John W. Pritchard

Magnetic domains driving a Q-switched laser

A 10-mm cavity length magnetooptically Q-switched Nd:GdVO4 laser was demonstrated using a single-crystalline ferrimagnetic rare-earth iron garnet film. To design the Q-switching system, the magnetic, optical, and magnetooptical properties of the garnet film were measured. The diode pumped solid-state laser cavity was constructed using a 190-μm-thick garnet film with 58% transmittance. The garnet film had maze-shaped magnetic domains, and the domain walls disappeared when a field of over 200 Oe was applied. Therefore, the polarization state of the transmitted light was modified by modulating the magnetization, and a Q-switched pulse output with a pulse width of 5 ns and peak power of 255 W was achieved in the 10-mm-long cavity. The physical limitation of the pulse width was discussed with the calculated results.

Magneto-optical Q-switching using magnetic garnet film with micromagnetic domains

High-power giant pulses can be used applied in various applications with Q-switched micro-lasers. This method can shorten the pulse duration; however, active control is currently impossible in micro-lasers. To achieve precise pulse control while maintaining compactness and simplicity, we exploit the magneto-optical effect in magnetic garnet films with micromagnetic domains that can be actively controlled by a pulsed magnetic field. Our Q-switching technique enhances the output power by a factor of 4 × 103. Moreover, the device itself is smaller than other Q-switching devices. This novel type of active Q-switch can be combined with a micro-laser to obtain megawatt-order pulses.

Improved Switching for Magneto-Optic Fiber-Based Technologies

A new method for magnetic field generation is presented that enhances the reliability of fiber-based interferometric switches. Suitable switching technologies have been proposed and implemented, but magneto-optic (MO) materials have shown promise in realizing all-optical switching with reasonable power, loss, and switching speed. However, bottlenecks in field generation drivers have limited the performance of MO devices in fiber-based switches. Improving the design of the field generation system will enhance this technology, ultimately realizing practical and reliable solutions. Conventional drivers in MO switching devices utilize one coil with a low number of turns to quickly magnetize the MO material. This, in effect, leads to a fast optical rise time. However, the optical fall time is determined by the response of the MO material and the decay rate of any trapped magnetic energy in the coil, which can be sluggish. The proposed design achieves fast optical fall time by better controlling the demagnetization of the MO material. In this paper, the design of the magnetic field generation system is presented and compared to other recently proposed systems, the electrical system is characterized, and the reliability of the optical output is investigated.

Magnetic Field Generator Design for Magneto-Optic Switching Applications

In optical communications, magneto-optic switching technologies are emerging alternatives, as well as complimentary solutions to their electro-optic counterpart. Their main attractions include low-power and low-cost solutions for signal routing used in fiber-based and all-optical circuits needed in fast dynamic communications systems. However, design of the magnetic field generator system required for these devices is a challenge that has limited their performance and integration onto silicon-based technologies. In this work, a novel approach to designing magnetic field generators for magneto-optic switching systems is provided. This practical field generation design method for magneto-optical interferometers highlights important trade-offs specific to different needs and applications. Example usage of this design process is provided in the application of a magneto-optic switch of ring resonator configuration. Optical and electrical results are also provided and discussed.

Demonstration of Magnetooptic Latching Router for All-Optical Networking Applications

In this paper, a novel fiber-based magnetooptic (MO) latching circuit using a bismuth-substituted yttrium iron garnet (Bi:YIG) is presented. Experimentation shows that nearly 90° of rotation of the state of polarization of incident light occurs between material latching states upon application of an external magnetic field greater than 500 G. This amount of rotation is enough to cause sufficient routing at the output of an optical interferometer of Sagnac configuration, which is presented in this paper. Due to the high coercivity of the Bi:YIG, the material remains in its magnetized state for very long periods of time and is thus latched. Reversing the applied magnetic field changes the state of the material, unlatching it. This capability has great importance for nonreciprocal all-optical devices requiring low power operation. In addition, having such control of the state of the nonreciprocal elements can allow for a wider diversification of small-scale and large-scale optical network design. A discussion of the experimental setup, the resulting measurement data, and its implication for future low power applications is presented.

Magneto-Optic Interferometric Switch With Resonator Configuration

All-optical resonators are candidates for next-generation, integrated, optical switching devices for communication purposes. Their simplicity in design can allow for easy integration using standard CMOS fabrication processes. Other switch configurations, such as the Mach-Zhender and the Sagnac, have been implemented but are more complicated. Traditionally, optical resonators have been used as optical all-pass filters. However, by including a Faraday rotator in the resonating loop with an actuating field, an all-optical switch can be realized. Optical resonator switches have often been proposed and implemented utilizing the electro-optic effect. This study reveals that magneto-optic equivalents show promise as alternatives. Here, a magneto-optical switch in a resonator configuration is proposed and implemented with theoretical analysis using the Jones calculus technique.

Randomly polarised beam produced by magnetooptically Q-switched laser

Diode-pumped solid-state micro lasers are compact (centimetre-scale), highly stable, and efficient. Previously, we reported Q-switched lasers incorporating rare-earth substituted iron garnet (RIG) film. Here, the first demonstration of the magnetooptical (MO) Q-switch in an Nd:YAG laser cavity is performed. We fabricate a quasi-continuous-wave (QCW) diode-pumped Nd:YAG laser cavity, which is shortened to 10 mm in length and which contains an RIG film and a pair of small coils. This cavity yields a 1,064.58-nm-wavelength pulse with 25-ns duration and 1.1-kW peak power at a 1-kHz repetition ratio. Further, the polarisation state is random, due to the isotropic crystal structure of Nd:YAG and the fact that the MO Q-switch incorporating the RIG film does not require the presence of polarisers in the cavity. This is also the first report of an MO Q-switch producing random polarisation.

The dynamic image of the engineer

In this work, engineering students are asked what engineering is and what it means to be an engineer. Their responses suggest that there may be an inconsistent development of the image of an engineer as the student progresses within their engineering program, and a lack of philosophical discussion that leads to a deeper understanding of their field. Additionally, non-engineering students are given the same questions, providing an interesting perspective. The survey questions are presented and an analysis of the results is provided with suggested approaches to improve the observed issues.