BOSA – What is it? How is it produced?

The most important and core thing in optical communication is the optical module. In the historical development of optical communication, the main thing is the innovation of the performance indicators of the optical transceiver module. The most basic function of the optical transceiver is to complete the optical-to-electrical or electro-to-optical conversion function of the optical signal, in other words, to complete the photoelectric conversion. Its interior mainly comprises optical devices, functional circuits, and optical interfaces.

Among them, optical devices are the main components of optical transceiver modules. One is TOSA (Transmitting Optical Sub-Assembly, light emitting component), and the other is ROSA (Receiving Optical Sub-Assembly, light receiving component).

The optical devices used in early optical modules were separate for receiving and transmitting. With the development of miniaturization, the two were combined into one to form BOSA (Bi-Directional Optical Sub-Assembly, light transmitting and receiving assembly).

What is BOSA?

Bi-Directional Optical Sub-Assembly (BOSA) refers to a single-fiber bidirectional optical device, which mainly consists of a transmitting laser, a receiving detector, an adapter, a filter, a base, an isolator and a die sleeve. TOSA and ROSA can also be integrated into the transceiver of the light source (LD and PIN/APD) through the coaxial coupling process, plus components composed of splitters, optical fibers, etc. The main function is to convert electrical signals and optical signals into each other.

BOSA Key Components

BOSA mainly contains the following key components:

BOSA Production Process

The main production process of BOSA is: marking - installing beam splitter - assembling LD - LD assembly surface inspection and spot welding - transmitting coupling - welding - receiving coupling - glue sealing - transmitting and receiving parameter detection.

1. Marking: A laser is used to print an“ID card”on the outside of the metal structure of the component, and its parameters are entered into the system to facilitate tracking and inspection.

2. Install the beam splitter: The role of the beam splitter is to separate the light received and emitted in the optical fiber. The LD is press-fitted into a metal structural part with a beam splitter mounted on it.

3. LD assembly surface inspection and spot welding: The assembled metal structural parts with LD are inspected under a microscope to check the press-fitting effect to see if there are any undesirable conditions such as pin tilt. After checking that there are no problems, the LD and structural parts will be laser spot welded to fix the LD.

4. Emission coupling and welding: By adjusting the relative position of the SC connector structural part and the LD, the light emitted by the LD is coupled into the optical fiber of the SC connector part as much as possible. After the adjustment is completed, the structural parts of the SC joint part and the structural parts with the LD pressed are fixed by laser spot welding.

5. Receiving coupling and sealing: It is to adjust the relative position of the PD and the structural parts equipped with LD so that more optical signals from the optical fiber are coupled to the PD to improve the receiving sensitivity of the PD. After the adjustment reaches the index requirements, the PD and structural parts are glued and sealed to fix the PD.

What is Optical Cross-Connection (OXC) in OTN?

Optical cross-connection (OXC) is a fundamental technology in optical transport networks (OTNs) that revolutionizes the way optical signals are switched and routed. OXC enables dynamic and flexible reconfiguration of optical paths, improving network efficiency, reliability, and scalability. Today, we will explore the concept, benefits, and implementation of OXC in OTN networks.

OTN, a high-speed optical networking technology, underpins the backbone of modern communication networks. OTN networks handle massive volumes of data traffic, including voice, video, and internet, over long distances with high bandwidth and low latency. OXC serves as the cornerstone of OTN networks, providing the means to dynamically establish, modify, and release optical connections in response to changing traffic demands and network conditions.

How Does OXC Work?

OXC devices, also known as optical cross-connects, are intelligent network elements that perform optical switching. They receive optical signals from multiple input ports and selectively direct them to specific output ports based on preconfigured switching tables. OXC devices leverage various technologies, such as wavelength-selective switches (WSS) and MEMS (microelectromechanical systems) switches, to achieve this switching functionality.

Technologies of OXC:

1. Wavelength-Selective Switches (WSS): WSS-based OXC devices employ a combination of gratings and mirrors to selectively switch optical signals based on their wavelengths. Each input signal is directed to a specific wavelength channel, enabling flexible routing to any output port.

2. MEMS Switches: MEMS-based OXC devices utilize tiny movable mirrors to redirect optical signals to different output ports. These mirrors are actuated by electrical signals, allowing for rapid and precise switching of optical paths. MEMS switches offer low insertion loss, high port count, and fast switching speeds.

Advantages of OXC in OTN Networks:

1. Network Flexibility: OXC enables dynamic reconfiguration of optical paths, allowing network operators to optimize traffic flow, avoid congestion, and reroute signals around network failures or maintenance activities.

2. Protection and Restoration: OXC plays a crucial role in implementing protection and restoration mechanisms in OTN networks. It facilitates rapid rerouting of optical signals in the event of a link or node failure, ensuring uninterrupted service and minimizing downtime.

3. Scalability: OXC simplifies network expansion and scale-out by providing a flexible way to add or remove network nodes and links. New services and traffic demands can be easily accommodated by reconfiguring OXC devices.

4. Cost Reduction: OXC reduces the need for costly and complex multiplexing and demultiplexing equipment, resulting in lower overall network costs. Additionally, OXC enables more efficient utilization of network resources, leading to operational cost savings.

5. Improved Network Performance: OXC contributes to improved network performance by reducing signal delay, minimizing jitter and latency, and optimizing overall network utilization.

Types of 400G Transceivers

400G optical transceivers are compact, high-performance devices designed to transmit and receive data at a staggering rate of 400 gigabits per second (Gbps). These modules serve as the essential interface between network equipment and optical fibers, converting electrical signals into light pulses and vice versa. By leveraging advanced optical technologies, 400G transceivers enable ultra-fast and reliable data transfer over long distances, catering to the ever-increasing demands of bandwidth-intensive applications.

As an important product in the field of optical communication transmission, optical modules are widely used in high-performance data centers, communication networks, large-scale computing, cloud computing and other fields. In the field of data centers, 400G optical modules can meet the needs for large bandwidth, low latency, and high reliability required for the development of cloud computing and big data. It is also suitable for scenarios such as long-distance transmission and high-speed transmission.

Several different types of 400G transceivers exist, each optimized for specific applications and network configurations. Some of the most common types include:

400G OSFP:

The full name of OSFP is Octal Small Formfactor Pluggable. Octal refers to 8, meaning octal, which means directly using 56G electrical signals, 856GbE, but the 56GbE signal is formed by a 25G DML laser under the modulation of PAM4. This standard is a new interface standard and is incompatible with existing optical and electrical interfaces.

OSFP comes with its own heat sink and has a slightly larger form factor than QSFP-DD but offers additional features such as enhanced thermal management and improved signal integrity. It also uses eight 50 Gbps lanes for data transmission.

400G QSFP-DD:

Q in QSFP-DD refers to "Quad", which means 4 channels. Each QSFP56 is 456Gbe, forming a 200G signal; DD refers to "Double Densiy", which means there are two QSFP56 in parallel, 2200G generates a 400Gbe signal, the full name It is Quad Smal Fom Factor Pluoable-Double Density. This solution is an expansion of QSFP. It adds one line to the original 4-channel interface and turns it into 8 channels. It is smaller in size than OSFP and is compatible with existing 40GbE QSFP and 100GbE QSFP28 interfaces. The original QSFP28 module can still be used, and you only need to insert another module to achieve a smooth upgrade.

This popular form factor offers high density and low power consumption, making it ideal for data center applications. It utilizes eight electrical lanes operating at 50 Gbps each to achieve the aggregate 400G data rate.

400G CFP8:

CFP8 is an expansion of CFP4. The number of channels is increased to 8 channels, and the size is also increased accordingly. Using 16 25G parallel signals can quickly complete the launch and application of 400G products, but the cost is high. You need to use 1625G optical devices, or use PLC splitters to reduce the number of lasers, but the LOSS of the splitters is very high. , which directly leads to a relatively large emission power of the laser, thus increasing the cost. The power consumption is also high, the panel interface density is too low, and the size is large.

This module is designed for longer-reach applications in telecommunication networks. It utilizes 16 electrical lanes operating at 25 Gbps each to achieve the 400G data rate.

400G optical modules also can be categorized based on their transmission mode and reach:

Single-mode vs. Multi-mode:

Single-mode modules transmit data over longer distances using a single light path, while multi-mode modules are suitable for shorter distances and utilize multiple light paths.

Short-reach vs. Long-reach:

Depending on the application, 400G modules can be optimized for different transmission distances, ranging from within data centers to across continents.

What is GPON?

Passive Optical Network (PON) technology has become one of the mainstream technologies for Fiber-to-the-X (FTTx) network construction. As users' demand for high bandwidth continues to grow, especially with the popularization of high-traffic applications such as OTT video and 4K TV, operators have included 10G GPON technology in their schedules to meet users' urgent need for faster and more reliable network connections. GPON is generally divided into GPON, XG-PON and XGS-PON.

Gigabit Passive Optical Network (GPON) is an optical fiber transmission technology that uses a single optical fiber line to transmit data to achieve high-speed, high-bandwidth network connections. The basic principles of GPON involve light transmission and the use of optical splitters. In the GPON network, an optical fiber line connects multiple users and distributes signals to different end users through optical splitters to achieve data transmission.

The architecture of GPON includes optical line terminal (OLT) and optical network unit (ONU). The OLT is responsible for communicating with the ONU on the user side, and the ONU is responsible for communicating with the user equipment. This distributed structure enables the GPON system to support a large number of users and be widely used in different fields.

1. GPON Technical Specifications

Among the technical specifications of GPON, one of the most prominent features is its high bandwidth requirements. GPON is typically capable of providing transmission rates of 1.25 Gbps (downstream direction) and 2.5 Gbps (upstream direction). This high bandwidth makes GPON excellent in supporting high-traffic applications such as high-definition video and large-capacity file transfer.

In addition, GPON also has certain advantages in distance. Fiber optic transmission allows signal transmission distances to reach tens of kilometers, which enables GPON to meet a wide range of network topology needs.

Since the uplink rate of GPON is relatively low, the cost of ONU's sending components (such as lasers) is also low, so the total price of the equipment is low.

2. GPON Features

High bandwidth: GPON can provide transmission rates of up to 2.5 Gbps (uplink) and 1.25 Gbps (downlink), which enables it to meet users' needs for high-speed broadband connections.

Point-to-multipoint architecture: GPON uses a point-to-multipoint optical fiber transmission architecture to connect an optical line terminal (OLT) and multiple optical network units (ONU) through an optical fiber line. This distributed architecture allows multiple users to share the same optical fiber, improving network resource utilization.

Symmetric and asymmetric transmission: GPON supports symmetric and asymmetric transmission, that is, the uplink and downlink transmission rates can be different. This enables the network to better adapt to the needs of different users and applications.

ITU-T standards: The technical specifications of GPON are formulated by the Telecommunications Sector of the International Telecommunications (ITU-T) and are specifically defined in the G.984.x series of recommendations. This provides a unified standard for equipment from different manufacturers and increases the interoperability of equipment.

3. GPON Advantages and Limitations

One of the advantages of GPON is its relatively low cost. Fiber optic networks are often more cost-effective than traditional copper cable networks, especially in large-scale deployments. In addition, GPON supports symmetric and asymmetric transmission, making it suitable for different application scenarios.

However, GPON also has some limitations. Due to its limitations in transmission rate and bandwidth, the network may face bandwidth bottlenecks when user demands continue to increase. Upgrading the GPON system to meet higher requirements may face some technical and economic challenges.

4. GPON Application Scenarios

Home broadband network: GPON provides home users with high-speed and stable broadband connections, supporting high-definition video streaming, online games and other needs.

Enterprise network: In an enterprise environment, GPON can provide reliable communication infrastructure to meet the needs of enterprises for daily office work and large-scale data transmission.

Government and campus networks: GPON is also widely used in government agencies and school networks, meeting the needs of these institutions for high-bandwidth and high-stability networks.

What Are the Key Components of Optical Transceiver Module?

The function of optical transceiver module is to perform photoelectric conversion, and its internal TOSA, ROSA and BOSA are the key components to realize the photoelectric conversion function. The optical device is composed of transmitter and receiver to complete the optical-electrical or electrical-optical conversion of optical signals.

The interior is composed of optical devices, functional circuits and optical interfaces. The optical device is the main component of the optical transceiver module.

The optical devices used for optical signal conversion are called TOSA and ROSA.

TOSA (Transmitting Optical Sub-Assembly) mainly completes the conversion of electrical signals into optical signals. With the light source (semiconductor light-emitting diode or laser diode) as the core, LD chip, monitor photodiode (MD) and other components are packaged in a TO coaxial package or butterfly package, which constitutes TOSA.

In TOSA, laser diode is the most commonly used semiconductor emitting device for optical transceiver modules. Threshold current (Ith) and slope efficiency (S) are the two main parameters. In order to make the LD work quickly, a DC bias current slightly greater than the threshold current must be provided to the LD, that is, the laser is emitted only when the forward current exceeds the threshold current.

ROSA (Resceiving Optical Sub-Assembly) optical receiving assembly, in the high data rate optical fiber module, PIN or APD photodiode and TIA are usually assembled in a sealed metal casing to form an optical receiving assembly.

The figure below is the schematic diagram of the optical module ROSA, which is composed of a photodetector (PIN/APD), a TIA pre-amplifier, and a limiting amplifier.

Photodetector, the main device of ROSA, is mainly used to convert optical signals into electronic signals through the photoelectric effect. The common photodetectors in optical communications are PIN photodiodes and avalanche photodiodes (APDs). APDs are high-sensitivity photodetectors that use the avalanche multiplication effect to double the photocurrent. Compared with PIN photodiode, the receiving sensitivity of APD can be improved by 6~10dB.

The weak signal current generated by the photodetector is converted into a signal voltage of sufficient magnitude by the preamplifier TIA, and then output. TIA is actually a voltage converter, which converts electro-optic current into voltage.

At this time, the voltage signal output by the TIA is still an analog signal, which needs to be converted into a digital signal before the signal processing circuit can recognize it. The function of the Poster Amplifier behind the TIA is to convert signals of different amplitudes into digital signals with the same amplitude.

After introducing TOSA and ROSA, let's take a look at what is BOSA?

With the development of process level technology, the modules can be made smaller. TOSA and ROSA integrate the transmission and reception of light (LD and PIN/APD) through the coaxial coupling process, plus splitters, optical fibers and other components, called BOSA (Bi-Directional Optical Sub-Assembly).

Nowadays, the high-speed optical transceiver module integrates high-performance DSP at the receiving end, and its performance in terms of dispersion and noise processing is really good.

Application of Magneto Optical Switch in Wind LiDAR

Basic principles of magneto-optical switch:

The magneto-optical switch is an optical switch that utilizes the Faraday magneto-optical effect. It changes the effect of the magneto-optical crystal on the polarization plane of the incident polarized light by changing the external magnetic field, thereby achieving the effect of optical path switching.

Compared with traditional mechanical optical switches, magneto-optical switches have obvious advantages. The switching speed of the magneto-optical switch reaches μs level and has the following advantages: low polarization sensitivity, no moving parts, small insertion loss, fast response speed, high degree of integration, small crosstalk, small size, etc.

It can meet the requirements of strong anti-interference ability, low driving voltage, high stability, simple and reliable circuit design, and long-term continuous operation.

Application in Wind LiDAR:

The laser emitted by the laser light source system is coupled to the optical antenna by an optical fiber. The radar is equipped with four light-emitting lenses, with an angle of 30° horizontally and an angle of 25° vertically. The four laser beams are switched at a frequency of 50HZ.

The lens in the optical antenna is focused to a fixed distance, where the energy is most concentrated and scatters with the aerosol at that point. The scattered returned light is coupled back into the optical fiber through the lens.

It is mixed with the local oscillator light generated by the laser light source system in the coupler, and then the optical signal is converted into an electrical signal by the photoelectric conversion module and amplified.

The data acquisition system collects electrical signals and performs spectrum processing, and then the data processing system calculates the spectrum to obtain the wind speed information of the single channel.