[14a-C301-1~9] 4.5 Information Photonics

▲ [14a-C301-4] Dual-wavelength digital holography using optical frequency synthesizer

〇(M2)Clement Trovato^1,2,3、Dahi Ghareab Abdelsalam^1,3、Takayuki Ogawa^1,3、Takeo Minamikawa^1,3、Hirotsugu Yamamoto^3,4、Emmanuel Abraham^2,5、Takeshi Yasui^1,3 (1.Tokushima Univ., Japan、2.Bordeaux Univ., France、3.JST, ERATO MINOSHIMA IOS、4.Utsunomiya Univ.、5.LOMA)

キーワード：Digital Holography, Optical frequency synthesizer

Digital holography (DH) has become a topic of growing interest which finds its spot in the three dimensional imaging, as well as biomedical imaging and metrology. One practical limitation in DH with a single wavelength light is that it can only handle smooth profiles and step height less than half a wavelength (lambda/2). To extend the dynamic range in depth over lambda/2, dual-wavelength DH has been proposed. In this method, DH is performed at two different wavelengths (lambda₁, lambda₂), and then the synthesized wavelength between them lambda_1,2 [= ( lambda₁.lambda₂) /| lambda₁-lambda₂|] is used to extend the dynamic range in depth up to lambda_1,2. However, since stable CW laser oscillates at only a few discrete wavelengths, such as 532 nm, 633 nm, or 780 nm, it is difficult to obtain an arbitrary lambda_1,2. Recently, optical frequency comb (OFC) has emerged as a new technique for optical frequency metrology. OFC can be used as an optical frequency ruler by phase-locking a carrier-envelope-offset frequency f_ceo and a repetition frequency f_rep to a frequency standard. One interesting application of OFC is an optical frequency synthesizer (OFS), which is a single-mode CW laser phased locked to one optical frequency mode of OFC. Furthermore, continuous tuning can be achieved by changing f_rep while keeping the phase-locking of CW laser to OFC. Such characteristics of OFS are attractive for dual-wavelength DH because lambda_1,2 can be arbitrarily generated from µm order to mm order over m order depending on the sample. We demonstrated dual-wavelength DH using OFS.