Nature Photonics 3, 91–94 (2009); published online: 11 January 2009; corrected online 15 April 2009.

The authors wish to correct equation (4) of the above Letter; it should have appeared as shown below. This also affects the final sentence in the third paragraph from the end of page 92, which should now read: For this device, our calculation indicates that over a frequency bandwidth of 1.2 THz, the contrast ratio between forward and backward transmission coefficients is above 40 dB.