Shuai Ci-jun

The relationship between IR characteristic peak and microstructure of the glass used as optical fiber

Based on the harmonic vibration equation, the relationship between IR characteristic peak of fiberglass and Si-O-Si bond angle was deduced, and 1 100 cm−1 characteristic peak was specifically studied. It is found that 1 100 cm−1 characteristic peak shifts to higher wave number when Si-O-Si bond angle increases. Taking fused biconical taper (FBT) coupler as an example, the microstructures of the fiber coupler manufactured at different drawing speeds were tested with micro infrared spectrum. According to the test results, it is found that the bond angle at the taper region is the largest, the one at the fused region is the second largest, and the one of bare fiber is the smallest. The characteristic peaks of fused—taper region shift to higher wave number when drawing speed increases.

Effect of technological parameters on optical performance of fiber coupler

To find out the influence of technological parameters on optical performance of fused optical fiber device, the fiber coupler was served as subject investigated by using the fused biconical taper machining as experimental setup. Fused fiber coupler’s optical performances such as insertion loss, excess loss, directivity and uniformity were tested with the optical test system that was constituted of tunable laser and optical spectrum analyzer. Especially the relationship between optical performance and drawing speed was investigated. The experimental results show that the optical performance is closely related to process conditions. At fused temperature of 1 200 °C, there exists a drawing speed of 150 μm/s, which makes the device’s performance optimum. Out of this speed region, the optical performance drops quickly. At drawing speed of 200 μm/s, the excess loss is relatively small when the fused temperature is above 1 200 °C. So the technological parameters have close relationship with optical performance of the coupler, and the good performance coupler can’t get until the drawing speed and fused temperature match accurately.

Experimental measurement and numerical analysis of fused taper shape for optical fiber coupler

To find out the effect of the shape of fused taper region on the optical fiber coupler, the fiber couplers were fabricated at different drawing speeds with a six-axes fiber coupler machine. The results, which were obtained from the shape of fused taper region measured with microscope, show that there is a close correlation between the cone angle and optical performance of fiber coupler. High-performance fiber coupler cannot be obtained until rheological shape is controlled accurately. The numerical analysis model, which was built based on generalized Maxwell viscoelastic theory, is resolved with ANSYS software. The calculated results accord with the experimental data. It can apply a theoretic basis for forecasting the shape of fiber coupler fabricated under the conditions of different technological parameters.

Novel manufacturing method of optical fiber coupler

Based on the coupling mode theory that the coupling ratio of fiber coupler changes periodically with center distance of two optical fibers, a novel manufacturing method of optical fiber couplers was developed with fused biconical taper experimental system. Its fabrication process is that the fiber is fused but not stretched when light begins to split, and the reduction of diameter of fiber is dependent on the rheological characteristic of the fused fiber-glass. The performance of the coupler was tested. The results show that the performance of the novel optical fiber coupler meets the performance expectations, and its diameter of coupling region (about 30 µm) is twice as long as that of classical fused biconical taper coupler (about 16 µm), so the default, that is, the device is easy to fracture, is restrained and the reliability is greatly improved.

Development of a Novel Optical Fiber Coupler

Using the theory that the coupling ratio of fiber coupler changes periodically with center distance of two optical fibers, in the fabrication process of fiber coupler, the fiber is fused but not stretched when light begin to split. The reduction of diameter of fiber is dependent of the theological characteristic of the fused fiberglass, and the light continues to split. A new manufacturing method of optical fiber couplers is developed with fused biconical taper experimental system. The tested results show that the performance of the novel optical fiber coupler complies with the performance indexes of fused biconical taper coupler, and its diameter of coupling region is double of classical fused biconical taper coupler.

Structure analysis of optical fiber coupler with infrared spectrometry

To obtain excellent performance optical fiber couplers, the structural difference of SiO2 in couplers with different manufacturing techniques was investigated. With 740-FT-IR infrared spectrometric analyzer, the infrared absorption spectrum of SiO2 in couplers at different drawing velocities was measured, and two characteristic peaks in the wavenumber range of 650–2000 cm−1 were observed. One characteristic peak is at about 943 cm−1, which is attributed to Si-O-Si bond asymmetric stretching vibration, the other is at about 773 cm−1, which is attributed to Si-O-Si bond symmetric stretching vibration. From the infrared spectrum, it is found that the intensity and wave-number of the characteristic peaks are related to the manufacturing technique of couplers. The characteristic peak at about 943 cm−1 becomes steeper when increasing the drawing velocity. At the drawing velocity of 150 µm/s, the distance between the two characteristic peaks is maximum, and then the optical fiber coupler has excellent performance, indicating that the performance of the optical fiber coupler has a close relationship with the wavenumber of the two characteristic peaks.