A Semiconductor Photon Bose-Einstein Condensate as a Practical Light Source for Ranging Finding

TL;DR

The paper addresses bridging fundamental photon BEC studies and practical metrology by demonstrating a room-temperature cw semiconductor photon BEC that emits with thermal statistics near threshold. Range sensing is implemented via Hanbury Brown–Twiss intensity correlations, using the peak of $g^{(2)}(\\tau)$, fit to $g^{(2)}(\\tau)=1+a\\exp(-|\\tau-\\tau_0|/\\tau_l)$ to extract the delay $\\tau_0$. Key results include range measurements up to 0.6 m with ~5 mm precision and a demonstration of multi-distance capability, alongside identification of an optimal pump regime balancing photon flux and coherence. The work indicates practical implications for LiDAR and depth imaging and outlines future improvements in cavity design and real-world target testing.

Abstract

Here we report the measurement of thermal photon statistics from a semiconductor photon Bose-Einstein condensate operating just above the condensation threshold. We identify a regime where coherent, single mode emission occurs while still demonstrating significant photon bunching. Taking advantage of the photon bunching, along with the continuous-wave operation and high photon flux, we demonstrate optical range sensing using a photon Bose-Einstein condensate. We characterise the precision of the range measurement and analyse the dependence on the condensate's pump power and resulting coherence properties.

Figures (4)

• Figure 1: Cavity and experimental setup. (a) Schematic diagram of the open semiconductor microcavity. (b) Schematic diagram of the experimental setup. A fibre-coupled laser is used to excite the semiconductor in the cavity through an objective lens (Obj.). A CCD camera (CCD) is used to monitor cavity length by imaging an interference pattern from a broadband LED. Emission (red line) is collimated by an objective lens (Obj.), sent through a 950 nm LP filter (950LP) and sent to the HBT interferometer, highlighted in the blue box. The first APD (APD1) starts the coincidence timer, and the second APD (APD2) stops the timer. The second APD is placed after a Michelson interferometer with a variable delay stage (STAGE). The second arm, indicated with a dashed line, is blocked unless otherwise stated. (c) Input-output curve for the photon BEC. Data (points) are from power measurements fit with a multimode rate equation model (dashed line), shown with the single mode component of the model (solid line) Schofield2024. The vertical line is $P=P_c$ and shaded region represents region of interest for this work.
• Figure 2: The height and width of the second-order correlation function $g^{(2)}(\tau)$ as a function of pump intensity. (a-c) $g^{(2)}(\tau)$ measurements at $P/P_c$ = 0.83, 1, 1.05 respectively. Data (points) are fit with the exponential decay shown in Eq. 1 (line). Labels in (d) and (e) indicate these measurements. (d) Height of the $g^{(2)}(\tau)$ as a function of power, where the Poissonian baseline value of 1 is subtracted. (e) Width of the $g^{(2)}(\tau)$ as a function of power.
• Figure 3: Distance measurement using thermal light. (a) Data (points) from two $g^{(2)}(\tau)$ measurements differing by approximately 1 m of optical delay, showing a clear shift in bunching feature. Data are fit with Eq. 1 (lines). (b) Measured distance (points) as a function of optical path delay. Dashed line is $x=y$. (c) Deviation from actual distance (points) as a function of distance. (d) Data (points) from two $g^{(2)}(\tau)$ measurement where one arm of the HBT interferometer has two paths differing by approximately 0.1 m (blue) and 1 m (red) of optical delay. The 0.1 m measurement looks like a single broadened peak, and the 1 m measurement shows two clear bunching features. Data are fit with Eq. 1 (line), modified to have two peaks. (e) Measured distance (points) as a function of actual distance, expressed as distance between objects. Dashed line is $x=y$. (f) Deviation from actual distance (points) as a function of distance.
• Figure 4: Dependence of error in distance measurement as a function of system parameters. (a) Error magnitude as a function of integration time (points) for no (blue) and 0.6 m (red) delay for $P= P_c$. Both tend to the same value showing independence of measurement error on distance. (b) Error magnitude as a function of $P/P_c$. (c) Average deviation and error magnitude for distance measurement as a function of timing resolution for $0.9 <P/P_c\leq 1$. Timing resolution is reduced through re-binning data.