Advantages of the One-Jumper Reference Method 15 July 2000 1

The Advantages of the One-Jumper Reference Method

Over the Two-Jumper Reference Method when Measuring Link Insertion Loss

Advantages of the One-Jumper Reference Method 15 July 2000 2

Why is the One-Jumper Reference Method So Important?

• It is specified in TIA-568 and ISO 11801. • It eliminates the insertion loss measurement error

of about 0.5 dB caused by the two-jumper method.• Insertion loss measurement accuracy is critical

when certifying multimode Gigabit Ethernet links, which have maximum channel loss requirements of only 3.2 to 4.0 dB.

Advantages of the One-Jumper Reference Method 15 July 2000 3

An optical fiber link comprises one (or more) sections of fiber plus an input and an output connection.

InputConnection

OutputConnection

NetworkEquipment

NetworkEquipment

Link

Optical Fiber *

* May comprise multiple fiber sections joined by other connections and splices.

Advantages of the One-Jumper Reference Method 15 July 2000 4

Measured optical fiber link insertion loss* must include the loss of both the input and output connections.

InputConnection

(0.5 dB)

OutputConnection

(0.5 dB)

NetworkEquipment

NetworkEquipment

Link Insertion Loss = 3.0 dB

Optical Fiber(2.0 dB)

* Insertion loss will be shortened to simply “loss” for the rest of the presentation.

Advantages of the One-Jumper Reference Method 15 July 2000 5

To measure link loss you need to know the power entering the near-end connection (PIN) and exiting of the far-end connection (POUT).

PIN (dBm) POUT (dBm)

Loss (dB) = PIN (dBm) – POUT (dBm)

Input patch cordor test jumper

Output patch cordor test jumper

Link

Advantages of the One-Jumper Reference Method 15 July 2000 6

Example:

PIN = -20 dBm POUT = -23 dBm

Loss = -20 dBm - (-23 dBm) = 3.0 dB

Link under test

Light Source Optical Power Meter(in dB loss mode)

3.0 dB

Advantages of the One-Jumper Reference Method 15 July 2000 7

When making a link loss measurement, PIN is the output of the light source jumper

Link under test

Light Source

PIN = -20 dBm

Advantages of the One-Jumper Reference Method 15 July 2000 8

Light Source

Optical Power Meter(set reference mode)

- 20 dBm

The transmit jumper has negligible loss.

Using the one-jumper method, the reference level stored by the power meter is PIN.

There is no loss at the power meter detector.

Therefore, the reference level stored by the power meter is PIN.

REF

Advantages of the One-Jumper Reference Method 15 July 2000 9

So measured loss is correct !

PIN = -20 dBm POUT = -23 dBm

Measured Loss = -20 dBm - (-23 dBm) = 3.0 dB

Link under test

Light Source Optical Power Meter(dB loss mode)

3.0 dB

Advantages of the One-Jumper Reference Method 15 July 2000 10

But using the two-jumper method the reference level stored by the power meter is PIN minus the loss of one connection.

Reference level stored by the power meter is PIN minus 0.5 dB.

Light Source

Optical Power Meter(set reference mode)

- 20.5 dBm REF

One connection loss(about 0.5 dB)

Advantages of the One-Jumper Reference Method 15 July 2000 11

So measured loss is understated by one connection loss or about 0.5 dB.

POUT = -23 dBm

Measured Loss = -20.5 dBm - (-23 dBm) = 2.5 dB

Link under test

Light Source Optical Power Meter(dB loss mode)

2.5 dBBut the power meter reference

level is -20.5 dBm!

PIN = -20 dBm

Advantages of the One-Jumper Reference Method 15 July 2000 12

Measured loss should be less than or equal to the typical loss of one connection, as specified by the connector manufacturer.

Light Source

Optical Power Meter(dB loss mode)

0.5 dB

One Final Point: After you have referenced your power meter and light source using the one-jumper method, you should always check the receive and transmit jumpers before making loss measurements, as shown below:

TransmitJumper

ReceiveJumper

Adapter

Advantages of the One-Jumper Reference Method 15 July 2000 13

Summary of One Jumper Method1. Attach the transmit jumper to the light source.

2. Connect the free-end of the transmit jumper to the optical power meter.

3. Remove the free-end of the transmit jumper from power meter without disturbing the end connected to the light source.

4. Attach the receive jumper to the power meter. You may change the adapter cap on the power meter at this point to accommodate the connector type on the receive jumper.

5. Connect the transmit and receive jumpers using a mating adapter.

6. Verify that loss is less than the typical loss of one connection.

7. Keeping the transmit jumper attached to light source and receive jumper attached to power meter, you can now measure insertion loss.

8. Re-reference your light source and power meter about once per day.