Design of an integrated optical pickup with NA of 0.85 for small form factor optical disk drives

We design an integrated optical pickup for small form factor optical disk drives. The specifications of the pickup are compatible with those of the Blu-ray disk (BD) in terms of numerical aperture (NA) of the objective lens, the wavelength of the laser diode, and the thickness of the cover layer. The objective lens unit with NA of 0.85 consists of two aspherical refractive lenses and a diffractive optical element for compensation of the chromatic aberration. Each element of objective lens unit will be fabricated on a wafer as an array type, and the three wafers will be aligned and bonded to form an objective lens array. Therefore, elements of the objective lens unit are designed to have sufficient alignment tolerances for various directions such as de-center and tilt. The optical performances of the objective lens unit are evaluated by simulation against various disturbances such as wavelength change of emitting light from laser diode, misalignments, etc. We also design a quarter wave plate, a polarized holographic optical element, and the shape of photodiode integrated circuit array to generate focusing and tracking error signals. The entire height of the pickup including working distance is 2 mm, and the effective pupil diameter of the objective lens unit is less than 1 mm.