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We demonstrate that ionic self-assembled multilayers (ISAMs) adsorbed on long period gratings (LPGs) function effectively as biosensors using biotin–streptavidin as a demonstration bioconjugate pair. Biotin, streptavidin, and anti-streptavidin were deposited onto the ISAM-coated LPG sequentially, each inducing a measurable resonant wavelength shift of the LPG. Control experiments verified the specificity of the biosensor system. Furthermore, we demonstrate that ISAM coated turnaround point LPGs could serve as highly sensitive biosensors that exhibit a change in transmitted intensity rather than resonant wavelength. Experimental measurements confirm that ISAM-coated LPGs provide an attractive platform for building efficient and high-performance optical sensors.

This paper describes the physics and properties of a novel optical fiber that would be attractive for building high-power fiber lasers and amplifiers. Instead of propagating light in the fundamental, Gaussian-shaped mode, we describe a fiber in which the signal is forced to travel in a single, desired higher order mode (HOM). This provides for several advantages over the conventional approach, ranging from significantly higher ability to scale mode areas (and hence laser powers) to managing dispersion for ultra-short pulses - a capability that is practically nonexistent in conventional fibers. Particularly interesting is the tact that this approach challenges conventional wisdom, and demonstrates that for applications requiring meter-length fibers (as in high-power lasers), signal stability actually increases with mode order. Using this approach, we demonstrate mode areas exceeding 3200 μm 2 , and propagate signals with negligible mode distortions over up to 50-meter lengths. We describe several pulse propagation experiments in which we test the nonlinear response of this fiber platform, ranging from managing dispersive effects in femtosecond pulse systems, to reducing Brillouin scattering impairments in systems operating with the nanosecond pulses.

We demonstrate an emulator that captures the coherent distributed nature of multipath interference in few-mode fiber devices. Coherent interference in these devices manifests in slow power fluctuations as well as relative intensity noise. Slow bit-error-rate drifts and attendant systems power penalty drifts, in timescales similar to the slow power fluctuations (/spl sim/10 s), are the dominant manifestations of this impairment.

By utilizing a novel high-temperature measuring method, we investigated thermal profile of graphite filament for fiber fusion splicing. The experimental results indicate its excellent uniformity with less than 6.42% temperature fluctuation over 1.5mm diameter area.

We demonstrate resonant grating couplers with the broadest bandwidth (565 nm) reported to date, using microbend gratings in dispersion-optimized few-mode fibers. Control of modal dispersion enables the demonstration of spectrally flat (< 0.25-dB ripple) coupling. This enables a compact (1 cm), broad-band (110 nm) variable optical attenuator, which is highly cost-effective, since device assembly simply involves pressing an as-drawn fiber between two corrugated blocks.

We present a novel technique for measuring the chromatic dispersion of the higher order mode of an optical fiber. The measurement technique is simple, accurate, and capable of measuring the dispersion of kilometer lengths of fiber without the need for mode converters. The dispersion of the LP/sub 02/ mode is measured for several different fibers, and accuracies of better than 1%, compared with a measurement with the modulation phase shift method, are achieved.

We demonstrate a novel tunable dispersion compensator that utilizes higher order mode fibers and switchable fiber gratings. The device is broad band and wavelength continuous, yielding a bit rate, bit format, and signal bandwidth as well as channel-spacing transparent adjustable dispersion compensator. The novel device design is free from tradeoffs between tuning range and bandwidth. The tuning range is 435 ps/nm, with a bandwidth of 30 nm. Its all-fiber configuration yields the lowest loss (average /spl sim/3.7 dB) tunable dispersion compensator reported to date. 40-Gb/s transmission tests reveal penalty-free operation.

It is demonstrated that the lateral resolution of a non-linear scanning multi-photon microscope can be improved significantly by using the light from an LP{in02} mode instead of a Gaussian-like beam.

Multiple higher-order-modes propagating simultaneously in large-mode-area optical fibers are measured and their relative power levels quantified using spatially and spectrally resolved imaging.

The stimulated Brillouin scattering (SBS) gain efficiencies were measured in the LP(08) and LP(01) modes of a higher-order-mode optical fiber. Gain efficiencies C(B) of 0.0085 and 0.20 (m-W)(-1) were measured for the LP(08) and LP(01) modes at 1083 nm, respectively. C(B) is inversely proportional to the optical effective area Aeff and the same core-localized acoustic phonon seeds the SBS process in each case. An acoustic modal analysis and a distributed phenomenological model are presented to facilitate the data analysis and interpretation. The LP(08) mode exhibits a threshold powerlength product of 2.5 kW-m.

Modelocking in an Yb-doped figure-eight fiber laser is demonstrated utilizing anomalous dispersion from an LP(02) higher-order-mode fiber for dispersion management. Outside the laser cavity, the pulses were re-compressed to 95 fs using a second HOM module, the shortest demonstrated pulses to date from an Yb-doped figure-eight fiber laser. Operation of the laser with HOM fiber in the cavity is compared to an Yb figure-eight laser that utilizes all-normal dispersion fibers.

Fiber devices that amplify light propagating in a single fundamental mode face several challenges in extracting ever-increasing powers. Here we explore the advantages and present results showing amplification of light in a single higher order mode.

Femtosecond fiber lasers are currently of great interest due to their small size, stable operation, long lifetime and low cost compared to bulk lasers. However, for operation in the 1 µm wavelength range of Yb lasers, a major obstacle has been the lack of suitable fibers with anomalous dispersion that can compensate for the normal dispersion of the conventional active and passive fibers used. However, a new promising fiber device using a higher order mode (HOM) with anomalous dispersion in the 1 μm range has recently been demonstrated. The device comprises integrated all fiber mode converters based on long period gratings (LPG), and hence has the potential to be low loss and easy to splice, while offering a large effective area, and the possibility of third order dispersion compensation. In this paper, optimization of HOM fibers with anomalous dispersion in the 1 μm range has been investigated theoretically and experimentally. Fibers with dispersion coefficients ranging from +50 to +300 ps/(nm·km) at 1060 nm have been fabricated and devices including integrated LPG mode converters have been characterized. Modeled and measured properties of the modules, such as dispersion, grating bandwidth etc., are found to correlate well. It is shown that there is a tradeoff between a high dispersion coefficient and the bandwidth of LPG mode converters. The characteristics of such HOM devices have been studied in a linear, passively mode-locked laser-cavity using SESAM as saturable absorber.

We present a mode-locked ytterbium fiber laser with a higher-order mode fiber compensating the group-velocity dispersion and partially the third-order dispersion of the single-mode fiber at a wavelength of 1 microm. The generated pulses had an energy of 0.5 nJ and could be dechirped externally to a pulse duration of less than 60 fs. The power spectrum shows a spectral full width at half-maximum of 57 nm.

We review the performance and applications of a recently demonstrated platform that utilises higher-order modes in few-moded fibers to facilitate robust, bend-resistant, long-length light-propagation in ultra-large modal areas.

An SBS gain efficiency of 0.0088 (m-W)-1 was measured in an LP08 higher order mode optical fiber at 1083 nm. Comparative measurements in a single mode fiber confirm that the SBS threshold scales with the inverse modal effective area of 1714 mum2 yielding a single frequency SBS threshold power-length product of 2.4 kW-m.

We demonstrate a method of generating short pulses at 1350 nm by exciting Cerenkov radiation in a higher-order-mode fiber with a 1064 nm femtosecond fiber laser. We measure a 106 fs, 0.66 nJ output pulse. Cerenkov radiation in fibers allows for energy transfer between a soliton and a dispersive wave, providing an effective and engineerable platform to shift the wavelength of a femtosecond source. With appropriate design of the higher-order-mode fiber, this method of generating short pulses at 1350 nm can be extended to other wavelengths and to higher pulse energies.

We demonstrate soliton self-frequency shift of more than 12% of the optical frequency in a higher-order mode solid, silica-based fiber below 1300nm. This new class of fiber shows great promise for supporting Raman-shifted solitons below 1300nm in intermediate energy regimes of 1 to 10nJ that cannot be reached by index-guided photonic crystal fibers or air-core photonic bandgap fibers. By changing the input pulse energy of 200fs pulses from 1.36 to 1.63nJ we observe Raman-shifted solitons between 1064 and 1200nm with up to 57% power conversion efficiency and compressed output pulse widths less than 50fs. Furthermore, due to the dispersion characteristics of the HOM fiber, we observe redshifted Cerenkov radiation in the normal dispersion regime for appropriately energetic input pulses.

We present a mode-locked ytterbium fiber laser with a higher-order mode fiber compensating the GVD and partially the TOD of the SMF. The pulse duration is 52 fs with a spectral FWHM of 57 nm.

We review the performance and applications of a recently demonstrated platform that utilises higher-order modes in few-moded fibers that achieves robust, bend-resistant, long-length light-propagation in ultra-large modal areas.

We demonstrate robust single-transverse-mode light propagation in higher-order modes of a fiber, with effective area A(eff) ranging from 2,100 to 3,200 microm(2). These modes are accessed using long-period fiber gratings that enable higher-order-mode excitation over a bandwidth of 94 mm with greater than 99% of the light in the desired mode. The fiber is designed such that the effective index separation between modes is always large, hence minimizing in-fiber mode mixing and enabling light propagation over lengths as large as 12 m, with bends down to 4.5 cm radii. The modal stability increases with mode order, suggesting that A(eff) of this platform is substantially scalable.

Light propagation in higher-order modes of fibers yields a promising schematic for arbitrarily increasing modal areas. We demonstrate this with modes of record A eff ranging from 2100 to 3100 μm2, which experience negligible loss or mode coupling.

We demonstrate propagation and compression of 14-nJ, 152-fs pulses in the 2100-μm2 effective area, LP 07 mode of an intentionally multi-moded fiber. The 12-m length of fiber was coiled to a radius of curvature of 7.5 cm.

We demonstrate the first all-solid (non-holey), silica-based fiber with anomalous-dispersion (+60ps/nm-km) at wavelengths (1080nm) where silica material dispersion is negative. We demonstrate its functionality as a critical enabler for an all-fiber, Yb-based, femtosecond ring laser.

We demonstrate a higher-order-mode fiber-based platform, to achieve low-loss, bend-resistant, mode-coupling-free light transmission over meter-length fibers, in a record A/sub eff/ of 2100 /spl mu/m/sup 2/. Its nonlinearity tolerance is demonstrated by compressing fiber-laser pulses to 64 fs, yielding 52-kW peak powers.

Delivery of high peak-power femtosecond pulses with fibers is constrained by nonlinear distortions accumulated during pulse propagation. We address this problem with a novel, to our knowledge, fiber schematic, where the pulse propagates in a small Aeff (18 microm2) but highly dispersive (record value of approximately -900 ps/nm km) medium, enabled by transmission in the LP02 mode of a few-mode fiber. The novel fiber yields a low dispersion-to-nonlinear-length ratio (due to its large dispersion) despite its small Aeff, hence enabling mitigation of nonlinearities. This enables fiber delivery of distortion-free150 fs, approximately 1 nJ, and 840 nm pulses--an order-of-magnitude improvement over single-mode fibers of similar Aeff.

Polarization dependence in microbend gratings is an inherent problem, even in perfectly circular fibers, since antisymmetric modes are almost degenerate linear combinations of four distinct, polarization-sensitive modes. We demonstrate a novel fiber design that lifts polarization degeneracies of the antisymmetric modes to solve this problem. By intentionally exacerbating the polarization splittings, we achieve coupling to only the polarization-insensitive doublet, over wavelength ranges exceeding 100?nm, thus demonstrating a device with practical usable bandwidths. This allows all previous applications envisaged with UV-induced long-period gratings to be realized with the significantly lower-cost microbend technology platform.

We have shown that ionic self-assembled multilayers (ISAMs) deposited on optical fiber long period gratings (LPGs) yield dramatic resonant-wavelength shifts, even with nanometer-thick films. Precise control of the refractive index and the thickness of these films was achieved by altering the relative fraction of the anionic and cationic materials combined with layer-by-layer deposition. We demonstrate the feasibility of this highly controllable deposition-technique for fine-tuning grating properties for grating applications. In addition, we confirm theoretically that the resonant wavelength shift can result from either the variation of the thickness of the film and/or the variation of its refractive index. Finally, we demonstrate that ISAMs adsorbed on LPGs function effectively as biosensors. These simulations and experimental results confirm that ISAM-coated-LPGs provide a thermally-stable, reusable, robust, and attractive platform for building efficient fiber optic sensors and devices.

We compare various techniques to measure MPI in devices exhibiting distributed coherent crosstalk. Such devices are susceptible to deterministic noise as well as intermittent fading, and the measurement technique employed must capture both these manifestations of MPI. We evaluate several measurement techniques used to characterise MPI in few mode fibers. The coherent, distributed nature of MPI in few-mode fibers leads to fast fluctuations, manifesting in deterministic noise, as well as slow variations, reminiscent of fading in mobile communications systems. Slow temporal intensity variations of a CW DFB laser captures most of the relevant information.

We present a study of loss and MPI contributions from various components in adjustable dispersion compensators utilizing HOM fibers. We demonstrate this technology scalability to offer fine dispersion tuning granularity while maintaining low loss and low MPI characteristics.

We present a technique for measuring the chromatic dispersion of the higher order modes in kilometer lengths of fiber. The LP/sub 02/ dispersion is measured for several different fibers, and accuracies better than 1% are achieved.

A new measurement technique, capable of quantifying the number and type of modes propagating in large-mode-area fibers is both proposed and demonstrated. The measurement is based on both spatially and spectrally resolving the image of the output of the fiber under test. The measurement provides high quality images of the modes that can be used to identify the mode order, while at the same time returning the power levels of the higher-order modes relative to the fundamental mode. Alternatively the data can be used to provide statistics on the level of beam pointing instability and mode shape changes due to random uncontrolled fluctuations of the phases between the coherent modes propagating in the fiber. An added advantage of the measurement is that is requires no prior detailed knowledge of the fiber properties in order to identify the modes and quantify their relative power levels. Because of the coherent nature of the measurement, it is far more sensitive to changes in beam properties due to the mode content in the beam than is the more traditional M(2) measurement for characterizing beam quality. We refer to the measurement as Spatially and Spectrally resolved imaging of mode content in fibers, or more simply as S(2) imaging.

We demonstrate propagation of 14 nJ femtosecond pulses through a large-mode-area, higher-order-mode (HOM) fiber with an effective area of 2100 microm2. The pulses propagate stably in the LP07 mode of the fiber through lengths as long as 12 m. The strongly chirped pulses exiting the amplifier fiber are dechirped by the high-order-mode fiber, resulting in pulses with a peak power of 61 kW after propagation in 5 m of the positive-dispersion fiber. A small amount of self-phase modulation is observed in the compressed pulses and is described well by a nonlinear Schrödinger equation model that takes into account the measured effective area and dispersion of the HOM fiber.

We demonstrate a novel device that comprises a pair of broadband and narrowband long-period gratings written in specially designed few-mode fibers to achieve in-fiber bandpass filtering. This device configuration opens the possibility of using long-period gratings for complex spectral shaping in a band-selection as opposed to the conventional band-rejection configuration. The devices are low loss (0.5dB) as well as tunable over large spectral ranges (26 nm). We demonstrate, for the first time to our knowledge, that the unique dispersive properties of long-period gratings allow for constructing dispersion-free bandpass filters with arbitrarily sharp spectral profiles.

The nonlinear properties of a nanosecond pulse in a higher-order-mode, Er-doped-fiber amplifier with 2440µm2 effective area are compared to a conventional 880 µm2 area fiber. Both 1480nm pump and 1554nm signal propagate in the LP09 mode.

Modelocking in Yb-doped figure-eight fiber lasers is demonstrated utilizing dispersion compensation from a higher-order-mode module with anomalous dispersion. Pulses were compressed to 91 fs. the shortest demonstrated pulses for a Yb-doped figure-eight fiber laser.

Higher order modes for large-mode-area high power fiber amplifiers are reviewed. Results from amplification in both Yb-doped HOM fiber at 1083 nm and Er-doped HOM fibers at 1550 nm are presented.

We demonstrate tuning of the output spectrum of an HOM fiber module by changing the dispersion curve. Spectral feature wavelengths can be changed systematically by changing the location of the zero-dispersion wavelength.

We demonstrate a method of generating femtosecond pulses at 1350 nm by exciting Cherenkov radiation in a higher-order-mode fiber with a 1064 nm source. We measure a 134 fs, 0.66 nJ output pulse.

We demonstrate that ionic self-assembled multilayers (ISAM) adsorbed on long period gratings (LPG) function effectively as biosensors. Theoretical simulations and experimental measurements confirm that ISAM-coated-LPGs provide a thermally-stable, reusable platform for building efficient optical sensors.