Risley prisms are widely used for beam pointing in several optical systems. The exact solution for the inverse problem does not exist, except using numerical methods. However, the errors introduced by misalignment are usually greater than the approximation errors. We present a novel method to compensate alignment errors in pointing systems based on Risley prisms. The prism model that we used is based on paraxial approximation with an additional vector to compensate typical alignment errors. Simulation and experimental results show that the improvement in pointing accuracy is achievable even in comparison with exact ray tracing methods.

A polymer optical Sagnac interferometer is proposed as a compact and low-cost refractive index sensor for the first time to our best knowledge. The Sagnac interferometer is fabricated by only one piece of fiber to facilitate its fabrication and to avoid losses due to misalignment or fusion. The coupler was developed based on chemical and twisting techniques of ∼ 5 c m of fiber. We modified the coupling ratio by varying the refractive index of media surrounding the coupler and consequently modified the transmission. For several values of mass percent concentration of sugar solutions surrounding the coupler, we found that transmittance decreases as the mass concentration increases. However, the decay is faster for the low concentration, while the decay is slower for higher concentrations. Two sets of experiments were carried out, at high ( ≥ 1 gm/100 ml) and low ( < 1 g m / 100 m l ) mass concentration of sugar solutions. The calibration of the sensor was done at 733 nm, where the response of the interferometer displays larger transmission variations for different solutions. The refractive index estimation was possible by correlation of the transmittance function (calculated by fitting the experimental data) with a linear refractive index model. The estimated resolution of the system is 0.057 weight percent of sugar solution, determined by the noise of the system.

High-performance megapixel focal plane arrays with small pixels have been widely used in modern optical remote sensing, astronomical, and surveillance instruments. In the prediction models applied in the traditional instrument performance analysis, the image of a point source is assumed to fall on the center of a detector pixel. A geometrical image of a point source in the realistic optical system may actually fall on any position on the detector pixel because the sensor’s line of sight includes pointing errors and jitter. This traditional assumption may lead to an optimistic error, estimated at between 10% and 20%. We present the critical factors that impact the performance estimate in a realistic instrument design based on the prediction for the noise-equivalent power (NEP). They are the optical centroid efficiency (OCE) and the ensquared energy, or more precisely, the energy on the rectangular detector pixel (EOD). We performed the simulation studies for imaging with an optical system with and without a generalized rectangular central obscuration.

The off-axis three-mirror optical system is derived from the classical Cooke triplet or a derivative of the inverse-telephoto lens. By properly arranging an internal reimaging mechanism or altering the location of the optical stop, one can create different versions of three-mirror optical systems. They include very compact configurations and wide field-of-view imagers. Insights into the optical design process, manufacturing, stray light management, and remote sensing applications are presented.

The Rotational Shearing Interforometer has been proposed for direct detection of extra-solar planets. This interferometer cancels the star radiation using destructive interference. However, the resulting signal is too small (few photons/s for each m²). We propose a novel method to enhance the signal magnitude by means of the star–planet interference when the star radiation is not cancelled. We use interferograms computationally simulated to confirm the viability of the technique.

In this work, we study a double-sense twisted low-birefringence Sagnac loop structure as a sound/vibration sensing device. We study the relation between the adjustments of a wave retarder inside the loop (which allows controlling the transmission characteristic to deliver 10, 100, and 300 $\mathsf{\mu }\mathrm{W}$ average power at the output of the system) and the response of the Sagnac sensor to vibration frequencies ranging from 0 to 22 kHz. For a 300 m loop Sagnac, two sets of experiments were carried out, playing at the same time all the sound frequencies mixed for ∼1 s, and playing a sweep of frequencies for 30 s. In both cases, the time- and frequency-domain transmission amplitudes are larger for an average power of 10 $\mathsf{\mu }\mathrm{W}$, and smaller for an average power of 300 $\mathsf{\mu }\mathrm{W}$. For mixed frequencies, the Fourier analysis shows that the Sagnac response is larger for low frequencies (from 0 to ∼5 kHz) than for high frequencies (from ∼5 kHz to ∼22 kHz). For a sweep of frequencies, the results reveal that the interferometer perceives all frequencies. However, beyond ∼2.5 kHz, harmonics are present each ∼50 Hz, revealing that some resonances are present. The results about the influence of the power transmission through the polarizer and power emission of laser diode (LD) on the Sagnac interferometer response at high frequencies reveal that our system is robust, and the results are highly reproducible, and harmonics do not depend on the state of polarization at the input of the Sagnac interferometer. Furthermore, increasing the LD output power from 5 mW to 67.5 mW allows us to eliminate noisy signals at the system output. in our setup, the minimum sound level detected was 56 dB. On the other hand, the experimental results of a 10 m loop OFSI reveal that the response at low frequencies (1.5 kHz to 5 kHz) is minor compared with the 300 m loop OFSI. However, the response at high frequencies is low but still enables the detection of these frequencies, yielding the possibility of tuning the response of the vibration sensor by varying the length of the Sagnac loop.