保偏分光比可調耦合器

Model 905 SM non-PM version

Model 905P PM version

Model 905(P)-M Remotely controlled version

Precise Ratio Adjustment

Low lossLow back reflectionLow polarization cross talkLarge operating bandwidthPolarization Maintaining (PM) or non-PM types

Variable ratio couplers are made with optically contacted polished fibers mounted in substrate blocks that have transverse motion in the contact plane to adjust core-to-core separation distance. In the case of PM fiber， the orientation of the fast and slow axes is preserved during the motion. A negligibly thick oil layer is used to lubricate the substrate blocks and ensure smooth motion. Long term ratio stability is better than 1% under laboratory conditions.

Fine transverse motion is accomplished by means of a micrometer and lever system. The 25:1 lever ratio gives approximately one micron of motion at the coupler center per 0.001 inch division on the micrometer.

This motion however， is not free of hysteresis or backlash and a particular micrometer reading or selected position for the remote 905-M driver will not correspond to a particular fixed ratio， only to a nominal ratio. Accurate ratio settings can only be made by observation of the outputs. (X and Y if input A or B). Hysteresis and backlash tend to be reduced if the device is used repeatedly.

Available fibers have cutoff wavelengths ranging from 450 nm to 1550 nm. For a particular fiber used in a variable coupler the useful bandwidth extends from the single mode cutoff wavelength to approximately 1.3 times the cutoff wavelength， where losses begin to occur.

905(P) / 905(P)-M Specifications

Polarization Isolation

(room temperature，measured after connectorization):

-24 dB typical

-22 dB guaranteed

Standard Coupling Ratio:

0-99% (other ranges upon request)

Excess Loss:

<0.15dB

Pigtails:

1m standard length (longer available)

sleeved in 900 micron HYTREL or 3mm sleeving

Wavelengths:

0.890 to 2.04um

Coupler Bandwidth

The coupler bandwidth， or change in coupling ratio with wavelength， is a complex function of coupling ratio. This is shown in the figure below， where the measured coupling ratio curves for a tunable coupler (model 905P) at the wavelengths 1537nm and 1552nm are superimposed.

The tunable coupler operates by varying the core separation between fibers; as the fiber cores approach， coupling increases. If the coupling increases to 100% before fiber core separation is minimized， the phenomenon called overcoupling occurs. Overcoupling causes light to couple back into the original fiber， hence reducing the coupling ratio. It is possible to have several overcoupling cycles for long interaction length and small separation.

As indicated by A on Figure 1， for the first 50/50 (3dB) setting， a 3% change in coupling occurs for 1% change in wavelength.The coupling position can also be set at the 150% (overcoupled) position， labeled B， which is more sensitive， with a 7.5% change in coupling.Measured coupling curves for more widely spaced wavelengths are shown in the following figure.

Low loss WDMs (model 954P-P)， such as those with ratios 1550/980 and 1060/810， can be manufactured taking advantage of such coupling relationships， as shown below.

Package:

905(P): 25 mm x 38 mm x 63 mm aluminum case， with micrometer projecting 28 mm 905(P)-E: 25 mm x 38 mm x 63 mm aluminum case， with micrometer projecting 28 mm， 35mm projection opposite micrometer

Terminations:

FC/SPC， FC/APC， LC/APC， SC/APC， SC/PC