OPTICAL FIBER PREFORM AND MANUFACTURING METHOD THEREOF

Abstract

In the process comprising manufacturing a glass fine particle deposit (soot) by injecting glass fine particles generated with a burner for glass fine particle synthesis to a starting material rotating around its central axis as an axis of rotation; and sintering the glass fine particle deposit to vitrify it into transparent glass by suspending and heating the glass fine particle deposit in a furnace core tube, it is characterized that a product of a time period (min) during which a part of the glass fine particle deposit is heated in a heating zone in the furnace core tube and a linear speed (m/min) of sintering gas flowing in the furnace core tube is 15.5 (m) or more.

Claims

1. A manufacturing method for an optical fiber preform, comprising: manufacturing a glass fine particle deposit (soot) by injecting glass fine particles generated with a burner for glass fine particle synthesis onto a starting material rotating around its central axis as an axis of rotation; and sintering the glass fine particle deposit to vitrify it into transparent glass by suspending and heating the glass fine particle deposit in a furnace core tube, wherein a product of a time period (min) during which a part of the glass fine particle deposit is heated in a heating zone in the furnace core tube and a linear speed (m/min) of sintering gas flowing in the furnace core tube is 15.5 (m) or more.

2. The manufacturing method for an optical fiber preform according to claim 1, wherein a product of a time period (min) during which a part of the glass fine particle deposit (soot) is heated in a heating zone in the furnace core tube and a linear speed (m/min) of sintering gas flowing in the furnace core tube is 17.6 (m) or more.

3. The manufacturing method for an optical fiber preform according to claim 1, wherein a product of a time period (min) during which a part of the glass fine particle deposit (soot) is heated in a heating zone in the furnace core tube and a linear speed (m/min) of sintering gas flowing in the furnace core tube is 21.7 (m) or more.

4. The manufacturing method for an optical fiber preform according to claim 1, wherein the sintering the glass fine particle deposit to vitrify it into transparent glass comprises heating the glass fine particle deposit (soot) by passing it through a heating zone in the furnace core tube.

5. The manufacturing method for an optical fiber preform according to claim 1, wherein the sintering the glass fine particle deposit (soot) to vitrify it into transparent glass comprises supplying helium gas as sintering gas.

6. The manufacturing method for an optical fiber preform according to claim 1, wherein a product of a time period (min) during which a part of the glass fine particle deposit (soot) is heated in a heating zone in the furnace core tube and a linear speed (m/min) of sintering gas flowing in the furnace core tube is 34.1 (m) or less.

7. The manufacturing method for an optical fiber preform according to claim 6, wherein a time period (min) during which a part of the glass fine particle deposit (soot) is heated in a heating zone in the furnace core tube is 60 (min) or less.

8. The manufacturing method for an optical fiber preform according to claim 1, wherein a linear speed (m/min) of sintering gas flowing in the furnace core tube is 0.36 (m/min) or more.

9. The manufacturing method for an optical fiber preform according to claim 1, wherein a heating temperature in the sintering is in a range from 1555? C. to 1605? C.

10. An optical fiber preform manufactured by: manufacturing a glass fine particle deposit (soot) by injecting glass fine particles generated with a burner for glass fine particle synthesis to a starting material rotating around its central axis as an axis of rotation; and sintering the glass fine particle deposit to vitrify it into transparent glass by suspending and heating the glass fine particle deposit in a furnace core tube, wherein a product of a time period (min) during which a part of the glass fine particle deposit is heated in a heating zone in the furnace core tube and a linear speed (m/min) of sintering gas flowing in the furnace core tube is 15.5 (m) or more.

11. The optical fiber preform according to claim 10, wherein a product of a time period (min) during which a part of the glass fine particle deposit is heated in a heating zone in the furnace core tube and a linear speed (m/min) of sintering gas flowing in the furnace core tube is 17.6 (m) or more.

12. The optical fiber preform according to claim 10, wherein a product of a time period (min) during which a part of the glass fine particle deposit is heated in a heating zone in the furnace core tube and a linear speed (m/min) of sintering gas flowing in the furnace core tube is 21.7 (m) or more.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] FIG. 1 is a schematic vertical cross-sectional view illustrating an example of a sintering machine.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0012] Although embodiments of the present invention are described below in reference to the examples of the present invention and comparative examples based on the drawing, the present invention is not limited to these embodiments, and various aspects are possible within the scope of claims.

[0013] The manufacturing method of the present invention is described in detail. Firstly, by means of the VAD method or the like, soot is manufactured by depositing glass fine particles generated with a burner for glass fine particle deposition. The synthesized soot is heated and sintered in a zone-heating furnace and vitrified into transparent glass to obtain the optical fiber preform. FIG. 1 is a schematic vertical cross-sectional view representing an example of the sintering machine for dehydrating and vitrifying the soot into transparent glass. In FIG. 1, the soot 3 coupled to an axial bar 2 is suspended in the furnace core tube 4 in the sintering machine 1. The axial bar 2 extends through an upper lid 5 and a motor is connected to the axial bar 2 for vertical movement and rotation of the axial bar 2 and the soot 3.

[0014] A heating furnace body 6 for heating the soot 3 is arranged around a part of the outer circumference of the furnace core tube 4, and the heating furnace body is provided with a cylindrical heater 7 and a thermal insulation material 8 covering it. A temperature sensor monitors the temperature inside the furnace, and a temperature controller 9 controls the temperature inside the furnace by adjusting the output of the heater 7. A sintering gas introduction conduit 10 is connected to the bottom of the furnace core tube 4 to supply the sintering gas necessary for dehydration and vitrification into transparent glass. The supplied sintering gas flows upwardly and is exhausted through an exhaust conduit 11 at the upper lid 5, so that pressure inside the furnace core tube is adjusted.

Examples

[0015] Soot with a length of 1650 mm and an outer diameter of 160 mm was manufactured by means of the VAD method. The soot was sintered in the sintering machine shown in FIG. 1. Specifically, the soot was suspended in the furnace core tube having an inner diameter of 272 mm, the heater temperature was set to 1200? C. while a mixture gas of chlorine gas and argon gas (chlorine concentration 3 mol %) for dehydration was supplied to the furnace core tube through the gas introduction conduit at the volumetric flow rate of 26 L/min, the soot was heated while being lowered at a lowering rate of 10 mm/min, and the soot was dehydrated. Once the entire soot was heated and dehydrated, the soot was lifted upwardly. Subsequently, the soot was sintered and vitrified into transparent glass, and studied for the presence or absence of unmelted areas.

[0016] To study the presence or absence of unmelted areas, examples 1 to 5 and comparative examples 1 and 2 were performed. Table 1 shows the respective conditions of the examples and the comparative examples in terms of the set temperature of the heater, the volumetric flow rate of the helium gas supplied, and the lowering rate. The soots were heated and vitrified into transparent glass based on these conditions applied as set values for respective examples and the comparative examples, and the presence or absence of unmelted areas was studied. Note that, assuming that the lowering rate of the soot is 5.0 mm/min, the heating time period, i.e. the time period during which a part of the soot passes through a heating zone with the height of 300 mm in the cylindrical heater arranged surrounding the furnace core tube, is calculated to be 60 min by dividing the heater height 300 mm by the lowering rate. Assuming that the volumetric flow rate of the helium gas is 33.0 L/min, a linear speed of the helium gas is calculated to be 0.57 m/min by dividing the volumetric flow rate by a cross-sectional area 0.058 m2 of the furnace core tube having an inner diameter of 272 mm. Note that although a helium gas linear speed down to three decimal places was used in calculation of a product of the helium gas linear speed and the heating time required for vitrification into transparent glass, the helium gas linear speed described was rounded to two decimal places for the sake of simplification.

TABLE-US-00001 TABLE 1 PRODUCT OF SET VOLUMETRIC LINEAR SPEED TEMPERATURE FLOW LINEAR HEATING OF HELIUM GAS OF THE RATE OF SPEED OF LOWERING TIME AND HEATING HEATER HELIUM GAS HELIUM GAS RATE PERIOD TIME PERIOD [? C.] [L/min] [m/min] [mm/min] [min] [m] EXAMPLE 1 1555 33.0 0.57 5.0 60.0 34.1 EXAMPLE 2 1555 21.0 0.36 5.0 60.0 21.7 EXAMPLE 3 1555 17.0 0.29 5.0 60.0 17.6 EXAMPLE 4 1570 21.0 0.36 6.0 50.0 18.1 EXAMPLE 5 1605 21.0 0.36 7.0 42.9 15.5 COMPARATIVE 1555 6.3 0.11 5.0 60.0 6.5 EXAMPLE 1 COMPARATIVE 1605 21.0 0.36 8.0 37.5 13.6 EXAMPLE 2

[0017] In example 1, a glass fine particle deposit manufactured was heated to around 1200? C. in a furnace core tube containing chlorine gas, and dehydrated. Then the heater temperature was set to 1555? C. and helium gas was supplied at a volumetric flow rate of 33.0 L/min and the soot was heated while being moved at the lowering rate of 5.0 mm/min and vitrified into transparent glass, to obtain a core glass rod. No occurrence of an unmelted area was observed in a product effective part of this core glass rod. Then, the core glass rod was provided with a cladding externally and drawn to form an optical fiber. The transmission loss of the optical fiber obtained was not problematic. Note that the product of the helium gas linear speed 0.57 m/min and the heating time 60 min required for vitrification into transparent glass was 34.1 m.

[0018] In example 2, a glass fine particle deposit manufactured was heated to around 1200? C. in a furnace core tube containing a chlorine gas, and dehydrated. Then the heater temperature was set to 1555? C. and helium gas was supplied at the volumetric flow rate of 21.0 L/min and the soot was heated while being moved at the lowering rate of 5.0 mm/min and vitrified into transparent glass, and then a core glass rod was obtained. No occurrence of an unmelted area was observed in a product effective part of this core glass rod. Then, the core glass rod was provided with a cladding externally and drawn to form an optical fiber. The transmission loss of the optical fiber obtained was not problematic. Note that the product of the helium gas linear speed 0.36 m/min and the heating time 60 min required for vitrification into transparent glass was 21.7 m.

[0019] In example 3, a glass fine particle deposit manufactured was heated to around 1200? C. in a furnace core tube containing a chlorine gas, and dehydrated. Then the heater temperature was set to 1555? C. and helium gas was supplied at the volumetric flow rate of 17.0 L/min and the soot was heated while being moved at the lowering rate of 5.0 mm/min and vitrified into transparent glass, and then a core glass rod was obtained. No occurrence of an unmelted area was observed in a product effective part of this core glass rod. Then, the core glass rod was provided with a cladding externally and drawn to form an optical fiber. The transmission loss of the optical fiber obtained was not problematic.

Note that the product of the helium gas linear speed 0.29 m/min and the heating time 60 min required for vitrification into transparent glass was 17.6 m.

[0020] In example 4, a glass fine particle deposit manufactured was heated to around 1200? C. in a furnace core tube containing a chlorine gas, and dehydrated. Then the heater temperature was set to 1570? C. and helium gas was supplied at the volumetric flow rate of 21.0 L/min and the soot was heated while being moved at the lowering rate of 6.0 mm/min and vitrified into transparent glass, and then a core glass rod was obtained. No occurrence of an unmelted area was observed in a product effective part of this core glass rod. Then, the core glass rod was provided with a cladding externally and drawn to form an optical fiber. The transmission loss of the optical fiber obtained was not problematic. Note that the product of the helium gas linear speed 0.36 m/min and the heating time 50 min required for vitrification into transparent glass was 18.1 m.

[0021] In example 5, a glass fine particle deposit manufactured was heated to around 1200? C. in a furnace core tube containing a chlorine gas, and dehydrated. Then the heater temperature was set to 1605? C. and helium gas was supplied at the volumetric flow rate of 21.0 L/min and the soot was heated while being moved at the lowering rate of 7.0 mm/min and vitrified into transparent glass, and then a core glass rod was obtained. No occurrence of an unmelted area was observed in a product effective part of this core glass rod. Then, the core glass rod was provided with a cladding externally and drawn to form an optical fiber. The transmission loss of the optical fiber obtained was not problematic. Note that the product of the helium gas linear speed 0.36 m/min and the heating time 42.9 min required for vitrification into transparent glass was 15.5 m.

[0022] In the comparative example 1, a glass fine particle deposit manufactured was heated to around 1200? C. in a furnace core tube containing a chlorine gas, and dehydrated. Then the heater temperature was set to 1555? C. and helium gas was supplied at the volumetric flow rate of 6.3 L/min and the soot was heated while being moved at the lowering rate of 5.0 mm/min and vitrified into transparent glass, and then a core glass rod was obtained. No occurrence of an unmelted area was observed in a product effective part of this core glass rod. However, an optical fiber, obtained by providing a cladding externally to this core glass rod and being drawn, tended to show high values of a transmission loss, which was a maximum 0.302 dB/km at the wavelength 1383 nm of a transmitted light. Note that the product of the helium gas linear speed 0.11 m/min and the heating time 60.0 min required for vitrification into transparent glass was 6.5 m.

[0023] In the comparative example 2, a glass fine particle deposit manufactured was heated to around 1200? C. in a furnace core tube containing a chlorine gas, and dehydrated. Then the heater temperature was set to 1605? C. and helium gas was supplied at the volumetric flow rate of 21.0 L/min and the soot was heated while being moved at the lowering rate of 8.0 mm/min and vitrified into transparent glass, and then a core glass rod was obtained. Occurrence of unmelted areas was observed in a product effective part of this core glass rod. Then, the core glass rod was provided with a cladding externally and drawn to form an optical fiber. The transmission loss of the optical fiber obtained was not problematic. Note that the product of the helium gas linear speed 0.36 m/min and the heating time 37.5 min required for vitrification into transparent glass was 13.6 m. According to the examples, it is possible to obtain the glass preform that has fewer unmelted areas and of which the transmission loss is not problematic in the optical fiber after being drawn, while requiring as little processing time as possible for vitrification into transparent glass and reducing as much as possible the volumetric flow rate of the sintering gas supplied during the process of vitrification into transparent glass.

EXPLANATION OF REFERENCES

[0024] 1: sintering machine [0025] 2: axial bar [0026] 3: soot [0027] 4: furnace core tube [0028] 5: upper lid [0029] 6: heating furnace body [0030] 7: heater [0031] 8: thermal insulation material [0032] 9: temperature controller [0033] 10: sintering gas introduction conduit [0034] 11: exhaust conduit.