180:'Return Loss' will be infinite. Conversely if the line is terminated in an open circuit, the reflected power will be equal to the incident power; all of the incident power will be lost in the sense that none of it will be transferred to a load, and RL will be zero. Thus the numerical values of RL tend in the opposite sense to that expected of a 'loss'.
316:
In practice, the sign ascribed to RL is largely immaterial. If a transmission line includes several discontinuities along its length, the total return loss will be the sum of the RLs caused by each discontinuity, and provided all RLs are given the same sign, no error or ambiguity will result.
179:
From a certain perspective 'Return Loss' is a misnomer. The usual function of a transmission line is to convey power from a source to a load with minimal loss. If a transmission line is correctly matched to a load, the reflected power will be zero, no power will be lost due to reflection, and
663:
799:
710:
to transmit signals over optical fiber, and a low optical return loss (ORL) can cause the laser to stop transmitting correctly. The measurement of ORL is becoming more important in the characterization of optical networks as the use of
300:
138:
172:(Γ). Increasing return loss corresponds to lower SWR. Return loss is a measure of how well devices or lines are matched. A match is good if the return loss is high. A high return loss is desirable and results in a lower
520:
440:
202:. However, return loss has historically been expressed as a negative number, and this convention is still widely found in the literature. Strictly speaking, if a negative sign is ascribed to RL, the ratio of
864:
833:
533:. Thus, a large positive return loss indicates the reflected power is small relative to the incident power, which indicates good impedance match between transmission line and load.
572:
721:
382:
445:
Return loss is the negative of the magnitude of the reflection coefficient in dB. Since power is proportional to the square of the voltage, return loss is given by,
715:
increases. These systems use lasers that have a lower tolerance for ORL, and introduce elements into the network that are located in close proximity to the laser.
692:
such as a fiber endface. At those interfaces, a fraction of the optical signal is reflected back toward the source. This reflection phenomenon is also called "
216:
59:
451:
390:
927:
961:
895:
838:
807:
712:
45:. This discontinuity can be caused by a mismatch between the termination or load connected to the line and the
993:
988:
983:
890:
658:{\displaystyle RL(\mathrm {dB} )=P_{\mathrm {i} }(\mathrm {dB} )-P_{\mathrm {r} }(\mathrm {dB} )\,}
46:
978:
794:{\displaystyle {\text{ORL}}(\mathrm {dB} )=10\log _{10}{P_{\mathrm {i} } \over P_{\mathrm {r} }}}
530:
952:
362:
169:
998:
544:), then the return loss in dB can be calculated as the difference between the incident power
367:
344:
8:
165:
295:{\displaystyle RL'(\mathrm {dB} )=10\log _{10}{P_{\mathrm {r} } \over P_{\mathrm {i} }}}
694:
526:
133:{\displaystyle RL(\mathrm {dB} )=10\log _{10}{P_{\mathrm {i} } \over P_{\mathrm {r} }}}
22:
885:
38:
689:
682:
30:
875:
515:{\displaystyle RL(\mathrm {dB} )=-20\log _{10}\left|{\mathit {\Gamma }}\right|}
173:
972:
880:
678:
435:{\displaystyle {\mathit {\Gamma }}={V_{\mathrm {r} } \over V_{\mathrm {i} }}}
42:
536:
If the incident power and the reflected power are expressed in 'absolute'
956:
563:
552:
537:
50:
317:
Whichever convention is used, it will always be understood that
16:
Measure of power reflected by a discontinuity in a line or fiber
674:
340:
34:
962:
Optical Return Loss
Testing—Ensuring High-Quality Transmission
707:
686:
347:
mismatch. The ratio of the amplitude of the reflected wave
343:
traveling down a conductor can occur at a discontinuity or
541:
842:
811:
841:
810:
724:
575:
454:
393:
370:
219:
62:
188:
As defined above, RL will always be positive, since
49:
of the line. It is usually expressed as a ratio in
858:
827:
793:
657:
514:
434:
376:
294:
132:
970:
681:) a loss that takes place at discontinuities of
339:In metallic conductor systems, reflections of a
859:{\displaystyle \scriptstyle P_{\mathrm {i} }}
828:{\displaystyle \scriptstyle P_{\mathrm {r} }}
654:
932:IEEE Antennas & Propagation Magazine
971:
928:"Definition and Misuse of Return Loss"
354:to the amplitude of the incident wave
29:is a measure in relative terms of the
706:Fiber optic transmission systems use
920:
13:
866:is the incident, or input, power.
849:
818:
783:
771:
737:
734:
647:
644:
634:
618:
615:
605:
589:
586:
503:
468:
465:
424:
412:
396:
371:
284:
272:
238:
235:
122:
110:
76:
73:
37:reflected by a discontinuity in a
14:
1010:
938:, iss.2, pp. 166–167, April 2009.
896:Optical time domain reflectometer
713:wavelength-division multiplexing
555:units) and the reflected power
164:Return loss is related to both
146:(dB) is the return loss in dB,
741:
730:
651:
640:
622:
611:
593:
582:
472:
461:
242:
231:
80:
69:
1:
908:
334:
7:
869:
835:is the reflected power and
10:
1015:
964:EXFO Application note #044
668:
153:is the incident power and
891:Time-domain reflectometer
903:
308:(dB) is the negative of
47:characteristic impedance
685:, especially at an air-
377:{\displaystyle \Gamma }
183:
160:is the reflected power.
953:Federal Standard 1037C
860:
829:
795:
659:
516:
436:
378:
363:reflection coefficient
296:
170:reflection coefficient
134:
994:Electrical parameters
861:
830:
796:
660:
517:
437:
379:
297:
135:
839:
808:
722:
573:
452:
391:
368:
217:
60:
166:standing wave ratio
989:Engineering ratios
856:
855:
825:
824:
791:
695:Fresnel reflection
655:
562:(also in absolute
512:
432:
374:
292:
210:power is implied;
130:
23:telecommunications
984:Radio electronics
886:Signal reflection
789:
728:
677:(particularly in
430:
324:can never exceed
290:
195:can never exceed
128:
39:transmission line
1006:
939:
926:Trevor S. Bird,
924:
865:
863:
862:
857:
854:
853:
852:
834:
832:
831:
826:
823:
822:
821:
800:
798:
797:
792:
790:
788:
787:
786:
776:
775:
774:
764:
759:
758:
740:
729:
726:
683:refractive index
664:
662:
661:
656:
650:
639:
638:
637:
621:
610:
609:
608:
592:
521:
519:
518:
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511:
507:
506:
493:
492:
471:
441:
439:
438:
433:
431:
429:
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417:
416:
415:
405:
400:
399:
383:
381:
380:
375:
361:is known as the
301:
299:
298:
293:
291:
289:
288:
287:
277:
276:
275:
265:
260:
259:
241:
230:
139:
137:
136:
131:
129:
127:
126:
125:
115:
114:
113:
103:
98:
97:
79:
1014:
1013:
1009:
1008:
1007:
1005:
1004:
1003:
969:
968:
967:
943:
942:
925:
921:
911:
906:
872:
848:
847:
843:
840:
837:
836:
817:
816:
812:
809:
806:
805:
782:
781:
777:
770:
769:
765:
763:
754:
750:
733:
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723:
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719:
671:
643:
633:
632:
628:
614:
604:
603:
599:
585:
574:
571:
570:
561:
550:
502:
501:
497:
488:
484:
464:
453:
450:
449:
423:
422:
418:
411:
410:
406:
404:
395:
394:
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389:
388:
369:
366:
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359:
352:
337:
330:
323:
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255:
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223:
218:
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194:
186:
159:
152:
121:
120:
116:
109:
108:
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93:
89:
72:
61:
58:
57:
17:
12:
11:
5:
1012:
1002:
1001:
996:
991:
986:
981:
979:Wave mechanics
966:
965:
959:
949:
948:
947:
941:
940:
918:
917:
916:
915:
910:
907:
905:
902:
901:
900:
899:
898:
888:
883:
878:
876:Hybrid balance
871:
868:
851:
846:
820:
815:
802:
801:
785:
780:
773:
768:
762:
757:
753:
749:
746:
743:
739:
736:
732:
699:," or simply "
670:
667:
666:
665:
653:
649:
646:
642:
636:
631:
627:
624:
620:
617:
613:
607:
602:
598:
595:
591:
588:
584:
581:
578:
559:
548:
540:units, (e.g.,
529:bars indicate
523:
522:
510:
505:
500:
496:
491:
487:
483:
480:
477:
474:
470:
467:
463:
460:
457:
443:
442:
426:
421:
414:
409:
403:
398:
373:
357:
350:
336:
333:
328:
321:
314:
313:
302:
286:
281:
274:
269:
263:
258:
254:
250:
247:
244:
240:
237:
233:
229:
226:
222:
199:
192:
185:
182:
174:insertion loss
162:
161:
157:
150:
140:
124:
119:
112:
107:
101:
96:
92:
88:
85:
82:
78:
75:
71:
68:
65:
15:
9:
6:
4:
3:
2:
1011:
1000:
997:
995:
992:
990:
987:
985:
982:
980:
977:
976:
974:
963:
960:
958:
954:
951:
950:
945:
944:
937:
933:
929:
923:
919:
913:
912:
897:
894:
893:
892:
889:
887:
884:
882:
881:Mismatch loss
879:
877:
874:
873:
867:
844:
813:
778:
766:
760:
755:
751:
747:
744:
718:
717:
716:
714:
709:
704:
702:
698:
696:
691:
688:
684:
680:
676:
629:
625:
600:
596:
579:
576:
569:
568:
567:
565:
558:
554:
551:(in absolute
547:
543:
539:
534:
532:
528:
508:
498:
494:
489:
485:
481:
478:
475:
458:
455:
448:
447:
446:
419:
407:
401:
387:
386:
385:
364:
360:
353:
346:
342:
332:
327:
320:
311:
307:
303:
279:
267:
261:
256:
252:
248:
245:
227:
224:
220:
213:
212:
211:
209:
205:
198:
191:
181:
177:
175:
171:
167:
156:
149:
145:
141:
117:
105:
99:
94:
90:
86:
83:
66:
63:
56:
55:
54:
52:
48:
44:
43:optical fiber
40:
36:
32:
28:
24:
19:
999:Fiber optics
946:Bibliography
935:
931:
922:
803:
705:
701:Fresnel loss
700:
693:
679:fiber optics
672:
556:
545:
535:
524:
444:
355:
348:
338:
325:
318:
315:
309:
305:
207:
203:
196:
189:
187:
178:
163:
154:
147:
143:
26:
20:
18:
957:MIL-STD-188
27:return loss
973:Categories
909:References
525:where the
335:Electrical
168:(SWR) and
955:and from
761:
690:interface
626:−
531:magnitude
504:Γ
495:
479:−
397:Γ
372:Γ
345:impedance
262:
204:reflected
100:
870:See also
566:units),
527:vertical
228:′
208:incident
51:decibels
669:Optical
564:decibel
553:decibel
538:decibel
33:of the
936:vol.51
804:where
708:lasers
675:optics
341:signal
304:where
142:where
53:(dB);
35:signal
914:Notes
904:Notes
687:glass
312:(dB).
31:power
697:loss
184:Sign
752:log
727:ORL
703:."
673:In
542:dBm
486:log
306:RL'
253:log
206:to
91:log
41:or
21:In
975::
934:,
930:,
756:10
748:10
490:10
482:20
384:.
331:.
310:RL
257:10
249:10
176:.
144:RL
95:10
87:10
25:,
850:i
845:P
819:r
814:P
784:r
779:P
772:i
767:P
745:=
742:)
738:B
735:d
731:(
652:)
648:B
645:d
641:(
635:r
630:P
623:)
619:B
616:d
612:(
606:i
601:P
597:=
594:)
590:B
587:d
583:(
580:L
577:R
560:r
557:P
549:i
546:P
509:|
499:|
476:=
473:)
469:B
466:d
462:(
459:L
456:R
425:i
420:V
413:r
408:V
402:=
358:i
356:V
351:r
349:V
329:i
326:P
322:r
319:P
285:i
280:P
273:r
268:P
246:=
243:)
239:B
236:d
232:(
225:L
221:R
200:i
197:P
193:r
190:P
158:r
155:P
151:i
148:P
123:r
118:P
111:i
106:P
84:=
81:)
77:B
74:d
70:(
67:L
64:R
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