JP2008256784A - Optical pulse multiplexing unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical pulse multiplexing unit configured to optionally set a pulse interval in an optical pulse string. <P>SOLUTION: The optical pulse multiplexing unit includes: a plurality of optical fibers 101a etc.; a demultiplexing/multiplexing part 120 to demultiplex/multiplex incident light; an optical fiber 201a etc., functioning as an optical path length adjusting part having an incident surface and an emitting surface. The demultiplexing/multiplexing part is formed in a position where the plurality of optical fibers 201a and 201b are most adjacent to each other or come in contact with each other. The plurality of optical fibers 201a include a first light guiding part having a first incident end surface and a first emitting end surface, and a second light guiding part having a second incident end surface and a second emitting end surface. The optical path length adjusting part is disposed on at least one of the following positions (a), (b) and (c), (a) at least one of the first light guiding part and the second light guiding part, (b) at least one light incident side of either of the first incident end face or the second incident end surface, and (c) at least one light emitting side of either of the first emitting end surface or the second emitting end surface. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical pulse multiplexing unit that generates an optical pulse train.

  Conventionally, as an optical pulse generator for generating an optical pulse train, for example, there is one proposed in Patent Document 1. FIG. 14 shows a schematic configuration of a conventional optical pulse generator. The optical pulse generator includes a pulse light source 51, a delay structure 52, a condenser lens 53, and a waveguide 54.

  As shown in FIG. 15, the delay structure 52 has a stepped shape. Therefore, the delay structure 52 can be regarded as a plurality of parallel plates having the same refractive index and different thicknesses. The parallel plates are arranged at equal intervals in a direction perpendicular to the optical axis. Further, the difference in thickness along the optical axis between adjacent parallel plates is constant.

When the light pulse emitted from the pulse light source 51 is incident on the delay structure 52 as a plane wave, the optical path length varies depending on the thickness of the parallel plate that is transmitted. In FIG. 15, as indicated by pulses 55 ₁ , 55 ₂ ,..., 55 _n , the wavefront is modulated stepwise.

  By collecting this pulse train through the condenser lens 53, the optical pulse train can be transmitted to the waveguide 54.

US Patent Application Publication No. 2003 / 0012236A1

  However, the delay structure disclosed in Patent Document 1 has the following problems. In Document 1, the length of the parallel plate is fixed. Therefore, it is difficult to change the pulse interval of the optical pulse train.

  In general, in the waveguide, unless the propagation mode of the propagating optical pulse is limited, it is difficult to keep the pulse interval of the optical pulse train constant due to the difference in propagation speed due to mode dispersion. The waveguide is preferably single-mode, but the optical coupling condition becomes very strict when it is single-mode. This is the same reason that optical coupling to a single mode fiber is difficult in optical communication technology.

  Here, the numerical aperture on the input side of the waveguide 54 is NA1, and the numerical aperture of the light pulse when condensed through the condenser lens 53 is NA2. In the configuration of FIG. 15, in order to increase the coupling efficiency, NA1 and NA2 must be substantially matched.

  However, in each optical pulse, the value of NA2 becomes very small, and the incident angle of the waveguide 54 to the incident angle 54 is different. As a result, it is difficult to simultaneously increase the coupling efficiency to the waveguide 54 for all the optical pulses transmitted through the parallel plates of the delay mechanism 52.

  Further, since the value of NA2 is reduced, there is a problem that the spot size when the light is condensed through the condenser lens 53 cannot be reduced.

  The present invention has been made in view of the above, and an object thereof is to provide an optical pulse multiplexing unit capable of arbitrarily setting the pulse interval of an optical pulse train. In that case, it aims at providing the optical pulse multiplexing unit which can obtain an optical pulse train with high coupling efficiency.

  In order to solve the above-described problems and achieve the object, according to the present invention, a plurality of light guide units, a demultiplexing / combining unit that demultiplexes and / or combines incident light, an incident surface, and an exit. An optical path length adjusting unit having a surface, and the demultiplexing / combining unit is formed at a position where the plurality of light guiding units are closest to or in contact with each other, and the plurality of light guiding units are connected to the first incident end surface and the first incident end surface. A first light guide section having one exit end face, a second light guide section having a second entrance end face and a second exit end face, and the optical path length adjusting section comprises: At least one light guide part of the light part and the second light guide part, (b) at least one light incident side of the first incident end face and the second incident end face, and (c) the first exit end face and the second. It is possible to provide an optical pulse multiplexing unit characterized in that it is provided on at least one of the light emission sides of at least one of the emission end faces.

  According to a preferred aspect of the present invention, the optical path length adjustment unit is the first light guide unit or the second light guide unit, and the length from the first incident end surface to the demultiplexing / combining unit is set. When L1, the refractive index of the first light guide unit is n1, the length from the second incident end surface to the demultiplexing / combining unit is L2, and the refractive index n2 of the second light guide unit is L1 × n1 And L2 × n2 are preferably different.

  According to a preferred aspect of the present invention, the optical path length adjusting unit is the first light guide unit or the second light guide unit, and the first incident end surface and the first exit end surface, or the second incident surface. It is desirable that the end face and the second exit end face face each other.

  According to a preferred aspect of the present invention, the optical path length adjustment unit is a plurality of light guide units including a first light guide unit and a second light guide unit, and each of the plurality of light guide units includes: When the length from the incident end surface to the demultiplexing / combining portion is L and the refractive index of the light guide portion is n, each of the plurality of light guide portions has L × n. Unlike other light guides, it includes a moving mechanism that moves at least two light guides among a plurality of light guides, and a demultiplexing / combining part may be formed by at least two light guides. desirable.

  According to a preferred aspect of the present invention, the optical path length adjusting unit has an incident end surface and an exit end surface, has a predetermined refractive index, and is disposed on at least one of the light incident side and the light exit side of the light guide unit. It is desirable that

  Moreover, according to a preferable aspect of the present invention, it is desirable that the optical path length adjusting unit has a refractive index larger than that of air.

  Moreover, according to the preferable aspect of this invention, it is desirable for an optical path length adjustment part to provide the reflective surface which reflects so that the light from an incident end surface may be guide | induced to an output end surface.

  According to a preferred aspect of the present invention, the optical path length adjustment unit includes a first optical path length adjustment element and a second optical path length adjustment element, and includes a first optical path length adjustment element from an incident end surface to an emission end surface. The length is D1, the refractive index of the first optical path length adjusting element is N1, the length from the incident end face to the exit end face of the first optical path length adjusting element is D2, and the refractive index of the second optical path length adjusting element is N2. , It is desirable that D1 × N1 and D2 × N2 are different.

  According to the optical pulse multiplexing unit of the present invention, the pulse interval of the optical pulse train can be arbitrarily set. At that time, an optical pulse train having high coupling efficiency can be obtained.

  Embodiments of an optical pulse multiplexing unit according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

  In the description of the optical pulse multiplexing unit of this embodiment, one or two optical pulses are used. Therefore, a configuration for generating two optical pulses will be described. FIG. 1 shows a configuration for generating two light pulses.

  The two optical pulses are generated using the first fiber coupler 100 as shown in FIG. The first fiber coupler 100 includes two optical fibers 101a and 101b as a light guide unit. The optical fibers 101a and 101b are arranged to face each other with the center line X interposed therebetween.

  A collimator lens 110a and a collimator lens 111a are disposed at both ends of the optical fiber 101a. Similarly, a collimator lens 110b and a collimator lens 111b are disposed at both ends of the optical fiber 101b. Therefore, the optical fiber and the collimator lens may be regarded as the light guide unit. The collimator lens is used to input pulsed light to an optical fiber or to output pulsed light from the optical fiber as collimated light.

  A demultiplexing / multiplexing unit 120 is formed at the center of the two optical fibers 101a and 101b. In the demultiplexing / multiplexing unit 120, the optical fiber 101a and the optical fiber 101b are close to or in contact with each other. The demultiplexing / multiplexing unit 120 can supply the optical pulse propagating through the optical fiber 101a to the other optical fiber 101b, in other words, the other optical fiber 101b can ooze light. In addition, the demultiplexing / multiplexing unit 120 can vary the amount of light pulse that leaks (corresponding to the branching ratio) by adjusting the distance (interval) between the optical fiber 101a and the optical fiber 101b.

  In the first fiber coupler 100, the incident end face of the optical fiber 101a and the incident end face of the optical fiber 101b coincide with the line Y1. Similarly, the exit end face of the optical fiber 101a and the exit end face of the optical fiber 101b coincide with the line Y2. In addition, what actually coincides with the line Y1 is the incident side lens surface of the collimator lens 110a and the incident side lens surface of the collimator lens 110b. Moreover, what actually coincides with the line Y2 is the exit side lens surface of the collimator lens 111a and the exit side lens surface of the collimator lens 111b.

Here, regarding one of the two light guides,
The length from the incident end surface to the demultiplexing / combining portion and the refractive index are respectively expressed as L1, n1,
The length and refractive index from the exit end face to the demultiplexing / combining part are respectively expressed as L1 ′, n1 ′,
And for the other light guide
The length from the incident end face to the demultiplexing / combining portion and the refractive index are expressed as L2, n2,
The length and refractive index from the exit end face to the demultiplexing / combining part are respectively expressed as L2 ′, n2 ′,
And

In addition, when the light guide part is composed of an optical fiber and a collimator lens, for one light guide part,
The length and refractive index from the incident end face of the optical fiber to the demultiplexing / combining part are respectively expressed as L1F, n1F,
The length and refractive index from the optical fiber exit end face to the demultiplexing / combining part are respectively expressed as L1′F, n1′F,
The center thickness and refractive index of the collimator lens on the incident end face side are respectively expressed as L1C, n1C,
The center thickness and refractive index of the collimator lens on the exit end face side are respectively expressed as L1′C, n1′C,
And for the other light guide
The length and refractive index from the incident end face of the optical fiber to the demultiplexing / combining part are respectively expressed as L2F, n2F,
The length and refractive index from the optical fiber exit end face to the demultiplexing / combining part are respectively expressed as L2′F, n2′F,
The center thickness and refractive index of the collimator lens on the incident end face side are respectively expressed as L2C, n2C,
The center thickness and refractive index of the collimator lens on the exit end face side are respectively expressed as L2′C, n2′C,
And

  The optical fiber is configured such that the refractive index of the core portion and the refractive index of the cladding portion are different. Hereinafter, the refractive index in the description relating to the optical fiber refers to the refractive index of the portion where the optical pulse propagates in the optical fiber, that is, the core.

And the relational expression regarding these parameters is as follows.
L1 × n1 = L1F × n1F + L1C × n1C,
L2 × n2 = L2F × n2F + L2C × n2C,
L1 ′ × n1 ′ = L1′F × n1′F + L1′C × n1′C,
L2 ′ × n2 ′ = L2′F × n2′F + L2′C × n2′C,

  In such a configuration, when a light pulse is incident from the collimator lens 110a, the incident light pulse reaches the demultiplexing / multiplexing unit 120. Here, a part of the incident optical pulse becomes an optical pulse that propagates through the optical fiber 101a as it is. On the other hand, the remainder of the incident light pulse oozes out to the optical fiber 101b by the demultiplexing / multiplexing unit 120. As a result, an optical pulse that propagates through the optical fiber 101b is generated. Thus, the demultiplexing / multiplexing unit 120 does not spatially demultiplex one optical pulse. That is, the demultiplexing / multiplexing unit 120 divides the optical pulse by amplitude, not by wavefront division. For this reason, the same optical pulse as the incident optical pulse can be generated except that the light intensity is different.

  In the configuration of FIG. 1, regarding the optical fiber 101a and the optical fiber 101b, the length from the incident end face to the demultiplexing / multiplexing section 120, the length from the exit end face to the demultiplexing / multiplexing section 120, and these The refractive index between is the same. The four collimator lenses have the same shape and material.

That is,
L1F = L2F
L1'F = L2'F
n1F = n2F
n1′F = n2′F
L1C = L1′C = L2C = L2′C
n1C = n1′C = n2C = n2′C
It is a relationship.

  For this reason, in the structure of FIG. 1, it becomes the relationship of L1 * n1 = L2 * n2 regarding two light guide parts. In this case, the light pulses propagated and guided in the respective optical fibers 101a and 101b are simultaneously emitted from the collimator lenses 111a and 111b. In this way, two light pulses can be generated from one light pulse. The two light pulses are spatially separated from each other in order to pass through different optical fibers. However, there is no time difference between the two pulses. That is, there is no time delay in one optical pulse in the other optical pulse.

  Next, the second fiber coupler 100 'will be described. The second fiber coupler 100 ′ has exactly the same configuration as the first fiber coupler 100. Therefore, the same number is attached | subjected to the same structure and description is abbreviate | omitted.

  In the first fiber coupler 100, when an optical pulse was incident from the incident end side of the optical fiber 101a, the optical pulse was emitted from the exit end of the optical fiber 101a and the exit end of the optical fiber 101b, respectively. The same phenomenon occurs when a light pulse is incident from the incident end side of the optical fiber 101b. That is, light pulses are emitted from the emission end of the optical fiber 101a and the emission end of the optical fiber 101b, respectively. Therefore, also in the second fiber coupler 100 ′, the light pulse is simultaneously emitted from the collimator lenses 111 a and 111 b.

  Thus, in the configuration of FIG. 1, light pulses are emitted from the emission end of the optical fiber 101a and the emission end of the optical fiber 101b, respectively. However, there is no time difference between the two light pulses. Therefore, a configuration that causes a time difference between two optical pulses, that is, a configuration that multiplexes optical pulses will be described next.

  FIG. 2 shows a schematic configuration of the optical pulse multiplexing unit according to the first embodiment. Hereinafter, in all the embodiments, the same components as those shown in FIG. 1 are denoted by the same reference numerals, and redundant description is omitted. The fiber coupler 100 is for generating two spatially separated optical pulses, and there is no time difference between the two optical pulses. Therefore, the fiber coupler 100 is not included in the optical pulse multiplexing unit (the same applies to other embodiments).

  The optical pulse multiplexing unit of this embodiment is a fiber coupler 200. The fiber coupler 200 includes an optical fiber 201a and an optical fiber 201b as light guide portions. The optical fiber 201a and the optical fiber 201b are disposed to face each other with the center line X interposed therebetween.

  In the optical fiber 201a, a collimator lens 210a is disposed on the incident end face side, and a collimator lens 211a is disposed on the exit end face side. Similarly, in the optical fiber 201b, a collimator lens 210b is disposed on the incident end face side, and a collimator lens 211b is disposed on the exit end face side. Therefore, you may consider the part of an optical fiber and a collimator lens as a light guide part. The collimator lens is used for inputting pulsed light into an optical fiber or outputting pulsed light from the optical fiber as collimated light.

  In addition, a demultiplexing / multiplexing unit 220 is formed at the center of the two optical fibers 201a and 201b. The structure and function of the demultiplexing / multiplexing unit 220 are the same as those of the demultiplexing / multiplexing unit 120.

  Further, the incident end face of the optical fiber 201a and the incident end face of the optical fiber 201b coincide with the line Y3. Similarly, the exit end face of the optical fiber 201a and the exit end face of the optical fiber 201b coincide with the line Y4. In addition, what actually coincides with the line Y3 is the incident side lens surface of the collimator lens 210a and the incident side lens surface of the collimator lens 210b. Moreover, what actually coincides with the line Y4 is the exit side lens surface of the collimator lens 211a and the exit side lens surface of the collimator lens 211b.

  In such a configuration, when a light pulse is incident from the collimator lens 110a, one light pulse is emitted from each of the collimator lenses 111a and 111b. These light pulses are incident on the optical fibers 201a and 201b from the collimator lenses 210a and 210b, respectively.

  Here, in the fiber coupler 200, the length L1F from the incident end face of the optical fiber 201a to the demultiplexing / multiplexing section 220 is different from the length L2F from the incident end face of the optical fiber 201b to the demultiplexing / multiplexing section 220. . Similarly, the length L1'F from the exit end face of the optical fiber 201a to the demultiplexing / multiplexing section 220 is different from the length L2'F from the exit end face of the optical fiber 201b to the demultiplexing / multiplexing section 220. Specifically, L1F> L2F and L1′F> L2′F.

  On the other hand, the refractive index of the optical fiber 201a is equal to the refractive index of the optical fiber 201b. Specifically, n1F = n2F and n1′F = n2′F. Note that n1F ≠ n1′F and n2F ≠ n2′F may be set, but n1F = n1′F and n2F = n2′F are more realistic.

  The four collimator lenses have the same shape and material.

Thus, for optical fiber and collimator lens,
L1F> L2F
L1'F>L2'F
n1F = n2F
n1′F = n2′F
L1C = L1′C = L2C = L2′C
n1C = n1′C = n2C = n2′C
It is a relationship.

  For this reason, regarding the two light guide portions, the relationship is L1 × n1> L2 × n2. Therefore, in terms of time, the optical pulse P2 propagating through the optical fiber 201b reaches the demultiplexing / combining unit 220 earlier than the optical pulse P1 propagating through the optical fiber 201a. Therefore, in the demultiplexing / multiplexing unit 220, the optical pulse P2 is demultiplexed before the optical pulse P1. Then, after the demultiplexing of the optical pulse P2, the optical pulse P1 is demultiplexed in the demultiplexing / multiplexing unit 220. As a result, two optical pulses P1 and P2 having a time difference can be generated. That is, a time delay can be caused in the optical pulse P1 with respect to the optical pulse P2.

  In this embodiment, the length of the path from the incident end face of the optical fiber to the demultiplexing / multiplexing unit 220 is different between the optical fiber 201a and the optical fiber 201b. Therefore, the optical path lengths in the two paths (the optical fiber 201a side and the optical fiber 201b side) are different. It can be said that the optical path length is adjusted using two fibers. Therefore, it can be said that both the optical fiber 201a and the optical fiber 201b correspond to the optical path length adjustment unit. Note that the optical path length of the other optical fiber is different from the optical path length of one optical fiber. From the point of view of this, either one of the optical fibers can be regarded as an optical path length adjusting unit. It is obvious that a collimator lens may be included in the optical path length adjustment unit.

  Thus, in this embodiment, the light guide section itself is an optical path length adjustment section. Therefore, it can be said that the light path length adjustment unit is provided in the light guide unit.

  Further, in the two optical fibers 201a and 201b, the refractive index is the same from the exit end face of the optical fiber to the demultiplexing / multiplexing unit 220 (n1'F = n2'F). However, the length between them is configured such that the optical fiber 201a is longer than the optical fiber 201b (L1′F> L2′F).

  For this reason, the optical pulses P1 and P2 propagating in the optical fiber 201a are emitted from the collimator lens 211a with a time delay from the optical pulses P1 and P2 propagating in the optical fiber 201b. Thereby, the optical pulses P1 and P2 are emitted from the collimator lens 211a, and the optical pulses P1 'and P2' are emitted from the 211b. At that time, the optical pulses P1 and P2 have a time delay with respect to the optical pulses P1 'and P2'. In this way, it is possible to obtain two light pulses that are temporally and spatially separated. At this time, since one optical pulse is not spatially demultiplexed, an optical pulse train having high coupling efficiency can be obtained.

  In addition, by adjusting the length of the optical fiber 201a, the interval (time delay amount) between the two optical pulses can be arbitrarily set. Or you may adjust the length of the optical fiber 201b, and also the length of two optical fibers.

  Further, as described above, the two optical pulses P 1 and P 2 have a time difference when they are demultiplexed (multiplexed) by the demultiplexing / multiplexing unit 220. Therefore, the length of the optical fiber, the thickness of the collimator lens after demultiplexing (combining), and the refractive index thereof may be set to arbitrary values.

  FIG. 3 shows a schematic configuration of an optical pulse multiplexing unit according to the second embodiment. In this embodiment, the positional relationship of the fiber with respect to the center line X and the positional relationship of the collimator lens with respect to the lines Y1 to Y4 are the same as those in the first embodiment. The functions of the optical fiber, collimator lens, and demultiplexing / combining unit are the same as those in the first embodiment.

  The optical pulse multiplexing unit of this embodiment is a fiber coupler 300. In the fiber coupler 300, the length L1F from the incident end face of the optical fiber 301a to the demultiplexing / multiplexing section 220 is the same as the length L2F from the incident end face of the optical fiber 201b to the demultiplexing / multiplexing section 220. . Similarly, the length L1′F from the exit end face of the optical fiber 301a to the demultiplexing / multiplexing section 220 is the same as the length L2′F from the exit end face of the optical fiber 201b to the demultiplexing / multiplexing section 220. It is.

  On the other hand, the refractive index of the optical fiber 301a is different from the refractive index of the optical fiber 201b. Specifically, n1F> n2F and n1′F> n2′F. Note that n1F ≠ n1′F and n2F ≠ n2′F may be set, but n1F = n1′F and n2F = n2′F are more realistic.

  The four collimator lenses have the same shape and material.

Thus, for optical fiber and collimator lens,
L1F = L2F
L1'F = L2'F
n1F> n2F
n1′F> n2′F
L1C = L1′C = L2C = L2′C
n1C = n1′C = n2C = n2′C
It is a relationship.

  For this reason, regarding the two light guide portions, the relationship is L1 × n1> L2 × n2. Therefore, in terms of time, the optical pulse P2 propagating in the optical fiber 201b reaches the demultiplexing / multiplexing unit 220 earlier than the optical pulse P1 propagating in the optical fiber 301a. Therefore, in the demultiplexing / multiplexing unit 220, the optical pulse P2 is demultiplexed before the optical pulse P1. Then, after the demultiplexing of the optical pulse P2, the optical pulse P1 is demultiplexed in the demultiplexing / multiplexing unit 220. As a result, two optical pulses P1 and P2 having a time can be generated. That is, a time delay can be caused in the optical pulse P1 with respect to the optical pulse P2.

  In the present embodiment, the refractive index from the incident end face of the optical fiber to the demultiplexing / multiplexing unit 220 is different between the optical fiber 301a and the optical fiber 201b. Therefore, the optical path lengths in the two paths (the optical fiber 301a side and the optical fiber 201b side) are different. It can be said that the optical path length is adjusted using two fibers. Therefore, it can be said that both the optical fiber 301a and the optical fiber 201b correspond to the optical path length adjustment unit. Note that the optical path length of the other optical fiber is different from the optical path length of one optical fiber. From the point of view of this, either one of the optical fibers can be regarded as an optical path length adjusting unit. It is obvious that a collimator lens may be included in the optical path length adjustment unit.

  Thus, in this embodiment, the light guide section itself is an optical path length adjustment section. Therefore, it can be said that the light path length adjustment unit is provided in the light guide unit.

  Further, in the two optical fibers 301a and 201b, the length from the exit end face of the optical fiber to the demultiplexing / multiplexing unit 220 is the same (L1′F = L2′F). However, the refractive index therebetween is configured to be larger in the optical fiber 201a than in the optical fiber 201b (n1′F> n2′F).

  For this reason, the optical pulses P1 and P2 propagating in the optical fiber 301a are emitted from the collimator lens 211a with a time delay from the optical pulses P1 and P2 propagating in the optical fiber 201b. As a result, light pulses P1 and P2 are emitted from the collimator lens 211a, and light pulses P1 'and P2' are emitted from 211b. At that time, the optical pulses P1 and P2 have a time delay with respect to the optical pulses P1 'and P2'. In this way, it is possible to obtain two light pulses that are temporally and spatially separated. At that time, an optical pulse train having high coupling efficiency can be obtained.

  In addition, by adjusting the refractive index of the optical fiber 301a, the interval (time delay amount) between two optical pulses can be arbitrarily set. Or you may adjust the refractive index of the optical fiber 201b, and also the refractive index of two optical fibers.

  Further, as described above, the two optical pulses have a time difference when they are demultiplexed (multiplexed) by the demultiplexing / multiplexing unit 220. Therefore, the length of the optical fiber, the thickness of the collimator lens after demultiplexing (combining), and the refractive index thereof may be set to arbitrary values.

  FIG. 4 shows a schematic configuration of an optical pulse multiplexing unit according to the third embodiment. In this embodiment, the positional relationship of the fiber with respect to the center line X and the positional relationship of the collimator lens with respect to the lines Y1 to Y4 are the same as those in the first embodiment. The functions of the optical fiber, collimator lens, and demultiplexing / combining unit are the same as those in the first embodiment.

  The optical pulse multiplexing unit of this embodiment is a fiber coupler 400. In the fiber coupler 400, the length L1F from the incident end face of the optical fiber 401a to the demultiplexing / multiplexing section 220 is different from the length L2F from the incident end face of the optical fiber 201b to the demultiplexing / multiplexing section 220. Further, the length L1′F from the exit end face of the optical fiber 401a to the demultiplexing / multiplexing section 220 is the same as the length L2′F from the exit end face of the optical fiber 201b to the demultiplexing / multiplexing section 220. . Specifically, L1F> L2F and L1′F = L2′F.

  On the other hand, the refractive index of the optical fiber 201a is equal to the refractive index of the optical fiber 201b. Specifically, n1F = n2F and n1′F = n2′F. Note that n1F ≠ n1′F and n2F ≠ n2′F may be set, but n1F = n1′F and n2F = n2′F are more realistic.

  The four collimator lenses have the same shape and material.

Thus, for optical fiber and collimator lens,
L1F> L2F
L1'F = L2'F
n1F = n2F
n1′F = n2′F
L1C = L1′C = L2C = L2′C
n1C = n1′C = n2C = n2′C
It is a relationship.

  For this reason, regarding the two light guide portions, the relationship is L1 × n1> L2 × n2. Therefore, in terms of time, the optical pulse P2 propagating in the optical fiber 201b reaches the demultiplexing / multiplexing unit 220 earlier than the optical pulse P1 propagating in the optical fiber 401a. Therefore, in the demultiplexing / multiplexing unit 220, the optical pulse P2 is demultiplexed before the optical pulse P1. Then, after the demultiplexing of the optical pulse P2, the optical pulse P1 is demultiplexed in the demultiplexing / multiplexing unit 220. As a result, two optical pulses P1 and P2 having a time difference can be generated. That is, a time delay can be caused in the optical pulse P1 with respect to the optical pulse P2.

  In the present embodiment, the distance of the path from the incident end face of the optical fiber to the demultiplexing / multiplexing unit 220 is different between the optical fiber 401a and the optical fiber 201b. Thereby, the optical path lengths in the two paths (the optical fiber 401a side and the optical fiber 201b side) are different. That is, it can be said that the optical path length is adjusted using two fibers. Therefore, it can be said that both the optical fiber 401a and the optical fiber 201b correspond to the optical path length adjustment unit. Note that the optical path length of the other optical fiber is different from the optical path length of one optical fiber. From the point of view of this, either one of the optical fibers can be regarded as an optical path length adjusting unit. It is obvious that a collimator lens may be included in the optical path length adjustment unit.

  Thus, in this embodiment, the light guide section itself is an optical path length adjustment section. Therefore, it can be said that the light path length adjustment unit is provided in the light guide unit. Furthermore, as will be described below, in this embodiment, the moving mechanism (stage ST) is included in the optical path length adjustment unit.

  In this embodiment, the fiber coupler 400 is provided with a stage ST. This stage is configured to be movable in the left-right direction (arrow direction) of the drawing. A collimator lens 210a is placed on this stage. Therefore, the collimator lens 210a is movable in the left-right direction on the paper surface by the stage ST.

  In this embodiment, the exit end face of the optical fiber 401a and the exit end face of the optical fiber 201b coincide with the line Y4, but the entrance end face of the optical fiber 401a and the entrance end face of the optical fiber 201b coincide with the line Y3. Absent. Actually, the incident side lens surface of the collimator lens 210a and the incident side lens surface of the collimator lens 210b do not coincide with the line Y3. Specifically, the incident-side lens surface of the collimator lens 210a is located on the fiber coupler 100 side by a distance m from the incident-side lens surface (reference line Y3) of the collimator lens 210b. On the other hand, in the fiber coupler 100, the exit end face of the optical fiber 101a and the exit end face of the optical fiber 101b coincide with the line Y2.

  Therefore, in this embodiment, the distance from the emission end face of the optical fiber 101a to the incident end face of the optical fiber 401a is different from the distance from the emission end face of the optical fiber 101b to the incident end face of the optical fiber 201b. Actually, the relationship between the distance m1 from the collimator lens 111a to the collimator lens 210a and the distance m2 from the collimator lens 111b to the collimator lens 210b is m1 <m2. And m1 can be changed by the movement of the stage ST.

  As described above, in this embodiment, L1 × n1 and L2 × n2 are different. Therefore, it is possible to emit two light pulses P1 and P2 that are temporally and spatially separated from the collimator lenses 211a and 211b, respectively. In addition, in this embodiment, a time difference of ml × n and m2 × n can be generated.

  Further, ml can be finely adjusted by the stage ST. This means that the difference between ml × n and m2 × n can be finely adjusted. Therefore, the time difference (temporal delay amount) between the two light pulses P1 and P2 can be arbitrarily set, and the time difference between the two light pulses P1 and P2 can be finely adjusted. At that time, an optical pulse train having high coupling efficiency can be obtained.

  Further, as described above, the two optical pulses P 1 and P 2 have a time difference when they are demultiplexed (multiplexed) by the demultiplexing / multiplexing unit 220. Therefore, the length of the optical fiber, the thickness of the collimator lens after demultiplexing (combining), and the refractive index thereof may be set to arbitrary values.

  FIG. 5 shows a schematic configuration of an optical pulse multiplexing unit according to the fourth embodiment. In this embodiment, the positional relationship of the fiber with respect to the center line X and the positional relationship of the collimator lens with respect to the lines Y1 to Y4 are the same as those in the first embodiment. The functions of the optical fiber, collimator lens, and demultiplexing / combining unit are the same as those in the first embodiment.

  The optical pulse multiplexing unit of this embodiment is a fiber coupler 500. In the fiber coupler 500, the incident end face and the exit end face of the optical fiber 501a, that is, the collimator lens 210a and the collimator lens 211a are arranged to face each other. Therefore, in this embodiment, the light pulse is incident only from the collimator lens 110b.

  When a light pulse is incident from the collimator lens 110 b, the incident light pulse reaches the demultiplexing / multiplexing unit 220. Here, a part of the incident light pulse becomes the light pulse P2 propagating as it is in the optical fiber 201b. On the other hand, the remainder of the incident light pulse oozes out into the optical fiber 501 a by the demultiplexing / multiplexing unit 220. As a result, an optical pulse P1 that propagates through the optical fiber 501a is generated.

  The light pulse P1 travels through the optical fiber 501a and is emitted from the collimator lens 211a. The emitted light pulse P1 enters the optical fiber 501a again through the collimator lens 210a. The optical pulse P1 incident on the optical fiber 501a reaches the demultiplexing / multiplexing unit 220 again. Then, it is demultiplexed in the same manner as the optical pulse P2. As a result, an optical pulse P1 'propagating through the optical fiber 201b is generated.

  Here, the total length L501 of the optical fiber 501a and the total length L201 of the optical fiber 201b may be the same or different. Also, the refractive index (n1F, n1′F) of the optical fiber 501a and the refractive index (n2F, n2′F) of the optical fiber 201b may be the same or different. Further, the shape (L1C, L1′C, L2C, L2′C) and the material (n1C, n1′C, n2C, n2′C) of the collimator lens may be the same or different.

  In this embodiment, the total length L501 of the optical fiber 501a is different from the total length L201 of the optical fiber 201b. Specifically, L501> L201 (502).

  Further, the refractive index of the optical fiber 201a is equal to the refractive index of the optical fiber 201b. Specifically, n1F = n2F and n1′F = n2′F. Note that n1F ≠ n1′F and n2F ≠ n2′F may be set, but n1F = n1′F and n2F = n2′F are more realistic.

  Also, the four collimator lenses are assumed to have the same shape and material.

Here, assuming that the incident end faces of the two optical fibers are common, for the optical fiber and the collimator lens,
L1F> L2F (L1F = L501 + L2F)
L1'F = L2'F
n1F = n2F
n1′F = n2′F
L1C = L1′C = L2C = L2′C
n1C = n1′C = n2C = n2′C
It is a relationship.

  For this reason, regarding the two light guide portions, the relationship is L1 × n1> L2 × n2. Therefore, in terms of time, the optical pulse P2 propagating in the optical fiber 201b reaches the demultiplexing / multiplexing unit 220 earlier than the optical pulse P1 propagating in the optical fiber 501a. Therefore, in the demultiplexing / multiplexing unit 220, the optical pulse P2 is demultiplexed before the optical pulse P1. Then, after the demultiplexing of the optical pulse P2, the optical pulse P1 is demultiplexed in the demultiplexing / multiplexing unit 220. As a result, two optical pulses P1 and P2 having a time difference can be generated. That is, a time delay can be caused in the optical pulse P1 with respect to the optical pulse P2.

  In this embodiment, the distance from the incident end face of the optical fiber to the demultiplexing / multiplexing unit 220 is made different between an optical path passing through the optical fibers 201b and 501a and an optical path passing only through the optical fiber 201b. Thereby, the optical path lengths in the two paths (the optical fiber 501a side and the optical fiber 201b side) are different. That is, it can be said that the optical path length is adjusted using two fibers. Therefore, it can be said that both the optical fiber 501a and the optical fiber 201b correspond to the optical path length adjustment unit. From the viewpoint of making the optical path length of the other optical fiber different from the optical path length of one optical fiber, either one of the optical fibers can be regarded as an optical path length adjusting unit. It is obvious that a collimator lens may be included in the optical path length adjustment unit.

  Thus, in this embodiment, the light guide section itself is an optical path length adjustment section. Therefore, it can be said that the light path length adjustment unit is provided in the light guide unit. Furthermore, as will be described below, in this embodiment, the moving mechanism (stage ST) is included in the optical path length adjustment unit.

  In this embodiment, the fiber coupler 500 is provided with a stage ST. This stage is configured to be movable in the left-right direction (arrow direction) of the drawing. A collimator lens 211a is placed on this stage. Therefore, the collimator lens 211a is movable in the left-right direction on the paper surface by the stage ST.

  Therefore, in this embodiment, the distance between the incident end face of the optical fiber 501a and the exit end face of the optical fiber 501a can be changed by moving the stage ST. Actually, the distance m 'between the collimator lens 211a and the collimator lens 210a can be changed. This means that the length from the incident end face of the optical fiber 501a to the demultiplexing / multiplexing unit 220 can be changed in the range from 0 to m '.

  As described above, in this embodiment, L1 × n1 and L2 × n2 are different. Therefore, it is possible to emit two light pulses P1 and P2 that are temporally and spatially separated from the collimator lenses 211a and 211b, respectively. In addition, in this embodiment, a time difference of m ′ × n can be generated.

  Further, m ′ can be finely adjusted by the stage ST. Therefore, the time difference (temporal delay amount) between the two light pulses P1 and P2 can be arbitrarily set, and the time difference between the two light pulses P1 and P2 can be finely adjusted. At that time, an optical pulse train having high coupling efficiency can be obtained.

  FIG. 6 shows a schematic configuration of an optical pulse multiplexing unit according to the fifth embodiment. In this embodiment, the positional relationship of the collimator lens with respect to the lines Y1 to Y4 is the same as that in the first embodiment. The functions of the optical fiber, collimator lens, and demultiplexing / combining unit are the same as those in the first embodiment.

  The optical pulse multiplexing unit of this embodiment is a fiber coupler 600. The fiber coupler 600 has a plurality of optical fibers as a light guide. In this embodiment, the fiber coupler 600 includes optical fibers 601a, 601b, 601c, 601d, and 601e.

  In addition, collimator lenses 610a, 610b, 610c, 610d, 610e, 611a, 611b, 611c, 611d, and 611e are disposed at both ends of each optical fiber.

  In addition, the incident end faces of the optical fibers 601a to 601e coincide with the line Y3. Similarly, the exit end faces of the optical fibers 201a to 601e coincide with the line Y4. In addition, what actually coincides with the line Y3 is the incident side lens surface of each of the collimator lenses 610a to 610e. Also, what actually coincides with the line Y4 is the exit side lens surface of the collimator lenses 611a to 611e.

  In this embodiment, the moving mechanism is provided at two places. The first moving mechanism is provided at the center of the optical fiber. The second moving mechanism is provided in the vicinity of the incident end face of the optical fiber.

  In this embodiment, two of the five optical fibers are selected. Then, the center portions of the two selected optical fibers are moved so as to be close to or in contact with each other in the vicinity of the center line X. In this way, the demultiplexing / multiplexing unit 620 is formed. The first moving mechanism is used for moving the central portion of the optical fiber.

  Further, it is necessary to make the incident end faces (two collimator lenses) of the two selected optical fibers face the collimator lenses 111a and 111b of the fiber coupler 100. As a result, the optical pulse from the fiber coupler 100 can be incident on the fiber coupler 600. Therefore, the second moving mechanism is used for moving the incident end face (collimator lens) of the optical fiber. The fiber coupler 100 may include a moving mechanism that moves the exit end face (collimator lens). In this case, the second moving mechanism is not necessary.

  In this embodiment, the length from the incident end face of each optical fiber to the demultiplexing / multiplexing unit 620 is the same. Similarly, the length from the exit end face of each optical fiber to the demultiplexing / multiplexing unit 620 is also the same.

  On the other hand, the refractive index of each optical fiber is different for each optical fiber.

  All collimator lenses have the same shape and material.

  Therefore, the configuration using the two selected optical fibers is the same as that of the second embodiment. Therefore, the relationship between the two light guides is L1 × n1> L2 × n2. Therefore, in terms of time, for example, the optical pulse P2 propagating in the optical fiber 601b reaches the demultiplexing / multiplexing unit 620 earlier than the optical pulse P1 propagating in the optical fiber 601a. Therefore, in the demultiplexing / multiplexing unit 620, the optical pulse P2 is demultiplexed before the optical pulse P1. Then, after the optical pulse P2 is demultiplexed, the optical pulse P1 is demultiplexed in the demultiplexing / multiplexing unit 620. As a result, two optical pulses P1 and P2 having a time difference can be generated. That is, a time delay can be caused in the optical pulse P1 with respect to the optical pulse P2.

  Thus, in this embodiment, the light guide section itself is an optical path length adjustment section. Therefore, it can be said that the light path length adjustment unit is provided in the light guide unit.

  Furthermore, in this embodiment, two optical fibers are selected from a plurality of optical fibers. This increases the number of combinations of the two fibers. Therefore, the time difference between the two light pulses P1 and P2 can be changed variously.

  However, in such a configuration, since the two optical fibers must be moved, the moving mechanism is complicated or increased in size.

  Therefore, the position of one optical fiber may be fixed and the remaining optical fibers may be moved. FIG. 7 shows a cross-sectional configuration in this case. As shown in FIG. 7, in the demultiplexing / multiplexing unit 620, the remaining four optical fibers 601b, 601c, 601d, and 601e are arranged in a cross shape with the optical fiber 601a as the center. The demultiplexing / multiplexing unit 620 is configured so that any one of the optical fibers, for example, the optical fiber 601c, approaches or contacts the optical fiber 601a.

  As described above, each optical fiber is composed of members having different refractive indexes. For this reason, for example, the optical pulse propagating in the optical fiber 601c is delayed in time from the optical pulse propagating in the optical fiber 601a.

  Thereby, the optical pulse emitted from the collimator lens 611c of the optical fiber 601c is delayed in time from the optical pulse emitted from the collimator lens 611a of the optical fiber 601a. By selectively selecting one optical fiber from the four optical fiber lights, the interval between the two optical pulses can be arbitrarily set.

  Thus, in this embodiment, L1 × n1 and L2 × n2 are different between the two selected optical fibers. Therefore, it is possible to emit two light pulses P1 and P2 that are temporally and spatially separated from the collimator lens. In addition, in this embodiment, the time difference between the two optical pulses P1 and P2 can be made different by changing the combination of the optical fibers.

  Thus, in this embodiment, the light guide section itself is an optical path length adjustment section. Therefore, it can be said that the light path length adjustment unit is provided in the light guide unit. Furthermore, in this embodiment, the moving mechanism (stage ST) is included in the optical path length adjustment unit.

  FIG. 8 shows a schematic configuration of an optical pulse multiplexing unit according to the sixth embodiment. In this embodiment, the positional relationship of the fiber with respect to the center line X and the positional relationship of the collimator lens with respect to the lines Y1 to Y4 are the same as those in the first embodiment. The functions of the optical fiber, collimator lens, and demultiplexing / combining unit are the same as those in the first embodiment.

  The optical pulse multiplexing unit of this embodiment is a fiber coupler 700. In the fiber coupler 700, parallel flat plates 310a and 310b are provided on the incident end face side of the optical fiber. Other configurations are the same as those of the fiber coupler 100 ′ of the first embodiment. The fiber coupler 100 is the same as the fiber coupler 100 of the first embodiment.

  In the present embodiment, the parallel plate 310a is provided at a position facing the optical fiber 101a with the collimator lens 110a interposed therebetween. A parallel plate 310b is provided at a position facing the optical fiber 101b with the collimator lens 110b interposed therebetween. In terms of the positional relationship with the fiber coupler 100, the parallel plate 310a is provided between the collimator lens 111a (fiber coupler 100 side) and the collimator lens 110a (fiber coupler 700 side). The parallel plate 310b is provided between the collimator lens 111b (on the fiber coupler 100 side) and the collimator lens 210b (on the fiber coupler 700 side).

  Each of the parallel plate 310a and the parallel plate 310b has an incident end surface and an exit end surface. Further, the parallel flat plate 310a and the parallel flat plate 310b are formed of a material having a predetermined refractive index. However, the length (thickness) from the incident end face to the exit end face is longer (thicker) in the length D2 in the parallel plate 310b than in the length D1 in the parallel plate 310a. The refractive index is the same for the refractive index N1 of the parallel plate 310a and the refractive index N2 of the parallel plate 310b. That is, regarding the two parallel flat plates, the relationship is D1 <D2, N1 = N2.

  As described above, except for the parallel plate 310a and the parallel plate 310b, the configurations of the fiber coupler 100 and the fiber coupler 700 are the same as those of the first embodiment. In the present embodiment, the optical fiber and the collimating lens in the fiber couplers 100 and 700 have the following relationship.

L1F = L2F
L1'F = L2'F
n1F = n2F
n1′F = n2′F
L1C = L1′C = L2C = L2′C
n1C = n1′C = n2C = n2′C

  Therefore, in a state where the parallel flat plate 310a and the parallel flat plate 310b are not arranged, the light guide unit has a relationship of L1 × n1 = L2 × n2. In this case, there is no time difference between the two light pulses P1 and P2. However, in the state in which the parallel flat plate 310a and the parallel flat plate 310b are arranged, the relationship of D1 × N1 = <D2 × N2 is established for the two parallel flat plates.

  In such a configuration (a state in which the parallel plate 310a and the parallel plate 310b are arranged), an optical pulse is incident from the collimator lens 110a of the fiber coupler 100. One light pulse is emitted from each of the two collimator lenses 111 a and 111 b in the fiber coupler 100. These light pulses are incident on the parallel plates 310a and 310b, respectively.

  As described above, the parallel plate 310b is thicker than the parallel plate 310a. Therefore, the optical pulse propagating in the row flat plate 310b is delayed in time from the optical pulse propagating in the parallel flat plate 310a. As a result, the light pulse P2 emitted from the parallel plate 310b is delayed in time from the light pulse P1 emitted from the parallel plate 310a. In this way, two optical pulses P1 and P2 having a time can be generated. That is, a time delay can be caused in the optical pulse P2 with respect to the optical pulse P1.

  The light pulse P1 emitted from the parallel plate 310a and the light pulse P2 emitted from the parallel plate 310b are incident on the collimator lenses 110a and 110b, respectively. The optical pulse P1 and the optical pulse P2 travel through the optical fibers 101a and 101b, respectively, and reach the collimator lenses 111a and 111b. Then, the light pulse P1 and the light pulse P2 are emitted from the collimator lenses 111a and 111b, respectively.

  In the present embodiment, the length (thickness) from the incident end face to the exit end face is different between the parallel flat plate 310a and the parallel flat plate 310b. Therefore, the optical path lengths in the two paths (the optical fiber 101a side and the optical fiber 101b side) are different. It can be said that the optical path length is adjusted using two parallel flat plates. Therefore, it can be said that both the parallel flat plate 310a and the parallel flat plate 310b correspond to the optical path length adjusting unit. From the viewpoint of making the optical path length of the other parallel flat plate different from the optical path length of one parallel flat plate, either one of the parallel flat plates can be regarded as the optical path length adjusting unit.

  As described above, in this embodiment, the optical path length adjustment unit is arranged at a place other than the light guide unit.

  As described above, two light pulses separated from each other in time and space are emitted from the collimator lenses 111a and 111b. In this embodiment, the interval between the two light pulses can be arbitrarily set by adjusting the thickness of the parallel plates 310a and 310b. At that time, an optical pulse train having high coupling efficiency can be obtained.

  One parallel flat plate may not be arranged. In the present embodiment, the two parallel plates are both arranged on the incident end face side of the optical fiber. However, the two parallel plates may be arranged on the exit end face side of the optical fiber. Further, one parallel plate may be arranged on the incident end face side of the optical fiber, and the other parallel plate may be arranged on the incident end face side of the optical fiber.

  Further, as described above, the two light pulses have a time difference when they pass through the parallel plate 310a and the parallel plate 310b. Therefore, the length of the optical fiber, the thickness of the collimator lens, and the refractive index thereof may be set to arbitrary values.

  FIG. 9 shows a schematic configuration of an optical pulse multiplexing unit according to the seventh embodiment. In this embodiment, the positional relationship of the fiber with respect to the center line X and the positional relationship of the collimator lens with respect to the lines Y1 to Y4 are the same as those in the first embodiment. The functions of the optical fiber, collimator lens, and demultiplexing / combining unit are the same as those in the first embodiment.

  The optical pulse multiplexing unit of this embodiment is a fiber coupler 800. In the fiber coupler 800, parallel flat plates 320a and 320b are provided on the incident end face side of the optical fiber. This arrangement place is the same as the parallel flat plates 310a and 310b of the sixth embodiment. Other configurations are the same as those of the fiber coupler 700 of the sixth embodiment. The fiber coupler 100 is the same as the fiber coupler 100 of the sixth embodiment.

  Each of the parallel plate 310a and the parallel plate 310b has an incident end surface and an exit end surface. Further, the parallel flat plate 310a and the parallel flat plate 310b are formed of a material having a predetermined refractive index. The length (thickness) from the incident end face to the exit end face is the same as the length D1 of the parallel flat plate 310a and the length D2 of the parallel flat plate 310b. On the other hand, the refractive index N2 of the parallel plate 310b is higher than the refractive index N1 of the parallel plate 310a. That is, regarding the two parallel plates, D1 = D2 and N1 <N2.

  As described above, except for the parallel plate 320a and the parallel plate 320b, the configurations of the fiber coupler 100 and the fiber coupler 800 (700) are the same as those of the sixth embodiment. Therefore, since the optical fiber and the collimating lens in the fiber couplers 100 and 800 (700) are the same as those in the sixth embodiment, the description thereof is omitted.

  In the state where the parallel flat plate 320a and the parallel flat plate 320b are not arranged, as in the sixth embodiment, the relationship of L1 × n1 = L2 × n2 is established for the light guide unit. In this case, there is no time difference between the two light pulses P1 and P2. However, in a state where the parallel flat plate 320a and the parallel flat plate 320b are arranged, the relationship of two parallel flat plates is D1 × N1 = <D2 × N2.

  In such a configuration (a state in which the parallel plate 320a and the parallel plate 320b are arranged), a light pulse is incident from the collimator lens 110a of the fiber coupler 100. One light pulse is emitted from each of the two collimator lenses 111 a and 111 b in the fiber coupler 100. These light pulses are incident on the parallel plates 310a and 310b, respectively.

  As described above, the refractive index of the parallel plate 320b is larger than the refractive index of the parallel plate 310a. Therefore, the optical pulse propagating in the parallel plate 320b is delayed in time from the optical pulse propagating in the parallel plate 320a. Thereby, the light pulse P2 emitted from the parallel plate 320b is delayed in time from the light pulse P1 emitted from the parallel plate 320a. In this way, two optical pulses P1 and P2 having a time can be generated. That is, a time delay can be caused in the optical pulse P2 with respect to the optical pulse P1.

  The light pulse P1 emitted from the parallel plate 320a and the light pulse P2 emitted from the parallel plate 320b are incident on the collimator lenses 110a and 110b, respectively. The optical pulse P1 and the optical pulse P2 travel through the optical fibers 101a and 101b, respectively, and reach the collimator lenses 111a and 111b. Then, the light pulse P1 and the light pulse P2 are emitted from the collimator lenses 111a and 111b, respectively.

  In this embodiment, the refractive index is different between the parallel plate 310a and the parallel plate 310b. Therefore, the optical path lengths in the two paths (the optical fiber 101a side and the optical fiber 101b side) are different. It can be said that the optical path length is adjusted using two parallel flat plates. Therefore, it can be said that both the parallel plate 320a and the parallel plate 320b correspond to the optical path length adjustment unit. From the viewpoint of making the optical path length of the other parallel flat plate different from the optical path length of one parallel flat plate, either one of the parallel flat plates can be regarded as the optical path length adjusting unit.

  As described above, in this embodiment, the optical path length adjustment unit is arranged at a place other than the light guide unit.

  As described above, two light pulses separated from each other in time and space are emitted from the collimator lenses 111a and 111b. In this embodiment, the interval between the two light pulses can be arbitrarily set by adjusting the refractive indexes of the parallel plates 320a and 320b. At that time, an optical pulse train having high coupling efficiency can be obtained.

  One parallel flat plate may not be arranged. In the present embodiment, the two parallel plates are both arranged on the incident end face side of the optical fiber. However, the two parallel plates may be arranged on the exit end face side of the optical fiber. Further, one parallel plate may be arranged on the incident end face side of the optical fiber, and the other parallel plate may be arranged on the incident end face side of the optical fiber.

  Further, as described above, the two light pulses have a time difference when they pass through the parallel plate 310a and the parallel plate 310b. Therefore, the length of the optical fiber, the thickness of the collimator lens, and the refractive index thereof may be set to arbitrary values.

  In Examples 6 and 7, the parallel plates 310a and 310b are arranged so that the normal line of the incident end face (the normal line of the exit end face) is parallel to the center line X. That is, the parallel plates 310a and 310b are arranged so that the incident end face is perpendicular to the center line X. However, at least one of the parallel plates 310a and 310b may be arranged such that the normal line of the incident end face (the normal line of the exit end face) is not parallel to the center line X.

  For example, when the angle formed between the normal line of the incident end face of the parallel plate 310a and the center line X is θ1, the parallel plate 310a is arranged so that θ1 ≠ 0 °. Further, when the angle formed between the normal line of the incident end face of the parallel plate 310b and the center line X is θ2, the parallel plate 310b is arranged so that θ2 ≠ 0 °. By setting θ1 ≠ θ2, even if D1 = D2, the optical path length of the parallel plate 310b can be made different from the optical path length of the parallel plate 310a.

  Further, at least one of the parallel plates 310a and 310b may be rotated around a predetermined rotation axis. In this case, the predetermined rotation axis is an axis perpendicular to the paper surface. By doing so, the optical path length can be changed. The predetermined rotation axis may be inside the parallel plates 310a and 310b (a position passing through the parallel plates) or may be a position away from the parallel plates 310a and 310b.

  When the parallel plates 310a and 310b are rotated, the position of the emitted light changes. In this case, it is necessary to change the positions of the collimator lenses 110a and 110b. Therefore, it is necessary to provide a moving mechanism that moves the collimator lens.

  Further, at least one of the parallel plates 310a and 310b may have a wedge shape (non-parallel shape). The optical path length can be changed by moving the wedge-shaped element on the paper surface so that the distance to the central axis X changes. Also in this case, the position of the emitted light changes as the wedge-shaped element moves. Therefore, it is necessary to provide a moving mechanism for moving the collimator lens.

  FIG. 10 shows a schematic configuration of an optical pulse multiplexing unit according to the eighth embodiment. In this embodiment, the positional relationship of the fiber with respect to the center line X and the positional relationship of the collimator lens with respect to the lines Y1 to Y4 are the same as those in the first embodiment. The functions of the optical fiber, collimator lens, and demultiplexing / combining unit are the same as those in the first embodiment.

  The optical pulse multiplexing unit of this embodiment is a fiber coupler 900. In the fiber coupler 900, optical fibers 330a and 330b are used instead of the parallel plates of the sixth embodiment.

  The optical fiber 330a and the optical fiber 330b have an incident end face and an exit end face, respectively. Moreover, the core part of the optical fiber 330a and the optical fiber 330b is formed with the material which has a predetermined refractive index. However, the length (thickness) from the incident end face to the exit end face is longer (thicker) in the length D2 in the optical fiber 330b than in the length D1 in the optical fiber 330a. The refractive index is the same for the refractive index N1 of the optical fiber 330a and the refractive index N2 of the optical fiber 330b. That is, for the two optical fibers, the relationship is D1 <D2, N1 = N2.

  In addition, collimator lenses 331a and 332a are disposed on both end faces of the optical fiber 330a. Similarly, collimator lenses 331b and 332b are disposed on both end faces of the optical fiber 330b. All collimator lenses have the same shape and material. Therefore, also in the present embodiment, the relationship of D1 × N1 = <D2 × N2 is established for the two optical fibers.

  As described above, in this embodiment, the parallel plate of the sixth embodiment is replaced with an optical fiber. Therefore, since the function, operation, and effect are the same as those of the sixth embodiment, description thereof is omitted.

  In this embodiment, at least one of the optical fibers 330a and 330b serves as an optical path length adjustment unit. The optical path length adjustment unit may include a collimator lens. As described above, in this embodiment, the optical path length adjustment unit is arranged at a place other than the light guide unit.

  FIG. 11 shows a schematic configuration of an optical pulse multiplexing unit according to the ninth embodiment. In this embodiment, the positional relationship of the fiber with respect to the center line X and the positional relationship of the collimator lens with respect to the lines Y1 to Y4 are the same as those in the first embodiment. The functions of the optical fiber, collimator lens, and demultiplexing / combining unit are the same as those in the first embodiment.

  The optical pulse multiplexing unit of this embodiment is a fiber coupler 1000. In the fiber coupler 1000, optical fibers 340a and 340b are used instead of the parallel plates of the seventh embodiment.

  Each of the optical fibers 340a and 340b has an incident end face and an exit end face. The core portions of the optical fibers 340a and 340b are formed of a material having a predetermined refractive index. Here, the length (thickness) from the incident end face to the exit end face is the same as the length D1 in the optical fiber 340a and the length D2 in the optical fiber 340b. On the other hand, the refractive index N2 in the optical fiber 340b is higher than the refractive index N1 in the optical fiber 340a. That is, regarding the two optical fibers, the relationship is D1 = D2 and N1 <N2.

  In addition, collimator lenses 331a and 332a are disposed on both end faces of the optical fiber 340a. Similarly, collimator lenses 331b and 332b are disposed on both end faces of the optical fiber 340b. All collimator lenses have the same shape and material. Also in the present embodiment, regarding the two optical fibers, the relationship is D1 × N1 = <D2 × N2.

  As described above, in this example, the parallel plate of Example 7 is replaced with an optical fiber. Therefore, since the function, operation, and effect are the same as those of the seventh embodiment, description thereof is omitted.

  In this embodiment, at least one of the optical fibers 340a and 340b serves as an optical path length adjusting unit. The optical path length adjustment unit may include a collimator lens. As described above, in this embodiment, the optical path length adjustment unit is arranged at a place other than the light guide unit.

  FIG. 12 shows a schematic configuration of an optical pulse multiplexing unit according to the tenth embodiment. In this embodiment, the positional relationship of the fiber with respect to the center line X and the positional relationship of the collimator lens with respect to the lines Y1 to Y4 are the same as those in the first embodiment. The functions of the optical fiber, collimator lens, and demultiplexing / combining unit are the same as those in the first embodiment.

  The optical pulse multiplexing unit of this embodiment is a fiber coupler 1100. In the fiber coupler 1100, a mirror unit 380 is used instead of the parallel plate of the sixth embodiment.

  In this embodiment, the mirror unit 380 is provided at a position facing the optical fiber 101b with the collimator lens 110b interposed therebetween. On the other hand, nothing is provided at a position facing the optical fiber 101a across the collimator lens 110a. In terms of the positional relationship with the fiber coupler 100, the mirror unit 380 is provided between the collimator lens 111b (fiber coupler 100 side) and 110b (fiber coupler 1100 side). Further, nothing is provided between the collimator lens 111a (on the fiber coupler 100 side) and 110a (on the fiber coupler 1100 side).

  The mirror unit 380 includes four reflection mirrors M1, M2, M3, M4 and a stage ST. The reflection mirror M1 corresponds to the incident end face, and the reflection mirror M4 corresponds to the exit end face.

  Here, the path on which the mirror unit 380 is not disposed is a path from the collimator lens 111a (on the fiber coupler 100 side) to 110a (on the fiber coupler 1100 side). On the other hand, the length of the path on which the mirror unit 380 is disposed is the path from the collimator lens 111b (fiber coupler 100 side) to 110b (fiber coupler 1100 side). Therefore, the length of the path where the mirror unit 380 is arranged is longer than the length of the path where the mirror unit 380 is not arranged. On the other hand, the refractive index between the two paths is the same. That is, regarding the two parallel flat plates, the relationship is D1 <D2, N1 = N2.

  Here, there is nothing in the path from the collimator lens 111a (fiber coupler 100 side) to 110a (fiber coupler 1100 side). Therefore, there is no entrance end face and no exit end face. Therefore, it is assumed that there are virtual incident end faces and emission end faces at the same positions as the positions of the reflecting mirror M1 and the reflecting mirror M4.

  As described above, except for the mirror unit 380, the configurations of the fiber coupler 100 and the fiber coupler 1100 are the same as those in the sixth embodiment. Therefore, since the optical fiber and the collimating lens in the fiber couplers 100 and 1100 are the same as those in the sixth embodiment, the description thereof is omitted.

  In the state where the mirror unit 380 is not disposed, as in the sixth embodiment, regarding the light guide unit, L1 × n1 = L2 × n2. In this case, there is no time difference between the two light pulses P1 and P2. However, in the state in which the mirror unit 380 is arranged, the relationship of D1 × N1 = <D2 × N2 is established for the two parallel plates.

  In such a configuration (a state in which the mirror unit 380 is disposed), an optical pulse is incident from the collimator lens 110a of the fiber coupler 100. One light pulse is emitted from each of the two collimator lenses 111 a and 111 b in the fiber coupler 100. These light pulses are incident on the parallel plates 310a and 310b, respectively.

  As described above, the length of the path where the mirror unit 380 is arranged is longer than the length of the path where the mirror unit 380 is not arranged. Therefore, the light pulse traveling through the mirror unit 380 is delayed in time from the light pulse traveling through the path without the mirror unit 380. Thereby, the light pulse P2 emitted from the mirror unit 380 is delayed in time with respect to the light pulse P1. In this way, two optical pulses P1 and P2 having a time can be generated. That is, a time delay can be caused in the optical pulse P2 with respect to the optical pulse P1.

  The light pulse P1 and the light pulse P2 emitted from the mirror unit 380 enter the collimator lenses 110a and 110b, respectively. The optical pulse P1 and the optical pulse P2 travel through the optical fibers 101a and 101b, respectively, and reach the collimator lenses 111a and 111b. Then, the light pulse P1 and the light pulse P2 are emitted from the collimator lenses 111a and 111b, respectively.

  Further, although the position of the reflection mirror M1 and the position of the reflection mirror M4 are fixed, the reflection mirrors M2 and M3 are configured to be movable in the vertical direction on the paper surface by the stage ST. Therefore, the distance from the reflection mirror M1 to the reflection mirror M2 and the distance from the reflection mirror M3 to the reflection mirror M4 can be changed. In this embodiment, the distance m ″ can be changed if the sum of both distances is m ″.

  As described above, in this embodiment, D1 × N1 and D2 × N2 are different. Therefore, it is possible to emit two light pulses P1 and P2 that are temporally and spatially separated from the collimator lenses 211a and 211b, respectively. In addition, in this embodiment, a time difference of M1 × n and M2 × n can be generated. In addition, in this embodiment, a time difference of m ″ × n can also be generated.

  Further, m ″ can be finely adjusted by the stage ST. Therefore, the time difference (temporal delay amount) between the two optical pulses P1 and P2 can be arbitrarily set and the time difference between the two optical pulses P1 and P2. In this case, an optical pulse train with high coupling efficiency can be obtained.

  In this embodiment, the length of the path where the mirror unit 380 is arranged is different from the length of the path where the mirror unit 380 is not arranged. Therefore, the optical path lengths in the two paths are different. It can be said that the optical path length is adjusted using the mirror unit 380. Therefore, it can be said that the mirror unit 380 corresponds to the optical path length adjustment unit.

  As described above, in this embodiment, the optical path length adjustment unit is arranged at a place other than the light guide unit.

  Note that another mirror unit may be arranged on the optical path where the mirror unit 380 is not arranged. In this embodiment, the mirror unit 380 is disposed on the incident end face side of the optical fiber. However, the mirror unit 380 may be disposed on the exit end face side of the optical fiber. Further, the mirror unit 380 may be arranged on the incident end face side of the optical fiber, and another mirror unit may be arranged on the incident end face side of the optical fiber.

  Further, as described above, the two light pulses have a time difference when one of the light pulses is emitted from the mirror unit 380. Therefore, the length of the optical fiber, the thickness of the collimator lens, and the refractive index thereof may be set to arbitrary values.

  FIG. 13 shows a schematic configuration of an optical pulse multiplexing unit according to the eleventh embodiment. In this embodiment, the positional relationship of the fiber with respect to the center line X and the positional relationship of the collimator lens with respect to the lines Y1 to Y4 are the same as those in the first embodiment. The functions of the optical fiber, collimator lens, and demultiplexing / combining unit are the same as those in the first embodiment.

  The optical pulse multiplexing unit of this embodiment is a fiber coupler 1200. In the fiber coupler 1200, an optical fiber unit 680 is used instead of the mirror unit 380 of the tenth embodiment.

  In this embodiment, the optical fiber unit 680 is provided at a position facing the optical fiber 101b with the collimator lens 110b interposed therebetween. On the other hand, the optical fiber 1201a is provided at a position facing the optical fiber 101a with the collimator lens 111a interposed therebetween. In terms of the positional relationship with the fiber coupler 100, the optical fiber unit 680 is provided between the collimator lens 111b (on the fiber coupler 100 side) and 110b (on the fiber coupler 1200 side). The optical fiber 1201a is provided between the collimator lens 111a (on the fiber coupler 100 side) and 110a (on the fiber coupler 1200 side).

  The optical fiber unit 680 includes four reflection mirrors M1, M2, M3, and M4. Furthermore, the optical fiber unit 680 includes three optical fibers 1201b, 1201c, 1201d, and a stage ST. Three optical fibers 1201b, 1201c, and 1201d are held on the stage ST.

  The stage ST is moved in the vertical direction on the paper surface. Accordingly, the optical fibers 1201b, 1201c, and 1201d move in the vertical direction on the paper surface. Thereby, the optical fibers 1201b, 1201c, and 1201d are alternatively arranged in the optical path between the reflection mirrors M2 and M3.

  Also in this embodiment, except for the optical fiber unit 680, the configurations of the fiber coupler 100 and the fiber coupler 1200 are the same as those in the sixth embodiment. Therefore, since the optical fiber and the collimating lens in the fiber couplers 100 and 1200 are the same as those in the sixth embodiment, the description thereof is omitted.

  Here, the four optical fibers 1201a, 1201b, 1201c, and 1201d have different refractive indexes and / or lengths.

  As described above, the three optical fibers 1201b, 1201c, and 1201d are configured to be movable in the vertical direction on the paper surface by the stage ST. In this embodiment, one of the three optical fibers 1201b, 1201c, and 1201d is selected and inserted into the optical path between the reflection mirrors M2 and M3.

  As for the selected optical fiber and the optical fiber 1201a, when the two optical fibers have different lengths but have the same refractive index, the configuration is the same as that of the eighth embodiment. When the two optical fibers have the same length but different refractive indexes, the configuration is the same as that of the ninth embodiment. Therefore, since the function, operation, and effect are the same as those of the eighth and ninth embodiments, the description thereof is omitted.

  In this embodiment, the optical fiber unit 680 serves as an optical path length adjustment unit. The optical path length adjustment unit may include a collimator lens. As described above, in this embodiment, the optical path length adjustment unit is arranged at a place other than the light guide unit.

  In each of the above embodiments, an optical fiber having a refractive index at the center (core) higher than that of the periphery (cladding) can be used. However, the present invention is not limited to this, and a member capable of guiding light, such as a waveguide, can also be used. Also, a desired number of optical pulse trains can be easily obtained by connecting three or more fiber couplers in series. As described above, the present invention can take various modifications without departing from the spirit of the present invention.

  As described above, the present invention is useful for an optical pulse multiplexing unit that can arbitrarily set the pulse interval of an optical pulse train.

It is a figure for demonstrating the basic composition of this invention. It is a figure which shows schematic structure of the optical pulse multiplexing unit which concerns on Example 1 of this invention. It is a figure which shows schematic structure of the optical pulse multiplexing unit which concerns on Example 2 of this invention. It is a figure which shows schematic structure of the optical pulse multiplexing unit which concerns on Example 3 of this invention. It is a figure which shows schematic structure of the optical pulse multiplexing unit which concerns on Example 4 of this invention. It is a figure which shows schematic structure of the optical pulse multiplexing unit which concerns on Example 5 of this invention. FIG. 10 is a diagram showing a cross-sectional configuration in the vicinity of a demultiplexing / combining portion in Example 5. It is a figure which shows schematic structure of the optical pulse multiplexing unit which concerns on Example 6 of this invention. It is a figure which shows schematic structure of the optical pulse multiplexing unit which concerns on Example 7 of this invention. It is a figure which shows schematic structure of the optical pulse multiplexing unit which concerns on Example 8 of this invention. It is a figure which shows schematic structure of the optical pulse multiplexing unit which concerns on Example 9 of this invention. It is a figure which shows schematic structure of the optical pulse multiplexing unit which concerns on Example 10 of this invention. It is a figure which shows schematic structure of the optical pulse multiplexing unit which concerns on Example 11 of this invention. It is a figure which shows the conventional optical pulse multiplexing unit. It is another figure which shows the conventional optical pulse multiplexing unit.

Explanation of symbols

100 First fiber coupler 110a, 110b, 111a, 111b, 210a, 210b, 211a, 211b Collimator lens 101a, 101b, 201a, 201b Optical fiber 301a Optical fiber 200 Fiber coupler 310a, 310b Parallel flat plate 320a, 320b Parallel flat plate 330a, 330b Optical fiber 331a, 331b, 332a, 332b Collimator lens 340a, 340b Optical fiber 400 Fiber coupler 401a, 401b, 401c, 401d, 401e Optical fiber 410a, 410b, 410c, 410d, 410e Collimator lens 411a, 411b, 411c, 411d, 411e Collimator lens 420 Demultiplexing / multiplexing unit 500 Fiber coupler 501a Optical fiber 601a, 60 1b, 601c, 601d Optical fiber 610a, 610b, 610c, 610d Collimator lens 611a, 611b, 611c, 611d Collimator lens 700, 800, 900, 1000, 1100 Fiber coupler 1201a, 1201b, 1201c, 1201d Optical fiber 1210a, 1210b, 1210c , 1210d Collimator lens 1211a, 1211b, 1211c, 1211d Collimator lens Y1, Y2, Y3, Y4 Reference line X Center line ST stage M1, M2, M3, M4 Reflection mirror 51 Pulse light source 52 Delay structure 53 Condensing lens 54 Waveguide 55 _{1 to} 55 _n pulses

Claims (8)

A plurality of light guides and a demultiplexing / combining unit for demultiplexing and / or combining incident light;
An optical path length adjustment unit having an entrance surface and an exit surface;
The demultiplexing / combining part is formed at a position where the plurality of light guide parts are closest to or in contact with each other,
The plurality of light guides include a first light guide having a first incident end face and a first exit end face, and a second light guide having a second entrance end face and a second exit end face. And
The optical path length adjusting unit is
(A) at least one of the first light guide and the second light guide;
(B) at least one light incident side of the first incident end face and the second incident end face;
(C) at least one light exit side of the first exit end face and the second exit end face;
An optical pulse multiplexing unit provided in at least one of the above. The optical path length adjustment unit is the first light guide unit or the second light guide unit,
The length from the first incident end face to the demultiplexing / multiplexing section is L1, the refractive index of the first light guide section is n1, and the length from the second incident end face to the demultiplexing / multiplexing section. 2. The optical pulse multiplexing unit according to claim 1, wherein L1 × n1 and L2 × n2 are different when a length is L2 and a refractive index n2 of the second light guide unit. The optical path length adjustment unit is the first light guide unit or the second light guide unit,
3. The optical pulse multiplexing unit according to claim 1, wherein the first incident end face and the first exit end face, or the second incident end face and the second exit end face are opposed to each other. The optical path length adjustment unit is the plurality of light guide units including the first light guide unit and the second light guide unit,
Each of the plurality of light guides has an incident end surface and an exit end surface,
When the length from the incident end surface to the demultiplexing / combining portion is L and the refractive index of the light guide portion is n, each of the plurality of light guide portions has L × n as another light guide portion. Unlike
A moving mechanism for moving at least two of the plurality of light guides;
The optical pulse multiplexing unit according to claim 1, wherein the demultiplexing / multiplexing unit is formed by the at least two light guide units. The optical path length adjusting unit has an incident end surface and an exit end surface, and has a predetermined refractive index,
2. The optical pulse multiplexing unit according to claim 1, wherein the optical pulse multiplexing unit is disposed on at least one of a light incident side and a light emission side of the light guide unit.   6. The optical pulse multiplexing unit according to claim 5, wherein the optical path length adjusting unit has a refractive index larger than that of air.   6. The optical pulse multiplexing unit according to claim 5, wherein the optical path length adjusting unit includes a reflecting surface that reflects light from the incident end surface so as to guide the light to the exit end surface. The optical path length adjustment unit includes a first optical path length adjustment element and a second optical path length adjustment element. The length from the incident end face to the exit end face of the first optical path length adjustment element is D1, and the first optical path length adjustment is performed. When the refractive index of the element is N1, the length from the incident end face to the exit end face of the first optical path length adjusting element is D2, and the refractive index of the second optical path length adjusting element is N2, D1 × N1 and D2 × N2 6. The optical pulse multiplexing unit according to claim 5, wherein the optical pulse multiplexing units are different from each other.

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