A Blu-ray Drive is a device that reads Blu-ray discs. It uses a blue laser as part of the process of reading or writing data to or from Blu-ray discs.

A BD drive

Many manufacturers produce them for Blu-ray players or computers, manufacturers include Sony, LG, Panasonic, ASUS, Pioneer, etc. 

A device that uses the drive is called a host (player or computer). 

BD drives read all types of Blu-ray Discs (BD-ROMs, BD-Rs, BD-REs) and are backwards compatible with CDs and DVDs. There are often internally inside and connected to the player's system-on-chip with a wired ribbon cable.

BD Drives for computers (Windows, Linux, Mac), often called "burners" or "writers", can write and burn data to BD-Rs, BD-REs, and other burnable discs. They also contain firmware, separate from the host's OS. There's usually two physical types of drives, internal and external. External drives are usually for laptops for portability and are connected using a USB. Internal drives is for desktops are connected using a SATA bus interface. They are capable of writing (burning) data into BD-Rs and BD-REs. Duplicator Towers, are professional burners that burn multiple BD-Rs/BD-REs at the time.

Comparison of laser resolution in a CD, DVD, and Blu-Ray Player. (Photos from Phillips)

The spectrum of optical disc lasers.

BD drives for consumer players are embedded components controlled by the player’s SoC via proprietary low-level signals over a ribbon cable.

BD drives for computers use the Multi-Media Command Set (unrelated to HDMV Commands.), a set of commands that allows the host to control the drive. It is based on the SCSI Multimedia Commands (MMC5), which defines a SCSI/ATAPI-based command set for accessing and controlling devices of type 05h.

How the Drive Works

• Numerical Aperture (NA) = 0.85 (vs 0.60 for DVD)
• Thin 0.1 mm transparent cover layer on the disc (vs 0.6 mm substrate on DVD) — this reduces spherical aberration at high NA.
• Track pitch = 0.32 µm  
• Minimum pit length ≈ 0.138 µm (27GB), 0.149 µm (25GB), 0.160 µm (23.3GB) - (17PP modulation code)

Details of the Laser Diode Package: LD (Laser Diode) – the forward current pin that drives the laser chip, COM (Common/Ground) – shared ground for both LD and PD, PD (Monitor Photodiode) – the rear-facet monitor sensor that measures laser output power for APC feedback

• 405 nm laser diode (plus usually 650 nm red + 780 nm IR lasers for backward compatibility with DVD/CD).  
• Objective lens (high-NA, often with actuator).  
• Photodetector array.  
• Focus and tracking actuators (voice-coil or similar).

Top-down view of a typical Blu-ray drive traverse mechanism.  The spindle motor spins the disc while the sled motor drives the worm gear/lead screw to move  the Optical Pickup Unit (OPU) radially. The OPU contains separate objective lenses for  Blu-ray and CD/DVD compatibility, plus focus and tracking voice-coil actuators. *NOTE: Some use gears as an alternative.

• Spindle motor: spins the disc at Constant Linear Velocity (CLV) — data rate stays constant as the laser moves outward.  
• Sled motor: moves the OPU radially across the disc.  
• Focus servo and tracking servo: keep the laser spot precisely on the data layer (critical because of the tiny 0.138 µm pits and high NA).