Simplified system based on photoelastic modulation technique for low-level birefringence measurement

Abstract

In this article, the authors present a new low-level birefringence detection (LLBD) system based on the use of a photoelastic modulator. This system uses a single modulator so that only one detector is required to capture all the frequency components in the optical beam. The design removes gain errors associated with the conventional dual-beam approach. In addition, we also incorporate a complete analytical signal-processing algorithm to enhance measurement accuracy by eliminating the requirement of small phase angle approximation. To demonstrate the operation of our LLBD system, we performed birefringence measurement on a silicon wafer to characterize the distribution of its internal stress. Results obtained from our experiments indicate that the instrument has high sensitivity and good repeatability. The birefringence measurement sensitivity of our system was found to be about 0.03° (or 0.096 nm at 1152 nm). Several samples with different levels of birefringence were studied using our LLBD system.

Phase‐sensitive surface plasmon resonance biosensors: methodology, instrumentation and applications

“…Ho and coworkers reported various configurations for phase measurement using photoelastic modulators since 2003 [56,59,44]. As shown in Fig.…”

“…By decomposing the detected signal using a lock-in amplifier with the input fed by reference signals at the first and second harmonic frequencies of the modulator, the amplitudes of first and second harmonics can be obtained and further processed to determine the phase retardation. This scheme was first used to determine the low-level birefringence [44], and later adopted for SPR biosensing [56]. Phase change with regard to varying concentration of glycerin in water were measured and the sensitivity was found to be 1.19 × 10 −6 RIU.…”

“…Here, three approaches to phase-sensitive measurements are possible. In the first approach, called SPR interferometry, phase information is extracted from an interference pattern between the "signal" p-polarized beam, reflected from the SPR-supporting film, and the "reference" beam presented by either an additional p-polarized beam [14][15][16]23,[40][41][42][43] or the unaffected s-polarized component of the same beam [17,19,[44][45][46][47][48][49]. Such approach makes possible the extraction of a pure phase response in sensing or 2D imaging geometries.…”

Polarization-sensitive surface plasmon enhanced ellipsometry biosensor using the photoelastic modulation technique

“…With all the necessary information already embedded in the frequency domain of the detected signal, the polarization state is extracted by analyzing the first and second harmonics of the modulated signal as well as the DC component simultaneously. In previous work we reported that the influence of residual birefringence to phase retardation of PEM [15,17]. In order to minimize this effect, the setup is located in an enclosed environment to ensure minimum temperature fluctuation caused by air circulation and proprietary frequency generator is used to provide stable modulation frequency.…”

Recent advances in surface plasmon resonance imaging: detection speed, sensitivity, and portability

“…Besides AOM, a photoelastic modulator (PEM) can also be used to modulate the laser frequency. Peng et al developed a single-beam approach where the input beam is modulated by a PEM and the SPR-induced phase change was obtained by an analytical signal-processing algorithm [38]. This single-beam system was then used for real-time monitoring of biomolecule binding reactions with detection sensitivity up to 6 × 10 −7 RIU or 15 ng/ml [39,40].…”