In on-chip optical interconnect, dielectric waveguide arrays are usually designed with pitches of a few wavelengths to
avoid crosstalk, which greatly limits the integration density. In this paper, we for the first time propose to use multipleinput
multiple-output (MIMO), a well-known technique in wireless communication, to recover the data from entangled
signals and reduce the waveguide pitch to subwavelength range. In the proposed on-chip MIMO system, there is
significant coupling among the adjacent waveguides in the high density waveguide region. In order to recover signals,
the N×N transmission matrix of N high-density waveguides is calculated to describe the relation between each input
ports and output ports. In the receiving part, homodyne coherent receivers are used to receive the transmitted signals, and
obtain the signal in phase and /2 out of phase with local oscillator. In the electrical signal processing, the inverse
transmission matrix is utilized to recover the signals in the electronic domain. To verify the proposed on-chip MIMO, we
used the INTERCONNECT package in Lumerical software to simulate a 10x10 MIMO system. The cross section of
each waveguide is 500 nm x 220 nm. The spacing is 250 nm. The simulation verifies the possibility of recovering 10
Gbps data from the heavily coupled 10 waveguides with a BER better than 10−12. The minimum input optical power for
a BER of 10−12 is greater than -18.1 dBm, and the maximum phase shift between input laser and local oscillator can
reach to 73.5˚.
The development of a 4-channel×10-Gbits/s optical interconnect module based on a silicon optical bench (SiOB) is presented. The 4-channel vertical-cavity surface-emitting laser (VCSEL) and photo diode (PD) arrays are flip-chip assembled onto the pedestals of SiOB using Au/Sn solder bumps to form an SiOB-based bi-directional optical sub-assembly (BOSA) configuration. The optical coupling of VCSEL-to-multi-mode fiber (MMF) and MMF-to-PD without adding coupled optics is −5.2 and −2 dB, respectively. The wide alignment tolerances of 1-dB power variation for the transmitting and receiver parts to be ±15 μm are achieved. The clearly open 10-Gbits/s eye patterns of transmitting part as well as the 10−12-order bit error rate (BER) at the receiving part verify the proposed SiOB-based module is suitable for the application of 4-channel×10-Gbits/s optical interconnects.
Transmitting part of optical interconnection module with three-dimensional optical path is demonstrated. In this module,
electronic-device and photonic-device are separated on the front and rear sides of SOI substrate. The key component of
this module are 45° micro reflector and trapezoidal waveguide which are fabricated by single-step wet etching on front
side of SOI substrate. High-frequency transmission lines for 4-channel × 2.5-GHz and VCSELs are constructed on rear
side of SOI substrate. In this module, the measurement result of optical coupling efficiency is -8.09 dB, and the 1-dB
alignment tolerances are 25 μm and 26 μm on the horizontal and vertical direction, respectively. Eye diagrams are
measured at data rate of 1-Gbps and 2.5-Gbps with the 215-1 PRBS pattern and the clearly open eyes are demonstrated.
SOI-based trapezoidal waveguide with 45° reflector for non-coplanar light bending is proposed and demonstrated. The
proposed structures include 45° micro-reflector and silicon trapezoidal waveguide. Due to the SOI-based trapezoidal
waveguide with 45° reflector, light wave can be coupled into silicon waveguide easily and have higher coupling
efficiency. All of structures are fabricated using a single-step wet etching process. The RMS roughness of waveguide
sidewall and 45° micro-reflector is about 30 nm. The coupling efficiency of proposed structure is -4.51 dB, and
misalignment tolerance are 42 μm at horizontal direction and 41 μm at vertical direction. The multi-channel trapezoidal
waveguide is also demonstrated. This device can transfer the light wave at the same time, and its cross talk is about -50
dB.
In this paper, a bi-directional 4-channel x 10-Gbps optoelectronic transceiver based on this silicon optical bench (SiOB)
technology is developed. A bi-directional optical sub-assembly (BOSA), fiber ribbon assembly, PCB with high
frequency trace design, transmitter driver, and receiver TIA IC are included in this transceiver. The BOSA and PCB also
have some specific design for conventional chip-on-board (COB) process. In eye diagram measurement, the transmitter
can pass 10-G Ethernet eye mask with 25% margin at room temperature; Bit-error-rate (BER) performance from the
transmitter to receiver via 10-meter fiber can achieve 10-12 order, which confirm the transceiver's ability of 10-Gbps data
transmission per a channel.
In this paper, the proposed polymer waveguides based on silicon optical bench (SiOB) including a Si-based 45° microreflector
and multi-channel polymer waveguides at cross-sectional dimension of 40 × 20 μm2 is demonstrated. The
proposed 45° micro-reflector is fabricated on an orientation-defined (100) silicon substrate by using the anisotropic wetetching
process. The optical performance of polymer waveguides with the propagation loss of -0.35 dB/cm and the
insertion loss of -2.5 dB for the SiOB-based bending structure with polymer waveguides has been experimented. The
multi-channels polymer waveguides based on the SiOB would be applied for the chip-to-chip optical interconnect.
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