal material treated by oxidation and blackening; and / or the light-tight sleeve is a metal material treated by oxidation and blackening.

6. The light blocking fixture of claim 1, wherein, The lens one is a G lens, and the lens two is a G lens or a C lens.

7. An optical fiber filter, comprising the light-blocking fixture according to any one of claims 1-6, and the lens one, the lens two and the filter unit fixedly arranged in the light-blocking fixture.

8. The optical fiber filter according to claim 7, further comprising a packaging structure for packaging the light-blocking fixture inside.

9. The fiber filter of claim 8, wherein, The packaging structure comprises an outer metal tube with an inner surface treated by oxidation and blackening.

10. The fiber filter of claim 7, wherein, The number of the light-blocking fixture and the lens one, the lens two and the filter unit inside the light-blocking fixture is two.

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