JPS59220625A - Method and apparatus for measuring transmission characteristic of optical fiber during production - Google Patents

Abstract

PURPOSE:To measure transmission characteristic of an optical fiber accurately in a non-destructive and continuous manner by irradiating a strong light from the side of an optical fiber after drawn from a matrix rod to excite a measuring light therein so that a propagated light is measured at the winding end thereof. CONSTITUTION:A demodulated output light of a light source 31 driven in modulation with a controlling signal generator 37 irradiates a bare fiber 1a from the side thereof. A Rayleigh scattered light with the wavelength the same as that lambda of the irradiation light is excited within the optical fiber 1a. The scatter angle of the Rayleigh scattered light covers the every bearing but the portion thereof only within the propagation angle propagates along the length thereof. The portion of the measuring scattered light propagating to the winding end thereof is connected direct to the end of an optical fiber 1 and received with a photoelectric converter 33 fixed on a winding drum 7. The electrical signal wave converted is introduced to a receiver 35 through a rotary connector 34 and processed with a signal analyzer 36. Thus, in the production and drawing process, the light transmission characteristic can be inspected and measured accurately online in a non-destructive and continuous manner.

Description

[Detailed Description of the Invention] [Technical Field to Which the Invention Pertains] The present invention is a method for inspecting and measuring optical transmission characteristics such as optical loss and frequency characteristics of a long communication optical fiber during the optical fiber manufacturing process. It is about the method.

[Description of prior art]

As optical transmission characteristics of an optical fiber, optical loss characteristics and baseband frequency characteristics are important, and the quality of the optical fiber is ultimately evaluated based on these characteristics.

Conventionally, as shown in FIG. 1, the method of measuring this optical transmission characteristic is to connect an excitation fiber 11 to an optical fiber 1,
A system is used in which a measuring optical signal is sent out from the optical fiber 2, the optical signal propagated through the optical fiber is detected by the photodetector 15, and is received by the receiver 16. The light source 12 and receiver 16 are controlled by a control oscillator 17. In the cut-puncture method, which is most commonly used to obtain optical loss, the amount of propagated light is measured at the receiving end of the optical fiber 1, and then the fiber is cut at the zero point on the sending end side, and the amounts of light are measured and compared. Although this method has good accuracy, it is a destructive method, and 1
Each time one piece of data is obtained, it is necessary to connect and disconnect the excitation optical fiber 11 and the optical fiber 1 to be measured, which is a complicated work.

As a method different from this, a laser pulse is sent out from the light source 12, and the backscattered light excited in the optical fiber 1 is received at the sending end side, and from the rate of change of the amount of received light with respect to the fiber length,
There is a backscatter method to determine optical loss. Although this method has the advantage of being a non-destructive method, it requires advanced optical circuit technology such as using an optical directional coupler to separate the reflected wave and the backscattered wave of the transmitted pulse, and it also requires two fiber lengths.
The measurement length is limited because the loss is measured for twice the length.

Conventional measurement methods such as these examples are performed completely separately from the drawing process that is used to manufacture optical fibers, and the measurements require a great deal of labor, which increases the price of optical fibers. This is a contributing factor.

Conventionally, it has been desired to measure transmission characteristics in order to monitor whether or not an optical fiber is being manufactured correctly during manufacturing in a drawing process as shown in FIG. However, a method to measure it online has not yet been realized. - As a proposal, the propagation component of the light emitted when the base material rod 2 is heated in the heating furnace 3 is detected from the side of the optical fiber wound on the winding drum 7, and the detected light is A method of looking at the rate of change is given.

However, this method cannot modulate the propagating light with the required signal, so it can only be used to monitor the presence or absence of breaks in the optical fiber.
It is not possible to evaluate the performance of optical fibers during manufacture.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a measurement method and apparatus that nondestructively and continuously accurately measure the transmission characteristics of an optical fiber that is in the process of being manufactured during a drawing process.

[Features of the invention]

The present invention irradiates strong light from the side of the optical fiber after it has been drawn from a base material rod to excite measurement light within the optical fiber, and the measurement light is emitted at the wound end of the optical fiber. It is characterized by measuring the propagated light.

As the measurement light, the Ray scattered light of the irradiated light can be used. Further, as the measurement light, Raman scattered light of the irradiated light can be used.

[Explanation based on examples]

FIG. 3 is a block diagram of a method and apparatus according to a first embodiment of the present invention. The end of the base material rod 2 is heated in a heating furnace 3, and the hardened portion is drawn into an optical fiber by a known method. The optical fiber 1 is passed through a resin 4 to form a protective resin layer on its surface, and further passed through a resin curing furnace 5 to harden this resin layer. This optical fiber 1 is controlled by the rotation of the capstan 6 and is wound around a winding drum 7.

Here, the feature of the present invention is that the powerful light source 31 (
In this example, the output light of a semiconductor laser (using a semiconductor laser) is irradiated onto the optical fiber 1a that has just been drawn and has not yet formed the resin layer, thereby exciting measurement light within the optical fiber 1a. . Further, a photoelectric converter 33 is connected to the winding end of the optical fiber 1 wound on the winding drum 7, and a photoelectric converter 33 is connected to the winding end to convert the light emitted from the optical fiber 1 into an electric signal. be. This electrical signal is transmitted to a rotary connector 34 provided on the rotating shaft of the winding drum 7.
The signal is input to the receiver 35 via the . The output of this receiver 35 is given to a signal analyzer 36. The light source 31 and receiver 35 are controlled by one control signal generator 37.

To explain the operation of the system configured in this way, the modulated output light of the light source 31 modulated and driven by the control signal generator 37 is irradiated from the side to the bare fiber 1a immediately after being drawn. As a result, as shown in FIG. 4, Rayleigh scattered light having the same wavelength as the wavelength λ of the irradiated light is excited into the optical fiber la. Although the scattering angle of this Raman scattered light covers all directions, only the components within the propagation angle remain in the optical fiber and propagate in the long direction within the optical fiber 1. Therefore, the angle of incidence of the irradiation light onto the optical fiber 1a may be set arbitrarily.

In order to increase the excitation efficiency, it is also possible to install a reflecting mirror around the optical fiber 1a and irradiate the optical fiber 1a with the irradiation light many times. A photoelectric converter 33 receives a component of this measurement scattered light that propagates to the winding end. For example, since the photoelectric converter 33 made of an APD is small and lightweight, it can be directly connected to the end of the optical fiber 1 and fixed to the winding drum 7. The signal wave converted into an electric signal is guided to a receiver 35 via a low-reflection connector 34, and is processed by a signal analyzer 36 to obtain optical loss or Haesnod frequency characteristics.

When the transmitted signal waveform is a pulse, a pulse waveform similar to that of the received signal as shown in FIG. 5 can be obtained. In this case, the base level is defined by the propagation component of the light emitted when the base metal mouth/nod 2 is heated in the heating furnace 3.
Since this is a constant level within the measurement time slot of the signal pulse, the output of the signal generator 32 causes the receiver 35 to
Separation and identification can be performed by synchronously detecting the signals, or by using techniques such as synchronous detection, filtering, bias method, and averaging.

FIG. 6 shows the change in the light reception level (in dB) of the photoelectric converter 33 with respect to the fiber length in the drawing process in the above system. That is, as the length of the optical fiber 1 increases with manufacturing, the light reception level decreases.

The rate of change A/i! This allows us to know the optical loss in any section of the fiber. Furthermore, if a sinusoidal modulation signal is used and the relationship shown in Fig. 6 is applied to each frequency component,
Haasband frequency characteristics can be measured. When pulsed light is used as measurement light, this amount of light is observed as a change in the waveform of the received light signal. Although the total length of the optical fiber to be drawn is several tens of kilometers, the optical signal can be detected to a measurable extent by averaging weak signal detection technology using pulsed light.

Next, a second embodiment of the measuring method and apparatus of the present invention will be explained by developing the above method with reference to FIG.

In this example, a plurality of light sources 31a to 31d having different wavelengths are arranged in accordance with the wavelength range in which the optical fiber is used, and irradiate light simultaneously from the side of the bare optical fiber 1a. As a result, Rayleigh scattered light having different wavelengths of λ1 to λ4 is excited and propagated within the optical fiber 1. At the winding end, the light of each wavelength is separated by a demultiplexer 71, and each wavelength is separated into separate photoelectric converters 33a.
This is detected by ~33d. The electrical signal obtained as this output is guided to the receiver 35 via the multi-channel low-reconnector 72, and data processed by the signal analyzer 36.

In this system, by applying the relationship explained in FIG. 6 to the signals of each wavelength, it is possible to measure on-line the optical loss wavelength characteristic peculiar to the optical fiber as shown in FIG. 8.

The method of exciting the Rayleigh scattered light by irradiating light from the side of a bare optical fiber is extremely simple.

Furthermore, since the mechanical precision of the side surface of the optical fiber 1a is extremely high, the excitation level can be maintained with high stability. Therefore, changes in the received signal due to changes in the optical fiber length due to manufacturing can be accurately captured. The method of measuring from the rate of change in the signal with respect to the change in fiber length has the advantage of being non-destructive and maintaining high measurement accuracy compared to conventional methods in which the fiber length is fixed.

In the above explanation, it is assumed that the measurement light is irradiated onto the bare fiber 18, but if the coating is thin and almost uniform, the measurement light may be applied to the bare fiber 18 after passing through the resin curing furnace 5. It is also possible to irradiate the area over the coating. In this case as well, the configuration of the receiving system, data processing method, etc. are the same as described above.

Next, if a high-power semiconductor laser or the like is used as a light source,
As shown in FIG. 9, it is well known that Ley scattered light having the same wavelength as the wavelength λ0 of the irradiated light and several types of Raman scattered light having different wavelengths are excited into the fiber Ia. In particular, Raman scattered light (Stokes lines) with a specific wavelength is likely to be excited by doping elements such as germanium in the core and a of the fiber. Although the scattering angle of the scattered light covers all directions, only the components within the propagation angle remain in the fiber and propagate in the long direction within the optical fiber 1.

Therefore, the angle of incidence of the irradiation light onto the fiber may be set arbitrarily. In order to increase this excitation efficiency, it is also possible to use a method in which a reflecting mirror is installed around the fiber and the fiber is irradiated with irradiation light many times. The component of this measurement scattered light propagating to the end of the winding is first separated by a demultiplexer 71 into each Stokes line by a detector having the same configuration as in FIG. 7, and then detected by separate photoelectric converters 33a to 33d. The only difference from FIG. 7 is that only one light source 31 for excitation is required.

In the above system, the change in light reception level (in dB) with respect to the fiber length in the drawing process is shown in FIG. 6 for the Stokes lines of each wavelength. The optical loss in any section of the fiber can be measured by the rate of change Δ/β. Also, using a sine wave modulation signal, the sixth
By applying the relationship shown in the figure, the baseband frequency characteristics at each wavelength can be measured. The total length of the optical fiber to be drawn is several tens of kilometers, which can be measured using a weak signal detection technique using averaging. With this method, it becomes possible to measure on-line the optical loss wavelength characteristic peculiar to an optical fiber as shown in FIG. 8 as well.

In this case, the Stokes lines λ′, λ″, λ″′ are λ2,
λ3, λ4. λ0 corresponds to λ1.

Next, the fourth embodiment of the present invention, which is a development of the above method, will be described in the 10th embodiment.
This will be explained using figures. A plurality of light sources 31a to 31d with significantly different wavelengths are arranged according to the wavelength range of the optical fiber used,
These are simultaneously irradiated from the sides of the bare optical fiber 1a. Raman scattered light based on each wavelength is excited in the optical fiber 1a.

As a result, measurement light including a large number of Stokes lines over a wide range of wavelengths is propagated within the optical fiber 1, and at the winding end, the splitter 71 is used to receive the measurement light in a wide range of wavelengths. It is possible to measure optical transmission characteristics across the range.

If the wide wavelength range demultiplexer 71 is too large to be fixed to the winding drum 7, as shown in FIG.
The duplexer 71 can be configured to be installed separately from the winding drum 7.

The method of exciting Raman scattered light for measurement with light irradiated from the side of the fiber is extremely simple.

Furthermore, the extremely high precision of the fiber sidewalls allows the excitation level to be maintained with high stability.

Therefore, changes in the received signal due to changes in fiber length can be accurately captured. The method of measuring from the rate of change in the signal with respect to the change in fiber length has the advantage of being non-destructive and maintaining measurement accuracy, compared to conventional methods in which the fiber length is fixed.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to nondestructively, continuously, and accurately inspect and measure optical transmission characteristics online during the production and drawing process of optical fibers. It is possible to significantly reduce the cost of inspecting fiber transmission characteristics, which has traditionally occupied a large portion of the cost. Also,
The configuration of the present invention does not require high training accuracy, is simple, and can be used to simultaneously measure a wide wavelength range, so it is expected to be used for further development. According to the invention,
It is possible to measure all of the various types of data required regarding the transmission characteristics of fibers only during the drawing process. As described above, the present invention has great effects in simplifying optical fiber measurement technology and reducing the cost of optical fibers, and contributes to economicalization of optical communications.

[Brief explanation of drawings]

FIG. F is a configuration diagram of a conventional off-line optical transmission measurement. FIG. 2 is an explanatory diagram of the optical fiber drawing process. FIG. 3 is a block diagram of the optical transmission characteristic method and apparatus according to the first embodiment of the present invention. FIG. 4 is a diagram showing Leh scattered light excitation due to light irradiation from the side of the optical fiber. FIG. 5 is a diagram showing an example of a received light waveform. FIG. 6 is a diagram illustrating measurement from the rate of change of the received light level with respect to the fiber length. FIG. 7 is a block diagram of a method and apparatus according to a second embodiment of the present invention, which uses a plurality of lights of different wavelengths. FIG. 8 is a diagram illustrating optical loss wavelength characteristics. FIG. 9 is a diagram showing Raman scattered light excitation due to light irradiation from the side of the optical fiber. FIG. DESCRIPTION OF SYMBOLS 1... Optical fiber, 2... Base material rod, 3... Heating furnace, 4... Resin, 5... Resin curing furnace, 6... Capstan, 7... Winding drum, 11... Excitation fiber, 12... Light source, 13... Signal generator,
15... Photodetector, 16... Receiver, 3I... Light source, 33... Photoelectric converter, 34... Low reconnector, 35... Receiver, 36... Signal analysis device, 37
... Control signal generator, 41... Optical low reconnector, 51... Reception pulse, 71... Duplexer,
72...Multi-channel rotary connector. Hi 3 Figures 1 Child 4 times Child 6th 7th Figure Now wavelength helmet 8 En

Claims (6)

[Claims] (1) Optical fiber transmission performed during a continuous optical fiber manufacturing process in which one end of the base metal rond is heated, an optical fiber is drawn from the base metal rond, and the drawn optical fiber is wound. Characteristic measurement method G includes a method of irradiating at least one excitation light from the side of the optical fiber after drawing to excite measurement light into the optical fiber; A method for measuring transmission characteristics of an optical fiber during manufacture, comprising: measuring light propagated through the optical fiber at a wound end of the optical fiber. (2) The measuring method includes a method of observing the amount of light appearing at the wound end of the optical fiber or the rate of change in the waveform as the length of the optical fiber increases during manufacture. The method for measuring transmission characteristics of an optical fiber under manufacture as described in (1). (3) A method for measuring transmission characteristics of an optical fiber under manufacture according to claim (1), wherein the excitation method includes a method of exciting Leh scattered light as the measurement light. (4) The method of excitation includes a method of exciting measurement light of multiple wavelengths using multiple light sources with different wavelengths, and the method of measurement includes a method of performing spectroscopy for each wavelength. A method for measuring transmission characteristics of an optical fiber during manufacture according to claim (3). (5) The excitation method includes a method of exciting several types of Stokes lines with different wavelengths using a high-power excitation light source, and the measurement method includes spectroscopy of each Stokes line. A method for measuring transmission characteristics of an optical fiber under manufacture according to claim (1), including a method for measuring. (6) means for exciting measurement light into the optical fiber from the side of the optical fiber after being drawn from the base material rod; and within the optical fiber that has been continuously drawn and wound from the base material rod. and means for measuring light excited by the measurement light, propagating within the optical fiber, and appearing at the wound end of the optical fiber.