JP2006337519A - Polarization maintaining optical fiber having circularly polarized light suitability, and magnetooptic trapping apparatus and atomic chip using same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make input/output of circularly polarized light or its transmission possible by using an ordinary polarization maintaining optical fiber, without twisting an optical fiber or installing a 1/4 wavelength plate on the outside of the optical fiber. <P>SOLUTION: In this optical fiber which circularly polarized light is made once linearly polarized light and transmitted, wherein the polarization maintaining optical fiber contains a first part, a second part that is continuous to the first part in a manner tilted at 45° around the optical axis, and a third part that is continuous to the second part in a manner tilted at 45° around the optical axis. The first and third parts include a length producing, in the polarization components, a retardation of 1/4 wavelength or its integer multiples, making the circularly polarized light enter from the first part, transmitting the linear polarized light in the second part, and transmitting the circularly polarized light in the third part to output it from the end thereof. Also, in the second part, a linear polarization element is inserted having a polarization characteristic along the polarization direction of the polarization maintaining optical fiber, improving the purity of polarization in the linear polarization part. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention is used for applications in which circularly polarized light is directly emitted from the tip of an optical fiber, or circularly polarized light is directly incident on an optical fiber, or where circularly polarized light is transmitted using an optical fiber. In particular, 1) connection of optical fibers in an optical communication network in which polarization maintaining optical fibers are used, and 2) in laser equipment and measuring instruments in which polarization maintaining optical fibers are used. Circularly polarized light that can be used to connect optical fibers, or 3) to supply a circularly polarized beam to an atomic optical device using the interaction between a magnetic field and laser light, such as an atomic clock, atomic laser, atomic chip, or atomic lithography The present invention relates to a polarization-maintaining optical fiber having compatibility, a magneto-optical trap apparatus using the same, and an atomic chip.

  It is known that it is difficult to transmit circularly polarized light having the same phase using an optical fiber as circularly polarized light. Single-mode optical fibers do not have the ability to stably transmit a fixed polarization state because the transmission characteristics do not depend on polarization. This is because the optical fiber is subjected to bending stress, vibration, uneven temperature distribution, etc., and irregular birefringence is induced in the optical fiber, and the polarization state of the incident light is greatly increased during the transmission of the optical fiber. This is because the polarization state of the beam that is broken and emitted is significantly different from the original one, and the polarization state fluctuates greatly over time.

  For this reason, in order to emit circularly polarized light from the tip of the optical fiber, a special device is required. For example, after transmitting laser light as linearly polarized light using a polarization maintaining optical fiber, circularly polarized light is obtained by passing the light emitted from the optical fiber through a quarter-wave plate and converting it into circularly polarized light. be able to. Conversely, in order to make circularly polarized light incident on the optical fiber, a quarter-wave plate is used to convert the circularly polarized laser light into linearly polarized light and then enter the polarization maintaining optical fiber. There is a need.

  Therefore, in the above example, in order to transmit circularly polarized laser light, quarter-wave plates are disposed at both ends of the polarization maintaining optical fiber. This configuration is structurally complex and unsuitable for miniaturization, and the optical fibers cannot be directly connected to each other, so that there is a problem that transmission characteristics are easily affected by mechanical vibration.

  In the above configuration, the polarization maintaining optical fiber is used. However, even in this case, the polarization maintaining optical fiber alone does not have the ability to stably transmit an arbitrary polarization state of incident light. An exception to this is linearly polarized light having an oscillation plane of an electric field vector that is parallel to or perpendicular to the optical axis of the polarization maintaining optical fiber.

  In addition, an optical fiber having a low birefringence characteristic has a lower birefringence than a normal single mode optical fiber, and the above situation is improved. An optical fiber having a low birefringence characteristic is commercially available, and the presence or absence of the effect can be easily confirmed. However, like the single mode optical fiber, the polarization state is still not maintained due to the birefringence caused by bending stress or the like.

  As a technique relatively similar to the present invention, the disclosure of Patent Document 1 can be cited. In Patent Document 1, circularly polarized light is transmitted using a single-mode optical fiber. In order to compensate for a polarization state disturbed by a disturbance, “to adjust according to the polarization depending on the bending of the optical fiber”. In addition, a stand having a tilt angle and roll angle adjustment function ”is used, and stable transmission of circularly polarized light is not realized with an optical fiber alone.

  Patent Document 2 also describes “Circularly Polarized Fiber”. This has the function of inducing circular birefringence by giving an “axial twist” to an ordinary single mode optical fiber and stably transmitting circularly polarized light using the single mode optical fiber. Fiber. Details of this principle are also described in Non-Patent Document 1.

  In the method of twisting a normal single mode optical fiber itself, it is necessary to devise to hold the optical fiber in the twisted state, and it is difficult to handle the optical fiber. Further, it is possible to give a twist in advance in the manufacturing process of the optical fiber, but a special preform and a special drawing tower are required for the manufacturing.

  The present invention realizes circularly polarized light input / output and transmission using a normal polarization maintaining optical fiber without using such a special optical fiber.

  Patent Document 3 discloses a depolarizer in which a part of a polarization maintaining optical fiber is melted and the melted portion is wound 45 degrees. This document also describes an optical fiber in which two polarization maintaining optical fibers are melted by rotating 45 degrees. However, since the length of the optical fiber melted by rotating 45 degrees is sufficiently longer than the coherence length of the laser light, this fiber does not have a function of inputting / outputting circularly polarized light.

  Further, there is a magneto-optical trap (MOT) technique to which the present invention can be effectively applied. In general, in MOT, atoms are put in a vacuum vessel and isolated, and atoms are trapped in the air by a magnetic field and an electric field of light. For this reason, since it is usually necessary to irradiate laser light from the outside of the vacuum container, it is indispensable to install a viewing port in the vacuum container, and it is difficult to reduce the size of the apparatus. Moreover, in order to irradiate circularly polarized light, a plurality of expensive wave plates had to be used. In addition, it is necessary to use a large electromagnet that generates a strong magnetic field and to flow a large current. In order to suppress power consumption, it is well known that a superconducting magnet may be used. However, since cooling is necessary, the apparatus becomes complicated. In addition, in order to capture or release neutral atoms, it is necessary to turn on and off the magnetic field. In practice, a normal electromagnet is generally easier to use. However, the necessity of flowing a large current as described above has made it difficult to reduce the size of the apparatus.

  On the other hand, it is known that a large magnetic field gradient that can be sufficiently used as a magnetic trap can be obtained very close to the wiring of the integrated circuit, generally within a few mm from the chip surface. This is because the value of the current flowing through the wiring of the integrated circuit is small, but the magnetic field becomes stronger in the vicinity. As described above, with respect to the magnetic field, the atomic chip technology using a fine circuit is practically advantageous, and the light irradiation portion is required to be miniaturized for practical use.

JP 2004-004579 A JP-T-2002-525647 Japanese Patent Laid-Open No. 06-337321

Hung-chia Huang "Microwave approach to Highly Irregular Fiber Optics" (Willey, 1998) P. Horak et al., "Possibility of single-atom detection on a chip," Physical Review A 67, 043806 (2003). P.A. Quinto-Su et al., "On-chip optical detection of laser cooled atoms," Optics Express 12, 5098 (2004).

  Enables the input / output of circularly polarized light or transmission using ordinary polarization-maintaining optical fiber without twisting the optical fiber or providing a quarter-wave plate outside the optical fiber. To do.

  The present invention relates to a polarization maintaining optical fiber having circular polarization compatibility, and it is possible to input / output circularly polarized light or transmit the polarization using a normal polarization maintaining optical fiber. Also, an optical isolator different from the conventional optical isolator can be realized. Furthermore, by using the polarization maintaining optical fiber of the present invention for the magneto-optical trap device, the vacuum vessel can be made smaller than the conventional one.

  The present invention provides a polarization-maintaining optical fiber that can change circularly polarized light into linearly polarized light, including a first portion and a second portion that is continuous with the first portion inclined at 45 degrees about the optical axis, The first part is shorter than the second part, and has a length that causes a phase difference corresponding to a quarter wavelength or a natural number plus a natural number of wavelengths between the intrinsic polarization components of light. Circularly polarized light is incident on the part, and linearly polarized light is propagated in the second part.

  The present invention also provides a polarization-maintaining optical fiber capable of changing linearly polarized light into circularly polarized light, including a second portion and a third portion that is continuous with the second portion inclined at 45 degrees about the optical axis, The third part is shorter than the second part, and has a length in which a phase difference corresponding to a quarter wavelength or a natural number plus a natural number of wavelengths is generated between the intrinsic polarization components of light. In the second part, linearly polarized light is propagated, and in the third part, the linearly polarized light is converted into circularly polarized light, and circularly polarized light is output from the end of the third part.

  Further, the present invention transmits circularly polarized light once into linearly polarized light, and is a polarization maintaining optical fiber, and a first portion and a second portion that is continuous with the first portion inclined at 45 degrees about the optical axis. And the second part includes a third part that is inclined at 45 degrees about the optical axis, and the first part and the third part have a quarter wavelength or a natural number between the intrinsic polarization components of the light. It has a length that produces a phase difference corresponding to the addition of a natural number of wavelengths to it, makes circularly polarized light incident on the first part, propagates linearly polarized light in the second part, and linearly polarized light in the third part. The light is converted into circularly polarized light, and circularly polarized light is output from the end of the third portion.

  The present invention also improves the polarization purity of the linearly polarized light portion, and the second portion has a polarization characteristic along the polarization axis direction of the polarization maintaining optical fiber or a direction perpendicular thereto. A linearly polarizing element is inserted.

  Further, the present invention performs connection between optical fibers at a circularly polarized portion. In the polarization maintaining optical fiber, the first portion and the first portion are continuously inclined at 45 degrees about the optical axis. The second part includes A having a length that produces a phase difference corresponding to a quarter wavelength or a natural number plus a natural number of wavelengths between the intrinsic polarization components of light, and a polarization. A wave-holding optical fiber including a third portion and a fourth portion that is continuous with the third portion inclined at 45 degrees about the optical axis, and the third portion includes a quarter wavelength between polarization components of light. B having a length that produces a phase difference of a fraction or a fraction of a natural number obtained by adding a natural fraction of a wavelength thereto, and connecting A and B, and linearly polarized light that has propagated through the first portion, When propagating through the second part, it is converted to circularly polarized light, transmitted from the second part to the third part as circularly polarized light, And converted into linearly polarized light in a portion, in the fourth part is to transmit to propagate linearly polarized light.

  In addition, the present invention makes it possible to use at a plurality of wavelengths, and the part that performs conversion between circularly polarized light and linearly polarized light is the intrinsic polarization component of light of each wavelength for a plurality of different wavelengths. The length is such that a phase difference corresponding to a quarter wavelength or a natural number plus a natural number of wavelengths is generated between them.

  Further, the present invention conserves the volume of the decompression vessel, and a plurality of polarization maintaining optical fibers having circular polarization compatibility are introduced into the decompression vessel so as to penetrate the decompression vessel wall, and a magneto-optical trap The polarization-maintaining optical fiber is arranged so as to be a light irradiation arrangement constituting the apparatus.

  Further, the present invention conserves the volume of the decompression vessel, and a plurality of polarization maintaining optical fibers having circular polarization compatibility are introduced into the decompression vessel so as to penetrate the decompression vessel wall, and surface magnetic optics The polarization-maintaining optical fiber is arranged so as to be a light irradiation arrangement constituting the trap device.

  In addition, the present invention realizes a fine atomic chip, and has the above-mentioned circular polarization compatibility with an atomic cloud captured by a magnetic trap formed by a wiring pattern on a flat substrate in a reduced-pressure atmosphere. Means for irradiating circularly polarized light emitted from the wave holding optical fiber is provided.

  Further, the means for irradiating circularly polarized light using the polarization maintaining optical fiber is an optical resonator formed by an output side end surface of the polarization maintaining optical fiber having circular polarization compatibility and a predetermined reflecting surface. Means for irradiating circularly polarized light.

  In the present invention, instead of twisting the optical fiber or providing a quarter-wave plate outside the optical fiber, a portion having a function of a quarter-wave plate is provided in a part of the optical fiber itself. Thus, circularly polarized light can be input and output using a normal polarization maintaining optical fiber. Embodiments of the present invention will be described below in detail with reference to the drawings. In the following description, devices having the same function or similar functions are denoted by the same reference numerals unless there is a special reason.

  FIG. 7 shows a cross-sectional structure of an example of the polarization maintaining optical fiber. This is called a PANDA fiber, and uses uniaxial birefringence induced in the core by the stress applying portion. FIG. 8A shows the state of the electric field vectors Px and Py of the light immediately after the circularly polarized light is incident on the polarization maintaining optical fiber. Since stress is always applied to this medium due to the presence of the stress-applying portion in FIG. 7A, and the refractive index varies depending on the vibration direction of propagating linearly polarized light, the light depends on the propagation distance. Various polarization states appear periodically in the fiber.

Assuming that the difference in refractive index is Δn, the wavelength of light is λ, and the length of the optical fiber is L, between the two intrinsic linear polarization components orthogonal to the vibration plane,
Δφ = (2π · Δn · L) / λ radians,
Phase difference occurs. This phase difference Δφ or Δn · L is referred to as retardation (hereinafter, Δφ is referred to as retardation). If the optical fiber has a refractive index dispersion, the above equation requires some correction but gives approximate results that are approximate. An optical fiber having a length L such that the value of Δφ is exactly π / 2 radians exhibits optical properties equivalent to a quarter-wave plate for light of this wavelength (FIG. 1). Hereinafter, such an optical fiber piece is referred to as a “quarter wavelength optical fiber”.

  Since the quarter-wavelength optical fibers are the same as ordinary polarization-maintaining optical fibers, they can be fused and connected to each other. A quarter-wave optical fiber can be made to function as a polarization state converter by fusion splicing with a normal polarization maintaining optical fiber with the optical axes inclined at 45 degrees. Hereinafter, the optical fiber module assembled by fusion-bonding with the optical axes inclined at 45 degrees in this way will be referred to as a “circularly polarized optical fiber”.

  By applying fusion processing of a quarter-wavelength optical fiber as a circularly polarized optical fiber to both ends of the polarization maintaining optical fiber 2, when circularly polarized light is incident, the circularly polarized light having exactly the same polarization state can be obtained. It is also possible to inject from the end (FIG. 2).

  It is assumed that a normal polarization maintaining optical fiber is used for the intermediate portion 2 of the above-mentioned circularly polarized light compatible optical fiber. Since the polarization state of light propagating through the intermediate portion is linearly polarized light, the polarization state does not change even when bending stress, temperature change, or the like is applied. If bending stress or the like is applied to the quarter-wavelength optical fiber part, the polarization state may change, but this part can usually be sufficiently short (several millimeters to several centimeters), It can be well protected. Moreover, since the circularly polarized light compatible optical fiber is not different from a normal polarization maintaining optical fiber in terms of material and appearance, it can be loaded into a widely used optical fiber connector. It is desirable to prevent the refractive index from changing easily by protecting the fragile quarter wavelength optical fiber part with a ferrule part such as a connector or a highly rigid sheath.

  It is also easy to interconnect the circularly polarized light compatible optical fibers via this connector. When interconnecting polarization-maintaining optical fibers via a connector, it was necessary to adjust the optical axis of the optical fiber precisely until now. Since it is injected, it is not necessary to align the direction of the optical axis when interconnecting the connectors.

  Further, linearly polarized light propagates in the intermediate portion 2 of the above-mentioned circularly polarized light compatible optical fiber, and the polarization direction thereof varies depending on the direction of rotation of the circularly polarized light that is incident or emitted. When circularly polarized light with different rotation directions is mixed, the purity of circularly polarized light is lowered and becomes elliptically polarized light. Therefore, as shown in FIG. 3, if the linear polarizer 4 is inserted in the middle part of the circularly polarized optical fiber, the incident light of low-purity circularly polarized light (elliptical polarized light) is converted into circularly polarized light with high purity. Can be operated as a circular polarizer (FIG. 3).

  Further, when the light propagating in the circularly polarized optical fiber is reflected backward at the end face of the connector, the direction of rotation of the circularly polarized light of the reflected light is opposite to that of the incident light. The direction of polarization when propagating in the opposite direction (as linearly polarized light) is perpendicular to that of the incident light. Therefore, this reflected light can be removed by using the linear polarizer 4 in the intermediate portion. That is, an optical isolator can be configured (FIG. 3). In a conventional optical isolator, a Faraday rotator is used. However, in the present invention, it is not necessary to use this, and the size can be easily reduced.

  If the quarter-wavelength optical fibers connected to both ends of the optical fiber 2 are connected so that the signs of the retardations are different from each other (that is, the directions of the optical axes are opposite to each other), It is possible to convert to left circularly polarized light and vice versa. In addition, a quarter-wavelength optical fiber connected to only one end of a normal optical fiber can be used to convert linearly polarized light into circularly polarized light and vice versa. More versatile than fiber.

  In addition, since the circularly polarized light compatible optical fiber does not require an expensive and large-volume optical element other than the optical fiber, the conventional optical system can be used as it is, and is installed separately from the optical fiber. By simply removing the half-wave plate, the performance of the optical system can be used as it is.

Quarter-wave optical fiber retardation,
Δφ = (2π · Δn · L) / λ is
When it changes with λ and Δφ coincides with (π / 2 + 2πm) where m is an integer, a circularly polarized light conforming type is obtained. There are an infinite number of such wavelengths λ as many as the integer m, but if two different wavelengths are given, the values of L and m are uniquely determined. In this way, by utilizing the high-order nature of the wave plate, it is possible to make a circularly polarized light compatible type at an arbitrary two wavelengths, for example, for 780 nm and 852 nm simultaneously.

  In addition, when connecting conventional polarization-maintaining optical fibers, the optical axes of the two optical fibers had to be precisely matched, but circularly-polarized optical fibers are a type of polarization-maintaining optical fiber. However, it is not necessary to make the optical axes coincide when connecting them, and at the same time, it saves the trouble of connecting, and at the same time prevents polarization crosstalk caused by imperfect optical axis adjustment Available at. An example of this connection is shown in FIG. The polarization maintaining optical fiber 11 and the quarter wavelength optical fiber 12 protected by the coating 15 are fused with an inclination of 45 degrees around the optical axis. Similarly, the quarter-wavelength optical fiber 13 and the polarization maintaining optical fiber 14 are fused with an inclination of 45 degrees around the optical axis. The quarter-wavelength optical fibers 12 and 13 are physically in contact with each other without providing a gap, or are connected with an antireflection filler 18 interposed therebetween, and this connection portion is a shield portion 16 of the connector. The left and right shield portions 16 are connected by a connection fitting 17. The length of the quarter-wavelength optical fiber 12 or 13 may be a quarter wavelength or a length obtained by adding a natural number of wavelengths to the quarter wavelength.

  As shown in FIG. 6, an example is shown in which a neutral atom is removed from a planar substrate by using a magnetic field generated by passing a current through a wiring pattern formed by etching or the like on a planar substrate placed in an ultrahigh vacuum. Can be captured in the very vicinity of the surface. This is a kind of magnetic trap that captures neutral atoms by a magnetic field, but the feature is that the trap can be miniaturized and integrated by using a flat substrate.

  In this way, a large number of small traps are formed on a single substrate, and the state of the captured atoms can be precisely controlled by irradiating the laser beam or modulating the trap current. The structure is called an “atomic chip”. As shown in FIG. 6, in addition to using a current flowing through the wiring pattern, the dipole is caused by the near-field light leaking through the optical waveguide formed on the chip, though not shown in the figure. There is also a way to capture using force.

  In addition, it is often necessary to optically detect atoms trapped in a large number of traps arranged closely side by side on the atomic chip and to optically control their states. In this case, it is extremely difficult to access a large number of traps at the same time by the method of condensing and irradiating laser light from the outside due to the size limitation of the optical component. Therefore, Non-Patent Document 2 or Non-Patent Document 3 proposes a method in which an optical fiber is introduced on an atomic chip and is integrated and arranged corresponding to each trap.

  In this case, although there is no restriction on the arrangement of the optical fibers, a pair of optical fibers are often arranged facing each other with an interval of several mm or less, and other optical elements are arranged between the facing optical fibers. It is difficult. In addition, as described in Non-Patent Document 2, an end face of a facing fiber may be coated with an increased reflectance coating so as to function as a Fabry-Perot resonator. In this case, it is necessary to bring the two optical fibers closer to a distance of several μm in order to expand the free spectrum range of the Fabry-Perot resonator and reduce the coupling loss.

  As is well known, when a linearly polarized light is irradiated to an atom, a transition in which the magnetic quantum number does not change occurs, and when a circularly polarized light is irradiated, a transition in which the magnetic quantum number changes by 1 is caused. That is, the change in the magnetic quantum number accompanying the transition can be controlled using the polarization state of the irradiated light. Such control is not only indispensable for the MOT capturing operation, but also extremely useful when the difference in magnetic quantum number is utilized as a qubit or memory.

  In order to enable control of the magnetic quantum number using the integrated optical fiber shown in FIG. 6, it is necessary to be able to output circularly polarized light from the tip of the fiber. In this case, it is not necessary to output an arbitrary polarization state from one fiber, and two or three optical fibers that can output a predetermined polarization state may be arranged side by side. The present invention has a configuration in which the function of the wave plate is added to a part of the optical fiber, so that circularly polarized light can be directly output from the tip of the optical fiber without adding an optical element other than the optical fiber. Therefore, it is suitable for the purpose of realizing an atomic chip that controls the magnetic quantum number using an optical fiber.

  The present invention relates to an atom using an interaction between a magnetic field and laser light, such as an atomic beam reducer, a two-dimensional or three-dimensional magneto-optical trap (MOT), an atomic polarization gradient cooling device, and an atomic clock. In the optical apparatus, the apparatus can be made small and inexpensive by reducing the number of parts in the portion to which the laser beam is supplied, and can be used for easy adjustment.

  Conventional MOTs, atomic beam reducers, etc. have an optical system installed outside the vacuum device, and laser light is introduced into the vacuum device, so the overall volume and weight of the device are large, and miniaturization is difficult. It was. If a circularly polarized light compatible optical fiber is used, most of the conventional optical system can be omitted by introducing the tip of the optical fiber directly into the vacuum device, making it suitable for miniaturization and weight reduction. It becomes. By using an optical fiber, adjustment work of the optical system becomes unnecessary and portability can be obtained.

  In the field of atomic optics, as described above, an optical fiber is integrated on an atomic chip to count the number of atoms passing through the cross section, and the quantum mechanical effect can be obtained by the effect of the resonator QED (quantum electrodynamics). However, for such purposes, it is convenient if circularly polarized light can be emitted directly from the end of the fiber, and a circularly polarized optical fiber is useful (FIG. 6).

  It is considered that the application range of the quantum information processing apparatus using the atomic chip is greatly expanded by the present invention.

It is a figure which shows the polarization maintaining optical fiber which has the function to convert linearly polarized light into circularly polarized light. An example of the structure and operation principle of a circularly polarized optical fiber. The figure which shows the circularly-polarized light polarizer which used the linear polarizer for the center part of a circularly polarized light compatible optical fiber, and operate | moves also as an optical isolator. It is a figure which shows the connection of a circularly polarized light compatible optical fiber, (a) is sectional drawing of a longitudinal direction, (b) is sectional drawing perpendicular | vertical to an optical axis. It is a figure which shows the mirror MOT (surface magneto-optical trap) apparatus comprised using the circular polarization compatible optical fiber. It is a figure which illustrates the atom chip to which the present invention is applied. It is a figure which shows the cross section of a PANDA fiber. It is a figure which shows the mode of the electric field vector of the light immediately after the circularly polarized light injects into the polarization maintaining optical fiber.

Explanation of symbols

1 1/4 wavelength optical fiber 2 polarization maintaining optical fiber 3 1/4 wavelength optical fiber 4 linear polarizer 11 polarization maintaining optical fiber 12 quarter wavelength optical fiber 13 1/4 wavelength optical fiber 14 polarization Wave holding optical fiber 15 Coating 16 Shield portion 17 Connection fitting 18 Antireflection filler

Claims (11)

A polarization-maintaining optical fiber, including a first part and a second part that is inclined by 45 degrees about the optical axis and is continuous with the first part;
The first part is shorter than the second part, and a phase difference is generated between the intrinsic polarization components of light by a quarter wavelength or by adding a natural number of wavelengths to the quarter wavelength. A polarization-maintaining optical fiber having circular polarization compatibility, characterized in that circularly polarized light is incident on a first portion and linearly polarized light is propagated in a second portion. A polarization-maintaining optical fiber, including a second part and a third part that is inclined at 45 degrees about the optical axis in the second part and is continuous,
The third part is shorter than the second part, and a phase difference is generated between the intrinsic polarization components of light by a quarter wavelength or by adding a natural number of wavelengths to the quarter wavelength. Circular polarization compatibility characterized by having a length, propagating linearly polarized light in the second part, and converting circularly polarized light into circularly polarized light in the third part and outputting circularly polarized light from the end of the third part A polarization maintaining optical fiber. A polarization-maintaining optical fiber, a first part, a second part that continues to the first part with an inclination of 45 degrees about the optical axis, and a third part that continues to the second part with an inclination of 45 degrees about the optical axis Including
The first part and the third part are shorter than the second part, and a part corresponding to a quarter wavelength or a part obtained by adding a natural number multiple of the wavelength to the quarter wavelength between the intrinsic polarization components of light. It has a length that causes a phase difference. Circularly polarized light is incident on the first part, linearly polarized light is propagated in the second part, and linearly polarized light is converted into circularly polarized light in the third part. A polarization-maintaining optical fiber having circular polarization compatibility, characterized by outputting circularly polarized light from   4. The circular polarization compatibility according to claim 3, wherein a linearly polarizing element having a polarization characteristic along the direction of the intrinsic polarization axis of the polarization maintaining optical fiber or a direction perpendicular thereto is inserted in the second portion. A polarization maintaining optical fiber.   The part that converts between circularly polarized light and linearly polarized light is a natural number of wavelengths for a quarter wavelength or a quarter wavelength between the intrinsic polarization components of light of each wavelength for a plurality of different wavelengths. The polarization maintaining optical fiber having circular polarization compatibility according to any one of claims 1 to 4, wherein the length is such that a phase difference corresponding to double is generated. The polarization maintaining optical fiber includes a first portion and a second portion that is inclined at 45 degrees about the optical axis in the first portion, and the second portion is a quarter of the intrinsic polarization component of light. A having a length that produces a phase difference corresponding to one wavelength or a quarter wavelength plus a natural number multiple of the wavelength;
The polarization maintaining optical fiber includes a third part and a fourth part that is inclined at 45 degrees about the optical axis in the third part, and the third part is a quarter of the intrinsic polarization component of light. B having a length that produces a phase difference corresponding to one wavelength or a quarter wavelength plus a natural number multiple of the wavelength; and
A and B are connected,
The linearly polarized light that has propagated through the first part is converted into circularly polarized light when propagating through the second part, is transmitted as circularly polarized light from the second part to the third part, and is linearly polarized when propagated through the third part. A polarization-maintaining optical fiber having circular polarization compatibility, characterized in that linearly polarized light is propagated and transmitted in the fourth part.   The part that converts between circularly polarized light and linearly polarized light is a natural number of wavelengths for a quarter wavelength or a quarter wavelength between the intrinsic polarization components of light of each wavelength for a plurality of different wavelengths. The polarization-maintaining optical fiber having circular polarization compatibility according to claim 6, wherein the length is such that a phase difference corresponding to double is generated.   A plurality of polarization-maintaining optical fibers having circular polarization compatibility according to any one of claims 2, 3, 4, and 5 are introduced into a decompression container so as to penetrate the decompression container wall, thereby forming a magneto-optical trap A magneto-optical trap, wherein the polarization-maintaining optical fiber is arranged so as to have a light irradiation arrangement.   A plurality of polarization-maintaining optical fibers having circular polarization compatibility according to any one of claims 2, 3, 4, and 5 are introduced into a decompression vessel so as to penetrate the decompression vessel wall, and a surface magneto-optical trap is provided. A magneto-optical trap characterized in that the polarization-maintaining optical fiber is arranged so as to constitute a light irradiation arrangement.   Polarized waves having circular polarization compatibility according to any one of claims 2, 3, 4, and 5 on atoms trapped by a trap formed of a wiring pattern or an optical waveguide on a flat substrate in a reduced-pressure atmosphere An atomic chip comprising: means for irradiating circularly polarized light from a holding optical fiber.   The means for irradiating circularly polarized light using the polarization-maintaining optical fiber is an optical resonator formed by an output side end face of a polarization-maintaining optical fiber having circular polarization compatibility and a predetermined reflecting surface. The atomic chip according to claim 10, which is means for irradiating circularly polarized light.

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