JPS60148185A - Semiconductor ring laser gyro - Google Patents

Abstract

PURPOSE:To miniaturize and lighten the titled gyro, to reduce power consumption and to improve reliability by forming the ring laser gyro consisting of a semiconductor laser with a ring type resonator, a waveguide and a Y type coupling element on a semiconductor substrate as one chip. CONSTITUTION:An InP clad layer 32, a non-doped InGaAsP active layer 33 and an InP clad layer 34 are grown on an InP substrate 31 in an epitaxial manner in succession. The active layer 33 is brought to thickness of 0.1-0.3mum in order to lower a threshold at that time. An oxide 35 patterned as an etching mask is formed to the substrate, and a ring-shape resonator section, a waveguide suction and a Y coupling section are etched through a normal photolithography technique. A crystal is grown while using the oxide 35 as a mask.

Description

[Detailed Description of the Invention] - 3-1c, Technical Field] The present invention relates to a ring gyro, and is a gyro in which a ring is formed of a semiconductor laser.

3-2 [Background Art] In mobile machines such as aircraft, ships, automobiles, and mobile robots, a gyro is an important sensor used for the purpose of detecting the rotational angular velocity of the machine. Mechanical devices are currently in use, but the laser light propagating on a loop-shaped optical path has an optical path difference between clockwise light (CW light) and counterclockwise light (CCW light) due to the rotation of the entire loop-shaped optical path. There is active research into optical sensors that utilize the Subnack effect that occurs.

CW light ccw inside an optical fiber wound into a loop An optical fiber gyro detects the optical path difference, and CW light ccw inside a ring laser having a ring-shaped resonator
A ring laser gyro uses the optical path difference of oscillated light. Among these, some ring laser gyros have been put into practical use and are installed on aircraft.

A gas laser oscillation tube 11 is configured in a ring shape, and a CW light 12 and a CCW light 13 are present inside the ring laser. Reference numeral 14 is a mirror, and one of the mirrors is partially used as a transmissive mirror 15 to allow the redirection oscillation waves to interfere with the outside. Inside the ring laser resonator, the CW light and the ccw light normally oscillate at the same frequency. However, when the entire resonator rotates, cw
An optical path difference occurs between the light and the ccw light. This optical path difference can be observed as a difference in the oscillation frequency of the CW light and the CCW light through the photodetector 17. When the CW light and the CCW light with different oscillation frequencies are superimposed, the output has a beat corresponding to the frequency difference. appears. Assuming that the beat frequency is △f, the rotational angular velocity Ω at that time is expressed as λL. Here, λ is the average wavelength of the ccw light and the cw light, L is the circumferential length of the ring resonator, and A is the area of the portion surrounded by the ring resonator. In this way, since the beat frequency and the rotational angular velocity are in a proportional relationship, the beat 1 of the output light
By counting 8 using an appropriate logic circuit, the rotational angular velocity can be easily obtained. (18 is logic
It is a counter. ) However, in the ring laser gyro using the gas laser described above, since pumping is normally performed by discharge, power of several W to several tens of W is required.

Further, an optical system that superimposes CW light and CCW light has drawbacks such as difficulty in adjustment and further difficulty in reducing size and weight.

3-3 [Object of the present invention] An object of the present invention is to provide a new gyro element that is small, lightweight, low power consumption, and highly reliable in the ring laser gyro described above.

It is manufactured as a single chip.

FIG. 2 shows a schematic diagram as an example of the present invention. A semiconductor laser having a ring-shaped resonator 22, a waveguide 23, and a Y-type coupling element 24 are integrated on a semiconductor substrate 21. The output beats 25 are detected by a photodetector 26 and counted by a signal processing electronic circuit 27.

The following will be explained step by step.

(1) Semiconductor Ring Laser A semiconductor ring laser is a well-known device in which the resonator of a semiconductor laser, which is usually made with a linear structure, is configured as a ring-shaped waveguide. A ring-shaped semiconductor laser medium that has some kind of light wave confinement mechanism and is capable of laser oscillation is manufactured. Spontaneous emission light generated by current injection propagates within the ring-shaped waveguide and is further amplified while causing stimulated emission. When the guided light goes around the ring waveguide once, the amplitudes of the guided light become in phase. That is, 2πr=
Light with a wavelength that satisfies Nλ becomes resonant within the ring waveguide and becomes capable of oscillation. Here, r is the radius of the ring resonator, λ is the wavelength within the semiconductor laser medium, and N is an integer. In a ring-shaped optical resonator, there is essentially a bending loss in the guided light depending on the bending radius r. Furthermore, there are losses such as scattering and reflection in the coupling portion for extracting light to the outside of the resonator. In addition, the waveguide that forms the resonator also has losses such as scattering depending on the absorption of the material and the shape of the waveguide.

Laser oscillation occurs when these losses and optical amplification caused by transmissive emission caused by injected carriers reach equilibrium. Therefore, in order to achieve a low laser oscillation threshold and low power consumption, it is necessary to use a resonator with as little loss as possible. Since the loss caused by bending increases with r, r is set as large as possible. Furthermore, the stronger the light confinement within the waveguide, the smaller the bending loss, so the larger the difference in refractive index between the waveguide medium and the cladding, the better. Furthermore, it is desirable that the injection current be efficiently injected into the laser oscillation region. Semiconductor lasers are made by sandwiching a region layer (active layer) that oscillates between p-type and n-type semiconductor layers, and then creating a so-called double hetero substrate with a band gap that is the smallest in the active layer. It is manufactured by incorporating a confinement mechanism in some way. Various methods have been reported, but the ring laser resonator uses a buried double heterostructure in which the laser oscillation layer is buried with oppositely oriented nopn layers to create a refractive index difference in the lateral direction and to further confine the current. is suitable. This will be explained in detail later in FIG.

(2) Coupling ring of laser light with the outside In a steady state, cw ccw light having the same frequency exists inside the laser oscillator. In order to take these out separately, a waveguide is created tangentially to the resonator. A directional coupling method in which the evanescent field seeping out of the ring resonator waveguide) is coupled to the external waveguide is also considered, but in order to reduce the loss of the laser resonator itself, it is necessary to strongly Bonding by oozing is considered impractical because a structure with less structure is desirable. The laser beam may be extracted by extending the active layer of the laser resonator as it is.

(3) Y-type coupling and waveguide to the outside of the element The cw c taken out to the outside of the resonator by the above waveguide
The cw oscillation light usually has the same frequency, but as the entire ring resonator rotates, the oscillation wavelength of the cw/ccw light changes depending on the rotational angular velocity. This frequency difference is measured as the beat frequency that occurs when the two lights interfere.

For this purpose, the CW light ccw optical waveguide is coupled using a Y-type coupling element, and the waveguide after the Y-type coupling portion becomes guided light with a beat caused by interference between the two lights. The change in intensity is measured by a photodetector placed outside.

The end face from which light waves are extracted to the outside is treated with an AR coating or with a scattering surface. If the external emission end face is a mirror surface, a new resonator including the mirror surface will be constructed, and oscillation may become unstable.

Next, the present invention will be explained with reference to materials and manufacturing methods using specific examples.

・The material used in this case may be any material as long as it is capable of laser oscillation, but the beat frequency obtained is based on the oscillation wavelength λ0.
Since λ0 is inversely proportional to
GaAlAs, which is epitaxially grown on a GaAs substrate, is generally used as an active layer of sP.

The manufacturing method is an example of an InGaAsP/InP embedded double heterostructure, and a perspective view of an element using InP as an example.
Using FIG. 3, an n-InP substrate 31, which will be described below, is
-InP lower cladding layer 32, non-doped InGaAsP
The active layer 33 and the P-InP upper cladding layer 34 are epitaxially grown in sequence.

At this time, the InGaAsP active layer 38 has a thickness of 0.1 to 03 μm in order to increase carrier injection efficiency and lower the threshold voltage.
Control the thickness to a certain degree. For epitaxial growth, a liquid phase method, a vapor phase method, a molecular beam evaporation method, an organometallic vapor phase method, etc. are generally used. A ring-shaped resonator section, a waveguide section, and a Y-coupling section are etched on the substrate on which the crystals have been grown in this manner using a mask having the same shape as shown in FIG. 2 by ordinary photolithography technology. On the board,
The crystal-grown layer remains in the shape shown in FIG. At this time, the etching mask is patterned with Sing.
Isooxide 35 is used. This oxide also acts as a selective growth mask for subsequent crystal growth. It can be used as a semiconductor laser or a waveguide element if the insulator is removed in this state and electrodes are formed, but p-
Since both ends of the n-junction interface are exposed to air, impurities tend to adhere to it, leading to deterioration of characteristics. Therefore, crystals are usually grown around InP, which has a p-n junction in the opposite direction to the laser oscillation p-n junction. , to ensure efficient current injection into the active layer and at the same time prevent deterioration of the interface. After the second crystal growth, oxide is deposited on the entire surface, the oxide on the laser oscillation part is removed, and electrodes are deposited on the entire surface.
The current is injected only into the buried part. n
The side ohmic electrode 36 is made of AnGeN i etc.
The side ohmic electrodes are made of AuZn or the like. As the current blocking layer, 38 represents P-1nP, and 39 represents n-InP.

The above is an example of an embedded double heterostructure, but
Other laser structures are also possible.

Other examples include gain waveguide type and ridge waveguide type.

Next, a photodiode integrated type device will be explained as another specific example of the present invention.

In the semiconductor laser gyro described above, a photodetector (usually a photodiode) is placed outside, but the active layer forming the laser portion and waveguide portion can be used as a photodetector as is. As shown in Figure 4, a groove 4 is etched in the final straight waveguide section in a direction perpendicular to the waveguide.
1, and provide air insulation. The light wave emitted from the waveguide (active layer is 4.2) (laser output is 4.2
3) Since a photocurrent 44 is generated in the pn junction portion separated from the sensor, the current value may be measured separately.

a-5, [Effects of the present invention] The following effects are produced by the present invention. In order to manufacture a ring laser gyro on a semiconductor device, the gyro, which currently requires a volume on the order of a cube with at least 10 crn on a side, can be made into a mathematical chip. Furthermore, since a semiconductor laser is used, the power required can be reduced from the current several watts to several tens of watts to several tens to several 5 mw. Excellent reliability and stability as no optical device is required. This effect is further enhanced in devices with integrated photodetectors.

[Brief explanation of the drawing]

FIG. 1 shows a conventional ring laser gyro, FIG. 2 shows a semiconductor ring laser gyro according to the present invention, and FIG. 3 shows an In
FIG. 4 is a diagram showing an example of the present invention constructed using P/InGaAsP as a material. FIG. 4 is a diagram showing an example of the present invention which is a semiconductor ring laser gyro with integrated photodetection elements. 11... Laser oscillation tube 12... CW light 13... CCW light 14... Mirror 15... Partially transmitting mirror 16... Prism mirror 17... Photodetector 18...・Logic counter 19... Beat 21... Semiconductor substrate 22... Ring resonator (ring laser) 23... Leading waveguide 24... Y-type coupling element 25... Output beat 26... Photo Detector 27...Signal processing electronic circuit 30...Injection current 31 -n-)np substrate 32...n-1nP (lower crat) 33...Non-doped InGaAsP (active layer) 34-P-InP
(Upper cladding) 35...Sing Insulating layer 36...N-side ohmic electrode 37...P-side ohmic electrode 38...P-InP leakage current blocking layer 39...n-InP leakage current blocking Layer 41...Groove by etching 42...Active layer 43...Laser output 44...Current diagram 3 Name of Semiconductor Ring Laser Gyro 3, Relationship with the person making the amendment Patent applicant address 5-15 Kitahama, Higashi-ku, Osaka Name (213
) President Tetsu Kawakami, President of Sumitomo Electric Industries, Ltd. Address: Inside Sumitomo Electric Industries, Ltd., 1-1-3 Shimaya, Konohana-ku, Osaka (Telephone: Osaka 461-1031) Name (7881) Patent attorney (first generation) Tetsu Tsukasa 5, Date of amendment order Spontaneous amendment 6, Detailed explanation of the invention column 7 in the specification subject to amendment, Contents of amendment (11 Change "redirection oscillation wave" to "bidirectional oscillation wave" on page 3, line 14 of the specification) ■ Correct the second line of page 4 of the specification. (3) Change “beat frequency and △f” to “beat frequency and △f” on page 4, line 4 of the specification.
and correct it. (4) From page 7, line 9 to page 7, line 10 of the specification, “the active layer of the band gear amplifier” is r activity 1m (7) t<
/do gap,” he corrected. The resulting waveguide light contains beats generated by the waveguide. Complement 11: do. (6) On page 9, line 13 of the specification, "active layer: GaAs substrate" is corrected to "active layer: GaAs substrate". (7) On page 9, line 18 of the specification, "n-1nP substrate described below" is replaced with "n-1nP substrate described below.
-1nP substrate".

Claims (4)

[Claims] (1) In a semiconductor laser device fabricated on a semiconductor substrate, a laser oscillator portion having a ring-shaped resonator and clockwise and counterclockwise oscillation waves generated within the ring-shaped semiconductor laser are extracted to the outside of the resonator. 2 with equal length
A straight waveguide, a Y-shaped optical coupling part for coupling clockwise and counterclockwise light extracted by both waveguides, and a straight waveguide for guiding the coupled guided light to the outside of the element;
Consisting of positive and negative electrodes for causing a ring-shaped laser oscillator to oscillate, the oscillation frequency difference between the clockwise and counterclockwise oscillation waves caused by the rotation of the ring resonator section is absorbed by the Y-type coupling section. A semiconductor ring laser gyro characterized by detecting a beat frequency due to the interference of both lights and obtaining a rotational angular velocity. (2) A semiconductor ring laser gyro according to claim 1, characterized in that a photodetecting element is fabricated in the straight waveguide portion after the Y-coupling portion to facilitate detection of guided light and improve reliability. . (3) The semiconductor ring laser gyro according to claims 1 and 2, characterized in that an InP--nGaAsP system is used as the semiconductor material. (4) The semiconductor ring laser gyro according to claims 1 and 2, wherein a GaAs-GaAlAs semiconductor is used.