1、 Copyright 2012 by THE SOCIETY OF MOTION PICTURE AND TELEVISION ENGINEERS 3 Barker Avenue, White Plains, NY 10601 (914) 761-1100 Approved August 1, 2012 Table of Contents Page Foreword . 2 Intellectual Property 2 Introduction 2 1 Scope . 3 2 Optical SDI Networks . 3 2.1 Optical Components . 3 3 Opti
2、cal Data Transmission . 12 3.1 Laser Modulation 12 3.2 Encoding/Decoding 12 3.3 Pathological Patterns . 12 4 Optical System Architecture . 13 4.1 Optical Fiber . 13 4.2 Fiber Connectors 17 4.3 Handling . 22 4.4 Splicing . 23 5 Fiber Optic Multiplexing 24 5.1 Time Division Multiplexing (TDM) 24 5.2 W
3、avelength Division Multiplexing (WDM) 24 6 SFP Modules 27 6.1 Pin Assignment 28 6.2 EEPROM 29 6.3 Digital Diagnostic Monitoring . 29 6.4 SFP Labeling 29 7 Link Budgeting . 30 7.1 Power Budget . 30 7.2 Calculating Link Distance . 32 8 System / Network Evaluation . 35 8.1 Receiver Testing 35 8.2 Trans
4、mitter Testing 38 8.3 System Testing 39 9 Safety and Regulatory Requirements . 41 Annex A Simple Optical Transmitter Design (Informative) 42 Annex B Simple Optical Receiver Design (Informative) 44 Annex C Bibliography (Informative) . 45 Annex D Glossary of Terms (Informative) 46 Page 1 of 52 pages S
5、MPTE EG 2069:2012 SMPTE ENGINEERING GUIDELINE SMPTE ST 297 Optical SDI Networks SMPTE EG 2069:2012 Page 2 of 52 pages Foreword SMPTE (the Society of Motion Picture and Television Engineers) is an internationally-recognized standards developing organization. Headquartered and incorporated in the Unit
6、ed States of America, SMPTE has members in over 80 countries on six continents. SMPTEs Engineering Documents, including Standards, Recommended Practices, and Engineering Guidelines, are prepared by SMPTEs Technology Committees. Participation in these Committees is open to all with a bona fide intere
7、st in their work. SMPTE cooperates closely with other standards-developing organizations, including ISO, IEC and ITU. SMPTE Engineering Documents are drafted in accordance with the rules given in Part XIII of its Operations Manual. SMPTE EG 2069 was prepared by Technology Committee 32NF. Intellectua
8、l Property At the time of publication no notice had been received by SMPTE claiming patent rights essential to the implementation of this standard. However, attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. SMPTE shall not be held r
9、esponsible for identifying any or all such patent rights. Introduction International standards for the real-time transmission of video, audio, data and metadata over optical digital interfaces have been in existence for a number of years. SMPTE ST 297 standardizes the requirements for a “Serial Digi
10、tal Fiber Transmission System for SMPTE ST 259, SMPTE ST 344, SMPTE ST 292-1 and SMPTE ST 424 Signals” which cover all SMPTE SDI rates up to and including 3 Gb/s. The design, installation, setup and evaluation of an optical digital interface used in professional broadcast applications, differs from
11、a typical coax (copper), digital interface and from optical interfaces used in datacom / telecom enterprise or carrier systems. Different optimizations in the network components used for optical connectivity for SDI interfaces must be considered in order to ensure a robust, reliable Optical digital
12、network. This Engineering Guideline outlines the key components of an optical digital Interface developed in accordance with SMPTE ST 297. It documents methods and best practice for the design, installation, setup and evaluation of SMPTE ST 297 optical digital interfaces, and illustrates how the rob
13、ustness of an optical SDI link can be evaluated. SMPTE EG 2069:2012 Page 3 of 52 pages 1 Scope This engineering guideline provides guidance on the implementation of SMPTE ST 297 optical SDI networks in the following areas: Network: - Basics components of an optical network - Multimode versus Single
14、mode fiber - Link budget how to calculate, important factors - Differences between Optical SDI interfaces and components and datacom interfaces and components - Issues arising from the use of non-optimized ST 297 optical components - Optical attenuators why are they required and when to use them - O
15、ptical isolators why are they required and when to use them Evaluation of an optical system and its components: - Test and measurement equipment - Test and measurement methodology - Important test parameters - Ensuring interoperability 2 Optical SDI Networks As broadcasters upgrade their facilities
16、to support the carriage and distribution of higher frame rate formats such as 1080p50/60; image formats with increased dynamic range such as 12-bits for digital cinema; the carriage of stereoscopic 3D image formats; “Quad-Full HD” images etc, an increasing number of fiber optic systems are being dep
17、loyed. Fiber based systems offer a number of advantages over coax based systems, including high performance over long link distances, virtually unlimited bandwidth, reduced sensitivity to electrical interference and smaller lighter trunking. To deploy a robust optical network, careful selection and
18、evaluation of the components is required. 2.1 Optical Components A basic optical transmission system consists of several components illustrated in the block diagram shown in Figure 1. The main components are: a) transmitter, containing the optical source and a means of modulating the optical output
19、from the source with the signal to be transmitted; b) the transmission medium; in this case, the optical fiber; c) a receiver, containing the photo-detector which converts the received optical power back into the electrical waveform; SMPTE EG 2069:2012 Page 4 of 52 pages Figure 1 Basic Optical Trans
20、mission System The following sections explore the main components of an optical transmission system as well as the different form factors used in a typical deployment. 2.1.1 Transmitters Optical transmitters are devices that include an optical source and signal conditioning electronics to inject a s
21、ignal into a fiber. The type of optical source used in the transmitter will affect the performance and ultimately the distance a signal can travel within the fiber. Although several types of optical sources have been (and are still used), in data transmission, lasers are the predominant sources in o
22、ptical SDI transmitters. See Annex A for more details on transmitter design. 2.1.1.1 Lasers Lasers are predominantly used as sources in an optical transmission system. LASERs, an acronym Light Amplification by the Stimulated Emission of Radiation produce a coherent light with a narrow spectral width
23、 through, as the name implies, stimulated emission. Applying current to a semiconductor laser excites electrons to produce photons with a very specific wavelength and phase. These photons collect in a cavity where they reflect off opposing mirrors to travel back and forth through the lasing medium.
24、In the process, they stimulate other electrons and can cause the emission of more photons of the same wavelength and phase. A cascade effect occurs, resulting in the propagation of many photons of the same wavelength and phase. Coherent light is emitted from two opposite faces. The front face couple
25、s to an optical fiber, while the back face is often used for power monitoring. The wavelengths and modes of light are determined by the makeup of the semiconductor materials and the size of the optical cavity. In SMPTE ST 297, Optical transmitters are separated into 3 main categories: Low-power (sho
26、rt haul), Medium-power (medium haul), and High-power (long haul). To achieve these different link distances, different laser types with different characteristics are commonly used. Table 1 provides a comparison of typical laser types, their usage and advantages / disadvantages. SMPTE EG 2069:2012 Pa
27、ge 5 of 52 pages Table 1 A comparison of optical sources VCSELs FP Laser DFB Laser Typical Link Distances 200m 400m 10km 30km 30km 80km Cost Low cost Mid cost High cost Advantages Typically used in lower cost, lower power multimode installations Ideal for low cost point to point on single mode fiber
28、 Used for medium and long haul applications, as well as in wavelength division multiplexing Disadvantages Shorter link distance over multimode fiber Not suitable for wavelength division multiplexing, dispersion limited at high data rates High cost Each laser type has different characteristics that i
29、mpact the performance of the optical transmitter. The laser type, and thus the transmitter, is generally selected based on link distance, however, there are many other parameters to be considered when selecting a transmitter for optical SDI transmission. The following sections discuss in more detail
30、 the different laser types and their unique properties. 2.1.1.2 VCSELs Vertical-cavity surface-emitting lasers (VCSELs) are laser sources with a monolithic laser resonator, where the emitted light leaves the device in a direction perpendicular to the chip surface. Because the light is emitted from t
31、he surface of the device and not from the edge as in other semiconductor laser types, tens of thousands can be fabricated simultaneously on a semiconductor wafer significantly reducing the cost. VSCELs have lower output powers and a wider spectral width than their FP (Fabry-Perot) and DFB (Distribut
32、ed Feed Back) cousins, and are generally used for applications that require transmission over hundreds of meters rather than 10s of kilometers. VCSELs typically emit light in the 650 nm to 1300 nm wavelength region. SMPTE EG 2069:2012 Page 6 of 52 pages Figure 2 VCSEL spectrum 2.1.1.3 Fabry-Perot La
33、sers Fabry-Perot (FP) Lasers are well suited for the propagation of information over fiber. They are capable of high output powers, have an output beam with a narrow angular spread which allows increased coupling efficiencies to single mode fiber and can be modulated directly at high frequencies. Th
34、e Fabry-Perot laser is the predominant laser found in medium haul optical SDI transmitters today. These transmitters are configured to meet SMPTE ST 297 Medium-power transmitter specifications usually with output power in the range of -5 dBm to 0 dBm. In this type of laser, a relatively broad wavele
35、ngth spectrum of light is emitted as shown in Figure 3. Each peak is a mode that resonates within the cavity with a spectral width ranging from 2-4 nm (RMS) The different wavelengths of light emitted by the FP laser, travel along the fiber at different speeds. This causes a spreading of the pulse of
36、 light over the length of the fiber. Eventually, the spreading of different wavelengths can overlap neighboring pulses. This is known as dispersion and limits the distance the pulse can travel in the fiber. The effects of dispersion are discussed further in Section 4.1.2.2. SMPTE EG 2069:2012 Page 7
37、 of 52 pages Figure 3 FP spectrum 2.1.1.4 Distributed Feedback Laser (DFB) A DFB laser is similar to an FP laser, but with a diffraction grating within the device which acts as an optical filter that selects a single wavelength with a tighter spectral width than is possible with an FP laser as seen
38、in Figure 4. This results in longer transmissions over an optical fiber due to the reduced dispersion effect of the single wavelength and tighter spectral width of the DFB laser. The DFB laser is used in long haul transmitters as well as CWDM transmitters as discussed in Section 5. SMPTE EG 2069:201
39、2 Page 8 of 52 pages Figure 4 DFB spectrum 2.1.2 Receivers As a signal travels along a fiber, degradation will occur (more on this in Section 4). Optical receivers extract the information that has been placed on the modulated light carrier by the distant transmitter and restores the information to i
40、ts original form. The signal arriving at the receivers is typically at a lower power than the power at which it was originally launched by the transmitter. The minimum power at which the receiver can detect and decode the signal is given by the receiver sensitivity. SMPTE ST 297 specifies receiver s
41、ensitivities of -17 dBm for SMPTE ST 424 signal rates (3 Gb/s nominal). That is, the receiver is able to detect and restore a signal arriving at the receiver with an optical power of -17 dBm with a bit error ratio of less than 10-12. When selecting a receiver, it is also important to ensure that the
42、re is no additional sensitivity penalty for SDI pathological signals if the over all system power will be close to the receiver sensitivity specification A simple receiver is made of a photo-detector, a Transimpedance Amplifier (TIA), and a limiting amplifier. See Annex B for more details on receive
43、r design. Overall system performance is heavily influenced by the optical sensitivity of the receiver. The types of optical detectors and quality of the TIA selected must be appropriate for the application. In all communication equipment there are two types of optical detectors used; the PIN photodi
44、ode and the APD photodiode. The PIN (Positive-Intrinsic-Negative) diode is a very small device (200 um x 200 um) which has a low bias voltage, is economical, and provides receiver sensitivities around -20 dBm. SMPTE EG 2069:2012 Page 9 of 52 pages The Avalanche PhotoDiode (APD) is more complex, larg
45、er, requires a large bias voltage, is much more expensive, but does result in a sensitivity of -30 dBm. An APD based receiver is typically used for long links where the input power at the receiver is low. Both PIN based receivers and APD based receivers are in use in optical SDI links for broadcast
46、video applications, but PIN based receivers are most prevalent mainly due to the lower cost. 2.1.3 Optical Isolators All lasers are susceptible to back reflection. Whenever there is a change in refractive index, back reflection or as it is sometimes called, optical return loss (ORL) will occur. ORL
47、is a phenomenon whereby a fraction of the transmitted optical power is reflected back toward the source. Splices, patches and defects in the fiber can all cause back reflections and these back reflections create undesirable effects that impact signal integrity and hence the link distance over which
48、data can be successfully recovered without error. SMPTE ST 297 (Section 3.6.2) specifies a minimum return loss of 20 dBm on multimode fiber, and 26 dBm on single mode fiber. Fiber with more than 20 dB of return loss (back reflection), is considered quite high. Optical isolators can be used on laser
49、sources where a return loss of 20 dB or more is expected. An isolator is an optical component which allows the transmission of light in only one direction. Light propagates through the isolator in the forward direction while light propagating in the reverse direction is absorbed or displaced. An optical Isolator protects laser sources from back reflections and signals that can cause instabilities and damage, thereby improving the signal to noise ratio for laser diode based transmitters. Isolators are available in bot
