Patent ID: 7894073

Claim:
A fiber optic gyroscope comprising: a broadband light source having an output fiber end; a directional coupler having a first optical fiber port, a second optical fiber port and a third optical fiber port, the first optical fiber port coupled to the light source output fiber end; wherein light entering the first optical fiber port is directed to the second fiber optical port, and light entering the second optical fiber port is directed to the third optical fiber port; a photodetector coupled to the third optical fiber port of the directional coupler; a polarization maintaining (PM) delay management fiber of length v, having a first end and a second end, wherein the first end of the polarization maintaining delay management fiber is coupled to the second optical fiber port of the directional coupler; an integrated optical circuit (IOC) having an input end coupled to the second end of the polarization maintaining delay management fiber via a first polarization maintaining fiber pigtail of length d 1 ; a first output end coupled to a second polarization maintaining fiber pigtail with length of d 2 ; a second output end coupled to a third polarization maintaining fiber pigtail with length of d 3 ; and a splitter that directs light coupled into the input end to the first output end and the second output end with substantially equal power; wherein the integrated optic circuit (IOC) comprises a polarization maintaining waveguide device having waveguide length of L IOC and comprise a polarizing element so that the total effective polarization extinction ratio (PER) of the integrated optic circuit is ε; a single mode optical fiber loop having a first end and a second end; and a depolarizer region coupled to said fiber loop, said depolarizer region including a first optical fiber section of length x, a second optical fiber section of length z, a third optical fiber section of length w and a fourth optical fiber section of length y, each comprising polarization maintaining fibers having a beat length of L B ; wherein the second optical fiber section is coupled to the first optical fiber section via a first splice, the first optical fiber section is coupled to the first end of the single mode optical fiber loop via a second splice, the fourth optical fiber section is coupled to the third optical fiber section via a third splice, and the third optical fiber section is coupled to the second end of the single mode optical fiber loop via a fourth splice and wherein x+z is substantially equal to w+y; wherein the lengths of v, x, y, d 1 and d 3 are proportioned to avoid regions of high bias instability defined by the expressions v=x −( L IOC +y+d 1 +d 3 ), v= 2 x −( L IOC +y+d 1 +d 3 ), v= 3 x −( L IOC +y+d 1 +d 3 ), and v= 4 x+y −( L IOC +y+d 1 +d 3 ).