Low cost InGaAIN based lasers
View Patent ↗A method and structure for producing lasers having good optical wavefront characteristics, such as are needed for optical storage includes providing a laser wherein an output beam emerging from the laser front facet is essentially unobstructed by the edges of the semiconductor chip in order to prevent detrimental beam distortions. The semiconductor laser structure is epitaxially grown on a substrate with at least a lower cladding layer, an active layer, an upper cladding layer, and a contact layer. Dry etching through a lithographically defined mask produces a laser mesa of length l c and width b m . Another sequence of lithography and etching is used to form a ridge structure with width w on top of the mesa. The etching step also forming mirrors, or facets, on the ends of the laser waveguide structures. The length l s and width b s of the chip can be selected as convenient values equal to or longer than the waveguide length l c and mesa width b m , respectively. The waveguide length and width are selected so that for a given defect density D, the yield Y D is larger than 50%.
1. A laser, comprising:
a substrate having at least one predetermined region of low defect density and at least one predetermined region of high defect density, said low and high defect density regions being in parallel bands;
an InGaAlN-based laser waveguide cavity formed on said substrate at an angle other than parallel to said bands, said cavity having a length l c and having a width w l , said laser cavity including:
a lower cladding layer;
an active region completely contained within said low defect density region;
an upper cladding layer;
at least one etched facet; and
wherein l c <400 μm and w l ≦4 μm.
2. The laser of claim 1 , wherein l c ≦300 μm.
3. The laser of claim 1 , wherein l c ≦200 μm.
4. The laser of claim 1 , wherein l c ≦100 μm.
5. The laser of claim 1 , wherein said etched facet is at or near a 45° angle to the substrate.
6. The laser of claim 5 , further including a lens formed above said 45° facet.
7. The laser of claim 5 , further including a grating positioned above said 45° surface and splitting the received laser light into a central beam and at least two sidebeams adjacent to said central beam.
8. The laser of claim 1 , further including a lithographically-defined facet reflectivity modification of said etched facet.
9. The laser of claim 1 , wherein said laser is incorporated in an optical storage system comprising:
an optical transmitter and shaper for directing and focusing radiation from said laser onto an optical storage medium;
an optical receiver for receiving reflected laser light from the optical storage medium and providing a data signal responsive thereto and position error signals indicative of the vertical and lateral position of the focused laser light relative to the data on said storage medium; and
an actuator for controlling the position of said focused laser light in response to said position error signals.
10. The laser of claim 9 , wherein said optical storage system further comprises:
an optical storage disk medium with a plurality of data tracks circumferentially oriented around the disk medium;
a controller for the laser intensity; and
an electronic reading of said data signal.
11. The laser of claim 1 , further including a second laser facet formed by etching a surface essentially perpendicular to the substrate plane.
12. The laser of claim 1 , wherein said substrate comprises GaN.