Fiber-based Interferometer Research Articles

Single photon locking of an all-fiber interferometer

We describe locking of a fiber-based Mach–Zehnder interferometer. This work used a coherent state as input with a mean of 0.1 photons per gating period of an avalanche photodiode operated in geiger mode. Feedback from the avalanche photodiode loop was used to lock the intensity of the interferometer such that the output was balanced. Details of the technique are discussed as well as locking fiber-based interferometers to arbitrary output states and using number states as input. Applications in quantum computing, quantum communications, and quantum key distribution are discussed.

A portable, low coherence interferometry based instrument for fine needle aspiration biopsy guidance

A portable, low coherence interferometry (LCI) based instrument for fine-needle aspiration biopsy guidance is presented. The instrument consists of a fiber-based low coherence interferometer, a data acquisition, processing and display unit, and a probe. The probe, consisting of a 250μm diameter single-mode optical fiber inserted within the bore of a fine needle, is used to illuminate tissue and collect light from tissue at the tip of the needle. Light returning out of the probe is detected by the LCI system, which is capable of measuring depth-resolved information (reflectivity, spectra, birefringence) with a spatial resolution of 10μm over a depth range of approximately 1.4mm. The LCI based instrument can be used to guide the fine needle during biopsy procedures to potentially diagnose neoplasms, infections, inflammations, or infiltrations. The design and performance of the instrument, as well as preliminary measurements on excised breast tissue specimens, are presented in detail.

Process Monitoring of a Thermosetting Resin Using Optical-Fiber Sensors in a Microwave Environment

Conventional means of curing thermosetting resins used in advanced fiber-reinforced composites involves heating the sample in an oven or autoclave where heat is transferred to the sample through conduction and convection. In general, the cure schedules that are used can be time consuming and expensive. Hence, significant attempts are being made to improve the processing efficiency and productivity of this class of material. Microwave-based processing has been claimed to offer the advantage of a significantly faster processing time. In this study, two remote (noncontact) sensor systems were designed and developed to facilitate spectral-based quantitative process monitoring inside a custom-modified commercial microwave oven. The two fiber-optic sensor systems were 1) a noncontact optical-fiber reflectance probe and 2) a reusable transmission probe assembly. Spectroscopic data were obtained using the fiber-optic probes at specified microwave power levels. Since conventional metal-based temperature monitoring devices cannot be used in the microwave oven, a low-cost disposable fiber-optic probe was developed. This design was based on an optical fiber-based extrinsic Fabry-Perot interferometer (FPI). The extrinsic FPI temperature sensor demonstrated an accuracy of /spl plusmn/0.5/spl deg/C over the range from ambient to 300/spl deg/C. The temperature of the resin system was also measured simultaneously, along with the spectral data, to monitor the progress of the chemical reaction (curing).

Comparison of fiber-based Sagnac interferometers for self-switching of optical pulses

Self-switching of ultrashort optical pulses in a gain-distributed nonlinear amplifying fiber loop mirror (NALM) is investigated numerically in the soliton regime. Switching characteristics of this device is compared to those of the nonlinear optical loop mirror (NOLM) and the conventional NALM that uses a lumped gain. We show that, as compared with the NOLM or the conventional NALM, the gain-distributed NALM can produce higher-quality pulses and permits more efficient pulse compression. We also show that the gain-distributed NALM has several advantages over the conventional NALM such as sharpened switching edges, flattened switching peak, and robustness to gain variations.

Investigation of 2-b/s/Hz 40-Gb/s DWDM Transmission Over 4>tex<$,times,$>/tex<100 km SMF-28 Fiber Using RZ-DQPSK and Polarization Multiplexing

We have investigated transmission of 14/spl times/40 Gb/s dense wavelength-division-multiplexing channels with 20-GHz spacing over 4/spl times/100 km of SMF-28 fiber. A spectral efficiency of 2 b/s/Hz was demonstrated by 4-b (8-state) per-symbol coding using return-to-zero differential quadrature phase-shift keying (RZ-DQPSK) and polarization multiplexing using polarization bit interleaving. All 12.5-Gsymbols/s transmitted channels included 25% overhead bandwidth reserved for forward-error correction (FEC) and showed uncorrected bit-error rate below the FEC threshold required for error-free operation. Demodulation of the RZ-DQPSK signal at the receiver was achieved using a fiber-based asymmetric Mach-Zehnder interferometer as well as a packaged integrated lithium niobate optical 90/spl deg/ hybrid.

Instantaneous quadrature low-coherence interferometry with 3 x 3 fiber-optic couplers.

We describe fiber-based quadrature low-coherence interferometers that exploit the inherent phase shifts of 3 x 3 and higher-order fiber-optic couplers. We present a framework based on conservation of energy to account for the interferometric shifts in 3 x 3 interferometers, and we demonstrate that the resulting interferometers provide the entire complex interferometric signal instantaneously in homodyne and heterodyne systems. In heterodyne detection we demonstrate the capability for extraction of the magnitude and sign of Doppler shifts from the complex data. In homodyne detection we show the detection of subwavelength sample motion. N x N (N > 2) low-coherence interferometer topologies will be useful in Doppler optical coherence tomography (OCT), optical coherence microscopy, Fourier-domain OCT, optical frequency domain reflectometry, and phase-referenced interferometry.

Fiber Sagnac interferometer temperature sensor

A modified Sagnac interferometer-based fiber temperature sensor is proposed. Polarization independent operation and high temperature sensitivity of this class of sensors make them cost effective instruments for temperature measurements. A comparison of the proposed sensor with Bragg grating and long-period grating fiber sensors is derived. A temperature-induced spectral displacement of 0.99 nm/K is demonstrated for an internal stress birefringent fiber-based Sagnac interferometer.

Sapphire optical fiber-based interferometer for high temperature environmental applications

Describes the development and testing of an extrinsic sapphire fiber-based sensor design intended for use in high-temperature environments, including the processing environments of advanced high-temperature materials and the in-situ operational environments of high-temperature adaptive materials and structures. In this sensor, a length of uncoated, unclad, single-crystal optical-quality multimode sapphire fiber is fusion-spliced to a single-mode silica fiber. Another sapphire fiber is placed end-to-end with the first sapphire fiber, so that the two adjacent end-faces of the sapphire fibers form a low-finesse Fabry-Perot cavity. This sensor is demonstrated to be useful for both strain and temperature measurement, with a 10-microstrain resolution over a range of 0-1150 microstrain, and a 3.5 degrees C temperature resolution over a range from 150 to 650 degrees C.