The applications of optical fibers are impeded in implantable medical diagnostics due to incompatibility with biological tissues, and immune reaction in vivo. The utilization of biocompatible materials to construct a photonic sensing platform can reduce the immune response in in vivo medical diagnostics. Here, we developed real-time optical fiber sensors to determine the volumetric modulation of stimuli-responsive polymers. Asymmetric microlens structures were replicated on stimuli-sensitive hydrogels as stand-alone sensors and were chemically attached to the tips of silica and biocompatible optical fibers. Quantitative measurements were carried out using a smartphone to demonstrate the ease, simplicity, and practicality of the readout methodology. To demonstrate the utility in real-time sensing, the fiber probe was investigated in various concentrations of ethanol, propan-2-ol, and dimethyl sulfoxide. Also, the fiber probe showed a rapid response to pH in the acidic region with a sensitivity of 40 nW pH-1. To develop biocompatible probes for physiological applications, a microlens array-imprinted polymer was attached to the tip of a hydrogel optical fiber. The optical fiber probe in the refection configuration showed a sensitivity of 7 nW pH-1. The developed hydrogel fiber probes may have application in point-of-care diagnostics, continuous biomarker monitoring, and critical care sensing devices.