外腔式可調多波長半導體雷射之研究

Abstract

本文首度報導連續波多波長外腔式半導體雷射。雷射外腔是由削角入射光柵、聚焦透鏡與數組不同設計之條型反射鏡所組成。 利用V型及其等分角線組成三個條型鏡的結構，此雷射可輸出與中心波長差由1.8nm至5nm的可調波長輸出。預計最小波長差為0.1nm，而最大波長差可達19.6nm。此三波長之線寬應小於儀器極限之92MHz。 利用多個等間距的條型鏡，我們首度報導由半導體雷射直接產生多達十個窄頻寬波長的連續波輸出，並驗證了條型鏡間距與模間距的對應關係。如將條型鏡偏離距焦透鏡，使光束橫向長度變長，則可獲得超過二十個波長的輸出。不同波長的輸出其遠端光分布並無明顯差異。我們並以時間閘門的方式研究各波長間的相互追跡，以對各波長間之同調性作一步瞭解及驗證。雷射未經控制的狀況下，各波長輸出之漂移量約為100MHz，而波長差之漂移量僅5MHz。

In this thesis we report for the first time generation of continuous wave (cw), multiple-wavelength, narrow-linewidth output from an external-cavity semiconductor laser diode. The laser cavity consists of a grazing-incidence grating, lens, and stripe-mirrors of diferent desing. Using a fan-shaped end mirror consisting of three stripe mirrors, the laser could produce tunalbe output with wavelength separation ranging from 1.8nm to 5 nm with respect to the center wavelength. We estimate that the minimum wavelenght separation is 0.1 nm. The maximum of the wavelength separation is≠19.6nm. The linewidth of the triplewavelength output should be under 92 MHz (Instrument limit). Using a number (>3) of stripe mirrors, we first report over ten cw narrow-bandwidth wavelengths produced directly from a semiconductor leaser diode. The wavelength separation is consistent with theoretical predictions. On the other hand, if we defocus the lens, over twentywavelength utput can be obtained. The far-fild distribution of the laser output at different wavelength is essentially identical. We also studied the tracking of modes with each other using time-gating method.The different wavelengths were found to track each other. For a free-running laser, the frequency drift of the individual wavelength is 100 MHz. The relative fluctuation between any pair of wavelengths is only 5 MHz.