A simple method for fabricating fiber-embedded boards using a grooving technique is described that is quite cost effective and fully compatible with conventional printed circuit board (PCB) processes with no necessity for a specially designed wiring machine. FR-4 plates are grooved using a dicing saw machine and followed by placing optical fibers into the grooves. The fiber-embedded PCBs are laminated by conventional PCB processes at a temperature of 180°C for 1 h under 47 kg/cm2 of pressure. The 50/125-µm glass fibers, and the polyimide-coated glass fibers are laminated successfully. In the fiber-embedded boards with a length of 10 cm, the variation of center positions of the embedded glass fibers is about ±5 µm. The transmitted optical power through the fiber-embedded boards shows a good uniformity of less than ±0.5 dB variation from the average value for the 12 fiber channels. Data transmission through the board at data rates of 2.5 Gbits/s is achieved. After confirming the successful laminations and the data transmission with the small-scale fiber-embedded boards, a large-scale prototype of the fiber-embedded board for a backplane application is successfully fabricated.
We demonstrated a new architecture of the optical interconnection system which can be applied in the waveguide-embedded optical printed circuit board (PCB). We used 45° ended optical connection rods as a medium to guide light paths perpendicularly between surface-emitting lasers (or photodiode) and waveguides. A polymer film of multimode waveguides with cores of 100μm x 65μm was sandwiched between conventional PCBs. We made through-holes with a diameter of ~140μm on the PCB, passing through the waveguide cores, using Ti-sapphire laser drill. The optical rods were made of the segment of multimode silica fiber ribbon. One end of the fiber segment was cut with 45° and the other end with 90° by using the high power laser cutting technique. These fiber rods were inserted into the through-holes formed in the PCB, adjusting the insertion depth to locate the 45°-end of rods near the waveguide core. From this interconnection system, we achieved 12channels optical transmission link through a waveguide with a channel pitch of 250μm in the optical PCB. This new interconnection structure using the optical connection rods is well compatible with the fabrication processes of conventional electronic PCB which is employing the through-hole formation by laser drill and the lamination of plastic films by compression.
2.5Gb/s optical transmitter IC for vertical-cavity surface-emitting lasers (VCSELs) was fabricated using the TSMC 2-poly 4-metal process of 0.35μm Si-CMOS. This IC has four channels with 250μm pitch for VCSEL array. The transmitter IC consists of four parts, i.e., buffer, differential amplifier, threshold current controller and modulation current controller. Modifying the threshold current and modulation current, we attained a wide range of the operation current from 1mA to 20mA. The measurement of the IC chip packaged with a 850nm VCSEL array, we obtained a maximum optical output power of 2dBm in 2.5Gb/s operation and an extinction ratio of 5~25dB.
We fabricated a low-power CMOS post amplifier for asynchronous transfer mode passive optical network system. In this amplifier the multistage feedforward type was employed for high-speed response. The circuit consists of adaptive threshold control with wide input range and limiting amplifier. This amplifier was fabricated in a standard 3.3V 0.35?m CMOS technology and showed a low power consumption of 80mW at the supply voltage of 3.3V. The limited output voltage swing was 200mVP-P .
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