JPS624800B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical information storage device that stores optical pulses.

Shaping and amplification of optical pulses are important issues in optical communications or optical digital information processing. Conventionally, to achieve this purpose, optical pulses were first converted into electrical signal pulses, and then the electrical signal pulses were shaped and amplified, and then converted back into optical pulses. In this way, conventional optical pulse shaping was achieved by energy conversion from light to electricity to light, making the entire system complex and expensive. Furthermore, high-speed optical pulses have problems such as the need for high-speed response of electronic circuits and broadband amplification when converted into electrical signal pulses.

On the other hand, various types of information storage devices using light have been proposed. Among these methods, there is a method in which an optical waveguide is used as a delay circuit and information is stored for a time corresponding to the delay time. In order to further develop this and store information for a long time, the optical output from the delay circuit is received by a photodetector, converted into an electrical signal, shaped and amplified, and then converted again. A method has been used in which a light source such as a laser is driven by an electric signal and a light pulse is again input to the delay circuit. However, as mentioned above, this long-term storage has a problem due to the conversion from light to electricity to light.

In order to solve the above-mentioned drawbacks, this invention utilizes the optical amplification effect of a semiconductor laser to solve problems such as complexity, high cost, high-speed response of electronic circuits, and broadband amplification caused by conventional optical-to-electrical-to-optical conversion. An object of the present invention is to provide an optical information storage device that solves the above problems.

According to this invention, an information pulse is given to a semiconductor laser, a light pulse from the semiconductor laser is made to enter a delay optical transmission line, and a reflected light pulse from the light transmission line is made to enter the semiconductor laser, thereby shaping the The amplified optical pulse is made to enter the optical transmission line again. At this time, a DC bias for the semiconductor laser is selected so that the optical pulse is repeatedly transmitted and received between the optical pulse and the optical transmission line.

FIG. 1 shows an example of an optical information storage device according to the present invention. Pulse information is applied to the semiconductor laser 1 from a pulse generator 2, and a DC bias is applied to the semiconductor laser 1 from a DC bias source 3. The output light pulse from one end face of the semiconductor laser 1 is incident on one end of an optical fiber 5 serving as a delay optical transmission line through lenses 4 and 4'. The light pulse traveling through the optical fiber 5
It is reflected by the mirror 6 at the other end and is connected to the optical fiber 5 again.
The light returns to the semiconductor laser 1 through the lenses 4' and 4.

On the other hand, the output light pulse from the other end facet of the semiconductor laser 1 is incident on a photodetector 8 via a lens 7, and the signal converted into electricity by the photodetector 8 is sent to a terminal via a gate 9 which is controlled as necessary. 10,1
It is read out as 0'.

The semiconductor laser 1 functions as an optical amplifier, and its characteristics can be described by rate equations of the respective densities of photons and electron carriers. FIG. 2 shows the operating characteristics of the optical output I vs. current J of the semiconductor laser. Jth is the threshold current, and Jb is the DC bias current. When a current is applied to the semiconductor laser in a normal state in which no DC bias current is applied, the optical output I suddenly increases when the current becomes larger than the threshold value Jth, as shown by the solid line a. threshold
When light of the same wavelength and mode is incident on the active layer of a semiconductor laser while applying a current bias current Jb that is slightly smaller than Jth, the photon density in the active layer increases and stimulated emission occurs. Note that since the DC bias Jb is applied near the threshold value Jth, the absorption of input light is so small as to be almost negligible. As a result of stimulated emission, the semiconductor laser operates along the dotted line b, and an optical output I ₀ is obtained.

In FIG. 1, an optical pulse train generated from a semiconductor laser 1 by a DC bias current from a DC bias power supply 3 and a pulse from a pulse current generator 2 propagates back and forth through a delay transmission path such as an optical fiber 5, and τ=
The light returns to the semiconductor laser 1 with a delay of 2L/v (where L is the length of the optical fiber 5 and v is the speed at which the light propagates through the optical fiber 5). When this optical pulse train is incident on the laser active layer, output light appears in accordance with the characteristics indicated by the dotted line b shown in FIG. The semiconductor laser 1 again emits an optical pulse train corresponding to the incident optical pulse train.

In this case, as schematically shown in FIG.
Due to the limitations of the baseband characteristics of the optical fiber 5, the pulse waveform of the transmitted light pulse train shown in FIG. 3 becomes dull when it returns to the semiconductor laser 1 as shown in FIG. bias current
By setting Jb so that a light pulse of a certain level or higher enters the semiconductor laser 1, laser oscillation occurs in the semiconductor laser 1, and the light pulse that is sent out again is as shown in Figure 3C. , the waveform becomes close to the original waveform.

For example, consider a case in which 100 words of information of 32 bits per word are stored in the apparatus shown in FIG. Using an optical fiber 5 with a refractive index of 1.5, the pulse width is 5 ns and the pulse is repeated to achieve a duty of 50.
%, one bit requires 10 ns, or a fiber length of 2 m, and a total of 3200 bits requires a length of 6.4 km. However, in the embodiment shown in Fig. The optical fiber 5 is necessary because the mirror 6 is attached to the end.
The length will be halved to 3.2km. Since this 3200-bit optical information is stored, the amplification gain of the semiconductor laser 1 is made to compensate for the round-trip loss of the entire optical feedback loop system. With current technology, it is easy to obtain an amplification gain of the semiconductor laser 1 of 15 to 20 dB, while the loss of the optical fiber 5 depends on the wavelength used, but is 0.85 dB.
It is easy to achieve 2.5dB/Km in the μm band and 0.5dB/Km in the 1.3μm band. Further, the loss of the mirror 6 and the loss of the optical system (lenses 4, 4') can be extremely reduced. Therefore, a loop length of 30 to 40 km (the length of the optical fiber 5 is 15 to 20 km) can be sufficiently realized using current technology. Also, the optical pulse width is currently 0.5nsec.
can be fully realized, so it is also possible to create an optical information storage device with a storage capacity of 2×10 ^-5 bits using current technology.

In order to read out the information, it is sufficient to input the optical pulse from the semiconductor laser 1 into the electric pulse at the photodetector 8, but the timing of reading can be controlled by the gate circuit 9. This reading has the great feature that the stored optical information signal can be read out without destroying it.

Note that in order to propagate high-speed optical pulses through an optical fiber with a length of several kilometers or more, the baseband band of the optical fiber becomes a problem, but if a single mode fiber is used as the optical fiber 5, at least
It can take a band of _100GHz /Km. Therefore, deterioration of the waveform of the stored optical pulse can be suppressed to a small extent, and information can be stored semi-permanently.

With an automatic adjustment function for the DC bias current Jb, a part of the light is branched and monitored on the photodetector 8 side, and the bias current Jb is adjusted based on the light intensity and waveform.
The stability of the system can be improved by controlling the temperature and by providing the semiconductor laser 1 with a temperature control function. In addition, the mirror 6 has a slight transmittance,
For example, if the optical information signal is extracted with a difference of 1% to several %, the optical information can be stored and simultaneously transmitted to a long distance. In addition, wavelength division multiplexing technology used in optical communications can be used to store different optical information by sharing a single optical fiber for multiple semiconductor lasers, or to create connections between semiconductor lasers and optical fibers. By inserting a light control element such as an ultrasonic optical deflector or an electro-optic modulator into the device, it becomes possible to add a signal processing function and perform various applications such as storing information. Further, if the optical delay circuit can be short, not only the optical fiber 5 but also an optical waveguide can be used in general.

As described above, according to the present invention, an optical information storage device is constructed using a semiconductor laser as an optical amplifier, so optical information can be stored without the conventional conversion from light to electricity to light, and the structure is simple. In addition, it is economical with low power consumption, has high reliability, and can store high-speed pulses.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an example of an optical information storage device according to the present invention, and Fig. 2 shows the optical output of a semiconductor laser.
FIG. 3 is a diagram showing current operating characteristics and a waveform diagram showing a transmitted light pulse and a feedback pulse. 1: Semiconductor laser, 2: Pulse generator, 3: DC bias source, 4, 4': Lens, 5: Optical fiber as delay optical transmission path, 6: Mirror, 7: Lens, 8: Photodetector, 9: Gate circuit, 10,1
0': Read terminal.

Claims (1)

[Claims] 1. A semiconductor laser, a pulse generator and a DC bias source for applying current to the semiconductor laser, an optical delay transmission line, a reflecting means provided at one end of the optical delay transmission line, and the semiconductor laser Means for making a light pulse from one end face enter the other end of the optical delay transmission line, reflected by the reflecting means, and returning the light pulse from the optical delay transmission line to enter the end face of the semiconductor laser. The semiconductor laser generates an optical pulse by a pulse from the pulse generator, and the pulse current of the pulse generator and An optical information storage device, wherein a bias value of the DC bias source is selected.