Application of reflective MEMS VOA in optical communication system
1 Introduction Variable Optical Attenuator (VOA) is an important optical passive device in optical fiber communication. It realizes real-time control of signals by attenuating transmitted optical power. It can be used with optical wavelength division multiplexer (WDM) and optical splitter Optical devices such as detectors (TAP PD) and erbium-doped fiber amplifiers (EDFA) constitute ROADM, VMUX, flat gain EDFA and other modules, and can also be directly used for overload protection of optical receivers. In addition, the measurement and calibration of optical power meters and other instruments also need to use VOA. With more and more applications of VOA in optical communications, the requirements for its functions are also getting higher and higher: VOA should be able to accurately control the power of optical signals and provide stable attenuation for each channel wavelength; in dynamic network nodes Above, its response time should be in the ms level; in ultra-long-distance DWDM systems, VOA must have sufficient sensitivity and reliability to compensate for changes in signal optical power caused by external factors such as the environment. According to the manufacturing process, the common VOA types are traditional mechanical type, liquid crystal type, planar waveguide type, Micro-Electro-Micromechanical System (MEMS) type, magneto-optical type, polymer tunable diffraction grating type and high Photoelectric coefficient material type. There are two types of MEMS VOA: reflective and light-blocking. The latter has a complicated manufacturing process and high cost. Reflective MEMS VOA is relatively mature in various technologies, and has obvious advantages such as fast response time, small size, light weight, low power consumption, large dynamic attenuation range, small insertion loss, large return loss, and high accuracy. It has been widely used use. 2 Reflective MEMS VOA Reflective MEMS VOA is a micro optical device based on MEMS chip packaging. The design idea comes from the traditional mechanical VOA. The difference is that the driving device is changed from a huge stepper motor to an electrostatic opening and closing bridge, electrostatic comb, tilting structure, piezoelectric The driving principle is shown in Figure 1. Figure 1 Schematic diagram of reflective MEMS VOA The structure of reflective VOA based on MEMS technology is mainly divided into two parts. One part is composed of a collimator composed of a double-core pin and a C lens, etc., which is used as a light input and reflection output channel. The parameters such as the angle of the bevel of the pin, the radius of curvature of the C lens and the material can be optimized and designed to produce MEMS VOA with different specifications. The other part is the MEMS seal, which is packaged in a stable and reliable sealed environment through precision processes such as patching, gold wire bonding, and vacuum capping. After applying a few volts or more than ten volts to the positive and negative pins of the device, due to the specific structure of the MEMS chip, an electrostatic force is generated between the gold-plated silicon-based surface and the gold-plated mirror surface, which drives the reflective surface of the MEMS chip at a slight angle The rotation causes the reflected light incident on the mirror surface of the MEMS chip to shift synchronously, resulting in a mismatch between the mode field of the returned light and the mode field of the coupled single-mode fiber, resulting in attenuation. As the applied voltage changes, the attenuation changes accordingly, continuously adjustable. When a reverse bias voltage is applied between the positive and negative electrodes, the device can still work normally. High-precision packaging is the key to MEMS VOA production. Guangxun Technology is one of the few domestic optical device companies with independent packaging to make reflective MEMS VOA. The size of the MEMS VOA device produced by it is only 5.4 & TImes; 25.4mm (excluding Length of pins for soldering). The technical indicators of VOA mainly include: operating wavelength range, operating temperature, dynamic attenuation range, insertion loss (IL), return loss (RL), polarization dependent loss (PDL), temperature characteristics and wavelength dependent loss (WDL), etc. The main indicators of MEMS VOA manufactured by Xun Technology are shown in Table 1, which has reached a high level of the same kind of products in the industry. Compared with similar companies, Guangxun devices also have better anti-static capabilities and long-term stability, and can flexibly provide products with different voltage (5V & 15V) requirements. In addition, its weight is less than 3g, the power consumption is less than 5mw, and the response time is generally 2 ~ 3ms, which is very conducive to module splicing and has made a significant contribution to the miniaturization and integration of optical communication systems. Table 1 Main performance indicators of Guangxun Technology MEMS VOA The polarization-dependent loss and temperature-dependent loss in the above table are tested in the entire attenuation range (0 ~ 30dB), and the wavelength-dependent loss can be customized according to requirements. At the same time, Guangxun Technology also provides Dark type MEMS VOA with power-off protection function, and the zero-voltage reset attenuation can reach more than 45dB, which can meet the application of more optical communication lines. ZhenHuan`s dimmable phase cut LED driver is constant voltage mode, UL class 2 rated and designed to operate with any standard MLV/Incandescent TRIAC (Leading edge) dimmer switch. The 12V Dimmable Led Driver is encased in a low profile aluminum enclosure with junction box that includes 2 knock-outs to enable easy installation makes it the perfect choice for under cabinet lights, tape lights and various LED fixtures installations. 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