JP2567164Y2 - Optical module and optical fiber fault point detector using the same - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION The present invention is applied to an optical modulator, an optical switch, an optical frequency shifter, and the like, and relates to an optical module using an acousto-optic modulator.

[0002]

2. Description of the Related Art FIG. 4 shows a conventional optical module of this kind. That is, the optical module 11 is an acousto-optic modulator 1
And an acousto-optic modulator 12 comprising an acousto-optic element 13 and an electro-acoustic transducer 14 for injecting acoustic waves into the acousto-optic element 13.
5 can control the application of the high-frequency electric signal.
A light beam can be incident on the acousto-optic element 13 from the first port 16, and a light beam can be incident on the acousto-optic element 13 from the second port 17 at an angle different from that of the light beam from the first port 16. Acousto-optic element 1
The light beam emitted from 3 can be emitted to the third port 18.

The incident light beam 19 from the first port 16 to the acousto-optic element 13 and the outgoing light beam 21 to the third port 18 are on the same straight line, that is, no high-frequency acoustic signal is incident on the acousto-optic element 13. In this state, the incident light beam 19 becomes the outgoing light beam 21. In a state where a high-frequency acoustic signal is incident on the acousto-optic element 13,
The light is diffracted in the inside and the incident light beam 2 from the second port 17
2 becomes the output light beam 21.

Accordingly, the high-frequency acoustic signal is transmitted to the acousto-optical element 13.
Can be used as an optical switch depending on whether or not it is applied, and because the intensity of the diffracted light changes according to the intensity of the high-frequency acoustic signal, it can be used as an optical modulator,
Further, since the wavelength of the diffracted light shifts corresponding to the frequency of the high-frequency acoustic signal, it can be used as an optical frequency shifter.

[0005] With respect to the incident angle θ of the light beam 22 with respect to the acousto-optic element 13, the diffraction angle 2θ is λf / v (λ: acousto-optic
Wavelength of light in element 13 , f: frequency of high-frequency acoustic signal,
v: the velocity of the acoustic wave in the acousto-optic element 13 ), the diffraction efficiency becomes maximum. Further, as shown in FIG. 5, the incident angle θ has a polarization dependence, and the incident angle θ is selected so that the polarization dependence becomes as small as possible, that is, the diffraction efficiencies of both polarized lights coincide. The third port 18 may be used as an input port, and the first and second ports 16 and 17 may be used as output ports.

[0006]

Conventionally, in order to reduce the polarization dependence of the optical module 11, for example, the optical module 11 is required to have a.
In order to make the incident angle θ less than or equal to 05 dB, it is necessary to finely adjust the incident angle θ with high accuracy, for example, with an accuracy of about 0.1 mrad.
Such fine angle adjustment has been difficult. For example, an optical switch used for an optical fiber fault point detector cannot detect correctly unless the polarization dependence is less than 0.05 dB.

[0007] The polarization dependence changes depending on the wavelength of light. On the other hand, the wavelength of the laser diode is usually ± 0.02μ.
There is a variation of about m, which is affected by this variation. In particular, two wavelengths (for example, 1.31 μm and 1.55 μm)
m), there is a difference of about 1 mrad in the incident angle at which the polarization dependence is minimum for both wavelengths, as shown in FIG. When the incident angle is matched with the above, the other has a large polarization dependence of about 0.2 to 0.3 dB .

[0008]

An optical module according to claim 1 wherein :
Light from different wavelengths incident at the same angle of incidence,
Light using an acousto-optic modulator modulated by a high-frequency modulated wave
The polarization dependence of diffraction efficiency in
According to the above wavelength, the oscillation frequency of the high-frequency modulator
The number is variable. The optical fiber failure detector according to claim 2 is
The incident light from the optical pulse generator is
Modulated at the high frequency of
Optical module that outputs backscattered light from the fiber to the light receiving unit
Module and an electric signal from the light receiving unit,
A display for displaying the state of the scattered light;
An air signal is input and the polarization dependence of the backscattered light is evaluated
Polarization dependence monitor and the polarization dependence monitor
Value output data so that the polarization dependence is reduced.
And the high-frequency oscillator whose serial RF frequency is controlled, the ingredients
Be prepared.

[0009]

FIG. 1 shows an embodiment of the present invention, in which parts corresponding to those in FIG. 3 are denoted by the same reference numerals. In this invention, a variable frequency high frequency oscillator 23 is provided, and a high frequency signal from the high frequency oscillator 23 can be applied to the electroacoustic transducer 14.

[0010] Figure 2 A, as indicated by the measured data of B, for example, the case where the wavelength of the light beam is 1.31 .mu.m, the frequency of the high frequency signal applied to the electroacoustic transducer 14 9
3.5MHz (Fig. 2A) to 90.5MHz (Fig. 2B)
Changes the characteristic of the polarization-dependent incident angle to the smaller θ along the θ axis (from about 17 mrad).
About 16 mrad). On the other hand, two wavelengths, for example when using a 1.31μm and 1.55 .mu.m, from the viewpoint of maximizing the diffraction efficiency, the frequency of the high-frequency signal as shown in Figure 5 was 80MHz respectively and 93.5MHz
In this case, the incident angles are about 16 mrad and about 17 mr, respectively.
ad is preferable. But waves from the same port
Changing the angle of incidence for incident light of different lengths is
Since it is impossible at present, the incident angle is fixed (for example, about 16 mrad).
), So that one incident light (for example, 1.31 μm)
On the other hand, as shown in FIG.
B gets worse. Therefore, as shown in FIG. 2B, the wavelength is 1.3.
In the case of 1 μm, assuming that the frequency of the high-frequency signal is 90.5 MHz, the incident angle θ of the minimum polarization dependence is 1.55 μm.
m (the frequency of the high-frequency signal is 80 MHz). Therefore, for both wavelengths, at the same angle of incidence,
The polarization dependence can be reduced to 0.05 dB or less. Note that, as described above, one incident light (for example, 1.31 μm)
Shift the frequency of the corresponding high-frequency signal (for example, 3 MHz)
Therefore, if the polarization dependence is minimized at both wavelengths , the incident angle is shifted from the incident angle at which the diffraction efficiency is maximum, but this level difference is about 0.2 to 0.3 dB. Can be more easily cleaned.

Further, as in the example for the wavelength of 1.31 μm, if the incident angle of the same wavelength deviates from the minimum value of the polarization dependence, the frequency dependence of the high-frequency signal is adjusted to sufficiently increase the polarization dependence. Can be smaller. In this example, the frequency of the high-frequency signal was changed by about 3 MHz in order to adjust the incident angle θ by about 1 mrad. Therefore, in order to make the polarization dependence 0.05 dB or less, 0.1
In order to adjust the incident angle θ with mrad accuracy, the frequency of the high-frequency signal may be adjusted with an accuracy of 300 kHz, and the frequency of the high-frequency signal is significantly easier to adjust than in the case of directly mechanically adjusting the incident angle θ. Can be done.

If the wavelength of the laser diode used changes due to a change in the ambient temperature, or the optical axis, that is, the incident angle θ changes, and the polarization dependence deviates from a required range, the output signal frequency of the high-frequency oscillator 23 is changed. The polarization dependency can be adjusted to a predetermined value or less. When the required polarization dependence is 0.05 dB or less and the wavelength is 1.31 μm, the frequency range of the high-frequency signal having the polarization dependence of 0.05 dB or less is 3.6 MHz, and when the wavelength is 1.55 μm, the frequency range is 4 MHz. .
6 MHz, as long as the frequency of the high-frequency signal can be set with an accuracy of about 1.0%.

FIG. 3 shows an example in which the optical module 11 of the present invention is applied to an optical fiber fault point detector as an optical switch.
Shown in The light pulse from the light pulse generator 24 enters the optical module 11 of the present invention, and the light pulse enters one end of the optical fiber 25. The backscattered light from the optical fiber 25 returns to the optical module 11 and is converted into an electric signal and amplified by the light receiving unit 26, and its output is converted into a digital signal by an AD converter 27. The adder 28 adds and averages the corresponding portion of the backscattered light for each light pulse to improve the S / N, and displays the output on a display 29.

The output of the adder 28 is used as a polarization-dependent monitor 31.
The polarization dependence of the optical module 11 is evaluated from the data of the backscattered light. In other words, the greater the polarization dependence, the greater the fluctuation of the intensity of the backscattered light corresponding to each reflection point. The oscillation frequency of the high-frequency oscillator 23 is feedback-controlled so as to reduce this fluctuation. In this way, even if the wavelength of the laser diode in the optical pulse generator 24 varies before the detection of the failure point of the optical fiber, the polarization dependency of the optical switch of the optical module 11 on the wavelength is sufficiently reduced. Thus, the high-frequency signal frequency of the high-frequency oscillator 23 is adjusted, and the fault point of the optical fiber can be correctly detected. Also, when the oscillation wavelength of the laser diode fluctuates or the optical axis fluctuates due to the fluctuation of the ambient temperature or the like during use, the oscillation frequency of the high-frequency oscillator 23 is similarly adjusted to change the polarization dependence. Can be made sufficiently small.

[0015]

As described above, according to the first aspect of the present invention, the frequency of the high-frequency signal applied to the electroacoustic element of the acousto-optic element can be changed. The dependence can be made sufficiently small, the adjustment is extremely easy compared with the case where the polarization dependence is made small by adjusting the incident angle, and the adjustment can be performed without skill and without fail. Another contract
According to the invention of claim 2, if the polarization dependence of the reflected light is minimized
By adjusting the high frequency signal frequency to
The detection accuracy of optical fiber failure detection can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention;

FIG. 2 is a characteristic diagram showing polarization dependence on a relative value of an incident angle.

3 is a block diagram illustrating an example of applying the embodiment of the second aspect of the invention the optical fiber fault point detector.

FIG. 4 is a block diagram showing a conventional optical module.

FIG. 5 is a diagram showing diffraction efficiency characteristics with respect to an incident angle using polarization as a parameter.

Claims (2)

(57) [Scope of request for utility model registration] 1. An input of different wavelengths incident at the same angle of incidence.
An acousto-optic modulator that modulates the emitted light with a high-frequency modulated wave
In the optical module used , the wavelength is adjusted to minimize the polarization dependence of diffraction efficiency.
The variable oscillation frequency of the high-frequency modulator
Optical module to feature. 2. An optical pulse generator, and an incident light from the optical pulse generator is transmitted from a high-frequency oscillator.
Modulated at the high frequency of
Optical module that outputs backscattered light from the fiber to the light receiving unit
And the electric signal from the light receiving section, the state of the backscattered light
A display for displaying the status and an electric signal from the light receiving unit are input, and the backscattered light is input.
A polarization dependence monitor to assess the polarization dependence, the evaluation output data from the polarization dependence monitor, the polarizing
The high frequency is controlled so that the dependence is small.
That the optical fiber fault point detector characterized by comprising the high frequency oscillator and, the.