High powered laser

Abstract: A method of reducing the amount of unwanted radiation emitted from a semiconductor laser device (2) involves coating a transparent portion the device intended to transmit radiation with a partially reflective layer (32). The transparent portion is typically the lens cap (30).

Description: This invention relates to the field of laser diodes, and more particularly to a high powered laser diode, such as a VCSEL (vertical cavity surface emitting laser). VCSELs inherently produce a high optical power output, and this output can be significantly higher than the maximum limit for eye safety applicable to many fiber optic systems, such as Fiber channel and Ethernet applications. As a result one of the problems that has been faced in the prior art is how to maintain adequate power when the VCSEL is coupled to an optical fiber while preventing the VCSEL from emitting dangerous radiation when not attached to a fiber. Various techniques have been used to make such a diode safe. One technique involves the use of an electromechanical shutter to cut off optical power when the fiber is detached and shut the VCSEL off. Another technique requires the use of a calibrated monitor diode. An object of the invention is to provide an effective means of controlling output radiation to maintain it at a safe level. According to the present invention there is provided a semiconductor laser device comprising a vertical cavity surface emitting laser, a transparent lens, and means for reducing the amount of radiation transmitted through the lens, characterized in that the means for reducing the amount of radiation is a chrome layer coated on the lens and having a transmissivity of about 20-25%. In a preferred embodiment the reflective layer is chrome, although other reflective coating materials can be used. The thickness of the reflective layer is chosen so as to make the amount of light passed safe to the human eye. Other reflective coating materials are examples and do not form, part of the invention. The chrome layer may be coated on the inside or outside of the lens in the cap of the device. The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings, in which:- Figure 1 is a plan view of a VCSEL device embodying the invention with the cap removed; Figure 2 is a side elevation of the device shown in Figure 1 with the cap in place. Referring now to Figures 1 and 2, the device comprises a base 1 on which is mounted a pedestal 6 supporting VCSEL laser diode 2 and a sensing photodiode 3, which is mounted laterally adjacent the laser diode 2 to provide a monitoring function of the radiation emitted by the laser. Bonding posts 20, 21, 22 are provided on the pedestal 6 in a manner known per se. A rectangular strip of window glass 7 having a refractive index of 1.5 and about 100 microns thick is placed over the laser diode 2 and photodiode 3 so as to be parallel to the emitting surface 5 of the laser diode 2. The glass strip 7 serves as a waveguide coupling light from the laser to a detector as described in our co-pending British application no. 9713607.1 (GB 2 326 760 A). A filler glue 8 optically couples the glass to the laser diode 2. The glass contains dispersant spheres 9. A cap 30 containing lens 31 is placed over the base in a conventional manner as shown in Figure 2. In accordance with the principles of the invention, a partially reflective layer of chrome 32 is place on the inside surface of lens 31. This chrome layer typically has a transmissivity of about 20 - 25%. The thickness of the chrome layer determines the transmissivity and this can be selected as desired for the particular application, an in particular to ensure that the radiation emitted is safe for the human eye. Typically for a 25% transmissivity, the chrome layer is 260nm (2600Å) thick and for a 20% transmissivity the chrome layer is 290nm (2900Å). A 300nm (3000Å) layer gives a transmissivity of about 19%, and a 265nm (2650Å) layer a transmissivity of about 23%. The chrome layer can be deposited by a conventional deposition technique. The invention is particularly applicable to 1300nm VCSELs, and combination VCSELs with an integral monitor function as described in our co-pending application referred to above. Another important effect of the reflective layer is that it can be used to reflect light to a sensor, such as a photodiode, laterally adjacent the VCSEL and serving a monitoring function. This can obviate the need for a special optical coupling arrangement.

Claims: A semiconductor laser device comprising a transparent lens (31), and means for reducing the amount of radiation transmitted through the lens (31), characterized in that the semiconductor laser is a vertical cavity surface emitting laser (2) and the means for reducing the amount of radiation is a chrome layer (32) coated on said lens (31) and having a transmissivity of about 20-25%. A semiconductor laser device as claimed in claim 1, characterized in that said chrome layer (32) is deposited on the inside surface of said lens (31). A semiconductor laser device as claimed in claim 1, characterized in that said chrome layer (32) is deposited on the outside surface of said lens (31). A semiconductor laser device as claimed in claim 1, wherein said VCSEL has an integral laterally adjacent monitoring device for monitoring the radiation emitted by the laser and disposed so as to receive radiation reflected from said chrome layer.

Inventors: OSKARSSON VILHELM, OSKARSSON, VILHELM
Applicants: MITEL SEMICONDUCTOR AB
Application year: 1998
Main classification: H01S5
IPC codes: G02B6, H01S5