Exactly. GA

At any point in either signal chains (A→B & A←B) the data can be lost. An additional complication with RS232 though is that one may also have handshaking communication in either direction not happening that is preventing signals from being generated. Software handshaking is great at validating sound communication but it can make hardware troubleshooting awkward.

How is he receiver end. Is the out output into MATLAB also?

yes

You say you are using a Laser...exactly what are you using? Are you also using fiber optic cable to transmit/receive? If so what fiber are you using? Singlemode/multimode? What distance? What is the wavelength of the Laser? Is the responsivity of the receiver device Ok for the Laser you are using? If you are sure that the signal going into the Laser is good, you will need an optical to electrical converter connected to your oscilloscope to see what type of signal you are receiving. What are you using for the receiver part of the circuit? I can give you a hint that you will require a pre-amp, amp, and comparator (yes, in those stages) to get a good enough signal to convert back to RS232. (yes I designed one such modem for a company I work for...but can't give intellectual property (ie circuit)...only 'hints'. It's about the size to fit into ones hand and plug directly to the PC port).

sir, if i am using this circuit for both transmitter and receiver , and i am connecting a laser torch to the laser output then, what must be the power of laser torch that i can connect? if i connect a 1mwatt laser,will i get any output? what about a 5mwatt torch?

You do not have enough power to drive an X-ray laser with this circuitry. This circuit is not suitable to drive any of the excimer lasers. You obviously can drive some lasers with this circuit. This circuit though is not a duplex circuit. This circuit is only a transmitter.

There is so much wrong here as to defy the point of making any helpful comment since what is indicated is that there is such a lack of even the most basic notion of what is required that to help would be to attempt to teach an entire discipline which is way beyond the scope of what could be done.

I have developed laser systems that transmit data in open air from a hand held targeting device at distances of 400 yards. I in fact developed some of the very first infrared proximity sensors used in automatic toilet flushing. Doing what you propose to do requires an understanding of numerous aspects of the technology you are attempting to use and from the schematic you show it is clear you have no basic handle on any of what is required.

If this is for a comercial application, find a qualified consultant. If you are just messing around to learn, get some data sheets on the optical parts you are using and study them. Find some application notes for things like remote controls and start there. You are trying to make fire with wet sticks and you have hardly figured out you need to rub them together. It's going to be a long road but study hard and good luck.

If it was my project I would at first check it without PCs using only static voltage levels. So you can be sure that the problem isn`t your Matlab interface or an incorrect RS-232 configuration (start/stop-bit, parity etc.). This test can be done only with a voltmeter and without scope.

Regard the polarity of the rs-232 signals in relation to the polarity of the TTL-signals, it`s an error source often disregarded.

If the error still exists I would replace the laser medium by a normal optocoupler - so you can see whether the problem is caused by the laser which may be the wavelength or the optical power (too high or too low).

Regards Uwe

' without PCs '

Exactly! GA
3 rules of fault finding, experimentation and desgin.
Simplify
Simplify
Simplify
Del

if tis is my circuit,will i get any output?

Unfortunately the image I can see from the CR4 is not clear enough for me to conclusively say what you are doing. The MAX 232 chip is an RS232 transmitter and receiver (unlike my earlier implication) that converts the logic levels of RS232 to and from nominal TTL +5V logic levels. What I can see though is that only one signal lead (the emitter of the PNP transistor) leaves this part of the schematic to presumably go to your fiber optics. This will probably be able to drive communication from the computer on the left out to something on the right, but return signals from the right have no path to return to the computer. So all I can say is that this maybe be useful for part of what you wish to do but you clearly need more for this to work.

Once again, I reiterate my prior comment. What is shown demonstrates a complete void of understanding of the technology of optical data transmission and reception. The only answer would be to offer a working design which would be a Cadillac and what he is showing is a skateboard with no wheels.

Given all the potentially critical information you have not told us, one could only guess which of a multitude of problems you may be having. Sending data optically is not a simple matter and merely "connecting" your RS232 feed to a laser offers many possible modes of failure that you haven't given adequate information to support a good diagnosis. Right off the top, if, in the unlikely event everything else that could go wrong hasn't, there is a critical alignment issue and if you happen to be using an infrared laser (we don't know from what you have said) then unless you have a sure means of verifying alignment, there's a good possibliity that is a dealbreaker. Also, if you are counting on on/off keying as your means of sending mark/space (1/0) info, the "what can go wrong" there is beyond a simple discussion especially considering that your discription of the problem does not give a clue as to what you may or may not know about successfully attempting to make this type of interface work. Please tell us more about the details of your transmission mode and the receiver end of the link.

TX_/¯\_/¯\_/¯\ . . .
. . . . . . . . . . . . .-=-=-= rx

DC offset

Plausible. From what the OP has provided it's also possible that the large black switch is in the 0 position to prevent a DC offset.

Where you able to pass data from one PC to another just using a cable in the first instance ie RS232 electrical?