JPS6150245B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical chopper for measuring weak optical power when measuring characteristics of optical communication systems and optical devices.

When measuring the characteristics of optical communication systems and optical devices (for example, when measuring the wavelength loss characteristics of optical fibers laid over long distances or the crosstalk of optical switches), extremely weak light of about -90 dBm is required. It is necessary to measure power, and for this purpose a highly sensitive optical power meter is required. In order to construct an optical power meter that operates stably with high sensitivity, the use of an optical chopper is unavoidable from the viewpoint of S/N ratio.

Conventionally, there is an optical chopper having the configuration shown in FIG. 1, which is mainly used for measuring the spectral characteristics of material parts. The motor 2 is rotated by the control device 3,
A notched disc 1 interrupts the light beam 4. In this case, the interrupted optical signal becomes as shown in FIG. Here, the input optical power is P ₀ and the intermittent period is T. Rise and fall time of optical signal τ
can be expressed as follows, where D is the diameter of the light beam interrupted by the disk 1, and S is the distance from the rotation center axis to the light beam.

τ=4T/πsin-1(D/4S)...(1) When the distance S to the light beam is sufficiently larger than the diameter D of the beam, τ~DT/-πS...(2). Since it is necessary for the fundamental wave component of the output waveform to be large in terms of the S/N ratio of the signal detection system, the optical chopper is required to output a rectangular wave optical pulse with a pulse occupancy rate of 50%. Therefore, (τ/
It is desirable that T) be small. For this reason, in the optical chopper shown in FIG. 1, it is necessary to make S sufficiently large, that is, to make the disk large, and the dimensions of the optical chopper become large.

Furthermore, in optical fibers and optical communication devices (directional couplers, optical attenuators, optical switches, etc.), light is emitted after being spread by an angle given by a numeric aperture (NA). Therefore, when using the above optical chopper to measure these characteristics, in order to obtain an optical pulse close to a rectangular wave, (2)
As is clear from the equation, the optical fiber must be placed as close as possible to the chopper disk, the beam diameter of the interrupted portion must be small, and the photodetector must be placed immediately behind the disk, making it difficult to use. It's inconvenient.

SUMMARY OF THE INVENTION An object of the present invention is to improve the above-mentioned drawbacks and provide an optical chopper that is small and easy to use, and is particularly suitable for measuring characteristics of optical communication systems and optical devices.

The principle of the present invention will be explained with reference to FIG. The optical chopper of the present invention consists of two lenses 5 and 6 and a cut-off device (not shown) having a portion 7 arranged between these lenses and cut off the light. The light beam enters the lens 5, is image-converted so as to form an image between the lenses 5 and 6, and is periodically interrupted by an interrupter having a portion 7 for interrupting the light at the imaging section C, and then passes through the lens. 6, the image is converted again and the light is emitted.
Note that reference numeral 8 indicates the direction in which the interrupting portion 7 moves. Assuming that the incident beam is a parallel beam of diameter D, this output beam has the rise and fall times of equation (2) when the chopper shown in FIG. 1 is used. On the other hand, in the optical chopper of the present invention, when using the same intermittent device (the motor and disk in Fig. 1), if the beam diameter of the imaging section is d, the rise and fall times of the output light are (d/ become D). In other words, it is possible to obtain an optical signal that is closer to a rectangular wave.

In addition, when the light emitted in a spread manner, such as the light emitted from an optical fiber, is to be interrupted, a lens 5 that forms an image between the lenses C as shown in FIG. 4 is used.

Further, when intermittent light is made to enter a photodetector or optical fiber having a small receiving diameter, a lens 6 is used which forms an image at the installation point B of the photodetector or optical fiber as shown in FIG.

Next, an embodiment of the present invention will be described with reference to FIG. The optical fiber 10 is an optical fiber (not shown).
Connectors 15, 16 and rod lens 1
A tuning fork vibrator 13 having shutters 1 and 12 and a shutter 14
It has The light connected to the connector 15 is image-converted by the lens 11 so that it is focused on the shutter 14 . Since the shutter 14 opens and closes at the natural frequency of the tuning fork vibrator 13, the light is interrupted and incident on the lens 16, and is focused by the lens 16 so as to be incident on the fiber connected to the connector 16. The tuning fork vibrator used has a resonant frequency
The amplitude (shutter part) is 400 μm when 20 Vpp (20 volts at peak) is applied at 280 Hz. Also,
The rod lenses are arranged to perform 1:1 image conversion between the lenses. Therefore, when a fiber with a core diameter of 60 μm is connected, the diameter of the image forming part is 60 μm.
It is m.

The rise and fall times of Honko Chiyotsupa are approximately 50μ
s, the pulse occupancy rate was 50±1%, and an optical output signal that could be sufficiently approximated as a rectangular wave pulse with a pulse occupancy rate of 50% was obtained. In addition, the dimensions of case 10 are 32
×25×105mm, insertion loss was 0.8dB.

As described above, the optical chipper of the present invention rises,
It can produce optical pulses that are very close to rectangular waves with a steep falling edge, and it is also compact. Furthermore, a lens having a connector for connecting an optical fiber on the outside of the lens is suitable for measuring characteristics of optical communication systems and optical devices, and is easy to handle. Therefore, the optical chopper of the present invention is extremely useful when used for measuring the characteristics of parts and materials, and especially for measuring the characteristics of optical communication systems and optical devices.

[Brief explanation of the drawing]

Figure 1 is a diagram showing an example of the configuration of a conventional optical chipper.
Figure 2 is a diagram explaining the output optical signal of the optical chopper.
3 and 4 are diagrams showing the principle of the optical chopper of the present invention, and FIG. 5 is a diagram showing an embodiment of the present invention. In Figures 1 to 5, 1...disc, 2...
...Motor, 3...Control device, 4...Light beam,
5, 6... Lens, 7... Light intermittent part of the intermittent device, 8... Direction, 11, 12... Rod lens, 13... Tuning fork vibrator, 14... Shutter, 1
5, 16...connector, 10...case.

Claims (1)

[Scope of Claims] 1. A means for intermittent light incident on the lens, comprising two lenses and an intermittent device disposed between the two lenses and having means for intermittent light. An optical chip, characterized in that the lens is arranged so as to form an image. 2. Two lenses, an intermittent device having a means for intermittent light disposed between the two lenses, and two connectors disposed outside the two lenses to be connected to an optical fiber. A light chiyotsupa characterized by being composed of.