Ultrahigh-speed line-scan SD-OCT for four-dimensional in vivo imaging of small animal models.

We report an ultrahigh-speed and high-resolution line-scan spectral-domain optical coherence tomography (SD-OCT) system that integrates a number of mechanisms for improving image quality. The illumination uniformity is significantly improved by the use of a Powell lens; Phase stepping and differential reconstruction are combined to suppress autocorrelation artifacts; Nonlocal means (NLM) is employed to enhance the signal to noise ratio while minimizing motion artifacts. The system is capable of acquiring cross-sectional images at more than 3,500 B-scans per second with sensitivities between 70dB and 90dB. The high B-scan rate enables image post-processing with nonlocal means, an advanced noise reduction algorithm that affords enhanced morphological details and reduced motion artifacts. The achieved axial and lateral resolutions are 2.0 and 6.2 microns, respectively. We have used this system to acquire four-dimensional (three-dimensional space and one-dimensional time) imaging data from live chicken embryos at up to 40 volumes per second. Dynamic cardiac tissue deformation and blood flow could be clearly visualized at high temporal and spatial resolutions, providing valuable information for understanding the mechanical and fluid dynamic properties of the developing cardiac system.

5-Gb/s optical transmitter based on incoherent-light-injected RSOAs with graceful upgrade capability for WDM PONs.

We propose and demonstrate a novel and cost-effective optical transmitter based on incoherent-light-injected reflective semiconductor optical amplifiers (RSOAs) which can be upgraded to higher data rate without discarding the existing low-data-rate transmitter. The transmitter is based on optical time-division multiplexing (OTDM) of return-to-zero modulated RSOAs and thus capable of upgrading the system capacity on an as-needed basis simply by adding RSOAs. By using the proposed transmitter, we experimentally demonstrate a capacity upgrade from 2.5 to 5 Gb/s/channel by using two RSOAs, each operating at 2.5 Gb/s. To the best of our knowledge, this is the highest reported data rate demonstrated using incoherent-light-injected RSOAs. We also demonstrate the performance of the proposed transmitter after 10-km transmission over standard single-mode fiber, and investigate the sensitivity penalty to the power level injected into the RSOAs as well as the optical delay for the OTDM.

Line coding to enhance the performance of 10-Gb/s CPFSK-ASK directly modulated signals.

The major drawback of frequency modulation (FM)-based directly modulated laser (DML) is its non-uniform FM response at low frequency range which gives rise to a severe pattern-dependent performance degradation. In this paper, we investigate the use of line coding to deplete the low-frequency spectral contents of the signal and thus to alleviate the degradation. We examine various line codes (8B/10B, 5B/6B, 7B/8B, 9B/10B, and 64B/66B) with continuous-phase frequency-shift keying/ amplitude-shift keying (CPFSK/ASK) signals generated using a DML and a delay interferometer. Experimental demonstrations are performed with a long pseudorandom bit sequence length of 2(20)-1 and the bandwidth expansion by each code is taken into consideration. The results show that among the five codes we tested, 9B/10B code outperforms the other codes in terms of receiver sensitivity an dispersion tolerance. We demonstrate successful transmission of 10-Gb/s CPFSK-ASK signals over 65-km standard single-mode fiber with a bandwidth expansion of only 11.1%.