Suyong Wu

Design of a superluminal ring laser gyroscope using multilayer optical coatings with huge group delay

We propose and analyze a superluminal ring laser gyroscope (RLG) using multilayer optical coatings with huge group delay (GD). This GD assisted superluminal RLG can measure the absolute rotation with a giant sensitivity-enhancement factor of ~103; while, the broadband FWHM of the enhancement factor can reach 20 MHz. This superluminal RLG is based on a traditional RLG with minimal re-engineering, and beneficial for miniaturization according to theoretical calculation. The idea of using GD coatings as a fast-light medium will shed lights on the design and application of fast-light sensors.

Spectral ripple effect in continuous-wave fold-type cavity ring down spectroscopy

A spectral ripple effect observed in fold-type continuous-wave cavity ring down spectroscopy is described and studied. Its period was measured as ∼0.02 cm−1 in a 49.1 cm long V-shaped glass ceramics cavity. To find its origin, various losses of high-reflectivity coating and their relations to the optical field in the V-shaped cavity, especially the optical field inside the folding mirror coating, have been discussed and analyzed according to the interference theory and the matrix calculation method. It is found that the ripple mainly comes from an interference effect at the folding mirror coating between the direct and the inverse light waves. The interference effect results in the periodic fluctuations of the scattering and absorption loss of the high-reflectivity coating, so it can be used to measure some special losses of the high-reflectivity coating and separate them from the total loss of the coating.

Monolithic Cylindrical Fused Silica Resonators with High Q Factors

The cylindrical resonator gyroscope (CRG) is a typical Coriolis vibratory gyroscope whose performance is determined by the Q factor and frequency mismatch of the cylindrical resonator. Enhancing the Q factor is crucial for improving the rate sensitivity and noise performance of the CRG. In this paper, for the first time, a monolithic cylindrical fused silica resonator with a Q factor approaching 8 × 105 (ring-down time over 1 min) is reported. The resonator is made of fused silica with low internal friction and high isotropy, with a diameter of 25 mm and a center frequency of 3974.35 Hz. The structure of the resonator is first briefly introduced, and then the experimental non-contact characterization method is presented. In addition, the post-fabrication experimental procedure of Q factor improvement, including chemical and thermal treatment, is demonstrated. The Q factor improvement by both treatments is compared and the primary loss mechanism is analyzed. To the best of our knowledge, the work presented in this paper represents the highest reported Q factor for a cylindrical resonator. The proposed monolithic cylindrical fused silica resonator may enable high performance inertial sensing with standard manufacturing process and simple post-fabrication treatment.

Approximation Characteristic Matrix of Slightly Inhomogeneous optical coating at Oblique Incidence

We derive 1st and 2nd order approximation characteristic matrix of slightly inhomogeneous optical coating at oblique incidence, and test its effectiveness, accuracy and speed by comparison with published results.

A developed method for surface testing based on the scattering interference effect

Light scattering is an important and classical method for optical surface testing. Typical scheme of light scattering measurement often uses a single laser beam incidence, and then evaluates the surface quality via detecting and analyzing the scattering signal. In this work, a developed method for optical surface testing is proposed and demonstrated, and whose measuring principle is based on the scattering interference effect. In this approach, a single longitudinal mode laser beam is divided into two beams, when these beams irradiate the optical surface, their respective scattering fields would interfere with each other. If the phase between these incidence lights is scanned periodically, their scattering light interference signal would fluctuate simultaneously. Through analyzing this kind of scattering signal, our method can not only determine the scattering loss of optical surface, but also scale its inhomogeneity performance. A simply set of experimental apparatus is built up and used to demonstrated this method, which uses a single mode laser as the light source. Furthermore, to modulate the phase difference between two incidence beams, a piezoelectric ceramic is used. Some typical cases are then experimented and discussed, the results show that this method can be used to calibrate the quality of optical surface.

Frequency stabilization based on high finesse glass-ceramic Fabry-Perot cavity for a 632.8-nm He-Ne laser

A frequency stabilization technique for a 632.8nm He-Ne laser with a high finesse Fabry-Perot cavity is introduced in this paper. The resonant frequency of the cavity is taken as the frequency standard .In this system the Fabry-Perot cavity is composed of a glass-ceramic spacer, with thermal expansion coefficient smaller than 2×10-8/°C ， which means an excellent thermal stabilization which greatly decreases the thermal impacts on the cavity length in the desired constant-temperature environment.The intra-cavity spherical mirror is specially designed, which makes the Fabry-cavity a sensor element in our subsequent experiments for a new practical optical accelerometer .Both cavity mirrors were custom made in our laboratory which have reflectivities greater than 99.995% at 632.8nm, so the Fabry–Perot cavity has a finesse of about 62830. The half-maximum transmission line width is about 55.48 KHz and the free spectral range is 3.5GHz .In the experimental setup, we adopt the frequency stabilization circuit with small dithering .With proper dithering voltage, the laser can be precisely locked to the Fabry-Perot cavity minimum reflection point. Theoretically the frequency stability can reach 10-10 order.

Influence of laser linewidth on spectral ripple in fold-type cavity ring-down measurement

So-called spectral ripple a special phenomenon only existing in fold-type cavity ring-down spectrometer, and it is believed as deriving from the interference effect of different lights on the folded mirror. To investigate the influence of this phenomenon, on fold-type cavity ring-down measurement, some representative instances of laser linewidth are simulated and analyzed, and some experiments are carried on. It is found that the increasing of laser linewidth can make the amplitude of the spectral ripple decrease, more importantly, which can make the ring-down signal no longer decay as a single exponential but as the double exponential function.

Interference effect of surface scatter at folded-mirror coating of V-shaped resonance cavity

Scatter property of folded-mirror coating in V-shaped cavity is studied with Kirchhoff diffraction theory. The interference effect of scatter lights can be used to explain the ripple effect existing in optical-feedback cavity ring-down spectroscopy.