The network application of tunable laser can be divided into two parts: static application and dynamic application. In static applications, the wavelength of the tunable laser is set during use and does not change with time. The most common static application is used as a substitute for source lasers, that is, used in dense wavelength division multiplexing (DWDM) transmission systems. Let a tunable laser act as a backup for multiple fixed wavelength lasers and flexible source lasers, which can reduce the use of To support the number of line cards required for all different wavelengths in the system. In static applications, the main requirements for tunable lasers are price, output power and spectral characteristics, that is to say, the line width and stability should be equivalent to the fixed-wavelength lasers it replaces. The larger the wavelength adjustable range, the better the cost performance, without the need for fast adjustment speed. At present, there are more and more applications of DWDM systems equipped with precision tunable lasers.
In the future, tunable lasers used as backups will also require fast response speeds. When a DWDM channel fails, a tunable laser can be automatically activated to make it work again. To achieve this function, the laser must be tuned to and locked at the failed wavelength within 10 milliseconds or less, so that the entire recovery time can be guaranteed to be shorter than the 50 milliseconds required by the synchronous optical network. In dynamic applications, the wavelength of the tunable laser is required to change regularly during operation to enhance the flexibility of the optical network. This kind of application generally requires the ability to provide dynamic wavelengths, so that a wavelength can be added or proposed from a network segment to adapt to the required changing capacity. People have proposed a simple and more flexible ROADMs structure: this is an architecture based on the simultaneous use of tunable lasers and tunable filters. Tunable lasers can add certain wavelengths to the system, and tunable filters can filter certain wavelengths from the system. Tunable lasers can also solve the problem of wavelength blocking in optical cross-connections. Currently, most optical cross-connects use optical-electrical-optical switching interfaces at both ends of the fiber to avoid this problem. If a tunable laser is used at the input end to input to the OXC, a certain wavelength can be selected to ensure that the light wave reaches the end in a clear path.