1. Field of the Invention
This invention addresses a multi-wavelength fiber optic transmitter related to directly modulated laser sources and multifunctional filters.
2. General Background and State of the Art
Fiber optic communication systems use a variety of transmitters to convert electrical digital bits of information into optical signals that are carried by an optical fiber to a receiver. In a directly modulated transmitter the output intensity of a laser is modulated by directly changing the injection current driving the laser. In an externally modulated transmitter, the intensity of a continous wave laser is modulated via the use of a modulator, which changes the intensity of the laser light. Directly modulated semiconductor lasers are typically compact, integrable, and have large responses to modulation. They are comparatively inexpensive than externally modulated transmitters, which require an intensity modulator following the laser source. However, directly modulated lasers may suffer from a drawback; namely, their outputs may be highly chirped. As a result, directly modulated lasers are normally used for short reach applications because the inherent chirp of the laser causes the transmitted pulses to be distorted after propagation in dispersive fiber. For longer reach applications, external modulation is used. However, external modulation requires a costly modulator that consumes power, introduces loss, and takes up board space.