Everyone in the industry knows that the light source plays a very important role in the hardware of the optical module, and it can even be said that the light source determines the transmission distance of the optical module. A basic simplex connection consists of a laser transmitter, an optical fiber, and an optical signal receiver. The laser of the optical module as a transmitter needs to be modulated by a suitable IC driving circuit according to the signal to be transmitted. There are many types of light sources, including VCSEL\DFB\EML\DML, they are all semiconductor lasers, and this article will introduce them.
The optical module hardware consists of optoelectronic devices (lasers such as DFB/VCSEL), functional circuits (IC and RF circuits) and optical receivers. The optoelectronic devices include two parts: transmitting TX (optical transmitter) and receiving RX (optical receiver). In short, the function of an optical module is the conversion of photoelectric signals. The transmitter modulates the signal in the IC chip into an optical signal, and after transmission through the optical fiber, the receiver receives the optical signal and converts it into an analog circuit signal through the chip.
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What is VCSEL?
VCSELs, known as Vertical Cavity Surface Emitting Lasers, are a popular high-speed network laser source that consists of two wafer surfaces parallel to the surface (DBR) whose active region consists of one or more quantum wells, resulting in laser. It combines high bandwidth with low cost, making it ideal for multi-mode network options from Gigabit to 10 Gigabit. Today, in addition to being a transmitter in optical modules, it is widely used in analog broadband signal transmission, laser printers, computer mice, biological tissue analysis, Face ID, and other applications.printers, computer mouse, biological tissue analysis, chip scale atomic clock, etc.
What is DFB
Also known as distributed feedback lasers, DFBs contain periodically structured elements or diffraction gratings in their active regions. The structure constructs a one-dimensional interference grating to generate Bragg scattering, which can provide optical reflection for the laser light. Such longitudinal diffraction gratings have periodic refractive index changes that result in reflections back into the cavity. Periodic changes can be stronger or weaker in refractive index. DFB lasers tend to be very stable and not easily affected by ambient temperature etc.
The simplest type of laser is the Fabry-Perot laser, which is also the most common one. It is often used in the vicinity of the wavelength of 850nm, and the transmission distance is within 500M.
Each of the above lasers has its own characteristics, and there is a considerable gap in cost. The cost of DFB/FP/VCSEL is generally much lower than that of DML/EML, and is used for short-distance transmission. The performance of EML is better than that of DML, and it is often used at a distance of more than 80km. We know these lasers very well, if you have more questions, you are welcome to contact global-fiber-optics.