Single-mode Wavelength-division Multiplexing Research Articles

Combining Harmonic Laser Beams by Fiber Components for Refractivity–Compensating Two-Color Interferometry

A perfect spatial overlap with multiple beams of different wavelengths is a prerequisite for multi–wavelength interferometry. Beam combination with the help of fibers seems to be an interesting method for this. We investigated three different types of fiber components, multi–mode wavelength division multiplexers (MM–WDMs), single–mode wavelength division multiplexers (SM–WDMs), and endlessly single–mode polarization maintaining photonic crystal fibers (PM–PCFs). All three seem potential candidates for a perfect spatial overlap of laser beams separated by an octave, i.e. fundamental and harmonic beams. We performed an experimental study on the impact of these components on polarization, wavefront, and coherence. These properties are essential for high–accuracy interferometry. As a test system, we used the fundamental and second harmonic beam of a Nd:YAG laser system at 1064 and 532 nm as a popular system in two–color interferometry for intrinsic refractive index compensation. The experimental results show the potential of PM–PCFs for this challenging application.

A 25 Gb/s Hybrid-Integrated Silicon Photonic Source-Synchronous Receiver With Microring Wavelength Stabilization

Single-mode wavelength-division multiplexing (WDM) optical links are an attractive technology to meet the growing interconnect bandwidth demand in data center applications. This paper presents a multi-channel hybrid-integrated photonic receiver based on microring drop filters and waveguide photodetectors implemented in a 130 nm SOI process and high-speed optical front-ends designed in 65 nm CMOS. The source-synchronous receiver utilizes an LC injection-locked oscillator (ILO) in the clock path for improved jitter filtering, while maintaining correlated jitter tracking with the data channels. Receiver sensitivity is improved with a large input-stage feedback resistor transimpedance amplifier (TIA) cascaded with an adaptively-tuned continuous-time linear equalizer (CTLE). In order to stabilize the microring drop filter resonance wavelength, a peak-detector-based thermal tuning loop is implemented with a 0.7 nm range at $43~\mu \text {W}$ /GHz efficiency. When tested with a waveguide photodetector with 0.45 A/W responsivity, the receiver achieves -8.0 dBm OMA sensitivity at a BER $= 10^{\mathrm {-12}}$ with a jitter tolerance corner frequency near 20 MHz and a per-channel power consumption of 17 mW including amortized clocking power.