Optical modules are available in various types to meet diversified requirements.
Classified by transmission rates
Depending on transmission rates, optical modules are classified into 100GE, 40GE, 25GE, 10GE, FE, and GE optical modules.
Classified by encapsulation types
The higher transmission rate an optical module provides, the more
complex structure it has. Optical modules are encapsulated in different
modes to provide different structures. Optical
modules come in the following encapsulation types: SFP, eSFP, SFP+, XFP,
SFP28, QSFP+, CXP, CFP, and QSFP28. All optical modules are hot
swappable.
SFP: small form-factor pluggable. SFP optical modules support LC fiber connectors.
eSFP: enhanced small form-factor
pluggable. An eSFP module is an SFP module that supports monitoring of
voltage, temperature, bias current, transmit optical power, and receive
optical power. Because all the SFP optical modules support these
monitoring functions, eSFP is also called SFP.
SFP+: small form-factor pluggable
plus, SFP with a higher rate. SFP+ modules are more sensitive to
electromagnetic interference (EMI) because they have a higher rate. To
reduce EMI, SFP+ modules have more springs than SFP modules and the
cages for SFP+ modules on a card are tighter.
XFP: 10 Gigabit small form-factor
pluggable. X is the Roman numeral 10, meaning that all XFP optical
modules provide a 10 Gbit/s transmission rate. XFP optical modules
support LC fiber connectors. XFP optical modules are wider and longer
than SFP+ optical modules.
SFP28: with the same interface size
as an SFP+ module. An SFP28 interface can use a 25GE SFP28 optical
module or 10GE SFP+ optical module.
QSFP+: quad small form-factor pluggable. QSFP+ optical modules support MPO fiber connectors and are larger than SFP+ modules.
CXP: hot-pluggable high-density
parallel optics transceiver form factor, which provides 12 channels of
traffic in each of the Tx and Rx directions. It applies only to short
multimode links.
CFP: C form-factor pluggable, a new
standard for high-speed, hot-pluggable optical transceivers that support
data communication and telecommunication applications. Dimensions of a
CFP optical module are 144.75 mm x 82 mm x 13.6 mm (W x D x H).
QSFP28: with the same interface size
as a QSFP+ module. A QSFP28 interface can use a 100GE QSFP28 optical
module or a 40GE QSFP+ optical module.
Classified by physical layer standards
Different physical layer standards are defined to allow data
transmission in different modes. Therefore, different types of optical
modules are produced to comply with these standards. For details, see Standards compliance of the specific optical module.
Classified by modes
Optical fibers are classified into single-mode and multimode fibers.
Therefore, optical modules are also classified into single-mode and
multimode modules to support different optical fibers.
Single-mode
optical modules are used with single-mode fibers. Single-mode fibers
support a wide band and large transmission capacity, and are used for
long-distance transmission.
Multimode optical modules are used
with multimode fibers. Multimode fibers have lower transmission
performance than single-mode fibers because of modal dispersion, but
their costs are also lower. They are used for small-capacity,
short-distance transmission.
Wavelength division multiplexing modules differ from other optical
modules in center wavelengths. A common optical module has a center
wavelength of 850 nm, 1310 nm, or 1550 nm, whereas a wavelength division
multiplexing module transmits lights with different center wavelengths.
Wavelength division multiplexing modules are classified into two types:
coarse wavelength division multiplexing (CWDM) and dense wavelength
division multiplexing (DWDM). Within the same band, DWDM modules are
available in more types and use wavelength resources more efficiently
than CWDM modules. DWDM and CWDM modules allow lights with different
center wavelengths to be transmitted on one fiber without interfering
each other. Therefore, a passive multiplexer can be used to combine the
lights into one channel, which is then split into multiple channels by a
demultiplexer on the remote end. This reduces the optical fibers
required. DWDM and CWDM modules are used for long-distance transmission.
The transmit power of a long-distance optical module is often larger
than its overload power. Therefore, when using such optical modules,
select optical fibers of an appropriate length to ensure that the actual
receive power is smaller than the overload power. If the optical fibers
connected to a long-distance optical module are too short, use an
optical attenuator to reduce the receive power on the remote optical
module. Otherwise, the remote optical module may be burnt.
