We present our design and fabrication methodology of planar photonic crystal wavelength switches and the optical micro-bench surrounding them. The core device is a channel add-drop multiplexer (CADM) whose pass/transfer element can be turned off and on in tens of nanoseconds. The photonic crystal consists of a regular triangular array of SiO2 -filled holes in an amorphous Ge3Si film. The film is sandwiched between two SiO2 cladding layers. The pass and transfer buses consist of linear extended defects in the crystal, with the pass bus and each drop bus separated by a cavity resonator defect tuned to each wavelength. There is a small region where an ECD-designed chalcogenide alloy is incorporated into each resonator. Switching is accomplished by changing the structure of the chalcogenide between amorphous and crystalline, using a short wavelength diode laser. The optical bench consists of photonic wire waveguides formed in the Ge3Si film and deep trenches in an underlying thick SOI film to accommodate bonded access fibers, both features being photolithographically co-aligned to the photonic crystal array. This, along with our impedance-matching interface designs, assures that there is low input-output power loss. The local reconfigurability in effect elevates the CADM to an all-optical router. Sub-100 nanosecond latency enables packet-level discernment. The large difference in optical constants of the two chalcogenide phases provides high on-off contrast (low crosstalk). The stability of the two phases gives complete latching nonvolatility. Our current progress in building and testing prototypes of our switches is also presented.
We describe a method to achieve phased array steering at the near infrared (i.e., optical) frequencies used in telecommunication (1550 nm) as an alternative to physical movement of standard mirrors. A stationary and planar multi-layer device utilizes a chalcogenide phase change material1,2 (PCM) as its active element whose refractive index changes by very large amounts (> 1.7X) between its amorphous and crystalline states. The optical phase angle upon reflection off this surface can change by more than 180° depending on physical state of the PCM. Phasor analysis is used to explain how such large phase angle shifts can be accomplished for a PCM layer only 20 nm thick. Not only can this be used to make rewritable diffractive elements, but since the phase taper can be made nearly continuous, the surface can also steer the beam in non-specular directions with no diffractive distortions. To date, we have steered a telecom beam 2° in one direction, and expect deflections by more than 10°. The steering is broad-banded, self latching, and potential switching speeds are expected to be less than 100 ns.