**2.1 CMOS chipsets for HDMI active optical cables**

High-performance networking and computing systems mandate high-speed optical interconnects to satisfy the extreme bandwidth requirements [1, 2]. Previously, parallel optical interconnects could provide terabit-per-second data bus in board scale [1] and also multi-gigabit-per-second data transport for mega-cloud systems, reaching a 100-m distance [2]. We have recently demonstrated active optical cables specified by HDMI 2.0 standard for true 4K video at 60-Hz resolution for 10-m distance, where 4-channel CMOS Tx and Rx chipsets were integrated on a printed circuit board (PCB) with pluggable connectors at its both ends to transport data via plastic optical fibers (POF) [3]. POF is well known for its benefits over costly glass optical fibers such as low cost, lightweight, resilient to bending, etc. [4]. In this section, we demonstrate a 10-m AOC utilizing graded-index POF with 60-dB/km loss characteristics that equips 4-channel CMOS transmitter and receiver chipsets to support HDMI 2.1 specification, i.e., true 8 Mpixel/60 fps display with no data encoding or compression. For this purpose, it is necessary to align optical devices, optical subassembly, and POF precisely within the tolerance range of 10 μm.

monitor for checking if each photodiode emits appropriate photocurrents to the

was carefully selected to be 400 μm to prevent extra coupling loss from

loss. Also, the thermal loss of a VCSEL diode is typically 2 dB at 70<sup>o</sup>

19.2% faster rising time in the output waveforms.

There are various sources of coupling loss occurred in its optical alignment. For example, 3-dB coupling loss occurs at the interface of a VCSEL diode to prism due to 50% coupling efficiency, whereas 1-dB coupling loss occurs at the interface of a photodiode to prism [5]. The optimal pitch between VCSEL diodes and photodiodes

Meanwhile, the low-cost POF shows 60-dB/km attenuation, resulting in 1-dB

**Figure 2** shows the schematic diagram of a 10-Gb/s VCSEL driver that consists of a main driver, a pre-driver, an EQ, and an input buffer. The main driver operates with two current sources, i.e., the bias current (IBIAS) and the modulation current (IMOD). When M5N in the main driver is turned off, the current sum (IBIAS+IMOD) flows through the VCSEL diode. When M5N is on, only IBIAS is supplied to the VCSEL diode. The feedforward preemphasis is conducted by using a capacitor (CFF) to alleviate the distortion effects of the output waveforms from the bond-wire inductance and the parasitic capacitance of a VCSEL diode. Simulations confirm

Considering the device reliability of VCSEL diodes, it is not clever to keep IBIAS

to flow continuously through the array chip because it will rise the device

optical power budget is set to 10 dB including 3-dB additional margin, which leads to the feasible assumption of 0-dBm Tx power and 10-dBm Rx sensitivity.

C. Hence, the

4-channel Rx array chip.

*CMOS Integrated Circuits for Various Optical Applications*

*DOI: http://dx.doi.org/10.5772/intechopen.92014*

*2.1.1 Optical power budget*

misalignment.

*2.1.2 VCSEL driver*

**Figure 2.**

**131**

*Schematic diagram of the VCSEL driver.*

**Figure 1** shows the block diagram of the 4-channel optical ICs, where a 4 channel Tx and Rx chipsets are separately integrated with optical devices. Here, we have employed a number of circuit techniques to optimize the performance, which include feedforward preemphasis at Tx for high-speed operations; input data detection (IDD) for automatic turning off each vertical-cavity surface-emitting laser (VCSEL) diode during its idle time to lower current consumption; double-gain feedforward transimpedance amplifier (TIA) for high gain; selective equalizer for either 6 or 10 Gb/s, depending upon desired HDMI specification; and photodiode

**Figure 1.** *Block diagram of the 4-channel optical ICs.*

monitor for checking if each photodiode emits appropriate photocurrents to the 4-channel Rx array chip.

### *2.1.1 Optical power budget*

**2. Circuit description**

*Integrated Circuits/Microchips*

range of 10 μm.

**Figure 1.**

**130**

*Block diagram of the 4-channel optical ICs.*

**2.1 CMOS chipsets for HDMI active optical cables**

High-performance networking and computing systems mandate high-speed optical interconnects to satisfy the extreme bandwidth requirements [1, 2]. Previously, parallel optical interconnects could provide terabit-per-second data bus in board scale [1] and also multi-gigabit-per-second data transport for mega-cloud systems, reaching a 100-m distance [2]. We have recently demonstrated active optical cables specified by HDMI 2.0 standard for true 4K video at 60-Hz resolution for 10-m distance, where 4-channel CMOS Tx and Rx chipsets were integrated on a printed circuit board (PCB) with pluggable connectors at its both ends to transport data via plastic optical fibers (POF) [3]. POF is well known for its benefits over costly glass optical fibers such as low cost, lightweight, resilient to bending, etc. [4]. In this section, we demonstrate a 10-m AOC utilizing graded-index POF with 60-dB/km loss characteristics that equips 4-channel CMOS transmitter and receiver chipsets to support HDMI 2.1 specification, i.e., true 8 Mpixel/60 fps display with no data encoding or compression. For this purpose, it is necessary to align optical devices, optical subassembly, and POF precisely within the tolerance

**Figure 1** shows the block diagram of the 4-channel optical ICs, where a 4 channel Tx and Rx chipsets are separately integrated with optical devices. Here, we have employed a number of circuit techniques to optimize the performance, which include feedforward preemphasis at Tx for high-speed operations; input data detection (IDD) for automatic turning off each vertical-cavity surface-emitting laser (VCSEL) diode during its idle time to lower current consumption; double-gain feedforward transimpedance amplifier (TIA) for high gain; selective equalizer for either 6 or 10 Gb/s, depending upon desired HDMI specification; and photodiode

There are various sources of coupling loss occurred in its optical alignment. For example, 3-dB coupling loss occurs at the interface of a VCSEL diode to prism due to 50% coupling efficiency, whereas 1-dB coupling loss occurs at the interface of a photodiode to prism [5]. The optimal pitch between VCSEL diodes and photodiodes was carefully selected to be 400 μm to prevent extra coupling loss from misalignment.

Meanwhile, the low-cost POF shows 60-dB/km attenuation, resulting in 1-dB loss. Also, the thermal loss of a VCSEL diode is typically 2 dB at 70<sup>o</sup> C. Hence, the optical power budget is set to 10 dB including 3-dB additional margin, which leads to the feasible assumption of 0-dBm Tx power and 10-dBm Rx sensitivity.
