Modulation transfer function of the imaging probe using an 8.8mm-long and 125µm-thick graded- index short multimode fiber

• Published in: Optics communications 2017-02, Vol.385, p.25-35
• Main Authors: Sato, Manabu, Shouji, Kou, Nishidate, Izumi
• Format: Article
• Language: English
• Subjects: Fiber GRIN lens; Imaging probe; Modulation transfer function; Phase screen
• ISSN: 0030-4018; 1873-0310
• DOI: 10.1016/j.optcom.2016.10.007

We measured the modulation transfer function (MTF) of a short multimode fiber (SMMF) probe and proposed the optical model including the thin random phase screen (TRPS) to explain degradations of imaging characteristics. SMMF is a graded index multimode fiber for optical communication. That length is 8.8mm and the diameter of core is 50µm. With the wavelength of 780nm, for spatial frequencies from128lp/mm to 228lp/mm MTFs were measured at 0.179–0.062 in reflection images and these contrasts were 19% to contrasts without TRPS. With parameters of σϕ of 1.5rad and W of 2–3.5µm calculated results almost correspond to measured ones. Dependences of contrasts on wavelength were also measured. With the spatial frequency of 200lp/mm, at the wavelength of 0.8µm the contrast decreased to 17% due to TRPS and at that of 0.5µm the contrast decreased to 6%. Measured dependences of contrasts on wavelength with the spatial frequency of 228 lp/mm approximately correspond to calculation results with 200lp/mm. These basic characteristics are useful to design the imaging optics by means of SMMF. •MTF of an imaging probe of 8.8mm-long and 125µm-thick graded-index short multimode fiber was evaluated.•Blurs of images were explained using the thin random phase screen model.•Dependences of contrast on wavelengths were discussed based on that screen model.