JPH02118613A - Semiconductor optical gate element - Google Patents

Abstract

PURPOSE:To improve a response speed by amplifying control light with a light amplifier to utilize the induction emission of a semiconductor and, thereafter, inputting it to the field effect type light modulator. CONSTITUTION:Since the light amplifier area is biased in a positive direction, the control light is amplified by the induction emission. An amplification factor at such a time is, for example, in a ten-fold degree, the amplified control light reaches the light modulator area, it is absorbed there, and an excited current is generated. Since the light modulator area is biased in a reverse direction, the induction emission is not generated. Since a voltage drop proportional to the excited current by the control light amplified in such a way is generated to a load resistance 10, an effective reverse bias voltage to an electrode 5 is made small, and signal light can pass the light modulator. Thus, the CR time constant of the photomodulator is reduced, and the response speed is improved.

Description

[Detailed Description of the Invention] [Summary] This invention relates to a semiconductor optical gate device using an electro-absorption type optical modulator.

The purpose is to improve the operating speed of the optical gate element.

an optical amplifier that utilizes stimulated emission of semiconductors by input light;
Equipped with an electric field absorption type optical modulator that utilizes changes in the optical absorption coefficient of the semiconductor layer due to applied voltage.

The semiconductor layer of the optical modulator is optically coupled so that the output light of the optical amplifier is input, and the optical amplifier amplifies the input control light and sends it to the optical modulator. , the optical modulator generates a photocurrent by the amplified control light, and since the photocurrent flows through a load resistor connected between the optical modulator and the power source, the voltage applied to the optical modulator increases. The configuration is such that as a result of the drop, the signal light input to the optical modulator can be output.

[Industrial application field]

The present invention relates to an optical gate element used in an optical communication system, and more particularly to a semiconductor optical gate element using an electroabsorption optical modulator that utilizes changes in the optical absorption coefficient of a semiconductor layer due to applied voltage.

[Conventional technology]

In optical communication systems currently in practical use, optical signal processing such as amplification, modulation, and switching involves first converting an optical signal into an electrical signal, processing this electrically, and then converting it back into an optical signal. A method of sending is adopted. However, this method cannot fully utilize the advantages of large-capacity optical transmission.

Not only does the circuit configuration become complicated because elements for optical-electrical and electrical-optical conversion are required.

There are limits to the miniaturization and reliability of the various devices that make up the system. Therefore, progress is being made in developing methods for processing optical signals as they are.

Furthermore, as the ultimate form of an optical communication system, it is desired that the control signals for processing optical signals also be optical.

For this reason, progress is being made in developing methods that allow optical signals to be processed as they are by using optical control signals.

[Problem to be solved by the invention]

An optical gate element shown in FIG. 4 has been proposed as a device for modulating the above optical signal with an optical control signal.

(Wakao et al., patent application No. 1983-083836. April 1983)
By the way, when a voltage is applied to a semiconductor, the absorption wavelength range for light that passes through it shifts to the longer wavelength side. The so-called electric field absorption effect is known.

By utilizing this effect, when light having a wavelength slightly longer than the absorption edge when no voltage is applied passes through the semiconductor, an optical gate can be obtained that turns on and off the light by applying a voltage to the semiconductor. Instead of controlling an externally applied voltage, the device shown in Figure 4 allows control light to be incident at the same time as the above light (signal light), and turns on/off the signal light depending on the presence or absence of this control light.
This is to turn it off. As the control light, light having a wavelength approximately equal to or shorter than the absorption edge when no voltage is applied to the semiconductor is used.

To explain the structure of Fig. 4 in a little more detail, 1. For example, n-type I
On an nP substrate 1, a non-doped InGaAsP layer 2p-type InP layer 3. P"-type InGaAsP- layers 4 are laminated in sequence, and an upper electrode 5 is formed thereon. On the other hand, a lower electrode 6 is formed on the back surface of the InP substrate 1. InGaAs 1' layer 2 + InP layer 3.InG
The aAsP layer 4 was processed into stripes, and these were formed on its sides. It has a structure embedded with a high resistance or semi-insulating TnP layer 7 doped with iron (Fe). Reference numeral 8 denotes an insulating layer made of, for example, SiO□. The InGaAsP layer 2 is surrounded by an InP substrate 1 having a larger band gap (Eg) and T
Since it has a structure surrounded by nPii3 and 7, light is confined inside the rnGaAsP layer 2.

For example, the lower electrode 6 is grounded, while a negative voltage (-■) is applied to the upper electrode 5 via the load resistor 10. That is, a reverse bias voltage is applied between the n-type InP substrate 1 and the p-type InP layer 3, and most of the electric field is applied to the InP layer 3.
It is concentrated in the GaAsP layer 2. Here, a signal light is inputted to the InGaAsP layer 2 from, for example, an optical fiber 11 . By applying the above bias voltage, InGa
The absorption edge of the AsP layer 2 is shifted to a longer wavelength side than the wavelength of the signal light. As a result, the signal light is InG
It is absorbed by the aAsP layer 2 and does not appear in the output optical fiber 12.

On the other hand, when control light having a wavelength shorter than the wavelength corresponding to the band gap (Eg) of the InCaAsP layer 2 is input from the optical fiber 11 to the InGaAsP layer 2 along with the signal light, excitation by this control light is performed. Then, an excitation current flows through the load resistor 10, resulting in a voltage drop.

As a result, the bias voltage applied to InCaAsP'Wt2 is relaxed, and the signal light is transferred to InGaAsP'Wt2.
It is not absorbed by layer 2 and appears on the optical fiber 12 side.

As described above, a gate operation is performed in which the signal light is transmitted to the output side when the control light is input, and is not transmitted when the control light is not input.

However, the response speed of the optical gate element shown in FIG. is limited by the CR time constant determined by .

The parasitic capacitance (C) is made as small as possible based on the structural design of the element. On the other hand, if the value of the load resistance 10 is decreased,
A sufficiently large voltage drop cannot be obtained with control light of the same intensity, resulting in a loss of the on/off ratio characteristics of the optical gate element. Incidentally, the parasitic capacitance in the conventional optical gate element described above is 3 pF, and the upper limit value f of the response speed when approximately 5Ω is used as the load resistance. is 10MHz
It was about.

An object of the present invention is to improve the response speed of a light gate element that can be controlled by light as described above.

[Means to solve the problem]

The above object includes an optical amplifier that utilizes stimulated emission of a semiconductor due to input light, and an electro-absorption optical modulator that utilizes changes in the optical absorption coefficient of the semiconductor layer due to applied voltage. is optically coupled so that the output light of the optical amplifier is input to the optical amplifier, and the optical amplifier amplifies the input control light and sends it to the optical modulator. A photocurrent is generated by the control light, and since the photocurrent flows through a load resistor connected between the optical modulator and the power source, the voltage applied to the optical modulator drops, resulting in the optical modulation. This is achieved by the semiconductor optical gate device according to the present invention, which is characterized in that the signal light input to the device can be outputted.

[For production]

In an optical device controlled by light.

By amplifying the control light in advance using an optical amplifier that utilizes the stimulated emission of semiconductors, and then inputting it to a field-effect optical modulator, a large excitation current can be obtained and the value of the load resistance connected to the optical modulator can be obtained. Even if g of the load resistance (R) is small, it is possible to generate a voltage drop of the size necessary to maintain the on/off operation of the optical gate element.
It is possible to improve the response speed by reducing the

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

In the following drawings, the same parts as in the previously shown drawings are designated by the same reference numerals.

FIG. 1 is a diagram illustrating the principle of the present invention, in which an optical amplifier that utilizes stimulated emission of a semiconductor is provided upstream of the same field-effect optical modulator as explained using FIG. 4. . That is, for example, a non-doped (nGaAsP layer 2 and a p-type T
The nP layer 3 is laminated, and upper electrodes 14 and 5 are formed in a region constituting an optical amplifier and a region constituting an optical modulator, respectively. Upper electrodes 14 and 5 are electrically isolated from each other. A lower electrode 6 is formed on the lower surface of the InP substrate 1 .

For example, the lower electrode 6 is grounded, and the upper electrode 14 is connected to a positive voltage (
+V+), while a negative voltage (-VZ) is applied to the upper electrode 5 via the load resistor 10. Due to this.

The optical amplifier region is forward biased and the optical modulator region is reverse biased. When signal light and control light are input to the InGaAsP layer 2 in this state, the signal light passes through the optical amplifier region and reaches the optical modulator region, but since the optical modulator region is reverse biased, It gets absorbed.

On the other hand, the control light is amplified by stimulated emission because the optical amplifier region is biased in the forward direction.

The amplification factor at this time is 5, for example, about 10 times. The amplified control light reaches the optical modulator region 1 where it is absorbed and generates an excitation current. Since the light modulator region is biased in the opposite direction, no stimulated emission occurs. In this way, a voltage drop proportional to the excitation current due to the amplified control light is generated across the load resistor 10. As a result, the effective reverse bias voltage applied to the upper electrode 5 becomes smaller, allowing the signal light to pass through the optical modulator.

As mentioned above, since the control light is amplified in the optical amplifier region, even if the value (R) of one load resistor 10 is reduced to 1/10,
A voltage drop equal to that in the case where the control light is not amplified is generated, and gate operation can be maintained. On the other hand, the value of load resistance 10 (R
) is reduced to 1/10, the C17 time constant of the optical modulator having the structure shown in FIG. 1 is reduced to about 1/10, and the response speed is improved to about 100 MHz.

FIG. 2 is a cross-sectional view of a main part showing the structure of an embodiment of the present invention, in which (a) is a side cross-sectional view, and (b) is a side view of (al viewed from the input direction of signal light; The same parts as in the previously published drawings are designated by the same reference numerals.

For example, n-type InP layers 21 . n-type InGaAs
P light guide layer 22. Non-doped InGaAsP active layer 2p type InPn chip 5 3. and p1 type InG
An a^sP cap layer 4 is formed. InGaAs
The compositions of the P operating layer 2 and the InGaAsP optical guide layer 22 have absorption edge wavelengths of 1.3 μm and 1.2 μm, respectively.
m.

In this embodiment, the InGaAsP active layer 2 has a structure in which an optical amplifier and an optical modulator are separated. In addition, from the InGaAsP camp layer 4 to the InGaAsP
The layers up to the optical guide layer 22 are processed to form a stripe-like meza as shown in FIG. structure.And TnGaAsP
Separate upper electrodes 14 and 5 corresponding to the optical amplifier region and the optical modulator region are disposed on the cap layer 4.
On the other hand, a lower electrode 6 is provided on the back surface of the InP substrate 1, and a voltage of +1V to 5 is applied to the upper electrode 14 and 5, respectively.
Bias voltages of about +2v and -3v to -4v are applied.

For InGaAsP layers 2 and 22 in the optical amplifier region.

Signal light with a wavelength of 1.4 μm and control light with a wavelength of 1.3 μm are input. The signal light passes through the InGaAsP layers 2 and 22 and reaches the optical modulator region, where it is absorbed.

After the control light is amplified approximately 10 times in the optical amplifier region.

reaching the light modulator area. InGaAsP light guide layer 22
Since the absorption edge wavelength of is 1.2 μm, the amplified control light efficiently propagates to the optical modulator region. As a result, a voltage drop occurs across the load resistor 10, and signal light is output from the optical modulator region. Note that the reason why the InGaAsP active layer 2 has a structure in which the optical amplifier region and the optical modulator region are separated is to electrically isolate the upper electrodes 14 and 5 from each other.

When the value of the load resistor 10 is 500Ω and the parasitic capacitance of the optical gate element is 3 pF, one response speed is about 100 MHz. Therefore, high-speed operation approximately one order of magnitude higher than that of the conventional optical gate element shown in FIG. 4 is possible.

FIG. 3 is a sectional view of a main part for explaining the manufacturing process of the optical gate element having the structure of the present invention shown in FIG.

Referring to FIG. 3 (al), lattice matching was performed on an n-type (100) InP substrate 1 (n.2 x 10'"cm-").

N-type InP buffer layer 21 (n=2×10Il1cm
-', thickness 2 μm) + n-type InGaAs1' optical guide layer 22 (absorption edge wavelength λ-1,2 pm, thickness 0.2 μm)
), non-doped 1rlGaAsP operating layer 2 (absorption edge wavelength λ-1.3 μm, thickness 0.2 pm Lp type rnP layer 23
(pm5 x 10” cm-, thickness 0.5 μm
)of.

For example, after epitaxial growth is performed sequentially using a liquid phase growth method, the InP layer 23 and the InGaAsP active layer 2 are selectively removed using ordinary photolithography and etching techniques, as shown in FIG. 3 (bl). .

A groove 24 having a width of about 20 μm is formed. As a result, as explained with reference to FIG. 2, the aAsP active layer 2
has a structure in which the optical amplifier region and the optical modulator region are separated. Note that the TnP layer 23 is provided for the purpose of protecting the InGaAsP layer 2 during etching for forming the groove 24.

Then, for example, using the liquid phase growth method again,
As shown in FIG. 2, a p-type rnP cladding layer 3 (p.5 x 10" cm-3, thickness 1 μm) is formed on the InGaAsP optical guide layer 22 exposed in the groove 24 and on the InP layer 2 layer 3. InGaAsP cap layer 4 (absorption edge wavelength λ
-1,37'm+p=I
For example, a 5iO7 film is formed and this 5i02 is selectively etched to form a striped 5i02 mask with a width of about 3 pm orthogonal to the groove 24. And the SiO□
4. InGaAsP cap layer in one exposed area using a mask. The rnP cladding layer 3, the TnGaAsP active layer 2, and the InGaAsP optical guide layer 22 are selectively etched away to obtain the structure shown in FIG. In the shape after the etching, reference numeral 25 is the 5iOz mask.

After the above process, a high-resistance InP layer 7 doped with, for example, iron (Fe) is formed using, for example, MOCVD (metal-organic chemical vapor deposition), as shown in FIG. 3(e). The InP layer 7 is not grown on the SiO□ mask 25, but is formed on the exposed InP buffer layer 2 and from the InGaAsP cap layer 4 processed into a striped mesa.
It grows only on the sides of each layer across the nGaAsP light guide layer 22. Therefore, TnGaAsP layers 2 and 2
2 has a structure embedded in the InP layer except for the portion that becomes the light input/output end face.

Thereafter, the 5i02 mask 25 is removed, and upper electrodes 14 and 5 and lower electrode 6 as shown in FIG. 2 are formed to complete the optical gate device of the present invention shown in FIG.

In the above embodiment, a structure is shown in which the signal light and the control light enter the optical amplifier region from the same direction, but a structure is shown in which the control light enters the optical amplifier region and the signal light enters the optical modulator region from different directions. It is also possible to do this. FIG. 5 is a perspective view and a top view showing the structure of another embodiment of the present invention.

An InGaAsP optical guide layer 22+ InGaAs was formed on two InP buffer layers and one layer in the same manner as in the above embodiment.
P operation layer 2. InP cladding layer 3 and InGaAsP
As shown in FIG. 5 (bl), the camp layer 4 is processed to form independent striped mesas for each of the optical amplifier region and the optical modulator region, and then embedded in the high-resistance InP layer 7. , and upper electrodes 14 and 5 are formed on the InGaAsP cap layer 4 belonging to each stripe.Similar to the previous embodiment,
Also apply a positive voltage (+V+) to the upper electrode 14.

A negative voltage (-VZ) is applied to the upper electrode 5 via the load resistor 10, and the lower electrode 6 is grounded, for example.

In this state, one control light and one signal light are made to enter the optical amplifier region and the optical modulator region, respectively, from directions substantially orthogonal to each other. The subsequent operations in the optical amplifier region and optical modulator region are similar to those in the previous embodiment. This embodiment has a structure in which an optical path for the signal light orthogonal to the traveling direction of the control light is added to the optical modulator region, so that the signal light can be input directly to the optical modulator, and the signal light in the optical gate element can be directly input to the optical modulator. This has the advantage of reducing optical loss and increasing the degree of freedom in designing the optical gate element and the device using the element. In addition, in the example shown in FIG.
I in each of the optical amplifier region and optical modulator region
nGaAsP light guide layer 22.

There is no problem even if it is processed into a stripe shape that intersects with each other.
This makes it possible to increase the propagation efficiency of the control light.

〔Effect of the invention〕

According to the present invention, by combining an optical amplifier using stimulated emission of a semiconductor and an optical modulator of the electro-absorption effect type, it is possible to improve the response speed of the optical modulator by one order of magnitude or more compared to the conventional one, The provision of the semiconductor optical gate device of the present invention comprising the above combination greatly contributes to the promotion of practical use of optical communication systems that control signal light using light.

[Brief explanation of drawings]

FIG. 1 is a diagram explaining the principle of the present invention. FIG. 2 is a sectional view of a main part showing the structure of an embodiment of the present invention. FIG. 3 is a sectional view of a main part for explaining an example of the manufacturing process of the optical gate element of the present invention shown in FIG. 2. FIG. 4 is a perspective view showing a conventional optical gate element that modulates signal light with control light. FIG. 5 is a perspective view and a top view showing the structure of another embodiment of the present invention. In fig. 1 is the rnP substrate. 2 is an InGaAsP active layer. 3 is an InP cladding layer 4 is an InGaAsP cap layer. 5 and 14 are upper electrodes. 6, the lower electrode 7 is a high resistance InP layer. 8 is an insulating layer. 10 is load resistance. 11 and 12 are optical fibers. 21 is an InP buffer layer. 22 is an rnGaAsP light guide layer. 23 is an InP layer. 24 is a groove. 25 is a SiO□ mask. Unexploded 88 Helmet Vouten Prefectural road schedule -4 ri 1] Figure 3 can "1'4 but ν" Diagram 4

Claims (3)

[Claims] (1) Equipped with an optical amplifier that utilizes stimulated emission of a semiconductor by input light and an electro-absorption optical modulator that utilizes changes in the optical absorption coefficient of the semiconductor layer due to applied voltage, the semiconductor layer of the optical modulator is Optical coupling is performed so that the output light of the optical amplifier is input, and the optical amplifier amplifies the input control light and sends it to the optical modulator. A photocurrent is generated by the control light, and the photocurrent flows through a load resistor connected between the optical modulator and a power source, so that the voltage applied to the optical modulator drops, and as a result, the optical modulator 1. A semiconductor optical gate device that is capable of outputting signal light input to the device. (2) Semiconductor substrate of one conductivity type (band gap E_g_
0) A first semiconductor layer (band gap E_g_1;
E_g_1<E_g_0), and a second semiconductor layer of an opposite conductivity type formed on the first semiconductor layer so as to lattice match with the substrate (band gap E_g_2; E_g_2>E
_g_1), two upper electrodes formed one each in an optical amplifier region and an optical modulator region respectively defined on the surface of the second semiconductor layer near the two side surfaces, and two upper electrodes facing the upper electrodes. and a lower electrode formed on the back surface of the semiconductor substrate. (3) A third semiconductor layer (band gap E_g_3; E_g_0>E_g_3) formed between the semiconductor substrate and the first semiconductor layer so as to be lattice matched with the semiconductor substrate.
3. The semiconductor optical gate device according to claim 2, characterized in that the semiconductor optical gate device has an intervening layer (>E_g_1).