The backward propagating light experiences 90° polarization rotation, i.e. In this way, forward propagating light experiences a total polarization rotation of 0° between the beam splitters, and goes into port#2. The Faraday rotator 104 always rotates the polarization axis of the incident light by 45° independent of the propagation direction, whereas the half-wave plate 106 rotates the polarization axis either by +45° or by −45° depending on its propagation direction. For each polarization path, light goes through a 45° Faraday rotator 104, a half wave plate 106, a second polarization beam splitter 108, and a second lens 110. The two orthogonal polarizations from input #1 will be split into two separate paths by a first polarization beam splitter 102. Light first goes through the lens 100 and becomes collimated. Most of the currently available polarization independent optical isolators and circulators are based on birefringent prisms or wedges, 45° Faraday rotators, and half-wave plates to spatially split, rotate the two orthogonal polarizations, and recombine the two split optical signals such as demonstrated in Shirasaki et al., “Compact polarization-independent optical circulator”, Appl. Such devices can be realized only via magneto-optic effects such as Faraday rotation. For example, dispersion compensators and optical add/drop multiplexers (OADMs), both important devices in dense wavelength division multiplexing (DWDM) systems, can be realized using circulators and Bragg gratings.īoth isolators and circulators are called nonreciprocal devices because the backward propagating optical signal does not follow the same path as the forward propagating optical signal.
port#1 to port#3, where the input from port#1 goes to port#2, the input from port#2 goes to port#3 and the input from port#3 goes to port#1. It is used, for example, to protect active devices such as lasers from back-reflected light, which makes them unstable.Īn optical circulator has multiple ports, e.g. The invention relates to optical isolators and optical circulators, important nonreciprocal devices in optical communications.Īn optical isolator transmits light in one direction and blocks it in the other direction. This application claims priority from provisional application Ser.
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