研究目的
To design a virtual reality display that addresses the vergence-accommodation conflict by generating a dense collection of depth/focal planes using high-speed tracking of a focus-tunable lens.
研究成果
The prototype demonstrates the ability to generate 1600 focal planes per second, enabling a multifocal display that resolves the vergence-accommodation conflict. Dense focal stacks provide higher spatial resolution and more natural focus cues compared to existing displays, with potential for miniaturization and broader applications in VR/AR.
研究不足
The proposed approach requires additional optics that increase bulk, leads to reduced peak brightness due to multiple focal planes per frame, and has low energy efficiency in the prototype due to the use of a DMD. Switching to OLED displays or other technologies could mitigate some issues.
1：Experimental Design and Method Selection:
The system involves driving a focus-tunable lens with a high-frequency input (e.g., triangular wave) to sweep focal lengths and tracking the focal length in real-time using an optical module with a position sensing detector (PSD). This allows rendering of dense focal stacks without waiting for the lens to settle.
2：Sample Selection and Data Sources:
A lab prototype is built and tested, with measurements taken using a camera (e.g., Nikon D3400) to capture images and evaluate performance.
3：List of Experimental Equipment and Materials:
Includes a focus-tunable lens (Optotune EL-10-30), PSD (OSI Optoelectronics SL15), DMD-based projector (TI DLP7000), FPGA (Altera DE0-nano-SOC), DAC (MCP4725), ADC (LTC2308), laser (Thorlabs CPS980S), dichroic mirrors (Edmund Optics 69-220), and other optical and electronic components.
4：Experimental Procedures and Operational Workflow:
The FPGA drives the lens with a triangular wave, reads the PSD output to trigger the display of focal planes, and coordinates the projector to show images at specific focal lengths. Calibration is performed using a camera to map PSD readings to focal depths.
5：Data Analysis Methods:
Images are captured and analyzed for blur kernel size to measure focal depths, and modulation transfer functions are computed to evaluate spatial resolution. Simulations compare different numbers of focal planes and filtering methods.
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Focus-tunable lens
EL-10-30
Optotune
To sweep through a range of focal lengths at high frequency for generating multiple focal planes in the display system.
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Position sensing detector
SL15
OSI Optoelectronics
To measure the deflection of a laser beam for real-time tracking of the focal length of the tunable lens.
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Digital-to-analog converter
MCP4725
Microchip
To drive the focus-tunable lens with the required voltage or current signals.
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Collimated infrared laser
CPS980S
Thorlabs
To provide a laser beam for probing the tunable lens and enabling focal length tracking.
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LED
XHP35A
Cree
To serve as the light source for the DMD-based projector in the display system.
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Digital micromirror device
DLP7000
Texas Instruments
To act as a high-speed display for rendering images at different focal planes.
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Field-programmable gate array
DE0-nano-SOC
Altera
To control the tunable lens, read PSD outputs, and coordinate the display system.
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Analog-to-digital converter
LTC2308
Linear Technology
To convert analog signals from the PSD to digital values for processing by the FPGA.
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Shortpass dichroic mirror
69-220
Edmund Optics
To separate visible and infrared light paths in the optical tracking module.
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LED driver
LM3409HV
Texas Instruments
To modulate the intensity of the LED for pulse-width modulation in the display.
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Operational amplifier
OPA-37
Texas Instruments
To amplify signals in the analog processing circuit for focal length tracking.
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Analog divider
MPY634
Texas Instruments
To compute the ratio of currents from the PSD for focal length estimation.
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Current buffer
BUF634
Texas Instruments
To buffer the current output for driving the focus-tunable lens.
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