Squeezed light from a diamond-turned monolithic cavity
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2016-02-19 |
| Journal | Optics Express |
| Authors | Alexandre Brieussel, Yong Shen, Geoff Campbell, Giovanni Guccione, JiĆĂ JanouĆĄek |
| Institutions | Tianjin University, University of Rostock |
| Citations | 8 |
| Analysis | Full AI Review Included |
Squeezed Light Generation: Material Analysis and Optimization using MPCVD Diamond
Section titled âSqueezed Light Generation: Material Analysis and Optimization using MPCVD DiamondâExecutive Summary
Section titled âExecutive SummaryâThis document analyzes a breakthrough application of precision diamond turning to create highly stable, compact monolithic optical parametric oscillators (OPOs) for squeezed light generation. The analysis highlights the limitations inherent in the incumbent material (Lithium Niobate) and outlines how 6CCVDâs expertise in high-purity MPCVD diamond (SCD) and ultra-precision polishing directly addresses these performance bottlenecks.
- Novel Resonator Design: Developed a monolithic, square-shaped LiNbO3 resonator utilizing total internal reflection (TIR) and fabricated via precision ductile-mode diamond turning.
- Performance Achieved: Successfully demonstrated 2.6 ± 0.5 dB of vacuum squeezing (4.7 dB corrected) at 1064 nm, using a double-resonant cavity configuration.
- Fabrication Precision: The use of ductile-mode diamond machining and subsequent mild polishing yielded surfaces of optical quality, with the cavity Q-factor limited primarily by bulk material absorption loss rather than surface scattering.
- Advanced Coupling: Achieved independent and highly tunable coupling rates for the pump (532 nm) and sub-harmonic (1064 nm) fields using birefringent calcite prisms in an evanescent coupling setup.
- Material Limitation: The experimental performance is ultimately constrained by the bulk absorption (Q-factor 3.1 x 107) and scattering losses of the LiNbO3 crystal, as well as mode perturbation arising from mechanical polishing.
- 6CCVD Value Proposition: The demonstrated requirements for ultra-high precision machining (ductile regime) and ultra-low loss operation necessitate the use of Optical Grade SCDâa core product of 6CCVDâto achieve the predicted performance improvements (Q > 109) required for next-generation quantum light sources.
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data points were extracted from the research paper detailing the performance metrics and physical characteristics of the diamond-turned monolithic resonator.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Squeezing Achieved (Measured) | 2.6 ± 0.5 | dB | Below shot noise level at 5 MHz sideband frequency. |
| Squeezing Achieved (Corrected) | 4.7 | dB | Corrected for 98% detector QE, 85% visibility, and 1.6% optics loss. |
| Sub-Harmonic Wavelength (Squeezed) | 1064 | nm | Output wavelength of the OPO. |
| Pump Wavelength (SHG) | 532 | nm | Required input wavelength. |
| Resonator Material | MgO-Doped LiNbO3 | - | Chosen for phase matching and diamond cutting compatibility. |
| Resonator Thickness | 200 | ”m | Wafer initial thickness. |
| Resonator Width (Nominal) | 2.5 | mm | Side length of the square cavity. |
| Mirror Curvature (Confinement) | 3 | mm | Curvature of the two spheroidal faces. |
| Mirror Curvature (Coupling) | 22 | mm | Curvature of the two prism coupling faces. |
| Free Spectral Range (FSR) | 18.7 ± 0.5 | GHz | Determined by cavity length (2.5 mm roundtrip). |
| Bulk Absorption Limited Linewidth (532 nm) | 9 ± 1 | MHz | Corresponds to the maximum intrinsic Q-factor of the material. |
| Bulk Absorption Limited Q-Factor | 3.1 x 107 | - | Calculated from the 532 nm linewidth. |
| Operating Temperature | 60 | °C | Phase-matching temperature for 1064/532 nm operation. |
| Self-Locking Bandwidth | ~40 | Hz | Roll-off frequency for noise reduction. |
| Electro-Optic Tuning Rate (Pump) | 40 | MHz/V | For the extraordinarily polarized 532 nm field. |
Key Methodologies
Section titled âKey MethodologiesâThe creation of this monolithic resonator required specific material and machining processes to achieve the necessary surface quality and mode geometry.
- Material Selection and Orientation: Used a 200 ”m thick Magnesium Oxide-doped Lithium Niobate (LN) wafer. The extraordinary optical axis was oriented normal to the disk plane to facilitate phase matching between 1064 nm and 532 nm via temperature tuning (set near 60 °C).
- Ductile Regime Diamond Turning: The square monolithic resonator (2.5 mm width) was produced in a single continuous cut using precision diamond turning. Critical control of the cutting process was maintained to ensure ductile (chip-free) material removal, avoiding chipping common in brittle materials.
- Surface Design: The geometry utilized four distinct smooth surfaces for Total Internal Reflection (TIR): two spheroidal surfaces (3 mm curvature) for optical mode confinement, and two nearly flat surfaces (22 mm curvature) for prism coupling.
- Post-Machining Polishing: Mild hand-polishing was applied after turning to reach final optical quality, ensuring that the resonator linewidth was limited by bulk absorption in the LN, rather than scattering from surface imperfections.
- Prism Evanescent Coupling: Custom-designed birefringent calcite prisms (Green for 532 nm pump, Red for 1064 nm sub-harmonic) were coupled evanescently to the resonator via piezo-actuated translation stages, allowing for independent tuning of the fundamental and second harmonic coupling rates.
- Self-Locking Stability: Passive frequency stabilization was achieved by utilizing the photo-thermal and photo-refractive effects present in the LN at high pump powers to self-lock the cavity near resonance, compensating for the high thermal and acoustic sensitivity of the long (0.5 m equivalent) bow-tie cavity alternatives.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & Capabilitiesâ6CCVDâs advanced MPCVD Diamond products and precision engineering services are optimally suited to overcome the material limitations encountered in this research, enabling higher Q-factors and superior stability necessary for next-generation quantum optics.
| Application Requirement (From Paper) | 6CCVD Diamond Solution | Technical Advantage (Sales Pitch) |
|---|---|---|
| Bulk Absorption Limitation (Q-factor limited to 3.1 x 107 by LiNbO3 intrinsic loss). | Optical Grade SCD (Single Crystal Diamond): Ultra-high purity, low nitrogen (N) concentration. | Diamondâs intrinsic absorption coefficients are orders of magnitude lower than LiNbO3, supporting Q-factors far exceeding 109. Utilizing SCD eliminates the primary limitation to squeezing performance cited in the paper. |
| Surface Scattering Loss (Residual losses due to surface imperfections, Ra < 5 nm required). | Ultra-Precision Polishing Services: Ra < 1 nm guaranteed for SCD wafers. | 6CCVD guarantees Ra < 1 nm surface roughness on SCD, significantly reducing surface scattering losses and preserving TEM00 mode purity, crucial for maximizing the escape efficiency of the squeezed field. |
| Custom Compact Dimensions (2.5 mm wide, 200 ”m thick plates required for monolithic design). | Custom Dimension & Thickness Control: SCD/PCD plates up to 125 mm diameter, and SCD thickness from 0.1 ”m to 500 ”m. | We routinely supply highly uniform SCD wafers in the exact 200 ”m (0.2 mm) thickness required for compact resonator fabrication, ensuring optimal geometry definition and TIR performance. |
| Future Integrated Electrodes (Need for advanced tuning/locking integration). | Internal Metalization Capabilities: Au, Pt, Pd, Ti, W, Cu. | 6CCVD can deposit custom metal patterns (e.g., Ti/Pt/Au) directly onto the diamond crystal, enabling integrated, photo-refractive-free electro-optic tuning, providing superior stability compared to external brass electrodes used in the experiment. |
| Thermal Management (LiNbO3 requires temperature control near 60 °C). | Diamondâs Thermal Properties: SCD exhibits the highest thermal conductivity of any bulk material. | While LN requires active thermal stabilization, replacing the host material with SCD provides intrinsic superior thermal management, reducing thermal drift and stabilizing the cavity resonance without complex ovens. |
Engineering Support
Section titled âEngineering Supportâ6CCVDâs in-house team of PhD material scientists and technical engineers specializes in advanced quantum and optical applications. We can assist researchers in material selection, crystal orientation optimization (e.g., maximizing the effective nonlinear coefficient in diamond substitutes or hybrid structures), and designing custom dimensions for next-generation Optical Parametric Oscillation (OPO) and non-linear optics projects.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
For some crystalline materials, a regime can be found where continuous ductile cutting is feasible. Using precision diamond turning, such materials can be cut into complex optical components with high surface quality and form accuracy. In this work we use diamond-turning to machine a monolithic, square-shaped, doubly-resonant LiNbO3 cavity with two flat and two convex facets. When additional mild polishing is implemented, the Q-factor of the resonator is found to be limited only by the material absorption loss. We show how our monolithic square resonator may be operated as an optical parametric oscillator that is evanescently coupled to free-space beams via birefringent prisms. The prism arrangement allows for independent and large tuning of the fundamental and second harmonic coupling rates. We measure 2.6 ± 0.5 dB of vacuum squeezing at 1064 nm using our system. Potential improvements to obtain higher degrees of squeezing are discussed.