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.

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 3000.76 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 0.3960×10 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.

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-3155Mbps/OC-12622Mbps/ OC-482.488Gbps , Security and Protection systems; also in Local Area Network (LAN), Wide Area Network (WAN), and Ethernet switches and router application.

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


Things You Should Know About PSM4

In current interconnection market, 100G QSFP28 transceiver has become a common trend of Ethernet due to its higher bandwidth, high data rate, lower cost and so on. To further keep pace with the market demands, many series of QSFP28 optical transceivers comes into data center, such as QSFP28 100GBASE-SR4/LR4, QSFP28 100GBASE-PSM4, QSFP28 100GBASE-CWDM4 and so on, in which 100GBASE-PSM4 is relatively cost-effective compared with other 100G series optics. Well, this article will have an introduction to things you should know about QSFP28 PSM4 from perspectives of 100G PSM4 definition, 100G PSM4 Specification, advantages of PSM4 and other else.
What’s 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.
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 PSM4
For QSFP28 PSM4 transceiver, Gigalight also launches one type: GQM-SPO101-IR4C(shown as the pic). 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.

QSFP28 PSM4, as the most cost-effective one type of QSFP28 series transceivers, it’s believed that it will play a key role in future data center by virtue of its various strengths, especially in cost. Simultaneously, it’s possible to be further improved in cost with the development of tech. Let’s expect it together.


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.

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 132. 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 1518dB, 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.

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 


Things We Should Know About SFP Transceiver

In today’s data center, fast Ethernet is out of date.  What takes the place of it is SFP transceiver. Although SFP transceiver is commonly applied in the data center, and there are still many people knowing little of it, such as SFP transceiver types, SFP applications, SFP use tips and so on. Now this article will introduce things we should know about it there.

What Is SFP Transceiver?
The small form-factor pluggable (SFP) is a compact, hot-pluggable optical module transceiver used for both telecommunication and data communications applications. The form factor and electrical interface are specified by a multi-source agreement (MSA) under the auspices of the Small Form Factor Committee. It is a popular industry format jointly developed and supported by many network component vendors.

SFP Transceiver

An SFP interface on networking hardware provides the device with a modular interface that the user can easily adapt to various fiber optic and copper networking standards. Existing SFP transceivers support SONET, gigabit Ethernet, Fibre Channel, and other communications standards. Due to its smaller size, the SFP has replaced the gigabit interface converter (GBIC) in most applications; the SFP is sometimes referred to as a Mini-GBIC. In fact, no device with this name has ever been officially defined in the MSAs.

Types of SFP Transceiver
SFP transceivers are available with a variety of transmitter and receiver specifications, allowing users to select the appropriate transceiver for each link to provide the required optical reach over the available optical fiber type. With the respect to SFP transceiver types, it can be sorted out according to transmission rate, wavelength. The introductions of them are as below:
Classified according to the SFP transceiver rate, it includes 155M/622M/1.25G/2.125G/4.25G/8G/10G, in which 155M and 1.25G are usually applied. Besides, 10G tech is maturely developed, and the demands for it tend to rise.
Sorted according to the SFP wavelength, it consists of 850nm/1310nm/1550nm/1490nm/1530nm/1610nm, in which 850nm wavelength belongs to multimode, and its transmission distance is less than 2KM; 1310nm/1550nm wavelength belongs to single mode, and the transmission distance is over 2KM. Relatively speaking, the prices of 850nm, 1310nm and 1550nm wavelength are lower than the other three types. Moreover, bare optical modules without signs are easy to get mixed up, thus manufacturers usually make a clarification in the colours of pull rings. For example, pull rings of  modules differ in colors, which means they distinguish in wavelengths. Black represents 850mn wavelength; blue represents 1310mn wavelength; yellow represents 1550mn wavelength; and purple represents 1490mn.
In addition, it can also be divided into these categories, such as Gigabit Ethernet SFP, Fast Ethernet SFP, BiDi SFP, CWDM SFP, DWDM SFP, Fiber Channel SFP and so on, in which Gigabit Ethernet SFP and CWDM SFP are relatively common ones (Gigalight will provide several ones for reference at the end of this article, shown as the tables)

SFP sockets are found in Ethernet switches, routers, firewalls and network interface cards. Storage interface cards, also called HBAs or Fibre Channel storage switches, also make use of these modules, supporting different speeds such as 2Gb, 4Gb, and 8Gb. Because of their low cost, low profile, and ability to provide a connection to different types of optical fiber, SFP provides such equipment with enhanced flexibility.

Use Tips
If module is improperly operated when used, it may not work. Once this situation happens, things that should be done first is to check it carefully and analyze the causes. The failure of optical transceiver usually includes these two types: the failure of transmitting terminal and receiving terminal. The commonly-seen reasons of failure are as below:
1.    The contaminated interface of fiber connector result in the secondary contamination of optic module’s optical port
2.    Optical port of optic module is exposed to the air, and dust into it brings about contamination.
3.    Optic fiber connector is with bad quality.

Although the needs for higher rate products will be increased with the development of tech, and SFP transceiver will still be in the optic market for a long time due to its advantages in miniaturization, port density and so on. This article have a relative comprehensive introductions to SFP transceiver, and it’s believed that it will be beneficial to us in the future use of SFP transceiver.

More Information :
1.    Gigalight Gigabit Ethernet SFP:
Gigalight Gigabit Ethernet SFP
Part Number

Compliant with the Gigabit Ethernet and 1000BASE-T standards as specified in IEEE 802. 3-2002 and IEEE 802.3ab, which supporting 1000Mbps data- rate up to 100 meters reach over unshielded twisted-pair category 5 cable.
Supporting data-rate of 1.25Gbps and 550m transmission distance with MMF. All modules satisfy class I laser safety  requirements.
Supporting data-rate of 1.25Gbps he transceiver consists of three sections: a DFB laser transmitter, a PIN photodiode
integrated with a and 40km transmission distance with SMF
Supporting data-rate of 1.25Gbps and 80km transmission distance with SMF. Compatible with SFP Multi-Source Agreement (MSA) and SFF-8472.

2.    Gigalight CWDM SFP Transceivers:
Gigalight CWDM SFP Transceivers
Part Number

Supporting data-rate of 155Mbps and 80km transmission distance with SMF. Compatible with SFP Multi-Source Agreement (MSA) and SFF-8472.
Supporting data-rate of 155Mbps and 80km transmission distance with SMF. Compatible with SFP Multi-Source Agreement (MSA) and SFF-8472.
Supporting data-rate of 155Mbps and 80km transmission distance with SMF. Compatible with SFP Multi-Source Agreement (MSA) and SFF-8472.
Supporting data-rate of 155Mbps and 80km transmission distance with SMF. Compatible with SFP Multi-Source Agreement (MSA) and SFF-8472.
Supporting data-rate of 155Mbps and 80km transmission distance with SMF. Compatible with SFP Multi-Source Agreement (MSA) and SFF-8472.
Supporting data-rate of 155Mbps and 80km transmission distance with SMF. Compatible with SFP Multi-Source Agreement (MSA) and SFF-8472.
Supporting data-rate of 155Mbps and 80km transmission distance with SMF. Compatible with SFP Multi-Source Agreement (MSA) and SFF-8472.

Note: Infiberone is the online store of Gigalight