Researchers in China have developed a rice-sized optical sensor that could give surgical robots and medical tools a sense of touch. The device measures force, pressure, and twisting in every direction using light instead of electronics.

The sensor measures just 1.7 millimeters. Researchers say it could help robots detect unsafe contact during delicate procedures and respond instantly. The team also demonstrated that the device could identify hidden structures beneath soft materials, including tumor-like objects embedded in tissue models.

The work came from researchers at Shanghai Jiao Tong University.

Light replaces electronics

Current robotic surgery systems rely heavily on imaging. However, they struggle to sense physical interaction in tight surgical spaces. Existing force sensors also remain too large for many miniature tools.

“Although modern imaging systems can show structures clearly, they do not provide information about physical interaction, such as force or torque, and existing force sensors are often too bulky or complex to fit into miniature tools,” said research team leader Jianlong Yang from Shanghai Jiao Tong University in China.

“By allowing machines to measure contact force, pressure, shear, and twisting, our technology could make it possible for robots to detect unsafe contact early and adjust their actions in real time, especially in small and sensitive environments.”

The researchers designed the sensor around an optical fiber with a soft elastomer tip. When the tip touches an object, it deforms slightly. That tiny movement changes the way light spreads inside the sensor.

A coherent fiber bundle then carries the light pattern to a camera. The system analyzes the captured image using data-driven methods to calculate force and torque in all directions.

The researchers said the setup avoids the wiring complexity found in conventional miniature sensors.

“Our sensor works differently from conventional miniature force sensors, such as fiber Bragg grating (FBG) systems that rely on multiple sensing elements and carefully designed structures to separate different force components,” said Yang.

“We are not measuring force piece by piece but are sensing the overall contact state in a single step. We believe this shift could make it easier to build compact tools that can both see and feel.”

The team tested the device under controlled loading conditions using known forces and twisting motions. The sensor delivered repeatable measurements with low hysteresis, meaning readings stayed consistent during loading and unloading cycles.

Researchers also tested the device in gelatin models containing stiff spherical objects designed to mimic tumors hidden beneath tissue. The sensor successfully detected and located the embedded structures.

The team believes the technology could improve tactile guidance in minimally invasive surgery. Surgeons using robotic systems often work through narrow pathways where accidental contact can damage delicate tissue.

“Robotic systems used in minimally invasive surgery operate in extremely tight spaces, such as inside the eye or through narrow surgical pathways,” said Yang. “By making tools and robots safer and more precise, this technology could make delicate medical procedures more controlled and reduce the risk of accidental damage.”

Path toward real-world use

The researchers now plan to improve manufacturing consistency and reduce calibration requirements before commercial deployment. They also aim to integrate the sensor into medical and industrial robotic systems for long-term testing under real operating conditions.

The team said additional work will focus on packaging the technology into compact systems that clinicians and engineers can deploy easily in practical environments.

The study is published in the journal Optica.