3.46, Photonic Materials and Devices Spring 2004 Prof. Lionel Kimerling Materials for Microphotonics

Lecture Comments

Optical Interconnection

1. insensitive to EMI (electromagnetic interference) - links don’t pick-up or create EM fields - receiver amplifiers can exchange noise ⇒ high Po , ∴ low gain required 2. No ground loops 3. No RC contribution to signal skew 4. Less complex signal processing - interconnect not designed into logic 5. Typical application: mainframe to mainframe - 1 Gb/s - MM fiber (low cost connectors) - 50 fibers/cable

Issues 1. Materials Selection & Processing 2. Process Integration 3. Speed (bandwidth) 4. Power dissipation 5. Footprint ( area of device/circuit) 6. Crosstalk (noise) 7. I/O (density, bandwidth) 8. Packaging (insertion loss)

Robust Design 1. Architecture

parallel microprocessors global electrical memory power supply

global photon clock source

The global view of the microprocessor

3.46, Photonic Materials and Devices Materials for Microphotonics Prof. Lionel Kimerling Page 1 of 7 Lecture Comments

An example of a transceiver: the silicon substrate supplies only electrical power and control signals to the InP substrate on which all the optical components are present.

2. Electronic/ Photonic Partitioning a) Switching speed of electronics - 50-200 GHz limit? - power dissipation - OE transduction - variation

b) Photonic Switching - speed : χ (3) (non resonant) - high power (non interactive bosons )

3.46, Photonic Materials and Devices Materials for Microphotonics Prof. Lionel Kimerling Page 2 of 7 Lecture Comments

3. Materials Selection c) Silicon - well developed technology - emerging optical applications - good thermal properties d) Compound Semiconductors - optical devices (direct gap) - LSI circuits (MMIC) c) Hybrid materials technology - monolithic (hetero-epitaxy) - hybrid: ‘wafer’ bonding - hybrid: solder bump

4. Process Integration a) Photonics requires dielectric confinement of devices and waveguides. wafer bonding – multilayer deposition – free space b) Materials compatibility c) - single crystal - Polycrystal - Glass

3.46, Photonic Materials and Devices Materials for Microphotonics Prof. Lionel Kimerling Page 3 of 7 Figure 3. Morphology of passive optical devices.

(a) is a waveguide having a curvature. The curved tube is made to have higher refractive index relative to the surroundings, and changes the direction of light in it.

(b) is a ring shaped waveguide. This works as a resonator when placed close to other waveguides.

(c) is a directional coupler. When two waveguides are close to each other, application of a field results in light switching from one waveguide to the other.

(d) is a Y junction. A building block in planar light wave circuits, it allows the light energy in a guided mode to be divided between two output waveguides.

(e) is an X bifurcation. The refractive index of the central portion can be changed to make this X bifurcation work as an optical switch.

(f) is a mirror. It can couple the device with external system.

(g) is a diffraction grating. It is often used in LDs to make reflectors.

(h-1) and (h-2) are two types of circular lenses. (h-3) is the top view for both (h-1) and (h-2). (h-1) is a convex dome, which has higher refractive index than the underlying layer. (h-2) is a concave dome, which provides longer optical path lengths.

3.46, Photonic Materials and Devices Materials for Microphotonics Prof. Lionel Kimerling Page 4 of 7 (i) and (j) are prisms. The fragmented meniscus and the triangular shaped parts have higher refractive index than the surrounding parts.

Physical and electrical properties of materials important to optoelectronic packaging.

Material CTE Thermal Young’s Dielectric Electrical Conductivity Modulus Constant Resistivity* (x 10-6/K) (W/m K) (GPa) (at 1 MHz) (Ω-cm) Silicon 2.7 130-150 113 12 >105 Alumina 6.3-9.1 12-26 360 8-10 >1014 Beryllia 5-7 200-280 350 5.8-6.7 1015 Glass 4.6 1.2 69 5 >1013 AIN 3.1 60-230 340 8-10 >1014 Silica 5-6 42 72 3.7 >1014 Diamond 1.5-2.8 400-2000 890-970 5.7 >1013 Silicon Nitride 1.3 238 300 6.1 >1011 GaAs 5.7 46 76 13.1 >108 InP 4.5 70 — 12.35 >106 Aluminum 2.4 238 62 — 2.7x10-6 Copper 16.8 398 110 — 1.7x10-6 Gold 14.3 315 74 — 2.2x10-6 *Intrinsic or near-intrinsic resistivity.

Optical coupling performance comparison for (a) cleaved standard and (b) lensed standard single-mode fiber. Lensed fiber offers higher maximum coupling efficiency at the expense of greater sensitivity to misalignment.

3.46, Photonic Materials and Devices Materials for Microphotonics Prof. Lionel Kimerling Page 5 of 7 Monolithic time-delay “unique-select” network integrating waveguides with 1.3µm detectors on GaAs substrate, by Hughes.

3.46, Photonic Materials and Devices Materials for Microphotonics Prof. Lionel Kimerling Page 6 of 7 (a)

(b) Sealed Windows

Optical Optical Axis Axis OEIC

(c ) Optical Fiber Seals

Optical Fiber Optical Fiber OEIC

An illustration of three techniques for sealing OEIC modules from the environment while allowing optical information free access.

3.46, Photonic Materials and Devices Materials for Microphotonics Prof. Lionel Kimerling Page 7 of 7