Four 45 Gbps PAM4 VCSEL based transmission through 300 m wideband OM4 fiber over SWDM4 wavelength grid.

We demonstrate successful transmission of four 45 Gbps PAM4 single-channels through OM4 multimode fibers (MMFs) and wideband MMF using a PAM4 PHY chip and four vertical cavity surface emitting lasers (VCSELs) with wavelengths ranging over short wavelength division multiplexing (SWDM) grid. Real-time bit error ratios (BERs) < 2 × 10-4 were achieved for all four 45 Gbps PAM4 SWDM grid channels over 100 m, 200 m, and 300 m of wideband OM4 MMFs. All four channel received PAM4 optical eyes are shown after propagating through 100 m, 200 m, and 300 m of wideband OM4 as well as 100 m and 200 m conventional OM4 MMFs. The measured BERs as a function of the inner eye optical modulation amplitudes (OMAs) are shown for all four SWDM grid channels. Inner eye OMAs ranged from -16.2 dBm to -13.5 dBm for different channels over different OM4 MMF types at the KP4 BER threshold of 2 × 10-4.

52 Gbps PAM4 receiver sensitivity study for 400GBase-LR8 system using directly modulated laser.

Real-time 52 Gbps PAM4 transmission is demonstrated over single mode fiber (SMF) using a directly modulated laser (DML) and a PHY chip. The inner eye optical modulation amplitude (OMA) receiver sensitivities were measured and compared using avalanche photodetector (APD) and PIN photodetector (PD) for the maximum and minimum chromatic dispersions (CDs) of 400GBase-LR8 link. The measured inner eye OMAs were -17.8 dBm and -18.8 dBm for + 10 ps/nm and -58 ps/nm of CDs at the KP4 bit error rate (BER) threshold of 2 × 10-4 using a PIN PD, respectively. The measured inner eye OMA was improved to -21.0 dBm for -58 ps/nm of CD at the KP4 BER threshold using an APD. Negligible OMA penalty (< 0.4 dB) was captured for operating DML at different bias currents of 40 mA and 60 mA using a PIN PD and an APD for both positive and negative CDs at the KP4 BER threshold.

In vivo human choroidal vascular pattern visualization using high-speed swept-source optical coherence tomography at 1060 nm.

PURPOSE: To investigate the retinal and choroidal vascular pattern, structure, and thickness using high-speed, high axial resolution, swept-source optical coherence tomography (SS-OCT) at 1060 nm, demonstrating enhanced penetration through all choroidal layers. METHODS: An ophthalmic SS-OCT system was developed operating at 57,000 A-lines/s with 5.9 µm axial resolution and was used to collect 3D images with scanning angles up to ∼70° × 35°. The similar features were observed in the choroidal layers by imaging three healthy volunteers. En face images, extracted at different depths, capture features of the retinal and choroidal vasculature networks and substructure. Retinal and choroidal thicknesses were measured over scanning angles of ∼14° × 14°, yielding retinal and choroidal thickness maps. RESULTS: The retinal layers, choriocapillaris (CC), Sattler's layer (SL), Haller's layer (HL), and the lamina suprachoroid layer (LSL) were delineated in 2D sagittal tomograms. The sagittal tomograms and en face reflectance images over a 2-cm(2) field of view captured the paraoptic, lateral and medial distal short posterior ciliary artery (SPCA) branches as well as the two lateral and medial long posterior ciliary arteries (LPCAs). En face images in the HL revealed the superotemporal, inferotemporal, superonasal, and inferonasal major choroidal vessels. CONCLUSIONS: High-speed, high-resolution SS-OCT centered at 1060 nm enables retinal and choroidal vasculature networks visualization, including retina vessels, posterior ciliary artery (PCA) branches, and venous vascular patterns. This technology offers diagnostic opportunities by monitoring change in these networks, substructure, and retinal and choroidal thicknesses during disease initiation and progression.

Logarithmic intensity and speckle-based motion contrast methods for human retinal vasculature visualization using swept source optical coherence tomography.

We formulate a theory to show that the statistics of OCT signal amplitude and intensity are highly dependent on the sample reflectivity strength, motion, and noise power. Our theoretical and experimental results depict the lack of speckle amplitude and intensity contrasts to differentiate regions of motion from static areas. Two logarithmic intensity-based contrasts, logarithmic intensity variance (LOGIV) and differential logarithmic intensity variance (DLOGIV), are proposed for serving as surrogate markers for motion with enhanced sensitivity. Our findings demonstrate a good agreement between the theoretical and experimental results for logarithmic intensity-based contrasts. Logarithmic intensity-based motion and speckle-based contrast methods are validated and compared for in vivo human retinal vasculature visualization using high-speed swept-source optical coherence tomography (SS-OCT) at 1060 nm. The vasculature was identified as regions of motion by creating LOGIV and DLOGIV tomograms: multiple B-scans were collected of individual slices through the retina and the variance of logarithmic intensities and differences of logarithmic intensities were calculated. Both methods captured the small vessels and the meshwork of capillaries associated with the inner retina in en face images over 4 mm(2) in a normal subject.