JPH05249525A - Microwave signal generator - Google Patents

Abstract

PURPOSE:To facilitate the generation of microwaves signals of a wide frequency band and to enable the easy execution of the arbitrary phase control of microwaves regardless of an oscillation frequency by utilizing an electrooptical effect by using two wavelength variable semiconductor lasers. CONSTITUTION:The light beams emitted from the semiconductor lasers 12, 13 pass optical waveguides 14. An electrode 15 is provided on the one optical waveguide. A difference in the refractive index between the optical waveguides proportional to an impressed electric field is generated by the electrooptical effect of GaAs when the electric field is impressed into the optical waveguides from the outside. The microwave of the wavelength corresponding to the difference is then formed. The microwave can be controlled in the frequency over the wide band by changing the one implantation current of the lasers 12, 13. The arbitrary phase control is enabled regardless of the oscillation frequency by changing the intensity of the electric field in the electrode 15. In addition, the signal processing function of the microwave is possible as well as an MMIC is formed in the part in the middle 18 of a microstrip line 17.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microwave signal generator capable of generating microwaves from two laser beams.

[0002]

2. Description of the Related Art The invention of modern laser light has made it possible to apply the technology used in the field of electricity to the field of light. Heterodyne detection is one of them. This technique has been actively used for the development of long-distance optical communication, but research has also been conducted in which the electric signal after heterodyne detection by two laser beams is simply used as a microwave signal. For example, IEEE TRANSACTION ON MICROWAVE THEO
RY AND TECHNIQUES, VOL.38, NO.5, MAY 1990 "Optical Generation, Distribution, and Control o"
f Microwaves Using Laser Heterodyne ", Nd: Y
Microwave generation is performed using heterodyne detection of an AG laser.

Conventionally, microwave generation by such an optical heterodyne method has been performed by a structure using a spatial optical system or an optical fiber. The configuration will be described below with reference to FIGS.

Laser light sources 21 and 22 that perform single-mode oscillation and have oscillation frequencies close to each other (31 and 3 in FIG. 3).
The light emitted from 2) is combined by the beam splitter 23 in FIG. 2 and the optical fiber coupler 33 in FIG. This combined light is made incident on the photodetector 24 (34 in FIG. 3). At this time, heterodyne detection is performed on the surface of the photodetector,
The difference between the frequencies of the two laser beams is generated as a microwave signal.

[0005]

In such a construction method, since each part is independent, it becomes a very large device, and the loss of light is large and impractical. Furthermore, the method shown in FIG. Then, there was a problem of inconvenience of alignment of the optical axis and optical axis shift due to vibration, and instability of the detection signal intensity due to polarization fluctuation in the optical fiber in the method of FIG. Also,
The frequency and phase could not be controlled independently.

The present invention is intended to solve the above problems and provides a wide frequency variable microwave signal generator having a small size, a light weight, a high stability and a low loss.

[0007]

A microwave signal generator according to the present invention combines output lights of two wavelength tunable semiconductor lasers formed on a single semiconductor substrate through an optical waveguide and outputs the combined light. It is characterized in that a microwave having a wavelength corresponding to a wavelength difference between the two output lights is created by applying the light to a photodiode formed on the semiconductor substrate.

[0008]

According to the present invention, all the elements are formed on a single substrate by the above-mentioned structure, so that it is very compact, lightweight, highly stable, and has low loss. Furthermore, this structure simplifies the phase control function and the signal processing function. It is possible to control the frequency and phase of the output microwave signal independently.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG.

In FIG. 1, the semiconductor substrate 11 is GaAs.
It consists of a temperature stabilizer and is kept at a constant temperature. Distributed feedback semiconductor lasers 12 and 13 for performing single-mode oscillation and a photodiode 16 are formed on the semiconductor substrate 11, and are optically connected by an optical waveguide 14. Furthermore, from the photodiode 16, it is connected to a microstrip line 17 for microwave transmission,
It is input to the MMIC 18 of the signal processing circuit. An electrode 15 for phase control is vapor-deposited on the optical waveguide 14 on the side of the one semiconductor laser 13.

The operation of the above arrangement will be described below. Since the semiconductor lasers 12 and 13 are stabilized in temperature, they emit light stably at frequencies close to each other. Consider the electric fields of the light waves at this time as shown in (Equation 1).

[0012]

[Equation 1]

Light emitted from the semiconductor lasers 12 and 13 passes through the optical waveguide 14, but an electrode 15 is provided on one of the optical waveguides.
Is provided. When an electric field is applied to the optical waveguide from the outside, a difference in refractive index of the optical waveguide proportional to the applied electric field as shown in (Equation 2) occurs due to the electro-optic effect of GaAs.

[0014]

[Equation 2]

Due to this difference in refractive index, a phase shift of the light wave can be obtained. This shift amount is shown in (Equation 3).

[0016]

[Equation 3]

Therefore, the electric field of the light wave at this time is as shown in (Equation 4).

[0018]

[Equation 4]

This light and the light emitted from the semiconductor laser 12 are
The light is multiplexed in the optical waveguide and heterodyne detection is performed in the photodiode 16. The DC component of the received light at this time is removed, and only the AC component is received by the microstrip line 1.
It passes through 7 and is taken out. This signal becomes a microwave and has a shape as given by (Equation 5).

[0020]

[Equation 5]

The microwave is generated by the semiconductor laser 1
By changing one of the injection currents of 2 and 13, frequency control can be performed in a wide band, and the electrode 15
By changing the electric field strength at, the arbitrary phase control is possible regardless of the oscillation frequency. In addition, the MMI is inserted in the middle 18 of the microstrip line 17.
C can be formed and a signal processing function of the generated microwave can be added.

[0022]

As described above, the present invention can realize a microwave signal generator having the following excellent effects.

(A) By using two wavelength tunable semiconductor lasers, it is possible to easily generate a microwave signal in a wide band, and by utilizing the electro-optic effect, an arbitrary microwave signal can be generated regardless of the oscillation frequency. Phase control can be easily performed.

(B) By integrating on a single substrate, a very small and lightweight device can be obtained.

(C) By using an optical waveguide for propagation and multiplexing of laser light, the stability of the optical system and the polarization stability of light are improved.

(D) An MMIC for microwave signal processing can be formed on the same substrate, and multifunctional microwave transmission can be performed.

[Brief description of drawings]

FIG. 1 is a block diagram of an integrated microwave signal generator according to an embodiment of the present invention.

FIG. 2 is a block diagram of a conventional microwave signal generation method using a spatial optical system.

FIG. 3 is a block diagram of a conventional microwave signal generation method using an optical fiber coupler.

[Explanation of symbols]

 11 GaAs Substrate 12, 13 Distributed Feedback Semiconductor Laser 14 Optical Waveguide 15 Phase Control Electrode 16 Photodiode 17 Microstrip Line 18 MMIC 21, 22 Laser Light Source 23 Beam Splitter 24 Photodetector 31, 32 Laser Light Source 33 Optical Fiber Coupler 34 Optical Detector

Claims (2)

[Claims] 1. An output light of two wavelength tunable semiconductor lasers formed on a single semiconductor substrate is multiplexed through an optical waveguide, and the combined light is applied to a photodiode formed on the semiconductor substrate. A microwave signal generation device, wherein a microwave having a wavelength corresponding to a wavelength difference between both output lights is created. 2. The micro according to claim 1, wherein an electrode is formed so as to cover a part of an optical waveguide for guiding the output light of the wavelength tunable semiconductor laser, and a variable voltage can be applied to the electrode. Wave signal generator.