Optical frequency averaging of light.

The use of averaging has long been known to reduce noise in statistically independent systems that exhibit similar levels of stochastic fluctuation. This concept of averaging is general and applies to a wide variety of physical and man-made phenomena such as particle motion, shot noise, atomic clock stability, measurement uncertainty reduction, and methods of signal processing. Despite its prevalence in use for reducing statistical uncertainty, such averaging techniques so far remain comparatively undeveloped for application to light. We demonstrate here a method for averaging the frequency uncertainty of identical laser systems as a means to narrow the spectral linewidth of the resulting radiation. We experimentally achieve a reduction of frequency fluctuations from 40 Hz to 28 Hz by averaging two separate laser systems each locked to a fiber resonator. Only a single seed laser is necessary here as acousto-optic modulation is used to enable independent control of the second path. This technique of frequency averaging provides an effective solution to overcome the linewidth constraints of a single laser alone, particularly when limited by fundamental noise sources such as thermal noise, irrespective of the spectral shape of noise.

Cooling of an integrated Brillouin laser below the thermal limit.

Photonically integrated resonators are promising as a platform for enabling ultranarrow linewidth lasers in a compact form factor. Owing to their small size, these integrated resonators suffer from thermal noise that limits the frequency stability of the optical mode to ∼100 kHz. Here, we demonstrate an integrated stimulated Brillouin scattering (SBS) laser based on a large mode-volume annulus resonator that realizes an ultranarrow thermal-noise-limited linewidth of 270 Hz. In practice, yet narrower linewidths are required before integrated lasers can be truly useful for applications such as optical atomic clocks, quantum computing, gravitational wave detection, and precision spectroscopy. To this end, we employ a thermorefractive noise suppression technique utilizing an auxiliary laser to reduce our SBS laser linewidth to 70 Hz. This demonstration showcases the possibility of stabilizing the thermal motion of even the narrowest linewidth chip lasers to below 100 Hz, thereby opening the door to making integrated microresonators practical for the most demanding future scientific endeavors.

Impact of laser frequency noise on high-extinction optical modulation.

In present literature on integrated modulation and filtering, limitations in the extinction ratio are dominantly attributed to a combination of imbalance in interfering wave amplitude, instability of control signals, stray light (e.g., in the cladding), or amplified spontaneous emission from optical amplifiers. Here we show that the existence of optical frequency noise in single longitudinal mode lasers presents an additional limit to the extinction ratio of optical modulators. A simple frequency-domain model is used to describe a linear optical system's response in the presence of frequency noise, and an intuitive picture is given for systems with arbitrary sampling time. Understanding the influence of frequency noise will help guide the design choices of device and system engineers and offer a path toward even higher-extinction optical modulators.

Operation of an optical atomic clock with a Brillouin laser subsystem.

Microwave atomic clocks have traditionally served as the 'gold standard' for precision measurements of time and frequency. However, over the past decade, optical atomic clocks1-6 have surpassed the precision of their microwave counterparts by two orders of magnitude or more. Extant optical clocks occupy volumes of more than one cubic metre, and it is a substantial challenge to enable these clocks to operate in field environments, which requires the ruggedization and miniaturization of the atomic reference and clock laser along with their supporting lasers and electronics4,7,8,9. In terms of the clock laser, prior laboratory demonstrations of optical clocks have relied on the exceptional performance gained through stabilization using bulk cavities, which unfortunately necessitates the use of vacuum and also renders the laser susceptible to vibration-induced noise. Here, using a stimulated Brillouin scattering laser subsystem that has a reduced cavity volume and operates without vacuum, we demonstrate a promising component of a portable optical atomic clock architecture. We interrogate a 88Sr+ ion with our stimulated Brillouin scattering laser and achieve a clock exhibiting short-term stability of 3.9 × 10-14 over one second-an improvement of an order of magnitude over state-of-the-art microwave clocks. This performance increase within a potentially portable system presents a compelling avenue for substantially improving existing technology, such as the global positioning system, and also for enabling the exploration of topics such as geodetic measurements of the Earth, searches for dark matter and investigations into possible long-term variations of fundamental physics constants10-12.

Clinical practice algorithm for Eaton's injury of the thumb.

Trapeziometacarpal joint instability is a well-recognised but under-diagnosed cause of basal thumb pain. A systematic approach with sound understanding of anatomy and clinico-pathological correlation is required to make a diagnosis. We discuss an overview of the principles of diagnosis and management of basal thumb joint instability. An evaluation algorithm for Eaton's injury of the thumb is proposed for clinical application with evidence in literature.

Strategies in reconfiguration of hand injuries management during COVID-19 pandemic.

During the COVID-19 pandemic there has been a re-organisation of care provided by the Trauma and Orthopaedic services in the United Kingdom. The National Health Service England (NHSE) speciality guide forms the primary responses to this pandemic, whilst British Society for the Surgery of Hand (BSSH) provides sub-specialty guidance on management of hand trauma. The orthopaedic community's responsibility of providing a continuity of care for patients has to be balanced with measures to reduce risk of viral transmission (e.g. reduce face to face consultations) and also protect ion of both the patients and staff. We highlight the strategies applied whilst reconfiguration of hand injury management following publication of COVID-19 British Society for the Surgery of Hand and Indian Orthopaedic Association (IOA) guidelines.

Modified Eaton-Littler's Reconstruction for Traumatic Thumb Carpometacarpal Joint Instability: Operative Technique and Clinical Outcomes.

Background Injuries to thumb carpometacarpal joint ligaments lead to instability. Eaton-Littler's ligament reconstruction traditionally uses a strip of flexor carpi radialis to stabilize the CMC joint. Study Description We have modified this technique to reproduce the direction of active action of the anterior oblique ligament by reconstructing both the volar and dorsoradial ligaments. In this prospective study, we evaluated patients with confirmed traumatic thumb CMC joint instability who underwent modified Eaton-Littler's reconstruction. Strength analysis, Michigan Hand Outcome Questionnaire, QuickDASH, and subjective outcome measures were collected pre- and postoperatively with minimum 3 years of follow-up. Eleven patients were included in the final analysis, with mean age of 29 years (range: 16-52) and average follow-up of 6.2 years (range: 3-11). There was a statistically significant improvement in all outcome measures. Clinical Relevance Our modified technique helps to simultaneously address both volar and dorsal ligaments and yields satisfactory clinical outcomes at medium term follow-up. Level of Evidence Level IV, case series.

Optical unmasking of spectrally overlapping RF signals.

When two signals having overlapping frequency content are received at the same time, they interfere to obstruct detection of the information carried by each individual signal. We introduce here a new nonlinear optoelectronic filtering technique that enables the ability to individually detect two concurrent and spectrally overlapping signals, even when the amplitude ratio between the signals is as high as 100,000. We demonstrate our system for application in steganography where we unveil the information carried by a hidden desired RF signal, while a dominant interferer signal is intentionally transmitted nearby and at the same frequency. Our signal recovery technique, which operates assuming no a priori knowledge of either signal, presents an additional pathway that can be used to control how information can be processed and communicated.

Microresonator Brillouin laser stabilization using a microfabricated rubidium cell.

We frequency stabilize the output of a miniature stimulated Brillouin scattering (SBS) laser to rubidium atoms in a microfabricated cell to realize a laser system with frequency stability at the 10-11 level over seven decades in averaging time. In addition, our system has the advantages of robustness, low cost and the potential for integration that would lead to still further miniaturization. The SBS laser operating at 1560 nm exhibits a spectral linewidth of 820 Hz, but its frequency drifts over a few MHz on the 1 hour timescale. By locking the second harmonic of the SBS laser to the Rb reference, we reduce this drift by a factor of 103 to the level of a few kHz over the course of an hour. For our combined SBS and Rb laser system, we measure a frequency noise of 4 × 104 Hz2/Hz at 10 Hz offset frequency which rapidly rolls off to a level of 0.2 Hz2/Hz at 100 kHz offset. The corresponding Allan deviation is ≤2 × 10-11 for averaging times spanning 10-4 to 103 s. By optically dividing the signal of the laser down to microwave frequencies, we generate an RF signal at 2 GHz with phase noise at the level of -76 dBc/Hz and -140 dBc/Hz at offset frequencies of 10 Hz and 10 kHz, respectively.

Phase steps and resonator detuning measurements in microresonator frequency combs.

Experiments and theoretical modelling yielded significant progress toward understanding of Kerr-effect induced optical frequency comb generation in microresonators. However, the simultaneous Kerr-mediated interaction of hundreds or thousands of optical comb frequencies with the same number of resonator modes leads to complicated nonlinear dynamics that are far from fully understood. An important prerequisite for modelling the comb formation process is the knowledge of phase and amplitude of the comb modes as well as the detuning from their respective microresonator modes. Here, we present comprehensive measurements that fully characterize optical microcomb states. We introduce a way of measuring resonator dispersion and detuning of comb modes in a hot resonator while generating an optical frequency comb. The presented phase measurements show unpredicted comb states with discrete π and π/2 steps in the comb phases that are not observed in conventional optical frequency combs.

A nonlinear optoelectronic filter for electronic signal processing.

The conversion of electrical signals into modulated optical waves and back into electrical signals provides the capacity for low-loss radio-frequency (RF) signal transfer over optical fiber. Here, we show that the unique properties of this microwave-photonic link also enable the manipulation of RF signals beyond what is possible in conventional systems. We achieve these capabilities by realizing a novel nonlinear filter, which acts to suppress a stronger RF signal in the presence of a weaker signal independent of their separation in frequency. Using this filter, we demonstrate a relative suppression of 56 dB for a stronger signal having a 1-GHz center frequency, uncovering the presence of otherwise undetectable weaker signals located as close as 3.5 Hz away. The capabilities of the optoelectronic filter break the conventional limits of signal detection, opening up new possibilities for radar and communication systems, and for the field of precision frequency metrology.

Modified Eaton-Littler's Reconstruction for Traumatic Dislocation of the Carpometacarpal Joint of the Thumb-A Case Report and Review of Literature.

Isolated traumatic dislocation of the carpometacarpal joint of the thumb is an uncommon injury. Left untreated, resulting mechanical instability of this joint interferes with normal function of the hand and can lead to articular degeneration of the joint. Most are amenable to closed reduction with or without supplementary pinning. We present a case of a 21 year old female patient with continual instability of the carpometacarpal joint of her right thumb, following closed reduction and pinning. Surgical stabilization was achieved by anterior oblique ligament reconstruction using a Modified Eaton- Littler's technique. At 1 year follow-up evaluation the patient was pain free with no clinico-radiological evidence of instability.

Low-noise RF-amplifier-free slab-coupled optical waveguide coupled optoelectronic oscillators: physics and operation.

We demonstrate a 10-GHz RF-amplifier-free slab-coupled optical waveguide coupled optoelectronic oscillator (SCOW-COEO) system operating with low phase-noise (<-115 dBc/Hz at 1 kHz offset) and large sidemode suppression (>70 dB measurement-limited). The optical pulses generated by the SCOW-COEO exhibit 26.8-ps pulse width (post compression) with a corresponding spectral bandwidth of 0.25 nm (1.8X transform-limited). We also investigate the mechanisms that limit the performance of the COEO. Our measurements indicate that degradation in the quality factor (Q) of the optical cavity significantly impacts COEO phase-noise through increases in the optical amplifier relative intensity noise (RIN).

Amplifier-free slab-coupled optical waveguide optoelectronic oscillator systems.

We demonstrate a free-running 3-GHz slab-coupled optical waveguide (SCOW) optoelectronic oscillator (OEO) with low phase-noise (<-120 dBc/Hz at 1-kHz offset) and ultra-low sidemode spurs. These sidemodes are indistinguishable from noise on a spectrum analyzer measurement (>88 dB down from carrier). The SCOW-OEO uses high-power low-noise SCOW components in a single-loop cavity employing 1.5-km delay. The noise properties of our SCOW external-cavity laser (SCOWECL) and SCOW photodiode (SCOWPD) are characterized and shown to be suitable for generation of high spectral purity microwave tones. Through comparisons made with SCOW-OEO topologies employing amplification, we observe the sidemode levels to be degraded by any amplifiers (optical or RF) introduced within the OEO cavity.

Bilateral recurrent wrist flexor tenosynovitis and rice body formation in a patient with sero-negative rheumatoid arthritis: A case report and review of literature.

INTRODUCTION: Rice body formation has been traditionally observed in the joint and tendon sheaths of patients with tuberculosis. Few case reports exist that describe rice body formation in patients with rheumatoid arthritis. We describe a case report of bilateral recurrent wrist flexor tenosynovitis with rice body formation in a patient with sero-negative rheumatoid arthritis. PRESENTATION OF CASE: This case report describes a 72 year old lady presenting with severe bilateral, flexor tenosynovitis of the wrists. Ultrasonography revealed significant echogenic fluid on the palmer aspect of wrist joint surrounding flexor tendons with intact neurovascular bundles and no bony erosion. Laboratory tests demonstrated elevated erythrocyte sedimentation rate (50 mm/h) and negative rheumatoid factor. A sequential subtotal flexor tenosynovectomy was carried out with decompression of the carpal tunnel. During the operation, multiple rice bodies among the flexor tendons with adherent synovitis were found. Histology revealed disrupted synovial tissue containing several areas of fibrinoid necrosis, bounded by a layer of vaguely pallisaded histiocytes but no epitheloid granulomata or germinal centre. A revision surgery with debulking of the fibro-osseous canal was undertaken following recurrence. The patient presently has complete resolution of symptoms at one year follow-up. DISCUSSION: The combined clinical, laboratory, ultrasound and histology findings of the patient indicated that the cause of the rice body formation was due to a sero-negative arthritis rather than tuberculosis. CONCLUSION: Rice body formation can be caused by sero-negative arthritis. Bilateral wrist flexor tensosynovitis can recur within five months of a previous synovectomy in a patient with sero-negative arthritis.

Primary septic arthritis of the acromio-clavicular joint: case report and review of literature.

Primary septic arthritis of the Acromio clavicular joint is an uncommon disorder and is rarely seen even in an immunocompromised individual. We report a case of primary septic arthritis of the acromio-clavicular (A-C) joint caused by Staphylococcus aureus without any predisposing factors. The patient was admitted with left shoulder pain, restricted movements and fever. Laboratory parameters showed high C-reactive protein, raised erythrocyte sedimentation rate and leucocytosis. Blood cultures were positive for Staphylococcus-aureus. Magnetic resonance imaging (MRI) using Gadolinium enhancement revealed marked effusion in the A-C joint. Aspiration from the A-C joint revealed a heavy growth of Staphylococcus-aureus. The patient was successfully treated with 8 weeks of appropriate antibiotics with complete resolution of infection and return to full function.

A novel and improved method of predicting hand grip strength in the adult Malaysian population.

Hand grip strength measurement is a recognized part of hand function assessment. The standard measurement using the Jamar dynamometer and comparing these results to the recommended normal values suggested by the manufacturers of the Jamar was questioned as these values were based on Western population. A study comparing a novel method of predicting grip strength using our software was conducted on 25 normal subjects using the LIDO kinetic workset (Group A and B ). These results were then compared against our predictive software (Group A) and the expected values supplied together with the Jamar Dynamometer (Group B). In another group, 22 normal subjects were tested using the Jamar (Group C and D) and then matched against the predicted values using their recommended chart (Group C). The last group (Group D) was tested using the Jamar but the values attained were compared to the results from our software. In group A, the predictability of our predictive method was 100% (both R & L) as compared to (R = 64%, L = 68%) in group B, (R = 27.3%, L = 59.1%) in group C and (R = 81.8%, L = 86.4%) in group D. The differences between the predictability of both methods were statistically significant. The data collected using both the Jamar and the LIDO kinetic workset correlated well to the data from our software but not to the values suggested by the manufacturers of Jamar. We conclude that our method of predicting hand grip values are superior to that suggested by the manufacturers of dynamometers. The standard reference for hand grip strength provided by the manufacturers is less accurate in predicting the grip strength of our local population.