Mode control of surface-emitting lasers using fib er Bragg grantings and its application to high-speed local area networks

垂直腔面发射激光器(VCSEL)是一种垂直发射光到半导体衬底上的激光器。由于输出光束具有圆形轮廓，因此垂直腔面发射激光器有利于与光纤耦合。如果它们排列成网格，则VCSEL也适用于大容量并行通信。另一方面，光纤布拉格光栅(FBG)是由两束相交的紫外光在光纤中形成的衍射光栅。光纤布拉格光栅反射布拉格波长的光，因此被应用于激光二极管的波长控制。在这项研究中，我们将FBG与VCSEL相耦合，并演示了对纵模和光谱窄化的控制。我们研究了利用数字信号调制的垂直腔面发射激光器的光纤传输。在实验中，我们制作了布拉格波长与垂直腔面发射激光器的振荡波长一致的FBG。布拉格波长约为840 nm，反射率为30-40%，光谱宽度为6-7 nm半高宽。然后，我们将FBG耦合到VCSEL。VCSEL的光谱宽度已经减少到没有FBG的一半。这种窄带激光器在光通信或光学测量中都有应用。接下来，我们利用多模光纤对数字传输特性进行了测量。在光纤长度为1公里的情况下，采用700Mb/S数据速率的FBG降低了误码率，功率损失降低了2dB。对于增加2公里的光纤长度，使用FBG，在300-400Mb/S的数据速率下，误码率略有降低。结果表明，在局域网等较短距离的高比特率通信中，使用FBG是有效的。改进的机理被认为是减小了抖动、波长色散和模式色散。

A vertical-cavity surface-emitting laser (VCSEL) is a laser that emits light vertically to a semiconductor substrate. As the output beam has a circular profile, a VCSEL is advantageous to coupling with optical fibers. A VCSEL is suitable also for high-capacity parallel communication if they are arranged in a grid. On the other hand, a fiber Bragg grating (FBG) is a diffraction grating in an optical fiber formed by two intersecting ultraviolet laser beams. FBGs reflect light at Bragg wavelengths, and thus they have been applied for wavelength control of laser diodes. In this study, we couple an FBG with a VCSEL and demonstrate control of longitudinal modes and spectral narrowing. We studied optical fiber transmission using the VCSEL modulated with digital signals. In the experiment, we fabricated FBGs that have Bragg wavelengths in agreement with oscillation wavelengths of VCSELs. The Bragg wavelength was about 840 nm, the reflectivity was 30-40%, and the spectral width was 6-7 nm FWHM. Then, we coupled the FBGs to the VCSELs. Spectral widths ofVCSELs have decreased to half of those without FBGs. Such a narrowband laser has an application to optical communication or optical measurement.Next, we performed measurement on digital transmission characteristics with multimode optical fiber. For a fiber length of 1 km, the bit error rate decreased by using an FBG at a data rate of700 Mb/s, and decrease in the power penalty by 2dB was obtained. For an increased fiber length of 2 km, the bit error rate somewhat decreased at a data rate of 300-400 Mb/s by using an FBG. It is concluded that use of an FBG is effective for relatively short distance high-bit rate communication such as local area networks. The mechanism of the improvement is considered to be decrease in jitter, wavelength dispersion, and modal dispersion.