tailieunhanh - Optical Networks: A Practical Perspective - Part 25

Optical Networks: A Practical Perspective - Part 25. This book describes a revolution within a revolution, the opening up of the capacity of the now-familiar optical fiber to carry more messages, handle a wider variety of transmission types, and provide improved reliabilities and ease of use. In many places where fiber has been installed simply as a better form of copper, even the gigabit capacities that result have not proved adequate to keep up with the demand. The inborn human voracity for more and more bandwidth, plus the growing realization that there are other flexibilities to be had by imaginative use of the fiber, have led people. | 210 Components Figure A two-state pop-up MEMS mirror from LGT98 shown in the popped-up position. The mirror can be moved to fold flat in its other position. Figure An analog beam steering mirror. The mirror can be freely rotated on two axes to deflect an incident light beam. of flexures to an outer frame. The flexures allow the mirror to be rotated freely on two distinct axes. This mirror can be controlled in an analog fashion to realize a continuous range of angular deflections. This type of mirror is sometimes referred to as an analog beam steering mirror a gimbel mirror or a 3D mirror. A mirror of this type can be used to realize a 1 x n switch. The control of these mirrors is not a trivial matter with fairly sophisticated servo control mechanisms required to deflect the mirrors to their correct position and hold them there. Switches 211 Figure An n x n switch built using two arrays of analog beam steering MEMS mirrors. Figure shows a large n x n switch using two arrays of analog beam steering mirrors. This architecture corresponds to the Spanke architecture which we discussed in Section . Each array has n mirrors one associated with each switch port. An input signal is coupled to its associated mirror in the first array using a suitable arrangement of collimating lenses. The first mirror can be deflected to point the beam to any of the mirrors in the second array. To make a connection from port i to port j the mirror i in the first array is pointed to mirror j in the second array and vice versa. Mirror j then allows the beam to be coupled out of port j. To make a connection from port i to another port say port k mirror i in the first array and mirror k in the second array are pointed at each other. Note that in order to switch this connection from port i to port k the beam is scanned from output mirror j to output mirror k passing over other mirrors along the way. This does not lead to additional crosstalk because a connection is .