Cem Ozturk

Total internal reflection mirror-based InGaAsP ring resonators integrated with optical amplifiers

Novel ring resonators combining very small multimode interference (MMI) couplers, low loss total internal reflection (TIR) mirrors, and a semiconductor optical amplifier in InGaAsP material system are reported for the first time. The MMI length of 113 /spl mu/m is among the shortest reported. Average TIR mirror loss is about 1.1 dB per mirror. The material platform and fabrication process used are the same used for other active and passive devices except for a deep etch step. Hence, such resonators are easily integrated with other active and passive devices. A free spectral range of approximately 2 nm is observed near 1568 nm along with an on-off ratio of 14 dB, a full-width at half-maximum of about 0.3 nm, a finesse of more than 6, and a Q-factor of more than 4900.

An Experimental Study on the Process Monitoring of Resin Transfer Molded Composite Structures Using Fiber Optic Sensors

Research conducted on in situ process monitoring of resin transfer molded composites with fiber optic sensors is presented. A laboratory scale resin transfer molding (RTM) apparatus was designed and built with the capability of embedding fiber optic sensors and visually observing the resin filling process. Both fiber Bragg grating (FBG) and etched fiber (EF) sensors are embedded into glass fiber reinforcements in the RTM mold and used to monitor the resin flow front and cure. The cure cycle of the resin system utilized in this work is also studied using a Fresnel reflection refractometer (FRR) sensor. The results of this study show that both the FBG and EF sensors can be used efficiently for flow and cure monitoring of the RTM process. The experimental results of the EF and FRR sensors agree with those of the FBG sensors for cure monitoring.

Rectangular Ring Lasers Based on Total Reflection Mirrors and Three Waveguide Couplers

Novel rectangular ring lasers containing active and passive sections are fabricated and characterized. The rectangular laser cavity is formed using four low-loss total internal reflection (TIR) mirrors and an output coupler made out of passive three coupled waveguides. The fabrication process is exactly the same as for other active and passive devices except for one deep etch step for TIR mirror fabrication. Two different lasers having active section lengths of 250 and 350 mum and total cavity lengths of 580 and 780 mum are fabricated. For both devices, lasing thresholds of 38mA are obtained at room temperature and under continuous-wave operation. Lasing is predominantly single-mode with a sidemode suppression ratio better than 20 dB. The power loss of a single TIR mirror is also determined to be about 0.5 dB. Such low-loss TIR mirrors enabled lasers with very small footprints

Multimode-interference-coupled ring resonators based on total-internal-reflection mirrors

We investigate the properties of a multimode-interference (MMI) coupled ring cavity resonator with total-internal-reflection (TIR) mirrors and a semiconductor optical amplifier (SOA) in an InGaAsP material system. The TIR mirrors were fabricated by the self-aligned process with a loss of about 1.4 dB per mirror. The resulting free spectral range (FSR) was approximately 0.8 nm (97 GHz) near 1569 nm. The on–off ratio and the full width at half maximum (FWHM) were 8 dB and 0.152 nm, respectively, corresponding to a finesse of 5.2 and a Q factor of 10,322. Hence, such resonators can be directly integrated with other devices making possible the fabrication of compact and highly functional photonic integrated circuits.

Study of Local and Transient Buckling in Glass Fiber Reinforced Composite Using Fiber Bragg Grating

Glass ber reinforced composites (GFRC) are widely used in load bearing industrialapplications. Failure can occur in GFRC due to matrix cracking, ber breaking, crack coupling,delamination, or combined e ects of these failure mechanisms, and it is important to study thefailure mechanisms for qualitative inspection of the material during its operation. In this paper,GFRC is manufactured using resin transfer molding, and ber Bragg grating is embeddedin the composite during the manufacturing step. A strain gage is surface mounted on thecomposite, to correlate the FBG measurement data. GFRC is subjected to continuous tension-compression load cycles at 1Hz using MTS 322 test-frame servo-hydraulic test machine. TheFBG is characterized in this loading regime, and its strain sensitivity calculated. The cyclicloading induces local buckling the composite. It is observed that the buckling does not leadto immediate failure. However, the initial local buckling is transient in nature and surfaces atcompression stage of the loading cycle. Continuous loading cycles, leads to permanent bucklingin the composite leading to complete failure of the composite, and is observed in real-time usingFBG.

Coupled polymer waveguides and substrate removed GaAs waveguides as tunable filters

Tunable filtering with low fiber to fiber insertion loss was demonstrated using hybrid integration of polymer waveguides and GaAs epilayers. The wavelength tuning can be done electronically and very fast utilizing electrooptic properties of GaAs.