A high-isolation polarization-independent optical circulator is reported. The circulator structure can sharply reduce isolation dependency on both the rotation error of a rotator and on extinction ratio of a polarizing beam splitter. As a result, the circulator has high isolation over a wide wavelength and temperature range. A 4-port circulator coupled with single-mode fibers was fabricated. Its measured insertion loss and isolation were 31.5 dB, respectively. Consequently, a loss ratio of over 29.7 dB has been realized. The isolation (which is free from reflections) was measured to be >45.1 dB. It is confirmed that the wavelength range for this kind of isolation over 40-dB is very wide. The measured range was wider than the measurement system limit of 90 nm. >

High-isolation polarization-independent quasi-optical circulator

An electrically controlled optical switch based on polarization principles is described. It uses a liquid crystal twist cell that rotates polarization by 90°, and it operates on an ac voltage that switches between 0.8 and 2.5 V rms. The switch has a loss of ~0.4 dB, neglecting reflections, in an unpolarized incoherent beam and a cross-talk ratio of ~−20 dB. It operates in collimated light, but it can be applied to multimode fibers using collimating lenses, which are expected to add <0.8 dB to the loss.

Electrically controlled optical switch for multimode fiber applications

The wavelength and temperature dependence of the Faraday rotation together with the optical loss spectra of yttrium, gadolinium, terbium, dysprosium, holmium, erbium and ytterbium iron garnets are reported for wavelengths in the range 1.1-1.7 mu m. It is demonstrated that the Faraday rotation of all the iron garnets decreases with increasing wavelength with the exception of ytterbium iron garnet which, for wavelengths in excess of approximately 1.3 mu m, possesses a wavelength independent Faraday rotation of 5.7+or-0.3 degrees mm-1. The performance of magneto-optic switches, isolators, modulators and deflectors constructed using each of these materials is discussed with particular emphasis on their operation at 1.3 mu m and 1.55 mu m, the wavelengths of interest in current optical fibre systems. It is concluded that whilst yttrium iron garnet or holmium iron garnet are best suited to the fabrication of devices operating at single wavelength, for broadband operation ytterbium iron garnet is to be preferred.

https://iopscience.iop.org/article/10.1088/0022-3727/17/3/015/pdf

Magneto-optic properties of rare earth iron garnet crystals in the wavelength range 1.1-1.7μm and their use in device fabrication

We present a detailed study of the polarization properties of a reflective fiber amplifier composed of a circulator, a normal single-mode Er-doped fiber and a Faraday rotator mirror. The amplifier can preserve an arbitrary input state of polarization regardless of any external perturbations, and is completely free from polarization effects. The effect of imperfections of the Faraday rotator mirror is also discussed. Finally, we demonstrate experimentally the polarization-stability of the amplifier and its ability to compensate polarization mode dispersion both in the circulator and in the single-mode Er-doped fiber.

Polarization properties of a reflective fiber amplifier employing a circulator and a Faraday rotator mirror

A high-isolation polarization-independent optical circulator is reported. The goal is to provide a simple structure that sharply diminishes the degradation on the isolation caused by imperfection of polarization separation in the polarizing beam splitters. The circulator structure is almost the same as that of a conventional circulator except that a birefringent plate is added to each port to achieve high isolation. The effectiveness of the added birefringent plate has been confirmed by calculation and experiment. Insertion loss and isolation of the fabricated circulator coupled with single-mode fibers have been measured to be 29.9 dB, respectively, for 1.299 mu m wavelength light. A loss ratio over 28.9 dB has been realized. >

High-isolation polarization-independent optical circulator coupled with single-mode fibers

A simple polarisation-independent optical circulator has been developed. The circulator consists of a 45°Y3Fe5O12 rotator and a quartz rotator and two polarising beam-splitting cubes. Measured insertion loss was about 1.3 dB at 1.32 ?m wavelength. The circulator was connected to graded-index multimode fibres using rod lenses.

Simple polarisation-independent optical circulator for optical transmission systems

PURPOSE:To obtain a vertical end surface by providing a optical active layer on a semiconductor substrate, forming a mask on one side surface of an epitaxial wafer having a p-n junction and an ohmic electrode on the other surface of the wafer, dipping it in an aqueous electrolyte solution and etching it with the ohmic electrode as a negative electrode. CONSTITUTION:An n type InP layer 22, an InGaAsP active layer 23, a p type InP layer 24, and an n type InGaAsP layer 25 are superposed on an n type InP substrate 21, an Zn diffused layer 26 is formed, and the prescribed ohmic electrodes 27, 28 are attached. A resist mask 31 is covered on a p type ohmic electrode 28, and the electrode 27 is secured to a glass plate 44 with conductive adhesive 43. It is then dipped in aqua regia solution, and etched in the prescribed current density with a Pt plate as a positive electrode and the wafer as a negative electrode. According to this method, the side surface etching amount of the active layer is largely reduced as compared with the chemical etching of no voltage, the flatness can be remarkably improved, and the undercut amounts of the layers 24, 25 are significantly reduced, and the vertical degree can be remarkably improved.

Kubodera Kenichi

Papers

Simple polarisation-independent optical circulator for optical transmission systems

Manufacture of semiconductor optical element