To achieve distributed reflectivity measurements along an optical fiber, we developed a simplified cost-effective configuration for optical correlation-(or coherence-) domain reflectometry based on a synthesized optical coherence function using sinusoidal modulation. By excluding the conventional optical heterodyne detection that accompanies the frequency shift (without using an acousto-optic modulator) and by exploiting the foot of the electrical Fresnel reflection spectrum, the electrical bandwidth required for signal processing is lowered to several megahertz. We evaluate the basic system performance and demonstrate its high-speed operation (10 ms for one scan) by tracking a moving reflection point in real time.

We develop a simplified configuration for optical correlation-domain reflectometry (OCDR) without an explicit reference path. Instead, the Fresnel-reflected light generated at the distal open end of the sensing fiber is exploited as a reference light. After the fundamental demonstration, the optimal incident power is found to be approximately 8 dBm. We also show that the loss near the distal end should not be applied, unlike in the case of Brillouin-based OCDR.

We develop a new configuration of simplified optical correlation-domain reflectometry using a proximal reflection point. The experimental setup is basically composed of standard silica fibers and includes neither an optical frequency shifter such as an acousto-optic modulator nor an explicit reference path. The light reflected at the proximal reflection point, which is artificially fabricated near an optical circulator, is used as the reference light. Unlike the conventional silica-based setup, this configuration can perform a distributed reflectivity measurement along the distal half of the sensing fiber. After demonstration of the basic operation, the incident optical power dependence of the reflectivity distribution is investigated, and the existence of the optimal incident power is clarified.

We develop a simplified configuration of optical correlation-(or coherence-) domain reflectometry (OCDR) using a polymer optical fiber (POF). The conventional reference light path is removed by using as reference light the Fresnel-reflected light caused at the interface between a silica single-mode fiber and the POF. We demonstrate its basic operation and investigate the dependences of the spatial resolution and signal-to-noise ratio (SNR) on the sweep time of the laser modulation frequency. The optimal sweep time is found to be 30 ms (corresponding to a repetition rate of 33 Hz), at which both the resolution and SNR are maintained at high values.

We demonstrate power-based refractive index (RI) sensing using an ultrasonically crushed polymer optical fiber (POF). This structure can be easily and cost-effectively fabricated within a short time (i.e., ∼1 s) without the need to employ external heat sources or chemicals. The only requirement is to simply press a horn connected to an ultrasonic transducer against part of the POF. The RI dependence of the transmitted power shows linear trends in RI ranges of ∼1.32 to ∼1.36 [coefficient: −62 dB/RIU (RI unit)] and ∼1.40 to ∼1.44 (coefficient: −257 dB/RIU). The temperature dependence of the transmitted power is also investigated.