JPH05322699A - High distance-resolution optical transmission line measuring device - Google Patents

Abstract

PURPOSE:To achieve a high distance resolution by providing a ring resonator optical circuit in that a ring waveguide path which has the same loop length as light pulse length and where a gain medium is added and a frequency shifter are formed on a crystal substrate. CONSTITUTION:An optical pulse modulator 2 converts irradiation light of a coherence light source 1 to an optical pulse with a specified pulse length. A synthesizer 3 synthesizes an excitation light from a light source 8 for excitation and that from the modulator 2 and then transmits it to a ring resonator optical circuit 4. The circuit 4 has an optical waveguide 44 and a ring waveguide 45 which has the same loop length as the incidence light pulse length and where a gain medium is added, a directional coupler 46 which connects the optical waveguide 44 and the waveguide 45, and a frequency shifter 47 which is inserted halfway through the waveguide 45 for shifting the frequency of a passage light on a crystal substrate 41, thus enabling an output light to be an equivalent continuous light which changes stepwise. Also, the loop length can be equal to 0.01mm, thus achieving a high distance resolution. Also, light pulse loss can be compensated by the waveguide 45 and the shifter 47 and loss in the circuit 4 can reduced to 0.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention measures a reflected light and a backscattered light of an optical pulse incident on an optical transmission line, and a high distance used for identifying a break point or a failure point generated in the optical transmission line. The present invention relates to a resolution optical transmission line measuring device.

[0002]

2. Description of the Related Art In a conventional optical transmission line measuring apparatus for searching for a break point or a failure point occurring in an optical transmission line, an optical time domain reflectometry method (hereinafter referred to as OTDR) is used. O
TDR measures the reflection position from the time it takes for an optical pulse to enter the optical transmission line and the reflected light goes back and forth and returns, and measures the degree of obstacle from its intensity. It is around 100m. However, in a measurement test of an optical transmission line of an optical subscriber system having many branch points and connection points, a higher distance resolution of about 1 m to 0.1 m is required.

The improvement of the distance resolution of the OTDR is realized by narrowing the width of the incident optical pulse and widening the bandwidth of the receiving system. However, when the reflected light is at a low level, the photosensitivity is deteriorated due to the increase of noise accompanying the widening of the band, and it may be impossible to measure the reflection position and the degree of obstacle. For this reason, there has been a limit to the high-distance resolution of OTDR.

On the other hand, an optical frequency domain reflection method (hereinafter referred to as OFDR) has been proposed as a technique that enables high distance resolution. The OFDR sweeps the frequency of a coherent light source linearly with respect to time, demultiplexes it into a signal light and a reference light, makes the signal light incident on a measured optical transmission line, and combines the reflected light with the reference light. Then, heterodyne detection is performed. At this time, the frequency difference between the reflected light and the reference light is proportional to the optical path length difference between the two lights, so that the reflected position can be specified by measuring the reflected light intensity distribution in the frequency domain.

In this OFDR, the range resolution can be improved by narrowing the bandwidth of the receiving system.
By improving the minimum amount of received light by narrowing the bandwidth, it is possible to easily perform reflection measurement with high distance resolution.

[0006]

By the way, OFDR
Requires extremely high frequency sweep accuracy, and particularly requires linearity of frequency sweep. However, at present, there is no light source that meets the demand, and it has not been put to practical use as a measurement technique.

According to the present invention, it is possible to realize high range resolution.
It is an object of the present invention to provide a high-distance resolution optical transmission line measuring device that can be used for practical purposes by improving frequency sweep accuracy in FDR.

[0008]

According to the present invention, as an optical frequency sweeping means, an optical pulse generating means for converting the light emitted from a coherent light source into an optical pulse having a predetermined pulse length, and the same pulse length as the optical pulse are used. A ring waveguide having a loop length and added with a gain medium, and a frequency shifter for giving a predetermined frequency shift to passing light in the ring waveguide are formed on a quartz substrate, and the light from the optical pulse generating means is formed. A ring resonator optical circuit that makes a pulse incident on the ring waveguide and sends the output light to the optical branching means is provided, and excitation light is made incident on the ring resonator optical circuit to It is characterized in that a pumping light injection means for compensating for the loss is provided.

[0009]

In the ring resonator optical circuit, by making the loop length of the ring waveguide equal to the pulse length of the incident light pulse and giving a predetermined frequency shift by the frequency shifter, the frequency of the output light is changed on the time axis. Thus, an equivalent continuous light that changes stepwise with the shift frequency as a unit can be output, and can be output as an optical pulse with high frequency sweep accuracy.

The optical pulse output from this ring resonator optical circuit is demultiplexed into a signal light and a reference light, the signal light is made incident on the measured optical transmission line, and the reflected light from the reference light and the measured optical transmission line. When the reflection position is measured by heterodyne detection of the and backscattered light, the distance resolution of the pulse length of the optical pulse (loop waveguide loop length) can be obtained.

[0011]

1 is a block diagram showing the configuration of an embodiment of the present invention. In the figure, a coherent light source 1, an optical pulse modulator 2, a multiplexer 3, a ring resonator optical circuit 4, directional couplers 5 and 6, and a measured optical transmission line 7 are connected in series.
A pumping light source 8 is connected to the other input terminal of the multiplexer 3, and a heterodyne detector 9, a spectrum analyzer 10, and a signal processing device 11 are connected in series in a branch path from the directional couplers 5 and 6. Connected to.

The optical pulse modulator 2 is a coherent light source 1.
The emitted light is converted into an optical pulse having a predetermined pulse length. The multiplexer 3 multiplexes the pumping light emitted from the pumping light source 8 and the optical pulse emitted from the optical pulse modulator 2 and sends them to the ring resonator optical circuit 4.

The ring resonator optical circuit 4 has an optical waveguide 44 connecting an input port 42 and an output port 43 on a quartz substrate 41, a loop length equal to the pulse length of an incident optical pulse, and A ring waveguide 45 to which rare earth (for example, erhium) ions are added as a gain medium, and an optical waveguide 4.
4 and the ring waveguide 45 are coupled to each other by a directional coupler 46.
And a frequency shifter 47 that is inserted in the middle of the ring waveguide 45 and shifts the frequency of the passing light in units of F [Hz]. As the frequency shifter 47,
An acousto-optic device, an optical phase modulator, etc. can be used.

Here, the loop length of the ring waveguide 45 is made equal to the pulse length of the incident light pulse, and the frequency shifter 4
By applying a frequency shift of F [Hz] at 7, the frequency of the output light of the ring resonator optical circuit 4 changes stepwise in units of F [Hz] on the time axis as shown in FIG. It may be equivalent continuous light. By forming the ring waveguide 45 on the quartz substrate 41, the loop length can be set to 0.1 m or less.

Further, by the amplifying action of the pumping light injected into the ring resonator optical circuit 4, it is possible to compensate the loss of the optical pulse generated by passing through the ring waveguide 45 and the frequency shifter 47. The loss in the resonator optical circuit 4 can be effectively reduced to zero.

The directional coupler 5 is a ring resonator optical circuit 4
The output light of 1 is split into a signal light and a reference light, the signal light is sent out to the measured light transmission line 7 through the directional coupler 6, and the reference light is sent out to the heterodyne detector 9.

The directional coupler 6 sends out the signal light to the measured optical transmission line 7 and branches the reflected light and the backscattered light from the measured optical transmission line 7 to the heterodyne detector 9.

The heterodyne detector 9 is a directional coupler 5.
The reflected light and the backscattered light input from the directional coupler 6 are coherently detected using the reference light input from the local oscillation light as local oscillation light, and the detected signal is sent to the spectrum analyzer 10 as an electric signal. The spectrum analyzer 10
The frequency of the detection signal in the heterodyne detector 9 is analyzed. The signal processing device 11 averages and adds the measured values to improve the signal-to-noise ratio.

Information for specifying the reflection position of the signal light incident on the optical transmission line 7 to be measured is generated based on the configuration described above. The frequency of the output light of the ring resonator optical circuit 4 is
In principle, since the frequency is swept with extremely high accuracy,
It is possible to solve the nonlinearity of the frequency sweep, which has been a problem in the conventional OFDR.

Further, by using the ring resonator optical circuit 4 whose main component is the ring waveguide 45 formed on the quartz substrate 41, instead of the resonator optical circuit using the optical fiber, the loop length is 0.1 m or less. Can be set, and can be a discrete step size related to the distance.
This means that the frequency difference between the reflected light and the reference light changes in units of F [Hz] every time the reflection position of the reflected light changes by 0.1 m, which corresponds to a distance resolution of 0.1 m. .. That is, the distance resolution can be dramatically improved.

[0021]

As described above, according to the present invention, it is possible to obtain the distance resolution corresponding to the loop length of the ring waveguide constituting the ring resonator optical circuit, but the ring waveguide is formed on the quartz substrate. Therefore, the loop length can be set to 0.1 m or less, and high range resolution can be easily achieved in OFDR.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.

FIG. 2 is a diagram showing frequency time dependence of an optical pulse.

[Explanation of symbols]

 1 Coherent light source 2 Optical pulse modulator 3 Multiplexer 4 Ring resonator Optical circuit 5, 6 Directional coupler 7 Optical transmission line under test 8 Excitation light source 9 Heterodyne detector 10 Spectrum analyzer 11 Signal processor 41 Quartz substrate 42 input port 43 output port 44 optical waveguide 45 ring waveguide 46 directional coupler 47 frequency shifter

Claims (1)

[Claims] 1. An optical frequency sweeping means for frequency-sweeping an output light of a coherent light source on a time axis and outputting the output light, the output light being demultiplexed into a signal light and a reference light, and the signal light being sent to a measured optical transmission line. Incident, optical branching means for branching and outputting reflected light and back scattered light emitted from the reference light and the measured light transmission path, the reference light as local oscillation light, heterodyne detection of the reflected light and back scattered light, In an optical transmission line measuring device provided with a measuring unit that specifies a reflection position of the measured optical transmission line by frequency analysis and predetermined signal processing, the optical frequency sweeping unit emits light from a coherent light source to a predetermined pulse length. An optical pulse generating means for converting the optical pulse to a light pulse, a ring waveguide having a loop length the same as the pulse length of the optical pulse and having a gain medium added thereto, and a predetermined pass light in the ring waveguide. A ring resonator optical circuit for forming a frequency shifter for giving a frequency shift on a quartz substrate, inputting an optical pulse from the optical pulse generating means to a ring waveguide, and sending the output light to the optical branching means. And a pumping light injection means for compensating for a loss of an optical pulse in the ring resonator optical circuit by injecting pumping light into the ring resonator optical circuit. measuring device.