We characterize an approach to make ultra-low-loss waveguides using stable and reproducible stoichiometric Si3N4 deposited with low-pressure chemical vapor deposition. Using a high-aspect-ratio core geometry, record low losses of 8-9 dB/m for a 0.5 mm bend radius down to 3 dB/m for a 2 mm bend radius are measured with ring resonator and optical frequency domain reflectometry techniques. From a waveguide loss model that agrees well with experimental results, we project that 0.1 dB/m total propagation loss is achievable at a 7 mm bend radius with this approach.

/pdf/ultra-low-loss-high-aspect-ratio-si3n4-waveguides-221dhugo3c.pdf

Ultra-low-loss high-aspect-ratio Si3N4 waveguides.

This paper describes the theory of a microfiber loop resonator (MLR) and experimentally demonstrates a high quality factor MLR in free space. The MLR is fabricated from the ∼ 1-μm diameter waist of a biconical fiber taper using the CO 2 laser indirect heating technique. The high coupling efficiency of an MLR is achieved through an adiabatically slow variation of the microfiber diameter in the coupling region. An MLR-loaded Q-factor of120 000 and an intrinsic Q-factor of 630 000 were demonstrated. As an application, the performance of an MLR as an ultrafast direct contact temperature sensor is also demonstrated. The MLR heating/cooling relaxation time was measured to be ∼ 3 μs, in good agreement with the developed theory.

The microfiber loop resonator : Theory, experiment, and application

This paper describes the theory of a microfiber loop resonator (MLR) and experimentally demonstrates a high quality factor MLR in free space. The MLR is fabricated from the /spl sim/1-/spl mu/m diameter waist of a biconical fiber taper using the CO/sub 2/ laser indirect heating technique. The high coupling efficiency of an MLR is achieved through an adiabatically slow variation of the microfiber diameter in the coupling region. An MLR-loaded Q-factor of 120 000 and an intrinsic Q-factor of 630 000 were demonstrated. As an application, the performance of an MLR as an ultrafast direct contact temperature sensor is also demonstrated. The MLR heating/cooling relaxation time was measured to be /spl sim/3 /spl mu/s, in good agreement with the developed theory.

The microfiber loop resonator: theory, experiment, and application

Planar waveguides with ultra-low optical propagation loss enable a plethora of passive photonic integrated circuits, such as splitters and combiners, filters, delay lines, and components for advanced modulation formats. An overview is presented of the status of the field of ultra-low loss waveguides and circuits, including the design, the trade-off between bend radius and loss, and fabrication rationale. The characterization methods to accurately measure such waveguides are discussed. Some typical examples of device and circuit applications are presented. An even wider range of applications becomes possible with the integration of active devices, such as lasers, amplifiers, modulators and photodetectors, on such an ultra-low loss waveguide platform. A summary of efforts to integrate silicon nitride and silica-based low-loss waveguides with silicon and III/V based photonics, either hybridly or heterogeneously, will be presented. The approach to combine these integration technologies heterogeneously on a single silicon substrate is discussed and an application example of a high-bandwidth receiver is shown.

Ultra‐low loss waveguide platform and its integration with silicon photonics

A transverse closed-loop fiber resonator (10) includes an inner cladding (102) having a surface (300) peripherally forming a closed-loop shape for confining light to the surface (300). The inner cladding has a first diameter thickness (104) and a first index of refraction profile in a cross-sectional portion of the transverse closed-loop fiber resonator (10). A ringed-core (120) corresponding to the closed-loop shape is disposed on the corresponding surface of the inner cladding (102). The ringed-core (120) has a second thickness (124) of material thinner than the first diameter thickness (104), and a second index of refraction profile greater than the first index of the inner cladding by an index delta in the cross-sectional portion of the transverse closed-loop fiber resonator such that the ringed-core can guide light within the ringed-core traversely around the closed-loop shape.

Transverse closed-loop resonator

Ring resonators (RRs) with a round-trip loss below 0.1 dB and a maximum free-spectral range (FSR) of 62.7 GHz were successfully fabricated. Single-mode waveguides of essentially square cross sections (/spl sim/2.6 /spl times/ 2.8 /spl mu/m/sup 2/) were patterned through reactive ion etching on a core layer of high Ge content doped silica deposited using plasma-enhanced chemical vapor deposition; they received a silica overclad. A propagation loss of 0.085 dB/cm was recorded for these waveguides. We strongly believe that our technology makes it possible to fabricate equally ultralow-loss RRs of even smaller bending radius, reaching an FSR of 100 GHz, thus opening the way to the design of filters for wavelength-division-multiplexing systems.

Ultralow loss ring resonators using 3.5% index-contrast Ge-doped silica waveguides

A plasma enhanced chemical vapor deposition process was developed to deposit SiO 2 -GeO 2 films suitable for high index contrast planar waveguides. These films were deposited in a standard parallel plate reactor from silane, germane, nitrous oxide, and a nitrogen carrier. The germania content of the film was equal to the mole fraction germane of the hydride precursors in the gas stream, and the refractive index of the film varied linearly with the mole fraction of germania. Low loss guides ranging from 1.5-4.0% Δ were fabricated. With standard photolithographic patterning, a 0.05 dB/cm propagation loss and minimum bend radius of 1.5 mm were measured for 2.0% A. Improvements to the photolithographic patterning to reduce sidewall roughness were required to achieve low propagation loss at higher Δ. This reduced the propagation loss for 3.5% Δ cores to 0.086 dB/cm. An average minimum bend radius of 570 μm was measured for 3.5% A, but modeling suggests the bend radius could be reduced below 500 μm with offsets to reduce transition loss. Ring resonator, fabricated from 3.5% A waveguides, exhibited a free spectral range as large as 62.7 GHz and a very low round trip insertion loss of 0.06 dB.

Ultralow Loss High Delta Silica Germania Planar Waveguides

We present a 3.5% index contrast Ge-doped silica planar technology with a propagation loss /spl les/0.10 dB/cm. This technology was used to fabricate ring resonators with a round-trip loss of 0.03 dB and a maximum FSR of 62.7 GHz.

E. Guiot

Papers

Ultralow loss ring resonators using 3.5% index-contrast Ge-doped silica waveguides

Ultralow Loss High Delta Silica Germania Planar Waveguides

High-index contrast Ge-doped silica waveguide technology: optical performance and application to ultralow-loss ring resonators