Re: [Vo]:Sagnac effect, optical gyroscope lock-in
The MM device does rotate sitting on a rotating Earth globe. It is not a translational movement. It can be seen as part of a Sagnac interferometer going around the globe. David On Sun, Jun 24, 2012 at 11:59 PM, Terry Blanton hohlr...@gmail.com wrote: The MM device does not rotate, right? T On Sat, Jun 23, 2012 at 10:36 AM, David Jonsson davidjonssonswe...@gmail.com wrote: Thanks for this reference. I thought lock in was also present in a optical fiber gyroscope or any type. Now I realize that the differences are big between different types of interferometers. Are you sure it is not involved in other types? What do you base your conclusion on that it isn't involved in the MM-interferometer? David On Tue, Jun 19, 2012 at 7:33 PM, Terry Blanton hohlr...@gmail.com wrote: On Tue, Jun 19, 2012 at 11:08 AM, David Jonsson davidjonssonswe...@gmail.com wrote: Hi Can someone refer me to the lock-in effect in optical gyroscopes? I have also heard the effect being mentioned as a phase lock loop effect. Could lock-in effect also be present in a straight interferometer like a Michelson-Morley-interferometer? http://en.wikipedia.org/wiki/Ring_laser_gyroscope end I don't think it relates to the MM experiment. T
Re: [Vo]:Sagnac effect, optical gyroscope lock-in
The MM device does not rotate, right? T On Sat, Jun 23, 2012 at 10:36 AM, David Jonsson davidjonssonswe...@gmail.com wrote: Thanks for this reference. I thought lock in was also present in a optical fiber gyroscope or any type. Now I realize that the differences are big between different types of interferometers. Are you sure it is not involved in other types? What do you base your conclusion on that it isn't involved in the MM-interferometer? David On Tue, Jun 19, 2012 at 7:33 PM, Terry Blanton hohlr...@gmail.com wrote: On Tue, Jun 19, 2012 at 11:08 AM, David Jonsson davidjonssonswe...@gmail.com wrote: Hi Can someone refer me to the lock-in effect in optical gyroscopes? I have also heard the effect being mentioned as a phase lock loop effect. Could lock-in effect also be present in a straight interferometer like a Michelson-Morley-interferometer? http://en.wikipedia.org/wiki/Ring_laser_gyroscope end I don't think it relates to the MM experiment. T
Re: [Vo]:Sagnac effect, optical gyroscope lock-in
Thanks for this reference. I thought lock in was also present in a optical fiber gyroscope or any type. Now I realize that the differences are big between different types of interferometers. Are you sure it is not involved in other types? What do you base your conclusion on that it isn't involved in the MM-interferometer? David On Tue, Jun 19, 2012 at 7:33 PM, Terry Blanton hohlr...@gmail.com wrote: On Tue, Jun 19, 2012 at 11:08 AM, David Jonsson davidjonssonswe...@gmail.com wrote: Hi Can someone refer me to the lock-in effect in optical gyroscopes? I have also heard the effect being mentioned as a phase lock loop effect. Could lock-in effect also be present in a straight interferometer like a Michelson-Morley-interferometer? http://en.wikipedia.org/wiki/Ring_laser_gyroscope end I don't think it relates to the MM experiment. T
Re: [Vo]:Sagnac effect, optical gyroscope lock-in
On Tue, Jun 19, 2012 at 11:08 AM, David Jonsson davidjonssonswe...@gmail.com wrote: Hi Can someone refer me to the lock-in effect in optical gyroscopes? I have also heard the effect being mentioned as a phase lock loop effect. Could lock-in effect also be present in a straight interferometer like a Michelson-Morley-interferometer? Principle of operation A certain rate of rotation induces a small difference between the time it takes light to traverse the ring in the two directions according to the Sagnac effect. This introduces a tiny separation between the frequencies of the counter-propagating beams, a motion of the standing wave pattern within the ring, and thus a beat pattern when those two beams are interfered outside the ring. Therefore the net shift of that interference pattern follows the rotation of the unit in the plane of the ring. RLGs, while more accurate than mechanical gyroscopes, suffer from an effect known as lock-in at very slow rotation rates. When the ring laser is hardly rotating, the frequencies of the counter-propagating laser modes become almost identical. In this case crosstalk in between the counter-propagating beams can allow for injection locking so that the standing wave gets stuck in a preferred phase, thus locking the frequency of each beam to each other rather than responding to gradual rotation. Forced dithering can largely overcome this problem. The ring laser cavity is rotated clockwise and anti-clockwise about its axis using a mechanical spring driven at its resonance frequency. This ensures that the angular velocity of the system is usually far from the lock-in threshold. Typical rates are 400 Hz, with a peak dither velocity of 1 arc-second per second. Dither does not fix the lock-in problem completely, as each time the direction of rotation is reversed, a short time interval exists in which the rotation rate is near zero and lock-in can briefly occur. In a technically more complicated solution the gyro assembly is not rotated back and forth, but in one direction only at a constant angular rate. A related device is the fibre optic gyroscope which also operates on the basis of the Sagnac effect, but in which the ring is not a part of the laser. Rather, an external laser injects counter-propagating beams into an optical fiber ring, and rotation of the system then causes a relative phase shift between those beams when interfered after their pass through the fiber ring proportional to the rate of rotation. This is therefore less sensitive than the RLG in which the externally observed phase shift is proportional to the accumulated rotation itself, not its derivative. However the sensitivity of the fiber gyro is enhanced by having a long optical fiber coiled for compactness, but in which the Sagnac effect is multiplied according to the number of turns. http://en.wikipedia.org/wiki/Ring_laser_gyroscope end I don't think it relates to the MM experiment. T
