# Integrated Components and Solutions for High-Speed Short-Reach Data Transmission
## 4 Some Integrated Solutions for Short-Reach Transmission Systems
### Transceiver Integration Scheme Based on Direct Detection  
For IM/DD systems, the easiest way to increase transmission rate is to transmit multi-channel data streams in parallel, but this kind of system needs to use multiple sets of tranmitter and receiver components, which would lead to the increase of system cost to a certain extent. For reducing cost constraints, a transceiver integration solution based on direct detection, which can generate, transmit and detect multi-channel intensity signals at the same time, had been designed as depicted in Figure 10. The transmitter part of the transceiver integration solution, which consisted of multiple lasers, multiple drivers, and multiple MZM modulators, can generate multi-channels optical signals. After fiber transmission, the receiver part including multiple single-end PDs and multiple TIAs, would be able to detect multi-channel transmission signals. Based on this principle, [PERSON] et al. successfully demonstrated a 16 channels 25-Gbit/s OOK optical transceiver on package  
Figure 8: The principle of the simplified detection scheme. PAM: pulse amplitude modulation; SMF: single mode fiber; Pol. : polarization; OBPF: optical band-pass filter; PD, photodetector; (From [103] © 2021 OSA). Figure 9: Twenty-five km transmission performance of the 2 \(\times\) PDM-PAM4 and the single PDM-PAM4 systems. (**a**) BER at 4 \(\times\) 20-Gbit/s and (**b**) 4 \(\times\) 40-Gbit/s. PDM: polarization division multiplexing; FEC: forward error correction; (From [101] © 2021 OSA). SiP [28]. The photographs of electronic integrated circuit (EIC) and photonic integrated circuit (PIC) of the high-density 16 channels optical transceiver where transmitter and receiver components were highly integrated in the chips were shown in Figure 11a,b. At the transmitter section of the transceiver, multiple wavelength lights emitting from 4 \(\times\) 4 channels laser diodes (LDs) were modulated by 2 \(\times\) 8 Mach-Zehnder interferometer (MZI) modulators under push-pull type, which were driven by 2 \(\times\) 8 electronic drivers, to generate 16 channels 25-Gbit/s OOK optical signals. Then, the multi-channel optical signals were fed into an array of 16 grating couplers by waveguides and coupled into 16 optical fiber transmission links, respectively. At the receiver side, multi-channel optical signals were coupled into the PIC waveguide through 16 grating couplers. Finally, the transmission signals were detected by 16 PDs and amplified by TIAs. Figure 11: Photographs of (**a**) electronic integrated circuit (EIC) and (**b**) photonic integrated circuit (PIC) of the high-density 16 channels optical transceivers where transmitter and receiver elements were highly integrated in the chips; 4 \(\times\) 4 channels laser diodes (LDs) were assembled and 32 channels (32 ch) grating couplers (GCs) were formed in the PIC; Ch_1: the first channel; Ch_2: the second channel; TIA: trans-impedance amplifier; (From [28] © 2021 IEEE). Figure 10: Block diagram of transceiver integration scheme based on direct detection. LD: laser diode; MZM: Mach-Zehnder modulator; RF: radio-frequency; SSMF: standard single mode fiber; TIA: trans-impedance amplifier; PD: photodetector. In here, the performance of multi-channel transceivers was further evaluated by the eye diagram and BER. Figure 12a shows the optical eye diagrams of all transmitter channels, which depicted clear eye openings. Subsequently, the inter-channel crosstalk penalty among multi-channel transmitters was measured by a commercially available receiver module. The channel 4 (ch_4) were selected as a victim channel to study the effect of a crosstalk penalty from other aggressor transmitter channels. As shown in Figure 12b, the sensitivity changes of ch_4 were measured at multi-channel transmitters operations. The total penalty between all channels driving and only ch_4 driving was about 1.4-dB, and it was considered to be negligible in high-density assembled configuration.