ArticlePublisher preview available

Self-pumped phase-conjugate fiber-optic gyro

Optica Publishing Group
Optics Letters
Authors:
To read the full-text of this research, you can request a copy directly from the authors.

Abstract and Figures

We describe a new type of phase-conjugate fiber-optic gyro that uses self-pumped phase conjugation. The self-pumped configuration is simpler than externally pumped configurations and permits the use of sensing fibers longer than the coherence length of the laser. A proof-of-principle demonstration of rotation sensing with the device is presented.
This content is subject to copyright. Terms and conditions apply.
686 OPTICS LETTERS / Vol. 11, No. 10 / October 1986
Self-pumped phase-conjugate fiber-optic gyro
Ian McMichael and Pochi Yeh
Rockwell International Science Center, 1049 Camino Dos Rios,
Thousand Oaks, California
91360
Received June 2, 1986; accepted July 30, 1986
We describe a new type of phase-conjugate fiber-optic gyro that uses self-pumped phase conjugation. The self-
pumped configuration
is simpler than externally pumped configurations
and permits the use of sensing fibers
longer
than the coherence length of the laser. A proof-of-principle demonstration of rotation sensing with the device is
presented.
Several types of phase-conjugate gyro
are described in
the literatures and we recently reported on the first
demonstration to our knowledge of rotation sensing
with a phase conjugate gyro.
5The passive phase-
conjugate fiber-optic gyros described in Refs. 3 and 5
are Michelson interferometers in which the arms con-
tain fiber-optic coils that are terminated by externally
pumped phase-conjugate mirrors. Since the phase-
conjugate mirrors produce time-reversed waves, all
reciprocal phase changes in the optical paths are com-
pensated for and do not effect the output of the inter-
ferometer. However, since the phase shift produced
by the Sagnac effect is nonreciprocal, the output of the
interferometer is sensitive to rotation and can be used
as a gyro.
Standard fiber-optic gyros6are Sagnac interferome-
ters that are inherently insensitive to reciprocal phase
changes and sensitive to nonreciprocal phase changes.
This is true only when their operation is restricted to a
single polarization mode,7and the best fiber-optic gy-
ros use polarization-preserving fibers and couplers.8
However, if the phase-conjugate mirrors in the phase-
conjugate fiber-optic gyro
preserve polarization,9then
nonpolarization-preserving single-mode fibers, and
even multimode fibers, can be used in the gyro.
In the externally pumped configurations described
in Ref. 3 and 5, the fiber-optic coils can be no longer
than the coherence length of the laser. This limits the
sensitivity of the device. It is true that longer coils
can
be used if a polarization-preserving fiber of equal
length is used to carry the pumping waves to the
phase-conjugate mirrors. However, this defeats the
above-mentioned advantage in that the phase-conju-
gate gyro can use inexpensive multimode fibers and
couplers. In this Letter we describe and demonstrate
a self-pumped configuration of the phase-conjugate
fiber-optic gyro
that is not only simpler than the exter-
nally pumped configurations but also allows for the
use of fiber-optic coils that are longer than the coher-
ence length of the laser.
Figure 1 shows a schematic of a self-pumped phase-
conjugate fiber-optic gyro. Light from a laser is split
by beam splitter BS into two fibers, Fl and F2. Fibers
F1 and F2 are coiled such that light travels clockwise
in F1 and counterclockwise in F2. Light waves tra-
versing fibers F1 and F2 experience reciprocal phase
shifts
O,= J k1d1
1, ¢kr
2= J k2d12,(1)
respectively, where d1l and d1
2are elements of length
along Fl and F2, and kl,2= 27rnl,
2/X. In addition, the
nonreciprocal phase shifts
qnrl =+27rR1LW/Xc, q5n,2
= -27rR 2L2Q/XC (2)
are due to the Sagnac effect, where R1,2and L1,2are the
radii and lengths of the fiber loops, respectively, and Q
is the rotation rate. The net phase shifts are then Gr1
+ 0,,, and 0r2 + Cknr2.On reflection of the light from
the phase-conjugate mirror, the phase shifts become
-br1-knr 1and -0r2-,nr 2, where we have dropped the
phase shift of the phase conjugator
1 0"' since it is com-
mon to both waves and we are interested only in the
phase difference. It should be noted that the phase
shift of the phase conjugator is common to both waves
D
/PCM
M
Fig. 1. Schematic of a self-pumped phase-conjugate fiber-
optic gyro. Light from a laser is split by beam splitter BS
into two fibers F1 and F2 that are coiled such that light
travels clockwise in F1 and counterclockwise in F2. Light
traversing the fibers experiences phase shifts due to thermal,
mechanical, and rotational effects. The self-pumped
phase-conjugate mirror PCM produces time-reversed waves
that compensate for the reciprocal phase changes produced
by thermal and mechanical effects but do not compensate
for the nonreciprocal phase shift produced by rotation (Sag-
nac effect). Therefore rotation can be sensed by measuring
the interference between the recombining waves at detector
D.
0146-9592/86/100686-03$2.00/0 © 1986, Optical Society of America
... A variety of nonlinear interactions have been used to produce coherent combination, including stimulated Brillouin scattering,'-3 four-wave mixing (FWM), and selfpumped phase conjugation in photorefractive materials.-10 For some applications, including coupling laser amplifiers, 9 fiber-optic gyros, 6 and image subtraction, 5 7 not only must the beams be coherent but the piston component of the phase difference between the beams must also be conjugated so that they recombine in phase at a reference plane. ...
Article
Full-text available
Coherent beam combination through multiple-beam self-pumped phase conjugation in BaTiO3 has been demonstrated to conjugate piston error to at least λ/10. The coupling is shown to occur by a copumping mechanism.
Conference Paper
Phase-conjugate fiber-optic gyros (PCFOG’s) use phase conjugation to compensate for reciprocal phase changes due to thermal and mechanical effects on the fiber, while at the same time. allowing for the measurement of the nonreciprocal phase shift produced by rotation. 1,2 Where the best standard fiber-optic gyros require polarization-preserving fibers and couplers to avoid polarization scrambling that is a source of noise and signal fading, the PCFOG can avoid this problem by using polarization-preserving phase conjugation. ³ This has the advantage of allowing for the use of inexpensive nonpolarization preserving, and even multimode fibers and components. ³⁻⁵ Our first objective was to demonstrate that the PCFOG is sensitive to the nonreciprocal phase shift produced by the Sagnac effect and can be used to sense rotation. A proof of concept experiment was set up for this objective using an externally-pumped crystal of barium titanate as the phase conjugator. This experiment, reported in Ref. 6, provided the first demonstration of rotation sensing with a PCFOG. In this proof of concept demonstration the length of the fiber-optic coil, and therefore the sensitivity of the gyro, was limited by the coherence length of the laser. To solve this problem we set up a PCFOG consisting of a Michelson interferometer in which the light beams from two arms travel as clockwise and counterclokwise beams respectively, in the same fiber optic coil and reflect from the same self-pumped phase-conjugator. We reported the demonstration of rotation sensing with this PCFOG in Ref. 7. Again, since phase conjugation can correct for modal scrambling, a PCFOG can use multimode fibers. However, complete correction of modal scrambling requires a polarization-preserving conjugator, ⁵ and the corresponding experimental setup of a PCFOG is complicated. To solve this problem we set up a PCFOG using a multimode fiber coil, a nonpolarization-preserving conjugator, ⁴ and a spatial filter to discriminate against the portion of the light reflected by the conjugator that does not correct for modal scrambling. This experiment, reported in Ref. 8, provided the first demonstration of rotation sensing with a PCFOG using multimode fiber.
Conference Paper
Modal scrambling is a source of noise and signal fading in fiber-optic gyros ¹ and therefore the best fiber-optic gyros use single-mode polarization preserving fiber and couplers ² . Phase-conjugation can be used to correct for modal scrambling ³⁻⁵ and to make fiber-optic gyros ⁶⁻⁹ . In this paper we describe and demonstrate the combination of these two possiblities; a phase-conjugate fiber-optic gyro using multimode fiber.
Article
In this paper, the grating dynamical theory of photorefractive in ring laser resonator is introduced. The condition and the reason of light beam frequency mismatching in the rotating ring resonator are researched. This rotating ring resonator can be used for optic-gyro. In the rotating process, the phase can be changed into the frequency mismatching. By measuring the frequency mismatching, the rotational angle of the ring resonator can be calculated.
Chapter
All the chapters of the book, except this one, deal with permanent diffractive optical elements, i.e. elements with relative permittivity (both the refractive index and absorption coefficient) that does not depend on the light intensity. In contrast, this chapter is devoted to dynamic optical elements, which are sensitive to light. When a light beam propagates in these elements, the spatial distribution of the refractive index is changed, affecting the propagation of the beam itself at subsequent times. Materials possessing such a property are known as nonlinear optical materials. Among the variety of nonlinear optical effects discovered so far, it is only the photorefractive effect that can be observed at low optical power densities (of the order of mW/cm2). The large effective optical nonlinearity in photorefractive materials has attracted much attention in the past few years. The main purpose of this chapter is to highlight some device potentials and possibilities of practical applications of photor
Article
We review the current status of photorefractive self-pumped optical phase conjugation in the tungsten bronze family of ferroelectric crystals. The tungsten bronze ferroelectrics have emerged as an important class of materials for performing optical phase conjugation in addition to the well known pyroelectric, piezoelectric, and electro-optic applications. The large electro-optic coefficients, open lattice structure, compositional flexibility, and good optical quality of these materials has made possible a new set of self-pumped phase conjugate mirrors. Our initial interest in this class of crystals arose from a number of enlightening discussions with Professor L. Eric Cross who pointed out the multitude of applications possible with the tungsten bronzes. We would like to acknowledge his assistance and encouragement by dedicating this paper to Professor Cross on the occasion of his 65th birthday.
Article
We present experiments demonstrating reciprocity for conjugation of highly scattered light; if a fraction eta of the total scattered light is incident on a phase-conjugate mirror having reflectivity rho, then a fraction rho eta(2) returns back through the scatterer as a phase-conjugate wave, with the remaining fraction rho (eta - eta(2)) being lost due to scattering. Low efficiency results from inability to gather a large fraction of scattering, but the efficiency is higher than is possible without conjugation.
Article
Full-text available
Amplification owing to holographic two-wave mixing in photorefractive crystals can be utilized to achieve unidirectional ring oscillation. Unlike for the conventional gain medium (e.g., He–Ne), the gain bandwidth of photorefractive two-wave coupling is very narrow (a few hertz for BaTiO3). Despite this fact, the ring resonator can still oscillate over a large range of cavity detuning. A theory is presented that describes how the oscillating mode attains the round-trip phase condition.
Article
Full-text available
The first demonstration of rotation sensing with a fiber-optic gyro that uses the phase-reversal property of polarization-preserving phase conjugation is reported. In this system, the severely scrambled waves are restored to their original state of polarization, and the signal fading and noise due to polarization scrambling is eliminated without the need for polarization-preserving fiber. In the experimental setup, an argon laser provides the pumping waves for degenerate four-wave mixing, and a phase-conjugate reflectivity of 50 percent and a response time of 0.1 s are obtained. The expected rotation-induced Sagnac phase shift is achieved within the experimental uncertainties.
Article
Full-text available
Expressions for the phase of reflection from a photorefractive phase-conjugate mirror are obtained as a function of the intensity and phase of the pump and the probe beams. The phase is independent of these parameters in common photorefractive conditions in which the index grating is spatially shifted 90° with respect to the light-interference pattern. Multiple solutions exist for the phase and intensity of the reflection at large coupling strength. Oscillation conditions involving frequency detuning are obtained for the double phase-conjugate resonator (resonator formed with two phase-conjugate mirrors).
Article
Full-text available
Using a single self-pumped crystal of barium titanate, we demonstrate a method for producing the phase conjugate of an incident wave having arbitrary polarization. Our experimental results show that the phase-conjugate wave produced by this method reproduces both the ellipticity and the helicity of the polarization of the incident wave.
Article
Full-text available
Photorefractive resonators exhibit an extremely small frequency difference (Δω/ω ~ 10⁻¹⁵) between the oscillating and pumping beams. The observed frequency difference is proportional to cavity-length detuning. This dependence is explained by a photorefractive phase shift that is due to slightly nondegenerate two-wave mixing that compensates for cavity detuning and satisfies the round-trip phase condition for steady-state oscillation. The measured onset or threshold of oscillation as a function of photorefractive gain and intensity agrees with theory.
Article
Full-text available
A new type of interferometer has been constructed that uses a beam splitter and two self-pumped BaTiO3 crystals as phase-conjugate reflectors in place of the usual interferometer mirrors. Counterpropagating beams of light are spontaneously generated between the two crystals, coupling the pair of phase conjugators. This optical oscillation locks the relative phase of the two phase-conjugate reflections such that they recombine at the beam splitter to form only a single beam as though they were truly time-reversed waves.
Article
Full-text available
A fiber gyroscope is reported that uses polarization-holding fiber in the coil, the phase modulator, and the coupler. The random-drift coefficient, calculated from rms noise levels, was 8 . 10 − 4 deg / h , within a factor of 2 of an experimentally determined quantum and thermal limit. White-noise behavior was observed for integration time constants from 1 to 40 sec. Device characteristics and performance are presented.
Article
Full-text available
Continuous-wave phase conjugation of an image-bearing beam is demonstrated using a single-domain crystal of BaTiO3 and nothing else. The device operates by four-wave mixing using the photorefractive effect but without any external pumping beams or external mirrors. The customary pumping beams are derived from the incident beam and are internally reflected inside the crystal adjacent to an edge. The device is self-starting and has a phase-conjugate reflectivity of 30%. Imaging applications are discussed.
Article
Full-text available
We present a theoretical analysis of a ring laser incorporating a wave-front-conjugating coupling element between the counterpropagating waves. Our results demonstrate the possibility both of using a homogeneously broadened laser, such as a solid-state or dye laser, and of a substantial reduction in lock-in frequency.
Article
A new optical rotation sensor is described. It is a ring passive phase conjugator in which the ring may consist of a multimode fiber. A nonreciprocal phase shift in the ‘‘passive’’ like fiber ring activates a grating movement and subsequent frequency detuning of the beams in a photorefractive four‐wave mixer. This device has the advantages of natural reciprocal behavior of phase conjugate beams (essential for rotation sensing) and has several adjustable controlling parameters. It reveals a new class of interferometry in which changes in the ring’s optical phases, the beam’s intensities and losses, and the mixing crystal’s efficiency and electric field modulate a frequency detuning of the oscillating beams.