In order to evaluate the spherical radius and fiber height of the end face of optical fiber connector, the shape of the end face of the connector must be measured first. Interferometer has the advantages of high measurement accuracy, high speed and low cost, and is an effective means to measure surface shape. Fig. 3 is a schematic system diagram of an interferometer for detecting the end face of an optical fiber connector. The light emitted by the light source is reflected by the semi-transparent and semi-reflective mirror to the micro-interference objective lens, and then focused on the end face of the tested optical fiber connector. After being reflected by the end face, it passes through the semi-transparent and semi-reflective mirror together with the light reflected by the micro-interference objective lens and is imaged on the CCD camera. At this time, interference fringes can be observed on CCD camera. The image measured by CCD camera is transmitted to the computer for analysis through the image card. We can get the measurement results we need. The computer controls the piezoelectric ceramic component (PZT) to move the micro-mirror interference objective to generate phase shift through the control card and control loop.
Fourier transform methods 2,3,4 and phase shift methods 5,6 can be used to analyze interference fringes. Fourier transform method has the advantages of simplicity, rapidity and low cost, but its accuracy is low, so it is generally used in simple measuring instruments. Generally, the phase shift method with high analytical accuracy is used to measure the end face shape of optical fiber connectors.
It must be pointed out that phase connection is a complicated process. Choosing different phase connection algorithms will lead to different calculation speed and stability.
(2) Tilt adjustment of the stage
The tilt adjustment of the stage is a key technology. If the tilt adjustment accuracy of the stage is not high, it will greatly affect the measurement accuracy of spherical vertex eccentricity, APC angle and positioning key angle. Fig. 4 is a summary of the relationship between tilt adjustment and measurement accuracy of eccentricity of spherical vertex. As shown in fig. 4(a), when the tilt adjustment of the workbench is completed, the optical axis of the interferometer optical system will be parallel to the central axis of the sleeve of the optical fiber connector to be tested. At this time, when the optical fiber connector to be tested is rotated, the spherical vertex of the end face of the optical fiber connector (the center of the annular interference fringe, such as point A or point B) will rotate around the center point O of the optical fiber to form a circle with the center point O. The measured vertex eccentricity OA or OB will be the same as the actual vertex eccentricity. That is to say, no matter what angle the optical fiber connector rotates, the measured vertex eccentricity will not change much. On the contrary, as shown in fig. 4(b), when the tilt adjustment of the stage is incomplete, the optical axis of the interferometer optical system will intersect with the central axis of the ferrule of the optical fiber connector to be tested at an angle. At this time, when rotating the tested optical fiber connector, the spherical vertex of the end face of the optical fiber connector (the center of the annular interference fringe, such as point A, point B, point C or point D) will rotate around the center O* different from the optical fiber center o, forming a circle with the center O*. Obviously, the vertex eccentricity values OA, OB or OC measured at different positions will be different from the actual vertex eccentricity OD. That is to say, the measured vertex eccentricity will change greatly after rotating the optical fiber connector. From this phenomenon, we can also get a method to check whether the tilt adjustment of the stage is completed. That is, rotate the optical fiber connector and measure the eccentricity of the vertex in turn. If the measured vertex eccentricity changes little, the tilt adjustment of the stage is completed. On the contrary, the tilt adjustment of the stage is incomplete. In order to improve the adjustment accuracy of the tilt of the stage, Fuji Photomechanical Co., Ltd. has developed high-precision and simple-to-operate tilt adjustment technologies (many patents have been applied for) 7 and 8, which can realize the adjustment accuracy much higher than that of the general adjustment methods.
(3) measurement reproducibility
The measurement repeatability has a great influence on the measurement accuracy of the optical fiber connector end face detector. Take the vertex eccentricity as an example. At present, the repeatability of optical fiber connector end face detectors produced by most manufacturers is about 5 μ m, and these data can be easily found on the websites of various manufacturers. Some manufacturers measure reproducibility by standard deviation σ. According to the calculation method of error theory, the maximum error of measuring reproducibility can reach 3 σ, which is about 6 μ m.
Generally, it is impossible to require the measurement accuracy of measuring instruments to be higher than the measurement reproducibility accuracy. Therefore, repeatability accuracy is one of the most important indexes to measure the measurement accuracy of measuring instruments.
The measurement repeatability accuracy of the optical fiber connector end-face detector is mainly determined by the measurement repeatability accuracy of the optical fiber connector end-face detection interferometer (determined by the phase shift accuracy of PZT, the accuracy of the A/D converter of CCD camera and image card, the noise of the measurement circuit, the measurement environment such as vibration and temperature change, etc.) and the positioning accuracy of the optical fiber connector fixing fixture on the workbench. In addition, due to the uncertainty of the rotation direction angle of the optical fiber connector (except APC optical fiber connector) inserted into the fixture, the tilt adjustment accuracy of the workbench will also affect the repeatability accuracy of the measurement.
For the measurement reproducibility of the interferometer, the optical fiber connector can be fixed on the fixture of the workbench, and the measurement can be repeated without pulling out the optical fiber connector. Then, the measured values are processed to evaluate the measurement reproducibility of the interferometer itself. Generally speaking, the interferometer based on modern interferometer measurement technology and interference fringe analysis technology has high measurement repeatability. However, due to improper optical design and optical path arrangement, some manufacturers' interferometers are very sensitive to vibration, which affects the measurement accuracy of interferometers.
For the positioning accuracy of optical fiber connector fixture, the tested optical fiber connector can be plugged and unplugged many times, and the same optical fiber connector can be measured repeatedly. Then, the measured values are processed to evaluate the positioning accuracy of the optical fiber connector fixing fixture. It must be pointed out that the tilt adjustment accuracy of the stage will also be affected by the positioning accuracy of the fixed fixture, because most standard devices, such as standard optical fiber connectors, are used to adjust the tilt of the stage. Therefore, improving the positioning accuracy of the fixture is the key to improve the measurement accuracy of the whole optical fiber connector end-face detector. In order to improve the positioning accuracy of the fixture, Fuji Photomachine Co., Ltd. has developed a lamp with high accuracy, simple operation and high reliability.
/element/ 10445% 2 ehtml & amp； p = cb6ff 9 15d 9 c 544 ee 0 fb3c 77 10e 1383 & amp； User = Baidu