With the rise of 5G technologies and massive deployment of 5G base stations, wireless access of terminals with high speed and large capacity is realized. Meanwhile, the traffic in optical fiber network increases rapidly. It is predicted that the current optical fiber network will become the bottleneck of information exchange in the future 12-18 months. The upgrading of optical fiber network is urgent. The representative trend is that the technologies for long-haul network (LHN) will be sunk to metropolitan area network (MAN), including DWDM (Dense Wavelength Division Multiplexing), ROADM (Reconfigurable Optical Add-Drop Multiplexer) and coherent receiving techniques. This paper discusses some of the passive optical devices for the coming 5G applications.
1. CDC ROADM Based on MCS The demand for increasing bandwidth promotes the upgrading of all-optical network (AON). As key parts of AON, the market of ROADM and related passive optical devices is expected to grow rapidly. In the nodes of optical fiber network, any wavelengths can be downloaded/uploaded via ROADMs. With the rapid growth of Internet traffic, the traditional ROADM nodes can’t meet the requirements. The new generation of ROADMs are required to be colorless, directionless and contentionless (CDC ROADM).
5G Application Scenarios The development of 5G networks starting in 2019 is generally believed to bring changes not limited to people’s daily life. It will support the evolution of Internet from mobile internet to intelligent internet, which will influence the industrial-ecology deeply.
The international standard organization 3GPP defined the three main application scenarios of 5G: eMBB (Enhance Mobile Broadband), uRLLC (Ultra-Reliable Low Latency Communications), mMTC (Massive Machine Type Communication). eMBB requires the bandwidth experienced by the customers to be more than 1Gbps supporting mobile broadband surfaces such as 3D and ultra-high definition video. uRLLC requires the transmitting delay to be <1ms supporting real time applications such as self-driving cars, industrial automation, and remote surgery. mMTC means application in massive internet of things (IOT) which requires high density terminal connection of more than one million per square kilometer.
Polarization maintaining(PM) optical fiber connectors are usually used for special applications, such as optical fiber sensing, interferometry, planar waveguides, coherent optical transmission, and long-distance bidirectional optical transmission systems. To understand polarization-maintaining connectors, we need to know what polarization-maintaining fibers are.
The PM fibers currently on the market basically have the following cross-sectional types:
CCWDM is Compact CWDM (Compact Coarse Wavelength Division Multiplexing), which is a wavelength division multiplexing technology based on TFF (Thin Film Filter). It works in the same way as CWDM modules, except that CCWDM uses free space technology (As shown in Figure 1), compared with the common CWDM fiber cascading method (as shown in Figure 2). The package size of CCWDM is smaller than CWDM and with lower insertion loss and better consistency. CCWDM can be used to replace the CWDM products in telecommunications, corporate networks, PON networks, cable TV and other fields. The lower insertion loss makes the CCWDM module have lower signal attenuation when used, thereby reducing the power requirements of the signal transmitter.
On March 31, with the last bucket of concrete poured, in the loud and festive firecrackers, the main building of the first phase project of HYC device production base was successfully topped off. This is a brand new milestone of the whole HYC building project.
In OFC 2020, the most exciting moment must be the commermorative event. Fifty years ago, two breakthrough technologies that laid the foundation for this year’s optical communications were born: low-loss optical fiber and room-temperature semiconductor lasers. For the first time in the past 20 years, OFC arranged a special celebration after the morning conference speech. David F. Welch, Chief Innovation Officer of Infinera, who will lead the audience to recall the 50 years of optical fiber communications and look forward to the future of optical communications.
With the rapid development of optical fiber, the traditional communication devices with electricity as the core is hardly to meet the needs of high-speed and large-capacity optical communication network. MEMS optical switch has become one of the important devices in all optical communication network due to its small size, easy integration and large capacity.
MEMS optical switch is based on Micro-Electro-Mechanical System(MEMS) technology, using the micromirrors to control and switch the optical path. Its function is shown in the following figure:
The research and application of fiber lasers flourish in recent years. Optical isolators are important devices to ensure the reliability of fiber lasers. Depending on the actual applications, different types of optical isolator are employed. For some applications under relatively low optical power, wedge-type in-line optical isolator is employed, just with more consideration on heat dissipation. While for some applications under high optical power, BD-type in-line optical isolator is employed instead of wedge-type. The reason is that the FR for telecom applications can’t be used anymore.
Birefringent crystals are widely used to fabricate optical passive devices such as optical isolator, optical circulator, polarization beam combiner/splitter, optical interleaver. The mostly used crystals are uniaxial, such as YVO4 and LiNbO3.
Birefringence in Uniaxial Crystal Wave normal K is the normal of equalphase surface which describes the transmission of wave phase. Ray S is the normal of wave front which describes the transmission of optical energy. When light incidents on the air-crystal (uniaxial) interface, there are usually two refractive rays, o-ray So and e-ray Se. The direction of each ray depends on the direction of corresponding wave normal.
Optical isolators are widely used in optical fiber communication systems, optical fiber sensing systems and fiber lasers. The basic and common principle for optical isolators is Faraday effect. However, the device structures and characteristics are variable, which are detailed as follow.
Free-space Optical Isolator The structure of a free-space optical isolator is shown in Fig.1, which comprises two polarizers, a Faraday rotator (FR) and a magnet ring. The transmission axes of the two polarizers are aligned with 45º angle and the FR has a fixed rotatory angle of 45º in a saturated magnetic field.