Hyperband electro-optic modulator based on a two-pulley coupled lithium niobate racetrack resonator.

Integrated optical modulators (IOMs) are crucial components of on-chip photonic circuits. However, most conventional IOMs are restricted to specific spectral bands. Here, we leveraged the wide transparency window of lithium niobate in conjunction with the two-pulley coupled resonator method. This approach led to the development of a hyperband electro-optic (EO) modulator that operates over an expansive spectral range from 775 to 1550 nm on a single device. The demonstrated EO modulator exhibits half-wave voltage-length products of 0.25, 0.93, and 0.68 V·cm at wavelengths of 1539.50, 969.70, and 775.17 nm, respectively.

Sub-10 nm Precision Engineering of Solid-State Defects via Nanoscale Aperture Array Mask.

Engineering a strongly interacting uniform qubit cluster would be a major step toward realizing a scalable quantum system for quantum sensing and a node-based qubit register. For a solid-state system that uses a defect as a qubit, various methods to precisely position defects have been developed, yet the large-scale fabrication of qubits within the strong coupling regime at room temperature continues to be a challenge. In this work, we generate nitrogen vacancy (NV) color centers in diamond with sub-10 nm scale precision using a combination of nanoscale aperture arrays (NAAs) with a high aspect ratio of 10 and a secondary E-beam hole pattern used as an ion-blocking mask. We perform optical and spin measurements on a cluster of NV spins and statistically investigate the effect of the NAAs during an ion-implantation process. We discuss how this technique is effective for constructing a scalable system.

Plug-and-play QKD architecture with a self-optical pulse train generator.

The commercialization of quantum key distribution (QKD), which enables secure communication even in the era of quantum computers, has acquired significant interest. In particular, plug-and-play (PnP) QKD has garnered considerable attention owing to its advantage in system stabilization. However, a PnP QKD system has limitations on miniaturization owing to a bulky storage line (SL) of tens of kilometers. And, the secure key rate is relatively low because Bob transmits the signal pulses only at the dedicated time slots to circumvent backscattering noise. This study proposes a new method that can eliminate the SL by realizing an optical pulse train generator based on an optical cavity structure. Our method allows Alice to generate optical pulse trains herself by duplicating Bob's seed pulse and excludes the need for Bob's strong signal pulses that trigger backscattering noise as much as the conventional PnP QKD. Accordingly, our method can naturally overcome the miniaturization limitation and the slow secure key rate, as the storage line is no longer necessary. We conducted a proof-of-concept experiment using our method and achieved a key generation rate of 1.6×10-3 count/pulse and quantum bit error rate ≤ 5%.

Electro-optic control of the external coupling strength of a high-quality-factor lithium niobate micro-resonator.

Controlling the optical coupling between a micro-resonator and waveguide plays a key role in on-chip photonic circuits. Here, we demonstrate a two-point coupled lithium niobate (LN) racetrack micro-resonator that enables us to electro-optically traverse a full set of the zero-, under-, critical-, and over-coupling regimes with minimized disturbance of the intrinsic properties of the resonant mode. The modulation between the zero- and critical-coupling conditions cost a resonant frequency shift of only ∼344.2 MHz and rarely changed the intrinsic quality (Q) factor of 4.6 × 105. Our device is a promising element in on-chip coherent photon storage/retrieval and its applications.

Diamond photonic crystal mirror with a partial bandgap by two 2D photonic crystal layers.

In this study, photonic crystals with a partial bandgap are demonstrated in the visible region using single-crystal diamonds. Quasi-three-dimensional photonic crystal structures are fabricated in the surface of the single-crystal diamonds using a tetrahedron Faraday cage that enables angled dry etching in three directions simultaneously. The reflection spectra can be controlled by varying the lattice constant of the photonic crystals. In addition, nitrogen-vacancy center single-photon sources are implanted on top of the diamond photonic crystals, and doubled collection efficiency from the light sources is achieved.

Reference-frame-independent, measurement-device-independent quantum key distribution using fewer quantum states.

Reference-frame-independent quantum key distribution (RFI-QKD) provides a practical way to generate secret keys between two remote parties without sharing common reference frames. On the other hand, measurement-device-independent QKD (MDI-QKD) offers a high level of security, as it is immune to all quantum hacking attempts to measurement devices. The combination of these two QKD protocols, i.e., RFI-MDI-QKD, is one of the most fascinating QKD protocols, since it holds advantages of both practicality and security. For further practicality of RFI-MDI-QKD, it is beneficial to reduce the implementation complexity. Here, we show that RFI-MDI-QKD can be implemented using fewer quantum states than those of its original proposal. We find that, in principle, the number of quantum states for one of the parties can be reduced from six to three without compromising security. Compared to conventional RFI-MDI-QKD where both parties transmit six quantum states, it significantly simplifies the implementation of the QKD protocol. We also verify the feasibility of the scheme with a proof-of-principle experiment.

Stokes and anti-Stokes Raman scatterings from frequency comb lines in poly-crystalline aluminum nitride microring resonators.

In optical microresonators, stimulated Raman scattering (SRS) competes with four-wave mixing process and impact Kerr comb generation. Here, we demonstrate Raman frequency combs in poly-crystalline aluminum nitride (AlN) microring resonators. The Raman shifts at transverse-electric (TE) and transverse-magnetic (TM) polarizations are characterized from AlN straight waveguides using backscattering geometries. In poly-crystalline AlN microring resonators, the frequency matching of cavity resonances with broad Raman gain enhances the SRS and leads to Raman-assisted frequency combs. As a result, comb lines near Raman scattering regions of AlN are generated.

High sensitivity temperature measurement via mask-free hybrid polymer long period fiber grating.

Long-period fiber gratings (LPFGs) are useful for environmental sensing under conditions of high corrosiveness and electromagnetic interference. Most LPFGs are fabricated by coherent or high-power UV illumination of an optical fiber under an amplitude mask, resulting in narrow and environmentally-dependent band rejection. We present a hybrid LPFG waveguide fabricated without an amplitude mask through polymer self-assembly under low-power incoherent UV illumination, which demonstrates high-temperature sensitivity in its transmission spectrum compared to LPFG sensors based purely on silica waveguides. A sensitivity of 1.5 nm °C -1 is obtained experimentally for attenuation near 1180 nm, and a sensitivity of 4.5 nm °C -1 with a low random error was obtained with a composite of attenuation bands. Finite element method simulations and coupling mode theory reveal this to be due to a thermo-optic coefficient one order of magnitude greater than that of fused silica. The device has potential for a simple and inexpensive transmission intensity based temperature sensor consisting of an infrared light source, the LPFG, a bandpass filter, and a photodiode.

High-fidelity cavity soliton generation in crystalline AlN micro-ring resonators.

Chip-scale mode-locked dissipative Kerr solitons have been realized on various materials platforms, making it possible to achieve a miniature, highly coherent frequency comb source with high repetition rates. Aluminum nitride (AlN), an appealing nonlinear optical material having both Kerr (χ3), and Pockels (χ2) effects, has immerse potential for comb self-referencing without the need for external harmonic generators. However, cavity soliton states have not yet been achieved in AlN microresonators. Here, we demonstrate mode-locked Kerr cavity soliton generation in a crystalline AlN microring resonator. By utilizing ultrafast tuning of the pump frequency through single-sideband modulation, in combination with an optimized wavelength scan and pump power-ramp patterns, we can deterministically elongate a ∼400 ns short-lived soliton to a time span as long as we wish to hold it.

Deuterated silicon nitride photonic devices for broadband optical frequency comb generation.

We report and characterize low-temperature, plasma-deposited deuterated silicon nitride films for nonlinear integrated photonics. With a peak processing temperature less than 300°C, it is back-end compatible with complementary metal-oxide semiconductor substrates. We achieve microresonators with a quality factor of up to 1.6×106 at 1552 nm and >1.2×106 throughout λ=1510-1600 nm, without annealing or stress management (film thickness of 920 nm). We then demonstrate the immediate utility of this platform in nonlinear photonics by generating a 1 THz free-spectral-range, 900 nm bandwidth modulation-instability microresonator Kerr comb and octave-spanning, supercontinuum-broadened spectra.

Influence of soft tissue balancing and distal femoral resection on flexion contracture in navigated total knee arthroplasty.

PURPOSE: The purpose of this study was to evaluate the influence of intra-operative soft tissue balancing and distal femoral cutting on flexion contracture in navigated TKA. METHODS: This was a prospective cohort study. Fifty-nine patients of primary navigation-assisted TKA were included with over 15° of flexion contracture and excluded valgus knees. Among the cases, 43 cases were performed with soft tissue balancing procedures only, and 16 cases were performed with soft tissue balancing and additional distal femoral bone cutting. The mean preoperative flexion contracture was 17.5° ± 2.7°. The angles of flexion contracture were recorded at each surgical step with navigation. RESULTS: The mean difference in flexion contracture angle between initial angle and angle after medial release was 5.2° ± 2.8°. The mean difference in flexion contracture angle between medial release step and after posterior cruciate ligament (PCL) release was 2.5° ± 2.2°. The mean difference in flexion contracture angle between PCL release step and after routine bone cutting was 3.1° ± 3.2°. The mean difference in flexion contracture angle between after trial insertion and after posterior clearing procedure was 2.7° ± 1.9°. Among the cases, TKA with 2 mm additional bone cutting were performed in 16 cases. The mean difference in flexion contracture angle after additional femoral bone cutting was 4.8° ± 2.1°. CONCLUSION: The medial release and 2 mm additional bone cutting could correct flexion contracture by 5°. The appropriate soft tissue balancing and bone cutting could correct flexion contracture intra-operatively up to 5° in each step. LEVEL OF EVIDENCE: II.

Phase-dependent interference between frequency doubled comb lines in a χ(2) phase-matched aluminum nitride microring.

Nonlinear optical conversion with frequency combs is important for self-referencing and for generating shorter wavelength combs. Here we demonstrate efficient frequency comb doubling through the combination of second-harmonic generation (SHG) and sum-frequency generation (SFG) of an input comb with a high Q, phase-matched χ(2) microring resonator. Phase coherence of the SHG and SFG nonlinear conversion processes is confirmed by sinusoidal phase-dependent interference between frequency doubled comb lines.

On-Chip Strong Coupling and Efficient Frequency Conversion between Telecom and Visible Optical Modes.

While the frequency conversion of photons has been realized with various approaches, the realization of strong coupling between optical modes of different colors has never been reported. Here, we present an experimental demonstration of strong coupling between telecom (1550 nm) and visible (775 nm) optical modes on an aluminum nitride photonic chip. The nonreciprocal normal-mode splitting is demonstrated as a result of the coherent interference between photons with different colors. Furthermore, a wideband, bidirectional frequency conversion with 0.14 on-chip conversion efficiency and a bandwidth up to 1.2 GHz is demonstrated.

In-resonator variation of waveguide cross-sections for dispersion control of aluminum nitride micro-rings.

We propose and demonstrate a dispersion control technique by combination of different waveguide cross sections in an aluminum nitride micro-ring resonator. Narrow and wide waveguides with normal and anomalous dispersion, respectively, are linked with tapering waveguides and enclosed in a ring resonator to produce a total dispersion near zero. The mode-coupling in multimoded waveguides is also effectively suppressed. This technique provides new degrees of freedom and enhanced flexibility in engineering the dispersion of microcomb resonators.

Electrical tuning and switching of an optical frequency comb generated in aluminum nitride microring resonators.

Aluminum nitride (AlN) has been shown to possess both strong Kerr nonlinearity and electro-optic Pockels effect. By combining these two effects, here we demonstrate on-chip reversible on/off switching of the optical frequency comb generated by an AlN microring resonator. We optimize the design of gating electrodes and the underneath resonator structure to effectively apply an electric field without increasing the optical loss. The switching of the comb is monitored by measuring one of the frequency comb peaks while varying the electric field. The controlled comb electro-optic response is investigated for direct comparison with the transient thermal effect.

Second-look arthroscopy after surgical treatment of Schatzker type II plateau fractures through the lateral submeniscal approach.

MAIN PROBLEM: To evaluate cartilage healing using second-look arthroscopic examination in tibia plateau fracture patients who have undergone open reduction and internal fixation with a submeniscal approach technique. METHODS: Between January 2007 and January 2010, we used second-look arthroscopy during 18-24-month follow-up of 20 patients with Schatzkar type II tibial plateau fractures who had undergone open reduction and internal fixation with a submeniscal approach technique. We classified patients according to step-off, knee range of motion, and Knee Society Score, and compared the results with those obtained by arthroscopy. RESULTS: Radiologically, 16 cases (80 %) were reduced within 2 mm of step-off. In 11 of these cases, according to the Outerbridge classification, we checked for chondromalacia from grade II to III. We observed 2 mm of step-off in four cases, and each had chondromalacia of at least grade III. The Knee Society Score was associated with chondromalacia grade (p < 0.05). CONCLUSION: Even in patients with normal joint range of motion and good clinical and radiological results, the actual condition of the articular cartilage varied significantly. Therefore, more long-term and regular follow-up is needed for proximal plateau fractures.

Optical frequency comb generation from aluminum nitride microring resonator.

Aluminum nitride (AlN) is an appealing nonlinear optical material for on-chip wavelength conversion. Here we report optical frequency comb generation from high-quality-factor AlN microring resonators integrated on silicon substrates. By engineering the waveguide structure to achieve near-zero dispersion at telecommunication wavelengths and optimizing the phase matching for four-wave mixing, frequency combs are generated with a single-wavelength continuous-wave pump laser. Further, the Kerr coefficient (n2) of AlN is extracted from our experimental results.

Less femoral lift-off and better femoral alignment in TKA using computer-assisted surgery.

PURPOSE: A comparison has been made between navigation-assisted and conventional measured resection total knee arthroplasty (TKA), under the hypothesis that navigation assistance would improve the precision and consistency of component alignment and femoral component rotation. METHODS: The following radiographic parameters were measured: mechanical femorotibial angle, coronal and sagittal component angle, and femoral component rotation. Femoral condylar lift-off was checked by axial radiographs, and thresholds for outliers were set at 1.0 mm. RESULTS: Clinical results obtained using Knee Society and Hospital for Special Surgery systems were not statistically different. The mean mechanical femorotibial angle was 2.2° (SD: 0.9) in the conventional group and 1.7° (SD: 0.7) in navigation group (p = 0.001). The mean coronal femoral component angle was 89.2° (SD: 2.2) in conventional group and 90.4° (SD: 1.8) in navigation group (p = 0.006). The mean transepicondylar-posterior condylar axis angle was 1.7° (SD: 0.9) in conventional group and 1.2° (SD: 0.5) in navigation group (p = 0.008). Femoral condylar lift-off greater than 1 mm occurred more frequently (p = 0.000) in conventional group. CONCLUSION: Coronal plane stability and precision of femoral component rotation were impacted by navigation system. The use of a navigation system with measured resection TKA can help optimize coronal stability and parallel component position. LEVEL OF EVIDENCE: Retrospective case control study, Level IV.

The isometry of two different paths for remnant-preserving posterior cruciate ligament reconstruction.

PURPOSE: It is reported that the length of the posterior cruciate ligament (PCL) fibres increases as the knee flexes, and the magnitude of the length change reaches up to 9.8 mm throughout the range of motion, which exceeds the range of failure strain. Therefore, we postulated that a compensatory mechanism must be recruited to overcome this large strain in order to maintain physiologic function as a key component of joint kinematics. Our main objective was to compare the length change pattern for the linear distance between the femoral and tibial tunnels with the length change patterns derived from a real isometer test of different curvatures. METHODS: We utilized ten intact cadaveric knees and created a vertical femoral tunnel (5 mm medial to the roof of the intercondylar notch and 5 mm proximal from the articular margin) and lateral tibial tunnels (5 mm proximal to the posterior bony ridge on the lateral side of the PCL fibre) and performed a 3D-CT scan at 0º, 30º, 60º, 90º, and 120º. The distances between the femoral and tibial tunnels were calculated from the 3D coordinates. Real isometry was checked both (1) over the PCL and (2) under the PCL using an isometer with an accuracy of 0.1 mm. RESULTS: The path over the PCL had the longest intra-articular length, followed by the path under the PCL, and the lengths measured by CT, respectively. The path over the PCL had a more curved path compared with the path under the PCL and the lengths measured by CT. The lengths measured by CT showed significantly larger excursion than the real isometer test. The path over the PCL showed the least excursion through the range of motion, followed by the path under the PCL, and the lengths measured by CT, respectively. CONCLUSION: Our findings suggested that a more curved PCL path has better isometry because the curvature of the PCL compensates for the length change between 0º and 60º flexion. In remnant preservation PCL reconstruction, the passage of graft over the PCL would have increased intra-articular length and better isometry compared with straight under the PCL path. LEVEL OF EVIDENCE: Basic science study.

Evaluation of tunnel position of posterolateral corner reconstruction using 3-dimensional computed tomogram.

PURPOSE: To evaluate the isometry of different tunnel positions in posterolateral corner (PLC) reconstruction using 3-dimensional computed tomography. METHODS: In 10 fresh-frozen cadaveric knees, fibular tunnels were made from the anterodistal surface of the fibular neck to the posteroproximal fibular tip. Tibial tunnels were made from just medial to the Gerdy tubercle to a point 1 to 1.5 cm medial to the proximal tibiofibular joint. Femoral condyles were marked at 3 different locations: (1) epicondyle, (2) 5 mm distal-anterior to the epicondyle, and (3) 18 mm distal-anterior to the epicondyle. All specimens were scanned by computed tomography at different ranges of motion. Relative length changes between the tunnels were calculated by use of medical imaging software, and the center of rotation (COR) of each distal tunnel was obtained by use of a least-squares circle-fitting algorithm. RESULTS: The anterior fibular tunnel to lateral epicondyle and the posterior fibular or posterior tibial tunnel to 5 mm distal-anterior to the lateral epicondyle showed the best results in terms of isometry. The COR of the posterior fibular tunnel is distal and anterior to the epicondyle, whereas the COR of the posterior tibial tunnel is distal and slightly posterior to the epicondyle (8.4 mm away from the epicondyle, with a -8.4° angle along the longitudinal axis of the femur). The COR of the anterior fibular tunnel is located posterior and distal to the epicondyle. CONCLUSIONS: Contrary to our hypothesis, the distal tunnels for PLC reconstruction each have different isometric points. The isometric point of the posterior fibular tunnel is distal and anterior to the epicondyle, whereas the isometric points of the posterior tibial and anterior fibular tunnels are distal and posterior to the epicondyle. CLINICAL RELEVANCE: The isometric pattern of each tunnel combination should be considered in PLC reconstruction; currently, popliteus tendon reconstruction is non-isometric.