Introduction of PLC Technology and Fabrication Processes

 

PLC is more known in the field of electronic technology. It is the acronym of the terminology ‘programmable logic controller’. However, in the field of optical communication, PLC is the acronym of another terminology, i.e. ‘planar lightwave circuit’, which is variable optical waveguide structures fabricated with integrated optics technologies. PLC technologies can implement functional devices as directional coupler (DC), Y-branch splitter, multimode interferometer (MMI), arrayed waveguide grating (AWG), optical interleaver (ITL), Mach-Zehnder (MZ) electro-optical modulator, thermo-optical variable optical attenuator (TO-VOA), thermo-optical switch (TO-SW), etc.

In the optical communication industry, the widely deployed PLC devices include optical power splitter, AWG, MZ electro-optical modulator and TO-VOA, etc. optical power splitter is a device consisting of Y-branch splitters in cascade and parallel connection. For example, a 1×16 power needs 15 Y-branch splitters. AWG is a device with 1×N ports, which separates tens of wavelengths from the input to each output. MZ modulator based on lithium niobate optical waveguide is the main approach for optical modulators. Meanwhile, modulators based on silicon optics are commercialized and become the first choice for high-speed modulators >50G. TO-VOA based on PLC technology is deployed in combination with AWG, which compose a VMUX module with functions of multiplexing/demultiplexing and dynamic channel equalization.

Optical communication devices based on PLC technology and widely deployed are variable. However, PLC is usually specified as optical power splitters in the industry, which is a most widely deployed passive optical device in the FTTH network. After the internet bubble in 2000, optical communication industry entered a period of depression. Then in 2004, Japan first invested on FTTH construction as a new infrastructure, although the application scenario of FTTH had not emerged yet. In 2008, China added in the construction of FTTH and reached the peak in 2012. FTTH network usually adopts PON structure. The key device is optical power splitter, which is widely deployed in the business and residential buildings. In our lives, the most approach to an optical power splitter is the modem for internet access. The pigtail of the modem was upgraded from twist-pair electrical wires to an optical fiber jumper, which is led to one of the ports of an optical power splitter. The optical fiber access can support transmission speed of 100-200M, which is much higher than 4M through electrical wires.

In the field of optical communication, PLC is the abbreviation of plane optical path, which is based on the integrated optical technology to prepare various optical waveguide structures, in order to achieve some functional devices. There are four kinds of fabrication processes for optical waveguides: ion exchange, ion implantation, chemical vapor deposition and flame hydrolysis.

1) Ion exchange

The principle of ion exchange process is to soak the glass material containing A⁺ ions in the solution containing B⁺ ions, and exchange the A⁺ ions in the glass with the B⁺ ions in the solution by using the property that the ions will diffuse from the high concentration area to the low concentration area. Because the glass material containing A⁺ ions has higher refractive index than the glass material containing B⁺ ions, high refractive index can be obtained in the region where ion exchange occurs, which can be used as the core layer of the optical waveguide, and the region where ion exchange does not occur can be used as the cladding layer of the optical waveguide to obtain the required optical waveguide structure.

The general process flow of preparing optical waveguide by ion exchange is shown in Figure 1:

1) A mask layer is covered on the glass substrate by evaporation or sputtering process;

2) Through photolithography and etching process, a window of waveguide structure is opened in the mask layer;

3) The glass material with the mask layer prepared and the window opened is immersed in the solution for ion exchange;

4) Through the electric field driving, the exchange ions distributed in the surface layer are driven to a certain depth to form the waveguide structure.

In the actual process, in order to better ensure the ion exchange effect, the above 3-4 steps need to be carried out at the same time, which depends on the specific process design.

Fig.1.  Fabrication of optical waveguides by ion exchange

In order to improve the ion exchange efficiency and obtain good optical waveguide characteristics, it is necessary to select two kinds of exchanged ions, optimize the glass formula, control the concentration and temperature of the solution, and apply the electric field appropriately.

2) Ion implantation

Ion implantation is a kind of material surface modification technology, which belongs to a standard processing technology in semiconductor industry. Ion implantation optical waveguide is to accelerate ions to tens of thousands to hundreds of thousands of electron volts of high energy by ion accelerator, bombard the surface of substrate materials, cause damage or defects on the surface of materials through the interaction between atoms or molecules, change the refractive index, and form optical waveguide structure.

The typical process of preparing optical waveguide by ion implantation is shown in Fig.2. The ion implanter is usually composed of ion source, ion extraction and pre acceleration, magnetic analyzer, back channel accelerator, electron scanning system, ion implantation cavity and vacuum system. In the cavity of the ion source, ions are generated by gas discharge. The electrode in the ion extractor is led out and pre accelerated. The magnetic analyzer controls the quality of the ion beam and obtains the ion beam with good directivity. The ion beam accelerated by the back channel is injected into the sample in the cavity under the control of the electron deflector.

Fig.2.  Fabrication of optical waveguides by ion implantation

 

The substrate material placed in the ion implantation cavity needs to be pretreated. The mask layer is prepared according to the optical waveguide pattern. After ion implantation, post-processing, such as annealing, is also needed to reduce the influence of material defects on the loss.

3) Chemical vapor deposition

Chemical vapor deposition (CVD) process is also a standard process in the semiconductor industry. The process of preparing optical waveguide by CVD process is shown in Fig.3. It is to successively deposit optical waveguide layers with different doping layers on silicon substrate (or quartz substrate). For example, the core layer is doped with phosphorus and boron to improve the refractive index, and the cladding layer is doped with germanium to reduce the refractive index. After the core layer is deposited and before the upper cladding layer is deposited, the mask layer needs to be prepared by photolithography to define the optical waveguide pattern. After each layer is deposited, annealing hardening process is needed to enhance the density and uniformity of the deposited layer and reduce the stress.

Fig.3.  Fabrication of optical waveguides by chemical vapor deposition

 

4) Flame hydrolysis deposition

The fabrication process of optical waveguide by Flame hydrolysis deposition (FHD) is similar to that by CVD, but the difference is only in the process conditions. CVD is a process in which various elements and compounds containing film elements are introduced into the cavity, and chemical reaction occurs at a certain temperature, so as to deposit the required film on the substrate surface. FHD is to pass volatile halides containing film elements, such as silicon tetrachloride, and halides containing various doping elements, such as phosphorus, boron and germanium, into a gas burner, and react with water in a high temperature flame to form a silicon dioxide film layer doped with various impurity elements.

5) Process comparison

Ion exchange and ion implantation can produce low-cost optical waveguides, but the control of the cross-section shape of the waveguides is slightly poor. They are mainly used to make optical splitters. The production efficiency of ion implantation is much higher than that of ion exchange. CVD and FHD can be used to fabricate high-end optical waveguide devices, such as arrayed waveguide grating (AWG). Among them, FHD is more suitable for thick film fabrication than CVD.

About HYC

Relying on 21 years of experience in OEM ODM manufacturing of optical communication passive basic devices, HYC has continuously achieved technological innovation, and established a complete range from chip post-process processing to overall coupling packaging technology, high-precision full-wavelength testing technology, and providing customers with a full series of PLC optical splitter products.

http://www.hyc-system.com

Know the type of fiber, fiber cable, jumper, pigtail, and connector

To understand the types of optical fibers, optical cables, jumpers, connectors, and adapters, you first need to know the relationship between these products.

 

Optical fiber

The optical fiber is drawn from silica glass through a complicated process, it is a highly transparent glass filament, which is also called optical fiber.

Optical fiber type

Optical fiber is divided into single mode fiber and multimode fiber according to the transmission mode. Light enters the optical fiber at a specific angle of incidence, and full emission occurs between the optical fiber and the cladding. When the diameter is small, only one direction of light is allowed to pass through, which is a single-mode optical fiber; when the diameter of the optical fiber is large, light can be allowed to inject and propagate at multiple angles of incidence, that is a multimode fiber.

Single mode optical fiber

Normally, there are two types of optical fiber: single mode and multi mode. Single-mode fiber is a single glass fiber strand used to transmit a single mode or ray of light. Single mode fiber with a relatively narrow diameter, through which all signals travel straight down the middle without bouncing off the edges. Single-mode fiber features only one transmission mode. Single Mode Fiber with a relatively narrow diameter of 8.5 to 9.5μm, through which only one mode will propagate typically 1310 or 1550nm. 

Multimode optical fiber

Multi mode fiber is an optical fiber that allows multiple guided modes to be transmitted. Multi-mode fiber has a larger diameter core, typically 50 or 62.5μm. This larger core allows multiple modes of light to propagate. The standard wavelengths of the multimode are 850 nm and 1300 nm. Multimode fiber is available in four classifications: OM1 (62.5/125 µm), OM2, OM3, OM4 (50/125 µm). There’s also a new multimode fiber standard known as WBMMF (wideband multimode fiber) which uses the wavelengths between 850nm and 953nm.

Both single mode fiber and multimode fiber have a cladding diameter of 125μm.

G652，G657 fiber

According to the ITU standard, there are seven kinds of fibers: G651, G652, G653, G654, G655, G656, G657, and G652 and G657 are commonly used.

G652 fiber is the most widely used fiber in the metropolitan area network. It is a standard single-mode fiber with a zero-point dispersion of 1300nm. G652 fiber is subdivided into four types: G652A, G652B, G652C and G652D. The main difference lies in PMD. Among them, G652D is more commonly used. Because of its low fiber dispersion at 1300nm operating wavelength, the transmission distance of the system is only limited by loss.

G657 is a bending loss-insensitive fiber, and it is the most commonly used fiber optic cable for FTTH because of its better performance. But G657 fiber is more expensive than G652D.

G651 is a multi-mode optical fiber, mainly used in multi-tenant, residential buildings, and enterprise networks in FTTH networks. Its bending radius is half that of G652 fiber. It is suitable for indoor and FTTH cabling.

OS1, OS2, OM1, OM2, OM3, OM4, OM5

OS1 and OS2 are both single-mode optical fibers. OS1: the ordinary single-mode optical fiber used earlier; OS2: the ordinary optical fiber in use now, the low-water peak optical fiber. In general, OM1 is conventional 62.5/125μm; OM2 is conventional 50/125μm; OM3 is 850nm laser-optimized 50μm core multimode fiber, and in 10Gb/s Ethernet with 850nm VCSEL, the fiber transmission distance can reach 300m; OM4 is an upgraded version of OM3. OM4 multimode fiber optimizes the differential mode delay (DMD) generated by OM3 multimode fiber during high-speed transmission. Therefore, the transmission distance is greatly improved, and the fiber transmission distance can reach 550m; OM5 is a new standard for fiber patch cords defined by TIA and IEC with a fiber diameter of 50/125μm. Compared to OM3 and OM4 fiber patch cords, OM5 fiber patch cords can be used for higher bandwidth applications. The bandwidth and maximum distance are different for different levels of transmission.

 

Optical cable

The optical fiber is drawn from pure quartz with a special process into a glass tube thinner than a hair with a few mediums in the middle. Its texture is brittle and fragile, so an additional protective layer is needed. The outer layer of the optical fiber is combined with a plastic protective tube and a plastic sheath to form an optical cable.

Optical cables include fibers. Broadly speaking, optical fibers are optical cables, which are all transmission media. But they are also difference. The difference between optical fiber and optical cable: optical fiber is a thin and soft medium that transmits light beams. Most optical fibers must be covered by several layers of protective structures before use, and the covered cables including fibers are called optical cables. Therefore, the optical fiber is the core part of the optical cable, and the optical fiber forms the optical cable through the protection of some components and the auxiliary protective layer.

The type of fiber optic cable

There are many classification methods to categorize fiber optic cables, such as:

Classified by material: LSZH, PVC, HYTREL 7246, HYTREL 7237, PE, TPU

According to the outer diameter: φ0.9, φ2.0, φ3.0……

Divided by mode field: single mode (9/125), multimode (50/125, 62.5/125)

Divided by color: single mode is yellow, multimode is orange (OM1/OM2), OM3 is aqua blue, OM4 is aqua blue or violet, OM5 is lime green.

According to the structure, it can be divided into: generally simplex or duplex, duplex in single-tube, mini multicore, branch cable

Optical fiber brands: Corning, YOFC, Fujikura, Sumitomo, OFS, etc.

 

Type of patch cord

The 0.9, 2.0, and 3.0 of the optical fiber jumper are used to distinguish the outer diameter of the optical cable. 0.9 means the outer diameter of the optical cable is 0.9mm, 2.0 means the outer diameter of the optical cable is 2mm, and 3.0 means the outer diameter of the optical cable is 3mm.

There are also single-mode fiber jumpers and multi-mode fiber jumpers. Single mode is indicated by yellow, and the transmission distance is longer; multimode is indicated by orange, and the transmission distance is shorter.

 

Pigtail

Only one end of the pigtail has a connector, and the other end is a broken end of an optical cable core, which is connected to other optical cable cores through fusion splicing. It often appears in the optical fiber terminal box and is used to connect the optical cable to the optical transceiver.

Type of connector

Divided by the connection mode: FC, SC, ST, MU, LC, MT, E2000, MTRJ

Divided by fiber end face: PC, UPC, APC, SPC

According to the number of cores of the optical cable, it can be divided into: single core, double core (with clip)

Commonly used connectors: FC/PC, SC/PC, SC/APC, LC/PC

According to the tail sleeve structure, it can be divided into: round tail sleeve, square tail sleeve, conventional tail sleeve, short tail sleeve

 

Why should the fiber end face be divided into PC,UPC,APC

There are many reasons to caused fiber loss caused during fiber connections, such as: different axis (single-mode fiber coaxiality is required to be less than 0.8μm), the end face is not perpendicular to the axis, the end face is not flat, the butt core diameter is not matched, and the splicing quality is poor.

In order to make the end faces of the two optical fibers better contact, the end faces of the ferrule of the fiber jumper are usually ground into different structures. Common grinding methods are mainly: PC, APC, UPC. PC/APC/UPC represents the front surface structure of the ceramic ferrule.

 

Different fiber end face finishes

PC (Physical Contact).The two end faces are polished to be slightly curved or microspherical, and the fiber core is at the highest point of the bending. This eliminates the air gap and forces the fibers into physical contact.

UPC (Ultra Physical Contact) is based on the PC to optimize the end face polishing and surface finish, the end face looks more dome-shaped. The end face of the UPC connector is not entirely flat, and there is a slight arc to achieve more accurate connecting.

APC (Angled Physical Contact). The end face of APC is usually polishing into an 8-degree angle. The 8° angled bevel makes the fiber end face tighter and reflects light through its beveled angle to the cladding instead of returning directly to the source, providing better connection performance. 

The APC fiber optic connector is usually green. UPC/PC connectors are easily identified by their blue color on the connector boot.

Type of adapter

Optical fiber adapters are used to convert various optical fiber equipment and optical fiber connection methods. With the wide application of fiber optic adapters in fiber optic connections, there are various fiber optic adapters with different interfaces to choose from to adapt to different environmental installation requirements. Common types of adapters are: LC adapter, FC adapter, SC adapter, ST adapter, E2000 adapter, MTP / MPO adapter, etc.

 

HYC is a leading passive optical component OEM/ODM manufacturer, focusing on providing customers with efficient manufacturing, high-quality products and in-depth research and development. The main products are: fiber optic connectors (high-density optical connectors for data centers), WDM wavelength division multiplexers, PLC optical splitters, MEMS optical switches and other four core optical passive basic devices, which are widely used in fiber to the home , 4G/5G mobile communications, Internet data centers, national defense communications and other fields.

What does WDM (Wavelength Division Multiplexing )stand for?

This article will include these subject.

What does WDM stand for?

The basic structure of WDM system

Advantages of WDM technology

What does Mux and Demux stand for?

The difference between WDM and optical splitter

The indicators that affect the WDM devices

How to understand the O, E, S, C, L, U band

What does CWDM stand for vs. DWDM, FWDM, LWDM, MWDM?

What does WDM stand for?

Wavelength Division Multiplexing(WDM) is one of the most common way of using wavelengths to increase bandwidth by multiplexing various optical carrier signals onto a single optical fiber. It combines a series of optical carrier signals with different wavelengths carrying various information and coupled to the same optical fiber for transmission at the transmitting end. At the receiving end, optical signals of various wavelengths are separated by a demultiplexer. This technique of simultaneously transmitting two or many different wavelengths in the same fiber is called wavelength division multiplexing, or WDM. 

As shown in the figure below, the traditional optical transmission method is that one fiber can only transmit one wavelengths of signal in a single time. If you want different services, you need countless different and independent optical fibers for transmission. However, if there is a large amount of services, a large number of optical fibers need to be laid for transmission, which poses a great challenge to cabling space and cost. The application of a WDM system can quickly solve the above problems. The WDM system can carry multiple signals through multiplexing and demultiplexing technologies, such as ATM, IP, etc., and multiple service signals can be transmitted through a single optical fiber, which greatly reduces the amount of optical fiber. The WDM system can carry multiple signals, such as ATM, IP, etc., through multiplexing and demultiplexing technology, the multiple service signals can be transmitted through a single optical fiber, which greatly reduces the amount of optical fiber. This is an ideal technology for capacity expansion. When introducing new broadband services such as CATV, HDTV, B-ISDN, etc., only one additional wavelength needs to be added.

The basic structure of the WDM system is mainly divided into two modes: dual-fiber unidirectional transmission and single-fiber bidirectional transmission. 

Unidirectional WDM is the transmission of all optical channels on a fiber propagating simultaneously in the same direction. Different wavelengths carry different optical signals, which are combined at the transmitting end for transmission through an optical fiber, and demultiplexed at the receiving end to complete multiple paths. In the opposite direction, a second optical fiber is needed. The transmission in the two directions is completed by two optical fibers respectively. 

Bidirectional WDM is the transmission of optical channels on a fiber propagating simultaneously in both directions, and the wavelengths used are separated from each other to achieve full-duplex communication between the two parties.

The general WDM system is mainly composed of five parts: network management system, optical transmitter, optical relay amplifier, optical receiver, and optical monitoring channel.

The simple WDM system mainly includes transceivers, WDM wavelength division multiplexers, patch cord, and dark fiber components.

In the entire WDM system, the multiplexer and demultiplexer are key components in the WDM technology, and their performance is decisive for the transmission quality of the system.

Advantages of WDM technology

Large capacity

An important feature of WDM is that it can make full use of the bandwidth resources of the optical fiber and increase the data transmission capacity without changing the existing network infrastructure, so that the transmission capacity of an optical fiber is multiple times that of a single wavelength. For example, the DWDM system can support up to 192 wavelengths in a pair of optical fibers, and the transmission capacity of each wavelength is as high as 100Gbit/s ~ 400Gbit/s and one Terabit/s.

Good compatibility

WDM has good compatibility with different signals. When transmitting signals with different properties such as image, data and voice, each wavelength is independent from each other and does not interfere with each other to ensure the transparency of transmission.

Flexibility, economy and reliability

WDM technology allows new channels to be connected as needed without changing the existing network, which makes upgrades easier. When upgrading and expanding the network, there is no need to renovate the optical cable line, and new businesses can be opened or superimposed by adding wavelengths. Optical fibers and 3R regenerators can be saved during large-capacity long-distance transmission, and the transmission cost is significantly reduced.

Wavelength routing

WDM technology is one of the key technologies for realizing all-optical networks. In the all-optical network that is expected to be realized in the future, by changing and adjusting the wavelength of the optical signal on the optical path, the up/down and cross-connection of various telecommunication services can be realized.

What does Mux and Demux stand for?

MUX

The main function of the combiner MUX is to combine multiple signal wavelengths into one fiber for transmission.  At the transmitting end, the N optical transmitters operate on N different wavelengths respectively, and the N wavelengths are separated by appropriate intervals, which are respectively recorded as λ1, λ2, ... λn. A multiplexer combines these optical wavelengths into a single-mode fiber. Since optical carrier signals of different wavelengths can be regarded as independent of each other (regardless of fiber nonlinearity), multiplexing transmission of multiple optical signals can be realized in one optical fiber. Through multiplexing, communication carriers can avoid maintaining multiple lines and effectively save operating costs.

DEMUX

The main function of DEMUX is to separate the multiple wavelength signals transmitted in one fiber. In the receiving part, the optical carrier signals of different wavelengths are separated by a Demux and further processed by the optical receiver to restore the original signal. A multiplexer (Demux) is a device that reverses the processing of a multiplexer.

In principle, the device is reciprocal (two-way reversible), that is, as long as the output and input of the demultiplexer are used in reverse, it is a multiplexer.

The difference between WDM and optical splitter

Many people cannot understand the difference between wavelength division multiplexing and optical splitters. In short, WDM separates and transmits light of multiple wavelengths in the line. Of course, it can also transmit light of multiple wavelengths together. The optical splitter divides the light of one wavelength into multiple beams according to the purpose. The power of the light depends on the specifications of the splitter used. The most important difference between the two is that the former can compositely transmit optical signals of various service wavelengths, while the latter can only transmit light of one wavelength to split light according to a specific splitting ratio.

The indicators that affect the WDM devices

Working band

Working bands of the multiplexer/demultiplexer. For example, there is three bands of 1550 wavelength: S-band (short-wavelength 1460~1528nm), C band (conventional band 1530~1565nm), L band (long-wavelength band 1565~1625nm).

Number of channels & channel spacing

The number of channels is the number of channels the device has to send information. This number can range from 4 to 160 with design enhancements adding more channels. The normal channels are 4, 8, 16, 32, 40, 48, etc. Channel spacing is the center-to-center difference in frequency between neighboring channels. It can be used to prevent inter-channel interference.

Insertion loss

Insertion loss is the attenuation caused by the insertion of wavelength division multiplexers (WDM) in an optical transmission system. The attenuation effect of wavelength division multiplexer directly affects the transmission distance of the system. In general, the lower the insertion loss, the less the signal attenuation.

Isolation

Isolation refers to the degree of isolation between individual channel signals. High isolation values can effectively prevent crosstalk between signals and cause distortion of the transmission signal.

Polarization dependent loss（PDL）

Polarization-dependent loss is the maximum deviation in insertion loss across all input polarization states.

In addition to the above, there are of course other performance parameters that affect the multiplexing/demultiplexing devices, such as operating temperature, bandwidth, etc. Generally, a multiplexer and a demultiplexer are combined into a single device allowing the device to process both incoming and outgoing signals. Or a single output of a multiplexer can be connected through a single channel to a single input of a demultiplexer. But mostly is the combined and complex devices for both directions transmission.

How to understand the O, E, S, C, L, U band

 

What is O band?

The O band is the original band with wavelength from 1260 to 1360nm. The O-band is the first wavelength band used in optical communications in history, and the signal distortion (due to dispersion) is minimal.

What is E band?

The E-band (extended wavelength band: 1360-1460 nm) is the least common of these bands. The E-band is mainly used for the expansion of the O-band, but it is rarely used, mainly because many existing optical cables show high attenuation in the E-band and the manufacturing process is very energy-intensive, so the use in optical communication is limited.

What is S band?

The optical fiber loss in the S-band (Short-wavelength Band, 1460-1530 nm) is lower than the loss in the O-band. The S-band is used as many PON (passive optical network) systems.

What is C band?

The C-band (Conventional Band) ranges from 1530 nm to 1565nm and represents the conventional band. Optical fiber shows the lowest loss in the C-band and occupies a large advantage in long-distance transmission systems. It is usually used in many metropolitan areas combined with WDM, long-distance, ultra-long-distance and submarine optical transmission systems and EDFA technology. As the transmission distance becomes longer, and fiber optic amplifiers are used instead of optical-to-electronic-to-optical repeaters, the C-band becomes more and more important. With the advent of DWDM (Dense Wavelength Division Multiplexing) that allows multiple signals to share a single fiber, the use of the C-band has been expanded.

What is L band?

The L-band (Long-wavelength Band, 1565-1625nm) is the second lowest-loss wavelength band, and is often used when the C-band is insufficient to meet the bandwidth requirements. With the wide availability of b-doped fiber amplifiers (EDFAs), DWDM systems have expanded upward to the L-band, and were initially used to expand the capacity of terrestrial DWDM optical networks. Now, it has been introduced to submarine cable operators to do the same thing-to expand the total capacity of submarine cables.

Due to its low transmission attenuation loss, C-band and L-band is usually selected to use in the DWDM system. Except for the O-band and L-band, there are two other bands, 850nm band and the U band (ultra-long band: 1625-1675 nm). The 850nm band is the main wavelength of the multimode optical fiber communication system, which combines VCSEL (Vertical Cavity Surface Emitting Laser). The U frequency band is mainly used for network monitoring.

WDM technology can be divided into WDM, CWDM, DWDM according to different wavelength modes. The wavelength range stipulated by ITU for CWDM (ITU-T G.694.2) is 1271 to 1611nm, but considering the attenuation of the 1270-1470nm band in the application, the band of 1470~1610nm is usually used. The channel space of DWDM is more closeness, so choose the C-band (1530 nm-1565 nm) and L-band (1570 nm-1610 nm) transmission windows. Ordinary WDM generally uses 1310 and 1550nm wavelengths.

What does CWDM stand for vs. DWDM, FWDM, LWDM, MWDM?

WDM solutions include coarse wavelength division multiplexing (CWDM), dense wavelength division multiplexing (DWDM), medium wavelength division multiplexing (MWDM), and Lan wavelength division multiplexing (LWDM).

CWDM (Coarse Wavelength Division Multiplexing)

The CWDM wavelength set consists of a series of 18 wavelengths spaced 20nm apart, from 1270nm to 1610nm. The biggest advantage of CWDM systems is the low cost, and the component cost is mainly reflected in filters and lasers. The wide wavelength spacing of 20 nm also gives CWDM the advantage of low specification of the laser and simplified structure of the optical multiplexer/demultiplexer. The structure is simplified, the yield is improved, so the cost is reduced.

DWDM（Dense Wavelength Division Multiplexer）

DWDM can carry 40, 80 or up to 160 wavelengths with a narrower spacing of 1.6/0.8/0.4nm (200/100/50GHz). The DWDM module further increases the system bandwidth and capacity by using tightly spaced wavelengths to carry more signals on the same fiber. DWDM is mainly due to the high cost of laser diodes and the cooling laser technology used to maintain wavelength stability. Compared with CWDM, DWDM with tighter wavelength spacing can carry 8 to 160 wavelengths on an optical fiber, which is more suitable for long-distance transmission. With the help of EDFA, DWDM system can work within thousands of kilometers.

FWDM（Filter Wavelength Division Multiplexing）

The filter type WDM is based on mature membrane filter technology. Filter-type WDM can combine or separate light of different wavelengths in a wide wavelength range, and are widely used in erbium-doped optical amplifiers, Raman amplifiers and WDM optical fiber networks.

MWDM（Medium Wavelength Division Multiplexing）

MWDM is proposed based on mature CWDM technology. CWDM has 18 wavelengths (1271~1611nm), but due to the relatively large attenuation of the 1270~1470nm band and cost considerations, usually only 6 wavelengths (1271nm, 1291nm, 1311nm, 1351nm, 1371nm) are used. MWDM reuses the first 6 wavelengths of CWDM, compresses the 20nm wavelength interval of CWDM to 7nm, and uses Thermal Electronic Cooler (TEC) temperature control technology to expand 1 wave into 2 waves. In this way, an increase in capacity can be achieved while further saving optical fibers. MWDM is based on the 6 wavelengths of CWDM, shifted by 3.5nm left and right to expand to 12 waves (1267.5, 1274.5, 1287.5, 1294.5, 1307.5, 1314.5, 1327.5, 1334.5, 1347.5, 1354.5, 1367.5, 1374.5nm).

 

LWDM（Lan Wavelength Division Multiplexing）

LWDM is based on the Ethernet channel wavelength division multiplexing Lan-WDM technology, also known as dense wavelength division multiplexing. Its channel interval is 200~800GHz, this range is between DWDM (100GHz, 50GHz) and CWDM (about 3THz). LWDM uses 12 wavelengths in the O-band range from 1269nm to 1332nm, with a wavelength interval of 4nm (Wavelengths including 1269.23, 1273.54, 1277.89, 1282.26, 1286.66, 1291.1, 1295.56, 1300.05, 1304.58, 1309.14, 1313.73 , 1318.35nm). The characteristic of LWDM working wavelength is that it is located near zero dispersion, with small dispersion and good stability. At the same time, LWDM can support 12-wave 25G to increase the capacity and save fiber.

HYC can provide customers with a one-stop optical network device and low-cost optical communication products, supplying a range of WDM products. HYC Co.,Ltd（HYC）is a national Hi-tech optoelectronics company engaged in R&D, manufacture and marketing of fiber optical products. Providing professional product and service for fiber connectivity,WDM, PLC splitter and high density datacom cabling. HYC products and solutions widely applied in 4G/5G, Data Center and Cloud Computing industry etc.

http://www.hyc-system.com

sales@hyc-system.com

HYC Launched A Full Range of High-speed Fiber Array Subassembly

 With the development of ultra-high-speed and integrated optical communications, optical transceiver modules are also expected to adopt smaller and more integrated solutions, which have high demand for parallel high-speed optical subassembly. Due to the high cost caused by strict material usage and processing technology, the optical fiber array has not been widely used for 10G transmission. With the rapid advance of 400G and 800G high-speed transmission, FA with high-density packaging can be said to be a more ideal solution.

Optical fiber arrays are most commonly used in the packaging of planar optical waveguide splitters (PLC) and arrayed waveguide gratings (AWG). With the explosive growth of data flow, the demand for optical fiber arrays in data centers and 5G commercial applications is growing rapidly, and FA has become more and more widely used in MEMS systems, sensors, silicon photonics and other fields.

Relying on the technical advantages and rich experience of ultra-precision component assembly, HYC quickly launched high-speed optical component products to meet market demand. Relying on the technical advantages and rich experience of ultra-precision component assembly, HYC quickly launches high-speed optical subassembly products to fullfit the market demand. Now, HYC has high-precision glass cutting,fiber array design, surface optical coating design, fiebr array bonding, convex surface fiber grinding and processing capabilities, and can provide customers with a full series of fiber array with various end-face grinding angles (such as 0 degree, 8 degree, 42.5 degree, 45 degree,and other customized angles). High precision pitch cores and low-cost high speed optical fiber array subassembly will be provided to meet different customer needs.

High-speed FA Subassembly Product Introduction

1. High-speed Optical Subassembly MT-FA

MT-FA is widely used in parallel transmission of optical transceiver modules, such as 100GPSM4 connection to an external port. HYC's MT-FA jumpers can achieve total reflection on the end surface by grinding the fiber array into a 42.5° angle reflector. It uses the low-loss MT ferrules, and the tolerance range of the V-groove spacing is ±0.5μm,which can provide the most compact parallel connection scheme for optical transceiver modules.

2. High-speed FA Subassembly in AWG , AWG-FA-Receptacle

Receptacle is usually combined with FA, Capillary, Isolator, etc. to form an optical connection device, which is used as the external connection optical port of the optical module to realize the connection and transmission of optical signals outside the module.

3. High-speed Optical Subassembly PM-FA

Polarization-maintaining PM-FA is widely used in coherent optical communication. The polarization state of light can be maintained during transmission, which can give full play to the advantages of coherent reception. The PM fiber array uses a V-shaped groove to install a polarization-maintaining fiber ribbon on the array substrate, which can achieve high-density parallel transmission while ensuring the stability of light wave polarization.

4. Silicon Photonics Integration Optical Subassembly, MFD(Mode field diameter) Conversion FA 

Mode field diameter conversion fiber array provides a low loss coupling method to a waveguide with a smaller mode field by using a small segment of ultra-high numerical aperture single-mode fiber (UHNA) stitched onto the pigtail of a standard SM or PM fiber to achieve mode field conversion. This product is an ideal solution for high-speed silicon photonic transceiver modules connections. HYC can provide customized fiber diameters, such as 3.2μm / 3.3μm / 4μm / 5.5μm to 9μm, using special assembly and polishing processes and high-precision V-slot substrates to achieve low insertion loss, high pitch-core, and wide temperature.

HYC uses precise processing technology or etching technology to achieve precise fiber array positioning and high reliability FA, and adopts sophisticated automation and testing equipment(e.g. DISCO cutting machine, Seiko FA core-pitch detector) to ensure product reliability. HYC will continue to increase R&D investment and expand a rich product line to meet the market demand for high-speed optical transmission passive device products for 5G and data center construction.

The working principle and application of MEMS optical switch

This article will including:

• What is optical switch?
• Working principle of MEMS optical switch
• Structure of MEMS fiber optic switch
• MEMS optical switch VS Mechanical optical switch
• The advantages of MEMS switch
• The applications of MEMS fiber optic switch
• The MEMS based optical switch in AON

What is optical switch?

Optical switch is a device that converts an optical signal from one optical channel to another optical channel within a certain range. It has one or more selectable transmission windows. Fiber optic switch is one of the core devices for optical cross-connection, optical add/drop multiplexing, network monitoring and automatic protection system.

Its implementation technologies are diverse, including: mechanical optical switches, thermo-optical switches, acousto-optic switches, electro-optical switches, magneto-optical switches, liquid crystal optical switches and MEMS optical switches. The traditional switch with electricity as the core is gradually unable to meet the demand for high-speed and large-capacity optical communication, which is why the all-optical switch appears in the market. Among them, MEMS optical fiber switches are widely used due to their small size, low power consumption, and good scalability.

Working principle of MEMS optical switch

What is MEMS? MEMS is shot for Micro-Electro-Mechanical System, which refers to a micro-device or system that can be mass-produced and integrate micro-machines, micro-actuators, signal processing and control circuits. The preparation process of micro-mechanical structures includes photolithography, ion beam Etching, chemical etching, wafer bonding, etc.

MEMS is driven by electronic technology, such as electrostatic attraction, electromagnetic force, electrostriction, and thermocouple. Among all the driving mechanisms of MEMS devices, the electrostatic attraction structure is the most widely used due to its simple preparation, easy control and low power consumption.

The MEMS optical switch is to engrave a number of tiny mirrors on the silicon crystal. The microarray is rotated by electrostatic force or electromagnetic force to change the propagation direction of the input light, thereby realizing the on and off function of the light path.

Generally speaking, MEMS based optical switch can be divided into two types in terms of spatial structure: 2D switches and 3D switches.

(a) 2-D (b) 3-D Source: researchgate.net

The rotating mirror of the 2D MEMS optical switch is monolithically integrated on the silicon substrate through surface micromechanical manufacturing technology, and the collimated light is connected to the designated output terminal through the rotation control of the micro mirror. When the micro mirror is horizontal, the light beam can pass through the micro mirror. When the micro mirror rotates perpendicular to the silicon substrate, it will reflect the light beam incident on its surface, so that the light beam can pass through the corresponding output port of the micro mirror. In the 3D MEMS optical switch, the micro mirror can rotate arbitrarily along two axes, so different angles can be used to change the output of the optical path. These arrays usually appear in pairs, and the input light reaches the first array mirror. It is reflected to the mirror surface of the second array, and then the light is reflected to the output port.

Structure of MEMS Fiber Optic Switch

Fiber optic switch is a multiport device. The port configurations include 2×2, 1×N, N×N. Optical switch with N×N ports is usually called OXC (optical cross connect). The structure of a MEMS-based 1×N optical switch is shown in Fig, which consists of a MEMS torsion mirror, a collimating lens and a multi-fiber pigtail. The MEMS mirror is usually assembled on a TO base, then the collimating lens is joint to the sub-assembly through the TO cap. Finally, the multi-fiber pigtail is actively aligned to the sub-assembly.

Structure of the 1×N MEMS optical switch

MEMS optical switch VS Mechanical optical 

The working principle of mechanical optical switches is to redirect optical signals by physically moving optical fibers with the help of mechanical equipment. By moving the prism or directional coupler, the light at the input end will be directed to the desired output port. There are three main types of mechanical optical switches: one is to use a prism to switch the optical path technology, the other is to use mirror switching technology, and the third is to switch the optical path by moving an optical fiber.

MEMS optical switches are based on micro-electro-mechanical systems, which use optical micro-mirrors or optical micro-mirror arrays to change the direction of light beams to switch optical paths. The principle of MEMS optical switches is very simple. When the light is exchanged, the angle of the MEMS micro-mirror is moved or changed by the drive of the electrostatic force or the magnetic force, and the input light is switched to the different output terminals of the optical switch to realize the switching and on-off of the optical path. 

The advantages of MEMS switch

The MEMS optical switch can realize the comprehensive remote control of the all-optical network, and has the main advantages of high integration, low power consumption and low cost. MEMS optical switches have the advantages of mechanical optical switches, such as low insertion loss, low crosstalk, low polarization sensitivity, high extinction ratio, high switching speed, small size and easy large-scale integration of waveguide switches. This will be the mainstream direction for the development of large-capacity switching optical network switches.

The applications of MEMS fiber optic switch

MEMS optical switches and the switch arrays have a wide range of applications in optical communications. Its application scope mainly includes: optical network protection switching system, light source control in optical fiber test, real-time monitoring system of network performance, optical device test, construction of switching core of OXC equipment, optical add/drop multiplexing, optical test, optical Sensing system, etc.

Applied in MCS (multicast switching optical switch)

MCS based on PLC technology and MEMS technology is a key component of the next generation reconfigurable optical add/drop multiplexing system (ROADM). Each functional unit is composed of M independent splitters and N independent MEMS optical switches, which provide connections from N upper (or lower) ports to M directions.

Applied in iODF (intelligent optical distribution)

Through optical switch cascade integration, it can be used in iODF to replace the traditional distribution frame in the industrial private network.

As the switching core of OXC (Optical Cross Connect) equipment

In the all-optical switching system, the optical switch is a key component of the OXC. Through optical switch cascade integration, it can be used in small OXC to meet the needs of industrial private networks and key lines in data centers.

Applied in optical performance monitoring

Integrated with TOF or OPM, combined with monitoring software, and through time division multiplexing OPM, it can be used to monitor the signal performance of the DWDM channel in the multi-core fiber in the optical cable. It is widely used in optical transmission network cable monitoring, ROADM network, DCI, etc.

Applied in optical cable monitoring

It is integrated with OTDR and combined with monitoring software to monitor the quality of multi-core optical fibers in the optical cable. It is widely used in PON network optical cable monitoring, optical transmission network optical cable monitoring, industry-specific network optical cable monitoring, etc.

Applied in optical fiber sensing

The main products used in Sensing field are 1x4 and 1x8 switch.

Applied in test instrumentation and factory automation

Applied in DWDM system

The MEMS based optical switch in AON

What is an all-optical network? AON is the abbreviation of All Optical Network, which means that the transmission and exchange process of the network is realized through optical fiber. This means that the data transmission process from the source node to the destination node is carried out in the optical domain, and the optical/electrical, electrical/optical conversion is only performed when entering and leaving the network. Since there is no need to implement electro-optical and photoelectric conversion, the network speed can be greatly increased. The main technologies of the all-optical network include optical fiber technology, SDH, WDM, optical switching technology, OXC, passive optical network technology and optical fiber amplifier technology.

Structure of AON

Among the various equipment of all-optical network, OXC and OADM (optical add-drop multiplexing equipment) are the core equipment technologies of all-optical network. Optical switches and optical switch arrays are the core technologies of OXC and OADM. The new optical switch made by MEMS technology is small in size, light in weight and low in energy consumption. It can be compatible with the manufacturing process of large-scale integrated circuits. It is easy to mass produce, integrate, and has low cost.

In recent years, as a MEMS optical switch manufacturer, HYC has focused on the research of large-channel multi-core fiber collimators, and has made achievements in the compact layout of high-density fibers. Now, we have the mass production capacity of 1×48 optical switches. HYC will officially release 1×64 MEMS optical switches or more channels.

HYC Showcases Hybrid Series Product at ECOC 2020 Virtual Event

 The European Optical Fiber Communication Exhibition ECOC is the largest optical fiber communication exhibition in Europe, which is held in EU countries every year. The event was originally scheduled to take place in Belgium in September, but due to the impact of the epidemic, it was rescheduled to take place online on December 7-9. HYC also participated in this virtual exhibition with the latest products and solutions. At the virtual exposition, visitors will have the opportunity to explore HYC’s high-density cabling solutions, micro-optic solutions, 5G Open-WDM solutions and more. 

In recent years, the integrated optical passive devices are smaller in size and more mature in technology, occupying a considerable part of the market share. As one of the key devices of optical communication, erbium-doped fiber amplifier (EDFA) has become the technical focus of competition among many manufacturers due to its integration, miniaturization, multi-function and low cost.  HYC has launched a series of customized small N in 1 integrated high-end devices that can be applied to ultra-small EDFAs to help realize the above-mentioned competitive advantages of EDFAs. The above competitive advantages of EDFA can be realized by integrating optical isolator, wavelength division multiplexing (WDM) devices, optical circulator and test access port (TAP) splitter into a hybrid device.

In addition to the above-mentioned Hybrid components, HYC also demonstrated full-band/dual-window/multimode/polarization-maintaining couplers, fiber optic circulators, MPO/MT-FA, AWG CWDM4 and other micro-optic solutions.

At this exhibition, HYC also highlighted the CEx wavelength coexistence WDM module used in the "Trip-play" network. The CEx WDM module is a transitional product in the evolution of PON technology.  At present, the main PON technologies can be divided into three types: TDM-PON, WDM-PON and OFDM-PON. The original proposal of CEx wavelength coexistence is mainly to allow G/EPON to realize system sharing with NG-PON1 and NG-PON2, so as to achieve a smooth upgrade and save costs.

For 400G transmission applications, HYC is also actively exploring new solutions, and has launched a series of AAWG products such as 50GHz 96CH AAWG and 75GHz 64CH AAWG. Arrayed waveguide gratings (AWGs) are key components of DWDM (Dense Wavelength Division Multiplexing Systems) networks that are rapidly developing. The AWG can obtain a large number of wavelengths and channel numbers, realize multiplexing and de-multiplexing of tens to hundreds of wavelengths, and can flexibly form multifunctional devices and modules with other optical devices. High stability and excellent cost performance are also one of the reasons why AWG has become the technology of choice for DWDM. Based on the array waveguide grating technology, it does not require additional power supply or temperature control, and is a pure passive module. The application of AAWG can greatly improve the propagation efficiency of optical fiber networks.

ECOC's online exhibition will be open until January 15. Customers from all over the world are welcome to visit HYC's online virtual booth to explore new technologies and directions in the optical communications industry.

About HYC Co., Ltd

HYC focuses on the design, development, manufacturing and sales of optical passive basic devices for optical communications, providing customers with one-stop product procurement and customized services. The production and sales of products include optical fiber connectors (high-density optical connection products for data centers), WDM wavelength division multiplexers, PLC optical splitters, MEMS optical switches, etc., and continue to explore new product areas, including Hybrid combination devices, optical fiber circulator and other Micro-optic device products. For details, please visit www.hyc-system.com

 OTDR is an Optical Time-domain Reflectometer. It is the main devices in optical fiber measurement. It uses to test detect problems that may exist in fiber links.

OTDR is widely used in carrier backbone networks. By analyzing the measurement curve, it can quickly detect the fault location of the optical fiber link and the fiber loss. The working principle is to use a laser light to send a higher power laser or light pulse to the test fiber. OTDR observes the power of the laser signal from each point on the fiber and records these results through a trace diagram. It can calculate the distance by recording the return time and transmission speed. 

In the PON (Passive Optical Network) network, especially the complex point-to-multipoint PON ODN (Optical Distribution Network) topology applications, rapid monitoring, and diagnosis of fiber fault locations is a challenging subject. At present, optical time-domain reflectometer (OTDR) tools are widely used for monitoring the fiber network. However, OTDR detection may not be so particularly sensitive to the attenuation of optical signals at the ends of some ODN branch fibers or ONU fibers. The application of FTTx terminal splitter to the main cable signal makes the traditional OTDR fiber optical detection techniques unable to achieve on-off detection. So a cost-effective and wavelength selective fiber optic reflector is a basic method of implementation of optical layer monitoring on the whole length of an FTTx network from the OLT to the ONT in real-time.

The working principle of the fiber optic reflector is mainly to use Fiber Bragg Grating (FBG) to reflect the test light pulse sent by OTDR with nearly 100% reflectivity. But the wavelength of normal passive optical network (PON) will pass with a small attenuation. The main purpose is to accurately calculate the return loss value of the reflected event at the end of each ONU branch by detecting whether the reflected OTDR test signal exists and the intensity of the optical signal. Therefore, it can easy to determine whether the optical link from the OLT side to the ONU side is normal. By detecting the reflected signal through OTDR, it can accurately grasp the fiber breakage, loss anomalies, fault location, and locate the error quickly.

The end-to-end OTDR measurement from the OLT to the ONT is usually difficult because the splitter brings high losses and complex networks. The application of optical fiber reflector is a cost-effective solution to help OTDR detection, and is the best way to realize real-time end-to-end (OLT to ONT) monitoring of optical networks in FTTx networks.

The optical fiber (FBG) reflector independently developed by HYC has the advantages of low insertion loss, high reflectivity, and convenient installation. It is widely used in PON network, OTDR testing, central computer room testing, FTTX and other fields. HYC offers customized pigtail or adapter type, such as LC, SC, APC/PC and so on.

HYC provides optical passive components OEM/ODM services. We welcome any inquiry for customized optical devices solutions for optical communication industry, including fiber optic connectors/adapters, WDM, PLC splitter, MEMS optical switch for data center, FTTx, Cloud Computing industry, 4G/5G networks .