1. Field of the Invention
The present invention relates generally to testing of semiconductors, and particularly to testing of laser bars, which are an intermediate structure in the manufacture of laser devices.
2. Technical Background
Laser devices, such as semiconductor diode lasers or laser chips, have become important commercial components. They are used in a wide variety of applications ranging from the readout sources in compact disks to the transmitters in optical fiber communication systems. While new applications in high-speed telecommunication networks continue to emerge, how to ensure that diode lasers are reliable and manufacturable is the most challenging issue. One proven approach to this issue is to deploy tight quality control by using laser bar testing systems that characterize diode lasers in many aspects and in an efficient manner.
Diode lasers are manufactured on wafers or substrates which are processed and further divided into sections or quarters. The sections are further divided into laser bars by breaking or cleaving the sections along the scribe lines, to form facets along the elongated sides of the sections. The laser bar contain many laser diodes.
During the process of diode laser fabrication from the wafer to the final packaging of individual laser devices or diodes, the first stage where these lasers exhibit both electrical and optical characteristics is when laser bars are formed. Therefore, it is desired to characterize lasers at this early stage by probing and testing all the lasers when they are still in the form of a laser bar. The laser devices that do not meet specifications will be scrapped before entering into further labor-costing or time-costing stages, i.e. packaging and life-testing or burn-in. Usually, a full procedure of bar testing includes six measurements for each laser that is being probed: front-facet light versus current, back-facet light versus current, voltage versus current, horizontal far field pattern, vertical far field pattern and an optical spectrum analysis. A system that performs one or all of these measurement functions is called a laser bar tester.
In a conventional laser bar tester, after a laser bar holder or chuck has been removed to load/unload laser bars at a remote station, the laser bar and a single long contact probe are mounted on a rotational stage and detectors are scattered around the laser bar. In order to make a specific measurement, i.e. light versus current, the laser under test or the selected laser device and the probe have to rotate to face one particular detector with the probe engaged. Thus testing of all characteristics involves moving the laser bar and probe many times. This mechanism enabling multiple movements of the probe and the laser bar is prone to vibration that can cause the lift-off of the probe from the laser surface of the selected laser device, potentially damaging the laser because of transient electrical discharges during or in-between measurements.
Therefore, there is a need to improve the laser bar tester to minimize damage to the laser devices due to the testing process while maximizing efficiency.
One aspect of the present invention is a tester for characterizing individual ones of a semiconductor laser devices of a laser bar, wherein the tester includes a holder for securing the laser bar in a fixed position. For moving in at least one relative direction with respect to the laser bar, a movable measurement system is provided for characterizing the individual ones of the semiconductor laser devices as a function of the at least one relative direction.
In another aspect, the present invention includes a pair of detectors, each moving in arc paths around the laser bar to sample the far-fields.
Additional features and advantages of the invention will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the invention as described herein, including the detailed description which follows, the claims, as well as the appended drawings.
It is to be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification. The drawings illustrate various embodiments of the invention and together with the description serve to explain the principles and operation of the invention.