Hyperfine wavelength division multiplexing (HWDM) based on the virtually-imaged phased-array (VIPA)
A modified Fabry-Perot etalon termed a virtually-imaged phased-array (VIPA) was recently introduced as an optical spectral disperser. One important application of the spectral disperser is in the area of wavelength division multiplexing (WDM) fiber communication. Current WDM is operated at channel spacing of tens of GHz (standard is 50 GHz or 100 GHz), which is referred as dense WDM (DWDM). Hyperfine WDM (HWDM) has been proposed by the industry to utilize the optical communication band more efficiently at channel spacing of several GHz. Such a narrow channel spacing is a big challenge for DWDM wavelength demultiplexers. In experiment using a solid VIPA at a 50 GHz free spectral range (FSR) and a single mode fiber array with eight ports, we have implemented an eight-channel hyperfine wavelength demultiplexer at 1.55 um, and we obtain a channel spacing around 3 GHz, more than or equal to 23 dB adjacent channel isolations and more than or equal to 30 dB nonadjacent channel isolations. Firstly, using the eight-channel wavelength demultiplexer, we test data detection at 622 Mbps (OC-12) in a HWDM system configuration. The single channel filtering effects as well as the adjacent channel crosstalk are studied in detail. DWDM transmitter consists of multiple laser diode array sources, which have a stable range of several GHz. The DWDM transmitter can't be used in HWDM as HWDM system requires highly stable channel sources. Here, we demonstrate a novel HWDM transmitter via sub-carrier multiplexing (SCM), where multiple RF/microwave sub-carriers are modulated on to an optical carrier for fiber transmission. For the first time to our knowledge, we demonstrate a 4-user, around 3 GHz-spaced hybrid SCM-HWDM system on a 50-km fiber link, in which the SCM is used to generate closely spaced channels in the transmitter, while a hyperfine wavelength demultiplexer is used at the receiver to separate the sub-carrier channels for optical direct detection. A hyperfine blocking filter is employed in the transmitter to realize optical single sideband (O-SSB) modulation with strong carrier suppression. This work is the first demonstration of a multiple-user HWDM system at the narrowest channel spacing around 3 GHz.
Weiner, Purdue University.
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