Optical power is an Important indicator of a WDM system and directly affects the transmission distance of signals. Therefore, the output optical power of a site must be as high as possible to ensure that signals can reach the peer site.

The statement is incorrect because while sufficient optical power is necessary to overcome fiber attenuation and ensure an adequate Optical Signal-to-Noise Ratio (OSNR) at the receiver, excessively high optical power introduces detrimental non-linear effects in the optical fiber. These effects, such as Self-Phase Modulation (SPM), Cross-Phase Modulation (XPM), and Four-Wave Mixing (FWM), distort the signal, increase the bit error rate (BER), and can ultimately limit the transmission distance and overall system performance. Therefore, optical power must be carefully managed within an optimal range, not simply maximized. The goal is to launch enough power to maintain a sufficient OSNR at the receiver while keeping the power below the threshold where non-linear penalties become significant.

The "True" option is incorrect because it presents an oversimplified and dangerous principle. It completely ignores the performance degradation caused by fiber non-linearities at high power levels. The fundamental principle of modern WDM system design is to balance the optical power to achieve the best possible system performance, which involves a trade-off between OSNR (favoring higher power) and non-linear penalties (favoring lower power).

1. Official Vendor Documentation: Huawei Technologies, HCIP-Transmission V2.5 Training Material. In the section covering "WDM System Transmission Technologies," it is explained that while higher optical power improves OSNR, it also increases the impact of non-linear effects. The documentation states, "When the optical power is excessively high, the non-linear effect occurs, which deteriorates system performance." This confirms that power should not be "as high as possible." (Reference: Huawei Certified ICT Professional Learning Guide, HCIP-Transmission V2.5, Chapter on WDM Principles).

2. Official Vendor Documentation: Huawei Technologies, OptiX OSN 8800/6800/3800 Product Documentation, WDM System Basic Concepts. This documentation details the physical limitations of optical transmission. In the section on "Non-linear Effect," it explicitly states that these effects are triggered when optical power density in the fiber exceeds a certain threshold, leading to signal degradation. This directly contradicts the idea that power should be maximized. (Reference: Huawei OptiX OSN Product Documentation, Section: WDM Principles > Transmission Impairments > Non-linear Effects).

3. Peer-reviewed Academic Publication / Foundational Textbook: Agrawal, G. P. (2021). Fiber-Optic Communication Systems (5th ed.). Wiley. In Chapter 5, "Nonlinear Impairments," Agrawal explains, "Although an increase in signal power improves the signal-to-noise ratio (SNR) at the receiver, it also enhances the impact of fiber nonlinearity, which becomes a limiting factor for lightwave systems... In fact, system performance can be degraded by increasing channel powers beyond a certain optimum level." (Reference: Chapter 5, Section 5.1, Introduction). DOI: https://doi.org/10.1002/9781119737339

4. University Courseware: MIT OpenCourseWare, Course 6.453J / 2.717J - Topics in Optical Communications, Spring 2006. Lecture notes on "Nonlinear Effects in Optical Fibers" describe how effects like SPM and XPM are dependent on optical intensity (power). The materials demonstrate that these effects induce phase shifts and spectral broadening that degrade signal quality, establishing that there is an upper limit to useful optical power in a transmission system. (Reference: MIT OCW, 6.453J, Lecture 10-12 Notes on Fiber Nonlinearities).