Tunable laser technology application in optical fiber communication
1, an overview of the optical communication field of traditional light source is based on the fixed wavelength laser module, with the continuous development of optical communication system and application promotion, the shortcoming of fixed wavelength laser gradually emerge: on the one hand, with the development of DWDM technology, the system achieved hundreds of wavelength number, the need to provide protection, each laser backup must be provided by the same wavelength of laser, so lead to increase in the number of backup laser, rising costs; Another aspect due to the need to distinguish between the fixed laser wavelength, so the type of laser wavelength as the increases with the increasing of the number of, make the management complexity and inventory level; Again if you want to support dynamic wavelength assignment in optical network, improve network flexibility, a large number of different wavelengths will be equipped with a fixed laser, but each laser utilization rate is very low, cause the waste of resources. Aiming at these deficiencies, along with the development of the semiconductor and related technology, people has successfully developed the tunable laser, namely on the same laser module to control the output must be within the bandwidth of different wavelengths, and the values of these wavelengths and interval are meet the itu-t T's request. For the next generation optical networks, the tunable laser is the key factor of the intelligent optical network, can provide operators with greater flexibility, supply speed faster wavelength, and zui to achieve lower costs. Future long wavelength optical network will be a dynamic system, the network can be realized in a very short period of time a new wavelength assignment, due to the long distance transmission technology without the use of regenerator, thereby saving a lot of money. Tunable laser is expected to provide new tools for the future communication network, is used to manage the wavelength, improve the efficiency of the network, and develop the next generation optical network. Zui attract an application can be reconfiguration of light plugged multiplexer ( ROADM) 。 Dynamic reconfiguration of the network system will appear in the network market, large adjustment range of tunable laser will gain greater demand. 2, principle and characteristics of tunable laser technology from the tuning principle of three kinds of control technology: current control, temperature control and mechanical control technology and other types. With electronic control technology is the wavelength tuning by changing the injection current implementation, have ns level tuning speed, wide tuning bandwidth, but the output power is small, mainly include the SG - based on electronic control technology DBR（ Sampling grating DBR) And GCSR ( Auxiliary sampling grating directional coupling of back reflection) Laser. Temperature control technology is active area by changing the laser refractive index, so as to change the wavelength of the laser output. The technology is simple, but the slow speed, adjustable belt width, only a few nm. Based on the temperature control technology are mainly DFB ( Distributed feedback) And the DBR ( Distributed Bragg reflection) Laser. Mechanical control is mainly based on MEMS ( Micro-electro-mechanical systems) Technology to complete the selection of the wavelength, with larger adjustable bandwidth, high output power. Based on the mechanical control technology mainly include DFB ( Distributed feedback) 、ECL（ External cavity laser) And VCSEL ( Vertical cavity surface emitting laser) Structures, etc. Below will be taken from these a few respects the principle of tunable laser. Which focuses on the current mainstream zui tunable technology & ndash; — Current tuning technology. 2. 1 the temperature control technology based on temperature control technology is mainly used in the DFB structure, the principle is to adjust the temperature of the laser cavity, which can make the launch of different wavelengths. A kind of technology on the basis of the principle of the tunable laser wavelength adjust depend on control InGaAsPDFB laser work change in a certain temperature range. Device through the built-in lock wave ( Etalon and monitoring detector) , the continuous laser light output can be locked on the 50 GHZ intervals specified by the ITU grid. General device encapsulated within two independent TEC, one is used to control the wavelength of laser chip, another to ensure that the device lock wave and power detecting probe temperature within the work. This kind of laser zui big advantage is that their performance is similar to the fixed wavelength laser, with high output power, wavelength stability is good, work the characteristics of simple, low cost and mature technology. But there are two main disadvantages: one is the individual components of tuning the width of a narrow, usually only a few nm, 2 it is tuning time is long, generally takes a few seconds of time tuning stability. 2. 2 machinery control technology based on MEMS to implement commonly used control technology. A kind of mechanical control technology based on tunable laser with MEMs - The DFB structure. Tunable laser, mainly including DFB laser array can be tilted MEMs lenses and other control and auxiliary parts. For DFB laser array area there are a number of DFB laser arrays, each array can generate bandwidth is about 1. 0 nm in the interval of 25 GHZ specific wavelengths. By controlling the MEMs mirror rotation Angle to need to choose a particular wavelength, thus output needs certain wavelengths of light.