Optical Waveguide Ring Resonator Research Articles

Alternative Approach to Design and Optimization of High-Q Ring Resonators for Membrane-Free Acoustic Sensors.

Membrane-free acoustic sensors based on new principle and structure are becoming a research hotspot, because of many advantages, e.g., their wide bandwidth and high sensitivity. It is proposed that a membrane-free acoustic sensor employs a semi-buried optical waveguide ring resonator (SOWRR) as a sensing element. Using air as the upper cladding medium, the excited evanescent field in the air cladding medium would be modulated by acoustic wave. On this basis, the acoustic sensing model is established. Taking high Q factor and resonance depth as design criteria, the optimal design parameters are given. The optimal values of the air/SiO2: Ge/SiO2 waveguide resonator length and coupling spacing are obtained as 50 mm and 5.6 μm, respectively. The Q factor of the waveguide resonator of this size is as high as 8.33 × 106. The theoretical simulation indicates that the frequency response ranges from 1 Hz to 1.58 MHz and that the minimum detectable sound pressure is 7.48 µPa using a laser with linewidth of 1 kHz. Because of its advantages of wide bandwidth and high sensitivity, the membrane-free sensor is expected to become one of the most promising candidates for the next-generation acoustic sensor.

Using DFB laser self-injection locked to an optical waveguide ring resonator as a light source of Φ-OTDR.

A distributed feedback (DFB) semiconductor laser self-injection locked to an optical waveguide ring resonator (OWRR) is used in a phase-sensitive optical time-domain reflectometry (Φ-OTDR) vibration sensing system as its light source. A frequency-hopping-free period of more than 100 s is realized. A spatial resolution of 13 m at 4700 m and simultaneous measurement of two vibration sources are realized. The measurable vibration frequency is from 8 Hz to the upper limit of the sampling theorem. These satisfactory performances demonstrate that the DFB laser locked to an OWRR is not only cost effective, but also stable and reliable for Φ-OTDR sensing.

High-finesse frequency tunability of optoelectronic oscillator based on SiO[formula omitted] optical waveguide ring resonator with the frequency locking technology

Fine tunability of oscillation frequency of optoelectronic oscillator (OEO) is crucial to its practicality. An approach of utilizing frequency locking technology is presented to realize the high-finesse tunable output of OEO based on SiO2 optical waveguide ring resonator (OWRR). Then the OEO system based on SiO2 OWRR is constructed, consisting of OEO loop and frequency locking loop. When the laser frequency is locked at the resonant frequency of the SiO2 OWRR, the stable single-mode oscillation is realized based on the filtering effect of SiO2 OWRR. The OEO oscillation frequency can be precisely tuned by adjusting the locking position of laser frequency, and a high-finesse tunable output of microwave signal is obtained with a tuning step of 20 kHz. Moreover, the change of locking position would not deteriorate the phase noise; for the generated signal at 2 GHz at different locking point, the phase noise is about -89.18 dBc/Hz at 10 kHz. These results show that the OEO based on SiO2 OWRR using frequency locking technology is feasible to obtain fine tunability of oscillation frequency. It indicates that the SiO2 OWRR has great potential in monolithic integrated OEO.

Comparison of Self-Injection Locking of DFB-LD by Optical Fiber and Optical Waveguide Ring Resonators

ABSTRACTUtilizing the frequency selection characteristic of ring resonators, self-injection-locking linewidth narrowing and frequency stabilization of distributed feedback laser diodes (DFB-LDs) can be achieved under the aid of ring resonators. In this paper, the self-injection-locking effects of a DFB-LD realized by two fiber ring resonators and an optical waveguide ring resonator are compared. The influences of the resonant peak bandwidth and transmission on linewidth narrowing are demonstrated. It is shown that the mode hopping can be significantly suppressed by employing the optical waveguide ring resonator. This is of great significance for practical applications and integration of the self-injection-locked DFB-LDs.

High quality factor silicon oxynitride optical waveguide ring resonators

In this manuscript, we report the design, manufacturing and characterization of silicon oxynitride (SiON) based optical waveguide ring resonators (OWRR) which achieve higher quality factors with respect to the state-of-the-art waveguide ring resonators. To improve the coupling efficiency, Bragg grating couplers are used at both ends of the designed resonators instead of the conventional directional couplers. In the proposed design, the core of OWRR structure was realized in the optimized refractive silicon oxynitride films deposited by liquid source chemical vapor deposition (LSCVD), under controllable composition ratio, time slot duration, and deposition temperature. The SiON based resonators have achieved a measured waveguide loss of 4.07 dB/cm and a quality factor of 0.93 × 105 in the transverse electric (TE) mode, and this by the way outperforms the results fulfilled with the state-of-the-art waveguide ring resonators.

Filtering effect of SiO2 optical waveguide ring resonator applied to optoelectronic oscillator.

Single-mode oscillation is crucial to the practicality of optoelectronic oscillator (OEO). Due to the limited by bandwidth and precision of radio frequency (RF) filters, it is difficult to be achieved for the OEO based on the long fiber-optic delay line. So instead of the long fiber-optic delay line, SiO2 optical waveguide ring resonator (OWRR) with high-Q and mode selection is first presented to be applied to OEO. The OEOs based on the minimum loop and SiO2 OWRR are constructed. The oscillation characteristics of the minimum loop OEO and the transmission characteristics of the SiO2 OWRR are simulated by MATLAB, respectively. The filtering effect of the SiO2 OWRR applied to the OEO is verified theoretically by comparing these simulation results. Subsequently, the contrastive experiments of the above two OEOs on oscillation modes are carried out. The oscillation mode spacing of 40.32 MHz and 2.137 GHz are obtained. These results show that the SiO2 OWRR can function as an excellent 'filter' in the minimum loop of the OEO. Moreover, the side mode suppression ratio and the phase noise of the OEO have been improved. Our experimental results demonstrate that the OEO adopting SiO2 OWRR is feasible to achieve the single-mode oscillation and obtain better performance microwave signals.

Tilted Waveguide Gratings and Implications for Optical Waveguide-Ring Resonator

In this paper, a novel optical waveguide-type ring resonator by inserting titled waveguide gratings (TWGs) with the Brewster's angle is proposed. Using the Marcatili approximation, the electric fields for a rectangular waveguide is obtained. Then, the volume current method (VCM) is first developed for rectangular-core TWGs. By the VCM, the feasibility of the TWGs to filter the s-polarized light propagating in the resonator is proved. When a 4-cm-long 45°-titled TWG is applied to a silica waveguide-ring resonator, a polarization extinction ratio of 40 dB is obtained. The influences of the angular misalignment as well as the grating period of the TWGs are also evaluated.

Transfer function of optical waveguide ring resonator in frequency domain for micro-optic gyro

Resonator micro optic gyro (R-MOG) is a high accuracy inertial rotation sensor based on the Sagnac effect. Optical waveguide ring resonator is the core-sensing element in R-MOG. According to the feature of the input signal, we established the transfer function of a Si-based ring resonator model in frequency domain for R-MOG with the coupled-mode theory. According to using the derived transfer function in the frequency domain, we analyzed the demodulation characteristics of R-MOG using Bessel function expansion based on laser frequency modulation spectrum technique. And we analyzed the relationship between the frequency modulation demodulation output signal and the resonant frequency deviation and obtained the best modulation coefficient applied in laser PZT drive. When the modulation coefficient M=2, the maximum linear interval slope, the demodulation curve is the best.

Current modulation technique used in resonator micro-optic gyro

Resonator micro-optic gyro (RMOG) is a promising candidate for the next generation inertial rotation sensor based on the Sagnac effect. A current modulation technique used in an external cavity laser diode is proposed to construct the gyroscope system for the first time. The resonance curves before and after eliminating accompanying amplitude modulation are theoretically analyzed, calculated, and simulated; the demodulation curves with different modulation currents are formulated theoretically; and the optimum modulation current corresponding to the maximum sensitivity is obtained. The experiment results from the established RMOG experimental setup demonstrate that a bias stability of 2.7 deg/s (10 s integrated time) over 600 s, and dynamic range of ±500 deg/s are demonstrated in an RMOG with a silica optical waveguide ring resonator having a ring length of 12.8 cm.

Influence of coupling conditions on the time delay characteristics of parallel-cascaded optical waveguide ring resonators

The influence of coupling conditions of parallel-cascaded waveguide ring resonators on the time delay application in the optically phased array antennas is analyzed. Two kinds of coupling conditions, over-coupling and restriction free are considered to achieve a certain target delay time by parallel-cascaded three ring resonators. The results show that the restriction free coupling condition is better than the over-coupling one to obtain a flat time delay response in the target delay bandwidth especially for the small target delay time, which is the advantage of ring-resonator-based tunable true time delay line. The influence of round-trip loss on the time delay response and the transmission amplitude response is also investigated, which indicates that ring resonators with low optical round-trip loss are preferred to achieve a high performance true time delay line.

Silicon Oxynitride Optical Waveguide Ring Resonator Utilizing a Two-Mode Interferometer Structure

Silicon oxynitride (SiOxNy, SiON) optical waveguide ring resonator, in which a two-mode interferometer is used to replace the directional coupler in a conventional ring resonator, has been designed and fabricated. Preliminary results exhibit the same of free spectral range of 100 GHz but different quality factors of 3700 and 3900 at 1550 nm for transverse electric (TE) and transverse magnetic (TM) mode, respectively. The extinction ratio is more than 18 dB over the entire C-band, and the insertion loss is lower than 9.5 dB for TE and TM mode.

Measurements of excess loss of the crossed waveguide using optical waveguide ring resonators

Crossed waveguide is widely used in optical devices, whose excess loss has a strong impact on multi-turn optical waveguide ring resonator and resonator integrated optic gyro. The resonance curve of the ring resonator is sharply dependent on the loss within the resonator. This paper presents how to get excess loss of the crossed waveguides nondestructively through the comparison of the resonance characteristics between one-turn and multi-turn optical waveguide ring resonators.

Silica waveguide ring resonators with multi-turn structure

Optical waveguide ring resonator is the basic element of resonator integrated optic gyro (RIOG). In this paper, we report a novel configuration of optical waveguide ring resonator using a multi-turn structure. The characteristic of the light propagating across the crossed waveguides is analyzed using the finite difference beam propagation method. The relationship between the propagation loss and the intersection angle for arbitrary intersecting angles has been analyzed. Some crossed waveguides are fabricated in silica waveguides to verify the theoretical results. On this basis, the influences of the loop numbers and the excess loss of the crossed waveguide on the limited sensitivity of the RIOG have been analyzed. There is a critical intersection angle for certain resonator, only when the intersection angle is bigger than the critical angle, the gyro sensitivity can be improved by increasing the loop numbers. This will be helpful to how to determine the optimum length in resonator for its application in RIOG.

Critical coupling, oscillation, reflection, and transmission in optical waveguide-ring resonator systems

We generalize an earlier published analysis of critical coupling in a single-ring resonator waveguide system [Electron. Lett.36, 321 (2000)] to multiple-ring resonator all-pass and channel-dropping filter structures. The fundamental analytical relationships among coupling coefficient, internal loss, and oscillation frequency for critical coupling and oscillation conditions are derived for two and three rings coupled to single- and double-bus waveguides using the transfer-matrix method and Sylvester's theorem. Furthermore, we derive the photonic band structure of an infinite periodic ring structure and show that, as the number of rings increases, the reflection band of the double-bus structure approaches the photonic bandgap.

Measurement of optical nonlinearity in silicon rich nitride waveguide ring resonators

The optical nonlinearities of amorphous silicon rich nitride corresponding to χ(3) in a static electric field have been measured by tracking wavelength shifts in the resonances of optical waveguide ring resonators as a function of an applied electrical field. The magnitude of the nonlinearity measured agrees well with expected values.

Critical coupling and its control in optical waveguide-ring resonator systems

The coupling of optical waveguides to ring resonators holds the promise of a new generation of switches (modulators) which employ orders of magnitude smaller switching (modulation) voltages (or control intensities). This requires a means for voltage (or intensity) control of the coupling between the waveguide and the resonator. Schemes for achieving such control are discussed.

Silica-based optical waveguide ring laser integrated with semiconductor laser amplifier on Si substrate

A compact and stable ring laser at 1.3 μm was demonstrated using an InGaAsP semiconductor laser amplifier (SLA) and a silica-based optical waveguide ring resonator with an FSR of 2 GHz on an Si substrate. Two end facets of the SLA were coupled to lensed optical fibres, the other ends of which were attached without alignment to the waveguide resonator through fibre guiding grooves. A low threshold current of 17 mA was obtained in the ring laser.