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Optical Characterization and Nanophotonics Laboratory

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Near-field Scanning Optical Microscopy of Laser Diodes

Members: M. Selim Ünlü

 

Alumni: Carey C. Cates, Hadi F. Ghaemi, Bennett B. Goldberg, William D. Herzog, Gökhan Ulu

 

Near-field Scanning Optical Microscopy (NSOM) involves scanning a subwavelength aperature to generate an image. We studyied the capabilities of NSOM to collect the highly diverging fields emanating from high-power, nearly diffraction limited lasers. In addition to establishing the validity of the technique, we have studied frequency locking in 980nm narrow stripe laser diodes. NSOM can be used to image the propagation of the laser mode (as seen to the left in the 6x6 micron images) and image the mode on the output facet. During frequency locking the mode shifts laterally on the facet. In the far-field, frequency locking is characterized by a pointing of the laser. This effect is detrimental to optimizing power coupled into a fiber or other optical components.

The beam waist has been fitted (image linecuts) and plotted below. We determined the astigmatism (distance between beam waist minima) and noticed focusing of the laser diode outside the device for the lateral dimension (in the plane of the p-n junction).

Below is data we collected on high power GRINSCH laser diodes. These images were obtained by scanning the tip over the output facet of the device and collecting the light being emitted by the laser diode.

These images show the laser mode moving on the laser facet due to frequency locking of lateral modes. The frequency locking occurs when the zeroth order and first order lateral modes are coherently coupled. When this occurs the beam "points" in the far-field, and "beats" along the cavity.

Publications

M. S. Ünlü, B. B. Goldberg, and S. B. Ippolito, "Optical Microscopy Beyond the Diffraction Limit: Imaging Guided and Propagating Fields," Proceedings of the 7th International Symposium on Advanced Physical Fields, November 2001

W. D. Herzog, G. Ulu, B. B. Goldberg, G. H. Vander Rhodes, M. S. Ünlü, L. R. Brovelli, and C. Harder, "Theoretical and Experimental Study of Near-Field Beam Properties of High Power Laser Diodes," Proceedings of the International Semiconductor Device Research Symposium (ISDRS), 11-13 December 1997

L. A. Peach, "Near-field microscopy profiles diode laser beam," Laser Focus World, May 1997

Staff Writer, "Near-Field Scanning Optical Microscopy Measures Diode Beam Properties," Photonics Spectra, April 1997

W. D. Herzog, M. S. Ünlü, B. B. Goldberg, G. H. Vander Rhodes, and C. Harder, "Beam divergence and waist measurements of laser diodes by near-field scanning optical microscopy ," Applied Physics Letters, Vol. 70, No. 6, 10 February 1997, pp. 688-690

L. A. Peach, "Near-field microscopy maps semiconductors," Laser Focus World, January 1997

W. D. Herzog, M. S. Ünlü, B. B. Goldberg, G. H. Vander Rhodes, and C. Harder, "Near-field Analysis of Beam Properties of InGaAs Ridge Lasers," Proceedings of IEEE Lasers and Electro-Optics Society 1996 Annual Meeting, Vol. 1, 18-19 November 1996, pp. 109-110

B. B. Goldberg, M. S. Ünlü, W. D. Herzog, H. F. Ghaemi, and E. Towe, "Near-field optical studies of semiconductor heterostructures and laser diodes," IEEE Journal of Selected Topics in Quantum Electronics, Vol. 1, No. 4, December 1995, pp. 1073-1081

M. S. Ünlü, B. B. Goldberg, W. D. Herzog, H. F. Ghaemi, and E. Towe, "Layer Composition and Mode Structure Analysis of Heterojunction Laser Diodes by Near Field Scanning Optical Microscopy," 53rd Annual Device Research Conference 1995, 19-21 June 1995, pp. 148-149

M. S. Ünlü, B. B. Goldberg, W. D. Herzog, C. C. Cates, H. F. Ghaemi, D. Sun, and E. Towe, "Characterization of Heterojunction Laser Diodes by Near Field Optical Scanning Microscopy: Layer Composition and Mode Structure Analysis," Proceedings of IEEE Lasers and Electro-Optics Society 1994 Annual Meeting, Vol. 2, 31-Nov. 3 October 1994, pp. 209-210


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