Claims
- 1. An optically controlled selector comprising:
- an optical coupler having a first input for an optical input signal, a second input for an optical control signal and an output for a combined signal, and
- an optical amplifier downstream of the output of the coupler and arranged to receive the combined signal,
- said optical amplifier including a resonant cavity containing an optically non-linear material of the type such that changes in the power of the optical control signal result in changes in the resonant frequency of the cavity, in use, the power of the optical control signal controlling the transmission or suppression of the optical input signal in the optical cavity.
- 2. A selector according to claim 1 in which the cavity is a Fabry-Perot cavity resonator which is completely filled by the optically non-liner material.
- 3. A selector according to claim 1 in which the optical cavity is formed by a semi-conductor laser amplifier.
- 4. A selector according to claim 3 in which the amplifier is of the Fabry-Perot type or of the distributed feedback type.
- 5. A selector according to claim 1 in which filtering means are located downstream of the optical cavity to separate the control signal from the, or the selected one of the, input signals.
- 6. A selector according to claim 5 in which the filtering means are formed by a monochromator.
- 7. An optical communication system including a selector in accordance with claim 1, 5 or 6.
- 8. An optically-controlled optical switch comprising:
- an optical signal input port for accepting optical input signals of frequency f.sub.1 ;
- an optical control signal source of frequency f.sub.2 which is different from f.sub.1 ;
- an optical signal coupler disposed to combine said optical signals of frequency f.sub.1 and f.sub.2 into a common optical signal path;
- an optical signal amplifier disposed in said common optical signal path and including a resonant cavity containing an optically non-linear material of the type such that selective changes in power of the optical control signal selectively change the resonant frequency of the cavity and thereby selectively control passage or non-passage of the input optical signal therethrough.
- 9. A method for selectively passing or blocking an input optical signal I.sub.1 of frequency f.sub.1, said method comprising the steps of:
- supplying said optical signal I.sub.1 of frequency f.sub.1 to an optical resonant cavity having non-linear optical properties which cause the cavity to have a resonant frequency response which changes as a function of input optical signal power; and
- supplying a control optical signal I.sub.2 to said resonant cavity and selectively controlling the magnitude of said control signal so as to change the resonant frequency response between (a) a first state in which said input signal frequency f.sub.1 falls within the resonant frequency response thereby passing the input optical signal to an output port of the cavity and (b) a second state in which said input signal frequency f.sub.1 falls outside the resonant frequency response thereby blocking the input optical signal from said output port.
Priority Claims (1)
| Number |
Date |
Country |
Kind |
| 8612955 |
May 1986 |
GBX |
|
Parent Case Info
Optical transmission systems are now widespread and it is becoming increasingly desirable to provide devices which are directly controllable by optical signals to enable control logic for a telecommunications system to be carried out entirely optically.
In this specification, the term optical is intended to refer to the visible region of the electromagnetic spectrum together with those parts of the infrared and ultraviolet regions at each end of the visible region which are capable of being transmitted by dielectric optical waveguides such as optical fibres.
According to this invention an optically controlled selector comprises an optical coupler having a first input for an optical input signal, a second input for an optical control signal and an output 4 for a combined signal, and a resonant cavity downstream of the output of the coupler and arranged to receive the combined signal, the resonant cavity containing an optically non-linear material so that changes in the power of the optical control signal result in changes in the resonant frequency of the cavity. In use, the power of the optical control signal controls the transmission or suppression of the optical input signal in the optical cavity.
Such a selector can act as a simple switch and, in this case, the input signal is usually monochromatic. When the control signal tunes the optical cavity to resonate at the frequency of the input optical signal the optical cavity transmits the input optical signal and so acts as a switch which is ON but when the optical control signal tunes the resonant frequency of the cavity to one other than that of the input signal, the input signal is suppressed by passage through the optical cavity so that the switch is OFF.
Alternatively the selector may be used to select one of a number of input signals having different frequencies. An example of this is where the input signal is a frequency or wavelength division multiplexed signal containing two or more separate signals each having a different wavelength. In this case, the control signal is used to set the resonance frequency of the optical cavity to match a particular one of the number of input signals so that this particular one signal is transmitted through the optical cavity whereas the remainder of the optical signals are suppressed. In this way the selector in accordance with the present invention forms the basis of an optically controlled de-multiplexer for a frequency or wavelength division multiplexed optical signal.
The cavity is preferably a Fabry-Perot cavity resonator and preferably it is completely filled by the optically non-linear material. It is possible to use passive non-linear materials such as zinc selenide or gallium arsenide. However, it is very much preferred that the optical material in the cavity is an active optical material so that the optical cavity acts as a resonance amplifier and provides a strong positive gain for optical signals whose frequency corresponds to the resonant frequency of the cavity. The use of an active non-linear optical material increases the selectivity of the selector and improves the ratio of discrimination between those signals transmitted and those suppressed in the optical cavity. When used with communication systems the optical cavity is typically formed by a semiconductor laser amplifier. Such an amplifier may be of the Fabry-Perot type or of the distributed feedback type.
The bias current applied to the laser amplifier, in use, biases the amplifier to a level below its lasing threshold. When both the optical input signal or signals and the optical control signal is fed into the amplifier this increases the power of the light passing through the amplifier and causes a change in its refractive index so tuning the amplifier to a different resonant frequency. When the laser amplifier is tuned by the optical control signal to resonate at the same frequency as that of the one or the selected one of the input signals that input signal is amplified and any others are suppressed.
The selector may also include biasing means such as a constant current source for supplying a bias current to the laser amplifier to bias it to a level just below its lasing threshold. In this case the biasing means preferably include control means which maintain the bias at a constant level.
Filtering means such as a monochromator are located downstream of the optical cavity to separate the control signal from the, or the selected one of the, input signals but filtering means are unnecessary when subsequent equipment downstream from the optical cavity which receives the output signals is only responsive to light of the or the selected one input signal frequency or, alternatively, is unaffected by the control signal. The filtering means also removes any spontaneous emission generated when the optical cavity is formed by a laser.
PCT Information
| Filing Document |
Filing Date |
Country |
Kind |
102e Date |
371c Date |
| PCT/GB87/00359 |
5/26/1987 |
|
|
1/19/1988 |
1/19/1988 |
| Publishing Document |
Publishing Date |
Country |
Kind |
| WO87/07396 |
12/3/1987 |
|
|
US Referenced Citations (5)
Non-Patent Literature Citations (2)
| Entry |
| Jewell et al., "Use of a Single Nonlinear Fabry-Perot Etalon as Optical Logic Gates"; Appl. Phys. Letters, vol. 44, No. 2, Jan. 15, 1984, pp. 172-174. |
| Electronics Letters, vol. 21, No. 21, Oct. 10, 1985, (Stevenage, Herts., GB), H. J. Westlake et al: "Measurement of Optical Bistability in an InGaAsP Laser Amplifier at 1.5 .mu.m", pp. 992-923. |
Patent Grant
4863230
