40 Gb/s silicon photonics modulator for TE and TM polarisations

Abstract

A key device in future high speed short reach interconnect technology will be the optical modulator. These devices, in silicon, have experienced dramatic improvements over the last 6 years and the modulation bandwidth has increased from a few tens of MHz to over 30 GHz. However, the demands of optical interconnects are significant. Here we describe an approach based on a self-aligned wrap around p-n junction structure embedded in a silicon waveguide that can produce high-speed optical phase modulation, whilst at the same time, capable of a high extinction ratio. An all-silicon optical modulator using a CMOS compatible fabrication process with a data rate of 40 Gb/s and extinction ratio up to approximately 6.5 dB for TE and TM polarisations is demonstrated. This technology is not only compatible with conventional complementary MOS (CMOS) processing, but is also intended to simplify and improve the reliability of, the fabrication process. Kaertner, and T. M. Lyszczarz, "High-speed silicon electro-optical modulator that can be operated in carrier depletion or carrier injection ©2011 Optical Society of America

Recent breakthroughs in carrier depletion based silicon optical modulators

“…Firstly, the waveguide should support only single mode propagation to avoid performance degradation in interferometric and resonant structures. Secondly, if polarisation independence is required without a polarisation diversity scheme, the dimensions should be chosen to support both fundamental TE and TM modes and the effective index and optical loss for both modes should be the same [38]. The waveguide geometry also affects the confinement of the optical mode within the waveguide and therefore the degree of interaction with the region of changing refractive index (depletion region).…”

“…To overcome this issue and to therefore create a design which is robust to fabrication variations and therefore results in a high yield, a fabrication process using selfaligned pn junction formation has been devised [37,38]. The process used by Thomson et al is shown in Figure 6.…”

“…Figure 7 Cross sectional diagrams of phase modulators produced using the self-aligned process [37]. Figure 8 Diagram showing how ions implanted at an angle can be used to position the pn junction within the rib waveguide whilst using a self-aligned fabrication process [38].…”

“…Gardes et al used this variant of the process to produce the phase modulator shown in the bottom of Figure 8 [38].…”

“…As mentioned when discussing the device of Gardes et al [38] as shown in Figure 8 (bottom) it is also possible to combine vertical and horizontal junction type devices. Such an approach has also been proposed by Spector et al [49] and demonstrated recently by Liow et al [42].…”