Mode-Multiplexed Transmission over Conventional Graded-Index Multimode Fibers

We present experimental results for combined mode-multiplexed and wavelength multiplexed transmission over conventional graded-index multimode fibers. We use mode-selective photonic lanterns as mode couplers to precisely excite a subset of the modes of the multimode fiber and additionally to compensate for the differential group delay between the excited modes. Spatial mode filters are added to suppress undesired higher order modes. We transmit 30-Gbaud QPSK signals over 60 WDM channels, 3 spatial modes, and 2 polarizations, reaching a distance of 310 km based on a 44.3 km long span. We also report about transmission experiments over 6 spatial modes for a 17-km single-span experiment. The results indicate that multimode fibers support scalable mode-division multiplexing approaches, where modes can be added over time if desired. Also the results indicate that mode-multiplexed transmission distance over 300 km are possible in conventional multimode fibers

Wavelength-Selective Switch with Direct Few Mode Fiber Integration

The first realization of a wavelength-selective switch (WSS) with direct integration of few mode fibers (FMF) is fully described. The freespace optics FMF-WSS dynamically steers spectral information-bearing beams containing three spatial modes from an input port to one of nine output ports using a phase spatial light modulator. Sources of mode dependent losses (MDL) are identified, analytically analyzed and experimentally confirmed on account of different modal sensitivities to fiber coupling in imperfect imaging and at spectral channel edges due to mode clipping. These performance impacting effects can be reduced by adhering to provided design guidelines, which scale in support of higher spatial mode counts. The effect on data transmission of cascaded passband filtering and MDL build-up is experimentally investigated in detail

All-fiber Real-time Ultrafast Ranging Lidar For Motion Management Of Patients During Stereotactic Radiotherapy

We report a fiber-optic-based ultrafast time-stretch laser detection and ranging (Lidar) sensor with 10 MHz speed and 10 μm accuracy with 30 mm dynamic range for head motion detection under the thermoplastic mask during image-guided radiotherapy procedures. The sensor (1) is miniaturized and fits under the mask, (2) is small enough not to cause attenuation in radiation beams, (3) has a spatial resolution of a tenth of a millimeter, (4) is real-time, and (5) is immune to electromagnetic radiation

Entangled Photon Pair Generation Via Spontaneous Intermodal Four-wave Mixing In A 25-km-long Few-mode Fiber

High degrees of security have been achieved in quantum communication over fiber using entangled photons. For communications applications, it is crucial to produce high-yield entangled photon pairs (EPPs) with the capacity to transmit them over telecommunication-length fiber distances and the ability to integrate and transmit them over existing classical communication systems. Since spatial division multiplexing (SDM) is currently being demonstrated to replace single-mode communication systems, it only makes sense to demonstrate the generation and transferring EPPs in various fiber modes suitable for generation and transmission in SDM fibers. We experimentally demonstrate EPP formation in a 25-km-long graded-index few-mode fiber (three modes) via the intermodal spontaneous four-wave mixing (SFWM) effect. Mode profile and phase matching condition have been confirmed through experiments

Head Motion Tracking for Stereotactic Radiotherapy Applications

Head motion detection and its correction in stereotactic radiotherapy are subjects of interest. In this paper a fiber optic sensor-based design is introduced for head motion detection with radiation immunity

Search for Ionization-Induced Modulation of Light Polarization for a New Direction to Improve Time Resolution of PET

In this work, we study whether ionizing radiation can induce a small component of non-polarized light in a crosspolarizer setup, where usually no light transmission would occur. Such ionization-induced modulation of polarization occurs at a sub-picosecond time scale, which could be exploited for fast timing applications, such as time of flight in positron emission tomography. We demonstrate the feasibility of this approach using ionization produced from a laser diode in high Z, high-density crystals. Results indicate that the signal strength, quantified by induced cross-polarized light due to ionization from 20 MHz UV pulses in BSO is 10x higher than that in CdTe

Model of Anti-Stokes Cooling in a Yb-Doped Fiber

We use a comprehensive model of cooling by anti-Stokes fluorescence in a single-mode fiber that includes the effects of fiber loss, concentration quenching, mode profiles, and amplified spontaneous emission to analyze the trends of cooling in single-mode Yb-doped ZBLANP fibers. Simulations demonstrate that heat extraction varies significantly along the fiber. There is an optimum pump power (58 mW at 1015 nm for the modeled fiber) for which the maximum heat extracted per unit length is at the start of the fiber. Launching more power moves the coolest point further down the fiber. At substantially higher powers, ASE has a significant heating effect, and coupled with the heating due to absorptive loss, the entire fiber warms up. For a given fiber length, the total extracted heat is maximized for a different pump power (430 mW for a 20-m length). The temperature change is then negative along the entire fiber, and the total extracted heat is 7.12 mW (1.65% cooling efficiency). When the fiber absorptive loss is negligible, this value increases to 30.5 mW for a 2-W pump, giving a 3.48% cooling efficiency, only slightly below the quantum limit (3.7%). The optimum dopant concentration has a similar trade-off: The total extracted heat is maximized for a Yb concentration of 2 wt.%, and the cooling efficiency for 0.5 wt.%. A model of ASF cooling in fiber lasers is also described and exploited to investigate how to select the fiber laser parameters to extract the most power output from a radiation-balanced fiber laser. It shows that increasing the cavity length increases cooling at the expense of laser efficiency, and that a low output coupler reflectivity enhances ASF cooling. Simulations predict that a large-mode-area fiber laser should produce 12.7 W of output power at 63% efficiency, a performance limited by the fiber\u27s absorptive loss, the core diameter (30 µm), and concentration quenching

High-Resolution Slow-Light Fiber Bragg Grating Temperature Sensor with Phase-Sensitive Detection

This Letter reports a slow-light fiber Bragg grating (FBG) temperature sensor with a record temperature resolution of ~0.3 m°C √Hz, a drift of only ~1 m°C over the typical duration of a measurement (~30 s), and negligible self-heating. This sensor is particularly useful for applications requiring the detection of very small temperature changes, such as radiation-balanced lasers and the measurement of small absorptive losses using calorimetry. The sensor performance is demonstrated by measuring the heat generated in a pumped Yb-doped fiber. The sensor is also used to measure the slow-light FBG\u27s very weak internal absorption loss (0.02m-1), which is found to be only ~2% of the total loss

Model of Anti-Stokes Fluorescence Cooling in a Single-Mode Optical Fiber

We report a comprehensive model that quantifies analytically and numerically the heat that can be extracted by anti-Stokes fluorescence (ASF) from a fiber doped with a quasi-two-level laser ion. This model is used to investigate the effects on cooling of all relevant fiber and pump parameters, as well as amplified spontaneous emission. Simulations of a typical Yb-doped ZBLANP single-mode fiber show that for short enough fibers the heat extraction is relatively uniform along the fiber length. There is an optimum pump wavelength and power that maximizes the heat extracted per unit length. At this power, the coolest point is at the fiber input end. At higher powers, the coolest spot moves further down the fiber. The total heat extracted from a fiber, important for payload cooling, depends on the fiber absorptive loss, the pump wavelength, and the pump power. Simple expressions are derived to predict the optimum dopant concentration that maximizes heat extraction and the maximum tolerable absorptive fiber loss above which cooling is unobtainable. In a fiber with negligible residual absorption, the cooling efficiency is predicted to be 3.7%. In the modeled fiber, it is reduced to 1.7% in part by concentration quenching, but mainly due to the fiber absorptive loss (∼15 dB/km). Since the total extracted heat increases linearly with core radius and dopant concentration (up to a limit determined by concentration quenching), highly doped multimode fibers are strong candidates for payload cooling. This model can be straightforwardly expanded to design and optimize fiber lasers and amplifiers that utilize ASF for cooling

305-Km Combined Wavelength and Mode-Multiplexed Transmission over Conventional Graded-Index Multimode Fibre

We present experimental results for mode-multiplexed WDM transmission over OM3 multimode fibres. We transmit 60 WDM channels and 3 spatial modes over a distance of 305 km. We use mode-selective photonic lanterns as mode couplers and for differential group delay compensation