JPS62115340A - Loss measuring method for optical fiber - Google Patents

Abstract

PURPOSE:To speed up and simplify measuring operation while reducing the influence of an error due to temperature variation by shortening the time of each wavelength sweep by employing a multi-sampling system which uses a fast wavelength sweep type spectroscope. CONSTITUTION:Light having a continuous wavelength spectrum is projected from a continuous wavelength light source 8. This light is wavelength-swept by the fast wavelength sweep type spectroscope 9 at a high speed, light passed through the spectroscope 9 is coupled with one end of an optical fiber 10 to be measured, and light projected from the other end of the optical fiber 10 is coupled with a photodetector 11. A sampling device 13 begins to operate on the basis of a wavelength sweep start signal sent by the spectroscope 9, which sends out a wavelength marker signal to the device 13 the moment indicated wavelength coincides with wavelength to be measured. An electric signal obtained from a photodetector 11 is sampled at a high speed in a synchronism with the marker signal and electric signal outputs at respective sampling points are read in by an integral processor 14 and integrated to measure the loss of the optical fiber.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for quickly and easily measuring loss wavelength characteristics of an optical fiber.

(Prior Art) Conventionally, a measuring device as shown in FIG. 3 has been used to measure the loss wavelength characteristics of an optical fiber.

In Fig. 3, 1 is a light source with uniform spectral intensity in the measurement wavelength region, 2 is a spectrometer for dispersing and monochromating light 8!1, and 3 is a constant output light from spectrometer 2. 4 is an optical fiber to be measured; 5 is a photodetector for detecting the output light of the optical fiber; 6 is only a signal of a frequency component equal to the frequency of chopper 3 among the signals of the photodetector; A lock-in amplifier that selectively amplifies the
is a control device that controls the wavelength of the output light from the spectrometer 2, reads the signal from the amplifier 6, and calculates the loss wavelength characteristics of the fiber under test 4.

In the conventional measurement method, the wavelength of the light emitted from the spectrometer 2 is set to one wavelength within the wavelength range to be measured, and the output of the amplifier 6 in this case is read. The wavelength characteristics of the intensity of the emitted light from the optical fiber 4 to be measured are determined by executing the measurement while changing the wavelength characteristics sequentially at intervals.

On the other hand, the important wavelength in normal optical fiber is 1 to 2 μm.
In loss measurement, a halogen lamp is generally used as the light source 1, but in this case, the light intensity reaching the photodetector 5 via the optical fiber 4 to be measured is weak, so the optical chopper 3 and the lock-in amplifier 6 are used. It is necessary to improve the signal-to-noise ratio in measurements by using However, the measurement method using such a lock-in amplification method has the disadvantage that several seconds are required to measure each wavelength, so the entire measurement requires several minutes or more. Furthermore, since measurement takes time, measurement errors are likely to occur due to fluctuations in the intensity of the light source and fluctuations in the sensitivity of the photodetector due to changes in ambient temperature.

(Problems to be Solved by the Invention) An object of the present invention is to provide a simple optical fiber loss measurement method that shortens the time required for measurement and reduces the influence of errors due to temperature fluctuations during measurement.

(Means for Solving the Problems) The present invention does not use a lock-in amplification method, but sweeps the wavelength of light having a continuous wavelength spectrum emitted from a light source at high speed using a spectrometer, and A marker signal tuned to the indicated wavelength is emitted, and the electrical signal obtained from the photodetector via the spectrometer and the optical fiber to be measured is synchronized with the marker signal emitted from the spectrometer using a sampling device to perform high-speed sampling and integration processing. The device reads the electrical signal output at each sampling point and performs an integral process to measure the loss in the optical fiber.

FIG. 1 is a diagram showing an embodiment of the present invention, in which 8 is a continuous wavelength light source, 9 is a high-speed wavelength sweep valve that can sweep the entire measurement wavelength range within approximately a few seconds, and 10 is an object to be measured. 11 is a photodetector; 12 is a DC amplifier for amplifying the photodetector signal; 13 is a sampling device that samples the photodetector signal in synchronization with the wavelength marker signal of the spectrometer 9; 14 is an optical fiber; This is an integral processing device that reads the electrical signal output at each sampling point and performs integral processing.

FIG. 2 is a timing chart of measurements according to the present invention. (A) is a diagram showing the relationship between the wavelength sweep start signal of the spectrometer and the wavelength marker signal in one wavelength sweep, and <8) is (
A> is enlarged in the time domain and shows the relationship between the wavelength marker signal and the sampling signal, where a is the output signal waveform of the photodetector, b is the wavelength sweep start signal of the spectrometer, and C is the wavelength sweep start signal of the spectrometer. The wavelength marker signal, d, represents the sampling signal of the sampling device.

As is clear from FIGS. 1 and 2, in the measurement method of the present invention, the spectrometer 9 first issues a wavelength sweep start signal to the sampling device 13, and based on this, the sampling device 13 starts operating. .

At the moment when the wavelength indicated by the spectrometer 9 matches the wavelength to be measured, the wavelength marker signal C is sent from the spectrometer 9 to the sampling device 13.

Normally, this wavelength marker signal C is sent out at equal intervals with respect to the wavelength, at wavelength intervals of several nm. Upon receiving the wavelength marker signal C, the sampling device 13 immediately emits a sampling signal d and starts sampling the detector signal. This sampling operation is continued until just before the next wavelength marker signal is transmitted to the sampling circuit, and the detector output at that wavelength is determined by averaging the detector outputs sampled during that time. By employing such an averaging method, it is possible to reduce the noise component of the output signal of the detector. It is also possible to roughly reduce the noise component by sweeping the spectrometer twice or more and averaging the measurement results.

In the measurement method of the present invention, the time required to sweep within the measurement wavelength range is within several seconds, making it possible to dramatically shorten the time compared to conventional methods. Therefore, it is possible to extremely reduce measurement errors due to fluctuations in the ambient temperature of the measurement system.

In the measurement method of the present invention, when wavelength sweep is performed two or more times to improve measurement accuracy, the time required for measurement increases by the number of times the measurement is performed. Although errors may occur, the fluctuations during one sweep are very small, so such errors do not have wavelength dependence.

Generally, when evaluating the measurement results of the loss wavelength characteristics of optical fibers, it is customary to correct errors that are not wavelength-dependent, so errors that are not wavelength-dependent pose a practical problem. It's not a thing.

(Effects of the Invention) As explained above, the measurement method of the present invention employs a multi-sampling method using a high-speed wavelength sweep type bulb instead of the conventionally used lock-in amplification. This has the advantage of shortening the wavelength sweep time per time during measurement, reducing the influence of errors due to temperature fluctuations during measurement, and achieving faster and simpler measurement.

[Brief explanation of drawings]

FIG. 1 is an embodiment of the present invention, and FIG. 2 is a timing chart of measurement according to the present invention.
A> is a diagram showing the relationship between the wavelength sweep start signal of the spectrometer and the wavelength marker signal in one wavelength sweep, (B) is a diagram showing the relationship between the wavelength marker signal and (A)
FIG. 3 is a diagram showing the relationship between the wavelength marker signal and the sampling signal when expanded in the time domain. FIG. 3 is a side view of the configuration of a conventional optical fiber loss measuring device. 1... Continuous wavelength light source 2... Spectroscope 3... Optical chopper 4... Optical fiber to be measured 5... Photodetector 6... Lock-in amplifier 7...
Control device 8... Continuous wavelength light source 9... High speed wavelength sweep valve light device 10... Optical fiber to be measured 11... Photodetector 12
... DC amplifier 13 ... Sampling device 14 ... Integral processing device a ... Output signal waveform of photodetector b ... Spectrometer wavelength sweep start signal C ... Spectrometer wavelength marker signal d... Sampling signal of sampling device Fig. 2 (A) Time Time

Claims (1)

[Claims] 1. Emit light with a continuous wavelength spectrum from a light source, sweep the wavelength of the light at high speed with a spectrometer, emit a marker signal tuned to the indicated wavelength at each moment, and emit light that passes through the spectrometer. is coupled to one end of the optical fiber to be measured, the light emitted from the other end of the optical fiber is coupled to a photodetector, and the electrical signal obtained from the photodetector is converted into a marker signal emitted from the spectrometer using a sampling device. A method for measuring loss in an optical fiber, characterized by performing high-speed sampling in synchronization with , reading the electrical signal output at each sampling point with an integral processing device, and performing integral processing to measure the loss in the optical fiber.