JPH09218098A - Automatic extinction ratio measuring equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure the extinction ratio of laser light accurately in a short time by delivering an output light, impinging on a rotating polarizer, to a photoelectric converter and subjecting an electric signal, amplified through a plurality of amplifiers, to A/D conversion thereby measuring the extinction ratio. SOLUTION: A polarizer 4 is fixed to a rotating disc 3 in the center thereof and a light to be measured is projected thereto. Output light from the polarizer 4 is received by a photodiode 5 which produces an electric signal subjected to photoelectric conversion. The electric signal is passed through amplifiers 7, 8 having different gain and subjected to A/D conversion before being processed by a signal processing computer 13.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a measuring instrument for measuring an extinction ratio which is one of the characteristics of the polarization state of laser light.

[0002]

2. Description of the Related Art In optical communication, optical information processing, and other laser research and applied fields, the polarization state of a spatially propagating laser beam or a light beam emitted from a fiber can be measured, and the real-time polarization state in the assembly process of optical parts The applications using polarized light such as the monitor and the shipping test of the emitted light of the semiconductor laser are increasing, but the problem at that time is the extinction ratio. Conventionally, the extinction ratio has been obtained by measuring the maximum light amount and the minimum light amount with optical power meters having different ranges. In addition, the polarizing element was manually rotated to find the maximum value and the minimum value while observing the light intensity value. Therefore, it takes a long time to perform the measurement, and the arrangement of the measuring device becomes large, which is very inconvenient to use as a simple monitor in the assembly process.

[0003]

In order to measure a large extinction ratio, the dynamic range of the ratio between the maximum light amount and the minimum light amount must be large. Therefore, it is necessary to devise a method for reading the minimum portion of the minimum light amount. Further, if the measurement by the optical power meter is used, the measurement time becomes long and the measuring device becomes large, so that it is necessary to use a small-sized photoelectric converter having a high response speed.

An object of the present invention is to make it possible to measure the extinction ratio in a short time, and to make the sensor unit small to facilitate the measurement.

[0005]

In order to solve the above problems, according to the present invention, a rotatable polarizing element, a rotating plate (or an angle encoder) for reading the angle, and the intensity of light passing through the polarizing element are measured. Photodiode, two or more amplifiers for amplifying the electric signal of the light quantity, and an analog / digital converter for converting the amplified electricity into a digital signal, and read it by a digital computer. It was done.

An amplifier having a high degree of amplification or an amplifier having multiple stages is used for measuring the minimum light, and an amplifier having a low degree of amplification is used for measuring the maximum light so that the gain is not saturated. It is configured so that accurate measurement can be performed. As the amplifier, it is possible to use multiple stages to increase the amplification degree, or to use a variable amplification type amplifier.

[0007]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows a basic configuration of an extinction ratio measuring instrument according to the present invention. The polarizer 4 is attached to the center of the rotating disk 3, and the light to be measured is incident on the polarizer. The light emitted from the polarizer 4 is received by the photodiode 5 and photoelectrically converted to output an electric signal. The photoelectrically converted signals are input to amplifiers 7 and 8 having different gains.
The signals from the amplifiers 7 and 8 are converted from analog to digital and then processed by the signal processing computer 13.

The LED 1 and the photodiode 2 are encoder portions provided for reading the angle. The motor 6 is provided to rotate the polarizer 4.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS When a polarizer is placed perpendicular to the propagation direction of the light to be measured, the amount of light transmitted through this polarizer is as shown in FIG. 2 with respect to the rotation angle.

When the extinction ratio is measured with an amplifier having a constant amplification factor in this state, the dynamic range is not so large and the limit is about 20 dB.

However, if the electric signal is amplified by an amplifier having a large amplification factor, the portion where the light quantity value is low can be enlarged as shown in FIG. When the electric signal value having a high amplification factor is analogically calculated to the electric signal value having a low amplification factor, the minimum light amount value can be calculated as the minimum light amount value in the amplifier measuring the maximum light amount value, and the extinction ratio can be calculated. In the present invention, particularly when the minimum light amount is measured, A / D converted and subjected to digital calculation processing, the minimum value is greatly amplified and A / D converted to enable more accurate measurement.

Further, at this time, the data of the same angle can be calculated with high accuracy by calculating the multiplication rate not only for one angle but for several points and averaging. Assuming that the light amount signal I1 of the amplifier 1 and the light amount signal I2 of the amplifier 2 are at the same angle, the multiplication rate A of the amplifier 2 with respect to the amplifier 1 is

## EQU1 ## A = I2 / I1 is given.

The maximum light quantity Imax is calculated from the light quantity data near the maximum light quantity measured by the amplifier 1 by the quadratic least squares method, and the minimum light quantity is calculated from the data near the minimum light quantity measured by the amplifier 2. Imin2 by multiplication
Is calculated and multiplied by the multiplication rate to determine Imin. Therefore, the extinction ratio is calculated by the following formula.

## EQU2 ## Extinction ratio P = Imin / Imax The amplification degree of the amplifier 2 may be designed to be larger than that of the amplifier 1 so that the minimum light amount can be accurately measured.

[0014]

According to the present invention, the extinction ratio can be measured easily and in a space-saving manner.
It is effective for monitoring the polarization state of light during the assembly of optical components, inspection of semiconductor lasers, etc., and contributes greatly to the research and application fields of optical communication optical information processing.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a change of an output optical signal of a polarizer with a rotation angle.

FIG. 3 is a diagram showing a signal obtained by amplifying a portion where the light intensity value of the output light shown in FIG. 2 is low.

[Explanation of Codes] LED 2. Photodiode 3. Disk 4. Polarizer 5. Photodiode 6. Motor 7. Amplifier 8. Amplifier 9. Sample & Board 10. Sample & Board 11. Switching device 12. AD converter 13. Signal processing computer 14. display

Claims (1)

[Claims] 1. A polarizer positioned on the central axis of the incident optical axis,
A rotating plate or encoder for reading the rotation angle of the polarizer, a photoelectric converter for reading the output light amount of the polarizer in synchronization with the rotation angle, and an electric signal of the light amount obtained by the photoelectric converter Or two or more amplifiers for amplifying the signal, an analog / digital converter for analog / digital converting the output signal of the amplifier, a digital electronic calculator for inputting the output signal of the analog / digital converter, and the digital electronic An automatic extinction ratio measuring instrument comprising: a display for displaying a calculation result of a computer.