RE: Standards for connectors and attenuators

["DAWE,PIERS (A-England,ex1)" <piers_dawe@xxxxxxxxxxx>]

Bob, great information.

At to S,T,U,V, here are extracts from G.691:

where "application" corresponds to the target distance: VSR- (very short
reach), I- (Intra-office), S- (Short-haul), L- (Long-haul), V- (Very
long-haul), and U- (Ultra long-haul).

>From the tables:
S	20 or 40 km
L	40 or 80
V	60 or 120 
U	160

Piers

> -----Original Message-----
> From: Bob Hughes [mailto:bhughes@xxxxxxxxxx]
> Sent: 05 November 2000 22:25
> To: piers_dawe@xxxxxxxxxxx; gary.bastin@xxxxxxxxxxxxxx;
> d_hanson@xxxxxxxxxxx; peter.ohlen@xxxxxxxxxxxxx; robert@xxxxxxxxx;
> petarp@xxxxxxxxxx; dkabal@xxxxxxxxxxxxx
> Subject: Standards for connectors and attenuators
> 
> 
> To all,
> 
> During the serial PMD specs telecon, 31 Oct 00, we briefly 
> discussed the
> return loss characteristics of the connectors used in long haul links.
> (See "Draft Minutes of serial PMD specs telecon 31 Oct 00", 
> by Piers Dawe,
> last paragraph.) As discussed, I am writing a brief summary of that
> information and providing some information on the 
> recommendations/standards
> for connectors and attenuators.
> 
> Connector Return Loss
> 
> The following anecdotal information is from the perspective 
> of the fiber
> plant "as shipped" to long-haul carriers, primarily for use 
> with long haul
> SONET installations. Persons working in other areas may have 
> a different
> perspective than this.
> 
> About 7 or 8 years ago, most of the transmission industry 
> switched over to
> "physical contact" connectors. ITU-T G.671 has the following 
> definition:
> "Physical Contact (PC): This finish is typically used in a 
> single fibre
> connector. The end face is polished to a spherical shape in 
> order to obtain
> a perfect contact between the two fibre cores and to improve the
> transmission performances of the connector. A typical 
> spherical radius is
> 10-25 mm"
> 
> PC terminations manufactured in the time frame of 2 - 8 years 
> ago will have
> a return loss of 45 dB or better. PC terminations 
> manufactured in the last
> two years will have a return loss of 50 dB or better. In 
> contrast, non-PC
> connectors manufactured more than 8 years ago could be 
> expected to have a
> return loss of  20 to 30 dB.
> 
> In order to help confirm this information, I asked a associate from
> the OTDR industry what levels of return loss he had seen in the
> installed plant. He has seen very few installations that are 
> worse than 30
> to 35 dB. He commented that any physical plant upgrade in the 
> last 6 to 7
> years would have 40+ dB of return loss.
> 
> As a side note, Angled Physical Contact (APC) connectors are 
> not typically
> used with SONET equipment - at least not with any 
> installations I know of.
> However, APC connectors do seem to be very popular with cable TV
> installations. The attractive feature of APC connectors is a very high
> return loss, e.g. 70 dB.
> 
> 
> Standards and Recommendations
> 
> It is my understanding that one of the goals of 802.3ae is 
> interoperability
> between equipment manufactured by various companies. It also 
> seems that in
> order to provide interoperability, it may be useful to specify the
> requirements of the fiber plant. This is especially true of 
> the 1550 nm PMD
> since it can be performance limited by attenuation and back 
> reflectance.
> Specifically, what I am proposing is that we reference an existing
> performance standard for attenuator and connector performance.
> 
> The standard frequently used in North America is Telcordia (formerly
> Bellcore) GR 326 "Generic Requirements for Single Mode Optical Fiber
> Connectors." However, since IEEE is an international 
> standards organization,
> it is probably more appropriate to cite an ITU standard.
> 
> There are three ITU standards (recommendations actually) that 
> I could find
> relevant to connector and attenuator performance. They are 
> listed below. I
> downloaded all three of these this week from the ITU 
> electronic bookstore.
> The cost is 20 CHF each (about USD$12).
> 
> ITU-T  Recommendation  G.671, "Transmission characteristics of passive
> optical components", 11/96
> ITU-T  Recommendation  L.31, "Optical fibre attenuators", 10/96
> ITU-T  Recommendation  L.36, "Single mode fibre optic 
> connectors", 10/98
> 
> As the title implies, G.671 contains performance 
> specifications for many
> types of passive components including connectors, attenuators, and
> isolators. The two "L" recommendations are specific to 
> outside plant and
> appear to have some overlap with G.671.
> 
> L.31 itself only contains environmental recommendations, e.g. 
> temperature,
> humidity. It references Table 6.3 in G.671 for optical performance
> specifications.
> 
> L.36 was published after G.671. In the Summary, L.36 states 
> "While taking
> into account Recommendation G.671 as far as the transmission 
> parameters are
> concerned, this Recommendation is based on the most recent 
> work carried out
> within IEC 86B Working Groups 4, 6 and 7, namely the future 
> IEC 1753-2-1 and
> the 61300-series." In specifying performance for optical 
> connectors, L.36
> appears to be more comprehensive. But, it is also more 
> complicated to use.
> For example, section 6.1.2 defines four different return loss 
> values for
> four different "Classes" of , i.e. Class S, Class T, Class U, 
> and Class V .
> The meaning or intended usage of these classes are not defined in the
> document.
> In contrast, G.671 contains a single table, section 6.9, that 
> specifies all
> of the connector performance parameters.
> 
> For all three ITU recommendations, as well as GR 326, there 
> is no connector
> type specified. The recommendations apply independent of the 
> connector type,
> e.g. SC, LC, etc. Thus, we do not have to get into the 
> connector wars in
> order to use these recommendations.
> 
> The G.671 performance recommendations for attenuators, and 
> connectors are
> shown below.
> 
> Attenuators
> 
> Insertion Loss Tolerance +/- 15%
> Optical Reflectance (dB) -40 Max
> Polarization Dependent Loss (delta dB) 0.3 Max
> 
> 
> Connectors
> 
> Insertion Loss (dB) 0.5 Max for single fibre (Note 1)
> Optical Reflectance (dB) -35 Max (Notes 1 and 2)
> Polarization Dependent Loss (delta dB) 0.1 Max
> NOTE 1 - When used over an extended operating temperature range, these
> values may be exceeded and are under study.
> NOTE 2 - For networks other than those covered by 
> Recommendation G.982,
> including other access networks, a value of -27 dB is allowed 
> however, care
> should be taken to insure system functionality in systems 
> implemented with
> several optical components with reflectance values at, or 
> near, this limit.
> In consideration of future network evolutions, a value of -40 
> dB is under
> study.
> 
> 
> My specific proposal
> 
> I would like to propose that within 802.3ae, we recommend 
> compliance with
> "ITU-T Recommendation  G.671, "Transmission characteristics of passive
> optical
> components", for attenuators and connectors used with the 
> 1310 and 1550 nm
> serial PMD. The purpose of including such a recommendation is 
> to give the
> end-users guidance in the performance specification of the 
> fiber physical
> plant to provide satisfactory end-to-end performance of the 
> 802.3ae system.
> 
> Thanks,
> Bob Hughes
> Telect
> bhughes@xxxxxxxxxx
> 
>