What Are Optical Modules?

Optical modules are the electronic modules that are used in optical communication systems. These modules can be found in several applications such as optical modulation, multiplexing, NRZ electrical interface and many more.

Optical modulation

When you want to use an optical module, you must ensure that its electrical interface is compatible with other components. To ensure this, your optical module must pass a number of parameter tests. This includes the average output optical power and the extinction ratio. These parameters directly affect the quality of the communication between the transmitting and receiving end.

An optical module can be configured with a digital or analog electrical interface. Most modules, including Ethernet, utilize an active electrical connection. In contrast, some optical modules use a passive connection.

Optical modules are typically soldered to a PCB assembly. The underlying waveguide is accessed through holes in the substrate. Optical modules can be built with polymer waveguides. However, polymer waveguides are more susceptible to signal loss. It is important to compensate for these losses.

An important design decision for any transceiver is the extinction ratio. For instance, if a module’s optical extinction ratio is greater than 50%, it is more likely to produce weaker signals. As a result, the maximum input optical power is reduced.

Optical modules use a variety of different forms of modulation, such as Dual Polarization Quad Phase Shift Keying (DPQPSK) and coherent optical modulation. They also can use tunable lasers. Tunable lasers can be used in network-based optical switching and mesh networks.

High-speed data lines are susceptible to signal loss. This occurs due to high-frequency roll-off of the PCB traces and intersymbol interference. Therefore, an ultrafast electrical driver is necessary to compensate for these losses.

Another issue is the signal return loss. This occurs due to crosstalk from adjacent lanes. Signal processing techniques can be used to mitigate this effect. A common solution is to use decision feedback equalization.

Other factors that impact the optical signal are the transmission line and IC pads. Polymer waveguides have high optical losses at longer wavelengths. Additionally, they are susceptible to connector loss. In addition, their yield is low.

For this reason, the economics of scale are critical. Hence, the price per port is less when fewer ports are required.

Several Multi-source Agreements have been developed in the optical module industry. Nevertheless, reliable manufacturing is needed to achieve wide adoption.

Multiplexing

Optical modules are critical components of an optical communication system. They monitor communication signals and provide a connection to a base station. These modules can be arranged in a number of ways. Some of these optical modules deliver an analog connection while others deliver an electrical interface. The latter is typically used when connecting to a top rack switch.

Multiplexing is a technique used to combine multiple signals into one shared channel. This helps to achieve redundancy features and advanced topologies. It has been used traditionally to share limited bandwidth. However, advancements in technology have allowed higher density and performance.

One example is the XFP (Extensible Fibre Platform). The XFP was defined in 2002. It is an extension of the SFP specification. XFP modules are interoperable with other XFP modules and appropriate connectors.

An example of an optical module that uses multiplexing is the ER-Lite, a pluggable transceiver. It includes a PAM4 DSP IC. The PAM4 DSP IC is used to drive a transmission photomultiplier.

ADC ICs are another popular component. optical module pcb The addition of an ADC IC increases the scalability of the channels and adds precision measurement.

In an optical module, the most common multiplexing technique is on-off keying. Other techniques include Dual Polarization Quad Phase Shift Keying (DPQPSK), QAM-16, and QPSK. Each of these signals has its own characteristics and can be influenced by the way the signal is received and passed through the transmission line.

Earlier, a single mode fiber optical coupling is used. This method has a small core diameter and requires a lens to focus the coupling. But it has a large tolerance. High-speed optical modules may require cross-hitting or collapsed lead laps to improve signal integrity.

COB (Compact Optical Block) packaging saves space and other components. This packaging process is important for the yield rate and stability of the production. optical module pcb There are two main process steps in COB package, optical coupling and die bonding.

A COB package also allows the PCB to directly connect with an LD. LDs are generally sealed in a metal box. To ensure the life of the LD in a COB module, limited hermetic sealing is used.

NRZ electrical interface

Optical modules have various electrical interface options. One type, the PAM4 scheme, is designed to achieve the same data transmission rate as the NRZ code. It also has several advantages over the NRZ scheme.

The PAM4 system uses a higher order modulation format than the NRZ. This allows the signal rate to be increased without increasing the cost. Using a higher order modulation format reduces the number of components required. Moreover, the same total noise power is spread over a wider frequency band, resulting in lower total signal loss.

The PAM4 system comprises a transmitting unit, an optical receiving unit, an interface unit, and a standard conversion unit. Each component is connected to the next one. The transmitting unit integrates a 25G direct modulation laser DML. A corresponding receiver, or DML optical transceiver, is also integrated.

The electrical interface for the optical module was originally analog. It was later replaced by a retimed digital interface. There were several Multi-source Agreements (MSAs) in the optical module industry. XPAK, or XAUI, was introduced in 2001. Although XPAK had a similar electrical interface to XENPAK, its mechanical properties differed. Moreover, it did not have the same level of efficiency as NRZ.

Another advantage of the PAM4 modulation scheme is the reduced jitter characteristics. However, this is not always the case. High-speed data lines on current printed circuit board technology are plagued with high-frequency roll-off. Consequently, the jitter and eye pattern of the signal are impacted. To mitigate this, a soft band is used to attenuate the high-frequency signal amplitudes.

In addition, a flip-chip process was used to realize an RF connection between the photodetector and the linear transimpedance amplifier. An inductor is also employed inside the IC to suppress the heat generated by the switching converters. Gold wire bonding is also used to connect the LD to the driver.

Finally, an integrated electro-absorption modulator is used to transmit the high-frequency signal. The resulting combination of a 25G linear DML driver and a 25G DML laser is a cost-effective solution. The module is compact and simple to implement.

The proposed high-speed PAM4 optical transceiver module enables a single 25G component to transmit a 25 Gbit/s signal. The use of a multilevel modulation format is likely to be adopted when practical electrical PCB trace length is considered.

Optical modules are additionally used in optical communication systems

There are several types of optical modules that are used in the various fields of optical communication. These include transmitter, receiver, and optical transceiver. A common optical module is used in a mobile communication base station or a data center.

The transmission distances of an optical module depend on the type of wavelength used and dispersion. DWDM and CWDM optical modules are often used for long distances. They save on the costs of the optical fiber. Optical modules are also commonly used in Ethernet networks.

Typically, an optical sub-module is packaged with a laser diode and other components. It is packaged in a metal or plastic housing. When an electrical signal is input to a receive optical bore, it is processed by an internal driver chip. After passing a preamplifier, the optical power is transmitted to the module’s receiving end.

Typical optical modulation techniques are based on on-off keying and pulse-amplitude modulation. In contrast, coherent optical modulation is used for high speed communications. This type of modulation is achieved by averaging the optical powers of a plurality of signal 1s. Several types of optical modulation techniques are used by optical modules, including Dual Polarization Quad Phase Shift Keying (DPQPSK), QAM-16, and PAM-4.

Optical modules have been used extensively in the higher rate interfaces of Ethernet. In the 5G era, the need for high-speed data transfer is greater than ever. Increasing data traffic has pushed the development of optoelectronic technologies. Thus, the bandwidth of circuits has grown.

Optical modules are mainly employed in the fields of data communication. Due to the rise of cloud computing and artificial intelligence, data traffic has increased rapidly. Furthermore, the Internet of Things has caused a large number of devices to be connected to the network. Therefore, the demand for high-speed optical transmission has risen.

Several Multi-source agreements have been signed in the optical module industry. One of the prominent shows is the ECOC show in Europe. An example of a typical optical forwarding module is a 200/300pin.

Optical modules are also used in backhaul in 5G bearer networks. They can be used in a wide range of applications, such as a fiber channel, SONET/SDH, or Gigabit Ethernet.