Optical SFP Transceiver

About data communication optical transceivers, how much do you know?

tranceiver introduction

With the rapid development of optical telecommunication, “Fiber replaces copper” already occurred in most countries, that means coaxial-cable or Ethernet cable were totally replaced by fiber. While optical transceiver is one of the core components of the fiber communication. If you do not know much about Data communication optical SFP transceiver (transceivers of switch, router, GPON OLT uplink and so on), this article is helpful for you to know it.

Structure of Optical Transceiver

Exactly speaking, optical Transceiver/module, is a general name of various modules, includes Transmitter, Receiver, Transceiver (optical transmitter and receiver) and Transponder. But nowadays, optical transceiver stands for all these parts. Transceiver works at physical layer, the bottom of OSI model, performs Electrical and Optical signal conversion.

Structure of Transceiver

Components of an optical transceiver:

  • Transmitting device (TOSA, optical laser)
  • Optical receiving device (ROSA, including optical detector),
  • Functional circuit
  • Optical (electrical) interface
Structure Diagram

Transceiver Structure

Optical module

  1. Handle   2. Receiver   3. Transmitter
  2. Shell    5. Label   6. Dust cap
  3. Spring    8. Module connector

At the transmitting end, the driver chip processes the original electrical signal, and then drives the semiconductor laser (LD) or light-emitting diode (LED) to emit modulated optical signals.

At the receiving end, light detection diode converts optical signal to electrical signals, After going through a pre-amplifier, there outputs electrical signal.

Five main factors of Optical Transceiver

1, Encapsulation mode
2, Rate

Encapsulation mode is the most important way to distinguish optical transceivers, usual encapsulation modes are GBIC, SFP, eSFP, SFP+, XFP, SFP28, QSFP, QSFP28, CFP, CFP2, QSFP-DD etc., encapsulation mode is relative to rate.

Below is the development course of transceiver, and corresponding transmission rate.

Encapsulation mode

GBIC, 1000M

GBIC, Giga Bitrate Interface Converter (1000M rate), before 2000, GBIC was the most popular optical module Encapsulation mode and the most widely used gigabit module form.

GBIC

 

SFP/eSFP, 1000M

SFP or eSFP, small Form-factor pluggable, half smaller size than GBIC, save more interface space, also 1000M rate, so GBIC is replaced when SFP comes out.

SFP

XFP, 10G

10-Gigabit Small Form-factor Pluggable, 10G rate.

XFP

SFP+, 10G

Also same rate as XFP 10G, but more compact than XFP (about 30% smaller), lower power consumption.

Huawei and 10G SFP+ modules for example are OMXD30000 02318169 850nm 10GE 0.3km LC Transceiver Module, OSX010000 02318170 1310nm 10GE 10km LC Transceiver Module.

SFP+

SFP28, 25G

Same size as SFP and SFP+, to some extend, 25G SFP28 is a compromise solution for high price period of 40G and 100G, but even now, some Huawei switch models have 25 ports, and some ISPs have requirement for 25G rate.

Huawei and Cisco 25G module for example, Huawei SFP-25G-LR 02312LSE 25G 10km LC Transceiver Module,  Cisco SFP-10/25G-CSR-S 850nm 10/25GBASE-CSR SFP28 Transceiver Module

QSFP/QSFP+/QSFP28/QSFP28-DD, 40G/100G/200G

Quad Small Form-factor Pluggable, 4-channel SFP ports.

QSFP can be divided into 4*10G QSFP+, 4*25G QSFP28, 8*25G QSFP28-DD

Taking QSFP28 as an example, suitable for 4*25G interface, it can across over 40G and upgrade from 25G to 100G directly, wiring simplified significantly and costing reduced largely.

QSFP-DD, published in Mar. 2016, DD refers to “Double Density”. It adds 4 channels based on QSFP 4 channels, total 8 channels, and compatible with the QSFP solution.
Each channel of QSFP-DD adopts 25Gbps NRZ or 50Gbps PAM4 signal format. It supports up to 400Gbps rate under PAM4 format.

Fo example Cisco QSFP-100G-CWDM4-S 1310nm 100GBASE CWDM4 QSFP Transceiver Module, Huawei QSFP-100G-CWDM4 02311MNN 100G 2km LC Transceiver Module

Remarks:

PAM4 (4 Pulse Amplitude Modulation) and NRZ (Non-Return-to-Zero) are Doubling technology
For transceivers, if rate needs to be increased the, either increasing channels quantity or increasing per channel rate.

CFP/CFP2/CFP4/CFP8, 100~400G

Centum gigabits Form Pluggable, rate can reach to 100~400G.

CFP is larger size than SFP, supports single 100G channel, or multi 40G channels.

CFP

CFP is 2-time size of CFP2 and CFP8, 4-time size of CFP4

CFP is the specific encapsulation mode of 400G, supports 25Gbps and 50Gbps, realizes 400Gbps through 16*25G or 8*40G electrical interface. 400G transceiver price is very high, since it is not commercial used in large scale.

CFP 2

3, Mode

SM, Single mode; MM, multi-mode

SM transceiver is suitable for long-distance transmission, while MM module is for short-distance.

Differences:

Items Single mode Multi-mode
Wavelength 1310nm, 1550nm  850nm
Distance Long distance

10, 40, 80, 120km

Short-distance

0.1, 0.3, 0.5km

Optical Fiber Type (diameter) 9/125μm 50/125μm or 62.5/125μm
Optical source LD or LED with narrow spectral line  light-emitting diode or laser
Applications lines with high rates and long distances (metropolitan network construction) Lines in short-distance transmission, and transmission with many network nodes and connectors
Price Expensive Cheap
4, Wavelength

Most common wavelength is 850nm, 1310nm, 1490nm, 1270nm 1550nm

5, Transmission distance

0.1, 0.3, 0.5, 10, 40 80km 120km for even longer distance.

Actually these five factors are inter-related, Short distance 0.1km 0.3km 0.5km=MM=850nm, long distance 10km 40km=SM=1310 1550nm

 

Basic Index of Optical Transceiver

Index Definition
Output optical power The output optical power of optical source at the transmitting end of the optical module
Max Sensitivity The minimum received optical power of the optical module under condition of a certain rate and bit error rate, unit: dBm.
Extinction Ratio The minimum ratio value of the average optical power of the signal to the average optical power of the space sign under the condition of full modulation
Optical saturation The Max input optical power when maintaining a certain bit error rate (10-10 to 10-12) at a certain transmission rate, unit: dBm

 

Other Special optical transceiver

DWDM CWDM Module

WDM, Wavelength Division Multiplexing, it multiplexes different wavelength optical signal into one fiber to transmission. DWDM, is Dense WDM; CWDM, is Coarse WDM.

WDM

Type Full Name Wavelength Wavelength Interval
CWDM Coarse WDM 1270~1610nm 20nm
DWDM Dense WDM 1528~1623nm 0.8/0.4nm

The advantage of WDM modules is long-distance transmission.

BIDI Module

BIDI(Bi-directional), it means Single Fiber Dual Directions. BIDI module is a module using WDM bidirectional transmission technology, which realizes bidirectional transmission in the optical channel on one optical fiber at the same time.

Dual fiber bidirectional module, one fiber transmit and the other receive.

 

BIDI module vs Dual fiber bidirectional module

1, BIDI module uses WDM technology, dual fiber module does not.

2, BIDI module works in pairs, dual fiber module does not.

4, BIDI module structure is more compatible than dual fiber module, and it has optical splitter and combiner.

5, Among BIDI modules, only one fiber is needed; dual fiber modules need two pieces fiber.

BIDI module is expensive then normal module, but the most obvious advantage is the cost of fiber infrastructure reduced.

Data communication optical transceiver is hot-product in the market, due to 5G and data center have large demands for it; above are the basic aspects about transceiver, if you have some comments or requirements for transceivers, welcome to contact fiberolt.com.

 

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