(Patent application no. - 634/MUM/2001, Mumbai, INDIA )

Optical Transceiver to transmit and receive multiple monochromatic lasers

Data transmission through variable intensity monochromatic lasers:
 
Optical transceiver consist multiple monochromatic lasers and each laser has variable intensities.

Variable intensity laser: – The intensity of laser is controlled by voltage input to the source that emits laser. Laser source emit light at any of 16 different levels of intensities. The first level of intensity is LEVEL 1, this state occurs when laser is off; the sixteenth level of intensity occurs when laser is ON and emits light with maximum intensity. 14 intermediate levels of intensities are between Level 1 and Level 16. These 16 levels are evenly spaced (the difference between intensities of two consecutive intensity levels is equal). A hexadecimal number is assigned to each intensity level. Table below shows 16 intensity levels of a laser and corresponding hexadecimal number.
 

 
Intensity of laser is controlled by voltage input to the source of laser. When the source emits laser at specific intensity level, the corresponding hexadecimal number assigned to that intensity level is transmitted. Four bit binary data is transmitted by one laser since each hexadecimal number is equivalent to 4 bit binary number.
Data transfer over optical signal through variable intensity monochromatic lasers

A variable intensity monochromatic laser transmits a hexadecimal number at every clock pulse.
 
The optical transmitter consists of four variable intensity monochromatic lasers. Each laser is of specific wavelength and no two lasers are of same wavelength. The intensity of each laser is controlled by voltage input to the source of that laser. Four lasers with 16 intensity levels each make
16⁴ = 65536 combinations of different intensities and wavelengths.
 
These combinations are sufficient to transmit 16-bit binary number at one instance. (Since combinations of 16 bit binary number (1s and 0s) = 2¹⁶ =65536).
 
Construction and working of transmitter
 
The transmitter consists of four lasers. Each laser is of specific wavelength. The wavelengths (colours) are RED, YELLOW, GREEN and BLUE. All four lasers are variable intensity lasers. The intensities of these lasers are controlled by voltage input to laser sources. Each source has an independent voltage input. The voltage input is provided by an input voltage controller circuit. The circuit generates separate voltage input for each laser depending upon hexadecimal number to be transmitted.
 
Sixteen bit binary data is converted into equivalent 4-digit hexadecimal number. Most significant digit of hexadecimal number controls input voltage of RED laser source. The second most significant digit of hexadecimal number controls input voltage of YELLOW laser source. The third most significant digit of hexadecimal number controls input voltage of GREEN laser source. And the least significant digit of hexadecimal number controls input voltage of BLUE laser source.
 
Sixteen hexadecimal numbers (0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, and F) are assigned to 16 intensity levels of each laser. A table below shows some 16-bit binary numbers, their equivalent hexadecimal number and corresponding combination of intensity levels of lasers (RED, YELLOW, GREEN and BLUE lasers).
 
 

The intensities of these laser change at every clock pulse in accordance to hexadecimal number to be transmitted. All lasers are transmitted through single optical fiber.

Construction and working of optical Receiver
 
The receiver consists of a prism. The optical signal (light) received is made incident on the prism. The prism divides the light in to different components depending upon the wavelengths. Each colour component is made incident on separate light sensor. The sensor generates electrical signal in proportion to the intensity of light incident on it. The sensor that senses intensity of RED light component generates electrical signal whose voltage is proportional to intensity of RED laser. Similarly for sensors those sense intensities of YELOW, GREEN and BLUE components generate electrical signals proportional to intensities of respective components incident on the sensors. Electrical signal generated by RED sensor represents most significant digit of four-digit hexadecimal number received in optical form. Similarly the electrical signals generated by YELLOW, GREEN and BLUE sensors represent second most, third most and least significant digits of the four digit hexadecimal number respectively. The outputs of all sensors are connected to a circuit that converts electrical signals into equivalent hexadecimal number. The four hexadecimal numbers together represent a 4-digit hexadecimal number received in optical form. The hexadecimal number is converted in to equivalent 16-bit binary number by hexadecimal to binary converter circuit. The 16-bit binary number obtained after conversion is 16-bit binary number transmitted by the transmitter. This 16-bit binary number is transmitted in one clock pulse time in optical form through single optical fiber.
 
Four lasers transmit a 4-digit hexadecimal number. The equivalent binary number transmitted at one clock pulse is 16-bit binary number. (16 bit binary number is equal to 2 bytes)