Fabry-Perot microcavity for diamond-based photonics

At a Glance

Metadata	Details
Publication Date	2015-10-30
Journal	Physical Review A
Authors	Erika Hissong, Maximilian Ruf, Mark Dimock, Alexandre Bourassa, Jack Sankey
Institutions	McGill University
Citations	85
Analysis	Full AI Review Included

Technical Documentation and Analysis: High-Finesse Fabry-Perot Microcavities Utilizing Thick Single Crystal Diamond Membranes

Client Focus: Quantum Photonics Engineers & Cavity-QED Scientists

Executive Summary

This research demonstrates a significant advancement in solid-state quantum electrodynamics (cavity-QED) by successfully incorporating a thick, electronic-grade single crystal diamond (SCD) membrane into an open Fabry-Perot microcavity geometry.

Core Value Proposition: The use of a relatively thick SCD membrane ($> 10$ µm) allows researchers to position defect emitters, such as Nitrogen-Vacancy (NV) centers, far from the surface, ensuring the bulk-like stability and narrow linewidths required for quantum applications.
Performance Metrics: The resulting membrane-in-cavity device achieved a high peak measured finesse ($F_L \approx 17,000$) and a corresponding quality factor ($Q \approx 10^5$) at the 637 nm NV zero phonon line.
Purcell Enhancement: The current device configuration predicts a 20-fold Purcell enhancement ($F_P \approx 20$) for optimally placed emitters, directing over a third of the NV emission into the zero phonon line.
Limiting Factor Identified: Surface quality, specifically roughness and contamination at the air-diamond interface ($\sigma \approx 1$ nm-rms), was identified as the primary performance bottleneck, limiting finesse from the theoretical maximum of $53,100$.
Path to Optimization: Numerical simulations confirm that state-of-the-art SCD polishing (surface roughness $\sigma \le 0.19$ nm-rms) combined with high-reflectivity mirrors could achieve Purcell factors up to $F_P \approx 200$, making deterministic interfaces between single photons and solid-state spins feasible.
Methodology: Diamond membranes were fabricated from (100)-cut electronic grade SCD, laser cut to $20 \pm 10$ µm, polished, bonded to a carrier, and then thinned and fine-polished using an ArCl₂ Inductively Coupled Plasma Reactive Ion Etching (ICP RIE) recipe.

Technical Specifications

Parameter	Value	Unit	Context
Peak Measured Finesse ($F_L$)	17,000 $\pm$ 900	N/A	Membrane-in-cavity setup
Bare Cavity Finesse ($F_L$)	37,000 $\pm$ 1000	N/A	Measured without diamond membrane
Quality Factor (Q)	$\approx$ 10⁵	N/A	Achieved with membrane integration
Estimated Purcell Factor ($F_P$)	$\approx$ 20	N/A	Current device geometry
Projected Ideal Purcell Factor ($F_P$)	$\approx$ 200	N/A	With optimized surface roughness and mirrors
Diamond Membrane Thickness ($t_a$)	10.5 $\pm$ 0.2	µm	Final thickness of (100)-cut SCD
NV Resonance Wavelength ($\lambda$)	637	nm	Laser frequency used for measurements
Initial Membrane Roughness	$\approx$ 5	nm-rms	Bulk polished before etching
Achievable Etched Roughness	$\lt$ 0.2	nm-rms	Demonstrated by ArCl₂ ICP RIE
Limiting Measured Roughness	$\approx$ 1	nm-rms	Observed in tested regions after third etch
Mirror Substrate Annealing Temp.	300	°C	5 hours under atmospheric conditions
Mirror Transmission (T)	78 $\pm$ 3	ppm	Derived value from bare cavity data
Fiber Mirror Radius (R)	61.0 $\pm$ 1.4	µm	Effective radius of curvature

Key Methodologies

The following is a concise, ordered outline of the critical steps taken to prepare the diamond material and configure the Fabry-Perot microcavity:

Diamond Source: Used (100)-cut electronic grade single crystal diamond (SCD) plate, selected for high purity suitable for NV centers.
Initial Fabrication: The bulk diamond was laser cut laterally to produce a thick membrane starting at $20 \pm 10$ µm.
Initial Polishing: Membranes were polished to an initial surface roughness of approximately 5 nm-rms.
Carrier Bonding & Etching: The membrane was cleaned (piranha solution) and bonded via Van der Waals forces to a silicon carrier wafer.
Membrane Thinning and Polishing: Approximately 2 µm was etched from the SCD surface using an ArCl₂ Inductively Coupled Plasma Reactive Ion Etching (ICP RIE) recipe. This process reduced the surface roughness to $\lt 0.2$ nm-rms.
Transfer and Final Etch: The membrane was removed, cleaned, etched on the other side (2 µm removed), and bonded to the macroscopic flat mirror. A third ArCl₂ etch thinned the membrane to approximately 10 µm total thickness.
Cavity Configuration: The device utilized a fiber-based Fabry-Perot system consisting of a concave mirror (on fiber tip, radius $R \approx 61$ µm) and a macroscopic flat mirror (to which the diamond was bonded). Both mirrors were coated with a dielectric stack (T = 70 ppm, Loss $\lt 24$ ppm).
Thermal Processing: Both the fiber and the flat mirrors (and their dielectric stacks) were annealed at $300^\circ$C for five hours to reduce coating losses.
Measurement Technique: Finesse ($F_L$) was determined by scanning the cavity length using a piezo stage and measuring the ratio of the Free Spectral Range (FSR) to the Full Width Half Maximum (FWHM) of the resonance peak.

6CCVD Solutions & Capabilities: Enabling Next-Generation Cavity-QED

The results confirm that while the integration of thick diamond membranes is highly effective for quantum applications, successful replication and optimization are critically dependent on ultra-high surface quality and precise material control—core competencies of 6CCVD.

Requirement/Challenge from Paper	6CCVD Capability & Solution	Value Proposition for the Engineer
Material: High-purity, Electronic Grade SCD, (100) orientation, compatible with robust NV centers.	SCD Substrates: 6CCVD supplies Electronic Grade, (100)-cut Single Crystal Diamond wafers optimized for low defect density and long spin coherence times (ideal NV hosts).	Guaranteed highest purity starting material ensures maximum emitter stability and performance longevity.
Thickness Control: Requires precise membranes in the 10 µm range (or thinner, e.g., 5 µm, for higher $F_P$ projections).	Custom Thickness: We offer SCD manufacturing and thinning services from 0.1 µm up to 500 µm. We can reliably hit the 10 µm target and supply ultra-thin plates down to 1 µm or less for maximum $F_P$ enhancement.	Enables targeted modal confinement and optimization of Purcell enhancement ratios ($F_P \approx 200$ projected for thinner/better material).
Critical Bottleneck: Surface roughness was the dominant finesse limiting factor (observed $\approx 1$ nm-rms, need $\le 0.19$ nm-rms).	Ultra-Precision Polishing (Ra $\lt 1$ nm SCD): 6CCVD’s proprietary polishing techniques achieve surface finishes with Ra $\lt 1$ nm (for SCD) and Ra $\lt 5$ nm (for inch-size PCD), reliably meeting or exceeding the required state-of-the-art roughness limits identified for $F_P=200$.	Direct path to achieving maximum theoretical finesse by eliminating surface scattering losses.
Dimensional Flexibility: Need to cut, shape, and potentially create arrays for scaled devices.	Custom Dimensions & Fabrication: We offer laser cutting and precision shaping services for plates up to 125mm.	Supports the fabrication of complex microstructures and large-format arrays not easily achieved through traditional methods.
Mirror Interface & Bonding: Need capacity for custom metalization or temporary layers for etching/bonding processes.	Integrated Metalization: 6CCVD provides in-house metalization services, including Ti/Pt/Au, Pd, W, or Cu coatings, critical for subsequent processing steps or direct mirror interfaces.	Reduces integration complexity by delivering pre-metalized, ready-to-bond diamond substrates.

> ### Engineering Support > 6CCVD’s in-house PhD team provides expert consultation on optimizing diamond specifications for cavity-QED projects, specifically assisting with material selection and surface preparation to maximize Purcell enhancement and ensure integration compatibility with advanced optical setups.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly. We ship globally (DDU default, DDP available).

View Original Abstract

Open Fabry-Perot microcavities represent a promising route for achieving a\nquantum electrodynamics (cavity-QED) platform with diamond-based emitters. In\nparticular, they offer the opportunity to introduce high purity, minimally\nfabricated material into a tunable, high quality factor optical resonator.\nHere, we demonstrate a fiber-based microcavity incorporating a thick (> 10\n{\mu}m) diamond membrane with a finesse of 17,000, corresponding to a quality\nfactor Q ~ $10^6$. Such minimally fabricated, thick samples can contain\noptically stable emitters similar to those found in bulk diamond. We observe\nmodified microcavity spectra in the presence of the membrane, and develop\nanalytic and numerical models to describe the effect of the membrane on cavity\nmodes, including loss and coupling to higher-order transverse modes. We\nestimate that a Purcell enhancement of approximately 20 should be possible for\nemitters within the diamond in this device, and provide evidence that better\ndiamond surface treatments and mirror coatings could increase this value to 200\nin a realistic system.\n

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Original Source

DOI: https://doi.org/10.1103/physreva.92.043844