JPS59160101A - Single mode optical fiber having circular polarization maintainability and its manufacture - Google Patents

Abstract

PURPOSE:To obtain a single mode optical fiber low in loss and superior in circular polarization maintainability by forming a spiral glass layer different in the thermal expansion coefficient from glass materials forming a core or a clad in the longitudinal direction in the boundary between the core and the clad or in the clad layer near the core. CONSTITUTION:An SiO2-GeO2 glass is used as the glass material of a core 1, SiO2 as that of a clad 2, SiO2-B2O3 as that of a spiral glass layer 3, and SiO2 as that of a jacket 4, respectively, and the spiral glass layer 3 is formed on the outer side of the cald 2 spirally in one revolution per 1cm fiber length. At that time, a right-handed spiral stress is applied to the core 1 and the clad 2, resulting in inducing right-handed spiral refringence in the clad and core glasses. When laser beams having a right-handed spiral circular polarization mode are cast into this circular polarization maintainable signal mode fiber, combination with a left-handed circular polarization causing pulse enlargement, that is, coupling and energy shift are found to be extremely small, and the right-handed polarization state is found to be the maintained extremely satisfactory.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a circularly polarization-preserving single mode optical fiber and a method for manufacturing the same.

The fundamental mode propagating in a single mode optical fiber is composed of two circularly polarized modes rotating in opposite directions. In normally manufactured fibers, minute structural disturbances (for example, the deviation of the core from a perfect circle) cause a propagation time difference between the two circularly polarized modes, so long-distance light is In transmission systems, this is a factor that causes the time spread of optical pulses.

Therefore, in order to reduce the pulse broadening due to the propagation time difference of this circularly polarized wave mode, a circularly polarized wave preserving single mode fiber is required. A twisted single mode fiber (hereinafter abbreviated as "twisted fiber") was devised. In this twisted fiber, multilayer IJi properties occur due to torsional stress, and since this is distributed in the longitudinal direction of the fiber (in a twisted state), the circularly polarized wave mode is preserved and propagated. Therefore, times'l1 in one direction
If only the 7i polarization mode is incident, the circularly polarized state is maintained, so that transmission is possible without pulse broadening.

However, since the above-mentioned twisted fiber requires periodic twisting in the longitudinal direction, there are problems in that the manufacturing process is complicated and it is difficult to achieve low loss.

In order to solve these drawbacks, the present invention creates a spiral glass layer in the longitudinal direction within the cladding layer at the core-crat boundary or near the core, which has a coefficient of thermal expansion different from that of the glass crystals forming the core or the crat. We have invented a single-mode fiber with circularly polarized wave monopresence, which is characterized by a constant polarization of An object of the present invention is to provide a one-mode optical fiber and a method for manufacturing the same.

FIG. 1 shows an embodiment of the present invention, in which (a) is a radial cross-sectional view of an IS# fiber, (b is a longitudinal cross-sectional view of a J fiber, 1 is a core, 2 is a cladding, and 3 is a sectional view in a longitudinal direction.
The core A5 and the cladding glass material have a small coefficient of thermal expansion, and 4 is the glass layer. Even if the circular polarization maintaining single mode fiber of the present invention shown in Fig. 1 is a3-(,'A1's glass material is 3i02-GeO2 and 3 mol%) glass, Clara j
The glass material of ~2 is n'5ioz, the glass material of the linear glass layer 3 is C8i○2-B2O3 (10 mol%), and the glass material of Jacques 1-4 is 5i02 (quartz tube or (yusynthesis)). A linear glass layer 3 is placed on the outside of the cladding 2, and the length of the fiber is 1.
If it is formed in a spiral shape (clockwise) at a rate of once per cm, a clockwise spiral stress strain is applied to the core or cladding, and therefore the stress strain in the core/Tararad glass (rightward rotation of the Kohara wire) is applied to the core or cladding. Birefringence is induced.Therefore, when a laser beam having a circularly polarized moat of Ij!I!U was input into the circularly polarized wave-maintaining single mode fiber shown in Figure 1, the cause of the pulse broadening was found. The coupling (Cubb link, energy transfer) to the left-handed circular 1.1 wave was extremely small, and the right-handed circular polarization state was extremely well preserved.

Fig. 2 shows the length (back 11) of the method for manufacturing the base material of the jli-t-todo optical fiber that determines the circular polarization preservation property of the present invention. In Fig. 2, 21 and 0.22 are = 17 - A core part and a clad part in a glass rod having a clad structure, 23 is a porous glass layer made of a glass composition with a thermal expansion coefficient different from that of the core/clara 1~, 24 is a composite 1 for forming the glass layer 25 is a rotating/supporting part, and 26 is a glass particle/flame flow. Now, in Example 1 of FIG. 2, Si 02-Ge 02 (
Using a glass base material synthesized by the VAD method having a glass core part 21 (3 mol%) and a SiO2 glass cladding part 22, while rotating at a rotation speed of 10 ppm,
5102-8203 glass fine particles synthesized by a synthesis torch 24 moving parallel to the axis of the glass base material are IW-milled on the side surface of the glass base material to form a porous glass layer 23 with parallel lines ν, When heated to 1500℃ and sintered, a transparent gap (Δ is 24qI is good, and this is stone attack 2, and it is X-tatsu;
By combining two fibers with a predetermined HB by a method such as IJL, a single-mode optical fiber motherboard having circular polarization preserving property according to the present invention can be obtained. In this way, calendar 1
When a circularly polarized single-mode optical fiber 7r was fabricated by heating the mother wire 4 to a high temperature and drawing it, the circularly polarized single-seven-mode optical fiber 1' had extremely good circular polarization preservation characteristics. , and was sufficiently usable for practical use.

In addition, in Example 1, by adjusting the transfer speed of the synthesis torch 2/I and the rotation speed of the nolas rods (21, 22), the helical pitch of the crow layer 23 to be formed can be freely changed. It will be done.

The width of the naori lath layer can also be controlled by adjusting the accumulated amount of lath fine particles.

FIG. 3 is a practical example 2 of the method for manufacturing a base material for a single mode optical fiber having circular polarization preserving properties according to the present invention. In Fig. 3, 31 is a synthesis torch for the core, 32 is a synthesis torch for the cladding, and 33 is a synthesis torch for forming the glass layer.
~-di, 34 is the synthesis for Shakera 1~, 35 is the core porous part, 36 (Maclara 1~ porous part, 37 is composed of a glass composition having a thermal expansion coefficient different from that of the core and the cladding) The lath layer 38 is a porous layer 818. Therefore, in Example 2 of FIG. 3, Si Cf14-Qe C
j2n (3'El%) at 100 cc/min, SiC, Qt, at 300 cc/min in the synthesis torch 32, Si CA < -BBR3 (10 mol%) in the synthesis torch 33,
) to 5Qcc per minute, 5iCf to the synthesis torch 34! , 4 at a rate of 500 cc per minute, and pulled up while rotating at 10 ppm to form a porous base material, 5iO
A spiral porous glass layer consisting of z-I3203 (10 mol %) glass is formed. Furthermore, when this porous glass is heated to 1500℃ and sintered, a transparent glass layer with a spiral Si 02-8203 glass layer is formed at the boundary between the crat part and the ψcut part. The result is a single-seventh fiber matrix 4A having circular polarization preservation properties.The circularly polarized/j) 1-mode fiber base material produced in this manner is heated to a high temperature, and the wire The single mode fiber obtained showed good circular polarization preservation characteristics.

In addition, the circularly polarized wave produced by the manufacturing method of Examples 1 and 2
The loss of a single moat fiber is +15 and 0 at 13 μm.
．． It was less than 56B/Km.

In this example, 3iQ2 was used as the glass element () of the spiral glass layer having a different coefficient of thermal expansion from the core/crat.
-B203 was used, but in addition to this, a glass material made of a combination of Si 02 and one or more of the following dopant toy A can be used.

That is, the dopant (A is GeO2゜B205
,3n 02 ,Pb O,F, 102°7rO2,
etc. can be mentioned.

As explained above, the present invention replaces twisted fibers with
The present invention provides a novel circularly polarized single mode fiber having a glass layer that induces spiral stress strain within the fiber, and a method for manufacturing the same.

Therefore, the present invention has the advantage of not only simplifying the manufacturing method but also manufacturing a single mode fiber with excellent circular polarization preservation and (It J (1 loss ↑ 1). According to the manufacturing method of 19, there is an advantage that a long circularly polarized wave single mode fiber with a small C can be manufactured.

[Brief explanation of the drawing]

FIG. 1 shows an embodiment of the present invention, (a) is a radial cross-sectional view of the circularly polarized single mode fiber of the present invention, (11
) is a sectional view in the longitudinal direction, FIG. 2 is a reverse view showing Embodiment 1 of the method for manufacturing a base material for a circularly polarized single mode optical fiber of the present invention, and FIG. FIG. 2 is a diagram illustrating a second embodiment of a method for manufacturing a preform for a wave/single mode optical fiber. 1... Core 2... Clad 3...
A linear glass layer 4 having a thermal expansion coefficient different from that of the core and the Talarad glass material...Jacket 21...A core portion 22 in a glass rod having a core-clad structure...A core-clad structure. A cladding part 23 in a glass rod having a core and a cladding are a porous lath layer 24 consisting of a glass composition having a small coefficient of thermal expansion... a synthetic torch for forming the glass layer 25... a rotating/supporting part 26...Crow fine particles/flame flow 31...
・Synthesis 1 to 32 for the core...Synthesis torch 33 for the cladding 33...Synthesis torch for forming the glass layer 34...Synthesis 1 to 35 for the jacket 36. ...Clara 1-Porous part 3Y...
Linear porous Y1 glass layer 38 made of a glass composition having a coefficient of thermal expansion different from that of the core and crat...Jafut porous portion. Patent applicant Nippon Telegraph and Telephone Public Corporation Figure 1 (a) rb) (, +2,112

Claims (1)

[Claims] 1. A linear glass layer having a coefficient of thermal expansion different from that of the glass material forming the core or cladding in the longitudinal direction at the core-cladding boundary or in the cladding layer near the core. Single mode optical fiber with circular polarization preserving property. 2. A glass rod for a rotating core or IJ) A glass rod having a cladding structure is made of a glass composition having a different thermal expansion coefficient from the core material or cladding material by flame hydrolysis in the longitudinal direction of the side surface of the glass rod. After forming a porous glass layer consisting of a spiral shape, heating and sintering it to a high temperature to produce a transparent base material, and further drawing the transparent base material into lines using a high-temperature electric furnace. A method for manufacturing a single mode optical fiber having polarization preserving properties. 3. Use another synthetic torch to heat the side of the core porous matrix or the porous matrix with a core-clad structure that is being formed in the axial direction by the VAD method, which is different from the glass material of the core-clad. A circle characterized by forming a porous glass layer made of a glass material with a coefficient of expansion into a spiral shape, sintering it to produce a transparent base material, and then drawing the transparent base material into a wire in a high-temperature electric furnace. A method for manufacturing a single mode optical fiber having polarization preserving properties.