We set the phase distribution (hereafter phase function) of the LCOS in a quadratic form Φ(x), as shown in Fig. The light reflected by the LCOS travels along the incoming light axis, re-enters the AWG, and is output from the AWG to the circulator. The LCOS, which has a large number of fine phase modulator pixels on the dispersion axis (x), modulates the wavefront of the incoming light. The signal is then focused onto the LCOS by a focusing lens in the x direction and by a focusing and collimating cylindrical lens in the y direction. ![]() An optical signal is fed into the AWG via a circulator and is dispersed by the AWG. The LCOS is placed on the image plane of a 2-f type focusing system. The configuration of a channelized TODC consisting of an AWG and an LCOS is shown in Fig. Single-pass channelized TODC: principle, design, and characteristics In addition to this configuration, we also describe a double-pass configuration that enabled us to increase the channel count of the channelized TODC without narrowing its transmission bandwidth and demonstrate 40-channel TODC operation with a 100-GHz channel spacing. We have demonstrated six-channel (6-ch) independent CD compensation using a single-pass optical configuration. In this report, we describe a spectrometer-based TODC consisting of an AWG as a spectrometer and an LCOS as the SLM. The AWG is fabricated using planar lightwave circuit (PLC) technology, which has several advantages including reliability, design flexibility and mass producibility. To obtain a large CD with a spectrometer-based TODC, it is advantageous to use a highly dispersive grating as the spectrometer, such as a virtually imaged phased array or an arrayed-waveguide grating (AWG). However, since a bulk grating was used as the spectrometer, it was difficult to obtain a large CD (~400 ps/nm) because the diffraction order of a bulk grating is small. In these studies, a microelectromechanical system (MEMS) mirror array, or a liquid-crystal-on-silicon (LCOS) device was used as the SLM. Channelized TODC operation in RODM node.Ĭhannelized TODCs with a spectrometer-based configuration consisting of various grating and spatial light modulator (SLM) devices have been demonstrated. ![]() ![]() 1(b)), which can set different CD values for different WDM channels independently, is attractive for use in such a system because it reduces the device count as well as the power consumption of the network.įig. 1(a), this approach is costly because it needs a large number of TODCs. TODCs have already been reported using a number of technologies including lattice filters, etalons, fiber-Bragg gratings, and spectrometer-based TODCs –.Ī conventional TODC compensates for an optical signal with a single CD value, so one TODC is required for each wavelength division multiplexing (WDM) channel to obtain a different compensation value for each channel independently. ![]() The TODC offers the adjustability needed to handle such CD changes. In such ROADM networks, the transmission length and chromatic dispersion (CD) vary when a routing path is switched at the ROADM node. A tunable optical dispersion compensator (TODC) is an indispensable device for a reconfigurable optical add/drop multiplexed (ROADM) network with a high transmission bitrate such as 40 Gbit/s or higher.
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