Scaling the effective area of higher-order-mode erbium-doped fiber amplifiers.

We demonstrate scaling of the effective area of higher-order mode, Er-doped fiber amplifiers. Two Er-doped higher-order mode fibers, one with 3800 µm(2) A(eff) in the LP(0,11) mode, and one with 6000 µm(2) effective area in the LP(0,14) mode, are demonstrated. Output beam profiles show clean higher order modes, and S(2) imaging measurements show low extraneous higher order mode content. CW and pulsed amplifier experiments are reported. Nanosecond pulses are amplified to 0.5 mJ pulse energy with 0.5 MW peak power.

Mode-locked picosecond pulse generation from an octave-spanning supercontinuum.

We generate mode-locked picosecond pulses near 1110 nm by spectrally slicing and reamplifying an octave-spanning supercontinuum source pumped at 1550 nm. The 1110 nm pulses are near transform-limited, with 1.7 ps duration over their 1.2 nm bandwidth, and exhibit high interpulse coherence. Both the supercontinuum source and the pulse synthesis system are implemented completely in fiber. The versatile source construction suggests that pulse synthesis from sliced supercontinuum may be a useful technique across the 1000 - 2000 nm wavelength range.

Visible continuum generation using a femtosecond erbium-doped fiber laser and a silica nonlinear fiber.

Supercontinuum extending to visible wavelengths is generated in a hybrid silica nonlinear fiber pumped at 1560 nm by a femtosecond, erbium-doped fiber laser. The hybrid nonlinear fiber consists of a short length of highly nonlinear, germano-silicate fiber (HNLF) spliced to a length of photonic crystal fiber (PCF). A 2 cm length of HNLF provides an initial stage of continuum generation due to higher-order soliton compression and dispersive wave generation before launching into the PCF. The visible radiation is generated in the fundamental mode of the PCF.

Demonstration of bend-induced nonlinearities in large-mode-area fibers.

We present what we believe to be the first direct measurements of enhanced nonlinearities in large-mode-area fibers due to bend induced reductions in effective area. Both Raman scattering and self-phase modulation are observed to increase in tightly coiled fibers. The measured increase in nonlinearity compares well with predictions from simulations of the modal effective area.

Grating phase matching beyond a continuum edge.

We show that fiber Bragg gratings can extend an optical continuum to spectral regions where continuum generation is very weak. Highly nonlinear fibers with Bragg grating resonances at 700, 750, and 800 nm were pumped with 70 fs pulses at 1580 nm and exhibited enhancement peaks up to 25 dB above the extremely weak continuum at these wavelengths, normally more than 40 dB below the average power in the continuum. We show that the grating peaks may be computed by treating the continuum pulse as an undepleted pump and including the grating dispersion as a phase-matching term.

Fiber-laser frequency combs with subhertz relative linewidths.

We investigate the comb linewidths of self-referenced, fiber-laser-based frequency combs by measuring the heterodyne beat signal between two independent frequency combs that are phase locked to a common cw optical reference. We demonstrate that the optical comb lines can exhibit instrument-limited, subhertz relative linewidths across the comb spectra from 1200 to 1720 nm with a residual integrated optical phase jitter of approximately 1 rad in a 60 mHz to 500 kHz bandwidth. The projected relative pulse timing jitter is approximately 1 fs. This performance approaches that of Ti:sapphire frequency combs.

Outcome of osteochondral autograft transplantation for type-V cystic osteochondral lesions of the talus.

The treatment of osteochondral lesions of the talus has evolved with the development of improved imaging and arthroscopic techniques. However, the outcome of treatment for large cystic type-V lesions is poor, using conventional grafting, debridement or microfracture techniques. This retrospective study examined the outcomes of 50 patients with a cystic talar defect who were treated with arthroscopically harvested, cored osteochondral graft taken from the ipsilateral knee. Of the 50 patients, 45 (90%) had a mean good to excellent score of 80.3 (52 to 90) in the Karlsson-Peterson Ankle Score, at a mean follow-up of 36 months (24 to 83). A malleolar osteotomy for exposure was needed in 26 patients and there were no malleolar mal- or nonunions. One patient had symptoms at the donor site three months after surgery; these resolved after arthroscopic release of scar tissue. This technique is demanding with or without a malleolar osteotomy, but if properly performed has a high likelihood of success.

Improved stabilization of a 1.3 microm femtosecond optical frequency comb by use of a spectrally tailored continuum from a nonlinear fiber grating.

We report significant enhancement (+24 dB) of the optical beat note between a 657 nm cw laser and the second-harmonic generation of the tailored continuum at 1314 nm generated with a femtosecond Cr:forsterite laser and a nonlinear fiber Bragg grating. The same continuum is used to stabilize the carrier-envelope offset frequency of the Cr:forsterite femtosecond laser and permits improved optical stabilization of the frequency comb from 1.0 to 2.2 microm. Using a common optical reference at 657 nm, a relative fractional frequency instability of 2.0 x 10(-15) is achieved between the repetition rates of Cr:forsterite and Ti:sapphire laser systems in 10 s averaging time. The fractional frequency offset between the optically stabilized frequency combs of the Cr:forsterite and Ti:sapphire lasers is +/-(0.024 +/- 6.1) x 10(-17).

Supercontinuum generation in ultraviolet-irradiated fibers.

We demonstrate that UV exposure of highly nonlinear, germanosilicate fibers causes a strong change in their chromatic dispersion and can significantly alter the infrared supercontinuum generation in these fibers. By varying the level of UV exposure to the fiber, we show that the dispersion zero and the short-wavelength edge of the supercontinuum can be changed by more than 100 nm. A nonlinear Schrödinger equation model of the continuum generation in the nonlinear fiber shows that the short-wavelength behavior of the continuum is primarily controlled by changes in the fiber dispersion caused by the UV-induced change in the refractive index of the fiber core.

High power, single mode, all-fiber source of femtosecond pulses at 1550 nm and its use in supercontinuum generation.

We present a source of high power femtosecond pulses at 1550 nm with compressed pulses at the end of a single mode fiber (SMF) pigtail. The system generates 34 femtosecond pulses at a repetition rate of 46 MHz, with average powers greater than 400 mW. The pulses are generated in a passively modelocked, erbium-doped fiber laser, and amplified in a short, erbium-doped fiber amplifier. The output of the fiber amplifier consists of highly chirped picosecond pulses. These picosecond pulses are then compressed in standard single mode fiber. While the compressed pulses in the SMF pigtail do show a low pedestal that could be avoided with the use of bulk-optic compression, the desire to compress the pulses in SMF is motivated by the ability to splice the single mode fiber to a nonlinear fiber, for continuum generation applications. We demonstrate that with highly nonlinear dispersion shifted fiber (HNLF) fusion spliced directly to the amplifier output, we generate a supercontinuum spectrum that spans more than an octave, with an average power 400 mW. Such a high power, all-fiber supercontinuum source has many important applications including frequency metrology and bio-medical imaging.

Fiber-laser-based frequency comb with a tunable repetition rate.

A phase-locked, self-referenced frequency comb generated by a mode-locked fiber soliton laser with a tunable repetition rate is presented. The spacing of the frequency comb is set by the laser's repetition rate, which can be scanned from 49.3 MHz to 50.1 MHz while one tooth of the comb is held phase-locked to a stable RF source. This variable repetitionrate frequency comb should be useful for wavelength and length metrology, synchronization of different fiber laser-based frequency combs, and the generation of precise swept wavelength sources.

Handwriting: current trends in occupational therapy practice.

The objective of this survey was to describe assessment and treatment approaches commonly used by occupational therapists for children exhibiting handwriting and related fine motor difficulties. Secondarily, the application of weights as a treatment modality was also explored. Fifty experienced paediatric occupational therapists from Ontario (46%), Quebec (22%) and six other Canadian provinces, were surveyed by telephone. The majority of therapists indicated that they evaluated gross/fine motor and perceptual skills, motor planning, quality of movement and sensory functioning for this population, while psychosocial and environmental factors were often not formally evaluated. Evaluations most commonly utilized included the Beery, Bruininks-Oseretsky and Gardner Tests. Standardized handwriting assessments were rarely employed. All used an eclectic treatment approach with sensorimotor most frequently selected (90%). Work setting and years of experience did not influence the treatment approach favoured.

Arthroscopic evaluation of the subtalar joint: does sinus tarsi syndrome exist?

This is a retrospective review of 49 subtalar arthroscopies performed between 1989 and 1996. Patients were evaluated in the following areas: (1) preoperative diagnosis, (2) preoperative tests and clinical evaluation, (3) intraoperative findings, (4) postoperative diagnosis,(5) complications, and (6) clinical outcome. Particular attention was paid to the accuracy of the preoperative diagnosis, subtalar instability, intraoperative findings in sinus tarsi syndrome, and clinical outcome. Overall, this study demonstrated a success rate of 94% good and excellent results in the treatment of various types of subtalar pathologic conditions with arthroscopic techniques. The Workers' Compensation cases reported 90% good and excellent results. The complication rate was low, with five minor complications reported. The most common complication was a transient neuropraxia involving branches of the superficial peroneal nerve. Of the 14 feet that had a preoperative diagnosis of sinus tarsi syndrome, all the diagnoses were changed at the time of arthroscopy. The postoperative diagnoses included 10 interosseous ligament tears, two cases of arthrofibrosis, and two degenerative joints. Based on these findings, "sinus tarsi syndrome" seems to be an inaccurate term that should be replaced with a specific diagnosis. Arthroscopy is the tool that will allow the orthopaedic surgeon to make a more accurate diagnosis.

A comparison of MRI and clinical examination of acute lateral ankle sprains.

Because of its excellent soft tissue contrast and ability to demonstrate soft tissue structures, magnetic resonance imaging is ideally suited to the evaluation of the soft tissues surrounding the ankle, including the lateral collateral ligaments. This study was undertaken to compare the clinical evaluation of 15 patients who suffered inversion injuries of the ankle with the results found on magnetic resonance imaging within 48 hours of the injury. Physical examination was found to be 100% accurate in the diagnosis of grade III ligament injuries but only 25% accurate in the diagnosis of grade II injuries. Clinicians most often underestimate the damage with a grade II ligament tear. Furthermore, other associated injuries, such as significant capsule ruptures and tendon damage, were often overlooked at physical examination.

Plantarflexion injury to the metatarsophalangeal joint ("sand toe").

This is a retrospective study of 12 cases of hyperplantarflexion injuries to the great toe and the lesser toes sustained in professional beach volleyball players. The hyperplantarflexion injury to the metatarsophalangeal joint, referred to as "sand toe," can result in significant functional disability. Push-off, forward drive, running, and jumping are compromised. The average player in this series took 6 months to fully recover from the injury, and the most common problem after injury was the loss of dorsiflexion, seen in six players. Five players had residual discomfort in the injured toe, and two demonstrated an unstable toe. Individuals who experience sand toe injuries should be treated conservatively, with taping, anti-inflammatory medications, shoe wear modification, ice, and rest. A toe strengthening program is also presented.

Arthroscopy of the subtalar joint.

The purpose of this study was to determine the position and relative safety of the anterior, posterior, and newly defined middle portals by measuring their distance from the neurovascular structures and tendons on the lateral side of the foot and ankle. Furthermore, this study demonstrates specific components of the posterior subtalar joint and arthroscopic access to each utilizing a technique that allows direct anatomic correlation. The 15 specimens were divided into three groups of five feet each, with one arthroscopic portal site and one instrumentation portal site per group. Group I used the anterior portal for the arthroscope and the posterior portal for the curette. Group II used the posterior portal for the arthroscope and the anterior portal for the curette. In group III, the arthroscope was inserted through the anterior portal and the curette through the middle portal. The sural nerve and small saphenous vein were at risk with posterior portal placement. The anterior portal presented a minor risk of injury to the dorsal intermediate cutaneous branch of the superficial peroneal nerve. The middle portal was without risk to surrounding structures. Group I provided the best access to the posterior facet of the subtalar joint. Group II provided excellent arthroscopic visualization of the posterior facet, but poor access for instrumentation via the anterior portal. Group III provided the best access to the sinus tarsi. No combination of portals allowed visualization or instrumentation of the middle or anterior facets.

Ankle arthroscopy: review and long-term results.

Ankle arthroscopy has evolved over the past decade as a diagnostic and an operative modality. Forty ankle arthroscopies were performed by the senior author (G.J.S.) for osteochondral fractures, chronic sprains unresponsive to conservative treatment, posttraumatic osteoarthritis, adhesions, locking, instability, synovitis, and ankle disability of undetermined cause. Thirty cases with at least 24 months of follow-up were reviewed. Complications occurred in two patients: reflex sympathetic dystrophy and a fibular fracture. Postoperatively, the patients were rated clinically as having 13% excellent, 60% good, 17% fair, and 10% poor results. However, 95% of the patients stated that they would undergo the same operation again if needed. Results were significantly better in those patients who had chondral or osteochondral defects as the diagnosis, and in noncompensation cases.