Large-scale passive laser gyroscope for earth rotation sensing

Abstract

Earth rotation sensing has many applications in different disciplines, such as for the monitoring of ground motions, the establishment of UT1 and the test of the relativistic Lense-Thirring effect on the ground. We report the development of a 1 m × 1 m heterolithic passive resonant gyroscope (PRG). By locking a pair of laser beams to adjacent modes of the square ring cavity in the clockwise and counter-clockwise directions, we achieve a rotation resolution of about 2 × 10 −9 rad/s at an integration time of 1000 s. The sensitivity of the PRG for rotations reaches a level of 2 × 10 −9 rad/s/ √ Hz in the 5-100 Hz region, currently limited by the detection noise, residual amplitude modulation and the mechanical instability of the cavity. Our initial results improve the reported rotation sensitivity of the PRGs and indicate that PRGs have a great potential for highresolution Earth rotation sensing.Many large scale ring laser gyroscopes (RLG) have been built over the last three decades with extremely high sensitivity and stability [1]. These large ring lasers along with the developed fiber optic gyros have found applications in different fields like geodesy [1], seismology [1][2][3][4] and fundamental physics tests [5][6][7]. The monolithic G-ring experimentally resolves a rotation rate of 3.5 × 10 −13 rad/s over 1000 s and detects the Chandler and the annual wobble of the Earth [8,9]. The successful operation of two really large heterolithic RLGs, namely UG-1 and UG-2 with enclosed areas of 367 m 2 and 834 m 2 , demonstrate the feasibility of constructing giant rotation sensors [10,11]. Laser gyros are also used to improve the seismic isolation system for ground-based gravitationalwave antennas [12,13]. Moreover, an ambitious plan named GINGER has been proposed, focusing on measurement of the Lense-Thirring effect in a terrestrial laboratory [14]. Highly sensitive interferometric fiber optical gyroscopes (I-FOG) are developed mainly for applications in navigation and platform control, with a sensitivity in the order of 10 −8 ∼ 10 −9 rad/s/ √ Hz. Such rotational sensors with low self-noise are also suitable for applications in geosciences [15][16][17].The measurement principle of RLGs is based on the Sagnac effect: the counter propagating beams in a ring cavity will see a different round trip time if the ring cavity is rotating in the optical plane. This effect was first described by Sagnac in 1913 [18]. In 1963, Macek and Davis utilized a ring cavity that contains He-Ne gas to lase at the 1.153 µm line, which demonstrated rotation sensing [19]. This is considered to be the first active RLG. A passive gyro was successfully realized by Ezekiel and Balsamo in 1977 [20], where an external laser is split into two beams and locked to a passive ring cavity in the clockwise (CW) and counter-clockwise (CCW) direction. The rotation rate is determined by measuring the resonance frequency difference of the ring cavity in the opposite directions. A modern PRG, used as a tilt sensor, recently reported a sensitivity of 10 −8 rad/s/...

Noise Analysis of a Passive Resonant Laser Gyroscope

“…The experimental setup is shown in Figure 1 [ 15 ]. The central part of our PRG is a square ring cavity, which is composed out of four super mirrors, which provide a quality factor of .…”

“…The Sagnac effect is useful in the detention of rotational signals. Instruments based on the Sagnac effect have many applications in different fields [ 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 ]. In particular, large-scale optical gyroscopes find applications in inertial navigation, geophysical study, seismic isolation, platform stabilization, etc.…”

“…Recently, micro-optical gyroscopes made of whispering gallery mode resonators have attracted much attention and are believed to have great potential to be applied to both industrial and navigational fields [ 12 , 13 ]. On the other hand, a branch of resonant laser gyroscopes has evolved from compact aircraft inertial sensors back into large-scale and complex laboratory setups for applications in the geosciences and fundamental physics in recent decades, with sensitivity as high as [ 4 , 7 , 14 , 15 , 16 ].…”

“…Another advantage of the PRG over the RLG is that it deals with an empty optical ring cavity, rather than an optical cavity filled with a gain medium, so in the absence of non-linear laser dynamics, it is easier to estimate the absolute accuracy in EOP measurements. However, the performance of the PRGs is still below that of the RLGs at this time, which suggests that there are still other obstacles to be overcome in the development of the PRGs [ 7 , 15 ]. Therefore, it is desirable to take a closer look at these instruments and to search for the limitations.…”

“…In this paper, we make a full investigation of the noise sources in a PRG with a size of developed at Huazhong University of Science and Technology (HUST) [ 15 ]. We find that the sensor noise in a PRG is dominated by the FSR drift and by laser frequency locking noise.…”