JPH04130316A - Optical flip-flop circuit - Google Patents

Abstract

PURPOSE:To obtain the optical flip flop circuit of a higher speed, lower voltage and higher reliability free from optical axis misalignment by using a semiconductor optical modulator and monolithically integrating all elements onto the same substrate. CONSTITUTION:The voltage applied on the optical modulating parts of optical nonlinear circuit parts 10, 12 increases and the exit light intensity decreases to P0T1 when the hold light of the intensity P0 is made incident on these optical modulating parts and the set light of intensity above PB is made incident on the photodetecting part of the optical nonlinear circuit part 10. The light of the intensity proportional to the intensity P0T1 passes an optical feedback part and is made incident on the photodetecting part of the optical nonlinear circuit part 12. The exit light intensity of the optical modulating part of the optical nonlinear circuit part 12 attains P0T2 when this light intensity is below PA. This state is maintained if the intensity P0T2 is above PB even after the shut off of the incidence. The flip flop operation is executed when the reset light exceeding the light intensity P0 is thereafter made incident on the photodetecting part of the optical nonlinear circuit part 12.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an optical flip-flop circuit driven and controlled by an optical signal.

(Prior art) In the conventional technology, as an element for optical flip-flop operation, a semiconductor laser is used as a hold light source, a set light source, or a reset light source, a semiconductor photodiode is used as a receiving part, and LtNbO, . . . is used as an optical modulation part. Elements using this are known.

However, since the optical flip-flop circuit uses LiNbO3 for the optical modulation section, there is a problem in that it is difficult to integrate it with a semiconductor element.

(Problems to be Solved by the Invention) In order to solve the above-mentioned problems, the present invention provides an optical flip-flop circuit that uses a semiconductor element as an optical modulation part and can be integrated with other parts.

(Means for Solving the Problems) FIG. 3 shows the principle of construction of an optical flip-flop according to the present invention. As shown in FIG. 3, the present invention is a circuit that performs a flip-flop operation by driving a pair of optical nonlinear circuit sections complementary to each other using a hold light, a set light, and a reset light.

The optical flip-flop circuit of the present invention includes a light modulating section and a light receiving section that are electrically connected in series with a hold light source, a set light source, and a constant voltage source. A first optical nonlinear circuit having a characteristic that the output intensity of the hold light from the optical modulation section changes nonlinearly, a hold light source, a reset light source, and an optical modulation section that are electrically connected in series and to which a constant voltage is applied. and a second optical nonlinear circuit section having a characteristic that the output intensity of the hold light from the optical modulation section changes nonlinearly depending on the incident state of the reset light incident on the light receiving section. an optical nonlinear circuit section, and a hold light emitted from the optical modulation section of the first optical nonlinear circuit section is made incident on the light receiving section of the second optical nonlinear circuit section, and the second optical nonlinear circuit section an optical feedback section that makes the hold light emitted from the optical modulation section of the first optical nonlinear circuit section enter the light receiving section of the first optical nonlinear circuit section; It consists of a light receiving section.

Further, in the optical flip-flop circuit of the present invention, the hold light source, set light source, and reset light source are semiconductor laser elements, and the semiconductor optical modulator, semiconductor light receiving element, and optical feedback section are monolithically integrated on the same substrate.

Since the optical flip-flop circuit of the present invention uses a semiconductor optical modulator, it can operate at higher speed and lower voltage than conventional elements using LiNbO3, and all elements are monolithically integrated on the same substrate. Therefore, it is possible to provide a highly reliable optical flip-flop circuit that is faster, lower voltage, and does not shift its optical axis.

(Function) Next, the function related to the present invention will be explained using FIGS. 3, 4, and 5.

FIG. 4 shows the optical input/output characteristics of the optical nonlinear circuit section shown in FIG. As shown in FIG. 3, the transmittance T of the light modulation section decreases as the voltage increases. Consider a case where a light modulator and a light receiver having such characteristics are connected in series and a constant voltage is applied. When no set light or reset light is incident on the light receiving section, the light receiving section is in a high resistance state, and most of the applied voltage is applied to the light receiving section.

Next, when the intensity of the set light or the intensity of the reset light incident on the light receiving section increases, the voltage applied to the light modulation section increases. Therefore, the transmittance of the light modulating section decreases, and the characteristics shown in FIG. 4 are obtained.

FIG. 5 shows the characteristics of this optical flip-flop. Consider a case where an optical flip-flop is constructed as shown in FIG. 3 using a nonlinear semiconductor element having the characteristics shown in FIG. 4. In FIG. 3, the intensity P. The hold light is the first
When the set light enters the optical modulation section of the second optical nonlinear circuit section and the light intensity exceeds Pa, the set light enters the light receiving section of the first optical nonlinear circuit section. The voltage applied to the light modulation section increases, and the output light intensity becomes Po
decreases to T+. At this time, the strength is P. Light with an intensity proportional to T1 enters the light receiving section of the second optical nonlinear circuit section through the optical feedback section. When this light intensity is below PA, the output light intensity from the light modulation section of the second optical nonlinear circuit section is P. T2
becomes.

Further, even after the incidence of the set light is cut off, the intensity P of the output light from the light modulation section of the second optical nonlinear circuit section remains constant. This state is maintained if T2 exceeds Pa.

After this, when the reset light whose optical intensity exceeds PR enters the light receiving section of the second optical nonlinear circuit section, the voltage applied to the optical modulation section of the second optical nonlinear circuit section increases, and the output light intensity increases. is P. T2 to P. decreases to T1. Therefore, the intensity of the light emitted from the optical modulation section of the first optical nonlinear circuit section is P
Increase from oT+ to POT2. Furthermore, this state is maintained even after the incidence of the reset light is cut off. This results in a flip-flop operation.

(Embodiment) FIG. 6 shows an embodiment of the semiconductor integrated structure of the light modulating section and the light receiving section of the nonlinear circuit section, in which the input/output direction of light is perpendicular to the substrate. The light modulating section 1 is a layer having p-type trench conductivity (
P layer), a layer with high resistance and electrical insulation (i layer), and a layer with n type conductivity (n layer), which generates a photocurrent and changes the applied voltage. , which has the function of changing the light transmittance in the i layer.
The light receiving section 3 is composed of an n diode, and has the function of generating a photocurrent and amplifying the photocurrent using a transistor structure.
It is composed of a pn phototransistor. Furthermore, as part 2 of the high-reflection mirror, two types of semiconductors with different refractive indexes are alternately laminated with a thickness of 1/4n of the operating wavelength (n is the refractive index). Provided in between
Bias light and control light can be separated.

By operating the nonlinear circuit section shown in FIG. 6 with a constant voltage power supply connected to both ends thereof, the characteristics shown in FIG. 4 can be obtained.

In the above description, a phototransistor was used as the light receiving section, but the invention is not limited to this.
It goes without saying that an optical oscillator can be constructed by using a diode, pin diode, or other device that can generate a photocurrent upon incidence of light.

Further, in the above example, an example is shown in which the nonlinear circuit has an integrated structure of the semiconductor light modulating element and the semiconductor light receiving element, but each may be separate.

FIG. 1 is a block diagram showing a first embodiment of an optical flip-flop circuit of the present invention.

In Figure 1, LDI and LD4 are lasers for hold light, LD2 is a laser for set light, LD3 is a laser for reset light, Fl-FIO is an optical fiber, PCI and Fe2 are optical fiber couplers, FCMI-FCM4 is a collimator lens, PBSI-PBS4 is a polarizing beam splitter,
■ is a light modulation part (1), 2 is a part of a high reflection mirror, 3 is a light receiving part), 4 is a light receiving part (2), 5 is a part of a high reflection mirror, 6 is a light modulation part (2) .

According to this embodiment, the hold light that has entered the polarizing beam splitter PBSI from the LDI through the optical fiber F1 and the collimator lens FCMI travels straight through the PBSI,
It passes through the λ/4 wavelength plate, enters the light modulation unit 1, is reflected by the high reflection mirror part 2, passes through the λ/4 wavelength plate again, and enters the PB.
It is bent at a right angle at SI and inputted from collimator lens FCM5 to optical fiber F5 and further to optical fiber coupler PCI. Here, the output light is branched into output light and feedback light, and the output light is output as an output Poutl from the optical fiber F9 at an intensity corresponding to the voltage applied to the optical modulation section of the first optical nonlinear circuit section.

Also, the feedback light is optical fiber F7, collimator lens FCM
7 and enters the light receiving section 4 of the second optical nonlinear circuit section. Similarly to the above case, the hold light from LD4 is also
After being modulated by the optical modulation section 6 of the second optical nonlinear circuit section,
The optical fiber coupler FC2 separates the output light and the feedback light, the output light is output from the optical fiber FIO as the output Pout2, and the feedback light is sent to the light receiving section 3 of the first optical nonlinear element.
incident on .

At this time, hold light is input from LDI and LD4 to the optical modulation section of each optical nonlinear circuit section, and then the LD
When the set light enters the light receiving section of the first optical nonlinear circuit section from 2, the light receiving section 3 of the first optical nonlinear circuit section has a low resistance, and a high voltage is applied to the optical modulation section 1. . Therefore, the transmittance of the optical modulator becomes low, and the intensity of the output Poutl from the optical fiber F9 becomes low. At this time, the second
Since the intensity of the feedback light incident on the light receiving section 4 of the second optical nonlinear circuit section is also small, the voltage applied to the optical modulation section 6 of the second optical nonlinear circuit section becomes small. Therefore, the transmittance of the optical modulation section becomes high, and the intensity of the output Pout2 from the optical fiber FIO becomes large (and the intensity of the feedback light incident on the light receiving section 3 of the first optical nonlinear circuit section also becomes large. Therefore, The transmittance of the light modulating section l of the first optical nonlinear circuit section remains low even after the set light from the LD 2 is removed, and the transmittance of the light modulating section 6 of the second optical nonlinear circuit section is high. will be retained.

Next, when the reset light from the LD 3 enters the light receiving section 4 of the second optical nonlinear circuit section, the resistance of the light receiving section 4 of the second optical nonlinear circuit section becomes low, contrary to the previous case. A high voltage is applied to the optical modulator 6. For this reason, Pout
The intensity of 2 becomes small, and the intensity of Poutl becomes large. Further, as described above, even after the reset light from the LD 3 is removed, the respective output light intensities are maintained as they are.

In this way, an optical flip-flop circuit using a semiconductor element as a light modulation section can be constructed.

FIG. 2 is a diagram showing a second embodiment of the present invention.

The difference from the first embodiment is that the optical modulation section and the light receiving section of the nonlinear circuit section are constructed of a waveguide structure, and furthermore, all the components are integrated on one substrate. Figure 2(a) is a plan view, Figure 2(b),
(C) and (d) are respectively indicated by the broken line ■ in Fig. 2 faj.
, ■, and ■ are cross-sectional views. LDI is a hold light laser for the light modulator 1 and light modulator 2, LD2 is a set light laser, and LD3 is a reset light laser. Second
As shown in the figure, the light modulating section 1 and the light receiving section 2 are optically coupled through an optical waveguide, and similarly the light modulating section 2 and the light receiving section 1 are also optically coupled. On the other hand, the light modulating section 1 and the light receiving section 1, and the light modulating section 2 and the light receiving section 2 are electrically coupled to each other. By doing so, optical flip-flops can be integrated on one substrate.

As a result, compared to elements using conventional LiNbO3,
It is possible to provide a highly reliable optical flip-flop circuit that can operate at high speed and low voltage, and whose optical axis does not shift.

Although a phototransistor is used as the light receiving section in Fig. 2, the phototransistor is not limited to this, and it is also possible to use other devices such as a pn diode, a pin diode, etc. that can generate a photocurrent when light is incident. It goes without saying that an oscillator can be constructed.

(Effects of the Invention) As described above, according to the present invention, an optical flip-flop circuit can be configured by using a pin diode as the optical modulation section of the optical nonlinear circuit section.

Since the optical flip-flop circuit of the present invention uses a semiconductor optical modulator, it can operate at higher speed and lower voltage than a conventional element using LiNbO3.

In addition, in the optical flip-flop circuit of the present invention, all elements are monolithically integrated on the same substrate, so a highly reliable optical flip-flop circuit with higher speed, lower voltage, and no deviation of the optical axis can be achieved. Can be provided.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a first embodiment of an optical flip-flop circuit according to the present invention, FIG. 2 shows a second embodiment of the present invention, FIG. 2(a) is a plan view, and FIG. b), (C), and (d) are respectively cross-sectional views at the dashed lines in aj, ■, ■, and ■,
Fig. 3 is a diagram of the configuration principle of the optical flip-flop circuit of the present invention, Fig. 4 is a diagram of optical input/output characteristics of the nonlinear circuit section shown in Fig. 3, and Fig. 5 is an optical flip-flop circuit of the present invention. FIG. 6 is a diagram showing an example of an integrated structure of a light modulating section and a light receiving section of the nonlinear circuit section. LDI, LD4...Laser LD2 for hold light...
・Laser LD3 for set light...Laser F1 for reset light ~FIO...Optical fiber PCI-FC4...Optical fiber coupler FCMI~F
CM8...Collimator lens PBSI~PBS4...
・Polarizing beam splitter...Light modulation section (1) 2.5...High reflection mirror part 3...Light receiving section (1) 4...Light receiving section (2) 6...Light modulation section ( 2) 7...Gold wire...Guide wave path 9...N substrate 10...First optical nonlinear circuit section 11...Optical feedback section 12...Second optical nonlinear circuit section 13, 16...Hold light source 14...Set light source 15...Reset light source

Claims (1)

[Claims] 1. Consisting of a light modulating section and a light receiving section electrically connected in series with a hold light source, a set light source, and a constant voltage source,
A first optical nonlinear circuit section having a characteristic that the output intensity of the hold light from the optical modulation section changes nonlinearly depending on the incident state of the set light incident on the light receiving section; a hold light source, a reset light source, and electrically connected in series. It consists of a light modulator and a light receiver connected to the light modulator and a constant voltage applied thereto, and has a characteristic that the output intensity of the hold light from the light modulator changes nonlinearly depending on the incident state of the reset light that enters the light receiver. a pair of optical nonlinear circuit sections including a second optical nonlinear circuit section, and a hold light emitted from an optical modulation section of the first optical nonlinear circuit section, and enters a light receiving section of the second optical nonlinear circuit section. and an optical feedback section that makes the hold light emitted from the optical modulation section of the second optical nonlinear circuit section enter the light receiving section of the first optical nonlinear circuit section, An optical flip-flop circuit characterized in that the light modulating section and the light receiving section are each composed of a semiconductor optical modulator and a semiconductor light receiving element. 2. Claim 1, wherein the hold light source, set light source, and reset light source are semiconductor laser elements, and the semiconductor optical modulator, semiconductor light receiving element, and optical feedback section are monolithically integrated on the same substrate. The optical flip-flop circuit described.