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A novel (to our knowledge) dual-core ytterbium (Yb(3+)) doped fiber, as an optically pumped amplifier, boosts the output power from a 1060 nm swept source laser beyond 250 mW, while providing a wavelength tuning range of 93 nm, for optical coherence tomography (OCT) imaging. The design of the dual-core Yb-doped fiber amplifier and its multiple wavelength optical pumping scheme to optimize output bandwidth are discussed. Use of the dual-core fiber amplifier showed no appreciable degradation to the coherence length of the seed laser. The signal intensity improvement of this amplifier is demonstrated on a multichannel in vivo OCT imaging system at 1060 nm.

We demonstrate high efficiency and wide bandwidth gain in a Ytterbium doped fiber amplifier. The highpowered amplifier has potential applications for use with a swept-source fiber ring laser in multi-channel optical coherence tomography (OCT) system. The ring cavity design includes a 976nm pumped dual core Yb doped fiber as the gain medium, where a rotating polygon mirror is used as a wavelength-sweeping filter for this source. The amplified spontaneous emission (ASE) had a spectral bandwidth of 1037-1145nm at -60dBm, where a tunable lasing bandwidth of the ring cavity ranged from 1057-1115nm. The highest output power, for both the ASE and lasing spectrum, with this configuration was ~200mW, however it is possible to have a larger bandwidth and a larger output power. Higher power, in the wattage range is achievable if free space components are employed. Pumped with 976nm light at 1.27W, the use of this novel dual core Yb doped fiber as an amplifier has been successfully demonstrated, as it provided a small signal gain of 29.6 dB at 1085nm, where the gain medium was successfully saturated during operation. This is important for the spectral shaping requirements of OCT to improve image quality. The gain was demonstrated for several different wavelengths and for several pumping powers at a 1085nm wavelength. Fourier domain mode locked operation (FDML) was achieved with a bandwidth of 15nm and a sweep rate of 51.4kHz. This laser source offers a low-cost, high power alternative for biomedical imaging with multi-channel optical coherence tomography.

In this study, a cascaded Raman fiber laser in Fourier domain mode lock operation (FDML) is presented. This laser utilizes a Ytterbium doped twin core pump laser source at 1109 nm. The pump light is directed to a cascaded Raman cavity, which consists of multiple cascaded fiber Bragg grating pairs and 3.86 km of dispersion compensation fiber, which provides Raman gain. The output wavelength of a cascaded Raman laser is determined by the Stoke's shift (≈ 60 to 70 nm in optical fiber) and the pump laser wavelength. The power build up in the cascaded Raman cavity and shift to higher Stoke's orders produce multiple spectral peaks. At higher Stoke's orders, the overlapping Raman peaks create broad bandwidth gain with relatively large gain ripples. FDML operation using a polygon-based tunable filter helps to suppress the ripples. The overall laser in linear operation has a bandwidth of 316 nm with a center wavelength of 1445 nm. An output optical power was measured to be (> 10 mW). On the other hand, the sweeping bandwidth was 35 nm with an output power in the micro-watt range. The utilization of broadband tunable lasers are important in applications such as swept-source optical coherence tomography for use in biomedical imaging.