Introduction to Optical Communication

With the rapid development of society, it seems that optical communication plays a key part in nearly all industry. Whether in one’ daily life or in one’ work, it exists everywhere. Although it’s commonly utilized, and maybe most people haven’t had a detailed knowledge of it. Then this article will have an introduction to optical communication in these aspects, such as optical communication definition, types of optical communication, and advantages of optical communication.



What’ s Optical Communication?
Optical communication, also known as optical telecommunication, is one type of communications in which light is used to carry the signal to the remote end, instead of electrical current. Optical communication relies on optical fibers to carry signals to their destinations. It can be performed visually or by using electronic devices. An optical communication system uses a transmitter for encoding a message into an optical signal, a channel for carrying the signal to its destination, and a receiver for  reproducing the message from the received optical signal. These form the blocks of the optical communications system. When electronic equipment is not employed, the 'receiver' is a person visually observing and interpreting a signal, which may be either simple (such as the presence of a beacon fire) or complex (such as lights using color codes or flashed in a Morse code sequence).

Types of Optical Communication
Optical communication can be divided into laser communication and non laser communication according to the characteristics of light source. At the same time, according to the different transmission media, optical communication can be divided into wired optical communication and wireless optical communication (also known as atmospheric optical communication). The commonly used types include those:
Atmospheric laser communications:  the information is transmitted along the atmosphere by a laser beam. It’s unnecessary to lay the line; the equipment is light in weight and convenient to maneuver; it’s with good confidentiality, with large-capacity information transmission. These information can be transmitted such as sound, data, image and so on. Atmospheric laser communication is easily influenced by climate and external environment, and is commonly used as the horizon communication among river and lake, valley, desert area and island.
Optical fiber communication: It is a kind of wired communication. The light wave transmits along optical fiber. The light source can be a laser (also called as a semiconductor laser diode) or a light-emitting diode. Optical fibre communication, which is with low transmission attenuation, large capacity, good confidentiality and is free from external interference, can be used in large capacity defense trunk communication and field operation communication.
Blue-green light communication: it’s a kind of communication way in which information is transmitted under the sea by utilizing a kind of laser whose wavelength is between the blue light and green light. At present, it’s the best communication method under the water.
Infrared communication: it transmits information by infrared(wavelength is 300～0.76 micron). These information can be transmitted, such as language, character, data, image and so on. It’s available in coastal islands, remote control at short range, interior of air vehicle and so on. It’s with these advantages such as with large capacity, good confidentiality, with high performance in anti-electromagnetic interference. Simultaneously, the device is with simple architecture, small in size, light in weight, low in price. However, it’s easy to get influenced by climate when transmitted in the atmosphere channel, and the transmission distance is only 4000m.
Ultraviolet communication: It transmits information via  ultraviolet (wavelength is 0.39～60×10 micron). Its communication theory is similar to that of infrared, and both belong to non-laser communication.

Advantages of Optical Communication
The main benefits of optical communication include high bandwidth, low loss, wide transmission range and no electromagnetic interference. Besides, it’s also with these merits as below:

1. Long Distance Transmission & Economic and Energy-saving

When 10Gb information(10 billions of signals) need to be transmitted in on second, if using telecommunication, the signal need to be adjusted every 100m. By comparison, if applying the optic communication, it's adjusted every over 100kms. The less the signals are adjusted, the less the machines are needed. Therefore, to some degree, it's economic and energy-saving.

2. Large-capacity Information Transmission at One Time

Lots of users can simultaneously receive the information they need, such as movies, news and so on. In one second, at most 10Gb information can be transmitted via the telecommunication. While at most 1Tb information can be transmitted via optic communication.

3. With High-speed Transmission Rate

Telecommunication will bring about mistakes due to electronic noises, which leads to the dropping of transmission rate. While the optic communication will not have such kind of troubles so that it can transmit signals at high speed.

Conclusion
In current society, more industries can hardly work without optical communication, especially IT industry, communication industry and so on. Meanwhile, the communication tech is always keeping improved and keeping pace with the market demands, in which the fiber optical communication is widely used among these optical communications. Maybe the introduction to fiber optic communication can be made in next article.

How Much Do You Know about QSFP28 CWDM4?

These years， data center has always been expanded at the high speed and higher rate of single port are required, which contributes to the wide applications of 100G in the data center. While in the practical use, many optical transceiver usually can’t meet the demands on the deployment of data center by the way of saving cost, on account of the variety  in the lengths of optic fiber channel. For it, 2 km 100G QSFP28 CWDM4 appears in the current optical components market. Well, this article will have an introduction to QSFP28 CWDM4  from perspectives of CWDM4 definition, CWDM4 MSA as well as advantages and applications of QSFP28 CWDM4 by Gigalight.

What’s CWDM4 Optical Transceiver?

The 100G QSFP28 CWDM4 optical transceiver is a full duplex, photonic-integrated optical transceiver module that provides a high-speed link with a maximum transmission distance of 2km for 100G Ethernet. CWDM4 interfaces with LC duplex connectors. It uses 4×25Gbps to achieve 100Gbps. Specifically speaking, four lanes with center wavelengths of 1270nm, 1290nm, 1310nm and 1330nm are controlled on the transmit side. On the receiving side, four lanes of optical data streams are optically de-multiplexed by an integrated optical demultiplexer. With an optical multiplexer and de-multiplexer, one just uses a duplex single-mode fiber to connect two 100G CWDM4 optical transceivers. CWDM4 has many advantages, such as low power consumption, high compatibility, Digital Diagnostic Monitoring (DDM) support and so on. Nowadays, it has been widely applied in Local Area Network (LAN), Wide Area Network (WAN), and Ethernet switches and router application.

 

What’s CWDM4 MSA ?

The CWDM4 MSA (Multi-Source Agreement) targets a common specification for low-cost 100G optical interfaces that run up to 2km in data center applications. The MSA uses CWDM technology with 4 lanes of 25Gbps optically multiplexed into and demultiplexed from duplex single-mode fiber. CWDM4 MSA targets the broad data center 100G interconnects that support FEC applications.

CWDM4 MSA’  members consist of Avago Technologies, Finisar Corporation, JDSU and Oclaro, Inc. The Multi-Source Agreement (MSA) defines 4 x 25Gbps Coarse Wavelength Division Multiplex(CWDM) optical interfaces for 100Gbit/s optical transceivers in Ethernet applications including 100GbE. Forward error correction (FEC) is required to be implemented by the host in order to ensure reliable system operation. Two transceivers communicate over single mode fibers(SMF) of length from 2 meters to at least 2 kilometers. The transceiver electrical interface is not specified by this MSA but can have four lanes in each direction with a nominal signaling rate of 25.78125Gbps per lane.

Different form factors for the transceivers are possible. Initial implementations are expected to use the CFP4 or the QSFP28 module form factors. Other form factors are possible and are not precluded by this MSA.

Advantages and Applications of QSFP28 CWDM4

CWDM4 has many advantages, such as low power consumption, high compatibility, Digital Diagnostic Monitoring (DDM) support, high transmission rate, long transmission distance and so on, in which the long transmission distance is its most highlighted feature. It adopts WDM (Wavelength Division Multiplex) tech, full-duplex LC connector and single-mode fiber, which are helpful to realize 2km reaches. Besides, on account of the adoption of WDM, it just needs two single-mode fibers to realize the transmission, which, to some degree, save the costs in fibers. At this time, compared with QSFP28 PSM4 in cost and transmission distance, QSFP28 CWDM4 is preferred.

As for its applications, by virtue of its various advantages, it’s widely utilized in many fields, such as CATV(Community Antenna Television), FTTH(Fiber To The Home), 1G and 2G fiber channel, Gigabit Ethernet, SONET (Synchronous Optical Network) OC-3（155Mbps）/OC-12（622Mbps）/ OC-48（2.488Gbps） , Security and Protection systems; also in Local Area Network (LAN), Wide Area Network (WAN), and Ethernet switches and router application.

Conclusion

Although CWDM4 transceiver is high in cost, and the it’s still an economical solution for long transmission distance. Whether in aspects of link’ lengths or cost savings, it can meet the needs in a cost-effective way by DWM. Maybe it will get improved with the advances in future tech. We will see.

Note: article resource from www.gigalight.com.

How to Choose QSFP28 Optical Transceiver For 100G Network?

It’s known that cost-effective 100G optics are in great demand, especially QSFP28 optical transceivers with low cost optical design package tech, widely applied in data center, LAN, WAN, Ethernet switches. However, among these optic fibre modules, which one is the most suitable for 100G Network? Well, this article will introduce how to choose QSFP28 optical transceivers.

For QSFP28 optical module, except that it’s a hot-pluggable optical module designed for 100G data rate, it integrates 4 transmitting and 4 receiving channels. And “28” means each lane carries up to 28G data rate. Meanwhile it can do 4x25G/2x50G/1x100G connection.

To some degree, the selection of 100G QSFP28 products depends on transmission distance. Therefore, it would be better to choose it from this perspective. For different applications, there are different requirements for transmission distance. The below is about its specific conditions and feasible measures:

1. When transmission distance is 100m or under 100m, QSFP28 SR4 is highly recommended. The QSFP28 SR4 supports links of 70 m (OM3) and 100m (OM4) over multimode fiber with MPO connectors. It offers 4 independent transmitting and receiving channels, and each is with 25Gbps able to be aggregated into 100Gbps. Meanwhile, the QSFP28 SR4 optic module is also ideal for the connections from rack to rack in the data center. 

2. When transmission distance is over 100m but under 10 km, QSFP28 LR4 is preferred. The QSFP28 LR4 is a fully integrated 4 × 25Gbit/s optical transceiver module, supporting distance up to 10 km. So for long span 100G deployment, such as cabling between two buildings, QSFP28 LR4 with duplex LC and single-mode fiber cable is the perfect option.

3. When transmission distance exceeds 10 km, QSFP28 ER4 is ideal for very long transmission distance. It provides superior performance for 100G Ethernet applications up to 30km links and converts 4 input channels of 25Gb/s electrical data to 4 channels of LAN WDM optical signals and then multiplexes them into a single channel for 100Gb/s optical transmission.

Of course, the above ways are just for the different transmission distance. But for the  same transmission distance, how to choose it? Maybe we can get the answer from the example of QSFP28 CWDM4 and QSFP28 PSM4.

The QSFP28 CWDM4 provides a 100G Ethernet high-speed link with a maximum transmission distance of 2 km, which interfaces with LC duplex connectors, and uses Mux/Demux technologies with 4 lanes of 25Gbps optically multiplexed into and demultiplexed from duplex single-mode fiber. While PSM4 does not need a MUX/DEMUX for each laser but it does need either a directly modulated DFB laser (DML) or an external modulator for each fiber. Besides, with an MTP interface, PSM4 modules can transmit data at 100Gb/s from point to point over 2 km or can be divided into dual 50Gb/s or quad 25Gb/s links for linking to servers, storage and other subsystems.

It’s seen from that both of QSFP28 CWDM4 and QSFP28 PSM4 are designed to meet the requirement for intermediate or mid-reaches for datacenter applications (500 m to 2 km). And they both use WDM and parallel single mode fiber technologies and support transmission distance up to 2 km.

When faced with such a situation, maybe we can make a decision from the two aspects. For one thing, from the aspect of an inner transceiver module structure, by comparison , PSM4 can be more cost-effective due to its lower component costs. For another thing, from the infrastructure viewpoint, PSM4 will be more expensive when the link distance is long, because PSM4 uses 8 optical single-mode fibers while CWDM uses only 2 optical single-mode fibers.

All in all, when choosing one QSFP28 optical transceiver for 100G network, one can take different solutions according to the practical demands in different situations.  The most suitable is the best.

Note: article resource from http://www.gigalight.com/.

100G QSFP28 PSM4: the Most Cost-effective Solution for 100G Ethernet

In data center, there are various QSFP28 optical transceivers for 100G Ethernet, such as QSFP28 100GBASE-SR4/LR4, QSFP28 100GBASE-PSM4, QSFP28 100GBASE-CWDM4, among which the most cost-effective one is the QSFP28 100GBASE-PSM4. On account of its advantage in cost, 100G QSFP28 PSM4 plays a key part in 100G optics market. Then this article will have an introduction to it in these aspect, such as 100G PSM4 definition, 100G PSM4 Specification, advantages of PSM4 and other else.

What Is 100G PSM4?
PSM4, the abbreviation of Parallel Single Mode 4-channels, is a type of single-mode transceiver that uses a parallel fiber design for reaches from up to 2 km and for reaches beyond the limits of 100-meter Short Reach 4-channel (SR4) multi-mode transceivers. It uses four lanes of parallel single fiber to deliver serialized data at a rate of 25Gbps per lane . PSM4 will be the transceiver that enables single-mode fiber to become popular in next-generation data centers due to its low cost and high configurability.
Moreover, PSM4 is built with one laser (instead of four), split into four paths or channels and separately modulated with electrical data signals. Each channel has its own fibers and is separated throughout the link. It doesn’t need a MUX/DEMUX for each laser but it does need a directly modulated DFB laser (DML) or an external modulator for each fiber. PSM4 uses eight-fibers, in which four fibers are for transmission and four fibers are for receiving. A PSM4 QSFP28 module supports link lengths of up to 500 meters over single-mode fiber with 12 fiber MTP/MPO connectors. The light source of PSM4 optic module is a single uncooled distributed feedback (DFB) laser operating at 1310nm.

Brief Introduction Of 100G PSM4 Specification
The 100G PSM4 specification, created by PSM4 MSA(Multi-Source Agreement) group, provides a low-cost solution for long-reach optical interconnects data center. With the data rates of optical interconnects increased, the growth in the scale of data center has created a need for low cost solutions available for at least 500m reaches. The 100G PSM4 Specification is targeted to service that need on a parallel single mode infrastructure, as a critical need of next-generation data centers.
This specification defines a four lane (per direction) 100Gb/s optical interface to single mode fiber(SMF) media. As shown in Figure 1, the 100G PSM4 transceiver module (100G PSM4 module) provides Transmit Optics and Receive Optics between the Host IC and the fiber optic media. A particular form factor, such as QSFP28 or CFP4, is not defined and the 100G PSM4 optical transceiver module may be implemented in various form factors. Since management and control interfaces are with dependent form factor, definition of these interfaces are outside the scope of this specification.

What’s the Advantages of PSM4?
In the aspect of QSFP28 PSM4 advantages, in addition to the common merits of QSFP28 transceiver module, such as high bandwidth, low insertion loss, high data rate and so on, the most prominent advantage of PSM4 is with the lowest cost. On one hand, the existing 100G Ethernet links with QSFP28 SR4 or LR4 are either too short in transmission distance or too expensive in cost. On the other hand, unlike CWDM4, PSM4 doesn’t need to use an optical multiplexer and de-multiplexer, operating around 1310nm with CWDM technology, as shown in the following picture. However, the high component count drives the cost of CWDM4 modules. Thus, by comparison, CWDM4 is more expensive than PSM4.

Gigalight 100G QSFP28 PSM4
For QSFP28 PSM4 transceiver, Gigalight also launches one type: GQM-SPO101-IR4C. Besides the characteristics and advantages that common transceiver has, Gigalight PSM4 has its own unique features. This high-performance module for data communication and interconnect applications, integrates four data lanes in each direction with 104Gbps bandwidth. Each lane can operate at 26Gbps up to 2km over G.652 SMF. The electrical interface uses a 38 contact edge type connector. In addition, this module incorporates Gigalight proven circuit and optical technology to provide reliable long life, high performance, and consistent service.

 

Conclusion

With the future development of tech, QSFP28 100G PSM4 is possible to be further improved in cost, to a large extent, which will promote the development of this product, and simultaneously strengthen its importance in the future optical industry. Let’s expect it together!

How Much Do You Know About BiDi Transceiver?

In today’s data center, higher bandwidth and larger capacity are required, which, to some degree,  brings about the increasing in the use of optic fiber cables. It’s known that two fiber cables are usually used in the process of data transmission, in which one is for transmitting data, and another one is for receiving data. After that, the cost in the fiber deployment of infrastructure is also increased with it. To solve this issue, BiDi transceiver（Bidirectional transceiver） comes out, such as BiDi SFP, BiDi SFP+, BiDi QSFP+ and so on. Then this article will have an introduction to BiDi transceiver.

What’s BiDi Transceiver?
BiDi transceiver is a kind of bidirectional fiber optic transceiver with single fiber, which transmits and receives different central wavelengths from two different directions by WDM tech, to realize bidirectional transmission of optical signal in one optic fiber. Different from common fiber optic transceiver with two ports, BiDi transceiver is only with one port. It filters wavelength via filter and simultaneously complete the transmission of 1310nm optic signal and receiving of 1550nm optical signal so that it need to be applied in pair. Usually, its wavelength consists of these types: 1310nm/1550nm; 1310nm/1490nm; 1510nm/1590nm.

Types of BiDi Transceiver
The common types of BiDi transceivers include the following ones:

1. BiDi SFP transceiver is typically applied for the high-performance integrated duplex data link on one optic fiber. It interfaces mother board of network device (such as a switch, router or similar device) to a optic fiber or unshielded twisted pair networking cable. In addition, the typical wavelength combination of it is 1310/1490nm, 1310/1550 nm, 1490/1550 nm and 1510/1570 nm. This SFP BiDi transceiver is used in both telecommunication and data bidirectional communications applications.
2. BiDi SFP+ transceiver is an enhanced SFP transceiver. It is designed for bi-directional 10G serial optical data communications such as IEEE 802.3ae 10GBASE-BX by using 1330/1270nm transmitter and 1270/1330nm receiver. And its transmission distance is up to 20 km.
3. BiDi QSFP+ transceiver is designed for high-density data center. With QSFP+ BiDi transceiver, 40G network can be achieved by the exiting 10G cabling. That is to say, if one wants to upgrade his 10G network to 40G network, there is no need to change the existing 10G duplex patch cords into MTP/MPO multifiber patch cords.
4. BiDi X2 transceivers, mainly used in Ethernet network, are designed for bi-directional 10G serial optical data communications, similar to BiDi SFP+ transceivers. The transceiver consists of two sections: the transmitter section and the receiver section. The transmitter section uses a multiple quantum well 1330/1270nm DFB laser. The receiver section uses an integrated 1270/1330nm detector preamplifier (IDP) mounted in an optical header and a limiting post-amplifier IC. This BiDi transceiver is mainly used in Ethernet network.

Advantages of BiDi Transceivers
On the one hand, due to that BiDi transceivers( also called as WDM transceivers) are able to reduce the number of fiber patch panel ports and the amount of tray space for fiber management, as well as to require less fiber cables, the adoption of BiDi transceivers is beneficial to save the cost in fiber cabling infrastructure. Meanwhile, it also makes it possible to save more precious space in data centers.
On the other hand, although the cost of BiDi transceivers are higher than that of common transceivers in the market, and BiDi transceivers utilize half the amount of fiber per unit of distance. For many networks, the saved costs can offset the higher purchase costs of BiDi transceivers. The deployment of BiDi transceivers instantly doubles the bandwidth capacity of the existing optical fiber infrastructure and helps customers to achieve economical and efficient performance for their fiber optic network. Besides, 40G connectivity becomes more reliable via BiDi transceiver.

How Does BiDi Transceiver Work?
Different from traditional optic fiber transceiver modules with two fibers, BiDi transceivers are equipped with Wavelength Division Multiplexing (WDM) couplers, also called as diplexers, which combine and separate data transmitted over a single fiber according to  the wavelengths efficiency. On account of this, BiDi transceivers are also referred to as WDM transceivers.
Furthermore, BiDi transceivers must be deployed in pairs to reach the efficiency, with their diplexers tuned to match the expected wavelength of the transmitter and receiver. For example, paired BiDi transceivers are used to connect device A (Upstream) and device B (Downstream), then the figures are shown as below:

1. Transceiver A’s diplexer must have a receiving wavelength of 1490nm and a transmit wavelength of 1310nm
2. Transceiver B’s diplexer must have a receiving wavelength of 1310nm and a transmit wavelength of 1490nm

 

Conclusion
BiDi transceiver may have a higher cost than common transceivers. However, if seen from a long-term view, it will decrease the costs spent in fiber cables to a large extent. BiDi transceiver is compatible with many data rates.


Note: article resource from http://www.gigalight.com/.

EPON vs. GPON: What Are the Differences?

With the advent of Ethernet tech, the requirements for the bandwidth, network capacity and transmission rate are higher. In recent years, more equipment manufacturers and operators tend to transfer their focus to the optical network access techs, which contributes to the development of FTTH(Fiber To The Home) to some degree. In future optical interconnection market, FTTH will be gradually developed into a trend of access networks. PON (Passive Optical Network) becomes the major tech to serve for it. To further keep pace with market’s demands, EPON (Ethernet Passive Optical Network )and GPON(Gigabit Passive Optical Network) emerges from PON and become  popular versions of it. Maybe one is curious about difference between EPON and GPON. Well, then an introduction will be made in the form of EPON vs. GPON by Gigalight.

What’s EPON?
As the name implies, EPON tech is a version of PON tech based on Ethernet, offering point-to-multipoint network access with lower installation and maintenance costs. EPON tech is standardized by IEEE802.3EFM group and endowed with a standard, IEEE802.3ah. In this standard, the PON tech is integrated with Ethernet tech and a new physical layer specification applied in the EPON system and extended Ethernet data link layer protocol to realize the TDM access of the Ethernet frame in the PON with point-to-multipoint architecture.
In the physical layer, single fiber WDM Technology (downstream wavelength is 1490 nm, upstream wavelength is 1310 nm) are specified for application in IEEE 802.3-2005to realize bidirectional transmission via single fiber. Meanwhile, the two PON optical interfaces, the 1000 BASE-PX-10 U/D and 1000 BASE-PX-20 U/D, are defined to respectively support the maximum transmission distances,10 km and 20 km. In the physical coding sublayer, the EPON system inherits the original standard of Gigabit  Ethernet, adopts 8B/10B line coding and standardized upstream and downstream symmetric 1 Gbit/s data rate (line rate is 1.25 Gbit/s).

What’s GPON?
GPON tech is the latest-generation broadband passive optical access tech based on ITU-TG.984.x standard, which is with high bandwidth, high efficiency, wide coverage, rich user interface and so on. It's considered as an ideal tech to realize broadband access network services.
GPON uses an IP-based protocol and either ATM or GEM (GPON encapsulation method) encoding. Data rates up to 2.5Gbps are specified and it is very flexible in what types of traffic it carries. GPON enables "triple play" (voice-data-video) and is the basis of most planned FTTP (Fiber to the Premises) applications in the near future. Simultaneously, it also applies optical wavelength division multiplexing (WDM) so that a single fiber can be used for both downstream and upstream data. A laser on a wavelength (λ) of 1490nm transmits downstream data. Upstream data are transmitted on a wavelength of 1310 nm. If TV is being distributed, a wavelength of 1550nm is used.

Gpon

Moreover, It’s with 1.25Gbit/s or 2.5Gbit/s downstream or upstream bandwidths scalable from 155Mbit/s to 2.5Gbit/s. GPON does not support multi-cast services, which makes support for IP video more bandwidth-consuming.
As the main forces of optical network access, EPON and EPON have their own advantages for competition, as well as compensate for each other. For the difference between EPON and GPON, it will be shown in the following EPON and GPON comparison.

EPON vs. GPON： Which One Is Better？

1. In data rate, GPON is higher  than EPON. EPON uses standard 802.3 Ethernet data frames: IEEE 802.3 standard, ratified as 802.3ah-2004 for 1.25 Gbps (1.0 Gbps prior to 8B/10B coding) and IEEE 802.3av standard for 10Gbps (10G-EPON). The upstream and downstream data rate of EPON is symmetrical. While GPON supports various bit rate options using the same protocol, including a symmetrical data rate of 622 Mbps in both downstream and upstream, a symmetrical data rate of 1.25Gbps in both streams, as well as a data rate of 2.5Gbps in downstream and a data rate of 1.25Gbps in upstream. 2.5Gbps of downstream bandwidth and 1.25Gbps of upstream bandwidth are the data rates supported by typical GPON systems. Thus, one can decide the upstream and downstream data rate depending on the requirements, and then choose the corresponding optical transceiver modules. It is more flexible than EPON.
2. In split ratio, GPON is neck and neck with EPON. Split ratio mainly limited by the performance index of optical modules means the quantity of ONU user port in one OLT interface. The standard split ratio of EPON is 1：32. While the split ratio of GPON includes these types: 1:32; 1:64; 1:128. Actually, the split ratio of EPON can also reach higher, such as 1:64; 1:128. And the control protocol of EPON can support more ONUs. The high split ratio will bring about  the sharp rising in costs. Although GPON is able to provide multiple options, and it has few benefits in costs. In addition, the insertion loss of PON tech is 15～18dB, and higher split ratio will shorten the transmission distance. When the split ratios are 1:16 and 1:32, the maximum physical distance of GPON can respectively reach 20km and 10km, which is same as that of EPON.
3. In the cost, the EPON is more cost-effective than GPON. Generally speaking, the cost of GPON or EPON deployment consists of that of OLT, ONU/ONT and passive optical components. An ODN is combined with fiber cable, cabinet, optical splitter, connector and so on. For the same amounts of users, the cost for the fiber and cabinet with EPON is similar to that of GPON. The cost of OLT and ONT is decided by the ASIC (Application Specific Integrated Circuit) and optical transceiver modules. The GPON chipsets available in the market are mostly based on FPGA (Field Programmable Gate Array), which is more expensive than the EPON MAC (Media Access Control) layer ASIC. There are only several chipset vendors who can provide GPON chipsets, and it is likely that the price of GPON equipment cannot be reduced rapidly. The optical module of GPON is also more expensive than EPON. When GPON reaches deployment stage, the estimated cost of a GPON OLT is 1.5 to 2 times higher than that of an EPON OLT, and the estimated cost of a GPON ONT will be 1.2 to 1.5 times higher than that of an EPON ONT.
4. In QoS(Quality of Service), GPON is superior to EPON. Ethernet protocol has no inherent QoS capability. On account that a PON system is not viable without QoS, most vendors provide it by using VLAN (Virtual Local Area Network) tags. Without automatic provisioning of VLAN tags, to a large extent, they are manually provisioned. GPON is integrated with QoS to make it better than EPON, due to that EPON QoS is with high cost relative to GPON.
5. In OMA(Operation Administration and Maintenance), GPON has more advantages than EPON. EPON does not take OMA into consideration, and just simply defines the remote failure indication for ONT, loopback and link monitoring. On the contrary, GPON defines the PLOAM(Physical Layer OAM) in physical layer and OMCI(ONT Management and Control Interface) in the high-level layer. GPON has OAM management in multi-layers. PLOAM is applied to realize the data encryption, state inspection, error code monitoring. OMCI is applied to manage the higher-level layer services, such as ONU functional parameters, the types and quantity of T-CONT, QoS parameters, information of appliance for deployment and performance statistics, to implement the OLT management for the ONT deployment, fault diagnosis, performance and safety.

Conclusion
Although both GPON and EPON have their own features and merits, and to some degree, they compensate for each other. In performance, GPON is superior to EPON, but inferior to EPON in costs. GPON is coming up from behind. For the future broadband access market, the co-existence and complementation principle should be kept rather than one replacing another one. In some certain sense, GPON seems to be more suitable for clients having higher requirements for bandwidth, services, QoS, security and ATM tech.

Advantages and Disadvantages of Optical Fiber Communication

Nowadays, optical fiber communication stands out in the optical communication industry to be the mainstay of modern communication. As an emerging tech, the development pace of optical fiber communication and wide range of applications are unprecedented in the communication industry. However, what does it make so? What are advantages and disadvantages of optical fiber communication? Well, we will get the answer from this article.

optical fiber communication

In modern communication network, there are three pillars: optic fiber communication, satellite communication, and radio communication, in which optic fiber communication is regarded as the principal sector of them. It’s due to that it has various outstanding benefits.

Advantages of Optical Fiber Communication

1. With Higher Bandwidth and Large Communication Capacity

The available bandwidth for fiber is about 50000GHz. 1.7Gb/s optic fiber communication system adopted in 1987, in which a pair of fibers can simultaneously transmit 24192 channels of telephones; 2.4Gb/s system can transmit 30000 channels of telephones. Bandwidth plays a key role in transmitting various kinds of broadband information. Otherwise, it will not meet the needs of future Broadband Integrated Services Digital Network (B-ISDN)

2. With Low Loss and Long transmission distance without Repeater

the loss of fiber is very low. When optic wavelength is about 1.55μm, the loss of silica fiber is lower than 0.2dB/km, which is lower than any transmission media. So the transmission distance without repeater can reach to tens of or hundreds of miles. On account of the low loss of fiber, the long-distance transmission without repeater can be achieved. In the optical fiber communication system consisting of silica fibers, the transmission distance without repeater can reach to over 2000km

3. Anti-Electromagnetic Interference

Optic fiber belongs to insulator material, not interfered by thunder, variation of the ionosphere, sunspot activity; as well as not interfered by industrial equipments, such as electrified railway wires, high voltage devices and so on. It can also be made into the compound cables with electric conductors.

4. No Crosstalk Interference and With Security

Transmitted in the optic fiber cable, optical wave is hard to leak out. Even if it’s in the turning and its bending radius is very short, the optical wave leaking out from the cable is also weak. If it’s coated with a layer of delustrant on the surface of fiber or  optic fiber cables,  the effect will be better. After that, even though there are many fibers in the fiber cables, it’s able to reach the effect that no crosstalk interference happens and the information transmitted in the fibers is not be intercepted out of optical fibers.

5. Light in Weight and Short in Diameter

The fiber diameter of optic fiber is very short, 0.1mm, only 1% the one of single-tube coaxial cables. In addition, the diameter of optic fiber cable is also short. The cross-sectional diameter of optic fiber cable with 8 fibers is 10mm; while the one of standard coaxial cable is 47mm. By making use of this advantage, the space of transmission system can be narrowed so that a matter of crowding underground pipes can be solved and the costs for constructing pipes are also saved. Moreover, the fiber cables are lighter than cables in weight. To some degree, it’s easier to produce and install.

6. Abundant in the Raw Materials of Optic Fiber

The main material of optic fiber is quartz, which is unlimited on the earth; while cable is made of copper, which is limited. If the fiber cable is in replace of cable, amounts of metal materials are able to be saved.
In addition, there are still other strengths, such as with high corrosion resistance, nuclear radiation resistance,  low resource consumption and so on.
Of course, there is no perfect things in the world. No matter how perfect one thing is, it still has its demerits. Optical fiber communication is without exception. The below is about its introduction.

Disadvantages of Optical Fiber Communication
Compared with the merits, the demerits are relatively less, as below:
l  With fragile material and poor mechanical strength
l  The bending radium of optic fiber cable can not be too short（>20cm).
l  Separation and coupling are not flexible
l  Requiring more protection around the fiber cable compared with copper cable

Conclusion
Obviously, advantages of optical fiber communication in various aspects contribute to the rapid development of optical fiber communication. Although it’s still with some disadvantages, and it will be improved with the future development of tech. Let’s expect it together.