A short history of optical electronic sensors

The image dissector was an early all-electronic television camera tube invented by Philo Farnsworth. Farnsworth's image dissector was successfully demonstrated and patent applications were made in 1927. This was the first successful demonstration of a fully electronic television system. Farnsworth continued making improvements to his system, and by 1929, image clarity and number of lines of resolution exceeded the achievements of the mechanical television systems.

Most experimental television systems in the 1920s and 1930s made use of an electromechanical system, usually a Nipkow disk combined with a single photoelectric cell for scanning an image and creating an electrical output. A similar device operating in reverse was used to project the image onto the picture screen. [wiki]

The Iconoscope invented by Vladimir Zworykin improved on Farnsworth's invention by combining the photosensitive material at each point with a capacitor so that all the electrons were captured. A separate beam of electrons was then used to scan over the image surface, resulting in an electrical current proportional to the quantity of stored electrons at each point.

The key aspect of the Iconoscope was that the image-sensitive target integrated, or collected the charge developed by the light hitting it between readout scans. [wiki]

The iconoscope was the primary camera tube used in American broadcasting from 1936 until 1946, when it was replaced by the image orthicon tube.

The image orthicon tube (often abbreviated as IO) was common until the 1960s. A combination of Farnsworth's image dissector and RCA's orthicon technologies, it replaced the iconoscope/orthicon, which required a great deal of light to work adequately.

While the iconoscope and the intermediate orthicon used capacitance between a multitude of small but discrete light sensitive collectors and an isolated signal plate for reading video information, the IO employed direct charge readings from a continuous electronically charged collector. The resultant signal was immune to most extraneous signal "crosstalk" from other parts of the target, and could yield extremely detailed images. For instance, IO cameras were used for capturing Apollo/Saturn rockets nearing orbit long after the networks had phased them out, as only they could provide sufficient detail.

A properly constructed image orthicon could take television pictures by candlelight owing to the more ordered light-sensitive area and the presence of an electron multiplier at the base of the tube, which operated as a high-efficiency amplifier. It also had a logarithmic light sensitivity curve similar to the human eye, so the picture looked more natural. Image orthicons were used extensively in the early color television cameras, where their increased sensitivity was essential to overcome their very inefficient optical system. An engineer's nickname for the tube was the "immy", which later was feminized to become the "Emmy" [wiki] A vidicon tube (sometimes called a hivicon tube) is a video camera tube design in which the target material is a photoconductor. The Vidicon was developed in the 1950's at RCA by PK Weimer, SV Forgue and RR Goodrich as a simple alternative to the structurally and electrically complex Image Orthicon. While the initial photoconductor used was Selenium, other targets -- including silicon diode arrays -- have been used. Prior to the design and construction of Galileo probe to Jupiter in the late 70s, NASA used Vidicon camera on most of their unmanned deep space probes equipped with the remote sensing ability. [wiki]

Mercury imaged by the mariner 10 spacecraft using a vidicon.

The required array consisting of CCD (charge-coupled device) technology was invented in 1969 by Willard Boyle and George E. Smith at AT&T Bell Labs. The lab was working on the picture phone and on the development of semiconductor bubble memory. Merging these two initiatives, Boyle and Smith conceived of the design of what they termed 'Charge "Bubble" Devices'. The essence of the design was the ability to transfer charge along the surface of a semiconductor. As the CCD started its life as a memory device, one could only "inject" charge into the device at an input register. However, it was immediately clear that the CCD could receive charge via the photoelectric effect and electronic images could be created. Today, they are most widely used in arrays of photoelectric light sensors, to serialize parallel analog signals. Not all image sensors use CCD technology; for example, CMOS chips are also commercially available. [wiki] Two important characteristics of CMOS (Complementary metal–oxide–semiconductor) devices are high noise immunity and low static power consumption. Significant power is only drawn when the transistors in the CMOS device are switching between on and off states. [wiki]