Sagi Varghese Mathai

Experimental demonstration of a balanced electroabsorption modulated microwave photonic link

A novel balanced electroabsorption modulated photonic link for simultaneous suppression of even-order distortions, third-order distortions, laser relative intensity noise (RIN), and common amplified spontaneous emission noise at the same modulator bias point was experimentally demonstrated for the first time. By biasing the balanced electroabsorption modulator at the third-order null, the third-order distortions were suppressed, while the balanced link architecture suppressed all even-order distortions and common mode noises. The fabricated balanced electroabsorption modulator (B-EAM) showed well-matched dc characteristics in terms of I-V and transfer curve. System experiments were performed to compare single-EAM and B-EAM links. In the B-EAM link, 2-dB suppression of laser RIN and 20-dB improvement in spurious free dynamic range over the single-EAM link were observed.

Distributed balanced photodetectors for broad-band noise suppression

A novel velocity-matched distributed balanced photodetector with a 50-/spl Omega/ coplanar waveguide output transmission line has been experimentally demonstrated in the InP/InGaAs material system. Distributed absorption and velocity matching are employed to increase the saturation photocurrent. A common-mode rejection ratio greater than 27 dB has been achieved. The radio-frequency (RF) link experiment conducted at 4.16 GHz shows that the relative intensity noise of the laser has been suppressed by more than 24 dB and shot-noise limited performance has been achieved. Significant improvement of signal-to-noise ratio has been observed over a wide range of frequencies and phase mismatch of input RF signals.

A High-Speed Optical Multi-Drop Bus for Computer Interconnections

Buses have historically provided a flexible communications structure in computer systems. However, signal integrity constraints of high-speed electronics have made multi-drop electrical busses infeasible. Instead, we propose an optical data bus for computer interconnections. It has two sets of optical waveguides, one as a fan-out and the other as a fan-in, that are used to interconnect different modules attached to the bus. A master module transmits optical signals which are received by all the slave modules attached to the bus. Each slave module in turn sends data back on the bus to the master module. Arrays of lasers, photodetectors, waveguides, microlenses, beamsplitters and Tx/Rx integrated circuits are used to realize the optical data bus. With 1 mW of laser power, we are able to interconnect 8 different modules at 10 Gb/s per channel. An aggregate bandwidth of over 25 GB/s is achievable with 10 bit wide signaling paths.

Generation of millimeter waves by photomixing at 1.55 /spl mu/m using InGaAs-InAlAs-InP velocity-matched distributed photodetectors

Millimeter-wave generation by photomixing at 1.55 /spl mu/m in long-wavelength velocity-matched distributed photodetector (VMDP) is experimentally demonstrated. The VMDP exhibits a dc responsivity of 0.25 A/W, a breakdown voltage of 7-9 V, and up to 15-mA dc photocurrent without damage. Millimeter-wave output powers of -21 dBm at 75 GHz and -24 dBm at 95 GHz were measured.

A High-Speed Optical Multidrop Bus for Computer Interconnections

Signal integrity constraints of high-speed electronics have made multidrop electrical buses infeasible. This high-speed alternative uses hollow metal waveguides and pellicle beam splitters that interconnect modules attached to the bus. With 1 mw of laser power, the bus can interconnect eight modules at 10 gbps per channel and achieves an aggregate bandwidth of more than 25 gbytes per second with 10-bit-wide signaling paths.

Low cost, injection molded 120 Gbps optical backplane

A low cost, blind mate, injection molded optical backplane is presented. The optical backplane consists of a 12 channel optical broadcast bus operating at 10 Gbps/channel with six blind mate optical output ports spaced 1U apart.

Electrothermally actuated free space board-to-board optical interconnect with zero power hold

We present an electrothermally actuated MEMS lens scanner for board-to-board free-space optical interconnect systems capable of zero standby power. U-shaped thermal brakes, and lens frames are designed, fabricated, and characterized with a vertical cavity surface emitting laser (VCSELs) for dynamic beam steering. We demonstrate up to 170 µm displacement, at a maximum speed of 350 µm/s. The mechanical brakes have a holding force of 1.6 mN with switching speeds of up to 100Hz. A telecentric (4-f) optical interconnect operating at 1.25 Gb/s is demonstrated. The microlens scanner increases the tilt tolerance of the board by 2.5°.

Rotational optical alignment for array based free space board-to-board optical interconnect with zero power hold

We present an electrothermally actuated, rotating microlens array for the application of aligning free-space optical interconnects. A bistable mechanical brake holds the rotating stage after alignment so it does not consume any power in steady state. A 4×4 double-sided microlens array is fabricated via micro-inkjet printing and is precisely mounted on the lens shuttle with alignment bumps. Our MEMS device has a maximum rotation angle of 2.3° at an average velocity of 5.75°/s, and is capable of correcting angular misalignment of the laser/photodetector array chips. Measured CCD images of a 1×4 VCSEL array are presented to demonstrate the function of the device.

Silicon-based monolithic 4/spl times/4 wavelength-selective cross connect with on-chip micromirrors

A monolithic 4/spl times/4 wavelength-selective cross-connect (chip area = 3.2/spl times/4.6 cm ) is realized by integrating four 4/spl times/1 MEMS wavelength-selective switches and four 1/spl times/4 passive splitters, together with a 4/spl times/4 waveguide shuffle network on a silicon-on-insulator. Wavelength-selective routing has been successfully demonstrated.

Long-wavelength velocity-matched distributed photodetectors

We have experimentally demonstrated an InGaAs-InAlGaAs-InP high-speed, high-power long wavelength velocity matched distributed photodetector (VMDP) using optical lithography. A 3-dB bandwidth of 18-GHz and an overall quantum effiency of 34% have been achieved.