Device and method for generating polarization-entangled photon pairs

Abstract

Device (1) for generating polarization-entangled photon pairs (5), preferably for use in optical communication, quantum cryptography and / or quantum informatics, wherein the device comprises a pump beam source (2) for generating a pump beam (3), and wherein the device comprises a non-linear element (4) for generating photon pairs (5) by pumping the non-linear element (4) with the pump beam (3), and wherein each photon pair (5) comprises a signal photon (10) and an idler photon (11), and the polarization of the signal photon (10) and the idler photon (11) differs from one another, characterized in thatthat a polarization-maintaining fiber (6) (Polarization Maintaining Fiber PMF) is arranged after the non-linear element (4) to compensate for a time delay of the signal photon (10) and the idler photon (11) of the photon pairs (5) and for polarization entanglement by temporal indistinguishability of the signal photon (10) and the idler photon (11).,

Description

[0001] The invention relates to a device for generating polarization-entangled photon pairs according to the features of the preamble of claim 1 and to a method for generating polarization-entangled photon pairs according to the features of the preamble of claim 14.

[0002] Many different types of sources for generating entangled photon pairs are known. In some known sources for generating polarization-entangled photon pairs, the polarization-dependent propagation velocity in a nonlinear crystal results in a temporal shift (temporal walk-off), a wavelength-dependent shift (spectral walk-off), and / or a spatial shift (spatial walk-off) between the generated photons with different polarizations of a photon pair. This shift can lead to the destruction of entanglement, for example, by making it possible to distinguish superposition possibilities of entangled photons before the actual measurement.

[0003] In known sources, a birefringent crystal, such as a KTP crystal or a polarization-sensitive interferometer, is used to compensate for the time shift. Both variants require precise alignment and stabilization of the system during operation.

[0004] US 2007 / 0 002 307 A1 describes a rangefinder using entangled photon pairs. The entangled photon pairs, each containing a signal photon and an idler photon, are generated in a source. The signal and idler photons are spatially separated after generation and before passing through a polarization-maintaining fiber, using a polarizing beam splitter.

[0005] The present invention is based on the object of providing an improved, more cost-effective and more robust device and method for generating entangled photon pairs.

[0006] The object is achieved according to the invention by a device for generating polarization-entangled photon pairs according to the features of claim 1.

[0007] According to the invention, a device for generating polarization-entangled photon pairs is proposed, preferably for use in optical communication, quantum cryptography and / or quantum informatics, wherein the device comprises a pump beam source for generating a pump beam, and wherein the device comprises a non-linear element for generating photon pairs by pumping the non-linear element with the pump beam, and wherein each photon pair comprises a signal photon and an idler photon, and the polarization of the signal photon and the idler photon differs from each other.

[0008] It is essential that a polarization maintaining fiber (PMF) is arranged after the non-linear element to compensate for a time delay of the signal photon and the idler photon of the photon pairs and to polarization entanglement by temporal indistinguishability of the signal photon and the idler photon.

[0009] Furthermore, the object is achieved according to the invention by a method for generating polarization-entangled photon pairs according to the features of claim 14.

[0010] According to the invention, a method for generating polarization-entangled photon pairs is proposed, preferably for use in optical communication, quantum cryptography and / or quantum informatics, wherein the method comprises the following steps: i) generating a pump beam, preferably in a pump beam source; ii) Generation of photon pairs in a non-linear element by pumping the non-linear element with the pump beam, wherein each photon pair comprises a signal photon and an idler photon, and the polarization of the signal photon and the idler photon differs from each other; iii) compensation of a time delay of the signal photon and the idler photon of the photon pairs for polarization entanglement by indistinguishability of the signal photon and the idler photon; What is important here is that the time delay of the signal photon and the idler photon of the photon pairs is compensated by transmission of the signal photon and the idler photon through a polarization maintaining fiber (PMF).

[0011] An advantage of the device and method according to the invention is the use of a polarization-maintaining fiber, which utilizes the birefringence in the polarization-maintaining fiber to compensate for the time delay. It is important to note that in known sources for generating polarization-entangled photon pairs, such polarization-maintaining fibers are always avoided to prevent the entanglement from being destroyed by the birefringence of the polarization-maintaining fiber.

[0012] An advantage of the device and method according to the invention is the precise adjustment of the compensation provided by the polarization-maintaining fiber. In the device and method according to the invention, the compensation can be precisely adjusted by selecting the fiber length and / or by the material and / or design of the polarization-maintaining fiber. In particular, due to the lower birefringence of polarization-maintaining fibers compared to the strength of the birefringence of a birefringent crystal and the precision of manufacturing a birefringent crystal, much more precise compensation can be achieved through the fiber length. A further advantage is that such a polarization-maintaining fiber is significantly more cost-effective than birefringent crystals or interferometers.

[0013] An advantage of the device and method according to the invention, based on the use of the polarization-maintaining fiber and the transmission through this polarization-maintaining fiber, is the reduced size of the device, as well as the simple alignment (e.g., by splicing the fiber), and the intrinsic stability. In contrast, polarization-sensitive interferometers or birefringent crystals in known sources require additional space for compensation, very precise alignment, and must be protected from external influences during the generation of the entangled photons.

[0014] Compensation of the temporal delay of the signal photon and the idler photon of the photon pairs for polarization entanglement by temporal indistinguishability of the signal photon and the idler photon can be understood as meaning that polarization entanglement can be detected by measuring the photon pairs after compensation of the temporal delay. Such detection can be achieved, for example, by separating the signal photons and the idler photons at a beam splitter and measuring the polarization of the signal photons and the idler photons in a known manner. After separation of the signal photon from the idler photon by such a beam splitter, the photon pairs can also be used for optical communication, quantum cryptography, and / or quantum computing. Furthermore, the degree of entanglement, described, for example, by the visibility, can depend, among other things, on the compensation of the temporal delay.

[0015] Polarization-maintaining fibers are used in a known manner to maintain the polarization of light during transmission through the polarization-maintaining fiber. This is achieved by creating birefringence between two opposing polarizations, for example, the linear horizontal polarization H and the linear vertical polarization V, in the polarization-maintaining fiber. The two polarizations have different phase velocities within the polarization-maintaining fiber, which are determined by the different refractive indices of the polarization-maintaining fiber. For reasons of space-independent orientation of the polarization, two polarization axes are specified for polarization-maintaining fibers, which are referred to as the fast axis with the lower refractive index n. s and slow axis with higher refractive index n l be referred to.

[0016] For example, in an optically negative uniaxial crystal, the fast axis runs parallel to the crystal's optical axis, and the slow axis is perpendicular to it. For example, in an optically positive uniaxial crystal, the fast axis runs perpendicular to the crystal's optical axis, while the slow axis coincides with the optical axis. This behavior of optically negative or positive uniaxial crystals can be applied similarly to the fast and slow axes of a polarization-maintaining fiber.

[0017] It can be provided that the time delay of the signal photon and the idler photon of the photon pairs is generated by the non-linear element, preferably by transmission of the signal photon and the idler photon through the non-linear element.

[0018] It can be provided that the temporal delay of the signal photon and the idler photon of the photon pairs is generated by polarization-dependent birefringence in the non-linear element. Due to such polarization-dependent birefringence, the signal photon and the idler photon of each photon pair propagate at different speeds in the non-linear element due to their different polarization. As a result, the signal photon and the idler photon exhibit a temporal offset from one another after transmission, depending on the location of the photon pair generation in the non-linear element, i.e., due to transmission through the non-linear element. The temporal delay can be understood as the temporal offset of the signal photon and the idler photon from one another after transmission through the non-linear element.

[0019] It can be provided that the temporal delay of the signal photon and the idler photon of a photon pair, preferably by the non-linear element, is understood to be the average temporal offset between the signal photon and the idler photon of the photon pairs after the non-linear element. It can be provided that the average temporal offset corresponds to half of a maximum temporal offset, wherein the maximum temporal offset is formed by the entire length of the non-linear element.

[0020] It can be provided that the compensation of the temporal delay is achieved by a compensation delay, preferably by the polarization-maintaining fiber (PMF). Compensation of the temporal delay of the signal photon and the idler photon preferably means the formation of a compensation delay, preferably by the polarization-maintaining fiber (PMF). The compensation delay counteracts the temporal delay.

[0021] It can be provided that the compensation delay is generated partially or completely by the polarization maintaining fiber (PMF).

[0022] The compensation delay can be configured to have an opposite sign to the time delay. The compensation delay thus counteracts the time delay.

[0023] It can be provided that the value of the compensation delay corresponds to the value of the time delay of the signal photon and the idler photon, preferably the average time offset between the signal photon and the idler photon of the photon pairs, most preferably half of the maximum time offset, wherein the maximum time offset is formed by the entire length of the non-linear element.

[0024] It can be provided that the polarization of the signal photon and the idler photon of each photon pair is orthogonal to each other. For example, the signal photon has a linear horizontal polarization H and the idler photon has a linear vertical polarization V.

[0025] The polarization-maintaining fiber (PMF) can be configured to generate polarization-dependent birefringence. The PMF can be configured to generate the compensation delay entirely or partially through the polarization-dependent birefringence.

[0026] It can be provided that, to compensate for the time delay, preferably to generate the compensation delay, a further birefringent element is arranged in addition to the polarization-maintaining fiber (PMF), preferably after the non-linear element. It can be provided that the further birefringent element is designed as a birefringent crystal, preferably as a KTP crystal. It can be provided that the further birefringent element is arranged before or after the polarization-maintaining fiber (PMF). It can be provided that the time delay of the signal photon and the idler photon is compensated by transmitting the signal photon and the idler photon through a polarization-maintaining fiber (PMF) and by transmitting the signal photon and the idler photon through the further birefringent element.The signal photon and the idler photon can be arranged to first transmit through the polarization-maintaining fiber (PMF) or first through the birefringent element. The polarization-maintaining fiber (PMF) can be arranged before or after the birefringent element. One advantage of this design is that it allows existing sources to be optimized and the polarization-maintaining fiber provides additional, highly precise compensation. One advantage of this design is that both excessive and insufficient compensation by the additional birefringent element can be corrected through the selection and design of the polarization-maintaining fiber (PMF).

[0027] It can be provided that the time delay through the non-linear element of length L NLof the non-linear element and / or the refractive index n sNL in the direction of the fast axis of the non-linear element and / or the refractive index n lNL in the direction of the slow axis of the non-linear element.

[0028] It can be provided that the compensation of the time delay, preferably the compensation delay, is achieved by the polarization maintaining fiber (PMF) with a length L PMF the polarization-maintaining fiber and refractive index n sPMF in the direction of the fast axis and the refractive index n lPMF in the direction of the slow axis of the polarization maintaining fiber (PMF).

[0029] The polarization-maintaining fiber (PMF) can be arranged behind the non-linear element such that the fast axis of the PMF is parallel to the slow axis of the non-linear element. Such an arrangement can be achieved by positioning the PMF or by placing an optical component between the non-linear element and the PMF for rotating the polarization of the signal photon and the idler photon, such as a waveplate. Such an arrangement creates a compensation delay with opposite signs to the time delay.

[0030] It can be provided that the polarization maintaining fiber (PMF) is arranged behind the non-linear element in such a way that both the signal photon and the idler photon are transmitted through the polarization maintaining fiber (PMF).

[0031] It can be provided that the polarization maintaining fiber (PMF) has a length L PMF has.

[0032] It can be provided that the polarization maintaining fiber (PMF) with length L PMF the compensation delay is generated completely or partially.

[0033] It may be provided that the length L PMF is determined, preferably calculated in step iii), by LPMF=ΔθLb2π with Δθ as the temporal compensation, preferably the compensation delay, by the polarization maintaining fiber (PMF) with Δθ=LNL2(nsNL−NLNL)2πλ, with L NL the length of the non-linear element and a beat-length L b which corresponds to the length of the polarization-maintaining fiber for a phase shift 2π between two orthogonal polarizations, preferably with Lb=λ|(nsPMF−nlPMF)|.

[0034] It can be provided that the length L PMF the temporal compensation is generated completely or partially, preferably the compensation delay is generated completely or partially. In the case of partial temporal compensation, preferably a partial compensation delay, the length L is determined PMF Additionally, the temporal compensation by the additional birefringent element must be included in the calculation.

[0035] As a non-exclusive example, the length L PMF a polarization-maintaining fiber (PMF) specified for polarization-entangled photon pairs at 1550 nm. In this non-exclusive embodiment, the compensation is achieved entirely by the polarization-maintaining fiber (PMF). For this purpose, a type-II ppLN (periodically poled lithium niobate LiNbO3) crystal is used as a nonlinear element at 40°C with a length L NL = 20 mm. The beat-length L b In this example, the polarization maintaining fiber (PMF) corresponds to 2 mm, which is in the range of a normal polarization maintaining fiber (PMF).

[0036] With these values, the length L PMF the polarization maintaining fiber (PMF) can be determined LPMF=ΔθLb2π=0.98 m

[0037] It can be provided that the pump beam source is designed as a laser and / or an optically active element for amplified spontaneous emission. It can be provided that in step i), the pump beam is generated by amplified stimulated emission in a laser and / or amplified spontaneous emission in an optically active element.

[0038] It can be provided that the non-linear element is designed as one or more non-linear crystals or one or more non-linear waveguides.

[0039] It can be provided that the polarization-entangled photon pairs are additionally entangled in time (time-bin) and / or orbital angular momentum.

[0040] It can be provided that in step ii) the photon pairs are generated by a nonlinear process in the nonlinear element, preferably by parametric fluorescence (spontaneous parametric down-conversion SPDC) or spontaneous four-wave mixing (SFWM). It can be provided that the nonlinear element is arranged in a Sagnac configuration, a linear configuration, a BBO configuration, or a four-wave mixing configuration, preferably with a cavity, to generate polarization-entangled photon pairs.

[0041] It can be provided that the non-linear element is connected as a waveguide via a fiber connection to the polarization maintaining fiber (Polarization Maintaining Fiber PMF), or The non-linear element serves as a waveguide, and a component for rotating the polarization and the polarization-maintaining fiber (Polarization Maintaining Fiber PMF) are connected to each other via fiber connections. Preferably, the component for rotating the polarization is arranged between the non-linear element and the polarization-maintaining fiber (Polarization Maintaining Fiber PMF). The advantage of these designs lies in the direct connection of the components via the fiber connections, which ensures high stability and easy adjustment.

[0042] It can be provided that the fiber connections are designed as fiber plug connections or as fiber splice connections.

[0043] It can be provided that the device for generating polarization-entangled photon pairs is designed as a linear Type II source, preferably with a periodically poled non-linear Type II crystal as a non-linear element, and a beam splitter, or that the device for generating polarization-entangled photon pairs is designed as a source with a bi-directionally pumped non-linear element.

[0044] It can be provided that the polarization maintaining fiber (PMF) is temperature stabilized.

[0045] It can be provided that the properties of the non-linear element which cause the time delay of the photons are the material of the non-linear element, and / or the polarity of the non-linear element, and / or the beam path of the non-linear element.

[0046] Further embodiments of the invention are illustrated in the figures and described below. The figures show one possible embodiment of the invention by way of example. This embodiment serves to illustrate a possible implementation of the invention and is not intended to be limiting. They show: Fig. 1: A schematic representation of a first embodiment of the device according to the invention with a polarization-maintaining fiber for compensation; Fig. 2: A schematic representation of a further embodiment of the device according to the invention with a polarization-maintaining fiber and a birefringent element for compensation; Fig. 3: A schematic representation of a further embodiment of a device according to the invention with fiber elements; Fig. 4: A schematic representation of the time delay and compensation.

[0047] Fig. 1 shows a schematic representation of a first embodiment of the device 1 according to the invention for generating polarization-entangled photon pairs.

[0048] The device 1 comprises a pump beam source 2, which generates a pump beam 3. The pump beam 3 is guided to a non-linear element 4. By pumping the non-linear element 4 with the pump beam 3, photon pairs 5 are generated through a non-linear process. Each photon pair 5 comprises a signal photon and an idler photon, with the polarization of the signal photon and the idler photon differing from each other.

[0049] What is important here is that the photon pairs 5 are generated within the non-linear element 4, and after generation, the signal photon 10 and the idler photon 11 of each photon pair 5 pass through the rest of the non-linear element 4. Due to polarization-dependent birefringence in the non-linear element 4, the transmission of the signal photon 10 and the idler photon 11 creates a time delay between the signal photon 10 and the idler photon 11 due to their different polarization. This time delay can also be described as a time offset after the non-linear element 4 between the signal photon 10 and the idler photon 11 of the photon pair 5.

[0050] Furthermore, the device according to the invention has Fig. 1 has a polarization-maintaining fiber 6 (Polarization Maintaining Fiber PMF). The signal photon 10 and the idler photon 11 of each photon pair 5 with the time delay then transmit through the polarization-maintaining fiber 6, wherein the polarization-maintaining fiber 6 has a certain length L PMF has.

[0051] The properties, orientation and length L PMF the polarization-maintaining fiber 6 is determined in such a way that the time delay is compensated by the transmission of the signal photon 10 and the idler photon 11 through the polarization-maintaining fiber 6.

[0052] By compensating for the time delay, the signal photon 10 and the idler photon 11 of each photon pair 5 are temporally indistinguishable. After the polarization-maintaining fiber 6, the signal photon 10 and the idler photon 11 can be spatially separated from each other in order to detect polarization entanglement by measurement, or to use the photon pairs for optical communication, quantum cryptography, and / or quantum computing. The spatial separation can be achieved, for example, by the Fig. 1 optional beam splitter 7 shown in dashed lines.

[0053] Fig. Figure 2 shows a schematic representation of a second embodiment of the device 1 according to the invention for generating polarization-entangled photon pairs 5. The embodiment of the Fig. 2 differs from the embodiment of the Fig. 1 only in that a birefringent element 8 is arranged between the non-linear element 4 and the polarization-maintaining fiber 6. The birefringent element 8 can, for example, be formed as a birefringent crystal.

[0054] In the embodiment of the Fig. 2, the time delay is compensated by a transmission of the signal photon 10 and the idler photon 11 of the photon pairs 5 through the birefringent element 8 and a transmission through the polarization-maintaining fiber 6. The disadvantage of the birefringent element 8 as birefringent crystals is that they cannot be manufactured very precisely. The advantage of the inventive embodiment of the Fig. 2 is that by combining the birefringent element 8 and the polarization-maintaining fiber 6, the precision of the compensation by using the polarization-maintaining fiber 6 can be significantly improved in known devices by correcting both excessive and insufficient compensation by the birefringent element 9 by appropriate selection and design of the polarization-maintaining fiber 6.

[0055] Fig. 3 shows a schematic representation of a third embodiment of the device 1 according to the invention for generating polarization-entangled photon pairs 5. The embodiment of the Fig. 3 differs from the embodiment of the Fig. 1 only in that the pump beam source 2, the non-linear element 4, the polarization-maintaining fiber 6, and the optional beam splitter 7 are designed as fiber elements and are connected to one another by fiber connections 9. The fiber connections 9 can be designed as fiber plug connections or as fiber splice connections. In this embodiment, the design of the non-linear element 4 as a waveguide is particularly advantageous.

[0056] Fig. Figure 4 shows a schematic representation of the signal photon 10 and the idler photon 11 of a photon pair 5 in the device 1 for generating polarization-entangled photon pairs 5, as well as the generation and compensation of the time delay. It is important to note that the polarization of the signal photon 10 and the idler photon 11 of the photon pair 5 differs.

[0057] In the example of Fig. 4, the signal photon 10 has, for example, a linear horizontal polarization, represented by the point in Fig. 4, which represents an arrow out of the image plane. The idler photon 11 points in Fig. 4 shows an example of a linear vertical polarization, represented by the arrow in the image plane in Fig. 4.

[0058] The schematic diagram in Fig. 4 the generation of the photon pair in the center of the non-linear element 4 is assumed. As in Fig. As shown in Figure 4, the photon pair 5 comprises the signal photon 10 and the idler photon 11.

[0059] After the generation of the signal photon 10 and the idler photon 11 in the non-linear element 4, the signal photon 10 and the idler photon 11 pass through the rest of the non-linear crystal 4. Due to the polarization-dependent birefringence in the non-linear element 4, the transmission of the signal photon 10 and the idler photon 11 causes a time delay between the signal photon 10 and the idler photon 11 due to their different polarization, as shown in the section after the non-linear element 4 in Fig. 4, separated by the dashed lines. This time delay, shown in Fig. 4 by the horizontal distance between the signal photon 10 and the idler photon 11, the polarization of the measured photon could already be determined in a measurement based on the temporal detection, which would lead to a destruction of the entanglement.

[0060] The signal photon 10 and the idler photon 11 then pass through the polarization-maintaining fiber 6, wherein the properties, orientation and length of the polarization-maintaining fiber 6 are determined in such a way that the transmission of the signal photon 10 and the idler photon 11 through birefringence in the polarization-maintaining fiber 6 compensates for the time delay caused by the non-linear crystal 4, as shown in Fig. 4 is shown in the right section. The polarization-entangled photon pairs 5 compensated in this way can be used for optical communication, quantum cryptography, and / or quantum computing. List of reference symbols 1 device 2 Pump beam source 3 pump jet 4 non-linear element 5 photon pairs 6 polarization maintaining fiber 7 beam splitters 8 birefringent element 9 Fiber connection 10 Signal-Photon 11 Idler-Photon

Claims

[1] Device (1) for generating polarization-entangled photon pairs (5), preferably for use in optical communication, quantum cryptography and / or quantum informatics, wherein the device comprises a pump beam source (2) for generating a pump beam (3), and wherein the device comprises a non-linear element (4) for generating photon pairs (5) by pumping the non-linear element (4) with the pump beam (3), and wherein each photon pair (5) comprises a signal photon (10) and an idler photon (11), and the polarization of the signal photon (10) and the idler photon (11) differs from each other, characterized by , that a polarization maintaining fiber (6) (Polarization Maintaining Fiber PMF) is arranged after the non-linear element (4) to compensate for a time delay of the signal photon (10) and of the idler photon (11) of the photon pairs (5) and to the polarization entanglement through temporal indistinguishability of the signal photon (10) and the idler photon (11). [2] Device (1) according to claim 1, characterized by that the time delay of the signal photon (10) and the idler photon (11) of the photon pairs (5) is generated by the non-linear element (4), preferably by transmission of the signal photon (10) and the idler photon (11) through the non-linear element (4). [3] Device (1) according to one of the preceding claims, characterized by that the time delay of the signal photon (10) and the idler photon (11) of the photon pairs (5) is generated by polarization-dependent birefringence in the non-linear element (4) [4] Device (1) according to one of the preceding claims, characterized bythat the compensation of the time delay is effected by a compensation delay, preferably that the compensation delay is generated partially or completely by the polarization maintaining fiber (6) (Polarization Maintaining Fiber PMF). [5] Device (1) according to claim 4, characterized by that the compensation delay corresponds to the time delay of the signal photon (10) and the idler photon (11), preferably the average time offset between the signal photon (10) and the idler photon (11) of the photon pairs (5), most preferably half the maximum time offset, wherein the maximum time offset is formed by the entire length of the non-linear element (4). [6] Device (1) according to one of the preceding claims, characterized byin that, in order to compensate for the time delay, preferably to generate the compensation delay, a further birefringent element (8) is arranged in the device (1) in addition to the polarization maintaining fiber (6) (Polarization Maintaining Fiber PMF). [7] Device (1) according to one of the preceding claims, characterized by that the compensation of the time delay, preferably the compensation delay, is provided by the polarization maintaining fiber (6) (Polarization Maintaining Fiber PMF) with a length L PMF the polarization-maintaining fiber (6) and refractive index n sPMF in the direction of the fast axis and the refractive index n lPMF in the direction of the slow axis of the polarization maintaining fiber (6) (Polarization Maintaining Fiber PMF). [8] Device (1) according to one of the preceding claims, characterized bythat the polarization maintaining fiber (6) (Polarization Maintaining Fiber PMF) has a length L PMF preferably that by the length L PMF the polarization maintaining fiber (6) (Polarization Maintaining Fiber PMF) the temporal compensation is generated completely or partially, preferably the compensation delay is generated completely or partially. [9] Device (1) according to one of the preceding claims, characterized by that the non-linear element (4) is designed as one or more non-linear crystals or one or more non-linear waveguides. [10] Device (1) according to one of the preceding claims, characterized by , that the non-linear element (4) is connected as a waveguide via a fiber connection (9) to the polarization maintaining fiber (6) (Polarization Maintaining Fiber PMF), or that the non-linear element (4) as a waveguide and a component for rotating the polarization and the polarization-maintaining fiber (6) (Polarization Maintaining Fiber PMF) are connected to one another via a fiber connection (9), preferably that the component for rotating the polarization is arranged between the non-linear element (4) and the polarization-maintaining fiber (6) (Polarization Maintaining Fiber PMF). [11] Device (1) according to claim 10, characterized by that the fiber connection (9) is designed as a fiber plug connection or as a fiber splice connection. [12] Device (1) according to one of the preceding claims, characterized bythat the device for generating polarization-entangled photon pairs (5) is designed as a linear Type II source, preferably with a periodically poled non-linear Type II crystal as a non-linear element (4), and a beam splitter, or that the device for generating polarization-entangled photon pairs (5) is designed as a source with a bi-directionally pumped non-linear element (4). [13] Device (1) according to one of the preceding claims, characterized by that the polarization maintaining fiber (6) (Polarization Maintaining Fiber PMF) is temperature stabilized. [14] Method for generating polarization-entangled photon pairs (5), preferably for use in optical communication, quantum cryptography and / or quantum computing, the method comprising the following steps: i) generating a pump beam (3), preferably in a pump beam source (2); ii) generating photon pairs (5) in a non-linear element (4) by pumping the non-linear element (4) with the pump beam (3), wherein each photon pair (5) comprises a signal photon (10) and an idler photon (11), and the polarization of the signal photon (10) and the idler photon (11) differs from one another; iii) compensation of a time delay of the signal photon (10) and the idler photon (11) of the photon pairs (5) for polarization entanglement by indistinguishability of the signal photon (10) and the idler photon (11); characterized by that the time delay of the signal photon (10) and the idler photon (11) of the photon pairs (5) is compensated by transmission of the signal photon (10) and the idler photon (11) through a polarization maintaining fiber (6) (Polarization Maintaining Fiber PMF). [15] Method according to claim 14, characterized by that a length L PMFthe polarization maintaining fiber (6) (Polarization Maintaining Fiber PMF) in step iii) is calculated by LPMF=ΔθLb2π with Δθ as the temporal compensation, preferably the compensation delay, by the polarization maintaining fiber (6) (Polarization Maintaining Fiber PMF) with Δθ=LNL2(nsNL−nlNL)2πλ, Δθ with L NL the length of the non-linear element (4) and a beat-length L b which corresponds to the length of the polarization-maintaining fiber (6) for a phase shift 2π between two orthogonal polarizations, preferably with Lb=λ|(nsPMF−nlPMF)|.

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