Microsoft Word - ecoc_pdp_090913

We demonstrate a 1×2 wavelength-division multiplexing switch for few-mode fiber based on a spatial light modulator. We measure its crosstalk, frequency roll-off, mode dependence and other transmission characteristics. Introduction In response to saturating capacity achievable in single-mode fiber, space-division multiplexing (SDM) has become an established research area. Parallelization and component integration can potentially reduce power consumption, device footprint and system cost. It is hoped that a combination of multi-core and multi-mode technology will enable up to two orders of magnitude increase in capacity per fiber. Longhaul transmission using few-mode fiber (FMF) has already been demonstrated, along with few-mode amplifiers that can simultaneously amplify parallel modal channels in a single doped FMF. Another key element in optical networks is the optical switch. Few-mode diplexers and wave blockers have been demonstrated to date. Ultimately, a practical switch should allow bandwidth allocation at a frequency granularity comparable with singlemode devices. Due to mode coupling, it is likely that systems based in FMF will continue using wavelength-division multiplexing (WDM), with all spatial modes of a wavelength being allocated as a spatial superchannel to allow multiple-input multiple-output (MIMO) processing at the receiver. We recently proposed a few-mode (FM) switch of this type, using a spatial light modulator (SLM) as the switching element. In this paper, we provide the first experimental demonstration of an SLM-based FM switch. Switch Architecture Fig. 1(a) and (b) show top and front views of our SLM-based few-mode switch. At the left are three graded-index FMFs terminated by 8 mm collimators. Two 45° prisms, (i) and (ii), are used to stack the three beams vertically at a mutual spacing of 4 to 5 mm. The port corresponding to the middle beam is designated as the input port, and the other two are outputs ports. The beams pass through three f = 200 mm lenses, a grating, and a polarization demultiplexer (PolDemux) before impinging on the SLM. Lens 1 focuses the vertically stacked beams to point A. The setup between A and the SLM (with the PolDemux removed) is a 4f system. The magnification factor from FMF to the SLM is (200/8) = 25, and the 1/e beam radius at the SLM is ~160 μm for the LP01 mode. The beams corresponding to Ports 1 and 2 impinge on the SLM at vertical angles of θ1 ≈ 1.2° and θ2 ≈ 1.4° relative to the input beam. Programming the SLM with a linearly varying phase in the vertical (y) direction will switch the input beam to the desired output port. Wavelength switching is enabled by a 940 lines/mm transmissive grating placed at the focus of Lens 2, while Lens 3 parallelizes the spectral components so they impinge the SLM at normal incidence in the horizontal plane at a wavelength resolution of