Makoto Shizuka

Optical correlation-domain reflectometry without optical frequency shifter

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.

Simplified optical correlation-domain reflectometry without reference path.

We develop a simplified configuration of optical correlation-domain reflectometry without involving an explicit reference path. The Fresnel-reflected light generated at the distal open end of the sensing fiber is exploited as a reference light.

Simplified optical correlation-domain reflectometry using polymer fiber

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 30ms (corresponding to a repetition rate of 33Hz), at which both the resolution and SNR are maintained at high values.

Refractive index sensing using ultrasonically crushed polymer optical fibers

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.

Locally pressed plastic optical fibers for refractive index sensing

Power-based refractive index (RI) sensing is demonstrated by exploiting an ultrasonically pressed plastic optical fiber (POF). We can be easily and cost-efficiently fabricate this structure, within a short while (∼1 s), without using external heat sources or chemical materials. We have only to simply press the horn connected to an ultrasonic transducer against part of the POF. The RI dependence of the transmitted power exhibits linear trends in the RI ranges from ∼1.32 to ∼1.36 (coefficient: −62 dB/RIU (RI unit)) and ∼1.40 to ∼1.44 (coefficient: −257 dB/RIU)). We also study the temperature dependence of the transmitted power.

Simplified optical correlation-domain reflectometry employing proximal reflection point

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.

Measurement of the optical path length difference in an interferometer using a sinusoidally frequency-modulated light source.

We develop a technique for measuring the optical path length difference (OPLD) in an interferometer using a frequency-modulated light source. Compared with conventional methods, this technique offers a high sampling rate, high precision, and cost efficiency, and is capable of determining which of the two optical paths is longer. In addition, we show that this technique works properly even when the OPLD is significantly longer than the coherence length of the light source.