Semiconductor laser apparatus for optical heads

Claim 2

A semiconductor laser apparatus (21) for an optical head, the apparatus (21) comprising a semiconductor laser chip (31) for radiating a beam from a radiant surface thereof, a photodetector (25) for detecting an incident beam and supplying a signal, and a beam splitter (27), characterised in that: said beam splitter (27) has a first surface (27a) inclined at a predetermined angle with respect to said radiant surface, and said beam splitter (27) is fixed on said photodetector (25).

Claim 3

An apparatus (21) according to claim 1 further comprising a window (32) for receiving a beam radiated from said semiconductor laser chip (31) and reflected by said first surface (27a) of said beam splitter (27), and for receiving the beam reflected by an optical recording medium (6) after transmission through said window (32).

Claim 4

An apparatus (21) according to claim 2 wherein said beam splitter (27) comprises a prism (27), and said photodetector (25) comprises four photodetecting portions (A, B, C, D) divided by two bisectors inclined at 45° in directions opposite to a ridge of said beam splitter (27), two pairs of said photodetecting-portions (A, B, C, D) arranged symmetrically with respect to an intersection of the two bisectors being arranged to generate outputs for deriving a focus error signal, the focus error signal being calculated as an astigmatism from a difference between a sum of the outputs from one pair of opposing photodetecting portions (A, B, C, D) and a sum of the outputs from the other pair of opposing photodetecting portions (A, B, C, D).

Claim 5

An apparatus (21) according to claim 3 wherein the total sum of the outputs from said photodetecting portions (A, B, C, D) forms as a reproduced signal.

Claim 6

An apparatus (21) according to claim 3 wherein there is further provided another photodetector (26), and said beam splitter (27) has a second surface (27b) for directing those rays of the beam radiated from said semiconductor laser chip (31) which are transmitted through said first surface (27a) of said beam splitter (27), towards said other photodetector (26), so that an output from said semiconductor laser chip (31) is monitored by a signal from said other photodetector (26).

Claim 7

An apparatus (21) according to claim 3 wherein said prism (27) comprises first and second triangular prisms (44, 45) having refractive indices different from each other.

Claim 8

An apparatus according to claim 1 wherein said semiconductor laser chip (31) and said photodetector (25) are arranged on a common substrate (47).