JPH10209485A - Optical semiconductor element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a tunable light receiving unit having simple structure by entering an energy light having wavelength larger than that of the band gap energy of a light absorption layer so that microwave oscillation takes place under such voltage application conditions as the breakdown field strength is higher than a specified value. SOLUTION: A light absorption layer 13 is formed in the center and provided with clad layers, i.e., a p-InGaAsP layer 12 and an n-InGaAsP layer 14, on the opposite sides thereof and then a p-i-n junction is formed and an n electrode 11 and P electrode 15 are provided. An energy light having wavelength larger than that of the band gap energy of the light absorption layer 13 is projected as an optical signal 16 and when a diode applying voltage Vg is applied between the n electrode 11 and p electrode 15 under conditions that the breakdown field strength is 90% or above, a photocurrent and a microwave signal are generated from a same electrode. The microwave oscillation frequency depends on the wavelength and power of the incident light and the element can function as a tunable light receiving unit by specifying the input conditions.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor optical device such as a semiconductor light receiving device, a semiconductor optical oscillation device, and a wavelength multiplexing device.

[0002]

2. Description of the Related Art Various structures have been devised for light receiving elements for detecting light current and photoelectromotive force generated by the incidence of light, which have been put into practical use. Devices that apply a high electric field to a semiconductor device from the outside and realize microwave oscillation caused by carrier transit time effects and avalanche breakdown phenomena are well known, such as gun diodes and impatt diodes. Widely used as elements. These are optical-electrical conversion and optical-
The energy conversion of microwave conversion is actively used. In both examples, there is no correlation between light and microwave energy conversion.

[0003]

With the increase in the optical system of the subscriber line of the communication line and the introduction of ISDN, expectations for an increase in the capacity of the communication network are increasing. To do that, we need to multiplex in the time, space or wavelength dimensions,
Time multiplexing (TDM) and spatial multiplexing (SD)
M) and wavelength division multiplexing (WDM), and it is essential to combine them to realize a very large capacity network. However, the ultra-high speed which has been actively developed in the past has also been reduced to 10 Gb due to the difficulty of speeding up peripheral technologies such as electronic circuits.
/ S is not practical in the high-speed region of more than / s, and the application of spatial multiplexing is limited due to physical restrictions.

In order to overcome these problems, it is most effective to introduce multiplexing in a wavelength region that makes full use of the broadband characteristics of light. WDM has features that flexible multiplexing is possible regardless of the transmission signal format and that the system scale can be expanded simply by increasing the number of wavelengths. Considering these points, all-optical WDM networking is considered to be the main trend in optical technology development.

There are various types of key devices for realizing a WDM network, and a tunable optical receiver is one of them in passive star coupling. In order to perform channel switching reception at high speed, it is essential to use an optical filter that can be electrically controlled, and a system that is considered to be optimal at present has not been realized.

1.3 for optical access networks
/1.55 μm WDM-photodiode (PD) module has recently been proposed (OECC '96 (199
6) 384, 518). This corresponds to a 1.3 μm band PD and 1.55
μm band PDs are arranged in series, 1.3 μm wavelength light is 1.3 μm PD on the front side, 1.55 μm wavelength light is 1.3 μm
The light passes through the PD and is incident on the 1.55 μm PD. The 1.3 μm PD has a filtering function. In this system, inconveniences frequently occur in terms of optical position matching and element dimensions, so that restrictions are imposed on system construction.

[0007]

SUMMARY OF THE INVENTION A tunable optical receiver needs to have a function of identifying a channel to be received. In the WDM, since the wavelength of each channel is different, the function of discriminating the wavelength of the received light is included. Although a hybrid assembly of individual components can do this for this purpose, monolithic integration is desirable from a cost performance standpoint.

[0008] There are a PIN type and an APD type which are usually used as light receiving elements in an optical network. Both of them have a structure in which the incident direction of light is parallel to the traveling direction of the generated carrier. .

On the other hand, a recently-invented side-incident PD (WG-P
D) achieves both the use efficiency of the incident light corresponding to the light sensitivity and the high frequency band characteristic, and has many advantages as compared with the conventional structure. A high electric field bias of 90% or more of the junction breakdown electric field strength is applied to this WG-PD,
It has been found that, when light having energy equal to or greater than the band gap of the light absorbing layer is incident, microwave oscillation occurs together with the photocurrent.

The conversion efficiency of the light-microwave is larger in the APD having the multiplying effect of the carrier than in the PIN structure. Further, the amplitude and frequency of the microwave are determined depending on the intensity and wavelength of the incident light. Particularly in the case of WG-APD, this tendency occurs remarkably. Therefore, the WG-PD that has received the incident light of a constant intensity filters the output frequency to operate as a tunable optical receiver.
Electrical frequency filtering is easier than optical filtering and is also suitable for integration.

This light receiving element operates as an optical microwave converter. In particular, since the wavelength of the incident light corresponds to a specific output frequency, the information of the input channel can be known from the information of the output frequency. Therefore, it functions as a tunable optical receiver with a simple structure. Under multi-wavelength input conditions, a monolithic tunable light receiver can be realized by introducing a frequency identification circuit on the output side.

[0012]

FIG. 1 shows a sectional structure of a waveguide PD by incidence of side light according to an embodiment of the present invention. The light absorption layer 13 formed at the center of the PD is, for example, 1.55.
i-In with low impurity doping concentration for light of μm wavelength
GaAs is used. The thickness depends on the diameter of the incident light beam,
For example, it is 2 μm. As a cladding layer on both sides, p
-InGaAsP layer 12 and n-InGaAsP layer 1
4 to form a pin junction structure. p layer, n
The thickness of each layer is of the order of 4 μm. An electrode 11 for n and a electrode 15 for p are provided as electrodes for applying a voltage to the diode.

The optical signal 16 is incident from the side surface, and the actual element shape is a ridge-shaped stripe having a cross-sectional area of 10 μm × 10 μm and a length of about 100 μm in a plane perpendicular to the incident direction. The diode applied voltage Vg is applied in a reverse bias direction between both electrodes, and a photocurrent and a microwave signal are detected from the same electrode.

The dc current-voltage characteristic of the diode is shown by curve 21 in FIG.
It looks like 2. Therefore, the bias voltage is set to 90 at the junction breakdown voltage.
% Was set to the operating point 23 corresponding to at least%, and when light was irradiated, microwave oscillation was observed through the current terminal.

This microwave oscillation can be displayed as a frequency spectrum by a spectrum analyzer connected to a diode. FIG. 3 shows an example of the result, in which the horizontal axis shows the oscillation frequency Fc and the vertical axis shows the microwave oscillation output Po.

The oscillation frequency depends on the wavelength λ of the incident light and the input power Pin of the incident light. For example, if the incident light wavelength is λ ₁
(1.3 μm) and λ ₂ (1.5 μm)
When the change of the oscillation frequency when the input light power was changed was measured, the result as shown in FIG. 4 was obtained. The oscillation frequency tended to increase as the energy wavelength of the incident light increased. As a result, when the wavelength and the power of the incident light are defined, the oscillation frequency is uniquely set, and the correspondence between the wavelength and the frequency is clarified.

FIG. 5 shows an example of application to a tunable photodetector for WDM as the next embodiment. In the figure, when the optical input power is kept constant and a plurality of optical input signals having different wavelengths are incident on the PD 51 according to the present invention through the fiber, microwave oscillation of a frequency corresponding to each wavelength is generated under a DC high electric field bias condition. . This signal is filtered by an electric filter circuit and transmitted to the next signal processing circuit.

In other embodiments, the conceptual configuration of the apparatus is the same as that of FIG. 5, but an APD having an amplifying effect is used for the PD. In this case, if a wavelength very close to the optical wavelengths of λ ₁ and λ ₂ is used, the output microwave signal has a heterodyne frequency of ΔF = F ₁ −F _{2 in} addition to the corresponding F ₁ and F ₂ frequencies. The components become noticeable. λ ₁ = 1.27 μm, Δ
At λ = 2Å, millimeter wave oscillation of ΔF = 74 GHz was observed. This optical mixing method has made it possible to easily oscillate millimeter waves and submillimeter waves, which were difficult with conventional high-frequency electronic circuit elements.

Although an InGaAs-based material has been described as an example, the same operation can be performed by appropriately combining the wavelengths of incident light even when another direct transition type compound semiconductor material is used.

[0020]

According to the present invention, in a waveguide type photodiode with side light incidence, a microwave having an energy wavelength larger than the band gap energy of the light absorption layer is incident under a high electric field bias application condition. Oscillation could be caused. In particular, the APD structure having a remarkable carrier amplification effect has a large light-to-microwave conversion efficiency.

In the optical device of the present invention, since the microwave oscillation frequency is determined depending on the wavelength of the incident light and the input power, it can be operated as a tunable light receiver by designating a predetermined input condition. This is excellent in economy, multi-functionality and simplicity as compared with a structure in which a conventional light receiver and various optical filters are combined.
It offers a great advantage in building an access network system.

Further, utilizing the optical heterodyne effect,
Millimeter waves can be generated by making light of a plurality of wavelengths incident on the WG-APD. This optical mixing operation facilitates millimeter-wave or submillimeter-wave oscillation, which has been difficult using conventional ultrahigh-frequency electronic circuits.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a composite semiconductor light receiving element with side light incidence showing an embodiment of the present invention.

FIG. 2 is a current-voltage characteristic diagram of the device of FIG.

FIG. 3 is an oscillation spectrum characteristic diagram of the device of FIG.

FIG. 4 is an oscillation frequency-optical input characteristic diagram of the device of FIG. 1;

FIG. 5 is an explanatory diagram showing an application example of the optical semiconductor device of the present invention to a wavelength division multiplexing device.

[Explanation of symbols]

11: electrode metal layer, 12: p-type cladding layer, 13: i-type light absorption layer, 14: n-type cladding layer, 15: electrode metal layer.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masato Shishikura 1-280 Higashi Koikekubo, Kokubunji-shi, Tokyo Inside the Central Research Laboratory of Hitachi, Ltd. In Central Research Laboratory (72) Inventor Shinji Tsuji 1-280 Higashi Koigakubo, Kokubunji City, Tokyo Inside Central Research Laboratory, Hitachi, Ltd.

Claims (4)

[Claims] In a semiconductor light receiving element having an electric signal input surface and an optical signal input surface, light having a wavelength energy larger than the band gap energy of a light absorbing layer is incident, and microwaves are applied under a voltage application condition of 90% or more of the breakdown electric field intensity. An optical semiconductor device characterized by generating oscillation. 2. An optical semiconductor device according to claim 1, wherein the oscillation frequency can be controlled by controlling the wavelength of the incident light and the light input energy. 3. An optical semiconductor device wherein a plurality of light beams having different wavelengths are incident and an output signal having a frequency corresponding to each wavelength is subjected to signal processing by frequency control. 4. An optical semiconductor device which generates a millimeter wave or a submillimeter wave by heterodyne optical mixing by a plurality of light incident on a waveguide type avalanche photodiode.