JPH08271758A - Assembling structure for optical connector with lens - Google Patents

Abstract

PURPOSE: To suppress the light loss by the axis misalignment between lenses to the extent of a permissible low level and to lessen the light loss by an angle deviation to a negligible level. CONSTITUTION: This assembling structure consists of ferrules 2a, 2b for holding optical fibers, lens holders 4a, 4b holding lenses, flanges 3a, 3b for fixing the lens holder and the ferrules to each other and a sleeve 6 for coupling the lens holders to each other. A difference is imparted between the focal lengths f1 and f2 of the two lenses 5a and 5b to be coupled. For example, distributed refractive index lenses having an equal outside diameter are used for the two lenses and are set at f1 /f2 ≈2/1 to 3/2. The corresponding end faces of the lens holders 4a, 4b are so formed as to be engaged with each other like a socket and spigot joint by projecting the one peripheral part in a ring form toward the other side and cutting the other peripheral side to a ring shape in correspondence thereto.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a combined structure of a pair of optical connectors with lenses, and more particularly to reduction of coupling loss due to axial deviation and angular deviation.

[0002]

2. Description of the Related Art In an optical cable for relaying a television camera, an optical connector must be repeatedly attached and detached in an environment with dirt and dust. In such an optical connector, a lens-equipped optical connector is used in which the influence of dirt and dust is reduced by enlarging the diameter of the light spot at the connection portion with a lens.

A conventional combined structure of this type of optical connector with a lens will be described with reference to FIG. The ferrule 2 is coaxially attached to each terminal of the pair of optical fibers 1a and 1b to be coupled.
a and 2b are attached, and flanges 3a and 3b are fitted and fixed to the outer peripheral surfaces of the ferrules. The lens 5 is placed in the hollow portion on one end side of the cylindrical lens holders 4a and 4b.
a and 5b are respectively held, and one end portions of the ferrules 2a and 2b are inserted into the hollow portions on the other end side, respectively.

The end faces of the optical fibers 1a and 1b are arranged at the centers of the facing end faces of the ferrules 2a and 2b, and the optical axes of the optical fibers 1a and 1b and the optical axes of the lenses 5a and 5b are aligned. After that, the end surfaces of the flanges 3a and 3b and the end surfaces of the lens holders 4a and 4b are joined and fixed by welding or the like. In the lens holders 4a and 4b, the end surfaces on the lens holding side are coaxially butted against each other, and a common cylindrical sleeve 6 is fitted to the outer peripheral surface of each.

The light beam between the lenses 5a and 5b is expanded to about 140 μm, for example, assuming that the light diameter of the optical fiber is 5.5 μm, and becomes parallel light because the focal lengths of the lenses are the same. The lenses 5a and 5b are cylindrical and have a refractive index that decreases toward the outer periphery as shown in FIG. 10, and a gradient index lens having the same function as a convex lens is often used. This gradient index lens has the property that its focal length is proportional to the length of the lens.

[0006]

In the conventional combined structure of the optical connector with a lens, the light beams between the lenses 5a and 5b are parallel, and the spot size is 5.5 μm of the optical fiber.
Since it is expanded to about 140 μm compared to m, the optical transmission loss due to the misalignment of the optical axes of the paired optical connectors is negligibly small, but it is only 0.1 deg between each optical axis. 1.5 dB even if the angle deviation of
It turned out that there is a drawback that a large transmission loss occurs.

An object of the present invention is to solve the above-mentioned conventional problems, to suppress the optical loss due to the axis deviation to a permissible level, and to reduce the optical loss due to the angular deviation to the extent that there is no problem. .

[0008]

[Means for Solving the Problems]

(1) In the invention of claim 1, a difference is provided between the focal lengths f ₁ and f ₂ of the first and second lenses. (2) The invention of claim 2 is the same as (1) except that the structure of the connector is defined in detail.

(3) In the invention of claim 3, in (1) or (2), the outer shapes of the first and second lenses are made substantially equal. (4) In the invention of claim 4, in the above (1) or (2), a gradient index lens is used as the first and second lenses. (5) In the invention of claim 5, in the above (2), one of the peripheral end faces of the first and second lens holders has a ring shape protruding toward the other end, and the other end corresponding to the other end face. The peripheral portions of the are cut off in a ring shape, and are formed so as to engage with each other in an uneven manner.

(6) In the invention of claim 6, in the above (4), the ratio of the focal lengths f ₁ and f ₂ of the first and second lenses is f ₁ / f ₂ ≈2 / 1 to 3/2. It is set.

[0011]

First, consideration will be given to positional deviation and angular deviation of the optical axis generated between optical connectors. With the current processing accuracy, it is unavoidable that there is a maximum dimensional difference of about 3.5 μm between the outer shape of the lens holders 4a and 4b and the inner diameter of the sleeve 6. Therefore, in the case of FIG. 2A in which only the angular deviation occurs between the lens holders 4a and 4b, the length of the sleeve 6 is about 8 mm, and therefore the angular deviation from the axis line L of the sleeve 6 of each lens holder. Is about 0.05 deg, and the angular deviation between both lens holders is about 0.1 deg, which is twice that.
Becomes

On the other hand, in the case of FIG. 2B in which only the axis shift occurs between both lens holders, the maximum axis shift from the axis L of the sleeve of each lens holder is about 3.5 / 2 μm, and the distance between both lens holders is large. Is about 3.5 μm. In this way, with the current processing accuracy, as the deviation of the optical axis between both lens holders,
In the worst case, it is unavoidable that an angular deviation of about 0.1 deg or a positional deviation of about 3.5 μm occurs.

Next, the theoretical optical transmission loss caused by this angular displacement or positional displacement will be considered. According to the technical document "Basics and Applications of Optical Coupling System" (Hyundai Engineering Co., Ltd.), the transmission loss L (dB) of light generated by the axis shift and the angle shift of two light beams is given by the following equation. ^{L = 10log {exp (-x 2} / ω 2 -π 2 θ 2 ω 2 / λ 2)} (dB) = 10 × 0.434 (-x 2 / ω 2 -π 2 θ 2 ω 2 / λ 2 ) (1) where x: axis deviation (μm) θ: angular deviation (rad) λ: wavelength of light (μm) ω: diameter of light (μm) (1) In case of only axis deviation (1) Substituting θ = 0 into L = 4.34 × (−x ² / ω ² ) ... (2) (1-1) If the lens is not used and the spot size is not enlarged, ≈5.5 μm, axis deviation x
= 3.5 μm, L = −4.34 × 3.5 ² /5.5 ² ≈−1.76 (dB) according to equation ( ² ) (3) (1-2) Parallel light between the two lenses,
When enlarging the beam diameter in omega ≒ 140 microns ^{is, L = -4.34 × 3.5 2/} 140 2 ≒ -0.003 (dB) ... (4) (2) For the angular deviation only (1) Substituting x = 0 into the equation, L = −4.34 × π ² θ ² ω ² / λ ² (5) (2-1) If no lens is used, wavelength λ≈1.3
When the light of μm is targeted, ω≈5.5 μm, θ = 0.1 (deg) = 1.75 × 10 ⁻³ (rad), L≈−0.002 (dB) (6) (2- 2) When parallel light is used between the two lenses and the beam diameter is expanded, ω≈140 μm, θ = 0.1 (deg) = 1.75 × 10 ⁻³ (rad), L≈−1.51 (DB) (7) As can be seen from the above numerical examples, in the conventional optical connector with a lens, the transmission loss of light is certainly improved with respect to the misalignment of the optical axis as compared with the case where no lens is used. However, it can be seen that the transmission loss significantly increases with respect to the angle deviation.

In the present invention, the optical loss due to the axis deviation is allowed.
It is kept as low as possible (about 0.5 dB) and there is no angle.
Provide a method to reduce the light loss due to this
It That is, as shown in the schematic view of FIG.
L₁, L₂So that the light between them is non-parallel light.
Z L₁, L₂Focal length f₁′, F₂’
In the example in the figure, f₁′ ＞ f₂'And l₁<F₁′, L
₃> F₂’ Radiation of light from optical fiber 1a
Angle α₁Angle of incidence α'on the optical fiber 1b ₂′ And
When making them almost equal, and when there is no axis deviation or angular deviation
F so that there is no light loss in an ideal optical system₁'When
f₂The values of'and are set. That is, f₁′, F₂′ Is light
Can be efficiently input from an optical fiber to another optical fiber
Is set as follows. l₁, L₃Are optical fibers 1a and 1b
And lens L₁, L₂Is the distance between. Note that FIG.
FIG. 3 is a schematic diagram of an example, which is provided for comparison with the present invention.
It Distance between two lenses l₂Is the case of this invention of FIG. 3B
For l₂≤l₁Or l₂≒ l₁It is said that Actually l
₁, L₂, L₃Is a very small distance. Between lenses
Is a non-parallel light beam, and the lens L₁Side light diameter ω
₁Is the lens L₂Side light diameter ω₂Slightly smaller. Only
Calculate the optical transmission loss L due to axis deviation or angle deviation
L₂Is a small value, so ω₁≒ ω₂age
Can be handled.

Whether the light beam emitted from the lens becomes parallel light as shown in FIG. 4A, the beam diameter increases as shown in FIG. 4B, or the beam diameter decreases as shown in FIG. 4C.
It is determined by the size relationship between the distance l between the optical fiber 1 and the lens L and the focal length f of the lens L. When 1 = f, the light becomes parallel light, when 1 <f, the beam diameter increases, and when 1> f, the beam diameter decreases. The case where the light enters the optical fiber 1 in FIG. 4 is the same as the case where the light is emitted.

In the case of FIG. 3B, as can be seen from the above description.
And the lens L₁For l₁<F ₁'And the lens L
₂For l₃> F₂'And the lens L₁Is enlarged in
Light is the lens L₂All is condensed by, so there is no light loss
I have to. 3A and 3B, both are l₁= L₃As
Light that enters or exits the optical fibers 1a and 1b
The radiation angle of is α₁= Α₂, Α₁′ ≒ α₂’

While the beam diameter ω of the optical fiber 1 is approximately 5.5 μm, the beam diameter ω _L between two conventional lenses is approximately 14
Although it is set to 0 μm, in the present invention, in order to reduce the transmission loss due to the conventional angle deviation, the beam diameter between the lenses is ω _L while the beam diameter of the optical fiber 1 is ω≈5.5 μm.
≈10 to 20 μm. Next, a numerical example of reducing transmission loss in this case will be described.

[0018] (1-3) axis deviation when the light was non-parallel light between the two lenses (a) if the _{ω L ≒ 10μm L = -4.34 ×} 3.5 2/10 2 = - 0.53 (dB) ... (8) if you and _{(b) ω L ≒ 20μm L = -4.34} × 3.5 2/20 2 = -0.13 (dB) ... (9) (2-3 ) Angle shift when light between two lenses is non-parallel light (a) When ω _L ≈10 μm θ = 0.1 deg = 1.75 × 10 ⁻³ rad, ω = 5.5 μm L≈− 0.008 (dB) (10) (b) When ω _L ≈ 20 μm L ≈ -0.031 (dB) (11) The optical loss due to axis misalignment when a lens is not used is given by the formula (3). L≈−1.76 (dB), and the optical loss due to the angle shift is L≈−0.002 dB in the equation (6). ω _L ≒ 10~20μ
When m is set, the optical loss due to the axis shift is reduced to about 1/3. On the other hand, the light loss due to the angle deviation slightly increases, but L≈−0.008 to −0.031 (dB)
Therefore, it is so small that it does not matter at all. It can be seen that the light loss is significantly reduced as compared with the conventional light loss L≈−1.51 dB in the case of parallel light. The optical transmission loss due to the axis deviation or the angle deviation described above is shown collectively in FIG.

(3) Regarding the focal lengths of the two lenses, next, with respect to the beam diameter ω ≈ 5.5 μm of the optical fiber,
The beam diameter ω to about 10 to 20 μm.
Focal length f of the two lenses required for₁, F ₂Seeking
It As the lens, a gradient index lens similar to the conventional example is used.
When used, as shown in FIG. 6, the optical fiber 1a (1b)
If the distance between the lens and the lens 5a (5b) is d, then "optical coupling
"Basics and applications of systems" (Hyundai Engineering Co.), ω_L= Ω / {(πω²/ Λ)²/ F²+ (1-d / f)²｝^1/2 The relationship of (12) holds.

(A) Focal length f when ω _L = 10 μm
₁ is ω = 5.5 μm, d = 1.06 mm, λ1.3 μ
m, f ₁ = 1.95 mm (13) (b) The focal length f ₁ when ω _L = 20 μm is similarly f ₁ = 1.56 mm (14) (c) Conventional When parallel light of ω _L = 140 μm is used, f ₁ = 1.24 mm (15) In order to obtain the focal length f ₂ of the other lens, first the focal length f _T of the two lenses as a whole is obtained. The focal length f _{T of the} entire two lens system is equal to the distance between the focus P and the lens L ₂ when parallel light is incident on the lens system as shown in FIG. 7B. This is the same as the case of FIG. 7A in which only one lens is used in the lens system.

The focal length f _{T of the} entire two lens system is 1 / f _T = 1 / f ₁ + 1 / f ₂ (16) = 2 / f ₁ (∵f in the conventional case using parallel light) ₁ = f ₂ ) (17) ∴f _T = f ₁ /2=0.622 mm (18) When ω _L ≈10 to 20 μm, the focal point of the entire lens system is also used in the case of the present invention using non-parallel light. The distance f _T needs to be set to be the same as in the case of using parallel light in order to allow light to efficiently enter from one optical fiber to the other optical fiber. Therefore, ( ₂ ) f _{2 in} the case of ω _L = 10 μm is calculated from the equation (16) as follows: 1 / f ₂ = 1 / f _T −1 / f ₁ = 1 / 0.622−1 / 1.95 = 1.09 ∴f ₂ = 0.92 mm (19) The ratio of the focal lengths of the two lenses is f ₁ / f ₂ = 1.95 / 0.92≈2 / 1 (20) (e) ω _L = 20 μm Similarly, f ₂ in the case is 1 / f ₂ = 1 / f _T −1 / f ₁ = 1 / 0.622−1 / 1.56 = 0.97 ∴f ₂ = 1.03 mm (21) ∴f ₁ / f ₂ = 1.56 / 1.03≈3 / 2 (22) The beam diameter ω of the optical fiber is ω = 5.5 μm by the lens ω
_{From the} expressions (20) and (22), it is understood that the focal length ratio f ₁ : f ₂ should be changed from about 2: 1 to 3: 2 in order to increase _L ≈ 10 to 20 μm.

In the case of a gradient index lens, the focus is
The point distance f is inversely proportional to the length of the lens in the optical axis direction. this
The combination structure of the optical connector with a lens of the invention is shown in FIG.
The same reference numerals are given to the parts corresponding to 9
Omit it. Outer diameter of lenses 5a and 5b and lens holder 4
Easy to manufacture by setting the outer diameters of a and 4b equal.
I have to. Ferrules 2a and 2b and lenses 5a and 5b
And each interval is 1 in FIG. 3B.₁, L₃Lens 5
The distance between a and 5b is l in FIG. 3B. ₂Is equivalent to

FIG. 5 is a graph showing the relationship between the angle deviation and the optical transmission loss according to the equation (5). It can be seen that the influence of the angle deviation is significantly reduced as compared with the conventional example using parallel light. At one end of the lens holder, one of the peripheral parts protrudes toward the other side in a ring shape, and the other peripheral part is scraped off in a ring shape correspondingly, and they engage with each other unevenly to provide sufficient coupling strength. Is getting

[0024]

As described above, according to the present invention, 2
By providing a difference in the focal lengths f ₁ and f ₂ of the _two lenses (the light between the lenses becomes non-parallel light), the light loss due to the axis deviation between the lenses is suppressed to an acceptable level, and the light due to the angle deviation is It is possible to reduce loss to the extent that there is no problem.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention.

FIG. 2 is a principle cross-sectional view of the combined structure of the conventional optical connector with a lens for explaining the angular deviation and the axial deviation between the lenses that occur in the combined structure.

FIG. 3 is a schematic diagram of an optical system for explaining the principle of the present invention.

FIG. 4 shows a case where when a focal length f of a lens is changed with respect to a distance 1 between an end face of one optical fiber and the one lens, one lens moves to the other lens (not shown) or the other lens. FIG. 3 is a schematic diagram of one optical system used for explaining how a light beam that is incident on one lens from a lens is spread.

FIG. 5 is a graph showing an increase amount of light loss due to an angular shift between lenses in the combined structure of the present invention and the conventional example.

FIG. 6 is a principle cross-sectional view of an optical system used to explain a change in a light beam diameter when a gradient index lens is used.

FIG. 7 is a schematic diagram of an optical system showing the focal length f _{T of the} entire two lenses in comparison with the focal length f of one lens.

FIG. 8 is a diagram showing data of loss of an optical system due to a shift of an optical axis or a shift of an angle.

FIG. 9 is a sectional view of the conventional combined structure.

FIG. 10 is a diagram showing a refractive index change characteristic of a gradient index lens.

Claims (6)

[Claims] 1. A first and a second ferrule attached to each end of a pair of optical fibers to be coupled, and a first and a second lens having different focal lengths disposed near each end face of the ferrule. And a combination structure of optical connectors with lenses, wherein the first and second lenses are arranged so as to closely face each other when the connectors are connected. 2. The first and second flanges are fitted and fixed to the outer peripheral surfaces of the first and second ferrules which are coaxially attached to the respective ends of the pair of optical fibers to be coupled, and are cylindrical. The first and second lenses are respectively held in the hollow portions on one end side of the first and second lens holders, and the distal end portions of the first and second ferrules are inserted into the hollow portions on the other end side, respectively. The end surfaces of the first and second flanges and the end surfaces of the first and second lens holders are joined and fixed, respectively, and the first and second lens holders have outer peripheral surfaces that are common to both ends of a cylindrical sleeve. A combined structure of an optical connector with a lens, into which the end faces on the side holding the first and second lenses are abutted coaxially with each other so that they can be inserted into and removed from the inside, and the focus of the first and second lenses If there is a difference between the distances f ₁ and f _2. And a combination structure of optical connectors with a lens. 3. The method according to claim 1, wherein the first,
A combined structure of an optical connector with a lens, wherein the outer shapes of the second lenses are made substantially equal. 4. The method according to claim 1, wherein the first,
A combined structure of an optical connector with a lens, wherein the second lens is a gradient index lens. 5. The end surfaces of the first and second lens holders facing each other according to claim 2, wherein one of the peripheral portions has a ring shape protruding toward the other side, and the other peripheral portion corresponds to the ring. A combined structure of an optical connector with a lens, characterized in that the optical connector with a lens is formed so as to be scraped off into a concave shape so as to engage with each other. 6. The method according to claim 4, wherein the ratio of the focal lengths f ₁ and f ₂ of the first and second lenses is set to f ₁ / f ₂ ≈2 / 1 to 3/2. A combination structure of optical connectors with lenses.