How does remote control in TV work?

How does remote control in TV work?
In earlier days, remote controls wre based on ultrasonics (sound frequency above the audible range of frequencies). The controlling circuitry included a hand held transmitter 9that transmits ultrasound) and a TV-based receiver circuit. Electronic filter and stepper motors were used to allow/select certain frequencies and perform various functions depending on the key pressed.

But the recent remote controls use infra-red(IR) rays and a special binary (0 and 1) coding mechanism. The code, intensity and wavelength of the IR wave, help to select different functions. Depending on the key pressed, a signal is sent out by IR source say, an injetion laser diode(ILD). It generates a code in parallel format. This is converted to a series format by s shift register. This signal is received by photo-sensitive devices such as an avalanche photo diode at the receiver.

Here another shift register is used to convert the code back to a parallel form. This operates a one-of-n decoder, which selects one function from a set of "n" predefined functions and executes it.