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Pulse Transformer for Injection Laser

IP.com Disclosure Number: IPCOM000082372D
Original Publication Date: 1974-Nov-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 3 page(s) / 61K

Publishing Venue

IBM

Related People

Rutz, EM: AUTHOR

Abstract

In designing a pulse transformer, great care must be taken to preserve good wave shape with fast rates of rise and high efficiency. A good pulse transformer design attempts to minimize the leakage inductance, by winding the secondary and primary closely together.

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Pulse Transformer for Injection Laser

In designing a pulse transformer, great care must be taken to preserve good wave shape with fast rates of rise and high efficiency. A good pulse transformer design attempts to minimize the leakage inductance, by winding the secondary and primary closely together.

An integrated unit is described where the low-impedance load is made part of the current path of the secondary winding. Advantage is taken of the continuity between the radial conduction current in the secondary winding of the transformer and the radial displacement current in a coaxial transmission line, to physically separate the load from the transformer and still maintain close coupling between the primary and secondary windings.

A step-down transformer is used to convert the 0.5 ohm impedance of the injection current pulse generator to the very low diode impedance of approximately 20x10/-3/ ohm. The pulse transformer holds the GaAs diode, and is an integral part of the laser device. The electrical parameter and the dimensions of the transformer are determined by the design specification of the laser device, where the GaAs laser diode is operated with an external resonator.

For two watts peak pulse power in the transverse electromagnetic (TEMoo) mode at room temperature, injection current pulses up to 150A are required. Thus, the secondary current in the step-down transformer can be as high as 150A. For a repetition frequency of 10kHz at room temperature, the duration of the injection current pulses is limited to 50ns to keep the temperature rise of the PN junction laser below a few degrees. The frequency band of the transformer, therefore, must extend to at least 25MHz.

For efficient impedance transformation, the laser diode must be placed directly in the current path of the secondary winding of the pulse transformer. To minimize the leakage inductance of the pulse transformer, the secondary winding must tightly enclose the primary winding which is wound on a toroidal core. The geometry of the pulse transformer must be commensurable with the configuration of the optical cavity of the GaAs laser device.

The design shown in the figure meets the requirement of efficient impedance conversion, but also makes it possible to place the laser diode at the optical axis of the external resonator. In the pulse transformer the coil of the primary winding (which has the form of a toroid) is wound on a toroidal core. The secondary winding consists of one turn only. To the secondary winding a low-impedance transmission line is coupled, which is terminated by the GaAs diode.

The secondary winding of one turn has circular syrmetry in reference to the primary winding. The conduction current induced by the magnetic field in the core is radial in the lower and upper part of the secondary winding. Efficient coupling between the secondary winding of the pulse transformer and the coaxial transmission line is accomplished, by the continuity of the radial...